Improved Tribological Performance of Co-Au Coatings Prepared by Sequential Chemical Plating Combined with Thermal Diffusion

Friction and wear significantly limit the performance and service life of mechanical components, yet metallic coatings remain essential for electrical and thermal conductivity in applications such as connectors. In this work, Co-Au coatings were fabricated on Ni-P-coated copper substrates via a chemical plating method, followed by thermal diffusion annealing at 350 °C for 1 h. The as-deposited coatings exhibit a continuous granular structure with an Au-rich top layer and a nanocrystalline Co-rich layer beneath, while annealing induces interdiffusion between Au and Co, forming a Co-Au solid solution. This microstructural evolution leads to enhanced hardness, optimized H/E ratio, and improved load-bearing capacity. Tribological tests reveal that annealed Co-Au coatings exhibit a reduced and stable coefficient of friction compared with Co and as-deposited Co-Au coatings under identical test conditions (~0.14), corresponding to a reduction of approximately 77% compared with the as-deposited Co-Au coatings (~0.60). Meanwhile, the wear track width decreases from ~138 μm to ~70 μm, indicating a reduction of about 49%. Corrosion resistance is improved after annealing, as evidenced by lower corrosion current density and a more positive open-circuit potential. The results demonstrate that the combination of chemical plating and thermal diffusion provides an effective strategy to produce structurally stable Co-Au coatings with excellent mechanical, tribological, and corrosion-resistant properties, suitable for complex-shaped conductive components.