Measurement of rapid mass transport along individual dislocations in aluminum

Abstract

Measurements were made of rapid mass transport by self-diffusion along individual dislocations in aluminum. Voids (200–400 Å in diameter) were first produced throughout thin film specimens, and a number of them were “hooked-up” to the specimen surfaces by individual dislocations which were of the usual slip type with Burgers vectors b = a 2〈110〉 . Upon subsequent annealing, electron microscope observations showed that atoms from the surfaces diffused rapidly along the dislocations to the hooked-up voids causing them to anneal out more rapidly than isolated voids which were otherwise similar. An analysis of void shrinkage rates measured between 50 and 180°C, assuming that the dislocation diffusion occurred via vacancies, yielded the expression Λ d v = AD T d ξ T d = 7.0 × 10 −17 exp(− 0.85eV kT ) cm 4Sec −1 for the average value of the self-diffusional mass transport parameter, Λ d v , for a considerable number of dislocations making angles, θ, with respect to b over the range at least 20° ⪯ θ ⪯ 80°. Here, A = effective dislocation area, D T d = dislocation tracer self-diffusivity and ξ T d = dislocation tracer correlation factor. A similar result, (within a factor of two) was obtained using a phenomonological analysis independent of mechanism. The Λ v d data for individual dislocations showed a relatively large scatter, and no systematic variation with θ was evident. It was concluded that any variation of Λ v d with θ in the range 20° ⪯ θ ⪯ 80° was less than a factor of ten. The results were compared to selected existing measurements of tracer self-diffusion along dislocations, and it was pointed out that the data were not inconsistent with a vacancy mechanism in which the correlation factor was relatively temperature independent and of magnitude of the order of a few tenths.