Dislocation density distribution at slip band-grain boundary intersections

Dr Ed Tarleton and Professor Angus Wilkinson from Oxford Materials have collaborated with Imperial College, University of Birmingham  and Oxford Engineering to study the mechanisms of slip transfer at a grain boundary, in titanium, using Differential Aperture X-ray Laue Micro-diffraction (DAXM). The paper ('Dislocation density distribution at slip band-grain boundary intersections') explores how the 3D characterisation tool enabled measurement of the full (9-component) Nye lattice curvature tensor and calculation of the density of geometrically necessary dislocations (GNDs). The team observed dislocation pile-ups at a grain boundary, as the neighbour grain prohibits easy passage for dislocation transmission. This incompatibility resulted in local micro-plasticity within the slipping grain, near to where the slip planes intersect the grain boundary, and bands of GNDs lying near the grain boundary were observed. Additionally, it was noted the distribution of GNDs can be significantly influenced by the formation of grain boundary ledges that serve as secondary dislocation sources. This observation highlights the non-continuum nature of polycrystal deformation and helped the team understand the higher order complexity of grain boundary characteristics.