Oxidation resistant zirconium diboride–silicon carbide coatings for silicon carbide coated graphite materials

• ZrB2–SiC/SiC coated graphite specimens were prepared by pack cementation.
• Weight loss of ZS50 sample was 2.9% after oxidation and 6.5% after 15 thermal shocks.
• Residual silicon is beneficial to oxidation resistance and thermal shock resistance.

Four ZrB2–SiC/SiC dual-layer coatings were prepared on the surface of graphite matrix by pack cementation to improve the oxidation and thermal shock resistance of graphite. The crystalline structure and morphology as well as the resistance to oxidation and thermal shock of these coatings were investigated. The results indicated that the weight loss of the ZS50 coating sample, whose pack powders contained 52.4 wt.% ZrB2, 39.2 wt.% Si and 8.4 wt.% graphite, was only 2.9% after oxidation in air at 1500 °C for 19 h and 6.5% after thermal shocks between 1500 °C and room temperature for 15 cycles. With the increasing silicon in pack powders, some residual silicon appeared in ZS50 coating, which was considered to be beneficial to oxidation resistance and thermal shock resistance because it can improve the density of coating and the SiO2 formed by oxidation of residual Si can heal the microcracks at high temperature.