A field in material science is tribology. For sliding interfaces, there is a significant lack of knowledge about the mechanics for the microstructure evolution. As tribological contacts have significant industrial relevance, gaining more knowledge about the materials science governing friction and wear will have key role. The initial phase in the life of a tribosystem is known as ‘running-in’, during which a mechanically altered layer grows into the material. This layer has often nanocrystalline character. Experiments have provided that the majority of the plastic deformation during sliding is carried by dislocation movement. This leads to an increase in dislocation density and to a decrease in grain size.
An ideal method to correlate this evolution with different elastic and plastic strains is to use samples with a morphological surface texture. We will concentrate on model materials like oxygen-free high-purity copper structured with a membrane-like texture. By varying the aspect ratios of these membranes we are able to produce different values of elastic / plastic strains.
These copper specimens are in contact with a sapphire disc. The experiment runs in reciprocating motion under dry condition.
We will present how, with increasing the aspect ratio and in this way different strain distribution, an annealed microstructure is transformed into a nanocrystalline surface layer. We follow this evolution with scanning electron and focused ion beam microscopy. Parallel to determining the contact mechanisms by recorded time laps videos, the calculation of the elastic strains will be based on the friction data telling us the static and dynamic friction forces deforming the membranes. Correlating the elastic and plastic behavior with the microstructure evolution depending on size effects, energetic and mechanistic considerations, the goal of this study will be the formulation of a model description in order to understand these changes and their influence on tribological properties.