Plasma-electrolytic synthesis of nanostructured graphene-containing composite coatings on D16 alloy

The influence of graphene nanoparticles on the physical and tribological properties of nanostructured composite coatings under plasma electrolytic oxidation (PEO) of aluminium alloy D16 in electrolytes with additives of graphene nanoparticles and graphene oxide was investigated. The structure of the coatings was analysed using micro-Raman spectroscopy with an excitation laser wavelength of 473 nm , along with optical and electron microscopy techniques. An abrasive wear test was conducted on a Calowear (CAW) machine using an aqueous diamond suspension as the abrasive. It was found that, the abrasive wear rate of the PEO coating with graphene nanoparticles is 15 –16 % lower than that of the PEO coating without additives. The micro-Raman spectroscopy showed significant differences in the structure of carbon nanoparticles in the upper soft and the following hard layer of the PEO coating. In the upper layer of the coating, the Raman spectra are close to those for graphene additives in the electrolyte. The micro-Raman spectra for the following hard layer indicate a significant disorder of graphene particles, a decrease in their size and the formation of SiC and carbon nanotubes inclusions. The micro-Raman spectroscopy shows amorphous structure of the top layer and crystalline α-Al2O3 inclusions in the following hard layer of the coatings. The found regularities explained within the framework on the significant influence of GNP particles on the PEO process.