Sintering of ZrO2 toughened mullite ceramics and its microstructure

Mullite/ZrO2 composite ceramics were fabricated from sol-gel derived powders. The effects of ZrO2 content and firing temperature on the densification and microstructure development have been investigated by means of SEM, TEM and XRD. It was clarified that the 5 to 25 vol% addition of ZrO2 to mullite improved the sinter-ability. The effect is more striking in the composites containing 10 or 15 vol% ZrO2. The growth of mullite grains was inhibited by dispersing ZrO2 particles. The effects were, especially, most predominant in the composite containing 15 vol% ZrO2+. However, in composites fired at 1650°C and above, remarkable grain growth was observed, and needle-like mullite grains having Al-rich composition appeared. These results may be ascribed to the coalescence of fine ZrO2 crystals.