Invited Lecture
Atomic interaction in grain boundaries and related phenomena

At the present talk the peculiarities were studied of grain boundary selfdiffusion in Cu connected with the effect of atomic pairs formation in GBs.

The molecular dynamics (MD) simulation of GB selfdiffusion was used taking semiempirical potential designed for Cu. To be sure in adequacy of the model proposed, the double product δD_gb of GB selfdiffusion was obtained based on mean square displacements (MSD) of free atoms at different temperatures (825, 900, 1000 and 1200K).

The results obtained for δD_gb and D_gb (GBD selfdiffusion coefficient) are in a good agreement with experimental results and other results of computer simulation.

The similar simulation was performed with the artificial addition energy of interaction (E) between identical atoms in arbitrary chosen pairs. To obtain reliable data on the MSD the used simulation cell consists of three thousands atoms, two symmetrical GBs Σ5 (001)(012) and 70 pairs of identical random Cu atoms in GBs bonded into pairs. It was required also that MD should run at least 100ps.

It was shown that the complexes formation leads to decrease of MSD for atoms bonded into the pair compared with free atoms. The pair interaction energy E=-0,2 eV/atom influences only slightly on D_gb which decreases to 15-45% comparing with E=0. The activation energy changes in limits of error. At E=-0,5 eV/atom Dgb decreases more than to order of magnitude and activation energy increases at 1,5 times comparing with E=0.

The results obtained involve also dependence the number of the stable pairs on time and temperature and show the possibility of pairs to condense into ternary, quarterly and more numerous complexes.