Si Bond Layer Prepared By Physical Vapor Deposition In Environmental Barrier Coatings

Carbon fiber reinforced silicon carbide composites（C_f/Si C composites）have excellent mechanical and thermal properties at high temperature and have great application potential in the field of aerospace materials.However,in the service environment,the presence of oxygen and high temperature water vapor will cause the oxidation of C fiber and the water-oxygen corrosion of Si C matrix,thus rapidly reducing the mechanical properties of the material,making the service life of the composite greatly reduced.Therefore,environmental barrier coatings to protect composite materials have been developed rapidly.Environmental barrier coatings（EBC）can reduce the erosion of matrix materials in oxygen and flowing water vapor environment.EBC coatings usually consist of a bonding layer and a ceramic surface layer（and sometimes with an intermediate layer）.The bonding layer can enhance the bonding force between substrate and ceramic coating and slow down the diffusion rate of oxygen.Atmospheric plasma spraying is the main method to prepare EBC in recent years.It has the characteristics of flexible preparation process,high spraying efficiency and good spraying structure.However,in the process of preparing Si adhesive layer,problems such as oxidation and volatilization will be brought,which will reduce the density and uniformity of the prepared Si adhesive layer,thus affecting the service ability of the entire EBC coating and reducing the reliability of the coating.In order to solve the above problems,this paper prepared pure Si bond layer on C_f/Si C composite substrate by physical vapor deposition（PVD）process of vacuum evaporation.The coating has good crystallinity,uniform density and smooth surface.The experimental results show that the larger the insulation area is,the higher the deposition power is,the lower the deposition position is,and the longer the deposition time is,the longer the thickness of the coating is.It is found that the deposition mainly occurred in the early stage of deposition.Through the study of deposition distribution is studied in the crucible,found deposits within the crucible from down to up into the no-deposition area,liquid phase deposition area,solid phase deposition area,oxide area,carbon felt heat preservation area and deposition power of ascension would increase overall temperature field and reduce temperature field of temperature gradient,the carbon felt the effects of heat preservation area is more significant.It is found that the uniform thickness of Si bond layer is mainly obtained by solid deposition.Three coating systems,Yb₂Si₂O₇,PVD-Si/Yb₂Si₂O₇ and APS-Si/Yb₂Si₂O₇,were prepared experimentally.It is found that the Si bonding layer prepared by physical vapor deposition can significantly improve the bonding property between ceramic surface layer and C_f/Si C matrix.At the same time,high temperature steam oxidation corrosion experiment was carried out to verify the resistance of EBC to high temperature water and oxygen corrosion,and confirm the effect of Si bonding layer to high temperature water and oxygen corrosion.