Stress-induced martensitic transformation in Fe-Mn-Si alloys is characterized by the transformation of the fcc matrix to the hcp phase, which is generally reversible. In this study, Debye rings obtained by monochromated X-ray diffraction using synchrotron radiation were used for analyzing the structural change of the fcc matrix to the hcp phase in a polycrystalline austenitic Fe-Mn-Si-Cr alloy that was deformed by the tensile test at room temperature. Structural changes resulting from the reverse transformation due to heating were also studied. The results showed that the occurrence of the stress-induced martensitic transformation was not uniform, but depended on the relationship between the orientation of polycrystalline grains and the tensile direction. The transformation appears to preferentially occur in grains with large Schmid factors for the shear of [ 2 211](111) in the fcc matrix, and the formation of hcp phases also depends on the orientation of grains. The reverse transformation due to heating does not necessarily occur in the crystallographically reversible route. This indicates that irreversible deformation induced by dislocations during the tensile test restricts the reversible transformation of the alloy.
Debye rings obtained by synchrotron X-ray diffraction were analyzed for investigating structural changes caused by stress-induced martensitic transformation and reverse transformation of a polycrystalline austenitic Fe-Mn-Si shape memory alloy. The chemical composition of the shape memory alloy was Fe-28 mass%Mn-6 mass%Si-5 mass%Cr. The results showed that a part of the austenitic phase was transformed to a martensitic " phase by room-temperature tensile deformation, and the " phase was reversely transformed by subsequent heating. Diffraction intensities in Debye rings changed non-uniformly on tensile deformation and heating, indicating that occurrences of the stressinduced and reverse transformation depend on the crystallographic orientations of grains with respect to the tensile direction. The optimum recovery strain induced by the reverse transformation was obtained for a sample deformed by about 10% tensile strain, which was consistent with the structural changes caused by the reverse transformation. X-ray diffraction lines were shown to be broadened by tensile strain. This indicated that irreversible deformation due to dislocations restricted the reverse transformation, leading to the optimum recovery strain.
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