Abstract:

Aluminum alloys have been the primary material of choice for structural components of aircraft,
among which Al-Li, Al-Ni, Al-Co and Al-Cu alloy have attracted much attention due to their
exceptional fracture toughness, corrosion resistance and so on. Understanding the relationships
among composition, processing, microstructural characteristics and properties can improve
strength and ductility of Al alloys that are important to aircraft applications. The phase diagram
is a crucial factor to design and improve mechanical properties of alloys based in these chemical
elements. Herein, we aim to accurately predict Al-based binary phase diagram from first
principles calculations and statistical mechanics considering the effect of configurational,
vibrational entropy and magnetic enthalpy.
The whole Al-Li and Al-Ni phase diagram is predicted from first principles calculations and
statistical mechanics. The formation enthalpy of different configurations at different
temperatures is accurately predicted by means of cluster expansions that were fitted from first
principles calculations. The vibrational entropic contribution of each configuration is determined
from the bond length vs. bond stiffness relationships for each type of bond and the Gibbs free
energy of the different phases is obtained as a function of temperature from Monte Carlo
simulations. The predicted phase diagram is in excellent agreement with the currently accepted
experimental one in terms of the stable and metastable phases, of the phase boundaries between
them and of the maximum stability temperature of line compounds. Finally, the influence of the
configurational entropy, vibrational entropy and magnetic enthalpy on the correct prediction of
the phase diagram was discussed. Overall, the methodology shows that accurate phase diagrams
of alloys of technological interest can be predicted from first principles calculations.
This first year assessment provides a theoretical guidance for the design and improve mechanical
properties of Al-based alloy. We will use first principle combined with statistical mechanics
method to predict Al-Co and Al-Cu phase diagram in the following work.