|Titanium and its Alloys|
1. Introduction: Although when 'pure' (99% - 99.5%) Titanium does not have a particularly high strength (UTS at room temperature: 330 - 650 MPa), when alloyed (with aluminium, copper, manganese, molybdenum, tin, vanadium, or zirconium) it's strength increases considerably (UTS at room temperature 800 - 1450 MPa). The elevated temperature strength properties of titanium and its alloys are also good.
Young's modulus for titanium and most of it's alloys is about 110 GPa (125 GPa for Ti-6Al-4V) and the shear modulus is about 45 GPa. The fatigue endurance strength at 107 cycles of 'pure' titanium is 0.5 times the UTS and for the alloys is 0.4 to 0.65 times the UTS.
When these mechanical properties are considered with it's very good corrosion resistance and a density of 4500 kg/m3 (slightly over half that of steel) it means that despite its high cost, it is used in a range of specialist areas.
Un-alloyed titanium is used for its corrosion resistance in chemical plant.
Applications for high strength alloys include components for aerospace - air frame and turbine parts - connecting rods in high performance engines, bolts, etc.
2. Classification of Titanium Alloys: Alloys can be classified according to the phases present. They are often referred to just by the nominal compositions. In the US there are ASTM and ASM specifications. In the UK the IMI Ltd. codes for the alloys are frequently used.
3. Typical Properties of some Alloys
|Alloy type, properties and use||Composition||IMI code||ASTM grade||UTS, MPa||0.2% Yield Strength, MPa||Elongation %||Fracture Toughness, MPa(m)0.5|
|Unalloyed. Non-heat treatable. Used for parts requiring high corrosion resistance.||commercially pure, >99% Ti||110, 115, 125, 130, 155, 160||1, 2, 3, 4||330 - 650||220 - 550||20 - 30||70 or more|
|Small addition of palladium increases the corrosion resistance||commercially pure, 0.05% - 0.2% Pd||260, 262||7, 11||480||350||28|
|Alpha and near alpha: Good high temperature strength||Ti-2.5Cu||230|
|Alpha and near alpha: these alloys have high strength and good creep resistance and are used in aircraft frames and jet engine components.||Ti-2.25Al-11Sn-1Mo-5Zr-0.2Si, Ti-6Al-5Zr-0.5Mo-0.25Si||679, 685||1000||900||50 - 60|
|Retains toughness and ductility at low temperature, hence extensively used in cryogenic applications.||Ti-5Al-2.5Sn-Extra low interstitial||>690||>620|
|Alpha-Beta: Heat treatable (solution treated, quenched and aged) good hot forming qualities. Creep strength not as good as most Alpha alloys.||Ti-6Al-v4, Ti-4Al-4Mo-2Sn-0.5Si||318, 550||900-1100||800-1000||14 - 17||40 - 60|
|Beta: Can be cold worked in solution and quenched condition (unlike alpha alloys) and then aged to give very high strengths.||Ti-11.5Mo-6Zr-4.5Sn, Ti-3Al-8V-6Cr-4Mo-4Zr||1400||1300||11||50|
For further information, link to Titanex Gmbh.
Reference: Titanium: A Technical Guide, by Donachie, ASM, 2000, ISBN: 0-87170-686-5.
David J Grieve. Revised 8th September 2004. Original December 2000
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