PREFERENTIAL ABSORPTION OF HYDROGEN INTO EPSILON-PHASE IN FE-MN ALLOYS

An X-ray diffraction study was performed on Fe-Mn (16 to 41%Mn) alloys charged cathodically with hydrogen. In the alloys with the gamma-single phase, a hydrogen-induced transformation to an hcp epsilon(H) Phase is found after hydrogen charging. On the other hand, in the alloys with the gamma and epsilon phases, there is little change in the gamma phase, but a considerable lattice expansion is observed for the epsilon phase. This means that the epsilon phase preferentially absorbs hydrogen. Especially in the Fe-27%Mn alloy, the epsilon phase gradually expands with increasing charging time, and finally the epsilon(H) Phase is separated from the epsilon phase. Therefore, the formation of the epsilon(H) phase should be regarded as a phase separation in the hcp matrix epsilon enriched with hydrogen, although it apparently seems to be a martensitic transformation.