Molecular Dynamics Studies of the Response of Symmetric Tilt Grain Boundaries to Deformation in Rocksalt Structured, Ionically Bonded Ceramics
Palko, James Wayne
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https://hdl.handle.net/2142/82773
Description
Title
Molecular Dynamics Studies of the Response of Symmetric Tilt Grain Boundaries to Deformation in Rocksalt Structured, Ionically Bonded Ceramics
Author(s)
Palko, James Wayne
Issue Date
2005
Doctoral Committee Chair(s)
Kieffer, John
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
This work is a computational investigation of the phenomena occurring near symmetric tilt grain boundaries during deformation under simple stress states in NaCl and some related rocksalt structured materials. The grain boundaries considered are those where the boundary in each crystal is an {n10} plane. Pure grain boundaries in NaCl, LiCl, and MgO are treated as well as doped boundaries possessing a thin amorphous interphase in the NaCl-CsCl system, and the mechanisms for formation of the amorphous phase are examined in detail. The results point to novel mechanisms active during deformation in these materials, such as: (i) formation of previously unknown hexagonal polymorphs of NaCl and LiCl under loading of the (310) grain boundary. (ii) creation of two dimensional, crack bridging, sheets under tension. (iii) decomposition of sessile dislocations into highly mobile 1/2 dislocations under hydrostatic pressure and a concomitant reduction in the slip resistance of grain boundaries formed from arrays of dislocations. (iv) mixing at amorphous grain boundaries formed by phase separation due to dislocation activity. Additionally, the atomic mechanisms of dislocation emission and absorption at these boundaries are elucidated.
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