Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B59/00—Obtaining rare earth metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
  • B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/20—Direct sintering or melting
  • B22F10/25—Direct deposition of metal particles, e.g. direct metal deposition [DMD] or laser engineered net shaping [LENS]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/20—Direct sintering or melting
  • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/023—Hydrogen absorption
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y80/00—Products made by additive manufacturing
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/001—Dry processes
  • C22B7/002—Dry processes by treating with halogens, sulfur or compounds thereof; by carburising, by treating with hydrogen (hydriding)
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
  • H01F41/0273—Imparting anisotropy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C2202/00—Physical properties
  • C22C2202/02—Magnetic
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
  • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
  • H01F1/0573—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes obtained by reduction or by hydrogen decrepitation or embrittlement

Definitions

• the present invention relates to the field of recycling permanent magnets based on rare earths. It relates in particular to a powder resulting from the recycling of neodymium magnets (NdFeB type) and a recycling process for obtaining said powder. The invention also relates to a process for producing a permanent NdFeB magnet from said powder.
• NdFeB type neodymium magnets
• Rare earth resources in particular, neodymium (Nd)
• Nd neodymium
• NdFeB type magnets are the most commonly used rare earth permanent magnets. They are mainly manufactured by sintering processes (solid magnets) or by injection or compression molding processes, the latter involving a polymer binder between the particles of NdFeB material (bonded magnets). Additive manufacturing techniques are also beginning to be implemented to manufacture NdFeB magnets, solid or based on polymer binders, with great flexibility in the shape of the magnet object.
• the present invention addresses the aforementioned problems. It relates in particular to a process for recycling solid NdFeB magnets, as well as an anisotropic and coercive powder resulting from this process, which is particularly suitable for the development of new high-performance NdFeB magnets, in particular by additive manufacturing.
• the invention relates to a process for recycling NdFeB magnets comprising the following steps: a) the recovery of waste comprising solid NdFeB magnets to be recycled, said NdFeB magnets having a magnetic Nd2FewB main phase and a non-magnetic intergranular secondary phase; b) the preheating of the waste to a preheating temperature of between 300°C and 500°C under an inert atmosphere, the waste being contained in a first enclosure raised to the preheating temperature in a first station equipped with heating means ; c) decrepitation with hydrogen, applied to the hot waste from step b), under a partial or total hydrogen pressure of between 0.1 bar and 10 bar, said hot waste being contained in a second enclosure arranged in a second station, separate from the first station, equipped with a hydrogen source and pumping means, the decrepitation taking place at a temperature between 200°C and 500°C, said temperature in the second chamber being maintained in this temperature range due to the exothermic nature of the hydr
• the first enclosure and the second enclosure are formed by a single enclosure, moved from the first station to the second station between steps b) and c), and connectable to the hydrogen source and to the pumping means of the second station;
• the waste recovered in step a) comprises metal parts integral with the NdFeB magnets to be recycled, the process comprising, during or after step c), a sieving step d) with a sieve size of 1cm, carried out to separating said parts and the first powder;
• the method comprises, during or after step c), a step d) of sieving the first powder
• the method comprises, after step c) or, during or after a sieving step d), a step e) of grinding the first powder or a fraction of the first powder, to obtain a second powder with particles having a size less than or equal to 500 microns;
• step e the grinding is carried out in a ball mill or by a ring mill or by a gas jet mill;
• At least one non-magnetic metal compound (without rare earth) having a low melting point (typically lower than or equal to that of the secondary inter-granular phase) is added to the first powder or to the second powder during the process of recycling, said compound being intended to promote the bond between NdFeB particles during the development of a new magnet;
• the method comprises a step f) of dehydrating the first powder or the second powder.
• the invention further relates to a powder resulting from the process for recycling NdFeB magnets as above, comprising particles composed of several grains of main magnetic phase Nd2FewB, separated from each other by the inter-granular secondary phase, and in which the grains of the same particle have a common crystallographic orientation which generates a magnetic anisotropy.
• the powder comprises a double particle size distribution:
• the powder comprises between 1% and 50% by volume of intergranular secondary phase. Even more preferentially, the powder comprises between 10% and 30% by volume of intergranular secondary phase.
• the powder comprises between 1% and 50% by volume of the non-magnetic metallic compound (without rare earth). Even more preferentially, the powder comprises between 1% and 20%, or even between 1% and 10% by volume of the non-magnetic metallic compound.
• the invention finally relates to a process for producing a permanent NdFeB magnet implementing, from a powder as mentioned above:
• the production process is based on an additive manufacturing technique involving melting of at least one phase of the powder, and the melting is carried out at a temperature below the melting temperature of the phase main NdaFewB, so as to melt all or part of the inter-granular secondary phase or of a non-magnetic metallic compound without rare earth if present, and not the main NdaFewB phase.
• the powder particles comprising the main phase are advantageously oriented before or during the consolidation of the NdFeB magnet in the form of a printed object, to confer magnetic anisotropy on said magnet.
• FIG. 2 presents an image by scanning electron microscopy (SEM) of the particles of the first powder and a graph illustrating a typical size distribution of the particles of the first powder, measured by laser diffraction, at the end of the step c) the recycling process;
• FIGS. 3a to 3c show images by scanning electron microscopy (SEM) of the particles of the second powder after step e) of the recycling process in accordance with the invention, for different grinding conditions;
• FIGS. 3a to 3c also present graphs illustrating the particle size distribution of the second powders obtained for said different grinding conditions, the size of the particles being measured by laser diffraction (FIGS. 3a and 3b) and image analysis (FIG. 3c );
• - Figure 4 shows a scanning electron microscopy image of the particles of the second powder after addition of particles of an intergranular phase compound rich in rare earths.
• the invention relates to a process for recycling massive magnets of the NdFeB type.
• a solid magnet as mentioned in the introduction, is only metallic, i.e. it does not contain any polymer binder in addition to the NdFeB alloy. In the present invention, the term solid magnet therefore excludes composite materials based on polymers such as for example plasto-magnets.
• this terminology includes any magnet of the NdFeB type, that is to say likely to include various additives and/or other rare earths than neodymium (for example example, dysprosium).
• a first step a) of the method consists in the recovery of waste comprising massive NdFeB magnets to be recycled.
• waste we mean solid NdFeB magnets, manufacturing scrap; we also mean any type of mechanical or electronic parts, at the end of their life or decommissioned in a manufacturing process, including NdFeB magnets whose material is likely to be recycled.
• the waste may consist of NdFeB magnets from hard drives attached to a steel leg, NdFeB magnets from electric motors, etc. Due to their magnetizing properties, these magnets are often very firmly attached to the mechanical part (metal) associated with previous use; it is nevertheless possible to obtain scrap NdFeB magnets alone, i.e. separated from the mechanical parts of previous use.
• NdFeB magnets from waste can be bare or covered with a protective layer, typically of a metallic nature (based on nickel or zinc for example) or polymer (epoxy).
• a massive NdFeB magnet to be recycled forms an alloy which comprises a magnetic NdaFewB main phase typically representing 85% (+/-10%) by volume of the alloy. The melting point of this main phase is around 1180°C.
• the alloy also comprises a non-magnetic secondary phase, called inter-granular because it serves to magnetically decouple (isolate) the NdaFewB main phase grains.
• the secondary phase is composed of several phases rich in rare earths, which have melting temperatures between 500°C and 800°C depending on the compositions of the alloy.
• the inter-granular secondary phase typically represents 15% (+/-10%) by volume of the alloy.
• the recycling process then comprises a step b) of preheating the waste 100 in a first chamber 10 to a preheating temperature of between 300° C. and 500° C., preferably between 350° and 450° C., in particular around 400°C (Fig. 1(b)).
• a preheating temperature of between 300° C. and 500° C., preferably between 350° and 450° C., in particular around 400°C
• the waste 100 is introduced into the first enclosure 10, which is placed in a first station 1 equipped with heating means 11 .
• the first station 1 can for example consist of an annealing furnace, in which the first enclosure 10, filled with waste 100, is placed.
• the first station 1 advantageously comprises a gas circuit 12,13 including at least one neutral gas source 12 and a gas discharge 13, which can be connected to the first enclosure 10, to adjust its internal atmosphere.
• the atmosphere in the first enclosure 10 is thus advantageously chosen to be inert, for example based on argon.
• the first enclosure 10 is preferably perfectly sealed, compatible with a pressure of a few bars and with temperatures typically up to 600° C. This preheating of the waste 100 is advantageous in that it promotes the demagnetization of the various materials contained in the waste and therefore the physical separation of parts potentially held together by magnetic attraction.
• the next step c) of the recycling process corresponds to hydrogen decrepitation, applied to the hot waste 101 , under a partial or total hydrogen pressure of between 0.1 bar and 10 bar, preferably between 1 and 4 bar , and at a temperature between 200°C and 500°C.
• the hot waste 101 is contained in a second enclosure 20 arranged in a second station 2, separate from the first station 1, equipped with a hydrogen source 21 and pumping means 22 (FIG. 1(c)).
• the first enclosure 10 and the second enclosure 20 are formed by a single and same enclosure, which is moved from the first station 1 to the second station 2 between step b) and step c), and which is connectable to the hydrogen source 21 and to the pumping means 22 of the second station 2.
• the enclosure 10 is disconnected from the gas circuit 12,13 of the first station 1 at the from step b), then when it is placed in or on the second station 2, it is connected to the hydrogen source 21 and to the pumping means 22.
• the hot waste 101 is transferred from the first enclosure 10 into the second enclosure 20, between step b) and step c). Care will be taken to limit the drop in temperature of the waste 101 during this transfer, so that their temperature remains greater than or equal to 250°C at the start of step c).
• the air is evacuated therefrom by the pumping means 22, before the enclosure 20 is supplied by the source of hydrogen 21.
• the second enclosure 20 is perfectly sealed, compatible with a pressure ranging at least up to 10 bars and with temperatures typically ranging up to 600°C. It is also advantageous to control the distribution of hydrogen by the hydrogen source, so as to maintain the hydrogen pressure in the second chamber 20 above a predefined threshold, for example a threshold at 25% in- below an initial pressure, throughout the duration of the decrepitation, as the hydrogen is absorbed by the NdFeB alloy of waste 100.
• the temperature in the second chamber 20 is self-sustaining without any heating means being required in the second station 2.
• the NdFeB magnets contained in the hot waste 101 that is to say at a temperature greater than or equal to 250° C.
• the decrepitation temperature is close to the preheating temperature, in practice it can be between 200°C and 500°C.
• steps b) and c), respectively in two separate stations 1, 2 greatly simplifies the equipment and infrastructure for implementing the recycling process, by decorrelating the heating needs (first station 1) of hydrogen supply (second station 2) and secures operations.
• Step c) typically lasts between a few minutes and 12 hours.
• the end of the hydriding reaction is detected, either by a drop in the temperature of the second enclosure 20 (measured via a temperature sensor immersed in the enclosure 20), or by measuring a pressure inside of the second enclosure 20 which tends to be constant, because the NdFeB magnets of the waste 100 no longer absorb hydrogen.
• the inter-granular secondary phase of the NdFeB alloy which is essentially hydride.
• the main Nd2Fei4B phase is not hydrided or very weakly, because the associated hydride is not stable above 200°C; indeed, the main phase absorbs hydrogen and creates a stable hydride at lower temperatures, typically between ambient and 150°C.
• This stage c) of decrepitation with hydrogen carried out between 200° C. and 500° C., preferably between 300° C. and 500° C., or even between 350° C. and 450° C., is to reduce the quantity of hydrogen (H2) required to carry out the hydriding, since only the secondary inter-granular phase is targeted and it generally represents less than a quarter by volume of the alloy.
• H2 hydrogen
• Another advantage comes from the fact that the main magnetic phase grains will be very little affected and modified by this step, and will thus retain their initial properties and structures (i.e. those they had in the magnet NdFeB to be recycled): in particular, within the same powder particle, the overall magnetic orientation of the grains will be the same.
• the second station 2 is advantageously equipped with a stirring system 23, able to transmit a movement to the second enclosure 20, during step c).
• the agitation system can consist of a vibrating system (vibration amplitude typically between 0.5 mm and 3 mm) or a wave-balancing system.
• the agitation of the second enclosure 20 favors the separation between the NdFeB magnets and the other parts, and the fragmentation of the NdFeB alloy by decrepitation with hydrogen.
• the NdFeB magnets of the waste 100 treated in step c) will thus evolve, as this step progresses, towards a powder (called first powder 110 hereafter) whose particles comprise the main phase Nd2FewB and/or of the inter-granular secondary phase, and have a size less than or equal to 5mm, or even less than or equal to 1mm.
• the recycling process comprises a step d) of sieving the first powder 110, carried out during or after step c) of decrepitation (FIG. 1 (d)).
• the hot waste 101 is placed on said sieve 31, and at the as the hydriding of the NdFeB alloy progresses, the particles of said alloy, of size less than the mesh of the sieve 31, fall into the part of the enclosure below the sieve.
• the fall of the alloy particles through the sieve 31 is favored by the agitation applied to the second chamber 20 arranged in the second station 2.
• the first NdFeB alloy powder and the other remains of waste (if any) obtained at the end of step c) are transferred from the second chamber 20 to a sieving device 30, for example via a hatch associated with a valve (not shown), arranged in the lower part of the second enclosure 20.
• the sieving device 30 can be fitted with one or more sieves 31 . It may optionally be arranged in the second station 2 and undergo, like the second enclosure 20, the movement of the agitation system 23, or be provided with its own agitation system 33 (FIG. 1(d)).
• the mesh of the sieve(s) 31 used for step d) of sieving may be 1cm, 5mm, 1mm, 500 microns, 300 microns, 150 microns, 100 microns, 50 microns, 10 microns or even lower .
• Balls of a size greater than that of the particles of the first powder 110 may optionally be added to the sieve 31 to carry out a pre-grinding and facilitate the sieving of said powder.
• step d) of sieving is carried out with a 1cm mesh, to separate said parts and the first powder 110. If the metal parts or other shavings generated during decrepitation (for example, shavings of a coating layer of the NdFeB alloy) have a smaller size, one can imagine sieving with a finer mesh, for example 1mm, 500 microns, 150 microns, 100 microns, or even less.
• step d) may comprise sieving the first powder 110 from step c) with a sieve size of between 800 microns and 100 microns, so as to separate a batch of powder of fine particle size 112, likely to be used directly for the subsequent manufacture of a new magnet and a batch of powder of coarse particle size 111, intended to undergo a subsequent grinding step that can be carried out in the recycling process according to the invention.
• the first powder 110 can sieve the first powder 110 through an ultrafine sieve, typically with a mesh size of less than 10 microns, or even less than 5 microns, for example approximately 1 micron.
• this ultrafine sieving makes it possible to separate them from the rest of the first recycled powder. They could possibly be replaced by intergranular phase particles of good quality or of optimized composition (recycled or new) to improve the properties of a new magnet made from recycled powder.
• the particles of the first powder 110 mostly have an angular shape (FIG. 2) and a typical example of particle size distribution, following a sieving step d) at 800 microns, is illustrated in FIG. 2.
• a particle's size is referred to here as its "Sauter's equivalent diameter".
• the “Sauter equivalent diameter” is the diameter of the sphere which would behave identically when measured by a defined technique, for example by laser diffraction.
• This first powder 110 can be adapted for certain processes for developing new magnets.
• the fraction of particles with a size of less than 50 microns is compatible with a conventional sintering technique for the development of a new magnet.
• the fraction of particles between 100 microns and 500 microns is compatible with conventional techniques for manufacturing plasto-magnets, by injection or by compression.
• NdFeB alloy particles of sizes typically less than 300 microns, or even less than 100 microns are favorable but it is preferable that their shape be less angular.
• the recycling process may comprise, after step c) and/or during step d) and/or after step d) , a step e) of grinding the first powder 110 (or a fraction thereof), which will lead to obtaining a second powder whose particles, of more rounded shape, have a size less than or equal to 500 microns, 300 microns, or even less than or equal to 100 microns, or even less than or equal to 50 microns.
• any known grinding means can be implemented in step e), in particular a ball mill, a ring mill or a gas jet mill (“jet milling” according to the Anglo-Saxon terminology). This last technique is known and usually implemented for the grinding of powders.
• Ring milling is achieved by circular and horizontal oscillation of a ring and a core on an oscillating plate. The sample is then fragmented under the forces of pressure, shock and friction to a size that can go below 20 microns.
• a ball mill comprises a rotating drum or rotating blades arranged in a fixed drum, in which all or part of the first powder 110 is placed, alone or accompanied by balls.
• the first powder 110 or the fraction thereof intended to undergo the grinding step will therefore be transferred from the second station 2 to a third grinding station.
• these balls can be chosen in stainless steel and advantageously have a diameter of between 1mm and 30mm, preferably between 1mm and 10mm, for example 5mm; the mass ratio between the first powder and the beads is preferably chosen between 0.5 and 3.
• the grinding of step e) advantageously takes place by applying a sequence of agitation with a drum rotation speed of between 100 rpm and 800 rpm, for example 450 rpm. min, for a period of between 10s and 1 h, for example 10 min, followed by a rest sequence, for a period of between a few seconds (typically 5s) and 40s, for example 20s.
• the agitation sequence and the rest sequence can be successively repeated, between 2 and 500 times, until a defined particle size of the second powder is obtained.
• FIGS. 3a, 3b, 3c correspond to SEM images of the particles of a second powder, at the end of step e) of grinding, for different repetitions of the agitation and rest sequences mentioned above, respectively 10 iterations, 30 iterations and 300 iterations; in these examples, the grinding was carried out with balls.
• the recycling process finally comprises a step f) of dehydration which can be applied to the first powder 110 (or to a sieved fraction thereof) or to the second powder resulting from step e) of grinding, in order to extracting the hydrogen present in the alloy particles.
• Dehydriding is carried out by heating the powder under a secondary vacuum, up to about 800° C. in a fourth chamber, arranged in a fourth station equipped with heating means and pumping means.
• the dehydridation consists of two successive stages during which the hydrogen is evacuated from the main phase NdaFewB (which may optionally be slightly hydrided during stage c)), around 200°C, then from the secondary phase inter- granular, between 350 and 800°C (depending on composition, temperature conditions and vacuum dynamics).
• the alloy particles contain a low hydrogen content, because it is essentially the inter-granular secondary phase which has been hydrided during step c) of decrepitation.
• Step f) of dehydriding is therefore faster than following the decrepitation steps usually carried out in the state of the art.
• the alloy powder (first or second powder) resulting from the recycling process according to the invention comprises particles composed of one or more grains of the main magnetic phase Nd2Fei4B; when there are several grains, they are separated from each other by the non-magnetic intergranular secondary phase, rich in rare earths.
• the strong advantage of the alloy powder according to the invention is that said grains included in the same particle have a common crystallographic orientation which generates magnetic anisotropy. These multi-grain particles can thus be used, like anisotropic single-grain particles, for the fabrication of new NdFeB magnets.
• An anisotropic powder is usually obtained by expensive and complex processes such as the HDDR process (hydrogenation-disproportionation-desorption-recombination); the recycling process according to the invention makes it possible to obtain an anisotropic powder of good quality, in a simple and economical manner.
• HDDR process hydrogenation-disproportionation-desorption-recombination
• the first 110 and the second powder, resulting from the recycling process according to the invention comprise between 1% and 50% by volume of inter-granular secondary phase, preferably between 10% and 30%. These powders can be directly used for the manufacture of NdFeB permanent magnets.
• particles consisting of a compound rich in rare earth(s) can be added to the second powder, to adjust its intergranular secondary phase content or modify its composition, if need.
• This addition can for example be made from neodymium (Nd) or other rare earth compounds including elements such as Nd, Dy, Tb, Pr, Co, Fe, Cu, Al, Nb, Zr, Ti, etc. .
• the following method can in particular be used to introduce the inter-granular secondary phase compound, rich in rare earth(s): - hydridation of the compound, for example at a temperature of 150° C. and under a pressure of 8 bars, to form hydrides;
• step e) of grinding of the recycling process grinding will easily make it possible to obtain a very fine particle size of the hydrides, i.e. particles having a size typically less than or equal to 10 microns, less than or equal to 2 microns, or even less than or equal to 1 micron. It should be noted that this grinding can be carried out during step e) of grinding of the aforementioned recycling process, by mixing the hydride compound with the first powder 110;
• step f) of the recycling process or independently for the rare earth compound and for the powder, which are mixed after the dehydriding.
• the SEM image in figure 4 gives an overview of the mixture obtained after this addition of intergranular phase compound particles to the second powder: the finest particles ( ⁇ 1 micron) correspond to the added intergranular phase, rich in rare earths. The larger particles are part of the second powder.
• a compound close to the composition of the initial magnet typically up to from 1% to 90%, preferably between 1% and 40%, or even more preferably between 2% and 15%.
• a compound consisting of magnetic phase of the TRaFewB type in particular NdaFewB.
• a non-magnetic metallic compound (without rare earth) having a low melting point (typically lower than or equal to that of the intergranular phase) may be added; its particles may for example have a particle size comparable to that of the particles of the second powder.
• a non-magnetic metallic compound (without rare earth) having a low melting point (typically lower than or equal to that of the intergranular phase) may be added; its particles may for example have a particle size comparable to that of the particles of the second powder.
• Such a compound is intended to promote the bond between NdFeB particles during the development of a new magnet, in particular by additive manufacturing.
• the added compounds can either be added to the waste and treated simultaneously according to the aforementioned recycling process, or be treated and modified in powder form, then added to the first or second powder according to the present invention. , at any stage of the process, before or after stage f) of dehydriding.
• the invention relates to a process for producing an NdFeB permanent magnet, from the first powder 110 (as mentioned above) or from the second powder according to the invention, implementing known techniques such as that :
• the invention relates to a process for producing an NdFeB magnet implementing a metal additive manufacturing technique, preferably from the second powder.
• powder bed fusion Selective Laser Melting - SLMTM” or “Laser Beam Powder Bed Fusion - LB-PBF” according to the Anglo-Saxon terminology
• EBAM electron beam melting
• MJ metal binder jetting
• DED directed energy deposition
• CCM cold spray additive manufacturing
• the metal powders are necessarily fine in order, for example, to meet the requirement of forming a bed of powder a few tens of microns thick.
• finer powders generally flow less freely than coarse ones. Maximum compactness is achieved with a distribution that includes both coarse and fine particles, with finer particles increasing density by filling in the gaps left by larger ones.
• the second powder according to the invention may prove to be particularly suitable when it has a double particle size distribution: namely, a first population of particles centered on a first size, and a second population of particles centered on a second size, the first size being one and a half times to ten times larger than the second size.
• the first size can be between 15 and 90 microns, and the second size between 1 and 15 microns.
• the first size is approximately 15 microns, and the second size is approximately 9 microns.
• Such a double distribution can in particular be obtained by applying a large number of grinding iterations, as described above in the recycling process.
• the presence of particles of a non-magnetic metallic compound without rare earth and/or particles of an intergranular phase compound rich in rare earths makes it possible to reduce the interactions between the magnetic particles and to greatly improve the flowability of the powder. This makes it possible to overcome the constraint of the shape of the particles and gives significant fluidities even with angular particles.
• the metal additive manufacturing techniques mentioned above provide significant energy which will allow the particles of the NdFeB alloy powder to be completely melted.
• the melting is carried out at a temperature below the melting temperature of the main phase NdaFewB, so as to melt all or part of the secondary inter-granular phase and/or of the metallic compound non-magnetic with no rare earth (if present), and not said main phase.
• This melting temperature is around 1180°C but can vary significantly depending on the composition of the NdFeB alloy.
• the melting point in the production process is therefore less than 1180°C, preferably less than or equal to 1000°C, or even less than or equal to 800°C, or even less than or equal to 600°C.
• the consolidation between the particles of the powder is thus obtained by partial melting of the NdFeB alloy. This has the advantage of not affecting the grains of the main magnetic phase, whether in terms of size, shape or composition. Thus, the intrinsic magnetic properties of the alloy of the second powder can be best preserved.
• the second powder therefore preferably comprises between 10% and 30% by volume of this phase.
• said compound can be formed from one or more elements chosen from among Al, Zn, Sn, In, Li, Bi, Cd, Pb, their alloys or other alloys without rare earth (eg Ag-Cu).
• This compound has a melting point typically less than or equal to 800°C.
• the powder comprises between 1% and 50%, between 1% and 20%, or even between 1% and 10% by volume of said non-magnetic metallic compound.
• Other properties specific to NdFeB magnet powder are necessary for the finished magnetic part to be a solid magnet that performs well.
• a magnet is mainly characterized by three main quantities: the coercivity (denoted Hc and expressed in kA/m), the remanence (or remanent magnetization, denoted Br and expressed in Tesla) and the maximum energy product (denoted BHmax and expressed in MGOe) .
• the coercivity corresponds to the resistance to demagnetization of the magnet when it is subjected to either a demagnetizing environment or to a high temperature (above 100°C).
• the remanence indicates the magnetization and therefore the magnetic force that the magnet can provide to the system.
• the maximum energy product is characteristic of the overall energy that the magnet can provide at its operating point.
• the second powder, resulting from the recycling process in accordance with the invention typically has a coercivity of between 500 kA/m and 2400 kA/m and a remanent magnetization of between 0.5 T and 1.4 T, magnetic characteristics very favorable to the development of a new permanent magnet.
• the remanence can be optimized at the time of the additive manufacturing, due to the crystallographic orientation of the grains of the main magnetic phase, thanks to a magnetic or mechanical orientation system of the particles. before their consolidation.
• the second powder comprises anisotropic particles (i.e. whose magnetic phase grains NdaFewB have a common crystallographic orientation generating magnetic anisotropy)
• a magnet or electromagnet (magnetic orientation system) judiciously placed around or near the object to be printed will make it possible to orient each particle comprising the main phase, just before its consolidation.
• the layer which has just been printed may be subjected to a forging operation in a direction perpendicular to the plane of the layer and with a strain rate of at least 8/s, so as to mechanically texture each powder particle. and/or magnetic phase grain, thus leading to an anisotropic magnetic orientation of the layer.
• This mechanical orientation system can optionally be coupled to the aforementioned magnetic orientation system.
• Another type of mechanical operation could possibly replace the forging operation (for example, implementation of a roller simulating rolling or of a vibratory system to obtain compaction), to achieve the anisotropic magnetic orientation and/ or to densify the powder bed (in particular to avoid porosity defects or cracks in the printed object).
• the coercivity will be all the greater if the grains of main magnetic phase are uniformly surrounded by inter-granular secondary phase, for effective magnetic decoupling of said grains, in the printed object.
• the coercivity will be developed on the condition of maintaining a quality inert atmosphere (oxygen level less than 0.1%) in the printing chamber.
• the fact that the temperature is kept below the melting temperature of the main magnetic phase makes it possible to preserve the magnetic qualities of the NdaFewB phase grains of the initial recycled magnet (good remanence) and simplifies the process of developing the new magnet.
• mere fusion of the secondary inter-granular phase (and/or of the non-magnetic metallic compound without rare earth, if present) promotes the coating of the grains of main magnetic phase, thus making it possible to obtain a high coercivity for the new printed magnet.
• the process for producing a solid permanent NdFeB magnet by additive manufacturing according to the invention can find applications in multiple fields, requiring high-performance permanent magnets in very varied forms of objects specifically accessible by 3D printing, for example the electronics, automotive, computer, etc.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Organic Chemistry (AREA)
• Power Engineering (AREA)
• Metallurgy (AREA)
• Mechanical Engineering (AREA)
• Environmental & Geological Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Hard Magnetic Materials (AREA)
• Processing Of Solid Wastes (AREA)
• Manufacturing Cores, Coils, And Magnets (AREA)
• Glanulating (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=76730772

Family Applications (1)

Country Status (4)

Family Cites Families (3)

• 2021
  • 2021-05-10 FR FR2104940A patent/FR3122665B1/fr active Active
• 2022
  • 2022-05-06 EP EP22724828.3A patent/EP4337803A1/de active Pending
  • 2022-05-06 JP JP2023569792A patent/JP2024520299A/ja active Pending
  • 2022-05-06 WO PCT/FR2022/050873 patent/WO2022238642A1/fr active Application Filing

Also Published As

Similar Documents

Legal Events