Grain Boundary Diffusion in Copper under Tensile Stress
Stress enhanced self-diffusion of Copper on the $Σ$3 twin grain boundary was examined with molecular dynamics simulations. The presence of uniaxial tensile stress results in a significant reduction in activation energy for grain-boundary self-diffusion of magnitude 5 eV per unit strain. Using a theoretical model of point defect formation and diffusion, the functional dependence of the effective activation energy $Q$ on uniaxial tensile strain $ε$ is shown to be described by $Q(ε)=Q_0-E_0V^*ε$ where $E_0$ is the zero-temperature Young's modulus and $V^*$ is an effective activation volume. The simulation data agree well with this model and comparison between data and model suggests that $V^*=0.6Ω$ where $Ω$ is the atomic volume. $V^*/Ω=0.6$ is consistent with a vacancy-dominated diffusion mechanism.