First-Principles Phase Stability Calculations of Pseudobinary Alloys of (Al,Zn)3Ti with L12, D022, and D023 Structures
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The thermodynamic and mechanical stability of intermetallic phases in the Al3Ti-Zn3Ti pseudobinary alloy system is investigated from first-principles total energy calculations through electronic density-functional theory within the generalized gradient approximation. Both supercell 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 D022 and D023 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.