Microstructural analysis of the stress-induced ε martensite in a Fe–Mn–Si–Cr–Ni shape memory alloy : Part II: Transformation reversibility

Abstract

The shape memory effect exhibited by some Fe–Mn–Si based alloys is related to the γ(f.c.c.)- ε(h.c.p.) martensitic transformation. In these alloys, the shape memory effect, incomplete even for low deformation rates, drastically decreases when the deformation rate increases. The evolution of the microstructure of the martensite, and particularly the interaction of martensite plates and grain boundaries, is studied in a Fe–Mn–Si–Cr–Ni alloy to determine the origin of the loss of shape memory. The influence of the back-stress created by the dislocations located at the tip of the martensite bands is pointed out. The reduction of the shape memory is attributed to the accommodation of this back-stress when the deformation rate, i.e. the martensite band width, increases. The same kind of analysis is used to analyse the problem of superelasticity.