平纹编织 SiC_f/SiC 复合材料的中温蠕变断裂时间及损伤机制

Silicon carbide fiber reinforced silicon carbide composites (SiC_f/SiC) have great potential to be used in the thermal structure of next-generation aero-engines. The creep rupture time t_u of SiC_f/SiC significantly reduced at intermediate temperatures (~800℃). Therefore, this paper investigated the creep rupture behaviors of a plain weave SiC_f/SiC (2D-SiC_f/SiC) at 500℃, 800℃ and 1000℃ with stresses of 100 to 160 MPa in air. The morphology, microstructure and compositions of the crept specimens were observed by scanning electron microscopy, transmission electron microscopy and an energy dispersive analysis system. The results show that the t_u of 2D-SiC_f/SiC is closely related to the applied temperatures and stresses. At the same temperature, t_u decreases with the increasing stresses at constant temperatures. When the temperature is 800℃ and the stress is greater than the proportional limit stress (PLS), embrittlement takes place for the 2D-SiC_f/SiC, which means the t_u and the total creep strain are much shorter than those at 500℃ and 1 000℃. The embrittlement mechanisms involve matrix cracking, oxidization of BN and formation of strong fiber/matrix interphase bonding by the filling of SiO₂, as well as for the 2D-SiC_f/SiC at intermediate temperatures. t_u vs. the applied stress follows linear relationship in logarithmic axis, whose transition appears when the applied stress equals to PLS.