Tribological evolution of materials interfaces: atomic-scale insights from computer simulations
Event details
| Date | 27.03.2019 |
| Hour | 16:00 › 17:00 |
| Speaker | Dr. Gianpietro Moras is deputy head of the “Multiscale Modelling and Tribosimulation” group at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg (Germany). He uses atomic-scale computer simulations to understand how the structure and chemistry of materials transform under tribological load and the effect of these transformations on friction and wear. Gianpietro received a master’s degree in Materials Engineering from the University of Trieste (Italy) and a PhD in Physics from King’s College London (UK). He held postdoctoral research positions at the Karlsruhe Institute of Technology and at Fraunhofer IWM (Germany). |
| Location | |
| Category | Conferences - Seminars |
Abstract: Materials interfaces under tribological load undergo chemical and structural transformations that tend to minimize their shear resistance. In spite of their crucial role in determining friction and wear, these material transformations are often not understood as they occur at buried interfaces that are hardly accessible by in situ experiments. In this seminar, I will show how computer simulations can be used to complement experiments and gain insights into the atomic-scale details of tribological processes. In particular, I will focus on tribological interfaces in silicon, diamond, diamond-like carbon (DLC). I will first present results on dry silicon and diamond systems in which covalent bonds form across the tribological interface. In order to minimize the shear resistance of the interface, the material undergoes plastic deformation and shear induces amorphization and recrystallization processes. Interestingly, despite the structural similarity between silicon and diamond, these non-equilibrium processes are different in the two materials. I will discuss these differences and relate them to the equilibrium properties of the two crystals. Next, I will move to lubricated tribological interfaces, where chemical surface passivation prevents the formation of covalent bonds across the interface, thus leading to lower friction. In particular, I will present results on how superlow friction coefficients can be achieved when diamond and DLC are lubricated by water or organic friction modifiers. Besides the commonly reported surface chemical passivation by dissociative chemisorption of the lubricant molecules, our simulations show a mechanochemical passivation process based on the formation of aromatic surface structures. Finally, I will talk about the role played by surface chemical terminations in friction. Specifically, both hydrogen and fluorine can be used as monoatomic chemical terminations for dangling bonds on carbon surfaces. It is often reported that the two different chemical terminations lead to different friction coefficients because of electrostatic effects. At odds with this explanation, I will show simulations results suggesting that differences in friction between hydrogen- and fluorine-terminated diamond/DLC depend on the different size of the two atoms rather than on the different polarity of the C-H and C-F bonds.
Practical information
- Informed public
- Free
Organizer
- LAMMM
Contact
- Géraldine Palaj