Аннотация
Metastable precipitate phase boundaries are difficult to ascertain experimentally and yet are important for controlling the microstructure of precipitation-hardenable alloys. We demonstrate how first-principles calculations of configurational and vibrational free energies can be used to predict precipitate phase boundaries of stable and metastable phases in Al–Cu alloys. Surprisingly, the formation entropy of a Cu impurity is found to be hugely positive(+2.7 k B /atom), leading to a dramatic enhancement in the solubility. The large entropy is dominated by the very low-frequency vibration of the small impurity atom (Cu) inside the large cage of the host (Al). The agreement between the GGA and experimental data is within 100 K for all phases, showing that accurate first-principles determination of metastable phase boundaries is now possible.
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