Thermally induced crystallization of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy

Abstract

Thermally induced crystallization of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy occurs in two well-separated stages: the first, around 475 °C, corresponds to formation of α-Fe(Si)/Fe3Si and Fe2B phases from the amorphous matrix, while the second, around 625 °C, corresponds to formation of Fe16Nb6Si7 and Fe2Si phases out of the already formed α-Fe(Si)/Fe3Si phase. Mössbauer spectroscopy suggests that the initial crystallization occurs through formation of several intermediate phases leading to the formation of stable α-Fe(Si)/Fe3Si and Fe2B phases, as well as formation of smaller amounts of Fe16Nb6Si7 phase. X-ray diffraction (XRD) and electron microscopy suggest that the presence of Cu and Nb, as well as relatively high Si content in the as-prepared alloy causes inhibition of crystal growth at annealing temperatures below 625 °C, meaning that coalescence of smaller crystalline grains is the principal mechanism of crystal growth at higher annealing temperatures. The second stage of crystallization, at higher temperatures, is characterized by appearance of Fe2Si phase and a significant increase in phase content of Fe16Nb6Si7 phase. Kinetic and thermodynamic parameters for individual steps of crystallization suggest that the steps which occur in the same temperature region share some similarities in mechanism. This is further supported by investigation of dimensionality of crystal growth of individual phases, using both Matusita–Sakka method of analysis of DSC data and texture analysis using XRD data.