High-temperature martensitic transformation of CuNiHfTiZr high- entropy alloys

One of the major challenges of near-equiatomic NiTi shape memory alloys is their limitation for high-temperature applications. To overcome this barrier, researchers have tried to enhance the transformation temperatures by addition of alloying elements or even by introducing the concept of high-entropy alloys (HEAs). In this study, the CuNiHfTiZr HEAs were developed for high-temperature shape memory effect. Based on their solubility and electron configurations, the alloying elements are divided into two groups, (CuNi)₅₀ and (HfTiZr)₅₀. The content of Cu in (CuNi)₅₀ is modulated to investigate the influences of Cu on martensitic transformation of the HEAs by studying structural evolution and transformation behavior. The results of x-ray diffraction and thermal expansion tests revealed that Cu₁₅Ni₃₅Hf_16.67Ti_16.67Zr_16.67 possesses high transformation temperature, narrow hysteresis temperature loops, and good dimensional stability within this HEA system.