Oxidation of HfB2-SiC-Ta4HfC5 ceramic material by a supersonic flow of dissociated air

The oxidation of an ultra-high-temperature ceramic material (HfB2-30 vol%SiC)-10 vol%Ta4HfC5 produced by reactive hot pressing at a temperature of 1800°C (pressure 30 MPa, holding time 30 min, Ar) under long-term exposure (2000s) to a supersonic flow of dissociated air was studied. It was found that the sample surface temperature, set during heating and oxidation on a high-frequency induction plasmotron, was significantly lower than for samples unmodified with super-refractory tantalum-hafnium carbide Ta4HfC5. It was also found that under similar exposure conditions there was no sharp temperature rise to 2500−2700°C – the temperature did not exceed 1850°C. Features of the oxidised material surface microstructure were noted, in particular, the existing gradient in the elemental composition and morphology of the oxide particles forming the surface. It was found that the main crystalline oxidation product was a complex hafnium-tantalum oxide Hf6Ta2O17, which had a phase stability up to temperatures of ∼2250°C, which set it apart from individual hafnium oxide.