Molecular Dynamics Studies of the Response of Symmetric Tilt Grain Boundaries to Deformation in Rocksalt Structured, Ionically Bonded Ceramics

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science and Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Palko, James Wayne

Contributors dc:contributor

• Kieffer, John

• Engineering, Materials Science

Language dc:language

eng

Identifier

(MiAaPQ)AAI3199109

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/82773