Characterization of Residual Stress Evolved in Iron-Based Shape Memory Alloys*

Abstract It is considered that complicated residual stresses may occur in shape memory alloys (SMAs) during deformation, as the matrix phase is transformed to martensitic phase during plastic deformation and the martensitic phase is reversely transformed by heating. Since the final shape of SMAs are influenced by residual stresses, it is important to characterize the residual stresses formed in SMAs during plastic deformation and annealing. The X-ray diffraction method was used to characterize the phase transformation and the residual stress formed in an Fe-Mn-Si-Cr SMA in this study. The samples were tensile-deformed to different strains and subsequently annealed. The results showed that a part of γ-phase with the face-centered cubic (fcc) structure was found to be transformed to ∊-phase with the hexagonal close-packed (hcp) structure by room-temperature tensile deformation in the SMA, and the ∊-phase was reversely transformed by subsequent heating. It has been also shown that the compressive stress occu...