Martensitic transformation fcc(gamma)->hcp(epsilon)

Criteria of the thermoelastic martensitic transformation are suggested, on the basis of which the martensitic transformation fcc(gamma)-->hcp(epsilon) in Fe-Mn-Si based alloys is classified as a semi-thermoelastic transformation. In contrast with the martensitic transformation fcc(gamma)-->bct(bcc)a' in iron-based alloys, the thermoelastic transformation in Cu-based alloys and the t-->m transformation in ceramics containing ZrO2, in gamma-->epsilon of Fe-Mn-Si, the strengthening and grain size of the parent phase will not markedly affect the M-s, and the internal friction peak indicating the martensitic transformation does not correspond to a significant lowering of the elastic modulus, implying that the nucleation of e-martensite may occur directly through the stacking fault and may not strongly depend on soft mode. A comparison between the thermal and stress induced epsilon martensites is made and a brief discussion is given.