Effects of processing parameters on phase, morphology, mechanical and corrosion properties of W-Cu nanocomposite powder prepared by electroless copper plating

Because of excellent physical properties and wide range of applications in electrodes, electrical connections, microelectronic packaging, and heating mineral, Tungsten-copper (W-Cu) composite powders have been significantly remarkable. The substantial differences in the density and lack of fusion of copper and tungsten in both solid and liquid phases, led to occur some problems in W-Cu composite powders. Among the various methods of preparing tungsten-copper composites, the electroless plating process is one of the conventional methods as it is easy to use, efficient, and inexpensive. In this paper, the copper electrolyte solution containing copper sulfate as the main salt, formaldehyde as the reducing agent, sodium ethylene diamine tetra-acetate as the sophisticated agent, has been employed in the electroless copper plating process of tungsten powder. The effects of main parameters of electroless copper plating including NaOH concentration, time and operating temperature, and pre-activation of tungsten powder on the amount of deposited copper layer were investigated. Then, the phase behavior, morphology, mechanical, and corrosion behavior were evaluated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy(EDS), Vickers hardness tester, and electrochemical impedance spectroscopy (EIS), respectively. Results demonstrated an improvement in the morphology and amount of the copper, which was deposited on the surface of the activated tungsten powder. Indeed, the defects formed on the surface of the tungsten powder increased the sites for nucleation and growth of copper particles. In agreement with the Fick's 2nd law, the maximum deposition rate of 7.9 vol% was obtained at 14 g/l NaOH, 100 degrees C and processing time of 90 min, with a (111) orientation on the activated tungsten powder surface. The higher capacitance and the charge transfer resistance along with the highest n(dl)at the 14 g/l NaOH concentration demonstrated the homogeneity and integrity of W-Cu composite, the lowest hardness of 149.0 +/- 2.8 Hv and a compressive strength of 187 +/- 11 MPa.