Characteristic Structural Changes in Stress-Induced Martensitic Transformation and Reverse Transformation of a Polycrystalline Fe-Mn-Si Alloy

Suzuki Shigeru, Senoo Shotaro, Maruyama Tadakatsu, Shinoda Kozo

doi:10.2320/matertrans.mra2008211

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 γ phase was transformed to a martensitic ε phase by room-temperature tensile deformation, and the ε 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 stress-induced 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.

Characteristic Structural Changes in Stress-Induced Martensitic Transformation and Reverse Transformation of a Polycrystalline Fe-Mn-Si Alloy

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