mechanical & aerospace engineering west virginia university ceramics

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Mechanical & Aerospace Engineering West Virginia University Ceramics

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Page 1: Mechanical & Aerospace Engineering West Virginia University Ceramics

Mechanical & Aerospace Engineering

West Virginia University

Ceramics

Page 2: Mechanical & Aerospace Engineering West Virginia University Ceramics

Mechanical & Aerospace Engineering

West Virginia University

2

• Properties: -- Tm for glass is moderate, but large for other ceramics. -- Small toughness, ductility; large moduli & creep resist.

• Applications: -- High T, wear resistant, novel uses from charge neutrality.

• Fabrication -- some glasses can be easily formed -- other ceramics can not be formed or cast.

Glasses Clay products

Refractories Abrasives Cements Advanced ceramics

-optical -composite reinforce -containers/ household

-whiteware -bricks

-bricks for high T (furnaces)

-sandpaper -cutting -polishing

-composites -structural

engine -rotors -valves -bearings

-sensors

Adapted from Fig. 13.1 and discussion in Section 13.2-6, Callister 7e.

Taxonomy of Ceramics

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• Need a material to use in high temperature furnaces.• Consider the Silica (SiO2) - Alumina (Al2O3) system.

• Phase diagram shows: mullite, alumina, and crystobalite as candidate refractories.

Adapted from Fig. 12.27, Callister 7e. (Fig. 12.27 is adapted from F.J. Klug and R.H. Doremus, "Alumina Silica Phase Diagram in the Mullite Region", J. American Ceramic Society 70(10), p. 758, 1987.)

Application: Refractories

Composition (wt% alumina)

T(°C)

1400

1600

1800

2000

2200

20 40 60 80 1000

alumina +

mullite

mullite + L

mulliteLiquid

(L)

mullite + crystobalite

crystobalite + L

alumina + L

3Al2O3-2SiO2

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Mechanical & Aerospace Engineering

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tensile force

AoAddie

die

• Die blanks: -- Need wear resistant properties!

• Die surface: -- 4 m polycrystalline diamond particles that are sintered onto a cemented tungsten carbide substrate. -- polycrystalline diamond helps control fracture and gives uniform hardness in all directions.

Courtesy Martin Deakins, GE Superabrasives, Worthington, OH. Used with permission.

Adapted from Fig. 11.8 (d), Callister 7e. Courtesy Martin Deakins, GE

Superabrasives, Worthington, OH. Used with permission.

Application: Die Blanks

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• Tools: -- for grinding glass, tungsten, carbide, ceramics -- for cutting Si wafers -- for oil drilling

bladesoil drill bits• Solutions:

coated singlecrystal diamonds

polycrystallinediamonds in a resinmatrix.

Photos courtesy Martin Deakins,GE Superabrasives, Worthington,OH. Used with permission.

Application: Cutting Tools

-- manufactured single crystal or polycrystalline diamonds in a metal or resin matrix.

-- optional coatings (e.g., Ti to help diamonds bond to a Co matrix via alloying) -- polycrystalline diamonds resharpen by microfracturing along crystalline planes.

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• Example: Oxygen sensor ZrO2

• Principle: Make diffusion of ions fast for rapid response.

Application: Sensors

A Ca2+ impurity

removes a Zr4+ and a

O2- ion.

Ca2+

• Approach: Add Ca impurity to ZrO2:

-- increases O2- vacancies

-- increases O2- diffusion rate

reference gas at fixed oxygen content

O2-

diffusion

gas with an unknown, higher oxygen content

-+voltage difference produced!

sensor• Operation: -- voltage difference produced when

O2- ions diffuse from the external surface of the sensor to the reference gas.

Page 7: Mechanical & Aerospace Engineering West Virginia University Ceramics

Mechanical & Aerospace Engineering

West Virginia University

Glass & Vitreous Ceramics

Vitreous Ceramics

Glass

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Mechanical & Aerospace Engineering

West Virginia University

High-performance Engineering Ceramics

Diamond: used as cutting tools, rock drills, abrasive, etc.

Generic High-performance Ceramics

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Mechanical & Aerospace Engineering

West Virginia University

Cement and Concrete

Cement: Mixture of lime (CaO), silica (SiO2) and alumina (Al2O3), which sets when mixed with water

Concrete: Sand and stones held together by cement.

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Mechanical & Aerospace Engineering

West Virginia University

Natural Ceramics

Page 11: Mechanical & Aerospace Engineering West Virginia University Ceramics

Mechanical & Aerospace Engineering

West Virginia University

Structure of Ceramics - Ionic

NaCl Structure

MgO Structure:Can be thought of as an fcc packing with Mg ions in octahedral holes.

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Mechanical & Aerospace Engineering

West Virginia University

Structure of Ceramics - Ionic

ZrO2: fcc packing of Zr with O in the tetrahedral holes

Al2O3: c.p.h packing of O with Al in 2/3 of the octahedral holes

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Mechanical & Aerospace Engineering

West Virginia University

Structure of Ceramics – Simple Covalent

Diamond: each atom has four neighbors.

SiC: diamond structure with half the atoms replaced by Si.

Page 14: Mechanical & Aerospace Engineering West Virginia University Ceramics

Mechanical & Aerospace Engineering

West Virginia University

Structure of Ceramics – Simple Covalent

Cubic SiO4: diamond structure with an SiO4 tetrahedron on each atom site.

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Mechanical & Aerospace Engineering

West Virginia University

Structure of Ceramics

Microstructure of Ceramics

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Mechanical & Aerospace Engineering

West Virginia University

Mechanical Properties of Ceramics

Elastic Moduli

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Mechanical & Aerospace Engineering

West Virginia University

Mechanical Properties of Ceramics

Strength, Hardness & Lattice Resistance

Normalised Hardness of Pure Metals, Alloys and Ceramics

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Mechanical & Aerospace Engineering

West Virginia University

Mechanical Properties of Ceramics

Dislocation Movement

Dislocation motion in covalent solids is intrinsically difficult because the interatomic bonds must be broken and reformed

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Mechanical & Aerospace Engineering

West Virginia University

Mechanical Properties of Ceramics

Dislocation Movement

Dislocation motion in ionic solids is easy on some planes, but hard on others. The hard systems usually dominate.

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Mechanical & Aerospace Engineering

West Virginia University

Mechanical Properties of Ceramics

Fracture Strength of Ceramics

The design strength of a ceramic is determined by fracture toughness and lengths of the microcracks it contains.

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Mechanical & Aerospace Engineering

West Virginia University

Mechanical Properties of Ceramics

Fracture Strength of Ceramics

(a) Tensile test measures tensile strength, TS

(b) Bend test measures modulus of rupture, r, typically 1.7 TS

(c) Compression test measures crushing strength, c, typically 15TS

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West Virginia University

Mechanical Properties of Ceramics- Fracture Strength

In compression, many flaws propagate stably to give general crashing

In tension the largest flaw propagates unstably

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West Virginia University

Mechanical Properties of Ceramics

Thermal Shock Resistance

ET = TS

Where E is the Young’s modulus, is the coefficient of expansion and TS is tensile strength. T represents the ceramic’s thermal shock resistance

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• Pressing:

GLASSFORMING

Adapted from Fig. 13.8, Callister, 7e. (Fig. 13.8 is adapted from C.J. Phillips, Glass: The Miracle Maker, Pittman Publishing Ltd., London.)

Ceramic Fabrication Methods-I

Gob

Parison mold

Pressing operation

• Blowing:

suspended Parison

Finishing mold

Compressed air

plates, dishes, cheap glasses

--mold is steel with graphite lining

• Fiber drawing:

wind up

PARTICULATEFORMING

CEMENTATION

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Sheet Glass Forming

• Sheet forming – continuous draw– originally sheet glass was made by “floating” glass on a pool of mercury

Adapted from Fig. 13.9, Callister 7e.

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• Quartz is crystalline SiO2:

• Basic Unit: • Glass is amorphous• Amorphous structure occurs by adding impurities

(Na+,Mg2+,Ca2+, Al3+)• Impurities: interfere with formation of crystalline structure.

(soda glass)

Adapted from Fig. 12.11, Callister, 7e.

Glass Structure

Si04 tetrahedron4-

Si4+

O2-

Si4+

Na+

O2-

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• Specific volume (1) vs Temperature (T):

• Glasses: -- do not crystallize -- change in slope in spec. vol. curve at

glass transition temperature, Tg

-- transparent - no crystals to scatter light

• Crystalline materials: -- crystallize at melting temp, Tm

-- have abrupt change in spec. vol. at Tm

Adapted from Fig. 13.6, Callister, 7e.

Glass Properties

T

Specific volume

Supercooled Liquid

solid

T m

Liquid(disordered)

Crystalline (i.e., ordered)

T g

Glass (amorphous solid)

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Glass Properties: Viscosity

• Viscosity, : -- relates shear stress and velocity gradient:

has units of (Pa-s)

y

v

d

d

velocity gradient

dv

dy

glass dvdy

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• Viscosity decreases with T• Impurities lower Tdeform

Adapted from Fig. 13.7, Callister, 7e.(Fig. 13.7 is from E.B. Shand, Engineering Glass, Modern Materials, Vol. 6, Academic Press, New York, 1968, p. 262.)

Glass Viscosity vs. T and Impurities

fused silica

96% silica

soda-lime

glass

Vis

cosi

ty [P

a s

]

1

102

106

1010

1014

200 600 1000 1400 1800 T(°C)

Tdeform : soft enough to deform or “work”

annealing range

Pyrex

Tmelt

strain point

• fused silica: > 99.5 wt% SiO2

• soda-lime glass: 70% SiO2 balance Na2O (soda) & CaO (lime)

• Vycor: 96% SiO2, 4% B2O3

• borosilicate (Pyrex): 13% B2O3, 3.5% Na2O, 2.5% Al2O3

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• Annealing: --removes internal stress caused by uneven cooling.

• Tempering: --puts surface of glass part into compression --suppresses growth of cracks from surface scratches. --sequence:

Heat Treating Glass

further cooled

tensioncompression

compression

before cooling

hot

surface cooling

hotcooler

cooler

--Result: surface crack growth is suppressed.

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• Milling and screening: desired particle size• Mixing particles & water: produces a "slip"• Form a "green" component

• Dry and fire the component

ram billet

container

containerforce

die holder

die

Ao

Adextrusion--Hydroplastic forming: extrude the slip (e.g., into a pipe)

Adapted from Fig. 11.8 (c), Callister 7e.

Ceramic Fabrication Methods-IIA

solid component

--Slip casting:

Adapted from Fig. 13.12, Callister 7e.(Fig. 13.12 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

hollow component

pour slip into mold

drain mold

“green ceramic”

pour slip into mold

absorb water into mold “green

ceramic”

GLASSFORMING

PARTICULATEFORMING

CEMENTATION

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Clay CompositionA mixture of components used

(50%) 1. Clay

(25%) 2. Filler – e.g. quartz (finely ground)

(25%) 3. Fluxing agent (Feldspar)

binds it together

aluminosilicates + K+, Na+, Ca+

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• Clay is inexpensive• Adding water to clay -- allows material to shear easily along weak van der Waals bonds -- enables extrusion -- enables slip casting

• Structure ofKaolinite Clay:

Adapted from Fig. 12.14, Callister 7e.(Fig. 12.14 is adapted from W.E. Hauth, "Crystal Chemistry of Ceramics", American Ceramic Society Bulletin, Vol. 30 (4), 1951, p. 140.)

Features of a Slip

weak van der Waals bonding

charge neutral

charge neutral

Si4+

Al3+

-OHO2-

Shear

Shear

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• Drying: layer size and spacing decrease.Adapted from Fig. 13.13, Callister 7e.(Fig. 13.13 is from W.D. Kingery, Introduction to Ceramics, John Wiley and Sons, Inc., 1960.)

Drying and Firing

Drying too fast causes sample to warp or crack due to non-uniform shrinkagewet slip partially dry “green” ceramic

• Firing: --T raised to (900-1400°C) --vitrification: liquid glass forms from clay and flows between SiO2 particles. Flux melts at lower T.

Adapted from Fig. 13.14, Callister 7e.(Fig. 13.14 is courtesy H.G. Brinkies, Swinburne University of Technology, Hawthorn Campus, Hawthorn, Victoria, Australia.)

Si02 particle

(quartz)

glass formed around the particle

micrograph of porcelain

70 m

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Sintering: useful for both clay and non-clay compositions.• Procedure: -- produce ceramic and/or glass particles by grinding -- place particles in mold -- press at elevated T to reduce pore size.

• Aluminum oxide powder: -- sintered at 1700°C for 6 minutes.

Adapted from Fig. 13.17, Callister 7e.(Fig. 13.17 is from W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to Ceramics, 2nd ed., John Wiley and Sons, Inc., 1976, p. 483.)

Ceramic Fabrication Methods-IIB

15 m

GLASSFORMING

PARTICULATEFORMING

CEMENTATION

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Powder PressingSintering - powder touches - forms neck & gradually neck thickens

– add processing aids to help form neck

– little or no plastic deformation

Adapted from Fig. 13.16, Callister 7e.

Uniaxial compression - compacted in single direction

Isostatic (hydrostatic) compression - pressure applied by fluid - powder in rubber envelope

Hot pressing - pressure + heat

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Tape Casting

• thin sheets of green ceramic cast as flexible tape

• used for integrated circuits and capacitors

• cast from liquid slip (ceramic + organic solvent)

Adapted from Fig. 13.18, Callister 7e.

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• Produced in extremely large quantities.• Portland cement: -- mix clay and lime bearing materials -- calcinate (heat to 1400°C) -- primary constituents: tri-calcium silicate di-calcium silicate• Adding water -- produces a paste which hardens -- hardening occurs due to hydration (chemical reactions with the water).• Forming: done usually minutes after hydration begins.

Ceramic Fabrication Methods-III

GLASSFORMING

PARTICULATEFORMING

CEMENTATION

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Applications: Advanced Ceramics

Heat Engines

• Advantages: – Run at higher temperature

– Excellent wear & corrosion resistance

– Low frictional losses

– Ability to operate without a cooling system

– Low density

• Disadvantages: – Brittle– Too easy to have voids-

weaken the engine– Difficult to machine

• Possible parts – engine block, piston coatings, jet engines

Ex: Si3N4, SiC, & ZrO2

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Applications: Advanced Ceramics

• Ceramic Armor

– Al2O3, B4C, SiC & TiB2

– Extremely hard materials » shatter the incoming projectile

» energy absorbent material underneath

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Applications: Advanced Ceramics

Electronic Packaging

• Chosen to securely hold microelectronics & provide heat transfer

• Must match the thermal expansion coefficient of the microelectronic chip & the electronic packaging material. Additional requirements include:

– good heat transfer coefficient

– poor electrical conductivity

• Materials currently used include:» Boron nitride (BN)

» Silicon Carbide (SiC)

» Aluminum nitride (AlN)• thermal conductivity 10x that for Alumina

• good expansion match with Si