We have studied the solubility at 1200°C of tungsten in Cu − Co melts and the growth kinetics of a W 6 Co 7 layer at the tungsten − melt interface. We have established the composition of the melt in the three-phase equilibrium tungsten − W 6 Co 7 − melt: 0.0195 Co, 4.8 ⋅ 10 −5 W, the rest is Cu (in atomic fractions). In the studied composition range for the melt, the solubility of tungsten is described well by the expression: lgX W = −7.117 + 25.7 ⋅ X Co 1/2 − 41.06 ⋅ X Co , where X W and X Co are the atomic fractions of the corresponding elements in the melt. We have determined the correlation between the growth rate for a layer of tungsten-containing phase at the tungsten − melt interface and the thermodynamic characteristics of the melt.The Cu − W system is used as a model system for studying the characteristics of processes occurring during liquid-phase formation of composite materials, in particular for studying the characteristics of the effect of small additions of a third component on compaction and structurizing processes. However, if the third component can form a new phase with tungsten at the temperature at which the material is formed, then to study such an effect we need to know the characteristics of the corresponding three-phase equilibrium and the growth kinetics of this phase. Using cobalt as the additive to tungsten-copper materials was suggested rather long ago in [1,2]. At their formation temperature (1200°C), formation of one intermediate phase is possible in the system: W 6 Co 7 [3]. So the aim of this work was to determine the composition of the liquid phase in the three-phase equilibrium tungsten − liquid phase − W 6 Co 7 and to study the growth kinetics of the phase W 6 Co 7 as a function of the cobalt content in the melt at 1200°C. The experimental procedure is described in detail in [4]. The starting materials were electrolytic cobalt (99.98% Co), monocrystalline tungsten (99.998% W) in the form of rods of diameter 10 mm, tungsten foil of thickness 20 μm (99.9% W), and copper (99.99% Cu). The solubility of tungsten in Cu − Co melts was determined under a vacuum of (2-4) ⋅ 10 −3 Pa: the tungsten specimens were immersed in the Co − Cu melt (120 g) of the specified composition (Table 1), and were removed from the melt after isothermal holding (up to 20 h) at 1200°C. The ratio of the surface area of the specimens to the volume of the melt was 1-0.6 cm −1 . According to previous experiments in [5], the indicated conditions ensure practically complete saturation of the melt with tungsten. To remove the Co − Cu melt from the surface of the specimens, they were transferred to a pure copper melt (120 g, 1200°C, 1 h). When the specimens were treated in this manner, the layer of W 6 Co 7 phase decomposed and was converted to a layer of tungsten sponge impregnated with copper. The copper was dissolved in nitric acid, and then the tungsten sponge was easily removed from the specimens by wiping with a cotton pad. The specimens were weighed and the solubility of tungsten in the Co − Cu melts was ca...

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Growth kinetics for a layer of W 6 Co 7 at the interfaces tungsten-cobalt and tungsten-melts based on copper and tin containing cobalt at 1200°C are studied. It is established that rate constant for growth of this layer in the system with participation of tin (k Sn ) is much greater than in the system with copper (k Cu ). Dependences are determined for these constants on cobalt activity in the melt (a Co ): k Cu (m 2 /sec) = = 1.72 ⋅ 10 -15 (a Co − 0.221) + 2.99 ⋅ 10 -14 (a Co − 0.221) 2 ; k Sn (m 2 /sec) = 1.8 ⋅ 10 -14 (a Co − 0.221) + + 9.077 ⋅ 10 -12 (a Co − 0.221) 3 .