Experimental investigations on the chlorine-induced corrosion of HVOF thermal sprayed Stellite-6 and NiAl coatings with fluidised bed biomass/anthracite combustion systems

Stellite-6 (Co-based) and NiAl coatings (Ni-based) were deposited via HVOF spraying onto 304 stainless steels and tested in a 20 kWth biomass fired bubbling fluidised bed (BFB) combustor for 20 hours and an industrial scale anthracite fired CFB boiler for 1630 hours. Stellite-6 showed excellent corrosion resistance in both fluidised bed combustion systems because of the formation of outermost Cr2O3 layer and the spinel CoCr2O4 beneath, whereas NiAl coatings' anti-corrosion performance was significantly depleted due to the chlorine attack, and the resultant formation of Al2O3 layer at the coating/substrate interface finally led to coating spallation in both systems