HOT-PRESSED AND DEFORMED MAGNET COMPRISING NONMAGNETIC ALLOY AND METHOD FOR MANUFACTURING SAME

Abstract

An R-TM-B hot-pressed and deformed magnet (here, R represents a rare earth metal selected from the group consisting of Nd, Dy, Pr, Tb, Ho, Sm, Sc, Y, La, Ce, Pm, Eu, Gd, Er, Tm, Yb, Lu, and a combination thereof, and TM represents a transition metal) of the present invention comprises flat type anisotropic magnetized crystal grains and a nonmagnetic alloy distributed in a boundary surface between the crystal grains, and thus the magnet of the present invention has an excellent magnetic shielding effect as compared with an existing permanent magnet since the crystal gains can be completely enclosed in the nonmagnetic alloy, so that a hot-pressed and deformed magnet with enhanced coercive force can be manufactured through a more economical process.

Claims

1. An R-TM-B (here, R means a rare earth metal selected from the group consisting of Nd, Dy, Pr, Tb, Ho, Sm, Sc, Y, La, Ce, Pm, Eu, Gd, Er, Tm, Yb, Lu, and a combination thereof, and TM means a transition metal) hot-pressed and deformed magnet comprising: (i) anisotropic plate-shaped crystal grains; and (ii) a non-magnetic alloy distributed at the interface of the crystal grains.

2. The magnet of claim 1, wherein the R-TM-B hot-pressed and deformed magnet is represented by the following Chemical Formula 1: [Chemical Formula 1] (R′.sub.1-xR″.sub.x).sub.2TM.sub.14B (here, R′ and R″ are a rare earth metal selected from the group consisting of Nd, Dy, Pr, Tb, Ho, Sm, Sc, Y, La, Ce, Pm, Eu, Gd, Er, Tm, Yb, Lu, and a combination thereof, and x is a real number with 0≦x≦1.0).

3. The magnet of claim 1, wherein the non-magnetic alloy is represented by the following Chemical Formula 2: [Chemical Formula 2] T.sub.aM.sub.1-a (here, T is any one element selected from the group consisting of Nd, Dy, Pr, Tb, Ho, Sm, Sc, Y, La, Ce, Pm, Eu, Gd, Er, Tm, Yb, Lu, and a combination thereof, M is any one metal element selected from the group consisting of Cu, Al, Sb, Bi, Ga, Zn, Ni, Mg, Ba, B, Co, Fe, In, Pt, Ta, and a combination thereof, and a is a real number with 0<a<1).

4. The magnet of claim 1, wherein the non-magnetic alloy comprises any one selected from the group consisting of Nd.sub.0.84Cu.sub.0.16, Nd.sub.0.7Cu.sub.0.3, Nd.sub.0.85Al.sub.0.15, Nd.sub.0.08Al.sub.0.92, Nd.sub.0.03Sb.sub.0.97, Nd.sub.0.8Ga.sub.0.2, Nd.sub.0.769Zn.sub.0.231, Nd.sub.0.07Mg.sub.0.93, Pr.sub.0.84 Cu.sub.0.16, Pr.sub.0.7Cu.sub.0.3, Pr.sub.0.85Al.sub.0.15, Pr.sub.0.08Al.sub.0.92, Pr.sub.0.03Sb.sub.0.97, Pr.sub.0.8Ga.sub.0.2, Pr.sub.0.769Zn.sub.0.231, Pr.sub.0.07Mg.sub.0.93, Bi, Ga, Ni, Co, and a combination thereof.

5. The magnet of claim 1, wherein the non-magnetic alloy has a melting point of 400° C. to 700° C.

6. The magnet of claim 1, wherein the crystal grains have a diameter of 100 nm to 1,000 nm.

7. A method for manufacturing an R-TM-B hot-pressed and deformed magnet, the method comprising the steps of: (a) preparing a magnetic powder from an R-TM-B (here, R means a rare earth metal selected from the group consisting of Nd, Dy, Pr, Tb, Ho, Sm, Sc, Y, La, Ce, Pm, Eu, Gd, Er, Tm, Yb, Lu, and a combination thereof, and TM means a transition metal) alloy; (b) manufacturing a sintered body by press sintering the magnetic powder; and (c) hot-pressing and deforming (hot deformation) the sintered body by applying heat and pressure, wherein the method comprises adding a non-magnetic alloy at the time of manufacturing the R-TM-B alloy in Step (a) or before the press sintering in Step (b).

8. The method of claim 7, wherein the magnetic powder comprises a magnetic powder manufactured by any one process selected from the group consisting of a hydrogenation disproportionation desorption and recombination (HDDR) process, a melt spinning process, a rapid solidification process, and a combination thereof.

9. The method of claim 7, wherein the non-magnetic alloy is added in an amount of 0.01 wt % to 10 wt % based on a weight of the magnetic powder.

10. The method of claim 7, wherein Step (b) is carried out at a temperature of 300° C. to 800° C.

11. The method of claim 7, wherein Step (c) is carried out at a temperature of 500° C. to 1,000° C.

12. The method of claim 7, wherein the non-magnetic alloy is added before the press sintering in Step (b), and is mixed with the magnetic powder.

13. The method of claim 12, further comprising a step of subjecting the sintered body to an additional heat treatment between Steps (b) and (c).

14. The method of claim 13, wherein the additional heat treatment is carried out at a temperature of 400° C. to 800° C.

15. The method of claim 7, wherein a deformation ratio of the hot-pressing and deformation in Step (c) is 50% to 80%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 illustrates the TEM observation photographs of the crystal grain interfaces of the permanent magnets manufactured in (a) Comparative Example 1, (b) Example 2, and (c) Example 3;

[0056] FIG. 2 illustrates the EDS-mapping analysis photographs of the permanent magnets manufactured in (a) Example 2 and (b) Example 3; and

[0057] FIG. 3 illustrates the SEM observation photographs of Example 4-3 (a) before the heat treatment and (b) after the heat treatment.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

[0058] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It will also be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[0059] Description will now be given in detail of a drain device and a refrigerator having the same according to an embodiment, with reference to the accompanying drawings.

[0060] Hereinafter, exemplary embodiments of the present invention will be described in detail such that a person skilled in the art to which the present invention pertains can easily carry out the present invention. However, the present invention can be implemented in various different forms, and is not limited to the exemplary embodiments described herein.

EXAMPLE

Example 1

Preparation of Magnetic Powder

[0061] An alloy in the form of a ribbon was prepared by melting an NdFeB-based powder (Nd.sub.30B.sub.0.9Co.sub.4.1Ga.sub.0.5Fe.sub.Bal.) being a raw material, and injecting the melt into a cooling roll which was rotated at high speed (a melt spinning process). A magnetic powder was prepared by milling an ingot in the form of a ribbon produced by the rolling process to pulverize the ingot into a size of about 200 μm.

Example 2

Manufacture of Hot-Pressed and Deformed Magnet Including Non-Magnetic Alloy

[0062] Nd.sub.0.84Cu.sub.0.16 as a non-magnetic alloy was added in an amount of each of 0.5 wt % (Example 2-1), 1.0 wt % (Example 2-2), and 1.5 wt % (Example 2-3) based on the weight of the magnetic powder, and the powders were mixed with each magnetic powder (the magnetic powder prepared in Example 1) by a dry method.

[0063] Thereafter, the mixed powders were injected into an extrusion mold for forming (press sintering) and were pressurized at a pressure of about 150 MPa and a temperature of about 700° C., and as a result, a press sintering was carried out by using a hot press, such that the relative density became 99%.

[0064] Subsequently, pressure was applied to a sintered body extruded and formed from the mold at about 750° C. by using a press device in which all directions were open, and as a result, a hot-press and deformation was carried out at a deformation ratio of about 70%, such that crystal grains in the magnetic powder became plate-shaped. Due to the pressurization, the magnetization direction of crystal grains included in each powder particle was aligned in one direction, thereby manufacturing anisotropic hot-pressed and deformed magnets including the non-magnetic alloy in an amount of 0.5 wt %, 1.0 wt %, and 1.5 wt %, respectively (Examples 2-1 to 2-3, respectively).

Example 3

Manufacture of Hot-Pressed and Deformed Magnet Including Non-Magnetic Alloy

[0065] An anisotropic hot-pressed and deformed magnet was manufactured in the same manner as in Example 2, except that Pr.sub.0.84Cu.sub.0.16 was used instead of Nd.sub.0.84Cu.sub.0.16 (wt %) as the non-magnetic alloy.

Example 4

Manufacture of Hot-Pressed and Deformed Magnet Subjected to Additional Heat Treatment

[0066] Hot-pressed and deformed magnets were manufactured in the same manner as in Example 2 (Examples 4-1 to 4-3, respectively), except that the sintered bodies subjected to press sintering in Example 2 (Examples 2-1, 2-2, and 2-3) were subjected to an additional heat treatment at a temperature of about 575° C. for about 2 hours.

Comparative Example 1

Manufacture of Hot-Pressed and Deformed Magnet To Which Non-Magnetic Alloy is not Added

[0067] A hot-pressed and deformed magnet was manufactured in the same manner as in Example 2, except that a non-magnetic alloy was not added to the magnetic powder prepared in Example 1.

Evaluation Example

[0068] 1) Observation of Internal Structure by Using Electronic Microscope

[0069] For the hot-pressed and deformed magnets in Examples 2 and 3 and the magnet in Comparative Example 1, photographs capturing the internal structures thereof are illustrated in FIG. 1 by using a transmission electron microscope (TEM). Through the photographs, it could be confirmed that the shape surrounding the crystal grains in the magnet in Comparative Example 1 could not be observed, but the Nd-rich phase was present at the crystal grain interface in the magnets in Examples 2 and 3.

[0070] 2) Analysis of Composition

[0071] For the hot-pressed and deformed magnets in Examples 2 and 3, an EDS-mapping analysis was carried out, and the results thereof are illustrated in FIG. 2. Through FIG. 2, it could be confirmed that an Nd-based compound or a Pr-based compound, which was a low-melting point metal compound, was contained inside the hot-pressed and deformed magnets in Examples 2 and 3.

[0072] 3) Evaluation of Magnetic Characteristics

[0073] For the hot-pressed and deformed magnets in Examples 2 to 4 and the sintered magnets in Comparative Examples 1 and 2, the coercive force and residual magnetic flux density being performance measures of a magnet were evaluated by using a vibrating sample magnetometer (VSM, Lake Shore #7410 USA), and the result values thereof are shown in the following Table 1.

TABLE-US-00001 TABLE 1 Before heat After heat Amount of non-magnetic treatment treatment alloy added (kOe) (kOe) Improvement (wt %) (Example 2) (Example 4) ratio (%) 0.0 (Comparative 14.2 15.2 7 Example 1) 0.5 (Examples 2-1 and 15.9 17.9 13 4-1) 1.0 (Examples 2-2 and 16.6 18.5 11 4-2) 1.5 (Examples 2-3 and 17.1 18.9 11 4-3)

[0074] Referring to Table 1, it could be confirmed that when the additional heat treatment was carried out as in Example 4, the non-magnetic alloy was more uniformly distributed at the interface of the crystal grains, and accordingly, the coercive force was improved by about 10% to about 15% than those in the magnets in Examples 2 and 3.

[0075] Further, through FIG. 3, it could be confirmed that the additive diffused in a larger amount into the crystal grain interface inside the powder after the heat treatment than before the heat treatment.

[0076] Through this, it could be confirmed that since the magnet in Comparative Example 1, in which the interface of the crystal grains was not surrounded by the non-magnetic alloy, failed to perfectly achieve the magnetic shielding, the Nd-rich phase was discharged outside the crystal grains, and as a result, the coercive force was exhibited at a low level, whereas it could be confirmed that in Examples 2 to 4 where the magnetic shielding was perfectly achieved by adding the non-magnetic alloy to surround the interface of the crystal grains, the coercive force was improved.

[0077] Although preferred examples of the present invention have been described in detail hereinabove, the right scope of the present invention is not limited thereto, and it should be clearly understood that many variations and modifications of those skilled in the art using the basic concept of the present invention, which is defined in the following claims, will also fall within the right scope of the present invention.