Evaluation of plasma-sprayed NiCrAlY/Cr3C2/h-BN coatings oxidation behavior on T22 boiler steel alloy

In the current work, a NiCrAlY/Cr₃C₂/h-BN composite coating applied on ASTM SA213-T22 boiler steel by plasma spray (APS) is examined for its hot cyclic oxidation behavior. In order to improve boiler steel components' resistance to oxidation in high-temperature oxidative conditions, a coating was created. 50 cycles of cyclic oxidation tests were conducted in static air at 700 °C. Each cycle consisted of an hour of heating and cooling to room temperature in order to replicate actual service conditions. The oxidation kinetics were ascertained by thermogravimetric measurements, and X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and emission scanning electron microscopy (FESEM) investigations were used to describe the oxide scale shape and composition. Diffusion-controlled oxide development was demonstrated by the NiCrAlY/Cr₃C₂/h-BN-coated specimen, which showed an oxidation rate 8.7 times lower than that of the untreated T22 substrate and a parabolic rate law. According to surface analysis, a thick, adherent, multi-layered oxide scale made up of NiO, CrO₃, and AlO₃ formed, effectively limiting the flow of oxygen. As a solid lubricant and diffusion barrier, hexagonal boron nitride (h-BN) reduced thermal stresses and inhibited the onset of cracks during cyclic exposure, further improving oxidation resistance. Oxides loaded with silicon and boron also helped to increase adhesion and scale stability under extended heat cycling. The development of continuous and protective oxide layers that preserved structural integrity and reduced mass gain during high-temperature exposure was the fundamental reason why the NiCrAlY/Cr₃C₂/h-BN coating showed higher cycle oxidation resistance at 700 °C overall.