The magnetic aspects of the gamma-alpha and gamma-epsilon martensitic transformations in Fe-Mn alloys

Fe100-xMnx alloys undergo fcc-bcc (gamma-alpha) and fcc-hcp (gamma-epsilon) transformations for about 0<x<10 at% and 15<x<30 at% respectively. The product phase in the region 10<x<15 at.% is mixed alpha+epsilon and epsilon+gamma. The gamma-alpha transformation in Fe-Mn is similar to that in Fe-rich Fe-Ni alloys where the transformation takes place between a high-temperature dense fee structure and a low-temperature more open bce structure. This anomalous volume increase at the martensite transformation temperature is closely related to short-range ferromagnetic correlations in the fee and bcc states. The gamma-epsilon transformation in Fe-Mn takes place between a high-temperature fee structure and a relatively denser packed low-temperature hcp structure. In this case there is no anomalous volume increase. In the present work we investigate the volumetric properties of Fe100-xMnx with x=8-30 at% and examine the influence of the: magnetic properties on the gamma-alpha and gamma-epsilon martensitic transformations. Results show that the gamma-epsilon transformation occurs with the simultaneous loss of ferromagnetic correlations in the gamma-phase.