The influence of the molar ratio of Al2O3 to Y2O3 on sintering behavior and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite

The influence of the molar ratio of Al2O3 to Y2O3 (i.e. M A l 2 O 3 / M Y 2 O 3 ) on sintering densification, microstructure and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite were studied. It was shown that the optimal value of M A l 2 O 3 / M Y 2 O 3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y3Al5O12) phase. When M A l 2 O 3 / M Y 2 O 3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When M A l 2 O 3 / M Y 2 O 3 was 3/2, materials existed in the two phases YAG (Y3Al5O12) and YAM (Y4Al2O9). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher.