Kinetic stages in the crystallization of deeply undercooled body-centered-cubic and face-centered-cubic metals

Crystallization velocities in several face-centered-cubic (fcc) and body-centered-cubic (bcc) metals are calculated using molecular dynamics computer simulations for the (1 0 0) and densely packed (1 1 1) or (1 1 0) planar interfaces. We show that the crystallization kinetics can be divided into high- and low-temperature regimes, separated at a crossover temperature, T_c, which is associated with kinetic arrest. In the high-temperature regime, the velocity in both fcc and bcc metals initially increases with the degree of undercooling before reaching a maximum somewhat above the glass temperature. The kinetics is characterized by a thermally activated process. In the low-temperature regime, stresses develop in the interface and reduce the apparent activation energies for interface mobility. For the fcc metals (Cu, Ni, Ag and Pt) the activation energies fall essentially to zero, indicating an athermal process. For bcc metals (Fe, Mo, V, Ta) the activation energies remain finite, varying from ≈0.013 eV (Ta) to ≈0.2 eV (Mo).