The magnetic aspects of the γ-α and γ-ε martensitic transformations in Fe-Mn alloys

Fe100-xMnx alloys undergo fcc-bcc (γ-α) and fcc-hcp (γ-ε) 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 α+ε and ε+γ. The γ-α transformation in Fe-Mn is similar to that in Fe-rich Fe-Ni alloys where the transformation takes place between a high-temperature dense fcc structure and a low-temperature more open bcc structure. This anomalous volume increase at the martensite transformation temperature is closely related to short-range ferromagnetic correlations in the fcc and bcc states. The γ-ε transformation in Fe-Mn takes place between a high-temperature fcc 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 γ-α and γ-ε martensitic transformations. Results show that the γ-ε transformation occurs with the simultaneous loss of ferromagnetic correlations in the γ-phase. (orig.)