Abstract
Plasma electrolytic oxidation (PEO) is a surface treatment process for obtaining oxide coatings with a high performance on valve metals. PEO is mostly performed in an aqueous solution electrolyte that limits the size of treated parts due to the fact that the system is heated. Therefore, the coating of large surfaces cannot be synthesized in an aqueous electrolyte. In the current work, an alternative approach of PEO treatment, whereby an aluminum 1050 alloy in nitrate molten salt at a temperature of 280 °C is applied, was investigated. The microstructure, phase and chemical compositions, and micro-hardness were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and micro-hardness tests. The obtained results show that formed coating contains from two sub-layers: one is the outer sub-layer of the α-Al2O3 phase and the second is its inner sub-layer. It was found that the formed coating was free of any contaminants originating from the electrolyte and had no cracks or pores, which are usually present in coatings formed by PEO treatment in an aqueous solution electrolyte.
Highlights
In the last two decades, plasma electrolytic oxidation (PEO) became one of the most attractive surface treatment methods of advanced ceramic coating formation on metallic compounds [1,2,3,4,5].This technological approach is usually applied in so-called valve metals as aluminum, magnesium, or titanium to obtain surface advanced properties such as high electrical insulation, corrosion and wear resistance, and excellent performance [6,7,8]
The basic principle of the PEO technology is a high-voltage application between the specimen subjected to the treatment and the electrode, while the micro-arc discharge migration points appear on the its surface
energy dispersive X-ray spectroscopy (EDS) results indicate that no additional compounds were incorporated into the results indicate that no additional compounds were incorporated into the coating, as it coating,as asititconfirmed confirmedisisusually usuallypresent presentafter aftertreatment treatmentin inaqueous aqueoussolutions solutionsoriginating originatingfrom fromthe the coating, confirmed is usually present after treatment in aqueous solutions originating from the electrolyte
Summary
In the last two decades, plasma electrolytic oxidation (PEO) became one of the most attractive surface treatment methods of advanced ceramic coating formation on metallic compounds [1,2,3,4,5].This technological approach is usually applied in so-called valve metals as aluminum, magnesium, or titanium to obtain surface advanced properties such as high electrical insulation, corrosion and wear resistance, and excellent performance [6,7,8]. In the last two decades, plasma electrolytic oxidation (PEO) became one of the most attractive surface treatment methods of advanced ceramic coating formation on metallic compounds [1,2,3,4,5]. The basic principle of the PEO technology is a high-voltage application between the specimen subjected to the treatment and the electrode, while the micro-arc discharge migration points appear on the its surface. These discharge points provide an additional impact to the thermal and plasmo-chemical effect, which causes the ceramic coating formation with a high adhesion to the metallic base [9,10,11]. The main disadvantages of the PEO treatment in aqueous solutions are a relatively low coating rate, a formation of a thick high porosity layer, a necessity of electrolyte cooling, and the presence of some undesirable compounds in the
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