Wear at the asperity level: An atomistic viewpoint

Tribological problems are particularly difficult to comprehend. Different physical mechanisms (including the environment, plastic deformation, third body interactions, phase transformations, recrystallization) interact at disparate length and time scales. Here, we will present some of our recent attempts to understand the origins of wear mechanism at the atomistic level. Macroscopically, the wear process, in terms of debris formation, is well described by the well-known Archard model [1]. As suggested, the wear rate is linearly proportional to the ratio of the applied force to the material hardness with a constant factor called wear coefficient which represents the probability of wear debris formation. This coefficient is the most important yet least understood parameter in the field of tribology. Since the physical origins of the debris formation process are still unclear, this coefficient cannot be estimated theoretically and must be only determined experimentally. In order to understand the physical origins of the debris formation process, we have performed a systematic set of molecular dynamics simulations employing a new family of interatomic potentials. These potentials allow us to independently modify physical properties such as hardness and surface energy where other parameters remains constant. Using that, we will discuss different wear mechanisms at the asperity level ranging from a gradual smoothing to a debris formation. Additionally, we elaborate the steady-state sliding regime in terms of frictional force, debris size and surface roughness and explore several influencing parameters such as applied load, sliding velocity and inter-facial adhesion [2]. The proposed framework opens up a new research path to implicitly model and explore the wear process and revisit classical models.