Alloy substituents for cost reduction in soft magnetic materials
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Amorphous and nanocrystalline soft magnets have been investigated extensively in the past two decades. Many materials with attractive soft magnetic properties contain boron, which improves the glass formability, thermal stability and prevents undesirable grain growth. The high price of boron, however, makes the development of new soft magnetic materials and alternative synthesis routes important. We report here a synthesis of cobalt-rich alloys by substituting boron carbide for elemental boron to achieve significantly lower cost. Ribbons produced with and without boron carbide substitution were observed to exhibit comparable soft magnetic properties while the former results in 31–48% cost reduction. Extrapolating this idea to commercial VITROVAC 6025 and 6150, the cost reductions were calculated to be 56 and 50%, respectively, while both synthesis routes produced ribbons of similar soft magnetic properties. Our work here provides an attractive route to reduce the cost and increase the market competitiveness of soft magnets.
I. INTRODUCTION
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ DOI: 10.1557/jmr.2015.56
carbide (B4C) as a precursor material7 following the reports by Sui et al. and Kou et al. who looked at the effects of carbon (C) substitution for boron (B) in this permanent magnet system.8–10 Other glass former substituents in the amorphous precursors to nanocomposite alloys have also been extensively studied and their role on crystallization kinetics and amorphous phase stability is of interest.11–14 The impact of boroncost on nanocomposite alloys has driven efforts to find substituents for boron (B) in nanocomposite precursors. For example, silicon (Si) substitution for boron (B) also helps reducing the alloy production cost due to the significantly lower price of the former.15,16 Okumura et al. and Zabransky et al. have explored this idea and looked at the structural, soft magnetic properties, and crystallization behavior of silicon-rich FINEMET.17,18 More recently, Long et al. have reported a study on the structural and soft magnetic properties of a boron-free iron-rich alloy.19 In this system, zirconium (Zr) and silicon (Si) were used to prevent over-crystallization. After thermal annealing treatment, an optimum grain size and relatively low power loss of ;10 nm and 19 W/kg, respectively, were observed. Using silicon (Si),17,19 phosphorus (P),20 or mixture of glass formers21 is common in bulk amorphous alloys to exploit the economic benefit of substitution for expensive boron (B). In iron-rich amorphous and nanocomposite materials, the economic benefit is not as large as in cobalt-rich materials. This is due to the readily available ferroboron (FeB) alloys, which reduce costs as compared with using elemental boron (B) a
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