NANOCRYSTALLIZATION OF AMORPHOUS FE-ZR-B-CU ALLOYS AND LOW-FREQUENCY SOFT-MAGNETIC PROPERTIES

In nanocrystalline alloys reported to date, Fe-Zr-B(-Cu) alloys shows the highest saturation magnetization (higher than Fe-B-Si amorphous alloys), they are thus expected to be applied to power transformers used at Bm = 1.3 similar to 1.4 T and f = 50 similar to 60 Hz. Usually they are expected to be used in high frequencies because of their excellent permeabilities. The low frequency (50 Hz) magnetic properties of Fe86ZrxB13-xCu1 nanocrystalline ribbons have been examined from the view-point of application to power transformers. Core loss W-13/50 (1.3 T, 50 Hz) = 0.07 W/kg was observed in the annealed Fe86Zr5B8Cu1 alloy. Magnetic induction B-1k (in a field of 1 kA/m) is 1.54 T for the same sample. In annealing Fe86ZrxB13-xCu1 (x = 5 similar to 7) amorphous alloys, ultrafine bcc-Fe grains about 15 nm in size were obtained with remaining stable amorphous phases. The stable amorphous phase makes the grains very fine. The stability of the amorphous phase is related to the liquidus temperature T-L that was measured during cooling and solidifying of the molten alloy of each composition in a furnace. When the grains grew during annealing, the amorphous phase changed its composition to exhibit lower T-L and became more stable. The core loss W-13/50 shows the W similar to D-6 dependence in the range of D = 15 similar to 25 nn. However, when the grain size was D = 8 nm, the core loss does not show the D-6 dependence. The nanocrystalline Fe-Zr-B-Cu ribbons shows poor ductility, which should be improved if the materials are to be used in actual pole transformers.