Ultra-low core loss and high core saturation magnetization of nanocrystalline Fe-B-P-Cu powder cores fabricated by using a hot-press process

Powder cores with low core loss and high flux density are in high demand for modern power-electronic applications. This study fabricated ultra-low core loss and high packing density powder cores composed of nanocrystalline Fe-B-P-Cu powder with high saturation magnetization of 1.74 T. By adopting a hot-press process, the packing density significantly increased to 89 % compared with 70 % of the conventional cold-press process, resulting in a high core saturation magnetization of 1.55 T. Moreover, by using the fine powder of 17 μm in diameter, the core loss at the frequency of 100 kHz and the excitation flux density of 100 mT decreased to 146 kW/m 3 from 852 kW/m 3 of the cold-pressed core using conventional powder of 28 μm in diameter. These properties are superior to, e.g., the SENDUST TM and Fe-Si powder cores widely used for power-electronics applications, and the recently reported powder cores using high saturation magnetization nanocrystalline alloys. Broadband core loss measurements and core loss analysis based on magnetization processes were employed for these cores. Consequently, the core loss component corresponding to the irreversible magnetization process, which is the sum of the hysteresis and excess losses, decreases significantly for the hot-pressed powder cores. Conversely, the core loss component corresponding to the reversible magnetization process in the high-frequency region, which is mainly the classical eddy current loss, depends only on the powder diameter.