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Stability and mobility of vacancy-H complexes in Al
Magnús Th Benediktsson1, Kjartan K G Mýrdal, Pramod Maurya
1Science Institute, University of Iceland, Reykjavík, 107, Iceland. Department of Applied Physics, Chalmers University of Technology, Göteborg, SE-41296 , Sweden.
Summary
Hydrogen loading significantly enhances the stability of vacancy-hydrogen complexes in aluminum. Higher hydrogen concentrations pin vacancies, increasing diffusion barriers and potentially forming new defects.
Area of Science:
- Materials Science
- Computational Materials Science
- Physical Chemistry
Background:
- Understanding the behavior of vacancies and hydrogen in metals is crucial for materials integrity.
- Vacancy-hydrogen complexes influence material properties, including mechanical strength and hydrogen embrittlement.
- Aluminum's interaction with hydrogen is a key factor in its performance in various applications.
Purpose of the Study:
- To investigate the impact of hydrogen loading on the stability and mobility of vacancy-hydrogen complexes in aluminum.
- To quantify the binding energies and diffusion barriers of these complexes under varying hydrogen concentrations.
- To elucidate the mechanisms behind the observed changes in stability and mobility.
Main Methods:
- Density Functional Theory (DFT) calculations were employed to model the system.
- The minimum-mode-following method was utilized to determine diffusion pathways and energy barriers.
- Calculations focused on vacancy-hydrogen complexes with varying hydrogen atom occupancies.
Main Results:
- Binding energy per hydrogen atom ranges from -0.36 eV/atom (1 H) to -0.34 eV/atom (8 H).
- Total binding energy reaches -2.72 eV for eight hydrogen atoms, with significant compensation of vacancy formation energy at just two hydrogen atoms (-0.70 eV).
- Vacancy mobility is significantly reduced (diffusion barrier increases to ≥1.03 eV) for complexes with four or more hydrogen atoms, indicating vacancy pinning.
Conclusions:
- Increased hydrogen loading enhances the stability of vacancy-hydrogen complexes in aluminum.
- Vacancy pinning and reduced mobility at higher hydrogen loads suggest these complexes can act as nucleation sites for extended defects.
- These findings have implications for understanding hydrogen-induced degradation and defect formation in aluminum alloys.
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