The Sintering Behavior and Mechanical Properties of the Al₂0₃-Cr₂0₃ Solid Solution

Abstract

The sintering behavior and mechanical properties of the alumina-chromia solid solution (chromia concentration: 0∼50 mol%) were studied at low partial pressure of oxygen (P₀₂≈10_-11atm) and in air in the temperature range from 1400 to 1700°C. The sintering behavior was strongly affected by the chromia concentration in the solid solution and also by the partial pressure of oxygen. The sintering characteristics were affected by the addition of small amount of chromia (5 mol%) at both atmospheres. This suggests that the additions of small amount of chromia to the alumina inhibits sintering. At the higher chromia concentration (10∼50mol%), the sintering behavior was complicated. At low oxygen pressure, the high er the chromia concentration, the higher the relative density. In air, the higher the chromia concentration, the lower the final density at 1500 and 1600°C. In contrast, at 1700° in air the whole sintering processes were accelerated, and the behavior was similar to that found in sintering at low oxygen pressure. These results suggest that the solid-state mechanism (s)(volume diffusion or/and grain boundary diffusion) occurs dominantly at low oxygen pressu re and that both the solid-state mechanism (s) and the evaporation condensation mechanism concurrently occur in air. The bending strength of the sintered body changed with its relative density. The relation between strength and porosity obtained for the specimens fired in air satisfied the Duckworth equation for each composition. Hypothetical strengthes of specimens without pore were estimated by extrapolation. Among the estimated strength the highest value was found for the specimen with 20 mol% chromia. When the firing temperature and sintering time were increased, the abnormal grain growth occurred and bending strength decreased.