Discontinuous Dissolution and Grain‐Boundary Migration in Al2O3‐Fe2O3 by Oxygen Partial Pressure Change

Abstract

When sintered 95Al2O3‐5Fe2O3 (wt%) specimens constituting corundum grains and iron aluminate spinel precipitates were annealed under high oxygen partial pressure (Po2) where only a corundum phase is stable, fast dissolution of particulate spinel precipitates occurred, together with the migration of corundum grain boundaries. Behind the migrating boundaries, a corundum solid solution enriched with Fe2O3 formed. Discontinuous dissolution (DD) of particulate spinel precipitates thus occurred by Po2 increase. In contrast, when 95Al2O3‐5Fe2O3 specimens constituting only corundum grains were annealed under low Po2 where both corundum and spinel phases are stable, grain boundaries migrated without spinel precipitation, leaving behind a corundum phase depleted of Fe2O3, similar to chemically induced grain‐boundary migration (CIGM) observed during solute depletion. The volatilization of Fe2O3 appeared to cause the boundary migration without precipitation. The observed CIGM and DD would suggest various possibilities of microstructure control in other oxide systems through oxygen partial pressure change.