Defects and diffusion in Al and Al-Cu alloy

Atomistic modeling and simulation plays an ever increasing role in understanding defects, segregation, and diffusion in a variety of materials systems. In this paper, we describe a newly-developed defect generation mechanism, namely the grain boundary Frenkel pair (GBFP) model, and corresponding diffusion mechanisms during electromigration developed using atomic molecular statics (MS), Monte Carlo (MC), and molecular dynamics (MD) simulation techniques in Al and Al-Cu. We contend that large numbers of interstitials and vacancies exist at grain boundaries and both contribute to mass transport. Cu preferentially segregates to the interstitial sites at grain boundaries via a Frenkel pair generation process and reduces the overall grain boundary diffusivity due to the strong binding in the Al-Cu dimer. Predictions from our models are in excellent agreement with available experimental data and observations. Implications of the GBFP model on grain boundary segregation, mass transport, and diffusion induced migration will be discussed.