Boron carbide (B4C), owing to a combination of desirable properties such as low density, excellent strength, high wear resistance, exceptional hardness, high elastic modulus, and good chemical inertness, has gained attention as a promising option for tribological applications. Accordingly, the aim of this research was to eva‎luate the effects of adding B4C nanoparticles to the Ni-P plating bath, resulting in the deposition of Ni-P-B4C composite coating on ST37 steel substrate. For this purpose, two low and high concentrations (0.5 g/L and 2.5 g/L) of B4C nanoparticles were added to the Ni-P plating bath. Corrosion tests were carried out in 3.5% NaCl solution at room temperature and tribological behaviour was investigated up to a distance of 1000 m under a load of 1.5 kg (critical load) and a speed of 0.14 m/s. In this research, the Schlotter bath (Germany) was used to prepare the Ni-P and Ni-P-B4C plating bath. The results demonstrated that adhesive and compact Ni-P-B4C composite coatings with a uniform morphology were successfully deposited on the steel substrate. The increase in the amount of B4C resulted in a higher percentage of B4C in the Ni-P-B4C composite. In the following, according to previous studies, the coatings were heat-treated at 400 °C for 1 hour under Ar atmosphere in an electric furnace. Findings revealed that all coatings were completely amorphous before the heat treatment. Heat treatment led to the formation of Ni3P in the crystalline Ni matrix. The hardness of the composite coatings was much higher than the Ni-P coating. Furthermore, the effect of heat treatment on the hardness of Ni-P-B4C composite coatings was considerably greater than that of Ni-P coatings. Heat treatment resulted in 100% increase in hardness for Ni-P-2.5B4C coating (2.5 g/L B4C in plating bath) and a 55% increase in hardness for Ni-P coating. Electrochemical measurements showed a substantial improvement in the corrosion resistance of the substrate after the deposition of electroless coatings. Additionally, Ni-P-B4C composite coatings exhibited higher corrosion resistance compared to Ni-P coating due to the inert nature of B4C. By increasing the amount of B4C in the coatings, the corrosion current density decreased. The corrosion current density of Ni-P, Ni-P-0.5B4C (0.5 g/L B4C in plating bath), and Ni-P-2.5B4C (2.5 g/L B4C in plating bath) coatings were 6.42 μA/cm2, 2.15 μA/cm2, and 0.6 μA/cm2, respectively. Tribological eva‎luations of the coatings indicated that by adding B4C, the wear resistance of electroless Ni-P coatings significantly improved, evidenced by a reduction in coefficient of friction (COF) and weight loss. With the increase in B4C concentration, the wear resistance of the coating increased. Overall, compared to the steel substrate, for the Ni-P-2.5B4C coating (2.5 g/L B4C in plating bath), the COF decreased by approximately 34%, and the weight loss decreased by almost 72%. The results of this research suggested that Ni-P-B4C composite electroless coatings can be a promising option for prolonging the lifetime of components exposed to wear and corrosion applications

محمود منير واقفي

علي شفيعي , عبدالمجيد اسلامي