Effect of Supersonic Nitrogen Flow on Ceramic Material Ta4HfC5–SiC

The behavior of the ceramic material Ta4HfC5-30 vol % SiC has been studied under the effect of supersonic flow of dissociated nitrogen, which is necessary to assess the potential application of these materials in oxygen-free gas environments at temperatures >1800°C. It has been found that as a result of heating the surface to ~2020°C in a few minutes there is a decrease to ~1915°C followed by a slow decrease to 188°C. This is probably due to the chemical processes occurring on the surface and the formation of an extremely rough microstructure. The ablation rate has been determined; it has been shown that neither at introduction of the sample into a high enthalpy nitrogen flow nor at sharp cooling (temperature drop to ~880°C in 9–10 s) cracking of the sample or detachment of the near-surface region has been observed. X-ray powder diffraction and Raman spectroscopy data allow us to conclude the complete removal of silicon carbide from the surface layer and the transformation of complex tantalum-hafnium carbide into the nitride.