  Tribological loading of metals induces microstructural changes by
dislocation-mediated plastic deformation. During continued sliding, combined
shear and lattice rotation result in the formation of crystallographic textures
which influence friction and wear at the sliding interface. In order to
elucidate the fundamental lattice rotation kinematics involved in this process
during the early stages of sliding, we conducted unlubricated, linear single
pass sliding experiments on a copper bicrystal using sapphire spheres. Electron
backscatter diffraction (EBSD) performed directly on the bulk surface of the
wear tracks in the vicinity of the grain boundary reveals crystal lattice
rotations by approximately up to 35{\deg}. Predominantly, the tribologically
induced crystal rotations appear to be kinematically constrained to rotations
around the transverse direction (TD) and occur in both grains, irrespective of
load (2 to 8 N). We demonstrate that inverting the sliding direction (SD)
inverts the sense of crystal rotation, but does not change the principal nature
of rotation for the majority of indexed EBSD data. A lower proportion of the
crystal lattice rotates much farther around TD (roughly up to 90{\deg}),
accompanied by a superimposed crystal rotation around +/-SD. Analysis reveals
that sliding direction and grain orientation exert a systematic influence of
how crystal rotations are accommodated. This is rationalized in terms of
geometry, anisotropic wear track profiles and slip traces. Under specific
conditions, combined crystal rotation and twinning are observed. These detailed
insights into the fundamental nature of tribologically induced lattice rotation
kinematics provide important guidance for applied research targeting materials
with superior tribological properties.
