Mechanical properties and shape memory behavior of Ti-Mo-Ga alloys

Mechanical properties and shape memory behavior of Ti-Mo-Ga alloys were investigated in order to develop Ni-free biomedical shape memory alloys. The Ti-Mo-Ga alloys were fabricated by arc melting method. The ingots were cold-rolled tip to 95% reduction in thickness. The cold-rolled specimens were heat treated in the temperature range 673-1273K for 60s-3.6ks. The martensitic transformation temperature decreased with increase in Mo and Ga content. The maximum shape recovery strain was obtained in a solution treated Ti-6 at%Mo-3 at%Ga alloy. Mechanical properties and shape memory behavior strongly depend on heat treatment condition in the Ti-6 at%Mo-3 at%Ga. Premature failure was observed in specimens heat treated in the temperature range 673-773 K. Ultimate tensile strength decreased and fracture strain increased with increasing heat treatment temperature. Shape memory effect was obtained in specimens heat treated in the temperature range 1073-1273 K. The shape memory effect was due to the stress induced martensitic transformation yielding tensile deformation and the reverse transformation upon heating after unloading. The martensitic transformation start temperature increased and the yield stress decreased with increasing heat treatment temperature and time. Stable superclastic behavior was obtained in a Ti-7 at%Mo-4 at%Ga alloy at room temperature by cyclic tensile tests. The recovery strain exceeding 4% was achieved in the pre-strained Ti-7 at%Mo-4 at%Ga alloy.