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AbstractÐGrain boundary diusion of Au and Cu was measured in a series of Cu bicrystals with symmetrical near AE 5, Â 36X98 310001 CSL tilt grain boundaries (GBs) using the radiotracer and the serial sectioning technique. The orientations of the bicrystals were very precisely determined with the Kossel technique where all three macroscopic parameters describing the orientations of the grains in the bicrystal were evaluated. The tilt angles ranged from 33.218 to 39.268. The GB diusion of the radiotracers 195 Au and 64 Cu was measured as a function of tilt angle and temperature. In the investigated temperature range 1030±661 K the orientation dependence of both radiotracers shows a characteristic cusp not exactly at but slightly below the ideal AE 5 CSL GB. The Arrhenius parameters, activation enthalpy and frequency factor, determined from lower temperature data adopt a maximum, again slightly before the ideal AE 5 CSL GB. These features are discussed with respect to the accidental small twist and second tilt orientations and the corresponding dislocation network inherent in the investigated real GBs. With increasing temperature a negative deviation from a straight Arrhenius behaviour is observed. This result indicates a certain change in the GB structure in the temperature range above 800 K. #

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