MICROSTRUCTURE AND FRACTURE-TOUGHNESS OF YTTRIA-DOPED TETRAGONAL ZIRCONIA POLYCRYSTAL MULLITE COMPOSITES PREPARED BY AN INSITU METHOD

Yttria-doped tetragonal zirconia polycrystal (Y-TZP)/mullite composites were prepared by three methods: in situ whisker growth (IS), physical mixing (PM) of zirconia powder and mullite whiskers, and reaction sintering (RS). Microstructures and fracture toughness values were compared. All the composites with 15 vol% of mullite could be densified to more than 97% relative density by firing at 1500° to 1550°C for 10 h. The fracture toughness of the composites as measured by the indentation method showed a clear enhancement compared with that of pure Y-TZP; the ranking was Y-TZP 2= RS composite IS composite. Enhancement of the fracture toughness in composites was found to relate strongly to the aspect ratio of mullite particles.