Development and Validation of Interatomic Potential for Sc and Al-Sc Alloys: Thermodynamics, Solidification, and Intermetallic Ordering

We present a second-nearest-neighbor Modified Embedded Atom Method (2NN–MEAM) potential for Scandium (Sc) and Aluminum-Scandium (Al–Sc) alloys that unifies cohesive, thermodynamic, and solidification behavior within a single transferable framework. The Sc component accurately reproduces cohesive energy, lattice constants, defect energetics, and the experimental melting point obtained from two-phase coexistence, demonstrating reliable description of both hcp and liquid phases. The Al–Sc binary interaction parameters were fitted using the L1$_2$–Al$_3$Sc reference and benchmarked against first-principles and calorimetric data. The potential reproduces the strong negative formation enthalpy of Al$_3$Sc (–0.45eVatom$^{-1}$), correct relative stability of competing phases, and realistic elastic properties. Mixing enthalpies of the liquid alloy agree with ideal-associated-solution and CALPHAD models, confirming that the potential captures exothermic Al–Sc association in the melt. Molecular-dynamics simulations of solidification reveal the expected temperature and composition dependence of homogeneous nucleation. Pure Al crystallizes readily, while Al–1~at.%~Sc exhibits a longer incubation and slower growth at the same absolute temperature due to reduced undercooling and solute drag. Within the alloy, ordered Al$_3$Sc-type L1$_2$ embryos appear spontaneously, with Sc atoms occupying cube-corner (B) sites surrounded by twelve Al neighbors. Energy–volume trajectories confirm that the potential links thermodynamics to microstructural evolution. Overall, the developed 2NN–MEAM potential provides a quantitatively grounded basis for modeling melting, solidification, and intermetallic ordering in Sc and Al–Sc systems, enabling future multicomponent alloy design and large-scale nucleation studies.

💡 Research Summary

This paper presents the development and comprehensive validation of a second-nearest-neighbor modified embedded atom method (2NN-MEAM) interatomic potential for scandium (Sc) and aluminum-scandium (Al-Sc) alloys. The primary goal was to create a unified, transferable computational framework capable of accurately describing cohesive, thermodynamic, and solidification behavior in this technologically important alloy system.

The potential was constructed in two key stages. First, the parameters for pure scandium were refined from an existing MEAM set to ensure reliable high-temperature behavior. The modified potential correctly reproduces Sc’s cohesive energy, lattice constants, defect energetics, and crucially, its experimental melting point through two-phase coexistence simulations, validating its description of both hcp solid and liquid phases. Second, the binary Al-Sc interaction parameters were meticulously fitted using the L1₂-structured Al₃Sc intermetallic compound as a primary reference. The resulting potential successfully captures the strong negative formation enthalpy of Al₃Sc (-0.45 eV/atom), the correct relative stability of competing phases, and realistic elastic properties. Furthermore, it demonstrates agreement with ideal-associated-solution and CALPHAD models for the mixing enthalpy of the liquid alloy, confirming its ability to model the exothermic Al-Sc association even in the melt.

The potential’s predictive power was rigorously tested using large-scale molecular dynamics simulations of solidification. Simulations revealed the expected temperature and composition dependence of homogeneous nucleation. Pure aluminum crystallized readily, while an Al-1 at.% Sc alloy exhibited a longer incubation time and slower growth rate at the same temperature, attributed to reduced undercooling and solute drag effects. A significant finding was the spontaneous appearance of ordered Al₃Sc-type L1₂ embryos within the solidifying alloy, with Sc atoms occupying the cube-corner sites surrounded by twelve Al neighbors. This observation directly links the potential’s thermodynamic foundation to the atomistic mechanisms of microstructural evolution during solidification.

In summary, the developed 2NN-MEAM potential provides a quantitatively robust and transferable tool for simulating complex phenomena in Sc and Al-Sc systems, including melting, solidification, and intermetallic ordering. It establishes a critical foundation for future computational studies aimed at multicomponent alloy design and large-scale investigations of nucleation kinetics, offering deep insights into the atomistic origins of the exceptional properties of Al-Sc alloys.