Electrochemical co-deposition of tungsten with cobalt and copper: Peculiarities of binary and ternary alloys coatings formation

Binary Cu-W, Co-W and ternary Co-Cu-W alloy coatings were electrochemically deposited onto stainless steel substrate from a citrate-borate electrolyte under potentiostatic mode at 20 and 60 °C. The cathodic polarization, current efficiency of co-deposition, chemical composition and structure of the prepared alloys as a function of deposition potential and temperature were studied and compared to those of binary Cu-W and Co-W alloys. All deposits were of uniform thickness, without cracks and well adhered to the substrate. The cathodic current efficiency increases with the bath temperature and cathodic deposition potential increase. The polarization studies revealed that Cu-W alloy deposition starts at more negative potentials than those of Co-W and Co-Cu-W that leads to the lowest current efficiency for Cu-W (20%) in comparison with up to ~ 90% obtained for Co-Cu-W and Co-W alloys electrodeposition. Also, this results in the low W content in the Cu-W coatings (< 6 at.%) that strongly depends on deposition potential and bath temperature. The morphology of deposited coatings depended rather on electrodeposition conditions than on W content in the alloys. X-ray diffraction analysis indicated that Cu-W alloy is a solid solution with typical Cu-type face centered cubic (fcc) lattice. Introduction of Co into this alloy resulted in the formation of additional hexagonal (hpc) Co XRD patterns for ternary Co-Cu-W alloy.