Microstructural and Phase Evolution of a Ni‐Rich Ni 45.2 Ti 29.8 Zr 20 Cu 5 Shape Memory Alloy

A recent study shows that a 5 at.% Cu addition to NiTi‐20 at.% Zr stabilizes the B19’ martensite phase and improves alloy processability, prompting further development of shape memory alloys with similar compositions. This study explores Ni 45.2 Ti 29.8 Zr 20 Cu 5 phases and microstructures to identify aging behavior and precipitation and investigate its potential as a cost‐effective actuator for aerospace applications. In situ and ex situ diffraction experiments were utilized to investigate phases present through annealing and increasing aging temperature. In situ experimentation revealed a single‐step transformation between cubic B2 austenite and monoclinic B19’ martensite with the second‐phase (Cu, Ni) 2 Zr present in Ni 45.2 Ti 29.8 Zr 20 Cu 5 , and ex situ diffraction patterns revealed the presence of H‐phase in aged Ni 45.2 Ti 29.8 Zr 20 Cu 5 . Transformation temperatures of Ni 45.2 Ti 29.8 Zr 20 Cu 5 follow an increasing trend in austenitic finish temperature, A f , for aging temperatures between 400°C and 600°C, with a maximum A f measured after aging at 600°C, which directly relates to the precipitation hardening trend observed with Vickers hardness, indicating increasing volume fraction of H‐phase with aging temperature and revealing the peak aged condition. Scanning transmission electron microscopy images and corresponding elemental maps revealed microstructural and compositional changes as a function of annealing and aging between Ni 50.2 Ti 29.8 Zr 20 and Ni 45.2 Ti 29.8 Zr 20 Cu 5 , highlighting H‐phase precipitation, which can be utilized to tune transformation temperatures in future alloy design.