Li Chunhong, Wang Pengjie, Duan Fangli
State Key Laboratory of Mechanical Transmission for Advanced Equipment, Chongqing University, Chongqing 400044, China.
Langmuir. 2024 Sep 9. doi: 10.1021/acs.langmuir.4c02569.
Sulfur-containing lubricant additives can chemically react with metal surfaces under extreme conditions, such as high temperature and high pressure, forming protective films on the surfaces. However, the formation mechanisms and the friction-reducing and antiwear properties of these films remain unclear. In this study, we investigated the friction process of sulfur-containing additives confined between two iron surfaces using reactive molecular dynamics simulations. Our research revealed that in systems with a higher S/C ratio, an iron sulfide layer formed on the iron surfaces with Fe-S-Fe bridging bonds at the interface, resulting in relatively smaller friction and wear even under higher loads. However, in systems with lower S/C ratios, the presence of numerous interfacial Fe-C-Fe bridging bonds, caused by the hydrocarbon radicals released from the additives, led to the formation of thick amorphous shearing bands at the interface between the two substrates. In this case, the distributed sulfur atoms also exhibited some effect in reducing the shear resistance of the amorphous shearing bands due to the weak strength of S-Fe bonds compared to the strength of C-Fe bonds. These atomic-level insights help understand the antiwear characteristics of sulfur-containing lubricant additives confined between iron substrates.
含硫润滑剂添加剂在高温高压等极端条件下能与金属表面发生化学反应，在表面形成保护膜。然而，这些膜的形成机制以及减摩和抗磨性能仍不清楚。在本研究中，我们使用反应分子动力学模拟研究了夹在两个铁表面之间的含硫添加剂的摩擦过程。我们的研究表明，在硫碳比更高的体系中，铁表面形成了一层硫化铁层，界面处存在铁硫铁桥键，即使在更高载荷下也能产生相对较小的摩擦和磨损。然而，在硫碳比更低的体系中，添加剂释放出的烃基导致大量界面铁碳铁桥键的存在，从而在两个基体之间的界面处形成了厚的非晶剪切带。在这种情况下，由于硫铁键的强度比碳铁键弱，分布的硫原子在降低非晶剪切带的剪切阻力方面也表现出一定作用。这些原子层面的见解有助于理解夹在铁基体之间的含硫润滑剂添加剂的抗磨特性。
