Dislocation cross-slip in face-centered cubic solid solution alloys

14.9.2018

Seminar Fraunhofer IWM, 14. September 2018, Seminarraum des Fraunhofer-Instituts für Werkstoffmechanik IWM in Freiburg, Dr. Wolfram Nöhring, IMTEK, Freiburg

Details: 

 

Was:                        Seminar Fraunhofer IWM: Dislocation cross-slip in face-centered cubic solid solution alloys

Wann                      14. September 2018, 11:15 Uhr

Wo:                         Seminarraum W9a des Fraunhofer Instituts für Werkstoffmechanik IWM in Freiburg

Vortragender:        Dr. Wolfram Nöhring, IMTEK, Freiburg

 

Many engineering alloys contain a significant concentration of substitutional solutes. Understanding how these solutes affect dislocation motion and macroscopic plastic behavior is required for developing predictive models of alloy strength.

The subject of this talk is the effect of solutes on dislocation cross-slip, i.e. the motion of a screw dislocation from one glide plane to another. Atomistic simulations of cross-slip of short (40b length) dislocation segments reveal that the energy barrier is controlled by local concentration fluctuations, and not by average alloying effects (e.g. a change of the average tacking fault energy). An analytical, parameter-free model of energy fluctuations during cross-slip is presented. Finally, cross-slip of long (100 nm to 1 μm long) dislocations is discussed using a statistical model. Cross-slip is modeled as a random walk, in which each step corresponds to movement of a 1b segment from the glide to the cross-slip plane. Associated with each step is a random change in solute binding energies, plus a deterministic energy during formation of the initial constriction.  The model reproduces the activation energy distribution of short dislocations. It is then used to predict the distribution and its sensitivity to stress for long dislocations. Results show that cross-slip is controlled by low activation barriers that are well below the average value. Thus, cross-slip in random alloys can be much faster than expected based on models that consider only average alloying effects.