Ternary alloys of cobalt with molybdenum and tungsten deposited from biligand citrate-pyrophosphate electrolyte by pulsed mode exhibit different compositions and surface morphologies depending on current density and on/off time. The structure of binary and ternary alloys was found to be amorphous crystalline, and intermetallic phases Co7W6 and Co7Mo3 were identified in deposits. The coherent-scattering region size of the amorphous part was detected of 2–8 nm. The amorphous structure of ternary alloys and significant content of alloying elements (Mo and W) predetermine improved high corrosion resistance. Corrosion resistance of binary and ternary deposits increases with total content of refractory metals, which associated with molybdenum and tungsten, enhancing corrosion resistance to pitting as well as decreasing in roughness and smoothing out the relief of ternary coatings. Ternary galvanic alloys of cobalt with molybdenum and zirconium with micro-globular morphology with low level of stress and cracks are formed at a current density of 4–6 A dm−2 and polarization on/off time 2/10 ms. High corrosion resistance of ternary coatings based on cobalt is caused by the increased tendency to passivity and high resistance to pitting corrosion in the presence of molybdenum and zirconium, as well as the acid nature of their oxides.
Part of the book: Applied Surface Science