FORMATION OF ALUMINA-CHROMIA-CHROMIUM COMPOSITES BY A PARTIAL REDUCTION REACTION

Metal-ceramic matrix composites were formed by the partial reduction of Al2O3-Cr2O3 solid solutions to form Cr metal particles in an Al2O3-Cr2O3 matrix which had a lower Cr2O3 concentration. In Al2O3-Cr2O3 solid solutions containing 10 and 25 wt.% Cr2O3, the microstructures produced by reduction are different from that expected from simple models of internal reduction or oxide scale formation. Grain boundary diffusion of individual grains. Small Cr particles were then observed to coarsen along some, but not all, grain boundaries by concomitant process known as 'discontinuous coarsening'. The mechanisms controlling microstructural evolution in this system were examined.