Deposition Of Cr-Al-Si Coatings On Zry-4 Alloy By Magnetron Sputtering Method And Its Oxidation Behaviors In High Temperature Steam

Since Fukushima nuclear accident happened in Japan on 2011,the concepts of Accident Tolerance Fuel(ATF)were proposed in nuclear power industry.One of the study directions of ATF is to improve the oxidation resistance of Zr alloy cladding tube in high temperature steam environment.In this study,Cr coating and CrAl and CrSi coatings with different contents were deposited on the surfaces of Zry-4 alloy by magnetron sputtering method.The oxidation behaviors of the coatings in 1000?-1200? steam environment were studied.The phase composition and microstructure of the oxidation products were determined by XRD and SEM.The main conclusions are as follows:(1)Deposition of Cr coating can protective Zry-4 alloy effectively,the oxidation rate constant of which was one order of magnitude lower than that of the blank alloy,when oxidized in 1000? and 1100? steam environment owing the formation of a continuous and dense Cr2O3 oxide layer.However,when oxidized in 1200?,cracks were found between the coating and the substrate,which reduced the oxidation resistance of the Cr coating.(2)An Al2O3+Cr2O3 mixed oxide layer formed on the surface of Cr0.68Al0.32 coating when oxidized in 1000? steam environment,and the oxidation rate constant was one order of magnitude lower than that of Zry-4 alloy;when the temperature increased to 1100?,cracks produced due to the thermal stress existing in the brittle Cr0.68Al0.32 coating consisted of A13Cr7 phase,which provided diffusion path for steam and oxygen to react with the substrate.The increasing of the thermal stress in Cr0.68Al0.32 coating resulted the further expanding of the cracks when oxidation temperature raised to 1200?,which caused the serve attacked of the substrate.While,the phases of Cr0.9Al0.1 and Cr0.95Al0.05 coatings were Cr(Al)solid solutions,which are less brittle,cracking and spallation did not occurred during the oxidation process of these two coatings.Meanwhile,owing to the additon of little amount of Al,the oxidation resistance of these two coatings were better than that of the pure Cr coaing.Cr and Zr mutually diffused to form Zr-Cr diffusion layer during the process of oxidation.Cr2O3/CrAl/Zr-Cr composite layers played an effective role in protecting the matrix.(3)CrSi coating performed excellent oxidation resistance in 1200? steam environment.The oxidation rate constants of Cr0.92Si0.08,Cr0.85Si0.15,Cr0.65Si0.35 coatings were one order of magnitude lower than that of Zry-4 alloy,and the oxidation weight gain were 1/16,1/21 and 1/33 of that of Zry-4 alloy,respectively.The Cr2?3/CrSi/Zr-Si composite layer formed during the oxidation process of CrSi coating had a good protective effect on the matrix.(4)For the M-Cr0.6aAl0.32 coatings dopped with different elements,Mo,Y and Ta elements had no positive effect on the oxidation resistance of Cr0.68Al0.32 coating in 1100? steam environment.While doping of V,Nb and Fe can improve the oxidation resistance of Cr0.68Al0.32 coating due to the reduction of cracks in the coating.