Properties and high‐temperature ablation behavior of pressureless sintered HfC‒SiC‒TaC ceramics

Abstract This study investigated the influence of TaC additions on the densification, mechanical properties, and ablation behavior of HfC–SiC composites fabricated via pressureless sintering. Incorporating TaC shows a measurable improvement in thermo‐mechanical performance. At 20 wt.% TaC, hardness increased from 13.0 ± 1.7 GPa to 18.0 ± 2.1 GPa, while flexural strength rose from 303 ± 30 MPa to 377 ± 18 MPa. Ablation testing using an oxyacetylene torch at ∼2400°C for 10 min further demonstrated improved thermal stability: thickness change improved from –0.05 ± 0.01 mm (0 wt.% TaC) to +0.24 ± 0.001 mm, while mass loss decreased from –0.20 ± 0.05 g to –0.15 ± 0.01 g for 20 wt.% TaC. Post‐ablation characterization revealed specific microstructural effects: TaC promoted silicon retention at the surface and facilitated the formation of protective oxides, notably HfSiO 4 and Hf 6 Ta 2 O 17 , together with Ta 2 C nanoparticles. These nanoparticles were found embedded within interlaced Hf‐rich and Si‐rich amorphous regions. This refined microstructure suppressed SiO volatilization, sealed surface porosity, and limited oxygen ingress, by developing a dense and adherent protective layer. The interplay of solid solution strengthening, oxide‐scale stabilization, and a network of finely distributed phases collectively accounts for the improved ablation resistance of HfC–SiC–TaC composites compared to baseline HfC–SiC. These findings set the stage for a deeper discussion of the context and significance within the field of ultra‐high‐temperature ceramics.