Metal amorphous nanocomposite (MANC) soft magnetic materials exhibit remarkably low iron loss and high saturation magnetization. However, they have not been widely used in electric motors largely due to a lack of demonstrated manufacturing processing methods and an absence of proven motor designs well suited for their use. Recent developments in these two areas have prompted the optimization study of flux-switching with permanent magnet motor topology using MANCs presented here. This study uses population-based optimization in conjunction with a simplified electromagnetics model to seek rare earth-free designs that attain or exceed the state of the art in power density and efficiency. To predict the maximum mechanically safe rotational speed for each design with minimal computational effort, a new method of quantifying the rotor assembly mechanical limit is presented. The resulting population of designs includes motor designs with a specific power of up to 6.1 kW/kg and efficiency of up to 99% without the use of rare earth permanent magnets. These designs, while exhibiting drawbacks of high electrical frequency and significant manufacturing complexity, exceed the typical power density of representative state-of-the-art EV motors while increasing efficiency and eliminating rare earth elements.

Given the promising high frequency magnetic properties of metal amorphous nanocomposite (MANC) soft magnetic materials (SMMs), recent efforts seek to use MANCs in electric motors to achieve high specific power utilizing elevated magnetic frequency. Such motors can operate at high rotational speed, as eddy current losses pose less limitations on their performance. It is thus important to understand mechanical stress distributions in a motor constructed from MANCs and to predict the likelihood of failure for such a machine at high speeds. Here, we model the residual stress due to the manufacturing process and the operating rotational stress of a MANC rotor. Previously reported failure distributions of laminated MANC ribbons are then used in conjunction with stress results to predict MANC motor failure rates. Because of brittle MANC failure, a design philosophy based on statistics rather than factor of safety (FOS) is used for a range of rotational speeds in our axial motor design. We estimate the probability of failure in a proof test as a function of operational speed. For our design, we determine that a failure rate of 1 in 10 5 at an operational speed of 12.5 kRPM can be achieved for a 45.8 kW motor.

Metal Amorphous Nanocomposite (MANC) materials offer low losses at high magnetic switching frequency, enabling high power density motors with increased rotational speed. While MANCs have high strength, they are brittle. The use of motor components such as a rotor consisting of brittle material presents a reliability concern. Here, a promising MANC alloy is subjected to tensile tests and failure is observed with high-speed photography. A method is developed to prepare tensile specimens of laminated MANC and epoxy layers, simulating the stacking of an epoxy-impregnated tape-wound core. Tensile tests are conducted for single layer ribbon and for five- and ten-layer stacks of laminated material with thin layers of thermosetting epoxy. Failure distributions are shown to have increasing Weibull modulus with increasing layer count. The composite MANC material system is modeled using chain-of-bundles models. Using a k-failure model, we show that single ribbon strength distribution data can be used to predict well the failure distribution of laminated stacks. The agreement occurs when the assumed ineffective length, over which load is recovered in a failed layer, is comparable to the observed interlaminar separation length.

In this work, we introduce a novel haptic device composed of a wearable fingertip sheath, fabricated using an oleogel loaded with magnetic particles, and an external electromagnet. The sheath is actuated using the external magnetic field provided by the electromagnet, which is equipped with a field-focusing pole piece. The oleogel composite used in this device has been optimized for the transfer of the magnetic force from the material to the skin to provide perceptible forces to the wearer. We compare our composite to composites created with materials commonly used in the literature and find the force transfer from our material, as measured by a force sensor, to be much greater when actuated under the same range of input voltages to the electromagnet. We also present a psychophysical user study that shows a linear relationship between this range of input voltages and perceptual magnitude. This result indicates that the device provides a range of tactile feedback that can be driven to a desired intensity of sensation through proportional voltage control.

Recently developed FeNi-based metal amorphous nanocomposites (MANCs) used in high-speed motors (HSMs) exhibit reduced eddy current losses while maintaining good mechanical properties and glass-forming abilities. Magnetic anisotropy in (Fe70Ni30)80Nb4B14Si2 amorphous magnetic ribbon (AMR) in the as-cast state and upon conventional ( $T_{\mathrm {CA}}$ ) and strain ( $T_{\mathrm {SA}}$ ) annealing heat treatment is investigated. From ribbon samples in as-cast condition, quenched in stress from planar flow casting (PFC) induced as-cast curvature derived uniaxial magnetic anisotropy. Stress relief by conventional furnace annealing at $T_{\mathrm {CA}} >$ 350 °C achieved isotropic properties in the bulk. Annealing about the primary crystallization temperature, $T_{\mathrm {CA}} \sim $ 450 °C, resulted in the formation of both face-centered cubic (FCC) and body-centered cubic (BCC) nanocrystallites and evolution to isotropic bulk magnetic properties confirming the random anisotropy model. In samples strain annealed at $T_{\mathrm {SA}}$ = 440 °C at various tensions, relatively large controlled induced uniaxial anisotropy is achieved. The largest magnetic anisotropy occurs in annealing under the stress of 250 MPa yielding an anisotropy field of $7.1\times 10^{4}$ A/m. Surface anisotropy observed by the magneto-optical Kerr effect (MOKE) differs from bulk anisotropy due to image contrast from closure domains. Epoxy coatings are important for improved bonding, mechanical properties, and resistivity in tape-wound MANC cores for HSMs. Using a sessile droplet method, the equilibrium contact angle of an epoxy droplet on a tensile stress-annealed MANC exhibits stress-dependent surface energies. Anisotropic wetting in FeNi-based MANC heat treated at $T_{\mathrm {CA}}$ = 440 °C mimics surface magnetic anisotropy observed by MOKE.

Following reports of attractive soft magnetic performance of an (Fe70Ni30)(80)B14Nb4Si2 alloy [1-3], improvement to this alloy is sought through substitution of small percentages of Co for Fe and/or Ni. Fifteen alloys in the ((FexNiyCo(100-x-y))(80)B14Nb4Si2 alloy system are fabricated by small batch planar flow casting and analyzed for various properties relating to their soft magnetic performance. Alloys synthesized are within the range x = 60-70 and y = 20-30. The most important properties studied here are saturation induction (Bsat), coercivity (Ht), saturation magnetostriction ( lambda(s)), and Curie temperature (T-c). These metrics are important to various aspects of electric motor design. High Tc improves a material's magnetic performance at elevated temperature, while lower Ht and lambda(s) reduce switching losses and larger Bsat is associated with higher torque capability. The resulting alloys have improved amorphous phase Tc of up to 414 celcius and a s reduction of up to 40%. This is achieved while keeping Ht of many compositions below 10 A/m and a calculated B-sat at T= 0 K of one alloy over 1.5 T. Given their improvements in the relevant properties, these new alloys present promise as soft magnets for electric motor applications. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

We report on a systematic investigation of newly developed (Fe70Ni30)(80)Nb4B14Si2 metal amorphous nanocomposites (MANCs) and the factors affecting their surface roughness, including oxide formation and phase evolution during the nanocrystallization process. Analysis of surface roughness using atomic force microscopy (AFM) revealed an average roughness of 9.33 nm after heat treatment compared with as-cast amorphous ribbons, which exhibited a roughness of 4.21 nm. A surface oxide layer thickness has been determined using X-ray photoelectron spectroscopy (XPS). For samples annealed at 400 degrees C for 1 h, 450 degrees C for 1 h, and 550 degrees C for 3 h in air, the average surface oxide layer thickness was determined to be 10.9, 11.7, and 54.4 nm, respectively. It was observed that oxygen is enriched at the outermost surface and decreases rapidly as the XPS sputtering depth increases. Fe-oxide appeared as a predominant metal oxide at the top surface, followed by the presence of Nb oxide. A boron content increase was observed at the interface between the top surface oxide layer and the bulk of the sample. A protective surface oxide layer on FeNi-MANCs, such as observed in this work, can provide sufficient electrical insulation to reduce interlaminate eddy current losses and lower overall losses in magnetic components. (C) 2022 The Author(s). Published by Elsevier B.V.

This chapter discusses ferrite structures and related phases. Ferrites knowledge is intertwined with the oxides of iron: magnetite, Fe 3 O 4 ; hematite, Fe 2 O 3 ; and wustite, FeO. The chapter explains the crystal structures of ferrites and related oxide materials considering: oxides and oxyhydroxides of iron, Fe; magnetic dipole moments, magnetization, exchange coupling, anisotropy, and magnetostriction; 2-3 and 4-2 cubic spinel ferrites; titanomagnetites; garnets; and low-symmetry hematite and hexaferrites. Finite size and surface effects in ferrite nanoparticles can include changes in the degree of inversion (cation preference for A- and B-sites), preferential breaking of like (B-B) or unlike (A-B) bonds at terminating surfaces, symmetry breaking, and chemistry changes at the surface. Chemical and structural changes influence such magnetic properties as surface superexchange interactions, dipole moments, and magnetic anisotropy.

The resulting nanocomposite microstructures of FeNi nanocrystallites under different heating and cooling rates (5 ?/min vs 400-500 ?/s) is investigated. Conventional furnace annealing under low heating rates and slow cooling resulted in both BCC alpha-FeNi and FCC gamma-FeNi nanocrystallites with an average grain size on the order of 25-27 nm whereas high heating rates achieved via flash annealing techniques have enabled a dramatically refined microstructure consisting of 5-7 nm grains with FCC gamma-FeNi phase and found to be the dominant phase following primary crystallization. Grain size refinement and phase identity optimization yielded low values of coercivities-17 A/m and high permeability similar to 11 x 10(3) measured at 400 Hz/1 kA/m in flash annealed samples at 450 ? for 5 s. The magnetic behavior and the underlying mechanism of optimal soft magnetic properties are discussed in terms of the critical role of the grain size in domain wall pinning and coercivity.

Thermal processing of soft magnetic amorphous and nanocrystalline alloys is explored under the influence of radio‐frequency induction‐heating techniques. Direct induction‐heating concepts based on longitudinal and transverse flux heating are examined and the details of electromagnetic fields interaction with metallic strips are discussed by analytical calculations as well as finite element analysis. Initial experimental results confirming spatial control of phase transformations and nanocrystallization within a single strip of Finemet Fe‐based amorphous ribbons are reported. The degree to which primary and secondary crystallization temperature are achieved depends on the spacing between the ribbon relative to the induction coil as well as the coil design and configuration. For transverse coil configurations, the local temperature and therefore microstructural evolution is different across the lateral dimension of processed ribbons, with reduced gap sizes producing enhanced peak temperatures and larger temperature distributions with greater spatial variation in microstructure. In addition, indirect susceptor‐based induction heating under tension is performed and the impact of microstructure is demonstrated. Herein, potential for exploiting spatially optimized phase transformations is illustrated through electromagnetic field–assisted processing in a scalable manufacturing process with amorphous and nanocrystalline soft magnetic alloys.

New interest in high performance soft magnetic materials (SMMs) have been fueled by the need to lower losses at higher operating frequencies while maintaining high flux density and tunable permeability in electrical motors, transformer, and generator applications. Conventional SMMs like electrical steels and Fe-based metal amorphous nanocomposite (MANC) alloys are dominated by eddy current losses at high frequencies. Recent breakthrough in high-performance FeNi MANC have shown promise in reducing eddy current losses as compared to electrical steels. Their intrinsic adherent native surface oxide layer provides sufficient electrical insulation to reduce interlaminate eddy current losses. However, notwithstanding advances in MANCs, there exists a gap in literature on investigations of the surface oxide layer responsible for significant reduction of interlaminate eddy current losses in magnetic cores. This work presents a detailed characterization of the surface oxide, oxidation behavior, and relationship between oxide thickness and resistivity of a new FeNi MANC alloy (Fe70Ni30)80Nb4B14Si2.

We report the pressure (P) dependent Curie temperature, Tc (P) in a FeCoNiCuMn high entropy alloy (HEA). We analyze Tc (P) in terms of d-orbital contraction to explain changes in magnetic exchange interactions (Jex). Considerations of the d-radius contraction inferred from the composition dependence of Tc in γ-Fe-Ni are combined with experimental data for P-dependent lattice constants and magnetic measurements of Tc (P), to calculate contributions of atomic spacing and d-orbital radii to Jex. We show the d-orbital contraction with P captures most of the Tc variation in this alloy.

Improved understanding of advanced manufacturing techniques is needed to fabricate next- generation soft magnetic tape-wound cores. These utilize metal amorphous nano-composites (MANCs) in the form of long thin ribbons. MANCs exhibit attractive soft magnetic properties for use in high frequency and high power density magnetic components. Of particular interest here, the permeability and hysteresis of MANC ribbons can be tuned in a strain annealing process. An unexpected consequence is that wider ribbons develop longitudinal wrinkle patterns. This can substantially reduce the tape-wound core stacking factor. However, when winding a wrinkled ribbon into a toroidal core, the wrinkles can completely flatten, or crinkle. By this phenomenon, the stacking factor can be recovered. To understand the crinkling effect we have developed analytical and finite element analysis (FEA) models. Experiments with known boundary conditions demonstrate the transition from wrinkled to crinkled versus winding curvature. The models utilize an elastic modulus measured via ribbon tensile testing and a ribbon thickness value measurement made by profilometry. The analytical model provides insight into the crinkling effect but cannot explain the length of the transition region from wrinkling to crinkling. With FEA, we successfully predict the transition region and depending on wrinkling amplitude can determine when a ribbon will wind into a useable core. Such mechanics-based insight provides critical feedback for allowable processing parameters in the strain annealing process.

Traditional manufacturing of tape wound cores with low effective permeability involves a cutting step to allow for gapping. While this process is well established, it is not without consequence. Gapped tape wound cores suffer reduced performance in terms of overall magnetic, thermal, and electrical properties. By working with a new class of Cobalt-rich metal amorphous nanocomposite alloys, the permeability can be controlled to a pre-determined value prior to winding into the final desired core shape, thus eliminating the gapping step. This new ability to tune the permeability of a core material opens opportunities to develop magnetic cores with reduced volume and improved thermal management, while eliminating the need for labor intensive gapping processes that also introduce variability and complexities such as fringing flux and excess losses. In this work, we present three permeability profiles (constant, ideally graded, and exponentially graded) in toroidal tape wound cores to allow for the greatest variation and control of the flux density. We also demonstrate the potential for manufacturing of large-scale permeability engineered inductors.

FeNi-based metal amorphous nanocomposite alloys are emerging soft magnetic materials with promise for high-speed motor applications. Here we demonstrate a technique to optimize magnetic properties in toroidal cores wound from strain annealed (Fe70Ni30)80Nb4Si2B14 amorphous metal ribbon (AMR). In-line strain annealing (SA) of the AMR yields a strip permeability that monotonically decreases with increasing SA tensions. After winding into toroidal cores, dramatic changes in magnetic properties are observed and determined to be of magnetostrictive origin. A procedure to re-anneal wound toroidal cores to reduce hysteresis and reverse magnetostrictive effects is developed inclusive of casting curvature effects. We investigate re-annealing temperatures between 300 – 470 °C for cores produced from each SA condition. Magnetic core loss, WL, coercivity, Hc, squareness ratio, Kr, and permeability, µr are measured as a function of (stress relief) re-annealing temperature to optimally achieve W1T,400 Hz = 0.51 W/kg, Hc = 2.42 A/m, Kr = 0.22, and µr = 35,300.

Soft magnetic metal amorphous nanocomposite alloys are produced through rapid solidification and thermal annealing yielding nanocrystals embedded within an amorphous precursor. Similar free energies in Co‐rich and FeNi‐based alloy systems result in multiple nanocrystalline phases being formed during devitrification. Studies of multi‐phase crystallization processes have been reported for Co‐rich alloys but relatively few have investigated FeNi‐based systems. A detailed characterization of compositional partitioning and microstructure of an optimally annealed FeNi‐based MANC (Fe70Ni30)80Nb4Si2B14 alloy is presented through complementary high‐resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). HRTEM demonstrates orientation relationships between FCC and BCC nanocrystals, suggesting heterogeneous nucleation of nanocrystals in the amorphous matrix or a cooperative mechanism of nucleation between BCC and FCC nanocrystallites. APT results show evidence for (i) the segregation of Fe and Ni between nanocrystals of different phases, (ii) B partitioning to the amorphous phase, and (iii) an Nb‐enriched shell surrounding nanocrystals.

Understanding the effects of viscoelastic relaxation of stresses is critical in electric motor and inductor applications, where the magnetic material is fully or partially comprised of an amorphous phase and impregnated in an epoxy. Magnetic Amorphous Nanocomposites (MANCs) are a class of recently developed high-frequency magnetic materials that exhibit low magnetic hysteresis, high saturation flux density and very low AC magnetic losses. MANCs are formed as long, thin ribbons, a shape factor that minimizes eddy current-induced self-heating. This feature, in addition to their 1 GPa strength, and makes them attractive candidates for high-speed, high-power density, electric motors. MANCs are used in the form of tape-wound cores (TWCs). During the manufacturing process, the cores are impregnated with liquid epoxy between each layer of ribbon. Validated knowledge of the stresses imposed by the manufacturing process and during operation is necessary to understand motor performance limitations with respect to strength. Magnetostriction, the strain imposed by reversal of the magnetic field, also affects performance. When the epoxy cures, it contracts volumetrically by 8%, imposing radial and circumferential stresses that vary along the radial direction. To date, these stresses have received little attention in the literature. Here, we model the stress distribution throughout a TWC due to epoxy curing. Strain gauge measurements reported here indicate substantially lower tangential strain than model values, which is beneficial and which we attribute to viscoelastic relaxation of the epoxy layers. We will incorporate a constitutive model of this viscoelastic relaxation, and conduct more detailed strain measurements to understand how this takes

Thermocalc simulations identified compositions with good glass-forming ability (GFA) by locating minima in liquidus temperature, and solidification range in (Fe70 Ni30)x(B-Si-Nb)100-x alloys with x = 82% and x = 85%, increased compared to previously developed x = 80% alloys. 3 compositions in the x = 82% system and 1 in the x = 85% system were successfully cast as amorphous magnetic ribbon. Magnetic properties of as-cast alloys showed improvements in Curie temperature and saturation induction, especially for the 85% alloy. Crystallization behavior in the 85% alloy was determined to occur as a 2-step process. Annealing studies showed (Fe70Ni30)82Nb2Si0B16 and (Fe70Ni30)82Nb3Si0B15 alloys to exhibit low coercivity and high Bs with annealing. TEM results show significant crystallization in as-cast ribbon. The (Fe70Ni30)85Nb0.5Si0B14.5 alloy as-cast has small, uniformly distributed grains, allowing a useful nanocrystalline alloy to be produced as cast. Finally, the parameter ΔTxg, the temperature range in which the material can be thermomechanically processed, was in the range of 12–23 °C.