Mechanical and Microstructural Characterization of Mullite and Mullite-SiC-Whisker and ZrO2-Toughened-Mullite-SiC-Whisker Composites

High‐purity mullite‐SiC‐whisker composites and mullite‐ZrO2‐SiC‐whisker composites were fabricated in situ by hot‐pressing using a matrix prepared by the alkoxide process. Varying degrees of ZrO2 stabilization were achieved by varying amounts of Y2O3 or MgO addition. Microstructural characterization was accomplished using SEM and energy dispersive analysis. Room‐temperature flexural strength and fracture toughness were determined as a function of SiC‐whisker content (0% to 30%) and ZrO2‐stabilizer content. The flexural strength of mullite varied with composition and was increased ∼50% by the addition of ∼30% ZrO2 phase. The flexural strength of mullite and mullite + 30% ZrO2 was increased ∼50% for 30% SiC‐whisker additions. The fracture toughness of mullite + 30% ZrO2 was nearly twice that of mullite. For a 30% SiC‐whisker addition, the fracture toughness of mullite was doubled, and the fracture toughness of mullite + 30% ZrO2 was increased 25% to 50%.