Oxidation of Porous HfB2-SiC Ultra-High-Temperature Ceramic Materials Rich in Silicon Carbide (65 vol %) by a Supersonic Air Flow

Porous HfB2-65 vol % SiC samples (porosity 34.5%) were produced by reactive hot pressing of HfB2-(SiO2-C) composite powder at 1800 degrees C (heating rate 10 deg/min, holding duration 15 min) and 30 MPa. Using a high-temperature induction plasmatron, their resistance to oxidation by a supersonic dissociated air flow was studied (the heat fluxes in the course of the experiment were varied from 363 to 779 W/cm(2)). The observation of the temperature distribution over the surface of the sample during the experiment showed that a sharp increase in temperature from 1770-1850 to 2600 degrees C in the samples under investigation occurred at lower heat fluxes and shorter treatment times than that in denser HfB2-30 vol % SiC samples (porosity 9-11%). This indicated that increasing the density of the HfB2-SiC material and also increasing the silicon carbide content reduced the oxidation resistance. However, the fact that the studied sample withstood 37-min exposure to a high-enthalpy dissociated air flow (including 27 min at a surface temperature of 2560-2620 degrees C) without destruction or complete oxidation makes it possible to assign it to ultra-high-temperature materials.