CORROSION RESISTANCE OF FERROUS COATINGS PRODUCED BY THERMAL SPRAY

Abstract

Three materials were deposited on AISI-SAE 4340 steel using the wire arc thermal spray technique. The deposited materials are commercially known as 140MXC (Fe, Nb, Cr, W), 530AS, which is a steel similar to AISI-SAE 1015, and 560AS, which is a steel similar to AISI-SAE 420. With the aim of evaluating the best strategy for increasing the corrosion resistance in the coating-substrate system, the coatings were deposited in three different ways: (1) homogeneous monolayers (single layers) of each material, (2) (Double layer) bilayers composed of a monolayer of 140MXC over a monolayer of either 530AS or 560AS, and (3) simultaneous monolayer-type (single layer) coatings achieved by depositing 140MXC + 530AS in the first case and 140MXC + 560AS in the second case. The coatings were characterized by optical microscopy and X-ray diffraction. The corrosion resistance was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization. The resistance to polarization of the material deposited in bilayers was increased through the congestion of defects with corrosion products, while the simultaneous monolayers achieved increased corrosion resistance by the reduction of defects with respect to 140MXC. The details and mechanisms of corrosion in the fabricated coatings are described in this study.