Creep Rupture of Siliconized Silicon Carbide

Creep and creep-rupture of siliconized silicon carbide were studied in flexure as a function of temperature and applied stress. The behavior of this material was dominated by the formation of cavities at the silicons-silicon carbide interface. At temperatures less than 1200°C, and applied stresses less than 300 MPa, cavity densities were low, and only transient creep was observed. The strength at room temperature and at the creep temperature were the same for these conditions. At 1300°C and stresses greater than ∼250 MPa, many large cavities formed on the tensile side of the specimen, effectively reducing the internal cross-section, and enhancing the rate of creep. These cavities lined up in rows to form cracks that limited specimen lifetime. A shift of the plane of zero strain from the geometric center towards the compressive surface of the specimen was also observed as a consequence of the creep and cavitation. Cavity formation during creep caused a significant reduction in the room temperature strength. By contrast, the strength at elevated temperatures did not decrease until extensive cavity linkage occurred at creep times that approached the creep-rupture life.