Pseudoelasticity and martensite phase plastic deformation in Cu-Al-Mn alloys produced by laser powder bed fusion

Cu-Al-Mn shape memory alloys (SMAs) are valuable for their large transformation strain and wide temperature range. However, high-performance Cu-Al-Mn alloys are typically single-crystalline or columnar-grained, while their polycrystalline, multi-variant alloys often exhibit limited pseudoelasticity with unfavorable reversibility due to the low yield strength. Here, fine-grained Cu-Al-Mn alloys were fabricated via laser powder bed fusion (L-PBF), and their deformation mechanisms were studied using in-situ tensile test. In-situ optical microscopy tensile testing was used to reveal distinct types of surface reliefs, including parallel bands, linear stripes, slip traces, and cracks. A multi-scale analysis was conducted to correlate these features with their underlying physical mechanisms. The formation and disappearance of parallel surface relief corresponds to the forward and reverse stress-induced martensitic transformation (SIMT). In contrast, the linear surface relief observed at grain boundaries arise from grain rotation driven by the strong anisotropy of the Cu-Al-Mn alloys. Furthermore, the activation of the {111}<011> slip system within the grains leads to the formation of slip traces, followed by the initiation of microcracks due to the operation of a new kind of <111> slip, ultimately resulting in material failure. These findings suggest that enhancing pseudoelasticity requires strengthening the matrix to suppress dislocation glide and grain rotation, thereby providing a theoretical basis for designing high-performance, fatigue-resistant Cu-Al-Mn alloys.