Study on the Application of Electric Arc Sprayed Duplex Coatings CrNi - Al for Anticorrosion Protection of Carbon Steel in Aqueous Acid Media

CrNi alloys are industrially well known with their good chemical resistance in many environments. With the wire electric arc metallization technology, the CrNi alloy coating can be easily applied on steel substrate for different anticorrosion purposes. However, due to the characteristics of the technology, the porosity of the coating would be as high as 10% or even more. It reduces significantly the protective properties of the coating once the reactive species from the outside environment attaint the interface with the steel substrate. To overcome the corrosive penetration process, a layer of a much less expensive Al coating over the CrNi alloy coating is applied. In this case, the Al coating plays a role of sacrificial material. Moreover, due to the passive possibility of the Al, the thin but dense Al2O3 oxide layer is quickly formed which give an additional barrier effect to slow down the ingress of the corrosion species.

In this work, the electrochemical behavior of the duplex coatings CrNi - Al in 4 popular inorganic acid solutions with pH 2 is studied. The change of the cross-section microstructure of the coating system is also investigated.