OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 6 No. 4 2024 Fig. 3. The mechanism of formation of “reptile skin” In order to establish the reasons for the low wear resistance of the experimental bits, the AGMK NPO carried out the research, aimed at developing optimal methods for manufacturing tungsten-cobalt teeth, its fi rm fi xation in the bit grooves and improving the technology of its assembly. According to literature sources [16, 17], the materials can be separated from the surfaces of carbide teeth in several ways: ● grinding of grains of the VK (W-Co) hard alloy and separation of fragments; ● separation of whole grains or parts of grains that lose its ability to be retained in the structure; ● grinding the mixture: VK (W-Co) hard alloy /rock binder and separation of fragments; ● tribochemical wear, scraping off corroded or oxidised surface layers of VK (W-Co) hard alloy; ● separation of composite fragments of VK (W-Co) grain groups together with the binder. A study of the microstructure of tungsten-cobalt teeth samples of the fi rst experimental batches showed that one of the reasons for the formation of a porous structure with depressions, prone to the formation of pits, cracks and chips, when the teeth are exposed to roughness of rocks, was the large size of tungsten carbide grains. The large size of tungsten grains is obtained as a result of using conventional metallic tungsten powder containing undesirable impurities of calcium, silicon, iron and Sulphur. Fig. 4 demonstrates the microstructure of a conventional sample of hard VK10 (90 %W; 10 % Co) alloy, the elemental composition of which revealed a signifi cant content of impurities that negatively aff ect the physical and mechanical properties of the alloy (Fig. 5). Fig. 6 shows the microstructure of the junction surface of a sample of conventional hard alloy VK10 (90 %W; 10 % Co). The hard alloy can be seen to be characterised by the presence of areas of inhomogeneity in the form of clusters of large spherical formations, as well as clearly foreign particles, exposed on the fracture surface of the VK10 (90 %W; 10 % Co) sample (Fig. 7). This explains the cause of the fracture. The areas of inhomogeneity and the presence of grains of foreign impurities negatively infl uence the bending strength, hardness, impact toughness and other physical and mechanical properties of the hard alloy VK10 (90 %W; 10 % Co), which should ultimately determine the operational wear resistance of manufactured carbide teeth. Fig. 4. Morphological features of the microstructure of a conventional sample of hard alloy VK10 (90 %W; 10 % Co)
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