The effect of the latter
most remarkably reflects on a decrease in the strain rate
sensitivity m through a decrease in s* and an increase
in s; the m value is not kept constant during deformation
but decreases with increasing strain. The present
results imply that a tensile test should be carried out at
a constant true strain rate to separate the strain rate
and strain hardening effects to correctly evaluate a
strain rate sensitivity m. The onset of local necking due
to the local strain concentration is suggested to be
triggered by the annihilation of dislocations into the
cavities formed by the sliding of grain boundaries
which were made serrated by interaction between subboundary
and original grain boundary.