Artificial permanent magnet and method for producing the artificial permanent magnet

Abstract

A method is provided for producing an artificial permanent magnet, in a powder preparation step a main phase powder, which includes a rare-earth transition metal compound with permanently magnetic properties and has a first average particle size, is prepared and an anisotropic powder, which has a higher anisotropy field strength than the main phase powder and has a second average particle size, is prepared, wherein the second average particle size is smaller than the first average particle size. In a subsequent powder mixing step, the main phase powder and the anisotropic powder are mixed together to form a powder mixture and, in a subsequent heat treatment step, this powder mixture with the main phase powder of the first average particle size and with the anisotropic powder of the second average particle size is sintered to form an artificial permanent magnet.

Claims

1. A method for producing an artificial permanent magnet, comprising, preparing a main phase powder, the main phase powder comprising a rare-earth transition metal compound with permanently magnetic properties and with a first average particle size, and an anisotropic powder, the anisotropic powder having a higher anisotropy field strength than the main phase powder and having a second average particle size which is smaller than the first average particle size, wherein mixing the main phase powder and the anisotropic powder together to form a powder mixture, generating a molded body using powder metallurgical methods subsequent to the mixing step, sintering the powder mixture with the main phase powder of the first average particle size and with the anisotropic powder of the second average particle size to form an artificial permanent magnet subsequent to the mixing step, wherein both the main phase powder and also the anisotropic powder are in each case mixtures of at least another two different powders, and wherein the main phase powder contains an SE.sub.2 (Fe, X).sub.14 B compound, where SE denotes rare earth elements, Fe denotes iron, B denotes boron and X denotes any desired chemical element including iron or a number of any desired chemical elements.

2. The method according to claim 1, wherein the main phase powder contains at least one rare-earth element.

3. The method according to claim 1, wherein the anisotropic powder contains at least one rare-earth element.

4. The method according to claim 1, wherein the anisotropic powder contains at least one SE.sub.2 (Fe, X).sub.14 B compound, where SE denotes rare earth elements, Fe denotes iron, B denotes boron and X denotes any desired chemical element including iron or a number of any desired chemical elements.

5. The method according to claim 1, wherein the first average particle size of the main phase powder is over 50% larger than the second average particle size of the anisotropic powder.

6. The method according to claim 1, wherein the first average particle size is between 3 μm and 10 μm.

7. The method according to claim 1, wherein the second average particle size is smaller than 3 μm.

8. The method according to claim 1, wherein the proportion of the anisotropic powder in the powder mixture is less than 50 percent by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below, embodiment examples of the inventive idea, which are represented in the drawings, are explained in further detail. In the drawings:

(2) FIG. 1 shows a diagrammatic representation of a sequence of method steps for producing an artificial permanent magnet according to the invention, and

(3) FIG. 2 shows a diagrammatic cross-sectional view through an internal region of an artificial permanent magnet according to the invention.

DETAILED DESCRIPTION

(4) In the method sequence represented diagrammatically in FIG. 1, in a powder preparation step 1, a main phase powder and an anisotropic power are prepared. The main phase powder comprises a rare-earth transition metal compound with permanently magnetic properties, for example, an SE (Fe, X).sub.1B compound. The anisotropic powder comprises particles with components or added elements which bring about a higher anisotropy field strength of the anisotropic powder in comparison to the main phase powder. Both the main phase powder and also the anisotropic powder may in each case be mixtures of at least another two different powders.

(5) The particles of the main phase powder have a first average particle size which is larger than the second average particle size of the particles of the anisotropic powder. The different average particle size can be preset by appropriate crushing or grinding processes, for example. It can also be obtained by sieving or fractionating a selection of particles having an appropriate particle size. In particular, if commercial powder mixtures are used, it is also conceivable that the desired particle size is already provided and can thus be selected accordingly.

(6) In subsequent powder mixing step 2, the main phase powder and the anisotropic powder are mixed together to form a powder mixture.

(7) In a pressing step 3, a pellet is produced from the powder mixture, which is suitable for subsequent heating and sintering and already has the shape of the desired artificial permanent magnet. In the process, it is possible to optionally add additional substances or, for example, a suitable binder to the powder mixture, in order to promote the production of the pellet and the subsequent sintering process. Moreover, components can be added, which, for example, influence and improve the strength or the temperature resistance of the artificial permanent magnet.

(8) In a subsequent heat treatment step 4, the powder mixture with n in powder of the first average particle size and with the anisotropic powder of the second average particle size as well as optionally with other components and added elements is sintered to form an artificial permanent magnet. In the process, the heat treatments which are conventional for a sintering process can be carried out.

(9) A cross-sectional view of an artificial permanent magnet 5 produced by the above-described method according to the invention is shown as an example in FIG. 2. The particles 6 of the main phase powder or of the main phase are embedded in a liquid phase 7 which is first liquefied and then crystallized again. The liquid phase 7 was generated during the sintering process from the anisotropic powder, which had melts early and is distributed in its liquid phase around the particles 6 of the main phase powder, surrounding these particles 6. During the heat treatment step 4, added elements penetrated into an edge region 8 of the particles of the main phase powder, and their concentration increased there. Due to the increase in concentration in the edge region 8, the anisotropic field strength of the permanently magnetic particles 6 of the main phase powder is increased, and magnetic interaction, in particular magnetic exchange interaction between adjacent particles of the main phase powder, is reduced. Since the chemical elements in question penetrate only into the edge region 8 of the particles 6 and not into a core region 9 of the particles, there is a concentration increase of only a small proportion of the components or added elements increasing the anisotropy field strength in the particles 6, and the concomitant influencing of the remanence of the particle 6 is kept low.

(10) With the embodiment example described below, it was possible to demonstrate a clear improvement of the magnetic properties in an artificial permanent magnet produced according to the invention. First, a main phase powder was produced from a ternary Nd—Fe—B alloy, where Nd denotes neodymium, Fe denotes iron and B denotes boron. The main phase powder was finely ground to an average grain size of approximately 6 μm. An anisotropic powder was produced from a second alloy consisting substantially of SE-TM-B, where SE denotes a rare-earth element and B denotes boron, and the component denoted TM also contained, in addition to iron, other chemical elements such as gallium, copper and aluminum, for example. The anisotropic powder was finely ground to an average grain size of approximately 3 μm. In both cases, before the grinding process, the starting materials were homogenized, hydrated and dehydrated according to the usual methods.

(11) From the main phase powder having the first average particle size of approximately 6 μm and the anisotropic powder having a second average particle size of approximately 3 μm, a powder mixture was prepared, consisting of approximately 90 percent by weight of the main phase powder and approximately 10 percent by weight of the anisotropic powder. Subsequently, a pellet was formed and an artificial permanent magnet was sintered.

(12) As reference object, another artificial permanent magnet was produced, in which the same materials of the main phase powder and of the anisotropic powder were prepared in each case with similar quantity proportions, but with a consistently lower particle size of 6 μm, and therefrom a reference permanent magnet was sintered.

(13) By measuring the respective demagnetization curves, it was possible to determine that both the artificial permanent magnet produced according to the invention and the reference permanent magnet exhibited an identical remanence, within the limits of measurement precision, both at room temperature and also at approximately 100° C. In contrast, at room temperature, the intrinsic coercive field strength of the permanent magnet according to the invention was approximately 10% higher than the intrinsic coercive field strength of the reference permanent magnet. Even in the case of heating to approximately 100° C., the intrinsic coercive field strength of the permanent magnet according to the invention was still clearly higher than the intrinsic coercive field strength of the reference permanent magnet.