Work Performance in the Ti–Hf–Zr–Ni–Cu–Co Shape Memory Alloys with Low, Medium, and High Configuration Entropy

The study examines the configuration entropy influence on the work output in the Ti–Hf–Zr–Ni–Cu–Co shape memory alloys and compare the results to those found in the binary NiTi alloy. The samples were pre-deformed at –196°C by 10%, unloaded, fixed to the bias elastic element and subjected to heating–cooling–heating with a system stiffness of 22 GPa. It was found that an increase in the concentration of doping elements (Hf, Zr, Cu, Co) led to non-monotonic variations in recoverable strain, recovery stress and work output. The maximum values were observed in the medium entropy alloys in which the work output was twice larger than in low-entropy Ti–Hf–Zr–Ni–Cu–Co alloys or in binary NiTi alloy. High-entropy alloys produced less work compared to the medium-entropy alloys due to a smaller volume fraction of the oriented martensite after pre-deformation as these materials demonstrate the superelasticity even at –196°C.