Microstructural development and mechanical properties of pressureless-sintered SiC with plate-like grains using Al₂O₃-Y₂O₃ additives

Abstract

Dense SiC ceramics with plate-like grains were obtained by pressureless sintering using Β-SiC powder with the addition of 6 wt% Al₂O₃ and 4 wt% Y₂O₃. The relationships between sintering conditions, microstructural development, and mechanical properties for the obtained ceramics were established. During sintering of the Β-SiC powder compact the equiaxed grain structure gradually changed into the plate-like grain structure that is closely entangled and linked together through the grain growth associated with the Β→α phase transformation. With increasing holding time, the fraction of Β→α phase transformation, the grain size, and the aspect ratio of grains, increased. Fracture toughness increased from 4.5 MPa m^1/2 to 8.3 MPa m^1/2 with increasing size and aspect ratio of the grains. Crack deflection and crack bridging were considered to be the main operative mechanisms that led to improved fracture toughness.