Heat transfer regimes and the electroplasticity effect: A molecular dynamics study

The reduction in the yield stress of metals without excess heating under the action of pulsed, high-density electric current is called the electroplasticity effect (EPE). One explanation of the EPE is Joule heating of dislocations. Increasing the temperature of dislocation cores allows them to detach from obstacles and overcome the Peierls-Nabarro potential, while the average sample temperature changes slightly. Therefore it is important to consider a balance between Joule heating of dislocations and energy flow from heated dislocations to cooler, defect-free areas of the crystal. We address this problem numerically using a molecular dynamics simulation of a two-dimensional lattice with a random distribution of substitutional atoms of different mass and analytically using the kinetic theory (in the ballistic limit, realized for the harmonic monatomic lattice). It is found that in the ballistic case, the temperature of the dislocation core under constant heating does not increase with time due to a rapid heat flow into the crystal volume. Substitutional atoms slow down the heat transfer and thus the temperature of the dislocation core increases linearly with time. The presented results are in agreement with known experimental facts and demonstrate the importance of the heat transfer problem in the discussion of EPE.