David Srolovitz - Grain boundary dynamics: a disconnection perspective

Описание: This talk was part of the Workshop “Modeling of Crystalline Interfaces and Thin Film Structures: A Joint Mathematics-Physics Symposium” held November 11 - 15, 2019 at the ESI.

The motion of grain boundaries (GBs) and the relative motion of crystals that meet at a GB are describable in terms of the motion of line defects that are constrained to the GB. These line defects (disconnections) are characterized by both a Burgers vector (dislocation character) and steps (step character). The set of possible disconnections {b,h} are determined by the relative orientations of the two grains that meet at the GB. At low temperature, GB dynamics is controlled by the disconnections with the lowest formation energies for any driving force. This gives rise to classical
shear coupling'' behavior. At high temperature, it is possible to form disconnections of multiple nodes (this is responsible for GB sliding). While single mode disconnection dynamics may be important in bicrystals, GB migration in polycrystals require the activation of multiple modes. A Kosterlitz-Thouless transition may occur at high temperature which changes the fundamental nature of how disconnections move. We present a combination of theory and molecular dynamics and kinetic Monte Carlo simulations to demonstrate these effects. While discrete disconnections dynamics can describe many of the fundamental behaviors, the goal is a continuum equation of motion for GBs and the junctions at which they meet. We present some recent results on the development of such continuum approaches. Some key references are listed below [1-7].
References

[1] J. Han, S.L. Thomas, D.J. Srolovitz. Grain-Boundary Kinetics: a unified approach. Progress in Materials Science
98
(2018), 386--476.
[2] S.L. Thomas, K.T. Chen, J. Han, P.K. Purohit D.J. Srolovitz. Reconciling grain growth and shear-coupled grain boundary migration. Nature Communications
8
(2017), 1764.
[3] L.C. Zhang, J. Han, Y. Xiang, D.J. Srolovitz. Equation of Motion for a Grain Boundary. Physical Review Letters
119
(2017), 246101.
[4] S.L. Thomas, C.Z. Wei, J. Han, Y. Xiang, D.J. Srolovitz, A disconnection description of triple junction motion. PNAS
116
(2019), 8756-8765.
[5] K.T. Chen, J. Han, S.L. Thomas, D.J. Srolovitz, Grain boundary shear coupling is not a grain boundary property. Acta Materialia
167
(2019), 241-247.
[6] C.Z. Wei, L.C. Zhang, J. Han, D.J. Srolovitz, Y. Xiang, Grain boundary triple junction dynamics: a continuum disconnection model. arXiv:1907.13469
(2019).
[7] C.Z. Wei, S.T. Thomas, J Han, D.J. Srolovitz, Y Xiang, A Continuum Multi-Disconnection-Mode Model for Grain Boundary Migration. arXiv:1905.13509
(2019).