Preparation And Properties Of Zr₂Al₃C₄ Coatings On Zr-Alloy Substrates

Zirconium alloys have been used in light water reactor(LWR)nuclear fuel cladding materials for decades,and shown good resistance to radiation damage.However,zirconium will react with water vapor at high temperature that generates a large amount of hydrogen,which will cause hydrogen explosion.Therefore,improving the reliability and safety of zirconium alloys under accident conditions has important research value and practical application significance.Zr-Al-C series ternary layered materials have excellent performance of ceramics and metals,and show good neutron economy and high temperature oxidation resistance,and have been widely concerned in the application of nuclear materials.The purpose of this work is to deposit the Zr₂Al₃C₄ coating on the surface of the Zr alloy in the Zr-Al-C system.At the same time,the coated zirconium alloy is subjected to high-temperature water vapor oxidation resistance and other performance evaluations to explore its use as a core cladding.The main contents of this article are:(1)Use the non-diffusion system as the substrate to explore the optimal preparation process of Zr₂Al₃C₄ phase coating.Normal temperature magnetron sputtering combined with subsequent high temperature annealing preparation technology is used to adjust the coating composition ratio with Si as the substrate.Based on Al₂O₃(0001),the preparation process was optimized by adjusting the C content,annealing temperature and holding time during the coating process.Combining EDS energy spectrum,X-ray diffraction,Raman spectroscopy and transmission electron microscopy to characterize the coating,it was determined that the high-purity Zr₂Al₃C₄phase was obtained when the element ratio was close to the Zr₂Al₃C₄ phase and annealed at 800°C for 3 h.(2)Combined with the intermediate layer process,a Zr₂Al₃C₄ phase coating is obtained on the surface of the zirconium alloy substrate.By adding a Mo-C/Al intermediate layer as a diffusion barrier layer,the diffusion of the coating layer and the substrate is effectively blocked and the generation of coating cracks is suppressed as well as the resulting Zr₂Al₃C₄ phase coating shows good crystallinity.(3)The performance of resulting coating was analyzed.The bonding force between the coating and the substrate is about 30 N and the thermal conductivity of the coating is 19.508 W/m K.In addition,the coating shows good resistance to water vapor oxidation at 1000°C and 1200°C.When the coated sample was oxidized for 10-45 min at 1200°C,the depth of the oxid layer was less than that of the uncoated zirconium alloy.At the same time, the oxidation-proof Al₂O₃oxide layer was detected in the oxidized coating.