Study On Preparation And Properties Of α-Al₂O₃Coatings Doped With Y By Low-temperature Plasma Composite Techniques

The preparation of α-Al₂O₃coatings on316L stainless steel can improve its tritium permeationresistance, what’s the key point is how to prepare high content of α-Al₂O₃coatings in low temperature,so that they can be used as penetration barriers of fusion reactor blanket. Therefore, it was proposed inthis work to prepared α-Al₂O₃coatings doped with Y on316L stainless steel by low-temperature（580℃） plasma composite techniques.Firstly, Al-Y coatings were produced on316L stainless steel by double glow plasma alloyingtechnique. The optimized parameters as follows were determined by single factor design: sourcevoltage700V, workpiece voltage350V, working pressure35Pa, parallel distance between twoelectrode25mm, and treatment time3h. Under these parameters, the prepared Al-Y coatings weredense, uniform, and no defects such as holes or cracks have been found. Besides, the composition ofthe Al-Y coatings from surface to interior is gradient distribution except Y element due to its rarecontent and particularity compared to the other sputtering alloy elements. What’s more, the coatingswere mainly composed of FeAl3, Fe2Al5, and FeAl phases, and exhibited excellent adhesive property,thermal shock resistance and corrosion resistance.Secondly, the oxide coatings were fabricated by means of three different oxidation treatments ata same temperature （580℃）. Compared with the thermal oxidation and double cathode plasmaoxidation, the oxide coatings prepared by single cathode plasma oxidation had much more compactmicrostructure and better performance, the adhesive force is65N. Meanwhile, α-Al₂O₃content in thecoatings reached highly62%. There is no generation of α-Al₂O₃on the thermal oxidation process atthis low temperature due to the lack of ion bombardment, and the appearance of cracks on the surfaceof the double cathode plasma oxide coatings were bad for their performance. After comprehensivecomparisons, single cathode plasma oxidation was finally choosed and the optimized parameters were:cathode voltage550V, working pressure40Pa, argon flow50sccm, oxygen flow10sccm, andoxidation time3h.Finally, the Al-Y alloy coatings and oxide coatings with different Y content were prepared byusing the different Y content Al-Y sputter targets. Characterized the Al-Y alloy coatings and theresults showed the best Al-Y coating was made by20%Y target but getting worse when the content ofY was less or more. It’s known that the presence of rare earth Y can improves the surface quality andrefine grain of the aluminized coating. Then the results of characterization of oxide coatings showed suitable addition of Y can refine the microstructure and made the oxide coatings’ surface uniform anddense. What’s more, adhesive property, thermal shock resistance and corrosion resistance of the oxidecoatings can also been promoted. Al₂O₃coatings which were made by20%Y sputter target got thehighest contents of α-Al₂O₃, accounted for65%. The oxide coatings had a uniform, dense surface andfine grain. Also, they had a good adhesive property with an adhesive force72N. No cracking wasfound after150cycles of thermal shock test. And the coatings showed excellent corrosion resistance.