Sintering behaviour and properties of SiCAION ceramics

Silicon carbide (SiC), aluminium oxycarbide (AI₂OC), and aluminium nitride (AlN) all have the same wurtzite crystal structure and can be processed so as to form SiCAION, an acronym for the solid solution. This paper describes processing of SiC-Al₂OC ceramics by pressureless reactive sintering and gives mechanical property data on the same. Experiments showed that densification occurred by a liquid-phase sintering mechanism. Both alpha and beta SiC up to a particle size of 5 μm were used to form the solid solution, boron additions were not necessary to promote densification, and densities greater than 97% of the theoretical were achieved by pressureless sintering. SiC-Al₂OC ceramics, containing minor amounts of AIN, were fabricated from conventional raw materials. Phase identification by X-ray diffraction and metallography showed that the materials consisted of two phases: SiCAION and SiC. Mechanical property data were obtained on pressureless sintered and hot-pressed materials. Hot-pressed materials had room-temperature strengths in excess of 600 MPa, hardness greater than 25 G Pa, and fracture toughness greater than 4 M Pa m^-1/2. Pressureless sintered bars had bend strengths in excess of 300 M Pa.