Effect of Poly Dimethyl Diallyl Ammonium Chloride‐Multiwalled Carbon Nanotubes Concentration on the Microstructure and Friction Behavior of Co‐Doped Diamond‐Like Carbon Films

A kind of wear‐resistant diamond‐like carbon (DLC) films doped with Ni, N, and multiwalled carbon nanotubes (MWCNTs) are synthesized on Ti–6Al–4V titanium alloy by a combined method of pulsed electrodeposition and liquid‐phase electrodeposition. The effect of different concentrations of MWCNTs on the microstructure and friction mechanism of Co‐DLC films is investigated. The results show that the polydimethyl diallyl ammonium chloride (PDDA)‐MWCNTs complex tend to deposit parallel to the substrate. Benefiting from the “bridging” effect of the MWCNTs between the cluster structures, it effectively reduces the protrusions on the surface of the films. When the concentration of MWCNTs is 0.06 g L⁻¹, the surface microstructure of the films is uniform and dense, and the films present a low I_D/I_G value (0.57) and a high sp³‐C content. The Raman and X‐ray photoelectron spectroscopy patterns reveal that the Ni/N/MWCNTs‐DLC films are typical amorphous carbon films. Furthermore, the micro‐indentation hardness of the Co‐DLC films reaches 513.24 HV. The lubricated Ni/N/MWCNTs‐DLC films significantly improve the frictional wear properties of the titanium alloy surface, which is mainly attributed to the homogeneous and dense structure and the low friction coefficient (0.146) and wear loss (1.40 × 10⁻⁵ kg m⁻¹).