OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 The hardness of the coatings was measured on a PMT-3M microhardness tester at a load of 0.5 N using the Vickers method. The wear resistance and coeffi cient of friction of the samples were tested following the ASTM G99-17 procedure under dry friction condition with speed of 0.47 ms–1 under load of 25 N. The testing time was 20 minutes. Discs made of M45 high-speed steel with a hardness of 60 HRC were used as a counterbody. Wear was measured gravimetrically. The sample of each type was tested three times. Results and discussion The study of mass transfer during ESD is important for establishing the fact of a positive weight gain of the cathode, otherwise ESD is not effective. In addition, the coating thickness is a function of the cathode weight gain [21]. During the ESD, electric discharges arose between steel granules and the substrate, which resulted in a liquid-phase transfer of the metal from the granules surface to the substrate. The powder particles that appeared on the surface of the electrodes at the moment of development of the discharge channel were fused with the metal. This was accompanied by a monotonous increase in the weight gain of the cathode (Fig. 2, a). With an increase in the processing time for all mixtures, a slowdown in the weight gain of the cathode was observed, which is also characteristic of the traditional ESD [22]. This is explained by the accumulation of defects in the coating and the intensifi cation of its electrical erosion with an increase in the specifi c number of discharges [23]. The largest gain of the cathode after 600 seconds of ESA was observed for the anode mixture of Cr5, and in the case of mixtures of Cr10 and Cr15, taking into account the error bars, the gain can be considered close. This behavior of mass transfer can be explained by the deterioration of the electrical contact and a decrease in the frequency of discharges with an increase in the powder concentration in a mixture of granules, which was previously observed for silicon powder [24]. Therefore optimal concentration of CrB2 powder in a mixture with iron granules is about 5 vol.% from the standpoint of achieving the maximum coating thickness. a b Fig. 2. AISI 304 stainless steel cathode weight gain during ESD (a) and X-ray diffraction patterns of deposited coatings (b) Figure 2, b shows the results of X-ray analysis of the prepared coatings. From this it follows that the composition of the coatings was dominated by a solid solution of chromium in iron, which forms a metal binder of the coating, and ceramic phases of chromium (Cr5B3, Cr2B) and iron (Fe23B6) borides are also present. This indicates that the original CrB2 phase was not retained in the coating due to its high reac-
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