Cluster structure and thermodynamics of formation of (nano)crystalline phases in disordered metastable metallic systems

Abstract

We have investigated the initial thermodynamic states, energetics, structures, and micromechanisms active in the transitions of complex metastable metallic systems to a more stable state from the viewpoint of spatially correlated distribution of rates of microprocesses controlling the transformation processes. Using a novel model-free continuous distribution approach we have obtained information about the overall distribution of rates of microprocesses as well as about the subprocesses active in different stages of the transition. From detailed analysis of the subprocesses by means of moment analysis we have obtained distributions of the true activation energies of the microprocesses and their temperature dependencies. This has allowed us to correlate the internal complexity of disordered systems obtained by rapid quenching, which induces a distribution of initial energetic states of the system, with short-range ordering (SRO) of atoms and with subsequent micromechanisms controlling the formation of (nano)crystalline phases. The main attention was focused especially on the origin of the amorphous structure, on the formation and stability of clusters, and on subsequent formation and phase selection of nanostructures. The analysis has enabled us to identify and compare microprocesses in the early stages of transformation, which have major influence on the entire process of nanocrystallization.