The Influence Of Alloy Element Y And Ion Bombardment On α-Al₂O₃Coatings

To prepare high content of α-Al₂O₃tritium permeation barrier in low temperature on structuralmaterials is a problem facing in the technology of fusion reactor blanket. Therefore, it was proposedin this work to prepare Al-Y coatings on316L stainless steel and oxidize it to get α-Al₂O₃tritiumpermeation barrier. The research focus on the influence of the microstructure and properties ofα-Al₂O₃coating caused by rare earth element Y and ion bombardment, it is of great importance on thepreparation of high quality α-Al₂O₃tritium permeation barrier in the low temperature.In this work, Al-Y coating was produced on316L stainless steel by magnetron sputtering.Through L16（43） orthogonal experiment, the optimized parameters were get as follows: sputteringpower300w, sputtering time3h, sputtering pressure5pa. Under these parameters, continuousamorphous membrane was made, the surface of the coatings was smooth, uniform and dense. Thenoxidize the Al-Y coatings respectively through plasma oxidation and ordinary thermal oxidation.Optimized parameters of plasma oxidation was get through L9（34） orthogonal experiment as follows:temperature800℃, oxygen flow50sccm, oxidation time3h, argon flow50sccm, cathode voltage830⁸40V, oxidation currents4.0⁴.5A, oxidation pressure55pa. Parameters of the ordinary thermaloxidation were: temperature900℃, the rest parameters are the same with the plasma oxidation.Results showed α-Al₂O₃was produced in both of the oxidations.The research studies the impact of the microstructure and properties of α-Al₂O₃coating causedby ion bombardment. It is found that compared with thermal oxidation, plasma oxidation can gethigher content of α-Al₂O₃in the same condition, and its microstructure is more compact. It is becauseion bombardment is an activate process, in this process, many crystal defects were generated, thesedefects would store some energy, this energy would be released in a certain temperature to counteractpart the reaction energy barrier, promotes the formation of α-Al₂O₃.Besides, the research was focused on the impact of the microstructure and properties of α-Al₂O₃coating caused by rare earth element Y. Results of X-ray diffraction showed that different oxidizedcoatings which have different Y content produced different content of α-Al₂O₃, and Al-Y oxidationcoatings which were made by30%Y sputter target can get the highest contents of α-Al₂O₃. It isprobable that when certain amount of Y was added, oxide particles of Y was formed in the early stagesof oxidation, these particles can apply nucleation points where Al element can form directly intoα-Al₂O₃, in this way, it promotes the formation of α-Al₂O₃. Through observation in the scanning electron microcopy, it was found that suitable addition of Y can refine the microstructure of α-Al₂O₃and made the coating’s surface uniform and dense. In addition, thermal shock test, scratch adhesiontest and anodic oxidation test showed that suitable addition of Y can promote adhesive property,thermal shock resistance and corrosion resistance of the coatings.