Ablation Resistance of ZrB₂-SiC-Si Composite Coatings Applied on Graphite Substrate by Spark Plasma Sintering

In this research, a protective composite coating made of ultra-high-temperature ceramics (UHTCs) was applied on the graphite substrate to boost the ablation resistance of the graphite substrate. Spark plasma sintering (SPS) was used to create such coatings on the graphite substrates. Efforts were made to identify the appropriate chemical composition for the composite coating and the conditions for the SPS (temperature, pressure and holding time). The coatings with a base composition of ZrB₂-15 vol.% Si-15 vol.% SiC as well as MoSi₂ and WC additives in the same amounts of 0 vol.%, 2.5 vol.% and 5 vol.% of each were applied on the graphite substrates under sintering conditions of final temperature of 1875 ± 25°C, initial pressure of 10 MPa, final load of 25 MPa and holding time of 5 min. The results obtained from the ablation test by oxyacetylene flame verified that the presence of the protective composite coating significantly increases the ablation performance of the graphite substrate. The sample without WC and MoSi₂ additives had the lowest mass reduction in longer ablation times, which indicates the high ablation resistance of the base sample compared to the samples with those additives.