Preparation And Properties Of Er₂O₃@Al₂O₃/FeAl Tritium Permeation Barrier Coatings

Because of high thermal stability,low cost and low permeability,Al₂O₃/FeAl coatings are seen as one of the most promising candidate materials for tritium permeation barriers.In the tritium breeder blanket,the liquid breeders,especially liquid Pb-Li breeder,is often used as tritium breeder for its a better thermal conductivity,adapt ability and tritium breeding capacity.However,the compatibility between Al₂O₃/FeAl coatings and high temperature liquid Pb-Li is poor,which affects the service life of the coatings.Therefore,improving the corrosion resistance of Al₂O₃/FeAl coatings in high temperature liquid Pb-Li is necessary.Due to the good compatibility between Er₂O₃and high temperature liquid Pb-Li,the compatibility of the Al₂O₃/FeAl coating with high temperature liquid Pb-Li is purposed to be improved by the addition of Er₂O₃.In this paper,Er₂O₃@Al₂O₃/FeAl coatings are prepared by"ionic liquid electrodeposition+ion injection+heat treatment+high temperature selective oxidation",and the composition structure and properties of the coating are also studied.The main results as follows:1.Continuous,dense and highly adhesive Al coatings are prepared on the surface of 316L stainless steel by ionic liquid electrodeposition.The influence of current density,electro-plating time,electro-plating temperature,stirring speed and electrochemical etching of the substrate,on coating structure are investigated in this paper.With the increase of current density,the grain size of the coating increases and the coating thickness decreases.With the increasing of electro-plating time,the thickness of the Al coating increases.With the increase of electro-plating temperature,particle uniformity is decrease.The stirring speed has little influence on the preparation of Al coatings,and only at a low stirring speed,the particle size of the Al coating is large.Electrochemical etching of the substrate effectively increases the adhesive between substrate and Al coatings.In addition,in the preparation of AlEr coatings by ion implantation,the effect of different Er content on Al layer was also investigated.With the increase of Er content,larger particles appear on the surface of Al coatings.2.The AlEr coating can be transformed into the Er@FeAl coating by heat treatment.It is found that with the increase of Er content,the surface morphology of the coating changes from large block to scale structure.In addition,with the increase of Er content,the Fe content on the coating surface decreases continuously.Er@FeAl coating can be transformed into the Er₂O₃@Al₂O₃/FeAl coating by high temperature selective oxidation.The thickness of the coating doped with 1×10¹⁷ ion·cm^-2 Er was about 150 nm.And no characteristic peak of Fe and Fe³⁺were detected the in the Al₂O₃ layer during the sputtering time of 0-30 min.However,the characteristic peaks of Fe and Fe³⁺appear in the Al₂O₃ layer of the coating without Er when the sputtering time reaches 25 min.3.In this work,Er₂O₃@Al₂O₃/FeAl coatings are prepared on 316L stainless steel,the deuterium permeability of the coating at 550-650℃reduced by 3 orders of magnitude.After the liquid Pb-Li corrosion test at 550℃for 1000 h,the surface of Er₂O₃@Al₂O₃/FeAl coatings with Er is uniform and dense,and a small amount of corrosion products were produced.However,the surface of the coating without Er become rough,and the corrosion products increase significantly.It shows that the addition of Er₂O₃effectively reduces the diffusion rate of Li ions and O ions along the grain boundaries to the interior,thus reducing the formation of corrosion products at the grain boundaries.After 50 cycles of hot and cold（750℃to room temperature）,no cracks and peelings of Er₂O₃@Al₂O₃/FeAl coatings happens,it shows that the coating has good thermal shock resistance.