MICROSTRUCTURAL ANALYSIS OF THE STRESS-INDUCED EPSILON-MARTENSITE IN A FE-MN-SI-CR-NI SHAPE-MEMORY ALLOY PART-II - TRANSFORMATION REVERSIBILITY

The shape memory effect exhibited by some Fe-Mn-Si based alloys is rel ated to the gamma(f.c.c.)-epsilon(h.c.p.) martensitic transformation. In these alloys, the shape memory effect, incomplete even for low defo rmation rates, drastically decreases when the deformation rate increas es. The evolution of the microstructure of the martensite, and particu larly the interaction of martensite plates and grain boundaries, is st udied 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 disloca tions located at the tip of the martensite bands is pointed out. The r eduction of the shape memory is attributed to the accommodation of thi s back-stress when the deformation rate, i.e. the martensite band widt h, increases. The same kind of analysis is used to analyse the problem of superelasticity. (C) 1998 Elsevier Science S.A.