Thermal stress relaxation creep and microstructural evolutions of nano-structured SiC ceramics by liquid phase sintering

We explored the thermal relaxation creep characteristics of nano-structured SiC ceramics by bend stress relaxation (BSR) method. The effects of the differences in microstructure and secondary phases by liquid phase sintering at 1800 or 1900 C were especially discussed, based on microstructural evolutions during the creep. The creep was characterized by the BSR ratio (m) of ∼ 0. 80 up to 1200 C, and the proportion of amorphous phase as a secondary phase was related to the creep resistance at 1300 C. The microstructural evolutions during the creep consisted firstly in the re-distribution of amorphous phase, probably as a consequence of its viscous flow, and secondly in an extensive nucleation and growth of cavities. Furthermore, the former enhanced inter-diffusion of Al-Y among intergranular areas above the ternary eutectic temperature, which caused the significantly reduced creep resistance, and the latter reflected the crystalline YAG decomposition as another secondary phase near 1500 C. (authors)