Spark Plasma Sintering of Al₂O₃–SiC Ceramics. Study of the Microstructure and Properties

The features of spark plasma sintering of submicron Al₂O₃ powders with different contents (0, 0.5, 1.5, 5 vol %) of β-SiC nanoparticles have been studied. The microstructure and hardness of Al₂O₃ + 5 vol % SiC ceramics obtained by sintering Al₂O₃ powders with β-SiC particles of various types (nanoparticles, submicron particles, fibers) have been studied. Sintering was carried out at heating rates (V_h) from 10 to 700°C/min. The sintering process of Al₂O₃ + SiC ceramics with low heating rates (V_h = 10–50°C/min) has a complex three-stage character, with a flat area in the temperature range of 1200–1300°C. At high heating rates (V_h > 250°C/min), the usual three-stage character of sintering is observed. The analysis of temperature dependences of compaction was carried out using the Young–Cutler model; it was found that the kinetics of powder sintering is limited by the intensity of grain boundary diffusion. It is shown that the dependence of the hardness of Al₂O₃ + SiC ceramics on V_h has a nonmonotonic character, with a maximum. In the case of pure alumina, an increase in V_h leads to a monotonic decrease in hardness.