Ultra-high temperature ceramics (UHTCs) based on transition metal (Zr, Hf) carbides and borides are key candidates for thermal protection components in aerospace applications due to their high melting points, excellent high-temperature mechanical properties, and superior ablation resistance. To achieve enhanced performance, multicomponent systems incorporating additional ceramic phases are essential; however, the vast compositional space and complex synergistic mechanisms among phases pose significant challenges to composition design. In this work, we establish a self-consistent thermodynamic database for the B-C-O-Si-Zr-Hf system and apply it to systematically evaluate the ablation resistance of UHTCs. Through extensive thermodynamic calculations, we propose the phase stability-based evaluation criteria for assessing oxidation behavior under service conditions. A novel phase fraction–oxygen partial pressure diagram is introduced to reveal the evolution of stratified ceramic structures during ablation and to predict critical oxidation thresholds. High-throughput thermodynamic calculations combined with multi-objective optimization are employed to screen over 3,000 initial compositions, from which 60 promising UHTC formulations with superior ablation resistance are identified. Experimental validation of two compositions (one randomly selected from the designed compositions while the one from the literature) via spark plasma sintering and ablation testing at 2773 K for 1000 s confirms that the designed composite exhibits excellent oxidation and ablation resistance, achieving a mass ablation rate of -0.001 mg·s -1 . In contrast, the chosen reference sample shows a significantly higher mass loss rate of -0.04 mg·s -1 . These results demonstrate the reliability and effectiveness of the proposed composition design methodology for developing superior ablation-resistant UHTCs.
Wang et al. (Mon,) studied this question.