Effect of yttria on mechanical and microstructural properties of reaction sintered mullite-zirconia composites

Mullite-zirconia composites containing 0 to 7 mol% yttria were prepared by reaction sintering process from Indian coastal zircon flour and calcined alumina. The main raw materials were attrition milled. Samples were isostatically pressed and sintered at temperatures of 1400 to 1650 degrees C with 2h soaking time. The resulting composites were characterised in terms of phase compositions, martensitic start (M-S) temperature, mechanical properties and microstructural features. The presence of yttria results in a dense composite material at a comparatively low temperature. Addition of yttria increases the tetragonal zirconia fraction and reduces the Ms temperature. Yttria goes into solid solution which was detected by EDX analyses. The effect of yttria on thermal expansion coefficient, room temperature flexural strength, hardness, fracture toughness is discussed. (C) 1998 Elsevier Science Limited. All rights reserved