OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 Ta b l e 1 Minimum size (nm) of tungsten W16,5 particles depending on mechanical activation mode Rotation speed, rpm Duration of mechanical activation, min 5 15 60 120 400 160 132 90 83 800 137 116 25 25 1,000 128 85 90 102 Fig. 2. Size distribution of tungsten particles after mechanical activation are aggregated. Alongside this, the material is exposed to work hardening, which hinders further milling. It can be seen fromTable 1 that increasing the duration of milling from 30 to 60 min practically does not lead to a decrease in particle size. Apparently, this is explained by work hardening of the particles. Increasing the rotation frequency leads to centrifugal forces and the kinetic energy of grinding media building up that results in the above milling processes getting intensifi ed. In particular, aggregation leading to large particle sizes mounts. Due to this, an increase in the carrier rotation frequency (from 800 to 1,000 RPM) does not give any positive effect. Effect of mechanical activation of tungsten on the structure of sintered Sn-Cu-Co-W materials Figure 3 shows the microstructure of two kinds of sintered materials: ones with tungsten not exposed to mechanical activation and ones with mechanically activated tungsten. Phase composition of the materials containing non-activated tungsten and its crystallization mechanism are described in works [3, 21]. After sintering, the materials contain the following phases: solid solution of tin and cobalt in copper (Cu), the Cu3Sn intermetallic compound, cobalt particles, and tungsten particles. Sintering of the materials at 820 °C proceeded with a large quantity of the liquid phase forming. Upon cooling after sintering, a Cu3Sn compound with a melting point of 755–798 °C was formed from the liquid phase [22]. X-ray microanalysis has shown that in the examined materials, the Cu3Sn intermetallic phase has almost the same composition, % wt.: 63.2 Cu; 33.5 Sn; 3.3 Co.
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