course specification for me251: materials engineering (2 ... · a5- what is meant by mechanical...
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Course Specification for ME251: Materials Engineering (2 hrs lectures +2 experimental+ 1 hrs Tutorials)
Instructor:
Dr. Mahmoud M. Tash E-mail: [email protected]
http://www.eng.cu.edu.eg/users/mtash/ http://faculty.ksu.edu.sa/mtash/default.aspx
Course Specification: Program: B. Sc. Mechanical Engineering Department: Mechanical Engineering Academic year: Level 4 A- Basic Information: Title: Materials Engineering Code: ME 251
Credit Hours: 3 (2,1,2) (lectures 2 + Experimental 2+ tutorials 1hrs) >>Total 5 hrs/week.
(Prerequisites: CHEM 101, PHYS 104)
B- Professional Information 1. Overall Aims of the course: Upon completion of the course the student should be able to:
• Learn what are engineering materials, their properties, processing and applications:
• Know the structure and characteristics of metals, polymers and ceramics. • Understand types of equilibrium-phase diagrams. • Microstructures of alloys • Understand the atomic imperfections and atomic movement(diffusion) • Understand what is meant by mechanical properties of metals, polymers and
ceramics. • Understand what is meant by heat treatment of plain-carbon steels, cast irons and
precipitation hardening. 2. Intended Learning Outcomes a. Knowledge and understanding By the end of the course the student should be able to: a1- Differentiate between the different behaviors of engineering materials.
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a2- Understanding of crystal structure for materials. a3- Understanding of phase diagram for alloy systems. a4- The basic of metallic heat treatment of ferrous and non ferrous alloys. a5- What is meant by mechanical properties of materials. a6-Understanding of polymeric, ceramic and composite materials and their applications b. Intellectual skills
b1- Identify materials in engineering parts used in daily life. b2- Be familiar with the crystal structure. b3- Be familiar with the phase diagrams b4- Design the heat treatment process. b5- Identify microstructure and properties of some important alloys b6-Understand the basic of material selections.
c. Professional and Practical Skills c1- Learning how are parts manufactured. c2- Selection of proper materials and process for specific industrial applications c3- Use of heat treatment process. c4- Use of materials testing for measuring mechanical properties.
d. General and Transferable Skills d1- Material selection and evaluations. d2- Present finding of scientific research in seminars
3. Course Content (Main Topics):
• Introduction to materials engineering • Structure and characteristics of metals • Polymers and ceramics • Equilibrium-phase diagrams • Microstructures of alloys • Imperfections and Diffusion • Mechanical properties of metals, polymers and ceramics • Heat treatment of plain-carbon steels, cast irons and precipitation hardening
Lecture Topic Outline
Week Topics No. of hours
Lec. Tutorial/lab 1 Introduction to Engineering Materials and Applications 2 3
2 Structure and Characteristics of Metals 2 3
3,4 Polymers and Ceramics 4 6
5,6 Equilibrium-Phase Diagrams 4 6
2
7 Microstructures of Alloys 2 3
8 Imperfections and Diffusion 2 3
9 Mid-Term Exam 2 3
10,11 Mechanical Properties of Metals, Polymers and Ceramics 4 6
12,13 Heat treatment of Plain-Carbon Steels, Cast Irons and Precipitation Hardening
4 6
14 Mid-Term Exam 2 3
4- Teaching and learning methods and Aids:
4.1- Blackboard/ whiteboard 4.2- OHP and power point data show 4.3- Laboratory experiment.
5 – Teaching and Learning methods for Disables 5.1- Extra office hours and additional lectures for tutorial.
6- Teaching and Learning Methods for Distinguished 6.1- Special discussions and seminars
7 - Student Assessment and Grading Basis Methods: Grading Basis: Attendance of lectures and tutorials is a most. Homework assignments will consist of essay questions and problem solving cases. There will be two quizzes and two midterm examination and one final test. Examinations are comprehensive, including subjects from all assigned readings, lectures, laboratory activities, and classroom demonstrations. Written exams to measure knowledge and understanding, Intellectual skills, and Professional skills. Term papers to measure Intellectual skills, Professional skills and General skills
7-1 Tools: Mid Term Exam 1 to measure Knowledge and understanding (a1-a3),
Intellectual skills (b1-b3), and Professional skills (c1-c2)
Mid Term Exam 2 to measure Knowledge and understanding (a4-a6), Intellectual skills (b3-b5), and Professional skills (c3)
Final Exam to measure Knowledge and understanding (a1-a7), Intellectual skills (b1-b5), Professional skills (c1-c4), and General Skills (d1-d2)
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Quizzes and Homework to measure Knowledge and understanding (a1-a7), Intellectual skills (b1-b5), Professional skills (c1-c4), and General Skills (d1-d2)
7-2 Assessment schedule:
Mid-term exam 1 Week 9 Mid-term exam 2 Week 13 Final exam Week 14 Homework Assigned at the beginning of each chapter and
collected one week after the end of each chapter
7-3 Grading system Mid-term exams 40% 40 Final term exam 40% 40 Section work Pop Quizzes (2)
10% 10%
10 10
Total 100% 100 8- List of References
8.1- Course Notes Lectures in Materials Science. 8.2- Required Books William D. Callister, Materials Sciences and Engineering- An Introduction, Jhon Wiley & Sons Inc. 1997. 8.3- Recommended Books Principles of Material Science, William Smith, 1996. Principles of Engineering Metallurgy, L. Krishna Reddy, 1996. Metallurgy for Engineers,4th edition, E.C.Rollason, 1973 8.4- Periodicals, Web Sites The Science and Engineering of Materials, 4th ed, Donald R. Askeland – Pradeep P. Phulé, © 2003 Brooks/Cole Publishing / Thomson Learning™ many internet web sites, 2002-2006
9- Facilities Required for Teaching and Learning
• Materials Laboratory • Workshop
Course Coordinator: Dr. Mahmoud M.Tash
Supervisor of Department: Dr. Habib Ben Bacha
Date: 8 /3 /2009
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Unit One: Introduction to Material Science and Engineering
Objective
- Field of materials science and engineering
- Classes of Engineering materials
Outline
- Introduction to Materials Science and Engineering
- Functional Classification of Materials
- Classification of Materials Based on Structure
- Properties of materials
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UNIT ONE: INTRODUCTION TO MATERIAL SCIENCE AND ENGINEERING
1.1 MATERIAL SCIENCE AND ENGINEERING
Materials science is primarily concerned with the search for basic knowledge about the
internal structure, properties, and processing of materials. Materials' engineering is
mainly concerned with the use of fundamentals and applied knowledge of materials so
that the materials can be converted into products necessary or desired by the society.
Materials in Industry: Industrial applications of materials science include materials
design, cost, processing techniques (casting, rolling, welding, ion implantation, crystal
growth, thin-film deposition, sintering, etc.) and analytical techniques (electron
microscopy, x-ray diffraction, calorimetry, backscattering, neutron diffraction, etc.).
1.1.1 Materials Processing:
• Casting
• Forging
• Extrusion
• Nanotechnology
• Sintering
1.1.2 Materials Properties: Physical behavior, Response to environment
• Mechanical (e.g., stress-strain)
• Thermal
• Electrical
• Magnetic
• Optical
• Corrosive
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1.1.3. Materials Characterization: Diffraction with x-rays, electrons, or neutrons
and various forms of spectroscopy and chemical analysis such as Raman
spectroscopy, energy-dispersive spectroscopy (EDS), chromatography,
thermogravimetric analysis, electron microscope analysis, etc., in order to
understand and define the properties of materials.
1.1.4. Materials Performance: Strength-to-weight ratio, formability, cost
Processing >> Structure >> Properties >> Performance
• Composition means the chemical make-up of a material.
• Structure means a description of the arrangements of atoms or ions in a material.
• Synthesis is the process by which materials are made from naturally occurring or
other chemicals.
• Processing means different ways for shaping materials into useful components or
changing their properties.
1.2 Functional Classification of Materials
• Biomedical (i.e. Hydroxyapatite, Titanium alloys, Stainless steels, plastics, PZT)
• Electronic Materials (i.e. Si, GaAs, Ge, BaTiO3, PZT, Al, Cu, W, Conducting
Polymers)
• Magnetic Materials (i.e. Fe, Fe-Si, NiZn and MnZn ferrites, Co-Pt-Ta-Cr)
• Aerospace (i.e. C-C composites, Sio2-Amorphous silicon, Al-alloys, Super alloys)
• Energy Technology and Environmental Technology (i.e. Uo2, Ni-Cd, ZrO2,
LiCoO2)
• Photonic or Optical Materials (i.e. Sio2, GaAs, Glasses, Al2O3)
• Smart Materials (i.e. PZT, NI-Ti shape memory alloys)
• Structural Materials (i.e. Steels, aluminum alloys, concrete, fiberglass, plastics,
wood)
• Ceramics, Glasses and Composites Materials
• Advanced Materials
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Biomaterials: Metals for implantation must be corrosion resistant, mechanical properties
must appropriate for desired application. Three main categories of metals for implants are
stainless steels, cobalt-chromium alloys and titanium alloys.
Electronic Materials: Materials such as semiconductors used to create integrated
circuits, storage media, sensors, and other devices. Semiconductors can be made into
transistors which can store a digital (on or off) signal. Semiconductors can also be made
to emit light by exposing them to an electric field (light emitting diodes (LEDs) and
diode lasers). Semiconductors are used in computers (45%), consumer products (23%),
communications equipment (13%), manufacturing industries (12%), automobiles (5%),
and by the military (2%).
Piezoelectric Materials: Piezoelectric materials are used in acoustic transducers, which
convert acoustic (sound) waves into electric fields, and electric fields into acoustic waves.
Quartz, a piezoelectric material, is often found in clocks and watches. An oscillating
electric field makes the quartz crystal resonate at its natural frequency. The vibrations of
this frequency are counted and are used to keep the clock or watch on time.
Magnetic Materials: Magnetic materials are used in electrical power applications such
as transformers and motors, in video monitor picture tubes to move electron beams, and
in computer disks or video or audio tapes to record information. Most materials can be
classified as diamagnetic, paramagnetic or ferromagnetic.
Superconductors: A superconductor can conduct electricity without electrical resistance
at temperatures above absolute zero. Superconductors are used in medical instruments
such as Magnetic resonance imaging (MRI) systems.
Ceramics and Glasses: High temperature materials including structural ceramics such
as, polycrystalline SiC and transformed toughed ceramics. Non-crystalline material
includes inorganic glasses, vitreous metals and non-oxide glasses.
Glass optical fibers: Including video, audio, images, and text, at speeds of over a billion
pulses of light every second.
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Optical Fibers: An optical fiber contains three layers: a core made of highly pure glass
with a high refractive index for the light to travel, a middle layer of glass with a lower
refractive index known as the cladding which protects the core glass from scratches and
other surface imperfections, and an outer polymer jacket to protect the fiber from
damage.
Composites Materials: Composites are formed from two or more types of materials.
Examples include polymer/ceramic and metal/ceramic composites. Reinforcing fibers can
be made of metals, ceramics, glasses, or polymers that have been turned into graphite and
known as carbon fibers.
Advanced Materials: Advanced engineered materials are playing a major role in the
rapid growth of the global telecommunication network. Fiber-reinforced composites are
used in some of the most advanced, and therefore most expensive, sports equipment, such
as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset
polymer matrix.
1.3 Classification of Materials-Based on Structure
• Crystalline material is a material comprised of one or many crystals. In each
crystal, atoms or ions show a long-range periodic arrangement.
• Single crystal is a crystalline material that is made of only one crystal (there are
no grain boundaries). Grains are the crystals in a polycrystalline material.
• Polycrystalline material is a material comprised of many crystals (as opposed to a
single-crystal material that has only one crystal). Grain boundaries are regions
between grains of a polycrystalline material.
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1.4 Properties of Materials
• Mechanical properties:
o Elasticity and Plasticity,
o Strength
o Toughness and,
o Fatigue.
• Electrical properties:
o Electrical conductivity and resistivity
• Magnetic properties:
o Paramagnetic,
o Diamagnetic, and
o Ferromagnetic properties.
• Dielectric properties:
o Capacitance,
o Ferroelectric, and
o Piezoelectric properties.
• Optical properties:
o Refractive index,
o Absorption,
o reflection,
o transmission, and
o Double refraction.
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UNIT TWO: CRYSTAL STRUCTURE, DEFECTS AND IMPERFECTIONS
Objective
- Relationships between structures-properties of engineering materials.
- Crystal structure
- Imperfections
Outline
- Crystal Structures
- Points, Directions, and Planes in the Unit Cell
- Point Defects
- Dislocations
- Surface Defects
- Importance of Defects
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UNIT TWO: CRYSTAL STRUCTURE, DEFECTS AND IMPERFECTIONS
2.1. Atomic Bonding
Bonding: There are two types of bonds: primary and secondary. Primary bonds are the
strongest bonds which hold atoms together. The three types of primary bonds are:
1. Metallic bond,
2. Covalent bond, and
3. Ionic bond
2.1.1. Metallic Bonds
Metallic bond forms when atoms give up their valence electrons, which then form an
electron sea. The positively charged atom cores are bonded by mutual attraction to the
negatively charged electrons. Elements in groups I and II of the periodic table, and some
in group III form metallic crystals. In a metal, the outer electrons are shared among all the
atoms in the solid. Each atom gives up its outer electrons and becomes slightly positively
charged. The negatively charged electrons hold the metal atoms together. Since the
electrons are free to move, they lead to good thermal and electrical conductivity.
Figure 2.1 Metallic bond
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2.1.2. Ionic Bonds
Atoms like to have a filled outer shell of electrons. Sometimes, by transferring electrons
from one atom to another, electron shells are filled. The donor atom will take a positive
charge, and the acceptor will have a negative charge. The charged atoms or ions will be
attracted to each other, and form bonds. Ionic bond is created between two unlike atoms
with different electro-negativities. When sodium donates its valence electron to chlorine,
each becomes an ion; attraction occurs, and the ionic bond is formed.
Figure 2.2 Ionic bond in NaCl
2.1.3. Covalent Bonds
The cohesive forces in covalent crystals arise from the sharing of an electron-pair
between each two atoms. Covalent bonds are called directional because the atoms tend
to remain in fixed positions with respect to each other. As a result, covalent bonds result
in poor electrical and thermal conductivity. Covalent bonding requires that electrons be
shared between atoms in such a way that each atom has its outer sp orbital filled. In
silicon, with a valence of four, four covalent bonds must be formed. Examples include
diamond. Silicon, germanium, and silicon carbide are among the crystals having the same
structure as that of diamond. Silicon has a valence of four and shares electrons with four
oxygen atoms, thus giving a total of eight electrons for each silicon atom. However,
oxygen has a valence of six and shares electrons with two silicon atoms, giving oxygen a
total of eight electrons. Tetrahedral structure of silica (Si02) contains covalent bonds
between silicon and oxygen atoms.
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Figure 2.3 Tetrahedral structure of silica (Si02) (covalent bonds between silicon and oxygen atoms)
2.1.4. Hydrogen Bonds
Hydrogen bonds are common in covalently bonded molecules which contain hydrogen,
such as water (H2O). Since the bonds are primarily covalent, the electrons are shared
between the hydrogen and oxygen atoms. However, the electrons tend to spend more
time around the oxygen atom. This leads to a small positive charge around the hydrogen
atoms, and a negative charge around the oxygen atom. When other molecules with this
type of charge transfer are nearby, the negatively charged end of one molecule will be
weakly attracted to the positively charged end of the other molecule. The attraction is
weak because the charge transfer is small. Van der Waals bonds are very weak compared
to other types of bonds. These bonds are especially important in noble gases which are
cooled to very low temperatures. At any given point in time, the electrons may be slightly
shifted to one side of an atom, giving that side a very small negative charge. This may
cause an attraction to a slightly positively charged atom nearby, creating a very weak
bond.
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2.2. Crystal Structures
Crystalline solids have a very regular atomic structure: that is, the local positions of
atoms with respect to each other are repeated at the atomic scale. These arrangements are
called crystal structures, and their study is called crystallography. All metals and alloys
are crystalline solids, and most metals assume one of three different lattice, or crystalline,
structures as they form: body-centered cubic (BCC), face-centered cubic (FCC), or
hexagonal close-packed (HCP). Lattice is a collection of points that divide space into
smaller equally sized segments. Unit cell is a subdivision of the lattice.
Figure 2.4 Atomic arrangement for simple cubic (SC), body centered cubic (BCC), and
face-centered cubic (FCC) unit cells.
A number of metals are shown below with their room temperature crystal structure
indicated.
Aluminum (FCC) Chromium (BCC) Copper (FCC) Iron (alpha) (FCC)
Iron (gamma) (BCC) Iron (delta) (BCC) Lead (FCC) Nickel (FCC)
Silver (FCC) Titanium (HCP) Tungsten (BCC) Zinc (HCP)
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2.2.1. Number of Lattice Points in Cubic Crystal Systems The number of lattice points per cell in the cubic crystal systems if there is only one atom
located at each lattice point can be calculated. The number of atoms per unit cell would
be 1, 2, and 4, for the simple cubic, body-centered cubic and face-centered cubic, unit
cells, respectively.
In the SC unit cell: lattice point / unit cell = (8 corners)1/8 = 1
In BCC unit cells: lattice point / unit cell = (8 corners)1/8 + (1 center)(1) = 2
In FCC unit cells: lattice point / unit cell = (8 corners)1/8 + (6 faces)(1/2) = 4
2.2.2. Relationship between Atomic Radius and Lattice Parameters
Referring to Figure 2.6, we find that atoms touch along the edge of the cube in SC
structures.
In BCC structures, atoms touch along the body diagonal. There are two atomic radii from
the center atom and one atomic radius from each of the corner atoms on the body
diagonal, so
In FCC structures, atoms touch along the face diagonal of the cube. There are four atomic
radii along this length—two radii from the face-centered atom and one radius from each
corner, so:
Figure 2.5 Relationships between the atomic radius and the Lattice parameter.
ra 20 =
34
0ra =
24
0ra =
16
2.2.3. Packing Factor Linear density - The number of lattice points per unit length along a direction. Packing
fraction - The fraction of a direction (linear-packing fraction) or a plane (planar-packing
factor) that is actually covered by atoms or ions. In a FCC cell, there are four lattice
points per cell; if there is one atom per lattice point, there are also four atoms per cell.
The volume of one atom is 4�r3/3 and the volume of the unit cell is a0 3
2.2.4. Density Example: Determine the density of BCC iron, which has a lattice parameter of 0.2866 nm. Atoms/cell = 2, a0 = 0.2866 nm = 2.866 ×××× 10-8 cm
Atomic mass = 55.847 g/mol
Volume of unit cell = = (2.866 ×××× 10-8 cm)3 = 23.54 ×××× 10-24 cm3/cell
Avogadro’s number NA = 6.02 ×××× 1023 atoms/mol
74.018)2/4(
)34
(4)( Factor Packing
24r/ cells,unit FCCfor Since,
)34
)(atoms/cell (4 Factor Packing
3
3
0
30
3
≅==
=
=
ππ
π
r
r
r
aa
32324 /882.7
)1002.6)(1054.23()847.55)(2(
number) sadro'cell)(Avogunit of (volumeiron) of mass )(atomicatoms/cell of(number
Density
cmg=××
=
=
−ρ
ρ
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2.3. Drawing Direction and Plane Draw (a) the [12-1] direction and (b) the [2-10] plane in a cubic unit cell.
Figure 2.6 Construction of a (a) direction and (b) plane within a unit cell
2.3.1. Miller Indices of points and Directions
Determine the Miller indices of directions A, B, and C
Figure 2.7 Crystallographic directions
and coordinates.
Direction B
1. Two points are 1, 1, 1 and 0, 0, 0
2. 1, 1, 1, -0, 0, 0 = 1, 1, 1
3. No fractions to clear or integers to reduce
4. [111]
Direction A
1. Two points are 1, 0, 0, and 0, 0, 0
2. 1, 0, 0, -0, 0, 0 = 1, 0, 0
3. No fractions to clear or integers to reduce
4. [100]
Direction C
1. Two points are 0, 0, 1 and 1/2, 1, 0
2. 0, 0, 1 -1/2, 1, 0 = -1/2, -1, 1
3. 2(-1/2, -1, 1) = -1, -2, 2
2]21[ .4
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2.3.2. Miller Indices of Planes Determine the Miller indices of planes A, B, and C
Figure 2.8 Crystallographic planes and intercepts
Plane B
1. The plane never intercepts the z axis, so x = 1, y = 2, and z =
2.1/x = 1, 1/y =1/2, 1/z = 0
3. Clear fractions:
1/x = 2, 1/y = 1, 1/z = 0
4. (210) Plane A
1. x = 1, y = 1, z = 1
2.1/x = 1, 1/y = 1,1 /z = 1
3. No fractions to clear
4. (111)
Plane C
1. We must move the origin, since the plane passes through 0, 0, 0. Let’s move the origin one lattice parameter in the y-direction. Then, x = � , y = -1, and z = �
2.1/x = 0, 1/y = 1, 1/z = 0
3. No fractions to clear.
4 (o1-o) Examples: --------------------
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2.4. Planar Density and Packing Fraction Calculate the planar density and planar packing fraction for the (010) and (020) planes in
simple cubic polonium, which has a lattice parameter of 0.334 nm.
Figure 2.9 Planer densities of the (010) and (020) planes in SC unit cells.
The planar packing fraction is given by:
However, no atoms are centered on the (020) planes. Therefore, the planar density and
the planar packing fraction are both zero. The (010) and (020) planes are not equivalent!
2142
2
atoms/cm 1096.8atoms/nm 96.8
)334.0(faceper atom 1
face of areafaceper atom
(010)density Planar
×==
==
79.0)2(
)()( atom) 1(
face of areafaceper atoms of area
(010)fraction Packing
2
2
20
2
==
==
rr
ra
π
π
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2.5. Imperfection in solids
Defects play a major role in determining the physical, electrical, optical and magnetic
properties of a material. Most crystalline materials are not perfect: the regular pattern of
atomic arrangement is interrupted by crystal defects. Defects affect the mechanical
properties via control of the slip or deformation process, strain hardening, and solid
solution and grain size strengthening.
� Point defects - Imperfections, such as vacancies, that are located typically at one
(in some cases a few) sites in the crystal. In some materials, neighboring atoms
actually move away from a vacancy, because they can better form bonds with
atoms in the other directions. This allows for increased atomic diffusion and
maintains charge balance.
� Vacancy - An atom or an ion missing from its regular crystallographic site. If a
neighboring atom moves to occupy the vacant site, the vacancy moves in the
opposite direction to the site which used to be occupied by the moving atom.
� Substitutional defect is a point defect produced when an atom is removed from a
regular lattice point and replaced with a different atom, usually of a different size.
� Interstitials are atoms which occupy a site in the crystal structure at which there
is usually not an atom. Small atoms in some crystals can occupy interstices
without high energy, such as hydrogen in palladium. Interstitial defect is a point
defect produced when an atom is placed into the crystal at a site that is normally
not a lattice point.
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Figure 2.10 Point defects: (a) vacancy, (b) interstitial atom, (c) small substitutional
atom, (d) large substitutional atom, (e) Frenkel defect, (f) Schottky defect.
� Line defects: Plane of atoms is displaced or dislocated from its regular lattice
space. Act to reduce the strength and stiffness of the solid as there is already an
increase in energy along the dislocation, so less energy must be added to move the
planes or break the bonds at this location. Many line defects will act to strengthen
a material as they interfere with the progression of dislocations
� Dislocations are linear defects around which some of the atoms of the crystal
lattice are misaligned. There are two basic types of dislocations, the Edge
dislocation and the Screw dislocation. ("Mixed" dislocations combining aspects
of both types are also common). Mixed dislocation - A dislocation that contains
partly edge components and partly screw components.
� Edge dislocation- A dislocation introduced into the crystal by adding an ‘‘extra
half plane’’ of atoms.
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Figure 2.11 The perfect crystal in (a) is cut and an extra plane of atoms is inserted (b).
The bottom edge of the extra plane is an edge dislocation (c). A Burgers vector b is
required to close a loop of equal atom spacings around the edge dislocation. (Adapted
from J.D. Verhoeven, Fundamentals of Physical Metallurgy, Wiley, 1975.)
� Screw dislocation- A dislocation produced by skewing a crystal so that one
atomic plane produces a spiral ramp about the dislocation.
Figure 2.12 the perfect crystal (a) is cut and sheared one atom spacing, (b) and (c). The
line along which shearing occurs is a screw dislocation. A Burgers vector b is required to
close a loop of equal atom spacings around the screw dislocation. (Adapted from J.D.
Verhoeven, Fundamentals of Physical Metallurgy, Wiley, 1975.)
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• Grain size: A larger grain size number (GS#) by ASTM standards indicates a higher
number of grains and grain boundaries per unit volume. In general, a fine-grained
structure is stronger than a coarse one for a given material at normal temperatures.
• Grain boundaries: At grain boundaries, there is a transition zone where atoms are
not aligned with either grain. Their size is typically 1 to 2 atomic distances wide. Less
efficient packing occurs at grain boundaries and they have higher energy. Surface
corrosion can occur at the grain boundaries. However, grain boundaries, which are
not aligned, also prevent slip planes from progressing and resulting in fracture at
normal temperatures. Grain boundaries interfere with the movement of atoms during
deformation. Grain boundaries are a source of weakness above temperatures where
atoms start to move significantly.
• Grain shape: the main types of grain shapeare;
o Equiaxed - approximately equal dimensions in 3 directions
o Plate-like - one dimension smaller than other two
o Columnar - one dimension larger than other two
o Dendritic (tree-like)
� Grain Orientation: Crystal orientations within grains are typically random for
metals. Preferred orientation can be manipulated to obtain improved material
properties (such as magnetic permeability)
Figure 2.13 (a) The atoms near the boundaries of the three grains do not have an
equilibrium spacing or arrangement. (b) Grains and grain boundaries in a stainless steel
sample. (Courtesy Dr. A. Deardo.)
� Anti phase boundaries occur in ordered alloys: in this case, the
crystallographic direction remains the same, each side of the boundary has an
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opposite phase: For example if the ordering is usually ABABABAB, an anti
phase boundary takes the form of ABABBABA.
� Stacking faults occur in a number of crystal structures, but the common example
is in close packed structures. Face centered cubic (fcc) structures differ from
hexagonal close packed (hcp) structures only in stacking order: both structures
have close packed atomic planes with six fold symmetry.
� Voids are small regions where there are no atoms, and can be thought of as
clusters of vacancies. Impurities can cluster together to form small regions of a
different phase. These are often called precipitates.
References Books:
1. Hagen Kleinert, Gauge Fields in Condensed Matter, Vol. II, "STRESSES AND
DEFECTS", pp. 743-1456, World Scientific (Singapore, 1989).
2. Van Vlack, L.H., Elements of Materials Science and Engineering, 5th Ed.,
Addison-Wesley Publishing Co., Reading, MA, 1985.
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UNIT THREE: PHASE DIAGRAMS & HEAT-TREATMENT
Objective
- Understand different types of Phase Diagrams - Know different types of Heat Treatment
o Annealing o Normalizing o Hardening and tempering o Understand Iron-carbon equilibrium diagram (Fe-C Phase Diagram)
Outline
- Engineering Alloys
o Phase Diagrams o Metallic Materials- Heat Treatment o Iron-carbon equilibrium diagram (Fe-C Phase Diagram)
- Types of Heat Treatments
o Annealing
o Normalizing
o Hardening and tempering
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UNIT THREE: PHASE DIAGRAMS & HEAT-TREATMENT
3.1. Engineering Materials
For convenience most engineering materials are divided into three main classes; metallic,
polymeric (plastics), and ceramic materials.
• Metals (ferrous and non ferrous)
• Ceramics, Glasses, glass- ceramics
• Polymers, Optical fibers,
• Composite materials, and
• Electronic Materials
3.2.Metals
• Iron and Steel
• Alloys and Superalloys (e.g. aerospace applications)
• Intermetallic Compounds (high-temperature structural materials)
3.2.1. Distinguishing features of Metals
• Atoms arranged in a regular repeating structure, Relatively strong and Dense
• Malleable or ductile: high plasticity, Resistant to fracture: tough
• Excellent conductors of electricity and heat
• Opaque to visible light and Shiny appearance
3.2.2. Applications of metals
• Electrical wiring, Structures: buildings, bridges, etc.
• Automobiles: body, chassis, springs, engine block, etc.
• Airplanes: engine components, fuselage, landing gear assembly, etc.
• Trains: rails, engine components, body, wheels
• Machine tools: drill bits, hammers, screwdrivers, saw blades, etc.
• Shape memory materials and Magnets
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• Examples of metal alloys include stainless steel which is an alloy of iron, nickel,
and chromium; and gold jewelry which usually contains an alloy of gold and
nickel.
• Pure metal elements (Cu, Fe, Zn, Ag, etc.)
• Alloys (Cu-Sn=bronze, Cu-Zn=brass, Fe-C=steel, Pb-Sn=solder, Nitinol)
• Intermetallic compounds (e.g. Ni3Al)
3.2.3. Properties of Metals and Metal Alloys
Density is defined as a material's mass divided by its volume. Most metals have
relatively high densities, especially compared to polymers.
Many metals and alloys have high densities and are used in applications which require a
high mass-to-volume ratio. Some metal alloys, such as those based on Aluminum or
magnesium, have low densities and are used in aerospace applications for fuel economy.
Melting point and strength: The strength of a metal derives from the electrostatic
attraction between the lattice of positive ions and the fluid of valence electrons in which
they are immersed. In general, the transition metals with their valence-level d electrons
are stronger and have higher melting points: Fe, 1535°C; Os 3700°C; W 3370°C.
Electrical conductivity: In order for a substance to conduct electricity, it must contain
charged particles (charge carriers) that are sufficiently mobile to move in response to an
applied electric field. The conductivity of an electrolytic solution decreases as the
temperature falls due to the decrease in viscosity which inhibits ionic mobility. Silver is
the most conductive metal, followed by copper, gold, and aluminum.
Thermal conductivity: The high thermal conductivity of metals is attributed to
vibrational excitations of the fluid-like electrons; this excitation spreads through the
crystal far more rapidly than it does in non-metallic solids which depend on vibrational
motions of atoms which are much heavier and possess greater inertia.
Appearance: When light falls on a metal, its rapidly changing electromagnetic field
induces similar motions in the more loosely-bound electrons near the surface. A vibrating
28
charge is itself an emitter of electromagnetic radiation, so the effect is to cause the metal
to re-emit, or reflect, the incident light, producing the shiny appearance.
Malleability and ductility: These terms refer respectively to how readily a solid can be
shaped by pressure (forging, hammering, rolling into a sheet) and by being drawn out into
a wire. The bonding within ionic or covalent solids may be stronger, but it is also
directional, making these solids subject to fracture (brittle) when struck with a hammer,
for example. A metal, by contrast, is more likely to be simply deformed or dented.
Fracture Toughness can be described as a material's ability to avoid fracture, especially
when a flaw is introduced. Many metal alloys also have high fracture toughness, which
means they can withstand impact and are durable. Many metals have high strength,
stiffness, and good ductility. Because each ion is surrounded by the electron fluid in all
directions, the bonding has no directional properties; this accounts for the high
malleability and ductility of metals.
Changing the properties of metals by alloying: alloying addition to the metals affect
properties of metals (i.e. density, strength, fracture toughness, plastic deformation,
electrical conductivity and environmental degradation).
3.3. Engineering Alloys
Metals and alloys have many useful engineering properties and so have wide spread
application in engineering designs. Iron and its alloys (principally steel) account for about
90 percent of the world's production of metals mainly because of their combination of
good strength, toughness, and ductility at a relatively low cost.
Each metal has special properties for engineering designs and is used after a comparative
cost analysis with other metals and materials. Alloys based on iron are called ferrous
alloys, and those based on the other metals are called nonferrous alloys. The study of
metallic alloys; ferrous (steels and cast irons) or non-ferrous, requires two basic topics;
phase diagram and heat treatment.
29
3.3.1. PHASE DIAGRAMS
Different crystalline structures exist within the same alloy. Each of these different
structures is called a phase, and the alloy-which is a mixture of these different crystalline
structures-is called a multiphase alloy. These different phases can be distinguished under
a microscope when the alloy is polished and etched.
Solutions: There are two types of solid solution: substitution solid solution and
interstitial solid solution. Solution based alloys are typically stronger than pure materials
as the solute atoms interfere with the movement of dislocations (solution hardening).
Solid solution alloys: Brass (zinc in copper solution), Bronze (tin in copper solution),
and Copper-nickel alloys (nickel in copper solution).
Substitutional Solid Solution: The new metal dissolves in the base metal to form a
substitutional solid solution when both atoms are similar in crystal structure (i.e. both are
FCC or BCC), difference in volume less than 15% and they are close to each other in the
emf series. Examples: copper dissolved in nickel, gold dissolved in silver,
Interstitial Solid Solution: The new metal dissolves in the base metal to form a
interstitial solid solution when both atoms are different in crystal structure, difference in
volume large than 15% and they are far from each other in the emf series. The result is
usually an increase in tensile strength and a decrease in elongation. Examples: carbon
and nitrogen dissolved in iron and other metals.
Mixtures: A mixture of two materials involves the combination of two different
structures of material without affecting either individual structure. It involves placing one
phase within another phase of the material either physically or by some chemical process.
Transition between solid solutions, various mixtures, and other phases (liquids or gases)
can be determined from phase diagrams. Define phases and combinations as a function of
temperature and % composition. Phase distribution and shape in a mixture also form part
of the microstructure. Examples: Stones in cement to form concrete and Graphite in
many forms of cast iron
30
Phase Diagrams: Describe the coexistence of phases of a material over a range of
temperatures and compositions. Can be used to determine (for a given temperature and
composition)
1. The stable phases of the material
2. The chemical compositions of the phases
3. The quantity of each phase present under equilibrium conditions
Each phase will have different properties at different compositions. Each mixture will
have different properties at different quantities of each phase. The properties of a phase
or mixture will also vary with temperature. Examples: Salt Water and Lead-Tin System
(Pb-Sn Solder)
1. To determine the phases present at a given temperature/composition:
• Find point on diagram corresponding to temperature/overall composition
• Look at region in which point falls
• Will list phases (ie. salt + water, or alpha + beta)
• A single listed phase indicates a solution (ie. brine)
• Two or more listed phases indicates a mixture (ie. salt + water)
• If temperature/composition point lies on a point of intersection between
three regions, this is termed a eutectic point and all three adjoining phases
are present
2. To determine the composition of the phases present:
For a solution: Composition of a solution is the same as the overall composition of the
material
For a mixture:
• Trace horizontal line across isotherm (temperature line) to each edge of
region
31
• Drop vertical line down to determine the composition of the phase (in
terms of component materials) at that temperature
• Composition of each phase of mixture is that of phase alone at the that
temperature where it transitions between existing as a pure solution and
existing as part of a mixture
1. To determine the amount of each phase present (mass fraction):
For a solutions: by definition, are composed of 100 percent of the single phase
For mixtures
- Perform a materials balance (inverse lever rule).
• Percent alpha = (C-beta - C-x)/(C-beta - C-alpha)
• C-x is the composition of the phase or mixture (x) in terms of one of the
two component materials (i.e. Amount of lead in alpha, beta, and the total
material)
• Percent beta = 1 - percent alpha
Examples:
1- Use the given Cu-Ni phase diagram to find the weight relative percentage of Liquid and Solid
in alloys containing: 20, 50 and 70 weight % Cu, at 1400, 1250, 1200 0 C, respectively.
32
Figure 3.1. Cu-Ni Phase Diagram
2- Use the given Pb-Sn phase diagram to find the weight relative percentage of Liquid and Solid
in alloys containing: 10, 40 and 80 weight % Sn, at 100, 200, 250 and 3000C, respectively.
Figure 3.2. Pb-Sn Phase Diagram
3. With reference to Fe-Fe3C phase diagram, answer the following questions:
i. Sketch the cooling curve and microstructure for alloys A (pretectic), E (eutectoid), B (hyper-eutectoid) and Eutectic
33
ii. The number of phases and relative amounts of each phase for the alloys containing 0.2, 0.4, 0.8% and 1 % carbon, at 1600, 950, 700, and after equilibrium cooling to room temperature. The structure of the alloys containing 0.2, 0.4 0.8% and 1 % carbon at RT.
Iron (Fe)-Iron Carbide (Fe3C) Phase Diagram
Figure. 3.3. Fe-Fe3C Phase Diagram (Materials Science and Metallurgy,
4th ed., Pollack, Prentice-Hall, 1988)
34
Heat Treatment
Steel � Carbon Steel:
� Low C < 0.2 �
� Medium 0.4 < C < 0.8 �
� High C > 1 �
Alloy Steel:
� Low, steel has < 2 � alloying additions as Cr, Mo, Ni, Mn.
� High, steel has > 2 � alloying additions as Cr, Ni in St.St.
Stainless steel:
� � St.St Cr > 12 � , Ni > 8 � with low carbon.
� � St.St Cr > 12 � with low carbon.
� M St.St Cr > 12 � , with high carbon.
TYPES OF HEAT TREATMENTS � ANNEALING � Annealing refers to heating the material to predetermined temperature, soaking at a
temperature, and then cooling it slowly, normally in furnace.
Aims of annealing & Types:
� Improvement of the mechanical properties " Full annealing"
� Homogenisation of ingots of steel and alloy steel "Homogenisation annealing"
� Restore ductility of cold work steel "recrystallisation"
� Improve the machinability and formability for steel "Spherodisation annealing"
� Relieve the internal stresses " stress relieve annealing" Temperature of annealing For hypo-eutectoid and eutectoid steel � Ac3 +50˚c Temperature of annealing For hyper-eutectoid steels � Ac1 + 50˚c
35
NORMALIZING � NORMALIZING is the process of heating steel to region to single phase austenitic
region to get homogenous austenite by soaking there for 20 min/cm of section and
allowing to cool freely in air.
Aims of normalizing:
� To refine the coarse grains of steel casting.
� To increase machinability of low carbon steel. -
� To improve the mechanical properties of plain carbon steel. -
Temperature of normalizing For hypo- eutectoid steels � Ac3 + 50˚c
Temperature of normalizing For hyper-eutectic and eutectoid steel� Ac1 +50
Fig 3.5 Effect of annealing and normalizing on steel
Annealing Normalizing
a-lower hardness with high ductility. b-grain size is coarser. c-microstructure is less uniform.
a-higher hardness with low ductility. b- grain size obtained is fine. c-microstucture is more uniform.
36
� HARDENING HARDENING is the process of heating steel to proper austeniting temperature and
soaking at this temperature to get fine grained and homogenous austenite. Austenite
transforms to martensite, and the steel become hard when cooling the steel at a rate faster
than the critical rate. Such cooling is called quenching, Carbon steel are quenched in
water and alloy steel in oil.
Figure 3.6 Hardening Temperature Range # Aims of hardening:
� Main aim of hardening is to induce high hardness.
� Many machine parts are hardened to induce high wear resistance.
� To develop high yield strength with good toughness and ductility Temperature of hardning For hypo- eutectoid steels � Ac3 +50˚c Temperature of hardning For hyper-eutectic and eutectoid steel � Ac1 +50
37
� TEMPERING
Quenching makes austenite to transform to martensite. Martensite is a hard and brittle.
Quenching stresses may cause cracks even later on when in use. We know that martensite
is a supersaturated solid solution of carbon in iron (BCT), it rejects on heating, carbon on
the form of fine carbide and these takes place some of decrease of hardness with increase
with ductility i.e. the properties of martensite can be modified
It is necessary, therefore, to warm the steel below the critical range in order to relieve
stresses and to allow the arrested reaction of cementite precipitation to take place. This is
known as tempering.
# Aims of Tempering:
� To relieve quenching stresses developed during hardening. -
� To restore ductility and toughness with decrease in hardness and strength.
� To improve magnetic properties
4.1.1 Stages of Tempering
• 150-250°C. The object is heated in an oil bath, immediately after quenching, to
prevent related cracking, to relieve internal stress and to decompose austenite
without much softening.
• 200-450°C. Used to toughen the steel at the expense of hardness. Brinell
hardness is 350-450.
• 450-700°C. The precipitated cementite coalesces into larger masses and the steel
becomes softer. The structure is known as sorbite, which at the higher
temperatures becomes coarsely spheroidised. Sorbite is commonly found in
heat-treated constructional steels, such as axles, shafts and crankshafts subjected
to dynamic stresses.
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UNIT FOUR: FERROUS AND NON FERROUS ALLOYS
Objective
- Understand different types of steels and cast irons - Know different application of steels and cast irons
Outline
- Steel Alloys o Carbon Steels
o Low Alloy Steels
o Tool Steels
o Stainless steels
- Applications of Steels
- Cast Iron - Nonferrous Alloys
39
UNIT FOUR: FERROUS AND NON FERROUS ALLOYS
4.1. Steel Alloys
Steel Alloys can be divided into five groups
1. Carbon Steels
2. High Strength Low Alloy Steels
3. Quenched and Tempered Steels
4. Heat Treatable Low Alloy Steels
5. Chromium-Molybdenum Steels
Carbon Steels
Carbon steels contain up to 2% total alloying elements and can be subdivided into low-
carbon steels, medium-carbon steels, high-carbon steels, and ultrahigh-carbon steels.
• Low-carbon steels include those in the AISI series C-1008 to C-1025, contain up
to 0.30 weight percent C. The largest category of this class of steel is flat-rolled
products (sheet or strip) usually in the cold-rolled and annealed condition. The
carbon content for these high-formability steels is very low, less than 0.10 weight
percent C, with up to 0.4 weight percent Mn. Typical uses are in automobile body
panels, tin plate, and wire products.
• Medium-carbon steels include those in the AISI series C-1020 to C-1050.
Similar to low-carbon steels except that the carbon ranges from 0.30 to 0.60
weight percent and the manganese from 0.60 to 1.65 weight percent. Increasing
the carbon content to approximately 0.5 weight percent with an accompanying
increase in manganese allows medium-carbon steels to be used in the quenched
and tempered condition. The uses of medium carbon-manganese steels include
shafts, axles, gears, crankshafts, couplings and forgings. Steels in the 0.40 to
0.60% C range are also used for rails, railway wheels and rail axles.
• High-carbon steels contain from 0.60 to 1.00 weight percent C with manganese
contents ranging from 0.30 to 0.90weight percent. High-carbon steels are used for
spring materials and high-strength wires.
40
• Ultrahigh-carbon steels are experimental alloys containing 1.25 to 2.0% C.
These steels are thermomechanically processed to produce ultrafine, equiaxed
grains of spherical, discontinuous proeutectoid carbide particles.
Low Alloy Steels
High-strength low-alloy (HSLA) steels, or microalloyed steels, are designed to provide
better mechanical properties and/or greater resistance to atmospheric corrosion than
conventional carbon steels. They are designed to meet specific mechanical properties
rather than a chemical composition. The HSLA steels have low carbon contents (0.50 to
~0.25 weight percent C) in order to produce adequate formability and weldability, and
they have manganese contents up to 2.0 weight percent. Small quantities of chromium,
nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium and zirconium are
used in various combinations.
HSLA Classification:
1. Weathering steels, exhibit superior atmospheric corrosion resistance
2. Control-rolled steels, hot rolled according to a predetermined rolling schedule,
designed to develop a highly deformed austenite structure that will transform to
a very fine equiaxed ferrite structure on cooling
3. Pearlite-reduced steels, strengthened by very fine-grain ferrite and precipitation
hardening but with low carbon content and no pearlite in the microstructure
4. Microalloyed steels, with very small additions of such elements as niobium,
vanadium, and/or titanium for refinement and/or precipitation hardening
5. Acicular ferrite steel, very low carbon steels with sufficient hardenability to
transform on cooling to a very fine high-strength acicular ferrite structure.
6. Dual-phase steels, processed to a micro-structure of ferrite containing small
uniformly distributed regions of high-carbon martensite, resulting in a product
with low yield strength and a high rate of work hardening, thus providing a
high-strength steel of superior formability.
41
• Low-alloy steels constitute a category of ferrous materials that exhibit mechanical
properties superior to plain carbon steels as the result of additions of alloying
elements such as nickel, chromium, and molybdenum. Total alloy content can
range from 2.07% up to levels just below that of stainless steels, which contain a
minimum of 10% Cr.
• Low Nickel Chrome Steels in this group include the AISI 3120, 3135, 3140,
3310, and 3316. In these steels, carbon ranges from 0.14-0.34%, manganese from
0.40-0.90%, silicon from 0.20-0.35%, nickel from 1.10-3.75% and chromium
from 0.55-0.75%. Thin sections of these steels in the lower carbon ranges can be
welded without preheat. A preheat of 100-1500C is necessary for carbon in the
0.20% range, and for higher carbon content a preheat of up 3200C should be used.
• Low Manganese Steels included in this group are the AISI type 1320, 1330,
1335, 1340, and 1345 designations. In these steels, the carbon ranges from 0.18-
0.48%, manganese from 1.60-1.90%, and silicon from 0.20-0.35%. Preheat is not
required at the low range of carbon and manganese. Preheat of 120-1500C is
desirable as the carbon approaches 0.25%, and mandatory at the higher range of
manganese. Thicker sections should be preheated to double the above figure. A
stress relief postheat treatment is recommended.
• Low Chromium Steels included in this group are the AISI type 5015 to 5160 and
the electric furnace steels 50100, 51100, and 52100. In these steels carbon ranges
from 0.12-1.10%, manganese from 0.30-1.00%, chromium from 0.20-1.60%, and
silicon from 0.20-0.30%. When carbon is at low end of the range, these steels can
be welded without special precautions.
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Summary: Below is a list of some SAE-AISI designations for Steel (the xx in the last
two digits indicate the carbon content in hundredths of a percent)
Carbon Steels
10xx Plain Carbon
11xx Resulfurized
12xx Resulfurized and rephosphorized
Manganese steels
13xx Mn 1.75
Nickel steels
23xx Ni 3.5
25xx Ni 5.0
Nickel Chromium Steels
31xx Ni 1.25 Cr 0.65-0.80
32xx Ni 1.75 Cr 1.07
33xx Ni 3.50 Cr 1.50-1.57
34xx Ni 3.00 Cr 0.77
Chromium Molybdenum steels
41xx Cr 0.50-0.95 Mo 0.12-0.30
Nickel Chromium Molybdenum steels
43xx Ni 1.82 Cr 0.50-0.80 Mo 0.25
47xx Ni 1.05 Cr 0.45 Mo 0.20 – 0.35
86xx Ni 0.55 Cr 0.50 Mo 0.20
Nickel Molybdenum steels
46xx Ni 0.85-1.82 Mo 0.20
48xx Ni 3.50 Mo 0.25
Chromium steels
50xx Cr 0.27- 0.65
51xx Cr 0.80 – 1.05
Tool Steels used for making tools, punches, and dies are perhaps the hardest, the
strongest, and toughest steels used in industry. Certain tool steels are made for producing
die blocks; some are made for producing molds, others are made for hot working, and
still others for high-speed cutting applications.
A list of tool and die steels.
43
AISI-SAE
Types Classification of Tools Steels
Composition %
C Cr V W Mo Other
W1 Water hardening 0.60 - - - - -
S5 Shock resisting 0.55 - - - 0.40 0.80 Mn- 2.00
Si
O1 Oil hardening 0.90 0.50 - 0.5 - -
A2 Cold work 1.00 5.00 - - 1.00 -
A4 Medium alloy air hardening 1.00 1.00 - - 1.00 2.00 Mn
D2 Cold work High carbon
High chromium 1.50 12.0 - - 1.00 -
M1 Cold work 0.80 4.00 1.00 1.5 8.00 -
M2 Molybdenum 0.85 4.00 2.00 6.0 5.00 -
H11 Hot work 0.35 5.00 0.40 - 1.50 -
P20 Die casting mold 0.35 1.25 - - 0.40 -
Stainless steels usually contain less than 30% Cr and more than 50% Fe. They attain
their stainless characteristics because of the formation of an invisible and adherent
chromium-rich oxide surface film. Chromium alloys can be passivated to give excellent
corrosion resistance. Some other alloying elements added to enhance specific
characteristics include nickel, molybdenum, copper, titanium, aluminum, silicon,
niobium, and nitrogen. Carbon is usually present in amounts ranging from less than
0.03% to over 1.0% in certain martensitic grades.
Stainless steels are commonly divided into five groups:
1. Martensitic stainless steels
2. Ferritic stainless steels
3. Austenitic stainless steels
4. Duplex (ferritic-austenitic) stainless steels
5. Precipitation-hardening stainless steels.
44
Selecting a Stainless Steel
There are a large number of stainless steels produced. Corrosion resistance, physical
properties, and mechanical properties are generally among the properties considered
when selecting stainless steel for an application. A more detailed list of selection criteria
is listed below:
• Corrosion resistance
• Resistance to oxidation and sulfidation
• Toughness
• Cryogenic strength
• Resistance to abrasion and erosion
• Resistance to galling and seizing
• Surface finish
• Magnetic properties
• Retention of cutting edge
• Ambient strength
• Ductility
• Elevated temperature strength
• Suitability for intended cleaning
procedures
• Stability of properties in service
• Thermal conductivity
• Electrical resistivity
• Suitability for intended fabrication
Applications of Steels
• Structural steels
• Pearlite Reduced Steel.
• Grain refinement.
• Precipitation Hardening.
• By controlled hot rolling
• Maraging Steels
• Alloy spring steels
• High and Low Thermal Expansion Steels
• Creep-resisting Steels for Use at Steam Temperatures:
45
4.2. CAST IRON
Cast iron has higher carbon and silicon contents than steel i.e. 2% C or more and 2-
3%Si. Carbon exists as free graphite in all types of cast iron except in white cast iron (as
intermetallic compound Fe3C called cementite). There are four basic types of cast iron:
1. White cast iron: hard, brittle, and not weldable.
2. Malleable cast iron: ductile, weldable, machinable and offers good strength and
shock resistance.
3. Gray cast iron: relatively soft, easily machined and welded. Main applications
(engine cylinder blocks, pipe, and machine tool structures).
4. Nodular or Ductile cast iron (spheroidal): ductile, malleable and weldable.
Graphite in nodules not flakes and matrix often pearlite.
1 2
3 4
Figure 4.1 Adapted from Fig. 11.3, Callister 7e Adapted from Fig. 11.3, Callister 7e
46
4.3.Non Ferrous Materials
Aluminum Alloys
The aluminum industry distinguishes one alloy from another through a standardized
numbering system. Wrought alloys use a four-digit designation while cast alloys use
three-digits. Various prefixes and suffixes are also used in both classes of aluminum.
Wrought Alloys: The first digit of the four-digits refers to the principal alloying element
used to identify the wrought aluminum alloy. For example, the fifth digit in a 5000-series
aluminum alloy indicates magnesium as the principal alloying addition. The second digit
refers to some particular modification of the original alloy composition. A suffix
consisting of a dash followed by a series of letters and numbers define the temper,
indicating certain properties and the process used to obtain them.
Age hardening alloy tempers
These suffixes begin with three possible letters: T - indicates a heat-treatable alloy, H -
indicates a non-heat-treatable alloy, O - indicates annealed material (not heat treated), F-
as fabricated, W: solution treated, but naturally aged, T1 to -T10: indicates a
combination of hot work, cold work, solution treatment, and aging
T1 Hot work, then naturally age
T2 Hot work, cold work, then naturally age
T3 Solution treat, cold work, then naturally age
T4 Solution treat, then naturally age
T5 Hot work, then artificially age
T6 Solution treat and artificially age
T7 Solution treat and stabilise (over age)
T8 Solution treat, cold work, then artificially age
T9 Solution treat, artificially age, then cold work
T10 Hot work, cold work, then artificially age
47
Cast Alloys: The first number in a three-digit cast alloy designation also indicates the
principal alloying element. However, this system does not parallel the one used for
wrought alloys. (The initial three indicates that the principal alloying element is
manganese in wrought alloys and silicon in cast alloys.) Modifications to a cast alloy
makeup are indicated by a letter prefix. Dash, letter, and number suffixes are also used to
describe the process in which to obtain particular mechanical properties. In both wrought
and cast aluminum materials, the particular alloying elements are critical to recycling but
temper states are not.
Aluminum alloy castings can be produced by virtually all casting processes in a very
large range of compositions possessing a wide variety of useful engineering properties.
The choice of a specific casting alloy depends on the chosen casting process (which
include: sand, permanent mold, die, lost foam, or squeeze), the product design, the
required properties of the product and other relevant factors.
Alloy Typical Applications
319.0 Manifolds, cylinder heads, blocks, internal engine parts
332.0 Pistons
356.0 Cylinder heads, manifolds
A356.0 Wheels
A380.0 Blocks, transmission housings/parts, fuel metering devices
383.0 Brackets, housings, internal engine parts, steering gears
B390.0 High-wear applications such as ring gears and internal transmission
parts
Cast products: Die castings are used for pistons, transmission housings, and suspension
components and aluminum metal matrix brake drums and rotors. Sand castings are used
for engine blocks, cylinder heads and manifolds. Structural castings are used for cross
members and body structures while, structural die castings are used for body structures.
Structural permanent mold castings are used for body structures and sub frames, and
permanent mold castings for wheels used on 45 percent of new passenger vehicles today.
48
Copper Alloys
Copper alloys are commonly used for their electrical and thermal conductivities,
corrosion resistance, ease of fabrication, surface appearance, strength and fatigue
resistance. Copper alloys can be readily soldered and brazed, and a number of copper
alloys can be welded by arc, and resistance methods. Color of copper alloys is a
significant reason for using them for decorative purposes. Copper is used extensively for
cables and wires, electrical contacts, and a wide variety of other parts that are required to
pass electrical current. Coppers alloys are used for automobile radiators, heat
exchangers, and home heating systems. Because of copper alloys corrosion resistance
they are used for pipes, valves, and fittings in systems carrying potable water, process
water, or other aqueous fluids.
Common classification of copper alloys is shown below:
Name Alloying elements
Coppers Cu
Brasses Cu-Zn
Leaded brasses Cu-Zn-Pb
Tin brasses Cu-Zn-Sn-Pb
Phosphor bronzes Cu-Sn-P
Leaded phosphor bronzes Cu-Sn-Pb-P
Copper-phosphorus and copper-silver-phosphorus alloys Cu-P-Ag
Aluminum bronzes Cu-Al-Ni-Fe-Si-Sn
Silicon bronzes Cu-Si-Sn
Copper-nickels Cu-Ni-Fe
Nickel silvers Cu-Ni-Zn
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Titanium and Titanium Alloys
The density of Titanium is roughly 55% that of steel. The density 4.5 g/cm3 as opposed to
7.9 g/cm3 for 316 SS and 8.3 g/cm3 for CoCrMo or 9.2 g/cm3 for CoNiCrMo alloys
Titanium alloys are extensively utilized for significantly loaded aerospace components.
Titanium is used in applications requiring somewhat elevated temperatures. Unalloyed
(commercially pure) titanium can be found in two crystallographic forms:
• Hexagonal close-packed (hcp) or alpha (�) phase is found at room temperature
• Body centered cubic (bcc) or beta (ß) phase is found above 883 °C (1621 °F)
The control of alpha (�) and beta (ß) phases through alloying additions and
thermomechanical processing is the basis for the titanium alloys used by industry today.
Titanium alloys are categorized as either alpha (�) alloys, beta (ß) alloys, or alpha+beta
(�+ß) alloys. Some common titanium alloys are listed below according to these
categories.
Alpha and near alpha alloys Alpha + Beta alloys Beta alloys
Ti-2.5Cu Ti-6Al-4V Ti-13V-11Cr-3Al
Ti-5Al-2.5Sn Ti-6Al-6V-2Sn Ti-8Mo-8V-2Fe-3Al
Ti-8Al-1V-1Mo Ti-6Al-2Sn-2Zr-2Cr-2Mo Ti-10V-2Fe-3Al
Ti-6242 Ti-3Al-2.5V Ti-15-3
One of the primary effect of alloying elements used in titanium production is the affect
on the alpha to beta transformation temperature. Some elements raise the alpha to beta
transformation temperature thereby stabilizing the alpha crystal structure. While other
elements lower the alpha to beta transformation temperature thereby stabilizing the beta
crystal structure. The effect of some elements is shown below:
Element Effect
Al and Sn alpha stabilizer
V, Mo, Cr, and Cu Beta stabilizer
50
Cobalt-Chromium Alloys
Two general compositions are: the first is CoCrMo which typically cast into the desired
form. Used for many years in dental implants and more recently used in artificial joints.
They have a good corrosion resistance. The second composition is CoNiCrMo which
normally hot forged. They have a high degree of corrosion resistance in salt water when
under stress. Cold-working can increase strength by more than 100 %. They have a poor
frictional properties and a higher fatigue and ultimate tensile strength than CoCrMo.
Good for components with long service life requirements. Cobalt and chromium are
dominant elements, forming a solid solution of up to 65 wt% Co. Molybdenum, when
added, produces finer grains.
Cobalt-Chromium Alloy Properties
Type Condition Tensile Strength
[MPa]
Yield Strength
[MPa] Elongation [%]
Cast CoCrMo (F76) 655 450 8
Wrought CoNiCrMo
(F562)
Solution
Annealed 795 - 1000 240 – 655 50
Cold-worked 1790 1585 8
Fully Annealed 600 276 50
References Physical metallurgy……………………………Vijendra Singh ENGINEERING MATERIALS 2…………….Michail F Ashby & David R H Jones
51
UNIT FIVE: POLYMERIC MATERIALS
Objective
- Polymeric Materials:
- Understand the mechanism of polymerization
- Polymer Processing
Outline
- Polymeric materials
� Main Applications and Examples
� Industrially Important Polymers
� Mechanisms of Polymerization
� The addition polymerization
� Condensation polymerization
- Classification of Polymers
� Thermoplastic polymers:
� Thermosetting polymers:
- Polymer Processing
52
UNIT FIVE: POLYMERIC MATERIALS
5.1- Polymeric materials:
Most polymeric materials consist of organic long molecular chains or networks.
Structurally, most polymeric materials are non-crystalline but some consist of mixtures of
crystalline & non- crystalline regions. The strength & ductility of polymeric materials
vary greatly. Because of the nature of their internal structure, most polymeric materials
are poor conductors of electricity. Some of these materials are good insulators and are
used for insulative applications. In general polymeric materials have low densities and
relatively low softening or decomposition temperatures. The term polymer is the correct
name for a group of materials commonly referred to as plastics. The reason these
materials are called plastics is that many of them exhibit plastic deformation or plastic
behavior. The term resin has also been used in reference to naturally occurring materials.
The terms; resins, Plastics and polymers are interchangeably used to describe these
materials. Polymer resins are a main component in many plastics. Most polymers are
synthetic materials that allow for a wide range of properties & applications.
Reinforced plastics constitute the most significant application of plastics (polymers) for
engineering structures, and their performance is limited by the properties of the plastics.
They composed primarily of C and H, and they have low melting temperature. Some are
crystals, many are not, and many have high plasticity. A few have good elasticity, some
are transparent, and some are opaque. Low density structures of non-metallic elements.
Poor thermal and electrical conductors
Main Applications and Examples
Main applications are films, foams, paints, fibers, and structural materials. The
microelectronics industry utilizes organic polymers in the fabrication of semiconductor
devices and as dielectrics between layers of semiconductors in advanced computer chips.
Plastics, Liquid crystals, Adhesives and glues, Containers, Moldable products (computer
casings, telephone handsets, disposable razors), Clothing and upholstery material (vinyls,
polyesters, nylon), Water-resistant coatings (latex), Biodegradable products, Biomaterials
53
(organic/inorganic intefaces), Low-friction materials (teflon), Synthetic oils and greases
and Gaskets and O-rings (rubber), Soaps and surfactants
Industrially Important Polymers
About 85% of the world plastics consumption is from just four polymers. These polymers
are produced in high volume at very low cost.
Polymer Repeat Unit Applications
Polyethylene (PE)
Electrical wire insulation, flexible tubing, squeeze bottles
Polypropylene (PP)
carpet fibers, ropes, liquid containers (cups, buckets,
tanks), pipes
Polystyrene (PS)
packaging foams, egg cartons, lighting panels, electrical
appliance components
Polyvinyl chloride
(PVC)
bottles, hoses, pipes, valves, electrical wire insulation,
toys, raincoats
5.1.1- Mechanisms of Polymerization
Since the properties and processability of the plastics depend on the structure and
chemical composition of the polymers from which it is made of, it is necessary to know
what the polymerization is.
Polymerization is the formation of chemical linkages between relatively small molecules
or monomers to form very large molecules or polymers. These linkages are formed by
either one or two of the following two types: addition or condensation. In the
polymerization process, a large unit molecule, the monomer, is added to another
monomer to form a larger chain, the polymer (referring to many parts), which has a
number of repeated units, mers. Mers are the smallest units recognizable in the chain. The
degree of polymerization is the number of the repeating units that have identical
structures within the chain formed by the polymer.
54
The addition polymerization process is characterized by the simple combination of
molecules without the generation of any by-products as a result of the combination. The
original molecules do not decompose to form reaction debris. When units of single
monomers are hooked together, the resulting product is a homopolymer, such as
polyethylene, that is made from the ethylene monomer. When two or more polymers are
used in the process, the product is a co-polymer. The formation of a homopolymer by
addition polymerization involves only one type of mer, where the formation of a co-
polymer involves more than one type and is referred to as co-polymerization.
Condensation polymerization involves the chemical reaction of two or more chemicals
to form a new molecule. The chemical union of two molecules can be only achieved by
the formation of a by-product molecule with atoms from the two molecules to create the
link for the polymerization to continue. This chemical reaction produces a condensate or
non-polymerizable byproduct, usually water. A catalyst is often required to start and
maintain the reaction. It can also be used to control the reaction rate.
Polymers are macromolecules, i.e., very large molecules. Large molecules entangle with
each other and lead to properties, such as the ability to form fibers and elastomers, which
can never be achieved with small molecules. Many polymer molecules are on the order of
hundreds of Angstroms in size, but others can be exceptionally large.
Polymer chains (organization of chain molecules within polymer) are typically; linear,
branched, or crosslinked. In a crosslinked polymer (also referred to as a network or
thermoset polymer), covalent bonds connect different chains, and quite literally the
molecular weight of such a material approaches infinity. Polymers that have covalent
crosslinks can either be soft (like a rubber band) or hard (like cured epoxy). Crosslinked
polymers are called thermosets because they cannot be re-processed into different shapes
upon heating without permanent chemical degradation. Linear and branched polymers
can be re-processed upon heating (or by dissolving them in a suitable solvent), and are
termed thermoplastics.
55
5.1.2- Polymeric structure
Polymers are a group of materials characterized by chains of molecules made up of
smaller units called monomers, a majority of which is joined artificially. Most polymers
are organic (carbon-based) materials that contain molecules composed of various
combinations of hydrogen, oxygen, nitrogen and carbon. These four elements are among
the most common found in organic polymers. Carbon forms the spine in the polymer
chain, and the other constituents attach themselves to the carbon. These polymer chains
become entangled and form irregular coils, which give them added strength.
Crystalline polymers usually contain regions of well-packed chains separated by
amorphous (liquid-like) regions. Pulling a fiber of a linear polymer causes the chains to
line up, and can induce crystallization. Besides viscosity, there are other factors that
influence the ability of a polymer to crystallize. One of them is the nature of the side
groups on the polymer chains. With very bulky side groups, or side groups that vary in an
irregular way, the chains have a hard time organizing into an ordered, crystalline solid.
This effect is important, because crystalline polymers tend to be much stiffer, harder, and
denser than amorphous polymers. A good example of this phenomenon is polypropylene,
which can be made in either atactic, isotactic, or syndiotactic forms.
56
The atactic form doesn't pack well and therefore is normally amorphous, and is used in
making garbage bags and other applications where flexible plastics are needed. The
isotactic form is crystalline at ordinary temperatures (its melting point is 160o), is
translucent and much stiffer, and is used to make jars, tupperware, etc. While small
molecules pretty much always form crystals upon cooling, polymers have another choice,
namely, they can form glasses. Crystallization requires quite a bit of chain re-orientation
(into a regular, ordered array), and if the chains are tangled enough or viscous enough,
then they will not "find" the crystalline arrangement before solidifying. The result is a
glassy solid in which the structure looks like the liquid, but the chains are no longer
mobile.
5.1.3- Classification of Polymers
The terms Thermoplastic and thermoset refer to the properties of polymers. Polymers are
separated into these two general classifications. In general, the properties of polymers
depend on the additives used, materials added to increase polymer's strength; the amounts
and properties of fillers used; coloring agents used; and plasticizers, which are added as
internal lubricants.
- Thermoplastic polymers:
Thermoplastic polymers are generally available in films, sheets, rods, tubing, and several
molded or extruded shapes. Thermoplastic polymers often exhibit plastic, ductile
properties. They can be formed at elevated temperatures, cooled, remelted, and reformed
into different shapes without changing the properties of the polymer. The properties of
thermoplastic polymers are determined by the bonding method between polymer chains;
in thermoplastic materials these bonds are weak. Common thermoplastic polymers
include acrylic, nylon, cellulose, polystyrene, fluorocarbons, and vinyl.
- Thermosetting polymers:
Thermosetting polymers have strong primary bonds, often formed by condensation
polymerization. Thermosetting polymers have strong primary bonds throughout, and their
structure resembles one large molecule. Once hardened, thermosets can not be softened
or reshaped, due to the loss of a part of the molecule during the curing process.
57
Important Characteristics of Polymers
Some important characteristics of polymers include their size (or molecular weight),
softening and melting points, crystallinity, and structure. The mechanical properties of
polymers generally include low strength and high toughness. Their strength is often
improved using reinforced composite structures.
Size: Single polymer molecules typically have molcular weights between 10,000 and
1,000,000 g/mol--that can be more than 2000 repeating units depending on the polymer
structure! The mechanical properties of a polymer are significantly affected by the
molecular weight, with better engineering properties at higher molecular weights.
Thermal Transitions: The softening point (glass transition temperature) and the melting
point of a polymer will determine which applications it will be suitable for. These
temperatures usually determine the upper limit for which a polymer can be used. For
example, many industrially important polymers have glass transition temperatures near
the boiling point of water (100C, 212F), and they are most useful for room temperature
applications. Some specially engineered polymers can withstand temperatures as high as
300 C (572 F).
Crystallinity: Polymers can be crystalline or amorphous, but they usually have a
combination of crystalline and amorphous structures (semi-crystalline).
Interchain Interactions: The polymer chains can be free to slide past one another
(thermoplastic) or they can be connected to each other with crosslinks ( thermoset or
elastomer). Thermoplastics can be reformed and recycled, while thermosets and
elastomers are not reworkable.
Intrachain Structure: The chemical structure of the chains also has a tremendous effect
on the properties. Depending on the structure the polymer may be hydrophillic or
hydrophobic (likes or hates water), stiff or flexible, crystalline or amorphous, reactive or
unreactive.
5.1.5-Polymer Processing
Extrusion, Film Blowing, Injection molding: Reports
58
UNIT SIX: CERAMICS MATERIALS
Objective - Classify Ceramic Materials
- Know the Main Application of Ceramic materials
- Glass-Ceramics
- Glasses
Outline
- Ceramic materials
- Industrially Important Ceramics
- Classification of Ceramics
- General Properties of Ceramics
- Ceramics Processing
- Glasses
59
UNIT SIX: CERAMICS MATERIALS
6.1-Ceramics
A ceramic is often broadly defined as compounds that contain both non-metallic and
metallic elements, as any inorganic nonmetallic material. Ceramic materials would also
include glasses; cement and rocks, and oxide structures. Ceramic fibers such as graphite
and aluminum oxide with their extremely high stiffness have led to the production of
fiber-reinforced composites. Ceramic materials are hard and brittle and good thermal and
electrical insulator, also resistant to high temperatures and severe environments. Most
have a regular arrangement of atoms (exception: glasses), Composed of a mixture of
metal and nonmetal atoms, Lower density than most metals, Stronger than metals (high
strength, stiffness, hardness, wear resistance), Low resistance to fracture: low toughness
or brittle, Single crystals are transparent and corrosion resistance. Ceramics are
crystalline compounds consisting of metallic and non-metallic elements whose properties
differ from the constituents. They are non-conducting and exhibit low thermal
conductivity. Ceramics are hard, brittle, and stiff. Ceramics have high melting points, up
to 38500 C (except for clay). Ceramics are highly resistant to compressive loads.
Ceramics are totally elastic and heat resistant. Abrasives, Windows, television screens,
optical fibers (glass), Corrosion resistant applications. Electrical devices: capacitors,
varistors, transducers, etc., Highways and roads (concrete), Biocompatible coatings
(fusion to bone), Self-lubricating bearings, Magnetic materials (audio/video tapes, hard
disks, etc.), Optical wave guides, Piezoelectric materials, Superconductors at very low
temperatures.
6.1.1-Classes of Ceramics
• Structural Ceramics (high-temperature load bearing)
• Refractories (corrosion-resistant, insulating), Whitewares (e.g. porcelains), Glass
• Electrical Ceramics (capacitors, insulators, transducers, etc.)
• Chemically Bonded Ceramics (e.g. cement and concrete)
60
Industrially Important Ceramics
Ceramics may be generally classified according to type or function, in various ways. In
industrial terms, they may be listed as pottery, heavy clay products, refractories, glasses
& vitreous enamels, and engineering ceramics. Engineering ceramics can also be
classified into three distinct material categories: 1) Oxides: Alumina, zirconia; 2) Non-
oxides: Carbides, borides, nitrides, silicides ; 3) Composites: Particulate reinforced,
combinations of oxides and non-oxides.
• Simple oxides (SiO2, Al2O3, Fe 2O3, MgO, etc.)
• Mixed-metal oxides (SrTiO3, MgAl2O4, YBa2Cu3O7-x, etc.)
• Nitrides (Si3N4, TiN, AlN, GaN, BN)
• Carbides (SiC, WC, TiC)
Ceramics Ex. Properties
Oxides
Aluminum oxide Al2O3 high strength, high stiffness, high thermal stability
Magnesium oxide MgO high thermal stability
Mullite Al6Si2O13 Low coefficient of thermal expansion, stability
silicon dioxide SiO2 Low density, transparency
Zirconium dioxide ZrO2 high toughness when transformation toughened
Carbides
Diamond C High stiffness, low coefficient of thermal expansion,
Graphite C high stiffness, low coefficient of thermal expansion
silicon carbide SiC high strength and hardness, high stiffness
tungsten carbide WC high strength and hardness
Nitrides
Boron nitride BN Very high strength and hardness, very high stiffness
silicon nitride Si3N4 High strength, stiffness and high thermal stability
ceramics Ex. Application
Carbides B4C Abrasives, helicopter and tank armor.
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Cr23C6 Wear-resistant coating
(SiC) Abrasives and as a refractory material.
TaC Wear-resistant coating
WC Cutting tools
VC Wear-resistant coating
Intermetallics NiAl Wear-resistant coating
Metalloids Ge Electronic devices
Si Electronic devices
Nitrides BN Insulator, a graphite-like one used as a lubricant, and a
diamond-like one used as an abrasive.
Si3N4 Wear-resistant coating, abrasive powder.
Oxides Al2O3 Electrical insulators
Cr2O3 Wear-resistant coating
MgO Wear-resistant coating
SiO2 Abrasives, glass.
TiO2 Pigment, semiconductor
UO2 Used as fuel in nuclear reactors
YBa2Cu3O7-
x,
And MgB2
high temperature superconductor
ZnO Semiconductor
ZrO2
Thermal insulation, Its high oxygen ion conductivity
recommends it for use in fuel cells,
Fe3O4 Ferromagnetic material, core of electrical transformers
and magnetic core memory.
Pb-Zr_Ti Ferroelectric material.
Ba-Ti-Sr-Ti In electromechanical transducers, ceramic capacitors,
and data storage elements.
Sulfides MoS2 Lubricant
W2S Lubricant
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6.1.3-Ceramic Materials:
Ceramic materials are inorganic materials consisting of metallic and non-metallic
elements chemically bonded together to form complex compounds. Ceramic materials
can be crystalline, non-crystalline, or mixture of both. Most ceramic materials have high
hardness and high temperature strength but tend to have mechanical brittleness. Lately,
new ceramic materials have been developed for engine applications. Advantages in
ceramic materials for engine applications are lightweight, high strength, high wear-
resistance, reduced friction, and insulative properties. Ceramics, because of their unique
properties, show great promise as engineering materials but, in practice, their production
on a commercial scale in specified forms with repeatable properties is often beset with
many problems.
They have a wide variety of applications, from pottery to brick, tile to glass, ovenware to
magnets, and refractories to cutting tools. Due to their high resistance to heat, ceramics
find application in furnace linings and tiles for the space shuttle. Ceramics are also used
in superconductivity applications. Ceramics are also used in the manufacture of space
shuttle tiles and furnace linings. The term ceramics comes from the Greek word
Keramos, which means burned stuff.
The introduction of engineering ceramics as engineering components in recent years has
been based upon considerable scientific effort and has revolutionized engineering design
practice. In general, the development of engineering ceramics has been stimulated by the
drive towards higher, more-energy-efficient, process temperatures, and foreseeable
shortage of strategic minerals. The new generation of engineering ceramics depends upon
the availability of purified and synthesized materials and upon close micro-structural
control during processing. Ceramics are subject to variability in their properties and
statistical concepts need to be incorporated into design procedures for stressed
components.
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6.3- General Properties of Ceramics
Mechanical properties
Ceramic materials are usually ionic or covalently-bonded materials, and can be
crystalline or amorphous. A material held together by either type of bond will tend to
fracture before any plastic deformation takes place, which results in poor toughness in
these materials. Additionally, because these materials tend to be porous, the pores and
other microscopic imperfections act as stress concentrators, decreasing the toughness
further, and reducing the tensile strength. These combine to give catastrophic failures, as
opposed to the normally much more gentle failure modes of metals.
• Electrical properties
There are a number of ceramics that are semiconductors. Most of these are transition
metal oxides that are II-VI semiconductors, such as zinc oxide. While there is talk of
making blue LEDs from zinc oxide, ceramicists are most interested in the electrical
properties that show grain boundary effects.
• Thermal properties
Increases in temperature can cause grain boundaries to suddenly become insulating in
some semiconducting ceramic materials, mostly mixtures of heavy metal titanates. The
critical transition temperature can be adjusted over a wide range by variations in
chemistry. In such materials, current will pass through the material until joule heating
brings it to the transition temperature, at which point the circuit will be broken and
current flow will cease.
6.4- Production of ceramics
Typically, ceramics manufacture involves blending fine starting materials with water to
form a plastic mass that can be formed into final shape. Although water is present, clay is
formable and exhibits high plasticity. Formation processes generally include extrusion,
pressing, and casting. With the invention of the potter's wheel clay cups, bowls, saucers,
and other round or cylindrical objects were produced.
64
After the material is formed, the product is dried to remove excess water. Dried clay
products are porous and not very strong. The material must be fired at elevated
temperatures to provide fusion and cause chemical reactions in the material that produce
the desired properties. The fusion process is called sintering. As a result of sintering, the
edges of the individual particles fuse together to form bonds. This bonding gives
ceramics their strong, brittle, rigid nature. After firing, a ceramic coating or glaze may be
applied to produce a smooth, impermeable surface on the product.
6.5-Glasses
A glass is an inorganic nonmetallic material that does not have a crystalline structure.
Such materials are said to be amorphous. Glasses have historically been used for low
technology applications such as soda bottles and window panes. However, glasses, like
ceramics, have recently found new application in high technology fields, particularly the
semiconductor microelectronics industry where silica is widely used as an insulator in
transistors and the fiber optic cable industry where high purity silica glass has made
advanced telecommunications possible. Three of the most common uses for glasses:
windows, liquid crystal displays, and optical fibers. Examples of glasses range from the
soda-lime silicate glass in soda bottles to the extremely high purity silica glass in optical
fiber. As with ceramics, the list of industrially important glasses also continues to grow.
Industrially Important Glasses
Silica glass SiO2 Used for optical fibers when it is very pure
Soda-lime glass SiO2-Na2O-CaO standard glass used for bottles and windows due to its
low cost and easy manufacturing
Borosilicate glassSiO2-B2O3 thermal shock resistance (glassware) and low
coefficient of thermal expansion
Lead glass SiO2-PbO high index of refraction
65
References
1. Van Vlack, L.H., Elements of Materials Science and Engineering, 5th Ed., Addison-Wesley Publishing Co., Reading, MA, 1985
2. ASTM Standard C 242-01 "Standard Terminology of Ceramic Whitewares and
Related Products": 3. ASM Engineered Materials Handbook â€" Vol 4, Ceramics and Glass 4. Introduction to Ceramics; Kingery, Bowen, and Ulhmann
5. Modern Ceramic Engineering, Properties, Processing, and Use in Design; D. W.
Richerson
6. Ceramic Fabrication Technology; Roy Rice
7. Ceramic Technology and Processing; A. G. King
66
UNIT SEVEN: COMPOSITE MATERIALS
Objective - Classify Composite Materials
- Know the Main Application of Composite materials
Outline
- Composite materials
- Industrially Important Composites
67
UNIT SEVEN: COMPOSITE MATERIALS
7.1- Composite Materials:
There are situations in which no single material has the required properties and
characteristics to suit an application. In these cases, to or more materials are combined
together to form a composite. Composites are composed of two or more combined
materials that exhibit improved properties over their individual components. Composites
are available in many varieties including fiber-resin, fiber-ceramic, carbon-metal, metal-
concrete, metal-resin, and wood plastic.
Composite materials are mixtures of two or more materials. Most composite materials
consist of selected fillers or reinforcing materials and a compatible resin binder to obtain
the specific characteristics and properties desired. Usually, the components do not
dissolve in each other and can be physically identified by an interface between the
components. Composites can be of many types. Some of the predominant types are
fibrous (composed of fibers in a matrix) and particulate (composed of particles in a
matrix). There are many different combinations of reinforcements and matrices used to
produce composite materials. Two outstanding types of modern composite materials used
for engineering applications are fiberglass reinforcing-materials in polyester or epoxy
matrix and carbon fibers in an epoxy matrix.
Composites are generally formed by suspending reinforcing fibers or particles in a
binding matrix. The matrix may be one of a number of materials, including
thermoplastics (T-plastics), thermosets (T-set), ceramics, and metals, thus the matrix is
either: ceramic, polymer or metal. The reinforcement is in fiber or particulate form, either
discontinuous; short fiber, whisker or particulate or continuous. Reinforcing fibers are
typically made from glass, kelvarTM, or a graphite material. The fibers are woven into
fabrics by intraply, interply, selective placement, or interply knitting. The reinforcement
has a higher strength and modulus than the matrix. When the reinforcement is in
particulate form the strengthening mechanism is by dispersion. The aspect ratio and
volume of the reinforcing material decide the strength of the composite. matrix is
required to surround and bind to the reinforcement material, giving the composite its
strength. The purpose of reinforcement is different for the different matrices. For metals,
68
it is usually to improve their high temperature creep properties and to improve their
hardness. For polymers, it is for the improvement of their stiffness and strength. For
ceramics, it is usually to improve their toughness.
Composites are manufactured in a variety of shapes using a variety of methods, including
hand lay-up, prepreg, resin transfer molding, ultimately reinforced thermoset reaction
injection, filament winding, and pultrusion. Composites are replacing other materials,
such as wood and metal, in many applications and will continue to do so in the future as
manufacturing costs & time are reduced.
7.2-Composites Materials
Composites are formed from two or more types of materials. Examples include
polymer/ceramic and metal/ceramic composites. Composites are used because overall
properties of the composites are superior to those of the individual components. For
example: polymer/ceramic composites have a greater modulus than the polymer
component, but aren't as brittle as ceramics. There are two types of composites; 1) Fiber
reinforced composites (e.g. fiberglass) and 2) Particulate composites. Reinforcing fibers
can be made of metals, ceramics, glasses, or polymers that have been turned into graphite
and known as carbon fibers. Fiber-reinforced composites are used in some of the most
advanced, and therefore most expensive, sports equipment, such as a time-trial racing
bicycle frame which consists of carbon fibers in a thermoset polymer matrix.
Applications
• Sports equipment , Aerospace materials
• Thermal insulation, Concrete and Brake materials
• Fiberglass (glass fibers in a polymer)
• Laminate composites
• Space shuttle heat shields (interwoven ceramic fibers)
• Paints (ceramic particles in latex)
• Tank armor (ceramic particles in metal)
69
This family of new materials include:
Polymer or resin matrix composites (PMC), e.g.; fiber-glass, carbon, or graphite
reinforced composites and typical products are tennis rackets, golf clubs, boats, and water
pipes, etc…. Ceramic matrix composites (CMC), And Metal matrix composites (MMC).
The following table shows different matrices, reinforcements and properties of composite
materials.
Table: Matrix, reinforcement, and properties of composite materials.
Matrix Material Reinforcement Material Properties Modified
Metal
Metal, Ceramic, Carbon, Glass
Fibers.
Elevated temperature strength.
Electrical resistance.
Thermal stability.
Ceramic Metallic and Ceramic Particles
and Fibers.
Elevated temperature strength.
Chemical resistance.
Thermal resistance.
Glass Ceramic Fibers and Particles. Mechanical strength.
Temperature resistance.
Chemical resistance.
Thermal stability.
Organics
Thermosets
Thermoplastics
Carbon, Glass, Organic Fibers,
Glass beads, Flakes, Ceramic
Plastics, and Metal Wires.
Mechanical strength.
Elevated temperature strength.
Chemical resistance.
Anti-static electrical resistance.
EMF shielding.
Flexibility.
Wear resistance.
Energy absorption.
Thermal stability.
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7.2.1 - Constituent materials for composites
Fiberglass-reinforced plastics were among the first structural composites. Composites
incorporating glass or relatively low modulus fibers (less than about 12 x 106 psi) are
used in many high-volume applications such as automotive vehicles because of their low
cost, and are sometimes referred to as basic composites. The so-called advanced
composites made from graphite, silicon carbide, polymer, boron, or other higher modulus
fibers are mainly used in more exotic applications such as aerospace structures where
their higher cost can be justified based on improved performance.
The advantages of advanced fibers over glass fibers and conventional bulk metallic
materials are higher modulus & lower density. In many applications such as aerospace
and automotive structures, structural weight is very important. Depending on whether the
structural design is strength-critical or stiffness-critical, the material used should
therefore have a high specific strength (strength to weight ratio) or a high specific
stiffness (stiffness to weight ratio).
Fiber materials:
- Glass fibers consist primarily of silica and metallic oxide modifying elements,
and are generally produced by mechanical drawing of molten glass through a
small orifice.
- Carbon fibers are the most widely used advanced fibers, especially in aerospace
structures. They are generally produced by subjecting organic precursor fibers to
a sequence of heat treatments, so that they are converted into carbon fibers.
- Aramid polymer fibers were originally developed for use in radial tires, but
other versions are used more extensively in structural composites. Unlike brittle
glass or graphite fibers, aramid polymers have excellent toughness, ductility, and
impact resistance.
- Boron fibers are actually consisting of a boron coating on a substrate of tungsten
or carbon. Boron fibers have much higher strength and stiffness, but they also
have a higher density.
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- Silicon carbide fibers are used primarily in high temperature metal and ceramic
matrix composites because of their oxidation resistance and high-temperature
strength retention.
Matrix and filler materials:
Polymers, metals, and ceramics are all used as matrix materials in composites, depending
on the particular requirements. The matrix holds the fibers together in a structural unit
and protects them from external damage, transfers and distributes the applied loads to the
fibers, and in many cases contributes some needed property such as ductility, toughness,
or electrical insulation. A strong interface bond between the fiber and matrix is obviously
desirable, so the matrix must be capable of developing a mechanical or chemical bond
with the fiber. The fiber and the matrix materials should also be chemically compatible,
so. Service temperature is often the main consideration in the selection of a matrix
material. The common matrix materials include polymers, epoxies, lightweight metals
and their alloys and intermetallics.
The third constituent material of a composite, the filler material, is mixed in with the
matrix material during fabrication. Fillers are not generally used to improve mechanical
properties but rather are used to enhance some other aspect of composite behavior. For
example, hollow glass micro-spheres are used to reduce weight, clay or mica particles are
used to reduce cost, and carbon black particles are used for protection against ultraviolet
radiation.
Examples Questions
Q1: What is the effect of adding a high modulus reinforcer to a lower modulus matrix?
Answer: Increases the stiffness of the overall composite compared to the matrix
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UNIT EIGHT: MECHANICAL TESTING
Objective
- Know the concepts of mechanical properties of materials.
- Be aware of the basic testing procedures that engineers use to evaluate many
of these properties.
Outline
- Mechanical Properties of Materials
- Stress-Strain Diagram & Properties
- Hardness Test of Materials
- Fatigue of Materials and Application
- Creep of metals
- Impact Testing of Materials
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UNIT EIGHT: MECHANICAL TESTING
8.1- Mechanical Properties of Materials: The tensile test and the engineering stress-strain diagram The tensile test is used to evaluate the strength of metals and alloys. In this test a metal
sample is pulled to failure in a relatively short time at a constant rate, Fig. 8.1 illustrates
schematically how the sample is tested in tension.
The force (load) on the sample being tested is plotted by the instrument on moving chart
graph paper, while the corresponding strain can be obtained from a signal from an
external extensomer attached to the sample and also recorded on the chart paper.
The type of samples used for the tensile test vary considerably. For metals with a thick
cross section such as plate, a 0.50-in-diameter round specimen is commonly used For
metal with thinner cross sections such as sheet, a flat specimen is used. A 2-in gage
length within the specimen is the most commonly used gage length for tensile tests (Fig.
8.2).
The force data obtained from the chart paper for the tensile test can be converted to
engineering stress data, and a plot of engineering stress vs. engineering strain can be
constructed. Figure 8.3 shows an engineering stress strain diagram for a high-strength
aluminum alloy.
Mechanical property data obtained from the tensile test and the engineering stress-
strain diagram
The mechanical properties of metals and alloys which are of engineering importance for
structural design and which can be obtained from the engineering tensile test are:
1. modulus of elasticity
2. yield strength at 0.2 percent offset
3. ultimate tensile strength
4. percent elongation at fracture
5. percent reduction in area at fracture
74
Modulus of elasticity
In the first part of the tensile test the metal is deformed elastically. That is, if the load on
the specimen is released, the specimen will return to its original length. For metals the
maximum elastic deformation is usually less than 0.5 percent. In general metals and
alloys show a linear relationship between stress and strain in the elastic region of the
engineering stress-strain diagram which is described by Hooke's law
σ (stress) = Eε (strain)
or E = (stress)/ε (strain) (units of psi or pa)
where E is the modulus of elasticity, or young's modulus.2
the modulus of elasticity is related to the bonding strength between the atoms in a alloy.
Metals with high elastic moduli are relatively stiff and do not deflect easily. Steels, for
example, have high elastic moduli values of 30 x 106 psi (207 Gpa)1, whereas aluminum
alloys have lower elastic moduli of about 10 to 11 x 106 psi (69 to 76 Gpa). Note that in
elastic region of the stress-strain diagram, the modulus does not change with increasing
stress.
Yield strength
The yield strength is a very important value of use in engineering structural design since
it is the strength at which a metal or alloy shows significant plastic deformation. Because
there is no definite point on the stress-strain curve where elastic strain ends and plastic
strain begins, the yield strength is chosen to be that strength when a definite amount of
plastic strain has occurred. For American engineering structural design, the yield strength
is chosen when 0.2 percent plastic strain has taken place, as indicated on the engineering
stress-strain diagram of Fig. 8.4.
The 0.2 percent yield strength, also called the 0.2 percent offset yield strength, is
determined from the engineering stress-strain diagram, as shown in Fig.8.4. First, a line is
drawn parallel to the elastic (linear) part of the stress-strain plot a 0.002 in/in (m/m)
strain, as indicated on Fig. 8.4. Then at the point where this line intersects the upper part
1�SI prefic G = giga = 109
75
of the stress-strain curve, a horizontal line is drawn to the stress axis. The 0.2 percent
offset yield strength is the stress where the horizontal line intersects the stress axis, and in
the case of the stress-strain curve of Fig.8.4, the yield strength is 78.000psi. It should be
pointed out that the 0.2 percent offset yield strength is arbitrarily chosen, and thus the
yield strength could have been chosen at any other small amount of permanent
deformation. For example, a 0.1 percent offset yield strength is commonly used in the
united kingdom.
Ultimate tensile strength
The ultimate tensile strength is the maximum strength reached in the engineering stress-
strain curve. If the specimen develops a localized decrease in cross-sectional area
(commonly called necking), the engineering stress will decrease with further strain until
fracture occurs since the engineering stress is determined by using the original cross-
sectional area of the specimen. The more ductile a metal is, the more the decrease in the
stress on the stress-strain curve beyond the maximum stress. For the high strength
aluminum alloy whose stress-strain curve is shown in Fig. 8.3, there is only a small
decrease in stress beyond the maximum stress because this material has relatively low
ductility.
An important point to understand with respect to engineering stress-strain diagrams is
that the metal or alloy continues to increase in stress up to the stress at fracture. It is only
because we use the original cross-sectional area stress at fracture. It is only because we
use the original cross-sectional area to determine engineering stress that the stress on the
engineering stress-strain diagram decrease at the latter part of the test.
The ultimate tensile strength of a metal is determined by drawing a horizontal line from
the maximum point on the stress-strain curve to the stress axis. The stress where this line
intersects the stress axis is called the ultimate tensile strength, or sometimes just the
tensile strength. For the aluminum alloy of Fig. 8.3, the ultimate tensile strength is 87.000
psi.
The ultimate tensile strength is not used much in engineering design for ductile alloys
since too much plastic deformation takes place before it is reached. However, the
76
ultimate tensile strength can give some indication of the presence of defects. If the metal
contains porosity or inclusions, these defects may cause the ultimate tensile strength of
the metal to be lower than normal.
Percent elongation
The amount of elongation that a tensile specimen under goes during testing provides a
value for the ductility of a metal. Ductility of metals is most commonly expressed as
percent elongation, starting with a gage length usually of 2 in (5.1 cm). In general the
higher the ductility 9the more deformable the metal is), the higher the percent elongation
is. For example, a sheet of 0.062-in (1.6-mm) commercially pure a aluminum (alloy
1100-0) in the soft condition has a high percent elongation of 35 percent, whereas the
same thickness of the-strength aluminum alloy 7075-T6 in the fully hard condition has a
percent elongation of only 11 percent.
As previously mentioned, during the tensile test an extensometer can be used to
continuously measure the strain of the specimen being tested. However, the percent
elongation of a specimen after fracture can be measured by fitting the fractured specimen
together and measuring the final elongation with calipers. The percent elongation can
then be calculated from the equation.
% elongation = %100
111
%100
x
xlengthinitial
lengthinitiallengthfinal
ο
ο−=
−
The percent elongation at fracture is of engineering importance not only as a measure of
ductility but also as an index of the quality of the metal. If porosity or inclusions are
present in the metal or if damage due to overheating the metal has occurred, the percent
elongation of the specimen tested may be decreased below normal.
Percent reduction in area
The ductility of a metal or alloy can also be expressed in terms of the percent reduction in
area. This quantity is usually obtained from a tensile test using a specimen 0.50 in (12.7
mm) in diameter. After the test, the diameter of the reduced cross section at the fracture is
77
measured. Using the measurements of the initial and final diameters, the percent
reduction in area can be determined from the equation.
% reduction in area = %100
%100area
xA
AA
xinitial
finalareaareainitial
ο
ο−=
−
The percent reduction in area, like the percent elongation, is a measure of the ductility of
the metal and is also an index quality. The percent reduction in area may be decreased if
defects as inclusion and/or porosity are present in the metal specimen.
Example problem
A 0.500-in-diameter round sample of a 1030 carbon steel is pulled failure in a tensile
testing machine. The diameter of the sample was 0.343 in at the fracture surface.
Calculate the percent reduction in area of the sample.
Solution:
% reduction in area =
( )
( )( )( )( ) ( )
( )( ) %53%10047.01
%100500.04/340.04/
1
%1001%100
2
2
=−=
��
���
�
ΠΠ−=
���
�
�−=
−
inin
A
Ax
A
AA ff
οο
ο
Comparison of engineering stress-strain curves for selected alloys
Engineering stress-strain curves for selected metals and alloys are shown in Fig. 8.5.
Alloying a metal with other metals or nonmetals and heat treatment can greatly affect the
tensile strength and ductility of metals. The stress-strain curves of Fig.8.5 show a great
variation in ultimate tensile strength (UTS). Elemental magnesium has a UTS of 35 ksi (1
ksi = 1000 psi), whereas SAE 1340 steel water-quenched and tempered at 700oF (370oC)
has a UTS of 240 ksi.
78
True stress, true strain
The engineering stress is calculated by dividing the applied force f on a tensile test
specimen by its original cross-sectional area Ao. Since the cross-sectional area of the test
specimen changes continuously during a tensile test, the engineering stress calculated is
not precise. During the tensile test, after necking of the sample occurs, the engineering
stress decreases as the strain increases, leading to a maximum engineering stress in the
engineering stress-strain curve. Thus, once necking begins during the tensile test, the true
stress is higher than the engineering stress. We define the true stress and true strain by the
following:
True stress σ1 = ( )
( )sampleofareationalcrossimumeousinssampletesttheonforceuniaxialaverageF
sec min tantanA
i −
True strain οο
εll
inldl i
t
tt
i
=
Where to is the original gage length of the sample and ti is the instantaneous extended
gage length during the test. If we assume constant volume of the gage-length section of
the test specimen during the test, then /oAo = liAi or
i
ii
i
i
AA
inll
inandAA
ll ο
ο
ο
ο
ε ===
Figure 8.6 compares engineering stress-strain and true stress-strain curves for a low-
carbon steel.
Engineering designs are not based on true stress at fracture since as soon as the yield
strength is exceeded, the material starts to deform. Engineers use instead the 0.2 percent
offset engineering yield stress for structural designs with the proper safety factors.
However, for research, sometimes the true stress-strain curves are needed.
79
Fig. 8.1 Tensile specimen being pulled.
Fig. 8.2 Tensile specimens
80
Fig. 8.3 Typical engineering stress-strain curve.
Fig. 8.4 Elastic range in stress-train curve
81
Fig. 8.5 Engineering stress-strain curves for some metals and alloys
Fig. 8.6 Comparison between engineering and tue stress-strain curve
82
8.2-Hardness Testing
Hardness is a measure of the materials resistance to localized plastic deformation (e.g.
dent or scratch). In general, hardness usually implies a resistance to deformation, and for
metals the property is a measure of their resistance to permanent or plastic deformation.
To a person concerned with the mechanics of materials testing, hardness is most likely to
mean the resistance to indentation, and to the design engineer it often means an easily
measured and specified quantity which indicates something about the strength and heat
treatment of the metal.
There are three general types of hardness measurements depending on the manner in
which the test is conducted. These are:
• Scratch hardness
• Indentation hardness, and rebound, or dynamic hardness.
Only indentation hardness is of major engineering interest for metals.
Scratch hardness is of primary interest to mineralogists. With this measure of hardness,
various minerals and other materials are rated on their ability to scratch one another.
Scratch hardness is measured according to the Mohs’ scale. This consists of 10 standard
minerals arranged in the order of their ability lo be scratched. The softest mineral in this
scale is talc (scratch hardness 1), while diamond has a hardness of 10. The Mohs’ scale is
not well suited for metals since the intervals are not widely spaced in the high-hardness
range. Most hard metals fall in the Mohs’ hardness range of 4 to 8.
In dynamic-hardness measurements the indenter is usually dropped onto the metal
surface, and the hardness is expressed as the energy of impact. The Shore seleroscope,
which is the commonest example of a dynamic-hardness tester, measures the hardness in
terms of the height of rebound of the indenter.
83
Brinell Hardness
The Brinell hardness test consists in indenting the metal surface with a 10-mm-diameter
steel ball at a load of 3,000 kg mass. For soft metals the load is reduced to 500 kg to
avoid too deep an impression, and for very hard metals a tungsten carbide ball is used to
minimize distortion of the indenter. The load is applied for a standard time, usually 30 s,
and the diameter of the indentation is measured with a low-power microscope after
removal of the load. The average of two readings of the diameter of the impression at
right angles should be made.
The Brinell hardness number (BHN) is expressed as the load P divided by the surface
area of the indentation. This is expressed by the formula:
where
P - applied load, N
D - diameter of ball mm
d - diameter of indentation, mm
t - depth of the impression, mm
It will be noticed that the units of the BHN are MPa.
Unless precautions are taken to maintain P/D2 constant, which may be experimentally
inconvenient, the BHN generally will vary with load. Over a range of loads the BHN
reaches a maximum at some intermediate load. Therefore, it is not possible to cover with
a single load the entire range of hardnesses encountered in commercial metals.
The relatively large size of the Brinell impression may be an advantage in averaging out
local heterogeneities. Moreover, the Brinell test is less influenced by surface scratches
and roughness than other hardness tests. On the other hand, the large size of the Brinell
impression may preclude the use of this test with small objects or in critically stressed
parts where the indentation could be a potential site of failure.
84
Meyer Hardness
Meyer suggested that a more rational definition of hardness than that proposed by Brinell
would be one based on the projected area of the impression rather than the surface area.
The mean pressure between the surface of the indenter and the indentation is equal to the
load divided by the projected area of the indentation. Meyer proposed that this mean
pressure should be taken as the measure of hardness. It is referred to as the Meyer
hardness.
Like the Brinell hardness, Meyer hardness has units of MPa. The Meyer hardness is less
sensitive to the applied load than the Brinell hardness. For a cold-worked material the
Meyer hardness is essentially constant and independent of load, while the Brinell
hardness decreases as the load increases. For an annealed metal the Meyer hardness
increases continuously with the load because of strain hardening produced by the
indentation. The Brinell hardness, however, first increases with load and then decreases
for still higher loads. The Meyer hardness is a more fundamental measure of indentation
hardness; yet it is rarely used for practical hardness measurements.
Meyer proposed an empirical relation between the load and the size of the indentation.
This relationship is usually called Meyer’s law.
P = kdn’
The parameter n’ is the slope of the straight line obtained when log P is plotted against
log d, and k is the value of P at d = 1. Fully annealed metals have a value of n’ of about
2.5, while n’ is approximately 2 for fully strain-hardened metals. This parameter is
roughly related to the strain-hardening coefficient in the exponential equation for the
true-stress-true-strain curve. The exponent in Meyer’s law is approximately equal to the
strain-hardening coefficient plus 2.
85
Vickers Hardness
The Vickers hardness test uses a square-base diamond pyramid as the indenter. The
included angle between opposite faces of the pyramid is 136°. This angle was chosen
because it approximates the most desirable ratio of indentation diameter to ball diameter
in the Brinell hardness test.
Because of the shape of the indenter, this is frequently called the diamond-pyramid
hardness test. The diamond-pyramid hardness number (DPH), or Vickers hardness
number (VHN, or VPH), is defined as the load divided by the surface area of the
indentation. In practice, this area is calculated from microscopic measurements of the
lengths of the diagonals of the impression. The DPH may be determined from the
following equation:
where
P - applied load, kg
L - average length of diagonals, mm
� - angle between opposite faces of diamond = 136°
Rockwell Hardness Test
The most widely used hardness test is the Rockwell hardness test. Its general acceptance
is due to its speed, freedom from personal error, ability to distinguish small hardness
differences in hardened steel, and the small size of the indentation, so that finished heat-
treated parts can be tested without damage.
This test utilizes the depth of indentation, under constant load, as a measure of hardness.
A minor load of 10 kg is first applied to seat the specimen. This minimizes the amount of
surface preparation needed and reduces the tendency for ridging or sinking in by the
indenter. The major load is then applied, and the depth of indentation is automatically
recorded on a dial gage in terms of arbitrary hardness numbers.
Hardened steel is tested on the C scale with the diamond indenter and a 150-kg major
load. The useful range for this scale is from about RC 20 to RC 70. Softer materials are
86
usually tested on the B scale with a 1/16-in-diameter steel ball and a 100-kg major load.
The range of this scale is from RB 0 to RB 100. The A scale (diamond penetrator, 60-kg
major load) provides the most extended Rockwell hardness scale, which is usable for
materials from annealed brass to cemented carbides. Many other scales are available for
special purposes.
Microhardness Tests
Many metallurgical problems require the determination of hardness over very small
areas. The measurement of the hardness gradient at a carburized surface, the
determination of the hardness of individual constituents of a microstructure, or the
checking of the hardness of a delicate watch gear might be typical problems.
The Knoop indenter is a diamond ground to a pyramidal form that produces a diamond-
shaped indentation with the long and short diagonals in the approximate ratio of 7:1
resulting in a state of plane strain in the deformed region. The Knoop hardness number
(KHN) is the applied load divided by the unrecovered projected area of the indentation.
The special shape of the Knoop indenter makes it possible to place indentations much
closer together than with a square Vickers indentation, e.g., to measure a steep hardness
gradient. The other advantage is that for a given long diagonal length the depth and area
of the Knoop indentation are only about 15 percent of what they would be for a Vickers
indentation with the same diagonal length. This is particularly useful when measuring the
hardness of a thin layer (such as an electroplated layer), or when testing brittle materials
where the tendency for fracture is proportional to the volume of stressed material.
Hardness at Elevated Temperatures
Interest in measuring the hardness of metals at elevated temperatures has been
accelerated by the great effort which has gone into developing alloys with improved
high-temperature strength. Hot hardness gives a good indication of the potential
usefulness of an alloy for high-temperature strength applications.
In an extensive review of hardness data at different temperatures, Westbrook showed that
the temperature dependence of hardness could be expressed by
87
H = Ae-BT
where
H = hardness, kg/mm2
T = test temperature, K
A,B constants
Plots of log H versus temperature for pure metals generally yield two straight lines of
different slope. The change in slope occurs at a temperature which is about one-half the
melting point of the metal being tested. Similar behavior is found in plots of the
logarithm of the tensile strength against temperature. Above mentioned figure shows this
behavior for copper. It is likely that this change in slope is due to a change in the
deformation mechanism at higher temperature.
Both tensile strength and hardness may be regarded as degree of resistance to plastic
deformation. Hardness is proportional to the tensile strength- but note that the
proportionality constant is different for different materials.
Fig. 8.7 Correlation between hardness and tensile strength
88
8.3-Fatigue of Metals
Failures occurring under conditions of dynamic loading are called fatigue failures,
presumably because it is generally observed that these failures occur only after a
considerable period of service. Fatigue has become progressively more prevalent as
technology has developed a greater amount of equipment, such as automobiles, aircraft,
compressors, pumps, turbines, etc., subject to repeated loading and vibration. Today it is
often stated that fatigue accounts for al least 90 percent of all service failures due to
mechanical causes.
A fatigue failure is particularly insidious because it occurs without any obvious warning.
Fatigue results in a brittle-appearing fracture, with no gross deformation at the fracture.
On a macroscopic scale the fracture surface is usually normal to the direction of the
principal tensile stress. A fatigue failure can usually be recognized from the appearance
of the fracture surface, which shows a smooth region, due to the rubbing action as the
crack propagated through the section, and a rough region, where the member has failed in
a ductile manner when the cross section was no longer able to carry the load. Frequently
the progress of the fracture is indicated by a series of rings, or "beach marks", progressing
inward from the point of initiation of the failure.
Three basic factors are necessary to cause fatigue failure. These are:
• maximum tensile stress of sufficiently high value,
• large enough variation or fluctuation in the applied stress, and
• sufficiently large number of cycles of the applied stress.
In addition, there are a host of other variables, such as stress concentration, corrosion,
temperature, overload, metallurgical structure, residual stresses, and combined stresses,
which tend to alter the conditions for fatigue. Since we have not yet gained a complete
understanding of what causes fatigue in metals, it will be necessary to discuss each of
these factors from an essentially empirical standpoint. Because of the mass of data of this
type, it will be possible to describe only the highlights of the relationship between these
factors and fatigue.
89
S-N-Curve
The most commonly used stress ratio is R, the ratio of the minimum stress to the
maximum stress (Smin/Smax).
• If the stresses are fully reversed, then R = -1.
• If the stresses are partially reversed, R = a negative number less than 1.
• If the stress is cycled between a maximum stress and no load, R = zero.
• If the stress is cycled between two tensile stresses, R = a positive number less
than 1.
Variations in the stress ratios can significantly affect fatigue life. The presence of a mean
stress component has a substantial effect on fatigue failure. When a tensile mean stress is
added to the alternating stresses, a component will fail at lower alternating stress than it
does under a fully reversed stress.
Fig. 8.8. Typical fatigue stress cycles. (a) Reversed stress; (b) repeated stress; (c)
irregular or random stress cycle.
90
The basic method of presenting engineering fatigue data is by means of the S-N curve, a
plot of stress S against the number of cycles to failure N. A log scale is almost always
used for N. The value of stress that is plotted can be �a, �max, or �min. The stress values
are usually nominal stresses, i.e., there is no adjustment for stress concentration. The S-N
relationship is determined for a specified value of �m, R (R=�min/�max), or A (A=�a/�m).
Most determinations of the fatigue properties of materials have been made in completed
reversed bending, where the mean stress is zero.
Fig. 8.9 Machine setup for fatigue test
The usual procedure for determining an S-N curve is to test the first specimen at a high
stress where failure is expected in a fairly short number of cycles, e.g., at about two-
thirds the static tensile strength of the material. The test stress is decreased for each
succeeding specimen until one or two specimens do not fail in the specified numbers of
cycles, which is usually at least 107 cycles.
Fatigue properties of a material (S-N curves) are tested in rotating-bending tests in
fatigue testing apparatus:
91
Fig. 8.10 S-N curves for ferrous materials
Fatigue limit (endurance limit) occurs for some materials (some Fe and Ti allows). In this
case, the S-N curve becomes horizontal at large N. The fatigue limit is maximum stress
amplitude below which the material never fails, no matter how large the number of cycle
is.
Fig. 8.11 S-N curves for non ferrous materials
The highest stress at which a runout (non-failure) is obtained is taken as the fatigue limit.
For materials without a fatigue limit the test is usually terminated for practical
considerations at a low stress where the life is about 108 or 5x108 cycles. The S-N curve
is usually determined with about 8 to 12 specimens.
92
8.4-Creep of metals
Creep is a time-dependent and permanent deformation of materials when subjected to a
constant load at a high temperature (>0.4Tm). Examples: turbine blades, stream
generators.
Fig. 8.12 Creep Testing setup
Fig. 8.13 Stages of Creep
93
Stages of Creep
1. Instantaneous deformation, mainly elstic.
2. Primary/transient creep. Slope of strain vs. time decreases with time: work-
hardening
3. Secondary/steady-state creep. Rate of straining is constant: balance of work-
hardening and recovery.
4. Tertiary. Rapidly accelerating strain rate up to failure: formation of internal
cracks, voids, grain boundary separation, necking, etc.
Parameters of creep behavior
The stage secondary/steady-state creep is of longest duration and the steady-state creep
rate =�/t is the most important parameter of the creep behavior in long-life
applications
Fig. 8.14 Parameters of creep behavior
Creep: stress and temperature effects
With increasing stress or temperature:
• The instantaneous strain increases
94
• The steady-state creep rate increases
• The time to rupture decreases
Fig. 8. 15 Creep stress and temperature effects
Mechanism of Creep
Different mechanisms are responsible for creep in different materials and under different
loading and temperature conditions.
The mechanisms include
• Stress-assisted vacancy diffusion
• Grain boundary diffusion
• Grain boundary sliding
• Dislocation motion
95
8.5-Fracture Toughness
Impact Fracture Testing
Two standard tests, the charpy and Izod, measure the impact energy (the energy required
to fracture a test piece under an impact load), also called the notch toughness.
Fig. 8. 16 Impact test Setup
96
UNIT NINE: METAL PROCESSING AND MECHANICAL WORKING
Objective
- Know the concepts of mechanical working of materials.
- Be aware of the basic forming processes that engineers use in industry.
Outline
- Metal Processing
- Cold and Hot Working
- Forming Processes
- Rolling,
- Forging,
- Stretching,
- Extrusion and
- Wire drawing.
- Deep drawing or Pressing,
- Roll forging,
- Spray forming.
- Metal Fabrication Methods
- Casting
97
UNIT NINE: METAL PROCESSING AND MECHANICAL WORKING
9.1-Metal Processing
Annealing: heating a material above a material-dependent temperature, allows
recrystalization (Temperature termed recrystalization temperature = 0.4-0.6 Tm where Tm
is the melting point). Time also plays a role in the amount of recrystalization at any given
temperature. Materials with more dislocations (higher energies) due to cold-working can
be recrystallized at lower temperatures.
Cold Working
Mechanical deformation at normal temperatures increases a material's strength (ultimate
and yield strengths, plus shear strength) and hardness. There is a corresponding decrease
in ductility and malleability as the metal strain hardens. Cold-working and annealing are
often cycled to assist in production. Advantages over hot working include a better quality
surface finish, closer dimensional control of the final article and improved mechanical
properties. The best combination of properties is usually found in the longitudinal
direction, and the worst in the short transverse direction.
Hot Working
Deformation is carried out at a temperature high enough for fast recrystallisation to occur.
A crude estimate for a hot working temperature T for a particular metal or alloy is that it
must be greater than 0.6Tm where Tm is the melting point in degrees Kelvin. This lower
bound for the hot working temperature varies for different metals, depending on factors
such as purity and solute content. Hot working achieves both the mechanical purpose of
obtaining the desired shape and also the purpose of improving the physical properties of
the material by destroying its original cast structure. The porous cast structure, often with
a low mechanical strength, is converted to a wrought structure with finer grains,
enhanced ductility and reduced porosity. Control of mechanical properties can be done by
metal working process. (Ex. Blowholes and porosity in a cast ingot may be eliminated by
hot-forging or hot-rolling and hence improvement of ductility and fracture toughness).
98
9.2-Forming Processes
Useful shapes such as tubes, rods and sheets may be generated in two basic ways:
• By plastic deformation processes: In which the volume and mass of metal are
conserved and the metal is displaced from one location to another.
• By metal removal or machining processes: In which material is removed in order
to give it the required shape
Forming processes include stamping, rolling, extrusion and forging, where deformation is
induced by external compressive forces or stresses exceeding the yield stress of the
material. Drawing is a fundamentally different process in that the external forces are
tensile in nature and hence the yield stress of the material cannot be exceeded. Metals or
alloys used in forming processes require a moderate level of ductility to enable plastic
deformation with no fracture. Classification of metal working process based on the type
of forces applied to the workpiece as it is formed into shape
1. Direct-compression-type processes
2. Indirect-compression processes
3. Tension type processes
4. Bending processes
5. Shearing processes
In direct-compression processes the force is applied to the surface of the workpiece and
the metal flows at right angles to the direction of the compression (ex. Forging and
rolling).
The indirect-compression processes include wiredrawing and tube drawing, extrusion,
and deep drawing of a cup. The primary applied forces are frequently tensile, but the
indirect compressive forces developed by the reaction of the workpiece with the die reach
high value. Therefore, the metal flows under the action of a combined stress state which
includes high compressive forces in at least one of the principal directions.
The best example of a tension-type forming process is stretch forming, where a metal
sheet is wrapped to the contour of a die under the application of tensile forces.
99
Bending involves the application of bending moments to the sheets. Shearing involves
the application of shearing forces of sufficient magnitude to rupture the metal in the plane
of shear.
Plastic working processes which are designed to reduce an ingot or billet to a standard
mill product of simple shape, such as sheet, plate, and bar, are called primary
mechanical working processes or processing operations. Forming methods which
produce a part to a final finished shape are called secondary mechanical working
processes or fabrication.
Metal forming is normally performed after the primary processes of extraction, casting,
and powder compaction and before the finishing processes of metal cutting, grinding,
polishing, painting, and assembly.
9.3-Common Industrial Processes
• Rolling,
• Forging,
• Stretching,
• Extrusion and
• Wire drawing.
• Deep drawing or Pressing,
• Roll forging,
• Spray forming.
Rolling
Rolling is the most widely used deformation process. It consists of passing metal between
two rollers, which exert compressive stresses, reducing the metal thickness, where simple
shapes are to be made in large quantity. Rolled products include sheets, structural shapes
and rails as well as intermediate shapes for wire drawing or forging. Circular shapes, ‘I’
beams and railway tracks are manufactured using grooved rolls.
100
Fig. 9.1 Rolling setup
Hot Rolling
Initial breakdown of an ingot or a continuously cast slab is achieved by hot rolling.
Mechanical strength is improved and porosity is reduced. The worked metal tends to
oxidise leading to scaling which results in a poor surface finish and loss of precise
dimensions. A hot rolled product is often pickled to remove scale, and further rolled cold
to ensure a good surface finish and optimise the mechanical properties for a given
application.
Cold Rolling
Cold rolling is often used in the final stages of production. Sheets, strips and foils are
cold rolled to attain dimensional accuracy and high quality surface finishes. With softer
metals such as lead and copper, a succession of cold-rolling passes can impose very large
deformations. For many materials, however, the rolling sequence has to be interrupted for
intermediate annealing in order to prevent fracture.
Forging
In this operation, a single piece of metal, normally hot, is deformed mechanically by the
application of successive blows or by continuous squeezing. Forged articles range in size
from nuts and bolts, hip replacement prostheses and crankshafts to (traditionally) gun
barrels. Most engineering metals and alloys can be forged readily and include most steels,
aluminium and copper alloys and certain titanium alloys. Strain-rate and temperature-
sensitive materials, such as magnesium and nickel based superalloys, may require more
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sophisticated forging processes such as radial forging. Forged articles have excellent
mechanical properties, combining fine grain structure with strengthening through strain
hardening.
Closed Die
A force is brought to bear on a metal slug or preform placed between two (or more) die
halves. The metal flows plastically into the cavity formed by the die and hence changes in
shape to its finished shape. Examples of the machinery used include hydraulic presses,
mechanical presses and hammers.
As metal flow is restricted by the die contours, closed-die forging can produce complex
shapes and higher tolerances than the shapes and tolerances achieved using open-die
forging processes.
Fig. 9.2 Closed-die forging
Open Die
Open-die forging is performed between flat dies with no pre-cut profiles. The dies do not
confine the metal laterally during forging. Deformation is achieved through movement of
the workpiece relative to the dies. Open-die forging comprises many process variations,
enabling an extremely broad range of shapes and sizes to be produced.
In addition to round, square, rectangular, hexagonal bar and other basic shapes, open-die
processes can produce: 1) Spindles or rotors, 2) hollows cylindrical in shape, and 3) ring-
like parts resembling washers or approaching hollow cylinders in shape.
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Fig. 9.3 Open-die forging
Extrusion
In extrusion, a bar or metal is forced from an enclosed cavity via a die orifice by a
compressive force applied by a ram. Since there are no tensile forces, high deformations
are possible without the risk of fracture of the extruded material. Extrusion products
include rods and tubes with varying degrees of complexity in cross-section.
There are two kinds of extrusion, direct and indirect or inverted. In the former case the
ram and die are at opposite ends of the billet and the metal is pushed up to and through
the die. With indirect extrusion the die is held at the end of a hollow ram and is forced
into the billet so that metal is extruded backwards through the die. Examples of metals
that can be extruded include lead, tin, aluminium alloys, copper, brass and steel. The
minimum cross-sectional dimensions for extruded articles are approximately 3 mm in
diameter for steel and 1 mm in diameter for aluminium. Some metals such as lead alloys
and brass lend themselves to extrusion rather than drawing or rolling.
Hot extrusion is carried out at a temperature T of approximately 0.6Tm and the pressures
required range from 35 to 700 MPa. Under these demanding conditions, a lubricant is
required to protect the die. Oil and graphite lubricants function well at temperatures up to
150°C, but borate glass or hexagonal boron nitride powders are favored at higher
temperatures where carbon-based lubricants oxidized.
Cold extrusion is performed at temperatures significantly below the melting temperature
of the alloy being deformed, and generally at room temperature. The process can be used
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for most materials, provided that sufficiently robust machinery can be designed. Products
of cold extrusion include aluminium cans, collapsible tubes and gear blanks.
Fig. 9.4 Extrusion setup
Wire Drawing
Metal rod is pointed at one end and then drawn through the tapered orifice of a die. The
rod entering the die has a large diameter and leaves with a smaller diameter. By using the
appropriately shaped orifice it is possible to draw a variety of shapes such as ovals,
squares, hexagons, etc., by this process.
A complete drawing apparatus may include up to twelve dies in a series sequence, each
with a hole a little smaller than the preceding one. In multiple-die machines, each stage
results in an increase in length and therefore a corresponding increase in speed is required
between each stage. This is achieved using “capstans” which are used both to apply the
tensile force and also to accommodate the increase in the speed of the drawn wire. These
speeds may reach 60 ms–1. A typical lubricant used for drawing is tallow, a soap/fat
paste-type material that has a formulation of 5 wt% soap, 25 wt% oil, 25 wt% water, and
45 wt% solids.
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Fig. 9.5 Drawing setup
Metals can be formed much closer dimensions by drawing than by rolling. Shapes
ranging in size from the finest wire to those with cross-sectional areas of many square
centimetres are commonly drawn. Drawn products include wires, rods and tubing
products.
Stretch Forming
This is essentially a process for the production of shapes in sheet metal. The sheets are
drawn over shaped formers to the extent that they deform plastically and assume the
required profiles. It is a cold-working process and is currently the least used of all the
working processes.
Stamping is used to make high volume parts such as aviation or car panels or electronic
components. Mechanical or hydraulic powered presses stamp out parts from continuous
sheets of metal or individual blanks. The upper die is attached to the ram and the lower
die is fixed. Whereas mechanical machinery transfers all energy as a rapid punch,
hydraulic machinery delivers a constant, controlled force.
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Fig. 9.6 Stamping setup
Deep Drawing and Pressing
For deep drawing, the starting sheet of metal is larger than the area of the punch. A
pressure plate, fixed to the machine, prevents wrinkling of the edges as the plug is drawn
into a top die cavity. The outer parts of the sheet are drawn in towards the die as the
operation proceeds. The process is limited by the possibility of fracture occurring during
drawing; the maximum sheet width is rarely more that twice the die diameter. Many
shapes are possible including cups, pans, cylinders and irregular shaped products.
Fig. 9.7 Deep drawing setup
A sheet of metal is deformed between two suitably shaped dies usually to produce a cup
or dish shaped component. A thick pad of rubber may replace one of the dies, giving
reduced tooling costs and allowing larger deformations to be imposed.
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Fig. 9.8 Pressing
Metal Fabrication Methods
Casting- mold is filled with metal
� Metal melted in furnace, perhaps alloying elements added. Then cast in a mold
� Most common, cheapest method
� Good production of shapes
� Weaker products, internal defects
� Good option for brittle materials
Sand Casting (large parts, e.g., auto engine blocks)
� trying to hold something that is hot
� What will withstand >1600ºC?
� Cheap - easy to mold => sand!!!
� Pack sand around form (pattern) of desired shape
Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades)
• Pattern is made from paraffin.
• Mold made by encasing in plaster of paris
• Melt the wax & the hollow mold is left
• Pour in metal
Die Casting (high volume, low T alloys)
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Continuous Casting: Report Powder Metallurgy: Report
Examples Questions
1. What would happen to a brittle metal such as white cast iron, if it were formed by
closed die forging?
Answer: It would shatter when the load was applied at high loading rate, and the final
object would be composed of shards pushed together – it would not be strong enough.
2. The melting temperature of a low-carbon steel is 1534°C. Above what
temperature can we use hot working to form it, and why?
Answer: Hot working requires the temperature to be >0.6Tm. In the case of this steel, Tm
is 1807 K so 0.6 Tm is 1084.2 K – hot working can be performed above this temperature.
Above this temperature, recovery, recrystallisation and grain growth occur as the
deformation process is happening. It is also interesting to note that the range of
temperature in which hot working can occur is mostly in the austenite field. Once a
sample of this steel has been hot worked for long enough for the transformation to take
place, it is austenitic and will again undergo the ferritic transformation on cooling to
room temperature. The properties of the steel will change between the end of hot working
and the piece’s use.
3. Do you think steel reinforcing bars for concrete are drawn or extruded?
Answer: They are extruded. If they were drawn they would end up coiled on a large
drum; they would then need to be unrolled and cut into lengths at the site. This would be
difficult because they are by necessity very stiff. If they are extruded they can be cut as
they emerge and this makes them easier to make into buildings.
Websites
• Forging Metal Forming Processes
• Metal casting technology
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DEPT. OF MINING, PETROLEUM AND METALLURGY MATERIALS SCIENCE FACULTY OF ENGINEERING TIME ALLOWED: 3 HRS. CAIRO UNIVERSITY 1st Year JUNE 2007 Examiner Dr. Mahmoud M. Tash _______________________________________________ FIRST QUESTION: (56 marks), Choose the Correct Answer:
1. Steels containing molybdenum are usually recommended for (a) High temperature applications. (b) Room
temperature applications. (c) Wear resistance applications. (d) High electrical conductivity. 2. Cast iron containing graphite flakes is called (a) White cast iron (b) Gray cast iron (c) Nodular cast iron
(d) Malleable cast iron 3. Cast iron containing spheroids of graphite is called (a) White cast iron (b) Gray cast iron (c) Nodular cast iron
(d) Malleable cast iron 4. The main difference between the carbon steels and the stainless steels is a) Carbon content. b) Nickel
content. c) Chromium content. d)All of the above. 5. Nodular cast iron is used in preference to gray cast iron for making (a) Motor housings (b) Tools (c)
Springs (d) Grinding balls 6. An important non-ferrous alloy is: - a) Al-Si alloy b) silicon carbide c) cast iron d) acrylic 7. Repars and structural parts are made from : - a) low carbon steel b) medium carbon steel c) High
carbon steel d) stainless steel 8. Pistons and some car engine parts are made from: -a) Al-Si alloy b) Cu-alloys c) low-carbon steel d) stainless steel 9. Precipitation hardening is a heat treatment given to aluminum alloys to increase their a) Ductility b) strength
c) toughness d) corrosion resistance 10. High C steels are used for making (a) Re-bars (b) cutting Tools (c) Springs (d) Automobile body sheets 11. Brasses are used in applications requiring (a) High thermal conductivity (b) High electrical conductivity (c)
resistance to corrosion (d) All of the above. 12. Bronzes are Cu-alloys containing (a) Mn (b) Sn (c) Zn (d) Non of the above. 13. The highest strength copper alloys are a) brasses b) bronzes c) pure copper d) monel 14. The main strengthening mechanism in the aluminium alloys is a) solution treatment (b) precipitation hardening
(c)annealing d) forming martensite. 15. Copper and its alloys posses …… and is thus suitable for marine applications. a)high corrosion resistance b) high
electrical and thermal conductivity c)high ductility d) all of the above. 16. Stainless steels are always recommended when Parts are (a) subjected to high temperature (b) exposed to acidic
media (c) carry high loads (d) work under frictional conditions. 17. Surgery tools are made from a) low carbon steel b) high carbon steel c) Tool steel d) stainless steel 18. Cu-Zn alloys are used for conditions requiring:-a) high corrosion resistance b) high wear resistance c) High
temperature applications d) high ductility 19. Cu-Sn alloys are used for conditions requiring: - a) high corrosion resistance combined with high strength b) High
strength c) high temperature applications d) high wear resistance 20. Mechanical properties of material may be enhanced by (a) heating (b) alloying (c) controlled heating and
cooling known as heat treatment (d) b & c. 21. Ni and Cr are added to steels to increase (a) melting temperature (b) electrical conductivity (c)corrosion resistance. 22. Most alloying elements contribute to strengthening steel by (a) forming martensite (b) solid solution strengthening (c)
raising their melting temperature. 23. Austenitic stainless steels are made of (a) <0.8% C 18%Cr 8% Ni (b) >0.8% C 18%Cr 8% Ni (c) <0.8% C 8%Cr
18% Ni. 24. The carbon content in carbon steel 1340 is (a) 0.6% (b) 0.2% (c) 0.4% (d) 0.8% 25. The alloy 0.15 %c is designated….. … (a) low C –(b) medium C – (c) high C steel. 26. The amount of phases present in the alloy contains 1.2%C after equilibrium cooling to room temperature is :-(a) 94%
martensite & 6% ferrite (b) 82% ferrite& 18% Fe3C (c) 80% austenite & 20% ferrite (d) 82 Fe3C & 18% ferrite 27. The critical temperature for hypoeutectoid alloys in heat treatment must (a) ensure the alloy is of 2 phases ferrite +
austenite (b) one phase ferrite (c) one phase austenite. 28. The stricture of the alloy containing 0.8% C after quenching would contain:- (a)100% pearlite
(b)100%martensite (c)50%ferrite + 50% Fe3C (d)50%ferrite+ 50% austenite 29. The eutectic alloy on the Fe-Fe 3 C Diagram contains (a) 4.3%C (b) 0.8%C (c) 2%C (d) 0.02%C. 30. Gray cast iron consists of (a) graphite fakes (b) graphite nodules (c) graphite needles in the alloy matrix. 31. Nodular cast iron consists of (a) graphite fakes (b) graphite nodules (c) graphite needles in the matrix. 32. White cast iron consists of (a) graphite fakes (b) graphite nodules (c) cementite needles in the matrix. 33. Nodular cast iron is made from (a) gray cast iron (b) white cast iron (c) steel. 34. One can produce a huge casting from mealable cast iron (a) true (b) false
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35. One can produce a huge casting from ductile cast iron (a) true (b) false 36. Tempering is done to (a) increase strength (b) optimize strength and toughness (c) increase ductility. 37. The structures of cast parts usually are (a) Isotropic. (b) Directional. (c) Relatively coarser (d) both a & c.
compared to those produced by hot working. 38. Parts produced by cold rolling usually display a structure of (a) Equal grains oriented in all directions. (b)Grains of
all sizes and orientations. (c) Fine grains oriented in one direction. (d) Coarse grains 39. Parts produced by forging include (a) Shafts. (b) Balls. (c) Chains. (d) All of the above. 40. Rebars and steel sheets are produced by (a) Casting. (b) Forging. (c) Drawing. (d) Rolling. 41. Electrical Copper cables are produced by (a) Casting. (b) Extrusion and wire drawing. (c) Extrusion. (d) Rolling. 42. The structure exhibited by hot rolling consists of (a) Recrystallized grains. (b) Fragmented grains
(c) Grains of all sizes and orientations (d) none of the above 43. Hot working operations are carried out whilst the workpiece is heated to (a) 1000 0C. (b) Melting temperature. (c)
Recrystallization temperature. (d) Any temperature above room temperature. 44. The mechanical properties of products manufactured by cold working compared with hot Working show: (a)Higher
hardness and strength. (b) Closer tolerance. (c) Better surface finish. (d) a,b and c. 45. Ceramics possess (a) high electrical and thermal conductivity (b) high heat and thermal resistance (c) high toughness. 46. Plastics or polymers are known best for their high (a) strength (b) ductility (c) heat resistance. 47. Thermoplastic polymers have a strong primary bond and are often formed by (a) addition (b) condensation
polymerization and they are recyclable. 48. Ceramic materials are (a) denser (b) more porous (c) similar to, when compared with metallic materials. 49. Ceramics gain their strength through (a) heat treatment (b) alloying (c) sintering process. 50. Polymers gain their strength through (a) heat treatment (b) sintering process (c) polymerization. 51. Ceramic materials a) Consist of organic long molecular chains or networks. b) Can be crystalline, non-crystalline,
or mixture of both. c)May contain non-metallic elements. d) Both (b) & (c). 52. Polymer materials a) Consist of organic long molecular chains or networks. b) Can be crystalline, non-crystalline. c)
Are inorganic substances composed of one or more metallic elements. d) Both A&b 53. Boron nitride is a ceramic material used in (a) Insulator (b) Lubricant (c) Electronic devices (d) Cutting tools 54. Fiber glass reinforced plastic is among the materials known as (a) metallic materials
(b) ceramic materials (c) composite materials (d) polymers. 55. Tungsten carbide used for manufacturing (a) Insulator (b) Lubricant (c) Electronic device (d) Cutting tools 56. Carbides are (a) ceramic ( b) composite materials (c) polymer (d) metals 57. A direct measure of ductility is the (a) Strain. (b) Percentage elongation. (c) Yield strength d) UTS 58. The resistance of a surface to abrasion or indentation is known as (a) Tensile strength. (b) Creep strength. (c)
Ductility. (d) Hardness. 59. The test used to find the endurance limit of a material is called:- a) Tension test b) hardness test b) fatigue test
d) creep test 60. The test used to find the resistance of the surface to indentation or plastic deformation is called a) Tension test b)
hardness test c) fatigue test d) creep test 61. The test used to measure the toughness due to sudden impact is called a) Impact test b) tension test
c) hardness test d) fatigue test 62. Strength of material are designated by (a) UTS (b) Yield stress (c) Toughness (d) a & b 63. The criteria of design for aircraft and automotive application is (a) light weight (b) high strength (c) strength to
weight ratio. 64. The property measured by loading a specimen from behind the notch by the impact of heavy Swinging pendulum is
the (a) UTS. (b) Fatigue strength. (c) Toughness. (d) Creep strength. 65. A proper selection of a material suitable for applications subjected to impact loads should be Based on the property
of (a) Impact toughness. (b) Hardness. (c) Ductility. (d) Toughness. 66. The impact test is used to measure the amount of energy absorbed for fracture under (a) Sudden impact. (b) Slow
loading conditions. (c) High temperature. (d) Changing loads. 67. Metals subjected to fluctuated or repeated forces fail at (a) Lower (b) Higher (c) The same d) none of the
above Stresses as those from the same metals carrying dead steady loads. 68. The fatigue limit is usually (a) 0.5 of the UTS. (b) 1.3 of the UTS. (c) The same as yield strength. 69. A proper selection of a material suitable for applications involving heavy frictional forces should be based on the
property of:- (a) Hardness. (b) Ductility. (c) Toughness. (d) Tensile strength. 70. A proper selection of a material suitable for applications carrying static dead loads should be based on the property
of: - (a) Hardness (b) Toughness (c) Yield strength (d) Fatigue limit 71. A proper selection of a material suitable for applications subjected to dynamic loading forces should be based on
the property of:- (a) Hardness. (b) Ductility. (c)Toughness (d) Fatigue strength. 72. When designing for high temperature service, one must consider (a) tensile properties only (b) fatigue properties
only (c) hardness properties only (d) creep properties as well as hardness and strength at considered temperature.
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73. If you are given two samples one made from a 0.2% C steel and the other made from 0.8% C steel and they got mixed is it possible that you identify which one is each? If you measured their Brinell hardness and impact toughness and obtained the data from Spec.1, i.e. hardness= 220 HB and Impact toughness=95 and data from Spec. 2, i.e. hardness = 280 and Impact tougness= 57. Answer, Spec. 1 is ------- a) 0.2% C b) 0.8%C
74. In Question one-Number 73, Spec.2 is -------- a) 0.2%C b) 0.8%C 75. One of the components of the composite material forms the matrix while the other present as particles or fibers
provides:- (a) The strength or hardness required. (b) The bonding required. (c) The toughness required d) The ductility required .
76. A proper selection of a material suitable for applications exposed to high temperatures for long times should be based on the property of:-(a) Hardness (b) Creep strength. (c) Ductility (d) Fatigue strength.
77. The maximum force that could be supported by a 50 mm diameter rod of yield strength 620 N/mm2 In static loading conditions using a factor of safety of 2 is :- (a) 610 MPa (b) 610 KN (c) 720 K d)720 MPa
78. The maximum force that could be supported by a 50 mm diameter rod of UTS 950 N/mm2 in dynamic loading conditions using a factor of safety of 3 (F.L=0.5 UTS) is (a) 310 KN (b) 310 MPa (c) 620K d) 620 Mpa.
79. The cross sectional area for apart made from steel of 0.2% offset yield strength 420 Mpa and ultimate tensile strength 600 Mpa, if it is required to carry a static load of 5000 KN (Note, W.S = Y.S/ F.S and F.S = 2) is :- a)1.5 cm2 b)2 cm2 c)2.38 cm2 d)3 cm2
80. During a tensile test on a cold worked brass the following data were obtained for force and corresponding extension. Answer the 0.2% offset yield strength is (a) 340 N/mm2 (b) 230 N/mm2 (c) 450 N/mm2 (D) 450KN .
Ext. mm 0.1 0.2 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2.0 2.5 3.0 4.0 Force KN 23 46 69 82 89 94 102 110 123 131 136 139 132
(Using the following information:, Diameter of test piece 16 mm., Gauge length 80 mm., Maximum load =139 KN., Break (fracture) load =118 KN., Final extension =4.3 mm.)
81. In Question one-number 80, UTS are: (a) 340 N/mm2 (b) 230 N/mm2 (c) 690 N/mm2 (d) 690KN 82. In Question one-number 80, % elongation of the material is (a) 20% (b) 5.4% (c) 10%. D) 15% 83. In Question one-number 80, What is the elongation exhibited by a 3mm wire made from the same
material, if carrying a load of 1 KN is a) 0.05% b)0.1% c)0.17% d) 0.25% 84. In Question one-number 80, What is the elongation if a 3 mm wire from the same material carry load of
2KN: a) 0.1% b) 0.2% C) 0.3% d) 0.4%
LIST YOUR CHOICE IN THIS TABLE, ANSWERS NOT IN THE TABLE WILL NOT BE CONSIDERED: 1 13 25 37 49 61 73 2 14 26 38 50 62 74 3 15 27 39 51 63 75 4 16 28 40 52 64 76 5 17 29 41 53 65 77 6 18 30 42 54 66 78 7 19 31 43 55 67 79 8 20 32 44 56 68 80 9 21 33 45 57 69 81 10 22 34 46 58 70 82 11 23 35 47 59 71 83 12 24 36 48 60 72 84
Total =
SECOND QUESTION: (34 marks), Answer questions , fill the space and Choose the Correct
Answer: 1. Draw the Engineering stress-strain curve for both 0.2 %C (plot one) and 0.4%C (plot two) indicating the most
significant points on the curve. Compare between plots in the curve? Strain (in/in) .001 .002 .005 .01 .02 .04 .06 .08 .10 .12 .14 .16 .18 Stress (Ksi) 0.2%C steel
0 30 55 60 68 72 74 75 76 73 69 65 56
Stress (Ksi) 0.4%C steel
0 55 60 68 82 90 93 95 97 93 90 86 75
(N.B. Stress in Ksi*7 =stress in Mpa, for 0.2%C steel (plot one): Break (fracture) stress = 51 Ksi and final strain = 0.19 in/in. On the other hand for 0.4%C steel (plot two): Fracture stress = 72 Ksi and final strain = 0.16 in/in.)
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i. For 0.2%C steel (plot one), answer the following: 1. 0.2% offset yield strength is--------------- a)30KN b)60KSi c)30Ksi d)68KSi 2. UTS is ---------------- a) 75KSi b) 76 Ksi c) 532 Mpa d) both b & c 3. % elongation of the material is--------------- a) 5% b) 10% c) 15% d) 19%.
ii. For 0.4%C steel (plot two), answer the following:
1. 0.2% offset yield strength is------------- a)60KSi b)55KSi c) 385MPa d)both b&c 2. UTS is --------------------------- a)75KSi b) 679MPa c)90KSi d)non of the above. 3. % elongation of the material is --------------------- :-a)10% b)13% c)16% d)20%
strain(�) in/in 2. Draw sketch for BCC and FCC unit cells identifying the following parameters:
i. Number of atoms per unit cell, coordination number and finally, calculate the atomic packing factor. ii. Relationship between the lattice constant and the atomic radius,
iii. Sketch the arrangement of the lattice points on a {111} type plane in a face centred cubic lattice and the same for a {110} type plane in a body centred cubic lattice.
iv. Iron has a density of 7.87 gm/cm3. The atomic radius [At. Wt. of Fe=55.85, A.N.=0.6002x10 24] is ------ a) r=2.24ºA b) r=3.24ºA c) r=1.24ºA d) r=0.24ºA
Q2-2: Answer BCC FCC Sketch
i. Number of atoms per unit cell i. coordination number i. Atomic packing factor. ii. Relationship a and r iii. Sketch {111}
{110}
iv. The atomic radius is------
Q2-1: Answer - comparison Plot--------------- have higher strength than plot ------------ Plot---------------have higher modulus of elasticity than plot----------------- Plot---------------have higher modulus of toughness than plot----------------- Plot---------------have higher ductility than plot-------------
Q2-1: Answer �-�
curve
stress
(�) ksi
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3. Use the given iron-iron carbon diagram to characterize each of the three alloys shown on the diagram by answering the related questions from i to iii.
Q2-3: Answer i. For alloy A: C%= The microstructure at RT consists of The microstructure at 14000F (7600C) consists of The microstructure at 22000F (12000C) consists of
(phases present and the percent of each phase). ii. For alloy E: C%= The microstructure at RT consists of The microstructure at RT after quenching the steel consists of The microstructure at 14000F (7600C) consists of
(phases present and the percent of each phase). iii. For alloy B: C%= The microstructure at RT consists of The microstructure at RT after quenching the steel consists of The microstructure at 14000F (7600C) consists of The microstructure at 22000F (12000C) consists of
(phases present and the percent of each phase).
iv. Hypoeutectoid alloys are those containing C in the range_____________, whereas hypereutectoid alloys are those containing C in the range _______________.
GOOD LUCK!
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Cairo University, 1st year Mining, Petroleum and Metallurgical Engineering, April, 2007 Faculty of Engineering Materials Science Time allowed: 1.5 h
Examiner: Dr. Mahmoud Tash
Q1: Crystal structure and defect i. Sketch BCC and FCC unit cells identifying the following parameters:
- Number of atoms per unit cell, - Relationship between the lattice constant and the atomic radius, - Sketch the arrangement of the lattice points on a {111} type plane in a face centred cubic lattice and the same for a {110} type plane in a body centred cubic lattice.
ii. The atomic radius of BCC tungsten is 1.4 Å. Calculate: The lattice parameter and b) The density of tungsten [At. wt = 183.8 g/g.mole] iii. Mention all type of defect and how can they affect properties
Q 2: Phase Diagrams and heat treatment 1. The eutectoid steel in Fe-C diagram has an austenite phase of composition ….. jusy below 1140C. (a) 4.3%C (b)
0.8%C (c) 2%C (d) 0.02%C (e) 6.6.7%C (f) none of the above. 1. The eutectic alloy on the Fe-Fe 3 C Diagram contains (a) 4.3%C (b) 0.8%C (c) 2%C (d) 0.02%C (e)
6.6.7%C (f) none of the above. 2. The eutectoid steel in Fe-C diagram is (a) Carbon tool steel of 0.6%C. (b)Carbon tool steel of 0.8%C. (c)
Carbon tool steel of 0.4%C. (d) None of the above 3. Annealing is usually performed to (a) Decrease hardness. (b) Increase ductility. (c) Relieve stresses. (d) All. 4. Quenching is (a) Heating to ferrite followed by air cooling. (b) Heating to austenite followed by water cooling.
c) Heating to austenite followed by air cooling. 5. Hardening and tempering produce optimum strength and toughness for (a) Steels of carbon content higher than
0.2%. (b) Al alloys. (c) Cu alloys. (d) All of the above. 6. Normalizing of steels is (a) Heating to ferrite followed by air cooling. (b) Heating to austenite followed by water
cooling. (c) Heating to austenite followed by air cooling. 7. Full annealing of steels is (a) Heating to ferrite followed by air cooling. (b) Heating to austenite followed by water
cooling. (c) Heating to austenite followed by furnace cooling. 8. Martensite is an unstable phase that appears due to non-equilibrium cooling conditions in ferrous alloys and it is
(a) of bct structure (b) of bcc structure (c) hard and brittle (d)hard and tough (e) both a and c (f) both a and d (g) both b and c (h) both b and d.
9. Non-equilibrium cooling conditions could be achieved in industrial conditions by (a) fast cooling (b) slow cooling (c) can not be achieved in industry.
10. Tempering of martensite makes it (a) more brittle (b) tougher (c) harder (d)of higher UTS . 11. The number of phases present in an alloy containing 0.4 % carbon, after equilibrium cooling to room temperature
are: (a) ferrite and cementite (b) ferrite and pearlite (c) ferrite and austenite 12. The structure of the alloy containing 0.8%C be after quenching in water consists of : (a)Ferrite and pearlite (b)
Ferrite and cementite (c) Martensite (d) None of the above 13. Quenching can be done in: (a)Water (b)Oil (c) Air (d)All of the above 15 The critical temperature for hypoeutectoid alloys in heat treatment must (a) ensure the alloy is of 2 phases ferrite +
austenite (b) one phase ferrite (c) one phase austenite. 16 Hardening temperature of hypo-eutectoid steels is (a)30-50 0C above upper critical temperature, (b)30-50 0C above
lower critical temperature, (c)30-50 0C above melting temperature, (d) 30-50 0C above recrystallization temperature. 17 The pearlite structure obtained in the eutectoid steel in Fe-C diagram contains …… at room Temperature. (a) 88%
Fe3C & 12% ferrite (b) 22% ferrite & 78% Fe3C c) 100% solid solution of carbon in gamma iron (d) 12%Fe3C & 88% ferrite
18 The 0.5%C steel contains less than 0.02%C in it’s ---- At 750ºC. (a) Austenite (b) Pearlite (c) Ferrite (d) Cementite 19 Upon cooling the eutectoid steel in Fe-C diagram from 1550ºC, the composition of the last trace of liquid phase at
the end solidification temperature is …%C (a) 0.4 (b) 0.8 (c) 4.3 (d) 1.6 20 The normalizing temperature in ºC of a hypoeutectoid steel having 88% Pearlite at room temperature is:- (a) 773ºC
(b) 1100ºC (c) 1250ºC (d) 1410ºC
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21 When the hypoeutectoid steel is heated to the normalizing temperature, the structure obtained is:- (a) Eutectic + Austenite (b) Pearlite +Fe3C (c) Fe3C + Austenite (d) None of the above
22 The number of phases of alloy containing 0.2%C after equilibrium cooling to room temperature is:- (a) One (b) two (c) three (d) four
23 The amount of phases of alloy contains 0.2% C after equilibrium cooling to room temperature is:- (a) 90% ferrite+ 10% austenite (b) 97% ferrite + 3%austenite (c) 97% ferrite + 3% Fe3C (d) 97% Fe3C + 3% ferrite
24 The number of phases of alloy contains 0.4%C after equilibrium cooling to room temperature is:- (a) One (b) Two (c) Three (d) Four
25 The amount of phases of alloy contains 0.4% C after equilibrium cooling to room temperature is:-(a) 94%austenite + 6% ferrite (b) 94% austenite +6%Fe3C (c) 94% Fe3C + 6% ferrite (d) 94% ferrite + 6% Fe3C
26 The number of phases of alloy containing 0.8%C after equilibrium cooling to room temperature is:- (a) One (b) Two (c) Three (d) Four
27 The amount of phases of alloy contains 0.8% C after equilibrium cooling to room temperature is:- (a)88% austenite + 12%ferrite (b) 60% ferrite + 40%Fe3C (c) 88% Fe3C + 12% ferrite (d) 88% ferrite + 12% Fe3C
28 The stricture of the alloy containing 0.8% C after quenching would contain:- (a)100% pearlite (b)100%martensite (c)50%ferrite + 50% Fe3C (d)50%ferrite+ 50% austenite
29 The upper critical temperature of the alloy containing 0.4%C is:- (a)723ºC (b)817ºC (c)863ºC (d)910ºC 30 The upper critical temperature of the alloy containing 0.8%C is:- (a)723ºC (b)817ºC (c)863ºC (d)910ºC 31 The upper critical temperature of the alloy containing 1.2%C is:-(a)723ºC (b)817ºC (c)863ºC (d)910ºC 32 The Fe-Fe3 C phase diagram is used to estimate ………. of Iron and steels. (a)Phases & microstructures (b)
Solidification sequence (c) Mechanical properties of C steels (d) (a) & (b). 33 The eutectic alloy on the Fe-Fe 3 C Diagram contains:- (a) 4.3%C (b) 0.8%C (c) 3.4%C (d) None of the above. 34 The pearlite structure obtained in the eutectoid steel in Fe-C diagram contains …… at room temperature. (a) 88%
Fe3C & 12% ferrite (b) 22% Fe3C & 78% ferrite (c) 22% ferrite & 78% Fe3C (d) 12%Fe3C & 88% ferrite 35 The structure of 0.5%C steel contains …… at 750C. (a) Ferrite & Pearlite (b) Ferrite and Austenite (c)
Ferrite & Cementite (d) Both (a) & (d) 36 The structure of 0.5%C steel contains two phases …… at room temperature (a) Ferrite & Pearlite (b) Ferrite
and Austenite (c) Ferrite & Cementite (d) Both (a) & (d) 37 The structure of 0.5%C steel consists of:- (a) 88% Fe3C & 12% ferrite (b) 22% Fe3C & 78% ferrite
(c) 22% ferrite & 78% Fe3C (d) 92.5%ferrite &7.5% Fe3C At room temperature after annealing. 38 The structure of the steel contains 0.5%C consists of (After water quenching to room temperature) (a) 88% Fe3C
& 12% ferrite (b) 37.5% pearlite and 62.5% martensite (c) 100% martensite (d) None of the above. 39 Upon cooling the eutectoid steel in Fe-C diagram from 1550 oC, it first transforms to:- (a) Liquid + ferrite (b)
Liquid +austenite (c) Ferrite + austenite (d) Austenite 40 The microstructure of hypo-eutectoid steel containing 0.2%C consists of :- (a) 90% pearlite and 10% ferrite (b)
75% Pearlite and 25% ferrite (c) 75% ferrite and 25% pearlite (d) 100% ferrite At room temperature 41 The upper critical temperature of a steel containing 0.4% C is:- (a) 7230 C (b) 7500 C (c) 8170 C (d) 9100 C 42 The structure of the alloy containing 0.8%C at 750 0 C consists of :- (a)100% Ferrite (b) 100% Austenite (c)
50% Ferrite + 50% Austenite (d) 100% Pearlite 43 Martensite has a structure of :- (a) BCC (b)FCC (c) BCT (d) HCP. 44 Normalizing is usually carried out to:- (a) Harden the steel (b) Soften the steel (c) Homogenize the properties (d)
Both a&c 45 The phases present in the alloy contains 0.4%C after equilibrium cooling to room temperature are:- (a) Austenite &
ferrite (b) Austenite &Fe3C (c) Ferrite & Fe3C (d) Ferrite & martensite 46 The phases present in the alloy contains 0.8%C after equilibrium cooling to room temperature are:-(a) Austenite &
ferrite (b) Austenite &Fe3C (c) Ferrite & Fe3C (d) Ferrite & martensite 47 The phases present in the alloy contains 1.2%C after equilibrium cooling to room temperature are:-(a) Austenite &
ferrite (b) Austenite &Fe3C (c) Ferrite & Fe3C (d) Ferrite & martensite 48 The amount of phases present in the alloy contains 0.4%C after equilibrium cooling to room temperature is :- (a)
94% martensite & 6% ferrite (b) 94% ferrite& 6% Fe3C (c) 94% austenite & 6% ferrite (d) 94% Fe3C & 6% ferrite
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49 The amount of phases present in the alloy contains 0.8%C after equilibrium cooling to room temperature is :-(a) 60% martensite& 40% ferrite (b) 88% ferrite& 12% Fe3C (c)80% austenite & 20% ferrite (d) 94% Fe3C & 6% ferrite
50 The amount of phases present in the alloy contains 1.2%C after equilibrium cooling to room temperature is :- (a) 94% martensite & 6% ferrite (b) 82% ferrite& 18% Fe3C (c) 80% austenite & 20% ferrite (d) 82 Fe3C & 18% ferrite
51 Annealing is usually performed to:- (a) Decrease hardness. (b) Increase ductility. (c) Relieve stresses. (d) All. 52 Tempering optimizes mechanical properties as it:- (a) Increases tensile strength and hardness (b) Increases
ductility and toughness. (c) Decreases tensile strength and hardness. (d) Both b & c. 53 Hardening and tempering produce optimum strength and toughness for:- (a) Steels of carbon content higher than
0.2%. (b) Al alloys. (c) Cu alloys. (d) All of the above. 54 Normalizing of steels is:- (a) Heating to ferrite followed by air cooling. (b) Heating to austenite followed by water
cooling. (c) Heating to austenite followed by air cooling. (d) Heating to austenite followed by furnace cooling 55 None-equilibrium cooling of Fe-C alloys by quenching yields a range of microstructure and mechanical properties
such as martensite having:- (a) High hardness and low toughness. (b) Low hardness and high toughness. (c) Low strength and high ductility. (d) Optimum combination of strength and hardness.
56 Full annealing of steels is: (a) Heating to ferrite followed by air cooling. (b) Heating to austenite followed by water cooling. (c) Heating to austenite followed by air cooling. (d) Heating to austenite followed by furnace cooling.
57 As the carbon content changes from 0.2 to 0.8%, the upper critical temperature:- (a) Increases (b) Decreases (c) Remains the same (d) critical temperature does not depend on carbon content
58 The effect of alloying elements on steel like Cr, Mo V, Ti, Si, etc. on heat treatment respond is:-(a)No effect (b) To increase hardenability (c) Make heat treatment with no effect (d) To decrease hardenability
59 We use the Fe-Fe3C diagram to predict the microstructure of steels: (a)Under equilibrium cooling conditions (b) Under all cooling conditions (c) At high temperatures only (d) After quenching
60 Equilibrium cooling of Fe-C alloys by slow cooling to room temperature yields a microstructure of:- (a)Ferrite and pearlite. (b)Austenite and pearlite. (c)Ferrite and Cementite. (d) Both b and c.
61 Tempering optimizes mechanical properties and it usually follows:- (a) Annealing. (b) Quenching. (c) Normalizing. (d) Both (b) and (c).
62 The number of phases present in an alloy containing 0.4 % carbon, after equilibrium cooling to room temperature are:- (a) 2 phases called ferrite and cementite (b) 2 phases called ferrite and pearlite (c) 2 phases called ferrite and austenite (d) None of the above
63 The structure of the alloy containing 0.8%C be after quenching in water consists of :- (a)Ferrite and pearlite (b) Ferrite and cementite (c) Martensite (d) None of the above
64 The upper critical temperature for the alloys containing 0.8C is:- (a) 850º C (b) 900º C (c) 773ºC (d) None. 65 The normalizing temperature in oC of a hypoeutectoid steel having 88% Pearlite at room temp. is :- (a)
773ºC (b) 960ºC (c) 793ºC (d) 910ºC 66 Steels Quenching is : (a) Heating to ferrite followed by rapid cooling. (b) Heating to austenite followed by rapid
cooling. (c) Heating to pearlite followed by rapid cooling. (d) All of the above 67 Quenching can be done in: (a)Water (b)Oil (c) Air (d)All of the above 68 .Martensite is an unstable phase that appears due to non-equilibrium cooling conditions in ferrous alloys and it is
(a) Of BCT structure (b) Of BCC structure (c) Of FCC structure (d) Of HCP structure 69 Martensite is an unstable phase that appears due to non-equilibrium cooling conditions in ferrous alloys and it is:-
(a)Hard and brittle (b) Hard and tough (c) Malleable (d) (a) & (c) 70 Non-equilibrium cooling conditions could be achieved in industrial conditions by:- (a) Fast cooling (b) Slow
cooling (c) Can not be achieved in industry. (d) None of the above 71 Tempering of martensite makes it:- (a) More brittle (b) Tougher (c) Harder (d) Of higher UTS . 72 Tempering is usually carried out by heating the steel to:- (a) Above 7230 C (b)Below 7 23ºC (c) Above
9100 C (d) Below 910 0 C. 73 Fine grain sizes are promoted by certain manufacturing conditions such as:- (a) High cooling rates (b) High
amounts of deformation (c) Certain alloying elements (d) All of the above
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74 Quenching is usually carried out to:- (a) Harden the steel ( b) Soften the steel (c) Homogenize the properties (d) Relief stresses
75 The normalizing temperature in 0 C of a hypoeutectoid steel having 75% Pearlite at room temperature Is:- (a) 773 (b) 1100-1250 (c) Above1410 (d) 850-900
76 Full annealing of steels corresponds to:- (a) Equilibrium cooling (b) Non-equilibrium cooling (c) Air cooling (d) Water cooling
77 Annealing made to highly alloyed castings should usually be conducted by cooling the parts in:- (a) Furnace (b) Air (c) Water (d)Oil
78 The normalizing temperature of eutectoid steel is:- (a) 700ºC (b) 773ºC (c) 850ºC (d) 910ºC 79 The tempering temperature for most steels must be below:- (a) 850ºc (b)800ºc (c)723ºc (d)910ºc 80 When the hypoeutectoid steel is heated to the quenching temperature, this temperature must ensure that the steel
enters the region of :- (a) Austenite phase (b) Ferrite (c) Pearlite (d)Fe3C. 81 Parts are furnace annealed to decrease their :- (a)-Brittleness & hardness (b)Ductility (c)Toughness
(d)None of the above 82 With reference to Fig. 1, answer the following questions: (Questions 82-88) From the Iron-carbon diagram to
determine the microstructure (phases present and the percent of each phase) for the following carbon-steel alloys : a) 0.15 % C after air cooling to room temperature b) 0.45% C after air cooling to room temperature c) O.83 % C after air cooling to room temperature, and 8000C d) 1.2 % C after air cooling to room temperature.
Fig. 1
83 for an alloy containing 0.12%C, answer questions (i-iv) i. The alloy is designated….. … (low C - medium C - high C) steel.
ii. This alloy contains ferrite and pearlite % at temperature below 700°C. iii. The alloy contains ferrite and cementite % at temperature below 700°C.
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84 The structure of a 0.15% C steel is composed of a. _____________ at 900 and b. _____________ at 800 and c. _____________at 700 0C .
85 The number of phases and relative amounts of each phase for the alloys containing 0.2,0.4 0.8% and 1 %
carbon, at 1600, 950, 700, and after equilibrium cooling to room temperature. 86 Sketch the cooling curve and microstructure for alloys A(pretectic), E(eutectoid), B(hyper-eutectoid) and
Eutectic 87 The atoms in the ferrite occupy positions in the lattice known as (BCC, FCC, BCT). 88 The structure of all hypoeutectoid alloys is (ferritic – pearlitic – austenitic) at 950oC.
89: With reference to Fig.2, answer the following questions: (Questions i-vii)
Fig.4.12
i. The amount of � in comparison with � (amount of �: amount of �) that forms if a 90%Pb-
10%Sn alloy is cooled to 0 C is (a). 45:4 (b) 4:45 (c) 8: 98 (d) 98:8 ii. The compositions of � and � phases at 170 C are … respectively (a) 98.5% Pb and 11% Pb
(b) 98.5% Sn and 11% Sn (c) 11%Pb and 98.5% Sn (d) None of the above iii. The amounts of � and � phases that form if the 30%Sn-70%Pb alloy is cooled to 0C are
……. respectively. (a) 100 � and 0% � (b) 71.5% � and 28.5 � (c) 0 � and 100% � (d) 28.5% � and 71.5% �
iv. The amount of primary � relative to the amount of eutectic for a 30%Sn-70%Pb alloy when it has been cooled to 0 C is (a)25% � (b) 75% � (c) 25% � (d) 75% �
v. For Pb-Sn alloy contains 25% Sn, what are the compositions of the phase in equilibrium at the eutectic temperature +0.5° C, and –0.5° C?
vi. For Pb-Sn alloy contains 45% Sn, which phases are in equilibrium at 100° C. What is the relative amount of each phase?
vii. For Pb-Sn alloy contains 15% Sn, what phases, compositions and amounts are present at 182° C, 150° C, and 50° C.
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Faculty of Engineering Materials Science Time allowed: 3 h Examiner: Dr. Mahmoud Tash (Cairo University-Engineering-Metallurgy) Part One: Answer the Following Questions:
1 Sketch BCC and FCC unit cells identifying the following parameters: a. Number of atoms per unit cell, b. Relationship between the lattice constant and the atomic radius, c. Sketch the arrangement of the lattice points on a {111} type plane in a face centred
cubic lattice and the same for a {110} type plane in a body centred cubic lattice. 2 The atomic radius of BCC tungsten is 1.4 Å. Calculate: The lattice parameter and b) The
density of tungsten [At. wt = 183.8 g/g.mole] 3 For Al-alloys, mention the different heat treatable alloys and what is the precipitation
hardening process? 4 What are the advantages of powder metallurgy? 5 What are the different types of cast iron and their engineering applications? 6 Mention (one or two ) engineering application for the following Cu-alloys: a)Brass b)Bronze
and c) Cu-Ni alloys Part Two: Answer the Following Questions: 1. Cu-alloys containing Zn are called (a)bronze (b)steel (c) brass (d) Non of the above. 2. Aluminium alloys posses a (a) higher or b) lower strength to weight ratio 3. Material made from mixture of two soluble components is called (a) Alloy (b) Composite. 4. Material made from matrix plus particles or fibers is called (a) Alloy (b)Composite. 5. Organic materials that contain molecules composed of hydrogen, oxygen and carbon are called
(a)ceramics (b)alloys (c)composites (d)polymers. 6. Electrical cables that require high electrical conductivity are usually made from (a) Steel
(b) Lead (c) Polymers (d) Copper or aluminum. 7. The strengthening in Al alloys is achieved by a heat treatment process known as:
(a)quenching (b) normalizing (c) solution treatment (d) precipitation hardening (e)annealing. 8. Low C steels are used mainly for (a) structural steels (b)machine parts (c)tool steels. 9. High C steels are used for making (a) Re-bars (b) cutting Tools (c) Springs (d)
Automobile body sheets (e) all of the above (f) both b and c. 10. The eutectoid steel in Fe-C diagram has an austenite phase of composition ….. jusy below 1140C.
(a) 4.3%C (b) 0.8%C (c) 2%C (d) 0.02%C (e) 6.6.7%C (f) none of the above. 11. The eutectic alloy on the Fe-Fe 3 C Diagram contains (a) 4.3%C (b) 0.8%C (c) 2%C
(d) 0.02%C (e) 6.6.7%C (f) none of the above. 12. The eutectoid steel in Fe-C diagram is (a) Carbon tool steel of 0.6%C. (b)Carbon tool steel of
0.8%C. (c) Carbon tool steel of 0.4%C. (d) None of the above 14 Sketch the cooling curve and microstructure for alloys A(pretectic), E(eutectoid), B(hyper-
eutectoid) and Eutectic 15 The number of phases and relative amounts of each phase for the alloys containing 0.2,0.4 0.8%
and 1 % carbon, at 1600, 950, 700, and after equilibrium cooling to room temperature. 16 The structure of the alloys containing 0.2,0.4 0.8% and 1 % carbon at RT. 17 Annealing is usually performed to (a) Decrease hardness. (b) Increase ductility. (c) Relieve
stresses. (d) All of the above. 18 Quenching is (a) Heating to ferrite followed by air cooling. (b) Heating to austenite followed by
water cooling. (c) Heating to austenite followed by air cooling. 19 Hardening and tempering produce optimum strength and toughness for (a) Steels of carbon
content higher than 0.2%. (b) Al alloys. (c) Cu alloys. (d) All of the above. 20 Normalizing of steels is (a) Heating to ferrite followed by air cooling. (b) Heating to austenite
followed by water cooling. (c) Heating to austenite followed by air cooling. 21 Full annealing of steels is (a) Heating to ferrite followed by air cooling. (b) Heating to austenite
followed by water cooling. (c) Heating to austenite followed by furnace cooling.
Dr. Mahmoud Tash