Plasma Oxidation of Additively Manufactured Monolithic and Multi‐Component Ultra‐High Temperature Carbides

ABSTRACT

Ultra‐high temperature ceramics (UHTCs) such as tantalum carbide (TaC) and multi‐component UHTCs (MCUHTCs) offer exceptional stability and oxidation resistance above 2500°C but remain difficult to manufacture into useful shapes using conventional routes. This study demonstrates a direct ink writing (DIW)‐based additive manufacturing (AM) pathway for fabricating high‐density TaC and (TaNbHfTi)C (MCUHTC) components with solid loadings up to 87 wt.% and 91 wt.%, respectively. Green bodies were consolidated via pressureless spark plasma sintering (PSPS) and graphite element‐based vacuum sintering (GVS) at 1900°C. PSPS yielded near‐theoretical densification (≈98%) and complete single‐phase solid‐solutioning in MCUHTC, while GVS resulted in phase segregation and lower densification ∼92%. Plasma‐jet oxidation tests revealed that PSPS‐processed MCUHTC exhibited 43% better oxidation resistance than monolithic TaC samples, forming a thin mixed‐oxide layer (∼75 µm) dominated by Hf ₆ Ta ₂ O ₁₇ , whereas TaC developed thicker erosive Ta ₂ O ₅ scales (∼133 µm). The MCUHTC samples from GVS fractured under thermal stress. Nanoindentation confirmed the superior mechanical performance of MCUHTC (hardness ≈ 14.5 ± 3.8 GPa, elastic modulus ≈ 300 ± 42.9 GPa) relative to TaC (≈ 11.7 ± 2.5 GPa, ≈ 251 ± 30.6 GPa). Overall, the results establish DIW combined with PSPS as a viable route to fabricate dense, oxidation‐resistant, multi‐component UHTC carbides for hypersonic, and plasma‐facing applications.