Design of shape memory alloys with low hysteresis via multiple phase coexistence

Shape memory alloys (SMAs) are the key components of actuators and sensors due to their shape memory effect and superelasticity. However, the thermal hysteresis associated with martensitic phase transformation limits their use in the long-duration precise control. We report a strategy that obtains SMAs with low hysteresis by constructing a composition-temperature pseudo phase diagram. This strategy is inspired by the physically parallel ferroelectric system where the hysteresis is minimized at the multiple phase coexistence point, due to the absence of energy barrier across different phases. Following this, an alloy in the phase diagram with a low hysteresis of about 5 K is synthesized. In contrast, those alloys compositionally different from the optimal one have large hysteresis. Microstructures characterization and diffraction analysis are employed to identify the multiple phase coexistence. The proposed strategy should be general and can shed light on the rational design of SMAs with low hysteresis.