Tribological behaviour of electrodeposited cobalt–tungsten coatings: dependence on current parameters.

The tribological behaviour of cobalt–tungsten alloy coatings electrodeposited under direct or pulse current mode from a cobalt sulphate–sodium tungstate bath was investigated. At a low average current density of 05 A dm^–2 the coatings contain a low amount of tungsten that leads to a milky appearance of the coatings. These coatings have a high roughness, a low hardness, and exhibit a high coefficient of friction and a high wear in sliding tests against corundum. In contrast, cobalt–tungsten coatings deposited at a higher average current density of 1 A dm^–2 also have a milky appearance but exhibit tribological properties comparable to the ones of electrodeposited hard chromium and physical vapour deposited TiN. [ABSTRACT FROM AUTHOR]