Impact of a Supersonic Dissociated Air Flow on the Surface of HfB2–30 vol % SiC UHTC Produced by the Sol–Gel Method

Abstract

A new method to produce ultra-high-temperature ceramic composites under rather mild conditions (1700°C, 30 MPa, treatment time 15 min) was applied to synthesize a relatively dense (ρrel = 84.5%) HfB2–30 vol % SiC material containing nanocrystalline silicon carbide (average crystallite size ∼37 nm). The elemental and phase compositions, microstructure, and some mechanical properties of this material and also its thermal behavior in an air flow within the temperature range 20–1400°C were investigated. Using a high-frequency induction plasmatron, a study was made of the effect of a supersonic dissociated air flow on the surface of the produced ultra-high-temperature ceramic composite shaped as a flat-end cylindrical sample installed into a copper water-cooled holder. On 40-min exposure of the sample to the supersonic dissociated air flow, the sample did not fail, and the weight loss was 0.04%. Although the heat flux was high, the temperature on the surface did not exceed 1400–1590°C, which could be due to the heat transfer from the sample to the water-cooled model. The thickness of the oxidized layer under these conditions was 10–20 μm; no SiC-depleted region formed. Specific features of the microstructure of the oxidized surface layer of the sample were noted.