Yttrium Oxyfluoride Coating Deposited with a Y5O4F7/YF3 Suspension by Suspension Plasma Spraying Under Atmospheric Pressure

Abstract

To develop the plasma-resistant coating of yttrium oxyfluoride using the suspension plasma spraying (SPS) process, a mixed Y5O4F7/YF3 suspension was developed for fluorine-rich yttrium oxyfluoride coating. The undesired cubic and monoclinic Y2O3 was formed in the yttrium oxyfluoride coating deposited with the Y5O4F7 suspension by the SPS process at atmospheric pressure. To minimize the formation of Y2O3, we inferred and proposed the mechanism of the SPS coating at atmospheric pressure and analyzed the coatings deposited by four suspensions with different mass ratios containing Y5O4F7 and YF3 particles. During the SPS process, the Y5O4F7 particles in the suspension reacted with hydrogen and oxygen through chemical reactions using the remaining thermal energy after the evaporation process, forming YOF and Y2O3 composites near the surface of the coating. Using x-ray diffraction (XRD) and a high-resolution three-dimensional x-ray tomography microscope system (HR-XRM), a relatively large amount of Y2O3 was found to have formed near the surface of the coating deposited with the Y5O4F7 suspension, whereas the formation of Y2O3 was minimized and the formation of yttrium oxyfluoride was maximized in the coating deposited with the mixed Y5O4F7/YF3 suspension at a mass ratio of 7:3. This coating containing a minimum amount of Y2O3 is expected to offer high plasma resistance.