WO2000019456A1

WO2000019456A1 - Magnetic material based on iron, cobalt, rare earths and boron and magnet based on said material

Info

Publication number: WO2000019456A1
Application number: PCT/FR1999/002184
Authority: WO
Inventors: Valérie ARCHAMBAULT; Charles Bounds; Theo Rijks; Cees De Kort
Original assignee: Rhodia Chimie; DE KORT, Alwine, Geraldine, Maria
Priority date: 1998-09-28
Filing date: 1999-09-14
Publication date: 2000-04-06
Also published as: AU5628099A; FR2783964A1

Abstract

The invention concerns a magnetic material based on iron, cobalt, rare earths and boron and a magnet based on said material, in particular a bound magnet. Said material is characterised in that it has a composition corresponding to the following formula: R1xR2yFe ¿100-x-y-z-v-w-tCozM?1vM2tBw wherein: R1 represents at least an element selected among lanthanum, cerium, praseodymium, neodymium, samarium and europium, at least one of the praseodymium and neodymium being present in majority; R2 represents at least an element selected among terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, at least one of the terbium and dysprosium elements being present in majority; M1 represents at least an element selected among titanium, vanadium, molybdenum, niobium, zirconium, hafnium, tantalum, manganese and tungsten; M2 represents at least an element selected among aluminium, copper, gallium, carbon and silicon; and wherein x, y, z, v, w and t verify the following relationships: 3 ≤ x ≤ 5, 0.1 ≤ y ≤ 1.5, 0 < z ≤ 15, 0 ≤ v ≤ 3, 15 ≤ w ≤ 25, 0 ≤ t ≤3.

Description

MAGNETIC MATERIAL BASED ON IRON. OF COBALT. RARE EARTH AND BORON AND MAGNET BASED ON THIS MATERIAL

The present invention relates to a magnetic material based on iron, cobalt, rare earths and boron and a magnet based on this material.

It is known that there is, in the field of magnets, an increasing need for a material whose performance is situated between those which are weak of magnets of the ferrite type and those high of the type sintered magnets based on neodymium, iron and boron. There are already magnets which partially satisfy this need. These are magnets bonded on the basis of neodymium, iron and boron and obtained by quenching on a wheel (melt-spining). Magnets with a lower rare earth content and a high remanence have also been proposed, but which are not entirely satisfactory because they have a coercivity which may be insufficient in certain applications. The object of the present invention is to provide a magnetic material with a low rare earth content and having improved magnetic properties and, in particular, increased coercivity.

For this purpose, the magnetic material of the invention is characterized in that it has the composition defined by the following formula:

R ¹ _χ R ² yf ⁼ eiOO-xyz ^ w-tCθ ₂ Ml _v M2 _t -3 _w (1)

in which

R ¹ represents at least one element chosen from lanthanum, cerium, praseodymium, neodymium, samarium and europium, at least one of the praseodymium and neodymium elements being present and predominant,

R ² represents at least one element chosen from terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, at least one of the elements terbium and dysprosium being present and predominant, M ¹ represents at at least one element chosen from titanium, vanadium, molybdenum, niobium, zirconium, hafnium, tantalum, manganese and tungsten,

M ² represents at least one element chosen from aluminum, copper, gallium, carbon and silicon, and where x, y, z, v, w and t satisfy the following relationships:

3 <x <5

0.1 <y <1, 5

0 <z <15 0 <V <3

15 <w <25

0 <t ≤3

The invention also relates to a magnet characterized in that it is based on the material defined above.

Other characteristics, details and advantages of the invention will appear even more completely on reading the description which follows, as well as various concrete but nonlimiting examples intended to illustrate it.

The material of the invention is first of all characterized by its composition. This composition corresponds to formula (1) given above. The proportions of the various constituent elements of the material of the invention are therefore expressed in atomic%.

R ^" ! Is chosen from the group of rare earths of the light rare earth type which has been defined above with the conditions, on the one hand, that the material comprises at least as element R ^" of praseodymium or neodymium or a combination of these two elements and, on the other hand, that the praseodymium, the neodymium or the combination of these two elements is in the majority, that is to say constitutes more than 50 atomic% of the set of rare earths constituting R The respective proportions of the neodymium and praseodymium with respect to each other can be any, the neodymium being more particularly in majority proportion. Preferably the rare earth R1 is neodymium.

R ^ is chosen from the group of rare earths of the heavy rare earth type which has been defined above with the conditions, on the one hand, that the material comprises at least as element R ^ terbium or dysprosium or a combination of these two elements and, on the other hand, that the terbium, the dysprosium or the combination of these two elements is in the majority, that is to say constitutes more than 50 atomic% of the set of rare earths constituting R ^. The respective proportions of the terbium and of the dysprosium with respect to each other can be arbitrary, the terbium possibly being more particularly in the majority proportion. Preferably, the rare earth R ^ is terbium. With regard to the respective proportions of the elements given above, it may be indicated that a rare earth content lower than the minimum content described induces an insufficient coercivity of the material and a content greater than the maximum content described results in a loss of coercivity, which can be total, of the material. The elements M ^ and M ² are used as additives. Too much of these additives can lead to a reduction in saturation magnetization. The boron content described makes it possible to obtain the phases in balance Fβ3B, Fe and (R ¹ , R ² ) 2Fei4-3. Apart from this content, this combination of phases is not formed. According to particular embodiments of the invention, the contents of elements R ¹ , R ² , Co, M ¹ , M ² and B can vary within more reduced ranges. Thus, the values of x and y can verify the relation 3,5 <x + y <4,5. In addition, the value of y can more particularly verify the relation 0,1 <y <1. According to another particular embodiment, z has the following value 1, 5 <z <7.5 and even more particularly 2.5 <z <7.5. In addition, v or t can have values of at most 1. Finally, w can vary more particularly in the following proportions: 17 <w ≤20.

Of course, the invention also includes the particular embodiment in which x, y, z, v, t and w simultaneously verify the relationships which have been given in the preceding paragraph.

The element M ² can more particularly be silicon and M ¹ and M ² can more particularly constitute a combination of copper and niobium. In the latter case, copper and niobium can be present in equal or substantially equal amounts. It will also be noted that the material of the invention does not contain chromium as a constituent element, with the exception however of possible traces of this element which can come from the raw materials used in the preparation of the material.

The material of the invention is generally in the form of a powder. Usually, this powder has an average particle size of between approximately 10 μm and approximately 500 μm, more particularly between 10 μm and 300 μm.

The material also consists of crystallites whose average size can be between 5nm and 300nm, preferably between 10 and 50nm.

A first process for preparing the material of the invention will now be described. This process includes the following steps:

- A starting mixture is melted comprising the constituent elements of the material in the necessary proportions;

- the molten mixture is cooled;

- The said product is optionally subjected to a heat treatment, whereby the magnetic material is obtained.

The starting mixture, for example an alloy of the different elements, is firstly melted, generally under an inert atmosphere, for example under argon. The second step in the process is to cool the molten mixture.

Different techniques can be used to do this, such as wheel quenching. Cooling rates are usually used which can vary between about 10 ^ and about 10 ⁷ ° C per second, preferably between 10 ^ and 10 ^ ° C per second. When the cooling is rapid, that is to say greater than 10 ^ ° C / s, we obtains an essentially amorphous product. The product thus obtained can optionally be ground.

In a final step, the product obtained previously can be subjected to a heat treatment. This treatment is not always necessary if the cooling rate is low, that is to say between 10 ⁴ ° C / s and 1θ5 ° C / s per second. On the other hand, such a treatment is useful in the case of a cooling rate greater than 10 ^ ^o C / s. In this case, crystallization is caused in the amorphous product and, more precisely, the appearance of fine crystallites. The temperature of this treatment can be between approximately 400 and approximately 800 ° C., more particularly between approximately 650 and approximately 750 ° C. The duration of the treatment can vary between approximately 0.001 seconds and approximately 2 hours, preferably between 0.01 seconds and approximately 10 minutes. The heating speed can vary from 0.1 ° C / s to 100 ° C / s. The treatment is preferably carried out under an inert gas such as argon.

Another process for preparing the material of the invention can also be used. The first step in this process consists in mechanically combining the constituent elements of the material in the necessary proportions. The mechanical alloying technique is known, it consists in grinding with high energy either powders of the separate elements concerned or premixes in the form of alloys of these elements. The heat treatment of the alloy obtained in the previous step is then carried out by implementing conditions similar to those which have been described for the first method.

A third process is possible. This method comprises, in a first step, a heat treatment under hydrogen of a starting mixture or alloy comprising the constituent elements of the material in the necessary proportions, then, in a second step, a heat treatment under vacuum.

The invention also relates to a permanent magnet which is based on a material such as that which has just been described or as obtained by the methods presented above. The preparation of such a permanent magnet is done in a known manner, for example by hot pressing or by sintering. In addition, the material of the invention is particularly suitable for the preparation of bonded permanent magnets. Such bonded magnets comprise the material of the invention as described above in a matrix formed of a non-magnetic material based for example on a glass, a polymer, a resin, such as an epoxy resin. or based on a second alloy with low melting point.

Examples will now be given.

The materials are obtained in the following manner. An alloy comprising the necessary quantities of the various elements is melted under atmosphere argon. The molten alloy is sprayed onto the external surface of a wheel maintained at ambient temperature and whose circumferential speed is between 20 and 40 m / s. A material is obtained in the form of a thin ribbon. The material is then subjected to a heat treatment at a temperature which is between 700 and 800 ° C. under argon.

The compositions of the materials of the various examples are shown in Table 1 below and in Table 2 the magnetic properties of these materials after the heat treatment. Example 20 is a comparative example because the material does not contain terbium or dysprosium. It can be seen that the materials according to the invention have a markedly improved coercivity with at least equal and generally improved remanence.

Table 1

Claims

1- Magnetic material, characterized in that it has the composition defined by the following formula:

R ¹ _χ R ² _y Fβ ₁₀ o. _x - _y - _z - _w - _w . _t Co _z M ⁱ _v M2 _t B _w (1)

in which

R ² represents at least one element chosen from terbium, dysprosium, holmium, Terbium, thulium, ytterbium and lutetium, at least one of the elements terbium and dysprosium being present and predominant,

M ¹ represents at least one element chosen from titanium, vanadium, molybdenum, niobium, zirconium, hafnium, tantalum, manganese and tungsten, M ² represents at least one element chosen from aluminum, copper, gallium, carbon and silicon, and where x, y, z, v, w and t verify the following relationships:

3 <x <5

0.1 <y <1, 5 0 <z <15

0 <v <3

15 <w <25

0 <t <3

2- Material according to claim 1, characterized in that x satisfies the following relation:

3.5 <x + y <4.5

3- Material according to claim 1 or 2, characterized in that y verifies the following relationship:

0.1 <y <1

4- Material according to one of the preceding claims, characterized in that z satisfies the following relationship: 1, 5 <z <7.5, more specifically 2.5 <z <7.5

5- Material according to one of the preceding claims, characterized in that w satisfies the following relation: 17 <w <20

6- Material according to one of the preceding claims, characterized in that the element M ² is silicon or in that M ¹ and M ² constitute a combination of copper and niobium.

7- Material according to one of the preceding claims, characterized in that it is in the form of a powder.

8- Material according to claim 7, characterized in that it is in the form of a powder of average particle size between about 10 microns and about

500μm, more particularly between 100μm and 300μm.

9- Material according to one of the preceding claims, characterized in that it consists of crystallites whose average size is between 5nm and 300nm.

10- Process for preparing a material according to one of the preceding claims, characterized in that it comprises the following steps:

- A starting mixture is melted comprising the constituent elements of the material in the necessary proportions; - the molten mixture is cooled;

11- Process for preparing a material according to one of claims 1 to 9, characterized in that it comprises the following steps:

- the constituent elements of the material are mechanically combined in the necessary proportions;

- The product obtained in the previous step is subjected to a heat treatment, whereby the magnetic material is obtained.

12- A method of preparing a material according to one of claims 1 to 9, characterized in that it comprises, in a first step, a heat treatment under hydrogen of a starting mixture or alloy comprising elements constitutive of the material in the necessary proportions then, in a second step, a heat treatment under vacuum.

13- Permanent magnet, characterized in that it is based on a material according to one of claims 1 to 9.

14- Magnet according to claim 10 characterized in that it comprises a binder.