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Abstract
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To obtain a fundamental understanding of the effect of structure and geometry of grain boundary on
the diffusion kinetics in nanocrystalline materials, the influence of grain boundary misorientation on
the effective diffusion coefficient (apparent diffusivity) in nanocrystalline aluminum was investigated
using molecular dynamics simulations. Nine series of [001] symmetric tilt grain boundaries,
including high and low symmetric boundary planes, were studied. The apparent diffusivity in the
samples was calculated in the temperature range from 423K to 823K by monitoring the mean square
displacement of atoms as a function of simulation time. A temperature dependence of the effective
diffusion coefficient according to the Arrhenius law was obtained for all samples. It is found that the
apparent diffusivity is anisotropic and it is a strong function of grain boundary misorientation at low
and high temperatures. At all temperatures, R29 [001]/(520) symmetric tilt grain boundary with
misorientation angle of 43.68 exhibits the highest effective diffusion coefficient among the
investigated grain boundaries. The simulation results show that the activation energy and preexponential
factor are affected significantly by the grain boundary misorientation angle. Moreover,
the results indicated that the misorientation dependence of activation energy for diffusion exhibits
two local maxima, which correspond to two symmetric tilt grain boundaries. Additional calculation
of misorientation dependence of the pre-exponential factor shows two local minima at the same symmetric
tilt grain boundaries. The misorientation dependence of the effective diffusion coefficient was
explained on the basis of grain boundary energy and the crystallographic structure of grain boundary.
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