MORPHOLOGICAL EVOLUTION OF ALPHA/GAMMA INTERFACE IN FE-MN-AL ALLOY

Series of multiphase diffusion couples were assembled with various terminal alpha and gamma alloys in a Fe-Mn-Al system. These couple series were employed to investigate the development of diffusion structures with planar and non-planar interfaces. Morphology in the diffusion interface was observed by scanning electron microscopy (SEM) and the concentration profile for the constituent element was obtained by electron probe X-ray microanalysis (EPMA) with the aid of quantitative analysis. Transitions from planar interfaces in the alpha/gamma two-phase diffusion couples were indexed by varying the compositions of the terminal alloys. Couples with planar alpha/gamma interfaces exhibited path crossings of the (alpha/gamma) two-phase region parallel to tie-lines. However, the two-phase path crossings for couples developing non-planar interfaces were inclined to tie-lines. The alpha/gamma phase boundary can be determined by the interfacial compositions of the diffusion couple in which the interface is planar.