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

摘要

The nanocrystalline Co-W alloy coatings were produced by dual-pulse electrodeposition from aqueous bath with cobalt sulfate and sodium tungstate (Na_2WO_4). Influence of the current density and Na_2WO_4 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 (100) 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.