Friction And Wear Properties Of Nickel-based Carbon Nanotubes Composite Coatings

Upon the application background of solid lubricants and wear resistant materials, the preparation and friction and wear properties of Ni-based CNT composite coatings on steel and aluminum substrates were investigated. And the effects of CNTs on friction and wear properties were also evaluated.Multi-walled carbon nanotubes were synthesized by chemical vapor deposition (CVD). Then the CNTs were purificated by nitric acid and shortened by ball milling. The microstructure of carbon naonotubes was observed using transmission electron microscope (TEM).The Ni-based CNT composite coatings with different volume fraction of CNT were prepared on steel and aluminum by electroless plating and electroplating separately. Then the composite coatings were treated at 400癈 for 1 hour. Microstructure analysis of the composite coatings before and after treated was identified by X-ray diffraction (XRD). It is found that the microstructure changes from amorphous feature to crystalline nickel, and Ni3P phase is formed. The surface morphology of the composite coatings was evaluated using scanning electron microscopy (SEM) and atomic force microscopy. It can be found that the composite coatings revealed a relatively smooth surface morphology and the CNTs appear well dispersed and are embedded in the nickel matrix.Microhardness of the composite coatings have been determined with a Vickers hardness indenter. The conclusion suggested that the volume fraction of CNT in Ni-CNT shows higher than Ni-P-CNT. Ni-based CNT composite coatings revealed a high microhardness and the hardness increases with the increasing volume fraction of carbon nanotubes. Friction and wear properties of the coatings were investigated using a pin-on-disk wear tester under unlubricated condition. It is found that the friction coefficients of the composite coatings were low, and the wear rate and the friction coefficient of the composite coatings showed a steadily decreasing trend with increasing volume fraction of CNTs. Thefavorable effects of CNTs on wear resistance are attribute to their excellent mechanical properties and reinforcement in the composite coating. Therefore, the addition of carbon nanotubes can improve the tribological properties of the Ni-based composite coatings greatly.