TEMPERATURE-DEPENDENCE AND ANISOTROPY OF GRAIN-BOUNDARY SELF-DIFFUSION ALONG SIGMA=5 [001] TILT BOUNDARIES IN AG

Using the radiotracer Ag-110m, grain boundary (GB) self-diffusion in n aturally grown, symmetrical Sigma = 5 [001] tilt boundaries has been s tudied in detail resulting in the first extended set of self-diffusion data for oriented high-angle GBs. A technique based on the Bridgman m ethod has been developed which allows production of GBs with large are a (similar to 8 x 60 mm). This allows the measurement of the diffusion behaviour parallel and perpendicular to the tilt axis in specimens cu t from the same bicrystal. The GB diffusivity was measured for diffusi on parallel and perpendicular to the tilt axis in the temperature rang e 593-876 K. The Arrhenius parameters determined for the theta = 53.1 degrees {012} GB were found to be drastically lower (1.23 x 10(-17) m( 3)s(-1); 37.4 kJ/mol) than for the theta = 36.9 degrees {013} GB (6.44 x 10(-13)m(3)s(-1); 109.1 kJ/mol). Furthermore, a slight anisotropy w as found for theta = 36.9 degrees, but no anisotropy was observed for theta = 53.1 degrees. This behaviour is rationalized using a three-dim ensional model of the atomic structure in the GB core region.