Significant improvement of shape memory effect in Co-Ni-based alloys through Si alloying

Abstract

We proposed that much lower forward martensitic transformation temperature (Ms) and lower yield strength were responsible for lower improvement of shape memory effect (SME) at room temperature (RT) in Co-based alloys than that in Fe-Mn-based alloys by Si alloying. To prove our opinion, the SME and martensitic transformation were investigated in Co-xNi-6Si (x = 15, 20, 25 wt%) alloys with higher Si content. The results confirmed that the Si addition could significantly improve the SME of Co-Ni-based alloys after adjusting the Ms temperature to around RT. The Co-20Ni-6Si alloy with Ms temperature close to RT showed the highest shape recovery of 80% after bent by 2.7%. This value was much higher than the ones in the Co-15Ni-6Si and Co-25Ni-6Si alloys whose Ms temperatures were much far from RT. The reduction in the Ms temperature by the Si addition augmented with increasing the Ni content.