Microstructure and functional properties of two-phase Ni-Mn-Fe-In shape memory alloys with small transformation hysteresis width

The microstructures, martensitic transformation behaviors, mechanical and shape memory properties of two types Ni-Mn-Fe-In shape memory alloys, including Ni50Mn36+xFe8In6−x (x = 0 and 2) and Ni52Mn34+yFe8In6−y (y = 0 and 2), were investigated. Typical two-phase microstructure consisted of the tetragonal martensite and fcc γ phase is observed for all the studied alloys. The results show that the mechanical properties are remarkably improved due to the presence of a mass of γ phase. The martensitic transformation is confirmed to be fully reversible, and the transformation temperatures almost linearly increase with the increase of e/a value of martensite. The transformation hysteresis widths of the studied alloys are very small, which are responsible for good shape memory effects of the alloys. Results further show that two-phase Ni-Mn-Fe-In alloys exhibit much better shape memory properties than those reported other two-phase shape memory alloys while the alloys have equal amount of γ phase.