NUCLEATION AND GROWTH-CHARACTERISTICS OF AMORPHOUS FE-SI-B-(CU)-(NB) ALLOYS DURING ISOTHERMAL CRYSTALLIZATION PROCESS

Isotherinal crystallization processes in amorphous Fe77.5Si13.5B9 allo y with the addition of 1% Cu and/or 3% Nb were investigated using diff erential scanning calorimetry and X-ray diffraction. A symmetric exoth ermal peak resulting from precipitation of crystalline alpha-Fe and Fe -B compounds in Fe74.5Si13.5B9Nb3, and an asymmetric peak originating from the formation of alpha-Fe(Si) solid solution in both Fe76.5Si13.5 B9Cu1 and Fe73.5Si13.5B9Cu1Nb3 have been observed. From the measured c urves of the crystallized volume fraction x(t) vs. the annealing time t, we have plotted the relationships of the local Avrami exponent n(x) and the local activation energy E(c)(x), respectively, varying with x (t), and have calculated the values of the activation energy E(g) for the growth of nuclei in the amorphous Fe74.5Si13.5B9Nb3, Fe73.5Si13.5B 9Cu1Nb3 and Fe76.5Si13.5B9Cu1 alloys. Changes in the average grain siz e of the alpha-Fe(Si) crystallite during the isothermal crystallizatio n process have also been examined. Based on these results, the effects of Cu and Nb on the nucleation and growth characteristics in amorphou s Fe-Si-B-(Cu)-(Nb) alloys have been further confirmed, i.e. Cu accele rates the nucleation process of the alpha-Fe phase and Nb suppresses g rowth of the alpha-Fe phase.