A first principles study of defects in titanium: interaction of twin boundaries with dislocations and oxygen interstitials

Ghazisaeidi, Maryam

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https://hdl.handle.net/2142/29557 Copy

Description

Title

A first principles study of defects in titanium: interaction of twin boundaries with dislocations and oxygen interstitials

Author(s)

Ghazisaeidi, Maryam

Issue Date

2012-02-01T00:55:19Z

Director of Research (if dissertation) or Advisor (if thesis)

Trinkle, Dallas R.

Doctoral Committee Chair(s)

Sofronis, Petros

Committee Member(s)

• Trinkle, Dallas R.
• Freund, Lambert B.
• Robertson, Ian M.

Department of Study

Mechanical Sci & Engineering

Discipline

Theoretical & Applied Mechans

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Defects
• Mechanical properties
• Computational Materials Science

Abstract

Interaction between gliding dislocations and twin boundaries affects the plastic deformation of hcp metals such as titanium. In addition, oxygen greatly affects both strength and twinning in titanium. Predictive models of strength and twinning rely on understanding of the underlying atomic scale mechanisms which are best captured through computer simulations. While recent first-principles methods predict dislocation core structures and boundary geometries and energies, modeling a dislocation near a boundary requires new techniques to treat the long range strain field of the dislocation near a boundary. Using flexible boundary conditions with a new method to compute the lattice Green’s function for crystals containing a planar interface, we present a general method to study line defects interacting with interfaces with a tractable number of atoms. This method is general in the sense that it can consider long range atomic interactions and reconstructions near the interface. We use the interfacial lattice Green’s function to model a screw dislocation interaction with Ti (10-12) twin boundary for the first electronic structure prediction of a dislocation in a boundary. We predict the dislocation core geometry in the twin boundary and compare with the core structure in bulk titanium. The first principles nature of this study makes it possible to consider interactions with solutes. The interaction energy of an oxygen interstitial with the Ti (10-12) is also computed. While we applied our method to a systematic study of defects interactions in titanium, the method is general and opens up the possibility of investigating line defects/interface interactions with chemistry changes in arbitrary systems.

Graduation Semester

2011-12

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http://hdl.handle.net/2142/29557

Copyright and License Information

Copyright 2011 Maryam Ghazisaeidi

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