AFM observation of microstructural changes in Fe-Mn-Si-Al shape memory alloy

We analyzed the surface relief caused by stress-induced hcp martensitic transformation in Fe-30Mn-5Si-1A1 shape memory alloy by atomic force microscopy. The alloy exhibits a good shape memory effect and an improved ductility due to a small addition of Al to a conventional Fe-30Mn-6Si shape memory alloy. The orientation of an austenite matrix was determined with surface traces of four {111}_f planes, which enabled us to determine the surface tilt angles for all twelve variants of hep martensites and deformation twins. On the basis of these values, stress-induced martensite and deformation twin coexisting in the same grain were identified by studying the surface tilt angles. The surface relieves caused by the stress-induced martensite recovered after heating above the reversed transformation temperature, however some relieves originating from the deformation twin remained.