Dislocation structures in high-purity copper under a unidirectional linear tribological loadTuesday (27.09.2016) 11:45 - 12:00 Part of:
Microstructure evolution underneath tribologically loaded surfaces is of great importance for the friction response and wear of the tribosystem, but still poorly understood, especially in the very early stages of sliding contact. As the microstructure change in later stages of sliding is directly based on or evolving from the microstructure in early stages, it is vital to investigate and understand the initial microstructural changes under tribological loading.
We investigated the microstructure evolution of high-purity copper in contact with a sliding sapphire sphere in a series of systematic experiments under mild wear conditions. The normal load was chosen between 0.5 N and 14 N corresponding to maximum Hertzian pressures of about 334 MPa and 1014 MPa, respectively. The trace number was varied starting from only one trace up to 20 traces.
Our results show the beginning of the dislocation self-organization and the emergence of a dislocation trace line parallel to the sliding surface at a depth of around 120 nm, irrespective of crystallographic orientation, creating a discontinuity in the subsurface area. The consistent appearance of this dislocation trace line, irrespective of experimental conditions, indicates that its formation mechanism is expected to be generic. The appearance of this dislocation trace line is explained as the result of a sign change in the contact stress field.
We interpret the dislocation trace line as the key feature demonstrating the elementary mechanism for the formation of a tribo-layer. Once these mechanisms are further understood, a model allowing to tailor a material’s microstructure for optimized friction and wear performance will be developed.