VOLUME AND GRAIN-BOUNDARY DIFFUSION OF IMPLANTED SN-113 IN ALUMINUM

Volume and grain boundary diffusion of Sn-113 in aluminium was investigated with the radiotracer method. The implantation technique was used for tracer deposition to avoid problems of tracer hold-up caused by the oxide layer always present on aluminium. The diffusion penetration was chosen large enough to permit serial sectioning of samples with the aid of a microtome. The temperature dependence of the volume diffusivity was determined as D(T) = 4.54 x 10(-5) x exp[-(114.5 +/- 1.2) kJ mol-1/RT]m2 s-1. This confirms previous measurements from our group which already showed that Sn is the fastest foreign metal diffusor so far investigated in aluminium. Grain boundary diffusion of Sn-113 in Al polycrystals was measured in the type-B kinetic regime. The grain boundary diffusion product P = s-delta-D(gb) (s = segregation factor, delta = grain boundary width, D(gb) = grain boundary diffusivity) was found to be strongly affected by the impurity content of aluminium. For Al polycrystals of 99.9992% nominal purity we obtained P5N(T) = 1.08 x 10(-8) exp [-(96.9 +/- 7.5) kJ mol-1/RT] m3 s-1 and for less pure Al polycrystals of 99.99% nominal purity P4N(T) = 3.0 x 10(-10) exp [90.1 +/- 4.2) kJ mol-1/RT] m3 s-1 was determined. The grain boundary diffusion product in the purer material is more than one order of magnitude higher than in the less pure material. Very likely this is an effect of co-segregation of non-diffusant impurities into the grain boundaries.