First-Principles Phase Stability Calculations of Pseudobinary Alloys of (Al,Zn)3Ti with L12, DO22 and DO23 Structures

The thermodynamic and mechanical stabilities of the Al3Ti-Zn3Ti pseudobinary alloy system is investigated from first-principles through density-functional theory calculations within the generalized gradient approximation. Both supercells calculations and sublattice cluster expansion methods are used to demonstrate that the addition of Zn to the Al sublattice of Al3Ti stabilizes the cubic L12 structure relative to the tetragonal DO22 and DO23 structures. This trend can be understood in terms of a simple rigid-band picture in which the addition of Zn modifies the effective number of valence electrons that populate bonding and anti-bonding states. The calculated zero-temperature elastic constants show that the binary end members are mechanically stable in all three ordered phases. These results point to a promising way to cost effectively achieve the stabilization of L12 precipitates in order to favor the formation of a microstructure associated with desirable mechanical properties.