Effects of Ni Content and Solution-Aging Treatment on Multi-Stage Transformations of TiNi Shape Memory Alloys

Abstract Effects of Ni content and solution-aging treatment on transformation type and transformation temperature of Ti 100- x Ni x ( x =33.3-75) alloys were investigated by differential scanning calorimeter (DSC). The results show that one-stage transformation B2→B19' of the solution-quenched Ti 100- x Ni x alloys occurs. The martensitic transformation temperature T M is constant at x = 40-49, decreases sharply at x = 49-52, increases gradually at x = 52-56, and is constant again at x = 56-70. The alloys after aging at 773 K for 3.6 ks and 36 ks will have the occurrence of one-stage transformation B2→B19' at x = 40-50.5, and the T M is constant first and then decreases suddenly with increasing of x ; when x = 50.5-52, the alloys have the occurrence of two-stage transformation B2· R · B19' and the T M decreases gradually with increasing of x ; when x =53-70,· the alloys have the occurrence of three-stage transformation and the T M1 and T M2 all increase first and then keep constant with increasing of x . All alloys after aging at 773 K for 360 ks have the occurrence of one-stage transformation B2→B19' except for Ti 49 Ni 51 and Ti 47 Ni 53 alloy, which will have the occurrence of two-stage transformation B2→R→B19' and three-stage transformation, respectively.