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MM: Fachverband Metall- und Materialphysik

MM 54: Topical Session: Interface-dominated phenomena - Crystallization and Microstructure Evolution

MM 54.3: Vortrag

Donnerstag, 19. März 2020, 12:15–12:30, IFW A

Shedding light on polymorph selection and seeding mechanisms during crystal nucleation in metals — •Grisell Díaz Leines and Jutta Rogal — Interdisciplinary Centre for Advanced Materials Simulation, Ruhr-University Bochum, Germany

Fundamental knowledge of the mechanism and the principles of polymorph selection during crystal nucleation is essential for the synthesis and control of materials with targeted properties. However, understanding the atomistic mechanism of crystallization poses a major challenge as many materials exhibit complex transitions with multiple steps, forming polymorphic structures. Here, we employ an advanced atomistic simulation method, transition path sampling, to investigate the formation mechanism of crystal clusters during homogenous and heterogeneous nucleation in metals. The analysis of the nucleation pathways in Ni shows that the formation of pre-ordered liquid regions with increased bond-orientational order facilitates the emergence of crystallites by decreasing the interfacial free energy. The pre-structured cloud acts as a precursor of crystallization and predetermines the polymorph selected. Furthermore, we explore how selected crystal seeds influence the polymorphic outcome and efficiency of the nucleation process in Ni. Our investigation reveals a novel mechanism of heterogeneous nucleation, demonstrating that the ability of small seeds to promote bond-orientational order fluctuations and template the formation of effective precursors in the liquid, is central to understand the enhancement of the nucleation probability and the selection of polymorphs during crystallization.