THE ROLE OF NB IN THE NANOCRYSTALLIZATION OF AMORPHOUS FE-SI-B-NB ALLOYS

The aging behavior of amorphous Fe84-xSi6B10Nbx alloys was investigate d using differential scanning calorimetry (DSC), transmission electron microscopy, and high-frequency magnetic measurements. A marked change in the peak morphology was observed on the DSC curve for the alloys c ontaining more than 3 at.% Nb. The right side of the first exothermic peak extended to the higher temperature side, while the second exother mic peak was drastically reduced in its intensity. After aging for 3.6 ks in the first exothermic temperature ranges, ail the alloys with a Nb content up to 6 at.% were composed of a mixed structure of the alph a-Fe phase and an amorphous matrix; however, the addition of more than 3 at.% Nb caused a significant grain refinement of the crystallizatio n-induced alpha-Fe particles. Furthermore, the low-temperature aging p roduced a notable increase in the effective permeability only for the alloys containing more than 3 at.% Nb, even though the amorphous phase remained unchanged without crystallization. Based on these results, t he mechanism of nanocrystallization was reasonably explained as being related to a change in the amorphous structure which occurs in the vic inity of 2-3 at.% Nb. (C) 1998 Acta Metallurgica Inc.