Vol 40, No 3 (2018)

The method is presented of producing a cubic phase of the silicon carbide β-SiC by anneling in the air a powder product of the electroarc synthesis, which consists of β-SiC, graphite and a small amount of silicon. Due to its high resistance of β-SiC to the oxidation in the air we succeeded in the purification of it during the process of combustion of the graphite phase burning in the temperature interval of ~ 700–900°C. According to the X-ray diffractometry, the obtained powder material contains β-SiC with the content close to 99% (by volume). In this case according to the results of the scanning electron microscopy, β-SiC is characterized by a wide (from ~ 0.1 to ~10 μm) distribution of particles by size and typical shape for this phase crystals. The method of the electroarc synthesis of β-SiC and its subsequent purification to the commercial purity for the first time is realized in the air without the use of protective inert gases.

The phase and chemical compositions, structure, thickness, microhardness, operational properties of the VK8 hard alloy with multilayer coatings produced by the methods of diffusion titanizing, titanoalitizing, nitriding, nitridotitanoalitizing have been studied. The last two methods combine the nitriding at a temperature of 540°C for 20 h followed by titanizing or titanonitriding. It has been established that the composition of TiN, TiC layers formed at the nitrotitanoalitizing fulfils barrier functions at the chemically thermal treatment. The produced barrier fully slows down the penetration of aluminium and oxygen into the basis and promotes the surface of the formation on the AlCoTi₂ compound, the microhardness of which due to dissolution of nitrogen, reaches 12.6 GPa. The maximum microhardness of the TiC layers is 31.0–35.5 GPa and of TiN layers 20–21.5 GPa. The stability of the nitrotitanoalitized polyhedral disposable carbide plates VK8 during cutting U8A steel grew by 10.5 times as compared with the initial stability.

The interaction of the cobalt melt with hot-pressed and synthesized polycrystalline WC samples was studied. It is shown that the polycrystalline WC-mesoelements are promising for the development of WC–Co mesostructural hard alloys produced by liquid-phase sintering.

The effect of phase composition of cutting inserts made of diamond–tungsten carbide nanocomposite on cutting forces, friction coefficient in the cutting zone, and acoustic emission signal in finish turning of aluminum alloys and brass has been studied. It has been found out that the amount of 30 to 40 wt % tungsten in the initial mixture ensures sintering of a tool composite with the most favorable phase composition for turning aluminum alloys and brass.

A mechanism of nucleation and formation of Ti–Cr coatings on synthetic diamond powders of grade HSD 90 has been revealed and investigated. The metal deposition has been found to occur selectively and heal surface defects (microcracks, steps, etc.). Ti is the matrix metal that forms the coating as a whole, while Cr is the alloying element. Thermal stability of metal-coated diamond powders has been studied by derivatography. It has been found out that in comparison to non-coated powders the coated ones have the oxidation resistance increased by 40°C and feature an interdiffusion at the coating–bond interface.

The corrosion resistance, structure and physico-mechanical properties of B₄C–VC hot-pressed composites are studied. Materials perspective for the use as the end seals at chemical productions.