Pressureless sintering of Al 2O 3/SiC w materials: Effect of the reducing atmosphere

Abstract

The effect of the temperature and the conditions of the reducing atmosphere on the sintering behavior of pressureless-sintered Al 2O 3/SiC w composites was studied by SEM, XRD and density measurements and analyzed throughout a thermodynamic study of the system. Different partial pressures of oxygen were 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 °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 Al 2O 3-Al 4C 3 binary system and liquid production by reaction of SiC and Al 2OC. The higher densities reached at 1800 °C than at 1700 °C were attributed to a liquid-phase assisted mechanism of sintering.