The effects of α″ and ω phases on the superelasticity and shape memory effect of binary Ti-Mo alloys

The superelasticity and shape memory effect of binary water-quenched and air-cooled Ti-10, 11, and 12 Mo (wt%) alloys are evaluated by tensile tests and linear dilatometry measurements. In addition to β phase, the water-quenched alloys consist of α″ and ω phases, while the air-cooled alloys contain a large amount of ω phase. The amounts of α″ and ω phases decrease with the increasing Mo content. After 3% pre-strain, the water-quenched Ti-12Mo alloy exhibits highest superelastic recovery strain of about 0.7%. Subsequent heating gives rise to obvious shape memory recoveries in the water-quenched Ti-11Mo and 12Mo alloys at 700 K. A total recovery strain of about 1% and a total recovery ratio of around 33% are obtained in the water-quenched Ti-11Mo and 12Mo alloys. Lower room temperature superelasticity and shape memory effect are present in the air-cooled alloys due to the decreased transformation temperatures compared with water-quenched alloys. The re-orientation of α″ martensite occurred in the water-quenched alloys and the stress-induced α″ martensitic transformation occurred in both the water-quenched and air-cooled alloys. The formation of ω phase is detrimental to the re-orientation of α″ martensite and the stress-induced α″ martensitic transformation, resulting in higher superelasticity when the Mo content increases.