Cluster Structure and Thermodynamics of the Formation of Nanocrystalline Phases

Abstract

The formation of amorphous metallic systems by rapid quenching is influenced in a significant manner by the detailed path of the corresponding alloy from the melt through undercooled liquid down to the amorphous state. The thermodynamic history of the formation of an amorphous system (quenching the liquid state with specific structure, interatomic bonding and short range ordering) forces a specific template, reflecting the presence of ordered polyatomic clusters, into its potential energy structure. Subsequent transitions from amorphous to the (nano)crystalline state which then take place respect the existing potential energy landscape with such quenched-in local-scale heterogeneities. It will be shown that using a model-free continuous approach for the estimation of the distributions of initial energetic states (reflecting the cluster structure) it is possible to obtain information about the types of micromechanisms controlling the transformation processes as well as to use this information to obtain control of the phase selection during the transformation into the nanocrystalline state. A generalized view of the process of nanocrystallization from a clustered amorphous state will be presented. A special focus will be put on the nucleation processes and on the methods of their quantification. Two methods will be discussed.