Spark plasma sintering of mullite-zirconia-TiO₂ ceramics

Spark plasma sintering (SPS) of an Al₂O₃-ZrSiO₄ mixture of fine powders in the presence of TiO₂ as an additive, which supplies a transient liquid during firing, has been studied. The effect of the sintering temperature, as well as the presence of the additive on the phase's evolution, microstructure and mechanical properties of the final sintered composite are analyzed in this work. Fast firing in the SPS process results in well densified bodies (> 99.5% relative density) at low temperatures (1380°C). However, it is necessary to increase the temperature to 1460°C in order to obtain bodies with full mullitization reaction. The K_IC of the composite is improved to 4.91 MPa·m ^1/2 , but a low tetragonal ZrO₂ content in the fired body indicates that reinforcement by ZrO₂ stress induced transformation is not the toughening mechanism. Therefore, another mechanism is responsible for toughening in this kind of composites.