Sm-Fe-N MAGNET MATERIAL AND Sm-Fe-N BONDED MAGNET

Abstract

The present invention relates to an SmFeN magnet material including: 7.0-12 at % of Sm; 0.1-1.5 at % of at least one element selected from the group consisting of Hf, Zr, and Sc; 0.1-0.5 at % of Mn; 10-20 at % of N; and 0-35 at % of Co, with the remainder being Fe and unavoidable impurities. The present invention also relates to an SmFeN bonded magnet including a powder of the SmFeN magnet material and a binder.

Claims

1. An SmFeN magnet material comprising: 7.0-12 at % of Sm; 0.1-1.5 at % of at least one element selected from the group consisting of Hf, Zr, and Sc; 0.1-0.5 at % of Mn; 10-20 at % of N; and 0-35 at % of Co, with the remainder being Fe and unavoidable impurities.

2. The SmFeN magnet material according to claim 1, further comprising 0.1-0.5 at % of Si.

3. The SmFeN magnet material according to claim 1, further comprising 0.1-0.5 at % of Al.

4. The SmFeN magnet material according to claim 2, further comprising 0.1-0.5 at % of Al.

5. The SmFeN magnet material according to claim 1, wherein a main phase thereof has a TbCu.sub.7-type crystal structure.

6. The SmFeN magnet material according to claim 2, wherein a main phase thereof has a TbCu.sub.7-type crystal structure.

7. The SmFeN magnet material according to claim 3, wherein a main phase thereof has a TbCu.sub.7-type crystal structure.

8. The SmFeN magnet material according to claim 4, wherein a main phase thereof has a TbCu.sub.7-type crystal structure.

9. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 1 and a binder.

10. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 2 and a binder.

11. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 3 and a binder.

12. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 4 and a binder.

13. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 5 and a binder.

14. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 6 and a binder.

15. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 7 and a binder.

16. An SmFeN bonded magnet comprising a powder of the SmFeN magnet material according to claim 8 and a binder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a graph that shows the decrease amounts of irreversible demagnetizing factors due to 2,000-hour holding at 120 C. from the initial demagnetizing factors, with respect to a plurality of samples differing in Mn content in Examples of the SmFeN bonded magnets according to the present invention and Comparative Examples.

[0026] FIG. 2 is a graph that shows changes in irreversible demagnetizing factor with the lapse of time in holding at 120 C., in Examples according to the present invention and Comparative Examples.

[0027] FIG. 3 is a graph that shows changes with the lapse of time in the decrease amounts of irreversible demagnetizing factors due to 120 C. holding from the initial demagnetizing factors in Examples according to the present invention and Comparative Examples.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Embodiments of the SmFeN magnet material and SmFeN bonded magnet according to the present invention are explained below.

[0029] The SmFeN magnet material of the present invention includes: 7.0-12 at % of Sm; 0.1-1.5 at % of at least one element (element T) selected from the group consisting of Hf, Zr, and Sc; 0.1-0.5 at % of Mn, 10-20 at % of N, and 0-35 at % of Co, with the remainder being Fe and unavoidable impurities. This SmFeN magnet material can be produced, for example, by the following method.

[0030] First, the components shown above, excluding N, are mixed together and melted to thereby produce a melt serving as a raw material. Next, this melt is jetted to the surface of a roll which is rotating at a high speed, thereby rapidly cooling the melt to produce a ribbon of an alloy. This ribbon is heat-treated in an inert atmosphere at a temperature in the range of 700-800 C. to thereby change some of the amorphous and metastable phases into a stable phase. This operation is conducted in order to enable the alloy to have a higher coercive force after the subsequent nitriding.

[0031] Thereafter, the ribbon is heated in a gas which contains molecules having nitrogen atoms to thereby obtain nitrided powder. This operation heightens the saturation magnetization, coercive force, and maximum energy product. A mixed gas containing ammonia and hydrogen is suitable for use as the gas containing molecules including nitrogen atoms. In this example, ammonia gas is the gas including molecules including nitrogen atoms. The heating temperature and pressure in the nitriding depend on the gas used. In an example, in cases when a gas containing ammonia and hydrogen in a volume ratio of 1:3 is used, a heating temperature of about 450 C. is used and the pressure is regulated to substantially atmospheric pressure (slightly higher than atmospheric pressure) by performing the treatment while passing the gas through the tube furnace. By regulating the time period of this nitriding, the content of N is regulated to 10-20 at %. Through the operations shown above, a powder-form SmFeN magnet material (hereinafter referred to as SmFeN magnet powder) is obtained.

[0032] As stated above, the SmFeN magnets generally include ones in which the main phase thereof has a Th.sub.2Zn.sub.17-type crystal structure and ones in which the main phase thereof has a TbCu.sub.7-type crystal structure. In this embodiment, an SmFeN magnet powder in which the main phase thereof has a TbCu.sub.7-type crystal structure is obtained by incorporating element T in an amount of 0.1-1.5 at %.

[0033] In the SmFeN magnet powder according to this embodiment, it is possible to further incorporate Si in an amount of 0.1-0.5 at % or to further incorporate Al in an amount of 0.1-0.5 at %. In the case of incorporating Si and/or Al, an SmFeN magnet powder may be produced in the same manner as described above. By incorporating Si and/or Al into the SmFeN magnet powder according to this embodiment, the SmFeN magnet produced from this SmFeN magnet powder can be more effectively inhibited from suffering thermal demagnetization over a long period than in the case where neither of the two elements is contained.

[0034] The SmFeN bonded magnet according to this embodiment can be produced by mixing the SmFeN magnet powder produced by the method described above with a binder and molding the mixture. As the binder, use can be made of a thermosetting resin such as an epoxy resin or a thermoplastic resin such as a nylon. For example, the SmFeN magnet powder according to the embodiment described above is mixed with 2% by mass of an epoxy resin, and this mixture is compression-molded. Thus, an SmFeN bonded magnet according to this embodiment is obtained.

EXAMPLES

[0035] Shown below are the results of an experiment in which SmFeN bonded magnets were actually produced and examined for magnetic property. In this experiment, an epoxy resin was added in an amount of 2% by mass to each of SmFeN magnet powders containing the respective elements in amounts shown in Table 1. Each mixture was kneaded, compression-molded into a cylinder having a diameter of 10 mm and a height of 7 mm, and then hardened. Thus, SmFeN bonded magnets were produced. Although the contents of Fe are omitted in Table 1, Fe accounts for the remainder of each magnet. In Table 1, nineteen samples of Examples have been sorted into four groups, G1 to G4, by the contents of Si and Al. In group G1, the contents of Si and Al are each 0.04 at % or less (less than 0.1 at % when the content values are rounded off by correcting the digits in the second decimal place). In group G2, the content of Si is 0.05-0.54 at % (0.1-0.5 at % when the content values are rounded off likewise), and the content of Al is 0.04 at % or less. In group G3, the content of Si is 0.04 at % or less, and the content of Al is 0.05-0.54 at %. In group G4, the contents of Si and Al are each 0.05-0.54 at %. The samples of Comparative Examples are ones in each of which the content of Mn is 0.04 at % or less or is 0.55 at % or higher (the content is less than 0.1 at % or exceeds 0.5 at %, when rounded off by correcting the digit in the second decimal place).

TABLE-US-00001 TABLE 1 T Sm Co N Mn Zr Hf Sc Si Al C G1 Example 1 7.37 3.83 13.6 0.14 1.02 0.04 0.04 0.08 Example 2 7.16 3.80 13.4 0.32 0.96 0.04 0.03 0.10 Example 3 7.54 3.82 13.2 0.48 0.97 0.03 0.03 0.12 G2 Example 4 7.29 3.76 13.3 0.05 1.01 0.12 0.03 0.06 Example 5 7.30 3.81 13.2 0.15 1.05 0.28 0.02 0.06 Example 6 7.44 3.79 13.5 0.31 0.99 0.52 0.04 0.04 Example 7 7.42 3.82 13.6 0.32 0.98 0.10 0.03 0.06 Example 8 7.30 3.82 13.3 0.35 1.41 0.21 0.03 0.04 Example 9 7.42 3.81 13.1 0.09 1.52 0.18 0.04 0.03 Example 10 7.35 3.83 13.7 0.12 1.28 0.22 0.04 0.04 Example 11 7.41 3.77 13.4 0.51 0.95 0.48 0.03 0.33 G3 Example 12 7.48 3.77 13.4 0.29 0.68 0.02 0.07 0.08 Example 13 7.43 3.82 13.3 0.07 1.03 0.04 0.31 0.09 Example 14 7.38 3.83 13.5 0.21 1.13 0.03 0.42 0.11 Example 15 7.35 3.85 13.2 0.45 1.04 0.04 0.34 0.14 G4 Example 16 7.30 3.75 13.6 0.30 0.70 0.28 0.08 0.04 Example 17 7.39 3.73 13.5 0.08 1.11 0.42 0.28 0.06 Example 18 7.41 3.84 13.4 0.23 1.02 0.06 0.45 0.03 Example 19 7.45 3.81 13.4 0.50 1.01 0.49 0.32 0.25 Comparative 7.36 3.84 13.5 0.02 0.93 0.02 0.03 0.03 Example 1 Comparative 7.32 3.82 13.6 0.73 0.97 0.02 0.04 0.06 Example 2 Comparative 7.37 3.81 13.5 0.03 0.90 0.23 0.03 0.04 Example 3 Comparative 7.37 3.76 13.2 0.73 1.03 0.43 0.04 0.05 Example 4 G1: 0.05-0.54 at % of Mn, up to 0.04 at % of Si, up to 0.04 at % of Al G2: 0.05-0.54 at % of Mn, 0.05-0.54 at % of Si, up to 0.04 at % of Al G3: 0.05-0.54 at % of Mn, up to 0.04 at % of Si, 0.05-0.54 at % of Al G4: 0.05-0.54 at % of Mn, 0.05-0.54 at % of Si, 0.05-0.54 at % of Al Comparative Examples: up to 0.04 at % or at least 0.55 at % of Mn * Note 1: The contents are given in terms of at %. * Note 2: The content of each element is shown with three effective digits (down to the first decimal place for N; down to the second decimal place for the other elements). * Note 3: The remainder of each sample is Fe and unavoidable impurities.

[0036] The samples of the Examples and Comparative Examples were each subjected to an experiment in which the sample was examined for magnetic flux after magnetization and after the magnetized sample was held in a 120 C. oven for 1 hour or for 2,000 hours and then cooled to room temperature. The initial demagnetizing factor and irreversible demagnetizing factor due to 2,000-hour holding were determined from the data obtained. Furthermore, the decrease amount of the irreversible demagnetizing factor due to 2,000-hour holding from the initial demagnetizing factor (hereinafter, the decrease amount is referred to as decrease amount through 2,000-hour holding) was determined as shown in FIG. 1 and Table 2.

TABLE-US-00002 TABLE 2 Irreversible Decrease demagnetizing amount of factor (%) irreversible Demag- Demagnetizing netizing factor due to factor 2000-hour Initial due to holding demag- 2000- from Initial netizing hour demagnetizing factor holding factor (%) G1 Example 1 6.68 8.78 2.10 Example 2 6.63 8.73 2.10 Example 3 6.63 8.71 2.08 G2 Example 4 6.70 8.70 2.00 Example 5 6.68 8.61 1.93 Example 6 6.63 8.61 1.98 Example 7 6.65 8.63 1.98 Example 8 6.67 8.62 1.95 Example 9 6.65 8.63 1.98 Example 10 6.66 8.66 2.00 Example 11 6.63 8.71 2.08 G3 Example 12 6.63 8.61 1.98 Example 13 6.64 8.64 2.00 Example 14 6.64 8.62 1.98 Example 15 6.63 8.71 2.08 G4 Example 16 6.63 8.61 1.98 Example 17 6.40 8.30 1.90 Example 18 6.35 8.11 1.76 Example 19 6.38 8.25 1.87 Comparative 6.93 9.32 2.39 Example 1 Comparative 6.75 9.10 2.35 Example 2 Comparative 6.91 9.25 2.34 Example 3 Comparative 6.86 9.16 2.30 Example 4

[0037] It can be seen from the graph shown in FIG. 1 that the Examples (data indicated by the solid squares, solid rhombs, open circles, and open triangles) are smaller in decrease amount through 2,000-hour holding than the Comparative Examples (data indicated by the symbols and +). Specifically, the decrease amounts through 2,000-hour holding in the Comparative Examples exceed 2.2%, whereas those in the Examples are 2.2% or less. This means that the Examples are higher in the stability of magnetic flux in high-temperature environments (i.e., thermal stability) and more suitable for long-term use in such environments than the Comparative Examples.

[0038] A comparison among the Examples in the graph of FIG. 1 shows that group G2 (solid rhombs) and group 3 (open circles) are smaller in decrease amount through 2,000-hour holding than group G1 (solid squares) and that group G4 (open triangles) are smaller in decrease amount through 2,000-hour holding than groups G2 and G3 (group G2 is substantially equal to group G3). This indicates that the thermal stability of SmFeN bonded magnets is enhanced by incorporating Si and/or Al thereinto in an amount of 0.05-0.54 at %. Meanwhile, among the Comparative Examples (Mn content: 0.04 at % or less), those containing 0.05-0.54 at % of Si (indicated by the symbol +) are each inferior in decrease amount through 2,000-hour holding to each of the Examples. It can hence be seen that Mn contributes more to thermal stability than Si.

[0039] FIG. 2 shows changes in irreversible demagnetizing factor with the lapse of time in holding at 120 C., with respect to the samples of Example 1, Example 17, Comparative Example 2, and Comparative Example 3. FIG. 3 shows changes with the lapse of time in the decrease amounts of irreversible demagnetizing factors due to 120 C. holding from the initial demagnetizing factors with respect to the same samples as in FIG. 2. Although demagnetization occurs at a relatively high rate during heating from room temperature to the holding temperature, it can be seen from the graphs of FIG. 2 and FIG. 3 that after the holding temperature has been reached, demagnetization occurs linearly with the logarithmic lapse of time. The samples of the Examples are smaller in the slope of the change in demagnetizing factor with the logarithmic lapse of time than the Comparative Examples. The same applies to the decrease amounts in irreversible demagnetizing factors from the initial demagnetizing factors. Thus, it can be seen also from the graphs of FIG. 2 and FIG. 3 that the Examples have better thermal stability than the Comparative Examples.

[0040] In Table 3 are shown the residual magnetic flux density B.sub.r, coercive force Ale, and maximum energy product (BH).sub.max of each sample determined at room temperature. With respect to the B.sub.r, iH.sub.c, and (BH).sub.max, there is no significant difference between the Examples and the Comparative Examples. It was ascertained from these experimental results that, in the SmFeN bonded magnets of Examples, thermal stability which is higher than those of the Comparative Examples can be obtained while obtaining room-temperature coercive force iH.sub.c and room-temperature residual magnetic flux density B.sub.r which are substantially equal to those of the Comparative Examples. Irrespective of Examples or Comparative Examples, the decrease amount of an irreversible demagnetizing factor from the initial demagnetizing factor can be reduced by heightening the room-temperature coercive force iH.sub.c by suitably setting the conditions (temperature, time period) for the heat treatment of the powder. In this case, however, the residual magnetic flux density B.sub.r decreases undesirably.

TABLE-US-00003 TABLE 3 B.sub.r (kG) iH.sub.c (kOe) (BH).sub.max (kOe) G1 Example 1 7.78 9.54 12.9 Example 2 7.85 9.36 12.9 Example 3 8.02 9.44 13.2 G2 Example 4 8.02 9.53 13.5 Example 5 8.01 9.43 13.4 Example 6 8.03 9.54 13.7 Example 7 8.02 9.36 13.3 Example 8 8.02 9.46 13.2 Example 9 7.98 9.45 13.1 Example 10 7.99 9.51 12.9 Example 11 8.04 9.55 13.5 G3 Example 12 8.03 9.43 13.1 Example 13 7.88 9.47 13.5 Example 14 7.96 9.51 12.9 Example 15 8.01 9.53 13.2 G4 Example 16 8.04 9.37 13.4 Example 17 8.12 9.41 13.6 Example 18 8.13 9.54 13.8 Example 19 8.10 9.49 13.7 Comparative 7.88 9.52 13.1 Example 1 Comparative 7.98 9.41 13.4 Example 2 Comparative 7.78 9.53 12.9 Example 3 Comparative 8.09 9.46 13.8 Example 4

[0041] The present application is based on Japanese patent application No. 2016-181262 filed on Sep. 16, 2016, and the contents of which are incorporated herein by reference.