Interaction of HfB2 + SiC + Cr Mixtures of Various Compositions with Carbon and Silicon Carbide Substrates

Graphite and SiC substrates have been coated with two layers via slurry spraying: an inner layer, consisting of Cr-SiC, and an outer layer, consisting of HfB2-SiC-Cr. Coating growth has been shown to involve the formation of a Cr5Si3Cx-based intermediate liquid. The phase composition and surface morphology of the coatings have been studied by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Single-layer coatings produced from Cr-SiC are tightly bonded to graphite substrates but peel off from SiC substrates. Bilayer coatings peel off from both graphite and SiC. Thermodynamic evaluation has made it possible to find the most plausible chemical reactions in the HfB2-SiC-Cr-C system at temperatures in the range 1300-1900 K. The experimental data have been shown to correlate with the calculation results.