FORMATION OF WEAR RESISTED HARDENED COATINGS ON THE SURFACE STEEL AT SUCCESSIVE ELECTRIC-SPARK ALLOYING BY CHROME AND COPPER IN THE PROTECTIVE ENVIRONMENT AND IN AIR
Journal Title: Проблеми тертя та зношування - Year 2018, Vol 79, Issue
Abstract
The purpose of this work is to study the microstructure, phase composition, microhardness and wear resistance of the steel (article 3) surface layers after the successive Electric-spark alloying (ESA) by carbide forming metal (Cr) and the metal that does not form carbides (Cu) in inert medium (argon) and in air in the following sequences of elements application: Cr-Cu and Cu-Cr. According to the results of the microstructural analysis, it was found that after ESA in air, lay-ers of 40 μm thickness were obtained for both doping sequences. ESA by Cr-Cu sequence leads to the creation of two layers on the surface: the first, with a microhardness of 1.8 GPa, and the second, with a microhardness of 3.6 GPa. At ESA in the sequence of Cu-Cr the hard-ness of the surface layer increases to 4.7 GPa. According to the X-ray diffraction analysis in the surface layer the phases are present: α-Fe, Cu and Cr. The wear resistance at ESA in the sequence of Cr-Cu is 10 times more than in the sample without processing, and when doped in a sequence of Cu-Cr in 9 times. Under ESA in the atmosphere of argon, Cr-Cu and Cu-Cr schemes alloyed layers of 50 and 60 μm in thickness, respectively were formed. ESA in the Cr-Cu sequence leads to the formation on the steel of layer with a microhardness of 3.9 GPa, and in the sequence of Cu-Cr – 7.7 GPa. X-ray diffraction analysis showed the presence of reflexes from α-Fe, Cu and Cr and Cr3C2. The wear resistance after ESA in the Cr-Cu sequence is 4 times more than in the sample with-out processing, and when doped in a sequence of Cu-Cr – in 5 times. An increase in the microhardness of a doped layer under ESA in argon, in comparison with ESA in the air, may be due to the formation of disperse carbides. ESA in air can lead to the binding of carbon by oxygen, and such a decrease in its concentra-tion may contribute to the reduction of the chromium carbide amount, which also leads to a decrease in the microhardness of the layer compared to treatment in argon, where oxygen is absent. The increase in the wear resistance of the doped layers obtained by ESA in air, compared with the wear resistance of the layers obtained in argon, is probably due to the formation of dis-persed nitrides and chromium oxides, which have high hardness and located in a soft compo-nent based on copper.
Authors and Affiliations
IE. V. IVASHCHENKO, G. G. LOBACHOVA, O. V. VOZNYUK
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