Effect of aging on isothermal ω/α″ growth and resulting mechanical behaviors of the Ti–Mo–Al high temperature shape memory alloys

Among β-Ti-based high-temperature shape memory alloys (HTSMAs), a Ti–Mo–Al alloy with a relatively high Al content of 14 mol%, which is much higher than that reported in previous studies, was designed to suppress the undesired ω-phase and to produce more promising HTSMAs. Ti–4.5Mo–14Al, Ti–5.5Mo–9Al, and Ti–6Mo–7Al (mol%) alloys, which possess almost identical reverse martensitic transformation temperatures of approximately 407 K, were aged at 393 K for various durations. The microstructures and deformation behaviors of the alloys were then investigated. Among all specimens, the solution-treated Al-rich Ti–4.5Mo–14Al specimen exhibited the largest lattice deformation strains. It was found that after aging, both the isothermal ω (ωiso)- and isothermal α″ (α″iso)-phases co-existed in all specimens. In the Al-rich Ti–4.5Mo–14Al alloy, the ωiso‐phase growth was suppressed to some extent while the α″iso‐phase grew. In contrast, in the Al-lean Ti–6Mo–7Al alloy, the ωiso-phase grew after aging. The deformation behavior of the aged Ti–4.5Mo–14Al alloys was little changed, with a slight increase in the yield stress. However, the deformation behavior of the aged Ti–6Mo–7Al alloy was completely altered, and its yield stress increased. Thus, it is concluded that for the utilization of Ti–Mo–Al alloys as HTSMAs, a high Al alloying concentration that successfully inhibits the growth of the ωiso-phase is preferred. [Display omitted] •A thermally stable Ti–Mo–Al alloy as high-temperature shape memory alloys is reached.•A 100% shape recovery was practiced by heating the Ti–Mo–Al alloys to 500 K.•Al-rich Ti–Mo–Al alloy exhibits larger lattice deformation strain than Al-lean one.•Al-rich alloy exhibits little deviation in mechanical behaviors after a 393 K aging.•Isothermal ω was inhibited while isothermal α″ domain grew in Al-rich alloy by aging.