Microstructural Evolution and Tribological Properties of Electroless Ni-P-B and Ni-P-B-W Polyalloy Coatings

Despite extensive research on Ni-P, Ni-B, and Ni-W systems, the combined Ni-P-B-W quaternary system has not been systematically examined under identical bath conditions, representing a significant gap in literature. In this study, sodium tungstate (Na2WO4) was added to a ternary Ni-P-B coating to investigate the effect of W on the tribological properties of an electroless ternary Ni-P-B polyalloy coating. All coatings' surface morphology, phase structure, hardness, and tribological properties were examined and compared while keeping the Ni-P-B and Ni-P-B-W bath parameters (pH, temperature, and deposition time) constant. The surface morphology of the Ni-P-B coating was transformed from spherical nodular to clear-shaped with the addition of W. All types of coatings resulted in a combination of amorphous and crystalline phases. The ternary Ni-P-B coating exhibited a higher hardness compared to the quaternary Ni-P-B-W coating, attaining a value of approximately 655±10 HV0.025. Dry reciprocating wear tests carried out against Al2O3 balls demonstrated that the quaternary Ni-P-B-W coating achieved up to a 31 % reduction in the friction coefficient and up to a 91 % reduction in specific wear rate compared to the ternary Ni-P-B coating.