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https://hdl.handle.net/2142/19462
Description
Title
Diffusion along twist grain boundaries in copper
Author(s)
Nomura, Miki
Issue Date
1996
Doctoral Committee Chair(s)
Adams, James B.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
Diffusion along twist grain boundaries was studied using the Embedded Atom Method (EAM). Six (100) twist grain boundaries (8.79$\sp\circ$-43.6$\sp\circ$) in Copper were investigated using energy minimization. Both vacancy and interstitial mechanisms were considered. Vacancy formation energies in all possible sites were calculated (0.14-0.76eV) and found to be directly related to the degree of coincidence with the neighboring crystal planes. The optimal migration paths were found to coincide with the screw dislocations which comprise the boundary. Vacancy migration energies were found to be low (0.02-0.52eV). The activation energies for self-diffusion at the boundaries were found to be less than half of the bulk value (2.07eV). Interstitial formation energies were found to be lower (0.26-0.78eV) than in the bulk also and migration energies were found to be comparable (0.01eV-0.24eV) to the bulk values (0.09eV). The vacancy mechanism was favored for low angle boundaries and the interstitial mechanism was favored for high angle boundaries. The total diffusion rate was calculated and agreed with the experimental value obtained from studies of polycrystalline Cu, and also, with experimental value for specific twist boundaries of Zn/Al. Molecular dynamics (MD) simulation of diffusion along high ($\Sigma$5 36.87$\sp\circ$) twist grain boundaries were carried out. Both ideal structures and boundaries with excess vacancies or excess interstitials were studied. A ring mechanism was observed during the simulation, but it did not contribute to long range diffusion. The mean square displacement of the atoms and defects were used to calculate the diffusion rate of the defects, and the results were in good agreement with the molecular statics calculations.
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