Twin-rich Ag coatings by additive rotary spray deposition manufacturing: Current-carrying friction machining to construct nanolamellar structures

In this study, a self-developed additive manufacturing technique, known as rotary spray deposition, was employed to uniformly deposit twin-rich Ag coatings onto Cu surfaces. The impact of the key deposition parameters, including spray distance, flow rate, and duration, on the surface morphology and thickness of the Ag coatings was meticulously investigated to achieve exceptionally high-quality coatings. These coatings exhibited a low resistivity of 1.711 × 10⁻⁸ Ω m and a high hardness of 145 HV, which was attributable to the high-density twins and stacking faults (SFs) induced by the rotary spray deposition process. Subsequently, nanolamellar structures were produced on the trilayers under extreme machining conditions of current-carrying friction, aided by the use of lubricating oil (polyalphaolefin). The tribological behavior and wear mechanisms of the Ag coatings were systematically examined to determine the optimal load and current parameters for the effective formation of nanolamellar structures within the optimally worn subsurface microstructures. The primary formation mechanism was identified as sliding-induced dynamic deformation, characterized by high strain rates and strain gradients during the current-carrying friction machining process. Moreover, the nanolamellar structures demonstrated a remarkable ability to absorb the stress and strain arising from the current-carrying friction process, thereby enhancing the wear resistance of the Ag coatings. As a result, this technique is anticipated to pave new pathways for the development of nanolamellar structures and high-strength metallic materials.