Supplementary Material: Nanodomain evolution and superelasticity of nonequilibrium solidified Cu-Al-Mn shape memory alloys fabricated by laser powder bed fusion

While Cu-Al-Mn shape memory alloys (SMAs) have excellent superelasticity, their cyclic stability is poor, mainly because of very high grain growth in the solution treatment step. Here, laser powder bed fusion (L-PBF) was used to produce Cu-Al-Mn SMAs. A predominantly austenite structure and a trace amount of the α phase, both resulting from rapid solidification, were observed at room temperature. Owing to the high temperature gradient in the melt pool, the austenite had a strong A texture and epitaxial columnar fine grains (12 μm × 30 μm) in the build direction. In particular, the austenite matrix contained randomly distributed nanodomains, which implied the transformation of the original austenite cubic lattice into a premartensitic state. These nanodomains reversibly transformed into martensite under stress and reverted to austenite upon unloading. Owing to their microstructures and a crack-free feature, the L-PBFed Cu-Al-Mn alloys exhibited enhanced superelasticity, high recoverable strain (>5%), and moderate stability (>600 cycles), with the lowest temperature sensitivity of critical stress (0.42 MPa/K) occurring between 183 and 323 K. Our results show that L-PBF has the potential to optimize both superelasticity and stability of Cu-Al-Mn SMAs, which could render these materials promising for use in deep space exploration probes.