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.
Highlights
NiTi shape memory alloys (SMAs) have deserved increasing attention in the domain of engineering since they possess shape memory effect and superelasticity
It is evident that the three NiTi-based SMAs are composed of B2 austenite and Ti2 Ni precipitate
SMA, Ti2 Ni and β-Nb precipitates occur in the matrix of B2 austenite
Summary
NiTi shape memory alloys (SMAs) have deserved increasing attention in the domain of engineering since they possess shape memory effect and superelasticity. Phase transformation temperature and mechanical property are the two critical factors influencing the application of NiTi SMA in engineering [1,2,3]. NiTi SMA so as to change its phase transformation temperature and mechanical property [4,5]. Typical ternary NiTi-based SMAs, such as NiTiCu, NiTiNb, and NiTiFe, have gone toward the engineering application. NiTiNb SMA possesses a broad transformation temperature hysteresis, so it is suitable for pipe coupling [9,10,11]. NiTiFe SMA is typically used for coupling pipe since it possesses a lower martensite transformation start temperature [12,13,14]. Some quaternary SMAs have become potential candidates for high temperature
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