Abstract
The influence of electrolysis regimes on the composition and morphology of the surface of binary Co (Fe)-W and ternary Fe-Co-W alloys has been established. It has been proven that coatings with binary alloys deposited in a pulse mode are distinguished by a more uniform distribution of components over the surface, a lower oxygen content and globular morphology. This is explained by the peculiarities of electrocrystallization of alloys under non-stationary electrolysis conditions: during a pulse, Fe3+ is reduced to Fe2+, tungstates to oxides of tungsten in an intermediate oxidation state. During the pause, the processes of adsorption of reagents, the reduction of Fe2+ to the metallic state, the chemical reduction of intermediate tungsten oxides by hydrogen atoms and the chemical reaction of ligand release are realized. The use of pulsed current allows precipitating Fe-Co-W ternary coatings with a more uniform surface and extends the range of the content of the refractory component in the alloy, and the process current efficiency rises almost twice to 70–75 % compared to galvanostatic. By the phase composition, binary coatings are shown to be solid solutions of tungsten in α-Fe or α-Co, while the ternary Fe-Co-W is amorphous-crystalline and contains the phases of Co7W6 and Fe7W6 intermetallic compounds, as well as α-Fe and Fe3C cementite. The possibility of controlling the composition and morphology of the surface of tungsten-containing coatings with iron and / or cobalt using various modes and parameters of electrolysis – direct and pulsed current with varying current density, pulse / pause duration has been proved. Pulsed electrolysis contributes to the increase in the content of the refractory component and the efficiency of electrolysis. Electrolytic alloys surpass the base of steel in microhardness by a factor of 3–4, and an increase in the content of tungsten provides an increase in mechanical characteristics due to the formation of intermetallic compounds and an amorphous structure of coatings. In terms of coating performance, Co(Fe)-W and Fe-Co-W alloys can be effectively used to strengthen surfaces made of steel and cast iron, as well as in repair technologies for restoring worn parts with giving the surface enhanced physical and mechanical properties.