Dynamics of self-interstitial structures in body-centred-cubic W studied by molecular dynamics simulation

This study concerns a molecular dynamics (MD) simulation, using the embedded-atom method (EAM), of the self-diffusion of an interstitial in the bcc metal tungsten (W) at 2000 K. It is found that the interstitial moves only along < 111 > diagonals and that the switches to other non-parallel directions take place through a two-dimensional process. The < 011 > dumb-bell is central to this process. Movement along the < 111 > diagonals takes place through < 111 > crowdions occupying 2-6 lattice sites. The probabilities of a direction switch and a move are 0.249 and 0.751, respectively. Translating the complicated movement mechanism into the simple picture of interstitial hopping between lattice points, the diffusion velocity is calculated to be 520 m s exp -1 , and the activation energy for the interstitial self-diffusion is calculated to be 0.54 eV/interstitial.