Preparation And Ablation Properties Of ZrC/ZrC(TaC)Composite Coating

In order to improve the ablation resistance performance of carbon/carbon (C/C) composites and meet the high and ultra-high temperature requirements of the aerospace field, ZrC/ZrC and ZrC/TaC composite coatings were successfully prepared by pack cementation and chemical vapor deposition (CVD).ZrC/ZrC composite coating was prepared by pack cementation and CVD, the microstructure and the ablation properties of the coating was investigated. The inner coating prepared by pack cementation method has a double structure of the inner dense layer and the outer porous layer; the CVD outer coating forms columnar crystal structure with convex cellular surface morphology. The porous layer and the CVD layer are mutually embedded and merged to form a mechanical interlocking structure, thus enhancing the interface bonding strength between the coatings.After30s ablation, the ablated coating has intact structure, the surface generates a porous ZrO2layer. The embedding porous ZrC layer can greatly ease and release strong thermal shock and thermal stress in the ablation process, improve the ZrC/ZrC coating’s thermal shock resistance, structural stability and reliability of the ablation.The ZrC/TaC coating was co-deposited in different ZrCl4/TaCl5ratio by CVD, the ablation properties were investigated. The coating accumulated with carbide particles has self-organized multilayer structural characteristic with composition fluctuation. After60s ablation, products are ZrO2and TaZr2.75O8, the mass and linear ablation rates of the coating prepared at4:1、2:1、1:1ZrCl4/TaCl5ratio are0.3×10-4g·s-1and0.5×10-4mm·s-1,0.6×10-4g·s-1and7.5×10-4mm·s-1、-0.2×10-4g·s-1and1.0×10-4mm·s-1, respectively. The multilayer structure can decrease the thermal shock of the internal coating and substrate because of the high temperature and high pressure environment, slowing down the oxidation rate of the internal coating. The existence of the TaC contribute to the coating to form a dense oxide layer and oxide melts in the ablation, which can withstand the flushing action of the high speed and high pressure air flow, avoiding the coating failure quickly. The amount of TaC can improve the ablation resistance of the ZrC/TaC composite coating.