Effect of supercritical drying method on microstructure and properties of Al₂O₃ composites reinforced with ultrafine SiC particulate

Mixtures of 95 vol% ultrafine γ-Al₂O₃ powder and 5 vol% ultrafine SiC powder, with average particle size of 40 nm, 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 Al₂O₃/5 vol%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.