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Point defect thermodynamics and diffusion in Fe3C: A first-principles study

Authors
Journal
Acta Materialia
1359-6454
Publisher
Elsevier
Publication Date
Volume
56
Issue
13
Identifiers
DOI: 10.1016/j.actamat.2008.03.012
Keywords
  • Steels
  • Carbides
  • Point Defects
  • Diffusion
  • First-Principle Electron Theory

Abstract

Abstract The point defect structure of cementite (Fe 3C) is investigated using a combination of the statistical mechanical Wagner–Schottky model and first-principles calculations within the generalized gradient approximation. Large 128-atom supercells are employed to obtain fully converged point defect formation energies. The present study unambiguously shows that carbon vacancies and octahedral carbon interstitials are the structural defects in C-depleted and C-rich cementite, respectively. The dominant thermal defects in C-depleted and stoichiometric cementite are found to be carbon Frenkel pairs. In C-rich cementite, however, the primary thermal excitations are strongly temperature-dependent: interbranch, Schottky and Frenkel defects dominate successively with increasing temperature. Using the nudged elastic band technique, the migration barriers of major point defects in cementite are also determined and compared with available experiments in the literature.

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