Factors influencing martensite transitions in Fe-based shape memory alloys

Abstract

Fe-14Mn-6Si-9Cr-5Ni (mass %) shape memory alloy (SMA) specimens were obtained by powder metallurgy in as-blended state (0_MA) and with particle volume fractions of 10 and 20 % MA’d powders, respectively. After hot rolling and solution treatment, between 973 and 1373 K, the specimens were pre-strained up to 4 %, on a tensile testing machine. The influences of: (i) MA’d fractions, (ii) solution treatment temperature and (iii) pre-straining degree were analysed by X-ray diffraction (XRD), optical (OM) and scanning electron (SEM) microscopy. In this purpose, the gauges of pre-strained specimens were cut and metallographically prepared. Dynamic mechanical analysis (DMA) was employed to emphasize the reverse transformation, during heating, of thermally induced martensite, obtained after solution treatment. The results proved that, as an effect of PM-MA processing, mechanical properties were improved, the amount of stress induced martensite increased and the reverse martensitic transformation was enhanced.