Diffusion and solute atom segregation in grain boundaries of copper and silver

Real materials are mostly used as polycrystalline components. Grain boundaries form planar defects in the polycrystalline structure. At temperatures below 0.5 of the melting temperature - the range in which materials are technologically applied - these defects are paths of strongly enhanced atomic mobility. Generally these interfaces are large angle grain boundaries. Impurity atoms inherent in the bulk material tend to segregate in the grain boundaries producing in this way under certain conditions brittleness and intergranular crack under load.

By investigating diffusion of impurities in grain boundaries under different, well defined kinetic conditions we are able to measure the grain boundary diffusion coefficients and the corresponding impurity segregation at the same time in the conditions of thermodynamic equilibrium. The most suitable method for these studies is the radiotracer technique, which is sufficiently sensitive to detect the very low absolute impurity concentration in the grain boundaries. From the shape of the diffusion profiles the conditions of linear versus non-linear segregation behaviour can be estimated. Segregation coefficients and segregation enthalpies were determined for several selected impurities in Cu and Ag grain boundaries.

Beteiligte Wissenschaftler:

Dr. S.V. Divinski, Prof. Dr. Chr. Herzig (Leiter), Dipl.-Phys. M. Lohmann, Prof. Dr. Y. Mishin (George Mason University, Fairfax, VA, USA)

Veröffentlichungen:

Mishin, Y., Chr. Herzig: Grain boundary diffusion: recent progress and future research, Materials Science and Engineering, A260, 55 (1999)

Divinski, S.V., M. Lohmann, Chr. Herzig: Ag grain boundary diffusion and segregation in Cu: measurements in the types B and C diffusion regimes, Acta mater., 49, 249 (2001)

Divinski, S.V., M. Lohmann, Chr. Herzig: On the physical meaning of the segregation coefficient determined by tracer diffusion measurements in Harrison's B-and C-type regimes - results on Ag in Cu polycrystals, Mat. Sci. Forum, in print