The complex characteristics of crystallization of the Fe75Si15B10 glassy ribbon

The Fe₇₅Si₁₅B₁₀ glassy ribbon was examined in the course of various isothermal and dynamic heat treatments. The number, type and mechanism of formation of the crystallization products formed during two crystallization stages in this alloy were determined by differential scanning calorimetry (DSC), thermomagnetometry, transmission electron microscopy and X-ray diffraction measurements. It is concluded that the first DSC peak is due to the crystallization of α-Fe(Si) or Fe₃Si and the composite microcrystals containing Fe₃B cores with α-Fe(Si) envelopes. The metastable Fe₃B subsequently transforms into the stable Fe₂B in the second DSC peak. The remaining amorphous matrix crystallizes by the eutectic reaction also in the second DSC peak forming the Fe₃Si and Fe₂B eutectic structures. The apparent activation energy E ₁ ^⊛ decreases 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 pre-nucleated sample. Simultaneously, the JMA exponent n ₁ decreases from 2.5 to 1.5. The apparent activation energy E ₂ ^⊛ depends on the temperature of the first crystallization stage. It decreases with increasing T _a from 384 to 282 kJ (g atom)^-1. This phenomenon was attributed to modification of the chemical composition of the remaining eutectic after the temperature dependent primary crystallization of Fe₃B within the composites. The value of n ₂ is 3. This revised version was published online in November 2006 with corrections to the Cover Date.