M. Seefeldt
Catholic University of Leuven,
Department of Metallurgy and Materials Engineering,
Kasteelpark Arenberg 44, B-3001 Heverlee, Belgium
Abstract
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Large strain plastic deformation of f.c.c. metals
at low homologous temperatures results in the subdivision of
monocrystals or polycrystal grains into mesoscopic fragments
and deformation bands. Stage IV of single crystal work-hardening
and the substructural contribution to the mechanical anisotropy
emerge at about the same equivalent strain at which the fragment
structure becomes the dominant substructural feature. Therefore,
the latter is likely to be the reason for the new features in
the macroscopic mechanical response. The present paper reviews
some experimental ant theoretical work on deformation banding and
fragmentation as well as a recent model which tackles the fragment
structure development as well as its impact on the macroscopic
mechanical response with the help of disclinations. Incidental or
stress-induced formation of disclination dipoles and non-conservative
propagation of disclinations are considered as "nucleation and growth"
mechanisms for fragment boundaries. Propagating disclinations get
immobilized in fragment boundaries to form new triple junctions with
orientation mismatches and thus immobile disclinations with long-range
stress fields. The substructure development is described in terms of
dislocation and disclination density evolution equations;
the immobile defect densities are coupled to flow or critical resolved
shear stress contributions.
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full paper (pdf, 376 Kb)