Creep and Microstructural Evolution at High Temperature of Liquid-Phase-Sintered Silicon Carbide

The compressive creep characteristics at 1625°C of liquid-phase-sintered silicon carbide ceramics containing 5 and 15 wt% of crystalline Y₃Al₅O₁₂ (YAG) as the secondary phase were studied. In the two cases, strains between 10% and 15% were reached without failure. The creep behavior was characterized by a stress exponent n ≈2, and the proportion of secondary phase was related to the creep resistance of the materials. The microstructural evolution during creep consisted firstly in the re-distribution of the secondary phase, probably as a consequence of its viscous flow at the creep conditions, and secondly an extensive nucleation and growth of cavities, which was more important for the highest YAG content. The latter reflects the carbothermal reduction that the secondary phase undergoes during creep.