Kinetic Study of the Crystallization of Free and Contact Surfaces of Fe77Ni1Si9B13 Amorphous-Alloy Ribbons under Low-Temperature Annealing

This study examines the differences in the crystallization kinetics of the free and contact sides of an Fe77Ni1Si9B13 amorphous-alloy ribbon at 400°C. X-ray phase analysis reveals that crystals based on α-Fe form on the contact side after just 5 min of annealing. In contrast, on the free side, reflections corresponding to α-Fe crystals are only detectable after 30 min of annealing. The relative content of the crystalline phase is determined using X-ray diffraction data, based on the relationship between the integral intensity of the reflection of the analyzed phase and its volume fraction. We explore the possible reasons for the observed differences in crystallization. Crystallization in the surface layers of both the contact and free sides of the ribbon occurs in two stages: the isotropic growth of existing nuclei with a decreasing rate of crystal formation, followed by the slowed anisotropic growth of already formed crystals. The first stage is satisfactorily described by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) thermodynamic formalism, whereas applying a kinetic equation to describe the second stage is not appropriate.