Mechanical and chemical wear components in environmental multi-asperity nanotribology

Running-in wear of MEMS can be described as a process which involves mechanical, chemical and physico-chemical phenomena at various scale levels. Extracting each sort of components would enable to better understand wear mechanisms in order to prevent it. Unfortunately, these components are generally hard to extract experimentally because their own time responses are generally not in the same order. A suitable approach is to combine multi-asperity nanotribological tests, using an in situ wear assessment, with numerical simulations using Movable Cellular Automata (MCA), which are able to interact together within the contact. Experimental tests enable to control the actual physico-chemical environment with an environmental enclosure, and MCA simulate the multi-asperity contact, where interactions between automata pairs can be controlled by various fracture and bonds criteria. There is generally an optimal set of interaction criteria which provides numerical results that match correctly with the experimental ones. By studying the influence of experimental environment on this optimal set, assumptions can be made about mechanical, chemical and physico-chemical phenomena that are likely to occur within the actual tribocontact. In this work, these assumptions have been studied for various samples like silicon wafers displaying various crystallographic orientations and nanostructures, and self-assembled monolayers grafted on silicon wafers, and carbon nitride coatings rubbing under different environmental conditions.