Microstructure and phase transformation behavior of a new high temperature NiTiHf-Ta shape memory alloy with excellent formability

Abstract

Microstructure, mechanical properties as well as phase transformation behavior of newly developed Ni49Ti36Hf15-xTa(x=0, 3, 6, 9, 12) high temperature shape memory alloys has been investigated. Ni49Ti36Hf15 alloy consists of (Ti,Hf)2Ni phase which is brittle and incoherent with the martensite matrix. However, addition of Ta in place of Hf suppresses the brittle (Ti,Hf)2Ni phase formation with white Ta rich phase. More than 70% reduction in area has been observed in Ta added Ni49Ti36Hf15 high temperature shape memory alloys. The austenitic transformation temperature is well above 200 °C (473 K) for lower Ta concentrations with up to 6 at. %; however; at higher Ta concentrations (i.e. above 9 at. %) decreases significantly. Overall, the addition of Ta greatly influences the hot deformation behavior and high temperature shape memory properties of Ni49Ti36Hf15 alloy. The present paper discusses the detailed investigation on Ni49Ti36Hf15-xTa(x=0, 3, 6, 9, 12) high temperature shape memory alloys.