ORIENTATION DEPENDENCE OF GE DIFFUSION ALONG SYMMETRICAL [111]-TILT GRAIN-BOUNDARIES IN AL

Grain boundary diffusion of Ge was measured in a series of Al bicrysta ls with symmetrical near Sigma = 7, Theta = 38.2 degrees (12(3) over b ar) [111] tilt grain boundaries (GBs). The actual orientations of the bicrystals were precisely measured with a modified Kossel-technique. A ll three macroscopic parameters describing the orientation of the grai ns in the bicrystals were determined. The tilt angles Theta ranged fro m 34.15 degrees to 41.41 degrees. GB diffusion measurements were perfo rmed parallel to the tilt axis in the type B kinetic regime in the tem perature interval 518-680 K using the radiotracer Ge-71 and the serial sectioning technique. A characteristic non-continuous dependence of t he measured GB diffusion parameter S delta D-GB on the tilt angle Thet a was observed for all five investigated diffusion temperatures. The G B diffusion parameter reveals a distinct minimum at the orientation of the ideal Sigma = 7, Theta = 38.2 degrees (12(3) over bar) [111] boun dary while the corresponding Arrhenius parameters (s(0)delta D-GB0) an d Q(GB) adopt a maximum. The orientation dependence of the GB diffusio n is discussed in terms of the diffusion concept of CSL boundaries. Di fferent from our previous GB diffusion investigation in near Sigma = 5 , Theta = 36.9 degrees (310) [001] Cu tilt GBs (Mater. Sci. Forum. 199 6, 207-209, 465) no specific influence of the furthermore determined o rientation parameters (twist angle, second tilt angle), on the GB diff usion, is observed. This feature is discussed with respect to the part icular dislocation network inherent in the present and previously inve stigated GBs. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Sc ience Ltd. All right reserved.