| The creep of a high strength, high toughness SiC, sintered with Al, B, and C (ABC-SiC), was investigated. For elevated temperature applications, the time-dependent deformation, creep response, must be fully characterized for candidate materials. The mechanisms responsible for high temperature deformation in ABC-SiC were evaluated. The creep response was compared to materials that have glassy grain boundary phases but do not have interlocked grains.; The creep mechanisms were assessed by calculating the stress exponent and apparent activation energy. For creep tests conducted between 1200–1500°C, 50–200 MPa, the stress exponent, n, was ∼1. The activation energy for the same temperature and stress range was Ea ∼ 225 kJ/mol. This data was utilized in conjunction with microstructural features to determine the operative creep mechanisms. Characterization revealed isolated grains containing dislocations after creep. However, these dislocations were not the controlling creep mechanism, as evidenced by the low stress exponent and lack of dislocation slip and climb. Grain boundary analysis revealed that the boundaries changed upon exposure at creep temperatures. The initial amorphous grain boundaries exhibited crystalline features after the heat treatments.; The controlling creep mechanism was determined to be grain boundary sliding accommodated by diffusion along the grain boundary interlayer/SiC interface. Parallel mechanisms of solution-precipitation and cavitation were also operative in ABC-SiC. Additionally, the dislocations were likely introduced at regions of grain-to-grain contact where the local stresses were high.; The high temperature strength and long exposure oxidation resistance were assessed. The four-point bend strength of ABC-SiC decreased by a factor of 5, from ∼515 MPa to 100 MPa, as the temperature was increased from room temperature to 1300°C. However, long heat treatments in Ar improved the high temperature strength at 1300°C from ∼100 MPa to almost 400 MPa, while also improving the room temperature strength. Crystallization of the grain boundary phase during annealing limited softening of the grain boundary glass and thus minimized subcritical crack growth. Little degradation was observed for ABC-SiC after oxidation at 1200°C for ∼9.5 days. |
