The effect of reduced graphene oxide concentration on the wear behaviour of reduced graphene oxide–nickel–boron (Ni–B–rGO) electroless coatings

In this article, the electroless nickel-boron coatings containing different rGO concentrations (0,6, 20.5, 35 and 40 mg/L) were deposited on AISI 4140 steel. Their structural properties were examined using X-ray diffraction, Raman spectroscopy, infrared spectroscopy, scanning electron microscopy and hardness analysis. Moreover, their friction coefficient and wear properties were studied using a pin-on-disc test. The results showed that as the rGO concentration increased, the structure of the coating changed from amorphous to semi-crystalline. Adding rGO up to 20.5 mg/L increased the hardness of the as-plated NiB coating from 519 to 863 Hv and reduced its specific wear rate from 1.28 × 10 −9 to 0.68 × 10 −9 kg/Nm. However, increasing the rGO concentration to 40 mg/L led to rGO agglomeration and increased the specific wear rate of the coating.