Effect of thermal cycling on microstructure and damping capacity of Fe–26Mn–4Si alloy

Abstract The microstructural changes, the volume fraction of coexistent phases, heat flow, and internal friction of the Fe–26Mn–4Si alloy are studied during thermal cycling over a range of reversible martensitic transition. The typical microstructure of this alloy at room temperature after various heat treatments is a mixture of γ-austenite (FCC, sp. gr. Fm3m) and e-martensite (HCP, sp. gr. P63/mmc) phases. In situ neutron diffraction tests reveal that after several thermal cycles, intensities of e-martensite diffraction peaks significantly decrease, whereas the intensities of γ-austenite peaks increase. The amount of the e-martensite in the cold rolled sample drops steeply from roughly 60%–30% after six thermal cycles and to 25% after 18 thermal cycles by EBSD analysis. This explains the change in the hardness and damping with thermal cycling by decreasing the ratio e/γ in the Fe–26Mn–4Si sample after cold rolling. According to TEM observation, many twins and stacking faults are observed within the retained γ-austenite matrix. Internal friction peak heights caused by phase transition increase with decreasing the frequency of forced vibration.