Effect of Kinds of Sintering Aids of Rare Earth Oxides on Si<sub>3</sub>N<sub>4</sub> Grain Size and Fracture Toughness of SiC Whisker/Si<sub>3</sub>N<sub>4</sub> Composite Ceramics

Abstract

In order to find the sintering aids for obtaining SiC whisker (SiC (w))/Si3N4 composite ceramics with high fracture toughness, the effect of nine rare earth oxides on the β-Si3N4 acicular grain size in the monolith was investigated in the first step. In the second step, the fracture toughness of SiC(w)/Si3N4 composite ceramics with addition of main four rare earth oxides was investigated in relation to the Si3N4 grain size. It was found that the Si3N4 grain size in the monolith was largely affected by the chemical species of rare earth oxides and that the order of the grain size was expressed as follows; Y2O3>Er2O3≅Dy2O3>Pr2O3>Sm2O3≅Gd2O3>Tb4O7>Nd2O3>MgO>Eu2O3. The Si3N4 grain size in SiC(w)/Si3N4 composites was nearly equal to that in the corresponding monolith with the same sintering aid, and the values of KIC of the composites were higher for larger β-Si3N4 grains than for the smaller β-Si3N4 grains, in the same manner as the monolith.