Effect of particle size on the characteristics of mULLITE-ZrO₂ ceramics produced by spark plasma reaction sintering

Zirconia-mullite composites were produced by spark plasma reaction sintering (SPRS) with a powder mixture of ZrSiO₄ + Al ₂O₃ + Al. The powder was milled in an attritor for 6 and 12 h in order to prepare two different particle sizes to evaluate the influence of the particle size on the formation of mullite and densification. The attrition-milled powders were calcined at 1100°C before the SPRS. They were consolidated at different temperatures up to 1580°C with a pressure of 40 MPa. The progress of the mullitization reaction and the densification was faster for the composites fabricated with the finer particles. The microstructure of the composites fabricated with the finer particles achieved almost full density and were completely mullitized. Their microstructure consisted of a homogeneous dispersion of tetragonal and monoclinic ZrO₂ particles in a mullite matrix. They achieved a hardness of 1533 MPa and a high Young's modulus. The flexural strength and toughness were 797 MPa and 5.93 MPa·m ^1/2, respectively.