Ultrahigh-temperature mechanical behavior and failure mechanisms of SiCf/SiC composites

SiCf/SiC composites are potential candidates in the aerospace fields for application as high-temperature structural components. Their mechanical properties and failure behaviors at ultra-high temperatures (above 1473 K) are important to obtain systematically. This work performed the in-plane compressive, bending, and interlaminar shear tests at 1573 K and 1773 K in an inert atmosphere. The results showed dramatically that the in-plane compressive and interlaminar shear strengths increased with the temperature increment from 1573 K to 1773 K. In contrast, a reduction in flexural strength was noticeable. To reveal the failure mechanisms, fracture surface microstructures of these SiCf/SiC samples were characterized. It was found that the fiber surfaces for the samples tested at 1773K were rougher than the samples tested at 1573K. It meant that, with the temperature increasing, the fiber-matrix interfaces enhanced, which resulted in increasing compressive and interlaminar strengths. For the bending tests, serious delamination occurred when the temperature increased to 1773K, which induced the flexural strength reduction. The numerical simulations of bending samples were developed to reveal the mechanism of strength degradation as the temperature elevated.