Microstructure And Properties Of Ceramic Coatings On Carbon Matrix Composites Prepared By Molten Salt Liquid Phase Method

In view of the shortcomings of the surface coating modification technology of carbon matrix composites,such as the uneven heat transfer and mass transfer of the solid-phase deposition method,and the low bonding strength of the interface of the vapor-phase deposition method,the molten salt liquid-phase method（molten salt reaction method and molten salt method）is adopted in this paper.Electrodeposition method)prepared tungsten and zirconium-based ceramic coatings on the surface of carbon-based materials.The microstructure and ablation behavior of tungsten-based ceramic coatings prepared on the surface of graphite materials by molten salt reaction（HSB）method have proved the feasibility of applying the HSB method to the modification technology of carbon-based material coatings.The ablation-resistant zirconium-based ceramic coating was prepared on the surface of carbon-based materials by HSB method,and the effect of process parameters on the microstructure of the materials was studied.The effects of deposition temperature,current density,deposition time,and substrate material on the microstructure and evolution of zirconium-based ceramic coatings prepared by molten salt electrodeposition（MSE）were studied,and the coating preparation process was optimized.The ablation resistance of zirconium-based ceramic coatings prepared by HSB method and MSE method at 3000℃was tested,and the ablation mechanism and ablation model were discussed.Obtain the following research results:（1）The HSB method has the controllability of coating components:the coatings prepared with Zr as raw materials are Zr C single-phase ceramic coatings;the coatings prepared with 0.7Zr0.3Si as raw materials are Zr C-Zr_xSi_y multiphase ceramic coating.The salt bath temperature has controllability on the phase composition of the tungsten-based coating.With the increase of temperature,the phase of the coating shows the transformation law of W→W₂C+WC→WC.（2）The suitable process conditions for the preparation of zirconium-based ceramic coatings by MSE method are:deposition temperature of750℃and current density of 100 m A/cm².The deposition temperature of750℃is conducive to the dynamic balance of nucleation and crystal growth.When the current density is 100 m A/cm²,the Zr C coating does not generate a large number of nodular structures on the surface,but also avoids the structure loosening caused by the fine grains.Slow growth and other problems;the prolongation of deposition time is conducive to the continuous thickening of the coating,and the growth rate of coating thickness decreases slowly with the increase of deposition time.（3）The mass ablation rate and line ablation rate of the zirconium-based single-phase ceramic coating prepared by HSB method after ablation for60 s were 0.805 mg/s and 2.900μm/s.The mass ablation rate and line ablation rate of the Zr C coating prepared by MSE method after ablation for30 s are 0.224 mg/s and 0.167μm/s,which can almost achieve zero ablation of the coating.（4）During the ablation process of the zirconium-based single-phase ceramic coating,the dense structure of the inner layer Zr C_xO_y coating and the high melting point Zr O₂ energy structure can achieve good thermal protection of the matrix,so that the material has excellent ablation performance.The zirconium-based multiphase ceramic coating can effectively protect the substrate for 60 s,and its thermal protection mechanism is related to the gasification endotherm after silicon phase oxidation and the Zr Si O₄ filled porous oxide layer formed by the reaction of part of Si O₂ and Zr O₂.The dense structure of the coating and the formation of dense and continuous Zr O₂ columnar crystals during the ablation process,a Zr Si O₄ wrapped Zr O₂ layer is formed at the transition interface between the Zr C layer and the SiC layer.