Performance of Chemical Vapor Deposition and Plasma Spray-Coated Stainless Steel 310 in Supercritical Water

In this study, aluminized and NiCrAlY plasma-sprayed AISI 310 stainless steel samples were tested in supercritical water (SCW) at 500°C. The microstructure after SCW exposure was analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Weight measurements were taken before and after exposure to provide quantitative comparison of the two coatings on AISI 310 base metal. The results showed that aluminized and bare 310 stainless steel experienced similar weight gain, in the range of $0.02–0.08mg/cm2$ after 1550 hr. The aluminized sample had a slight weight decrease as exposure progressed. Oxide formation, in the forms of $Al2O3$ and $(Fe,Cr)2O3$⁠, was found on the aluminized surface along with surface cracking after 1550 hr testing in SCW. NiCrAlY-coated 310, however, had the most consistent weight increase and oxide formation (mainly $Al2O3$⁠) on the surface. Based on the results from this study, the aluminized coating has limitations in providing surface protection due to surface cracking and weight loss. The NiCrAlY plasma-sprayed coating with alumina formation on the surface has the potential to provide long-term surface protection to the substrate material in SCW.