The structure of an in-situ formed titanium-boron-carbon coating on a graphite substrate

A titanium-boron-carbon coating was fabricated on a graphite substrate by heating TiB₂ powder on a graphite surface above the eutectic temperature. The coating consisted of a pure graphite layer on the outer surface and a TiB₂-C alloy layer inside. The graphite layer had many wrinkles due to the difference in the thermal expansion coefficients of TiB₂ and graphite. The TiB₂-C alloy layer had a continuous three-dimensional interpenetrating network microstructure. The d₀₀₂ value of the graphite in the alloy layer was 0.335 6 nm, which was quite close to that of single crystal graphite (0.335 4 nm). Raman and X-ray photoelectron spectroscopy indicated that the graphite in both layers was doped substitutionally with boron atoms. A water quench thermal shock test verified a high adhesion strength between the coating and the substrate. This method is promising for the fabrication of thermal barrier coatings on carbon materials.