No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Abstract
The influence of high-pressure sintering conditions on density and grain size of α-Fe phase was investigated to obtain Fe86Zr5.5Nb5.5B3 nanocrystalline bulks. Results show that single phase α-Fe nanocrystalline (16.3 nm) bulk of 98.3% relative density could be acquired with precursor amorphous powders prepared by melt-spinning and then ball milling, and under the sintering conditions of P=5.5 GPa/t=3 min. With the increment of Pw and t, its relative density and grain size slightly increased. The specific saturate magnetization σs and coercive force Hc of the nanocrystalline bulk alloy was 119.6 emu/g and 63.8 Oe, respectively.
ResearchGate has not been able to resolve any citations for this publication.
We obtained Fe84Nb7B9 bulk alloys by extruding amorphous powders at temperatures (Te) between 653 and 723 K and pressures (Pe) of 820 to 1210 MPa, and Fe90Zr7B3 bulk alloys by extruding at Te of 673 to 698 K and Pe of 920 to 940 MPa. Subsequent annealing of these bulk alloys at 923 K for 3.6 ks causes the formation of a nanocrystalline bcc phase with grain sizes of 9 to 11 nm for Fe84Nb7B9 and 20 to 30 nm for Fe90Zr7B3. The bcc Fe84Nb7B9 bulk alloy exhibits a magnetization (B800) of 1.40 T, a permeability (μe) of 1120 at 300 Hz, and a coercive force (Hc) of 48 A/m in the extrusion condition of Te = 698 K and Pe = 870 MPa. Similarly, the B800, μe and Hc of the bcc Fe90Zr7B3 bulk alloy prepared at Te = 698 K and Pe = 923 MPa are 1.57 T, 1880 and 29 A/m, respectively. The soft-magnetic properties of the bcc Fe90Zr7B3 bulk alloy are superior to those of the bcc Fe84Nb7B9 bulk alloy, presumably because of the formation of a more homogeneous bcc structure for the former alloy.
For the production of nanocrystalline soft-magnetic compacts with high saturation magnetization, we investigated the densification behavior of amorphous and nanocrystalline Fe86Zr7B6Cu1(at. %) powders using a hot-pressing machine, and the magnetic properties of the compacts. The density of the compacts produced from the nanocrystalline powder was 90.4%. However, nanocrystalline compacts with a high density of 99.9% were obtained by hot pressing the amorphous powder under 1.5 GPa and 853 K. We constructed the densification map of the amorphous and nanocrystalline powders. The pressure required to produce dense compacts, which was estimated from this map, is 3.0 GPa for the production of amorphous compacts, and 4.4 GPa for the consolidation of the nanocrystalline powder into nanocrystalline compacts, and only 1.5 GPa for the direct consolidation of the amorphous powder into nanocrystalline compacts. The consolidation of the amorphous powder through the crystallization is the most appropriate method for the production of dense nanocrystalline compacts. The dense nanocrystalline compacts exhibited good soft-magnetic properties which were superior to those of Fe-based amorphous compacts, in addition to a high saturation magnetization of 1.56 T. The coercive force, effective permeability at 1 kHz and 0.8 A/m, and core loss at 10 kHz and 0.1 T were 33 A/m, 1300 and 37 W/kg, respectively.
A bulky Fe84Nb7B, alloy was obtained by extruding the powders ground from amorphous ribbon, at temperatures T(e) between 563 K and 723 K at pressures P(e) between 824 MPa and 1208 MPa and at a speed of 5 mm s-1. The bulk Fe84Nb7B9 alloy extruded at T(e) = 698 K and P(e) = 1208 MPa is in a fully consolidated state and has a density of about 99%. The bulk alloy is composed of a mostly single b.c.c. phase with a grain size of about 10 nm after annealing for 3.6 ks at temperatures between 873 K and 973 K, and its soft magnetic property tends to be better for the bulks extruded at lower pressures. The bulk alloy extruded at T(e) = 698 K and P(e) = 824 MPa exhibits a high saturation magnetization B(s) of 1.40 T and a low coercive force H(c) of 64 A m-1 after annealing at 698 K.