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

Abstract

The shape memory effect in Cu–Al–Ni alloys iscaused by martensitic transformations between a metastablematrix (β phase) and one or more martensitic phases. Inthese alloys, when diffusion becomes significant, precipitationof thermodynamically stable α and γ occurs. Whileseveral transmission electron microscopy (TEM) works havefocused on the characterization of γ, α phase has receivedminimal attention, likely due to experimental challenges inachieving sufficient TEM image contrast. In this work, weemployed a combination of advanced electron microscopytechniques and, for the first time, we were able to identifysmall α particles with an unprecedented morphology.