Plasma Electrolytic Oxidation of Arc-Sprayed Aluminum Coatings

Different posttreatment methods, such as heat treatment, mechanical processing, sealing, etc., are known to be capable to improve microstructure and exploitation properties of thermal spray coatings. In this work, a plasma electrolytic oxidation of aluminum coatings obtained by arc spraying on aluminum and carbon steel substrates is carried out. Microstructure and properties of oxidized layers formed on sprayed coating as well as on bulk material are investigated. Oxidation is performed in electrolyte containing KOH and liquid glass under different process parameters. It is shown that thick uniform oxidized layers can be formed on arc-sprayed aluminum coatings as well as on solid material. Distribution of alloying elements and phase composition of obtained layers are investigated. A significant improvement of wear resistance of treated layers in two types of abrasive wear conditions is observed. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Express method for determining the presence of defects of the surface of oxide-ceramic coatings

Using a multiresolution relevance function for the localization and subsequent segmentation of surface objects of oxide-ceramic coatings, we propose an express method for determining their number and sizes.     

Optical currents in vector fields

We present the results of computer simulation of the spatial distribution of the Poynting vector and illustrate motion of microparticles and nanoparticles in spatially inhomogeneously polarized fields. The influence of phase relations and the degree of mutual coherence of superimposing waves on the characteristics of the microparticle's motion has been analyzed. For the first time, we have shown experimentally the possibility of diagnostics of optical currents in liquids caused by polarization characteristics of an optical field alone, using test metallic particles of nanoscale.     

Spectral analysis of an electrolytic plasma in the process of synthesis of aluminum oxide

The process of synthesis of oxides on the surface of aluminum placed in an electrolytic plasma is analyzed spectroscopically. It is established that electrolyte constituents and working-electrode constituents appear in the plasma. We describe their state, detect adhesion of electrons to ions of alkali metals, and investigate the thermodynamic state of the plasma and the influence of the oxides on the relative intensity of emission lines, the temperature and density of electrons, and the electric field intensity. These results give deep insight into the processes in an electrolytic plasma and enable one to clarify the mechanism of synthesis of oxide-ceramic coatings in an electrolytic plasma.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 3, pp. 70–81, May – June, 1994.     

Corrosion and wear behavior of alumina coatings obtained by various methods

Alumina coatings are widely used in a range of industrial applications to improve corrosion protection, wear and erosion resistances, and thermal insulation of metallic surfaces. Refined alumina surfaces with long-term use are obtained from various efficient and adjustable processes. It can be seen that costefficient arc-sprayed Al coatings post-treated by plasma-electrolytic oxidation (PEO) form Al₂O₃ -layers with remarkable corrosion protection, hardness, bonding strength, and abrasion resistance, as well as with the extended service time. The properties of these coatings are compared with alumina coatings obtained by flame spraying and atmospheric plasma spraying.     

Influence of Additions of Water on the Quality of Filled Anodic Oxide Coatings

We investigate the influence of anion-cation composition of an aqueous medium on the etching rate in an acid electrolyte and the resistance of the insulation of a filled oxide coating. We reveal the cations and anions of the aqueous medium that increase the etching rate of the coating and decrease its insulation resistance. We establish that Al³⁺ and Mg²⁺ cations and SiO ₃ ^2- anions have a considerable effect on the quality of the filled coating. A high-quality coating is obtained if their concentrations in the aqueous medium are at most (mg/liter) 100 for Al³⁺, 700 for Mg²⁺, 800 for Cl^–, and 13 for SiO ₃ ^2- . The optimum pH of the environment is equal to 6 and the time of treatment of a coating in distilled water is equal to 60 ± 5 min.