SOLUTE SEGREGATION AT GRAIN-BOUNDARIES IN POLYCRYSTALS WITH DOMINATING MASS-TRANSPORT BY COMPLEXES

Isothermal segregation of an impurity from a finite-size grain to the interface or the external free surface under predominant mass transfer by (vacancy-impurity atom) complexes is studied at low temperatures, A modified equation is obtained for an impurity with the effective dif fusion coefficient containing the diffusion coefficients of the impuri ty and complexes with different weights. The temporal evolution of the impurity concentration is determined for planar, spherical, and cylin drical grains (which are close in shape to conventional grains) in the case of a dilute solution at an arbitrary temperature. Simple algebra ic equations are obtained for the impurity concentration at the interf ace as a function of time. These equations are also valid for a concen trated solution of the impurity at the interface, The kinetics of impu rity redissolution, i.e., the enrichment or depletion of the interface with the impurity (the departure of impurity to the bulk of the grain ) is considered. (C) 1997 American Institute of Physics.