Cluster Structure of the Amorphous State and (NANO)Crystallization of Rapidly Quenched Iron and Cobalt Based Systems

Abstract

Micromechanisms and energetics of transitions from metastable to more stable state were investigated in complex metastable disordered systems prepared by rapid quenching from the melt from the viewpoint of spatially (structurally) correlated distribution of transformation rates of individual microprocesses controlling the transition process. Using a novel, model-independent method for determination of continuous distributions of process rates it was possible to obtain information on distributions of true activation energies of these microprocesses. Detailed analysis of subdistributions of microprocesses active at each stage a of transition yielded also the information on temperature dependence of the activation energies.

We have analyzed different nanocrystal-forming iron and cobalt based systems with the focus on the origin of the clustered amorphous state. New information was obtained with respect to the original local ordering of atoms in the amorphous state and its influence on the formation of nanostructures. Additional information was extracted which allowed comparison of the processes in the early stages of nanocrystallization with those activated at the end of this transformation. The origin of distributions of microprocess rates or, alternatively, of activation energies, i. e. dynamically heterogeneous behaviour, is discussed and correlated with the expected clustered structure of the amorphous state, i. e. spatial heterogeneities having distinct ordering within the disordered matrix.