Study of crystallization processes in Gd-substituted Finemet alloys

Abstract

The crystallization processes that occur in amorphous melt-spun ribbons of nominal composition Fe 73.5Cu 1Nb 3Si 13.5B 9 with Gd addition in different concentrations are studied by differential scanning calorimetry (DSC). The aim of Gd addition is to study the changes induced in the calorimetric behavior of Finemet alloys, the crystallization sequences at intermediate stages of annealing as well as the nature of obtained crystallization products. The nature and structural properties of the phases formed at the end of the calorimetric process are investigated using X-ray diffraction (XRD) and Mössbauer spectrometry (MS). The crystallization sequence and also the phase composition at different stages of annealing were investigated for the Fe 68.5Gd 5Cu 1Nb 3Si 13.5B 9 alloy. Structure and magnetic properties of resulting crystallized samples have been thoroughly investigated. It is shown that in the above-mentioned composition, the decomposition at around 690 °C of the metastable Gd 3Fe 62B 14 phase formed at incipient stages of crystallization leads to the co-existence of Gd 2Fe 14B, Fe 2B and α-Fe(Si) phases. Magnetic measurements of as-cast and annealed samples are in good agreement with the XRD and MS results and with the proposed crystallization sequences and decomposition of intermediate metastable phases.