Molecular dynamics simulation of the diffusion behaviour in Ti–Ag using diffusion couple method

Abstract

The diffusion behaviour of the Ti–Ag system was investigated using classical molecular dynamics by simulating a diffusion couple at various temperatures. One bulk of the diffusion couple consisted of titanium atoms arranged in a hexagonal close-packed (hcp) structure, i.e., α-Ti, and the other consisted of silver atoms arranged in a face-centred cubic (fcc) structure. The modern second nearest-neighbour modified embedded-atom method (2NN-MEAM) interatomic potential was used. The mean square displacement (MSD) of Ti atoms diffusing into Ag and Ag atoms into α-Ti was recorded during the simulation. Diffusion coefficients were determined from the slopes of lines fit to linear regions of MSD dependence on time. The Arrhenius relation was used to determine the activation energy and the frequency of attempts. The activation energy of Ti was 0.61eV and frequency of attempts 1.90⋅10−8m2s−1. The determined activation energy of Ag and frequency of attempts were not considered reliable because the Ag diffusion coefficient did not grow exponentially with temperature. Ti atoms penetrated deeper and greater amounts into Ag than Ag into α-Ti and also had a greater diffusion coefficient at all temperatures. The results were compared with the available experimental data, and for these purposes, self-diffusion in α-Ti and Ag was further investigated. Finally, it was determined that Ag diffuses in α-Ti by hopping over interstitial positions and Ti in Ag via vacancies.