Structure and composition heterogeneity of a FeAl alloy prepared by one-step synthesis and consolidation processing and their influence on grain size characterization

This paper aims to characterize a bulk dense FeAl (47 at.%) alloy synthesized and consolidated by one-step current-activated pressure-assisted processing of nanocrystalline elemental powders. The end-product was analyzed using a combination of scanning (SEM) and transmission electron microscopies (TEM), electron back-scattering diffraction (EBSD) as well as electron probe microanalysis (EPMA). Special attention was paid to verify the grain size (32–89 nm) previously determined by X-ray diffraction peak profile analysis. It has been found that this material displays equiaxed grains (0.8–4 μm in size) and contains limited structural defects like subgrains and dislocations. The EPMA result reveals that a variability in Al content (36–47 at.%) is present within the synthesized FeAl phase. Thus, the local variation of lattice parameters resulting from this heterogeneity accounts for the broadening of X-ray diffraction peaks instead of the common idea that the broadening is due to the small grain size. The formation mechanisms of the structure and the composition heterogeneity are also discussed and related to the combustion reaction process.