Manufacturing method for high-coercivity magnets

Abstract

The present invention is a method for manufacturing a high coercivity magnet, comprising the following steps: a) - Magnetic phase TR2Fe 14 First powder containing crystal grains of B, - heavy rare earth elements and magnetic phase TR2Fe 14 The present invention relates to a manufacturing method comprising the steps of: a) preparing a second powder containing crystal grains of B; b) subjecting the second powder to a hydrogenation-disproportionation treatment; c) mixing the first powder with the second powder obtained at the end of step b); d) subjecting the mixture obtained at the end of step c) to a compression step to obtain a compressed portion; e) subjecting the compressed portion obtained at the end of step d) to a pre-calcination step; and f) subjecting the pre-calcined portion obtained at the end of step e) to a calcination step.

Description

[Technical Field]

[0001] This invention relates to a method for producing high-coercivity magnets, preferably from recycled magnets. More specifically, this invention relates to TRFeB-based permanent magnets. [Background technology]

[0002] In the context of this invention, "high coercivity magnet" means a magnet whose coercivity exceeds 1400 kA / m at room temperature.

[0003] In the context of this invention, "TR" means an element selected from rare earth elements (especially rare earth elements: La, Ce, Pr, Nd, Dy, Gd, Tb, Ho) or a combination of two or more elements.

[0004] TR is primarily neodymium (Nd). Therefore, the most common example of these permanent magnets is the crystalline phase Nd2Fe. 14 This is an NdFeB-based magnet, an alloy of neodymium, iron, and boron in which B is the dominant phase, i.e., it forms a tetragonal crystal system.

[0005] Due to their excellent magnetic properties, including good coercivity (i.e., resistance to demagnetization) and high residual magnetism (i.e., high magnetic force), NdFeB-based permanent magnets are commonly used in a variety of applications, particularly in motors for electric or hybrid vehicles, electrical equipment (e.g., household appliances or air conditioning equipment), electronic devices (e.g., hard drives), and magnets for wind turbine motors.

[0006] However, given the current issues of environmental protection and the depletion of natural resources, particularly rare earth elements, in order to satisfy the ever-increasing demand for these permanent magnets for these various prior arts, which may exceed supply forecasts, it is necessary to limit the manufacture of these magnets to only virgin materials extracted from reserves, so that the magnets contained in these various devices, apparatuses, or motors can be recycled immediately and efficiently when these devices become obsolete.

[0007] In the context of this invention, "recycled magnets" means - Magnets recovered for reuse purposes from equipment, devices, motors, or other products containing magnets that are no longer in use (e.g., during waste sorting operations). - Magnets that correspond to manufacturing scrap, for example, scrap from the manufacturing of magnets (because they are particularly defective), and therefore magnets that correspond to recycled manufacturing scrap. It means...

[0008] There are various recycling routes for NdFeB-based permanent magnets.

[0009] One of these channels is so-called "direct" recycling, where magnets recovered after one or more surface and mechanical treatments (e.g., from end-of-life equipment) are reused in block form. In other words, through this route, magnets are manufactured directly from recycled magnets. There are no essential treatments that would alter the physicochemical properties of the recycled magnets, other than simple light surface treatment or cutting to achieve the desired shape. However, it is possible to modify the physicochemical properties, and therefore the magnetic properties, mainly coercivity, of these magnets by performing rare-earth diffusion treatments from their surfaces.

[0010] The second recycling route is a so-called "indirect" or "long" route in which the chemical elements constituting the recovered magnets (e.g., from end-of-life equipment) are separated in the form of oxides through dry or wet smelting processes. These resulting oxides are then reintroduced upstream into the production of new magnets as raw materials in the synthesis of metals and subsequent precursor alloys.

[0011] A third known recycling route is the so-called "powder" route, which involves reducing recovered magnets (e.g., those from end-of-life devices) into a powder. These powders are then diluted in a polymer to produce bonded magnets, or they are densified by heat treatment to obtain sintered magnets.

[0012] The so-called "powder" route has the advantage of allowing for a certain degree of freedom in the final shape of new magnets, as it is possible to readjust the composition of new magnets manufactured from recycled magnets using mixtures of various powders. Furthermore, in the case of sintered magnets, this recycling route is based on a powder metallurgy magnet manufacturing process that is already implemented and fully controlled.

[0013] However, this so-called "powder" recycling route (and the so-called "direct" route) does not allow for the optimal utilization of heavy rare earth elements (Dy or Tb) that substantially exist as substitutes for neodymium (and to a lesser extent, praseodymium) in the magnetic phase of certain permanent magnets to improve their coercivity and temperature resistance. For example, the Dy content can increase to an average of up to 10 mass% at operating temperatures of 150 to 180°C. This is because heavy rare earth elements can increase the magnetic crystal anisotropy of the magnetic phase, and therefore its demagnetizing resistance. In this regard, the two categories of rare earth elements are as follows: - Heavy rare earth elements including europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y), - Light rare earth elements including lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), and samarium (Sm) It should be remembered that they are distinguished as such.

[0014] Magnetic phase TR2Fe 14Methods for manufacturing permanent magnets containing heavy rare earth elements are known, in which the replacement of the entire neodymium (and, to a relatively small amount, praseodymium) with heavy rare earth elements is achieved by using a mixture of powders with low and high heavy rare earth content, or by a reduction in residual magnetism that can be limited by diffusing the heavy rare earth elements from the surface of the sintered magnet and along the grain junctions. In this way, the heavy rare earth elements are preferably localized around the magnetic grains, i.e., in the region where demagnetization is most critical, to obtain a structure known as a "core-shell". Thus, the region around the magnetic grains is the region in which the heavy rare earth elements have diffused during the manufacture of the magnet.

[0015] In other words, knowledge regarding the manufacturing method of magnets containing heavy rare earth elements highlights the importance of including heavy rare earth elements in the peripheral regions of magnetic crystal grains to improve the increased magnetic performance of the magnets obtained in this way, while also having the advantage of limiting the amount of heavy rare earth elements required for their manufacture.

[0016] However, during the so-called "powder" recycling route, it is possible to co-sinter several types of powder, and at least one type of powder among them may be obtained from recycled magnets that originally contained heavy rare earth elements. However, in this case, since a large proportion of these heavy rare earth elements may not be able to diffuse out of the crystal grains, they may remain in the magnetic phase of the powder rather than providing the core-shell effect around the crystal grains that initially did not contain heavy rare earth elements. Therefore, in order to obtain magnetic performance equivalent to that obtained by a method for producing a permanent magnet containing heavy rare earth elements derived from virgin raw materials, it is known to add heavy rare earth elements derived from a main supply source (in other words, heavy rare earth deposits) during this so-called "powder" recycling route. Alternatively, when it is desired to recycle magnets rich in heavy rare earth elements (usually with a content exceeding 2.5% by mass), it is also known to mix a first powder derived from these recycled heavy rare earth-rich magnets with a second powder that does not contain heavy rare earth elements, or at least has a low content of heavy rare earth elements (usually with a content of less than 1% by mass). The step of co-sintering these two types of powder only diffuses a small portion of the heavy rare earth elements contained in the first powder. The increase in coercive force achieved by the mixture of the above powders is on the order of 150 kA / m per percentage of added heavy rare earth elements. Summary of the Invention Problem to be Solved by the Invention

[0017] The inventors of the present invention have sought to optimize the utilization of heavy rare earth elements present in permanent magnets recycled through the so-called "powder" recycling route.

[0018] Accordingly, the present inventors aim to improve the so-called "powder" recycling route by presenting a novel method for producing a high-coercivity magnet that is of the TRFeB type and contains heavy rare earth elements, preferably from recycled permanent magnets. This novel production method relies on this recycling route, and further has other unique technical features detailed below, which enable: - obtaining a magnet having high magnetic performance (i.e., excellent coercivity while maintaining high residual magnetism) without necessarily adding heavy rare earths derived from virgin raw materials (for example, derived from deposits), which minimizes environmental load and has higher energy efficiency, - optimally reprocessing a permanent magnet containing a high content (for example, between 2.5% by mass and 10% by mass) of heavy rare earths derived from end-of-life devices (that is, recycled magnets), - enabling the use of 10% to 50% by mass of recycled magnet powder relative to the total mass of the powder used for producing the magnet, - enabling the use of existing production lines for magnet manufacturing. [Means for Solving the Problem]

[0019] A method for producing a high-coercivity magnet, preferably a method for producing a high-coercivity magnet from recycled magnets, relies on a so-called "powder" recycling route. In order to obtain good coercivity while maintaining high residual magnetism, and further by optimizing the magnetic performance of the recycled magnets containing the above-mentioned heavy rare earths compared to their magnetic performance, the method enables obtaining a magnet in which heavy rare earths are present around crystal grains of a magnetic phase. [Mode for Carrying Out the Invention]

[0020] The present invention provides a method for producing a high-coercivity magnet (preferably derived from recycled magnets), comprising at least the following steps: a) - a first powder comprising magnetic phase TR₂Fe 14 B crystal grains, a grain boundary phase rich in metal-based compounds and rare earths, and optionally crystal grains of non-magnetic phase TRFe₄B₄, wherein the first powder contains no heavy rare earths, or a mass content of heavy rare earths expressed relative to the mass of the first powder is less than 1%; - a second powder containing heavy rare earths (preferably obtained from recycled magnets), wherein a mass content of heavy rare earths expressed relative to the mass of the second powder is between 1% and 10%, preferably between 2% and 5%, and the second powder comprises magnetic phase TR₂Fe 14A second powder containing crystal grains of B. The process of preparing, b) The second powder is subjected to a hydrogenation-disproportionation treatment to obtain the magnetic phase TR2Fe 14 B is chemical formula TRH x The process involves decomposing a rare earth hydride, in which x is the atomic ratio H / TR, for example between 2 and 3, into a mixture containing iron, iron boride (Fe2B), and a so-called beta phase containing TR, iron, and boron, wherein the above hydrogenation-disproportionation treatment is performed - Temperature between 850°C and 950°C and hydrogen pressure between 0.3 bar and less than 0.5 bar, - Or a temperature between 925°C and 1025°C and a hydrogen pressure of 0.5 bar or more but less than 1 bar, - Or a temperature between 950°C and 1100°C and a hydrogen pressure of 1 bar or more and 10 bar or less. The process to be carried out in one of the following locations, c) A step of mixing the first powder with the second powder obtained at the end of step b) in a mass ratio that depends on the heavy rare earth content of the second powder to obtain a mixture, d) A step of subjecting the mixture obtained at the end of step c) to a compression step to obtain a compressed portion, e) A step of subjecting the compressed portion obtained at the end of step d) to a pre-firing step, wherein the pre-firing step is the following sub-step: - A sub-step involves heating from room temperature to a first temperature between 200°C and 400°C at a heating rate of 1°C to 5°C / minute, - A sub-step in which the temperature is maintained at the above first temperature between 200°C and 400°C for a period of time between 1 and 3 hours, - A sub-step involves heating from a first temperature between 200°C and 400°C to a second temperature between 400°C and 500°C at a heating rate of 1°C to 5°C / minute, - A sub-step involves maintaining the temperature at the second temperature between 400°C and 500°C for a period of time between 1 and 3 hours. - A sub-step involves heating from the second temperature between 400°C and 500°C to a third temperature between 550°C and 650°C at a heating rate of 1°C to 5°C / min, - A sub-step in which the temperature is maintained at the above third temperature between 550°C and 650°C for a period of time between 1 and 3 hours, - A sub-step involves heating from the third temperature between 550°C and 650°C to a fourth temperature between 650°C and 750°C at a heating rate of 5°C to 10°C / min, - A sub-step in which the temperature is maintained at the above fourth temperature between 650°C and 750°C for a period of time between 10 and 30 minutes. Processes including, f) A step of obtaining a magnet by subjecting the pre-fired portion obtained at the end of step e) to a firing step, wherein the above firing step is the following sub-step: - A sub-step involves heating from the fourth temperature between 650°C and 750°C to a fifth temperature between 850°C and 1050°C at a heating rate of 5°C to 25°C / min, - A sub-step in which the temperature is maintained at the above fifth temperature between 850°C and 1050°C for a period of time between 2 and 24 hours. Processes and This includes methods.

[0021] Since the second powder contains heavy rare earth elements, heavy rare earth hydrides are formed during step b) of the manufacturing method according to the present invention.

[0022] The mass ratio in step c) can be determined as follows. For example, if the second powder contains X% heavy rare earth elements and a total content of Y% is desired in the final magnet, then the mass ratio of the mass m2 of the second powder to the mass m1 of the first powder is m2 / m1 = Y / (XY).

[0023] During step f) of calcining the mixture of the first powder and the second powder, the first powder contains various metal-based compounds, a TR-rich phase, and a magnetic phase TR2Fe. 14A liquid phase is formed (by a eutectic reaction) between B and optional non-magnetic phase TRFe₄B₄. This liquid phase has a high mass content of rare earths, on the order of 90 mass% at 700°C, 80 mass% at 900°C and 70 mass% at 1000°C. During temperature rise under vacuum, the rare-earth hydrides formed in step b), especially heavy rare-earth hydrides, dissolve in said liquid phase and are converted into heavy rare-earth metals, increasing their concentration in the liquid phase. Then, these heavy rare earths, which are in the form of heavy rare-earth metals, can form a so-called "core-shell" structure around the crystal grains of the first powder during the densification of the first powder and the second powder that occurs during the sintering step, as described above.

[0024] Thus, thanks to step b) of the production method according to the present invention, the heavy rare earths present in the second powder (preferably the second powder obtained from recycled magnets) are extracted from the magnetic phase while being converted into hydrides. This increases the chemical activity of the heavy rare earths. The reason for this is that when the temperature rises under vacuum during the sintering step, conversion of these hydrides to heavy rare-earth metals can occur in the liquid phase, which is also formed during the sintering step.

[0025] In this way, step b) of the production process according to the present invention allows these heavy rare earths to be extracted from the magnetic phase TR₂Fe of the second powder 14 to be distributed into the B crystal grains via a diffusion step, which is a low-speed process and can form a concentration gradient in the heavy rare earth-rich crystal grains of the second powder. This can ultimately make it possible to reprocess only a small amount of said heavy rare earths. Furthermore, in the diffusion in this case, the heavy rare earth content around the crystal grains of the first powder can be lower than the heavy rare earth content in the crystal grains of the second powder.

[0026] Conversely, according to the production method of the present invention, extraction of heavy rare earths from the magnetic phase of the second powder increases their chemical potential. At the end of step f), the heavy rare earths have a higher content in the magnetic phase TR₂Fe of the first powder than the heavy rare earth content in the crystal grains of the second powder (preferably obtained from recycled magnets) 14It is present around the crystal grains of B, and the coercivity of the magnet obtained in this way increases significantly, while the magnet contains a small amount of heavy rare earth elements.

[0027] During the pre-calcination step e), the compressed section obtained at the end of step d) is dehydrated. This operation aims to remove almost all of the hydrogen contained in the compressed section. Hydrogen is substantially TRH with x around 2. x It exists in the form of a hydride. The purpose is to reduce the overall hydrogen content in the compressed section, from, for example, on the order of 2000 ppm (0.2 mass%) to, for example, less than 100 ppm (0.01 mass%), preferably less than 50 ppm (0.005 mass%). This operation results in better magnetic properties after firing.

[0028] More specifically, in order to properly dissolve NdFeB magnets, the hydrogen present inside must first be completely removed before optimal densification can occur. This hydrogen desorption is carried out during the pre-sintering step e). However, the magnetic phase Nd2Fe 14 It is known that the recombination of B can occur simultaneously with the total desorption of hydrogen. This is problematic because heavy rare earth elements may be re-trapped in the magnetic phase, making it difficult to diffuse the crystal grains of the first powder around them. In that case, the advantages provided by the hydrogenation-disproportionation step b) may be lost even before reaching the calcination step.

[0029] To overcome this problem, the magnetic phase Nd2Fe is used as much as possible. 14 This is why it is essential to ensure that there is no correlation between the recombination of crystal grains B and hydrogen desorption.

[0030] Contrary to all predictions, the inventors discovered that the selection of temperature and pressure intervals in step b) detailed above makes it possible to obtain a beta phase in which the mass content expressed relative to the total mass of the second powder can be advantageously between 5% and 50%. This beta phase contains almost all boron. However, the presence of almost all boron in the beta phase extends its diffusion distance during the calcination process, which is the magnetic phase Nd2Fe14 This contributes to the loss of correlation between the recombination of crystal grains B and hydrogen desorption.

[0031] Furthermore, the selection of temperature and pressure intervals in step b) makes it possible to obtain micron-sized crystal grains, preferably ranging from 1 μm to 20 μm, at the end of step b). This micron size extends the diffusion distance of boron, iron, and rare earth elements during the firing process, thereby avoiding premature recombination of the crystal grains and allowing for proper diffusion of heavy rare earth elements around the crystal grains.

[0032] Finally, and surprisingly, the inventors discovered that performing the pre-calcination steps e) and f) described above also contributes to the desorption of hydrogen without recombining the magnetic phase.

[0033] More specifically, carrying out these pre-calcination steps e) and calcination steps f) according to the parameters described above maximizes the amount of heavy rare earth elements in the liquid phase immediately after desorption is complete, and, as a further advantage, allows the calcination level to be reached as quickly as possible thanks to the heating gradient to reach this stage described above. This is because, as explained above, the heavy rare earth hydrides are converted to heavy rare earth metals, allowing the heavy rare earth elements to diffuse around the crystal grains of the first powder.

[0034] Thus, thanks to the selection of the above-mentioned parameters for carrying out the hydrogenation-disproportionation step b), and the pre-calcination step e) and calcination step f), the originality of the present invention lies in the magnetic phase Nd2Fe 14 The objective is to eliminate the correlation between the recombination of crystal grains in B and hydrogen desorption.

[0035] In the context of the present invention, a further advantage is that the first and second powders are co-calcined at a lower temperature, where the heavy rare earth elements are already present in the magnetic phase TR2Fe of the second powder. 14This is because it was extracted from the crystal grains of B. Therefore, it is possible to place the heavy rare earth elements at the outermost periphery of the crystal grains of the first powder, and in this way a very distinctive "core-shell" structure is obtained that can exceed the increase in coercivity obtained by a magnet added at a certain amount of heavy rare earth elements, i.e., a mass of 150 kA / m when approximately 1 mass% of heavy rare earth elements is added.

[0036] This increase in dilution from the manufacturing method according to the present invention is particularly interesting because it allows for the consideration of short-term recycling of recycled magnets rich in heavy rare earth elements, which are expected to remain limited in the future, and because it enables the production of large quantities of highly magnetically efficient magnets with minimal supply of essential raw materials.

[0037] The technical features of the manufacturing method according to the present invention are described in more detail below.

[0038] In the context of the present invention, "grain boundary phase rich in TR" means a metallic phase containing more than 70% by mass of rare earth elements in combination with a metal, such as a metal selected from iron, copper, and aluminum.

[0039] The first powder metal-based compound may contain a metal selected from iron, copper, aluminum, gallium, titanium, and zirconium.

[0040] The first powder is expressed as a mass percentage relative to the mass of the first powder. - TR2Fe between 90% and 99%, preferably between 95% and 97% 14 Crystal grains of the magnetic phase of system B, - Between 0.5% and 3%, preferably between 0.5% and 2%, a metal-based compound. - A grain boundary phase rich in rare earth elements, preferably between 1% and 10%, and preferably between 2% and 5%. - Optionally, 0.1% to 5%, preferably 0.1% to 1%, of the non-magnetic phase grains of the TRFe4B4 system. It may also include.

[0041] The first powder is expressed as a mass percentage relative to the mass of the first powder. - Rare earth elements between 27% and 35% - Boron between 0.9% and 1.2% - At least one metallic element M selected from the group consisting of Fe, Co, and Ni, either alone or in a mixture thereof, making up to 100% of the remainder, wherein the combined mass percentage of Ni and Co is 5% or less, and optionally, either alone or in a mixture thereof, Fe is partially replaced by at least one substitutional element selected from the group consisting of Al, Cu, Ga, Nb, Zr, Ti, Mo, V, Hf, Ta, W, and Sn, with the content of the substitutional element being 3% or less, wherein at least one metallic element M It may also include.

[0042] As explained above, the mass content of heavy rare earth elements is 1% or less in the first powder.

[0043] The particle size of the first powder is preferably between 3 μm and 7 μm.

[0044] The first powder is, - Virgin raw materials (e.g., pure metals and / or alloys) that contain no heavy rare earth elements at all, or whose mass content is less than 1%, or - Recycled magnets that contain no heavy rare earth elements at all, or whose mass content is less than 1%, or - A mixture of virgin raw materials containing no heavy rare earth elements or less than 1% by mass, and recycled magnets. It may also be obtained from [another source].

[0045] If the first powder is obtained whole or partially from virgin raw materials, the latter is selected from pure metals and / or alloys. These are preferably pure metals.

[0046] If the first powder is obtained whole or partially from virgin material, the latter is processed as follows: - Casting process on the wheel, followed by - Decrepitation and / or gas jet milling (also known as jet milling) process under hydrogen. It may also be used for that purpose.

[0047] First, a mixture of virgin raw materials (in other words, "base inputs") is heated to a temperature, preferably between 1350°C and 1550°C, preferably under the partial pressure of a neutral gas or under vacuum, to obtain a molten material bath.

[0048] Next, the molten material bath is poured onto a cooled rotating wheel. This causes the molten material to solidify due to quenching. The cooling rate may be between 500 K / sec and 5000 K / sec. The thickness of the resulting molten strip may be between 0.1 and 0.5 mm, preferably between 0.15 and 0.35 mm.

[0049] The decrepitation process under hydrogen conditions makes it possible to obtain a first powder with a particle size ranging from 50 μm to several millimeters.

[0050] Declepitation under hydrogen conditions may be carried out at temperatures between 10°C and 500°C, preferably between 20°C and 150°C, and at hydrogen pressures between 0.01 MPa and 5 MPa, preferably between 0.08 MPa and 0.25 MPa.

[0051] The duration of the decrepitation process under hydrogen may be between 1 and 5 hours.

[0052] The gas jet milling process makes it possible to obtain a first powder in which the median diameter is between 2 μm and 10 μm, preferably between 3 μm and 6 μm, and the ratio of the particle size of 90% of the total particles to the particle size of 10%, or in other words, the "D90 / D10" ratio is less than 10, preferably less than 5. Commercial equipment such as mills sold by Hosokawa-Alpine under trade names AFG100, AFG200 and AFG400 can be used in this gas jet milling process. They include a sealed chamber in which an inert gas is introduced through three tapered nozzles under a pressure between 2 and 8 bar, allowing control of the feed rate of the powder to be milled by a hopper. The powder is released by riding on the gas stream and passing through a vortex created by a system called a "cyclone". To improve particle size, the equipment may incorporate an inertial selector to prevent the largest particles from leaving the milling chamber.

[0053] If the first powder is obtained from a magnet that has been recycled whole or partially, the latter may have been subjected to a decrepitation and / or gas jet milling process under hydrogen.

[0054] The technical characteristics of the hydrogen decrepitation and gas jet milling processes may be described in the case of obtaining a first powder from virgin raw materials.

[0055] In step c) of the manufacturing method according to the present invention, in order to facilitate mixing of the first powder with the second powder, it is preferable that the particle size of the second powder be the same as that of the first powder. The particle size of the second powder is preferably between 3 μm and 7 μm.

[0056] The second powder is expressed as a mass percentage relative to the mass of the second powder mentioned above. - 27% to 35% rare earth elements, including heavy rare earth elements between 1% and 10%, preferably between 2% and 5%. - Boron between 0.9% and 1.2% - At least one metallic element M selected from the group consisting of Fe, Co, and Ni, either alone or in a mixture thereof, making up to 100% of the remainder, wherein the combined mass percentage of Ni and Co is 5% or less, and optionally, either alone or in a mixture thereof, Fe is partially replaced by at least one substitutional element selected from the group consisting of Al, Cu, Ga, Nb, Zr, Ti, Mo, V, Hf, Ta, W, and Sn, with the content of the substitutional element being 3% or less, wherein at least one metallic element M It may also include.

[0057] This means that the second powder contains heavy rare earth elements in a mass percentage of 1% to 10%, preferably 2% to 5%, relative to the mass of the second powder.

[0058] The second powder is, - Virgin raw materials (e.g., pure metals and / or alloys) having a heavy rare earth content of 1% to 10%, preferably 2% to 5%, or - Recycled magnets having a heavy rare earth content of 1% to 10%, preferably 2% to 5%, or - A mixture of virgin raw materials and recycled magnets, with a heavy rare earth content between 1% and 10%, preferably between 2% and 5%. It may also be derived from [another source].

[0059] As explained above, the magnet manufacturing method according to the present invention preferably uses recycled magnets.

[0060] Therefore, in a preferred embodiment of the present invention, the second powder is obtained solely from recycled magnets. These recycled magnets contain heavy rare earth elements. The mass percentage of these heavy rare earth elements relative to the mass of the second powder is between 1% and 10%, preferably between 2% and 5%.

[0061] Advantageously, the second powder is subjected to the following treatment: - Decrepitation process under hydrogen, optionally followed by - Gas jet milling It is obtained from recycled magnets that were used for [a specific purpose].

[0062] The decrepitation process under hydrogen conditions makes it possible to obtain a second coarse powder with a particle size ranging from 50 μm to several millimeters.

[0063] The technical features of the hydrogen decrepitation and gas jet milling steps for obtaining the second powder may be described in the case of obtaining the first powder from virgin raw materials or recycled magnets.

[0064] If the second powder is obtained whole or in part from recycled magnets, the latter may be subjected to a hydrogen decrepitation and / or gas jet milling process. The technical features of the hydrogen decrepitation and gas jet milling process may be described for the case in which the first powder is obtained from virgin raw materials.

[0065] If the second powder is obtained whole or partially from virgin material, the latter is processed as follows: - Casting process on the wheel, followed by - Decrepitation and / or gas jet milling process under hydrogen conditions It may also be used for that purpose.

[0066] The technical characteristics of the wheel-based casting process, the declépitation process under hydrogen, and the gas jet milling process may be those described above for obtaining the first powder from virgin raw materials.

[0067] The hydrogenation-disproportionation treatment can be carried out under vacuum, i.e., by heating the second powder to the above temperature under vacuum before introducing hydrogen. In another embodiment of the present invention, the second powder is heated to the above temperature after introducing hydrogen.

[0068] The second powder may be heated at a heating rate between 1°C / min and 30°C / min until the desired temperature is obtained in step b) as described above.

[0069] In step b), the above temperature is preferable because it does not cause aggregation between particles.

[0070] In step b), the above pressure is appropriate because it does not cause loss of the magnet's texture.

[0071] For example, at a pressure of 0.8 bar, the processing temperature in step b) may be between 925°C and 1025°C.

[0072] The hydrogenation-disproportionation treatment time may range from 10 minutes to 3 hours. This time depends on the hydrogenation-disproportionation treatment temperature, being shorter at higher temperatures. This is because excessively long treatment times at high temperatures can introduce visible inhomogeneities into the microstructure of the magnets produced by the manufacturing method.

[0073] At the end of the hydrogenation-disproportionation treatment, the elements recombine to form the magnetic phase TR2Fe. 14 This prevents the reformation of B, thereby maintaining the chemical formula TRH until room temperature (i.e., approximately 20°C). x In order to preserve the mixture of rare earth hydrides, iron, iron boride (Fe2B), and the beta phase, the second powder can be cooled under hydrogen.

[0074] Optionally, before carrying out step c) of the manufacturing method according to the present invention, the second powder is broken up to improve contact between the rare earth hydride and the liquid phase during step f) so that the heavy rare earth metal dissolves best in the liquid phase. This step may be necessary not only if the particles of the second powder reaggregate during the hydrogenation-disproportionation treatment, but also if their microstructure is suboptimal, i.e., if the hydride is located within the grains rather than around them. The second powder may be broken up by at least one grinding method selected from gas jet milling, planetary milling, attrition milling, and cryogenic milling.

[0075] The mixing step c) of the first powder and the second powder obtained after step b) is advantageously carried out for at least 30 minutes, preferably more than 1 hour, in order to obtain a homogeneous mixture.

[0076] The mixture obtained at the end of step c) may be poured into a mold (having the negative shape of the magnet to be manufactured) to carry out step d) compression.

[0077] The compression step d) may be carried out using transverse compression, axial compression, cold isostatic pressing, or isostatic pressing using rubber (also known as "RIP," an acronym for "Rubber Isostatic Pressing") to obtain a compressed section called the "green part." For example, the mixture is compressed by applying a uniaxial pressure between 50 MPa and 300 MPa.

[0078] The density of the compressed section obtained at the end of step d) is preferably between 50% and 70% of the theoretical density of the final magnet.

[0079] In an advantageous embodiment of the present invention, at the end of step c) and before carrying out the compression step d), the mixture obtained at the end of step c) is subjected to a magnetic field to orient the crystal grains of the mixture and ultimately obtain an anisotropic magnet having high residual magnetism. Preferably, the magnetic field is higher than 1 Tesla, more preferably higher than 2 Tesla. Preferably, the magnetic field should not exceed 8 Tesla. This magnetic field can be applied when the mixture obtained at the end of step c) is poured into a mold.

[0080] Preferably, the pre-sintering step e) is carried out under secondary vacuum and in the presence of hydrogen to avoid demixing of the TRFeB phase. The secondary vacuum is 10 -4 Less than mbar, preferably 5.10 -5 This corresponds to pressures below mbar.

[0081] Next, the firing process f) is carried out to obtain a magnet. This includes compaction of the compressed section by heat treatment, and in some cases, some of its components melt (however, not all of the components melt, so the compressed section does not deform into a liquid).

[0082] The firing process f) is advantageously carried out in an environment that is substantially free of oxygen, water, or hydrogen, preferably under a secondary vacuum.

[0083] At the end of step f) of the manufacturing method according to the present invention, the density is advantageously 7.4 g.cm³. -3 A super magnet can be obtained.

[0084] In an advantageous embodiment of the present invention, at the end of step f), the magnet thus obtained is subjected to cooling. Preferably, this involves rapid cooling, i.e., rapid cooling from the firing temperature to room temperature at more than 20°C / min, more preferably about 30°C / min, or, if applicable, rapid cooling to the start temperature of any of the annealing steps described below.

[0085] The magnet obtained at the end of step f) can be subjected to an annealing step, if cooling is performed and applicable at the end of that step.

[0086] This is because the annealing process enhances the demagnetizing resistance of the magnet. Those skilled in the art are familiar with the conditions for carrying out the annealing process.

[0087] For example, when a magnet is subjected to rapid cooling to a temperature of 50°C, the annealing process exhibits the following thermal profile: - A process of heating from 50°C to 820°C at a rate of 5°C / min, - A process of maintaining the temperature at 820°C for 2 hours, - A process of cooling from 820°C to 50°C at a rate of 20°C / min, - A process of heating from 50°C to a temperature between 460°C and 650°C at a rate of 5°C / min, - A process of maintaining a temperature between 460°C and 650°C for 2 hours, - A process of cooling from a temperature between 460°C and 650°C to 50°C at a rate of 30°C / min. It may include.

[0088] In an advantageous embodiment of the present invention, at the end of the firing process f), if applicable at the end of the cooling process if one is performed, or if applicable at the end of the annealing process if one is performed, the magnet may undergo machining and / or surface treatment, for example, polishing or coating to prevent oxidation and corrosion.

[0089] At the end of the above manufacturing method, the magnet itself is not magnetized. Thus, the magnet may be magnetized complementaryly. For example, the magnet may be exposed to a magnetic field parallel to the alignment direction of the magnetic field used to orient the crystal grains of the mixture to obtain the anisotropic magnet described above. The magnetic field may have an intensity of more than 4 Tesla, preferably more than 5 Tesla. These high values ​​are usually achieved in pulse mode.

[0090] In other words, at the end of firing step f), the magnet thus obtained is subjected to the following steps (i.e., one of these steps or any combination thereof): - Cooling, for example, the cooling process as described above, - Annealing process, for example, the annealing process as described above, - Surface machining and / or treatment process, for example, the surface machining and / or treatment process as described above, - Complementary magnetization process, for example, the complementary magnetization process as described above and It can be provided to at least one selected from the following.

[0091] Any of these steps performed after the firing process f) are entirely within the capabilities of a person skilled in the art.

[0092] The present invention can be better understood by referring to the detailed description of the experimental section below, which explains one embodiment of the method for manufacturing a magnet according to the present invention by non-limiting examples.

[0093] Laboratory Department: Preparation of the first powder This is expressed as a mass percentage relative to the mass of the first powder mentioned above. - A mixture of 33.5% of two rare earth elements, Nd and Pr (according to the mass percentages below: 75% Nd and 25% Pr, these mass percentages are expressed relative to the total mass of the two rare earth elements), - B:0.99%;Co:0.5%;Al:0.2%;Cu:0.12%;Ga:0.10%, - Impurities: O: 160 ppm, N: 13 ppm, H: 14 ppm, C: 180 ppm, S: 28 ppm - Remaining portion up to Fe:100, A first powder containing the following was prepared according to the following procedure.

[0094] The virgin raw materials initially consisted of the various solid metals mentioned above, available in the quantities described above (i.e., "base inputs").

[0095] The base material was heated. To obtain the molten bath, melting was carried out in an alumina crucible at a maximum temperature of 1450°C under a partial pressure of argon (400 mbar).

[0096] A molten material bath was cast onto a water-cooled copper-based wheel having a rotational speed that allowed for obtaining crystallized strips with thicknesses ranging from 150 μm to 400 μm and an average thickness of 250 μm.

[0097] The strips obtained in this way were collected in a tank cooled by water circulation in order to cool them to room temperature.

[0098] Next, the strip was placed inside the sealed oven enclosure for the decrepitation process.

[0099] The decrepitation process was carried out as follows: The enclosure was subjected to a primary vacuum (i.e., less than 1 mbar, preferably 10 mbar). -2 After bringing the pressure down to less than mbar, hydrogen was added to reach a pressure of 2 bar. The enclosure was then placed under primary vacuum to evacuate the hydrogen, followed by heating at 550°C for 2 hours to partially dehydrate it, and then cooling to room temperature (i.e., about 20°C) under argon.

[0100] Next, the crude powder obtained in this manner was homogenized in a mixer into which 0.05% by mass of zinc stearate was introduced. The percentage of zinc stearate is expressed relative to the mass of the crude powder. Zinc stearate is a lubricant that facilitates the construction of a fluidized bed during the jet milling process. This homogenization was continued for 1.5 hours.

[0101] Next, the homogenized powder thus obtained was introduced into a fluidized bed gas jet mill. The gas used was nitrogen. The milling pressure, nozzle diameter, and selector speed were adjusted to obtain a first powder with a median particle size of 5 μm, as measured in-line by a laser particle meter.

[0102] Preparation of the second powder This is expressed as a mass percentage relative to the mass of the second powder mentioned above. - Nd: 21.7%, - Pr: 6.6%, - Dy: 4.0%, - B: 1.07%, - Co: 1.01%, - Al: 0.69%, - Cu: 0.15%, - Fe: Remaining portion up to 100%, A second powder containing the following was prepared as follows:

[0103] The first recycled magnets available had dimensions of 8 x 28 x 5 mm and contained the aforementioned metals in the specified quantities.

[0104] For the decletti process, recycled magnets were placed inside a sealed oven enclosure. After placing the enclosure under primary vacuum, hydrogen was added to reach a pressure of 0.8 bar. This process not only formed hydrides throughout the material but also allowed for the removal of the metal coating.

[0105] The crude powder thus obtained was heated under 0.8 bar of hydrogen at a 5°C / min heating gradient, followed by heating at 950°C for 3 hours in the same chamber under hydrogen. The entire mixture was then allowed to cool naturally to room temperature under hydrogen.

[0106] Next, the obtained powder, along with 8 mm diameter stainless steel beads, were introduced into a milling bowl under a controlled atmosphere in a bead / powder ratio of 1:2. This bowl was immersed in a liquid nitrogen bath until heated. The entire mixture was then ground in a vibrating mill, and the contents of the bowl were transferred to a glove box. The size of the second powder ranged from 1 μm to 20 μm.

[0107] Next, in accordance with step c) of the manufacturing method, the first powder was mixed in a mixer for 30 minutes in a controlled atmosphere within a housing at a mass ratio dependent on the heavy rare earth content of the second powder, with the second powder obtained at the end of step b).

[0108] The mass ratio of the second powder's mass m2 to the first powder's mass m1 was equal to m2 / m1 = 25 / 75.

[0109] Next, the mixture obtained from step c) was introduced into various cylindrical rubber molds with a height of 22 mm and an inner diameter of 14 mm, and the particles were oriented by subjecting them to a 7 Tesla magnetic field.

[0110] Next, the mixture contained in these various molds was subjected to a cold isostatic press at 1500 bar to perform the compression step d) of the manufacturing method according to the present invention, thereby obtaining a compressed section.

[0111] Next, pre-sintering step e) of the manufacturing process according to the present invention was performed on these compressed sections under secondary vacuum according to the following thermal profile: - Heat from room temperature to a first temperature of 300°C at a rate of 5°C / min, then maintain at the first temperature of 300°C for 2 hours. - Heat from a first temperature of 300°C to a second temperature of 500°C at a rate of 5°C / min, and then maintain at the second temperature of 500°C for 2 hours. - Heat from the second temperature of 500°C to the third temperature of 600°C at a rate of 5°C / min, then hold at 600°C for 2 hours. - Heat from the third temperature of 600°C to the fourth temperature of 700°C at a rate of 5°C / min, and then maintain the fourth temperature of 700°C for 30 minutes.

[0112] Next, the thermal profile is as follows: - A step of heating from the fourth temperature of 700°C to the fifth temperature of 975°C at a rate of 10°C / min, - A step of maintaining the temperature at the above fifth temperature of 975°C for 12 hours. Accordingly, firing step f) of the manufacturing process according to the present invention was performed on these pre-fired sections under secondary vacuum.

[0113] At the end of this final step at the first temperature of 975°C mentioned above, argon was introduced until an absolute pressure of 2 bar was reached to obtain the magnet.

[0114] Next, the magnet was cooled from 975°C to 30°C at a cooling rate of 15°C / minute.

[0115] The following is the thermal profile of the magnet: - A process of heating from 50°C to 820°C at a rate of 5°C / min, - A process of maintaining the temperature at 820°C for 2 hours, - A process of cooling from 820°C to 50°C at 20°C / min, - A process of heating from 50°C to 500°C at a rate of 5°C / min, - A process of maintaining the temperature at 500°C for 2 hours, - A process of cooling from 500°C to room temperature at 15°C / min The material was subjected to an annealing process under secondary vacuum conditions.

[0116] A cylindrical magnet obtained using a grinder and diamond wheel was machined to remove the oxide layer and obtain a parallel surface.

[0117] Furthermore, a so-called "comparative" magnet was manufactured from 100% of the first powder using the same method as these magnets of the present invention.

[0118] The magnetic properties of the magnet of the present invention and the comparative magnet are described in detail in Table 1 below [in the table, - Br is the remanent magnetism (represented by T). - Hcj is the coercivity (expressed in kA / m). - (BH) The maximum value is the maximum energy output (kJ / m³ 3 (represented by), - Dy represents the mass content of dysprosium (expressed as a percentage). - Increase in coercivity (expressed in kA / m).

[0119] [Table 1]

[0120] To understand the interesting aspects of this invention, it is necessary to estimate the increase in coercivity due to the percentage of Dy in the final magnet. Compared to a comparative magnet, the increase in coercivity of the magnet of this invention is 191 kA / m. In relation to the amount of Dy introduced, this represents an increase of 191 kA / m / %Dy. As explained above, it is known that when Dy derived from virgin material is introduced into the manufacture of a magnet, this increase in coercivity is only about 150 kA / m / %Dy. This value is lower than the increase in coercivity obtained from magnets manufactured by the manufacturing method of this invention. These experiments demonstrate that this invention makes it possible to obtain magnets with an optimized increase in coercivity.

Claims

1. A method for manufacturing a high coercivity magnet, comprising at least the following steps: a) - Magnetic phase TR ２ Fe １４ Crystal grains of B (where "TR" represents an element selected from rare earth elements or a combination of two or more elements), metal-based compounds, and grain boundary phases rich in rare earth elements, and optionally, a non-magnetic phase TRFe ４ B ４ A first powder containing crystalline grains of a, which does not contain heavy rare earth elements, or whose mass content of heavy rare earth elements, expressed relative to the mass of the first powder, is less than 1%. - A second powder containing heavy rare earth elements, wherein the mass content of the heavy rare earth elements relative to the mass of the second powder is between 1% and 10%, preferably between 2% and 5%, and the magnetic phase TR ２ Fe １４ A second powder containing crystal grains of B. The process of preparing, b) subjecting the second powder to a hydrogenation-disproportionation treatment to obtain the magnetic phase TR ２ Fe １４ B into a rare earth hydride represented by chemical formula TRH ｘ , wherein x is an atomic ratio H / TR, iron, iron boride (Fe ２ B) and a so-called beta phase containing TR, iron and boron, wherein the hydrogenation-disproportionation treatment is - Temperature between 850°C and 950°C and hydrogen pressure of 0.3 bar or more and less than 0.5 bar, - Or a temperature between 925°C and 1025°C and a hydrogen pressure of 0.5 bar or more but less than 1 bar, - Or a temperature between 950°C and 1100°C and a hydrogen pressure of 1 bar or more and 10 bar or less. The process to be carried out in one of the following locations, c) A step of mixing the first powder with the second powder obtained at the end of step b) in a mass ratio that depends on the heavy rare earth content of the second powder to obtain a mixture, d) A step of subjecting the mixture obtained at the end of step c) to a compression step to obtain a compressed portion, e) A step of subjecting the compressed portion obtained at the end of step d) to a pre-firing step, wherein the pre-firing step is the following sub-step: - A sub-step involves heating from room temperature to a first temperature between 200°C and 400°C at a heating rate of 1°C to 5°C / minute, - A sub-step of maintaining the temperature at the first temperature between 200°C and 400°C for a period of time between 1 and 3 hours, - A sub-step of heating from the first temperature between 200°C and 400°C to a second temperature between 400°C and 500°C at a heating rate of 1°C to 5°C / min, - A sub-step of maintaining the temperature at the second temperature between 400°C and 500°C for a period of time between 1 and 3 hours, - A sub-step of heating from the second temperature between 400°C and 500°C to a third temperature between 550°C and 650°C at a heating rate of 1°C to 5°C / min, - A sub-step of maintaining the temperature at the third temperature between 550°C and 650°C for a period of time between 1 and 3 hours, - A sub-step of heating from the third temperature between 550°C and 650°C to a fourth temperature between 650°C and 750°C at a heating rate of 5°C to 10°C / min, - A sub-step of maintaining the temperature between 650°C and 750°C for a period of 10 to 30 minutes. Processes including, f) A step of obtaining a magnet by subjecting the pre-fired portion obtained at the end of step e) to a firing step, wherein the firing step is the following sub-step: - A sub-step of heating from the fourth temperature between 650°C and 750°C to a fifth temperature between 850°C and 1050°C at a heating rate of 5°C to 25°C / min, - A sub-step of maintaining the temperature at the fifth temperature between 850°C and 1050°C for a period of time between 2 hours and 24 hours. Processes and A manufacturing method characterized by including the following.

2. The first powder is expressed as a mass percentage relative to the mass of the first powder, - Between 90% and 99%, preferably between 95% and 97%, TR ２ Fe １４ Crystal grains of the magnetic phase of system B, - Metal-based compounds in an amount between 0.5% and 3%, preferably between 0.5% and 2%. - Between 1% and 10%, preferably between 2% and 5%. The grain boundary phase rich in rare earth elements, - Optionally, the TRFe in a concentration between 0.1% and 5%, preferably between 0.1% and 1%. ４ B ４ Crystal grains of the nonmagnetic phase of the system The manufacturing method according to claim 1, characterized by including

3. The first powder is expressed as a mass percentage relative to the mass of the first powder. - Rare earth elements between 27% and 35% - Boron between 0.9% and 1.2% - At least one metallic element M, selected from the group consisting of Fe, Co, and Ni, which constitutes the remainder up to 100% either alone or in a mixture thereof, wherein the combined mass percentage of Ni and Co is 5% or less, and optionally, either alone or in a mixture thereof, Fe is partially replaced by at least one substitutional element selected from the group consisting of Al, Cu, Ga, Nb, Zr, Ti, Mo, V, Hf, Ta, W, and Sn, with the content of the substitutional element being 3% or less, A manufacturing method according to claim 1 or 2, characterized by including the following:

4. The second powder is expressed as a mass percentage relative to the mass of the second powder, - Contains 27% to 35% rare earth elements, including heavy rare earth elements between 1% and 10%, preferably between 2% and 5%. - Boron between 0.9% and 1.2% - At least one metallic element M, selected from the group consisting of Fe, Co, and Ni, which constitutes the remainder up to 100% either alone or in a mixture thereof, wherein the combined mass percentage of Ni and Co is 5% or less, and optionally, either alone or in a mixture thereof, Fe is partially replaced by at least one substitutional element selected from the group consisting of Al, Cu, Ga, Nb, Zr, Ti, Mo, V, Hf, Ta, W, and Sn, with the content of the substitutional element being 3% or less, A manufacturing method according to any one of claims 1 to 3, characterized by including

5. The first powder is - Virgin raw materials that contain no heavy rare earth elements at all, or whose mass content is less than 1%, - Recycled magnets that contain no heavy rare earth elements at all, or whose mass content is less than 1%, or - A mixture of virgin raw materials and recycled magnets that contain no heavy rare earth elements or have a mass content of less than 1%. A manufacturing method according to any one of claims 1 to 4, characterized in that it is obtained from

6. The aforementioned virgin raw material is processed in the following steps: - Casting process on the wheel, followed by - Decrepitation and / or gas jet milling process under hydrogen The manufacturing method according to claim 5, characterized in that it is used for [a specific purpose].

7. The manufacturing method according to claim 5, characterized in that the recycled magnet has been subjected to a declepitament and / or gas jet milling process under hydrogen.

8. The second powder described above is - Virgin raw material having a heavy rare earth content of 1% to 10%, preferably 2% to 5%, or - Recycled magnets having a heavy rare earth content of 1% to 10%, preferably 2% to 5%, or - A mixture of virgin raw materials and recycled magnets, wherein the mass content of heavy rare earth elements is between 1% and 10%, preferably between 2% and 5%. A manufacturing method according to any one of claims 1 to 7, characterized in that it is obtained from

9. The second powder is subjected to the following treatment: - The decrepitation process under hydrogen conditions is optional, followed by - Gas jet milling The manufacturing method according to claim 8, characterized in that it is obtained from recycled magnets that have been used for [a specific purpose].

10. The manufacturing method according to any one of claims 1 to 9, characterized in that the second powder is destroyed by at least one grinding method selected from gas jet milling, planetary milling, friction milling, and cryogenic milling.

11. The manufacturing method according to any one of claims 1 to 10, characterized in that, at the end of step c) and before carrying out the compression step d), the mixture obtained at the end of step c) is subjected to a magnetic field, preferably a magnetic field greater than 1 Tesla.

12. The manufacturing method according to any one of claims 1 to 11, characterized in that the magnet obtained at the end of the firing step f) is subjected to at least one step selected from cooling, annealing, machining and / or surface treatment and complementary magnetization steps.

13. The manufacturing method according to any one of claims 1 to 12, characterized in that the time of the hydrogenation-disproportionation treatment in step b) is between 10 minutes and 3 hours.

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