Self-healing and failure behavior of yttrium silicate coated SiC_f/SiC composites in air at elevated temperatures

In this study, self-healing and failure behavior of yttrium silicate (YS)-coated silicon carbide fibers-reinforced silicon carbide matrix (SiC_f/SiC) composites were systematically investigated at temperatures ranging from 1000 to 1400 °C for 100 h in air. The self-healing mechanism involves the filling of cracks with SiO₂ glass and Y₂Si₂O₇ (oxidation product). The three-point bending strength of samples before and after oxidation was determined in order to clarify the self-healing performance. The strength and strength retention of YS-coated SiC_f/SiC composites after oxidation were consistently higher than those of the oxidized SiC_f/SiC composites. The strength retention rate of YS-coated SiC_f/SiC composites was found to be 110% at 1100 °C, while the corresponding value for SiC_f/SiC composites was only 68%. According to the Deal and Grove oxidation kinetic model, the oxidation activation energy of YS-coated SiC_f/SiC composites was ∼377 kJ mol⁻¹, which is higher than that of SiC_f/SiC composites (306 kJ mol⁻¹). These results indicate that the YS coating can protect SiC_f/SiC composites in oxidizing environments. Moreover, the degradation mechanisms of YS-coated SiC_f/SiC composites were expounded by finite element analysis.