There are three structural types of titanium alloys:
• Alpha Beta
The attributes of titanium alloys of prime importance to the design engineer are:
• Outstanding corrosion resistance
• Excellent erosion resistance
• High heat transfer capability
• Superior strength-to-weight ratios
Titanium alloys are also used because of their:
• Low thermal expansion co-efficient
• Non-magnetic character
• Fire resistance
• Short radioactive half life
Alpha Titanium Alloys
Commercially pure titanium and alpha alloys of titanium are non-heat treatable and are genarally very weldable . They have:
• 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 Beta Titanium Alloys
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
• Many alloys can be superplastically formed
The most commonly used alpha beta alloy is Ti6Al4V, developed in many variations of the basic formulation for the widest possible choice of key properties and for many widely differing applications.
Beta Titanium Alloys
Beta or near beta alloys are:
• Fully heat treatable
• Generally weldable
• Capable of high strengths
• Possess good creep resistance up to intermediate temperatures
• Excellent formability can be expected in the beta alloys in the solution treated condition
Beta-type alloys have good combinations of properties in sheet, as fasteners and are ideal for sporing applications. Some alloys offer uniform property levels through heavy sections.
The higher alloy content of beta alloys increases the density of beta alloys typically by 7-10% compared to Ti6Al4V.
Typical beta alloys include:
Ti3Al8V6Cr4Mo4Zr ASTM Grade 19
Ti10V2Fe3Al AMS 4983, 4984, 4987
Ti15Mo3Nb3Al2Si ASTM Grade 21
Ti15V3Cr3Sn3Al AMS 4914
Correctly, it is only the metastable beta alloys which are heat treatable by solution treatment and ageing. Fully stable beta alloys can only be annealed.