Atomic Mechanisms of Crystallization in Nano-Sized Metallic Glasses

Understanding crystallization mechanisms in nano-sized metallic glasses (MGs) is important to the manufacturing and application of these new nanomaterials that possess a unique combination of structural and functional properties. Due to the two-dimensional projections and limited spatial and/or temporal resolutions in experiments, significant questions (e.g., whether nucleation takes place on the free surface or in a near-surface layer) regarding this subject remain under debate. Here, we address these outstanding questions using molecular dynamics simulations of crystallization in MG nanorods together with atomistic visualization and data analysis. We show that nucleation in the nano-sized MGs predominantly takes place on the surface by converting the high-energy liquid surface to a lower-energy crystal surface (the most close-packed atomic plane). This is true for all the nanorods with different diameters studied. On the other hand, the apparent growth mode (inward/radial, lateral or longitudinal) and the resulting grain structure are more dependent on the nanorod diameter. For a relatively big diameter of the nanorod, the overall growth rate does not differ much among the three directions and the resulting grains are approximately semispherical. For small diameters, grains appear to grow more in longitudinal direction and some grains may form relatively long single-crystal segments along the length of the nanorod. The reasons for the difference are discussed. The study provides direct atomistic insights into the crystallization mechanisms in nano-sized MGs, which can facilitate the manufacturing and application of these new advanced materials.

Automated summary

Understanding the crystallization mechanisms in nano-sized metallic glasses (MGs) is crucial for the manufacturing and application of these new nanomaterials with unique structural and functional properties. Through molecular dynamics simulations and atomistic visualization, we address important questions regarding nucleation and growth modes in MG nanorods. Our study shows that nucleation predominantly occurs on the surface of nano-sized MGs, while the growth mode and resulting grain structure depend on the nanorod diameter. This atomistic insight provides valuable information for the development and utilization of nano-sized MGs.