M. Murakami, H. Fujiwara, M. Koyama, Shibaura Institute of Technology, Tokyo, Japan; T. Sawaguchi, National Institute for Materials Science, Tsukuba, Japan; T. Maruyama, Awaji Materia, Tokyo, Japan
Fe-Mn-Si shape memory alloys can be used for applications of structural materials such as pipe joints and fish plates. Compared to other SME materials, however, a recoverable strain of Fe-Mn-Si alloys is rather small and commonly in the range of 2 -3 %. This value is much smaller than the ideal value that can be expected for fcc → hcp martensitic transformation. Such discrepancy may be ascribed to polycrystalline nature. In this study, we observed microstructures of commercial Fe-28Mn-6Si-5Cr alloys in the pristine state, in the as-deformed state, and in the shape-recovered state after heat treatment. For microstructural observations, squares about 500mm in side length were grooved on the sample surface using focused ion beams. Through observing the deformation of these squares, one can easily determine how the samples are locally deformed. In addition, the photographs of the initial state and that in the recovered state were superimposed, so that one can identify where the shape recovery was hindered. It was found that the sample with 3% tensile strain almost recovered its original shape upon heating at 600°C, although some permanent strains were detected at grain boundaries. It was also interesting to note that the sample could almost recover 5% deformation in some local area.
Summary: Shape memory effects of Fe-Mn-Si-Al alloys were characterized by superimposing the photo for the initial state and that after shape recovery. Squares were grooved with focused ion beam on the sample surface, which made it possible to indentify the regions where shape recovery was hindered.
