JP2005285795A - Rare-earth magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare-earth magnet having a sufficiently excellent corrosion resistance, and to provide a method of manufacturing the magnet. <P>SOLUTION: The method of manufacturing the rare-earth magnet forms a reformed area near the surface of an elemental magnet body 10 containing a rare-earth element by irradiating an ion beam upon the surface of the elemental magnet body 10. In this way, a reformed layer 20 is formed on the surface of the elemental magnet body 10. Since the elemental magnet body 10 is protected by the reformed layer 20 in the rare-earth magnet 1 obtained by the method, the magnet 1 can obtain the sufficiently excellent corrosion resistance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rare earth magnet and a method for manufacturing the same.

  In recent years, so-called R—Fe—B based magnets (where R represents a rare earth element such as Nd) have been developed as permanent magnets having a high energy product of 25 MGOe (Mega Gauss Oersted) or more. For example, Patent Document 1 discloses an R—Fe—B based magnet formed by sintering. Patent Document 2 discloses an R—Fe—B magnet formed by rapid quenching. However, R-Fe-B magnets contain a rare earth element and iron, which are relatively easily oxidized, as main components, and therefore have relatively low corrosion resistance. Therefore, there have been problems such as deterioration in performance as a magnet at the time of manufacture and use, and / or reliability of the manufactured magnet is relatively low. For the purpose of improving the corrosion resistance of such R-Fe-B magnets, proposals for forming various protective layers on the magnet surface have been heretofore described, for example, as described in Patent Documents 3 to 9. Has been made.

More specifically, for example, in Patent Document 8, R (R is at least one of rare earth elements including Y) 8 atomic% to 30 atomic% for the purpose of improving the corrosion resistance of the R—Fe—B based magnet. There has been proposed a permanent magnet in which a corrosion-resistant thin film is coated on the surface of a permanent magnet body mainly composed of B2 atom% to 28 atom% and Fe 42 atom% to 90 atom% and the main phase is a tetragonal phase. Examples of materials constituting such a corrosion-resistant thin film include SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ , TiN, AlN, and TiC.
JP 59-46008 A JP-A-60-9852 JP-A-60-54406 JP-A-60-63901 JP 60-63902 A Japanese Patent Laid-Open No. 61-130453 JP-A-61-166115 JP 61-166116 A JP 61-270308 A

However, the present inventors have studied in detail the conventional rare earth magnets containing the rare earth elements including those described in Patent Documents 1 to 9, and such conventional rare earth magnets are sufficient. It was found that it does not have corrosion resistance. That is, it has been found that a conventional rare earth magnet provided with a SiO ₂ film or the like as a protective layer tends to generate cracks or the like in the protective layer. Further, in these conventional rare earth magnets, the constituent materials are different between the protective layer and the magnet body, so that stress due to the difference in thermal expansion coefficient occurs at the interface between the protective layer and the magnet body. As a result, it became clear that the adhesion between the protective layer and the magnet body tends to be insufficient. From these facts, a rare earth magnet having a conventional protective layer is not necessarily excellent in corrosion resistance in an actual use environment in which corrosion-causing substances (oxygen, moisture, salt water, sulfide) are present.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a rare earth magnet having sufficiently excellent corrosion resistance and a method for manufacturing the same.

  In order to solve the above-mentioned problems, the method for producing a rare earth magnet of the present invention is characterized in that a modified region is formed in the vicinity of a surface of a magnet body containing a rare earth element by irradiating the surface with an ion beam. And

  In the rare earth magnet obtained by this manufacturing method, since the magnet body is protected by the modified region, sufficiently excellent corrosion resistance can be obtained. One possible cause is that the constituent material of the magnet body becomes amorphous due to the energy of the ion beam. Furthermore, for example, when an oxidizing gas is present in the atmosphere around the magnet body, a passive layer is formed on the surface of the magnet body by irradiation of the ion beam, so that a stable layer is formed. It is possible. The rare earth magnet is a polycrystalline body containing a rare earth element that is easily oxidized. One of the crystals constituting the rare earth magnet is a rare earth rich phase which is a crystal mainly composed of a rare earth element. Due to the contribution of the rare earth-rich phase, the rare earth magnet has strong magnetic properties. However, the rare earth-rich phase is very easily corroded, and this phase is considered to have a great influence on the corrosion resistance of the rare earth magnet.

  In the present invention, the present inventors presume that the rare earth-rich phase existing in the vicinity of the surface of the magnet body is amorphized selectively or together with other crystal phases by ion beam irradiation. As a result, the rare earth-rich phase, which is a highly corrosive crystal existing near the surface of the magnet body, disappears, and it is considered that the obtained rare earth magnet has sufficient corrosion resistance.

  Here, “amorphous” refers to an amorphous individual assembled without forming a crystal having an amorphous state, that is, a regular spatial arrangement. Further, “amorphous” includes substantially amorphous. That is, the amorphous may include a crystal that is difficult to detect by a known electron diffraction method or X-ray diffraction method. In general, the electron diffraction method is a method in which an electron wave is irradiated to a substance, and an electron wave scattered by each atom constituting the substance interferes with a phase difference determined by the mutual positional relationship between the atoms from a diffraction image of the substance. The structure is analyzed. The X-ray diffraction method is an analysis of the structure of a substance by taking an X-ray diffraction image from a certain range of crystals and observing a local change in reflection intensity.

  In addition, in the rare earth magnet obtained by the above manufacturing method, the adhesion between the magnet body and the modified region is improved, so that the corrosion resistance is further improved. As a factor that improves the adhesion, the main component elements of the constituent materials are the same in the modified region and the magnet body.

  In the method of manufacturing a rare earth magnet, it is preferable to irradiate an ion beam so that the temperature of the magnet body does not exceed 200 ° C.

  The magnetic properties of rare earth magnets tend to deteriorate when the temperature of the magnet body exceeds 200 ° C. For this reason, if the ion beam is irradiated so that the temperature of the magnet body does not exceed 200 ° C., the magnetic properties of the obtained rare earth magnet can be further prevented from deteriorating.

  Further, at least one of the ion beam irradiation time, the ion beam acceleration voltage, the ion beam current, the ion beam incident angle, and the rotation speed of the magnet body so that the temperature of the magnet body does not exceed 200 ° C. It is more preferable to adjust one and irradiate the ion beam.

  Thereby, the temperature of the magnet body can be maintained at 200 ° C. or lower more easily.

  The rare earth magnet of the present invention includes a magnet body containing a rare earth element and a modified layer provided on the surface of the magnet body, and the modified layer is a magnet material contained in the magnet body. It contains the same element as the main component element.

  In this rare earth magnet, since the magnet body is protected by the modified layer, sufficiently excellent corrosion resistance can be obtained. This modified layer is formed, for example, by irradiating the surface of the magnet body with an ion beam and modifying (changing) a region near the surface. As the constituent material of the modified layer, for example, a material in which the constituent material of the magnet body is made amorphous can be considered. Further, for example, when the modified layer contains oxygen atoms, the constituent material of the modified layer may be one in which a passive state is formed by combining with the oxygen atoms at the same time as the amorphization. However, the constituent material of the modified layer is not limited to these.

  Here, the “main component element of the magnet material” refers to an element required to function as a magnet. For example, when the rare earth magnet of the present invention is an R—Fe—B based magnet, the “main component elements of the magnet material” are R, Fe and B, and when the rare earth magnet is an Sm—Co based magnet, “ The “main component elements of the magnet material” are Sm and Co, and in the case of the Sm—Fe—N magnet, the “main component elements of the magnet material” are Sm, Fe and N.

  In the rare earth magnet, the modified layer may further contain at least one element of Ti, Si, Zr, Ar, Mo, Zn, Al, Mn, and Ni.

  These elements are formed by, for example, irradiating the surface of the magnet body with an ion beam and remaining the constituent elements of the ion beam implanted in the vicinity of the surface. In such a rare earth magnet, the corrosion resistance is further improved.

  According to the present invention, it is possible to provide a rare earth magnet having sufficiently excellent corrosion resistance and a method for manufacturing the same.

  Hereinafter, a rare earth magnet according to a preferred embodiment of the present invention and a manufacturing method thereof will be described with reference to the drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  First, a configuration of a rare earth magnet according to a preferred embodiment of the present invention will be described with reference to FIGS.

<Rare earth magnet>
FIG. 1 is a schematic perspective view of a rare earth magnet according to a preferred embodiment of the present invention, and FIG. 2 is a diagram schematically showing a cross section that appears when the rare earth magnet of FIG. 1 is cut along line II. is there. As is clear from FIGS. 1 and 2, the rare earth magnet 1 of the present embodiment includes a magnet body 10 and a modified layer 20 provided on the surface of the magnet body 10.

(Magnet body)
The magnet body 10 contains, for example, R, iron (Fe), and boron (B). R represents one or more rare earth elements, specifically, one or more selected from the group consisting of scandium (Sc), yttrium (Y) and lanthanoids belonging to Group 3 of the long-period periodic table. Indicates an element. Here, lanthanoids are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy). , Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

  The composition of the above-described elements in the magnet body 10 is preferably as described below when the magnet body 10 is manufactured by a sintering method.

  R preferably includes one or more elements of Nd, Pr, Ho, and Tb among those described above, and further includes 1 of La, Sm, Ce, Gd, Er, Eu, Tm, Yb, and Y. It is also preferable to include more than one element.

  The content ratio of R in the magnet body 10 is preferably 8 to 40 atomic% with respect to the total amount of atoms constituting the magnet body 10. When the content ratio of R is less than 8 atomic%, the crystal structure becomes a cubic structure having the same structure as α-iron, so that the rare earth magnet 1 having a high coercive force (iHc) tends not to be obtained. Further, when the content ratio of R exceeds 40 atomic%, the R-rich nonmagnetic phase increases, and the residual magnetic flux density (Br) of the rare earth magnet 1 tends to decrease.

  The content ratio of Fe in the magnet body 10 is preferably 42 to 90 atomic% with respect to the total amount of atoms constituting the magnet body 10. If the Fe content is less than 42 atomic%, the Br of the rare earth magnet 1 tends to decrease, and if it exceeds 90 atomic%, the iHc of the rare earth magnet 1 tends to decrease.

  The content ratio of B in the magnet body 10 is preferably 2 to 28 atomic% with respect to the total amount of atoms constituting the magnet body 10. If the B content is less than 2 atomic%, the crystal structure has a rhombohedral structure, so the iHc of the rare earth magnet 1 tends to be insufficient. If it exceeds 28 atomic%, there are many B-rich nonmagnetic phases. Therefore, the Br of the rare earth magnet 1 tends to decrease.

  Further, the magnet body 10 may be configured by replacing part of Fe with cobalt (Co). By adopting such a configuration, the temperature characteristics tend to be improved without impairing the magnetic characteristics of the rare earth magnet 1. In this case, the content ratio of Fe and Co after substitution is preferably such that Co / (Fe + Co) is 0.5 or less on an atomic basis. If the amount of substitution of Co is larger than this, the magnetic properties of the rare earth magnet 1 tend to deteriorate.

  Furthermore, even if a part of B is replaced with one or more elements selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu), the magnet body 10 is configured. Good. With this configuration, the productivity of the rare earth magnet 1 is improved, and the production cost tends to be reduced. In this case, the content of C, P, S and / or Cu is preferably 4 atom% or less with respect to the amount of all atoms constituting the magnet body 10. When the content of C, P, S and / or Cu is more than 4 atomic%, the magnetic properties of the rare earth magnet 1 tend to deteriorate.

  Further, from the viewpoint of improving the coercive force of the rare earth magnet 1, improving productivity, and reducing the cost, aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), bismuth ( Bi), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel (Ni), silicon ( The magnet body 10 may be configured by adding one or more elements of Si), gallium (Ga), copper (Cu), and / or hafnium (Hf). In this case, it is preferable that the addition amount of the element is 10 atomic% or less with respect to the total amount of atoms constituting the magnet body 10. When the added amount of these elements exceeds 10 atomic%, the magnetic properties of the rare earth magnet 1 tend to deteriorate.

  In the magnet body 10, oxygen (O), nitrogen (N), carbon (C), and / or calcium (Ca), etc. as unavoidable impurities are included in the amount of all atoms constituting the magnet body 10. And may be contained within a range of 3 atomic% or less.

  As shown in FIG. 3, the magnet body 10 includes a main phase 50 having a substantially tetragonal crystal structure, a rare earth-rich phase 60 containing a relatively large amount of rare earth elements, and a boron rich material containing a relatively large amount of boron. And the phase 70 is formed. The particle size of the main phase 50 which is a magnetic phase is preferably about 1 to 100 μm. The rare earth-rich phase 60 and the boron-rich phase 70 are nonmagnetic phases and exist mainly at the grain boundaries of the main phase 50. These nonmagnetic phases 60 and 70 are usually contained in the magnet body 10 by about 0.5 volume% to 50 volume%.

(Modified layer)
In the present embodiment, the modified layer 20 is formed by irradiating the surface of the magnet body 10 with an ion beam. That is, when an ion beam is irradiated, a modified region having resistance to a corrosion factor substance is formed near the surface of the magnet body 10. Since this modified region already has a phase and / or elemental composition different from that of the magnet body 10, it is formed as a modified layer 20 on the surface of the magnet body 10. By such a modified layer 20 covering the magnet body 10, the magnet body 10 is protected from a corrosion factor substance. Therefore, the rare earth magnet 1 has sufficiently excellent corrosion resistance. Furthermore, it is preferable that the modified layer 20 covers the entire surface of the magnet body 10 because the corrosion resistance of the rare earth magnet 1 is further improved.

  As one of the factors that the modified layer 20 has excellent resistance to the corrosion factor substance, it can be considered that the modified layer 20 is amorphized, for example. As a result, the present inventors speculate that the rare earth-rich phase 60, which is a very corrosive phase, is difficult to be contained in the modified layer 20, so that the resistance of the modified layer 20 is improved. Alternatively, it is also considered that the rare earth-rich phase 60 that is relatively unstable as a crystal phase is amorphized selectively or together with another crystal phase by the collision energy of the ion beam. Further, for example, when the modified layer 20 contains oxygen atoms, the constituent material of the modified layer 20 may be one in which a passive state is formed by being combined with oxygen atoms at the same time as amorphization. However, the factors are not limited to these.

  It is also presumed that a crystal phase (crystal particles) and an amorphous phase (amorphous particles) are mixed near the boundary between the magnet body 10 and the modified layer 20. In this case, the modified layer 20 may include a crystal phase that is difficult to detect by a known electron diffraction method or X-ray diffraction method, as described above. Furthermore, the content ratio of the crystal phase in the crystal phase and the amorphous phase may continuously change from the magnet body 10 to the modified layer 20. In this case, the modified layer 20 in the present embodiment may include crystals that are difficult to detect by a known electron diffraction method, X-ray diffraction method, or the like, as described above.

  As described above, although the modified layer 20 has a phase and / or element composition different from those of the magnet body 10, the main component of the magnet material contains the same element. Specifically, when the magnet body 10 contains R, iron (Fe), and boron (B), the modified layer 20 contains R, iron (Fe), and boron (B). In this case, since the adhesion between the magnet body 10 and the modified layer 20 is improved, the rare earth magnet 1 having even better corrosion resistance can be obtained. This is presumably because the modified layer 20 is firmly bonded to the magnet body 10 and distortion at the boundary surface can be prevented.

  Furthermore, it is preferable that the composition ratio of each main component contained in the modified layer 20 is substantially the same as the composition ratio described for the magnet body 10 described above. In this case, the modified layer 20 is more firmly bonded to the magnet body 10, so that the corrosion resistance of the rare earth magnet 1 is further improved.

  Moreover, it is preferable that the modified layer 20 contains at least one element of Ti, Si, Zr, Ar, Mo, Zn, Al, Mn, and Ni because the corrosion resistance of the rare earth magnet 1 is further improved. These elements are implanted into the modified layer 20 by, for example, irradiating the surface of the magnet body 10 with an ion beam related to these elements. One of the factors that further improves the corrosion resistance of the rare-earth magnet 1 is that these elements further stabilize the modified layer 20 chemically, but is not limited thereto.

  In particular, when the modified layer 20 contains at least one element of Si and Zr, the sulfide resistance of the rare earth magnet 1 is improved, and as a result, the corrosion resistance of the rare earth magnet 1 is further improved.

  Note that these elements may be ionized or may not be ionized. The modified layer 20 may contain elements other than those described above.

  Further, the content ratio of each element contained in the magnet body 10 is not particularly limited. However, for example, when the constituent material of the magnet body 10 is Nd—Fe—B, if the constituent material of the modified layer 20 has an elemental composition represented by the following general formula (1), the corrosion resistance is further improved. From the viewpoint of Here, A represents a constituent element of the implanted ions. Examples of A include Ti, Si, Zr, Ar, Mo, Zn, Al, Mn, and Ni.

_{Nd x Fe y B z A 17} -x-y-z ... (1)
(1.8 ≦ x ≦ 2.2, 13.8 ≦ y ≦ 14.2, 0.8 ≦ z ≦ 1.2)

  In order to confirm the presence of the modified layer 20, for example, a cross-sectional SEM or TEM can be used. Thereby, the film thickness of the modified layer 20 can also be confirmed. The film thickness of the modified layer 20 is preferably about 30 to 300 nm from the viewpoint of further improving the corrosion resistance.

  The content of each constituent material in the modified layer 20 is EPMA (X-ray microanalyzer method), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) or EDS (energy dispersive X-ray fluorescence spectroscopy). It can be confirmed using a known composition analysis method such as (Method). Further, the composition analysis method described above is applied to the section of the magnet body 10 and the modified layer 20 in the rare earth magnet 1 exposed by using a known technique such as etching, or by cutting the rare earth magnet 1. By using and analyzing, the composition distribution of the constituent materials of the magnet body 10 and the modified layer 20 can be grasped.

  In the rare earth magnet 1 according to the present embodiment, sufficiently excellent corrosion resistance can be obtained without forming a protective layer on the surface of the magnet body 10. In this case, since no stress is generated at the interface between the protective layer and the magnet body, the problem that the protective layer peels can be avoided. Furthermore, deterioration of the magnet body due to the occurrence of cracks in the protective layer can be avoided.

  The rare earth magnet 1 described above includes line printers, automobile starters and motors, special motors, servo motors, disk drives for magnetic recording devices, linear actuators, voice coil motors, motors for devices, industrial motors, speakers, and nuclear magnetic resonance. It is suitably used for diagnostic magnets. In particular, when used in an environment where oil such as an automobile motor is splashed, it is more preferable that the modified layer 20 has resistance to various corrosive substances such as sulfides, moisture and salt water.

  Next, a method for manufacturing the rare earth magnet 1 according to a preferred embodiment of the present invention will be described. The rare earth magnet 1 is obtained, for example, through the following steps in order.

<Rare earth magnet manufacturing method>
(Magnet body preparation process)
The magnet body 10 is manufactured, for example, by a sintering method as described below. First, a desired composition containing the constituent elements of the magnet body 10 is cast to obtain an ingot. Subsequently, the obtained ingot is roughly pulverized to a particle size of about 10 to 100 μm using a stamp mill or the like, and then finely pulverized to a particle size of about 0.5 to 5 μm using a ball mill or the like to obtain a powder. .

Next, the obtained powder is preferably molded in a magnetic field to obtain a molded body. In this case, the magnetic field strength in the magnetic field is preferably 10 kOe or more, and the molding pressure is preferably about 1 to 5 ton / cm ² .

  Subsequently, the obtained molded body is sintered at 1000 to 1200 ° C. for about 0.5 to 5 hours and rapidly cooled. The sintering atmosphere is preferably an inert gas atmosphere such as Ar gas. And preferably, the magnet body 10 as described above is obtained by performing heat treatment (aging treatment) at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere, followed by magnetization.

  In addition to the above, the magnet body 10 can be prepared by, for example, a well-known super rapid cooling method, a warm brittle processing method, a casting method, or a mechanical alloying method. Further, a commercially available magnet body 10 may be prepared.

(Modified layer formation process)
Next, the surface of the magnet body 10 is irradiated with an ion beam. As a result, a modified region is formed in the vicinity of the surface of the magnet body 10, thereby forming a modified layer 20 provided on the surface of the magnet body 10.

  FIG. 4 is a diagram schematically showing an ion beam processing apparatus 200 for performing ion beam processing. The ion beam processing apparatus 200 includes a beam processing chamber 210 that irradiates the magnet body 10 with a beam, and a plasma generation chamber 220 that generates plasma serving as a beam source. In the beam processing chamber 210, a stage 212 for placing the magnet body 10 is installed so as to face the plasma generation chamber 220. Between the plasma generation chamber 220 and the stage 212, a grid 250, a new riser 260, and a shutter 270, which will be described later, are arranged in this order from the plasma generation chamber 220 side. The beam processing chamber 210 is connected to an exhaust system (not shown) such as a TMP (turbomolecular pump) and a cryopump via a valve 214, and is inside the beam processing chamber 210 and the plasma generation chamber 220. Is adjusted to a predetermined vacuum level.

  In the plasma generation chamber 220, for example, the source gas introduced into the plasma generation chamber 220 from the cylinder 230 is transferred between the thermoelectron emission filament 222 in the plasma generation chamber 220 and the plasma generation chamber wall surface 224 also serving as an anode. Plasma is generated by ionization by arc discharge. At this time, the filament 222 is heated by the filament power source 226, and an arc voltage for arc discharge is applied between the filament 222 and the plasma generation chamber wall surface 224 from a DC arc power source (ionization power source) 228. Yes. A gas obtained by evaporating and ionizing a metal member by heating may be used as a source gas.

  Furthermore, since a magnetic field is formed in the plasma generation chamber 220 by the magnet 240 provided outside the plasma generation chamber 220, the plasma can be confined in the plasma generation chamber 220. As a result, a high electric field necessary for starting discharge can be obtained even in a low gas pressure region, and plasma generation can be promoted.

  Ions in the generated plasma are accelerated toward the beam processing chamber 210 side by the grid 250 disposed at the boundary between the plasma generation chamber 220 and the beam processing chamber 210, whereby an ion beam is generated. The grid 250 includes, for example, three porous electrodes, ie, an extraction electrode, an acceleration electrode, and a deceleration electrode, and a predetermined voltage is applied thereto. This voltage becomes the acceleration voltage of the ion beam.

  Then, the ion beam that has passed through the grid 250 collides with the magnet body 10 on the stage 212, and the surface of the magnet body 10 is processed (ion bombardment).

  In order to form the modified layer 20 using such an ion beam treatment, the magnet body 10 is irradiated with an ion beam for a predetermined time, and the other surface of the magnet body 10 faces the shutter 270. The same processing is performed. By repeating such treatment and irradiating all six surfaces of the magnet body 10 in the same manner, the modified layer 20 covering the entire surface of the magnet body 10 is formed. The rare earth magnet 1 is manufactured as described above.

  In the rare earth magnet 1 obtained by the method for producing a rare earth magnet according to the present embodiment, the magnet element body 10 is protected by the modified layer 20, and thus sufficiently excellent corrosion resistance is obtained. As a factor for forming such a modified layer 20, as described above, for example, the constituent material of the magnet body 10 may be made amorphous by the collision energy of the ion beam. As a result, the present inventors speculate that the rare earth-rich phase 60, which is a very corrosive phase, is difficult to be contained in the modified layer 20, so that the resistance of the modified layer 20 is improved. Alternatively, it is also considered that the rare earth-rich phase 60 that is relatively unstable as a crystal phase is amorphized selectively or together with another crystal phase by the collision energy of the ion beam. For example, when an oxidizing gas is present in the atmosphere around the magnet body 10, a passive layer is formed on the surface of the magnet body 10 by irradiation with an ion beam, so that a stable layer is formed. It is thought that it is done. However, the factors are not limited to these.

  In the ion beam treatment, it is preferable to irradiate the ion beam so that the temperature of the magnet body 10 does not exceed 200 ° C. In general, the magnetic properties of rare earth magnets tend to deteriorate when the temperature of the magnet body exceeds 200 ° C. For this reason, if the ion beam is irradiated so that the temperature of the magnet body 10 does not exceed 200 ° C., the magnetic properties of the obtained rare earth magnet 1 can be sufficiently prevented from deteriorating. One of the causes of the deterioration of the magnetic properties of the rare earth magnet 1 is that the rare earth rich phase 60 in the entire magnet body 10 becomes unstable and the orientation of the main phase is disturbed.

  In order to maintain the temperature of the magnet body 10 at 200 ° C. or less, at least one of the irradiation time of the ion beam, the acceleration voltage of the ion beam, the beam current of the ion beam, the incident angle of the ion beam, and the rotation speed of the magnet body It is more preferable to adjust one and irradiate the ion beam. Further, from the viewpoint of maintaining the temperature of the magnet body 10 at 200 ° C. or lower, the acceleration voltage of the ion beam is preferably 200 to 800 V, and the beam current of the ion beam is preferably 1 to 180 mA. The ion beam irradiation time is preferably 1 to 30 minutes. The incident angle of the ion beam is preferably 0 to 45 °. Here, the incident angle of the ion beam means an angle (acute angle) between the incident direction of the ion beam and the normal direction of the surface of the magnet body 10 on which the ion beam is incident. The rotational speed of the magnet body 10 is preferably 10 to 30 rpm.

  Note that the acceleration voltage of the ion beam can be adjusted by the grid 250. The incident angle of the ion beam can be adjusted by inclining the stage 212 with respect to the incident direction of the ion beam. The rotational speed of the magnet body 10 can be adjusted by changing the speed at which the stage 212 is rotated. The stage 212 rotates with the incident direction of the ion beam as a rotation axis. The ion beam irradiation time can be adjusted by opening and closing a shutter 270 disposed in front of the magnet body 10.

Examples of the source gas introduced into the plasma generation chamber 220 include inert gases (Ar, N ₂ , Xe, Ne, etc.), metal elements (Ti, Si, Zr, Ar, Mo, Zn, Al, Gas containing Mn, Ni, etc.). For example, when Ar is used as the source gas, an ion beam containing Ar ions is generated. In addition, when a gas containing Ti is used as the source gas, an ion beam containing Ti ions is generated.

  When a gas containing a metal element is used as the source gas, the modified layer 20 containing the metal element is formed. The rare earth magnet 1 having such a modified layer 20 is more excellent in corrosion resistance. As one of the factors, it is considered that these elements further chemically stabilize the modified layer 20, but the present invention is not limited to this.

  In particular, when a gas containing at least one element of Si and Zr is used as the source gas, the modified layer 20 containing at least one element of Si and Zr is formed. Since the rare earth magnet 1 having the modified layer 20 has improved sulfidation resistance, as a result, the corrosion resistance of the rare earth magnet 1 is further improved.

  Note that the element implanted into the modified layer 20 may be ionized or may not be ionized.

  Moreover, in the rare earth magnet 1 obtained by the method for producing a rare earth magnet according to the present embodiment, sufficiently excellent corrosion resistance can be obtained without forming a protective layer on the surface of the magnet body 10. For this reason, when forming a protective layer, the problem that the pinhole generate | occur | produces in the protective layer by the particle | grains which consist of the constituent material of the said protective layer can be avoided. Moreover, the periodic cleaning operation | work of the protective layer forming apparatus required by such a particle adhering in a protective layer forming apparatus becomes unnecessary. From the above, if the method for producing a rare earth magnet according to the present embodiment is used, productivity can be improved and production cost can be reduced.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

  For example, the shape of the rare earth magnet according to another embodiment of the present invention is not limited to the rectangular parallelepiped as illustrated, and may have a shape corresponding to the application. Specifically, when used in a drive portion of a hard disk device or a motor for an automobile, a column shape having an arc-shaped section may be used. Moreover, when used for an industrial processing machine, a ring shape or a disk shape may be sufficient.

Moreover, as a constituent material of the magnet body 10 of another embodiment, a material containing one or more rare earth elements and Co, or a material containing one or more rare earth elements, Fe, and nitrogen (N) Etc. Specifically, for example, a material containing Sm and Co such as Sm—Co ₅ system or Sm ₂ —Co ₁₇ system (the number represents an atomic ratio), or Sm such as Sm—Fe—N system. And those containing Fe, N and the like. When the magnet body 10 contains Sm and Co, the modified layer 20 also contains Sm and Co. When the magnet body 10 includes Sm, Fe, and N, the modified layer 20 also includes Sm, Fe, and N.

  Even when the above constituent materials are used, it is preferable that the composition ratio of the elements contained in the modified layer is substantially the same as the composition ratio of the main component elements contained in the magnet body. Specifically, for example, in the case of an Sm—Fe—N magnet, the composition ratio of the elements in the magnet body and the modification of Sm, Fe and N, which are the main elements of the magnet body, are modified. It is preferable that the composition ratio of these elements in the layer is substantially the same.

  In the rare earth magnet of another embodiment, a protective layer may be provided on the surface of the modified layer 20. In this case, the corrosion resistance of the rare earth magnet is further improved.

  Moreover, in the manufacturing method of the rare earth magnet of another embodiment, you may irradiate an ion beam to the molded object before magnetization. Even in this case, since the rare earth magnet provided with the above-mentioned modified layer is obtained, the corrosion resistance of the rare earth magnet can be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the following Example.

<Rare earth magnet manufacturing method>
(Example 1)
First, a sintered body having a composition of 14Nd-1Dy-7B-78Fe (the number represents an atomic ratio) manufactured by powder metallurgy was subjected to heat treatment at 600 ° C. for 2 hours in an Ar gas atmosphere. Next, the sintered body after the heat treatment was cut into a substantially rectangular parallelepiped having a size of 56 × 40 × 8 (mm), and further chamfered by barrel polishing to obtain a magnet body.

  Next, the obtained magnet body was washed with an alkaline degreasing solution, and then the surface of the magnet body was activated with a 3% nitric acid aqueous solution and further thoroughly washed with water.

Subsequently, using the same ion beam processing apparatus as shown in FIG. 4, the surface (all six surfaces) of the magnet body was subjected to ion beam processing for 10 minutes. At this time, after the pressure in the beam processing chamber and the plasma generation chamber is reduced to 2 × 10 ⁻⁶ Pa, Ar gas is introduced into the plasma generation chamber at a flow rate of 20 sccm, the filament power source is 50 V, 20 A, the ionization power source is 20 V, 0.5 A. A plasma was generated. A voltage of about 1 kV was applied to the grid to generate an ion beam containing Ar ions. The incident angle of the ion beam was 15 °, and the rotational speed of the magnet body (stage) was 15 rpm. Thus, the rare earth magnet of Example 1 was obtained.

(Example 2)
Until the magnet body was sufficiently washed with water, the magnet body was produced and the surface thereof was washed in the same manner as in Example 1.

Subsequently, using the same ion beam processing apparatus as that shown in FIG. 4, the surface of the magnet body was subjected to ion beam processing for 5 minutes. At this time, after depressurizing the beam processing chamber and the plasma generation chamber to 1 × 10 ⁻⁴ Pa, a BN crucible on which a Ti metal member is placed is placed in the plasma generation chamber, and the Ti metal member is evaporated and ionized by resistance heating. Then, the filament power supply was set to 40 V and 50 A to generate plasma. A voltage of about 1 kV was applied to the grid to generate an ion beam containing Ti ions. In this way, a rare earth magnet of Example 2 was obtained.

(Comparative Example 1)
Until the magnet body was sufficiently washed with water, the magnet body was produced and the surface thereof was washed in the same manner as in Example 1.

  Thereafter, a nickel plating layer (protective layer) having a thickness of 15 μm was formed on the surface of the magnet body by plating with nickel. In this way, a rare earth magnet of Comparative Example 1 was obtained.

<Evaluation and results>
(Confirmation of crystal state)
The rare earth magnet of Example 2 was cut. And the TEM observation was performed about the cross section exposed by this cutting | disconnection. As a result, it was confirmed that Ti was present in the vicinity of the surface of the magnet body (modified region) in the rare earth magnet of Example 2.

(Corrosion resistance evaluation)
The obtained rare earth magnets of Examples 1 and 2 and Comparative Example 1 were subjected to a humidification high temperature test (PCT test) to evaluate the corrosion resistance of the rare earth magnet. In the PCT test, the sample was stored in a steam atmosphere, 120 ° C., 2 atm humidified high temperature environment for 24 hours, and then the corrosion state was confirmed.

  In the rare earth magnets of Examples 1 and 2, as a result of the above corrosion resistance evaluation, no abnormality in appearance such as corrosion and weight reduction were observed. Furthermore, the magnetic flux of each rare earth magnet after the PCT test was measured, and the reduction rate (flux loss, magnetic flux loss) with respect to the magnetic flux (initial value) before the PCT test was measured. As a result, in each of the rare earth magnets of Examples 1 and 2, the flux loss was 0.24% or less, which was within the measurement error range.

  On the other hand, in the rare earth magnet of Comparative Example 1, as a result of the corrosion resistance evaluation, an appearance abnormality such as rusting of the magnet body and a weight reduction of 0.21% were recognized. Furthermore, as a result of measuring the flux loss of the rare earth magnet after the PCT test, in the rare earth magnet of Comparative Example 1, the flux loss was a large value of 12.5%.

  Moreover, the rare earth magnets of Examples 1 and 2 and Comparative Example 1 were stored for 100 hours in a humid atmosphere at 120 ° C. and 2 atm. Then, as a result of measuring the flux loss of the rare earth magnet, the flux loss was 0.5% and 0.2% in the rare earth magnets of Examples 1 and 2, respectively. On the other hand, in the rare earth magnet of Comparative Example 1, the flux loss was 3.5%.

  From the result of the corrosion resistance evaluation, it was confirmed that the rare earth magnets of Examples 1 and 2 had sufficient corrosion resistance as compared with the rare earth magnet of Comparative Example 1.

It is a schematic perspective view which shows the rare earth magnet which concerns on suitable embodiment of this invention. It is a schematic sectional drawing which shows the rare earth magnet which concerns on suitable embodiment of this invention. It is a model enlarged view which shows the phase structure of a R-Fe-B type magnet. It is a figure which shows typically the ion beam processing apparatus used for the manufacturing method of the rare earth magnet which concerns on suitable embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 10 ... Magnet body, 20 ... Modified layer.

Claims (5)

A method for producing a rare earth magnet, comprising forming a modified region in the vicinity of a surface of a magnet body containing a rare earth element by irradiating the surface with an ion beam. 2. The method for producing a rare earth magnet according to claim 1, wherein the ion beam is irradiated so that the temperature of the magnet body does not exceed 200 ° C. The irradiation time of the ion beam, the acceleration voltage of the ion beam, the beam current of the ion beam, the incident angle of the ion beam, and the rotation speed of the magnet body so that the temperature of the magnet body does not exceed 200 ° C. The method for producing a rare earth magnet according to claim 2, wherein the ion beam is irradiated after adjusting at least one of them. A magnet body containing a rare earth element;
A modified layer provided on the surface of the magnet body;
With
The rare earth magnet, wherein the modified layer contains the same element as a main component element of a magnet material contained in the magnet body. The rare earth magnet according to claim 4, wherein the modified layer further contains at least one element of Ti, Si, Zr, Ar, Mo, Zn, Al, Mn, and Ni.

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