METHOD FOR PRODUCING A PERMANENT MAGNET FROM A MAGNETIC STARTING MATERIAL

Abstract

The invention relates to a method for producing a permanent magnet from a magnetic base material, wherein the magnetic base material is shaped, wherein a raw form is created, wherein the raw form is subjected to grain refinement, wherein the raw form is sintered, wherein the permanent magnet is produced.

Claims

1. Method for producing a permanent magnet from a magnetic base material, wherein the magnetic base material is shaped, wherein a raw form is created, wherein the raw form is subjected to grain refinement, wherein the raw form is sintered, wherein the permanent magnet is produced.

2. The method according to claim 1, wherein as magnetic base material is used a material comprising particles of R.sub.xT.sub.yB alloy and preferably particles of rare-earth-rich phase.

3. The method according to claim 1, wherein the magnetic base material is mixed with an organic binder, wherein a mixture of the magnetic base material and the organic binder is obtained, wherein the raw form is prepared from the mixture, wherein the organic binder is at least partially, preferably completely, removed from the raw form prior to grain refinement.

4. The method according to any claim 1, wherein the magnetic base material is mixed with an organic solvent, wherein a mixture of the magnetic base material and the organic solvent is obtained, wherein the raw form is prepared from the mixture, wherein the organic solvent is at least partially, preferably completely, removed from the raw form prior to grain refinement.

5. The method according claim 1, wherein the grain refinement comprises a hydrogen intercalation step and a recombination step, wherein in the hydrogen intercalation step the raw form, in particular the particles of the magnetic base material of which the raw form consists of, is reacted with hydrogen, wherein in the recombination step the hydrogen is at least partially, preferably completely, removed.

6. The method according to claim 1, wherein the hydrogen intercalation step is carried out in an atmosphere comprising hydrogen under a predetermined intercalation-pressure for a predetermined intercalation-duration, wherein the raw form is heated to a predetermined intercalation-temperature during the hydrogen intercalation step.

7. The method according to claim 1, wherein the recombination step is carried out in an atmosphere comprising an operation gas or consisting of the operation gas under a predetermined recombination-pressure and a predetermined recombination-temperature for a predetermined recombination-duration.

8. The method according to claim 1, wherein the operation gas is selected from a group consisting of hydrogen, argon, and helium.

9. The method according to claim 1, wherein the raw form is cooled to a predetermined cool-down temperature during or after the recombination step.

10. The method according to claim 1, wherein the raw form is produced by a method selected from a group consisting of injection moulding, additive manufacturing, extrusion, cold pressing, and hot pressing.

11. The method according to claim 1, wherein the raw form is produced in an externally applied magnetic field.

12. The method according to claim 1, wherein the raw form is sintered at a predetermined sinter-pressure and at a predetermined sinter-temperature, preferably a temperature of at least 900 C. to at most 1200 C., in an atmosphere consisting of a process gas for a predetermined sinter-duration.

13. The method according to claim 1, wherein the process gas is selected from a group consisting of argon and helium.

14. The method according to claim 1, wherein the sintered raw form is posttreated by hot isostatic pressing.

Description

[0064] The invention is explained in more detail below with reference to the drawing. Thereby show:

[0065] FIG. 1 a flow diagram of a method for producing a permanent magnet,

[0066] FIG. 2 a schematic representation of an embodiment of a grain refinement in a first embodiment of a raw form, and

[0067] FIG. 3 a schematic representation of a second embodiment of a raw form.

[0068] FIG. 1 shows a flow diagram of a method for producing a permanent magnet.

[0069] In step a), the magnetic base material is provided, preferably in powdered form. Preferably, the powdered magnetic base material is obtained by grinding a cast ingot, a melt-spun material or a recycled magnetic material. Preferably, the base material is embrittled by hydrogen embrittlement prior to milling. Preferably, the magnetic base material comprises particles of an R.sub.xT.sub.yB alloy, preferably an Nd.sub.2Fe.sub.14B alloy, and preferably particles of a rare-earth-rich phase.

[0070] In step b), the magnetic base material is shaped, wherein a raw form 1 shown in FIG. 2 a) is created. The raw form 1 is preferably produced by a method selected from a group consisting of injection moulding, additive manufacturing, extrusion, cold pressing, and hot pressing. Optionally, the raw form 1 is produced under an externally applied magnetic field. Preferably, the magnetic field is generated by a switchable electromagnet and/or a permanent magnet.

[0071] In step c), grain refinement is carried out on the raw form 1. The grain refinement process step preferably comprises a hydrogen intercalation step, in particular step c1), and a recombination step, in particular step c2). Preferably, in the hydrogen intercalation step, the raw form 1, in particular the particles of the magnetic base material constituting the raw form 1, is reacted with hydrogen. Preferably, the hydrogen intercalation step is performed in an atmosphere comprising hydrogen under a predetermined intercalation-pressure for a predetermined intercalation-duration. During the hydrogen intercalation step, the raw form 1 is heated to a predetermined intercalation-temperature.

[0072] Preferably, in the subsequent recombination step, the hydrogen is at least partially, preferably completely, removed from the raw form 1. Preferably, the recombination step is carried out in an atmosphere comprising or consisting of an operation gas, preferably hydrogen, argon, and/or helium, under a predetermined recombination-pressure and a predetermined recombination-temperature for a predetermined recombination-duration. Optionally, the raw form 1 is cooled to a predetermined cool-down temperature during or after the recombination step, in particular during or after step c2).

[0073] In step d), the raw form 1 is sintered, wherein the permanent magnet is produced. Preferably, the raw form 1 is sintered at a predetermined sinter-pressure, preferably at least 10.sup.5 mbar absolute to at most 50 mbar above atmospheric pressure, at a predetermined sinter-temperature, preferably at a temperature of at least 900 C. to at most 1200 C., in an atmosphere consisting of a process gas, preferably argon and/or helium, for a predetermined sinter-duration, preferably at least 30 minutes to at most 240 minutes.

[0074] Between step a) and step b), process step e) may optionally be carried out. In step e), the magnetic base material is mixed with an organic binder or an organic solvent, wherein a mixture of the magnetic base material and the organic binder or the organic solvent is obtained. In this case, the raw form 1 is created from the mixture in step b). An organic binder is preferably used if the raw form 1 is created by injection moulding. An organic solvent is preferably used if the raw form 1 is created by means of wet cold pressing.

[0075] If step e) is carried out, process step f) is obligatorily carried out between step b) and step c). In step f), the organic binder or the organic solvent which was added to the magnetic base material in step e) is at least partially, preferably completely, removed.

[0076] Optionally, an additional process step g) can be carried out between step b) and step c) or between step f) and step c). In step g), the raw form is hydrogenated in an atmosphere comprising hydrogen, in particular a hydrogen atmosphere or in pure hydrogen, preferably at a pressure of at least 50 mbar absolute to at most 50 mbar above atmospheric pressure, and preferably at a temperature of at least 600 C. to at most 900 C., preferably for a duration of at least 30 minutes to at most 180 minutes.

[0077] Optionally, an additional process step h)individually or in combination with process steps e), f) and g)can be carried out after step d). In step h), the sintered raw form 1 is post-processed by hot isostatic pressing to post-compress the permanent magnet. Hot isostatic pressing is carried out at a pressure of preferably at least 800 bar to at most 2000 bar and at a temperature of preferably at least 900 C. to at most 1200 C. for a duration of preferably at least 30 minutes to at most 240 minutes.

[0078] FIG. 2 shows a schematic representation of an embodiment of a grain refinement in a first embodiment of a raw form 1. The first embodiment of a raw form 1 comprises particles of an Nd.sub.2Fe.sub.14B alloy.

[0079] In FIG. 2 a), a section 3 of a single large Nd.sub.2Fe.sub.14B grain 5, as part of the magnetic base material, is shown. The Nd.sub.2Fe.sub.14B grain 5 comprises a magnetic axis 7. The raw form 1 shown in FIG. 2 a) is subjected to a hydrogen intercalation step. In this process, hydrogen is incorporated into the raw form 1 and the particles of the Nd.sub.2Fe.sub.14B alloy, in particular the Nd.sub.2Fe.sub.14B grain 5 shown, are split according to the chemical reaction (1).

[0080] FIG. 2 b) shows the section 3 after the chemical reaction (1), in particular after the hydrogen intercalation step. The Nd.sub.2Fe.sub.14B grain 5 has been split into a plurality of NdH.sub.x grains 9, a plurality of Fe grains 11, a plurality of Fe.sub.2B grains 13 and a plurality of Nd.sub.2Fe.sub.14B grains 15. Only the plurality of Nd.sub.2Fe.sub.14B grains 15 comprises the magnetic axis 7. The plurality of NdH.sub.x grains 9, the plurality of Fe grains 11, and the plurality of Fe.sub.2B grains 13 do not have magnetic axis. Advantageously, the NdH.sub.x grains 9, the Fe grains 11, the Fe.sub.2B grains 13, and the Nd.sub.2Fe.sub.14B grains are each smaller than the initial Nd.sub.2Fe.sub.14B grain 5. For clarity, only one grain 9, 11, 13, and 15 and one magnetic axis 7 are each provided with a reference sign. The raw form 1 from FIG. 2 b) is subjected to a recombination step in which the hydrogen is at least partially, preferably completely, removed from the raw form 1. The recombination step is carried out in accordance with the chemical reaction (2).

[0081] FIG. 2 c) shows the section 3 after the chemical reaction (2), in particular after the recombination step. By removing the hydrogen, the individual grains of the plurality of NdH.sub.x grains 9, the plurality of Fe grains 11, the plurality of Fe.sub.2B grains 13, and the plurality of Nd.sub.2Fe.sub.14B grains 15 combine to form another plurality of new Nd.sub.2Fe.sub.14B grains 17. Each grain of the plurality of Nd.sub.2Fe.sub.14B grains 17 comprises the magnetic axis 7. For clarity of illustration, a grain 17 and a magnetic axis 7 are indicated by a reference sign. Advantageously, the Nd.sub.2Fe.sub.14B grains 17 are each smaller than the initial Nd.sub.2Fe.sub.14B grain 5 of FIG. 2 a).

[0082] Advantageously, the magnetic axis 7or the sum of the magnetic axes 7is almost unchanged before, during and after grain refinement as shown in FIG. 2.

[0083] FIG. 3 shows a schematic representation of a second embodiment of a raw form 1. The raw form 1 consists of Nd.sub.2Fe.sub.14B grains 5, 17 and a plurality of particles 19 of a rare-earth-rich phase, preferably a neodymium-rich phase, which is preferably present as a hydride. The magnetic axes 7 of the Nd.sub.2Fe.sub.14B grains 5, 17 exhibit almost the identical direction. For a clearer representation, an Nd.sub.2Fe.sub.14B grain 5, 17, a rare-earth-rich particle 19 and a magnetic axis 7 are indicated by a reference sign.