Classifications

• • 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
• • 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
• • 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
  • H01F1/06—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 in the form of particles, e.g. powder
  • H01F1/065—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 in the form of particles, e.g. powder obtained by a reduction

Definitions

• the invention relates to an improved process intended to optimize the magnetic properties of a material endowed with permanent magnet properties, with a view to obtaining a product with high magnetic performance and presenting itself in finely divided form. More specifically, it relates to a process capable of increasing the internal magnetic energy of such a material, of the rare earth / iron / boron alloy type, obtained after decrepitation by hydriding-dehydriding procedure. Finally, it also relates to the products obtained by this process.
• bonded magnets are carried out fundamentally by the introduction of a large amount of magnetic material in the most divided form possible, in an organic continuous matrix, generally made of a synthetic polymer. This step is carried out in a traditional manner using a twin screw, at the polymer melting temperature. In this way, in order to obtain high performance bonded magnets, it is sought to introduce into the matrix the greatest possible quantity of magnetic material. In the context of optimizing such magnets, the aim is to minimize the size of the "particles" constituting the magnetic material, while increasing the magnetic properties, and in particular the coercivity of said "particles".
• this small distribution, and the effective size of the "particles” obtained depend on the one hand, on the dispersibility of the powders, namely, their ability to disperse homogeneously, for example in the matrix or coating resin, and on the other hand their orientability, namely, their ability to orient themselves under magnetic field, and more precisely to align their direction of easy magnetization with the direction of the applied magnetic field, and this by rotation mechanical.
• One of the aims of the present invention is to propose a process capable of manufacturing such powders, having a high coercivity.
• the object of the invention consists, starting from materials having qualities of permanent magnets - intrinsically self, or potentially (example amorphous product) - to obtain powders having the same magnetic properties as their precursors by applying heat treatments meeting particular conditions.
• the invention also aims to obtain powder of small homogeneous particle size, endowed with these magnetic properties.
• a second thermal treatment is applied at a temperature close to 600 ° C., that is to say a temperature higher than the hydride desorption temperature of the main phase of the material.
• this thermal post-treatment makes it possible to obtain a dehydriding of the set of phases constituting the base alloy. Indeed, as we know, whatever the method of obtaining the latter, we must go through a step of melting the base material in order to obtain an alloy in mas sive form. This fusion not being congruent, there exists between the preponderant entities, constitutive of the "magnetic" phase proper, one or more secondary phases with eutectic behavior, richer in rare earth elements. In fact, the subsequent heat treatments aim to dehydrate this or these secondary phases. Finally, by a third heat treatment, the aim is to reshape the envelope with a concentration rich in rare earth elements.
• primary vacuum is meant in the sense of the invention a vacuum preferably less than 10 -2 to 10 ⁇ * millimeters of mercury (or about 1 to lu -2 Pa). This primary vacuum is intended to allow the evacuation of hydrogen gas as it is formed. The duration of the thermal dehydration treatments is moreover linked to the restoration of the initial primary vacuum.
• the duration of the dehydriding treatment depends on the base material used. It is followed by cooling at constant speed, speed also depending on the starting material.
• this first post-treatment can be followed by a thermal plateau, then by subsequent thermal treatments, the purpose of which is similar to the first.
• Another approach consists on the contrary of starting from an isotropic powder of fine and uniform particle size obtained for example by decrepitation with hydrogen at very high temperature (600 to 900 ° C), then to subject this powder to a treatment of plastic deformation type that hot (analogous to that carried out in the previous case at the level of the precursor) intended to induce in the said powder a certain degree of anisotropy without risk of cause it to sinter.
• plastic deformation type that hot (analogous to that carried out in the previous case at the level of the precursor) intended to induce in the said powder a certain degree of anisotropy without risk of cause it to sinter.
• a mode of treatment has been aimed at associated with a suitable precursor composition making it possible to induce a maximum rate of magnetic anisotropy at the level of this precursor.
• a technique of particle size reduction has been used, such as decrepitation with hydrogen practiced under moderate temperature conditions, followed by an appropriate post-treatment of dehydrogenation, capable of fully preserving the very strong anisotropy. of the precursor used for this purpose.
• the starting product therefore plays a fundamental role both in terms of its composition and its isotropic or anisotropic character, the latter being preserved through successive stages of decrepitation and post-treatments.
• this product is advantageously a rare earth / iron / boron alloy, the fe being able to be partially substituted by cobalt or by other transition elements (3d, 4d, 5d).
• part of this iron or cobalt element can be substituted by other elements such as copper or aluminum.
• a highly anisotropic precursor is obtained (in terms of its magnetic characteristics) if the o uses materials derived from "powder metallurgy", a technique described in more detail in document EP-A-0 101 552, or if we start from massive magnet falls.
• magnetic anisotropic precursors resulting from a specific hyper-tempering treatment.
• Massive precursors or in ribbons having contrary isotropic magnetic properties are obtained in the framework of the process of hot-working made by spinning, also described in the document 87/07425, or in the hyper-quenching process on roll described in particular in the document EP-A-0 108 474.
• the invention also relates to the product obtained. It is a product having good magnetic properties, typically an internal energy (HB) m greater than or equal to 80 kJ / m 3 for isotropic powders and 240 kJ / m 3 for anisotropic powders, with a small homogeneous particle size, typically close to ten micrometers, or less, and in any event less than fifteen (15) micrometers.
• these products have a remanent magnetization typically of at least 40 Am 2 / kg for isotropic powders and 80 Am 2 / kg for oriented anisotropic powders and a high coercivity of at least 700 kA / m.
• the grains of the products obtained have characteristic facies in the form of broken crystallites typical of the morphology resulting from this process of re-reading.
• Products with magnetic properties are also known, having a homogeneous and small particle size, the limit of which can be less than 0.1 ⁇ m. These products are for example obtained by means of the procedure described in the document already cited EP-A-0 173 588. As already said, the decrepitation of the products by hydriding dehydrating certainly allows to obtain products of small particle size but with a significant loss magnetic properties.
• the starting material is a material having the massive state already of high magnetic properties.
• the method according to the invention aims, following a decrepification having reduced its magnetic properties, to restore them to result in magnetic properties, in particular in coercivity, and residual induction, close to those of the starting crude product.
• the starting product is an isotropic or anisotropic polyphase alloy depending on the destination of the final product, of rare earth / iron / boron composition.
• the iron can be substituted with cobalt, in particular with a view to increasing the Curie point of the final product or with other 3d transition metals, such as copper, or 4d and 5d.
• iron can also be partially substituted by other metallic elements such as aluminum, and this cumulatively with the transition elements.
• This alloy is, as already said, in polyphase form, respectively a magnetic phase with high anisotropy, corresponding to the general formula R ⁇ -M i4 -B, and one or more other phases with a concentration mainly in rare earth elements, consecutive to the embodiment of the basic material.
• the method of obtaining these starting materials will not be described in detail. As already said, they can be obtained according to the so-called "rapid quenching" technique, mechanical hot grinding or corroying, or even by the powder metallurgy technique, ie sintered powders previously oriented under field magnetic.
• this basic material is firstly hydrided by absorption of hydrogen under pressure (1 to 5 MPa) for example in an autoclave made of special steel, and generally at room temperature.
• pressure 1 to 5 MPa
• thermal activation is necessary.
• one or a few thermal cycling during the hydrogenation phase ensure better chemical and particle size homogeneity of the material.
• This hydriding results in the frag ⁇ mentation of the material, which thus becomes very easily dispersible.
• the revelation of the pulverulent form of the material can be obtained by simple mechanical agitation, or by simple grinding.
• the hydrogenated pulverulent material undergoes three treatment phases:
• a partial dehydrogenation is carried out, which concerns phase principa ⁇ the hydrided R 2 -M i4 -BH x (where x is between 1 and 5), the latter being transformed into R 2 -M r4 -B.
• the dehydriding must be carried out under primary vacuum at a temperature below their demixing temperature, otherwise, the formation of rare earth hydrides, of iron and a poorly defined iron-boron phase, the magnetic properties of the material then being definitively and unacceptably altered.
• the temperature of this partial dehydriding which can start under primary vacuum around 150 ° C, and q increases around 300 ° C, must not exceed 520 ° demixing temperature of hydrides R ⁇ -M ⁇ -BH ,,.
• q is carried out at a temperature of the order of 600 ° C.
• complete dehydration of the decrepit material can be carried out, in particular at the level of the eute tick rich in rare earths , which constitutes the film envelope of the magnetic domains
• This second phase is also carried out under primary vacuum.
• the dehydrated powder thus obtained can be subjected in a third phase to an annealing treatment between 450 and 1000 ° C., aimed at completely restoring the magnetic properties, in particular the coer civity.
• the treatment can advantageously be supplemented with an in-situ passivation by introducing argon under normal pressure, before bringing the product to normal temperature.
• the final heat treatments aim at optimizing at the level of the elementary particles the cohesion of the granular material, namely the phase of type R 2 -M i4 -B and its eutectic intergranular envelope.
• the different parameters of these heat treatments are a function of the composition of the base material and their metallurgical synthesis process.
• We choose different types of starting materials in the sense of the metallurgy of their preparation), depending on whether we want to favor the magnetization properties or coercivity properties.
• the choice of the starting material also depends on the desired anisotropy of the final product. This choice comes both in its composition and in its synthesis process.
• Figure 1 a block diagram that the different stages involved in the production of a bonded magnet.
• the powders obtained after the various heat treatments are dispersed before being coated in a resin, then oriented in the field.
• Example 1 Phase a
• An isotropic compound corresponding to the following chemical formula is used as precursor material: obtained by hyper-quenching at the speed of 50 m / s. Sintered in massive form, such a material is known to present good magnetic properties, such as: remanent induction: 85 Am 2 / kg. Coercive field: 1,250 kA / m
• This material undergoes a decrepitation treatment by hydriding, and the desorption is carried out by a thermal treatment above 180 ° C.
• This treatment aimed at desorbing the hydrogen from the main phase, is carried out at a speed of 300 ° C / hour. It constitutes the so-called dehydriding phase, carried out under primary vacuum. It is followed by a thermal plateau for 1 hour at 520 ⁇ C and finally by cooling at the speed of 150 ⁇ C / hour.
• a residual induction of 42 Am 2 / kg is obtained, but a very reduced coercive field of 120 kA / m, which makes this material not usable for shaping in the state of bound magnet.
• phase a from the same material, then the latter is subjected to a second heating phase at 600 ° C., temperature obtained at the speed of 300 ° C./hour.
• This treatment is followed by heating to 640 ° C, temperature obtained at the speed of 50 ⁇ C / hour, the thermal plateau at 640 ° C being maintained for 30 minutes.
• This phase is followed by rapid cooling down to 600 ° C, at a speed of 1000 ° C / hour, followed by a temperature decrease of 150 ⁇ C / hour.
• results obtained are respectively:. a residual induction of 56 Am ⁇ / kg on a non-oriented sample of compaction 0.4; and a coercive field of 1,100 kA / m.
• Nd x6 Fe 77 AlB 6 obtained by hot working by spinning, with a working rate of 12.
• This material has the following magnetic characteristics in a solid state:. Residual induction: 75 Am 2 / kg. Coercive field: 950 kA / m This material is decrepit and then heat treated, in the same manner as that described in the Example.
• Example 1 The same precursor material which has undergone the treatment of Example 1 (phase a), then undergoes heating at 10,600 ° C., temperature obtained at the speed of 300 ° C./h
• Nd X5 DyFe ⁇ B6 obtained by spinning and forging by hot working (working rate 25: 10).
• the initial magnetic characteristics of the material in massive form are respectively:
• the material is decrepit by hydriding, then heated to 520 G C under primary vacuum, temperature obtained at the speed of 300 ° C / hour. It undergoes a thermal plateau lasting one hour at this temperature then is
• the sample in the form of a non-oriented anisotropic powder of compaction 0.4, exhibits a residual induction of 40 Am 2 / kg for a coercive field of 1,200 kA / m.
• Example 4 We start from an anisotropic precusor material corresponding to the crude formula:
• Nd i6 Cu_.Fe 76 B 6 obtained by forging by hot working, with a working rate of 10.
• the initial magnetic characteristics of this material in massive form are respec ⁇ tively:
• Residual induction 116 Am 2 / kg.
• Coercive force 1.030 kA / m
• Example 3 This material is then treated as indicated in Example 3.
• the powder thus obtained is obtained as magnetic properties, in the non-oriented state, with a compaction of 0.4:
• Persistent induction 53 Am 2 / kg.
• Coercive field 720 kA / m.
• This powder is then heat treated at 1000 ° C and then at 500 ° C and is then coated in a resi ⁇ ne under magnetic field.
• the characteristics of the oriented powder thus introduced become:. Residual induction: 96 Am 2 / kg. Coercive field: 720 kA / m.
• the powders thus obtained taking into account their small homogeneous particle size on the one hand, and their high magnetic properties on the other hand, enabled the production of anisotropic bonded magnets, for which the measured remanent induction is increased by 30 at 40% compared to the anisotropic bonded magnets available today, and this for substantially the same charge of magnetic material.

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• Crystallography & Structural Chemistry (AREA)
• Inorganic Chemistry (AREA)
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• 1990
  • 1990-07-02 FR FR9008582A patent/FR2664086A1/fr active Granted
• 1991
  • 1991-06-28 EP EP91912597A patent/EP0538320B1/fr not_active Expired - Lifetime
  • 1991-06-28 WO PCT/FR1991/000517 patent/WO1992000595A1/fr not_active Ceased
  • 1991-06-28 JP JP3511665A patent/JPH06501135A/ja active Pending
  • 1991-06-28 AT AT91912597T patent/ATE106600T1/de not_active IP Right Cessation
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