Advanced structure research methods of amorphous Co69Fe4Cr4Si12B11 microwires with giant magnetoimpedance effect: Part 1 – Crystallization kinetics and crystal growth

Abstract

The initial stage processes of nucleation and growth of crystalline phases in Co-based amorphous microwires in a glass shell were studied by processing kinetic curves using various theoretical models. The results of X-ray diffraction for research of the microstructure evolution at Synchrotron Radiation Source and High Resolution Transmission Electron Microscopy were considered. The study of the crystallization process kinetics was carried out by a non-conventional method, in particular based on data of sample magnetization changes over time and with temperature at a unique in situ vibromagnetometer. The analysis of the kinetic curves for isothermal and non-isothermal crystallization process led to the similar conclusions and made it possible to establish the values of the Avrami exponent for the initial stage of surface and bulk crystallization, to establish the dimensionality of crystal growth, and to conclude that there was no nucleation in the process of crystal growth. Based on the analysis of kinetic curves by three methods, the activation energy of the primary crystallization process was determined, its high value is associated with the presence of chromium in the alloy, which determines its nanocrystallization. The microstructure and shape of crystals were analyzed.