ABSTRACT
As an aid to understanding the high-temperature microstructures of
rocks, the development of microstructures in the hexagonal organic material,
octachloropropane, was studied with in-situ optical microscopy. It was
found that the deformation behavior of grains in hard and soft orientations
for slip is different during simple shearing, although they both grow.
Strain heterogeneity is induced by partitioning of deformation into relatively
increased components of rigid-body rotation and translation in hard grains
and strains in soft grains.
A steady-state foliation, having a constant intensity and orientation
was observed in simple shearing. The steady state is maintained by a balance
between foliation-strengthening and -weakening processes. The major foliation-strengthening
process is intragranular strain, and the major foliation-weakening process
is dynamic recrystallization including migration of straight or slightly
wavy grain boundaries, grain dissection and rotational recrystallization.
Other minor weakening processes are grain amalgamation, relative rigidity
of hard grains and grain boundary sliding. Foliation intensity is lower
than the axial ratio of the bulk strain ellipse by a factor 0.2 - 0.4 at
a total shear strain of 1.3 - 1.8, indicating that grain-shape foliations
of this type cannot be used for strain calculation.
Subgrain boundaries which appear similar under optical microscopy originate
in seven different ways. They are classical polygonization, kinking, misorientation
reduction, grain coalescence, impingement of migrating subgrain boundaries,
edgewise propagation, and static development of subgrain boundaries from
optically strain-free grains. The preferred orientation of subgrain boundaries
with respect to the grain-shape foliation is symmetric in pure-sheared
samples and asymmetric in simple-sheared samples.
Grain boundary sliding can occur by discontinuities in the strain,
rotation and/or translation components of deformation across the boundary
in deforming samples. Grain boundary diffusion and intragranular plastic
deformation are found to be effective in accommodating grain boundary sliding.
Grain boundary openings can develop in association with grain boundary
sliding, preferentially along grain boundaries at a low angle to the shortening
direction. Once grain boundary openings occur, they continuously change
their shape and are eventually closed by thrusting of sliding grains and
grain overgrowth into the openings. An approximately equal volume of new
openings grow in other places, however, maintaining a steady ratio of 0.5-3%
of the sample volume without development of any large scale fracture. The
opening and closing of grain boundaries usually involve neighbor switching
of surrounding grains.
Ree, J-H., 1991. High temperature deformation of octachloropropane:
a microstructural study.
Unpublished PhD dissertation, State University of New York at Albany.
216pp., +xiii
University at Albany Science Library call number: SCIENCE MIC
Film QE 40 Z899 1991 R443
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