OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 3 2023 because iron inflowed to the coating during the melting of the base material. The compositions of the used powder mixtures are shown in Table 1. The prepared mixtures were put on the surfaces of a steel workpieces with a packed density of 0.8 g/cm2. The main technological modes of surfacing that affect the energy density are presented in Table 2. The workpiece motion speed and the electron beam current were selected in such a way as to provide the equiatomic composition of the CoCrFeNiMn coating without CrB particles (1st mode). Modes 3, 4, and 5 provided increased electron beam current to compensate for the rise in the melting temperature of the powder mixture. Ta b l e 1 Compositions of surfacing powder mixtures No. Surfacing powders, wt. % Flux, wt. % 1 CoCrNiMn 70% CaF2 30% 2 (CoCrNiMn : CrB 95:5) 70% 3 (CoCrNiMn : CrB 90:10) 70% 4 (CoCrNiMn : CrB 80:20) 70% 5 (CoCrNiMn : CrB 70:30) 70% Ta b l e 2 Technological modes of surfacing No. Composition Beam current, mА Accelerating voltage, MeV Workpiece motion speed, cm/s Energy density, kJ/cm2 1 CoCrNiMn 25 1.4 1.5 4.67 2 CoCrNiMn : CrB 95:5 25 3 CoCrNiMn : CrB 90:10 26.5 4.95 4 CoCrNiMn : CrB 80:20 26.5 5 CoCrNiMn : CrB 70:30 26.5 The microstructure of the coatings was studied in transverse sections prepared according to the standard method: grinding using abrasive papers with a gradual decrease in grit from P180 to P4000 and final polishing using an alumina suspension with a particle size of 0.3 μm. To reveal the structure, prepared samples were chemically etched with a solution consisting of 10 ml HNO3 + 10 ml HF + 15 ml H2O for 10–60 sec. The microstructure was studied using a Carl Zeiss AxioObserver Z1.m optical microscope and a Carl Zeiss EVO50 XVP scanning electron microscope equipped with an Oxford Instruments INCA X-Act system for X-ray energy dispersive microanalysis. The phase composition of the coatings was studied by a Bruker D8 ADVANCE X-ray diffractometer using Cu Kα radiation. The diffraction patterns were recorded in the range of 2Θ = 15–90° with a step of 0.02°. The dwell time was 0.2 s per point. The diffraction patterns were analyzed using the ICDD PDF4+ database. The microhardness of the coatings was determined by the Vickers method with a WolpertGroup 402 MVD hardness tester on polished transverse sections. The load on the indenter was 100 g, the dwell time was 15 s.
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