Synergistic strengthening and solid-lubrication effects of hydroxyl-functionalized boron nitride nanosheets in Ni-Mo composite coatings

Abstract In the present work, hydroxyl-functionalized boron nitride nanosheets (BNNS-OH) synthesized via alkaline-assisted high-energy ball milling were co-electrodeposited into Ni-Mo alloy coatings to examine their effects on grain refinement, hardness, friction coefficient, and wear resistance. Ni-Mo/BNNS-OH composite coatings with BNNS-OH contents ranging from 0 to 0.5 g l −1 were produced using direct current electrodeposition. It was observed that the incorporation of BNNS-OH refined the grain structure, increased nucleation density, and promoted a uniform nanosheet distribution within the Ni-Mo matrix. At an optimal loading of 0.3 g l −1 , the composite coating achieved a microhardness of 523.69 ± 9.86 HV, a stable friction coefficient of 0.28–0.35, and a reduced wear rate of 8.72 × 10 −6 mm 3 /Nm, outperforming pristine Ni-Mo. The performance enhancements were rationalized by synergistic contributions of microstructural strengthening and solid-lubrication effects. Excessive BNNS-OH content led to nanosheet agglomeration and a subsequent decline in mechanical and tribological properties. These findings highlight BNNS-OH as a promising reinforcement strategy for developing environmentally benign, high-durability coatings for advanced tribological applications.