Tailoring the mechanical properties of silicon carbide ceramics by modification of the intergranular phase chemistry and microstructure

Liquid-phase-sintered SiC has attracted increasing interest for its ability to form an in-situ toughened material and its potentially superior mechanical properties relative to the solid-state-sintered SiC. In the present work, a submicron-size β-SiC powder was densified with additives of various combinations of rare-earth oxides (RE2O3; RE=La, Nd, Y and Yb) and alumina by hot-pressing, and the hot-pressed materials were further annealed at higher temperatures. The phase compositions, microstructures and mechanical properties of the hot-pressed and the annealed materials were characterized. It was found that the mechanical properties were strongly influenced by the type of the sintering additives. The additives also affected the microstructural development during annealing. While the fracture toughness of all the annealed materials continuously increased with increasing annealing temperatures, however, the flexural strength either increased or decreased with annealing temperatures, depending on the kinds of the RE2O3 additives. By using appropriate rare-earth oxides, e.g. La2O3 or Nd2O3, fracture toughness and flexural strength synergetically improved after an annealing treatment.