On the kinetics of crystallization of the free and contact sides of Fe₇₇Ni₁Si₉B₁₃ amorphous alloy ribbons at low-temperature annealing

The differences between the kinetics of crystallization of the free and contact sides of the ribbon of the amorphous Fe₇₇Ni₁Si₉B₁₃ alloy at 400°C were considered. As a result of X-ray phase analysis, it was found that crystals based on α-Fe were formed on the contact side even after annealing for 5 min. In the case of the free side, reflections related to α-Fe crystals could be detected on the free side only after annealing for 30 min. The relative content of the crystalline phase was determined from X-ray diffraction data using the relationship between the integral intensity of the reflection of the analyzed phase and its volume fraction. Possible reasons for the observed differences in crystallization were considered. Crystallization in the near-surface layers of both the contact and free sides of the ribbon was shown to occur in two stages (isotropic growth of existing nuclei at a decreasing rate of crystal nucleation and slow anisotropic growth of already formed crystals). The first stage was satisfactorily described within the framework of the Johnson–Mel–Avrami–Kolmogorov thermodynamic formalism, but for the second stage it was unlawful to apply the kinetic equation.