OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 One of the methods for enhancing the properties of sintered materials is mechanical activation of powders. It provides milling of the powders, changing its energy state, intensifi ed sintering of the powder materials, and forming a fi ne-grained structure in it [4–7]. When certain powders are mechanically activated in planetary centrifugal mills, nanoparticles having a high reactivity can be formed [8]. Works [9–13] demonstrate that addition of nanoparticles into metallic binders ensures dispersion hardening of the binders and helps enhance operational properties of the diamond tools considerably. For this purpose, nanopowders of carbon-based materials, boron nitride, and high-melting oxides and carbides (ZrO2, WC) are used. The melting temperature of nanoparticles is known to be lower than that of micropowders [14]. So, to ensure dispersion hardening, nanoparticles have to be preserved in the structure of the material after sintering. An important characteristic of metallic binders is its adhesion activity to diamond, which provides strong retention of diamond grains in the binders. Nanoparticles located on the matrix-fi ller interface are known to be able to produce a considerable effect on mechanical properties of the composite material [15–17]. With regard to this, one can suppose that addition of nanodispersed particles of carbide-forming metals to the binder will allow enhancing its adhesion to diamond essentially. One more factor contributing to adhesion activity of binders can be the changed energy state and higher reactivity of the powders after its mechanical activation. Tungsten is one of the most refractory metals. Annealed tungsten of high purity has the hardness of 225–300 HB, ultimate strength of 800–1,200 MPa, and its relative elongation is close to zero [18]. Such properties make it possible to mill tungsten mechanically to nanosized particles [8, 19]. The authors of this work have conducted preliminary experiments [20] demonstrating the possibility of obtaining 25–90 nm sized particles of tungsten in milling the PVT and W16,5 grade powders with a planetary centrifugal mill. With tungsten being a carbide-forming element, adding it into the powder material enhances diamond adhesion activity of the binder. However, under certain conditions, the additive can prevent the binder from sintering, which leads to increase in its porosity while also reducing its hardness and strength [21]. The objective of this work is to study the effect of mechanical activation of tungsten particles on the structure and properties of the sintered Sn-Cu-Co-W powder material. Research technique For the experiments, the following powders were used: PO1 tin powder (up to GOST 9723-73), PMS-1 copper powder (up to GOST 4960-75), and Diacob-1600 cobalt powder with the particle size of 1–2 μm (by Dr. Fritsch Kg., Germany). It was the W16,5 special tungsten powder (by Pobedit JSC) containing not less than 99.9% W with particles sized 19–24 μm (technical specifi cations TU 48-19-417-8) that was exposed to mechanical activation. Mechanical activation was performed in the AGO-2U planetary centrifugal mill for 5, 15, 60, and 120 minutes at the carrier rotation frequencies of 400, 800, and 1,000 RPM. Using the above powders, mixtures were prepared containing two kinds of tungsten powders – mechanically activated and non-activated; the proportion of the components was as follows (% wt.): 20 Sn; 43 Cu; 30 Co; 7 W. The 20 g weighted samples were compacted by single-action static pressing in an all-steel mould at the 12 t/cm2 press power. The resulting cylindrical samples of 21 mm diameter were sintered in vacuum at the temperature of 820 °C for 20 minutes. After that, the sintered samples were weighed with the Adventurer AR2140 assay balance (by OHAUS) to fi nd out its density as the ratio of weight to volume. Next, the structure of sintered materials was examined by scanning electron microscopy and optical metallography. For this, the authors used the JSM-7500F (by JEOL) ultrahigh resolution
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