  Determining the full five-parameter grain boundary characteristics from
experiments is essential for understanding grain boundaries impact on material
properties, improving related models, and designing advanced alloys. However,
achieving this is generally challenging, in particular at nanoscale, due to
their 3D nature. In our study, we successfully determined the grain boundary
characteristics of an annealed nickel-tungsten alloy (NiW) nanocrystalline
needle-shaped specimen (tip) containing twins using Scanning Precession
Electron Diffraction (SPED) Tomography. The presence of annealing twins in this
face-centered cubic (fcc) material gives rise to common reflections in the SPED
diffraction patterns, which challenges the reconstruction of
orientation-specific virtual dark field (VDF) images required for tomographic
reconstruction of the 3D grain shapes. To address this, an automated
post-processing step identifies and deselects these shared reflections prior to
the reconstruction of the VDF images. Combined with appropriate intensity
normalization and projection alignment procedures, this approach enables
high-fidelity 3D reconstruction of the individual grains contained in the
needle-shaped sample volume. To probe the accuracy of the resulting boundary
characteristics, the twin boundary surface normal directions were extracted
from the 3D voxelated grain boundary map using a 3D Hough transform. For the
sub-set of coherent Sigma 3 boundaries, the expected {111} grain boundary plane
normals were obtained with an angular error of less than 3{\textdegree} for
boundary sizes down to 400 nm${}^2$. This work advances our ability to
precisely characterize and understand the complex grain boundaries that govern
material properties.
