Transformation and Deformation Characterization of NiTiHf and NiTiAu High Temperature Shape Memory Alloys

NiTiHf and NiTiAu are exciting candidates amongst an emerging class of high temperature shape memory alloys (HTSMAs), exhibiting properties conducive to actuator applications in demanding automotive and aerospace environments. NiTiHf can be tailored to achieve a highly favorable balance of properties, including high strength, stability, and work output at temperatures up to 300C, yet at a reduced cost compared to Pt, Pd, and Au containing counterparts [1]. NiTiAu shows potential for work output at much higher temperatures -where the benefits may offset cost -but additional research is needed. These investigations focus on developing a fundamental understanding of the inherent microstructure-property relationships for these NiTi-based HTSMAs. The attractive characteristics seen in many of these systems are strongly influenced by the formation of nano-scale precipitates. Advanced electron characterization techniques are used to explore the interaction of these precipitates with martensite at low temperature, and with dislocations at higher temperature. These insights are further incorporated into microstructural modeling frameworks with the aim of developing accurate simulations of polycrystalline functional response.