UDC 621.797; 621.793.7We study electric-arc coatings of the Fe-Cr-C and Fe-Cr-B systems. It is shown that chromium content of 12 wt.% is insufficient to guarantee higher corrosion resistance of the coatings in neutral aqueous solutions (as compared with steels) caused by the formation of chromium-based oxides, carbides, and borides. Therefore, the indicated chromium content of the compounds should be taken into account and compensated in finding the chemical composition of powder wires. Its unjustified increase is not reasonable because powder wires are characterized by filling coefficients restricting the possibility of their filling with alloying elements. Therefore, the content of each alloying element in the charge of powder wires should be well justified and determined. For this purpose, we propose to use the relations taking into account the nonlinear distribution of chromium in the lamellas of the coatings caused by their high microheterogeneity and the depletion of their solid solution of the indicated element as a result of the formation of oxides, carbides, and borides on its base.At present, the electric-arc metallization is extensively used in machine building, power-generating industry, mining industry, and other branches of national economy as the cost-effective, most productive, and simple method of gas-thermal spraying [1]. As electrode materials, it is possible to use both solid and powder wires. The powder wires are used to get coatings with high mechanical characteristics and, first of all, high hardness (up to 1300 HV) [2]. The procedure of electric-arc metallization can be used for the restoration of various worn-out articles, improvement of the properties or protection of the metallic and nonmetallic surfaces against the abrasive or corrosion wear [3,4]. However, at present, there exists a need in coatings of combined action (wear-and corrosion-resistant simultaneously). Various parts of the critical aggregates made of structural materials (the rods of hydraulic cylinders of the mining equipment and freight transport, parts of the sheet-output mechanisms of the printing equipment, rods of the stop valves, etc.) and protected by wear-resistant electrolytic chromium operate under the conditions of abrasive wear and boundary friction. The procedure of electrolytic chrome plating is ecologically dangerous and, therefore, the leading researchers throughout the world give much attention to the possibility of its replacement by gas-thermal spraying [5,6]. This is economically efficient because the amount of the required electric energy decreases, the time of application of the coating becomes much by (8-10 times) smaller, the necessity of utilizing toxic wastes disappears, and the material for the coating can be chosen depending on requirements imposed on the coatings.

The mechanical properties (hardness, cohesion, and residual stresses) of arc coatings designed for operation under conditions of boundary friction and corrosive-abrasive wear are analyzed. The coatings were formed by arc spraying cored wires (CW) with different charge compositions (the content of carbon, aluminum, and boron in CW charge varied). It is shown that the hardness of the coatings increases with an increase in the carbon content in them up to 1 wt. %, and then decreased due to an increase in the content of residual austenite in their structure. The level of residual stresses of the first kind in such coatings increased by four times with an increase in the carbon content to 2 wt. %. The hardness of the coatings and the level of residual tensile stresses in them also increase with a decrease in the aluminum content in them. In this case, the cohesive strength of the coatings increased due to the implementation of aluminothermic reactions in the droplets of the CW melt during their flight and crystallization on the sprayed surfaces. However, then, with an increase in the aluminum content in the coatings of more than 2 wt. %, their cohesive strength decreased. The level of residual tensile stresses in coatings with a high content of retained austenite decreased after heat treatment (tempering) of the specimens. Sometimes, after tempering, these stresses even transformed into residual compressive stresses (in particular, under using CW C1.4Cr14Ni2). At the same time, the tempering of specimens with a predominance of ferrite in the coating structure increased the level of residual tensile stresses in them, which is due to the precipitation of finely dispersed carbides or borides. It has been shown that the addition of boron-containing components (ferrochromium-boron, chromium-boron) to the composition of the CW charge leads to a significant increase in the hardness of the coatings. Thus, an increase in the boron content in coatings from 0 to 4 wt. % leads to an increase in their hardness from 320 HV to 1060 HV. However, this is accompanied by an increase in tensile residual stresses in the coatings and a decrease in their cohesive strength.

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