Microstructure, Mechanical Property, and Phase Transformation of Quaternary NiTiFeNb and NiTiFeTa Shape Memory Alloys

Abstract

Based on ternary Ni45Ti51.8Fe3.2 (at %) shape memory alloy (SMA), Nb and Ta elements are added to an NiTiFe SMA by replacing Ni element, and consequently quaternary Ni44Ti51.8Fe3.2Nb1 and Ni44Ti51.8Fe3.2Ta1 (at %) SMAs are fabricated. The microstructure, mechanical property, and phase transformation of NiTiFeNb and NiTiFeTa SMAs are further investigated. Ti2Ni and β-Nb phases can be observed in NiTiFeNb SMA, whereas Ti2Ni and Ni3Ti phases can be captured in NiTiFeTa SMA. As compared to NiTiFe SMA, quaternary NiTiFeNb and NiTiFeTa SMAs possess the higher strength, since solution strengthening plays a considerable role. NiTiFeNb and NiTiFeTa SMAs exhibit a one-step transformation from B2 austenite to B19’ martensite during cooling, but they experience a two-step transformation of B19’-R-B2 during heating.

Keywords

• shape memory alloy
• mechanical property
• microstructures
• phase transformation