Nanocomposite soft magnetic alloys with high temperature stability

Abstract

The inventive concept includes compositions and methods of manufacturing cobalt (Co)-based nanocomposite ribbons, as well as iron-cobalt (Fe-Co)-, iron-nickel (Fe-Ni)-, iron-cobalt-nickel (Fe-Co-Ni)-, and cobalt-nickel (Co-Ni)-based nanocomposite ribbons, which are all magnetically tunable and stable at high temperatures. The inventive soft magnetic materials operate at high temperatures due to their temperature stability for extended operation at frequencies greater than 1kHz. Exemplary preferred embodiments of the cobalt-based nanocomposites include 50 atomic % or less of a metal selected from iron and nickel, 20 atomic % or less of a metalloid selected from boron, silicon, phosphorous and carbon, 5 atomic % or greater of one or more metals selected from tantalum, niobium, vanadium, aluminum, and molybdenum, 5 atomic % or less of the total of manganese, zirconium, and hafnium, and a remainder of cobalt.

Description

NANOCOMPOSITE SOFT MAGNETIC ALLOYS WITH HIGH TEMPERATURE STABILITYSTATEMENT OF GOVERNMENT INTEREST

[0001] This invention was made with government support under grant 80NSSC 22K0415 awarded by NASA. The government has certain rights in the invention.CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This non-provisional patent application claims a benefit of priority based on the provisional patent application having U.S. Application Serial No. 63 / 560,306, entitled “NANOCOMPOSITE SOFT MAGNETIC ALLOYS WITH HIGH TEMPERATURE STABILITY”, filed in the United States Patent and Trademark Office on March 1, 2024; the contents of which are herein incorporated by reference in their entirety.1. Field of the Invention

[0003] The inventive concept relates to compositions and methods of manufacturing cobalt (Co)- based nanocomposite ribbons, as well as iron-cobalt (Fe-Co)-, iron-nickel (Fe-Ni)-, iron-cobalt- nickel (Fe-Co-Ni)-, and cobalt-nickel (Co-Ni)-based nanocomposite ribbons, which are all magnetically tunable. Preferred embodiments show excellent stability for high temperatures of at least 300 °C, more preferably for high temperatures of at least 400 °C, and most preferred for high temperatures of at least 450-550 °C. The inventive soft magnetic materials operate at high temperatures for extended operation times due to their temperature stability, and are of particular relevance for extended operation at frequencies greater than approximately 1kHz.2. Background

[0004] Nanocomposite soft magnetic materials are critical in passive electronic components such as inductors, and transformers used in the conditioning and conversion of electrical power due to their tunable magnetic permeability and low core losses at high frequencies. The inventive concept pertains to compositions and methods of manufacturing Fe-Co-based, Fe-Ni-based, Fe- Co-Ni-based, Co-Ni-based and Co-based, nanocomposite ribbons that are magnetically tunable and stable at high temperatures. There are no current soft magnetic materials that can operate forextended operation times at frequencies > 1kHz at high temperatures approaching 400 °C and greater with low losses due to limited temperature stability for extended operation.

[0005] There is a need in the art for the inventive concept which includes new alloy nanocomposites that exhibit an increased temperature stability compared to the prior art. The maximum continuous service temperature for amorphous and nanocomposite materials is typically on the order of 150 to 200 °C in Fe-based alloys. By altering the chemical composition of these new alloys, primary and secondary crystallization temperatures are increased while achieving high Curie temperatures of the crystalline and amorphous phases, allowing for higher temperature stability without significant degradation of magnetic properties, for application at high temperatures and extended operation, particularly, at frequencies greater than 1kHz.SUMMARY OF THE INVENTION

[0006] In one aspect, the inventive concept provides an alloy nanocomposite including an alloy selected from a Co-based alloy comprising cobalt, a Fe-Co-Ni-based alloy comprising iron, cobalt and nickel, a Fe-Ni-based alloy comprising iron and nickel, a Fe-Co-based alloy comprising iron and cobalt, and a Co-Ni-based alloy comprising cobalt and nickel, the alloy further comprising one or more metal selected from niobium and tantalum; and optionally, one or more metalloid selected from boron, silicon, phosphorous, and carbon; wherein the alloy has an amorphous phase Curie temperature of about 350 to about 800 °C or greater, saturation magnetization of about 0.5 T or greater, and a primary crystallization temperature from about 400 °C to about 600 °C or greater, and secondary crystallization temperature from about 500 °C to about 800 °C or greater.

[0007] In certain embodiments, the alloy comprises 50 atomic % or less of a metal selected from iron and nickel; 20 atomic % or less of a metalloid selected from boron, silicon, phosphorous and carbon; 5 atomic % or greater of one or more metals selected from tantalum, niobium, vanadium, aluminum, and molybdenum; 5 atomic % or less of the total of manganese, zirconium, and hafnium; a remainder atomic % of cobalt.

[0008] In certain embodiments, the alloy comprises from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % ofeach of one or more of tantalum and niobium; from 0 to 5 atomic % or 0 to 2 atomic % of manganese; and a remainder of cobalt.

[0009] In certain embodiments, the alloy is selected from Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Ta>4.0-10.0, or Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Nb>4.0-10.0, or Fe2.5Co75.5B8Si6Mn2Ta6, or Fe2.5Co75.5B8Si4Mn2Nb8.

[0010] In certain embodiments, the alloy further comprises one or more of copper and silver at up to 2 atomic % of each.

[0011] In certain embodiments, the amorphous Curie temperature is selected from about 350 to about 450 °C or about 450 to about 550 °C or about 550 to about 650 °C or about 650 to about 700 °C or about 700 to about 750 °C, and a secondary crystallization temperature of about 650 °C or greater.

[0012] In certain embodiments, the nanocomposite has primary and secondary crystallization temperatures that allow for higher temperature stability without significant degradation of magnetic properties for application at temperatures of about 400 °C to 500°C or greater, or about 450 °C to 550°C or greater, or about 500 °C to 600°C or greater.

[0013] In certain embodiments, the nanocomposite has a form of a ribbon or strip.

[0014] In certain embodiments, the one or more of silicon, chromium and aluminum are present in the alloy and provide properties of oxidation and corrosion resistance. In certain embodiments, manganese is absent from the alloy.

[0015] In certain embodiments, wherein a ribbon produced from the alloy annealed to its final use state is bendable with a zero curvature radius through 180 degrees without fracture.

[0016] In another aspect, the inventive concept provides a cobalt-based alloy nanocomposite, including from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % of each of one or more of tantalum and niobium (Nb); from 0 to 5 atomic % or 0 to 2 atomic % of manganese; and a remainder of cobalt.

[0017] In certain embodiments, the alloy is selected from Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Ta>4.0-10.0, or Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Nb>4.0-10.0, or Fe25Co75 5B8Si6Mn2Ta6, or Fe2.5Co75.5BsSi4Mn2Nb8.

[0018] In yet another aspect, the inventive concept provides a method of preparing a cobalt- based alloy nanocomposite. The method includes preparing an alloy composition, comprising analloy selected from a Co-based alloy comprising cobalt, a Fe-Co-Ni-based alloy comprising iron, cobalt and nickel, a Fc-Ni-bascd alloy comprising iron and nickel, a Fc-Co-bascd alloy comprising iron and cobalt, and a Co-Ni-based alloy comprising cobalt and nickel, the alloy further comprising one or more metal selected from niobium and tantalum; and optionally, one or more metalloids selected from boron, silicon, phosphorous, and carbon; forming an amorphous structure of the alloy composition; and annealing to form the nanocomposite structure, wherein the alloy has an amorphous phase Curie temperature of about 350 to about 800 °C or greater, saturation magnetization of about 0.5 T or greater, and a primary crystallization temperature from about 400 °C to about 600 °C or greater, and secondary crystallization temperature from about 500 °C to about 800 °C or greater.

[0019] In certain embodiments of the method, the alloy comprises 50 atomic % or less of a metal selected from iron and nickel; 20 atomic % or less of a metalloid selected from boron, silicon, phosphorous and carbon; atomic % or greater of one or more metals selected from tantalum, niobium, vanadium, aluminum, and molybdenum; 5 atomic % or less of the total of manganese, zirconium, and hafnium; a remainder atomic % of cobalt.

[0020] In certain embodiments of the method, the alloy comprises from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % of each of one or more of tantalum and niobium; from 0 to 5 atomic % or 0 to 2 atomic % of manganese; and a remainder of cobalt.

[0021] In certain embodiments of the method, the alloy composition is selected from an alloy selected from Fe2.0-3.oCo70.0-80.oB5.0-10.0Si2.0-8.oMno-5.oTa>4.0-10.0, or Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0- 8.oMno-5.oNb>4.0-10.0, or Fe2.5Co75.5BsSi6Mn2Ta6, or Fe2.5Co75.5BgSi4Mn2Nb8.

[0022] In certain embodiments, the method further comprises the step of planar-flow casting to produce a plurality of amorphous strips or ribbons.

[0023] In certain embodiments, the method further comprises annealing to form a nanocomposite structure comprised of a primary crystalline phase and a remaining amorphous precursor. The annealing may be selected from stress annealing and field annealing. The stress annealing can comprise transverse spool-to- spool annealing for 2 seconds or greater through the hot zone at stresses from 50-400 MPa., and wherein the field annealing can comprise annealingunder saturating magnetic field for up to 1 hour at a temperature from 400 to 550 °C. The stress annealing temperature can be from about 450 to about 700 °C.

[0024] In certain embodiments of the method, improved oxidation resistance is shown following operation in air at time for 7 to 20 days

[0025] In certain embodiments of the method, the as-cast nanocomposite is magnetically tunable and stable at high temperatures for extended operation at frequencies greater than 1kHz.

[0026] In still another aspect, the inventive concept provides a method of preparing a cobaltbased alloy nanocomposite including preparing an alloy composition, comprising from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % of each of one or more of tantalum and niobium; from 0 to 5 atomic % or 0 to 2 atomic % of manganese; and a remainder of cobalt; forming an amorphous structure of the alloy composition; and annealing to form the nanocomposite structure.

[0027] In certain embodiments of the method, the alloy composition is selected from Fe2.0- 3.oCo70.0-80.oB5.0-10.0Si2.0-8.oMno-5.oTa>4.0-10.0, or Fe2.0-3.oCo70.0-80.oB5.0-10.0Si2.0-8.oMno-5.oNb>4.0-10.0, or Fe2.5Co75.5BsSi6Mu2Ta6, or Fe2.5Co75.5BsSi4Mn2Nb8.BRIEF DESCRIPTION OF THE FIGURES

[0028] FIG. 1 shows a plot of heat flow versus temperature, in accordance with certain embodiments of the inventive concept.

[0029] FIGS. 2 through 6 show plots of onset crystallization temperature difference corresponding to various alloys, in accordance with certain embodiments of the inventive concept.

[0030] FIG. 7 shows a plot of intensity versus 2 theta for a reference composition and compositions #1 thru #10 of the inventive concept.

[0031] FIG. 8 shows a plot of intensity versus 2 theta for composition #18 of the inventive concept.

[0032] FIG. 9 shows a plot of intensity versus 2 theta for a reference composition and compositions #2, #9, #12 and #16 of the inventive concept.

[0033] FIG. 10 shows a plot of M / Ms versus temperature for reference compositions and composition #67 of the inventive concept.

[0034] FIG. 11 shows a plot of amorphous Curie temperature corresponding to various alloys, in accordance with certain embodiments of the inventive concept.

[0035] FIG. 12 shows a plot of Ms corresponding to various alloys, in accordance with certain embodiments of the inventive concept.

[0036] FIG. 13 shows a plot relating to dwell time for a reference alloy and alloy #18 according to certain embodiments of the inventive concept.

[0037] FIG. 14 shows a plot of weight gain for a reference composition and compositions #8, #10, #15, #19 and #26 according to the inventive concept.

[0038] FIG. 15 are images that illustrate the surface and cross section of magnetic ribbons for a reference sample and samples #16 and #18, in accordance with certain embodiments of the inventive concept.

[0039] FIGS. 16 and 17 show plots of intensity versus 2 theta for a reference composition and compositions #16 and #18 of the inventive concept.

[0040] FIG. 18 shows images of large and small grains and related plots for a reference composition and composition 16 of the inventive concept.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] The inventive concept relates to compositions and methods of manufacturing Co-based nanocomposite ribbons, as well as iron-cobalt (Fe-Co)-, iron-nickel (Fe-Ni)-, iron-cobalt-nickel (Fe-Co-Ni)-, and cobalt-nickel (Co-Ni)-based nanocomposite ribbons, that are magnetically tunable and stable at high temperatures. Preferred embodiments show excellent stability for high temperatures of at least about 300 °C, or about 400 °C or greater, or from about 200 °C to 400 °C, or from about 200 °C to 500 °C, or from about 300 °C to 400 °C, or from about 300 °C to 500 °C or greater. The inventive soft magnetic materials operate at high temperatures greater than 350°C due to their temperature stability where the preferred microstructure of small homogenous primary crystallite grains are present, and arc of particular relevance for extended operation at frequencies greater than approximately 1kHz. Preferred embodiments show coercivity (He) < 200 A / m, or even more preferred <100A / m, for saturating B-H curves measured at 1kHz at ambient temperature. Additional preferred embodiments show coercivity (He) < 200A / m, or even more preferred <100 A / m, for saturating B-H curves measured at 1kHz at the elevated operating temperature. Exemplary preferred embodiments also have a response to atransverse field anneal or a stress anneal which results in a shear magnetization loop. Exemplary preferred embodiments have a hard-axis permeability after transverse field annealing or stress annealing which changes by <10% at 500 °C for operation times of 24 hours without a longitudinal excitation.

[0042] In certain embodiments, soft magnetic materials are made through planar-flow casting to create thin metallic strips with an amorphous structure. The thickness of these ribbons is from about 10 to about 35pm. Further, in certain embodiments, subsequent annealing processes may be carried out which cause nanocrystalline development with grains smaller than about 100 nm, embedded within an amorphous matrix. These amorphous magnetic alloys typically have a base of Fe, Co, or Ni and contain metalloids such as phosphorus (P), carbon (C), boron (B), and silicon (Si) to promote the formation of the amorphous matrix on casting. Additional early transition metals may be added to promote small nanocrystalline grain formation upon annealing. Previous or known materials were limited to alloys functioning at lower frequencies, and I or with lower Curie temperatures of the continuous phase (e.g. the amorphous phase of nanocomposites), and / or with lower primary and secondary crystallization temperatures, with the majority of alloys being Fe-based.

[0043] The compositions of the inventive high-temperature alloys described in this disclosure follow a combination (TE-M-TE) of late transition metals (TL), metalloids (M), and early transition metals (TE) and, in certain embodiments, are produced by planar- flow casting. Further, in certain Co-based embodiments, these nanocomposites include 50 atomic % or less of each of iron (Fe) and / or nickel (Ni), 20 atomic % or less of each of one or more of boron (B), silicon (Si), phosphorous (P), and carbon (C), at least 5 atomic % or more of each of one or more of tantalum (Ta), niobium (Nb), vanadium (V), and molybdenum (Mo), 5 atomic % or less of each of manganese (Mn), zirconium (Zr), and hafnium (Hf), the remaining atomic % is cobalt (Co). In certain embodiments, additional noble metals such as copper (Cu) or silver (Ag) up to 2 atomic % of each are added to promote finer grain structures. In certain embodiments, the nanocomposites include a total of more than 1 atomic % of passivating elements such as silicon (Si), aluminum (Al), and chromium (Cr) to promote oxidation resistance. In other certain embodiments, the nanocomposites include more than 5 atomic % of passivating chromium (Cr) as in a stainless steel alloy for oxidation and corrosion resistance amongst other properties.

[0044] Further, in certain Co-rich embodiments, these nanocomposites include from 2 to 25 atomic % or from 2 to 10 atomic % of iron (Fc), from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron (B) and silicon (Si), from greater than 4 to 10 atomic % or from greater than 4 to 10 atomic % of each of one or more of tantalum (Ta) and niobium (Nb), from 0 to 5 atomic % or 0 to 2 atomic % of manganese (Mn), and the remaining is cobalt (Co). In certain embodiments, the Co-rich embodiments include an absence of manganese.

[0045] Furthermore, in certain Co-rich embodiments, these nanocomposites include the following atomic percent nanocomposites: Fe2.0-3.oCo70.0-80.oB5.0-10.0Si2.0-8.oMno-5.oTa>4.0-10.0, or Fe2 o-3 oCo7o o-8o oB5 o-io oSi2 o-8 oMno-5 oNb>4o-ioo, or Fe25Co755BsSi6Mn2Ta6, or Fe2.5Co75.5BsSi4Mn2Nb8.

[0046] Without being bound by any particular theory, it is believed that the high Co content increases the Curie temperature of the amorphous phase, increasing the temperature stability. In certain preferred embodiments, the amorphous phase of the nanocomposite alloy has a primary crystallization temperature (Txl) above about 450°C and a secondary crystallization temperature (Tx2) above about 650°C, setting this group of alloys apart from previous or known inventions. There is usually a tradeoff between temperature stability and magnetic properties, but the alloys in this compositional range maintain high saturation polarization greater than about 0.5T, and an amorphous Curie temperature of about 400°C or higher. In certain embodiments, excellent stability is shown for Curie temperatures from about 300 °C to about 500 °C or from about 500 °C to about 800 °C.

[0047] In certain embodiments, permeabilities of less than 3000 can be achieved through field annealing and permeabilities of less than 300 can be achieved through strain annealing with applied stress of less than lOOMPa. In other certain embodiments, permeabilities of less than 500 can be achieved by field annealing and permeabilities of less than 100 can be achieved through strain annealing with applied stress of less than lOOMPa. In yet more certain embodiments, permeabilities of less than 300 can be achieved by field annealing and permeabilities of less than 50 can be achieved through strain annealing with applied stress of less than lOOMPa.

[0048] Further, in certain Fe-Co-or Fe-Ni- embodiments, these nanocomposites include 75 atomic % or less of cobalt (Co), 75 atomic % or less of nickel (Ni), a total of 20 atomic % or less of one or more of boron (B), silicon (Si), phosphorous (P), and carbon (C), a total of at least 5atomic % or more of one or more of tantalum (Ta), niobium (Nb), vanadium (V), and molybdenum (Mo), a total of 5 atomic % or less of manganese (Mn), zirconium (Zr), and hafnium (Hf), the remaining atomic % is iron (Fe). In certain embodiments, additional noble metals such as copper (Cu) or silver (Ag) up to 2 atomic % of each are added to promote finer grain structures. In certain embodiments, the nanocomposites include a total of more than 1 atomic % of passivating elements such as silicon (Si), aluminum (Al), and chromium (Cr) to promote oxidation resistance. In other certain embodiments, the nanocomposites include more than 5 atomic % of passivating chromium (Cr) as in a stainless steel alloy for oxidation and corrosion resistance amongst other properties.

[0049] High crystallization temperatures allow for increased temperature stability in extreme environments or high temperature operations. The ideal annealing temperature to develop small ferromagnetic nanocrystallites is above the primary crystallization temperature but below the secondary crystallization temperature. The secondary crystallization temperature allows for nonmagnetic intermetallic phases to precipitate causing a rapid deterioration in magnetic properties and therefore, should be as high as possible to broaden the processing window (the temperature range between the primary and secondary crystallization temperatures). For the purpose of clarity, the primary and secondary crystallization temperatures specified are found through differential scanning calorimetry at a constant heating rate of 20°C per min.

[0050] The ribbons can be annealed as single strips in a furnace at temperatures higher than primary crystallization temperature and lower than secondary, to develop ferromagnetic crystals from the amorphous matrix. The ribbon to be annealed may begin pre- wound into the final core geometry, or may be annealed locally in strip form as part of a continuous, reel-to-reel based process. Both field annealing and strain annealing (alternatively called stress annealing) are techniques which modify the preferred directions of magnetization in the alloy and thus alter the shape of the hysteresis loop. The first consists of application of a saturating magnetic field during annealing, usually during the same anneal which develops the crystalline phase, although field annealing can also be performed at temperatures below primary crystallization. The preferred direction of magnetization can be controlled by the direction of the applied field. Stress annealing is performed by application of a tensile stress (typically >~ 50 MPa, but should not be considered limiting) along the ribbon axis during annealing, usually during the same anneal which develops the crystalline phase, although stress annealing can also be performed attemperatures below primary crystallization. The preferred direction of magnetization is largely composition-dependent in stress annealing.EXAMPLES

[0051] Alloys were prepared by melting a metal ingot of the desired alloy composition to then be used in a melt spinner to produce ribbons ~20pm thick and 1cm wide. Samples 1-90 as shown in Table 1 were prepared and tested as follows. Conventional annealing was performed by wrapping single strips of ribbon in Al foil and annealing at set temperatures and times. Oxidation studies were performed by annealing small ribbon strips in air for set times and temperatures. Transverse field annealing was performed by wrapping a ribbon segment approximately 2 m in length into a toroidal core geometry, before placing in a custom permanent magnet-based yoke which supplies a saturating magnetic field along the transverse axis. The yokes were then placed inside a furnace and annealed at set temperature and time. Stress / strain annealing was performed by clamping one end of a ribbon segment to a fixture and suspending a load from the other end to supply a given stress calculated from the ribbon dimensions. The ribbon was then pressed between two metal strips preheated to a given temperature and held for a specified time. The ribbon was then removed from the preheated strips prior to the load being removed. Stability of the permeability / induced anisotropy was performed in two ways. In a simple, high-volume test, the permeability and saturation inductions of strips of previously transverse field annealed or stress annealed ribbon 10-20 cm in length were measured. The strips were then placed on an aluminum foil tray and reannealed in a furnace at a specified time and temperature. The strips were removed and then their permeability and saturation induction were measured again. A more advanced test involved taking a previously transverse field annealed or stress annealed ribbon segment > 3 m in length and wrapping into a toroidal core geometry. This core was placed in a ceramic core box and wound with high temperature magnet wire. The core was placed in a furnace, with wires as well as a thermocouple (placed such that the thermocouple tip sits in the center of the core box) entering the furnace through a chimney. The furnace was heated up to a specified dwell temperature, held for a specified dwell time, and then allowed to cool through natural convection. Throughout the heat, dwell, and cool cycles, a current excitation of specified amplitude, frequency, and waveform (for example, but not limited to: sinusoidal with no de bias, square, sinusoidal with de bias) was supplied to the primary winding via a waveform generatorand amplifier. A power analyzer was used to record primary winding current and secondary winding induced voltage. These were used to calculate a magnetization loop for a given timestep, from which the longitudinal (typically a hard-axis) permeability was measured. Other measured / calculated quantities captured included but are not limited to: measured maximum magnetic field and induction, root-mean- square voltage and / or current, phase between current and voltage, coercivity of the magnetization loop, and measured core losses. The excitation was supplied continuously, however, waveforms were only collected for analysis once every timestep, which is typically 15-120 s based on length of test and desired density of data.

[0052] As illustrated in the plot in FIG. 1, the reference material identified in Table 1 (i.e., “Ref’), from previously developed (known) alloy systems, shows peaks at lower temperatures while alloy #18 (according to Table 1 of the inventive concept) has much higher primary and secondary crystallization temperatures.

[0053] The list of primary crystallization temperatures, secondary crystallization temperatures and crystallization onset difference of the primary and secondary temperatures along with peak temperatures, are summarized in Table 1 and plots illustrated in FIGS. 2, 3, 4, 5 and 6 of Cobased alloys where each segment of the plot and shape relating to a different element being investigated, with the pentagon referring to the reference, upside-down triangle to Si and B alterations, diamond to Zr alterations, circle to Ta alterations, triangle to Nb alterations, square to late ferromagnetic element alterations, right triangle Mn alterations, and star to Cr an Al alterations. Not only are the crystallization temperatures high but also the difference between the primary and secondary crystallization temperatures is large, providing for a larger processing range to allow development of ideal nanocrystals within the amorphous matrix.

[0054] Another example of the difference between the reference alloy (i.e. , “Ref” in Table 1) and an (inventive) alloy with high crystallization temperatures is illustrated through x-ray diffraction. Select alloys (#1 through #10 of Table 1) were annealed at 500°C for one hour and compared, showing all were stable showing some primary crystallization in FIG. 7. FIG. 8 shows x-ray diffraction patterns of both alloy #18 and the reference alloy (i.e., “Ref’ in Table 1) annealed at 550 °C for 1 hour, and the diffraction peaks show that alloy #18 has a strong peak attributed to remaining amorphous matrix and primary crystallization development. Due to the high stacking fault nature of these materials and the non-crystalline matrix, it can be difficult to characterize primary crystallization. The reference alloy, however, showed secondary crystallization due to the many sharp peaks corresponding to C023M6 and C021TE2M6 phases. FIG. 9 shows a direct relationship between chemical composition change and the microstructural stability of a select number of alloys annealed at 550 °C for 1 hour. These results show that there is an increased temperature stability for the alloys of the inventive concept compared to the prior art. By altering the chemical composition of these alloys, in accordance with the inventive concept, primary and particularly secondary crystallization temperatures are increased in temperature allowing for higher temperature stability without significant degradation of magnetic properties for application at high temperatures.

[0055] To ensure magnetic stability at high temperatures, select alloys were tested using high temperature vibrating sample magnetometry (VSM). FIG. 10 illustrates a comparison of magnetization versus temperature results of the reference alloy (i.e., “Ref’ in Table 1), alloy #32 (reproduced from a known alloy having composition Fes.aCoeeBe.sSiieM^.eCuo.e), and alloy #18under this inventive compositional range. Using this data, a Brillouin curve was fit using nonlinear regression to extrapolate the first heating curves down to zero to predict the Curie temperature of the amorphous phase and these values are reflected in Table 1. Results from various tests can be seen in Table 1, FIG. 11, and FIG.12, where both amorphous Curie temperature and saturation magnetization of the amorphous phase are represented. Alloys below the 400°C threshold include alloy #32, and alloys #26 and #27 due to the increased Cr content for corrosion resistance. This data further demonstrates that the inventive compositional space is uniquely stable for high temperature applications.

[0056] The ability to tune the magnetic properties of these inventive high-temperature alloys through secondary processing also has been demonstrated, such as, but not limited to stress or field annealing. Stress annealing response was determined by annealing strips of the as-cast ribbon for 1 minute under an applied load of 100 MPa at 510 °C, or for 1 minute under an applied load of 300 MPa at 500 °C, or for 1 minute under an applied load of 500 MPa at 500 °C. These temperatures were chosen to be well above Txl but below Tx2. The annealed strips were then characterized by single strip magnetic testing to measure the average hard axis (longitudinal) permeability under sinusoidal excitation at a frequency of 1kHz (measured at a field amplitude of H = 1 kA / m), as listed for selected compositions (see Table 2). Compositions that do not appear in this table either exhibited a non-shear loop after stress annealing, were too mechanically brittle to stress anneal, or were not stress annealed. A large number of alloys had permeabilities lower than the reference alloy (prior publication after stress annealing at 100 MPa at 510 °C for 1 min, and fifteen (15) alloys had permeabilities less than 50 after stress annealing at 100 MPa at 510 °C for 1 min. as tabulated in reference to Table 1, eighteen (18) alloys had anisotropy energies higher than #32 and thirty-two (32) alloys had anisotropy energies higher than the reference alloy when stress annealed at 100 MPa at 510 °C for 1 min. A preferred embodiment for the alloys stress annealed at 100 MPa at 510 °C for 1 min is #16 which demonstrated an induced anisotropy energy over 3.7x that of the reference and over 2.3 x that of #32. Transverse field annealing response was determined by annealing ribbon strips under a saturating magnetic field across the transverse ribbon axis using custom permanent magnetbased yokes at 500 °C for 1 hour and resulting permeabilities were measured via the same method as above for the stress-annealed alloys. Resulting permeabilities and calculated anisotropy energies are tabulated in Table 2. Compositions which did not show a shear loop haveinduced anisotropies listed as NOT SHEAR. A large number of alloys had permeabilities lower than that of the reference alloy and seven (7) alloys had anisotropy energies higher than that of the reference alloy after transverse field annealing. A preferred embodiment for the transverse field annealed alloys is #39, with an anisotropy energy 1.36x that of the reference alloy. Alloy #16 is also preferred, with anisotropy energy 1.32x that of the reference alloy. The highest responses to transverse field annealing and stress annealing resulted in alloys with Xpe= 2.5 at.% and low Ni content (< 2.5 at.%).

[0057] A unique feature of the inventive alloys is the high stability of the induced anistropy even after extended periods at high temperatures and under a longitudinal magnetic field. In select case, a preferred embodiment (#18) is compared to the reference. Both alloys were subjected to a transverse field anneal at 500 °C for 1 hour to develop the initial anisotropy. Then, each alloy was placed in a ceramic core box and wound with high-temperature magnet wire and placed inside a box furnace. As the furnace is heated, the cores were excited with a 100 mT, 1 kHz, sinusoidal (with zero de bias) excitation supplied by a waveform generator / amplifier. Supplied current on the primary winding and induced voltage on the secondary winding were measured using a power analyzer, allowing for conversion into magnetization loops and thus calculation of permeability and induced anisotropy. The cores were heated to a temperature of 500 °C and then held for a period of 24 hours before being allowed to naturally cool back to room temperature, all under excitation. The changes in permeability during the 24 hr dwell are plotted in FIG.13. After 24 hr, the permeability of the reference alloy increased by -10.7% relative to the value at the beginning of the dwell, while that of alloy #18 increased by only 6.4% relative to the value at the beginning of the dwell. Additionally, it is evident that at the end of the dwell the rate of increase of the permeability in #18 is significantly smaller than that of the reference alloy (Ref from Table 1), indicating larger differences in stability that would manifest under longer dwell times.Finally, a secondary method of measuring permeability / induced anisotropy stability was used to enable estimates for a select larger number of alloys, although not under longitudinal excitation. Previously transverse field annealed alloys had initial permeability measured, then were placed in a box furnace and reannealed at 500 °C for 24 hr, then the permeability was measured again. Results are found in Table 3. Though the reference alloy was not measured for comparison, in all cases the induced anisotropy changed by less than 10%, and in thirteen (13) out of twenty-four (24) alloys the induced anisotropy changed by less than 2%, and in seven (7) out of twenty-four (24) alloys the induced anisotropy changed by less than 1%.

[0058] Another unique feature of the inventive alloys is their oxidation resistance at high temperatures. The reference alloy and alloys 8, 15, 19, 26 and 10 were annealed at 500°C for 7, 14, and 21 days to observe the oxidation behavior through weight gain. The image FIG. 14. highlight the difference in weight gain where the reference alloy had the largest oxide layer formation while alloys 8, 15, 19, 26 and 10 had smaller weight gain due to high levels of Si, Nb, Cr and / or Al. Alloys #16 and #18 (according to the invention) showed superior thermal stability and magnetic properties resulting in further testing, where samples were annealed at 500°C for 7 days to compare microstructure stability to the reference material. Using SEM, the three alloys were imaged and compared, where the reference alloy showed large oxide nodules on the ribbon surface as well as large grains that developed, while 16 and 18 had no visible grains, seen in FIG.15.

[0059] The microstructural stability of select alloys were investigated for longer annealing times. FIG. 16 shows x-ray diffraction plots of the reference alloy, #16 and #18 that were annealed at 500°C for Ihr, Iday, 7days, 21days, where secondary crystallites became most prominent at the 21 day anneals. This showed that these alloys had a stable, preferred microstructure for extended times at high temperatures. These anneals were repeated for the same three alloys and times but at 550°C seen in FIG. 17. When annealing at 55O°C the reference alloy started to show secondary crystallites in the first hour and the peaks became more intense as time went on, showing its immediate instability. Alloys 16 and 18 stalled to show secondary crystallite peaks at the 7days anneals, showing an improvement of stability compared to the reference as they were able to withstand secondary crystallization for longer times. Further detailed microstructural investigation was performed with TEM of the reference alloy and 16 annealed at 500°C for 7 days. The two alloys were imaged and compared where the reference alloy showed abnormal large grain growth and secondary crystallites resulting in its instability while the grains in alloy 16 were primary crystallites which remained small and homogeneous throughout, seen in FIG.18. The small grains in alloy 16 reinforce the feature of high temperature stability in comparison to previous known alloys.

[0060] According to the invention, these exemplary Co-based alloys have shown high primary and secondary crystallization temperatures (Txl > 450 °C, Tx2 > 650 °C) while maintaining stable magnetic properties (Is >0.5T, Tcurie Amorphous > 400 °C) which has not been previously shown. Additionally, some preferred embodiments have shown a strong response to field and / orstrain annealing. In certain preferred embodiments, permeabilities of less than 3000 can be achieved through field annealing and permeabilities of less than 300 can be achieved through strain annealing with applied stress of less than lOOMPa. In other certain preferred embodiments, permeabilities of less than 500 can be achieved by field annealing and permeabilities of less than 100 can be achieved through strain annealing with applied stress of less than lOOMPa. In yet more certain preferred embodiments, permeabilities of less than 300 can be achieved by field annealing and permeabilities of less than 50 can be achieved through strain annealing with applied stress of less than lOOMPa.

[0061] Whereas particular’ embodiments of the invention have been described herein for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details may be made without departing from the invention as set forth in the appended claims.References:[1] Leary, Alex, et al. “Stress induced anisotropy in Co-rich magnetic nanocomposites for inductive applications” Journal of Materials Research, vol. 33 (2016).[2] Polak, Christian, Alloy and method for producing a nanocrystalline metal strip (W02023020945A1) Feb. 2023

Claims

We claim:

1. An alloy nanocomposite, comprising: an alloy selected from a Co-based alloy comprising cobalt, a Fe-Co-Ni-based alloy comprising iron, cobalt and nickel, a Fe-Ni-based alloy comprising iron and nickel, a Fe-Co-based alloy comprising iron and cobalt, and a Co-Ni-based alloy comprising cobalt and nickel, the alloy further comprising: one or more metal selected from niobium and tantalum; and optionally, one or more metalloid selected from boron, silicon, phosphorous, and carbon; wherein the alloy has an amorphous phase Curie temperature of about 350 to about 800 °C or greater, saturation magnetization of about 0.5 T or greater, and a primary crystallization temperature from about 400 °C to about 600 °C or greater, and secondary crystallization temperature from about 500 °C to about 800 °C or greater.

2. The alloy nanocomposite of claim 1, wherein the alloy comprises:50 atomic % or less of a metal selected from iron and nickel;20 atomic % or less of a metalloid selected from boron, silicon, phosphorous and carbon;5 atomic % or greater of one or more metals selected from tantalum, niobium, vanadium, aluminum, and molybdenum;5 atomic % or less of the total of manganese, zirconium, and hafnium; a remainder atomic % of cobalt.

3. The alloy nanocomposite of claim 1, wherein the alloy comprises: from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % of each of one or more of tantalum and niobium; from 0 to 5 atomic % or 0 to 2 atomic % of manganese; anda remainder of cobalt.

4. The alloy nanocomposite of claim 1, wherein the alloy is selected from Fe2.0-3.0C070.0-80.0B5.0- io.oSi2.0-8.oMno-5.oTa>4.0-10.0, or Fe2.0-3.oCo70.0-80.oB5.0-10.0Si2.0-8.oMno-5.oNb>4.0-10.0, or Fe2.5Co75.5BsSi6Mn2Ta6, or Fe2.5Co75.5BsSi4Mn2Nb8.

5. The alloy nanocomposite of claim 2, further comprising one or more of copper and silver at up to 2 atomic % of each.

6. The alloy nanocomposite of claim 1, wherein the amorphous phase Curie temperature is selected from about 350 to about 450 °C or about 450 to about 550 °C or about 550 to about 650 °C or about 650 to about 700 °C or about 700 to about 750 °C, and a secondary crystallization temperature greater of about 650 °C or greater.

7. The alloy nanocomposite of claim 1, wherein said nanocomposite has primary and secondary crystallization temperatures that allow for higher temperature stability without significant degradation of magnetic properties for application at temperatures of about 400 °C to 500°C or greater, or about 450 °C to 550°C or greater, or about 500 °C to 600°C or greater.

8. The alloy nanocomposite of claim 1, wherein said nanocomposite has a form of a ribbon or strip.

9. The alloy nanocomposite of claim 1, wherein one or more of silicon, chromium and aluminum are present in the alloy and provide properties of oxidation and corrosion resistance.

10. The alloy nanocomposite of claim 2, wherein manganese is absent from the alloy.

11. The alloy nanocomposite of claim 2, wherein a ribbon produced from the alloy annealed to its final use state is bendable with a zero curvature radius through 180 degrees without fracture.

12. A cobalt-based alloy nanocomposite, comprising:from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % of each of one or more of tantalum and niobium (Nb); from 0 to 5 atomic % or 0 to 2 atomic % of manganese; and a remainder of cobalt.

13. The cobalt-based alloy nanocomposite of claim 12, comprising an alloy selected from Fe20-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Ta>4.0-10.0, or Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Nb>4.0-10.0, or Fe2.5Co75.5B8Si6Mn2Ta6, or Fe2.5Co75.5B8Si4Mn2Nb8.

14. A method of preparing a cobalt-based alloy nanocomposite, comprising: preparing an alloy composition, comprising: an alloy selected from a Co-based alloy comprising cobalt, a Fe-Co-Ni-based alloy comprising iron, cobalt and nickel, a Fe-Ni-based alloy comprising iron and nickel, a Fe-Co-based alloy comprising iron and cobalt, and a Co-Ni-based alloy comprising cobalt and nickel, the alloy further comprising: one or more metal selected from niobium and tantalum; and optionally, one or more metalloids selected from boron, silicon, phosphorous, and carbon; forming an amorphous structure of the alloy composition; and annealing to form the nanocomposite structure, wherein the alloy has an amorphous phase Curie temperature of about 350 to about 800 °C or greater, saturation magnetization of about 0.5 T or greater, and a primary crystallization temperature from about 400 °C to about 600 °C or greater, and secondary crystallization temperature from about 500 °C to about 800 °C or greater.

15. The method of claim 14, wherein the alloy, comprises:50 atomic % or less of a metal selected from iron and nickel;20 atomic % or less of a metalloid selected from boron, silicon, phosphorous and carbon;5 atomic % or greater of one or more metals selected from tantalum, niobium, vanadium, aluminum, and molybdenum;5 atomic % or less of the total of manganese, zirconium, and hafnium; a remainder atomic % of cobalt.

16. The method of claim 15, wherein the alloy, comprises: from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % of each of one or more of tantalum and niobium; from 0 to 5 atomic % or 0 to 2 atomic % of manganese; and a remainder of cobalt.

17. The method of claim 16, wherein the alloy composition is selected from an alloy selected from Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Ta>4.0-10.0, or Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Nb>4.0-10.0, or Fe2.5Co75.5B8Si6Mu2Ta6, or Fe2.5Co75.5B8SuMn2Nb8.

18. The method of claim 14, further comprising the step of planar- flow casting to produce a plurality of amorphous strips or ribbons.

19. The method of claim 14, further comprising annealing to form a nanocomposite structure comprised of a primary crystalline phase and a remaining amorphous precursor.

20. The method of claim 14, further comprising annealing selected from stress annealing and field annealing.

21. The method of claim 20, wherein the stress annealing comprises transverse spool-to-spool annealing for 2 seconds or greater through the hot zone at stresses from 50-400 MPa., andwherein the field annealing comprises annealing under saturating magnetic field for up to 1 hour at a temperature from 400 to 550 °C.

22. The method of claim 20, wherein the stress annealing temperature is from about 450 to about 700 °C.

23. The method of claim 20, wherein improved oxidation resistance is shown following operation in air at time for 7 to 20 days24. The method of claim 14, wherein the as-cast nanocomposite is magnetically tunable and stable at high temperatures for extended operation at frequencies greater than 1kHz.

25. A method of preparing a cobalt-based alloy nanocomposite, comprising: preparing an alloy composition, comprising: from 2 to 25 atomic % or from 2 to 10 atomic % of iron; from 5 to 15 atomic % or from 2 to 10 atomic % of each of one or more of boron and silicon; from greater than 4 to 10 atomic % or from greater than 4 to 8 atomic % of each of one or more of tantalum and niobium; from 0 to 5 atomic % or 0 to 2 atomic % of manganese; and a remainder of cobalt; forming an amorphous structure of the alloy composition; and annealing to form the nanocomposite structure.

26. The method of claim 25, wherein the alloy composition is selected from Fe2.0-3.0CO70.0-80.0B5.0-10.0Si2.0-8.0Mno-5.oTa>4.0-10.0, or Fe2.0-3.0Co70.0-80.0B5.0-10.0Si2.0-8.0Mn0-5.0Nb>4.0-10.0, or Fe2.5Co75.5B8Si6Mn2Ta6, or Fe2.5Co75.5B8Si4Mn2Nb8.

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