Effects of vacancy-solute clusters on diffusivity in metastable Fe-C alloys

Mukul Kabir, Timothy T. Lau, Xi Lin, Sidney Yip, and Krystyn J. Van Vliet
Phys. Rev. B 82, 134112 – Published 15 October 2010

Abstract

Diffusivity in defected crystals depends strongly on the interactions among vacancies and interstitials. Here we present atomistic analyses of point-defect cluster (PDC) concentrations and their kinetic barriers to diffusion in ferritic or body-centered-cubic (bcc) iron supersaturated with carbon. Among all possible point-defect species, only monovacancies, divacancies, and the PDC containing one vacancy and two carbon atoms are found to be statistically abundant. We find that the migration barriers of these vacancy-carbon PDCs are sufficiently high compared to that of monovacancies and divacancies. This leads to decreased self-diffusivity in bcc Fe with increasing carbon content for any given vacancy concentration, which becomes negligible when the local interstitial carbon concentration approaches twice that of free vacancies. These results contrast with trends observed in fcc Fe and provide a plausible explanation for the experimentally observed carbon dependence of volume diffusion-mediated creep in ferritic (bcc) Fe-C alloys. Moreover, this approach represents a general framework to predict self-diffusivity in alloys comprising a spectrum of point-defect clusters based on an energy-landscape survey of local energy minima (formation energies governing concentrations) and saddle points (activation barriers governing mobility).

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  • Received 19 April 2010

DOI:https://doi.org/10.1103/PhysRevB.82.134112

©2010 American Physical Society

Authors & Affiliations

Mukul Kabir1, Timothy T. Lau1,*, Xi Lin2, Sidney Yip1,3, and Krystyn J. Van Vliet1,†

  • 1Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
  • 2Department of Mechanical Engineering and Division of Materials Science and Engineering, Boston University, Boston, Massachusetts 02215, USA
  • 3Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

  • *Present address: Stanford Law School, Stanford, California 94305, USA.
  • Corresponding author.

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Vol. 82, Iss. 13 — 1 October 2010

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