Microstructural Evaluation of Graphene-Reinforced Nickel Matrix Ni-P-Gr Coating on Ti-6Al-4V Alloy by the Electroless Coating Method

Abstract

Titanium alloys are widely used in many industrial applications, from aerospace to automotive, and from defense to medical, as they combine superior properties such as high strength and low density. Still, titanium and its alloys are insufficient in environments with friction and wear because of their weak tribological properties. In the literature, numerous research works on improving the surface quality of titanium alloys have been conducted. Electroless coatings, on the other hand, are one of the most widely used surface improvement methods due to its homogeneous thickness achievement, high hardness, and good corrosion resistance. The autocatalytic reduction in the coating process enhances the surface quality of the material or alloy considerably. In addition, many studies in the literature aim to carry the properties of electroless coatings to a higher point by creating a composite coating with the addition of extra particles. In this study, graphene-reinforced nickel matrix Ni-P-Gr coating was applied to the surface of Ti-6Al-4V alloy, in order to enhance weak tribological behaviors, by the electroless coating method. Moreover, the coated and uncoated, heat-treated, and non-heat-treated specimens were subjected to abrasion in linear reciprocating ball-on-plate configuration to observe tribological properties. Microstructure examination of the samples was performed using a scanning Electron Microscope (SEM), X-ray Diffractometer (XRD), X-ray Photon Spectrometry (XPS), and Raman Spectroscopy. Specific wear rates of specimens were calculated using microstructural analysis and the hardness of the produced samples was measured using the Vickers hardness test. Results indicate that both the coating and the heat treatment improved the microstructure and tribological properties significantly. With the graphene-reinforced Ni-P coating via electroless coating process, the hardness of the substrate increased by about 34%, while it increased by approximately 73% using subjected heat treatment. Furthermore, the wear rate of the Ti-6Al-4V substrate was approximately 98% higher than that of the heat-treated nanocomposite coating. The highest wear resistance was obtained at the heat-treated nanocomposite coating.