HfB2-SiC (10-20 vol %) ceramic materials: Manufacture and behavior under long-term exposure to dissociated air streams

Ultra-high-temperature composite materials HfB2-SiC containing 10, 15, and 20 vol % SiC were prepared by spark plasma sintering. The behavior of the samples prepared under long-term exposure to subsonic dissociated airstreams of a high-frequency induction plasmatron was studied. The total test time per sample was 35-42 min. Under certain exposure conditions (which were dependent on the composition of a sample), some regions of the sample were found to experience a rapid increase in temperature up to 2700A degrees C. These regions enlarged over time, so that most of the surface area of the sample experienced exposure to temperatures of up to 2500-2700A degrees C for 19-38 min, while the rest of the surface had a temperature of up to 1800-1900A degrees C during almost the entire duration of the experiment. The joint use of optical microscopy, scanning electron microscopy (with EDX analysis), and X-ray powder diffraction enabled us to study the microstructure and composition of a structurally complex oxidized layer.