Influence Of Solution Temperature On Gamma ->Epsilon Transformation And Damping Capacity Of Fe-19mn Alloy

Due to the high damping capacity and excellent mechanical properties, Fe-Mn alloy is considered to be a promising high damping alloy, and suitable for constructional and vehicle metal parts application, which can enhance the fatigue property of structures and metal parts, and also improve the working and living environment. It's generally accepted at present that damping capacity of Fe-Mn alloy is influenced by the stacking fault boundaries in gamma-austenite and epsilon-martensite, gamma/epsilon phase boundaries and epsilon/epsilon variant boundaries; another view is that boundaries of the above damping sources are made up of partial dislocations, so the damping capacity of Fe-Mn alloy is caused by the motion of partial dislocations, and interpreted by G-L dislocation pinning model and stacking fault probabilities calculation. But there is no distinction between the probabilities of different type stacking faults. Both deformation stacking fault and growth stacking fault can be formed in gamma-austenite and epsilon-martensite, and the change of process parameters has different influence on them, which will lead to different changes of deformation and growth stacking fault probabilities. So it's necessary to analyze whether boundaries of different stacking fault types will have different effects on damping capacity of Fe-Mn alloy. Based on that, a hot-rolled Fe-19Mn alloy is prepared and then solution treated between 950 similar to 1100 degrees C. Damping capacity is measured by dynamic mechanical analyzer (DMA). The microstructure evolution is observed by OM and TEM, and XRD is used to analyze phase constitution and to measure stacking fault probabilities. The results reveal that Fe-19Mn alloy shows amplitude-dependent damping capacity which almost linearly increases with amplitude, and frequency-independent damping capacity. From G-L plot, the variation of damping capacity below the critical amplitude A' (A'approximate to 30 mu m) is interpreted by G-L model, while it's associated with micro-plastic deformation when above A'. As the increase of solution treatment temperature, the damping capacity of Fe-19Mn decreases, and possesses the best performance at 950 degrees C; furthermore, it shows different characteristics in different amplitude ranges: when the amplitude is lower than 170 mu m, damping capacity decreases in exponential form, which changes similarily with deformation stacking fault probability in epsilon-martensite, so it can be considered the boundaries of deformation stacking fault as the main damping source; when the amplitude is higher than 170 mu m, damping capacity decreases linearly, which changes similarily with the relative length of gamma/epsilon phase boundary, so it can be considered gamma/epsilon phase boundary as the main damping source. Based on TEM observation of stacking faults in gamma-austenite, it can be inferred that stacking fault boundaries in gamma-austenite have no obvious contribution to the change of damping capacity of Fe-19Mn with amplitude.