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

摘要

We proposed that much lower forward martensitic transformation temperature (M-s) 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 M-s temperature to around RT. The Co-20Ni-6Si alloy with M-s 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 M-s temperatures were much far from RT. The reduction in the M-s temperature by the Si addition augmented with increasing the Ni content. (C) 2019 Elsevier B.V. All rights reserved.