Dimples on Nanocrystalline Fracture Surfaces As Evidence for Shear Plane Formation

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Science  06 Jun 2003:
Vol. 300, Issue 5625, pp. 1550-1552
DOI: 10.1126/science.1084284

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Tensile experiments of fully dense nanocrystalline structures with a mean grain size of less than 100 nanometers demonstrate a considerable increase in hardness but a remarkable drop in elongation-to-failure, indicating brittle behavior. However, dimple structures are often observed at the fracture surface, indicating some type of ductile fracture mechanism. Guided by large-scale atomistic simulations, we propose that these dimple structures result from local shear planes formed around clustered grains that, because of their particular misorientation, cannot participate in the grain boundary accommodation processes necessary to sustain plastic deformation. This raises the expectation that general high-angle grain boundaries are necessary for good ductility.

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