Nucleation and Cross-Slip of Partial Dislocations in FCC Metals
- Author(s): Liu, Gang
- Advisor(s): Xu, Guanshui
- et al.
Nucleation of partial dislocations at a crack and cross-slip of partial dislocations under general loading in FCC metals are analyzed based on a multiscale model which incorporates atomic information into continuum-mechanics approach. In both analyses, the crack and the slip planes are modeled as surfaces of displacement discontinuities embedded in elastic media. The atomic potentials between the adjacent atomic layers along the slip planes are assumed to be the generalized stacking fault energies, which are obtained based on atomic calculations. The relative displacements along the slip planes, corresponding to the configurations of partial dislocations and stacking faults, are solved through the variational boundary integral method. The energetics of partial dislocation nucleation at the crack and cross-slip in FCC metals Al and Cu are comparatively studied for their distinctive difference in the intrinsic stacking fault energy.
For the analysis of nucleation of partial dislocations at a crack, several new features have emerged compared with nucleation of perfect dislocations in previous studies. Among them, the critical stress and activation energy for nucleation of partial dislocations are markedly lowered. Depending on the value of stacking fault energy and crack configuration, the saddle-point configurations of partial dislocations can be vastly different in terms of the nucleation sequence and the size of the stacking fault. The implications of these new findings on mechanical behavior of nanostructured crystalline materials are elaborated.
For the analysis of cross-slip of partial dislocations, the conclusion from previous studies that cross-slip in FCC metals can be influenced by intrinsic stacking fault energy is confirmed. Furthermore, it is found that in Al, the preference of the gliding plane depends on the competition between the two resolved shear stresses on the slip planes. In Cu, the most preferred loading condition for cross-slip is that a lager compressing Escaig shear stress on the primary slip plane is accompanied with stretching Escaig shear stress on the cross-slip plane. The analysis of activation energy indicates that thermal motion plays an important role in cross-slip in FCC metals.