Tribological performance of plasma-nitrided self-lubricant electroless Ni-B-graphite composite coatings.

We developed a nickel-boron-graphite (Ni-B-Gr) composite coating with self-lubricating properties and investigated its tribological behavior. We employed an electroless bath to deposit the Ni-B-Gr coatings on AISI 4140 steel. The Ni-B matrix serves as a hard matrix, while graphite (<20 µm) at varying concentrations (0.05 to 0.5 g/L) act as the self-lubricant. We subjected the composite coating to plasma nitriding (PN) at 400 °C for 1 h in a mixture of 25% nitrogen and 75% hydrogen. Our analysis involved microstructural examination, hardness testing, toughness assessment, and tribological evaluations. The PN Ni-B-0.275Gr composite demonstrated a 65% reduction in wear rate and a 25% decrease in coefficient of friction. Furthermore, incorporating graphite altered the wear mechanism, shifting from adhesive to oxidation wear. [Display omitted] • Electroless Ni-B-Gr composite coatings were developed to enhance tribological performance. • Integration of plasma nitriding and graphite improves bonding and wear resistance. • Plasma nitrided Ni-B-0.275Gr coatings exhibit a reduction in wear rate and COF. • Graphite incorporation transforms the wear mechanism by reducing adhesive wear. [ABSTRACT FROM AUTHOR]