N. V. Dmitrieva

Fe- and co-based nanocrystalline soft magnetic alloys modified with Hf, Mo, and Zr: Magnetic properties, thermal stability, and structure. Alloys (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1

Nanocrystalline alloys (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1 have been investigated to obtain materials with improved thermal stability and new features. In order to make the alloys produced by melt quenching on a rotating wheel nanocrystalline, they have been subjected to heat (HT) and thermomechanical (TMechT) treatments. The effect of HT and TMechT conditions on the magnetic properties, thermal stability, and structure of the alloys has been studied. The optimal HT conditions for obtaining the minimum values of the coercive force (Hc) in the alloys have been determined. It is shown that TMechT of the alloys leads to the induced longitudinal magnetic anisotropy with the axis of easy magnetization along the long side of the ribbon in the studied temperature range of 520–620°C. It has been established that the alloys (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1 are thermally unstable at temperatures above 500°C.

Magnetic properties, thermal stability, and structure of the nanocrystalline soft magnetic (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy with induced magnetic anisotropy

The effect of magnitude of tensile stresses (σ) applied to the (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy with refractory-metal additions during its nanocrystallization at 620°C for 20 min on the magnetic properties, structure, and thermal stability of the alloy is studied. It has been found that, during the nanocrystallization of the alloy under the effect of tensile stresses of 6–250 MPa, longitudinal magnetic anisotropy with an easy magnetization axis parallel to the long size of ribbon is induced in the alloy. The thermal stability of magnetic properties of the alloy under study has been shown to be determined by the thermal stability of induced magnetic anisotropy and to depend on the magnitude of tensile stresses applied during nanocrystallizing annealing (NA). The better thermal stability of magnetic properties has been observed for the alloy subjected to NA at σ = 170 MPa. After annealing at 570°C for 25 h, the magnetic properties of the alloy are unchanged.

Fe- and co-based nanocrystalline soft magnetic alloys modified with Hf, Mo, and Zr: Magnetic properties, thermal stability, and structure. Alloy (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1

The alloy (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 is studied to obtain materials with improved thermal stability. The effect of the nanocrystallization conditions that occur during heat treatment (HT) and thermomechanical treatment (TMechT) in air at temperatures of 520–620°C on the structure of the alloy, as well as its magnetic properties and their thermal stability, is considered. Longitudinal magnetic anisotropy is shown to be induced in the alloy in the course of TMechT; the easy magnetization axis of the anisotropy is parallel to the long side of the ribbon. The alloy specimens subjected to heat and thermomechanical treatment have different magnetic characteristics. The (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy is found to surpass the (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1 alloys studied in [1] in the thermal stability of the magnetic properties. The magnetic properties of the alloy after nanocrystallization, which occurs in the course of TMechT (σ = 250 MPa) at 620°C for 20 min, hardly change during annealing at 550°C for 26 h.

Thermal stability of magnetic properties of nanocrystalline (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy with induced magnetic anisotropy

The effect of nanocrystallizing annealing in the presence of an ac magnetic field (magnetic heat treatment) and tensile stresses (thermomechanical treatment), as well as in the presence of both tensile stresses and an ac magnetic field (complex thermomechanical magnetic treatment) on the magnetic properties of the nanocrystalline (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy and their thermal stability has been studied. It has been found that the nanocrystallization of the studied (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy in the course of magnetic heat treatment, thermomechanical treatment, and thermomechanical magnetic treatment at low tensile stresses (6–30 MPa) leads to about a threefold decrease in the coercive force, but does not ensure the thermal stability of magnetic properties at high temperatures. In nanocrystallization, in the course of thermomechanical treatment at 620°С for 20 min under tensile stresses σ = 250 MPa has been found to be optimum for the high-temperature application (up to 550°С) of the studied alloy.

Magnetic properties, thermal stability, and structure of soft magnetic (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy that underwent high-temperature nanocrystallization

The effect of the temperature of nanocrystallizing annealing (NA) at temperatures of 670–750°C on the magnetic properties, structure, and thermal stability of the (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy has been studied. The NA was performed both in the presence of tensile stresses applied to samples and in the absence of stresses. It was found that the nanocrystallization of the alloy under applied tensile stresses induces the longitudinal magnetic anisotropy with an easy magnetization axis parallel to the long side of the ribbon. The optimum conditions for nanocrystallization of the alloy, which stabilize its magnetic properties at a fairly high temperature of 570°C, have been determined.

Induced magnetic anisotropy and the structure of nanocrystalline Fe-Co-Cu-Nb-Si-B alloys with different content of Co: II structure of alloys with an induced magnetic anisotropy

A connection has been established between the structural state (phase composition) of the nanocrystalline alloys Fe73.5 − xCoxCu1Nb3Si13.5B9 (x = 0, 10, 20, 30) and the type of the induced magnetic anisotropy (IMA), which is formed in the process of thermomechanical treatment (TMechT), on the one hand, and its thermal stability, on the other hand. It is shown that the addition of cobalt entails a decrease in the quantity of Fe-Si grains and the formation of phases that contain Fe-Co-B. The induced magnetic anisotropy depends on the volume fractions of structural components, their elastic properties, and coherent bonding of their crystal lattices.

Magnetic properties and thermal stability of the soft magnetic alloy (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 nanocrystallized in the presence of an alternating magnetic field

For the purpose of developing materials with optimum magnetic properties for high-temperature applications (500–600°C), we have investigated the magnetic properties and structure of a nanocrystalline (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy. The alloy was subjected to nanocrystallizing annealing (NA) at 620°C in the presence of an alternating magnetic field (magnetic heat treatment, MHT). The influence of the duration of the NA and of the amplitude value Hamp of the ac magnetic field on the magnetic properties of the alloy and on their thermal stability has been studied. It has been established that the MHT carried out at 620°C is most efficient after holding in a magnetic field for 20 min. In this case, a decrease in the coercive force and an increase in the remanence have been observed. An increase in the time of the holding upon the MHT from 20 min to 4 h decreases the efficiency of the treatment. It has been shown that the MHT carried out at 620°C for 2 h and Hamp = 9 kA/m leads to the smallest changes in the magnetic properties of the alloy after the subsequent holding at a temperature of 550°C for 30 h. However, this treatment does not ensure the thermal stability of the magnetic properties of the alloy at 550°C achieved earlier after the nanocrystallization of the alloy at 620°C for 20 min in the presence of tensile stresses (250 MPa).

Nanocrystalline Soft Magnetic (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 Alloy with Enhanced Thermal Stability of Magnetic Properties

Magnetic properties, structure and thermal stability of the (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy ribbon after its nanocrystallization at 620-750°C for 0-20 min in the presence or absence of tensile stresses σ were studied. It was shown that under the effect of tensile stresses a longitudinal magnetic anisotropy with an easy magnetization axis parallel to the long size of the ribbon was induced in the alloy. A better thermal stability of magnetic properties was observed for the alloy subjected to the nanocrystallization annealing at 620° for 20 min with σ = 170 MPa. After the subsequent annealing at 570°C for 25 h without σ, the magnetic properties of the alloy are unchanged. Increasing of the nanocrystallization annealing temperature up to 670-750°C did not result in improvement of the thermal stability of magnetic properties.

Nanocrystalline Soft Magnetic Fe-, Co-Based Alloys Doped by Hf, Mo and Zr with Enhanced Thermal Stability of Magnetic Properties

Magnetic properties, thermal stability and structure of the alloys - (Fe0.6Co0.4)86Hf7B6Cu1 (1), (Fe0.7Co0.3)88Hf7B4Cu1 (2) and (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 (3) obtained in the form of ribbons quenched from the melt were investigated after their nanocrystallization in the course of the thermal (TA) and stress (SA) annealings in the air at different temperatures. In all three alloys SA resulted in the induction of magnetic anisotropy with an easy axis along the direction of the ribbon. It is established that the alloy 3 after SA at 620°C for 20 min has the best thermal stability of magnetic properties, which remained practically unchanged after the subsequent annealing at 550°C for 26 hours. Magnetic properties of the alloys 1 and 2 subjected to SA under the same conditions did not change after annealing at 500°C.

Induced magnetic anisotropy and structure of nanocrystalline Fe-Co-Cu-Nb-Si-B alloys with different content of Co: I. Stress-annealing-induced magnetic anisotropy and its thermal stability

It is shown that the substitution of Co for Fe in the amorphous Fe73.5Cu1Nb3Si13.5B9 alloy leads to the change in the type of magnetic anisotropy induced in the alloy as a result of a thermomechanical treatment at 520°C. The type of the induced magnetic anisotropy determines the functional characteristics of these alloys as soft magnetic materials. With the content of Co in the alloy equal to 10 at % Co, there is induced a magnetic anisotropy with the direction of the easy axis across the ribbon axis (transverse induced magnetic anisotropy), just as in the alloy without Co. Upon the introduction of 20–30 at % Co into the alloy, the induced magnetic anisotropy becomes longitudinal, with the easy-axis direction along the ribbon axis. The thermal stability of the magnetic properties of the alloys with induced magnetic anisotropy has been investigated.