THE COMPLEX CHARACTERISTICS OF CRYSTALLIZATION OF THE FE75SI15B10 GLASSY RIBBON

The Fe75Si15B10 glassy ribbon was examined in the course of various is othermal and dynamic heat treatments. The number, type and mechanism o f formation of the crystallization products formed during two crystall ization stages in this alloy were determined by differential scanning calorimetry (DSC), thermomagnetometry, transmission electron microscop y and X-ray diffraction measurements. It is concluded that the first D SC peak is due to the crystallization of alpha-Fe(Si) or Fe3Si and the composite microcrystals containing Fe3B cores with alpha-Fe(Si) envel opes. The metastable Fe3B subsequently transforms into the stable Fe2B in the second DSC peak. The remaining amorphous matrix crystallizes b y the eutectic reaction also in the second DSC peak forming the Fe3Si and Fe2B eutectic structures. The apparent activation energy E-1 decr eases during the first crystallization stage from 480 kJ (g atom(-1)), characteristic of the Johnson-Mehl-Avrami (JMA) nucleation-and-growth kinetics of the as-quenched sample, to 350 kJ (g atom)(-1) implying a dominance of the diffusion-controlled growth of iron in the already p re-nucleated sample. Simultaneously, the JMA exponent n(1) decreases f rom 2.5 to 1.5. The apparent activation energy E-2 depends on the tem perature of the first crystallization stage. It decreases with increas ing T-a from 384 to 282 kJ (g atom)(-1). This phenomenon was attribute d to modification of the chemical composition of the remaining eutecti c after the temperature dependent primary crystallization of Fe3B with in the composites. The value of n(2) is 3.