UDC 621.762 The tribological and corrosive characteristics of binary and ternary alloys electrodeposited from CoW, FeW, CoMoP, and CoWP citrate solutions are studied. The tungsten content of CoW alloys reaches 31 at.% and of FeW alloys 34 at.%. The introduction of phosphorus into the alloys reduces the content of tungsten from 26.7 to 19.7 at.% (at 4.5 at.% P). The molybdenum content of CoMoP alloys is 0.7-1.0 at.% at 5 to 8 at.% P. The electrolytic tungsten alloys are nanocrystalline and subgrains are 4 to 7 nm in size. The nanohardness of tungsten-rich alloys (∼13 GPa) is comparable with that of electrolytic chromium coatings. The wear resistance of the deposited alloys is quite high and is commensurable with that of hard coatings such as TiB 2 , TiN, and TiAlN. The tribooxidation of FeW alloys in dry friction is revealed. The corrosion resistance of the coatings is similar to that for electrolytic chromium.
A correlation has been found between the composition, structure, and corrosion resistance of electrolytic Co-W coatings (on the basis of voltammeter and impedance measurements at pH-6.0 in a chloridesulfate model solution) deposited at various densities of direct current from citrate electrolyte with a high concentration of sodium tungstate with addition of boric acid at a temperature of 58 ° C. It is found that these coatings possess a high corrosion resistance that is only insignificantly inferior to that of electrolyte chromium coatings. We have determined the interval of current densities of electrodeposition in which corrosion resistance of the coatings is maximum.
The given research was driven by prospects to design Mo-rich coatings with iron group metals electrodeposited from a highly saturated ammonium acetate bath. The obtained coatings could be employed as prominent electrodes for the hydrogen evolution reaction (HER). It was found that the Mo content in Ni–Mo alloys can be tuned from 30 to 78 at.% by decreasing the molar ratio [Ni(II)]:[Mo(VI)] in the electrolyte from 1.0 to 0.25 and increasing the cathodic current density from 30 to 100 mA/cm2. However, dense cracks and pits are formed due to hydrogen evolution at high current densities and that diminishes the catalytic activity of the coating for HER. Accordingly, smoother and crack-free Ni–54 at.% Mo, Co–52 at.% Mo and Fe–54 at.% Mo alloys have been prepared at 30 mA/cm2. Their catalytic behavior for HER has been investigated in a 30 wt.% NaOH solution at temperatures ranging from 25 to 65 °C. A significant improvement of electrocatalytic activity with increasing bath temperature was noticed. The results showed that the sequence of electrocatalytic activity in alkaline media decreases in the following order: Co–52 at.% Mo > Ni–54 at.% Mo > Fe–54 at.% Mo. These peculiarities might be linked with different catalytic behavior of formed intermetallics (and active sites) in electrodeposited alloys. The designed electrodeposited Mo-rich alloys have a higher catalytic activity than Mo and Pt cast metals.
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