Modeling hardening and softening due to high-angle grain boundaries in crystalline solids (English shop)

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Xiaohui Zeng’s dissertation investigates the mechanisms of strengthening and softening caused by high-angle grain boundaries in crystalline materials. The research develops a statistical dislocation model to describe the plastic deformation behavior of coarse-grained and ultrafine-grained copper. The model incorporates dislocation generation, storage, and annihilation within grain interiors and at grain boundaries. Numerical simulations examine the effects of grain size, temperature, and strain rate on steady-state deformation resistance. The results demonstrate that high-angle grain boundaries promote strengthening at low temperatures in accordance with the Hall–Petch relationship. At elevated temperatures, thermally activated dislocation annihilation can instead cause material softening. Comparisons with experimental observations confirm important trends predicted by the model, although quantitative deviations remain. The study contributes to understanding the microstructural mechanisms governing plastic deformation in ultrafine-grained metals.