Microstructure and tribological property of nanocrystalline Co-W alloy coating produced by dual-pulse electrodeposition

The nanocrystalline Co-W alloy coatings were produced by dual-pulse electrodeposition from aqueous bath with cobalt sulfate and sodium tungstate (Na2WO4). Influence of the current density and Na2WO4 concentration in bath on the microstructure, morphology and hardness of the Co-W alloy coatings were investigated using an X-ray diffraction, a scanning electronic microscope and a Vickers hardness tester, respectively. In addition, the friction and wear properties of the Co-W alloy coating electrodeposited under different condition were evaluated with a ball-on-disk UMT-3MT tribometer. The correlation between the electrodeposition condition, the microstructure and alloy composition, and the hardness and tribological properties of the deposited Co-W alloy coatings were discussed in detail. The results showed that the microhardness of the deposited Co-W alloy coating was significantly affected by its average grain size, W content and crystal orientation. Smaller grain size, higher W content and strong hcp (1 0 0) orientation favor the improvement of the hardness for Co-W alloy coatings. The deposited Co-W alloy coating could obtain the maximum microhardness over 1000 kgf mm(-2) by careful control of the electrodeposition conditions. The tribological properties of the electrodeposited Co-W alloy coating were greatly affected by its grain size, microhardness, surface morphologies and composition, and could be significantly improved by optimizing the electrodeposition condition. (C) 2012 Elsevier B.V. All rights reserved.