Length-scale effects in the nucleation of extended dislocations in nanocrystaline Al by molecular-dynamics simulation.
The nucleation of extended dislocations from the grain boundaries in nanocrystalline aluminum is studied by molecular-dynamics simulation. The length of the stacking fault connecting the two Shockley partials that form the extended dislocation, i.e., the dislocation splitting distance, r{sub split}, depends not only on the stacking-fault energy but also on the resolved nucleation stress. Our simulations for columnar grain microstructures with a grain diameter, d, of up to 70 nm reveal that the magnitude of r{sub split} relative to d represents a critical length scale controlling the low-temperature mechanical behavior of nanocrystalline materials. For r{sub split}>d, the first partials nucleated from the boundaries glide across the grains and become incorporated into the boundaries on the opposite side, leaving behind a grain transected by a stacking fault. By contrast, for r{sub split}<d two Shockley partials connected by a stacking fault are emitted consecutively from the boundary, leading to a deformation microstructure similar to that of coarse-grained aluminum. The mechanical properties of nanocrystalline materials, such as the yield stress, therefore depend critically on the grain size.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); FOR
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 943277
- Report Number(s):
- ANL/MSD/JA-38817; ACMAFD; TRN: US200916%%631
- Journal Information:
- Acta Materialia, Vol. 49, Issue 14 ; Aug. 16, 2001; ISSN 1359-6454
- Country of Publication:
- United States
- Language:
- ENGLISH
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