Cr Based Films Prepared By Magnetron Sputtering And Their Properties

In the world energy structure,the position of nuclear energy is rising day by day.The economics and safety of nuclear energy have always been an important topic of nuclear energy research and development.Fuel cladding is the first barrier of nuclear energy safety.Zirconium alloy is used as fuel cladding material for nuclear power reactors because of its high temperature oxidation performance and radiation resistance,and it is also the most mature cladding material at present.After Fukushima nuclear accident in Japan in 2011,accident resistant fuel(ATF)was proposed in the United States to further improve the high temperature water vapor oxidation resistance of zirconium alloy cladding tubes.A complete,compact and well-bonded protective coating on the surface of the existing zirconium alloy cladding tube can effectively reduce the steam oxidation rate at high temperature.At present,there is no mature coating technology for cladding tube in China.In this paper,the effect of magnetron sputtering on the microstructure of Cr and CrAl coatings and the high temperature steam oxidation properties of the coatings were studied,and the preparation process of Cr coatings on zirconium cladding tubes was explored.When the preheating temperature is more than 400℃,Cr and CrAl films have uniform thickness,compact structure and good bonding with the matrix 24.2 at.%Al element added,the film grain coarsening,thermal expansion coefficient increases,resulting in CrAl film easy to crack.With the increase of sputtering power,Cr film becomes smooth and compact.The cracks on the surface of CrAl film are reduced.Both Cr and CrAl films grow in lamellar and island binding mode,and grow in lamellar form at the early deposition stage,and island form is the main growth when the film reaches a certain thickness.After water vapor oxidation at 1200℃/1h,the thickness of the oxide film on the zirconium substrate is about 100 μm,and the thickness of the Cr film surface is about 4 μm dense Cr2O3 layer.The thickness of the composite oxide layer of Cr2O3 and Al2O3 on the surface of CrAl film is about 0.8 μm,and Al element has obvious surface and interface segregation,resulting in the formation of a large number of new phases with the size of hundreds of nanometers inside the film.Both Cr and CrAl films show good oxidation resistance at high temperature.The optimal parameters for preparing Cr and CrAl films are preheating temperature of substrate 450℃ and sputtering current 0.5A.The Cr film was prepared on the surface of zirconium alloy coated tube by ring target magnetron sputtering system.The bonding strength of Cr film to matrix and the structural stability of Cr film after 360℃/30d aging treatment were analyzed.The results show that the Cr film becomes more dense with-100V bias.Both bias and sputtering power increase the bonding force between the film and the substrate,and the grain size of the film increases and the grain orientation diversities.After aging at 360℃for 30 days,the density of Cr film increases,and the interface between Cr film and zirconium alloy matrix has no obvious change.Cr film is relatively stable at service temperature.