The temperature dependence of grain boundary self-diffusion in polycrystals was investigated by using the 64Cu radiotracer and serial sectioning. Two different high-purity materials were studied at 1066 to 720K (5N8) or from 973 to 784K (5N). A significant dependence of the grain boundary self-diffusion upon material purity was observed:

5N8:     D (m3/s) = 3.89 x 10-16 exp[-72.47(kJ/mol)/RT]

5N:     D (m3/s) = 1.16 x 10-15 exp[-84.75(kJ/mol)/RT]

The differences in grain boundary diffusion coefficient and activation enthalpy were explained in terms of strong impurity-Cu atom bonding in the boundary.

T.Surholt, C.Herzig: Acta Materialia, 1997, 45[9], 3817-23