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Abstract
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To obtain fundamental understanding on the effect of grain boundaries on the diffusion
kinetics, molecular dynamics simulations (MD) were carried out on single crystal and
nanocrystal (with a mean grain size of 2.5 nm) bcc iron using the second nearestneighbor modified embedded atom method (2NN-MEAM) interatomic potential. Selfdiffusion coefficient in single crystal and nanocrystal samples were calculated in the
temperature range from 350 K to 1000 K. A temperature-dependence of the diffusion
coefficient according to the Arrhenius law was obtained for both lattice and grain boundary
diffusion. By doing so, activation energies as well as pre-exponential factors were derived
from the diffusion coefficients and compared to experimental data. MD simulation results
show that diffusion rate of iron atoms in nanocrystal sample is 6 to 28 orders of magnitude
greater than single crystal. The trajectory of iron atoms during diffusion process verified
that diffusion occurs mostly in the grain boundaries of nanocrystal iron; suggesting that
grain boundary diffusion is dominant in nanocrystal iron. Based on the obtained results
pure grain boundary diffusion coefficient was calculated
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