The mechanisms of microstructure formation in a nanostructured oxide dispersion strengthened FeAl alloy obtained by spark plasma sintering

A bulk dense nanostructured material, obtained by spark plasma sintering (SPS) of Y2O3 dispersion strengthened milled Fe-40Al powder, is characterized in detail using scanning (SEM) and transmission electron microscopies (TEM) in order to investigate the mechanisms of its microstructure formation. The sintered material displays a fairly heterogeneous microstructure that covers nano- and ultrafine together with large micrometric grains. The fine grains result from recovery and recrystallization, while the larger ones from grain growth or local melting. Under the present SPS conditions, large temperature differences in the range 570-670 °C, due to rapid heating-cooling and also to no holding stage applied, essentially account for such a structural heterogeneity. Controlling SPS of the milled powder thus provides a feasible processing route to get dense hetero-nanostructured material. In addition, complex oxide particles formed in the material are analyzed to be related to precipitation reaction and oxide evolution at different sintering temperatures.