MICROSTRUCTURE OF Fe-14Mn-6Si-8Cr-5.5Ni RIBBONS OBTAINED BY RAPID SOLIDIFICATION

In Fe-Mn-Si alloys, the shape memory effect (SME) is related to a stress-induced martensitic transformation. The transformation proceeds from the austenite phase, normally retained at room temperature, to a hexagonal-close-packed martensite: (FCC) -> (HCP). However, when ribbons of a Fe-14Mn-6Si-8Cr-5.5Ni alloy are manufactured by rapid solidification, the high temperature ferritic phase can be retained. As a consequence, not only decreases the materials capacity to recover its shape, but weakens the material, as well. In melt-spinning techniques, the thickness of the ribbons as well as the stable or metastable phases that result from the process, depend mainly on the gas ejection pressure, liquid temperature, and wheel temperature and rotation speed. In this work, we used optical microscopy and transmission and scanning electron microscopy, to investigate the microstructures obtained for various melt-spinning process variables. We also analyzed the effect of heat treatments applied in order to stabilize the austenite at room temperature and to optimize the shape memory behavior.