Including state-of-the-art physical understanding of thermal vacancies in Calphad models

Area of Science:

• Materials Science
• Computational Materials Science
• Thermodynamics

Background:

• Accurate thermodynamic modeling is crucial for predicting material behavior.
• Existing models often do not explicitly account for thermal vacancies.
• This limitation affects the accuracy of phase stability predictions, especially at higher temperatures.

Purpose of the Study:

• To present a physically sound thermochemical model incorporating explicit thermal vacancies.
• To extend the capabilities of the Calphad (Calculation of Phase Diagrams) formalism.
• To improve thermodynamic databases for elements and alloys.

Main Methods:

• Developed a model based on ab initio calculations for enthalpy of vacancy formation.
• Incorporated two parameters for excess heat capacity of vacancy formation.
• Validated the model using elements like Ag, Al, Cu, Zn, Ni, Ti, W and the Cu-Zn binary system.

Main Results:

• Achieved excellent agreement with experimental temperature-dependent vacancy concentrations and heat capacities.
• Ensured reasonable extrapolation of phase stability to high temperatures.
• Resolved the Neumann-Kopp related issue in multicomponent systems within the Calphad community.

Conclusions:

• The new model provides a robust framework for including thermal vacancies in thermodynamic databases.
• It enhances the predictive power of phase stability for alloys.
• This advancement is significant for computational materials science and alloy design.