DuringECApressing, grain refinement is achieved by two
different paths depending on the route of pressing. In route
A, only one set of GNBs forms in a lamellar shape, evolving
from low-angle to high-angle in successive pressing
due to accumulation of dislocations, and thus, misorientation
across the boundaries. In route BC, two sets of GNBs
form due to the 90◦ rotation in between each pass. Some
GNBs follow the course of microstructural evolution in
the case of the route A. However, in most areas, decomposition
and rearrangement of pre-existing GNBs result
in equiaxed subgrains that evolve into grains with highangle
boundaries upon collection of dislocations. In this
process, a few pre-existing GNBs are persistent, and thus,
produce larger-than-average grains, a microstructural heterogeneity.