BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:Tribological evolution of materials interfaces: atomic-scale insig hts from computer simulations DTSTART:20190327T160000 DTEND:20190327T170000 DTSTAMP:20260407T041925Z UID:89e453e0e0c571a61e18ef156db1462fecee1ed2d71716dded417f8c CATEGORIES:Conferences - Seminars DESCRIPTION:Dr. Gianpietro Moras is deputy head of the “Multiscale Model ling and Tribosimulation” group at the Fraunhofer Institute for Mechanic s of Materials IWM in Freiburg (Germany). He uses atomic-scale computer si mulations to understand how the structure and chemistry of materials trans form under tribological load and the effect of these transformations on fr iction and wear. Gianpietro received a master’s degree in Materials Engi neering from the University of Trieste (Italy) and a PhD in Physics from K ing’s College London (UK). He held postdoctoral research positions at th e Karlsruhe Institute of Technology and at Fraunhofer IWM (Germany).   \ nAbstract: Materials interfaces under tribological load undergo chemical a nd 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 semi nar\, I will show how computer simulations can be used to complement exper iments and gain insights into the atomic-scale details of tribological pro cesses. In particular\, I will focus on tribological interfaces in silicon \, diamond\, diamond-like carbon (DLC). I will first present results on dr y silicon and diamond systems in which covalent bonds form across the trib ological interface. In order to minimize the shear resistance of the inter face\, the material undergoes plastic deformation and shear induces amorph ization and recrystallization processes. Interestingly\, despite the struc tural similarity between silicon and diamond\, these non-equilibrium proce sses 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 result s on how superlow friction coefficients can be achieved when diamond and D LC are lubricated by water or organic friction modifiers. Besides the comm only reported surface chemical passivation by dissociative chemisorption o f the lubricant molecules\, our simulations show a mechanochemical passiva tion process based on the formation of aromatic surface structures. Finall y\, I will talk about the role played by surface chemical terminations in friction. Specifically\, both hydrogen and fluorine can be used as monoato mic chemical terminations for dangling bonds on carbon surfaces. It is oft en reported that the two different chemical terminations lead to different friction coefficients because of electrostatic effects.  At odds with th is explanation\, I will show simulations results suggesting that differenc es in friction between hydrogen- and fluorine-terminated diamond/DLC depen d on the different size of the two atoms rather than on the different pola rity of the C-H and C-F bonds.  LOCATION:ME B1 B10 https://plan.epfl.ch/?room=MEB1B10 STATUS:CONFIRMED END:VEVENT END:VCALENDAR