Quick and easy process for producing graphene material in liquid phase using high-power-density ultrasonication technique for preparing high microhardness nickel/graphene composite coating

In this paper, we present a rapid and straightforward method for producing graphene material in the liquid phase using a high-power-density ultrasonication technique. The graphene exfoliation process was considered with varying ultrasonication times, ranging from 1 to 5 h. The obtained results indicated that graphene nanoflakes, exfoliated under a power density of 1600 W/L for a short duration (5 h), exhibited a thickness of fewer than 10 layers, with an average flake size of ~ 300 nm. The production yield measured 30.6 mg h⁻¹, and the dispersed concentration reached 0.459 mg ml⁻¹. Furthermore, the exfoliated graphene nanoflakes displayed remarkable stability, as evidenced by a zeta potential value exceeding 30 mV. The resulting graphene material was used directly as a reinforcing element in nickel electroplating without the need for any additional surface modification steps. The results demonstrated a significant 53% increase in microhardness compared to the nickel coating. Structural characterizations of the few-layers graphene and nanocomposite coatings were elaborately investigated and presented.