On the mechanism of diffusion-induced recrystallization: Comparison between experiment and molecular dynamics simulations

Recent experimental results on diffusion-induced recrystallization (DIR) in size-mismatched thin film metallic diffusion couples are summarized in this paper. As the most striking feature, newly formed grains reveal a preferred concentration which is characteristic for a given couple. Based on a suggested thermoelastic interpretation, stress in front of a migrating grain boundary is calculated from observed characteristic compositions. A remarkable relation between derived stresses and shear strength of respective parent matrix is discovered: plane stress in the diffusion zone amounts consistently to about 80% of the ideal shear strength. To elucidate this relation, molecular dynamics simulations are performed in the copper–gold system applying the embedded-atom method. Simulations indicate a break of coherency within the nanometric diffusion zone when a critical diffusor concentration is reached. Both experiment and simulation show in close agreement that maximum stress in the diffusion zone is of the order of the ideal shear strength and hence far above the yield strength of the material. It is deduced that the limit of coherency controls the observed characteristic concentration levels of DIR.