Effect of CNTs concentration on the microstructure and friction behavior of Ni-GO-CNTs composite coatings

A kind of novel anti-wear and self-lubricating Ni-GO-CNTs composite coatings were deposited on the surface of AZ91D magnesium alloys substrates by an integrative method involved electrophoresis and electrodeposition with various CNTs (carbon nanotubes) concentration. The surface and cross-sectional morphologies of Ni-GO-CNTs composite coatings were studied by scanning electron microscope equipped with an energy dispersive spectroscope. The micro-indentation hardness as well as friction and tribological properties of Ni-GO-CNTs composite coatings were tested by micro-hardness tester, friction and wear tester separately. Results showed that the Ni-GO-CNTs composite coatings prepared successfully were strongly combined with the copper coating and the magnesium alloys substrates. The maximal micro-indentation hardness value of Ni-GO-CNTs composite coating was obtained with 0.04 g/L CNTs added. The wear resistance of Ni-GO-CNTs composite coating increased initially and then decreased with increasing the CNTs concentration. When the concentration of CNTs was 0.04 g/L, the friction coefficient and wear capacity of the composite coating exhibited the minimum value, which is mainly due to the cross-linking effect of CNTs and GO (graphene oxide) that enhanced the physicochemical properties of the CNTs and GO, indicating better mechanical properties of Ni-GO-CNTs coating.