CORROSION RESISTANCE AND SURFACE CHARACTERISTICS OF PLASMA ELECTROLYTIC OXIDATION COATING PRODUCED ON STEELS

摘要

Plasma Electrolytic Oxidation (PEO) is one of the most promising treatments used to improve the corrosion and wear properties of a wide range of metals. In particular, the process produces the growth of an oxide ceramic film on the surface of metals and this film is a strong barrier against corrosion. In this work, PEO process was applied on various steels using different solutions as electrolytes. In particular, were used base alkaline solutions containing mainly silicates and aluminates. The corrosion resistance of the PEO coated samples was studied with potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in chloride and sulphate environment, using the untreated sample as comparison. EIS data were fitted using the software Z-view with an appropriate equivalent circuit. The morphology and chemical composition of the obtained coatings were studied using a scanning electron microscope equipped with EDS. The phase composition was studied with X-ray diffraction (XRD). The corrosion properties of the PEO coated steels are improved if compared with the uncoated samples, in particular using aluminates in the electrolyte. The surface presents the typical porous morphology of the plasma electrolytic oxidation treated surfaces.