Comparison microstructure and sliding wear properties of nickel–cobalt/CNT composite coatings by DC, PC and PRC current electrodeposition

Abstract

Nickel–cobalt (Ni–Co) alloys and Ni–Co/multiwalled carbon nanotube (MWCNT) composite coatings were prepared under direct current (DC), pulse current (PC) and pulse reverse current (PRC) methods. The effect of different deposition currents on the surface microstructure, crystallographic structure, microhardness, and reciprocating sliding wear behavior were investigated. MWCNT co-deposition caused to modify Ni–Co surface morphology, decrease in grain size, and increase in surface roughness, since MWCNTs effected the deposition mechanisms of Ni–Co alloy. The nanocomposite coatings deposited using PC and PRC deposition exhibited significant improvement in microhardness and wear resistance due to unique enhanced reinforcement of MWCNTs in Ni–Co coatings. Reciprocating sliding wear tests evidenced that co-deposition of MWCNTs provided effective load bearing ability and self-lubrication between the friction surfaces. However, the friction coefficient increases for all the nanocomposites produced with DC, PC and PRC methods showed to be increased. In the Ni–Co alloy coatings, the predominant wear mechanisms was delamination caused by fatigue micro cracking whereas in the MWCNT co-deposited composites wear mechanism showed abrasive grooves and plastic deformation due to decreased real contact area.