Deformation twins as a probe for tribologically induced stress states

Friction and wear of metals are critically influenced by the microstructures of the bodies constituting the tribological contact. Understanding the microstructural evolution taking place over the lifetime of a tribological system therefore is crucial for strategically designing tribological systems with tailored friction and wear properties. Here, we focus on the single-crystalline High-Entropy Alloy CoCrFeMnNi that is prone to form twins at room temperature. Deformation twins feature a pronounced orientation dependence with a tension-compression anisotropy, a distinct strain release in an extended volume and robust onset stresses. This makes deformation twinning an ideal probe to experimentally investigate the complex stress fields occurring in a tribological contact. Our results unambiguously show a grain orientation dependence of twinning under tribological load. It is clearly shown, that twinning cannot be attributed to a single crystal direction parallel to a sample coordinate axes. With deformation twins in the microstructure, stress field models can be validated to make them useable for all different tribological systems.