Effect of hydrogen and argon shrouding gas flow rate on high-temperature oxidation behavior of NiCrAlY coating by solid shielding shrouded plasma spray (SSPS)

Abstract

This paper investigates the effect of hydrogen and argon shrouding gas flow rates in solid shielding shrouded plasma spray (SSPS) method on in-flight oxidation, formation and growth of the TGO layer and high-temperature oxidation behavior of NiCrAlY coating. With this in mind, NiCrAlY coating was applied on the Hastelloy X substrate by solid shielding shrouded plasma spray (SSPS) and compared with the conventional atmospheric plasma spray (APS). High-temperature oxidation was carried out at 1000 °C for 200 h. Microstructure of the coatings before and after oxidation was evaluated by scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). To study the effect of solid shielding shrouded plasma spray on the properties of metallic coatings, the variable parameters such as the shroud gas nature (Ar, H2), the gas injection method (internal, external or both) and their flow rates, were examined. The results indicated the better operation of the coatings deposited under the protection of internal argon shroud gas with a flow rate of 75SLPM, which could be due to better protection of the metallic particles against in-flight oxidation. This sample represented the lowest thickness of the TGO layer (2.25 μm). The formation and growth of the TGO layer were higher in APS coating (3.82 μm) than that of SSPS. Consequently, this can prove by the preservation of mono-layered TGO of SSPS coating even after 200 h oxidation without the formation of any CSN clusters.