Tribological Properties of Tungsten Doped Graphite Coating/Castor Oil Acid Solid Liquid Composite Lubrication System

The solid-liquid composite system composed of tungsten doped graphite like coating and castor oil acid has excellent friction and wear performance, and is expected to be widely used in fields such as rail transit, aerospace, and mechanical equipment. This article used magnetron sputtering technology to prepare tungsten doped graphite like coatings. Field emission scanning electron microscopy was used to analyze and characterize the surface, cross-sectional morphology, and element distribution of the tungsten doped graphite like coating prepared by magnetron sputtering technology. The hardness, elastic modulus and elastic recovery coefficient of the coating were measured using a nanoindentation instrument. The tungsten doped graphite like coating was characterized using a Raman spectrometer to observe whether it had typical GLC characteristics. The friction and wear performance of the coating was evaluated using a CSM friction and wear tester, and its friction coefficient was measured. The tribological properties of the tungsten doped graphite like coating under trace lubrication conditions of castor oil acid were studied. The Fourier transform infrared spectrometer was used to characterize the castor oil acid lubricant. By examining whether its characteristic functional groups were consistent with the known chemical formula, X-ray diffraction was used to analyze the chemical bond structure at the wear marks of tungsten doped graphite like coatings lubricated with castor oil acid. This further inferred the friction lubrication mechanism of the solid-liquid composite lubrication system. A three-dimensional contour instrument was used to characterize the morphological characteristics of the wear marks of tungsten doped graphite like coatings lubricated with castor oil acid, Raman spectroscopy was used to characterize the changes in tungsten doped graphite like coatings before and after friction under the action of castor oil acid lubricant. Through the use of a series of equipment for experimental analysis and characterization, the results showed that the friction coefficient of the solid-liquid composite lubrication system composed of tungsten doped graphite like coating and castor oil acid was as low as about 0.02, and the wear rate was about 6.25 × 10⁻¹⁹ m³/(N·m), which was higher than that of tungsten doped graphite like coating and polyalphaolefin (PAO). Within the range of the three-dimensional profilometer, almost no wear traces were observed, achieving ultra-low wear. Raman spectroscopy characterization revealed that the structural characteristics of tungsten doped graphite like coatings did not change before and after friction. Fourier transform infrared spectroscopy was used to characterize the lubricants collected after the lubrication experiment, and it was found that the functional groups did not change before and after the friction experiment. X-ray diffraction analysis revealed that there were residues of hydroxyl groups and oxygen at the wear marks. The oligomers of –(CH₂–CH₂)_n– generated by the friction decomposition of castor oil acid adsorbed and passivated the sp² fragments of the surface coating with hydroxyl groups. Therefore, the solid-liquid composite system had excellent anti-friction and anti-wear performance. The results of this study provided a research foundation and theoretical support for the future application and development of carbon based coatings/castor oil acid solid-liquid composite systems.