OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 2 2023 a solution of silicon oxide with a grain size of 0.04 μm. The microstructure of the samples was studied using an Olympus GX-51 optical microscope (Olympus, Japan) equipped with the OLYMPUS Stream Image Analysis Stream Essentials 1.9.1 software for measuring the porosity of materials, as well as a Carl Zeiss EVO50 XVP scanning electron microscope with an EDS X-Act microanalyzer. The phase composition was studied using an ARL X’TRA X-ray diffractometer in CuKα radiation. The diffraction patterns were recorded at the time t = 3 s with a step Δ2θ = 0.05º. To reveal the phase composition, a layer about 50 μm thick was removed from each sample from the side of the coating. The microhardness of the structural components of the coatings was evaluated on a Wolpert Group 402MVD microhardness tester at a load of 100 g [21]. Wear tests were carried out in accordance with ASTM G65. The cermet coatings were spraying on steel plates with the size of 25×75×3 mm. The coatings thickness was 300–350 µm. During the test, the abrasive material (electrocorundum) was fed into the friction zone and pressed against the sample by a rotating rubber roller. The sample was pressed against the roller with a lever (a force of 44 N). The rotational speed of the roller was 60 rpm. Based on the results of weighing, the arithmetic mean value of the weight loss was determined. To assess the adhesion of the coatings, the samples were bent with 180° around a guide roll with a diameter of 10 mm according to ASTM E-290. Results and discussion Coatings microstructure Fig. 1 shows XRD spectra of the initial powder and coatings formed by different spraying modes. The main phases of the powder are tungsten carbide WC (51-939) and cobalt Co (15-806) (Fig. 1, a). The X-ray patterns of all coatings (Fig. 1, b–g) are almost the same: the main phases are WC (65-4539) and W2C (35-776). The peak intensity of the WC phase in the coatings is lower than in the powder, which indicates its lower volume fraction. It could indicate its lower volume fraction. The W2C phase is formed as a result of decarburization of WC according to the reactions [22]: 2WC ↔W2C + C; 2WC + O2 ↔W2C + CO2. The shift of the diffraction peak of the W2C phase could indicate a change in the interatomic distances. The absence of cobalt in the coatings’ X-ray diffraction patterns is explained with the fact that, during spraying part of the WC is dissolved in the cobalt matrix, and then upon rapid cooling an amorphous or nanocrystalline supersaturated Co(W,C) solid solution is formed on a cold substrate or already solidified splats. Its formation is indicated by a wide diffraction halo in the range 2θ = 37–47°. According to the data of [22–24], the formation of η phases (Co3W3C, Co2W4C, or Co6W6C) is also possible in the matrix, although we did not identify it with X-ray diffraction analysis. Fig. 2, a–f shows the cross-sectional images of the WC-Co coatings fabricated by different modes. Its average thickness is 150–200 µm. All coatings are characterized with high density and good adhesion Ta b l e 1 The modes of HV-APS Spraying distance, mm Arc current, A Spraying modes 170 140 170/140 170 170/170 200 170/200 250 140 250/140 170 250/170 200 250/200
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