Revisiting first-principles thermodynamics by quasiharmonic approach: Application to study thermal expansion of additively-manufactured Inconel 625

TL;DR

This paper introduces a refined quasiharmonic DFT approach for accurately predicting thermodynamic properties, demonstrated on additively manufactured Inconel 625, with results aligning well with experimental data.

Contribution

The study develops an improved method for calculating thermodynamic properties using a model selection approach, enhancing accuracy and efficiency for complex materials.

Findings

Predicted thermal expansion matches experimental measurements.

Model selection with AICc improves fitting accuracy.

Sensitivity analysis reveals effects of structural variations on properties.

Abstract

An innovative method is developed for accurate determination of thermodynamic properties as a function of temperature by revisiting the density functional theory (DFT) based quasiharmonic approach (QHA). The present methodology individually evaluates the contributions from static total energy, phonon, and thermal electron to free energy for increased efficiency and accuracy. The Akaike information criterion with a correction (AICc) is used to select models and model parameters for fitting each contribution as a function of volume. Using the additively manufactured Inconel alloy 625 (IN625) as an example, predicted temperature-dependent linear coefficient of thermal expansion (CTE) agrees well with dilatometer measurements and values in the literature. Sensitivity and uncertainty are also analyzed for the predicted IN625 CTE due to different structural configurations used by DFT, and hence different equilibrium properties determined.