Influence of mechanically alloyed fraction and hot rolling temperature in the last pass on the structure of Fe-14Mn-6Si-9Cr-5Ni (mass. %) shape memory alloys processed by powder metallurgy

Abstract

Samples of Fe-14Mn-6Si-9Cr-5Ni (mass. %) shape memory alloy were sintered from two powder mixtures: (i) as blended (0_MA) and (ii) equal amounts of as blended and mechanically alloyed (MA’d) powders (50_MA). In order to increase the compactness degree, different specimens were hot rolled at 1373 K and the last rolling pass was performed at four different temperatures: (i) room temperature (RT); (ii) 873 K; (iii) 1073 K and (iv) 1373 K. In order to emphasize the influence of both MA’d fraction and rolling final temperature, the eight resulting specimens were analysed by X-ray diffraction (XRD) as well as by scanning electron microscopy (SEM). XRD results allowed the qualitative and quantitative identification of the three component phases, namely γ (face centred cubic, fcc)-parent phase, ε-(hexagonal close packed, hcp) martensite and α’- (body centred tetragonal, bct) martensite. SEM micrographs enabled to observe the influence of MA’d fraction on the relative amounts of the three phases. The results suggest that the presence of MA’d fraction contributes to destabilization of α’(bct) martensite and increase of the amount of ε(hcp) martensite, with favourable effects on shape memory behaviour.status: publishe