First Principles Calculation of Phase Diagrams of Alloys of Technological Interest Including Configurational and Vibrational Entropic Contributions

The phase diagram of different alloys of technological interest is predicted from first principles calculations and statistical mechanics including the effect of configurational and vibrational entropy. The formation enthalpy of different configurations was accurately predicted as a function of temperature 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.<br/><br/>The strategy was applied to determine the phase diagram of Al-Cu, Al-Li, Al-Cu-Li alloys and the computed phase diagrams were compared with the current experimental phase diagrams in the literature. Overall, the calculated phase diagrams were in good agreement with the currently accepted experimental phase diagrams and, moreover, they provided new insights and information that is sometimes missing in the experimental phase diagrams due to the limitations imposed by the kinetics of phase changes. This additional information can be very important to optimize the microstructure of these alloys by means of heat treatments.