Development and Mechanical Testing of Low Hysteresis Shape Memory Alloys

Shape memory alloys (SMAs) have the ability to convert thermal energy into work output through a cyclic phase transformation from martensite to austenite. The amount of thermal energy needed per cycle is directly associated with the hysteresis width, where a narrower gap requires a lower amount of energy to produce the work needed. A narrower hysteresis is linked with a strong coherence between the austenite/martensite interface. It has been shown that elemental additions to NiTi-based SMAs can further improve this coherency. The primary goal of this project is to identify and develop low hysteresis shape memory alloys (LHSMAs) for actuator applications. To accomplish this goal, elemental additions of Cu, Co, Hf, and Pd to NiTi-based SMAs are investigated using differential scanning calorimetry, scanning electron microscopy with energy dispersive spectroscopy, thermo-mechanical testing, and, if necessary, synchrotron radiation X-ray diffraction to evaluate them as potential LHSMAs.