arXiv subjects

Gang Lu

Publications and source records attributed to Gang Lu.

40 records · Page 3Linked to original sources

arXiv2001

Hydrogen-enhanced local plasticity in aluminum: an ab initio study

Dislocation core properties of Al with and without H impurities are studied using the Peierls-Nabarro model with parameters determined by ab initio calculations. We find that H not only facilitates dislocation emission from the crack tip but also enhances dislocation mobility dramatically, leading to macroscopically softening and thinning of the material ahead of the crack tip. We observe strong binding between H and dislocation cores, with the binding energy depending on dislocation character. This dependence can directly affect the mechanical properties of Al by inhibiting dislocation cross-slip and developing slip planarity.

cond-mat.mtrl-sci↗

arXiv2001

Interaction of vacancies with grain boundary in aluminum: a first-principles study

We present a theoretical study of the interaction of vacancies with a tilt grain boundary in aluminum based on the density functional theory. The grain boundary volume expansion and vacancy induced contraction are calculated and compared for the nearest-neighbor atoms from the defects, and the former is found to be smaller than the latter. The formation energy of a vacancy placed at various layers in the grain boundary has been calculated and we find that the grain boundary does not always act as sinks for vacancies. In fact, it costs more energy to form a vacancy at the boundary plane than in the bulk, although the rest of the grain boundary region does attract vacancies. The microscopic mechanisms of grain boundary sliding and migration are investigated thoroughly with and without a vacancy. We find that although the vacancy can hinder the grain boundary motion by tripling the energy barrier of sliding and migration, it can not inhibit or even delay the migration process. The vacancy placed at the first layer from the interface is found to be trapped at the layer and not able to follow the migrating interface.

cond-mat.mtrl-sci↗

arXiv1999

A Critical Reexamination of the Peierls-Nabarro Model

We reexamine two essential issues within the Peierls-Nabarro model which are critical in obtaining accurate values for the Peierls stress. The first issue is related to the sampling scheme of the misfit energy across the glide plane and the second one is the effect of relaxation on the Peierls stress. It is shown that most of the current applications of the Peierls-Nabarro model do not treat properly the two issues and therefore are not able to predict reliable values for the Peierls stress. We argue that the double counting scheme for the misfit energy at both sides of the glide plane is physically more reasonable, and it can predict more accurate values for the Peierls stress, especially for dislocations with equal spacing between alternating atomic rows. We also show the importance for allowing atomic relaxation when a dislocation traverses the Peierls barrier, which in turn lowers the Peierls stress for narrow dislocations by an order of magnitude.

cond-mat.mtrl-sci↗

arXiv1999

Generalized stacking fault energy surfaces and dislocation properties of aluminum

We have employed the semidiscrete variational generalized Peierls-Nabarro model to study the dislocation core properties of aluminum. The generalized stacking fault energy surfaces entering the model are calculated by using first-principles Density Functional Theory (DFT) with pseudopotentials and the embedded atom method (EAM). Various core properties, including the core width, splitting behavior, energetics and Peierls stress for different dislocations have been investigated. The correlation between the core energetics and dislocation character has been explored. Our results reveal a simple relationship between the Peierls stress and the ratio between the core width and atomic spacing. The dependence of the core properties on the two methods for calculating the total energy (DFT vs. EAM) has been examined. The EAM can give gross trends for various dislocation properties but fails to predict the finer core structures, which in turn can affect the Peierls stress significantly (about one order of magnitude).

cond-mat.mtrl-sci↗