respectively. Due to the rotation of specimen in
between passes, two sets of geometrically necessary boundaries were formed during the route BC pressing. The mechanism of grain refinement
during the route A pressing was evolution of high-angle geometrically necessary boundaries from the low-angled ones, while that during
the route BC pressing was decomposition and rearrangement of pre-existing boundaries. The yield stress of severely deformed specimens
increased with the reducing grain size according to a Hall–Petch relationship.
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