Effect of warm-working rate on shape memory properties in Ti–49.7 at.%Ni alloy

This study investigated the effect of warm-working rate on the shape memory properties of Ti–49.7 at.%Ni alloy. The ingot was prepared by using an arc melting method and then warm-rolled at 673 K to reduce the thickness by 77%, 85%, and 89%. For comparison, an ingot was cold-rolled at room temperature to reduce the thickness up to 30%. The warm-worked specimens were annealed at 623–723 K for 3.6 ks, and the cold-worked specimens were annealed at 673 K for 3.6 ks. The transformation behavior was analyzed by means of differential scanning calorimeter (DSC) and tensile tests. The critical stress for slip increases with increasing warm-working rate and decreasing annealing temperature. The martensitic transformation temperature (TR→M) and the reverse transformation temperature (TM→B2) increase with decreasing warm-working rate and increasing annealing temperature. The critical stress for slip in the warm-worked specimens is higher than that of the specimens annealed at 673 K after cold-working. Therefore, warm-working at 673 K improves the shape memory characteristics of Ti-rich Ti–Ni alloys. This suggests that Ti-rich Ti–Ni alloys are good candidate materials for actuators.

► TR→M, TB2→R and TM→B2 increases with increasing working rate.
► The critical stress for slip increases with increasing working-rate.
► Comparing the specimen rolled at room temperature and at 673 K.
► TR→M and TM→B2 of the rolled at 673 K were higher than those of the rolled at room temperature.
► The critical stress for slip of the rolled at 673 K was higher than that of the rolled at room temperature.