Microstructural implications of non-random nucleation protocols in nanocrystallized metallic glasses

Macroscopic properties of nanocrystallized metallic glasses are dependent of their nanostructure. The knowledge of the crystallization kinetics and its effect on the nanostructure are then essential in designing production and annealing protocols. Deviations from the Avrami kinetics in many of such systems are often interpreted in terms of either non-random nucleation or soft impingement due to overlapping concentration gradients. In this work, simple simulations of non-random nucleation processes allow us to evaluate the main features of both kinetic parameters and the nanostructure. It is shown that although non-random nucleation highly affects the nanostructure, it has a small effect on the transformed fraction evolution. Consequently, the decreasing Avrami exponents often reported in primary crystallization of metallic glasses have to be associated to a time dependent growth rate. Moreover, as similar kinetic behaviors are observed for different nucleation and growth protocols the understanding of the kinetics-nanostructure relationship becomes fundamental in studying such systems.