Phase selection in aluminum rare-earth metallic alloys by molecular dynamics simulations using machine learning interatomic potentials

L Tang and MJ Kramer and KM Ho and CZ Wang, PHYSICAL REVIEW MATERIALS, 7, 025601 (2023).

DOI: 10.1103/PhysRevMaterials.7.025601

Aluminum rare-earth (Al-RE) metallic alloys and glasses with Al-rich compositions have attracted much attention owing to their high strength- to-weight ratio and superior thermal stability. However, differences in phase selection and formation upon using light-or heavy-RE elements are still not well understood. Using Al90Ce10 and Al90Tb10 as prototype Al- rich light-RE and heavy-RE alloys, we study the similarity and difference of phase selection and glass-formation ability (GFA) in the two metallic glasses by molecular dynamics (MD) simulations using accurate machine learning (ML) interatomic potentials and cluster alignment analysis. We show that the glass-forming structural short- range order (SRO) motifs are much stronger in Al90Tb10 glass than in Al90Ce10 glass (77% vs 47%). On the other hand, there is a noticeable fraction of Al11RE3 and hexagonal Al3RE crystalline SRO motifs in Al90Ce10 glass that are almost absent in Al90Tb10. The origin of the SRO difference is investigated by comparing the structure-energy landscapes in these two systems, where unique competing metastable structures are obtained from an adaptive genetic algorithm search. MD simulations using the ML potentials and a solid/liquid interface model are also performed to show that the crystal growth speed in the Al-Ce is about 2-3 times faster than that in the Al-Tb system at similar undercooling conditions. The diffusion constant in the undercooled liquids and the latent heat of several competing crystalline phases and their liquids are also calculated to elucidate the different crystallization behaviors in the two systems. Moreover, chemical order preference in the two systems is also analyzed. Our results suggest that the different phase selection and GFA in the two systems can be attributed to the relative energetic stabilities of various competing metastable phases which lead to different structural and chemical SROs and different crystallization driving forces which influence the phase selection kinetics of the two systems.

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