  We study the mechanisms of slip transfer at a grain boundary, in titanium,
using Differential Aperture X-ray Laue Micro-diffraction (DAXM). This 3D
characterization tool enables measurement of the full (9-component) Nye lattice
curvature tensor and calculation of the density of geometrically necessary
dislocations (GNDs). We observe dislocation pile-ups at a grain boundary, as
the neighbor grain prohibits easy passage for dislocation transmission. This
incompatibility results in local micro-plasticity within the slipping grain,
near to where the slip planes intersect the grain boundary, and we observe
bands of GNDs lying near the grain boundary. We observe that 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 helps us understand the
higher order complexity of grain boundary characteristics.
