Structure forming of Cu–W pseudoalloys prepared in different routes

Abstract

The microstructures of alloys formed during the sintering of tungsten powder mixtures (PV2, 3.8–6.0 μm average particle size) and copper (PMS-11, 45–60 μm fraction) prepared by various methods were compared. The methods included simple metal powder mixing, mechanical activation (MA) of metal powders, copper precipitation from the solution of its sulfate (CuSO4·5H2O) on tungsten powder with simultaneous mechanical activation. The molar ratio of metals in mixtures Cu/W = 1. An aqueous solution for copper deposition included diethylene glycol (up to 30 %), glycerin (up to 8 %), hydrofluoric acid (up to 0.1 %), wetting agent OP-10 (up to 0.8 %). Mechanical activation was carried out in an AGO-2 planetary mill with 200 g of steel balls charged into the drums rotating at 2220 rpm for 5 min. Reduced copper in the solution and in the air rapidly oxidizes to the Cu2O oxide, so the composite powders obtained were washed, dried, and stored in an argon atmosphere. Samples pressed from the powders obtained (tablets 3 mm in diameter, 1.5–2.0 mm in height with a density of 7.7–8.0 g/cm3) were sintered in argon at atmospheric pressure and temperatures from 1000 to 1500 °C. During the sintering of Cu–W composite particles, several areas of the process can be distinguished. «Solid phase» sintering occurs at the contact points of composite particles at temperatures lower than the copper melting point. When samples are heated from the melting point to 1200 °C, samples are sintered by the liquid-phase mechanism from the conventional mixture of metal powders to form a low-porous cake. When composite powders obtained by MA during the copper deposition and MA of metal powder mixtures are sintered, samples are delaminated with the formation of large pores elongated perpendicular to the pressing axis and partially filled with copper melt. When samples obtained by powder MA are heated above 1400 °C, phase separation occurs and almost all copper is displaced from the sample to the surface.