Sm—Fe—N magnet material and Sm—Fe—N bonded magnet

Abstract

An Sm—Fe—N magnet material includes from 7.0 at % to 12 at % of Sm, from 0.1 at % to 1.5 at % of at least one element selected from the group consisting of Hf and Zr, from 0.05 at % to 0.5 at % of C, from 10 at % to 20 at % of N, and from 0 at % to 35 at % of Co, with a remainder being Fe and unavoidable impurities.

Claims

1. An Sm—Fe—N magnet material, comprising: from 7.0 at % to 12 at % of Sm; from 0.1 at % to 1.5 at % of at least one element selected from the group consisting of Hf and Zr; from 0.05 at % to 0.09 at % of C; from 10 at % to 20 at % of N; from 0 at % to 35 at % of Co; and at least one element selected from the group consisting of Al in a range from 0.1 at % to 0.5 at % and Si in a range from 0.15 at % to 0.5 at %, with a remainder being Fe and unavoidable impurities, wherein, when the Sm—Fe—N magnet material is maintained for 2,000 hours at 120° C. in atmosphere, an absolute value of a reduction rate from an initial demagnetizing factor is in a range from 1.8% to 2.2%, and wherein the Sm—Fe—N bonded magnet has a residual magnetic flux density (Br) of B.sub.r≥8.00 kG.

2. An Sm—Fe—N bonded magnet comprising a powder of the Sm—Fe—N magnet material according to claim 1 and a binder.

3. The Sm—Fe—N magnet material according to claim 1, wherein, when the Sm—Fe—N magnet material is maintained for 2,000 hours at 120° C., an irreversible demagnetizing factor is in a range from 1.8% to 2.0%.

4. The Sm—Fe—N magnet material according to claim 1, wherein the Sm—Fe—N magnet material includes Zr in a range from 0.1 at % to 1.5 at %.

5. The Sm—Fe—N magnet material according to claim 1, wherein a content of Co in the Sm—Fe—N magnet material is more than 0 at %.

6. An Sm—Fe—N magnet material, consisting of: from 7.0 at % to 12 at % of Sm; from 0.1 at % to 1.5 at % of at least one element selected from the group consisting of Hf and Zr; from 0.05 at % to 0.09 at % of C; from 10 at % to 20 at % of N; from 0 at % to 35 at % of Co; and at least one element selected from the group consisting of Al in a range from 0.1 at % to 0.5 at % and Si in a range from 0.15 at % to 0.5 at %, with a remainder being Fe and unavoidable impurities, wherein the Sm—Fe—N bonded magnet has a residual magnetic flux density (B.sub.r) of B.sub.r≥8.00 kG.

7. The Sm—Fe—N magnet material according to claim 6, wherein from 0.1 at % to 0.5 at % of Al is provided.

8. The Sm—Fe—N magnet material according to claim 7, wherein from 0.15 at % to 0.5 at % of Si is provided.

9. The Sm—Fe—N magnet material according to claim 6, wherein from 0.15 at % to 0.5 at % of Si is provided.

10. The Sm—Fe—N magnet material according to claim 6, wherein, when the Sm—Fe—N magnet material is maintained for 2,000 hours at 120° C., an irreversible demagnetizing factor is in a range from 1.8% to 2.2%.

11. The Sm—Fe—N, magnet material according to claim 6, wherein, when the Sm—Fe—N magnet material is maintained for 2,000 hours at 120° C., an irreversible demagnetizing factor is in a range from 1.8% to 2.0%.

12. The Sm—Fe—N magnet material according to claim 6, wherein the Sm—Fe—N magnet material includes Zr in a range from 0.1 at % to 1.5 at %.

13. The Sm—Fe—N magnet material according to claim 6, wherein a content of Co in the Sm—Fe—N magnet material is more than 0 at %.

14. An Sm—Fe—N magnet material, comprising: from 7.0 at % to 12 at % of Sm; from 0.1 at % to 1.5 at % of at least one element selected from the group consisting of Hf and Zr; from 0.05 at % to 0.09 at % of C; from 10 at % to 20 at % of N; from 0 at % to 35 at % of Co; from 0.1 at % to 0.5 at % of Al; and, from 0.15 at % to 0.5 at % of Si, with a remainder being Fe and unavoidable impurities, wherein, when the Sm—Fe—N magnet material is maintained for 2,000 hours at 120° C. in atmosphere, an absolute value of a reduction rate from an initial demagnetizing factor is in a range from 1.8% to 2.2%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A to 1E are diagrams illustrating the production method of the Sm—Fe—N magnet material that is one embodiment of the present invention.

(2) FIG. 2 is a graph illustrating the relationship of the content of C in the samples of Examples and Comparative Examples with the recovery ratio obtained in experiments.

(3) FIG. 3 is a graph illustrating the relationship of the content of C in the samples of Examples and Comparative Examples with the residual magnetic flux density B.sub.r and maximum energy product (BH).sub.max obtained in experiments.

DETAILED DESCRIPTION OF THE INVENTION

(4) The embodiments of the Sm—Fe—N magnet material and Sm—Fe—N bonded magnet according to the present invention are described by referring to FIGS. 1A to 1E, FIG. 2 and FIG. 3.

(5) The Sm—Fe—N magnet material of the present embodiment includes from 7.0 to 12 at % of Sm, from 0.1 to 1.5 at % of at least one element (hereinafter, referred to as “element T”) selected from the group consisting of Hf and Zr, from 0.05 to 0.5 at % of C, from 10 to 20 at % of N, and from 0 to 35 at % of Co, with the remainder being Fe and unavoidable impurities. This Sm—Fe—N magnet material can be produced, for example, by the following method.

(6) First, metal raw materials as simple substances of respective elements of Sm, the element T, Co (excluding the case where a Co content is 0 at %) and Fe, or an alloy raw material including two or more elements among the elements described above, and graphite as C are blended and melted by heating to afford the composition of an Sm—Fe powder before nitriding for an Sm—Fe—N magnet material to be manufactured, while taking into account the yield of each element, whereby a melt 11 is manufactured (FIG. 1A). Next, the melt 11 is jetted from an injection nozzle 12 onto the surface of a high-speed rotating roll 13, thereby being rapidly cooled, and a ribbon formed upon collision of the melt 11 with the roll 13 is pulverized by hitting it against a metal-made collision member 14 present on the path to a recovery vessel 16 and recovered as a powder 15 in the recovery vessel 16 (FIG. 1B). The powder 15 is heat-treated in an inert atmosphere at a temperature ranging from 700 to 800° C. (FIG. 1C), whereby an amorphous phase slightly contained before heat treatment is crystallized to enhance the crystallinity of the material. Incidentally, this operation is performed in order to achieve a higher coercive force after the subsequent nitriding treatment.

(7) Thereafter, the powder 15 is heated in a gas containing molecules having nitrogen atom (FIG. 1D) to thereby nitride the powder 15. As such a gas, a mixed gas of ammonia and hydrogen may be suitably used. The heating temperature and pressure during the nitriding treatment vary depending on the gas used, but as an example, in the case of using a gas in which the volume ratio of ammonia and hydrogen is 1:3, the heating temperature is set to about 450° C. and as for the pressure, a substantially atmospheric pressure (slightly higher than the atmospheric pressure) is created by performing the treatment while passing the gas through, for example, a tube furnace 17. Here, the nitriding treatment time is adjusted to afford an N content in the powder of 10 to 20 at %. Incidentally, when the amount of the powder 15 is large, in order to achieve homogenization and improve the reaction efficiency, the nitriding is conducted while stirring the powder 15 in a rotary heating furnace. Through these operations, a powdered Sm—Fe—N magnet material 10 is obtained (FIG. 1E).

(8) As described above, in general, the Sm—Fe—N magnet material includes a magnet material in which the main phase thereof is a Th.sub.2Zn.sub.17-type crystal structure, and a magnet material in which the main phase thereof is a TbCu.sub.7-type crystal structure, but in the Sm—Fe—N magnet material 10 of the present embodiment, an isotropic Sm—Fe—N magnet material in which the main phase thereof is a TbCu.sub.7-type crystal structure is obtained by incorporating from 0.1 to 1.5 at % of the element T and performing rapid cooling by the melt quenching method.

(9) In the Sm—Fe—N magnet material 10 of the present embodiment, a melt 11 containing C is manufactured at its production and therefore, the surface tension of the melt 11 is reduced. Accordingly, minute inclusions such as Sm.sub.2O.sub.3 slightly produced in the melt 11 are hardly aggregated in the melt 11 and are dispersed throughout the melt 11. Consequently, inclusions can be prevented from accumulating inside or around the hole of the injection nozzle 12 and clogging the injection nozzle 12.

(10) In the Sm—Fe—N magnet material 10 of the present embodiment, it is preferable to further contain from 0.15 to 0.5 at % of Si and/or from 0.1 to 0.5 at % of Al. Thanks to these elements, reduction in the magnetic flux density (thermal demagnetization) under a high temperature environment can be suppressed. Here, when both Si and Al are contained at the contents described above, thermal demagnetization can be more successfully suppressed.

(11) The Sm—Fe—N bonded magnet of the present embodiment can be produced by mixing a binder with the powder, i.e., the Sm—Fe—N magnet material 10 manufactured by the method described above, and subjecting the mixture to compression molding or injection molding. As the binder, a thermosetting resin such as epoxy resin, and a thermoplastic resin such as nylon or polyphenylene sulfide (PPS) resin, can be used respectively for compression molding and for injection molding. For example, the Sm—Fe—N bonded magnet of the present embodiment is obtained by mixing 2 mass % of an epoxy resin with the powder, i.e., the Sm—Fe—N magnet material 10 of the present embodiment, and subjecting the mixture to compression molding.

EXAMPLES

(12) In the following, the results of experiments of actually manufacturing an Sm—Fe—N magnet material and an Sm—Fe—N bonded magnet using the Sm—Fe—N magnet material are described. In this experiment, first, a powder of an Sm—Fe—N magnet material containing Sm, the element T (Zr, Hf), C, N, Co, Fe, Al and Si in the ratio shown in Table 1 was manufactured by the above-described method. In Examples 1 to 16, each of Sm, the element T, C, N, Co and Fe was contained at a content satisfying the requirement of the present invention, and each of Al and Si was contained at a content within the preferable addition requirement described above or within the allowable range as an impurity. Of these, in Examples 13 to 16, the content of Al was within the range of 0.1 to 0.5 at % which was the preferable addition requirement described above. In Examples 2 to 5 and 16, the content of Si was within the range of 0.15 to 0.5 at % which was the preferable addition requirement described above. On the other hand, in Comparative Examples 1 to 4, the content of C was smaller than the range of 0.05 to 0.5 at % which was the requirement of the present invention (indicated as “lack of C” in Table 1). In addition, in Comparative Example 5, the content of C was larger than the requirement of the present invention (indicated as “excess of C” in Table 1).

(13) At the manufacture of these powders before nitriding for the Sm—Fe—N magnet material by the melt quenching method, out of raw materials used, the amounts of raw materials which could be recovered as a powder of the Sm—Fe material were determined as a mass ratio and shown in mass percentage as the recovery ratio (yield) in Table 1. If inclusions accumulate inside or around the hole of the injection nozzle 12 in the process of manufacture and the injection nozzle 12 is clogged, the melt 11 cannot be jetted from the injection nozzle 12 and consequently, the recovery ratio decreases.

(14) After adding 2 mass % of epoxy resin to each of the powders of Sm—Fe—N magnet materials of Examples 1 to 16 and Comparative Examples 1 to 5 obtained above and subjecting the mixture to compression molding, a hardening treatment was performed to manufacture an Sm—Fe—N bonded magnet. With respect to each Sm—Fe—N bonded magnet manufactured, the residual magnetic flux density Br, the coercive force .sub.iH.sub.c, and the maximum energy product (BH).sub.max were measured.

(15) The composition and recovery ratio of the manufactured Sm—Fe—N magnet material and the results of measuring the magnetic properties of the Sm—Fe—N bonded magnet are shown in Table 1.

(16) TABLE-US-00001 TABLE 1 Composition of Sm—Fe—N Magnet Material [at %] (*remainder: Fe) Magnetic Properties Element T Recovery B.sub.r .sub.iH.sub.c (BH).sub.max Sm Zr Hf C N Co Al Si ratio [%] [kG] [kOe] [MGOe] Remarks Example 1 7.34 1.04 0.06 13.5 3.82 0.03 0.06 82 7.95 9.42 13.3 Example 2 7.25 1.03 0.07 13.2 3.81 0.02 0.31 88 8.03 9.35 13.5 Si content: 0.15-0.5 at % Example 3 7.34 1.05 0.08 13.5 3.80 0.04 0.16 83 8.05 9.42 13.3 Si content: 0.15-0.5 at % Example 4 7.32 0.96 0.09 13.2 3.68 0.02 0.17 84 8.15 9.40 13.2 Si content: 0.15-0.5 at % Example 5 7.39 1.08 0.09 13.1 3.86 0.04 0.18 85 8.05 9.45 13.4 Si content: 0.15-0.5 at % Example 6 7.34 1.09 0.09 13.5 3.81 0.02 0.08 88 8.03 9.34 13.1 Example 7 7.40 0.95 0.53 12.9 3.75 0.03 0.1 95 7.90 9.53 13.2 Example 8 7.35 1.03 0.11 13.4 3.81 0.04 0.13 91 8.07 9.20 13.3 Example 9 7.31 1.35 0.13 13.5 3.73 0.03 0.08 92 8.05 9.56 13.1 Example 10 7.37 1.07 0.43 13.3 3.91 0.02 0.07 95 8.10 9.45 13.4 Example 11 7.42 1.02 0.33 13.7 3.76 0.04 0.03 96 7.94 9.43 13.3 Example 12 7.37 0.96 0.19 13.2 3.75 0.02 0.04 94 8.04 9.36 13.3 Example 13 7.45 1.11 0.32 13.4 3.83 0.13 0.13 97 8.05 9.47 13.4 Al content: 0.1-0.5 at % Example 14 7.42 1.21 0.12 13.3 3.75 0.38 0.11 88 8.03 9.50 13.2 Al content: 0.1-0.5 at % Example 15 7.43 1.02 0.12 13.4 3.79 0.26 0.06 92 8.06 9.41 13.3 Al content: 0.1-0.5 at % Example 16 7.36 1.14 0.19 13.3 3.81 0.32 0.15 93 8.01 9.30 13.4 Si content: 0.15-0.5 at % Al content: 0.1-0.5 at % Comp. Ex. 1 7.32 1.02 0.03 13.2 3.79 0.03 0.05 70 8.03 9.45 13.2 lack of C, recovery ratio: small Comp. Ex. 2 7.28 1.12 0.02 13.4 3.81 0.03 0.06 65 8.14 9.53 13.4 lack of C, recovery ratio: small Comp. Ex. 3 7.34 1.04 0.03 13.3 3.82 0.03 0.32 72 8.04 9.39 13.2 lack of C, recovery ratio: small Comp. Ex. 4 7.22 0.98 0.04 13.2 3.81 0.04 0.13 71 8.03 9.43 13.3 lack of C, recovery ratio: small Comp. Ex. 5 7.32 1.02 0.63 13.1 3.83 0.04 0.05 95 7.50 9.44 12.1 excess of C, B.sub.r and (BH).sub.max: small

(17) As seen in Table 1 and FIG. 2, in all of Examples 1 to 16 where the content of C was within the range of the present invention and in Comparative Example 5 where the content of C was higher than that, the powder of the Sm—Fe—N magnet material could be obtained at a recovery ratio on the 90% or 80% level, while in Comparative Examples 1 to 4 where the content of C was lower than the range of the present invention, the recovery ratio remained at the 60% or 70% level. From these recovery ratio data, it was confirmed that the recovery ratio can be increased by the addition of C to the Sm—Fe—N magnet material and in turn, the yield is enhanced.

(18) On the other hand, among magnetic properties of the Sm—Fe—N bonded magnet manufactured, the residual magnetic flux density B.sub.r and the maximum energy product (BH).sub.max were, as seen in Table 1 and FIG. 3, lower in Comparative Example 5 where the content of C was higher than the range of the present invention, as compared with Examples 1 to 16. Accordingly, it is appropriate to set the content of C in the Sm—Fe—N magnet material to be from 0.05 to 0.5 at % which is the range of the present invention. Incidentally, as to the coercive force .sub.iH.sub.c, there was no significant difference between Examples and Comparative Examples.

(19) Next, with respect to Examples 3 to 5 where the content of Si is from 0.15 to 0.5 at %, Examples 14 and 15 where the content of Al is from 0.1 to 0.5 at %, Example 16 where the contents of both Si and Al are within the respective ranges described above, and Example 1 and Comparative Example 1 where the contents of both Si and Al are smaller than the respective ranges described above, the results of measuring the irreversible demagnetizing factor are described below. At the beginning, the irreversible demagnetizing factor is described. In general, a magnet after being magnetized decreases in the magnetic flux density as the temperature rises. When the temperature once rises and then drops to room temperature, the magnetic flux density may be partially recovered but is not completely recovered. Such a decrease in the magnetic flux density caused upon heating from room temperature is referred to as “thermal demagnetization”. Out of thermal demagnetization, the portion in which the magnetic flux density recovers when returning to room temperature is referred to as “reversible demagnetization”, and the portion in which the magnetic flux density does not recover is referred to as “irreversible demagnetization”. In this experiment, the Sm—Fe—N bonded magnets of Examples 1, 3 to 5 and 14 to 16 and Comparative Example 1 were magnetized; the magnetic flux ϕ.sub.0 of each of these Sm—Fe—N bonded magnets was measured; after holding in a furnace at 120° C. for the later-described holding time and then cooling to room temperature, the magnetic flux ϕ.sub.T of each of the Sm—Fe—N bonded magnets was measured; and the irreversible demagnetizing factor was determined according to (ϕT−ϕ.sub.0)/ϕ.sub.0)×100=ΔM.sub.T.

(20) Here, an experiment employing a holding time of 1 hour and an experiment employing a holding time of 2,000 hours were performed. In general, the magnetic flux of a magnet greatly decreases with a temperature rise and slowly decreases during a period of holding a predetermined temperature after reaching the temperature. A magnet is usually selected by anticipating in advance a large decrease of the magnetic flux at the initial stage and therefore, in order to obtain stable properties at high temperatures, the decrease rate at the time of slow decrease of the magnetic flux during the period of maintaining a predetermined temperature after a large decrease at the initial stage is preferably as small as possible. Accordingly, in this experiment, (ΔM.sub.2000−ΔM.sub.1) determined by subtracting the demagnetizing factor ΔM.sub.1 (this is referred to as initial demagnetizing factor) obtained in the experiment employing a holding time of 1 hour from the demagnetizing factor ΔM.sub.2000 obtained in the experiment employing a holding time of 2,000 hours was evaluated. Although (ΔM.sub.2000−ΔM.sub.1) takes a negative value due to the definition thereof, a smaller absolute value means that stable properties are obtained at high temperatures.

(21) The experimental results of the irreversible demagnetizing factor are shown in Table 2.

(22) TABLE-US-00002 TABLE 2 Irreversible Demagnetizing Factor Demag- netizing Initial De- Factor in Content Content magnetizing 2000 Hours ΔM.sub.2000 − of Al of Si Factor ΔM.sub.1 ΔM.sub.2000 ΔM.sub.1 [at %] [at %] [%] [%] [%] Example 3 0.04 0.16 −6.71 −8.89 −2.18 Example 4 0.02 0.17 −6.60 −8.76 −2.16 Example 5 0.04 0.18 −6.66 −8.77 −2.11 Example 14 0.38 0.11 −6.63 −8.71 −2.08 Example 15 0.26 0.06 −6.74 −8.93 −2.19 Example 16 0.32 0.15 −6.58 −8.52 −1.94 Example 1 0.03 0.06 −6.78 −9.16 −2.38 Comparative 0.03 0.05 −6.82 −9.12 −2.30 Example 1

(23) These results reveal that in Examples 3 to 5 and 14 to 16 where the content of Si was within the range of 0.15 to 0.5 at % and/or the content of Al was within the range of 0.1 to 0.5 at %, the absolute value of (ΔM.sub.2000−ΔM.sub.1) was smaller as compared with Example 1 and Comparative Example 1 where the contents of Si and/or Al were lower than the ranges described above, and stable properties were obtained at high temperatures. Incidentally, in order to obtain stable properties at high temperatures, the irreversible demagnetizing factor (ΔM.sub.2000−ΔM.sub.1) is suitably from −2.2% to −1.8% and falls within this range in all of Examples 3 to 5 and 14 to 16. In order to more successfully obtain stable properties at high temperatures, the irreversible demagnetizing factor (ΔM.sub.2000−ΔM.sub.1) is suitably from −2.0% to −1.8% and falls within this range in Example 16.

(24) The present invention is not limited to the above-described embodiments, and changes can be made therein within the scope of the gist of the present invention.

(25) The present application is based on Japanese patent application No. 2018-034276 filed on Feb. 28, 2018, and the contents of which are incorporated herein by reference.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

(26) 10: Sm—Fe—N magnet material 11: Melt 12: Injection nozzle 13: Roll 14: Collision member 15: Powder 16: Recovery vessel 17: Tube furnace