Microstructural and tribological characterization of Ni–P coatings reinforced with functionalized ZnO nanoparticles

Purpose This study aims to explore the effect of incorporating both normalized zinc oxide (n-ZnO) and functionalized zinc oxide (f-ZnO) nanoparticles into Ni–P matrices to enhance the mechanical and tribological performance. Design/methodology/approach Functionalized ZnO particles were chemically treated to improve their dispersion and interfacial bonding within the Ni–P matrix. Composite coatings were synthesized through electroless deposition on EN31 steel, with varying ZnO concentrations (0.1–0.5 g/l) and post-deposition heat treatments (250–550°C). X-ray diffraction, transmission electron microscopy and scanning electron microscopy analyses were performed to evaluate the structural integrity, particle dispersion and surface morphology of the Ni–P composite coatings. Tribological testing was conducted using a pin-on-disc tribometer to assess the wear rate and coefficient of friction under dry sliding conditions. Findings Morphological techniques confirmed phase formation, nanoparticle distribution and coating uniformity essential for enhanced mechanical and tribological properties. Tribological testing indicated that coatings reinforced with f-ZnO performed better than those with n-ZnO across all concentrations. The optimal condition was 0.3 g/l f-ZnO with a 450°C heat treatment, which achieved the lowest wear rate and coefficient of friction, attributed to the formation of a stable tribolayer and effective load distribution. The mechanical property through Vickers microhardness results also peaked under this condition at 574 HV, reflecting the combined effect of refined grain structure and strong matrix–reinforcement bonding. Originality/value The main contribution of the work is to improve the mechanical and wear characteristics of Ni–P coatings by f-ZnO and making them suitable for applications where enhanced durability is required.