Growth front nucleation in a hydrodynamic model of crystallization (HPFC)

Structural aspects of crystal nucleation in undercooled liquids are explored using a nonlinear hydrodynamic theory of crystallization proposed recently [G. I. Tóth et al., J. Phys.: Condens. Matter 26, 055001 (2014)], which is based on combining fluctuating hydrodynamics with the phase-field crystal theory. We show that in this hydrodynamic approach not only homogeneous and heterogeneous nucleation processes are accessible, but also growth front nucleation, which leads to the formation of new (differently oriented) grains at the solid-liquid front in highly undercooled systems. Formation of dislocations at the solid-liquid interface and interference of density waves ahead of the crystallization front are responsible for the appearance of the new orientations at the growth front that lead to spherulite-like nanostructures.

Article: Physical Review E 95, 052801, (2017)

Slide No. 1:

Polycrystalline solidification in the HPFC model supplemented with momentum noise within the metastable (ϵ < ϵc) and unstable liquid (ϵ > ϵc) regimes. Here ϵc = 0.1178 is the linear stability limit of the liquid phase, and ψ0 = −0.1982 is the initial density of the liquid. Note that in all cases, crystallization was started by placing a single potential well of the atomic size at the center of the simulation box. The time elapsed between subsequent snapshots was 10000 timesteps for the upper and central rows, whereas 50000 timesteps for the bottom row.

Slide No. 2:

Polycrystalline growth in the HPFC model: Two mechanisms are observed for creating new orientations at the solidification front: (a) nucleation of dislocations preferably in cusps of the interface and (b) nucleation near the front due to density waves emanating from the solid-liquid interface. The right and the lower side of the roughly hexagonal crystal (displayed in the red rimmed insert) are shown magnified in the upper and lower rows of the animations,