Design for Precipitation Strengthening in NiTi-based Shape Memory Alloys

A thermodynamically-driven systems design approach can be used to optimize desired properties by controlling the microstructure and processing of shape memory alloys (SMAs). The introduction of coherent nanoprecipitates based on the Heusler phase in a NiTi-base matrix is hypothesized to strengthen the parent phase. This hypothesis is validated by a detailed description of the effect of particle size on the thermo-mechanical properties, illustrating the direct correlation between processing, microstructure, and properties. Differential scanning calorimetry was used to determine the transformation temperatures and thermal cyclic stability of each alloy. Also, microstructural characterization was performed using X-ray diffraction, optical microscopy, scanning electron microscopy, and transmission electron microscopy. A new generation of alloys is proposed to show promising properties for actuator applications.