  Microstructure and crystallography of {\delta} phase hydrides in as-received
fine grain and 'blocky' alpha large grain Zircaloy-4 (average grain size ~11
{\mu}m and >200 {\mu}m, respectively) were examined using electron backscatter
diffraction. Results suggest that the the matrix-hydride orientation
relationship is {0001}{\alpha}||{111}{\delta};<11-20>{\alpha}||<110>{\delta}
for all the cases studied. The habit plane of intragranular hydrides and some
intergranular hydrides has been found to be {10-17} of the surrounding matrix.
The morphology of intergranular hydrides can vary depending upon the angle
between the grain boundary and the hydride habit plane. The misfit strain
between {\alpha}-Zr and {\delta}-hydride is accommodated by high density of
dislocations and twin structures in the hydrides, and a mechanism of twin
formation in the hydrides has been proposed. The growth of hydrides across
grain boundaries is achieved through an auto-catalytic manner similar to the
growth pattern of intragranular hydrides. Easy collective shear along <1-100>
makes it possible for hydride nucleation at any grain boundaries, while the
process seems to favour grain boundaries with low (<40{\deg}) and high
(>80{\deg}) c-axis misorientation angles. Moreover, the angle between the grain
boundary and the adjacent basal planes does not influence the propensity for
hydride nucleation.
