Wear Mitigation by Antiwear Additives in Simulated Valve Train Wear

Friction Mechanism of Sulfur-Containing Lubricant Additives Confined between Fe(100) Substrates

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-Cn-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.

3D tribo-nanoprinting using triboreactive materials

Tribology: the science of friction, wear and lubrication has never been associated in a positive way with the ability to manufacture at the nanoscale. Triboreactivity, when the contact between two surfaces promotes a chemical reaction, has been harnessed in this study to create highly tenacious nano-features. The reported 3D tribo-nanoprinting methodology has been demonstrated for organic and inorganic fluids on steel and silicon substrates and is adaptable through the interface tribology. The growth rate, composition and shape of the printed features were all found to be dependent on the nature of the printing liquid and shearing interfaces in addition to the applied temperature and contact force. The reported methodology in this study opens unprecedented future possibilities to utilize the nanoprinted films for the expanding fields of microelectronics, medical devices, flexible electronics and sensor technologies.