CORROSION BEHAVIOR OF LASER MELTED PLASMA-SPRAYED COATINGS ON 12-PERCENT CHROMIUM DUAL-PHASE STEEL

Plasma sprayed Mo and Cr coatings on a dual phase 12 wt-%Cr steel (3CR 12) were laser surface melted using a continuous wave CO2 laser. The m orphology and corrosion behaviour of the plasma sprayed and laser surf ace melted coatings were then studied using scanning electron microsco py (SEM), potentiodynamic scan and linear polarisation resistance meas urements. SEM observations showed that interconnected pores were forme d in the Cr and Mo plasma spray coatings. These pores were responsible for high general corrosion rates of both Cr and Mo plasma spray coati ngs exposed to sulphuric acid solutions. Under optimum laser processin g conditions the modified Cr surface had a very low corrosion rate and a small critical current density for passivation when exposed in sulp huric acid solutions. These improvements in corrosion properties appea r to be related to the removal of residual pores by laser surface melt ing and the formation of a Cr enriched surface alloy on 3CR12 steel.