Effect of Supercritical Drying Method on Microstructure and Properties of Al2O3 Composites Reinforced with Ultrafine SiC Particulate

Mixtures of 95vol% ultrafine γ-Al2O3 powder and 5vol% ultrafine SiC powder, with average particle size of 40nm, were mixed wet-ball milling and prepared by drying their slurry with a supercritical drying method and a microwave drying method. Al2O3 specimens dispersed with ultrafine-SiC particles as the secondary phase were hot-pressed, their powders being prepared by both the above drying methods. Difference between the superitical drying and the microwave drying method on the microstructure of Al2O3/5vol% SiC composites was investigated. Dense Al2O3/SiC composites were obtained at lower hot-pressing temperatures when the mixture was prepared by supercritical drying method. Influence of the drying method on the γ- to α-Al2O3 transition behavior was also examined. Al2O3/SiC powder dried by the supercritical drying method showed narrow particle size distribution and the formation of soft agglomerates. Al2O3/SiC composite sintered by hot-pressing the powder dried with the supercritical drying method indicated relatively higher strength, whereas the strength of Al2O3/SiC composite through microwave drying method was low and had the large scatter.