Date of Award

2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Frederic Sansoz

Abstract

Σ3{111} coherent twin boundary (CTB) in face-centered-cubic (FCC) metals and alloys have been regarded as an efficient way to simultaneously increase strength and ductility at the nanoscale. Extensive study of dislocation-CTB interaction has been carried out by a combination of computer simulations, experiments and continuum theory. Most of them, however, are based on the perfect CTB assumption. A recent study [Wang YM, Sansoz F, LaGrange T, et al. Defective twin boundaries in nanotwinned metals. Nat Mater. 2013;12(8):697-702.] has revealed the existence of intrinsic kink-like defects in CTBs of nanotwinned copper through nanodiffraction mapping technique, and has confirmed the effect of these defects on deformation mechanisms and mechanical behavior. One of the deformation mechanisms proposed therein, i.e. general hard dislocation slip intersecting with kink line is studied here in detail by molecular dynamics (MD) simulation. Simulations are performed using copper bicrystal models with a particular focus on the interaction of a screw dislocation with 0 degree and 60 degree kinked CTBs. It is found that kink-like defects have a profound impact on screw dislocation - CTB interaction mechanisms, resulting in significant strengthening or softening effects.

Language

en

Number of Pages

68 p.