Arc-jet testing on HfB2 and HfC-based ultra-high temperature ceramic materials

The behaviour of pressureless sintered HfC and HfB2 ceramics, when exposed to high enthalpy plasma flows typical of atmospheric re-entry environment, was investigated with an arc-jet facility at temperatures exceeding 2000 °C. The surface temperature and emissivity of the materials were evaluated during the test. The microstructure modifications were analysed after exposure. Fluid dynamic numerical simulations were carried out to evaluate the catalytic atom recombination efficiencies of the materials at the experimental conditions. Surface and cross sections of the samples showed the formation of scales mainly consisting of HfO2 and SiO2. For the HfB2-based composite numerical results correlated quite well with experimental ones assuming a low catalytic surface behaviour. For the HfC-based material the surface behaviour changed from low catalytic to partially catalytic as the temperature increased. The post-test analyses confirm the potential of these composites to endure re-entry conditions with temperature approaching 2000 °C or even higher.