| YANG Xing,WANG Yongfu,ZHANG Junyan,ZHANG Bin,LI Ruiyun.Preparation and Solid Superlubricity of Two-dimensional Nanocomposite Coating on Bearing Ball Surfaces[J],53(21):14-22 |
| Preparation and Solid Superlubricity of Two-dimensional Nanocomposite Coating on Bearing Ball Surfaces |
| Received:August 11, 2024 Revised:September 26, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.21.003 |
| KeyWord:two-dimensional nanopowder structural superlubricity graphene molybdenum disulfide heterojunction coating bearing balls |
| Author | Institution |
| YANG Xing |
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou , China |
| WANG Yongfu |
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou , China |
| ZHANG Junyan |
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou , China |
| ZHANG Bin |
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou , China |
| LI Ruiyun |
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou , China;State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing , China |
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| Abstract: |
| Structural superlubricity has been limited in nanoscale and microscale, which needs more efforts to achieve macroscale superlubricity. At present, two-dimensional nanopowders produced on an engineering scale have attracted more and more attentions. However, it is difficult to achieve macroscopic superlubricity as their single crystal state due to strong edge effects and friction-induced complex contact restructuration. Here, a strategy based on ball milling method under humidity environment was proposed to incorporate graphene edge oxygen for weakening the edge pinning effect of two-dimensional nanoflakes, to promote the conversion of two-dimensional nanopowder to heterojunction and the macroscale superlubricity at wide ranges of load and speed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) characterizations were used to compare the structures and compositions of two types of samples obtained under vacuum and humidity environments. The results showed that about 10% oxygen could be doped in the graphene edge to form C—O—C bonds during the humidity ball milling process, which weakened the edge pinning effect and retained the smooth interlayer slipping between two-dimensional materials. This finally induced the layered assembly and good mixing of two-dimensional nanosheets on the bearing ball surface, promoting the formation of the coexistent structure containing countless heterojunctions and homojunctions. As a contrast, the sample obtained under vacuum environment showed a poor mixing of graphene and MoS2. As expected, the humidity-milling sample exhibited a lower frictional coefficient (0.007) and wear under Ar environment than the vacuum-milling sample when paired with the amorphous carbon film. Combining the wear scar and track results of the ball milling samples, the friction behavior of humidity-milling sample was contributed by the contact restructuration of heterojunctions and homojunctions rather than the interaction between the sample and the amorphous carbon film. Raman spectra before and after the friction test showed that the humidity-milling sample had the negligible change of MoS2 and graphene signals, proving the existence of homojunction-heterojunction conversion. But for the vacuum-milling sample, the ID/IG of graphene increased after friction (1.41 for original film vs 1.62 for post-friction film), indicating the deterioration of the surface structure. To estimate the potential of the humidity-milling sample in engineering application, a variety of loads and velocities were considered for friction tests. The results showed that macroscale superlubricity could be achieved under 3-9 cm/s and 5-9 N. The minimum (0.007) of frictional coefficient could be obtained at 5 cm/s and 7 N. The classic molecular dynamic (MD) simulations exhibited that the edge atoms of graphene had higher potential energy than in-plane atoms, indicating high chemical activity of graphene edge and strong edge-pinning effect. Meanwhile, the edge-oxygen incorporated graphene exhibited higher potential energy than oxygen-free graphene when forming heterojunctions with MoS2, showing lower interaction with MoS2 and weaker edge-pinning effect. All results reveal that graphene edge oxygen incorporation strategy is effective to weaken graphene edge-pinning effect, promote the layered slipping of two-dimensional nanoflakes, and finally achieve the conversion of two-dimensional nanopowder to heterojunction and the macroscale superlubricity, which is of great significance for the scale-up and engineering application of superlubricity. |
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