Structure and micro-journal bearing working life of electroless Ni–P plating by varying pH value, ultrasonic assistance

Abstract Ni–P coatings were electroless deposited on brass substrates at various pH levels (ranging from pH 4 to pH 9) with ultrasonic assistance (20 to 40 kHz). The study analyzed the coatings' morphology, microstructure, hardness, corrosion resistance, fatigue life, and the working life of micro-journal bearings. XRD and TEM analyses confirmed that the Ni–P coating had a non-crystalline structure. XPS was employed to study the bonding states and chemical composition of the coating. As the pH increased, the deposition rate rose (film thickness increasing from 0.84 μm to 1.10 μm after 10 min of plating), and the phosphorus content decreases, indicating that the Ni–P coating became denser, thereby improving surface morphology and mechanical properties. Ultrasound-assisted electroless plating enhanced ion movement and mass transfer effects, resulting in a denser coating and improved the coating film's surface properties. The coating's mechanical features, wear, and corrosion resistance were enhanced. The hardness, corrosion potential, and fatigue life increased from 6.25 to 8.43 GPa, –0.524 to –0.250 V SCE , and 111.3 to 130.5 cycles, respectively. Additionally, the wear rate and micro-journal bearing wear decreased from 1.88 × 10⁻⁶ to 1.50 × 10⁻⁶ g/m and from 1.53 to 0.95 mg, respectively.