OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 of the white micron-sized inclusions in the WC20 and WC40 coatings suggest that they are original tungsten carbide WC particles. The cross-sectional images clearly show that the size of micron-sized WC inclusions increases with an increase in the WC powder fraction in the electrode. The diameter of the micron grains was smaller than the median particle diameter in the original W20 and W40 powders (Fig. 1, c, d). This suggests that the original powder particles were agglomerates of carbides, which disintegrated into fragments when wetted by the Fe-Ni-Al melt in the discharge pool and dissolved upon interaction with iron. The submicron inclusions in Fig. 4 likely formed via WC crystallization from the melt, as they resemble the diamondshaped inclusions of the WCn sample, and reaction 1 is reversible. Micron inclusions could also act as WC crystallization centers, growing further during crystallization of the melt microbath after the discharge ceased. The distribution of aluminum, nickel, and iron is uniform, indicating a homogeneous composition of the coating matrix. The light grey areas in Fig. 4 are likely the result of tungsten carbide decarburization, as described in Eq. 1. According to EDS analysis, the coatings contain tungsten, nickel, aluminum, and iron (Fig. 5, a–c). The source of iron is both the granules and the substrate. The concentration of elements remained relatively constant throughout the coating thickness. Fluctuations in tungsten concentration can be attributed to the presence of tungsten carbide grains in the path of the scanning electron beam. As the powder fraction size in the NE increased, the aluminum content in the coating matrix increased, while the iron (Fe) content decreased from 58 to 27 at.% (Fig. 5). The formation of the ESD coating inevitably involves the substrate as a source of iron. It is worth noting that the use of iron granules results in comparable iron concentrations in the coating to those obtained when using Ni and Al granules [10]. This can be explained by the fact a b c Fig. 5. Metal concentration distribution of across coating height, according to the results of EDS analysis: a – WCn; b – WC2; c – WC40
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