Formation of Nanocrystalline Metastable Phases in Fe-Ni-Zr-B Amorphous Alloys

Abstract

The paper presents a comprehensive review of our recent experimental and theoretical investigations in the processing of nanocrystalline soft magnetic materials made from an amorphous precursor with a nominal chemical composition of Fe81 – x –yNixZr7B12Au1, x = 10-40, 64; y = 0, 1. The transformation from the amorphous into the nanocrystalline state was investigated by means of structural (DSC, XRD, TEM) measurements as well as by transmission and conversion electron Mössbauer spectroscopy (CEMS). Additionally, magnetic (VSM) measurements were performed. The annealing favours the emergence of a fine grain fraction of magnetically ordered metastable cubic FexNi23 – xB6 phase in an amorphous matrix. The relationship between the structures of the metastable and equilibrium phases and their transformations are discussed. The magnetic behaviour of pure Ni23B6 and Fe23B6 phases was studied theoretically using the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. Anomalously high magnetic moments of Fe atoms were found in some inequivalent positions in the crystal structure. The possibilities of increasing the saturation magnetization value by applying an optimal chemical composition and a crystal structure as well as decreasing the coercive force of the nanocrystalline alloys utilizing intergranular exchange coupling are discussed.