Tuning the stress induced martensitic formation in titanium alloys by alloy design

Two novel titanium alloys, Ti–10V–2Cr–3Al and Ti–10V–1Fe–3Al (wt%), have been designed, fabricated, and tested for their intended stress-induced martensitic (SIM) transformation behavior. The results show that for Ti–10V–1Fe–3Al the triggering stress for SIM transformation is independently affected by the β domain size and β phase stability, when the value of the molybdenum equivalent is higher than ~9. The triggering stress was well predicted using the equations derived separately for the commercial Ti–10V–2Fe–3Al alloy. For samples containing β with a lower molybdenum equivalence value, pre-existing thermal martensite is also present and this was found to have an obstructive effect on SIM transformation. In Ti–10V–2Cr–3Al, the low diffusion speed of Cr caused local gradients in the Cr level for many heat treatments leading even to martensite free zones near former β regions.