Oxidation response of a SiCf/SiC CMC with a HfB2-based coating in an arc jet test

Abstract

The behaviour of a SiC-fibre-reinforced composite with a graded matrix was investigated in an arc jet facility. The graded matrix was comprised of several layers of silicon carbide that transition to a mixed SiC-HfB2 top layer and was sealed with an HfB2-SiC coating. Samples were exposed to maximum specific total enthalpy hypersonic flow between 14 and 17 MJ kg−1 under stagnation pressures between 2700 and 3050 Pa for hold times of between 137 and 395 s. The resulting sample surface temperatures ranged between 1600 and 1950°C. Spectral emissivity at about 1 μm was calculated using a pyrometer capable of switching between one and two color modes and was shown to decrease with oxidation and removal of SiO2 from the surface. The impacts of the surface chemistry changes during oxidation and of active oxidation were investigated.