High temperature ablation-oxidation performance of SiC nanowhisker toughened-SiC/ZrB2-SiC ultra-high temperature multilayer coatings under supersonic flame

Ablation behavior of SiC nanowhisker toughened-SiC/ZrB2-SiC ultra-high temperature multilayer coatings was evaluated under supersonic flame at similar to 2173 K for 120s. SiC nanowhisker toughened-SiC/ZrB2-SiC coatings were prepared on graphite substrate by two-step reactive melt infiltration (RMI) method. The ZrB2-SiC outer coating was prepared on the SiC coated graphite surface by in-situ and ex-situ methods. In ex-situ processing, ZrB2 powder was directly introduced into the powder mixture as a raw material. In in-situ processing, ZrB2 phase was formed in the coating by in-situ reaction between ZrO2 and B2O3. The linear and mass ablation rates for the in-situ ZrB2-SiC coating after 120s ablation under supersonic flame were 1.75 mms(-1) and 0.083 x 10(-3) g cm(-2) s(-1) respectively. For the ex-situ ZrB2-SiC coating the linear and mass ablation rates were 1.5 mms(-1) and 0.064 x 10(-3) g cm(-2) s(-1). The results showed that, the ablation resistance of in-situ ZrB2-SiC coating is very close to ex-situ ZrB2-SiC coating which can provide stable protection for the carbon substrate. Moreover, The SiC nanowhisker network structure in both in-situ ans ex-situ ZrB2-SiC coatings not only improved the toughness of the protective film by crack bridging, crack deflection and crack impedance, but also enhanced the bonding ability of protective film by the pinning and framework effects. (c) 2018 Elsevier B.V. All rights reserved.