Study On High-entropy Alloy Coating AlCrCuFeMo(Nb_x,Ni_x) For Nuclear Fuel Cladding

Since the Fukushima-Daiichi accident in 2011,Accident Tolerant Fuel（ATF）cladding has become a research topic around the world to further enhancing safety margins of nuclear power plants during severe accidents.Its ultimate objective is to improve the water vapor oxidation resistance of the cladding to improve the accident tolerance capability and to maintain or improve the fuel performance under normal working conditions.In current research strategies,preparing a protective coating on the surface of Zirconium alloy cladding can improve the resistance against high temperature water vapor oxidation without changing the design of the reactor structure,which is the best solution in the short term.According to the performance requirements of nuclear fuel cladding tubes,Al Cr Cu Fe Mo（Nb_x,Ni_x）high entropy alloy coating is prepared on zirconium alloy substrate by magnetron sputtering,and the influence of different element on the microstructure and performance of the coating is studied.The results are as follows:（1）The phase structure of high-entropy alloy coating AlCrCuFeMoNb_x（x=0.5,0.8,1.4,2.0）is regarded as amorphous;With the increase of the Nb content,both the hardness and elastic modulus of the coating showed an overall upward trend.The hardness and elastic modulus of Nb_2.0both reach the maximum value of 11.38GPa and 186.05GPa respectively;It is known from the nanoscratch experiment:The coating combines well with the substrate;With the increase of the Nb target power,The droplet contact angle on the coating surface first increases and then decreases,When the Nb target power reaches 70w,The hydrophobic properties of the coating are optimal;With the increase of the Nb content,The salt water corrosion resistance of the coating is gradually enhanced and better than the zirconium alloy substrate;When x reaches 0.8,The dense oxidation film Cr₂O₃and Cr Nb O₄generated from the coating surface hindered the diffusion of oxygen ions,The pure water corrosion weight gain of the coating is only 5.10 mg/dm²,The weight gain of per unit area decreased by56.4%compared to the uncoated zirconium alloy;In terms of accident fault tolerance,when x=0.5,the dense oxidation film Cr₂O₃and Cr Nb O₄reduce the diffusion rate of oxygen ions.Compared with the uncoated zirconium alloy,the oxidation weight gain of the coating decreased by 84.02%in a high temperature steam environment at T>1,200℃,which shows excellent accident fault tolerance performance.（2）With the increasing of Ni content,the structure of AlCrCuFeMoNi_x（x=0.5,0.8,1.4,2.0）high entropy alloy coating evolves from amorphous phase to FCC;With the increase of the Ni content,the coating showed an overall decrease in hardness and elastic modulus,and when x=0.5,both hardness and elastic moduli reached a maximum of 8.57GPa and170.75GPa respectively;It is known from the nanoscratch experiment:The coating combines well with the substrate;With the increase of the Ni power,The droplet contact angle on the coating surface showed an overall decreasing trend,When the Ni target power reaches 70w,The hydrophobic properties of the coating are optimal;With the increase of the Ni content,The salt water corrosion resistance of the coating is gradually reduced but better than the zirconium alloy substrate;When x reaches 0.5,The dense iron-chromium rich oxide generated from the coating surface hinders the diffusion of oxygen ions,The pure water corrosion weight gain of the coating is only 1.96 mg/dm²,The weight gain of per unit area decreased by 83.2%compared to the uncoated zirconium alloy;In terms of accident fault-tolerance performance,When x reaches 1.8,The dense Al₂O₃and oxide of the spinel structure generated on the coating surface reduces the diffusion rate of the oxygen ions,In a high-temperature steam oxidation environment at T>1200℃,The oxidative weight gain of the coating was decreased by 70.41%compared to the uncoated zirconium alloy,which shows excellent accident fault tolerance property.By controlling the sputtering power of Nb and Ni targets,the component proportion elements can be effectively adjusted,thus affecting the microstructure of and ultimately change the performance of the coating.AlCrCuFeMoNb_xhigh entropy alloy coating has better mechanical properties and accident-tolerance capability,while in contrast,AlCrCuFeMoNi_xhigh entropy alloy coating has better salt water corrosion resistance and high temperature and high pressure water corrosion resistance.Based on the experimental results,the accident-tolerance performance of high entropy alloy coating is far better than that of zirconium alloy.As an accident-tolerant cladding material,it will have great development potential in the future.