Dislocation-mediated and twinning-induced plasticity of CoCrFeMnNi in varying tribological loading scenarios.

Coarse-grained, metallic materials undergo microstructure refinement during tribological loading. This in turn results in changing tribological properties, so understanding deformation under tribological load is mandatory when designing tribological systems. Single-trace experiments were conducted to understand the initiation of deformation mechanisms acting in various tribological systems. The main scope of this work was to investigate the influence of normal and friction forces as well as crystal orientations on the dominating deformation mechanism in a face-centred cubic concentrated solid solution. While varying the normal force is easily realised, varying friction forces were achieved by using several counter body materials paired against CoCrFeMnNi. The subsurface deformation layer was either mediated through dislocation slip or twinning, depending on the grain orientation and on the tribological system. A layer dominated by dislocation-based deformation is characterised by lattice rotation, the formation of a dislocation trace line or subgrain formation. Such behaviour is observed for tribological systems with a low friction coefficient. For systems dominated by deformation twinning, three types of twin appearance were observed: small twins interacting with the surface, large twins and grains with two active twin systems. Two different twinning mechanisms are discussed as responsible for these characteristics.