Ultra low fatigue shape memory films

Functional shape memory alloys need to operate reversibly and repeatedly. This is especially crucial for many future applications such as artificial heart valves or elastocaloric cooling, where more than ten million transformation cycles will be required. Here we report on the discovery of an ultra-low fatigue shape memory alloy film system based on TiNiCu that allows at least ten million transformation cycles. We found these films contain Ti2Cu precipitates embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle. In addition we found an almost perfect fulfillment of the compatibility conditions in TiNiCuCo thin films that also show ultra low fatigue.