Study on High-Temperature Oxidation Behavior of Electrodeposited Ni/Cr Coating on Zr Alloy Surface
Cr coatings on zirconium(Zr)alloy surface for nuclear fuel cladding in nuclear reactor cores is considered to be the most likely technique for commercial application in a short term.The molten salt electrodeposition technique is expected to solve the problem of efficient and low cost preparation of high quality Cr coatings on the surface of Zr alloy claddings.This research adopted aqueous solution electrodeposition and molten salt electrodeposition methods to prepare Ni transition layer and Cr coating on the surface of Zr alloy substrate sequentially,and carried out the characterization of the microstructure,the bonding force and nano-hardness test as well as the study of the high-temperature oxidation behavior of the Zr/Ni/Cr specimens obtained from the preparation.The results show that the Ni/Cr coating on the surface of Zr alloy is uniform and dense,and the bonding force between the coating and the substrate is about 151 N.The hardness and elastic modulus of Zr/Ni/Cr increase gradually from the inner layer to the outer one with a quasi-gradient transition.The surface roughness of the Cr coating is about 2 μm,and the hardness and elastic modulus are 2.86 GPa and 172.86 GPa,respectively.The Zr/Ni/Cr specimen shows nearly parabolic and nearly linear patterns during steam oxidation at high temperatures of 1000 and 1200 ℃,respectively,indicating that the Ni/Cr coating is able to provide good protection to the Zr alloy matrix at 1000 ℃.The high-temperature oxidation failure mechanism of Ni/Cr coating on Zr alloy surface is closely related to the rapid diffusion of the Ni transition layer,the oxidation and diffusion depletion of the Cr layer,and the weakening of the Cr layer due to the rapid diffusion of Zr along the Cr grain boundaries.
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