Remarkable improvement of shape memory effect in a Co–31Ni–3Si alloy by training treatment

The influence of training cycles consisting of deformation by 5% at room temperature and subsequent annealing at different temperatures on the shape memory effect was studied in a Co–31Ni–3Si alloy to improve its shape memory effect. The results showed that the optimal annealing temperature in training was 973 K. A large recovery strain of 2.3% was obtained after one training cycle at the optimal annealing temperature and then bend by 3.7% at 77 K. The training promoted the stress-induced epsilon martensitic transformation and suppressed the occurrence of slip deformation due to the increase in yield strength. These results revealed that the shape memory effect in Co–Ni-based alloys stems from the stress-induced epsilon martensitic transformation. Their low yield strengths account for their poor shape memory effect.