On some structural characteristics of Fe-base shape memory alloys

Two different types of Fe-base shape memory alloys (SMAs), obtained by different processing methods, were comparatively analyzed from the point of view of: (i) structural characterization, (ii) morphologic aspects and (iii) mechanical behaviour. For this purpose, heat treated specimens of Fe-9Cr-4Ni-0.33C and in Fe-28Ni-17Co-11.5 Al-2.5 Ta (mass. %) were produced and prepared for X-ray diffraction (XRD) and scanning electron microscopy (SEM) observations, which enabled to detect the presence of alpha' thermally induced martensite and gamma austenite and to observed their respective morphologies. By means of micro-indentation tests, the variations of load vs. depth were recorded and the presence of pseudoelastic behaviour was confirmed, being ascribed to the presence of stable alpha' martensite. When alpha' martensite was stress-induced from y austenite, being unstable upon unloading, a superelastic response was obtained, as was the case for Fe-28Ni-17Co-11.5 Al-2.5 Ta alloy.