Nucleation of L12-Al3M (M = Sc, Er, Y, Zr) Nanophases in Aluminum Alloys: A First-Principles ThermodynamicsStudy

High-performance Sc-containing aluminum alloys are limited in their industrial application due to the high cost of Sc elements. Er, Zr, and Y elements are candidates for replacing Sc elements. Combined with the first-principles thermodynamic calculation and the classical nucleation theory, the nucleation of L12-Al3M (M = Sc, Er, Y, Zr) nanophases in dilutealuminum alloys were investigated to reveal their structural stability. The calculated results showed that the critical radius and nucleation energy of the L12-Al3M phases were as follows: Al3Er > Al3Y > Al3Sc > Al3Zr. The Al3Zr phase was the easiest to nucleate in thermodynamics, while the nucleation of the Al3Y and Al3Er phases were relatively difficult in thermodynamics. Various structures of Al3(Y, Zr) phases with the radius r < 1 nm can coexist in Al-Y-Zr alloys. At a precipitate’s radius of 1–10 nanometers, the core–shelled Al3Zr(Y) phase illustrated the highest nucleation energy, while the separated structure Al3Zr/Al3Y obtained the lowest one, and had thermodynamic advantages in the nucleation process. Moreover, the core–shelled Al3Zr(Y) phase obtained a higher nucleation energy than Al3Zr(Sc) and Al3Zr(Er). Core–doubleshelled Al3Zr/Er(Y) obtained a lower nucleation energy than that of Al3Zr(Y) due to the negative ΔGchem of Al3Er and the negative Al3Er/Al3Y interfacial energy, and was preferentially precipitated in thermodynamics stability.