Formation of coherent, core-shelled nano-particles in dilute Al-Sc-Zr alloys from the first-principles

We present a systematic first-principles based study on the formation of coherent L1(2)-phase nanoparticles in dilute Al-Sc-Zr alloys. Bulk structures and properties, solute substitution, interface formation energies, and interfacial coherent strains are all calculated. Nucleation modeling and relevant energetic calculations are performed on various possible structures of L1(2)-phase nano-precipitates, i.e. individual L1(2)-Al3Sc and L1(2)-Al3Zr, homogeneous L1(2) -Al-3(Sc,Zr1-x) and the core-shelled L1(2)-Al3Sc(Al3Zr) and L1(2)-Al3Zr(Al3Sc). The following insights are obtained. Matrix-dissolved Sc or Zr strongly prefers to substitute the X sublattice sites in L1(2)-Al3X (X= Zr or Sc), while the inter-substitution between L1(2)-Al3Sc and Al3Zr is only weakly feasible. The cube-on-cube orientation with the (100)/(100) contacting facets is the most energy favored for the Al/Al3Sc(L1(2)), Al/Al3Zr(L1(2)) and Al3Sc (L1(2))/Al3Zr(L1(2)) interfaces. All these interfaces are highly coherent, with fairly low formation energy. And particularly, the Al3Sc(L1(2))/Al3Zr(L1(2)) interface has essentially zero formation energy. Ternary L1(2)-A1(3)(ScxZr1-x) precipitates tend to form a Al3SC-based core and Al3Zr-based shell structure, with a relatively sharp inner interface of Al3Sc(L1(2))/Al3Zr(L1(2)). This core-shelled structure becomes energetically more favorable for the particle size R >1-2 nm. The potential influence of the Sc/Zr ratio and temperature on the relative stabilities of L1(2)-phases in Al is also evaluated and discussed. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.