Advancements in High Entropy Shape Memory Alloys: Thermo-mechanical Processing of Ti16.6Zr16.6Hf16.6Co10Ni20Cu20

High entropy shape memory alloys (HE-SMAs) combine unique high entropy-based properties with the functional advantages of shape memory alloys. Specifically, they feature enhanced strength, adjustable transition temperatures, high recoverable stresses and thermal stability. However, common challenges in multicomponent alloy design such as segregation and secondary phases hinder their functionality. The effectiveness of conventional heat treatments in overcoming these challenges is often limited, resulting in sub-optimal performance of promising alloy systems. This study investigates the benefits of thermo-mechanical processing (TMP) as a strategy to control the homogeneity and microstructure of HE-SMAs and thereby increasing their functionality. It focusses on the NiTi-related alloy Ti16.6Zr16.6Hf16.6Co10Ni20Cu20, evaluating the effects of TMP on its microstructural evolution and mechanical performance with the goal to establish reliable functionality. By employing TMP via hot-extrusion, significant improvements in microstructural homogeneity and both mechanical and functional properties were achieved. The effects of TMP included enhanced structural integrity after forming, a 25% increase in ultimate compressive stress, a 20% increase in transformation energy and a significantly improved functional fatigue resistance compared to solely heat-treated states. These findings underscore the critical importance of controlled TMP in overcoming existing limitations and positioning HE-SMAs as next-generation, high-performance materials. Graphical Abstract