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 L12-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 L12-phase nano-precipitates,i.e.individual L12-Al3Sc and L12-Al3Zr,homogeneous L12-Al3(ScxZr1-x)and the core-shelled L12-Al3Sc(Al3Zr)and L12-Al3Zr(Al3Sc).The following insights are obtained.Matrix-dissolved Sc or Zr strongly prefers to substitute the X sublattice sites in L12-Al3X(X=Zr or Sc),while the inter-substitution between L12-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(L12),Al/Al3Zr(L12)and Al3Sc(L12)/Al3Zr(L12)interfaces.All these interfaces are highly coherent,with fairly low formation energy.And particularly,the Al3Sc(L12)/Al3Zr(L12)interface has essentially zero formation energy.Ternary L12-Al3(ScxZr1-x)precipitates tend to form a Al3Sc-based core and Al3Zr-based shell structure,with a relatively sharp inner interface of Al3Sc(L12)/Al3Zr(L12).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 L12-phases in Al is also evaluated and discussed.