Effect of Process Conditions on the Microstructure and Properties of Supercritical Ni-Gqds Coatings

Abstract

In this study, Ni-GQDs nanocomposite coatings were prepared using a double-pulse electrodeposition process with graphene quantum dots (GQDs) as the second-phase additive under supercritical CO2 conditions. The effect of different electrodeposition processes and GQDs on the coatings was also investigated by comparing with the Ni-GQDs nanocomposite coatings prepared by the DC electrodeposition process, single-pulse electrodeposition process, and pure Ni coatings prepared using double-pulse electrodeposition process. The results show that the Ni-GQDs nanocomposite coatings prepared by double-pulse electrodeposition process under supercritical CO2 conditions with GQDs as the second phase additive are more excellent. The composite coatings layer has a flat surface, dense organization, fewer defects of GQDs in the coating layer, and higher quality. Compared to the pure Ni coating, the composite coating has a smaller grain size of 4.58 nm, a significant reduction of 33.4%. The hardness is higher at 867.2 HV, a significant increase of 11.4%. Roughness is lower at 0.236 μm, a significant reduction of 44.9%. Lower coefficient of friction and volumetric wear of 0.26 and 3.395×107 µm3, respectively, a significant reduction of 41% and 27.6%, respectively. The self-corrosion voltage of the composite coatings was higher at -139 mV, a significant increase of 30.5%. The self-corrosion current density was smaller at 3.19×10-7 A/cm2, which was significantly reduced by 82.9%. The Rct value was 31594.53 Ω·cm2 and the Ndl value was 0.862, which significantly increased by 51.7% and 9.7%, respectively. It shows that the Ni-GQDs nanocomposite coatings have excellent mechanical properties and corrosion resistance.

Keywords: Supercritical CO2, Graphene quantum dots (GQDs), Double-pulse electrodeposition, Microstructure, Mechanical properties, Corrosion resistance