Ar. Yavari et O. Drbohlav, THERMODYNAMICS AND KINETICS OF NANOSTRUCTURE FORMATION IN SOFT-MAGNETIC NANOCRYSTALLINE ALLOYS (OVERVIEW), Materials transactions, JIM, 36(7), 1995, pp. 896-902
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.