High-Temperature Reusability and In Situ Ceramization Mechanism of Alumina Fiber/Boron Phenolic Resin Composites Modified with ZrSi2 and TiB2

This research developed a ZrSi2-TiB2-modified alumina fiber/boron phenolic resin ceramizable composite intended to fulfill the criteria for high-temperature resistance, oxidation resistance, and structural load-bearing capacity in reusable thermal protection systems. The composite exhibits a low thermal conductivity of 0.405 W·m−1·K−1, a reduced density of 2.11 g·cm−3, and a high mass retention rate of 89.45% after heat treatment at 1200 °C in air. During thermal cycling at 1200 °C with a 30 min dwell time, it consistently demonstrates excellent stability, mass retention, and mechanical properties, indicating its potential for applications in reusable thermal protection systems. Following 20 cycles, the variation in length and width remains below 0.6%, the mass retention surpasses 80%, and the flexural strength remains above 20 MPa after 15 cycles. Microstructural evolution and thermodynamic analysis disclose that the in situ ceramization reaction of ZrSi2 and TiB2 consumes oxygen, inhibits oxygen diffusion, and fills pores and microcracks with oxidation products (SiO2 and B2O3), thereby forming self-healing and densifying phases. This synergistic mechanism of self-healing and densification ensures the reusability of the composite. The research illustrates the performance evolution patterns and strengthening mechanisms of the composite under extreme thermal conditions, confirming its outstanding performance in repeated usage evaluations.