Microstructural self-organization triggered by twin boundaries during dry sliding wear

A novel microstructural self-organization reaction is observed near the surface of a Cu-Ni-Sn bronze subjected to dry sliding wear. Scanning electron microscopy using electron-backscattered diffraction reveals the formation of near periodic patterns comprising domains with alternating orientation separated by narrow boundaries. Remarkably, orientation patterning takes place only near twin boundaries intercepting the sliding surface, and only on a specific side of the boundaries. The domain period, which ranges from a few to tens of micrometers, increases with the applied load. This orientation patterning is suppressed by promoting steady sliding using solid lubricants such as Ag and self-generated oxide-bearing tribolayers. Transmission electron microscopy reveals planar dislocation glide in the orientation domains, with multiple active slip systems. A rationalization of these results is offered based on an instability triggered by the interaction of elastic stick-slip waves with pre-existing twin boundaries.