Shape memory alloys (SMAs), otherwise referred to as ‘smart’ alloys, have incredible potential for use in the aerospace industry due to their ability to return to their original shape when heated above a certain critical temperature or to recover from deformation during unloading (Lobo, 2015; Costanza, 2020). This ability is responsible for the solid-state actuation unique to SMAs. Research on high temperature and ultra-high temperature SMAs (HTSMAs and UHTSMAs, respectively) is currently being conducted to help extend the range of temperatures where solid-state actuation can be used (AbuJudom II, 1992; Eckelmeyer, 1976).

NiTi-Zr holds potential as a practical and economical solution for the commercial use of HTSMAs in the aerospace industry compared to other NiTi-based HTSMAs with other ternary alloying additions (Eckelmeyer, 1976; Carl, 2017; Carl, 2018). Further research is required to identify NiTi-Zr HTSMA compositions which optimize the processability and solid-state actuation properties while increasing transformation temperatures for the use of SMAs at high temperatures and ultra-high temperatures (Frenzel, 2010; Frenzel, 2015). In addition to Zr, the addition of Cu to NiTi-based SMAs is used to tune the thermal hysteresis and enhance the fatigue response.

The purpose of this research is to investigate the phase transformation and stability of NiTi-Zr and NiTi-Zr,Cu HTSMAs and to control the precipitation of Ti2Ni-type and Ni4Ti3-type precipitates in Ni-lean and Ni-rich compositions, respectively. This work will help to determine these alloys' potential for high temperature solid-state actuation for aerospace applications. The results from this study will be coupled with thermal hysteresis curves (DSC) which can be used to determine the transformation temperatures, microstructural images and elemental maps using SEM with EDS to observe precipitation and grain evolution, and thermomechanical data from hardness and fatigue life testing. Experimental results will be compared with high temperature CALPHAD predictions.