The diffusivity of 71Ge was measured (tables 17 and 18) in a series of bi-crystals with symmetrical near Σ =7 θ = 38.2º (12¯3)[111] tilt grain boundaries. The precise orientations of the bi-crystals were measured by using a modified Kossel technique. The tilt angles ranged from 34.15 to 41.41º. Boundary diffusion measurements were performed by serial sectioning parallel to the tilt axis, in the type-B kinetic regime, at temperatures ranging from 518 to 680K. A characteristic non-continuous dependence of the measured grain-boundary diffusion parameter upon the tilt angle was observed at all temperatures. The grain-boundary diffusion parameter exhibited a distinct minimum at the orientation of the ideal Σ =7 θ = 38.2º (12¯3)[111] boundary, while the corresponding Arrhenius parameters were at their maxima. The orientation dependence of the grain-boundary diffusion was explained in terms of the concept of CSL boundaries. No clear effect of twist angle or second tilt angle upon grain-boundary diffusion was observed.

T.Surholt, D.A.Molodov, C.Herzig: Acta Materialia, 1998, 46[15], 5345-55

Table 19

Diffusivity of H in Al