The effect of nitrogen plasma treatment and reduced graphene oxide concentration on wear behavior of Ni-B-rGO electroless coatings

In this article, nickel-boron-reduced graphene oxide (Ni-B-rGO) coatings with concentrations of 0, 6.0, 20.5, and 40 mg of reduced graphene oxide (rGO) were deposited on AISI 4140 steel. Following the electrodeposition process, the samples were nitrogen-plasma treated in an atmosphere containing 25% nitrogen and 75% hydrogen for 120 minutes at a temperature of 400 °C, and their structure and wear behavior were examined. The structural properties of the coatings were investigated using X-ray diffraction tests, scanning electron microscopy and hardness tests. Additionally, the coefficient of friction and wear resistance of the samples were studied using a pin-on-disk tester. The results indicate that increasing the rGO concentration changes the coating structure from an amorphous to a semi-crystalline state, and the addition of rGO increases the hardness and enhances the wear resistance of the coating. Adding rGO up to a concentration of 20.5 mg/L improves the wear resistance and reduces the coefficient of friction. Moreover, the plasma nitrogen treatment leads to the crystallization of the coatings due to the formation of Ni2B, Ni3B, and h-BN phases. Furthermore, a two-hour plasma nitrogen treatment increased the coating hardness from 863 Vickers to 1490 Vickers. The wear resistance of the coatings increased after the plasma nitrogen treatment, resulting in a decrease in the specific wear rate from 0.75 × 10-9 kg/Nm (untreated sample) to 0.24 × 10-9 kg/Nm.