The disclosure relates to soft magnetic materials and techniques for forming soft magnetic materials.
Magnetic materials, including both hard magnetic materials and soft magnetic materials, are used in many different applications. Soft magnetic materials possess relatively low coercivity, while hard magnetic materials possess relatively high coercivity. For example, soft magnetic materials may be used in transformer and inductor cores, magnetic recording write heads, microwave devices, magnetic shielding, and the like.
The disclosure describes soft magnetic materials including α″-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α″-Fe16N2 or α′-Fe8N and at least one of α″-Fe16Z2 or α′-Fe8Z, where Z includes at least one of C, B, or O, and x is a number greater than zero and less than one and techniques for forming such materials. The soft magnetic materials may be formed using a technique that includes melt spinning of a molten iron-containing material. The molten iron-containing material may include elemental Fe, and Fe-based alloy, an Fe—Z mixture, an iron-N mixture, or an iron-Z—N mixture. Thus, the melt-spun ribbons may include elemental Fe, an Fe-based alloy, an Fe—Z mixture, an Fe—N mixture, or an Fe—Z—N mixture. The melt-spun ribbons may be further processed, such as by introducing nitrogen atoms, Z atoms, or both, to form a material that includes Fe, Z, and N. The material that includes Fe, Z, and N may be the soft magnetic material that includes α′-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α′-Fe16N2 or α′-Fe8N and at least one of α′-Fe16Z2 or α′-Fe8Z, where Z includes at least one of C, B, or O, and x is a number greater than zero and less than one, or may be annealed to form the soft magnetic material. In some examples, the soft magnetic material then may be consolidated with other soft magnetic material to form a bulk soft magnet.
In some examples, the disclosure describes a method that includes forming a soft magnetic material by a technique comprising melt spinning, wherein the soft magnetic material comprises at least one of at least one of an α″-Fe16(NxZ1-x)2 phase domain or an α′-Fe8(NxZ1-x), wherein Z includes at least one of C, B, or O, and wherein x is a number greater than zero and less than one; or at least one of an α′-Fe16N2 phase domain or an α′-Fe8N phase domain, and at least one of an α″-Fe16Z2 phase domain or an α′-Fe8Z phase domain.
The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
The disclosure describes magnetic materials including α″-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α″-Fe16N2 or α′-Fe8N and at least one of α″-Fe16Z2 or α′-Fe8Z, where Z includes at least one of C, B, or O, and x is a number greater than zero and less than one and techniques for forming such materials. In some examples, the magnetic material including α″-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α″-Fe16N2 or α′-Fe8N and at least one of α″-Fe16Z2 or α′-Fe8Z, may include a relatively high magnetic saturation, such as greater than about 219 emu/gram, greater than about 242 emu/gram, or greater than about 250 emu/gram. In addition, in some examples, the magnetic material including α″-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α″-Fe16N2 or α′-Fe8N and at least one of α″-Fe16Z2 or α′-Fe8Z may include a relatively low coercivity. For example, the coercivity of the magnetic material may be less than about 10 Oersted. In some examples, magnetic materials with a coercivity of less than about 10 Oersted may be referred to as soft magnetic materials. The combination of relatively high magnetic saturation and relatively low coercivity may make the magnetic material an attractive soft magnetic material for use in transformer and inductor cores, magnetic recording media write heads, microwave devices, magnetic shielding, and the like. In some examples, the magnetic material including α″-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α″-Fe16N2 or α′-Fe8N and at least one of α″-Fe16Z2 or α′-Fe8Z also may possess high magnetic permeability, high frequency response, and the like.
The soft magnetic materials may be formed using a technique that includes melt spinning of a molten iron-containing material. The molten iron-containing material may include elemental Fe, an Fe-based alloy, an Fe—Z mixture, an Fe—N mixture, or an Fe—Z—N mixture. Thus, the melt-spun material may include elemental Fe, an Fe-based alloy, an Fe—Z mixture, an Fe—N mixture, or an Fe—Z—N mixture. The melt-spun material may facilitate further processing of the material to form the soft magnetic material described herein. For example, the melt-spun material may facilitate further processing to introduce Fe atoms, Z atoms, or both, to the material due to nano-pores formed in the surface and/or interior of melt-spun ribbons after heat treatment.
The melt-spun material may be further processed to result in a material including Fe, Z, and N, such as by introducing N atoms, Z atoms, or both. The material that includes Fe, Z, and N may in some examples be annealed to form the soft magnetic material that includes α″-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α″-Fe16N2 or α′-Fe8N and at least one of α″-Fe16Z2 or α′-Fe8Z, where Z includes at least one of C, B, or O, and x is a number greater than zero and less than one. In other examples, N and/or Z introduction may be performed at conditions that directly result in the soft magnetic material.
The technique of
The precursor that includes iron and carbon may be placed in the arc melting furnace (or other furnace used to melt the precursor). In some examples, the arc melting furnace may heat the mixture including iron and carbon at a temperature above about 1500° C., or above about 1600° C., or above about 2000° C.
The precursor then may be mixed to form a molten mixture in which the carbon is substantially homogeneously mixed throughout the iron. For example, in some implementations in which the precursor includes cast iron pellets encapsulated in iron foils, the molten mixture may be flipped a plurality of times (e.g., about 6 to 10 times) to approach a homogeneous composition.
Once the molten mixture including iron and carbon is formed, the molten mixture may be melt spun to form iron-carbon ribbons (14). The melt spinning parameters may be selected to form ribbons having a selected size (e.g., thickness). For example, the melt spinner may be configured with a gap distance of about 0.3 mm and a wheel speed of about 50 Hz.
The operating temperature of the melt spinner may be selected based on the Fe—C phase diagram. For example, the melt spinner may be operated at a temperature of between about 1,300° C. and about 1,500° C.
The resulting ribbons include a mixture of iron and carbon (e.g., iron-carbon ribbons), and the mixture may be substantially homogeneous (e.g., a concentration of carbon varies by less than about 2 at. % throughout the volume of the ribbons. In some examples, the ribbons may have a thickness between about 30 micrometers and about 60 micrometers. The ribbons may include alpha phase iron carbide and gamma phase iron carbide.
The iron-carbon ribbons then may be nitrided to introduce nitrogen and form iron-nitrogen-carbon ribbons (20). However, in some examples, the iron-carbon ribbons may optionally be reduced (18), and, if reduced, may optionally be oxidized (16).
The iron-carbon ribbons may be exposed to a reducing environment (18) to reduce or substantially eliminate oxides in the iron-carbon ribbons. The oxides may be from the precursor material or may form during subsequent processing and/or handling. The oxides may include iron oxides, and may affect magnetic properties of the soft magnetic material. As such, in some implementations, the oxides may be removed by exposing the iron-carbon ribbons to a reducing environment. The reducing environment may include gaseous hydrogen or another reducing gas. Further, the reducing environment may include an elevated temperature, such as a temperature between about 300° C. and about 400° C., such as about 350° C. The reduction process may be performed for any suitable time, such as at least one hour, or about 2 hours.
In some examples, prior to exposing the iron-carbon ribbon to the reducing environment (18), the iron-carbon ribbon optionally may be exposed to an oxidizing environment (16). The oxidizing environment may cause oxides to form on and/or in the iron-carbon ribbon, such as iron oxides. Exposure to the reducing environment (18) then may remove most or all of these oxides, leaving nano-pores in the surface and/or interior of the iron-carbon ribbon. This may facilitate nitriding of the iron-carbon ribbons to form iron-carbon-nitrogen ribbons.
The oxidizing environment may include an oxidizing gas, such as air or oxygen, and a high temperature, such as between about 900° C. and about 1000° C., for a sufficient time to form a desired concentration of oxides. For example, the time may be about 30 minutes.
In other examples, the oxidation (16) may be omitted and the iron-carbon ribbons may be exposed to the reducing environment (18).
After the optional oxidation (16) and/or reduction (18), the iron-carbon ribbons may be nitrided (20). For example, the iron-carbon ribbons may be exposed to a source of atomic nitrogen, such as nitrogen (N2), gaseous ammonia (NH3), ammonium nitrate (NH4NO3; solid), an amide (liquid or solid), or hydrazine (liquid). Amides include a C—N—H bond and hydrazine includes an N—N bond. Ammonium nitrate, amides and hydrazine may serve as a nitrogen donor for forming the powder including iron nitride. Example amides include carbamide ((NH2)2CO; also referred to as urea), methanamide (Formula 1), benzamide (Formula 2), and acetamide (Formula 3), although any amide may be used.
In some examples, amides may be derived from carboxylic acids by replacing the hydroxyl group of a carboxylic acid with an amine group. Amides of this type may be referred to as acid amides.
The iron-carbon ribbons and the source of atomic nitrogen also may be heated to decompose the source of atomic nitrogen and enable the nitrogen atoms to diffuse into the iron-carbon ribbons.
The nitrogen may be diffused into the iron-carbon ribbon so that a collective concentration of nitrogen and carbon is between about 8 atomic percent (at. %) and about 14 at. %, such as about 11 at. %. The concentration of nitrogen and carbon in iron may be an average concentration and may vary throughout the volume of the iron-carbon-nitrogen ribbon. In some examples, the atomic ratio of iron to the combination of nitrogen plus carbon is between about 11.5:1 (iron:nitrogen+carbon) and about 5.65:1 (iron:nitrogen+carbon). For example, the atomic ratio of iron to the combination of nitrogen and carbon may be about 9:1 (iron:nitrogen+carbon), about 8:1 (iron:nitrogen+carbon), or about 6.65:1 (iron:nitrogen+carbon).
The iron-carbon-nitrogen ribbons may be quenched to room temperature by a quenching medium, such as water, ice water, oil, or brine. The iron-carbon-nitrogen ribbons then are cryo-treated using a cryogenic coolant, such as liquid nitrogen or liquid helium (24). The cryo-treatment may facilitate formation of martensite phase iron nitride, iron carbide, and/or iron-nitride-carbide.
After the cryo-treatment, the iron-carbon-nitrogen ribbons may be annealed (26). The annealing technique may be performed using a crucible heating stage, a plasma arc lamp, a radiation heat source, such as an infrared heat lamp, an oven, or a closed retort. The annealing technique may facilitate magnetic material including at least one of α″-Fe16(NxZ1-x)2 phase (where Z includes at least one of C, B, or O) or a mixture of α″-Fe16N2 phase and α″-Fe16Z2 phase. The annealing technique allows diffusion of N+ ions, C+ ions, or both within iron to form at least one of α″-Fe16N2, α″-Fe16C2, or α″-Fe16(NxC1-x)2. In some examples, annealing at relatively low temperatures allows transformation of partial Fe8N disordered phase into α″-Fe16N2 ordered phase. Similarly, annealing at relatively low temperatures is expected to allow transformation of partial Fe8C disordered phase into α″-Fe16C2 ordered phase and partial Fe8(NxC1-x) disordered phase into α″-Fe16(NxC1-x)2 ordered phase.
In some examples, the annealing technique may be carried out at a temperature below about 300° C., such as between about 120° C. and about 300° C., between about 120° C. and about 220° C., or between about 150° C. and about 220° C. The annealing technique may be performed in a nitrogen (N2) or argon (Ar) atmosphere, or in a vacuum or near-vacuum.
The temperature and duration of the annealing step may be selected based on, for example, a size of the ribbons and diffusion coefficient of nitrogen atoms in iron and carbon atoms in iron at the annealing temperature. Based on these factors, the temperature and duration may be selected to provide sufficient time for nitrogen atoms and carbon atoms to diffuse to locations within the iron-carbon-nitrogen ribbons to form Fe16N2 domains, α″-Fe16C2 domains, and/or α″-Fe16(NxC1-x)2 domains.
Additionally, the temperature and duration of the annealing technique may be selected based on a desired volume fraction of the respective phase domains in the ribbons. For example, at a selected temperature, a longer annealing technique may result in a higher volume fraction of α″-Fe16N2, α″-Fe16C2, and/or α″-Fe16(NxC1-x)2. Similarly, for a given annealing technique duration, a higher temperature may result in a higher volume fraction of α″-Fe16N2, α″-Fe16C2, and/or α″-Fe16(NxC1-x)2. However, for durations above a threshold value, the additional volume fraction of α″-Fe16N2, α″-Fe16C2, and/or α″-Fe16(NxC1-x)2 may be limited or eliminated, as the volume fraction of α″-Fe16N2, α″-Fe16C2, and/or α″-Fe16(NxC1-x)2 reaches a relatively stable value. For example, at a temperature of about 150° C., after about 20 hours, the volume fraction of α″-Fe16N2 reaches a stable value. The duration of the annealing step may be at least about 5 hours, such as at least about 20 hours, or between about 5 hours and about 100 hours, or between about 5 hours and about 80 hours or between about 20 hours and about 80 hours, or about 40 hours.
In some examples, rather than using ribbons throughout the processing, the ribbons may be milled to form a powder, and the powder subsequently processed to form the soft magnetic material described herein.
Like the technique of
During the ball milling, a milling apparatus may be manipulated to cause agitation of milling media, such as milling spheres, which impact the iron-carbon ribbon and eventually wear the iron-carbon ribbon into powder. The milling media may be formed of a sufficiently hard material, such as steel, stainless steel, or the like. In some examples, the material from which the milling media are formed may not chemically react with the iron-carbon ribbon or powder. In some examples, the milling media may have an average diameter between about 5 millimeters (mm) and about 20 mm.
Once ball milling (32) is complete, the iron-carbon powder may have a relatively small average diameter. For example, the average diameter may be on the order of hundreds of nanometers, such as between about 100 nm and about 1 micrometer, or between about 300 nm and about 500 nm.
The iron-carbon powder then may be nitrided (38). However, in some examples, the powder optionally may be oxidized to form oxides in and/or on the iron-carbon powder (34), and/or may be exposed to a reducing atmosphere to reduce any oxides present in the iron-carbon powder (36). Each of these steps may be similar to or substantially the same as the corresponding steps described with reference to
The iron-carbon powder may be nitrided using a high temperature technique as described with reference to
The iron-carbon-nitrogen powder then may optionally be annealed, as described with reference to
In some examples, rather than using an iron-carbon precursor material, an iron-containing precursor (that does not include sufficient (or any) carbon or nitrogen) may be used as a starting material.
The technique of
During the carburizing and nitriding, the iron-containing ribbons may be heated, for example, in a furnace, an autoclave, or the like. Pressure exerted in an autoclave may stabilize α″-Fe16(NxZ1-x)2 or α′-Fe(NxZ1-x), or a mixture of at least one of α″-Fe6N2 or α′-Fe8N and at least one of α″-Fe6Z2 or α′-Fe8Z, where Z includes at least one of C, B, or O.
The carburizing and nitriding each may be performed at relatively high temperatures, like the technique described with reference to
The nitrogen and carbon may be diffused into the iron-containing ribbons so that a collective concentration of nitrogen and carbon is between about 8 atomic percent (at. %) and about 14 at. %, such as about 11 at. %. The concentration of nitrogen and carbon in iron may be an average concentration and may vary throughout the volume of the iron-carbon-nitrogen ribbon. In some examples, the atomic ratio of iron to the combination of nitrogen plus carbon is between about 11.5:1 (iron:nitrogen+carbon) and about 5.65:1 (iron:nitrogen+carbon). For example, the atomic ratio of iron to the combination of nitrogen and carbon may be about 9:1 (iron:nitrogen+carbon), about 8:1 (iron:nitrogen+carbon), or about 6.65:1 (iron:nitrogen+carbon). In some examples, the carbon concentration is about 6 at. %.
The iron-carbon-nitrogen ribbons may be quenched to room temperature by a quenching medium, such as water, ice water, oil, or brine. The iron-carbon-nitrogen ribbons then are cryo-treated using a cryogenic coolant, such as liquid nitrogen or liquid helium (24). This step may be similar to or substantially the same as the corresponding step described with reference to
After the cryo-treatment, the iron-carbon-nitrogen ribbons may be annealed (26). This step may be similar to or substantially the same as the corresponding step described with reference to
During the ball milling, a milling apparatus may be manipulated to cause agitation of milling media, such as milling spheres, which impact the iron-containing ribbon and eventually wear the iron-containing ribbon into powder. The milling media may be formed of a sufficiently hard material, such as steel, stainless steel, or the like. In some examples, the material from which the milling media are formed may not chemically react with the iron-containing ribbon or powder. In some examples, the milling media may have an average diameter between about 5 millimeters (mm) and about 20 mm.
Once ball milling (62) is complete, the iron-containing powder may have a relatively small average diameter. For example, the average diameter may be on the order of hundreds of nanometers, such as between about 100 nm and about 1 micrometer, or between about 300 nm and about 500 nm.
The iron-containing powder then may be carburized and nitrided (68). However, in some examples, the powder optionally may be oxidized to form oxides in and/or on the iron-containing powder (64), and/or may be exposed to a reducing atmosphere to reduce any oxides present in the iron-containing powder (66). Each of these steps may be similar to or substantially the same as the corresponding steps described with reference to
The iron-containing powder may be carburized and nitrided using a high temperature technique as described with reference to
The iron-carbon-nitrogen powder then may optionally be annealed, as described with reference to
In some examples, a material that includes carbon and nitrogen may be used as the precursor material for forming the soft magnetic material described herein.
The technique of
During the carburizing, the iron-nitrogen ribbons may be heated, for example, in a furnace, an autoclave, or the like. Pressure exerted in an autoclave may stabilize α′-Fe16(NxZ1-x)2 or α′-Fe8(NxZ1-x), or a mixture of at least one of α′-Fe16N2 or α′-Fe8N and at least one of α′-Fe16Z2 or α′-Fe8Z, where Z includes at least one of C, B, or 0.
The carburizing may be performed at a relatively high temperature, such as between about 960° C. and about 1100° C., or a relatively lower temperature, such as between about 700° C. and about 750° C.
The carbon may be diffused into the iron-nitrogen ribbons so that a collective concentration of nitrogen and carbon is between about 8 atomic percent (at. %) and about 14 at. %, such as about 11 at. %. The concentration of nitrogen and carbon in iron may be an average concentration and may vary throughout the volume of the iron-carbon-nitrogen ribbon. In some examples, the atomic ratio of iron to the combination of nitrogen plus carbon is between about 11.5:1 (iron:nitrogen+carbon) and about 5.65:1 (iron:nitrogen+carbon). For example, the atomic ratio of iron to the combination of nitrogen and carbon may be about 9:1 (iron:nitrogen+carbon), about 8:1 (iron:nitrogen+carbon), or about 6.65:1 (iron:nitrogen+carbon). In some examples, the carbon concentration is about 6 at. %.
The iron-carbon-nitrogen ribbons may be quenched to room temperature by a quenching medium, such as water, ice water, oil, or brine. The iron-carbon-nitrogen ribbons then are cryo-treated using a cryogenic coolant, such as liquid nitrogen or liquid helium (24). This step may be similar to or substantially the same as the corresponding step described with reference to
After the cryo-treatment, the iron-carbon-nitrogen ribbons may be annealed (26). This step may be similar to or substantially the same as the corresponding step described with reference to
During the ball milling, a milling apparatus may be manipulated to cause agitation of milling media, such as milling spheres, which impact the iron-containing ribbon and eventually wear the iron-containing ribbon into powder. The milling media may be formed of a sufficiently hard material, such as steel, stainless steel, or the like. In some examples, the material from which the milling media are formed may not chemically react with the iron-containing ribbon or powder. In some examples, the milling media may have an average diameter between about 5 millimeters (mm) and about 20 mm.
Once ball milling (92) is complete, the iron-containing powder may have a relatively small average diameter. For example, the average diameter may be on the order of hundreds of nanometers, such as between about 100 nm and about 1 micrometer, or between about 300 nm and about 500 nm.
The iron-nitrogen powder then may be carburized (98). However, in some examples, the powder optionally may be oxidized to form oxides in and/or on the iron-nitrogen powder (94), and/or may be exposed to a reducing atmosphere to reduce any oxides present in the iron-nitrogen powder (96). Each of these steps may be similar to or substantially the same as the corresponding steps described with reference to
The iron-nitrogen powder may be carburized using a high temperature technique as described with reference to
The iron-carbon-nitrogen powder then may optionally be annealed, as described with reference to
α″-Fe6N2 has high saturation magnetization and magnetic anisotropy constant. The high saturation magnetization and magnetic anisotropy constants result in a magnetic energy product that may be higher than rare earth magnets. Additionally, iron and nitrogen are abundant elements, and thus are relatively inexpensive and easy to procure.
Calculations show that the magnetocrystalline anisotropy of α″-Fe16N2 may be about 1.6×107 erg/cm3. α″-Fe16N2 also has a relatively high theoretical magnetic saturation moment of about 2.3 Bohr magnetons per iron atom B/Fe.
Similarly, when X includes at least one of C, B, or O (Z atoms) α″-Fe6Z2 may be a hard magnetic material when the Z atoms are ordered within the iron crystal lattice. Like α″-Fe16N2, the Z atoms (C, B, or O) in ordered α″-Fe6Z2 may be positioned at octahedral interstitial sites within the iron crystal. However, in ordered α″-Fe16Z2, the lattice parameters may be different than the lattice parameters of α″-Fe16N2. For example, while not wishing to be bound by any theory, the presence of carbon atoms is expected to reduce the distance between the C atoms and the surrounding Fe atoms lying in the (002) (iron) crystal planes from 3.74 Angstroms to 3.68 Angstroms. This is expected to increase p-d mixing, which is expected to increase bandwidth and lower the density of states. This is expected to reduce the magnetocrystalline anisotropy of α″-Fe16C2 to a negative value. Similar results may be expected for B and O atoms.
Ordered α″-Fe16Z2, such as when Z is carbon (C), may exhibit magnetocrystalline anisotropy with a magnetic easy axis lying in the a-b plane (e.g., [100]; perpendicular to the c-axis). Hence, the direction of magnetocrystalline anisotropy in α″-Fe6Z2 may be substantially perpendicular to the direction of magnetocrystalline anisotropy in α″-Fe16N2. Calculations show that the magnetocrystalline anisotropy in ordered α″-Fe16C2 may be about −1.4×107 erg/cm3. α″-Fe16C2 also has a relatively high theoretical magnetic saturation moment of about 2.1 μB/Fe.
Hence, when ordered α″-Fe16C2 is mixed in predetermined quantities with α″-Fe16N2 with c-axes of the respective α″-Fe16C2 and α″-Fe16N2 crystals oriented in substantially the same direction, the magnetocrystalline anisotropies of α″-Fe16C2 and α″-Fe6N2 may substantially cancel. This may result in a material with a magnetocrystalline anisotropy value of near zero (depending on the volume ratio of α″-Fe16C2 to α″-Fe6N2), while providing a theoretical magnetic saturation moment of, e.g., about 2.2 pB/Fe (the average of the theoretical magnetic saturation moments of α″-Fe6N2 and α″-Fe16C2). For example, a magnetic material including a volume ratio of α″-Fe6N2 to α″-Fe16C2 of about 4.667:5.333 may have a magnetic anisotropy of about 0 (e.g., less than about 10 Oersteds) and a theoretical magnetic saturation moment of about 2.2 μB/Fe. In this way, a mixture of predetermined volumes of α″-Fe6N2 domains and α″-Fe16C2 domains may produce a soft magnetic material with a magnetocrystalline anisotropy value of near zero and a relatively high magnetic saturation moment. Similar results may be expected when B, O, or both are substituted for C, based on the similar atomic radii of C, B, and O.
In some examples, the soft magnetic material formed by any of the techniques described herein may be similar to that shown in
In other examples, rather than all of the respective domains of α″-Fe16N2 102 having their magnetic easy axes lying in substantially the same direction, the respective easy axes of the respective domains of α″-Fe16N2 102 may be substantially randomly distributed. Similarly, the respective easy axes of the respective domains of α″-Fe16Z2 104 may be substantially randomly distributed. This also may lead to a soft magnetic material 100 with high saturation magnetization and low magnetocrystalline anisotropy.
In some examples, soft magnetic material 100 including a mixture of domains of α″-Fe16N2 12 and domains of α″-Fe16Z2 104 may not include only domains of α″-Fe16N2 102 and domains of α″-Fe16Z2 104. For example, soft magnetic material 100 may include at least one Fe16(NxZ1-x)2 phase domain in addition to domains of α″-Fe16N2 102 and domains of α″-Fe16Z2 104. The size of the domains may be between about 1 nm and about 100 micrometers. The average domain size distribution may influence the permeability of the material as evidenced by the slope of the hysteresis loop. In some examples, soft magnetic material 100 including a mixture of domains of α″-Fe16N2 102 and domains of α″-Fe16Z2 104 may include other iron phases, other iron nitride phases, other iron carbide phases, or other phases including other constituents (e.g., dopants or impurities) present in the soft magnetic material. Dopants may include, for example, Cu, Co, Ti, Mn, Al, V, Cr, Zn, Ga, Ge, Zr, nNb, Mo, P, Si, Mg, or the like. Dopants may be used to fine tune the microstructure and magnetocrystalline anisotropy of the soft magnetic material. In some examples, the dopants may be present in an amount between about 0.1 atomic percent and about 15 atomic percent.
In some examples, the structure shown in
In some examples, rather than including discrete domains of α″-Fe6N2 and α″-Fe16Z2, a material may include one or more crystals of α″-Fe16(NxZ1-x)2, where Z includes at least one of C, B, or O, and x is a number greater than 0 and less than 1. In these examples, rather than forming discrete domains, the iron, nitrogen, and Z atoms form a crystalline structure in which some interstitial locations are filled by nitrogen atoms and some interstitial locations are filled by Z atoms. For example,
In some examples, the soft magnetic material including Fe16(NxZ1-x)2 may not include only Fe16(NxZ1-x)2. For example, the soft magnetic material may include at least one α″-Fe6N2 phase domain or at least one α″-Fe6Z2 domain in addition to at least one Fe16(NxZ1-x)2 phase domain. In some examples, the soft magnetic material including Fe16(NxZ1-x)2 may include other iron phases, other iron nitride phases, other iron carbide phases, or other phase including other constituents (e.g., dopants or impurities) present in the soft magnetic material.
In some examples, a soft magnetic material including at least one α″-Fe16(NxZ1-x)2 phase domain may include at least about 35 volume percent α″-Fe16(NxZ1-x)2 phase domain(s). In other examples, the soft magnetic material may include at least about 40 volume percent, at least about 50 volume percent, or at least about 60 volume percent α″-Fe16(NxZ1-x)2 phase domain(s). Similarly, a soft magnetic material including a mixture of α″-Fe16N2 and α″-Fe16Z2 may include at least about 35 volume percent of the combination of α″-Fe16N2 and α″-Fe16Z2 phase domains. In other examples, the soft magnetic material may include at least about 40 volume percent, at least about 50 volume percent, or at least about 60 volume percent of the combination of α″-Fe16N2 and α″-Fe16Z2 phase domains.
In some examples, the soft magnetic material including Fe16(NxZ1-x)2 or a mixture of α″-Fe16N2 and α″-Fe16Z2 may have a saturation magnetization of at least about 219 emu/gram, which is the saturation magnetization of pure iron. In some examples, the soft magnetic material including Fe16(NxZ1-x)2 or a mixture of α″-Fe16N2 and α″-Fe16Z2 may have a saturation magnetization of at least about 242 emu/gram, which is the saturation magnetization of Fe65Co35. In some examples, the soft magnetic material including Fe16(NxZ1-x)2 or a mixture of α″-Fe16N2 and α″-Fe16Z2 may have a saturation magnetization of at least about 250 emu/gram.
In some examples, the soft magnetic material including Fe16(NxZ1-x)2 or a mixture of α″-Fe16N2 and α″-Fe16Z2 may have a soft magnetic coercivity of less than or equal to about 10 Oersteds. In some examples, the soft magnetic material including α″-Fe16(NxZ1-x)2 or a mixture of α″-Fe16N2 and α″-Fe16Z2 also may possess high magnetic permeability, high frequency response, or the like.
The soft magnetic materials described herein may be formed into bulk soft magnetic materials by assembling multiple ribbons, powders, or the like. The ribbons, powders, or the like may be assembled using compaction, resins or adhesives, or the like. In some examples, the ribbons, powders, or the like may be assembled in a relatively low temperature process, e.g., a process performed at less than about 200° C., to reduce or substantially avoid affecting the magnetic properties of the soft magnetic materials. The bulk soft magnetic material may be formed with any desired shape during the assembly process, e.g., depending on the final use of the bulk soft magnetic material.
In some examples, the soft magnetic materials that are assembled into bulk soft magnetic materials may include oxide coatings or shells. For instance, as described above, during some preparation techniques, the material is oxidized and, optionally, reduced. The oxidation may form an oxide (e.g., iron oxide) outer layer or shell, which may be left (i.e., not reduced) or may be not fully reduced (i.e., reduction is performed, but at conditions that result in some oxide remaining). Alternatively, the material may be oxidized after forming the soft magnetic material including α″-Fe6(NxZ1-x)2 or a mixture of α″-Fe16N2 and α″-Fe6Z2, e.g., using an intentional reaction process or by exposing the material to ambient air. The oxide coating or shell may be useful when the bulk soft magnetic material is used in some applications, e.g., high frequency electromagnetic applications.
In some examples, a powder including a soft magnetic material including α″-Fe16(NxZ1-x)2 or a mixture of α″-Fe16N2 and α″-Fe16Z2 may be used for electromagnetic shielding. For instance, the powder may be spray coated on a component with any selected shape to form an electromagnetic shield for all or part of the component.
Clause 1: A method comprising: forming a soft magnetic material by a technique comprising melt spinning, wherein the soft magnetic material comprises at least one of: at least one of an α″-Fe6(NxZ1-x)2 phase domain or an α′-Fe8(NxZ1-x), wherein Z includes at least one of C, B, or O, and wherein x is a number greater than zero and less than one; or at least one of an α″-Fe16N2 phase domain or an α′-Fe8N phase domain, and at least one of an α″-Fe16Z2 phase domain or an α′-Fe8Z phase domain.
Clause 2: The method of clause 1, wherein forming the soft magnetic material by the technique comprising melt spinning comprises: forming a molten mixture comprising iron and carbon; melt spinning the molten mixture comprising iron and carbon to form iron-carbon ribbons; and nitriding the iron-carbon ribbons to form an iron-carbon-nitrogen material.
Clause 3: The method of clause 2, wherein nitriding the iron-carbon ribbons comprises exposing the iron-carbon ribbons to a nitrogen source at a temperature of between about 650° C. and about 900° C.
Clause 4: The method of clause 3, wherein the nitrogen source comprises at least one of ammonia, ammonium nitrate, urea, an amide, or hydrazine.
Clause 5: The method of any one of clauses 2 to 4, further comprising cryo-treating the iron-carbon-nitrogen material in liquid nitrogen.
Clause 6: The method of any one of clauses 2 to 5, further comprising annealing the iron-carbon-nitrogen material in a nitrogen-containing atmosphere at a temperature between about 100° C. and about 210° C. for between about 5 hours and about 100 hours.
Clause 7: The method of any one of clauses 2 to 6, further comprising, prior to nitriding the iron-carbon ribbons, exposing the iron-carbon ribbons to a reducing atmosphere to reduce a concentration of oxides in the iron-carbon ribbon.
Clause 8: The method of clause 7, further comprising, prior to exposing the iron-carbon ribbons to the reducing atmosphere, exposing the iron-carbon ribbons to an oxidizing atmosphere to form oxides in the iron-carbon ribbons, wherein exposing the iron-carbon ribbons to the reducing atmosphere removes at least some of the oxides and forms pores in the iron-carbon ribbons.
Clause 9: The method of any one of clauses 2 to 8, further comprising, prior to nitriding the iron-carbon ribbons, leaching some carbon from at least a surface of the iron-carbon ribbons to create porosity in the iron-carbon ribbons.
Clause 10: The method of clause 1, wherein forming the soft magnetic material by the technique comprising melt spinning comprises: forming a molten mixture comprising iron and carbon; melt spinning the molten mixture comprising iron and carbon to form iron-carbon ribbons; ball milling the iron-carbon ribbons to form iron-carbon powder; and nitriding the iron-carbon powder.
Clause 11: The method of clause 10, wherein nitriding the iron-carbon powder comprises exposing the iron-carbon powder to a nitrogen source at a temperature between about 100° C. and about 210° C. for between about 5 hours and about 100 hours.
Clause 12: The method of clause 11, wherein the nitrogen source comprises at least one of ammonia, ammonium nitrate, urea, an amide, or hydrazine.
Clause 13: The method of any one of clauses 10 to 12, further comprising, prior to nitriding the iron-carbon powder, exposing the iron-carbon powder to a reducing atmosphere to reduce a concentration of oxides in the iron-carbon powder.
Clause 14: The method of clause 13, further comprising, prior to exposing the iron-carbon powder to the reducing atmosphere, exposing the iron-carbon powder to an oxidizing atmosphere to form oxides in the iron-carbon powder, wherein exposing the iron-carbon powder to the reducing atmosphere removes at least some of the oxides and forms pores in the iron-carbon powder.
Clause 15: The method of any one of clauses 10 to 14, further comprising, prior to nitriding the iron-carbon powder, leaching some carbon from at least a surface of the iron-carbon powder to create porosity in the iron-carbon powder.
Clause 16: The method of any one of claims 2 to 15, wherein forming the molten mixture comprising iron and carbon comprises melting cast iron.
Clause 17: The method of clause 16, wherein the cast iron is encapsulated in elemental iron.
Clause 18: The method of any one of clauses 2 to 17, wherein the molten mixture comprises a substantially homogeneous distribution of carbon.
Clause 19: The method of clause 1, wherein forming the soft magnetic material by the technique comprising melt spinning comprises: forming a molten mixture comprising iron; melt spinning the molten mixture comprising iron and carbon to form iron ribbons; and carburizing and nitriding the iron ribbons to form an iron-carbon-nitrogen material.
Clause 20: The method of clause 19, wherein carburizing and nitriding the iron ribbons comprises exposing the iron ribbons to a nitrogen source at a temperature of between about 650° C. and about 900° C.
Clause 21: The method of clause 20, wherein the nitrogen source comprises at least one of ammonia, ammonium nitrate, urea, an amide, or hydrazine.
Clause 22: The method of any one of clauses 19 to 21, wherein carburizing and nitriding the iron ribbons comprises exposing the iron ribbons to a carbon source.
Clause 23: The method of clause 22, wherein the carbon source comprises at least one of urea, graphite, carbon monoxide, carbon dioxide, or methane.
Clause 24: The method of clause 19, wherein carburizing and nitriding the iron ribbons comprises exposing the iron ribbons to a carbon-nitrogen source.
Clause 25: The method of clause 24, wherein the carbon-nitrogen source comprises a carbamide.
Clause 26: The method of any one of clauses 19 to 25, further comprising cryo-treating the iron-carbon-nitrogen material in liquid nitrogen.
Clause 27: The method of any one of claims 19 to 26, further comprising annealing the iron-carbon-nitrogen material in a nitrogen-containing atmosphere at a temperature between about 100° C. and about 210° C. for between about 5 hours and about 100 hours.
Clause 28: The method of any one of clauses 19 to 27, further comprising, prior to carburizing and nitriding the iron ribbons, exposing the iron ribbons to a reducing atmosphere to reduce a concentration of oxides in the iron ribbon.
Clause 29: The method of clause 28, further comprising, prior to exposing the iron ribbons to the reducing atmosphere, exposing the iron ribbons to an oxidizing atmosphere to form oxides in the iron ribbons, wherein exposing the iron ribbons to the reducing atmosphere removes at least some of the oxides and forms pores in the iron ribbons.
Clause 30: The method of any one of clauses 19 to 29, further comprising, prior to carburizing and nitriding the iron ribbons, leaching some carbon from at least a surface of the iron ribbons to create porosity in the iron ribbons.
Clause 31: The method of clause 1, wherein forming the soft magnetic material by the technique comprising melt spinning comprises: forming a molten mixture comprising iron; melt spinning the molten mixture comprising iron to form iron ribbons; ball milling the iron ribbons to form iron powder; and carburizing and nitriding the iron powder to form an iron-carbon-nitrogen material.
Clause 32: The method of clause 31, wherein nitriding the iron-carbon powder comprises exposing the iron-carbon powder to a nitrogen source at a temperature between about 100° C. and about 210° C. for between about 5 hours and about 100 hours.
Clause 33: The method of clause 32, wherein the nitrogen source comprises ammonia, ammonium nitrate, urea, an amide, or hydrazine.
Clause 34: The method of any one of clauses 31 to 33, wherein carburizing and nitriding the iron ribbons comprises exposing the iron ribbons to a carbon source.
Clause 35: The method of clause 34, wherein the carbon source comprises at least one of urea, graphite, carbon monoxide, carbon dioxide, or methane.
Clause 36: The method of clause 31, wherein carburizing and nitriding the iron ribbons comprises exposing the iron ribbons to a carbon-nitrogen source.
Clause 37: The method of clause 36, wherein the carbon-nitrogen source comprises a carbamide.
Clause 38: The method of any one of clauses 31 to 37, further comprising, prior to carburizing and nitriding the iron powder, exposing the iron powder to a reducing atmosphere to reduce a concentration of oxides in the iron powder.
Clause 39: The method of clause 38, further comprising, prior to exposing the iron powder to the reducing atmosphere, exposing the iron powder to an oxidizing atmosphere to form oxides in the iron powder, wherein exposing the iron powder to the reducing atmosphere removes at least some of the oxides and forms pores in the iron powder.
Clause 40: The method of clause 1, wherein forming the soft magnetic material by the technique comprising melt spinning comprises: forming a molten mixture comprising iron and nitrogen; melt spinning the molten mixture comprising iron and nitrogen to form iron-nitrogen ribbons; and carburizing the iron-nitrogen ribbons to form an iron-carbon-nitrogen material.
Clause 41: The method of clause 40, wherein nitriding the iron-nitrogen ribbons comprises exposing the iron-nitrogen ribbons to a carbon source.
Clause 42: The method of clause 41, wherein the carbon source comprises at least one of urea, graphite, carbon monoxide, carbon dioxide, or methane.
Clause 43: The method of any one of clauses 40 to 42, further comprising cryo-treating the iron-carbon-nitrogen in liquid nitrogen.
Clause 44: The method of any one of clauses 40 to 43, further comprising annealing the iron-carbon-nitrogen material in a nitrogen-containing atmosphere at a temperature between about 100° C. and about 210° C. for between about 5 hours and about 100 hours.
Clause 45: The method of any one of clauses 40 to 44, further comprising, prior to carburizing the iron-nitrogen ribbons, exposing the iron-nitrogen ribbons to a reducing atmosphere to reduce a concentration of oxides in the iron-nitrogen ribbon.
Clause 46: The method of clause 45, further comprising, prior to exposing the iron-nitrogen ribbons to the reducing atmosphere, exposing the iron-nitrogen ribbons to an oxidizing atmosphere to form oxides in the iron-nitrogen ribbons, wherein exposing the iron-nitrogen ribbons to the reducing atmosphere removes at least some of the oxides and forms pores in the iron-nitrogen ribbons.
Clause 47: The method of any one of clause 40 to 46, further comprising, prior to carburizing the iron-nitrogen ribbons, leaching some nitrogen from at least a surface of the iron-nitrogen ribbons to create porosity in the iron-nitrogen ribbons.
Clause 48: The method of clause 1, wherein forming the soft magnetic material by the technique comprising melt spinning comprises: forming a molten mixture comprising iron and nitrogen; melt spinning the molten mixture comprising iron and nitrogen to form iron-nitrogen ribbons; ball milling the iron-nitrogen ribbons to form iron-nitrogen powder; and carburizing the iron-nitrogen powder.
Clause 49: The method of clause 48, wherein carburizing the iron-nitrogen powder comprises exposing the iron-carbon powder to a carbon source.
Clause 50: The method of clause 49, wherein the carbon source comprises at least one of urea, graphite, carbon monoxide, carbon dioxide, or methane.
Clause 51: The method of any one of clauses 48 to 50, further comprising, prior to carburizing the iron-nitrogen powder, exposing the iron-nitrogen powder to a reducing atmosphere to reduce a concentration of oxides in the iron-nitrogen powder.
Clause 52: The method of clause 51, further comprising, prior to exposing the iron-nitrogen powder to the reducing atmosphere, exposing the iron-nitrogen powder to an oxidizing atmosphere to form oxides in the iron-nitrogen powder, wherein exposing the iron-nitrogen powder to the reducing atmosphere removes at least some of the oxides and forms pores in the iron-nitrogen powder.
Clause 53: The method of any one of clauses 48 to 52, further comprising, prior to carburizing the iron-nitrogen powder, leaching some carbon from at least a surface of the iron-nitrogen powder to create porosity in the iron-nitrogen powder.
Clause 54: The method of any one of claims 40 to 53, wherein the molten mixture comprises a substantially homogeneous distribution of nitrogen.
Cast iron ingots with known carbon concentrations were wrapped in pure iron foils with selected thicknesses to achieve a desired carbon concentration. The ingots were melted in an arc melting machine (a SP-MSM20-7 compact vacuum arc melting system, available from MTI Corporation) at a temperature of about 1600° C. at 700 mTorr. Between 6 and 10 flips of the molten material were made to approach a homogeneous composition.
The molten material was then melt spun using a Melt Spinner SC, available from Edmund Buhler GmbH. The gap distance was set at 0.3 mm and the wheel speed was about 50 Hz. The melting temperature was between about 1300° C. and about 1500° C., depending on the carbon content.
The resulting ribbons are shown in
The iron-carbon powder was then ball milled in a Retsch PM100 planetary ball mill, available from Retsch GmbH, Haan, Germany.
Various samples were prepared using melt spinning of iron-carbon mixtures, followed by oxidation, reduction, and nitriding. Table 1 summarizes the processing parameters:
The molten material was then melt spun using a Melt Spinner SC, available from Edmund Buhler GmbH. The gap distance was set at 0.3 mm and the wheel speed was about 50 Hz. The melting temperature was between about 1300° C. and about 1500° C., depending on the carbon content. The sample included some iron nitride, such as Fe3N, Fe16N2, austenite iron nitride, and alpha Fe.
The molten material was then melt spun using a Melt Spinner SC, available from Edmund Buhler GmbH. The gap distance was set at 0.3 mm and the wheel speed was about 50 Hz. The melting temperature was between about 1300° C. and about 1500° C., depending on the carbon content. The sample was prepared by oxidizing at 975° C. for 30 minutes and reducing at 350° C. for 2 hours in hydrogen gas prior to the nitriding in ammonia. The sample included some iron nitride, such as Fe3N, Fe16N2, austenite iron nitride, and alpha Fe.
The molten material was then melt spun using a Melt Spinner SC, available from Edmund Buhler GmbH. The gap distance was set at 0.3 mm and the wheel speed was about 50 Hz. The melting temperature was between about 1300° C. and about 1500° C., depending on the carbon content. The sample was prepared by oxidizing at 975° C. for 30 minutes and reducing at 350° C. for 2 hours in hydrogen gas prior to the nitriding in ammonia. The sample included some iron nitride, such as Fe3N, Fe16N2, austenite iron nitride, and alpha Fe.
The molten material was then melt spun using a Melt Spinner SC, available from Edmund Buhler GmbH. The gap distance was set at 0.3 mm and the wheel speed was about 50 Hz. The melting temperature was between about 1300° C. and about 1500° C., depending on the carbon content. The sample was prepared by oxidizing at 975° C. for 30 minutes and reducing at 350° C. for 2 hours in hydrogen gas prior to the nitriding in ammonia. The sample included some iron nitride, such as Fe3N, Fe16N2, austenite iron nitride, and alpha Fe.
The molten material was then melt spun using a Melt Spinner SC, available from Edmund Buhler GmbH. The gap distance was set at 0.3 mm and the wheel speed was about 50 Hz. The melting temperature was between about 1300° C. and about 1500° C., depending on the carbon content. Iron-carbon-nitrogen ribbons were then formed by nitriding iron-carbon ribbons at 660° C. at 80 sccm H2 and 20 sccm NH3 for 2 hours, followed by water cooling and, optionally, liquid nitrogen cryo-treatment.
The disclosure of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, in its entirety.
This application claims the benefit of U.S. Provisional Patent Application No. 62/914,230, titled, “MAGNETIC MATERIAL INCLUDING α″-Fe16(NxZ1-x)2 OR A MIXTURE OF α″-Fe16Z2 AND α″-Fe16N2, WHERE Z INCLUDES AT LEAST ONE OF C, B, OR O,” filed Oct. 11, 2019, the entire content of which is incorporated herein by reference.
This invention was made with government support under DE-AR0000199 awarded by the United States Department of Energy. The government has certain rights in the invention.
Number | Date | Country | |
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62914230 | Oct 2019 | US |