The effect of Hf on the microstructure, transformation temperature, and the shape memory properties of Zr–Cu-based high-entropy shape memory alloys

Abstract

The microstructures, phase transformation temperatures, and shape memory properties of Hf-modified Zr50−xHfxCu25Ni7.5Co17.5 and Zr50−xHfxCu25Ni10Co15 high-entropy shape memory alloys (SMAs) were investigated. Hf additions can alter the valence electron concentration, strengthen the alloy matrix, and introduce more secondary phase particles, which significantly influence the properties of the alloys. The results reveal that high austenitic transformation temperature (over 600 K) with very small thermal hysteresis (70–80 K) can be achieved by tailoring the Hf contents, and the best shape memory recovery strain (up to 2.44%) compared with other Zr–Cu-based SMAs could be obtained in Zr42Hf8Cu25Ni10Co15 alloy. This study demonstrated that high-performance Zr–Cu-based high-entropy SMAs can be realized by incorporating Hf additions.