L12-phase nano-structures and their stabilities in dilute Al-Zr-Y alloys: A first-principles study

We present an interface-level first principles study on the formation of L12-phase nano-structures in dilute Al-ZrY alloys. All energetics, relevant to bulk substitution, interface formation, interfacial coherent strain and segregation, were calculated and used to evaluate the nucleation and relative stabilities of various possible L12 nano-structures. The following new insights were obtained. Only matrix-dissolved solutes Y and Zr can strongly substitute the X sublattice sites in L12-Al3X (X = Zr or Y), while the inter-substitution of Al3Zr(L12) and Al3Y(L12) is energetically forbidden. Solute Zr strongly segregate to the Al/Al3Y interface, in favor to develop a Zr-rich shell surrounding L12-Al3Y. Further energetics analyses based on the classic homogeneous nucleation theory clarified the intricate correlation of the formation of complex L12-phase nano-structures with the Zr/Y atom ratio and the aging temperature. Based on which, the experimental observed L12-phase nano-structures in dilute Al-Zr-Y alloys were also explained.