Kinetics of a fast moving twin boundary in nickel

A complete description of high-rate dynamic deformation of metals demands, in part, the fundamental understanding and characterization of twin boundary (TB) kinetics. We use molecular dynamics (MD) to characterize the TB kinetics in nickel, which serves as a model material for understanding TB kinetics in face-centered cubic metals. The kinetics of twinning dislocations (TD) fundamentally govern the TB kinetics. Propagation kinetics for a TD shares many common features with full dislocation kinetics, including non-linear kinetics, stable propagation regimes and forbidden velocities. However, a TD experiences an additional drag (as compared to a full dislocation) due to damping interactions with the TB; these characteristics are reflected in the TB kinetics. We show that, in Ni, TB velocities are limited to ∼650m s-1, well below the shear wave speed. The insights gained from the MD simulations inform our proposed kinetic relations for TD and TB, and we show how these kinetic relations may be utilized in both macroscopic and crystal plasticity formulations.