Abstract
Amorphous ferromagnetic microwires fabricated by water-quenching have been assessed to show favorable properties for next-generation high-frequency electric machines as compared to those of conventional amorphous magnetic alloys in sheet or ribbon form. Here, water-quenched amorphous Fe75Si10B15 microwires were subjected to a range of aging times of up to 5 years in the air at room temperature. While both newer and aged microwires are X-ray amorphous, the aged microwires do exhibit a slight degree of crystallinity, a lower initial susceptibility and a reduced enthalpy change for full devitrification. These small differences (typically < 5%) are attributed to the formation of minor surface oxidation products such as iron oxides and SiO2 which modify the surface strain state. The resultant stress couples to magnetostriction to promote the formation of radial magnetic domains that impair the magnetic reversal process. These results demonstrate that while amorphous ferromagnetic microwires are essentially stable against aging in the air, consideration of their surface state will be significant for advanced applications.
Highlights
The most significant feature in the X-ray diffraction (XRD) patterns of the as-quenched samples is the broad Bragg peak located at 2θ ∼ 45○; the magnitude of this Bragg peak for the aged microwires is significantly higher than that observed for the newer microwires
After heating in the Differential Scanning Calorimetry (DSC), sharp Bragg peaks with high intensities appear on the XRD patterns of both samples (Figure 1b)
The lattice parameters of the Fe3Si phase of both devitrified microwires are larger by approximately 1.5% than the reference value; it is noted that the Fe3Si lattice parameter in the aged microwires shows a yet larger value which returns a unit cell volume expansion by ∼1.75% over the reference value
Summary
In 2017, approximately 40% of primary energy usage in the United States was attributed to electricity, with 67% of this total electrical energy rejected in the form of waste heat. To reduce energy waste and the associated dependence on limited natural resources, it is crucial to promote the development of new energy-efficient electrical machines, which in part relies on the advancement of soft magnetic materials. Recently, amorphous magnetic microwires have been assessed to show favorable properties as compared to conventional amorphous magnetic alloys in sheet or ribbon form, due to the enhanced magnetization alignment, unique magnetoelastic interactions and diverse magnetic domain structure derived from the constrained and micro-scaled geometry of these materials. To better understand the long-term performance aspects of amorphous magnetic microwires as a new class of core materials in electrical machines, this work seeks to understand the effects of room-temperature long-term aging on their structural and magnetic characteristics. To reduce energy waste and the associated dependence on limited natural resources, it is crucial to promote the development of new energy-efficient electrical machines, which in part relies on the advancement of soft magnetic materials.. To better understand the long-term performance aspects of amorphous magnetic microwires as a new class of core materials in electrical machines, this work seeks to understand the effects of room-temperature long-term aging on their structural and magnetic characteristics. Numerous studies of Fe-based amorphous alloys have been carried out, advancing knowledge of the stability of this class of alloys in simulated marine environments.. Numerous studies of Fe-based amorphous alloys have been carried out, advancing knowledge of the stability of this class of alloys in simulated marine environments.4,5 These studies reported the formation of surface oxides that altered the magnetic response of these alloys. Little attention has been directed to assess the structural and magnetic modification of Febased amorphous microwires when exposed to air for an extended period
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