Chemical interactions in Cu-Al-Mn shape-memory alloy during low-temperature aging treatment: XAS and DFT study

Abstract

Low-temperature aging significantly affects the mechanical properties and martensitic transformation temperatures of Cu-Al-Mn (CAM) alloys. In this study, X-ray absorption spectroscopy (XAS) and density functional theory (DFT) were used to investigate the local order changes in a CAM shape-memory alloy during low-temperature aging treatment. The as-quenched CAM alloys were inhomogeneous, in which the average local Mn exhibited an L2₁-like structure and Cu predominantly occupied the first-nearest-neighbor positions around Al. Conversely, the Cu exhibited a D0₃-like local structure. During the 373 K aging treatment, the average local Mn atoms tended to form an L2₁ structure, and the arrangement of Mn atoms changed in two stages: formation of Mn-rich structures and reduction during 423 K aging treatment, whereas no significant change was observed for Al. Using XAS and magnetic measurements, phase separation was detected in the sample treated at 423 K for 120 min. This observation aligns well with the formation energy based on DFT calculations, which explains the transition from disordered to ordered structures during low-temperature aging driven by the aggregation and diffusion of Mn atoms with antipapal spin moments.