Lattice parameters of metastable structures in quenched Fe-Mn alloys. PartII: hcp phase

In this work the lattice parameters of the hexagonal close-packed (hcp) eps ilon phase have been investigated as a function of the composition using an X-ray technique. With the present results, reliable trends in the composit ion dependence of the axes a and c are established, which are significantly simpler than those suggested by early measurements. In addition, new extra polations to 0 at.% Mn are performed, which are compared with other indirec t information on the hcp phase of Fe at room temperature and atmospheric pr essure. Finally, by combining the present measurements on the hcp phase wit h those on the face-centred cubic (fcc) phase reported in the first paper o f this series, a detailed analysis is made of the changes in the interatomi c distances as well as the relative volume change associated with the fcc - -> hcp martensitic transformation. According to the present results such vo lume change is essentially independent of the Mn content, which should be i nteresting in modelling the energetics of the fcc --> hcp transformation.