First-principles calculations, experimental study, and thermodynamic modeling of the Al-Co-Cr system

Area of Science:

• Materials Science
• Thermodynamics
• Computational Materials Science

Background:

• Understanding phase relations and thermodynamic properties is crucial for designing advanced alloys.
• The Al-Co-Cr system is important for high-performance applications, but its phase behavior requires detailed investigation.

Purpose of the Study:

• To investigate the phase relations and thermodynamic properties of the condensed Al-Co-Cr ternary alloy system.
• To develop a CALPHAD-based thermodynamic description using DFT calculations and experimental data.
• To accurately model key phases like bcc-A2, B2, fcc-γ, and tetragonal-σ.

Main Methods:

• First-principles calculations based on density functional theory (DFT).
• Phase-equilibria experiments including X-ray diffraction (XRD) and electron probe micro-analysis (EPMA).
• CALPHAD method incorporating DFT and experimental data, utilizing special quasirandom structures (SQS) and a partitioning model for A2/B2 transitions.

Main Results:

• DFT calculations and experiments revealed key phase equilibria in the Al-Co-Cr system.
• A robust thermodynamic description was developed, accurately modeling the bcc-A2, B2, fcc-γ, and tetragonal-σ phases.
• Predicted a significant bcc-A2 (disordered)/B2 (ordered) miscibility gap, consistent with experimental findings.

Conclusions:

• The developed thermodynamic model provides a reliable description of phase equilibria in the Al-Co-Cr system.
• The model accurately captures the order-disorder transitions within the A2/B2 phases.
• This work contributes to the fundamental understanding and computational design of Al-Co-Cr alloys.