Transformation of the Surface of HfB2–SiC–C(graphene) Ultrahigh-Temperature Ceramics in a High-Velocity Flow of Dissociated Nitrogen

The effect of a high-velocity flow of dissociated nitrogen on a sample of HfB2–30 vol % SiC ultrahigh-temperature ceramic materials modified with low amounts of reduced graphene oxide was studied to evaluate the potential of these materials in creating aerospace equipment intended for use in N2-based atmospheres. It was determined that, under the selected treatment conditions during a stepwise increase in the anode supply power of the plasma torch and, accordingly, in the acting heat flux at certain process parameters, the surface temperature of the sample sharply increases from ~1750 to 2000–2100°C. A further increase in the heat flux does not have an obvious and proportional effect on the surface temperature of the sample, which may indicate its high catalyticity with respect to surface recombination reactions of atomic nitrogen. It was shown that the surface layers of the material undergo a chemical transformation (removal of silicon-containing substances and formation of a new phase based on HfN), which is accompanied by a significant change in the microstructure (formation of dendrite-like structures), affecting the optical and catalytic characteristics of the surface.