Research On High Temperature Protection Coatings Of Nb-Si By Eb Cladding

The Nb-Si coating on the niobium-based alloy Nb-W substrate was preparedby fused slurry method. The high-temperature oxidation resistance of the obtainedcoating is limited because of the coating contains defects, such as holes, cracks andhigh surface roughness. To improve the high temperature thermal stability and heatresistance of Nb-Si coating, a new compound coating with different thermalradiation properties on both sides has prepared by electron beam in this paper. Themicrostructure and properties were evaluated by XRD，SEM， EDS and RamanSpectrometer. The influence of the electron beam on microstructural modification inNb-Si coating, low-emissivity coating and high-emissivity coating was studied inthis paper. Also the high temperature oxidation resistance at1300℃of claddingcoating and the oxidation resistance mechanism have been researched.The results showed that the sintered coating structure was divided into threelayers. Both the outer and inner layers are mainly composed of NbSi2, and thetransition layer takes Nb5Si3as main content. After EB treatment, the structure ofthe cladding coating changed slightly. The surface roughness was decreased and lessdefects. The grain has been refined and the oxidation resistance of Nb-Si coatingimproved by EB. The cladding Nb-Si coating is oxidation resistant at1300℃for atleast25h.Two types of coating, Cr coating with low radiation and C coating with highradiation, have been fabricated by EB on two sides of Nb-Si coating. Researchshows that larger electron beam, the more serious the elements reactions are, thecoating structure denser is. As the thickness of the deposited coating increases, theweaker action of the electron beam. The thermal radiation test shows that Cr layerhas low radiation and C layer has high radiation. According to the Kirchhoff Law,under the same condition a low radiation coating radiates and absorbs less energy,while a high radiation coating is on the contrary. Thus, the compound coating canreduce the heat absorption from the high-temperature heat source by Cr coating andincrease the heat radiation to the outer environment by C coating. Ultimatelyimprove the high temperature thermal stability and heat resistance of the sinteredNb-Si coating.