EP0478674B1 - Method for preparing permanent magnets based on neodymium-iron-boron - Google Patents

Abstract

Method for preparing permanent magnets from a massive alloy containing a mixture based on neodymium-iron-boron which, for a range of temperatures, has a range within which said alloy undergoes two phases, one solid and fragile and the other liquid, characterized in that it involves: partially substituting copper atoms for iron and/or neodymium atoms from said alloy, then, forging the newly produced alloy at a temperature within said range of temperatures, to obtain a forging grade of at least ten, in order to refine the constituent grains of the alloy to particles of a few micrometers; and, finally, subjecting the forged alloy to an annealing and/or tempering treatment.

Description

The present invention relates to a new improved process for the preparation of high-performance permanent magnets based on Neodymium-Iron-Boron. It relates more particularly to a process for manufacturing permanent magnets by the technical process known as wrought.

By "wrought" means a mechanical treatment applied to a metal alloy and intended to cause refinement of the constituent grains of this alloy. The wrought is then defined by its wrought rate. The mechanical treatments likely to induce a wrought are essentially forging, hammering, rolling, spinning, vibro-tamping (tamping by vibration), etc.

In European patent EP-A-0 106 948, a process has been described for obtaining magnets based on an iron-cobalt-boron-rare earth alloy by the technique known as powder metallurgy. While the magnets obtained have interesting magnetic properties, on the other hand, this process proves to be particularly complicated and dangerous, in fact it requires numerous precautions to be taken, and in particular to work in a controlled atmosphere. In addition, the cost price of the magnets thus obtained is relatively high. Finally, although the use of Cobalt in the base mixture makes it possible to increase the Curie temperature significantly, therefore the temperature of use of these magnets, on the other hand, there is a decrease in the coercivity and properties magnetic in general.

In the publication SHIMODA et al (J.Appl. Phys. 64 (10) 1988), it has been proposed to produce permanent magnets based on a Praseodymium-Iron-Boron-Copper mixture, and this with a low rate of deformation , especially less than ten. This production process is carried out by hot pressing under an inert atmosphere at around 1000 ° C. However, this method only makes it possible to obtain high magnetic properties for small magnets. What is more, taking into account their production process, in particular by sheath rolling, which certainly results in a refinement of the grains (however insufficient with a deformation rate of less than ten), with an inhomogeneous microstructure and a magnetic orientation, only the Praseodymium provides good results. In fact, it has been shown that by replacing Praseodymium with Neodymium, the magnetic properties dropped drastically, making the addition of Copper completely unnecessary. However, Praseodymium is much rarer on the earth's surface than Neodymium, hence the cost price of magnets based on Praseodymium much higher (typically in a ratio of 5 to 1 compared to Neodymium).

A hot-working process has also been described in European patent EP-A-0 269 667 which makes it possible to obtain permanent magnets in industrial quantities under high safety conditions having good magnetic performance. These magnets, based on Fer-Bore and Rare Earths, have a relatively low production cost given the process used. Anyway, we wanted to improve their magnetic properties. And this is the object of the present invention. The document EP-A-302 947 describes an alignment of the grains of the alloy by "hot working". The "hot working" according to this document has the sole purpose of aligning the grains of magnetic materials.

The present invention relates to an improved process for the preparation of high-performance permanent magnets from a solid alloy containing a mixture based on Fer-Boron and Neodymium which, for a temperature range, has a domain inside of which said alloy is in two phases, one solid and fragile and the other liquid,
the iron and / or neodymium atoms of said alloy being partially substituted by copper atoms,
characterized in that it consists in wrenching the new alloy thus produced at a temperature included in said temperature range, in order to obtain a wrought rate of at least ten, so as to refine the grains constituting said alloy into particles a few micrometers;
- Then, to subject the alloy thus wrought to an annealing and / or tempering treatment.

In other words, the present invention consists in replacing, in a solid alloy based on Neodymium-Iron-Boron, some of the Iron and / or Neodymium atoms with Copper atoms, and then subjecting this alloy to a treatment hot working. While the use of copper was known per se with a view to improving certain magnetic properties, on the other hand, it was clearly shown that the use of copper in an iron-boron alloy of rare earth, in which rare earth was Neodymium did not make it possible to obtain permanent magnets with high magnetic properties.

• l'alliage comporte de 0,5 à 4 % atomique de Cuivre; on a en effet constaté que si la quantité atomique de Cuivre est inférieure à 0,5 %, on observait une chute des propriétés magnétiques de l'aimant ainsi réalisé. En d'autres termes on n'observait pas d'amélioration notable par rapport aux aimants obtenus selon le procédé décrit dans le brevet européen EP-A-0 269 667. En revanche, si la quantité de Cuivre dépasse 4 % atomique, on affecte la rémanence du fait de la diminution de la quantité de matériau magnétique ;
• l'alliage comporte de 1 à 2,5 % atomique de Cuivre de préférence 2 % ;
• l'alliage à base de Néodyme-Fer-Bore-Cuivre comporte également du Dysprosium (Dy) ;
• le Dysprosium est présent à raison de 0,5 % à 2 % atomique.

Advantageously in practice:

• the alloy comprises from 0.5 to 4 atomic% of copper; it has in fact been observed that if the atomic amount of copper is less than 0.5%, a fall in the magnetic properties of the magnet thus produced is observed. In other words, there was no noticeable improvement compared to the magnets obtained according to the method described in European patent EP-A-0 269 667. On the other hand, if the amount of Copper exceeds 4 atomic%, the remanence is affected due to the decrease in the amount of magnetic material;
• the alloy comprises from 1 to 2.5 atomic% of copper, preferably 2%;
• the alloy based on Neodymium-Iron-Boron-Copper also comprises Dysprosium (Dy);
• Dysprosium is present at a rate of 0.5% to 2 atomic%.

The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the following exemplary embodiments, given by way of indication and not limiting in support of the appended figure.

The various examples which follow show the production of permanent magnets on the one hand in accordance with the invention by means of a relatively simple installation as described in particular in European patent EP-A-0 269 667, and on the other hand , and for comparison in accordance with the method described in the publication J. Appl. Phys. 64 (10).

Briefly, and as can be seen in Figure 1, the installation according to the invention comprises an anvil (1), on which rests a retaining ring (2), surrounded by a glass enclosure (3), defining a sealed chamber (4), connected to the inlet (5) of a source of argon not shown. The top of the chamber has an opening (6) through which the hammer (7) of the external impact assembly (8) can pass, by means of a seal sealing (9). The sample (10) rests on the anvil (1) inside the ring (2) in which the hammer (7) slides. The glass enclosure (3) is surrounded by induction coils (11).

Example 1

• 76 atomes de Fer,
• 16 atomes de Néodyme,
• 6 atomes de Bore,
• 2 atomes d'Aluminium.

A massive sample is prepared (washer, cylinder, molded ..., shot) in an alloy constituted by a mixture of Iron, Neodymium, Boron and Aluminum. The atomic concentration for 100 alloy atoms of the different elements is:

• 76 Iron atoms,
• 16 Neodymium atoms,
• 6 Boron atoms,
• 2 Aluminum atoms.

This massive sample thus placed is placed on the anvil (1) of the installation, inside the ring (2). Argon is then injected at (5) and by induction (11) the sealed chamber (4) is heated to 800 ° C for five minutes. When this temperature is reached, the sample (10) is hammered with three hammer blows. This forging thus carried out induces a rate of wrought close to ten, sufficient to break the magnetic crystals.

An annealing is then carried out under neutral gas, or possibly under vacuum, at a temperature of 650 ° C.

The magnetic element thus obtained has an intrinsic coercive field of 756 kilo-amperes per meter (756 kA / m) and a residual induction of 0.8 Tesla. The internal energy obtained in this case is of the order of 103.5 kilo-joules per cubic meter (103.5 kJ / m³).

The element obtained has in known manner a quadratic crystal structure.

Example 2

Example 1 is repeated but in which the two aluminum atoms are replaced by two cobalt atoms. The sample is subjected to the same treatment. We then obtain an intrinsic coercive field of 597 kA / m for an emanation induction of 0.88 Tesla. There is therefore a significant drop in the coercive field and a slight increase in the residual induction. The role of Cobalt is essentially to increase the Curie temperature, therefore the temperature of use of the permanent magnets thus produced.

Example 3

• 16 atomes de Néodyme,
• 78 atomes de Fer,
• 6 atomes de Bore.

Example 1 is repeated but in which the base alloy is no more than a ternary mixture of Neodymium, Iron and Boron. The atomic composition for 100 atoms of the mixture is:

• 16 Neodymium atoms,
• 78 iron atoms,
• 6 Boron atoms.

The intrinsic coercive field obtained is then 600 kA / m and the residual induction of 0.9 Tesla. The internal energy obtained is in this case close to 95.5 kJ / m³.

Example 4

Permanent magnets are then produced by the process known as "hot pressing". The production process and the composition of the base alloy are described in the publication (SHIMODA et al) mentioned above J.Appl. Phy. 64 (10). This example and the following two are given for comparison.

• 17 atomes de Praséodyme,
• 7,5 atomes de Fer,
• 5 atomes de Bore,
• 1,5 atomes de Cuivre.

In the present case, the atomic centesimal composition of the basic mixture is:

• 17 Praseodymium atoms,
• 7.5 iron atoms,
• 5 Boron atoms,
• 1.5 Copper atoms.

The intrinsic coercive field obtained is 800kA / m and the residual induction of 1.25 Tesla. The internal energy obtained is 288 kJ / m³.

It is therefore observed that according to this process and with this composition, excellent anisotropic magnets are obtained.

Example 5

• 17 atomes de Néodyme,
• 76,5 atomes de Fer,
• 5 atomes de Bore,
• 1,5 atomes de Cuivre.

The same process is used, but the percentage composition of the initial mixture is:

• 17 Neodymium atoms,
• 76.5 iron atoms,
• 5 Boron atoms,
• 1.5 Copper atoms.

The intrinsic coercive field obtained is 230kA / m and the residual induction of 0.19 Tesla. The internal energy obtained is 72.8 kJ / m³. We thus observe a drastic fall in magnetic properties when we replace Praseodymium with Neodymium.

Example 6

In the same publication, another method known as pouring is used. This process, applied to the composition of the previous example, makes it possible to obtain permanent magnets with an intrinsic coercive field of 48 kA / m for a residual induction of 0.29 Tesla. The maximum internal energy obtained is 3.2 kJ / m³. It is therefore observed that according to one or other of the methods used in the context of this publication, the fact to introduce Copper into the Neodymium-Iron-Boron mixture, far from increasing the magnetic properties of the magnets thus produced, on the contrary, causes it to fall.

Example 7

• 17 atomes de Néodyme,
• 76 atomes de Fer,
• 5 atomes de Bore,
• 2 atomes de Cuivre.

The process according to the invention is repeated, using as base composition of the base mixture:

• 17 Neodymium atoms,
• 76 Iron atoms,
• 5 Boron atoms,
• 2 copper atoms.

The intrinsic coercive field obtained is 950 kA / m and the residual induction of 1.01 Tesla. In this way, an internal energy close to 200 kJ / m³ is obtained. This produces excellent permanent anistrop magnets with very high performance.

Example 8

• 15 atomes de Néodyme,
• 76 atomes de Fer,
• 5 atomes de Bore,
• 2 atomes de Cuivre.

The previous example is repeated with the atomic centesimal composition of the following basic mixture:

• 15 Neodymium atoms,
• 76 Iron atoms,
• 5 Boron atoms,
• 2 Copper atoms.

The intrinsic coercive field obtained is 835kA / m for a residual induction of 1.15 Tesla. The internal magnetic energy obtained is then 238 kJ / m³.

It is therefore observed that, despite the reservations formulated in the publication mentioned above, the use of Neodymium in the context of the process according to the invention makes it possible to obtain permanent magnets with very high magnetic performance.

Example 9

• 17 atomes de Néodyme,
• 77 atomes de Fer,
• 5 atomes de Bore,
• 1 atome de Cuivre.

The previous example is repeated with the atomic centesimal composition of the following basic mixture:

• 17 Neodymium atoms,
• 77 iron atoms,
• 5 Boron atoms,
• 1 atom of Copper.

The magnetic properties obtained are slightly lower than the two previous examples, in fact there is an intrinsic coercive field of 800 kA / m for a residual induction of 1 Tesla, the internal magnetic energy obtained being 159 kJ / m³.

Example 10

• 74 atomes de Fer,
• 4 atomes de Cuivre.

The previous example is repeated, respectively modifying the compositions of Iron and Copper, namely:

• 74 Iron atoms,
• 4 copper atoms.

The intrinsic coercive field obtained is then 835 kA / m for a residual induction of 0.95 Tesla. The maximum internal energy obtained is 243 kJ / m³. It is therefore observed in the context of the strict use of the four elements Neodymium-Iron-Boron-Copper, that the maximum of the magnetic properties is located for a centesimal atomic concentration of Copper close to 2.

It should be noted that the temperature of the wrinkling is at least equal to 500 ° C. in order to be situated at least at the level of the melting of the Neodymium-Copper eutectic. However, it has been found that around 800 ° C., the results are appreciably the best.

These different results are grouped in the following table.

It is therefore observed that the introduction of copper into the base mixture, at a rate of approximately 2 atomic%, allows a significant increase in the coercivity and hence the persistence of the magnets thus obtained, consequence of the increase in the anisotropy of the magnets obtained. In particular, there is a large increase in the internal energy of the magnets.

In all the previous examples it is also possible to introduce Dysprosium at a rate of 0.5 to 2 atomic%, in particular in the context of the use of these magnets at higher temperatures. Indeed the latter increases the coercivity therefore the operating temperature of the magnets obtained.

In addition, it is possible to replace the Copper with other metals such as Silver, Gold or Paladium.

The process according to the invention has many advantages over the process mentioned in the preamble. We can note the possibility of using a simple and inexpensive process using Neodymium, Rare Earth much more abundant than Praseodymium and in fact allowing the obtaining of permanent magnets with properties: magnetic equal, or even superior, to those described in the other methods, but of a much lower production cost. In fact, taking into account the relative abundance of Neodymium in nature, the cost price of such magnets can be reduced by a factor of 5.

One can also cite the other advantages inherent in the process proper of the invention, in particular the absence of danger to the environment such as the risks of explosion or fire, since no metallurgy is used. powders.

In other words, this process using a Neodymium-Iron-Boron-Copper base mixture, makes it possible to obtain permanent magnets of reduced cost, with high magnetic performance, and capable of being produced in industrial quantities in an easy manner. .

Claims (5)

1. Improved process for the preparation of permanent magnets from a bulk alloy containing a mixture based on neodymium-iron-boron which, for a temperature range, has a region in which the said alloy occurs as two phases, the one a solid and brittle phase and the other a liquid phase, the iron and/or neodymium atoms of said alloy being partially substituted by copper atoms, characterized in that it consists :

   - in welding the novel alloy thus produced at a temperature within the said temperature range, until a welding rate of at least ten is obtained, in such a manner as to refine the constituent grains of the alloy into particles of a few micrometers;

   - and then, in subjecting the alloy thus welded to an annealing and/or tempering treatment.
2. Improved process according to Claim 1, characterized in that the alloy comprises 0.5 to 4 atomic % of copper.
3. Improved process according to Claim 1, characterized in that the alloy comprises 1 to 2.5 atomic % of copper and preferably 2 atomic %.
4. Improved process according to one of Claims 1 to 3, characterized in that the alloy based on neodymium-iron-boron-copper also comprises dysprosium.
5. Improved process according to Claim 4, characterized in that the alloy comprises dysprosium at a level of 0.5 to 2 atomic %.

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