Pressureless sintering of sol–gel alumina matrix composites

Abstract

The effect of the temperature and the conditions of the reducing atmosphere on the sintering behaviour of pressureless-sintered sol–gel alumina matrix composites are studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and density measurements. The results are compared with those obtained with fine commercial alumina/SiC W composites, and analyzed by means of a thermodynamic study of the system. A notable improvement in sintering behaviour and a more extensive grain growth as the sintering temperature increases are determined for sol–gel alumina matrix samples. The amount of melt observed in the microstructural analysis of sol–gel alumina matrix materials is lower than that detected in fine alumina matrix samples. The mechanisms of formation of the glassy phase due to the reducing conditions of the atmosphere can operate in both series of samples, but the higher content of impurities in fine alumina matrix materials produces a more extensive liquid formation. The presence of glassy phase, higher starting densities, and lower weight losses during sintering, contribute to the higher final densities of fine alumina matrix composites.