Identification and Characterization of Elusive α Precipitates in Cu–Al–Ni Shape Memory Alloys with Combined Electron Microscopy Techniques

The shape memory effect in Cu–Al–Ni alloys is caused by martensitic transformations between a metastable matrix (β phase) and one or more martensitic phases. In these alloys, when diffusion becomes significant, precipitation of thermodynamically stable α and γ occurs. While several transmission electron microscopy (TEM) works have focused on the characterization of γ, α phase has received minimal attention, likely due to experimental challenges in achieving sufficient TEM image contrast. In this work, we employed a combination of advanced electron microscopy techniques and, for the first time, we were able to identify small α particles with an unprecedented morphology.