Effect of carbon on the shape memory mechanism in FeMnSiCrNi SMAs

Fe-Mn-Si-Cr-Ni alloys are Fe-based shape memory alloys (SMA), which make use of the γ ↔ ε stress induced martensitic transformation. In the present study, the effect of C addition on the shape memory effect was reported. The characterization of the martensitic transformation and the phase components was carried out by using light optical microscopy, X-ray diffraction, internal friction measurements and transmission electron microscopy (TEM). C is often mentioned to improve the shape memory behaviour. Present results show, however, an opposite effect. It is believed that the relative position between the deformation temperature and the Ms temperature for the two alloys is of key importance when looking for an explanation for the presented experimental results. The lower Ms temperature for the high C alloy causes more slip and less transformation of the austenite. The microstructural characterization showed a lower amount of formed ε martensite during deformation for the high C alloy. (author)