ZrO₂-induced crack-healing mechanism of ZrB₂-SiC-Graphite composite in high temperature atomic oxygen environment

The ZrO₂-induced crack-healing mechanism of ZrB₂-SiC-Graphite (ZSG) composite is investigated under high temperature atomic oxygen atmosphere, which characterizes the real condition of hypersonic flight. This differs greatly from the borosilicate glass-induced crack-healing mechanism in previous studies. The cracks are healed limitedly in high temperature atomic oxygen condition with a 39.09% maximum improvement in residual strength compared to the pre-cracked specimens. The crack-healing is induced by ZrO₂, and the crack-healing mechanism involves three main aspects: A. Local particle rearrangement, which is induced by expansion from the chemical reaction (ZrB₂→ZrO₂), the phase transition (t-ZrO₂→m-ZrO₂), and the thermal expansion. B. The crack volume filling by ZrO₂ driven by the liberation of the reaction gases. C. Diffusion controlled sintering around the ZrO₂ sintering temperature. The spontaneous crack-healing ability in high temperature atomic oxygen atmosphere is helpful to improve the reliability of ZSG composites in service.