ND-FE-B PERMANENT MAGNETIC MATERIAL AND PREPARATION METHOD THEREOF

Description

[0001] The present invention relates to an Nd-Fe-B permanent magnetic material and a preparation method thereof.

BACKGROUND

[0002] Because of their magnetic properties, low cost and ample reserves, Nd-Fe-B permanent magnetic materials are widely used in vehicles, computers, electronics, mechanical and medical devices, etc. In addition, because of their high performance/price ratio, Nd-Fe-B materials have been the ideal materials to produce magnetic devices with high efficiency, small volume and light mass. However, as the continuous expansion of application fields and the development of technology, requirements for performance, operating temperature and corrosion resistance of permanent magnetic materials become higher and higher.

[0003] WO 2009/057742 A1 discloses a permanent magnet, comprising SmFeN type of magnetic material and Co ferrite, obtained by mixing those materials, orientating in a magnetic field, sintering and heat treating.

[0004] JP 2002 164205 A discloses a bonded composite magnet including R-T-B-type and magnetoplumbite ferrite powders. JP 2005 159054 A discloses a sintered magnet including R-T-B-type and Ba/Sr ferrite powders.

SUMMARY

[0005] In view thereof, the present invention is directed to provide an Nd-Fe-B permanent magnetic material, according to claim 1, with good high temperature and corrosion resistance properties, and further to provide a preparation method of the Nd-Fe-B permanent magnetic material, according to claim 5.

[0006] A permanent magnetic material with good high temperature and corrosion resistance properties is provided, which comprises an Nd-Fe-B alloy and an additive comprising a cobalt ferrite.

[0007] A method of preparing the permanent magnetic material is also provided, which comprises the steps of mixing an Nd-Fe-B alloy and an additive including at least a cobalt ferrite to obtain a mixture; magnetically orienting and pressing the mixture in a magnetic filed; and sintering and tempering the mixture under protection of vacuum or an inert gas.

[0008] The cobalt ferrite is 0.5 wt % to 10 wt % of the Nd-Fe-B alloy.

[0009] An average particle diameter of the cobalt ferrite is in a range of 10 nanometers to 150 nanometers.

[0010] The cobalt ferrite is represented by a general formula of Co_nFe_3-nO₄, and n is in a range of 0.1≤n≤2.0.

[0011] The Nd-Fe-B alloy is represented by a general formula of Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d, where: Re is at least one element selected from a group consisting of Pr, Dy, Tb, Ho, Gd, La, Ce and Y; M is at least one element selected from a group consisting of Co, Al, Cu, Zr, Ga, Nb and Mo; and a, b, c, and d are atomic weight ratios, in which a is in a range of 1 ≤ a ≤ 10, b is in a range of 5 ≤ b ≤ 12, c is in a range of 5 ≤ c ≤ 8, and d is in a range of 0 ≤ d ≤ 15.

[0012] Additional aspects and advantages of the embodiments of present invention will be given in part in the following descriptions, become apparent in part from the following descriptions, or be learned from the practice of the embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] These and other aspects, solutions and advantages of the invention will become apparent and more readily appreciated from the following descriptions.

[0014] A permanent magnetic material is provided, which comprises an Nd-Fe-B (neodymium-iron-boron) alloy and an additive including at least a cobalt ferrite. The inventors of the present invention have found: by adding particles of a cobalt ferrite and distributing them uniformly along the grain boundary of the Nd-Fe-B alloy, the over-growth of the grain and magnetic domain size of the Nd-Fe-B alloy may be inhibited (i.e. pinning effect), thus improving the operating temperature effectively, and the cobalt element itself and neodymium can produce stable intergranular additional structure, thus improving the corrosion resistance property. The content of the heavy metal cobalt may be reduced because of adding a nano-cobalt ferrite, thus lowering the cost. An appropriate amount of oxygen in the cobalt ferrite may improve the high temperature resistance properties of the permanent magnetic material. Meanwhile, due to the presence of the cobalt ferrite, the corrosion resistance property of the permanent magnetic material may be improved greatly.

[0015] The cobalt ferrite is 0.5 wt % to 10 wt % of the Nd-Fe-B alloy. The average particle diameter of the cobalt ferrite ranges from 20 nanometers to 60 nanometers. The cobalt ferrite is represented by a general formula of Co_nFe_3-nO₄, in which n is in a range of 0.1≤n≤2.0. The particles of the cobalt ferrite are distributed uniformly along the grain boundary of the main phase of the Nd-Fe-B alloy, thus forming the pinning effect. However, the content of cobalt may not exceed 20 wt % of the total weight of the Nd-Fe-B permanent magnetic material, otherwise the coercive force may be seriously reduced.

[0016] In some embodiments, the Nd-Fe-B alloy is represented by a general formula of Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d, where Re is at least one element selected from the group consisting of Pr, Dy, Tb, Ho, Gd, La, Ce and Y; M is at least one element selected from the group consisting of Co, Al, Cu, Zr, Ga, Nb and Mo; and a, b, c, and d are atomic weight ratios, in which a is in a range of 1 ≤ a ≤ 10, b is in a range of 5 ≤ b ≤ 12, c is in a range of 5 ≤ c ≤ 8, and d is in a range of 0 ≤ d ≤ 15.

[0017] In a second aspect of the present invention, an embodiment of the present invention provides a method of preparing a permanent magnetic material, comprising steps of: mixing an Nd-Fe-B alloy and an additive including at least a cobalt ferrite to obtain a mixture; magnetically orienting and pressing the mixture in a magnetic filed; and sintering and tempering the mixture under protection of vacuum or an inert gas. The sintering and tempering are performed under the protection of vacuum, alternatively under the protection of an inert gas. The method of preparing a permanent magnetic material employing the sintering process may include without limitation one or more of the following steps: formulating, melting, crushing, milling, magnetically orienting and pressing in a magnetic field, sintering in vacuum, mechanical processing and electroplating.

[0018] Some of the steps of the method are described as follows:

(1) The Nd-Fe-B alloy is crushed and milled to form a powder. The crushing process is a hydrogen decrepitation process or a mechanical crushing process using a crusher. In some embodiments, jet milling and ball milling under an inert gas may be utilized to produce a powder with an average particle diameter of 2 microns to 10 microns. The Nd-Fe-B alloy is an Nd-Fe-B alloy ingot or a strip casting flake, both of which are commercially available. The Nd-Fe-B alloy ingot is prepared by a casting process, and the strip casting flake is prepared by a strip casting flaking process. The Nd-Fe-B alloy is represented by the following general formula: Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d, where Re is at least one element selected from the group consisting of Pr, Dy, Tb, Ho, Gd, La, Ce and Y; M is at least one element selected from the group consisting of Co, Al, Cu, Zr, Ga, Nb and Mo; and a, b, c, and d are atomic weight ratios, in which a is in a range of 1 ≤ a ≤ 10, b is in a range of 5 ≤ b ≤ 12, c is in a range of 5 ≤ c ≤ 8, and d is in a range of 0 ≤ d ≤ 15.
The casting process is known to those skilled in the art, and comprises steps of casting a melted alloy melt in a water-cooled copper mould. The Nd-Fe-B alloy ingot comprises columnar crystals, where the columnar crystals are separated by Nd-rich phase thin layers. Particularly, the distance between two adjacent Nd-rich phase layers ranges from 100 microns to 1500 microns.
The strip casting flaking process is known to those skilled in in the art, and comprises the steps of pouring a melted alloy onto a rotating copper roller surface, with a rotating linear velocity of the copper roller surface ranging from 1 (meter per second) m/s to 2 m/s, and then rapidly cooling the melted alloy to form flakes with different widths and with a thickness ranging from 0.2 millimeter to 0.5 millimeter. The columnar crystals in the flakes may have a width ranging from 5 microns to 25 microns.
The hydrogen decrepitation process using a hydrogen decrepitation furnace is known to those skilled in the art, for example, one method comprises the steps of placing an Nd-Fe-B alloy with fresh surfaces into a stainless steel vessel, filling the vessel with high purity hydrogen until one atmospheric pressure after vacuumizing, and then maintaining at the pressure for 20 minutes to 30 minutes until the alloy decrepitates and the temperature the vessel increases, this is resulted from the decrepitation of the alloy due to the formation of a hydride after the alloy absorbs hydrogen, and finally vacuumizing and dehydrogenating the hydride for 2 hours to 10 hours under the temperature 400 °C to 600 °C.
The mechanical crushing process is known to those skilled in the art, for example, a process comprises the steps of rough crushing in a jaw crusher, followed by mechanical crushing in a fine crusher.
The jet milling is known to those skilled in the art, and comprises the steps of accelerating powder particles to a supersonic speed using an air flow, and then causing the particles to clash with each other to break up.

(2) The Nd-Fe-B alloy powder and the additive are mixed uniformly using a mixer to obtain a mixed powder.
The additive comprising a cobalt ferrite is subject to decentralized processing in advance. The amount of the cobalt ferrite is 0.5 wt % to 10 wt % of the total weight of the Nd-Fe-B matrix powder. The cobalt ferrite has an average particle diameter of 10 nanometers to 150 nanometers, particularly 20 nanometers to 60 nanometers.
The alloy and the additive are mixed in the presence of an antioxidant, or in the presence of an antioxidant and a lubricant. Based on the weight of the Nd-Fe-B alloy, the amount of the antioxidant ranges from 0.1 wt % to 5 wt %, and the amount of the lubricant ranges from 0 wt % to 5 wt %. There is no special limit to the antioxidant, for example, the antioxidant is at least one selected from the group consisting of: polyethylene oxide alkyl ether, polyethylene oxide monofatty ester and polyethylene oxide alkenyl ether, For example, an antioxidant commercially available from the Shenzhen Deepocean Chemical Industry Co. Ltd, P.R.C. The lubricant is at least one selected from the group consisting of gasoline, oleic acid, stearic acid, polyhydric alcohol, polyethylene glycol, sorbitan, and stearin.
The mixing process is known to those skilled in the art. For example, the mixing process is carried out in a mixer.

(3) The mixed powder obtained is oriented and pressed in a magnetic field to form a parison.
Pressing the mixed powder in a magnetic filed to form a parison is achieved by using a well known process and a magnetically orienting-forming-pressing machine. The orienting magnetic field has an intensity of 1.2 Tesla (T) to 3.0 T, and the pressing is carried out under a pressure of 10 megapascals (MPa) to 200 MPa for 10 seconds to 60 seconds. The orientation degree of the magnetic powder may be improved by further increasing the magnetic field intensity. The formation of the parison is performed in a completely closed glove box with isolating the magnetic powder from the air, thus avoiding the fire risk due to the oxidation and heat generation of the magnet and reducing the content of oxygen in the final magnet.

(4) The parison is sintered and tempered under protection of vacuum or an inert gas to obtain the Nd-Fe-B permanent magnetic material.

[0019] The sintering and tempering process is known to those skilled in the art. The sintering and tempering process are carried out under protection of vacuum or an inert gas. The inert gas is any gas that does not participate in the reaction, for example, one selected from the group consisting of: nitrogen, helium, argon, neon, krypton and xenon. The parison is sintered at a temperature of 1030 °C to 1120 °C for a period of 2 hours to 8 hours, then tempered in a first tempering step at a temperature of 800 °C to 920 °C for a period of 1 hour to 3 hours, and finally tempered in a second tempering step at a temperature of 500 °C to 650 °C for a period of 2 hours to 4 hours. The second tempering step may further improve the coercive force. Because the cobalt ferrite has a melting point above 1120°C, when sintered at the above temperature, the cobalt ferrite may not be decomposed and melted.

[0020] The present disclosure will be described in detail with reference to the following examples.

EXAMPLE 1

[0021] 

(1) An Nd-Fe-B alloy represented by the formula (PrNd)_10.61Dy_3.5Tb_1.3Fe_77.55 B_5.87Co_1.68Al_0.5Cu_0.16Ga_0.13 (a%) was prepared by a strip casting flaking process with a rotating linear velocity of a copper roller surface of 1.5 meters per second. The flake had a thickness of 0.3 millimeter.

(2) The alloy was crushed by a hydrogen decrepitation process in a hydrogen decrepitation furnace. After absorbing hydrogen to saturation at room temperature and being dehydrogenated at 550 °C for 6 hours to prepare a crushed powder, the crushed powder was milled via jet milling under a nitrogen atmosphere to produce a powder with an average particle diameter of 3.5 microns.

(3) CoFe₂O₄ with an average particle diameter of 50 nanometers and an antioxidant (commercially available from the Shenzhen Deepocean Chemical Industry Co. Ltd, P.R.C.) were added to the Nd-Fe-B alloy powder. Based on the weight of the Nd-Fe-B alloy powder, the amount of the CoFe₂O₄ was 1 wt % and the amount of the antioxidant was 0.5 wt %.

(4) The mixed powder was pressed by using a magnetically orienting-forming-pressing machine in a closed glove box filled with a nitrogen gas to form a parison. The intensity of the orienting magnetic field was 1.6 T, the pressure was 100 MPa, and the pressing time was 30 seconds.

(5) The compacted parison was sintered in a vacuum sintering furnace under a degree of vacuum of 2×10^-2 Pa at a temperature of 1080 °C for 3 hours, then tempered at 850 °C for 2 hours, and finally tempered at 550 °C for 3 hours to prepare an Nd-Fe-B permanent magnetic material labeled as T1.

COMPARATIVE EXAMPLE 1

[0022] In the process of the COMPARATIVE EXAMPLE 1, no nano-sized cobalt ferrite CoFe₂O₄ was added, and the other steps are substantially similar to those of EXAMPLE 1.

[0023] The Nd-Fe-B permanent magnetic material obtained was labeled as CT1.

EXAMPLE 2

[0024] The process of this example was substantially similar to that of EXAMPLE 1, except that Co₂Fe₁O₄ was used as the additive in stead of CoFe₂O₄, and the amount of Co₂Fe₁O₄ was 5 wt % of the Nd-Fe-B alloy powder.

[0025] The Nd-Fe-B permanent magnetic material obtained was labeled as T2.

EXAMPLE 3

[0026] The process of this example was substantially similar to that of EXAMPLE 1, except that the average particle diameter of the CoFe₂O₄ was 100 nanometers.

[0027] The Nd-Fe-B permanent magnetic material obtained was labeled as T3.

EXAMPLE 4

[0028] The process of this example was substantially similar to that of EXAMPLE 1, except that the amount of the CoFe₂O₄ was 10 wt % of the Nd-Fe-B alloy.

[0029] The Nd-Fe-B permanent magnetic material obtained was labeled as T4.

COMPARATIVE EXAMPLE 2

[0030] The process of this example was substantially similar to that of EXAMPLE 1, except that Co was used as the additive instead of CoFe₂O₄, and an average particle diameter of the Co was 50 nanometers.

[0031] The Nd-Fe-B permanent magnetic material obtained was labeled as CT2.

TEST

1. Corrosion resistance property

[0032] Cylindrical samples with a diameter of 10 millimeters and a length of 7 millimeters were prepared from the permanent magnetic materials T1-T4, CT1 and CT2, and then tested on a HAS-70CP type Highly Accelerated Stress Tester commercially available from Terchy Environmental Technology Ltd, with a temperature of 130 °C, a humidity of 95%, a steam pressure of 2.7 bar, and a period of 10 days. The mass loss (W_loss) of the permanent magnetic materials T1-T4, CT1 and CT2 were recorded in Table 1.

2. Maximum operating temperature

[0033] Cylindrical samples with a diameter of 10 millimeters and a length of 7 millimeters were prepared from the permanent magnetic materials T1-T4, CT1 and CT2 , and then heated using a curve measurement system NIM200C (National Institute of Metrology, P.R.C.) from a temperature of 60°C with a 2°C increment each time. When the line started to bend at a certain temperature, the permanent magnetic materials reached the maximum operating temperature.

[0034] Test results were shown in Table 1.

Table 1

No.	Wloss (mg/cm2)	Inflection Temperature (°C)
T1	2.1	190
T2	1.8	186
T3	2.5	186
T4	1.5	188
CT1	8.2	160
CT2	2.7	170

[0035] It can be seen from the results of Table 1 that T1 has a W_loss of 2.1 mg/cm² and a inflection temperature 190°C and CT2 has a W_loss of 2.7 mg/cm² and an inflection temperature 170°C, so that the permanent magnetic material according to the embodiments of the present disclosure exhibited a better corrosion resistance and higher temperature resistance properties.

Claims

1. A permanent magnetic material, comprising:

an Nd-Fe-B alloy; and

an additive including at least a cobalt ferrite, characterized in that the cobalt ferrite is 0.5 wt % to 10 wt % of the Nd-Fe-B alloy.

2. The permanent magnetic material of claim 1, wherein an average particle diameter of the cobalt ferrite is in a range of 10 nanometers to 150 nanometers.

3. The permanent magnetic material of claim 1, wherein the cobalt ferrite is represented by a general formula of Co_nFe_3-nO₄, where n is in a range of 0.1≤n≤2.0.

4. The permanent magnetic material of claim 1, wherein the Nd-Fe-B alloy is represented by a general formula of Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d, where:

Re is at least one element selected from a group consisting of Pr, Dy, Tb, Ho, Gd, La, Ce and Y;

M is at least one element selected from a group consisting of Co, Al, Cu, Zr, Ga, Nb and Mo; and

a, b, c, and d are atomic weight ratios, in which a is in a range of 1 ≤ a ≤ 10, b is in a range of 5 ≤ b ≤ 12, c is in a range of 5 ≤ c ≤ 8, and d is in a range of 0 ≤ d ≤ 15.

5. A method for preparing a permanent magnetic material, comprising steps of:

mixing an Nd-Fe-B alloy and an additive including at least a cobalt ferrite to obtain a mixture;

magnetically orienting and pressing the mixture in a magnetic filed; and

sintering and tempering the mixture under the protection of vacuum or an inert gas; characterized in that the cobalt ferrite is 0.5 wt% to 10 wt% of the Nd-Fe-B alloy.

6. The method of claim 5, wherein the cobalt ferrite is represented by a general formula of Co_nFe_3-nO₄, where n is in a range of 0.1≤n≤2.0.

7. The method of claim 5, wherein the mixing step comprises mixing the Nd-Fe-B alloy and the additive in the presence of an antioxidant, in which based on the weight of the Nd-Fe-B alloy, the amount of the antioxidant is about 0.1 wt % to about 5 wt %, and the amount of the lubricant is 0 wt % to 5 wt %.

8. The method of claim 5, wherein the mixing step comprises mixing the Nd-Fe-B alloy and the additive in the presence of an antioxidant and a lubricant, in which based on the weight of the Nd-Fe-B alloy, the amount of the antioxidant is about 0.1 wt % to about 5 wt %, and the amount of the lubricant is 0 wt % to 5 wt %.

9. The method of claim 5, wherein the Nd-Fe-B alloy is represented by a general formula of Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d, where:

Re is at least one element selected from a group consisting of Pr, Dy, Tb, Ho, Gd, La, Ce and Y;

M is at least one element selected from a group consisting of Co, Al, Cu, Zr, Ga, Nb and Mo; and

a, b, c, and d are atomic weight ratios, in which a is in a range of 1 ≤ a ≤ 10, b is in a range of 5 ≤ b ≤ 12, c is in a range of 5 ≤ c ≤ 8, and d is in a range of 0 ≤ d ≤ 15.

10. The method of claim 5, wherein an average particle diameter of the cobalt ferrite is in a range of 10 nanometers to 150 nanometers.

11. The method of claim 5, wherein an average particle diameter of the Nd-Fe-B alloy is in a range of 2 microns to 5 microns.

12. The method of claim 5, wherein the magnetically orienting and pressing is performed under a magnetic filed intensity of 1.2 T to 3.0 T and a pressure of 10 MPa to 200 MPa for a period of 10 seconds to 60 seconds; the sintering is performed at a temperature of 1030 °C to 1120 °C for a period of 2 hours to 8 hours; and wherein the tempering steps comprising a first tempering step and a second tempering step, in which the first tempering step is performed at a temperature of 800 °C to 920 °C for a period of 1 hour to 3 hours, and the second tempering step is performed at a temperature of 500 °C to 650 °C for a period of 2 hours to 4 hours.

Ansprüche

1. Permanentmagnetmaterial, umfassend:

eine Nd-Fe-B-Legierung; und einen Zusatzstoff, der mindestens einen Cobaltferrit beinhaltet, dadurch gekennzeichnet, dass der Cobaltferrit 0,5 Gew.-% bis 10 Gew.-% der Nd-Fe-B-Legierung beträgt.

2. Permanentmagnetmaterial nach Anspruch 1, wobei ein durchschnittlicher Teilchendurchmesser des Cobaltferrits in einem Bereich von 10 Nanometern bis 150 Nanometern ist.

3. Permanentmagnetmaterial nach Anspruch 1, wobei der Cobaltferrit durch eine allgemeine Formel Co_nFe_3-nO₄ dargestellt ist, wobei n in einem Bereich von 0,1 ≤ n ≤ 2,0 ist.

4. Permanentmagnetmaterial nach Anspruch 1, wobei die Nd-Fe-B-Legierung durch eine allgemeine Formel Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d dargestellt ist, wobei:

Re mindestens ein Element ist, das aus einer Gruppe ausgewählt ist, die aus Pr, Dy, Tb, Ho, Gd, La, Ce und Y besteht;

M mindestens ein Element ist, das aus einer Gruppe ausgewählt ist, die aus Co, Al, Cu, Zr, Ga, Nb und Mo besteht; und

a, b, c und d Atomgewichtsverhältnisse sind, wobei a in einem Bereich von 1 ≤ a ≤ 10 ist, b in einem Bereich von 5 ≤ b ≤ 12 ist, c in einem Bereich von 5 ≤ c ≤ 8 ist und d in einem Bereich von 0 ≤ d ≤ 15 ist.

5. Verfahren zum Herstellen eines Permanentmagnetmaterials, umfassend die Schritte:

Mischen einer Nd-Fe-B-Legierung und eines Zusatzstoffs, der mindestens einen Cobaltferrit beinhaltet, um ein Gemisch zu gewinnen;

magnetisches Ausrichten und Verpressen des Gemisches in einem magnetischen Feld; und

Sintern und Anlassen des Gemisches unter dem Schutz von Vakuum oder einem Inertgas;

dadurch gekennzeichnet, dass der Cobaltferrit 0,5 Gew.-% bis 10 Gew.-% der Nd-Fe-B-Legierung beträgt.

6. Verfahren nach Anspruch 5, wobei der Cobaltferrit durch eine allgemeine Formel Co_nFe_3-nO₄ dargestellt ist, wobei n in einem Bereich von 0,1 ≤ n ≤ 2,0 ist.

7. Verfahren nach Anspruch 5, wobei der Mischschritt das Mischen der Nd-Fe-B-Legierung und des Zusatzstoffs in Gegenwart eines Antioxidationsmittels umfasst, wobei die Menge des Antioxidationsmittels auf Grundlage des Gewichtes der Nd-Fe-B-Legierung etwa 0,1 Gew.-% bis etwa 5 Gew.-% beträgt und die Menge des Schmiermittels 0 Gew.-% bis 5 Gew.-% beträgt.

8. Verfahren nach Anspruch 5, wobei der Mischschritt das Mischen der Nd-Fe-B-Legierung und des Zusatzstoffs in Gegenwart eines Antioxidationsmittels und eines Schmiermittels umfasst, wobei die Menge des Antioxidationsmittels auf Grundlage des Gewichtes der Nd-Fe-B-Legierung etwa 0,1 Gew.-% bis etwa 5 Gew.-% beträgt und die Menge des Schmiermittels 0 Gew.-% bis 5 Gew.-% beträgt.

9. Verfahren nach Anspruch 5, wobei die Nd-Fe-B-Legierung durch eine allgemeine Formel Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d dargestellt ist, wobei:

Re mindestens ein Element ist, das aus einer Gruppe ausgewählt ist, die aus Pr, Dy, Tb, Ho, Gd, La, Ce und Y besteht;

M mindestens ein Element ist, das aus einer Gruppe ausgewählt ist, die aus Co, Al, Cu, Zr, Ga, Nb und Mo besteht; und

a, b, c und d Atomgewichtsverhältnisse sind, wobei a in einem Bereich von 1 ≤ a ≤ 10 ist, b in einem Bereich von 5 ≤ b ≤ 12 ist, c in einem Bereich von 5 ≤ c ≤ 8 ist und d in einem Bereich von 0 ≤ d ≤ 15 ist.

10. Verfahren nach Anspruch 5, wobei ein durchschnittlicher Teilchendurchmesser des Cobaltferrits in einem Bereich von 10 Nanometern bis 150 Nanometern ist.

11. Verfahren nach Anspruch 5, wobei ein durchschnittlicher Teilchendurchmesser der Nd-Fe-B-Legierung in einem Bereich von 2 Mikrometern bis 5 Mikrometern ist.

12. Verfahren nach Anspruch 5, wobei das magnetische Ausrichten und das Verpressen unter einer magnetischen Feldstärke von 1,2 T bis 3,0 T und einem Druck von 10 MPa bis 200 MPa während eines Zeitraumes von 10 Sekunden bis 60 Sekunden durchgeführt werden; das Sintern bei einer Temperatur von 1.030 °C bis 1.120 °C während eines Zeitraumes von 2 Stunden bis 8 Stunden durchgeführt wird; und wobei die Anlassschritte einen ersten Anlassschritt und einen zweiten Anlassschritt umfassen, wobei der erste Anlassschritt bei einer Temperatur von 800 °C bis 920 °C während eines Zeitraumes von 1 Stunde bis 3 Stunden durchgeführt wird und der zweite Anlassschritt bei einer Temperatur von 500 °C bis 650 °C während eines Zeitraumes von 2 Stunden bis 4 Stunden durchgeführt wird.

Revendications

1. Matériau magnétique permanent, comprenant :

un alliage de Nd-Fe-B ; et un additif comprenant au moins une ferrite de cobalt, caractérisé en ce que la ferrite de cobalt représente de 0,5 à 10 % en poids de l'alliage de Nd-Fe-B.

2. Matériau magnétique permanent selon la revendication 1, dans lequel le diamètre de particule moyen de la ferrite de cobalt est compris dans la plage allant de 10 nanomètres à 150 nanomètres.

3. Matériau magnétique permanent selon la revendication 1, dans lequel la ferrite de cobalt est représentée par la formule générale Co_nFe_3-nO₄, où n est compris dans la plage de 0,1 ≤ n ≤ 2,0.

4. Matériau magnétique permanent selon la revendication 1, dans lequel l'alliage de Nd-Fe-B est représenté par la formule générale Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d où :

Re est au moins un élément choisi dans le groupe constitué par Pr, Dy, Tb, Ho, Gd, La, Ce et Y ;

M est au moins un élément choisi dans le groupe constitué par Co, Al, Cu, Zr, Ga, Nb et Mo ; et

a, b, c et d sont des rapports en poids atomique, où a est compris dans la plage de 1 ≤ a ≤ 10, b est compris dans la plage de 5 ≤ b ≤ 12, c est compris dans la plage de 5 ≤ c ≤ 8 et d est compris dans la plage de 0 ≤ d ≤ 15.

5. Procédé de préparation d'un matériau magnétique permanent, comprenant les étapes consistant à :

mélanger un alliage de Nd-Fe-B et un additif incluant au moins une ferrite de cobalt pour obtenir un mélange ;

orienter magnétiquement et compresser le mélange dans un champ magnétique ; et

fritter et réaliser une trempe du mélange sous la protection d'un vide ou d'un gaz inerte ;

caractérisé en ce que la ferrite de cobalt représente de 0,5 à 10 % en poids de l'alliage de Nd-Fe-B.

6. Procédé selon la revendication 5, dans lequel la ferrite de cobalt est représentée par la formule générale Co_nFe_3-nO₄, où n est compris dans la plage de 0,1 ≤ n ≤ 2,0.

7. Procédé selon la revendication 5, dans lequel l'étape de mélange comprend le mélange de l'alliage de Nd-Fe-B et de l'additif en présence d'un antioxydant, dans lequel en fonction du poids de l'alliage de Nd-Fe-B, la quantité de l'antioxydant est d'environ 0,1 % en poids à environ 5 % en poids, et la quantité du lubrifiant est de 0 % en poids à 5 % en poids.

8. Procédé selon la revendication 5, dans lequel l'étape de mélange comprend le mélange de l'alliage de Nd-Fe-B et de l'additif en présence d'un antioxydant et d'un lubrifiant, dans lequel en fonction du poids de l'alliage de Nd-Fe-B, la quantité de l'antioxydant est d'environ 0,1 % en poids à environ 5 % en poids, et la quantité du lubrifiant est de 0 % en poids à 5 % en poids.

9. Procédé selon la revendication 5, dans lequel l'alliage de Nd-Fe-B est représenté par la formule générale Nd_aRe_bFe_{(100-a-b-c-d)}B_cM_d où :

Re est au moins un élément choisi dans le groupe constitué par Pr, Dy, Tb, Ho, Gd, La, Ce et Y ;

M est au moins un élément choisi dans le groupe constitué par Co, Al, Cu, Zr, Ga, Nb et Mo ; et

a, b, c et d sont des rapports en poids atomique, où a est compris dans la plage de 1 ≤ a ≤ 10, b est compris dans la plage de 5 ≤ b ≤ 12, c est compris dans la plage de 5 ≤ c ≤ 8 et d est compris dans la plage de 0 ≤ d ≤ 15.

10. Procédé selon la revendication 5, dans lequel le diamètre de particule moyen de la ferrite de cobalt est compris dans la plage allant de 10 nanomètres à 150 nanomètres.

11. Procédé selon la revendication 5, dans lequel le diamètre de particule moyen de l'alliage de Nd-Fe-B est compris dans la plage allant de 2 µm à 5 µm.

12. Procédé selon la revendication 5, dans lequel l'orientation magnétique et la compression sont réalisées sous une intensité de champ magnétique de 1,2 T à 3,0 T et une pression de 10 MPa à 200 MPa pendant une période de 10 secondes à 60 secondes ; le frittage est réalisé à une température de 1030 °C à 1120 °C pendant une période de 2 heures à 8 heures ; et dans lequel les étapes de trempe comprennent une première étape de trempe et une seconde étape de trempe, la première étape de trempe étant réalisée à une température de 800 °C à 920 °C pendant une période de 1 heure à 3 heures, et la seconde étape de trempe étant réalisée à une température de 500 °C à 650 °C pendant une période de 2 heures à 4 heures.