Analysis of plastic strain-enhanced diffusivity in nanocrystalline iron by atomistic simulation

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Abstract
Plastic deformation may affect bulk diffusion in nanocrystalline materials by altering the rates of point defect production and annihilation. In the present work, a detailed analysis of this phenomenon is given by a series of molecular dynamics (MD) simulations to clarify the effect of preplastic strain on the diffusivity of iron atoms. The embedded atom method interatomic potential was used to perform MD simulations. The self-diffusion coefficient of iron atoms in unstrained and prestrained samples was measured over temperatures ranging from 600 to 1000 K and at total strains of 5%–20%. The results reveal that the diffusivity is indeed enhanced as a result of plastic straining, especially at low temperatures. The calculated diffusion coefficient of iron atoms in the prestrained samples is 10–80 times higher than that in the unstrained samples. The atomic structure analysis results indicated that the generation of excess vacancies and unstructured region by preplastic deformation contributes to the enhancement of self-diffusion under plastic straining conditions. At low temperatures, preplastic straining has a considerable effect in the peak shifting and broadening of the radial distribution function, which probably lowers the activation barrier height for diffusion.

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