Fracture-Resistant and Thermally Insulating Ultrahigh-Temperature Carbide Foams

Dense ultrahigh-temperature ceramics (UHTCs) carbides are recognized as potential materials for thermal protection systems (TPS) owing to properties beyond existing structural materials' capabilities. Recent advances in UHTCs have enabled the development of multiscale porous microstructures. Herein, it is highlighted that the porosity in UHTCs are no longer treated as a defect but as a functional property specifically tailored for thermal insulation. It is a promising solution to design and fabricate bulk UHTC foams via a freeze-drying (FD) approach followed by calibrated pressureless spark plasma sintering. Herein, monolithic TaC and HfC UHTC foams and their composite show the partial solid-solution formation of (Ta, Hf)C with porosity & GE;50%. TaC-HfC foam (& AP;80-92 N) shows an intermediate load-bearing capability compared to monolithic TaC (& AP;120-135 N) and HfC (& AP;28-35 N) foams, with no evident cracking on the sample surface. The thermal conductivity of partial solid-solution TaC-HfC foam increases up to fivefold compared to parent UHTC foams. In the results, solid solutions' efficacy and pores' unidirectionality in providing thermal insulation to TaC-HfC while maintaining its high-load bearing capability are illustrated. The developed technique establishes a new paradigm shift in UHTCs, expanding their potential for TPS in extreme environments. The study illustrates the fabrication of ultrahigh-temperature carbides (UHTCs) foams via freeze-drying (FD) technique followed by pressureless spark plasma sintering (PSPS). PSPS represents a promising strategy to retain the foam structure obtained during FD method. The partial solid-solutioning in mixed UHTC during PSPS improves the mechanical strength and thermal insulation. This fabrication technology can be applied to other structural ceramics.image & COPY; 2023 WILEY-VCH GmbH