The Preparation Of Inorganic Fullerene-like Molybdenum Disulfide And Its Friction And Wear Performance Of Composite Coatings

Upon the application background of solid lubricants and wear resistant materials, the synthesis of inorganic fullerene-like MoS₂ as a solid lubricant, the preparation and tribological properties of Ni-P-(IF-MoS2) composite coatings on medium carbon steel substrates were investigated. The formation mechanism of IF-MoS₂ was discussed and the effects of IF-MoS₂ on the friction and wear properties were also evaluated.Amorphous MoS₃ precursor was prepared by precipitation method with addition of polyethylene glycol (PEG) as surface dispersant agent, and then IF-MoS₂ nanoparticles were obtained by desulphurizing the precursor in a mixed gas of hydrogen-argon at 900°C for 8h. The as-prepared IF-MoS₂ nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and particle size analyzer. The formation mechanism of IF-MoS₂ was discussed including the influence of the surface dispersant agent, the temperature and the holding time. It can be found that addition of PEG could disperse the precursor and prevent the agglomeration of MoS₂ nanoparticles during desulphurizing. The average diameter of MoS₂ decreased with increasing the mass of PEG With increasing the desulphurizing temperature and prolonging the time, the crystallization of MoS₂ particles went better while the size and the morphology of the particles remained unchanged. However, when it was overheated, most of the spherical particles changed to layered structures.Ni-P-(IF-MoS2) composite coatings were deposited on medium carbon steel substrate by electroless plating and then treated at 400°C for 2h. Microstructure of the composite coatings before and after treatment was identified by X-ray diffraction (XRD) and the surface morphology of the composite coatings was characterized by scanning electron microscopy (SEM). The thickness and the mass of composite coatings were measured by optical microscope and electronic balance and by comparing with the density of Ni-P coating the volume fractions of IF-MoS₂ in the composite coatings were calculated. It can be found that the plating speed and the volume fraction of IF-MoS₂ in the composite coatings increased with increasing the concentration of IF-MoS₂ nanoparticles in the plating bath. After annealing the microstructure of the coatings changed from amorphous feature to crystalline nickel and Ni₃P phase was formed. The surface of the composite coating was relatively smooth and IF-MoS₂ nanoparticles appeared well dispersed and were embedded in the nickelmatrix.Microhardness of the composite coatings and the adhering force with the substrates have been determined with Vickers hardness indenter and scratch tester. The results indicated that Ni-P-(IF-MoS2) composite coatings revealed high microhardness and the hardness increased with increasing the volume fractions of IF-M0S2 nanoparticles, and the composite coatings adhered well to the substrates. Friction and wear properties of the coatings were investigated using pin-on-disk and ball-on-disk wear testers, respectively, and the morphology of the worn surfaces was characterized by scanning electron microscopy (SEM). The friction coefficients of the composite coatings were low. The wear rate and the friction coefficient of the composite coatings showed a steadily decreasing trend with increasing the volume fraction of IF-M0S2. The favorable effects of IF-M0S2 on wear resistance and antifriction are attributed to their unique fullerene-like structure. Ni-P-(IF-MoS2) composite coatings also exhibited good tribological properties both in humid air and vacuum, implying the good stability of IF-M0S2 in different environments.