Establishing relationships between electrodeposition techniques, microstructure and properties of nanocrystalline Co–W alloy coatings

Nanocrystalline cobalt–tungsten (Co–W) alloy coatings with varying microstructures were produced by different electrodeposition techniques. The properties, including hardness, friction and wear behavior, and the resistance to electrochemical corrosion, of the nanocrystalline Co–W alloy coatings are strongly dependent on their microstructures and compositions that are determined by the electrodeposition techniques used. The hardness of the coatings increases with decreasing average crystallite size and increasing W content in alloy. The increasing W content and decreasing surface roughness favor the improvement of the resistance to corrosion for Co–W alloy coatings. The tribological properties and the corresponding wear mechanisms of the coatings are closely related to their hardness and microstructures. The wear rates of the coatings are in accordance with Archard’s law at high applied load of 10.0 N, that is, their wear rates are linearly proportional to the inverse hardness. However, the surface roughness and morphology of the coatings greatly affect this accordance at the low load of 5.0 N. In general, various pulse electrodepositions is better than the direct current (DC) plating to produce Co–W alloy coatings with smaller crystallite size, higher hardness and the improved wear resistance. The nanocrystalline Co–W alloy coating produced by the bipolar pulse electrodeposition has the highest hardness and the best resistance to wear and corrosion. Finally, the electrodeposition mechanisms involved in these electrodeposition techniques are explained and account for the differences in the microstructure and the properties for these deposits.

► Nanocrystalline Co–W alloy coatings are synthesized by four electrodeposition techniques.
► Relationships between electrodeposition techniques, microstructure and properties established.
► Pulse electrodepositions are better than DC plating to improve the structure and properties.
► Bipolar pulse electrodeposition gives high hardness and resistance to wear and corrosion.
► The electrodeposition mechanism involved in these electrodeposition process are explained.