Controlling polymorph selection during nucleation by tuning the structure of metallic melts

Area of Science:

• Materials Science
• Crystallization Science
• Computational Materials Science

Background:

• Controlling crystal polymorphism is vital for designing metallic materials with tailored properties.
• The atomistic mechanisms governing polymorph selection during crystallization are not fully understood.
• Polymorphism significantly impacts material performance and applications.

Purpose of the Study:

• To explore the atomic mechanisms of polymorph selection during the nucleation of FCC aluminum and copper.
• To elucidate the role of free-energy surfaces and precursor symmetry in nucleation pathways.
• To provide theoretical guidance for controlling nucleation and polymorph selection in practice.

Main Methods:

• Employed molecular dynamics (MD) simulations.
• Utilized well-tempered metadynamics simulations to explore free-energy landscapes.
• Investigated nucleation processes in undercooled FCC aluminum and copper melts.

Main Results:

• Distinct nucleation pathways for FCC metals arise from different free-energy surfaces and precursor symmetries.
• The initially formed phase typically possesses symmetry closest to that of the nucleation precursors.
• Tiny seeds with specific symmetries can induce ordered precursors, lowering the nucleation barrier and promoting nucleation.

Conclusions:

• Precursor symmetry is a critical factor in determining the selected crystal polymorph during nucleation.
• Controlling polymorph selection can be achieved by tuning precursor symmetry using tailored seeds.
• Findings offer fundamental insights into polymorph selection and practical strategies for controlling crystallization.