Characterizations of nanocrystalline Co and Co/MWCNT coatings produced by different electrodeposition techniques

Nanocrystalline cobalt (Co) and cobalt/multi-walled carbon nanotube (Co/MWCNT) coatings were synthesized by direct current (DC) and pulse reverse current (PRC) electrodeposition from aqueous bath containing cobalt sulfate and MWCNTs, etc. Effect of the functionalization of MWCNTs and electrodeposition techniques, i.e. DC and PRC, on the microstructure and properties of these coatings was evaluated. The results show that the incorporations of MWCNTs, particularly the functionalized MWCNTs, substantially improve the hardness and the resistance to wear and corrosion of the deposited coatings. PRC electrodeposition produces Co and Co/MWCNT coatings that are featured by small grain size, low surface roughness and more uniform distribution of MWCNTs in matrix, and consequently display the higher hardness and better resistance to wear and corrosion. The functionalization of MWCNTs favors the co-deposition of MWCNTs with Co ions, and then improves the hardness and the corrosion and wear resistance of the produced composite coatings. Among all samples, the composite coating incorporated with functionalized MWCNTs produced by PRC electrodeposition has the highest hardness around 1180 kgf.mm(-2) and the best resistance to wear and corrosion. The differences in friction and wear behavior of these nanocrystalline Co and Co/MWCNT coatings as a function of treatment of MWCNTs or electrodeposition techniques are attributed to their different hardness, microstructures and the corresponding wear mechanisms. (c) 2012 Elsevier B.V. All rights reserved.