Characterization and mechanical behavior of electroless Ni-P and Ni-Co-P plating using ultrasonic-assisted

Brass is widely used in industrial components owing to its excellent machinability and conductivity; however, its relatively low hardness, wear resistance, and corrosion resistance limit its durability in demanding environments. In this study, the incorporation of CoSO₄ (30 g/L) into the Ni-P plating bath to form Ni-Co-P coatings on brass micro-journal bearings with an inner diameter of only 2 mm can enhance mechanical properties and corrosion protection. Electroless plating was selected for its advantage of depositing a uniform coating on complex geometries and micro-scale inner structures. The experimental apparatus includes a plating bath, a constant-temperature heater, a stirring device, and a pH-monitoring and exhaust system. The results confirm that Ni-Co-P coatings exhibit superior performance compared with Ni-P coatings, demonstrating the beneficial effect of Co incorporation. Ultrasonic-assisted electroless plating eliminates hydrogen-bubble accumulation and enhances mass transfer effect via acoustic cavitation, refining the microstructure to yield a denser coating with fewer defects. These findings greatly improve the coating’s hardness, corrosion resistance, and fatigue life, highlighting its significant potential to enhance coating reliability in mechanical and corrosive environments.