Preparation And Properties Of Al-Y-Si Oxide Coatings And Al₂O₃-SiO₂ Composite Coatings By Composite Glow Discharge Plasma Technique

α-Al2O3 coatings prepared on 316 L stainless steel can improve its tritium permeation resistance. Therefore, it is pivotal to prepare high content of α-Al2O3 coatings at a lower temperature as penetration barriers of fusion reactor blanket. In this study, double glow plasma discharge surface alloying and plasma oxidation were carried out respectively to prepare aluminide layer and alumina coatings on the surface of 316 L stainless steel with Al-Y-Si alloy cathode targets. Moreover, in order to improve comprehensive properties of Al2O3 coatings, Al2O3-Si O2 composite coatings were prepared on the surface of 316 L stainless steel by double glow plasma discharge surface alloying and plasma oxidation.The processing parameters were optimized by orthogonal experiment. The microstructures and compositions of the coatings were studied by X-Ray diffraction(XRD), scanning electron microscope(SEM) and energy dispersive spectrometer(EDS) respectively. Furthermore, the adhesion strength, corrosion resistance and thermal shock resistance of the oxide coatings were tested by scratch adhesion test, electrochemical workstation and thermal shock test. Moreover, the influence of Y on the aluminide coatings, plasma oxidation process and properties of alumina coatings were discussed. The main conclusions were drawn as follows:Al-Y-Si alloy coatings were successfully prepared at 580 ℃. The coatings were dense with a Fe Al3/Fe Al/Fe3 Al construction at the interface, obtaining metallurgical bonding. Y and Si were well-distributed in the coatings, and the relative content of which increased with that in the targets. When the target possessed 10% Y, the prepared coating had the maximum bonding force of 69.2 N with the substrate. The prepared coating exhibited excellent thermal corrosion resistance and shock resistance.Alumina coatings were prepared through plasma oxidation of the aluminide coatings with Y and Si at 580 ℃. XRD results showed that the alumina coatings mainly consisted of α-Al2O3、γ-Al2O3、θ-Al2O3 and α-Fe2O3。The alumina coatings with the content of 65 wt.% α-Al2O3 which was 10% more than that obtained by the oxidation of pure Al at the same condition, was obtained after plasma oxidation by using the alloy target dopted with 10% Y. When the target possessed 10%Y, the coatings had the maximum bonding force of 70.5 N with the substrates, and metallurgical bonding was obtained at the interface, which also the coatings exhibited excellent thermal corrosion resistance and shock resistance.Al2O3-Si O2 composite coatings were prepared on the surface of 316 L stainless steel by double glow plasma discharge surface alloying and plasma oxidation. The oxide coatings mainly consisted of cristobalite(Si O2), α-Al2O3 and γ-Al2O3. When prepared at 500 ℃, the coatings were continuous and compact without cracks and hole, having the maximum bonding force of 66.8 N with the substrates. In addition, the coatings exhibited excellent thermal corrosion resistance and shock resistance.