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M: Metallphysik

M 18: Mechanische Eigenschaften IV

M 18.1: Fachvortrag

Dienstag, 27. März 2001, 15:15–15:30, S5.3

Orientation gradient theory in plastically strained crystals — •D. Raabe, Z. Zhao, and F. Roters — Max-Planck-Institut für Eisenforschung, Max-Planck-Str. 1, 40237 Düsseldorf

We present a theory of in–grain orientation gradients in plastically strained metals. It explains why initially uniformly oriented crystals can under gradient-free external loadings build up in–grain orientation gradients during plastic deformation and how this phenomenon depends on intrinsic factors (crystal orientation) and extrinsic factors (neighbor grains). The intrinsic origin of grain fragmentation is investigated by quantifying the change in crystal reorientation upon small changes in initial orientation. This is formulated by applying a divergence operator to reorientation rate vector fields calculated by strain–rate homogenization theory. The extrinsic origin of grain fragmentation (influence of grain–neighbor interaction) is addressed using a crystal plasticity finite element bicrystal model. The simulations show that a significant dependence of grain fragmentation on the neighbor crystals occurs for grains with high positive divergence. The subdivision behavior of grains with close to zero or negative divergence is less sensitive to the neighbor orientations. It is further observed that the grain fragmentation tendency increases with decreasing strain compatibility between neighbor grains. The approaches are applied to bcc and fcc crystals.