Internally segmented magnets

Abstract

Internally segmented magnet comprising the following: a first layer of a permanent magnetic material; a second layer of a permanent magnetic material; and an insulating layer that separates the first and second layers and consists of a binary ceramic mixture with a molar ratio of 30% to 70% CaF2 and 30% to 70% MgF2 as well as 5 wt% to 15 wt% iron.

Description

TECHNICAL FIELD

[0001] This disclosure relates to segmented magnets, for example internally segmented neodymium magnets. GENERAL STATE OF THE ART

[0002] Permanent magnet motors are common and can be used in electric vehicles. Due to the high conductivity of sintered Nd-Fe-B magnets and the groove / tooth harmonics, eddy current losses can be generated within the magnets. This can increase the magnet temperature and degrade the performance of the permanent magnets, leading to a corresponding reduction in motor efficiency. In an attempt to address these problems and allow the magnets to operate at elevated temperatures, high coercive force magnets can be used in motors. These magnets typically contain expensive heavy rare earth elements (HRE), such as Tb and Dy. Reducing eddy current losses can increase motor efficiency and reduce material costs.

[0003] To reduce eddy current losses, the resistivity of the magnets must be increased. There are typically two approaches to increasing resistivity. The first is to increase the overall resistivity of the magnet by mixing high-resistivity materials into the magnet. However, this generally results in a deterioration in the magnetic properties. The second approach is to segment the magnet by separating the Nd-Fe-B magnets into thin slices with insulating materials in between. Such magnets are typically manufactured by bonding the sliced ​​magnets together using a polymer. This magnet segmentation process involves multiple manufacturing steps and increases the manufacturing cost of the magnet.

[0004] US 2015 / 0 155 082 A1 discloses laminated, composite permanent magnets consisting of layers of permanent magnets separated by layers of dielectric or high-resistivity materials, wherein the laminated magnets have an increased electrical resistance compared to a magnet that does not contain layers of dielectric or high-resistivity material. The dielectric layers contain fluorides such as CaF X and mixtures thereof. Furthermore, the materials with high electrical resistance may contain iron.

[0005] US 5 858 124 A describes a high-resistivity rare earth magnet having a metal structure in which a rare earth magnet phase is dispersed in a compound phase containing at least one compound selected from the group consisting of fluorides and oxides of Li, Na, Mg, Ca, Ba and Sr. SUMMARY OF THE INVENTION

[0006] According to the invention, an internally segmented magnet is provided, comprising: a first layer of a permanent magnetic material; a second layer of a permanent magnetic material; and an insulating layer separating the first and second layers and consisting of a binary ceramic mixture with a molar ratio of 30% to 70% CaF2 and 30% to 70% MgF2 and 5% to 15% by weight of iron.

[0007] In at least one embodiment, an internally segmented magnet is provided. The magnet may include a first layer of a permanent magnetic material, a second layer of a permanent magnetic material, and an insulating layer separating the first and second layers and including a ceramic mixture of at least a first ceramic material and a second ceramic material having a melting point of up to 1100°C.

[0008] In one embodiment, the first or second ceramic material may include a compound having the formula AH2, where A is an alkaline earth metal and H is a halogen. The halogen may include fluorine or chlorine, and the alkaline earth metal may be selected from the group consisting of magnesium (Mg), calcium (Ca), and strontium (Sr). In another embodiment, the first or second ceramic material may include a compound having the formula MH3, where M is a metal having an oxidation number of +3 and H is a halogen. In another embodiment, the first or second ceramic material may include a compound having the formula BH, where B is an alkali metal and H is a halogen.

[0009] The ceramic mixture may have a melting point lower than a melting point of both the first and second ceramic materials. The insulating layer may further include a metal or metal alloy. The metal or metal alloy may include iron, aluminum, copper, rare earth metals, or alloys thereof. In one embodiment, the metal comprises less than 20 wt.% of the insulating layer.

[0010] In at least one embodiment, a method for forming an internally segmented magnet is provided. The method may include forming a first layer of a powdered permanent magnetic material, depositing an insulating layer over the first layer including a ceramic mixture of at least a first ceramic material and a second ceramic material, depositing a second layer of a powdered permanent magnetic material over the insulating layer to form an internally segmented magnet stack, and sintering the magnet stack.

[0011] In one embodiment, the first and second ceramic materials may be selected from the group consisting of: a compound having the formula AH2, wherein A is an alkaline earth metal and H is a halogen, a compound having the formula MH3, wherein M is a metal having an oxidation number of +3 and H is a halogen, and a compound having the formula BH, wherein B is an alkali metal and H is a halogen.

[0012] The ceramic mixture may have a melting point lower than a melting point of both the first and second ceramic materials. The insulating layer may further include a metal or metal alloy. The metal or metal alloy may include iron, aluminum, copper, rare earth metals, or alloys thereof, and the metal may comprise less than 20 wt.% of the insulating layer.

[0013] The insulating layer may further include a low melting point (LMP) material having a melting point of 30°C to 400°C.

[0014] The LMP material may have a boiling point lower than a sintering temperature of the sintering step. The insulating layer may be pressed into a sheet prior to the first deposition step. The insulating layer may be pressed into the sheet at a temperature greater than the melting point of the LMP material and lower than the boiling point of the LMP material. The method may also include a hot-pressing step prior to the sintering step, wherein the hot-pressing step includes heating the magnet stack to a temperature below the melting point of the LMP material.

[0015] In at least one embodiment, an internally segmented magnetic green compact is provided. The green compact may include a first layer of a powdered permanent magnetic material, a second layer of a powdered permanent magnetic material, and an insulating layer separating the first and second layers and including a ceramic mixture of at least a first ceramic material and a second ceramic material, and a low melting point (LMP) material having a melting point of 30°C to 400°C. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-section of an internally segmented magnet according to one embodiment, Fig. Figure 2 is an example of a binary phase diagram including a eutectic reaction for a mixture of CaF2 and MgF2, Fig.3 is an SEM image comparing a CaF2 insulating layer and an insulating layer including CaF2 and MgF2, Fig. 4 is a schematic of a method of forming an internally segmented magnet according to one embodiment, and Fig. 5 is an image of an internally segmented magnet according to one embodiment. DETAILED DESCRIPTION

[0016] As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0017] To reduce processing costs, an alternative method for segmenting magnets has been developed, known as the internal segmentation technique. This technique allows the magnet to be segmented by placing insulating layers within the green compact during sintering. The insulating materials can be selected so that they do not degrade the magnetic properties, so the insulating layer does not react with the hard magnetic phase. However, the mechanical properties of internally segmented magnets have been shown to be very poor, especially when the insulating layer is thick and uniform, so that the hard magnetic phase is completely isolated.Accordingly, internally segmented magnets have been formed with very thin insulating layers, where the insulating layer is too thin to be continuous, resulting in a very limited increase in resistivity due to insufficient insulation. For example, the insulating layers can only provide a 2- to 3-fold increase in resistivity compared to the magnetic phase. To adequately insulate the magnetic material, the resistivity must be much higher, such as thousands, millions, or billions of times higher than the magnetic material itself.

[0018] The disclosed internally segmented magnets and methods for forming the same can improve / enhance the mechanical properties of the internally segmented magnet. To improve the mechanical properties, both "adhesive" and "cohesive" forces must be enhanced, given the heterogeneous nature of such materials. The former, adhesive, may refer to the interaction near the interface between the magnet and the insulating layer(s) (IL). The latter, cohesive, may reflect the mechanical properties of the insulating materials forming the IL. In a stacked magnet-IL-magnet structure, the adhesive force may be the interaction between the insulating materials and the magnetic materials (e.g., Nd-Fe-B), while the cohesive force may be based on the mechanical properties of the insulating layer itself.The insulating materials for the internally segmented magnet can be ceramic, which does not react with the main phase of the magnet and thus cannot degrade the magnetic properties. However, this lack of interaction may mean that there are no chemical bonds formed between the insulating layer and the Nd-Fe-B. The adhesion force may therefore consist of the relatively weak electrostatic interaction between these two materials, also called the van der Waals force. It has been discovered that if the insulating materials are melted during sintering, the mechanical properties can be improved. It is believed that the improvement is due to the insulating materials spreading thinly and wetting the surfaces of the magnetic phase well, thereby improving the adhesion force.

[0019] With reference to Fig.1, an internally segmented magnet 10 is shown in cross-section. The magnet 10 may have multiple magnetic layers 12 and one or more insulating layers (IL) 14. The insulating layers 14 may be disposed between the magnetic layers 12 to increase the electrical resistance of the magnet 10 and reduce eddy current losses. The insulating layers 14 may be in direct contact with two spaced-apart and opposing magnetic layers 12. The magnetic and / or insulating layers 14 may have a uniform or substantially uniform thickness (e.g., within 5% of the average thickness). There may be multiple insulating layers 14, for example, one insulating layer 14 between each pair of adjacent magnetic layers 12. In one embodiment, if there are "x" magnetic layers 12, there may be "x-1" insulating layers 14. In the Fig. In the example shown in Figure 1, there are four magnetic layers 12 and three insulating layers 14, but there may be any suitable number of both layers. The magnet may include at least two magnetic layers 12 separated by an insulating layer 14. However, there may be 3, 4, 5, 10, or more magnetic layers 12, including corresponding 2, 3, 4, 9, or more insulating layers 14 disposed between each pair of magnetic layers 12.

[0020] In at least one embodiment, the insulating layer(s) 14 may be relatively thin. For example, the insulating layer(s) may have a thickness (e.g., average thickness) of 1 to 1,000 μm, or any subrange therein. In one embodiment, the insulating layers 14 may have a thickness of 5 to 500 µm, 5 to 300 µm, 5 to 200 µm, 5 to 150 µm, 5 to 100 µm, 5 to 50 µm, 5 to 25 µm, 10 to 500 µm, 10 to 250 µm, 10 to 150 µm, 25 to 250 µm, 25 to 150 µm, 50 to 250 µm, 100 to 250 µm, or 150 to 250 µm. However, thicknesses outside these ranges may also be possible. In one embodiment, the thickness may be sufficiently thick to provide a continuous layer of resistive material regardless of the surface roughness of the magnetic layers 12.

[0021] The magnetic layers 12 may be formed from any suitable hard or permanent magnetic material. In one embodiment, the magnetic material may include a rare earth (RE) element, such as neodymium or samarium. For example, the magnetic material may be a neodymium-iron-boron (Nd-Fe-B) magnet or a samarium-cobalt (Sm-Co) magnet. The specific magnetic material compositions may include Nd2Fe 14 B or SmCo5, however, it should be understood that variations of these compositions or other permanent magnetic compositions may also be used. Other materials and / or elements may also be included in the magnetic material to enhance the properties of the magnet (e.g., magnetic properties such as coercivity), for example, heavy rare earth elements such as Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0022] The insulating layers 14 can be formed from any suitable material having an electrical resistance greater than that of the magnetic layers 12. In one embodiment, the insulating layers 14 can include a ceramic material. One example of a material that has been tested is calcium fluoride (CaF2). However, it has been found that insulating layers of CaF2 must be relatively thick to ensure adequate resistivity. However, thick layers of CaF2 are brittle and result in a magnet with poor mechanical properties.

[0023] It has been discovered that mixtures of ceramic materials can be used in insulating layers, which may have lower melting points than the individual ceramics. These mixtures can utilize eutectic reactions. Although ceramics tend to have high melting points, the eutectic reaction between ceramics can significantly lower the melting point of a ceramic mixture. Even if the overall composition of a system is not at or near the eutectic point, the melting point at the surface of the mixture's particles can be significantly lowered. For the densification process of ceramics, the formation of a liquid phase can improve the densification rate and therefore increase the cohesive strength of the insulating layers.In liquid-phase sintering, material transport through a continuous liquid grain boundary film is much faster, aided by capillary forces resulting from voids in the liquid located in the interstices between particles. Furthermore, increasing the volume of the liquid phase during sintering can also improve the interaction between the magnetic and insulating layers.

[0024] In one embodiment, the insulating layers may include a mixture (e.g., two or more) of compounds including an alkaline earth metal and a halogen. These compounds may have the formula AH2, where A is an alkaline earth metal and H is a halogen. The alkaline earth metals may include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The halogens may include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). In at least one embodiment, the alkaline earth metal may be calcium and / or magnesium. In at least one embodiment, the halogen may be fluorine (F) or chlorine (Cl). Mixtures may be formed from two or more of any combination of the above. For example, the mixture may include MgF2 and CaF2. A phase diagram showing a mixture of MgF2 and CaF2 is shown in Fig.2. The eutectic temperature for this system is about 980°C, which is much lower than either of the individual melting points of 1410°C (CaF2) and 1252°C (MgF2).

[0025] In addition to compounds of an alkaline earth metal and a halogen, the mixture may include one or more compounds that include an alkali metal and a halogen. The alkali metals may include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs). Accordingly, the mixture may include compounds such as LiF, NaF, KF, LiCl, NaCl, KCl, or any other combination. These compounds may have a formula BH, where B is an alkali metal and H is a halogen. The mixture may also include one or more compounds of other metals, such as transition or basic metals, and halogens. For example, the metals may include aluminum (Al), zirconium (Zr), titanium, or others. The compounds may include AlF3, AlCl3, ZrF4, ZrCl4, or others.

[0026] The above compounds can be mixed in any combination to form binary, ternary, or quaternary systems, or more (e.g., systems having 2, 3, 4, or more constituents). The systems can all include one type of compound (e.g., a binary or ternary system where all are alkaline earth metal-halogen or all are alkali metal-halogen compounds), such as a binary MgF2 and CaF2 system or a ternary LiF-NaF-KF system. Or the systems can be mixed, such as a binary system with one alkaline earth metal-halogen or one alkali metal-halogen compound, or a ternary system with two of one and one of the other. Similarly, metal-halogen compounds can be included in any of the above.

[0027] These binary, ternary, or quaternary, or more systems can be eutectic systems. The overall composition used for the insulating material mixture can be at or near the eutectic point, so that the melting point of the mixture is lower than that of the individual components. For example, the composition can be within a specific molar ratio of the eutectic point, such as 5%, 10%, 15%, 20%, 25%, or 30%. This is easiest to describe for a binary system, such as MgF2 and CaF2. The eutectic point of this system is approximately 50% CaF2 and 50% MgF2; therefore, for a composition within 20% of the eutectic point, the composition can be from 30% to 70% CaF2 and 30% to 70% MgF2.As described above, even if the composition of the mixture is not eutectic, melting may occur at the surface of the particles or powder at temperatures below the melting point. Accordingly, even relatively small amounts of a second or additional compound can enhance sintering. Therefore, the composition may include at least 5 mol%, for example, at least about 10 mol%, 15 mol%, 20 mol%, or 25 mol%, of a second or additional compound. The second or additional compound may be one of the compounds in a binary system. For example, if the second compound in the MgF2 and CaF2 system is present at 20 mol%, the composition may be either 20 mol% MgF2 or 20 mol% CaF2. The same may apply to other binary systems, or to ternary or quaternary systems.

[0028] In other words, the overall composition used for the insulating material mixture may be at or near the eutectic point, so that the melting point of the mixture is at or near the eutectic point temperature. For example, the composition may be configured such that the melting point is within a certain temperature of the eutectic point temperature, such as within 5°C, 10°C, 25°C, 50°C, 75°C, or 100°C. Accordingly, if the composition is configured to have a melting point within 50°C of the eutectic point temperature for a mixture of MgF2 and CaF2 (eutectic point of 980°C), then the composition may have a melting point of 930°C to 1030°C.However, since the eutectic point typically represents a minimum melting point (or at least a local minimum), the composition may have a melting point from the temperature of the eutectic point (980°C) to 1030°C.

[0029] Depending on the composition of the mixtures used for the insulating layers, the melting point can vary. The composition of the insulating material mixture can be configured such that the melting point can be less than or equal to 1100°C, 1050°C, or 1000°C, for example, from 850°C to 1100°C, 850°C to 1000°C, 900°C to 1050°C, 950°C to 1100°C, or 950°C to 1000°C. The melting point of the mixture can be lower than a sintering temperature of the magnetic material. In one embodiment, the sintering temperature of the magnetic material can be from 1000°C to 1100°C, for example, 1025°C to 1075°C or about 1060°C. As described above, even if the composition of the mixture is not a eutectic composition (e.g.a molar ratio of about 1:1 for MgF2 and CaF2), but melting can occur at the surface of the particles or powder, thereby improving the transport of materials and densification during sintering.

[0030] By reducing the melting temperature of the insulating layer material, the cohesive force of the insulating layer can be improved. Increased cohesive force can allow the insulating layer to be thicker without compromising its mechanical properties. Accordingly, the internally segmented magnet can have thicker and therefore more resistive insulating layers while still providing a stable and mechanically sound structure. For example, the insulating layers can have a resistivity of at least 10 6 Ωm, 10 7 Ωm or 10 8 Ωm.

[0031] An example of an internally segmented Nd-Fe-B magnet with an insulating layer of CaF2 + MgF2 is shown in Fig. 3. The mixture of CaF2 and MgF2 had a molar ratio of 3:7 and was sintered at 1060°C for four hours. The effect of the eutectic reaction (right) can be seen from the SEM image when compared to the magnet insulated only by CaF2 (left). There is obvious grain growth in the insulating layer, which includes a mixture of CaF2 and MgF2, which can improve the mechanical properties of the insulating layer and the magnet. In contrast, the CaF2 particles, with a melting temperature significantly higher than the sintering temperature, did not melt, sinter, or undergo grain growth. Accordingly, the insulating layer on the left has very low cohesive strength and is very brittle.

[0032] In another embodiment, the insulating layers may include a mixture of one or more compounds including an alkaline earth metal and a halogen, and one or more metals. The former compounds may have the formula AH2, where A is an alkaline earth metal and H is a halogen. These may be similar to those described above. In general, metals may have a lower melting point than ceramics. In addition, some metals may enhance the magnetic properties of the magnetic material. However, metals typically have very low electrical resistance, and including them in an insulating layer may defeat the purpose of the insulating layer.

[0033] However, it has been discovered that the conductivity of a mixture of metallic and dielectric materials can be controlled by percolation theory. Therefore, the conductivity can be modulated by controlling the amount of metal or alloy powders in the mixture. If the volume ratio of the metallic component is less than a threshold value, the conductivity of the mixture can be close to zero. If the volume ratio of the metallic component is above the threshold value, the conductivity of the mixture of a dielectric and a metallic component can be approximately expressed as: σ~(p−pc)μ

[0034] If µ is the critical exponent that describes the behavior of conductivity with changing volume ratio of metal and insulating materials, p can be seen as the volume ratio of the metal component, and p cis the threshold value indicating the formation of long-range conductivity in the metal phase. Therefore, metallic powders can be mixed with insulating powders to improve the mechanical properties of an internally segmented magnet by enhancing interfacial reaction. If the volume ratio of the metallic powders is below the threshold value, the insulating layer would still be dielectric.

[0035] The metal(s) included in the mixture may have relatively low melting temperatures compared to the ceramic insulating materials and the magnetic materials. For example, the metals may have a melting point lower than the sintering temperature of the magnetic material (e.g., less than 1060°C). Examples of metals that can be mixed with the insulating material mixture include iron, aluminum, copper, gallium (Ga), titanium (Ti), indium (In), rare earth metals (e.g., cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y)), or others. Alloys of the above materials (with each other or with other elements) may also be used.

[0036] A table of resistivity values ​​for various exemplary insulating material mixtures is shown below. The mixtures include CaF2 and varying amounts of iron. As shown, at a point between 15 wt% and 20 wt%, there is a change from dielectric behavior to a measurable resistance. From 5 wt% to 15 wt%, the mixture acts as a dielectric, and from 20 wt% to 40 wt%, the mixture decreases sharply in resistivity. However, including up to 15 wt% of metal in the insulating material can lower the overall melting temperature of the insulating material (which, as described above, improves cohesiveness and interfacial bonding) while also improving the magnetic properties of the magnetic material. These improvements can be achieved without sacrificing the resistivity of the insulating layer.While the mixture has been described with a single AH2 compound, a mixture of compounds, such as those described above, may also be used. As previously described, a mixture of compounds can further reduce the melting temperature of the insulating layer(s). Materials Specific resistance (Ω cm) CaF2+5 wt% Fe nz CaF2+10 wt% Fe nz CaF2+15 wt% Fe nz CaF2+20 wt% Fe 1,501×10 5 CaF2+30 wt% Fe 1,46×10 3 CaF2+40 wt% Fe 2,6×10 4

[0037] In the above embodiments, the insulating layers may be applied or deposited as a suspension or powder onto a magnetic layer. For example, the insulating material may be in a suspension which is then sprayed onto a magnetic layer. Alternatively, the insulating material may be a powder, and the powder may be applied or deposited directly onto a magnetic layer. Accordingly, formation of the magnetic structure prior to sintering may include depositing or depositing a layer of magnetic powder (e.g., Nd-Fe-B powder), for example, in a mold or die, and then applying a layer of insulating material onto the magnetic powder. This process may be repeated to form alternating layers of unsintered magnetic material and insulating material.The layers can be compacted or pressed down before a subsequent layer is applied. Alternatively, the layers can be pressed only after each magnetic layer is applied. In one embodiment, at least the magnetic material can be deposited into the mold or die in a non-reactive atmosphere, such as argon or nitrogen, or protected from oxidation using another method. Once all layers have been deposited, the magnet can be pressed into a green compact and sintered.

[0038] While the above loose or non-rigid application of the insulating layer material (e.g., spray or powder) can be effective, the use of a sheet or other preformed layer for the insulating layer can make it easier to control the thickness and uniformity of the layer. When a loose insulating material is applied to a pressed but unsintered magnetic layer, it can be difficult to ensure a uniform thickness of the insulating layer or to ensure that there are no gaps or cracks in the insulating layer. It has been discovered that a preformed insulating layer, for example, a sheet, can provide improved control of the thickness and uniformity of the insulating layer, as well as easier handling. However, insulating layers can be formed from ceramics, which are very brittle and difficult to fabricate in very thin layers.In addition, these layers can be easily broken during pressing, which can significantly reduce the resistivity.

[0039] With reference to Fig.4 shows a schematic of the assembly of an internally segmented magnet 20. The magnet 20 can be formed with magnetic layers 22, which can be similar to those described above (e.g., powder of Nd-Fe-B), and insulating layers 24, which can be preformed insulating tracks 26. As shown, a first magnetic layer 22 can be deposited, for example, in a mold or die. The magnetic layer 22 can then be pressed, and an insulating track 26 can be applied or inserted on or over the magnetic layer 22 (e.g., in direct contact). Because the track 26 is preformed, it can have a predetermined thickness that is uniform or substantially uniform. After the insulating track 26 is inserted, another magnetic layer 22 can be deposited on or over the insulating track 26 (e.g., in direct contact).This layer of magnetic material may be pressed similarly to the first deposited layer, but heat may be applied during any or all of the pressings performed once the insulating sheet(s) 26 have been inserted. As explained in more detail below, the applied heat may prevent or reduce cracking or tearing of the insulating sheet(s) 26. Additional layers of magnetic material and insulating sheets may be added to the die or mold in alternating sequence to form a finished internally segmented green compact.

[0040] As described above, insulating sheets formed from ceramics are generally brittle and difficult to form into thin layers. It has been discovered that more pliable or moldable insulating sheets can be formed by blending the insulating material with a soft, low-melting-point (LMP) material. The LMP material can act as a binder or adhesive to improve the formability of the sheets, prevent them from cracking / tearing, and improve their handling. In one embodiment, the LMP material can have a melting point slightly above room temperature (e.g., above about 25°C). Accordingly, the LMP material can be solid when the sheet is prepared and handled, but can begin to melt without the application of large amounts of heat. However, processing can be performed below room temperature, so the melting point can be lower than room temperature.In one embodiment, the LMP material may have a melting point of 0°C to 500°C or any subrange therein. For example, the melting point of the LMP material can be from 10°C to 450°C, 20°C to 400°C, 25°C to 400°C, 30°C to 400°C, 30°C to 350°C, 30°C to 300°C, 30°C to 250°C, 30°C to 200°C, 30°C to 150°C, 30°C to 100°C, 35°C to 90°C, 40°C to 90°C, 45°C to 85°C, 45°C to 80°C, 50°C to 80°C, 55°C to 80°C, 55°C to 75°C, 60°C to 75°C, 60°C to 70°C or about 64°C (e.g., ± 3°C).

[0041] In one embodiment, the LMP material may have a relatively low boiling point, which may be lower than a sintering temperature of the magnetic material (e.g., 1060°C). For example, the boiling point of the LMP material may be no higher than 500°C, such as less than or equal to 450°C, 400°C, 350°C, 300°C, 250°C, 200°C, 150°C, 125°C, or 100°C. The boiling point of the LMP material may be from 100°C to 500°C or any subrange therein, such as 100°C to 450°C, 150°C to 400°C, 150°C to 350°C, 150°C to 300°C, 175°C to 300°C, 175°C to 250°C, 175°C to 225°C, or about 200°C (e.g., ± 5°C).

[0042] The ratio of the LMP material to the insulating material mixture can be any suitable amount to bond and retain the insulating material to a web. In one embodiment, the LMP material can be 1 to 50 wt.% of the insulating web, or any subrange therein. For example, the LMP material can comprise 1 to 40 wt.%, 5 to 50 wt.%, 5 to 40 wt.%, 10 to 40 wt.%, 10 to 35 wt.%, 15 to 35 wt.%, 20 to 30 wt.%, or about 25 wt.% (e.g., ± 5 wt.%).

[0043] When mixed with the insulating material (e.g., powders), the adhesive-like LMP materials can combine or bond the powders together. The LMP material and the insulating material can be heated and pressed to form a sheet. The mixture can be heated to a temperature that is above the melting point of the LMP material but below the boiling point of the LMP material. The mixture can be heated to a temperature that is above, but within a certain temperature of, the melting point, such as within 5°C, 10°C, 20°C, or 50°C. For example, if the melting point of the LMP material is 60°C and the mixture is to be heated to within 20°C of the melting point, it can be heated to between 60°C and 80°C. Alternatively, the LMP material can be heated to the above temperatures and then mixed with the insulating material (e.g.,The materials can be mixed, then heated, or heated and then mixed. The sheets can be sized for a specific magnet, or they can be larger and later cut to size. Pressing into a sheet can increase the density of the insulating materials and therefore the resistivity of the magnet.

[0044] After the tracks are pressed and (if necessary) sized, they can be inserted into a mold or die on top of a pressed magnetic layer (e.g., Nd-Fe-B powder). Another layer of magnetic material can be deposited on top of the insulating track, and then the layers can be pressed. As described with reference to Fig.As described in Figure 4, the pressing may be a "hot" pressing. Any pressing performed on the unsintered magnet stack that includes one or more insulating tracks may be a hot pressing. The temperature of the hot pressing may be close to, but below, the melting point of the LMP material. This may soften the insulating track and cause the tracks to have increased formability during the hot pressing process.

[0045] In one embodiment, the hot press may have a temperature that is from 50% to 99% of the melting point of the LMP material, or any subrange therein. For example, the hot press may have a temperature that is from 60% to 99%, 70% to 99%, 75% to 99%, 80% to 99%, 85% to 99%, or 90% to 99% of the melting point of the LMP material. In other words, the hot press may be performed at a temperature that is within, but below, a certain number of degrees of the LMP material melting point. In one embodiment, the hot press may be performed at a temperature that is within, but below, 100, 75, 50, 40, 30, 20, or 10 degrees of the LMP material melting point. In another embodiment, the hot press may have a temperature that is above the melting point of the LMP material.

[0046] Once the alternating layers of magnetic powder and insulating sheets have been pressed into a finished green compact, the magnet can be sintered. Accordingly, the bonding between the magnetic and insulating layers can occur without any adhesive or resin, such as polymers or epoxies. The insulating layer, in one embodiment, can consist of only inorganic materials (e.g., ceramics) and metal(s). As described above, the sintering temperature can depend on the composition of the magnetic material. In one embodiment, the sintering temperature of the magnetic material can be from 1000°C to 1100°C, for example, 1025°C to 1075°C, or about 1060°C. However, other sintering temperatures can be used depending on the material.Because the LMP material may have a boiling point below the sintering temperature, the LMP material may evaporate during the sintering process. This may leave the insulating material behind to form a high-resistivity layer(s) between the magnetic layers, thereby reducing eddy current losses.

[0047] In one embodiment, the sintering temperature may be ramped up slowly, or there may be a two-stage sintering process with a lower temperature and a higher temperature. This may prevent the LMP material from evaporating quickly, which can render the remaining insulating layer unstable. If, instead, the LMP material is heated slowly or initially to a lower temperature, the insulating material within the insulating layer may be allowed to rearrange and therefore be more stable as the LMP material evaporates. The lower temperature may be close to or above the boiling point of the LMP material, but below the melting point of any phases of the magnet.

[0048] In the preformed sheet embodiments, the insulating material(s) may be any of the materials or material mixtures disclosed above. For example, the insulating material may be a mixture of MgF2 and CaF2 powders or a mixture of an AH2 compound and one or more metals (e.g., Fe, Al, Cu, Re). The adhesive-like or LMP material may be any material that has the disclosed relatively low melting point and relatively low boiling point. The LMP material may be a wax, which may be natural or synthetic. Examples of typical waxes that may be used include animal waxes (e.g., beeswax), vegetable waxes (e.g., carnauba wax), mineral waxes (e.g., peat wax), mineral oil waxes (e.g., paraffin wax), or synthetic waxes (e.g., polyethylene wax). The LMP material may contain other materials, such as thermoplastics (e.g.,polyolefins, such as PE or PP), or be formed from them.

[0049] In an example given in Fig. As shown in Figure 5, a magnet was formed having two Nd-Fe-B magnetic layers separated by an insulating layer.

[0050] The insulating layer included beeswax as the LMP material, which has a melting point of 64°C and a boiling point of 200°C, meaning it evaporates at 200°C. The preformed sheet was prepared by mixing the beeswax with a mixture of CaF2 and MgF2 powders at a ratio of 2:8 (e.g., approximately 20 mol% CaF2). The ratio of LMP material to insulating material (a mixture of MgF2 and CaF2) was 1:3. The insulating sheet mixture was then heated to 80°C and pressed. The layer thickness was approximately 150 µm. The insulating sheet was placed on top of a first pressed segment of Nd-Fe-B magnetic powder, and then Nd-Fe-B powder was placed on top of the insulating sheet and pressed. The second / final pressing was performed at a temperature of 30°C. The green compact was then sintered for 30 minutes at 220°C and then for four hours at 1060°C.The sintered magnet produced according to the above steps is . Fig. 5 shown.

[0051] The disclosed magnets can be used in any magnetic application where hard / permanent magnets are used. The magnets can be useful where eddy currents are generated. In one embodiment, the magnets can be used in electric motors or generators, such as those in hybrid or electric vehicles. The disclosed magnets and methods for forming them can reduce the temperature of the magnet, so a lower coercive force is required for the magnet. Therefore, fewer HRE materials are required, reducing the cost of electric motors. It also saves energy, which can increase the MPG (miles per gallon) or electric range of electric vehicles. The internally segmented magnet and method can also reduce the machining costs associated with externally segmented magnets.

[0052] While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. Furthermore, the features of various implementations may be combined to form further embodiments of the invention.

[0053] It further describes: A. Internally segmented magnet comprising: a first layer of a permanent magnetic material; a second layer of a permanent magnetic material; and an insulating layer separating the first and second layers and including a ceramic mixture of at least a first ceramic material and a second ceramic material, the mixture having a melting point of up to 1100°C. B. The magnet of A, wherein the first or second ceramic material includes a compound having the formula AH2, where A is an alkaline earth metal and H is a halogen. C. Magnet according to B, wherein the halogen is fluorine or chlorine and the alkaline earth metal is selected from the group consisting of magnesium (Mg), calcium (Ca) and strontium (Sr). D. The magnet of A, wherein the first or second ceramic material includes a compound having the formula MH3, where M is a metal having an oxidation number of +3 and H is a halogen. E. The magnet of A, wherein the first or second ceramic material includes a compound having the formula BH, where B is an alkali metal and H is a halogen. F. The magnet of A, wherein the ceramic mixture has a melting point lower than a melting point of both the first and second ceramic materials. G. The magnet of A, wherein the insulating layer further includes a metal or a metal alloy. H. Magnet according to G, wherein the metal or metal alloy includes iron, aluminum, copper, rare earth metals or alloys thereof. I. Magnet according to G, wherein the metal comprises less than 20 wt.% of the insulating layer. J. A method of forming an internally segmented magnet comprising: forming a first layer of a powdered permanent magnetic material; depositing an insulating layer over the first layer including a ceramic mixture of at least a first ceramic material and a second ceramic material; depositing a second layer of powdered permanent magnetic material over the insulating layer to form an internally segmented magnetic stack; and the sintering of the magnet stack. K. The method of J, wherein the first and second ceramic materials are selected from a group consisting of: a compound having the formula AH2, where A is an alkaline earth metal and H is a halogen; a compound having the formula MH3, where M is a metal having an oxidation number of +3 and H is a halogen; and a compound having the formula BH, where B is an alkali metal and H is a halogen. L. The method of J, wherein the ceramic mixture has a melting point lower than a melting point of both the first and second ceramic materials. M. The method of J, wherein the insulating layer further includes a metal or a metal alloy. N. The process of M, wherein the metal or metal alloy includes iron, aluminum, copper, rare earth metals or alloys thereof and the metal comprises less than 20 wt.% of the mixture. O. The method of J, wherein the insulating layer further includes a low melting point (LMP) material having a melting point of 30°C to 400°C. P. The method of O, wherein the LMP material has a boiling point lower than a sintering temperature of the sintering step. Q. Method according to O, wherein the insulating layer is pressed into a web before the first deposition step. R. The method of Q, wherein the insulating layer is pressed into the web at a temperature greater than the melting point of the LMP material and less than the boiling point of the LMP material. S. The method of P, further comprising a hot pressing step prior to the sintering step, wherein the hot pressing step includes heating the magnet stack to a temperature below the melting point of the LMP material. T. Internally segmented magnetic blank comprising: a first layer of a powdered permanent magnetic material; a second layer of a powdered permanent magnetic material; and an insulating layer separating the first and second layers and including: a ceramic mixture of at least a first ceramic material and a second ceramic material; and a low melting point material (LMP) that has a melting point of 30°C to 400°C.

Claims

[1] Internally segmented magnet comprising: a first layer of a permanent magnetic material; a second layer of a permanent magnetic material; and an insulating layer separating the first and second layers and consisting of a binary ceramic mixture with a molar ratio of 30% to 70% CaF2 and 30% to 70% MgF2 and 5% to 15% by weight of iron.

Images