[SY-C1] A random walk model of screw dislocation cross-slip in face-centered cubic solid solution alloys
The energy barrier for cross-slip of screw dislocations in FCC solid solution alloys is controlled by local fluctuations in the solute distribution [1]. Here, a random-walk-like model of cross-slip in solid solution alloys is presented. Cross-slip is treated as a discrete process, where on each step a one Burgers vector long dislocation segment moves from the glide to the cross-slip plane. Each step causes (i) a random energy change due to the random change in solute-dislocation and solute-solute binding energies, and (ii) a deterministic energy change due to constriction formation and stress effects. The random walk model allows to calculate the distribution of cross-slip activation energies for long (several 100 to 1000 Burgers vector long) dislocations, which is relevant for deformation of real materials, but not easily accessible by direct atomistic calculations. At zero stress, thermally activated cross-slip of long dislocations is unlikely because high activation energies become more frequent with increasing length. However, at moderate stresses (few MPa), these barriers disappear; the remaining barriers are typically well below the average barrier that one would expect if considering only average alloying effects (average change in stacking fault energy, elastic constants, etc.). Moreover, cross-slip becomes a weakest-link problem, meaning that the activation energy distribution for a long dislocation under stress can be estimated from a reference distribution for a short (40 Burgers vectors) dislocation at zero stress, whose determination is computationally inexpensive and needs to be done only once.
[1] Nöhring, W.G.; Curtin, W.A. Acta Materialia 2017, 128, 135–148.
[1] Nöhring, W.G.; Curtin, W.A. Acta Materialia 2017, 128, 135–148.