Composition-dependent Ta-Hf-C solid-solution ceramics derived from solvothermally synthesized powders and their laser ablation behavior above 3000 °C

Although Ta 4 HfC 5 ceramic has a highest melting point reported, it ablates rapidly in oxidative environment because Ta 2 O 5 has a low melting point of 1872 °C. In this work, ultrafine Ta-Hf-C solid-solution powders (49∼70 nm) with tunable Ta/Hf ratio were synthesized via a solvothermal route combined with carbothermal reduction using a liquid-phase precursor. Ta-Hf-C solid-solution bulks with relative densities of 98–99% were subsequently obtained by an ultra-fast pressure sintering technique. The effects of Ta/Hf ratio on densification behavior, mechanical properties, and oxidation–ablation resistance were systematically evaluated. Among all compositions, the 1TaC-4HfC ceramic exhibited the lowest mass and linear ablation rates of 0.422 mg/s and 14.237 μm/s after 120 s exposure to laser irradiation at a heat flux of 30 MW/m 2 , with a surface temperature up to 3800 °C. During ablation, a dense protective oxide layer formed through the reaction between HfO 2 and Ta 2 O 5 , generating Hf 6 Ta 2 O 17 coatings on the HfO 2 framework, while molten Ta 2 O 5 acted as a liquid bonding phase to wet and integrate the oxide phases with the residual carbide skeleton. This synergistic HfO 2 /Hf 6 Ta 2 O 17 /Ta 2 O 5 composite structure effectively suppressed oxygen permeation and enhanced high-temperature stability above 3000 °C.