Mechanisms in creep and hot working to high strain; microstructural evidence, inconsistencies.

Abstract

The dislocation mechanisms of dynamic
recovery (DRV) in metals of high stacking fault
energy (SFE) give rise to steady-state straining
dependent on temperature and strain rate
due to development of constancy in the
spacings of subgrain boundaries (wS, SGB)
and of the dislocations within both the SGB
and the subgrains. When the grains are large
compared to subgrains, the interactions of
grain boundaries with SGB are limited to
s e rration formation but when one-grain
dimension is reduced to about twice the SGB
spacing, the interactions begin to define a
minimum grain dimension. However, the
cellular size defined by the mixture of SGB
and GB remains constant at wS along with
the stress. In metals of low SFE, the above is
seldom attained since dynamic
recrystallization (DRX) intervenes to provide
new grains more than twice the subgrain size.
On a larger scale, transition boundaries
between deformation bands lying between
diff e rently slipping and rotating bands,
become permanent and rapidly rise in angle
and take on GB behavior in both DRV
(serrations) and in DRX (nucleation sites). The
evidence became more precise as techniques
advanced through polarized optical,
scanning and transmission electron and
orientation imaging microscopies; however,
deficiencies in each technique often created
confusions that were resolved only through
detailed comparison of the evidence.