Samuel J. Kernion

High Induction, Low Loss FeCo-Based Nanocomposite Alloys With Reduced Metalloid Content

We present a comparative study of reductions in metalloid and early transition metal content aimed at increasing inductions in FeCo-based nanocomposite alloys. Metalloid B and early transition metal Nb glass formers were replaced with magnetic late transition metals to determine the limits of amorphous and nanocrystalline formation and increase the magnetic flux density. Alloys of composition (Fe65Co35)80+x+yB13-xNb4-ySi2Cu1 (x=0-3, y=0,3) were cast by melt-spinning 50g batches into 2.5 mm wide, 30 μm thick ribbons. Ribbons were nanocrystallized and screened for their magnetic flux densities. The highest magnetic flux density of 1.85 T for quality ribbon was realized for the alloy with x=1, y=3. Magnetization as a function of temperature is reported for amorphous alloys to illustrate the effects of metalloid and early transition metal content on high temperature stability of magnetic properties and crystallization temperatures. Notable alloys were also synthesized by planar flow casting into 2.54 cm wide, 20 μ m ribbons and annealed under a 2.0 T transverse magnetic field. AC magnetic property measurements include permeability, coercive field, and core loss. The x=3, y=0 alloy demonstrated low core loss of 5.1 W/kg under a 0.2 T field and 20 kHz frequency with a high flux density of 1.70 T.

Increased induction in FeCo-based nanocomposite materials with reduced early transition metal growth inhibitors

We report on new high-saturation induction, high-temperature nanocomposite alloys with reduced glass formers. The amounts of the magnetic transition metals and early transition metal growth inhibitors were systematically varied to determine trade-offs between higher inductions and fine microstructures with consequently lower magnetic losses. Alloys of nominal composition (Fe65Co35)79.5+xNb4−xB13Si2Cu1.5 (x=0–4) were cast into a 28 mm wide, 20 μm thick ribbon from which toroidal cores were wound. Inductions and magnetic losses were measured after nanocrystallization and stress relief. We report technical magnetic properties: permeability, maximum induction, remanence ratio, coercive field, and high frequency magnetic losses as a function of composition and annealing temperature for these alloys. Of note is the development of maximum inductions in excess of 1.76 T in cores made of alloys with the x=4 composition and maximum inductions in excess of 1.67 T in alloys with the x=3 composition, which also exhibi...

Two-current model of the composition dependence of resistivity in amorphous (Fe100−xCox)89−yZr7B4Cuy alloys using a rigid-band assumption

Composition dependence of resistivity is studied in amorphous (Fe100−xCox)89−yZr7B4Cuy (0 ≤ x ≤ 50, y = 0, 1) alloys. The two-current model proposed by Mott for crystalline materials is extended to a disordered amorphous system where s-d scattering is dominant in electron conduction. A rigid-band assumption is made due to the small atomic number difference between Fe and Co. Band structures with a constant density of states (DOS), parabolic distributed DOS, and Gaussian distributed DOS were investigated to fit experimental data. The Gaussian distributed DOS was found to simulate the resistivity maximum and magnetic moment maximum in the Fe-rich region. The basic concepts presented here can potentially provide insight into the optimization of FeCo-based HITPERM alloys for applications at increased frequencies.

Crystallization behavior and high temperature magnetic phase transitions of Nb-substituted FeCoSiBCu nanocomposites

The effect of Nb substitution on the nanocrystallization process and high temperature magnetic properties of FeCoSiBCu nanocomposites is reported. Magnetization changes accompany the primary crystallization of α-Fe(Co) nanocrystals and the secondary crystallization of (FeCo)23B6 and (FeCo)2B phases. With increasing the Nb fraction in the alloys, the diffusion barrier to growth of α-Fe(Co) nanocrystals increases, resulting in an increase of thermal stability and a delay of Fe(Co) dissolution required for (FeCo)23B6 phase formation. The transmission electron microscopy images reveal finer grains with increasing Nb content.

Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)81+xB12Nb4−xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x = 0, 1, 1.5, 2, and 3, we report field induced anisotropy, KU, after annealing at temperatures of 340–450 °C for 1 h in a 2 T transverse magnetic field. The anisotropy field, HK, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructure related anisotropy mechanism in which the amorphous phase exhibits a higher HK than the crystalline phase. A high saturation induction nanocrystalline phase and high HK amorphous phase were achieved by low temperature annealing resulting in a value of KU exceeding 14 × 103 erg/cm3, more than twice that reported previously for Fe-rich amorphous and nanocomp...

Effect of P addition on nanocrystallization and high temperature magnetic properties of low B and Nb containing FeCo nanocomposites

The P content dependencies of the nanocrystallization behaviors and high temperature magnetic properties of the Fe54.6Co29.4Si2.8(B0.8−YPY)14Nb1Cu1 (Y = 0, 0.2, and 0.3) alloys have been investigated. Alloys were prepared by melt spinning and subsequently annealed in an argon atmosphere to induce nanocrystallization. P addition increases primary crystallization temperature (Tx1), thermal stability (ΔTx), and activation energy (QJMA) for secondary crystallization in as-cast alloys. The saturation induction (Bs) of 1.68 T for as-cast P free alloy decreases continuously with the addition of P. However, the soft magnetic properties are enhanced for P added alloys. The XRD pattern reveals that grain refinement increases with increasing P contents. Alloys annealed at 430 °C confirm primary nanocrystallization of α-FeCo in the amorphous matrix, while annealing at 550 °C causes secondary crystallization of other non-magnetic phases as well. The magnetic moment of as-cast and annealed alloys, measured by vibrating...

Secondary crystallization in (Fe65Co35)79.5+xB13Nb4−xSi2Cu1.5 and (Fe65Co35)83B10Nb4Si2Cu1 nanocomposite alloys

Here, secondary crystallization kinetics of high induction, low loss HTX002-type nanocompositealloys with the compositions (Fe65Co35)79.5+xB13Nb4−xSi2Cu1.5 (x = 0-4) and (Fe65Co35)83B10Nb4Si2Cu1 are reported. The magnetization of the alloys was measured through the thermal cycle of 50 °C-700 °C-300 °C-800 °C-300 °C-900 °C-200 °C by vibrating sample magnetometry. In (Fe65Co35)79.5+xB13Nb4−xSi2Cu1.5alloys, the stability of the (Fe,Co,Nb)23B6 (23-6) phase is increased with increasing Nb content. In the x = 4 alloy, (Fe,Nb)2B is the only secondary crystalline phase to form, demonstrating that Nb is necessary for the 23-6 phase to form. The (Fe65Co35)83B10Nb4Si2Cu1alloy forms the 23-6 phase more readily than the x = 0 alloy, likely due to the lower B content. The kinetics of secondary crystallization are important to assess long-term ageing effects on the metastable microstructure at elevated temperatures.

The Influence of Pressure on the Phase Stability of Nanocomposite Fe89Zr7B4 during Heating from Energy Dispersive X-ray Diffraction

Nanocomposite materials consisting of small crystalline grains embedded within an amorphous matrix show promise for many soft magnetic applications. The influence of pressure is investigated by in situ diffraction of hammer milled Fe89Zr7B4 during heating through the α → γ Fe transition at 0.5, 2.2, and 4.9 GPa. The changes in primary and secondary crystallization onset are described by diffusion and the energy to form a critical nucleus within the framework of classical nucleation theory.

Reduced losses in rolled Fe73.5Si15.5Nb3B7Cu1 nanocrystalline ribbon

Eddy currents in magnetic components undergoing high frequency switching can be mitigated by reducing the thickness of the component. Planar flow cast Fe73.5Si15.5Nb3B7Cu1 ribbon was plastically deformed by cold rolling, resulting in a thickness reduction of 38%. Shear band formation was seen and the coercivity was dramatically higher in the rolled ribbon. After crystallization, the hysteresis loop of the rolled ribbon was nearly identical to a non-rolled ribbon and losses were lower in the rolled ribbon above 25 kHz. Reductions in thickness by this method can lead to increases in operating frequency for power conversion applications.

In-situ investigation of phase formation in nanocrystalline (Co97.5Fe2.5)89Zr7B4 alloy by high temperature x-ray diffraction

Crystallization and phase evolution in an (Co97.5Fe2.5)89Zr7B4 amorphous alloy was studied by high temperature x-ray diffraction (HTXRD) and transmission electron microscopy (TEM). Co-based nanocomposite alloys have zero magnetostriction and a strong response to magnetic field annealing making them interesting for sensor and high frequency power applications. Amorphous alloys, synthesized by single roll melt-spinning, develop a nanocomposite structure after primary crystallization. After annealing at 540 °C for 1 h, TEM images and diffraction patterns confirm a grain size of 19 nm and the presence of at least two phases. HTXRD results show preferential body centered cubic (bcc) nucleation and formation of multiple phases at various stages of crystallization. Only the face centered cubic (fcc) phase remained at temperatures above 600 °C. On heating, the lattice parameter of the fcc phase increases at a rate higher than expected from thermal expansion. This is partially explained by an increase in the Fe-co...