Year

2015

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials and Mechatronics Engineering

Abstract

Grain boundary (GB), a special solid-solid interface in materials, exists in all polycrystalline materials, thereby being closely related to physical, chemical and mechanical properties (conductivity, catalysis, segregation, corrosion, ductility and strength etc) of the polycrystalline materials, especially in ultra fine and nano crystalline materials. In the present study, the molecular dynamics method has been used to simulate the grain boundary deformation behaviours, which include grain boundary sliding (GBS) behaviour, grain boundary coupling behaviour and the interaction between grain boundaries and dislocations. The following results have been obtained.

First, grain boundary sliding behaviour was strongly sensitive to the temperature. At low temperature, the GBS was very sensitive to the imposed ways of external applied forces. However, at high temperature, the two grains smoothly slid away from each other in the way of viscous grain boundary sliding under the shear deformation. Regardless of the type of driving force and misorientation, the bicrystal system tended to resist the applied force by GB rotation. Moreover, the grain boundary rotated among some of the Σ5 asymmetrical and symmetrical tilt GB boundaries under shear deformation and led to the normal stress σxx in the bicrystal system. Under particular circumstances, reaction of the grain boundary dislocations during shear deformation could release uncommon edge lattice dislocations from the grain boundary. The uncommon edge lattice dislocations with/2 Burgers vectors have the [001] line direction and glide on the {110} planes.

FoR codes (2008)

0912 MATERIALS ENGINEERING, 0913 MECHANICAL ENGINEERING

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.