Effect of controlling residual moisture in atmospheric plasma spray-Y2O3 coatings on random defect generation by halogen-based plasma

The fluorine-based plasma resistance properties of atmospheric plasma spray (APS)-Y 2 O 3 coatings were investigated based on residual moisture control levels. APS-Y 2 O 3 coatings at different moisture levels are exposed to F-poor (Ar, NF 3 , and O 2 ) and F-rich (NF 3 and O 2 ) plasma. Outgassing varies with the residual moisture control level. When the plasma supplies sufficient energy, internal moisture reacts with the coating surface to form Y-OH, accelerating the coating degradation. This confirms the decreasing random defect occurrence in the moisture-controlled coatings. The F radical preferentially binds to Y-OH bonds, which have a lower strength than Y-O bonds in F-poor plasma, and reacts with Y-OH and Y-O bonds to form YO x F y in F-rich plasma. YO x F y formed by Y-OH bonds is vulnerable to plasma owing to its low binding strength, which accelerates the formation of random defects. This study highlights the importance of reducing random defects by effective moisture control. • Plasma resistance of atmospheric plasma sprayed-Y 2 O 3 coatings is studied. • Coatings with various moisture levels are exposed to F-poor and F-rich plasma. • The occurrence of random defects is accelerated under F-poor plasma. • A thick YO x F y layer with fewer random defects is formed in F-rich plasma. • Internal moisture in coatings correlates with the occurrence of random defects.