Preparation and characterization of a TiB₂/ZrB₂-C eutectic coating

74μm TiB₂, and 74μm and 1μm ZrB₂ powders were heated with isostatically pressed carbon blocks at 2550℃, which is above the eutectic temperature of TiB₂-C and ZrB₂-C, to form eutectic coatings, which are named TIB, ZRB-1 and ZRB-2, respectively. Results showed that the surface and the inner part of the coatings were different. The surface of the coatings was composed of B-doped highly ordered graphite, and the inner part was composed of TiB₂-C or ZrB₂-C alloy. The d₀₀₂ values of graphite in samples TIB, ZRB-1 and ZRB-2 were 0.3359, 0.3360 and 0.3354 nm, respectively, which are almost the same as that of single crystal graphite(0.3354 nm), indicating the formation of highly ordered graphite. The features of the Raman spectra of these three coatings such as the appearance of D and D' bands, low intensity 2D bands and the shift of G bands to higher wave numbers are ascribed to B-doping in the graphene layers of the graphite. The small particle size of the ZrB₂ powder favored the relaxation of the stress formed inside the surface of the coatings.