PhysRevLett.89.105501

Introduction

• Study on the interaction of vacancies with dislocations in aluminum (Al) using semidiscrete variational Peierls-Nabarro model.

• Confirmation of vacancy lubrication effect on dislocation motion, potentially resolving a long-standing debate in dislocation theory for face-centered cubic (fcc) metals.

Key Findings

• Vacancy Lubrication Effect: The presence of vacancies enhances dislocation mobility.

• Dislocation splitting is predicted to increase in the presence of vacancies.

• Weak repulsion observed between vacancies and dislocations, independent of dislocation character.

Background

• Dislocations and Vacancies: Vacancies are point defects that interact with line defects (dislocations); traditionally thought to hinder dislocation movement.

• Previous studies (Benoit et al.) indicated vacancies may enhance dislocation mobility at low temperatures.

• Controversy exists regarding Peierls stress (p) values obtained from different experimental contexts.

Research Methodology

• Employed the semidiscrete variational Peierls-Nabarro (SVPN) model with ab initio surface data.

• The model effectively predicts dislocation properties when compared to direct atomistic simulations.

Energy Functional

• Stability and characteristics of dislocations analyzed through energy minimization of the dislocation energy functional:

  • ( U_{disl} = U_{elastic} + U_{misfit} + U_{stress} + Kb^2 ext{ln}L )

  • Core energy defined as ( U_{core} = U_{elastic} + U_{misfit} ).

Vacancy Effects

• Vacancy Concentration: Simulated a 4 at.% vacancy concentration representative of localized regions around dislocations.

• The effect of vacancies significantly alters core structures, impacting dislocation dynamics.

Results

• Peierls Stress Values: Lowered Peierls stress observed in dislocations when vacancies are present, confirming the theoretical lubrication effect:

  • p for Al and Al with vacancies shows a reduction by over an order of magnitude.

• Dislocation Core Width: Introduced vacancies increase dislocation core width by 60% to 90%, indicating enhanced mobility due to weakened lattice restoration forces.

• The introduction of vacancies lowers kink pair formation energy, relating to the observed decrease in Peierls stress.

Conclusions

• Confirmed the experimental suggestion of the vacancy lubrication effect in Al.

• Vacancies provide significant influence on dislocation mobility, bridging gaps between observed Peierls stress from different methods.

• Future technologies in material processing may exploit vacancy effects to enhance material properties.