Corrosion behaviour of laser melted plasma sprayed coatings on 12% chromium dual phase steel

Abstract

Plasma sprayed Mo and Cr coatings on a dual phase 12 wt-%Cr steel (3CR12) were laser surface melted using a continuous wave CO₂ laser. The morphology and corrosion behaviour of the plasma sprayed and laser surface melted coatings were then studied using scanning electron microscopy (SEM), potentiodynamic scan and linear polarisation resistance measurements. SEM observations showed that interconnected pores were formed in the Cr and Mo plasma spray coatings. These pores were responsible for high general corrosion rates of both Cr and Mo plasma spray coatings exposed to sulphuric acid solutions. Under optimum laser processing conditions the modified Cr surface had a very low corrosion rate and a small critical current density for passivation when exposed in sulphuric acid solutions. These improvements in corrosion properties appear to be related to the removal of residual pores by laser surface melting and the formation of a Cr enriched surface alloy on 3CR12 steel.