OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 strengthening phases of carbides, silicides, and borides chaotically located in the ferritic (for coating 1) and austenitic (for coating 2) matrices. The aim of this layer is to provide high wear resistance and thermal oxidation resistance due to the formation of protective SiO2 and Cr2O3 oxide films. The second layer is produced by plasma flux spraying of a mixture of heat-resistant self-fluxing powders and an iron powder in the 1:1 ratio for providing a smooth transition of properties from the oxygencontaining to metallic layers. The thickness of this layer is 250 μm, and its microhardness is 800 HV 0.05. It consists of the same phases as the first layer, but with an additional number of ferrite grains free from strengthening phases. The third (metal-oxide) layer formed by plasma spraying of iron powder in an oxidizing environment is meant for the recovery of the surface oxide layer after wear at operating temperatures of piercing mandrels. It has a thickness of 350 μm and a microhardness of 300 HV 0.05. The layer is a mechanical mixture of ferrite grains and iron oxides. The fourth (surface) layer of the FeO+Fe2O3+Fe3O4 oxide mixture is produced by oxidizing the surface of the metal oxide third layer by means of a plasma torch. The aim of this layer is to reduce the friction coefficient of piercing mandrels during operation and to decrease their surface temperature. References 1. Baldaev L.Kh., Borisov V.N., Vakhalin V.A., Gannochenko G.I., Zatoka A.E., Zakharov B.M., Ivanov A.V., Ivanov V.M., Kalita V.I., Kudinov V.V., Puzryakov A.F., Sborshchikov Yu.P., Khamitsev B.G., Shkol’nikov E.Ya., Yaroslavtsev V.M. Gazotermicheskoe napylenie [Thermal spray]. Moscow, Market DS Publ., 2007. 344 p. ISBN 978-5-7958-0146-9. 2. Budinovsky S.А., Muboyadzhyan S.A., Gayamov A.M., Matveev P.V. Development of ion-plasma refractory metallic layers of heat-insulating coatings for cooled turbine rotor blades. Metal Science and Heat Treatment, 2014, vol. 55, pp. 652–657. DOI: 10.1007/s11041-014-9684-2. 3. Tarasenko Yu.P., Tsareva N.N., Berdnik O.B. The structure and physical-mechanical properties of the heatresistant Ni-Co-Cr-Al-Y intermetallic coating obtained using rebuilt plasma equipment. Thermophysics and Aeromechanics, 2014, vol. 1, no. 5, pp. 641–650. DOI: 10.1134/S0869864314050138. 4. Cherepanov A.N., Orishich A.M., Malikov A.G., Drozdov V.O., Ovcharenko V.E., Pshenichnikov A.P. Influence of modifying nanoadditives on the properties of a multilayer composite coating obtained by laser surfacing. The Physics of Metals and Metallography, 2019, vol. 120, iss. 1, pp. 101–106. DOI: 10.1134/S0031918X190100225. 5. Chen L., Wang H., Zhao C., Lu S., Wang Z., Sha J., Chen S., Zhang L. Automatic remelting and enhanced mechanical performance of a plasma sprayed NiCrBSi coating. Surface and Coatings Technology, 2019, vol. 369, pp. 31–43. DOI: 10.1016/j.surfcoat.2019.04.052. 6. Guzanov B.N., Kositsyn S.V., Pugacheva N.B. Uprochnyayushchie zashchitnye pokrytiya v mashinostroenii [Hardening protective coatings in mechanical engineering]. Ekaterinburg, Ural Branch of the RAS Publ., 2004. 244 p. ISBN 5-7691-1405-3. 7. Shevchenko O.I., Trekin G.E., Farber V.M. Distribution of chemical elements in structural components of a facing of a self-fluxing nickel alloy. Metal Science and Heat Treatment, 1997, vol. 39, iss. 6, pp. 233–235. DOI: 10.1007/bf02467225. 8. Otsubo F., Era H., Kishitake K. Structure and phases in nickel-base self-fluxing alloy coating containing high chromium and boron. Journal of Thermal Spray Technology, 2000, vol. 9, iss. 1, pp. 107–113. DOI: 10.1361/10599 6300770350131. 9. Du H., Lee S.W., Shin J.H. Study on porosity of plasma-sprayed coatings by digital image analysis method. Journal of Thermal Spray Technology, 2005, vol. 14, iss. 4, pp. 452–461. DOI: 10.1361/105996305X76450. 10. Odhiambo J.G., Li W., Zhao Y., Li C. Porosity and its significance in plasma-sprayed coatings. Coatings, 2019, vol. 9 (7), pp. 460–479. DOI: 10.3390/coatings9070460. 11. Zhou C.G. Yu Q.H. Nanostructured thermal barrier coatings. Thermal Barrier Coatings. Cambrige, UK, Woodhead Publishing, 2011, pp. 75–96. 12. Kornienko E.E., Nikulina A.A., Bannov A.G., Kuz’min V.I., Mildebrath M., Bezrukova V.A., Zhoidik A.A. Vliyanie temperatury oplavleniya na strukturu i svoistva samoflyusuyushchikhsya pokrytii na osnove nikelya [The influence of flowing temperature on the structure and properties of the self-fluxing coatings]. Obrabotka metallov
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