Common titanium alloy is designated as Ti6Al4V, a.k.a. Ti64. This alloy is versatile and used across many industry sectors due to its high strength-to-weight ratio; it’s comparable to steel but at almost half the weight.
This alloy has a single top level alloy specification, but is actually used in two grades, the more common Grade 5, and the Extra Low Interstitial (ELI) Grade 23. The composition of the latter differs since there are much tighter controls on the amounts of allowed Oxygen and Nitrogen.
The metallurgy of Ti64 is complex and many different international standards exist to cover the properties that develop after a part undergoes one of a number of heat treatment cycles. The first AM standard that was published for this alloy under ASTM F42 was broad enough to allow the production by any laser powder bed fusing method and subsequently virtually any allowable heat treatment due to the large number of already existing standards for this alloy.
Residual stress is a particular problem for Ti64. Therefore, it’s difficult to state particular material properties in the as-built condition. Most vendors publish data after the test sample has undergone a stress relieving cycle.
There are many different stress relieving heat treatment cycles and each will result in different mechanical properties. For instance, the Medical and Dental Products Division at Renishaw has developed a custom heat treatment cycle that leads to very high levels of flexibility in the ELI alloy, which is now produced under the trademark name of X-Flex.
Other titanium alloys for AM include commercially pure alloys covered by the group name of Ti-CP, the medical alloy Ti7Al7Nb, and high temperature or high strength alloys such as, Ti-6242.
This information is excerpted from a Renishaw paper The status quo of metal alloys for additive manufacturing.