Effect of silicon/graphite ratio and temperature on oxidation protective properties of SiC/ZrB2-SiC coatings prepared by pack cementation

To investigate the silicon/graphite ratio and temperature on preparation and properties of ZrB2-SiC coatings, ZrB2, silicon, and graphite powders were used as pack powders to prepare ZrB2-SiC coatings on SiC coated graphite samples at different temperatures by pack cementation method. The composition, microstructure, thermal shock, and oxidation resistance of these coatings were characterized and assessed. High silicon/graphite ratio (in this case, 2) did not guarantee higher coating density, instead could be harmful to coating formation and led to the lump of pack powders, especially at temperatures of 2100 and 2200 degrees C. But residual silicon in the coating is beneficial for high density and oxidation protection ability. The SiC/ZrB2-SiC (ZS50-2) coating prepared at 2000 degrees C showed excellent oxidation protective ability, owing to the residual silicon in the coating and dense coating structure. The weight loss of ZS50-2 after 15 thermal shocks between 1500 degrees C and room temperature, and oxidation for 19 h at 1500 degrees C are 6.5% and 2.9%, respectively.