Microstructure and Property of Al₂O₃ Tritium Resistance Coating with Different Ratios of α/γ Phase Sprayed by Supersonic Atmospheric Plasma Spraying

Al₂O₃ tritium resistance coatings with different ratios of α/γ phase were sprayed on China-low activation martensitic steels by supersonic atmospheric plasma spraying technology. The effects of ratio of α/γ phase on microstructures and properties of Al₂O₃ coatings were investigated. GIXRD and SEM were carried out to characterize the microstructures of the Al₂O₃ coatings, tensile test and nano-indentation test were performed to measure mechanical properties of the Al₂O₃ coating, and the potentiodynamic polarization method was performed to test the property of corrosion resistance. The results show that the content of α phase in the Al₂O₃ coating is controlled from 78.6% to 24.4% by adjusting the critical plasma spray parameters (CPSP). And the porosity of the Al₂O₃ coatings decreases from 2.8% to 1.5%. The hardness is (11.500±0.575) GPa of the sample with α phase content of 78.6%, which is about twice the hardness of the coating with γ phase content of 75.6%. Compared with the Al₂O₃ coating with γ phase content of 75.6%, the corrosion current density of Al₂O₃ coating with α phase content of 78.6% decreases by one order of magnitude. The above results indicate that the Al₂O₃ coating with high α phase content of 78.6% displays better mechanical properties, electrochemical corrosion resistance and Cl^- diffusion penetration resistance, and possesses potential application in the tritium resistance coatings on the surface of structural materials of fusion reactor.