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

Microstructure, mechanical properties as well as phase transformation behavior of newly developed Ni₄₉Ti₃₆Hf_15-xTa_{(x=0, 3, 6, 9, 12)}high temperature shape memory alloys has been investigated. Ni₄₉Ti₃₆Hf₁₅alloy 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 Ni₄₉Ti₃₆Hf₁₅high 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 Ni₄₉Ti₃₆Hf₁₅alloy. The present paper discusses the detailed investigation on Ni₄₉Ti₃₆Hf_15-xTa_{(x=0, 3, 6, 9, 12)}high temperature shape memory alloys.