Preparation And Properties Of Rare Earth Oxides Doped Si-B Oxidation Resistance Coatings On Molybdenum Surface

MoSi₂ is widely used in high temperature oxidation resistant coatings of molybdenum and molybdenum alloys because it can form dense and uniform SiO₂ protective film in high temperature oxidation environment.However,MoSi₂ coating will undergo"Pesting"oxidation in low temperature oxidation environment,which limits the application of MoSi₂ in molybdenum and molybdenum alloys.The introduction of B element into MoSi₂ can delay the diffusion of Si to the substrate and improve the oxidation resistance of the coating,but can also leads the problem of peeling in multilayer coatings.It is found that the addition of a small amount of rare earth elements to the B modified MoSi₂ coatings can increase the adhesion between the coating and the substrate,refine the coating grain and improve the preparation efficiency.In addition,the common co-deposition method for Si-B coatings has problems such as inhomogeneous structure and poor oxidation resistance,which seriously affects the service life of the coating.Based on the above analysis,the Y₂O₃/CeO₂ doped Si-B composite coatings were prepared on the surface of Mo substrate by a two-step pack cementation process.The surface phase and cross-section morphology of the coating were systematic characterized.The oxidation resistance of Si-B composite coatings in 1150°C atmosphere before and after doping was studied.The mechanism of Y₂O₃/CeO₂ doping in the coating was investigated by analyzing the evolution of the phase,morphology and oxidation kinetics of the doped coating before and after oxidation.It was found that the CeO₂ doped MoB coating with uniform and dense microstructure,well adhesion to the substrate was prepared on the surface of molybdenum substrate.The Y₂O₃/CeO₂ doped Si-B composite coating with two layer structure of MoB/MoSi₂ on the basis of CeO₂ doped MoB was prepared by two-step pack cementation process.The microstructure of doped Si-B composite coating showed the characterization of uniform,dense and well adhesion between different layers.During the preparation of compiste coatings,Y₂O₃/CeO₂ exhibited excellent catalytic cementation effect?especially with doping amount of Y₂O₃ at 2wt%?.Compared with undoped coating,the Y₂O₃/CeO₂ doped Si-B composite coating showed a lower mass change and oxidation rate constant after oxidation at 1150?.In addition,the oxidation rate constant of the CeO₂ doped Si-B composite coatings(1.02×10^-4mg²/?cm⁴·h?)was lower than that of Y₂O₃ doped coatings(3.89×10^-4mg²/?cm⁴·h?).