High-temperature oxidation behavior of NiCrA1Y bond coats and Stellite-6 plasma-sprayed coatings

Ni-22Cr-10Al-1Y and Stellite-6 coatings were deposited on boiler-tube steels, namely ASTM-SA210-Grade A1, ASTM- SA213-T-11 and ASTM-SA213-T- 22, by a shrouded plasma-spray process. The NiCrAlY alloy powder was also sprayed as a bond coat before applying a Stellite-6 coating. The cyclic-oxidation behavior of the NiCrAlY bond coats and Stellite-6 coating were evaluated at 900 degrees C. Visual observations and gravimetric data were measured at the end of each cycle. Finally, the scale was analyzed using X-ray Diffraction, Scanning-Electron Microscope, Energy-Dispersive X-Ray Studies and Electron-Probe Micro-Analyzer techniques. The coatings were found to be effective in increasing resistance to oxidation at the test temperature of 900 degrees C. The protection is higher in the case of the Stellite-6 coating. The protection is lesser for both coating types when T22 steel was the substrate and higher in the case of GrA1 steel. The deleterious behavior of Mo present in the T22 steel is perhaps responsible for conferring lesser protection.