Study On Preparation Technology And Properties Of Aluminum Oxide Tritium Resistant Coating On 316L Stainless Steel Surface

With the imminent depletion of non-renewable resources,controlled fusion has become one of the most promising solutions to future energy problems.Nuclear fusion reactors use tritium and deuterium as feedstock to produce helium and emit large amounts of heat.However,tritium has a small atomic radius,very active physicochemical properties,and is radioactive,so it is easy to diffuse and permeate in the candidate structural materials of fusion reactors represented by 316L stainless steel.It causes leakage and loss of reaction materials and generates radioactive pollution in the environment.How to stop the diffusion and permeation of tritium in structural materials has become one of the key problems for the construction of controlled fusion reactors.Currently,the preparation of a tritium barrier coating on the surface of structural materials is an effective solution,and the Fe-Al/Al₂O₃composite coating has excellent tritium barrier properties and can alleviate the thermal mismatch between the coating and the substrate and self-healing function,which has become the focus of research work in various countries.The development of Fe-Al/Al₂O₃composite coatings and their preparation processes are important for developing and applying controlled fusion energy.In this paper,Fe-Al/Al₂O₃composite coatings were successfully prepared on the surface of 316L stainless steel by the process of pack aluminizing+in-situ oxidation,and the tritium diffusion and permeation behaviors of the substrate material and the composite coating material were investigated experimentally.The main results of the study are as follows.The effects of aluminizing temperature and time on the cross-sectional morphology,phase composition,and composition distribution of the aluminized layer when AlCl₃was used as the encapsulated aluminizing catalyst were investigated,and the kinetic analysis of the aluminizing process was performed.The results show that the overall cross-section of the coating is flat and dense,without cracks and holes,and tightly connected with the substrate material.In low-temperature aluminizing,the material phase of an aluminizing layer mainly consists of high-alumina phase Fe Al₃;at 750℃,the three-layer structure of the outer layer,outer transition layer,and inner transition layer start to appear;at 900℃,the content of Al element decreases from the surface of the aluminizing layer to the substrate,which indicates that the formation of an aluminizing layer mainly relies on the inward diffusion of Al element;at high-temperature aluminizing,the outer layer of an aluminizing layer mainly consists of high-alumina phase.The transition layer contains a variety of phases such as Fe₂Al₅and Fe Al.There is no difference in the phase composition of the aluminized layer when the aluminizing time is changed,and the coating thickness gradually becomes thicker with the extension of the aluminizing time,but there is no obvious change in the inner and outer transition layers.The kinetic analysis of the aluminizing process is carried out,the relationship between coating thickness and the aluminizing temperature is fitted,and the activation energy of aluminizing of 316L stainless steel is obtained as 79.23 k J/mol;meanwhile,the relationship between aluminizing time and coating thickness is fitted as h=14.585t^1/2+19.514.The diffusion permeation behavior of deuterium gas was studied for the base material and composite coating samples.In the base material test,the instantaneous diffusion flux at different diffusion temperatures at a carrier gas pressure of 40 k Pa was obtained,and the diffusion permeation activation energy of deuterium gas in the 316L substrate material is calculated to be 65.5 k J/mol.The relationship between the diffusion flux J and the carrier gas pressure P at each temperature is fitted by varying the carrier gas pressure on the high-pressure side.In this test,the matrix diffusion process plays a dominant control role in the diffusion permeation of deuterium molecules between 316L stainless steel.Two rounds of diffusion-permeation tests were performed on the composite coating samples,and the PRF values are used to evaluate the tritium barrier performance of the coating.It was found that the PRF value of Fe-Al/Al₂O₃coating decreased from 227 to 18 with the increase of the diffusion-permeation reaction temperature.The reason is that after a long time and high-temperature diffusion-permeation reaction,holes appeared on the surface of the composite coating,which led to the decrease of the tritium barrier performance.