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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Volume diffusion of 14C in high purity α‐Fe single crystals is measured in the wide temperature range of 1168 to 596 K applying the radiotracer technique and serial sectioning of the samples. In the temperature range in which the present tracer and previous Snoek‐effect measurements overlap a good agreement is found between the directly and indirectly measured diffusion coefficients. From this it is concluded that in the whole temperature range C‐atoms diffuse interstitially only via octahedral sites in α‐Fe. The data reveal a dependence on temperature which is typical for the influence of the magnetic phase transition on diffusion. The interstitial C diffusion responds more strongly to the stiffening of the lattice, which is related to the magnetic ordering, than the vacancy mediated self‐diffusion. Grain boundary diffusion of C in α‐Fe is observed below 740 K. The evaluation of the diffusion profiles results in Pc = sδD gbC which is 8 to 9 orders of magnitude larger than PFe = δD gbFe measured for grain boundary self‐diffusion in the same Fe‐material. Taking into account the segregation coefficient s, the still large difference between D gbC and D gbFe leads to the conclusion that C diffuses interstitially also in α‐Fe grain boundaries.

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