Research On Preparation And Properties Of One-dimensional Of Si-based Materials Toughened Silicate Coating For C/C Composites

Carbon/carbon?C/C?composites are outstanding materials for applications in aerospace industry due to their ultra high temperature stability and high-temperature mechanical properties.Unfortunately,oxidation of C/C composites above 450 °C in oxidizing atmosphere limits their applications in the field of high temperature and oxidizing atmospheres.Appling multilayer ceramic coatings have been proved as an effective method for addressing this issue.However,the inherent brittleness of the mullite ceramic coatings limits their application at high temperature,which will result in the formation of cracks during thermal cycles between room and high temperature.This project focused on the problem of high temperature oxidation resistance coating for carbon/carbon?C/C?composites.To improve the toughness of ceramic coatings,one-dimensional of silica-based materials toughened silicate coating was prepared by various method.The phase composition,microstructure,interface bonding strength,the toughening mechanism,as well as the thermal shock resistance and the toughening mechanism of the coating.The results are as follows:?1?The single phase ?-Y₂Si₂O₇ whiskers were synthesized via a facile molten salt method.The phase composition,microstructure,formation mechanism and the phase transformation of the ?-Y₂Si₂O₇ whiskers were investigated,as well as the thermal properties of the corresponding ?-Y₂Si₂O₇ ceramic.Results show that the obtained ?-Y₂Si₂O₇ whishers possess low thermal conductivity?1.84 W·m-1·K-1?and low thermal expansion coefficient?3.88×10-6·K-1?.?2?The Si C/?-Y₂Si₂O₇ whisker-toughened Y₂SiO₅/YAS multi-layer oxidation protective coating for carbon/carbon composites was prepared by pulse arc discharge deposition?PADD?and hot dipping.The phase composition,microstructure,adhesion strength,thermal shock resistance and oxidation resistance of the coating were investigated.The results showed that the weight loss of the coated samples was only 1.05% after 50 thermal cycles,and the weight loss of the coated samples was only 0.86% after oxidation in air at 1400 °C for 176 h.?3?The mullite whisker-toughened silicate glass coating for SiC pre-coated carbon/carbon composites?SiC-C/C?which was prepared by a novel molten salt and hot dipping.The microstructure,adhesion strength and thermal shock resistance of the coating were investigated.Results showed that preparing the transition mullite whisker layer and incorporating the mullite whisker could effectively improve the coating interface bonding and decrease the size of microcracks.The as-prepared coating has an enhanced thermal shock resistance and the weight loss of the coated samples was only 2.21% after 100 thermal cycles.?4?An oxidation resistant SiC nanowire-toughened mullite coating for SiC pre-coated carbon/carbon composites?SiC-C/C?was prepared by a two-step technique of hydrothermal electrophoretic deposition?HEPD?with a later pulse arc discharge deposition?PADD?.SiC nanowires could efficiently decrease the size of microcracks and baffle the propagation of the microcracks by various toughening mechanism including devitrification,crack deflection,bridging and pullout of SiC nanowires.The results showed that the weight loss of the coated samples was only 0.03% after 50 thermal cycles,and the weight loss of the coated samples was only 107 g·m-2 after oxidation in air at 1500 °C for 235 h.The failure of the coating is due to the volatilization of glass layer and the formation of microholes in the coating.