The measurement of grain boundary diffusion by the method of autoradiography

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Abstract
The method of autoradiography is used in the quantitative measurement of grain boundary diffusion. The autoradiographic image is examined using the Joyce-Loebl isodensitracer to produce an accurate two-dimensional density map of the grain boundary region sufficient in detail to allow a more extensive analysis of grain boundary diffusion. Tracer diffusion of the very high, medium and very low energy isotopes antimony-124, silver-110 and nickel-63 into copper bicrystals misorientated at 45° is studied over the temperature ranges 605°c to 720°c, 543°c to 757°c and 675°c to 850°c respectively. The data show that the technique can be applied over a wide range of experimental conditions, and also reveal the limitations of the technique. A method of interpretation is derived, based on matching the experimental density distribution to a distribution that is computed from an assumed theoretical model, and takes into account the energy of radiation of the isotope. The method also allows some comparison of the experimental with the theoretical distributions to indicate the extent of the agreement with the Suzuoka and the Whipple solutions. In each case an Arrhenius plot of the results indicates a linearity over most of the range covered, and this gives an activation energy half that of volume diffusion, but at low temperatures there is an enhancement of grain boundary penetration which cannot be given a satisfactory explanation by the factors that are discussed.