Gibbs energy functions with the vacancy complexes in the Al-Cu binary system

Area of Science:

• Materials Science
• Thermodynamics
• Computational Materials Science

Background:

• CALPHAD-type thermodynamic assessments are vital for materials development.
• Understanding point defects like vacancies is crucial for predicting material behavior.
• Previous models did not fully account for vacancy-solute interactions.

Purpose of the Study:

• To provide comprehensive Gibbs energy functions for the Al-Cu binary system.
• To incorporate the effects of monovacancies, divacancies, and vacancy-solute pairs into thermodynamic models.
• To enable calculation of vacancy fractions under various conditions, including metastable states.

Main Methods:

• Utilized CALPHAD-type thermodynamic assessment data.
• Incorporated formulations for monovacancy (Va), divacancy (VaVa), and Va-solute pairs.
• Modeled divacancies as associates in FCC solid solutions.
• Included Va-solute pair contributions via ternary excess Gibbs energy.

Main Results:

• Developed Gibbs energy functions accounting for various vacancy types in the Al-Cu system.
• Established a framework for calculating monovacancy and divacancy fractions.
• Demonstrated the ability to predict vacancy behavior even in metastable conditions.

Conclusions:

• The provided Gibbs energy functions enable accurate calculation of vacancy fractions in the Al-Cu system.
• The thermodynamic database is compatible with standard software like OpenCalphad.
• This work offers a valuable resource for researchers studying Al-Cu alloys and defect behavior.