THERMODYNAMICS AND KINETICS OF NANOSTRUCTURE FORMATION IN SOFT-MAGNETIC NANOCRYSTALLINE ALLOYS (OVERVIEW)

Thermodynamic and kinetic conditions for nanocrystallization of Fe-bas ed amorphous precursors into a duplex structure of alpha-Fe nanocrysta ls within a residual amorphous matrix are considered in view of recent literature. The effect of copper addition on nanograin size is explai ned in terms of the CuFe metastable phase diagram and the nature of th e various heteroatomic interactions. Addition of larger atoms such as Nb and Zr that are rejected together with boron atoms at the alpha-Fe nanocrystallization interface is found to generate diffusion double-la yers with sharp concentration gradients. The diffusion double-layers e xplain measured differences in Curie temperatures T-c of the remaining grain boundary amorphous phase and bulk glasses of the same compositi on. They also successfully predict the occurence of a broad maximum in T-c of the remaining amorphous phase during nanocrystallization annea ling. The concentration gradients have an additional thermodynamic sta bilization effect on the amorphous interlayers by reducing the driving force for the formation of intermetallics.