Structure Formation of Cu–W Pseudo Alloys Upon Various Methods of Their Production

This article compares the microstructures of alloys formed upon the sintering of powdered mixtures of tungsten (PV2, average particle size 3.8–6.0 μm) and copper (PMS–11, particle-size fraction 45–60 μm) produced by various methods: the simple mixing of powdered metals, the mechanical activation (MA) of powdered metals, and the deposition of copper from a solution of its sulfate (Cu 2 SO 4 ·5H 2 O) on powdered tungsten with simultaneous mechanical activation. The molar ratio in metals in mixtures is Cu/W = 1. The aqueous solution for copper deposition is comprised of diethylene glycol (up to 30%), glycerol (up to 8%), hydrofluoric acid (up to 0.1%), and the OP-10 wetting agent (up to 0.8%). Mechanical activation is carried out in an AGO-2 planetary mill with a drum load of 200 g of steel balls and a drum rotation speed of 2220 rpm for 5 min. Reduced copper in the solution and in air is rapidly oxidized to Cu 2 O; therefore, the composite powders were washed, dried, and stored in an argon environment. The samples pressed from the powders (tablets with a diameter of 3 mm, height of 1.5–2.0 mm, and density of 7.7–8.0 g/cm 3 ) are sintered in argon at ambient pressure and in a temperature range from 1000 to 1500°C. During the sintering of Cu–W composite particles, it is possible to highlight several regions of the progress of the process. At temperatures below the melting point of copper, solid-phase sintering in the contact points of composite particles occurs. Upon heating from the melting points to 1200°C, the samples from the mixture of powdered metals are sintered according to the liquid-phase mechanism, forming a low porous cake. Sintering of composite powders produced by MA upon copper deposition and the MA of mixtures of powdered metals results in the segregation of samples with the formation of coarse pores extended perpendicularly to the axis of pressing and are partially filled with molten copper. Upon the heating of samples produced by the MA of powders above 1400°C, phase separation occurs and all copper is displaced from the sample to the surface.