The problem of the optimal selection of multilayer coating structures, i.e. number, material, and arrangement of layers in the coating, is discussed. A systematic description of the influence of the external environment on the coating and the coating resistance to these influences is offered. With its help the necessary properties of coating layers can be determined in accordance with the coating operation conditions. The formal order for the search of the optimal structure of multilayer coatings and the algorithm for computer aided design of multilayer coatings are developed. The structures of wear resistance coatings are found for diverse schemes of loading. The design of an antifriction multilayer coating, produced with the PVD technique, is carried out to coat the piston rings of internal combustion engines.

The process of preferential hydrogen release on the anode in the course plasma electrolytic oxidation is a result of the thermochemical reaction between aluminum dispersed in spark discharges and water vapor. It is shown that the products of interaction are aluminum hydroxides or oxides. In this case, the degree of oxidation and the maximum efficiency of the plasma electrolytic oxidation are attained in the case of inhibition of the reaction of hydration of the metal and the presence of sufficient amounts of oxygen in the reaction zone. It is discovered that the compounds present in the electrolyte capable of adsorption on aluminum and the cathodic current component suppress the reaction of aluminum hydration and promote the formation of oxides. Plasma electrolytic oxidation (PEO) is a quite promising procedure of deposition of corrosion-[1], wear-[2], and heat-resistant [3] coatings on aluminum, titanium, and magnesium. As usual, the process is accompanied by the intense release of gases on the anode. Moreover, the composition of these gases and their "anomalous" amount could not be explained [4] within the framework of the available electrochemical regularities. The results of multiple measurements of discharges performed by using different methods [5-8] gave a common knowledge of their parameters (a duration of 0.2-1.0 sec, a temperature of 10 3 -10 4°K , and a pressure near the crater of 10 2 -10 3 MPa [9]) but did not clarify the nature of thermochemical processes in them. The experimental data obtained earlier [10,11] reveal large amounts of hydrogen in the anodic gas under the conditions of anodic polarization, which can be explained only by the conversion of aluminum.In the present work, we study the rate of gas release in the course of plasma electrolytic oxidation of aluminum and analyze the nature of thermochemical processes running in spark discharges. Experimental ProcedureThe process of plasma electrolytic oxidation was studied in an installation depicted in Fig. 1. The role of anode is played by BS 6082 aluminum alloy (0.4-1.0 wt.% Mn; ≤ 0.5 Fe; 0.6-1.2 Mg; 0.7-1.3 Si; ≤ 0.1 Cu; ≤ 0.2 Zn; ≤ 0.1 Ti; ≤ 0.25 Cr; balance Al). The areas of the specimens varied within the range 900-1600 mm 2 . The electrolysis was carried out in a solution containing 1 g/liter KOH, 2 g/liter Na 2 SiO 3 , and 1.5 g/liter Na 4 P 2 O 7 ⋅10 H 2 O . The temperature of electrolyte was held at 30°C with the help of a water heat exchanger.

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