  Precipitation during high temperature aging of Al-Cu alloys is analyzed by
means of the integration of classical nucleation theory and phase-field
simulations into a multiscale modelling approach based on well-established
thermodynamics principles. In particular, thermal stability of ${\theta}''$,
${\theta}'$ and ${\theta}$ precipitates was assessed from first principles
calculations of the Helmholtz free energy while homogeneous and heterogeneous
nucleation of ${\theta}''$ and ${\theta}'$ was analysed using classical
nucleation theory. Precipitate growth was finally computed by means of
mesoscopic phase-field model. The model parameters that determine
quantitatively the driving forces for each transformation were obtained by
means of first principles calculations and computational thermodynamics. The
predictions of the models were in good agreement with experimental results and
provided a comprehensive understanding of the precipitation pathway in Al-Cu
alloys. It is envisaged that the strategy presented in this investigation can
be used in the future to design optimum microstructures based on the
information of the different energy contributions obtained from first
principles calculations.
