Theoretical ab initio predictions of L12-Al3Zr structure stabilization by vacancy incorporation on the Zr sublattice

This work studies the effect of Zr sublattice vacancy (V_Zr) incorporation on the L1₂-Al₃Zr structure stabilization by first-principles calculations. It is revealed that incorporation of such vacancies in the metastable L1₂ phase is thermodynamically favored, with the energetically most preferred L1₂-Al₃Zr_(1-x)(V_Zr)_x configuration significantly reducing the L1₂ → D0₂₃ transformation driving force at experimentally relevant temperatures. The absence of experimental observation of any significant V_Zr concentration in L1₂ is proposed to result from an unfavorable Zr sublattice vacancy incorporation at the dispersoid-matrix interface, coupled with restrictive diffusion paths of Zr in the precipitate, with calculations providing potential support for this hypothesis. The present findings suggest that a circumvention of this dispersoid-matrix interface barrier to V_Zr incorporation may notably increase the thermal stability of L1₂, representing an important feature on an alternative route to the development of castable Al alloys with superior thermal stability.