Abstract
In contrast with amorphous alloys, nanocrystalline soft magnetic materials show improved thermal stability and higher soft magnetic properties. The nanocrystalline soft magnetic composites are usually fabricated by partially crystallizing from parent amorphous alloys. This paper reports our experimental observation on the sequence of crystallization in metallic glass under a high magnetic field (HMF). An application of a HMF to bulk metallic glass (BMG) of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 prioritizes the precipitation of α-(Fe,Co) phase separated from the subsequent precipitation of borides, (Fe,Co)23B6, upon isothermal annealing at a glass transition temperature. Furthermore, it was observed that, through the annealing treatment under a HMF, a soft magnetic nanocomposite, in which only α-(Fe,Co) phase uniformly distributes in amorphous matrix, was achieved for boron-bearing BMG. The promotion of the α-Fe or (Fe,Co) phase and the prevention of the boride phases during the isothermal annealing process help to produce high-quality soft magnetic nanocomposite materials. The mechanism by which a HMF influences the crystallization sequence was interpreted via certain changes in Gibbs free energies for two ferromagnetic phases. This finding evidences that the annealing treatment under a HMF is suitable for enhancing the soft magnetic properties of high B content (Fe,Co)-based bulk amorphous and nanocrystalline materials.
Highlights
Soft magnetic materials with low core losses, high magnetization, and low cost are the key components for transformers with improved energy efficiency, especially in higher frequency and elevated temperature operation conditions [1,2]
The nanocrystalline soft magnetic materials were usually fabricated via partially crystallization from parent amorphous alloys
Given a heating rate of 5 K/min, a preliminary Differential scanning calorimeter (DSC) experiment was done on a sample of as-melt-spun (AMS) [(Fe0.5 Co0.5 )0.75 B0.2 Si0.05 ]96 Nb4
Summary
Soft magnetic materials with low core losses, high magnetization, and low cost are the key components for transformers with improved energy efficiency, especially in higher frequency and elevated temperature operation conditions [1,2]. Since the 1970s, greatly reduced core loss has been achieved in amorphous and nanocrystalline alloys [3,4,5,6,7,8]. Because of a lack of magnetic domain walls, the soft magnetic properties of amorphous alloys deteriorate rapidly under operation frequency from tens to hundreds of kilohertz. In contrast with amorphous alloys, nanocrystalline soft magnetic materials show improved thermal stability, higher magnetization, and lower core loss [6,7,8]. The nanocrystalline soft magnetic materials were usually fabricated via partially crystallization from parent amorphous alloys. A large number of randomly oriented nanocrystalline phases (usually α-Fe, Fe3 Si, or α- or α’-(Fe,Co) phase with cubic symmetry) have been formed in the amorphous matrix at a primary
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