DIFFUSION ALONG [001] TILT BOUNDARIES IN THE AU/AG SYSTEM .2. ATOMISTIC MODELING AND INTERPRETATION

The low temperature boundary diffusion data obtained in Part I were modeled using elementary vacancy, interstitialcy and interstitial defect mechanisms. First, boundary structures were calculated using the embedded atom method. Point defect formation energies at different boundary sites and migration energies between them were then calculated, and values of delta(b)D(b) were determined using recently developed expressions for this quantity. The results indicate that the diffusion is dominated by a small number of jumps having relatively small activation energies and large partial correlation factors. Also, interstitial-related mechanisms make important (and perhaps dominant) contributions to the diffusion. Both the data and modeling indicate Arrhenius pre-exponential factors considerably smaller than those reported at high temperatures. It is suggested that additional jumps (possessing higher effective activation energies) exist, and that their contributions become dominant at high temperatures. Finally, the observed delta(b)D(b) vs misorientation behavior is found to be qualitatively consistent with the structural unit model.