DE29521549U1 - Magnetic material and permanent magnet of the NdFeB type - Google Patents

Description

Magnet factory
Schramberg GmbH & Co.
Max-Planck-Str. 15

78713 Schramberg

Magnetic material and permanent magnet of IMdFeB type

The invention relates to a magnetic material and a permanent magnet of the Nd FeB type.

Since the NdFeB materials became known, attempts have been made to use additives to improve the intrinsic properties such as remanence, coercive field strength or temperature coefficients as well as extrinsic properties such as corrosion resistance. Progress has been made by adding e.g. Mo, Cu and Ai (EP 0430278 B1), by mixing different powders (EP 0601943 A1), by the possible addition of almost all metals and subsequent coating (EP 0345 092 B1), by adding refractory metals, Co and Ga (EP 0421 488 B1), by the effect of nitrogen (DE 90 18 099 U1), by adding Ga

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or Bi {DE 4135403 AD, as well as by the addition of Co and Cu (Crucible lecture AD-08, Intermag 95/San Antonio).

The improvements achieved increased corrosion resistance, but did not represent a real breakthrough. The corrosion sensitivity of NdFeB materials continues to severely limit their use, so protective coatings are still necessary (EP 0345092 B1). Without coatings, NdFe-B materials can only be used in non-critical environmental conditions (room temperature, air humidity up to 50%, no condensation, see Vacuumschmeize GmbH product description PD-002,04/95, p.32 ff). The additional step of polymer or metallic coating causes additional costs and risks due to detachment, which can lead to failure.

Materials with comparable absolute magnetic properties at higher temperatures are known, but are based on different compositions. The materials commonly offered on the market for high-temperature applications start with relatively high remanence values, but are subject to a stronger temperature dependence (coefficients with an amount >0.1%/K, see Vacuumschmeize GmbH product description PD-002,04/95, p. 1Of).

The aim of the invention is to develop a corrosion-resistant magnetic material based on NdFeB materials for applications from room temperature to above 200° C with good absolute magnetic properties at low temperatures and superior magnetic properties at higher temperatures.

This object is achieved with the features of claims 1 and 11 respectively. Advantageous compositions are mentioned in the subclaims.

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In the magnetic materials or permanent magnets specified, the additives known per se are for the first time coordinated in such a way that decisive improvements in both the intrinsic and extrinsic properties are achieved, whereby a stable microstructure is produced.

The materials used, i.e. permanent magnets, have coefficients of approximately -0.08%/K up to a room temperature of 100 ^° C or -0.085%/K up to a room temperature of 150 ^° C. This means that comparatively excellent flux values are achieved at temperatures above 100 ^° C. The lower temperature coefficients are a clear advantage, as the temperature influence is lower and the system design is simpler.

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The thumb magnet can be used in damp environments without any additional protective measures. For specific applications, the material can be coated using conventional and easy-to-implement methods without the risk of the coating coming off under the influence of temperature and moisture.

The well-known and proven corrosion-resistant Sm2(TM) 17 materials served as a benchmark for durability and high-temperature properties, although they are only of limited use due to more expensive raw materials and more cost-intensive manufacturing parameters.

It can be clearly shown that the new material has a corrosion resistance comparable to that of Sm2 (TM) 17 materials. Its magnetic properties (magnetic flux) are higher at temperatures of up to approx. 200 ⁰ C than those of Sm2{TM)17 materials. Its production is more cost-effective. Compared to conventional NdFeB materials, its corrosion resistance is improved many times over. In the pressure cooker test (130 ⁰ C, 3 bar, saturated steam) only small material losses of on average about 0.1 mg per cm ² per day and decreasing further occur, while the material loss with commercially available

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Permanent magnets of the NdFeB type are in the range of 10 to 100 mg per cm ² and day (factor 100 to 1000!).

The invention is explained below using exemplary embodiments, with reference to the curves shown in Figures 1 to 3.

Alloy compositions and the process for manufacturing permanent magnets based on rare earth metals (RE)-transition metals (TM)-boron (B) are described. The material is characterized by extremely high corrosion resistance, which is unusual for materials in this group. The corrosion resistance achieved is comparable to that of Sm2 (TM) 17 materials. It is achieved by the targeted addition of additives such as Dy, Co, Nb, Al, Ga and Cu to the base alloy made of NdFeB, which creates intrinsic and structural corrosion resistance. An adapted overall composition leads on the one hand to a minimization of the corrosion-sensitive grain boundary phase and, with the help of the additives, improves its corrosion resistance. On the other hand, the formation of stable intermetallic phases in the grain boundary area creates barriers that prevent corrosion-causing substances from penetrating into the interior of the magnet. Material losses that occur at the beginning of corrosion stress are extremely small and gradually decrease to zero through mechanisms similar to passivation. These mechanisms also work at higher temperatures (see pressure cooker test below). A previously unknown level of corrosion stability is achieved.

Due to the high corrosion resistance, an additional coating is not required for standard applications. If protective layers are nevertheless required for application-related reasons, the new material is characterized by a high level of insensitivity to the corrosion that occurs during e.g. galvanic

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The coating is therefore unproblematic and can be applied in conventional galvanic plants without any special technological measures. The applied coatings are highly stable against temperature stress and moisture.

Improved temperature coefficients of remanence and, with a suitable choice of alloy, high coercive field strengths even at high temperatures enable use up to over 200 ⁰ C. Higher magnetic flux densities in the temperature range up to 200 ⁰ C can replace the proven but more expensive Sm2(TM)17 materials in a wide range of applications.

The materials described can be manufactured in standard production facilities in the magnet industry. The process parameters differ only slightly from those of the previously known NdFeB materials.

Examples:

Compounds were melted, homogenized, ground to approx. 3.5 //m (FSSS), pressed isostatically (A) or axially in the tool (B), sintered at temperatures between 1050 and 1150 ⁰ C (vacuum, 2.5 h), homogenized, heat treated (600 ⁰ C, 3 h) and then magnetized. The final densities are between 7.4 and 7.7 g/cm ³ .

Compositions in weight proportions:

A1: Nd20 Dy10 Co3 B0.95 NbO.8 AI0.2 Ga0.2 Cu0.1 FeRemainder
A2: Nd29 Co3 B0.9 NbO.8 AI0.2 Ga0.15 Cu0.1 FeRemainder
A3: Nd25 Dy5 Co3 BI NbO,8 AI0,2 Ga0,2 Cu0,1 FeRest
B1: Nd20 Dy11 Co3.3 B0.9 NbO.7 AI0.3, Ga0.1 Cu0.15 FeRemainder

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B2: Nd21 Dy11 Co3 B1 NbO,8 AlO, 1 GaO,3 CuO,2 FeRest
B3: Nd21 DyIO Co2 B0.9 NbO,6 GaO,4 Cu0.05 FeRest.

Corrosion properties:

In the pressure cooker test (130 ⁰ C, 3 bar, saturated steam), the samples were tested in 10 steps for 24 hours each. The corrosion products that appeared were then mechanically removed and the magnet was weighed. The test variable is the weight loss per surface and day.

A sample of Sm2(TM)17 (density 8.3 g/cm ³ ) and a sample of conventional NdFeB material are used for comparison. This can be shown in the diagram in Fig. 1. However, the values of the new materials and of Sm2{TM)17 cannot be resolved. The curve for the conventional NdFeB material shows a progressive development, the course is catastrophic.

All examples of the new materials show excellent corrosion properties (diagram in Fig. 2). Weight losses in this range can hardly be resolved using conventional gravimetric methods. A protective mechanism similar to passivation takes place. Alloy A1 shows better resistance than Sm2(TM)17 shortly after the start of the test. After a few days, practically no further corrosion can be detected in any of the similar compounds. The initial values are extremely low, so that we must already speak of extremely good stability here. Intermetallic phases occur in the microstructure in the grain boundary areas. The proportion of free Nd is reduced to the minimum necessary for sintering. The remaining amount of grain boundary phase is stabilized. All of this was achieved by specifically matching the additives to the basic composition.

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Magnetic properties:

A1: Remanence (150 ⁰ C) = 1000 mT Coercive field strength (150 ⁰ C) = 1050 kA/m Temperature coefficient (RT up to 100 ⁰ C) = -0.08 %/K Temperature coefficient (RT up to 150 ⁰ C) = -0.085 %/K.

The diagram in Fig. 3 shows the demagnetization curves of this alloy. These are curves at 25, 50, 100 and 150 ⁰ C. The measured values and test parameters are as follows.

8 ^{i 2 3 4}

."7 »1.089 i.069 1.023 .979 &Ggr;

^H cB =843.1 &THgr;25.8 784.1 742.8

>M80.1 M448.3 1416.5 910 2 2287 220.6 200.2 181 .'9

25 50 500 !50

A2: Remanence (room temperature) = 125OmT Coercive field strength (room temperature) = 900 kA/m

A3: Remanence (room temperature) = 118OmT Coercive field strength (room temperature) = 1500 kA/m Temperature coefficient (RT up to 100 ⁰ C) = -0.08 %/K Temperature coefficient (RT up to 150 ⁰ C) = -0.085 %/K.

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B1: Remanence (150 ⁰ C) = 910 mT

Coercive field strength (150 ⁰ C) = 900 kA/m Temperature coefficient (RT to 100 ⁰ C) = -0.08 %/K Temperature coefficient (RT to 150 ⁰ C) = -0.085 %K

B2: Remanence (150 ⁰ C) = 920 mT

Coercive field strength (150 ⁰ C) = 800 kA/m

φ Temperature coefficient (RT to 100 ⁰ C) = -0.08 %/K

Temperature coefficient (RT to 150 ⁰ C) = -0.085 %/K

B3: Remanence (150 ⁰ C) = 910 mT

Coercive field strength (150 ⁰ C) = 900 kA/m Temperature coefficient (RT up to 100 ⁰ C) = -0.08 %/K Temperature coefficient (RT up to 150 ⁰ C) = -0.085 %K.

The following variations in composition are possible:

Nb can be completely or partially replaced by other refractory metals such as Mo, V, Cr, W , Ta, etc.

Al can be partially or completely replaced by Ga or Bi. Cu can be partially or completely replaced by Ag or Au.

With Dy contents > 5 wt.%, excellent high-temperature properties and temperature coefficients for room temperatures up to 100 ⁰ C or up to 150 ⁰ C > - 0.09 can be achieved.

Claims (11)

-9- 8 Nov. 1995 Claims 1. Magnetic material with 27 to 33 wt.% RE, where RE stands for Pr, Nd, Dy or Tb or combinations thereof, other RE as unavoidable impurities and with at least two elements from the following group and with the following proportions 0 to 6 wt% Co 0.8 to 11.3 wt% B O to 2.0 wt% Nb 0 to 1.5 wt% Al 0 to 1.5 wt% Ga 0 to 1.0 wt.% Cu as well as unavoidable impurities and Fe as residue. 2. Magnetic material according to claim 1, characterized in that the proportions of the elements of the group 1 to 4 wt.% Co 0.9 to 1.0 wt.% B 0.1 to 1.0 wt.% Nb 0.1 to 0.5 wt.% Al 0.1 to 0.5 wt.% Ga -10- 8 Nov 1995 and 0.05 to 0.5 wt.% Cu. 3. Magnetic material according to claim 2, characterized in that the proportions of the elements of the group 2.5 to 3.5 wt% Co 0.95 to 1.0 wt% B 0.5 to 0.9 wt% Nb 0.1 to 0.3 wt% Al 0.1 to 0.4 wt% Ga and 0.05 to 0.2 wt% Cu be. 4. Magnetic material according to claim 3, characterized in that the proportions of the elements of the group 3.0 wt% Co 0.95 wt% B 0.8 wt% Nb 0.2 wt% Al 0.2 wt% Ga and 0.1 wt% Cu be. - 11 - 8 Nov 1995 5. Magnetic material according to one of the preceding claims, where Nb is completely or partially replaced by other refractory metals. 6. Magnetic material according to claim 5,
characterized, that the refractory metals are Mo, V, Cr or Ta or a combination thereof. 7. Magnetic material according to one of the preceding claims, characterized in that Al is completely or partially replaced by Ga and/or Bi. 8. Magnetic material according to one of the preceding claims, characterized in that Ga is completely or partially replaced by Al and/or Bi. 9. Magnetic material according to one of the preceding claims, characterized in W that Cu is completely or partially replaced by Ag and/or Au. 10. Magnetic material according to one of the preceding claims, characterized in that the Dy content is at least 5 wt.%. 11. Permanent magnet made of a magnetic material according to one of the preceding claims. 2. Permanent magnet according to claim 11,
characterized,
that it is coated.