Comparison of reverse transformation behaviors of thermally-And deformation-induced ϵ-martensite in Fe-28Mn-6Si-5Cr shape memory alloy

Abstract

Reverse transformation behavior and the microstructures of ϵ-martensite induced by two different methods of cooling and deformation in Fe-28Mn-6Si-5Cr shape memory alloy was investigated. In situ heating X-ray diffraction (up to 673 K) was applied to the cooled and deformed specimens to observe the reverse transformation behavior. The microstructures in the cooled and deformed specimens were analyzed by electron backscattering diffraction. From X-ray diffraction patterns, the reverse transformation start temperature (As) in the deformed specimens was found to be lower than that in the cooled specimen, while the reverse transformation finish temperature (Af) in the deformed specimens was higher than that in the cooled specimen. The electron back-scattering diffraction (EBSD) analysis revealed a higher fraction of low-Angle misorientation boundaries in γ-Austenite and ϵ-martensite in the deformed specimens than in the cooled specimens. Intersections of different ϵ-martensite variants with ϵ-Twin were observed in the deformed specimens, while such intersections were not observed in the cooled specimens. A heterogeneous mixture of plastically deformed ϵ-martensite and γ-Austenite were found in deformed specimens. It is considered that the heterogeneity of the microstructures led to the difference in reverse transformation temperatures of As and Af in the thermally-induced and deformation induced maretnsites.