Hot Corrosion Study of Plasma-Sprayed Optimized WC-NiCrB-Al-Co Coating Mixture on Stainless Steels for Boiler Environment

Hot corrosion study boiler grade materials SS304 and SS316 through optimized WC-NiCrB-Al-Co coating by Plasma spray technique was investigated for 50 cycles at 800°C in Na₂SO₄-60% KCl molten salt environment. I-Optimal was used to optimize the wt.% of alloying metal powders with Microhardness and porosity as response parameters. The morphology of experimented samples was studied through SEM/EDS, EDS Mapping, and corrosion by thermogravimetric analysis. Layers of the coat were observed to be parallel to the substrate's surface, resulting in a significantly stratified appearance. The porosity of the coating on the substrates was found to be 1.549 and the microhardness was found to be increased to 1.27 times the uncoated substrate. The experimental investigations demonstrated that the uncoated stainless steel (SS) experienced corrosion in the form of oxide scale flaking and residue. EDAX and elemental mapping show larger WC, Ni, and Cr distributions and lower Al, Co, S, Cl, K, and Na distributions. The strong WC matrix formed protective oxides that inhibited further oxidation and weight growth. Thus, the WC-NiCrB-Al-Co coated SS surface exhibited exceptional resistance to corrosion formation. The weight gain of coated SS316 and SS304 was observed to be reduced by 67% and 28% even in corrosive salt media when comparison to their respective uncoated SS.