TITANIUM ALLOYS & IT'S TITANIUM ALLOYS & IT'S PROPERTIESPROPERTIES

TITANIUM ALLOYS & IT'S TITANIUM ALLOYS & IT'S PROPERTIESPROPERTIES

Prepared byANAND PRABHU P

TITANIUM ALLOYSTITANIUM ALLOYS

• Titanium has the best strength to weight ratio among the metals.

• Titanium is very reactive, and because of this it is often used for alloying and deoxidizing other metals.

• High yield strength compared to other metals

• Titanium also features excellent corrosion resistance, which stems from a thin oxide surface film

• Titanium is difficult to fabricate because of its susceptibility to oxygen, nitrogen, and hydrogen impurities which cause the titanium to become more brittle.

• Titanium can also be cast, which must be done in a vacuum furnace because of titanium's reactive nature.

• Metallurgical stability at elevated temperature

• Fine particles of titanium can ignite and burn

• Work hardening characteristics similar to SS

• Low Thermal conductivity

Characteristics of Titanium

Structural Efficiency:Structural Efficiency:

Structural Efficiency:Structural Efficiency:

Effect of low thermal conductivity

• Cutting tool life is reduced

• Burning of chips

TITANIUM ALLOYSTITANIUM ALLOYSDescription

• Pure titanium undergoes an allotropic transformation from the hexagonal close-packed alpha phase to the body-centered cubic beta phase at a temperature of 882.5°C (1620.5°F).

• Alloying elements can act to stabilize either the alpha or beta phase.

• Titanium alloys are generally classified into three main categories:

Alpha alloyswhich contain neutral alloying elements (such as Sn) and/or alpha stabilizers (such as Al, O) only and are not heat treatable

Alpha + beta alloys, which generally contain a combination of alpha and beta stabilizers and are heat treatable to various degrees

Beta alloyswhich are metastable and contain sufficient beta stabilizers (such as Mo, V) to completely retain the beta phase upon quenching, andcan be solution treated and aged to achieve significant increases in strength.

• do not generally respond to heat treatment,

• but they are weldable

• Low to medium strength

• Good notch toughness

• Reasonably good ductility

• Excellent mechanical properties at cryogenic temperatures

• Pure titanium and alpha alloys possess the highest corrosion resistance.

• More highly alloyed near-alpha alloys offer optimum high temperature creep strength and oxidation resistance.

Alpha Alloys:Alpha Alloys:

• Titanium alpha alloys are alloys typically contain aluminum and tin.

• They can also contain molybdenum, zirconium, nitrogen, vanadium, columbium, tantalum, and silicon.

• commonly used for cryogenic applications, airplane parts, and chemical processing equipment.

PropertiesTi-8Al-1Mo-1V Ti-2.5Cu (IMI 230) Ti-6Al-2Sn-4Zr-2Mo Ti-6Al-5Zr-0.5Mo-0.2Si (IMI 685)

• Alpha-beta alloys can be strengthened by heat treatment and aging,

• The alloys are used in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware, and prosthetic devices.

Alpha-Beta Alloys:Alpha-Beta Alloys:

Properties

Alpha Beta alloys are heat treatable and most are weldable. Typical properties include:

•Strength levels are medium to high•High temperature creep strength is not as good as most alpha alloys•Cold forming may be limited but hot forming qualities are normally good

•The most commonly used alpha beta alloy is Ti6Al4V

Ti-6Al-4V Ti-6al-6V-2Sn (Cu+Fe) Ti-6Al-2Sn-4Zr-6Mo Ti-4Al-4Mo-2Sn-0.5Si (IMI 550) Ti-4Al-4Mo-4Sn-0.5Si (IMI 551) Ti-5Al-2Sn-2Zr-4Mo-4Cr Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.25Si

• The smallest group of titanium alloys• Beta alloys have good hardenability, good cold formability when they

are solution-treated• Exhibit high strength when they are aged. • Beta alloys are slightly more dense than other titanium alloys, having

densities ranging from 4840 to 5060 kg/m3. • They are used for heavier duty purposes on aircraft.

Beta Alloys:Beta Alloys:

Properties

• Fully heat treatable• Generally weldable• Capable of high strengths• can have yield strengths up to 1345 MPa.• They are the least creep resistant alloys, Possess good creep resistance up

to intermediate temperatures• Excellent formability can be expected in the beta alloys in the solution

treated condition

Ti-13V-11Cr-3Al Ti-11.5Mo-6Zr-4.5Sn (Beta III) Ti-3Al-8V-6Cr-4Mo-4Zr (Beta C) Ti-10V-2Fe-3Al Ti-15V-3Al-3Cr-3Sn

Ti-6Al-4VTi-6Al-4V

Salient FeaturesElement Max

Titanium Balance

Nitrogen 0.05

Carbon 0.1

Hydrogen 0.125

Oxygen 0.2

Aluminium 6

Iron 4

Vanadium 3.5-4.5

Other elements 0.1

• Ti 6Al-4V is known as the "workhorse" of the titanium industry because it is by far the most common

• Ti alloy, accounting for more than 50% of total titanium usage. It is an alpha+beta alloy that is heat treatable to achieve moderate increases in strength.

• Ti 6Al-4V is recommended for use at service temperatures up to approximately 350°C (660°F).

• Ti 6Al-4V offers a combination of high strength, light weight, formability and corrosion resistance

• which have made it a world standard in aerospace applications

Material UTS (Mpa) Specific Strength (mx103 )

Ti 6Al-4V STA 1172 27.0

Ti 6Al-4V Annealed 924 21.3

4130 steel 1379 17.9

7075 T6 Aluminium 538 19.6

2024 T3 Aluminium 441 16.1

Inconel 718 1276 15.3

Reason for the wide use of Ti 6AL 4VReason for the wide use of Ti 6AL 4V

• Strong Chemical affinity at high temperature• Highly reactive• Material gets welded on the tool• Galling of machined surface

Other features of Titanium Alloys:Other features of Titanium Alloys:

Alloying Tendency

• Distortion can occur• Springness is more• Creates problems while machining

Modulus of Elasticity

Material Modulus of elasticity (Gpa)

Steel 200

Aluminium 70

Titanium 110

PTFE 1

• Immediately and spontaneously forms a stable, continuous, tightly adherent oxide film

• Ti 6Al-4V is highly resistant to general corrosion in aqueous solutions including seawater, as well as in oxidizing acids, rocket propellants and alkalis.

• Conditions under which Ti 6Al-4V is susceptible to general corrosion are in the presence of reducing acids or dry chlorine gas.

• Stress-corrosion cracking (SCC) and crevice corrosion have been shown to occur in environments containing chlorides or other halide ions.

• it is general practice to avoid the use of chlorinated solvents, cutting fluids, etc., in processing titanium.

Corrosion Resistance

Stress-corrosion cracking (SCC)

• Titanium and its alloys, including Ti 6Al-4V, are susceptible to hydrogen embrittlement.

• Gaseous or cathodic hydrogen can diffuse into the metal, forming brittle hydrides.

• It is important to minimize hydrogen pickup during processing, particularly heat treating and acid pickling.

• Specifications for Ti 6Al-4V mill products typically specify a maximum hydrogen limit of about 150 ppm.

Hydrogen Embrittlement

• Strongly susceptible to surface damages.

• Micro cracks on the surface can result in fatigue failure

Surface damage susceptibility

• Shows work hardening characteristics similar to SS

work hardening

Using the rating system based on AISI B1112 steel, the machinability of Ti 6Al-4V is rated at 22% of B1112.

Machinability

Material Machinability rating

Aluminium Alloy 300

B1112 steel 100

302 stainless steel 35

Ti-6Al-4V 22

HS25 (Cobalt based) 10

• Use low cutting speeds

• Maintain high feed rates

• Use a generous quantity of cutting fluids

• Use water based coolants or large volumes of oil based coolants

• Chlorinated cutting fluid should not be used

• Maintain sharp tools

• Prevent accumulation of chips

• Never stop feeding when tool and titanium are in moving contact.

• Use rigid setups

• Proper selection of cutting tool material – K10 grade is preferable, If HSS T type is preferred

Guidelines for machining TitaniumGuidelines for machining Titanium

Modern machining TechniquesModern machining Techniques

Cryogenic Machining

• cryogenic system delivers liquid nitrogen through the tool at a low flow rate, which has the effect of turning the tool into a heat sink.

• The white mist of liquid nitrogen/CO2 turning to gas as soon as it touches the air.

• It lowers the temperature at the tool tip

• This method of tool cooling has delivered dramatic gains in tool life, particularly in heat-resistant metals

Machining using liquid Nitrogen Machining using liquid CO2

• Ti 6Al-4V wrought products are typically used in either a mill annealed or solution treated and aged condition. Rapid quenching following solution treatment (water quench or equivalent) is important inorder to maximize the formation of alpha' martensite phase, which in turn maximizes the aging response.

• Other heat treatments used on Ti 6Al-4V include stress relieving for formed or welded parts,and beta annealing, which is used for improving damage tolerance.

• Ti 6Al-4V, like other titanium alloys, has a high affinity for gases including oxygen, nitrogen and hydrogen. Absorption of oxygen results in the formation of an extremely hard, brittle oxygen-stablized alpha phase layer known as alpha case upon heating in air.

• Intermediate and final annealing of Ti 6Al-4V mill products is often performed in a vacuum or inert gas atmosphere to avoid alpha case formation and the associated material loss.

• Vacuum annealing can also be used to remove excess hydrogen pickup, a process known as vacuum degassing. Parts to be vacuum heat treated must be thoroughly cleaned

Heat TreatmentHeat Treatment

Hot Working

•Ti 6Al-4V can be hot worked by standard methods such as hot rolling, forging, and hot pressing.

•Typically, hot working is done high in the alpha/beta temperature range, at approximately 870-980º C (1600-1800ºF).

•Care must be taken to prevent the formation of excessive alpha case, and alpha case must be removed after processing. Hot forming of sheet is typically done at temperatures around 650ºC (1200ºF).

•"Warm" Working: The yield strength of Ti 6Al-4V in both the annealed and STA conditions drops off rapidly with temperature, making it readily formable at intermediate temperatures. For example, heating to just 427°C (800°F) results in approximately a 40% reduction in yield strength. Warm forming is used extensively in the manufacture of many products, including fasteners, aircraft components, and medical devices.

Workability

Cold Working

•Ti 6Al-4V can be cold drawn and extruded, although the cold workability is somewhat limited.

•Cold forming is sometimes used for parts such as brackets and clips.

•Due to the low modulus of titanium, springback is an issue in room-temperature forming.

•Theoretically, it can be compensated for by over-bending; however, in practice hot sizing is often used to correct for the variability that occurs.

Weldability

•Ti 6Al-4V can be welded using Ti 6Al-4V filler metal. •Inert gas shielding techniques must be employed to prevent oxygen pickup and embrittlement in the weld area. •Gas tungsten arc welding is the most common welding process for Ti 6Al-4V. •Gas metal arc welding is used for thick sections. •Plasma arc welding, spot welding, electron beam, laser beam, resistance welding and diffusion welding have all been used successfully in Ti 6Al-4V welding applications.

Wear Resistance

•Ti 6Al-4V, and Ti alloys in general, have a tendency to gall and are not recommended for wear applications.

Descaling (Cleaning)

•Following heat treatment in air, it is extremely important to completely remove not only the surface scale but the underlying layer of brittle alpha case as well. •This removal can be accomplished by mechanical methods such as grinding or machining, or by descaling (using molten salt or abrasive)•followed by pickling in a nitric/hydroflouric acid mixture.•Titanium alloys are also susceptible to hydrogen embrittlement, and care must be taken to avoid excessive hydrogen pickup during heat treating and pickling/chemical milling.

• Ti 6Al-4V may be considered in any application where a combination of high strength at low to moderate temperatures, light weight and excellent corrosion resistance are required.

• Some of the many applications where this alloy has been used include aircraft turbine engine components, aircraft structural components, aerospace fasteners, high-performance automotive parts, marine applications, medical devices, and sports equipment.

ApplicationsApplications

Pressure vessel Application:Pressure vessel Application:

For pressure-critical components and vessels for industrial applications,titanium alloys are qualified under numerous design codes and offer attractive design allowables up to 315°C (600°F)Some common pressure design codes include the

•ASME Boiler and Pressure Vessel Code (Sections I, III, and VIII),•ANSI (ASME) B31.3 Pressure Code•BS-5500 •CODAP•Stoomwezen and Merkblatt European Codes,•Australian AS 1210•Japanese JIS codes.

THANK YOUTHANK YOU