The effect of TiO2 additive on sinterability and properties of SiC-Al2O3-Y2O3 composite system

In the current research, the effects of TiO₂ additive on mechanical and physical properties of SiC bodies, sintered by liquid phase methods were investigated. Al₂O₃ and Y₂O₃ were used as sintering-aids (10?wt% in total) with an Al₂O₃/Y₂O₃ ratio of 43/57 to provide liquid phase during Sintering. TiO₂ was also used as the oxide additive with an amount ranging from 0 to 10?wt%. After scaling and mixing the starting materials by a planetary mill, the obtained slurry was dried at 100?℃ for four hours. The derived powders were finally pressed under a pressure of 90?MPa. The samples were then pyrolyzed and sintered at 600?℃ and 1900?℃, respectively under argon atmosphere for 1.5?h. Phase analysis showed no trace of TiO₂ after the sintering process, demonstrating the complete TiO₂ to TiC transformation. The results showed that an increase in TiO₂ content up to 5?wt%, led an improvement in all the measured properties including the relative density, hardness, Young's modulus, bending strength, indentation fracture resistance and the brittleness factor, reaching to 96.2%, 24.4?GPa, 395.8?GPa, 521?MPa, 5.8?MPa?m^1/2 and 286.5?×?10^?6 m^?1, respectively. However more than 5?wt% additive resulted in a decrease in all the above-mentioned properties. Microstructural studies demonstrated that crack deflection and crack bridging were the major mechanisms responsible for an increase in the indentation fracture resistance.