Electrodeposition of nanocrystalline chromium-carbon alloys from electrolyte based on trivalent chromium sulfate using pulsed current

The effect of the parameters of pulsed electrolysis on the current efficiency, nanocrystal size, composition, hardness, friction coefficient, and wear resistance of nanocrystalline Cr-C coatings obtained from electrolyte based on Cr(III) sulfate containing carbamide and formic acid is studied. It is shown that coatings contain ∼9 wt % of carbon; the current density and pulse ratio produce practically no effect on their composition. It is found that a maximum appears on the dependence of current efficiency on pulse ratio in the case of the pulse ratio of ∼1.05–1.1. Thereby, current efficiency greatly exceeds the value implemented in the steady-state current mode. It is shown that, if the microhardness of Cr-C deposits obtained at constant current is close to 850–900 HV, the microhardness may increase to ∼1200−300 HV when pulsed electrolysis is used in certain modes. It is found that application of pulsed electrolysis allows a significant decrease in the friction coefficient of chromium-carbon coating (steel counterbody) both under the dry friction conditions and in the case of boundary lubrication and also results in an increase in the deposit wear resistance.