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 kW(th) biomass fired bubbling fluidised bed (BFB) combustor for 20 h and an industrial scale anthracite fired CFB boiler for 1630 h. Stellite-6 showed excellent corrosion resistance in both fluidised bed combustion systems because of the formation of the 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.

Automated summary

Stellite-6 demonstrated excellent corrosion resistance with the formation of protective Cr2O3 and CoCr2O4 layers, while NiAl coatings showed significantly reduced anti-corrosion performance due to chlorine attack, resulting in the formation of Al2O3 layer and eventual coating spallation in both systems.