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I.

INTRODUCTION

IN recent studies, nanocrystalline (NC) FeCuNbSiB soft magnetic materials produced in as-cast (AC) state from the amorphous precursor by the primary crystallization of bcc Fe have been found remarkable as they have superior magnetic properties.[1–3] To obtain the NC state, primary crystallization should be achieved via a heat treatment above the crystallization temperature.[4] Such produced ribbons enabling efficient usage in many electronic and electromechanical circuits have been widely investigated in terms of both magnetic properties[1,5–7] and microstructures.[8–12] NC FeCuNbSiB alloys are commonly known by the lowest coercivity, Hc (< 1 A/m), a fulfilling permeability, l (> 1 9 105), a very low magnetostriction, ks (< 1 ppm), and a sufficient saturation polarization, Bs ( 1.25 T).[1,2,13] Knowing the composition of NC alloys would be a significant source for making a

TAYLAN GUNES is with the Department of Energy Systems Engineering, Yalova University, 77100, Yalova, Turkey. Contact e-mail: [email protected] Manuscript submitted February 20, 2019.

METALLURGICAL AND MATERIALS TRANSACTIONS A

prediction regarding their magnetic behavior and crystallization temperature based on their Fe content percentage.[14] The balance ratio of Cu and Nb would also provide approximate prior knowledge of the mean grain size of FeSi grains.[15,16] Thus, the addition of sufficient Cu contributes obviously to the uniformity of grain dispersion.[17,18] Ohnuma et al.[19] pointed out that Cu clusters are closely related to bcc a-Fe primary crystals so that their grain size directly influences the permeability of the alloy. Therefore, the relevant ratio of Cu and Nb makes it possible to obtain a uniform NC microstructure evaluation. Even though Finemet, Nanoperm, and Vitroperm are prominent and commonly known members of the class of NC FeCuSiBNb(Zr, P) alloys, the ratio of elemental percentages in their composition varies depending on the area of usage or the customer demands. For instance, magnetic cores of several inductive components such as chokes or transformers may lead to various desired magnetic properties, e.g., higher values of permeability (l), saturation induction (Bs), and lower core loss (Hc). No matter what the usage purpose of NC soft magnetic materials, one of the most significant requirements is generally a quite low (< 1 ppm) or vanishing ( 0) magnetostriction (ks), which reduces magneto-elastic anisotropies (Kr).[20–22] The key to the

understanding of a higher permeability level of NC alloys is the easy rotation of magnetization and easy domain wall motion, which originate from low magnetocrystalline anisotropy (K) and low ks.[23] Such microstructural refinement after some mechanical and/ or thermal treatments have been implemented would reveal superior soft magnetic properties, such as average grain size (D), lower Hc, high Bs, and small pinning forces.[5] On the other hand, all these different requirements necessarily restrain the selection of the alloy. Kuhnt et al.[21] reported that the ks of