Pressureless sintering of Al2O3/SiCW materials: Effect of the reducing atmosphere

The effect of the temperature and the conditions of the reducing atmosphere on the sintering behavior of pressureless-sintered Al2O3/SiCW composites was studied by SEM, XRD and density measurements and analyzed throughout a thermodynamic study, of the system. Different partial pressures of oxygen rr!ere estimated for two ways of arrangement of the samples, between graphite disks or packed in an SiC bed, the former being lower. A higher amount of glassy phase was observed when pressureless sintering was conducted with samples between graphite disks and at the highest sintering temperature studied (1800 degrees C). Taking into account the reactions that can occur at the partial oxygen pressures thermodynamically estimated, the formation of a high amount of liquid was explained throughout two mechanisms, formation of a melt with the composition of the eutectic of the Al2O3-Al4C3 binary, system and liquid production by reaction of sic and Al2OC. The higher densities reached at 1800 degrees C than at 1700 degrees C were attributed to a liquid-phase assisted mechanism of sintering. (C) 1997 Elsevier Science Limited.