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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.

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.

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.

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.

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.

The power losses in high power-density motors due to high rotational speed and/or high pole counts may be reduced adopting metal amorphous nanocomposites (MANCs) featuring low power loss and a relatively high flux density ($\sim$1.3 T). We recently proposed a flux switching permanent magnet (FSPM) motor with a rating of 2.5 kW at 1400 Hz electrical speed that incorporates low loss (

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.

Real-time temperature mapping that solves local overheating problems is important for obtaining an optimized thermal design for high-efficiency power transformers. Internal temperature monitoring of operating power transformers can also be leveraged for asset monitoring applications targeting at fault detection enabling condition-based maintenance. Transformers present a variety of challenging sensing environments such as high levels of electromagnetic interference and limited space for conventional sensors to operate. Immersion of power transformers in insulation oils for thermal management during operation and the presence of relatively large and time-varying electrical and occasional magnetic fields make sensing technologies requiring electrical wires or active power at sensing locations highly undesirable. In this work, we investigate thermal response of a standard telecom fiber instrumented on compact transformer cores by using an optical frequency-domain reflectometry scheme. Correlation between conventional temperature sensing methods and fiber-optic sensing results as well as tradeoffs between spatial resolution and temperature measurement accuracy is discussed and spatially resolved real-time monitoring of temperatures in energized transformers is experimentally demonstrated.

Metal amorphous nanocomposite alloys, with compositions (Fe70Ni30)80-xNb4Si2B14TEx (0 ≤ x ≤ 5), where TE is a transition element, and (Fe70Ni30)80-yNb4+ySi2B14 (0.5 ≤ y ≤ 2) were synthesized. Samples were annealed at 440 °C and strain-annealed at 440 °C and 300 MPa. Resistivity was found to increase with small substitutions of TE elements. Increasing V resulted in reduced Bs from 1.2 T to 0.5 T. Further Mo additions lowered Bs to 0.6 T, and consistently reduced the permeability. For Cr and Nb, resistivity increased, and strain-annealed permeability was lower than the annealed permeability. Lastly, toroidal core losses on (Fe70Ni30)79.5Nb4Si2B14V1 yielded W1.0/400 = 2.1 W/kg, and W1.0/1 k = 6.0 W/kg.

The solid-state transformer (SST) is an emerging technology which is gaining increasing importance for future power distribution systems. Here, we present 2-D finite-element analysis (FEA) of single-phase SSTs for operating frequencies of 50 kHz. We consider designs to benchmark materials aimed at controlling high-frequency losses to achieve higher power densities. The FEA model is solved in the time domain for frequencies of 50 kHz, at a fixed 800 V input voltage and 10 kW output power for the first four cycles. This paper analyzes the influence of leakage inductance on the waveform with an increasing number of turns and discusses how to calculate the leakage inductance of the different winding topologies by FEA. In addition, transformer topologies are coupled to a power analysis using a Steinmetz parameterization of magnetic losses capturing induction and field scaling for transformer losses for FeNi-based metal amorphous nanocomposites (MANCs) for SST applications and their benchmarking with amorphous and other MANCs and ferrites. Recently, discovered FeNi-based MANCs allow smaller transformers at equivalent power as compared to Si steels, Metglas, and Co-based MANCs. These Fe-rich and non-Co containing MANCs also offer economies based on lower raw materials costs as compared with Co-based MANCs and significantly improved mechanical properties with respect to commercially available Fe-based MANCs.

Metal amorphous nanocomposites (MANCs) offer lower losses than silicon steels and higher saturation inductions than amorphous alloys. Their application in motors will require a detailed understanding of their mechanical properties. Co74.6Fe2.7Mn2.7Nb4Si2B14 was studied by nanoindentation and tensile testing to determine hardness, elongation, Young's modulus, ultimate tensile strength (UTS), and Poisson's ratio. Young's modulus was observed to increase with crystallization at 50 MPa, and then decrease when annealing under applied stress. Annealing at even higher stress resulted in no significant change in Young's modulus. This trend was replicated in nanohardness results. The UTS and elongation decrease with crystallization and show a large increase in standard deviation. Reduction in UTS and elongation has been attributed to embrittlement, as well as the high surface roughness of the ribbon material. Poisson's ratio remained relatively constant at 0.31–0.33 for all samples. X-ray diffraction (XRD) was performed on annealed samples, revealing fine nanocrystals. Profilometry indicates significant surface roughness, which contribute to reduction of UTS and elongation. Hardness, UTS, and elongation compare favorably to existing materials, but embrittlement of the material needs to be addressed to allow use in electric motor applications.

This chapter provides a review of soft magnetic materials (SMM’s) beginning with a cursory discussion of fundamental and technical magnetic properties followed by a summary of technically important soft magnetic materials classes. This is followed by a review of measurement techniques which are important for materials characterization in emerging SMM’s.

The use of the advanced manufacturing technique of strain annealing for nanocomposite magnetic ribbons enables control of relative permeabilities and spatially dependent permeability profiles. Tuned permeability profiles enable enhanced control of the magnetic flux throughout magnetic cores, including the concentration or dispersion of the magnetic flux over specific regions. Due to the correlation between local core losses and temperature rises with the local magnetic flux, these profiles can be tuned at the component level for improved losses and reduced steady-state temperatures. We present analytical models for a number of assumed permeability profiles. This work shows significant reductions in the peak temperature rise with overall core losses impacted to a lesser extent. Controlled strain annealing profiles can also adjust the location of hotspots within a component for optimal cooling schemes. As a result, magnetic designs can have improved performance for a range of potential operating conditions.

We review the materials paradigm for metal amorphous nanocomposite (MANC) soft magnetic materials to showcase in solid state transformers (SSTs). We report 2D finite element analysis (FEA) of 3-phase SSTs operating at 50 Hz–10 kHz frequencies. We benchmark materials in designs to control high frequency losses and achieve higher power densities. FEA models are solved in the time domain for line frequencies of 50 Hz–10 kHz and 100 KW output power for the first 4 cycles. Transformer topologies are coupled to a power analysis using a Steinmetz parameterization of magnetic losses capturing induction and field scaling for transformer grade Si steel as compared to Metglas, Ferrite, FINEMET, Co- and FeNi-based MANCs. Recently discovered FeNi-based MANCs allow smaller transformers at equivalent power as compared to Si steel, Metglas, and Co-based MANCs. Fe-rich and non-Co containing MANCs also offer economies based on lower raw materials costs compared with Co-based MANCs.

Metal amorphous nanocomposites (MANCs) are promising soft magnetic materials (SMMs) for power electronic applications offering low power loss at high frequency and maintaining a relatively high flux density. While applications in certain motor designs have been recently modeled, their widespread application awaits scaled manufacturing of MANC materials and proliferation of new higher speed motor designs. A hybrid motor design based on permanent magnets and doubly salient stator and rotor is reported here to develop a compact (a factor of 10 smaller than currently possible in Si steels), high-speed (>1 kHz, electrical), high-power (>2.5 kW) motor by incorporating low loss ( $2.2 \times 10^{5}$ A/m sustainable, for example, with a high-grade hard ferrite magnet.

Metal amorphous nanocomposite (MANC) alloys are an emerging class of soft magnetic materials showing promise for a range of inductive components targeted for higher power density and higher efficiency power conversion applications including inductors, transformers, and rotating electrical machinery. Magnetization reversal mechanisms within these alloys are typically determined by composition optimization as well as controlled annealing treatments to generate a nanocomposite structure composed of nanocrystals embedded in an amorphous precursor. Here we demonstrate the concept of spatially varying the permeability within a given component for optimization of performance by using the strain annealing process. The concept is realized experimentally through the smoothing of the flux profile from the inner to outer core radius achieved by a monotonic variation in tension during the strain annealing process. Great potential exists for an extension of this concept to a wide range of other power magnetic components and more complex spatially varying permeability profiles through advances in strain annealing techniques and controls.

Fe-Ni based metal amorphous nanocomposites (MANCs) are investigated in the pseudo-binary alloys (Fe100 − xNix)80Nb4Si2B14. To optimize the soft magnetic properties of the nanocomposites, primary and secondary crystallization kinetics must be understood. As such, primary and secondary crystallization temperatures are determined by differential scanning calorimetry, and activation energies are calculated, along with the resulting crystalline phases. Time-temperature-transformation diagrams for primary and secondary crystallization in (Fe70Ni30)80Nb4Si2B14 are presented. Saturation magnetization and Curie temperature are determined. Lastly, the shape of magnetization vs. time curves for (Fe30Ni70)80Nb4Si2B14 at various temperatures suggest that the secondary crystal product often consumes some of the primary crystalline product.

This paper explores the FeCoNiCuMn high-entropy alloy system, where small departures from equiatomic composition have yielded technologically interesting 300-K Curie temperatures ( $$T_{\mathrm{c}}$$ ), making them promising for magnetocaloric applications. We also demonstrate that the small deviations from equiatomic compositions do not affect the structural stability of our single-phase fcc-based solid solutions. Room-temperature Mossbauer spectroscopy measurements provide evidence for the distributed exchange interactions ( $$J_{\mathrm{ex}}$$ ) occurring between the magnetic elements, which contribute to a broadened magnetocaloric effect observed for these alloys. The average hyperfine field observed in the Mossbauer spectra decreases as the $$T_{\mathrm{c}}$$ of the alloys decrease, confirming direct current magnetic measurements. Multiple peaks in the hyperfine field distribution are interpreted considering pairwise ferromagnetic or antiferromagnetic $$J_{\mathrm{ex}}$$ between all elements except the Cu diluent as contributing to overall magnetic exchange in the alloy.

Fe-Ni-based metal amorphous nanocomposites with a range of compositions (Fe100−x Ni x )80Nb4Si2B14 (30 ≤ x ≤ 70) are investigated for motor and transformer applications, where it is beneficial to have tunable permeability. It is shown that strain annealing offers an effective method for tuning permeability in these alloys. For an Fe-rich alloy, permeability increased from 4000 to 16,000 with a positive magnetostriction. In a Ni-rich alloy, permeability decreased from 290 to 40 with a negative magnetostriction. Significant elongations (above 60%) are observed during strain annealing at high stress. Crystallization products have been determined in all alloys heated to 480°C. γ-FeNi is formed in all alloys, while (Fe30Ni70)80Nb4Si2B14 also undergoes secondary crystallization at temperatures of approximately 480°C to form a phase with the Cr23C6-type structure and a likely composition of Fe21Nb2B6. Toroidal losses have been measured for (Fe70Ni30)80Nb4Si y B16−y (0 ≤ y ≤ 3) at various annealing temperatures. At an induction of 1 T and frequency of 400 Hz and 1 kHz, the toroidal losses obtained are W1.0T, 400 Hz = 0.9 W/kg and W1.0T, 1 kHz = 2.3 W/kg, respectively. These losses are lower than losses recently reported for state of the art 3.0% and 6.5% silicon steels, a Metglas Fe-based amorphous alloy, and some Fe-based nanocomposites.

Cobalt ferrite nanoparticles were exposed to mechanochemical activation, with and without equimolar amounts of graphene nanoparticles, for time periods ranging from 0 to 12 h. Their structural and magnetic properties were detailed from Mӧssbauer spectroscopy and magnetic measurements. The Mӧssbauer spectrum corresponding to the unmilled cobalt ferrite powder was analyzed using 2 sextets, corresponding to the tetrahedral and octahedral sites of ferrites. The rest of the spectra was deconvoluted using an additional quadrupole-split doublet, with an abundance close to 30% and was assigned to superparamagnetic particles. Moreover, the spectra corresponding to milling with graphene at the longest times needed a third sextet, which could be assigned to iron carbide. The degree of inversion was determined from the Mӧssbauer spectra and found to decrease with milling time, both for the set with and that without graphene. The canting angle was derived and studied as function of the ball milling time for both sets of samples. Hysteresis loops were recorded at 5 K in an applied magnetic field of 5 T and was found to exhibit a wasp-waist shape. Magnetization was plotted as function of temperature in the range 5–300 K with an applied magnetic field of 200 Oe using zero-field-cooling-field-cooling (ZFC-FC) measurements. These made it possible to determine the blocking temperature of the samples. Our data exhibit new characteristics of the cobalt ferrite nanopowders milled with and without graphene nanoparticles.

Magnetic nanocomposites, annealed under stress, are investigated for application in inductive devices. Stress annealed Co-based metal/amorphous nanocomposites (MANCs) previously demonstrated induced magnetic anisotropies greater than an order of magnitude larger than field annealed Co-based MANCs and response to applied stress twice that of Fe-based MANCs. Transverse magnetic anisotropies and switching by rotational processes impact anomalous eddy current losses at high frequencies. Here we review induced anisotropies in soft magnetic materials and show new Co-based MANCs having seven times the response to stress annealing as compared to Fe-based MANC systems. This response correlates with the alloying of early transition metal elements (TE) that affect both induced anisotropies and resistivities. At optimal alloy compositions, these alloys exhibit a nearly linear B–H loop, with tunable permeabilities. The electrical resistivity is not a function of processing stress but trends in electrical resistivity and induced anisotropy with choice and concentration of TE content are clearly resolved. Previously reported and record-level induced anisotropies, Ku, ∼20 kJ/m3 (anisotropy fields, HK ∼ 500 Oe), in stress annealed Co-rich MANCs are increased to Ku ∼ 70 kJ/m3 (HK > 1800 Oe) in new systems.

(Fe65Co35)83.5−xB13NbxSi2Cu1.5 amorphous ribbons with (4 at.%) and without (0 at.%) growth inhibitor Nb were Joule annealed at low current intensity to avoid bulk crystallization, and their surface domain structure, bulk and surface magnetization, and high frequency magneto-impedance (MI) were systematically investigated. Magneto-optic Kerr effect (MOKE) microscopy and longitudinal MOKE evidenced the development of a longitudinal surface anisotropy in the ribbon without Nb (Nb0) as a result of the Joule annealing treatment, while the 4 at.% Nb (Nb4) ribbon developed an anisotropy 30° from the transverse direction. The increased transverse ac permeability at the surface of Nb4 was evident in MI measurements by a higher [ΔZ/Z]max as compared to Nb0 at frequencies greater than 200 MHz. A correlation between the surface domain structure, induced anisotropy and high frequency MI in the ribbons was established.

High entropy alloys (HEAs) are useful in applications that requir high strength, oxidation resistance, and high temperature stability. Research on HEAs for magnetocaloric applications focuses on increasing the refrigeration constant and controlling the Curie temperature $({{T}}_{c})$ . Here we investigate the effect of metal additions on exchange interaction distributions in eqiatomic ferromagnetic alloys of Fe, Co, and Ni. The metal additions are (a) noble metals (e.g., Cu, Ag), (b) antiferromagnetic transition metals (e.g., Mn), (c) Stoner-enhanced transition metals (e.g., Pt), and (d) early transition metals (e.g., Mo) that contribute to the virtual bound states. We are able to: 1) stabilize a ferromagnetic face-centered cubic $\gamma$ -phase with equiatomic compositions in 4-, 5-, and 6-component systems, 2) make slight departures from equiatomic compositions to a chosen alloy to bring its ${T}_{c}$ closer to room temperature, and 3) measure the role of alloying on exchange interaction distributions. We present a simple model to predict ${T}_{c}$ in HEAs using the Bethe–Slater curve and binary phase diagrams of alloy constituents. Compared to the rare-earth-based magnetocaloric materials, the HEAs investigated here have significantly lower costs.

Nickel ferrite nanoparticles were subjected to mechanochemical activation for ball milling times ranging from 0 to 12 h. The milling was performed with and without the addition of equimolar concentrations of graphene nanoparticles. Characterization of resulting nano-powders was undertaken by Mӧssbauer spectroscopy and magnetic measurements. The hyperfine magnetic field was studied as function of milling time for octahedral and tetrahedral sites. An additional quadrupole split doublet represented the occurrence of superparamagnetic particles in the as-obtained and milled specimens. A new phase was obtained in the graphene-milled set of samples, which could be assigned to carbon-rich particles. The degree of inversion and canting angle were derived from the Mӧssbauer measurements and studied as function of ball milling time. The degree of inversion was found to decrease with milling time, especially for the set without graphene and evidenced a transition from inverse to normal spinels. The canting angle decreased with time for the graphene milled nanoparticles. The recoilless fraction was determined as function of milling time and was consistent with the observation – for the first time in literature – of a distribution of recoilless fractions in the studied specimens. The saturation magnetization, remanence magnetization and coercive field were derived from the hysteresis loops, recorded at 5 K and 5 T. The zero-field-cooling-field-cooling measurements were obtained in a magnetic field of 200 Oe and the blocking temperature was determined. Our results show new features of the behavior of nickel ferrite nanoparticles under mechanochemical activation with and without graphene.

xHfO2-(1-x)α-Fe2O3 (x = 0.1, 0.3, 0.5 and 0.7) nanoparticles system was obtained using mechanochemical activation by high energy ball milling for time periods ranging from 0 to 12 h. X-ray diffraction patterns revealed the presence of two phases, a hafnium-doped hematite and an iron-doped hafnia, which competed with each other to form a solid solution. The trend observed in the lattice parameters using Rietveld refinement was consistent with differences in ionic radii between Hf and Fe. Crystallite sizes for both hematite and hafnia were analyzed as function of milling time using the Scherrer method and found to decrease down to ~15 nm for all molar concentrations used. Mossbauer spectroscopy revealed the presence of 1–5 sextets corresponding to different numbers of Hf nearest neighbors of Fe in the hematite structure. The different hyperfine magnetic fields could be resolved in the model of local atomic environment. Substitutions of Fe in hafnia gave rise to a nonmagnetic phase represented by a quadrupole split doublet, whose abundance was found to increase with ball milling time. Hysteresis loops recorded at 5 K showed that the Hf-doped system does not saturate in an applied magnetic field of 5 T. The Morin transition was observed during zero-field-cooling-field cooling (ZFC-FC) in an external magnetic field of 200 Oe. Differential scanning calorimetry with thermal gravimetric analysis (DSC-TGA) evidenced an exothermic peak for the starting oxides and an endothermic peak for the solid solution.

In this work, we present characterization of surface oxidation and crystallization behavior of Metal Amorphous Nanocomposite (MANC) (Fe70Ni30)80Nb4Si2B14 alloys via complementary x-ray diffraction, electron microscopy, and x-ray photoelectron spectroscopy techniques. An adherent amorphous oxide of roughly 15–20 nm in thickness is observed on the wheel side of the ribbon, enriched in Fe relative to Ni and with significant content of Si and Nb as would be expected based upon a comparison of the Gibbs free energy of formation of the stable oxide phases. The amorphous character of the oxide is likely to result from the significant Si-content coupled with the amorphous and nanocrystalline character of the underlying metallic layer. Higher density of FeNi-enriched nanocrystals is also observed within ∼100 nm of the wheel-side surface, presumably due to reduction in local glass former concentration. A rough, crystalline copper oxide layer is also present and forms through contact between the copper wheel and the solidifying melt during the rapid solidification process. On the air side of the ribbon, a crystalline oxide layer of ∼15–20 nm is formed as well as intergranular oxidation that penetrates along the grain boundaries between highly textured surface crystallites of ∼50–100 nm in size. The crystalline nature of the oxide on these surfaces is asserted to result from the lack of significant Si-content and the pre-existing surface crystallites that form during the rapid solidification process which promote a crystalline oxide surface layer. These results shed new insights into the details of surface oxidation and can help to inform processing and alloy composition adjustments which seek to tailor surface properties.

Alloys in a (Fe70Ni30)80(B–Si–Nb)20 system, with good glass forming ability (GFA), were identified using Thermocalc software to simulate liquidus temperatures (T's) and solidification ranges (areas between the liquidus and solidus in a binary phase diagram,a line at fixed T). A region with excellent GFA was identified at 14–18% B and 0–7% Si with the balance Nb, showing minima in liquidus and solidification range. A region with a solidification range minimum, but no corresponding liquidus minimum was identified at 3–8% B and 5–10% Si but had lower GFA. A shallow liquidus minimum, with no minimum in solidification range, at 3–5% B and 1–3% Si had the lowest GFA and did not produce amorphous material. Measured GFA was ranked using parameters Trg, ΔTxg, and γm, defined herein. Only the reduced glass transition temperature, Trg, was predictive for the alloys. Differential Scanning Calorimetry (DSC) data showed liquidus T's to agree. Curie temperatures, Tc's were observed to increase with B/Nb ratio. Simulations of liquidus and solidification range for alloys with 18 and 15% glass formers do not show regions with minima in both, indicating good GFA is not expected.

Nanoparticle-sized powders have seen more and more use in many of today’s applications. As particle size decreases, many properties change including the ability to embed the small particles in liquids and other media. With decreasing size, however, surface energy becomes more important and can dictate the final shape of the particle. In applications based on polar molecules attaching to the nanoparticle surface, the surface morphology can become a key design parameter. A nucleation and growth model has been constructed for truncated body-centered cubic derivative materials, along with an update to previously published work on face-centered cubic materials. The model shows that for (110)- and (111)-truncations of a cube with a specified surface energy for each surface, the critical nuclei and equilibrium growth shapes are the same, supporting the theory of self-similar growth that had only been mentioned previously, but never proven. In this analysis, saddle points play an important role in determining the critical nuclei for comparison with the equilibrium growth shapes.

We explore amorphous soft-magnetic alloys as candidates for electric motor applications. The Co-rich system combines the benefits of low hysteretic and eddy-current losses while exhibiting negligible magnetostriction and robust mechanical properties. The amorphous precursors can be devitrified to form nanocomposite magnets. The superior characteristics of these materials offer the advantages of ease of handling in the manufacturing processing and low iron losses during motor operation. Co-rich amorphous ribbons were laser-cut to build a stator for a small demonstrator permanent-magnet machine. The motor was tested up to ~30,000 rpm. Finite-element analyses proved that the iron losses of the Co-rich amorphous stator were ~80% smaller than for a Si steel stator in the same motor, at 18,000 rpm (equivalent to an electric frequency of 2.1 kHz). These low-loss soft magnets have great potential for application in highly efficient high-speed electric machines, leading to size reduction as well as reduction or replacement of rare earths in permanent-magnet motors. More studies evaluating further processing techniques for amorphous and nanocomposite materials are needed. Fil: Silveyra, Josefina María. University Of Carnegie Mellon; Estados Unidos. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina Fil: Xu, Patricia. University Of Carnegie Mellon; Estados Unidos Fil: Keylin, Vladimir. University Of Carnegie Mellon; Estados Unidos Fil: DeGeorge, Vincent. University Of Carnegie Mellon; Estados Unidos Fil: Leary, Alex. University Of Carnegie Mellon; Estados Unidos Fil: McHenry, Michael. University Of Carnegie Mellon; Estados Unidos

Amorphous and nanocrystalline soft magnetic alloys have garnered interests in academia and industry due to their potentials for applications, such as power transformers, electric motors, and sensors. To achieve good glass formability, thermal stability, and prevent grain overgrowth, elements such as B, Nb, Ta, and Hf are used in many soft magnetic systems. However, the high price of these precursors results in expensive soft magnetic alloys. Herein, we report on substituting Ta and Hf with TaC and HfC, respectively, to significantly reduce the cost of Fe-based FINEMET and Co-based HTX005 alloys. Soft magnetic properties of these alloys are studied. The effect of thermal annealing and strain annealing on TaC and HfC substituted alloys are also investigated. Lastly, we discuss the cost analysis on these alloys. Using the synthesis route presented here, a cost reduction of up to 74% can be achieved.

Electric and magnetic properties, including saturation induction, resistivity, Curie temperature, and others, that make soft magnetic materials attractive for applications such as power converters and electric machines depend on local alloy composition. In this paper, we address this dependence quantifiably. First, we correlate the crystallization state to local composition with a novel mass balance. Second, we perform atom probe tomography on (Fe65Co35)79.5B13Si2Nb4Cu1.5 magnetic nanocomposites to explore local compositional evolution with devitrification and test predictions. Precise 3-D atom maps of constituent elements are constructed from as-cast, intermediate, and late stage crystallized samples. Local compositions and final crystal fraction predicted from mass balances are tested. Analysis of chemical partitioning during growth quantifies the depletion of glass formers (GFs) in nanocrystals, and enrichment of GFs and depletion of Fe and Co in the amorphous phase. Finally, we demonstrate the direct measurement of local composition on a nanometer scale and present predictive models necessary to deduce intrinsic constituent phase properties and investigate the proposed shell interfacial phases.

Amorphous and nanocrystalline soft magnets have been investigated extensively in the past two decades. Many materials with attractive soft magnetic properties contain boron, which improves the glass formability, thermal stability and prevents undesirable grain growth. The high price of boron, however, makes the development of new soft magnetic materials and alternative synthesis routes important. We report here a synthesis of cobalt-rich alloys by substituting boron carbide for elemental boron to achieve significantly lower cost. Ribbons produced with and without boron carbide substitution were observed to exhibit comparable soft magnetic properties while the former results in 31–48% cost reduction. Extrapolating this idea to commercial VITROVAC 6025 and 6150, the cost reductions were calculated to be 56 and 50%, respectively, while both synthesis routes produced ribbons of similar soft magnetic properties. Our work here provides an attractive route to reduce the cost and increase the market competitiveness of soft magnets.

Sn–Ag–Cu (SAC) alloys are regarded as the most promising alternative for traditional Pb–Sn solders used in electronic packaging applications. However, the higher reflow temperature requirement, possible intermetallic formation, and reliability issues of SAC alloys generate several key challenges for successful adoption of Pb-free solder for next generation electronic packaging needs. Localized heating in interconnects can alleviate thermal stresses by preventing subjection of entire package to the higher reflow temperatures associated with the SAC solders. It had been demonstrated that SAC solder–FeCo magnetic nanoparticles (MNPs) composite paste can be reflowed locally with AC magnetic fields, enabling interconnect formation in area array packages while minimizing eddy current heating in the printed circuit board. Solder/magnetic nanocomposite pastes with varying MNP concentration were reflowed using AC magnetic fields. Differential scanning calorimetry results show a reduced undercooling of the composite pastes with the addition of MNPs. TEM results show that the FeCo MNPs are distributed in Sn matrix of the reflowed solder composites. Optical and SEM micrographs show a decrease in Sn dendrite regions as well as smaller and more homogeneous dispersed Ag3Sn with the addition of MNPs. The MNPs promote Sn solidification by providing more heterogeneous nucleation sites at relatively low undercoolings. The mechanical properties were measured by nanoindentation. The modulus, hardness, and creep resistance, increase with the MNP concentration. The enhanced mechanical properties are attributed to grain boundary and dispersion strengthening. The reflow of solder composites have been modeled based on eddy current power loss in the substrate and magnetic power losses in the solder bumps. Induction reflow of pure solder bumps ( In this article we review lead-containing and lead-free solder systems, and the electronic packaging technologies pertinent to soldering process. Recent research on the effects of MNPs on localized heating, microstructure evolution, mechanical properties, and thermomechanical reliability are summarized.

INSPEC Accession Number: 15298193 We have designed and fabricated a microelectromechanical device, based on the alternating field gradient concept, to measure surface magnetic field gradient on planets. Its sensitivity is 4 10 -4 T/m, which is appropriate for magnetite outcrops and areas with rocks formed at different stages recording geomagnetic field reversals. We present the results obtained with three different prototypes. The work of J. L. Mesa was supported by INTA training Grant TS09/12. This work has been done in the frame of PRI-PIBUS-2011-1150 and 1182 grants of the subprogram of international and bilateral projects of the Spanish Ministry of Science and Innovation. The work at CMU is supported by the National Science Foundation through Materials World Network under Grant DMR1106943. Peerreview

Real-time temperature mapping is important to offer an optimized thermal design of efficient power transformers by solving local overheating problems. In addition, internal temperature monitoring of power transformers in operation can be leveraged for asset monitoring applications targeted at fault detection to enable condition based maintenance programs. However transformers present a variety of challenging environments such as high levels of electromagnetic interference and limited space for conventional sensing systems to operate. Immersion of some power transformers within insulation oils for thermal management during operation and the presence of relatively large and time varying electrical and magnetic fields in some cases also make sensing and measurement technologies that require electrical wires or active power at the sensing location highly undesirable. In this work, we investigate the dynamic thermal response of standard single-mode optical fiber instrumented on a compact transformer core by using an optical frequency-domain reflectometry scheme, and the spatially resolved on-line monitoring of transformer core temperature rise has been successfully demonstrated. It is found that spectral shifts of the fiber-optic sensor induced by the temperature rises are strongly related to the locations inside the transformer as would be expected. Correlation between thermal behavior of the transformer core as derived from standard IR-based thermal imaging cameras and fiber-optic sensing results is also discussed. The proposed method can easily be extended to cover situations in which high accuracy and high spatial resolution thermal surveillance are required, and offers the potential for unprecedented optimization of magnetic core designs for power transformer applications as well as a novel approach to power transformer asset monitoring.

Titanomagnetites (TMs) [pseudobinary (1 - x)Fe 3 O 4 · xFe 2 TiO 4 oxides, where, e.g., TM75 corresponds to x-0.75] are magnetic minerals with a spinel structure. Ulvospinel (Fe 2 TiO 4 ) and TMs were made using a solid-state synthesis technique, and transmission electron microscopy (TEM) characterization and measurement of the TM samples were performed to further confirm the homogeneity of the samples and cation site occupancies. The Mossbauer spectra in the TMs exhibited an anomalous composition dependence at x=0.95, when fitted with two instead of three quadrupole split doublets. This result was reinforced by the obtained dependence of the recoilless fraction on the composition, which exhibited an extremum at x=0.95.

A nanoscale-driven crystal growth of magnetic hexaferrites was successfully demonstrated at low growth temperatures (25-40% lower than the temperatures required often for crystal growth). This outcome exhibits thermodynamic processes of crystal growth, allowing ease in fabrication of advanced multifunctional materials. Most importantly, the crystal growth technique is considered theoretically and experimentally to be universal and suitable for the growth of a wide range of diverse crystals. In the present experiment, the conical spin structure of Co2Y ferrite crystals was found to give rise to an intrinsic magnetoelectric effect. Our experiment reveals a remarkable increase in the conical phase transition temperature by ∼150 K for Co2Y ferrite, compared to 5-10 K of Zn2Y ferrites recently reported. The high quality Co2Y ferrite crystals, having low microwave loss and magnetoelectricity, were successfully grown on a wide bandgap semiconductor GaN. The demonstration of the nanostructure materials-based "system on a wafer" architecture is a critical milestone to next generation microwave integrated systems. It is also practical that future microwave integrated systems and their magnetic performances could be tuned by an electric field because of the magnetoelectricity of hexaferrites.

Giant magnetoimpedance (GMI)-based devices offer potential as next-generation low-cost, flexible, ultrasensitive sensors. They can be used in applications that include current sensors, field sensors, stress sensors, and others. Challenging applications involve operation at high temperatures, and therefore studies of GMI temperature dependence and performance of soft magnetic materials are needed. We present a high-temperature GMI study on an amorphous soft magnetic microwire from room temperature to 560°C. The GMI ratio was observed to be nearly constant at ∼86% at low temperatures and to decrease rapidly at ∼290°C, finally reaching a near-zero value at 500°C. The rapid drop in GMI ratio at 290°C is associated with a reduction in the long-range ferromagnetic order as measured by the spontaneous magnetization (M) at the Curie temperature (Tc). We also correlated the impedance with the magnetic properties of the material. From room temperature to 290°C, the impedance was found to be proportional to the square root of the magnetization to magnetic anisotropy ratio. Lastly, M(T) has been fit using a Handrich–Kobe model, which describes the system with a modified Brillouin function and an asymmetrical distribution of exchange interactions. We infer that the structural fluctuations of the amorphous phase result in a relatively small asymmetry in the fluctuation parameters.

New power conversion systems that offer promise to transform electricity grids into unified interactive supply networks require high-resistivity soft-magnetic materials to allow for switching of magnetic materials at frequencies approaching 100 kHz for power transformation in the megawatt range. Amorphous and nanocomposite soft-magnetic materials, which represent the state of the art in terms of high power densities and low losses at high frequencies, have resistivities that depend on the structures and spatial distributions of multiple phases in thin ribbons. We present a multiphase resistivity model applicable to nanocomposite materials by considering an equivalent circuit approach considering paths through an amorphous, crystalline, and growth inhibitor shell phase. We detail: (a) identification of amorphous, crystalline, and shell phases; (b) consideration of the role of the morphology of each phase in an equivalent circuit model for the resistance; (c) a two-band model for the Fe/Co composition dependence of the resistivity in crystalline and amorphous phases; (d) a virtual bound state model for resistivity to explain increased resistivity due to early transition-metal growth inhibitors in the shell surrounding the nanocrystalline phase; and (e) disorder effects on amorphous phase resistivity. Experimental design and results for systems of interest in high-frequency power transformation are discussed in the context of our model including: (a) techniques for measurements of cross-section and density, (b) four-point probe and surface resistivity measurements, and (c) measurements in Fe- and Co-rich systems comparing amorphous and nanocomposite materials.

Nanocrystalline powders of (Fe70Ni30)100−xMox (x = 1 to 4) were produced by high-energy (SPEX) mechanical alloying. Increasing the Mo content was found to stabilize the face-centered cubic phase in mechanically alloyed nanopowders. To obtain a single γ-phase, a powdered sample was solution annealed in the γ-phase field and water quenched. The Curie temperature, TC, of the alloys was lowered with Mo addition, without decreasing the refrigeration capacity (RC), due to the additional temperature broadening of the magnetic entropy change. Based on previous study on the role of disorder, the additional temperature broadening was attributed to increased positional disorder and changes in the distribution of ferromagnetic exchange bonds introduced by Mo addition into the γ-FeNi system. (Fe70Ni30)97Mo3 and (Fe70Ni30)96Mo4 alloys have RCFWHM values of ∼440 J/kg and ∼432 J/kg at 5 T, comparable to other prominent magnetic refrigerants operating near room temperature. The economic viability of these alloys, along with their competitive magnetocaloric properties and potential for scalable production, make them good candidate magnetic refrigerants without critical rare-earth materials.