In Situ Raman Observation of the Graphitization Process of Tetrahedral Amorphous Carbon Diamond-Like Carbon under Boundary Lubrication in Poly-Alpha-Olefin with an Organic Friction Modifier

Abstract

The graphitization process of a tetrahedral amorphous carbon (ta-C) film under lubrication was investigated using a laboratory-built in situ Raman tribometer. The coating was lubricated with poly-alpha-olefin (PAO), PAO with an added friction modifier (FM), glycerol mono-oleate (GMO). Friction tests were carried out using a ball-on-disk setup, in which a 19-mm diameter ta-C-coated ball was loaded and rubbed against a steel disk that was immersed in a lubricant solution. In situ optical microscopy and Raman spectroscopy were used to monitor the graphitization process and wear tracks of the ta-C-coated ball. Raman analysis was conducted on the rubbed surface of the rotating ta-C-coated ball when it was located under an objective lens every three minutes during sliding. In this study, the degree of graphitization of the ta-C surface was estimated by calculating the intensity ratio of the D-peak and G-peak (ID/IG) in the Raman spectra of the ta-C film during friction tests with different lubricants. All our results suggest that the friction modifier inhibits the progression of graphitization of DLC films by reducing friction, in other words, reducing the contact temperature, and the wear progression of DLC films under boundary lubrication can be induced by graphitization of DLC surfaces at the sliding contact.

Synergistic effects of hexagonal boron nitride nanoparticles and phosphonium ionic liquids as hybrid lubricant additives

“…A WITec alpha300R+ confocal Raman microscope was employed to obtain the Raman spectrum of PAO 32 and the three ILs. As can be observed in Figure S1 and S2, a Raman band is detected around 2800-3000 cm -1 with peaks at 2857 and 2908, 2909 and 2930 cm -1 assignable to C-H stretching [41]; other peaks at 1310, 1314 and 1322 cm -1 correspond to δ(CH2) vibration and at 1451, 1456 and 1457 cm -1 assignable to the δ(CH3) vibrations [42]. Additional peaks at 894, 899, 1082, 1086, 1089 and 1094 cm -1 can be attributed to ν(CC) aliphatic chain vibrations [42].…”

Properties and Classification of Diamond-Like Carbon Films

“…The D peak at ~1355 cm −1 , which is characteristic of amorphic carbon, was the breathing mode of A 1g symmetry due to phonons near the K zone boundary [ 72 ]; this has been thoroughly discussed in terms of the phonon dispersion [ 73 ]. In addition, the relationship between Raman spectroscopy and the physical properties of the film has been examined, e.g., the G-peak position decreases by a magnitude of one as the sp 3 ratio increases, and then, it increases with a minimum sp 3 ratio of ~20%; further, the Young’s modulus of the film is proportional to the G-peak dispersion [ 19 , 74 , 75 , 76 ]. In addition, the FWHM of the G peak increases when the grain size of sp 2 decreases [ 77 ].…”

Tribological Improvement of Low-Viscosity Nanolubricants: MoO3, MoS2, WS2 and WC Nanoparticles as Additives

“…An intense Raman band is found between 2800 and 3000 cm −1 with peaks associa C-H stretching [21] and other peaks around 1310 cm −1 and 1440 cm −1 related to δ(CH δ(CH3) vibrations, respectively [22]. Further peaks at 890 and 1080 cm −1 can be ascri ν(C-C) aliphatic chain vibrations [22]. Regarding the nanoadditives, four different commercial nanoparticles (US Re Nanomaterials, Houston, USA) were utilized as additives for the PAO4 ba Molybdenum oxide nanopowder (MoO3, 1313-27-5) had 99.9% purity, with a size be 13 and 80 nm and with an orthorhombic structure.…”

“…Furthermore, the Raman spectrum of PAO4 can be seen in Figure 2b. An intense Raman band is found between 2800 and 3000 cm −1 with peaks associated to C-H stretching [21] and other peaks around 1310 cm −1 and 1440 cm −1 related to δ(CH 2 ) and δ(CH 3 ) vibrations, respectively [22]. Further peaks at 890 and 1080 cm −1 can be ascribed to ν(C-C) aliphatic chain vibrations [22].…”