National University of Science and Technology “MISIS”, Moscow, Russia:
E. N. Avdeenko, Engineer of Scientific-Education Center of SHS, e-mail: avdeenko.misis@mail.ru
E. I. Zamulaeva, Research scientist of Scientific-Education Center of SHS
A. A. Zaitsev, Senior research scientist of Scientific-Educational Center of SHS

Ultra-coarse-grained WC - Co hardmetals with WC grain size 5 μm are currently the materials of choice in rock drilling as possess higher wear resistance compared to that of fine-grained or medium-grained alloys having an equivalent hardness. In this study, we conducted a series of processes aimed at deagglomeration of ultra-coarse-grained tungsten carbide powder in a ball mill in different experimental modes. Two drum rotation speeds (“the rolling” and “the waterfall” modes) at two ratios between the weights of the grinding media and the powder (2:1 and 5:1) were studied; five different milling durations were used for each drum rotation speed and each ratio. The powder morphology and structure were studied by optical and scanning electron microscopies in the entire experimental design matrix. The optimal deagglomeration mode (5:1, nwaterfall = 64 rpm, milling time, 10 h) was determined by calculating the agglomeration index, which is equal to the ratio between the average agglomerate size and the average size of a monocrystal, and by measuring the granulometric composition of the powders, with the target 5–15 μm fraction isolated. In this mode, the percentage of the target fraction is 50 %, while the percentage of grains > 15 μm in size is 4%. The optimal mode of centrifugal air separation was selected: rotor speed = 3330 min^–1 and the number of powder passage = 7 cycles. The powder was monocrystalline tungsten carbide with the percentage of the 5–15 μm fraction >95%. The WC grain size was maintained constant during subsequent mixing of tungsten carbide with cobalt. In the sintered WC – 6 % Co hardmetal >90% carbide grains belong to the size range of 6–13 μm.
The work was carried out with the support of the Ministry of Education and Science of the Russian Federation, Agreement No. 14.575.21.0156, Project RFMEFI57517X0156, Federal Target Program of “Research and development in priority areas of the scientific and technological complex of Russia for 2014–2020”.

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