First principles prediction of the Al-Li phase diagram including configurational and vibrational entropic contributions

TL;DR

This paper presents a first-principles approach to accurately predict the entire Al-Li phase diagram, including configurational and vibrational entropy effects, aligning well with experimental data.

Contribution

It introduces a comprehensive methodology combining cluster expansions and Monte Carlo simulations to predict alloy phase diagrams from first principles, accounting for entropy contributions.

Findings

Predicted phase diagram matches experimental data.

Accurately determined phase boundaries and stability temperatures.

Highlighted the importance of vibrational entropy in phase stability.

Abstract

The whole Al-Li phase diagram is predicted from first principles calculations and statistical mechanics including the effect of configurational and vibrational entropy. The formation enthalpy of different configurations at different temperatures was accurately predicted by means of cluster expansions that were fitted from first principles calculations. The vibrational entropic contribution of each configuration was determined from the bond length vs. bond stiffness relationships for each type of bond and the Gibbs free energy of the different phases was obtained as a function of temperature from Monte Carlo simulations. The predicted phase diagram was in excellent agreement with the currently accepted experimental one in terms of the stable (AlLi, Al2Li3, AlLi2, Al4Li9) and metastable (Al3Li) phases, of the phase boundaries between them and of the maximum stability temperature of line compounds. In addition, it provided accurate information about the gap between Al3Li and AlLi solvus lines. Finally, the influence of the vibrational entropy on the correct prediction of the phase diagram is discussed. Overall, the methodology shows that accurate phase diagrams of alloys of technological interest can be predicted from first principles calculations.