Low-Temperature Sintering of Mullite/Yttria-Doped Zirconia Composites in the Mullite-Rich Region

Mullite/Y-TZP composites in the mullite-rich region, using powders of mullite prepared via the hydrazine method and a commercially available zirconia compound (ZrO₂(2Y)), have been fabricated by sintering for 3 h at 1450°C in air. The grain sizes of mullite and ZrO₂(2Y) are changed with increased ZrO₂(2Y) content; the former decreases from 0.25 µm to 0.13 µm, and the latter increases from 0.21 µm to 0.35 µm. High strength (780 MPa) and fracture toughness (5.4 MPam^1/2) are obtained in the 50/50 (vol%) mullite/ZrO₂(2Y) composite with 99.6% of theoretical density.