Magnetic core properties and their thermal stability in a BCC Fe‐Zr‐B‐Cu alloy with nanoscale grain size

Abstract

AbstractA mostly single bcc phase with nanoscale grain size of 10 to 20 nm has been found to form by annealing amorphous Fe‐Zr‐B, Fe‐Hf‐B and Fe‐M‐B‐Cu (M = Ti, Zr, Hf, Nb and Ta) alloys. It has further been clarified that the newly developed nanocrystalline bcc alloys exhibit high permeability (μe) combined with high saturation magnetization (Bs).Subsequently, the possible application potentials of the bcc alloys were investigated. The core loss is as small as 66 mW/kg at 1 T and 50 Hz for a nanocrystalline bcc Fe86Zr7B6Cu1 alloy obtained by annealing for 3.6 ks at 873 K. This value is 45 and 95 percent smaller than those for amorphous Fe86Si9B13 alloy and Fe‐3.5 percent Si alloy, respectively, which are presently in use as core materials in electric power transformers. The frequency dependence of the core loss for the bcc alloy at 0.2 T is almost the same as that for an amorphous Co70.5Fe4.5Si10B15 alloy with zero magnetostriction.In the frequency range of 10 to 300 kHz, the core loss for the bcc alloy is slightly smaller than the Co base amorphous which has been used as core material in high‐frequency transformers. Furthermore, the core losses of the nanocrystalline Fe86Zr7B6Cu1 alloy also were found to have high stability against thermal aging. Thus, nanocrystalline bcc Fe‐Zr‐B‐Cu alloys with the advantages of high Bs, high μe, and low core loss is expected to be used as a core material in various transformers.