Anisotropic magnetic powder, magnet thereof and method of producing same

Abstract: A the magnetically anisotropic magnetic powder having an average particle size of 1-1000µm and made from a magnetically anisotropic R-TM-B-Ga or R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron, Ga gallium, and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn. This is useful for anisotropic resin-bonded magnets with high magnetic properties.

Description: BACKGROUND OF THE INVENTION The present invention relates to a magnetically anisotropic magnetic powder composed of a rare earth element-iron-boron-gallium alloy powder, and a permanent magnet composed of such alloy powder dispersed in a resin, and more particularly to a resin-bonded permanent magnet having good thermal stability composed of a magnetically anisotropic rare earth element-iron-boron-gallium permanent magnet powder having fine crystal grains dispersed in a resin. Typical conventional rare earth element permanent magnets are SmCo₅ permanent magnets, and Sm₂Co₁₇ permanent magnets. These samarium·cobalt magnets are prepared from ingots produced by melting samarium and cobalt in vacuum or in an inert gas atmosphere. These ingots are pulverized and the resulting powders are pressed in a magnetic field to form green bodies which are in turn sintered and heat-treated to provide permanent magnets. The samarium·cobalt magnets are given magnetic anisotropy by pressing in a magnetic field as mentioned above. The magnetic anisotropy greatly increases the magnetic properties of the magnets. On the other hand, magnetically anisotropic, resin-bonded samarium·cobalt permanent magnets are obtained by injection-molding a mixture of samarium·cobalt magnet powder produced from the sintered magnet provided with anisotropy and a resin in a magnetic field, or by compression-molding the above mixture in a die. Thus, resin-bonded samarium·cobalt magnets can be obtained by preparing the sintered magnets having anisotropy, pulverizing them and then mixing them with resins as binders. Recently, neodymium-iron-boron magnets have been proposed as new rare earth magnets surmounting the samarium·cobalt magnets containing samarium which is not only expensive but also unstable in its supply. JP-A-59-46008 and JP-A-59-64733 disclose permanent magnets obtained by forming ingots of neodymium-iron-boron alloys, pulverizing them to fine powders, pressing them in a magnetic field to provide green bodies which are sintered and then heat-treated, like the samarium·cobalt magnets. This production method is called a powder metallurgy method. Also, it was reported to obtain a resin-bonded magnet having magnetic anisotropy by pulverizing an ingot to 0.5-2µm and then solidifying it with a wax (Appl. Phys. Lett. 48 (10), Mar. 1986, pp.670-672). With respect to the Nd-Fe-B permanent magnet, GENERAL MOTORS has proposed an alternative method to the above-mentioned powder metallurgy method. This method comprises melting a mixture of neodymium, iron and boron, rapidly quenching the melt by such a technique as melt spinning to provide fine flakes of the amorphous alloy, and heat-treating the flaky amorphous alloy to generate an Nd₂Fe₁₄B intermetallic compound. The fine flakes of this rapidly-quenched alloy is solidified with a resin binder (JP-A-59-211549). However, the magnetic alloy thus prepared is magnetically isotropic. Then, JP-A-60-100402 discloses a technique of hot-pressing this isotropic magnetic alloy, and then applying high temperatures and high pressure thereto so that plastic flow takes place partially in the alloy thereby imparting magnetic anisotropy thereto. The conventional Nd-Fe-B permanent magnets, however, have the following problems. First, although the above powder metallurgy can provide magnetic anisotropy and magnetic properties of (BH)max= 2.8 - 3.6 x 10⁵TA/m , the resulting magnets essentially have low Curie temperature, large crystal grain size and poor thermal stability. Accordingly, they cannot be suitably used for motors, etc. which are likely to be used in a high-temperature environment. Second, although molding is relatively easy by compression molding if rapidly-quenched powder is mixed with a resin, the resulting alloy is isotropic, so that its magnetic properties are inevitably low. For instance, the magnetic properties are (BH)max of 2.4 - 4 x 10⁴TA/m for those obtained by injection molding and (BH)max of 6.4 - 8 x 10⁴TA/m for those obtained by compression molding, and further the magnetic properties vary widely depending upon the strength of a magnetic field for magnetizing the alloy. To achieve (BH)max of 6.4 x 10⁴TA/m , the magnetic field should be 40 kA/cm or so, and it is difficult to magnetize the alloy after assembling for various applications. In addition, although hot pressing of the rapidly-quenched alloy powder serves to increase the density of the alloy, eliminating pores from the pressed alloy powder to improve weathering properties thereof, the resulting alloy is isotopic so that it is disadvantageous just like the permanent magnet prepared by mixing rapidly-quenched alloy powder with a resin. (BH)max of the resulting alloy is improved in proportion to the increase in the density, and it can reach 9.6 x 10⁴TA/m or so. However, it is still impossible to magnetize it after assembling. By the method of hot-pressing rapidly-quenched alloy powder and then causing plastic flow therein, anisotropy can be achieved like the powder metallurgy method, providing (BH)max of 2.72 - 3.2 x 10⁵TA/m , but annular magnets, for instance, magnet rings of 30mm in outer diameter, 25mm in inner diameter and 20mm in thickness cannot easily be formed because die upsetting should be utilized to provide anisotropy. Finally, with respect to magnets prepared by pulverizing ingots and solidifying them with wax, powders used are so fine that they are likely to be burned, making it impossible to handle them in the atmosphere. Also since the magnets show a low squareness ratio in the magnetization curve, they cannot have high magnetic properties. Incidentally, we tried to provide anisotropic resin-bonded magnets by pulverizing anisotropic sintered magnets prepared by the powder metallurgy method, mixing the pulverized particles with resins and molding them while applying a DC magnetic field, but high magnetic properties could not be achieved. OBJECT AND SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the problems peculiar to the above conventional techniques, thereby providing an anisotropic resin-bonded magnet having good thermal stability and easily magnetizable after assembling, and magnetic powder usable therefor and a method of producing them. To achieve the above object, the present invention comprises the following technical means. That is, the object of the present invention has been achieved first by forming magnetically anisotropic magnetic powder having an average crystal grain size of 0.01-0.5µm from an R-Fe-B-Ga alloy, wherein R represents one or more rare earth elements including Y, Fe may be partially substituted by Co to include an R-Fe-Co-B-Ga alloy, and one or more additional elements (M) selected from Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn may be contained to include an R-Fe-B-Ga-M alloy and an R-Fe-Co-B-Ga-M alloy, second by forming a pressed powder magnet therefrom, and third by forming a resin-bonded magnet from powder of the above alloy having an average particle size of 1-1000µm. The present invention is based on our finding that a thermally stable, anisotropic resin-bonded magnet can be obtained from magnetic powder of an average particle size of 1-1000µm prepared by pulverizing a magnetically anisotropic R-Fe-B-Ga alloy having an average crystal grain size of 0.01-0.5µm. It has been found that gallium (Ga) is highly effective to improve the thermal stability of the magnet. Thus, the magnetically anisotropic magnetic powder according to the present invention has an average particle size of 1-1000µm and is made from a magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron and Ga gallium. The method of producing a magnetically anisotropic magnetic powder according to the present invention comprises the steps of rapidly quenching a melt of an R-TM-B-Ga alloy, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron and Ga gallium, to form flakes made of an amorphous or partially crystallized R-TM-B-Ga alloy, pressing these flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to form a magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5µm, heat-treating it to increase a coercive force thereof, and then pulverizing it. The method of producing a magnetically anisotropic magnetic powder according to the present invention comprises the steps of rapidly quenching a melt of an R-TM-B-Ga alloy, wherein R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron and Ga gallium, to form flakes of an amorphous or partially crystallized R-TM-B-Ga alloy, pressing the flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to provide a magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5µm, and then pulverizing it without heat treatment. The magnetically anisotropic pressed powder magnet according to the present invention is made of magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron and Ga gallium, the magnetically anisotropic R-TM-B-Ga alloy having an axis of easy magnetization aligned in the same direction. The magnetically anisotropic resin-bonded magnet according to the present invention is composed of 15-40 volume % of a resin binder and balance R-TM-B-Ga alloy powder having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron and Ga gallium, the magnetically anisotropic R-TM-B-Ga alloy having an axis of easy magnetization aligned in the same direction. The magnetically anisotropic magnetic powder according to the present invention an average particle size of 1-1000µm and is composed of an R-TM-B-Ga-M alloy powder having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron, Ga gallium and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn. The method of producing a magnetically anisotropic magnetic powder according to the present invention comprises the steps of rapidly quenching a melt of an R-TM-B-Ga-M alloy, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron, Ga gallium, and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn, to form flakes made of an amorphous or partially crystallized R-TM-B-Ga-M alloy, pressing these flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to form a magnetically anisotropic R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5µm, heat-treating it to increase a coercive force thereof, and then pulverizing it. The method of producing a magnetically anisotropic magnetic powder according to the present invention comprises the steps of rapidly quenching a melt of an R-TM-B-Ga-M alloy, wherein R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron, Ga gallium, and M one or more elements selected from the group consisting of Nb, W, V, Ta, Si, Aℓ, Zr, Hf, P, C and Zn to form flakes of an amorphous or partially crystallized R-TM-B-Ga-M alloy, pressing the flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to provide a magnetically anisotropic R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5µm, and then pulverizing it without heat treatment. EPA-0 216 254, EPA-0 248 981 and EPA-0 258 609, which belong to the state of the art in the sense of Art. 54(3) EPC, disclose magnetically anisotropic powders, methods of producing them, and magnets made therefrom, which are similar to present claims 1, 7, 11 and 12 but differ therefrom in the average crystal grain size. SUMMARY OF THE INVENTION It is an object of the present invention to enable the production of anisotropic resin-bonded magnets which have good thermal stability and are easy to magnetise. This object is met by the features included in claims 1, 7, 11 and 12. The present invention is based on our finding that a thermally stable, anisotropic resin-bonded magnet can be obtained from magnetic powder of an average particle size of 1-1000µm prepared by pulverizing a magnetically anisotropic R-Fe-B-Ga alloy having an average crystal grain size of 0.01-0.5µm. It has been found that gallium (Ga) is highly effective to improve the thermal stability of the magnet. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the variation of irreversible loss of flux with heating temperature of the magnets (a), (b) and (c), wherein (a) denotes the magnet prepared by rapid quenching, heat treatment and resin impregnation, (b) the magnet prepared by rapid quenching, heat treatment and hot pressing, and (c) the magnet prepared by rapid quenching, HIP and die upsetting; and Fig. 2 is a graph showing the comparison in thermal stability of the anisotropic resin-bonded magnet (a) of Example 8, the anisotropic sintered magnet of Sm₂Co₁₇ (b) and the anisotropic sintered magnet having the composition of Nd₁₃DyFe 76.8 Co 2.2 B₆Ga 0.9 Ta 0.1 (c). DETAILED DESCRIPTION OF THE INVENTION The above alloy has preferably a composition of 11-18 atomic % of R, 5 atomic % or less of Ga, 4-11 atomic % of B, 30 atomic % or less of Co and balance Fe and inevitable impurities, and further preferably a composition of 11-18 atomic % of R, 0.01-3 atomic % of Ga, 4-11 atomic % of B, 30 atomic % or less of Co and balance Fe and inevitable impurities. This alloy may contain one or more additional elements M selected from Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn. The amount of the additional element M is 3 atomic % or less and more preferably 0.001-3 atomic %. The addition of the additional element M and Ga in combination is effective to further improve the coercive force of the alloy. Of course, the addition of Ga only is effective in some cases. The R-Fe-B alloy is an alloy containing R₂Fe₁₄B or R₂(Fe,Co)₁₄B as a main phase. The composition range desirable for a permanent magnet is as follows: When R (one or more rare earth elements including Y) is less than 11 atomic %, sufficient iHc cannot be obtained, and when it exceeds 18 atomic %, the Br decreases. Thus, the amount of R is 11-18 atomic %. When B is less than 4 atomic %, the R₂Fe₁₄B phase, a main phase of the magnet is not fully formed, resulting in low Br and iHc. On the other hand, when it exceeds 11 atomic %, a phase undesirable for magnetic properties appears, resulting in low Br. Thus, the amount of B is 4-11 atomic %. When Co exceeds 30 atomic %, the Curie temperature increases but the anisotropy constant of the main phase decreases, making it impossible to obtain high iHc. Thus, the amount of Co is 30 atomic % or less. When Ga exceeds 5 atomic %, the saturation magnetization 4πIs and the Curie temperature Tc decrease extremely. Ga is preferably 0.01-3 atomic %, and more preferably 0.05-2 atomic %. The addition of one or more additional elements of Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn is effective to further increase the coercive force of the alloy, but when it exceeds 3 atomic %, undesirable decrease in 4πIs and Tc takes place. Preferably, the additional element is 0.001-3 atomic %. Incidentally, the alloy of the present invention may contain Aℓ contained as an impurity in ferroboron, and further reducing materials and impurities mixed in the reduction of the rare earth element. In the present invention, when the average crystal grain size of the R-Fe-B-Ga alloy exceeds 0.5µm, its iHc decreases, resulting in irreversible loss of flux of 10% or more at 160°C which in turn leads to extreme decrease in thermal stability. On the other hand, when the average crystal grain size is less than 0.01µm, the formed resin-bonded magnet has low iHc so that the desired permanent magnet cannot be obtained. Therefore, the average crystal grain size is limited to 0.01-0.5µm. An average ratio of an average size (c) of the crystal grains in perpendicular to their C axes to an average size (a) thereof in parallel to their C axes is preferably 2 or more. To provide an anisotropic resin-bonded magnet with high magnetic properties, the R-Fe-B-Ga alloy to be pulverized is required to have a residual magnetic flux density of 8kG or more in a particular direction, namely in the direction of anisotropy. The R-TM-B-Ga or R-TM-B-Ga-M alloy is given anisotropy by pressing or compacting flakes obtained by a rapid quenching method by hot isostatic pressing (HIP) or hot pressing, and then subjecting the resulting pressed body to plastic deformation. One method for giving plastic deformation is die upsetting at high temperatures. The magnetically anisotropic R-TM-B-Ga or R-TM-B-Ga-M alloy means herein an R-TM-B-Ga or R-TM-B-Ga-M alloy showing anisotropic magnetic properties in which the shape of a 4πI-H curve thereof in the second quadrant varies depending upon the direction of magnitization. A pressed powder body produced by the hot isostatic pressing of flakes has usually a residual magnetic flux density of 0.75T or less, while by using an R-TM-B-Ga or R-TM-B-Ga-M alloy having a residual magnetic flux density of 0.8T or more, the resulting resin-bonded magnets have higher magneticproperties such as residual magnetic flux density and energy product than isotropic resin-bonded magnets. The method of producing anisotropic magnetic particles and anisotropic powder or resin-bonded magnets will be explained below. In the present invention, the alloy flakes are pulverized to 100-200µm or so. The coarse powder produced by pulverization is molded at room temperature to obtain a green body. The green body is subjected to hot isostatic pressing or hot pressing at 600-750°C to form a compacted block having a relatively small crystal grain size. The block is again subjected to plastic working such as die upsetting at 600-800°C to provide an anisotropic flat plate. This is called herein an anisotropic pressed powder magnet. Depending upon applications, this may be used without further treatment or working. It may be heat-treated but the heat treatment can be omitted by adding Ga, because the addition of Ga increases iHc sufficiently enough in some cases. The more working, the higher anisotropy the resulting alloy has. If necessary, the flat plate may be heat-treated at 600-800°C to improve iHc thereof. Pulverization of this flat plate can provide coarse powder foranisotropic resin-bonded magnets. By plastic working, the anisotropic R-Fe-B-Ga alloy has crystal grains flattened in the C direction. The crystal grains desirably have an average ratio of an average size (c) thereof in perpendicular to their c axes to an average size (a) thereof in parallel to their C axes of 2 or more, so that the magnet has a residual magnetic flux density of 0.8T or more. Incidentally, the average crystal grain size is defined herein as a value obtained by averaging the diameters of 30 or more crystal grains, which are converted to spheres having the same volume. When the plastic working is die upsetting while heating, particularly high magnetic properties can be obtained. By heat-treating the R-Fe-B magnet which is given anisotropy by the plastic working, it can have an increased coercive force. The heat treatment temperature is desirably 600-900°C, because when it is less than 600°C, the coercive force cannot be increased, and when it is higher than 900°C, the coercive force rather decreases than before the heat treatment. The heat treatment is conducted for a period of time needed for keeping a sample at a uniform temperature. Taking productivity into consideration, it is 240 minutes or less. The cooling rate should be 1°C/sec or more. When the cooling rate is less than 1°C/sec, the coercive force decreases before the heat treatment. Incidentally, the term "cooling rate" used herein means an average cooling rate from the heat treatment temperature (°C) to (heat treatment temperature + room temperature) / 2 (°C). However, the addition of Ga makes the heat treatment unnecessary in some cases, in which the heat treatment is not only unnecessary but also large magnets used for voice coil motors, etc. suffer from substantially no cracking nor oxidation. In the present invention, an average particle size of the pulverized powder is 1-1000µm for the following reasons: When it is less than 1µm, the powder is easily burned, making it difficult to handle it in the air, and when it exceeds 1000µm, a thin resin-bonded magnet of 1-2mm in thickness cannot be produced, and also it is not suitable for injection molding. The pulverization may be carried out by a usual method by a disc mill, a brown mill, an attritor, a ball mill, a vibration mill, a jet mill, etc. The coarse powder can be blended with a thermosetting resin binder and compression-molded in a magnetic field and then thermally cured to provide an anisotropic resin-bonded magnet of a compression molding type. Further, the coarse powder can be blended with a thermoplastic resin binder and injection-molded in a magnetic field to provide an anisotropic resin-bonded magnet of an injection molding type. As materials usable as the above binders, thermosetting resins are easiest to use in the case of compression molding. Thermally stable polyamides, polyimides, polyesters, phenol resins, fluorine resins, silicone resins, epoxy resins, etc. may be used. And Aℓ, Sn, Pb and various low-melting point solder alloys may also be used. In the case of injection molding, thermoplastic resins such as ethylene-vinyl acetate resins, nylons, etc. may be used. Example 1 An Nd₁₅Fe₇₇B₇Ga₁ alloy was prepared by arc melting, and this alloy was formed into thin flakes by a single roll method in an argon atmosphere. The peripheral speed of the roll was 30m/sec., and the resulting flakes were in irregular shapes of about 30µm in thickness. And as a result of X-ray diffraction measurement, it was found that they were composed of a mixture of amorphous phases and crystal phases. These thin flakes were pulverized to 32 mesh or finer and then compressed by a die at 6 kbar without applying a magnetic field. The resulting compressed product had a density of 5.8 g/cm³. The compressed product body was hot-pressed at 750°C and 2 kbar. The alloy after hot pressing had a density of 7.30 g/cm³. Thus, a sufficiently high density was provided by hot pressing. The bulky product or pressed powder body having a higher density was further subjected to die upsetting at 750°C. The height of the sample was adjusted so that a compression ratio was 3.8 before and after the upsetting. That is, h₀/h=3.8 , wherein h₀ was a height before the upsetting and h a height after the upsetting. The upset sample was heated in an Ar atmosphere at 750°C for 60 minutes, and then cooled by water at a cooling rate of 7°C/sec. The magnetic properties before and after the heat treatment are shown in Table 1. The heat-treated sample was pulverized to have a particle size range of 250-500µm. The resulting magnetic powder was mixed with 16 vol. % of an epoxy resin in a dry state, and the resulting powder was molded in a magnetic field of 8 kA/cm in perpendicular to the direction of compression. Next, by thermally curing it at 120°C for 3 hours, an anisotropic resin-bonded magnet was obtained. The resulting anisotropic resin-bonded magnet had magnetic properties of Br=0.76T, bHc=5.44 kA/cm, iHc=15.2 kA/cm and ( BH)max=1.08 x 10⁵TA/m when measured at a magnetization intensity of 20 kA/cm. For comparison, rapidly quenched thin flakes having the composition of Nd₁₇Fe₇₃B₈Ga₂ was heat-treated at 600°C for one hour in vacuum, pulverized to 250-500µm and formed into a resin-bonded magnet in the same manner as above. Incidentally, since this resin-bonded magnet was isotropic, no magnetic field was applied in the compression molding step. The magnetic properties thereof measured at a magnetization intensity of 20 kA/cm was Br of 0.63T, bHc of 4.16 kA/cm, iHc of 17.68 kA/cm and (BH)max of 5.44 x 10⁴TA/m (Comparative Example 1). It is clear from the above that the anisoprotic resin-bonded magnet of the present invention has better magnetization and higher magnetic properties than the isotropic resin-bonded magnet. For comparison, an ingot having the composition of Nd₁₅Fe₇₇B₇Ga₁ was pulverized in the same manner as in the above Example, mixed with a binder, molded in a magnetic field and heat-set. The magnetic properties thereof measured at a magnetization strength of 20 kA/cm were Br of 0.38T and bHc of 0.24 kA/cm (Comparative Example 2). Thus, anisotropic resin-bonded magnets prepared from ingots cannot be utilized as practical materials because high iHc cannot be achieved. The results of Example 1 and Comparative Example are summarized in Table 2 below. Example 2 Next, the influence of a compression ratio in die upsetting on final anisotropic resin-bonded magnets will be shown. With respect to composition and conditions of rapid quenching, hot pressing, molding in a magnetic field in perpendicular to the direction of compression, heat treatment and curing, this Example was the same as Example 1. The results are shown in Table 3. The magnetic properties shown in Table 3 are values obtained at a magnetization intensity of 20 kA/cm. As is shown in Table 3, the increase of the compression ratio serves to increase the magnetic properties of the resulting anisotropic resin-bonded magnet. Incidentally, when the compression ratio h₀/h was 5.6 or more, cracking appeared in the periphery of the samples after die upsetting, but no influence took place on the final anisotropic resin-bonded magnets of the compression molding type. Example 3 Magnetic powder was prepared from an Nd₁₄Fe₇₉B₆Ga₁ alloy in the same manner as in Example 1. The magnetic powder was blended with 33 volume % of EVA to form pellets. The pellets were injection-molded at 150°C. A test piece produced by the injection molding was in a circular shape of 20mm in diameter and 10mm in thickness, and the magnetic field applied during the injection molding was 6.4 kA/cm. The magnetic properties of the test piece was Br of nearly 0.71T, bHc of nearly 4.64 kA/cm, iHc of nearly 14.8 kA/cm and (BH)max of nearly 8.4 x 10⁴TA/m when measured at a magnetization intensity of 20 kA/cm. Example 4 Anisotropic resin-bonded magnets having the compositions as shown in Table 4 were prepared in the same compression molding method as in Example 1. The magnetic properties measured are shown in Table 4. Sameple Nos. 1-5 show the influence of Nd, Sample Nos. 6-10 show the influence of B, and Sample Nos. 11-19 show the influence of Ga. And Sample Nos. 20-23, 24-27, 28-31, 32-35, 36-39, 40-43, 44-47, 48-51, 52-55, 56-59, 60-63 and 64-67 respectively show the effects of additional elements, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C, Zn and Nb. It is clear from this table that Nd is preferably 11-18 atomic %, boron 4-11 atomic %, Ga 5 atomic % or less and each additional element 3 atomic % or less. Incidentally, the same effects of Ga and the additional element M were appreciated in the so-called sintering method. Example 5 An alloy having the composition of Nd 14.3 Fe 70.7 Co 5.1 B 6.9 Ga 1.7 W 1.3 was prepared by arc melting, and rapidly quenched by a single roll method. The resulting flaky sample was formed into bulky products by the following three methods: (a) Heat-treating at 500-700°C, impregnating with an epoxy resin and die molding. (b) Heat-treating at 500-700°C, and hot pressing. (c) Hot isostatic pressing, and die upsetting to produce a flatten product. The magnetic properties of the resulting samples are shown in Table 5. After heating each sample at various temperatures for 30 minutes, the variation of open flux was measured to investigate the thermal stability of each sample. Incidentally, the sample measured was worked to have a permeance coefficient Pc=-2. The results are shown in Fig. 1. It is shown that the upset flat product (c) had a small average crystal grain size and good (BH)max. Example 6 An alloy having the composition of Nd 14.1 Fe 73.0 Co 3.4 B 6.9 Ga 1.7 W 0.9 was prepared by arc melting and then rapidly quenched by a single roll method. The resulting flaky sample was compressed by HIP and upset by a die to provide a flatten product. The resulting bulky sample was pulverized to 80µm or less, impregnated with an epoxy resin and then molded in an magnetic field. The resulting magnet had magnetic properties of Br=0.71T, iHc=17.6 kA/cm and (BH)max=8.88 x 10⁴TA/m . Example 7 An Nd₁₅Fe 72.7 Co 3.2 B₇Ga 1.8 Nb 0.3 alloy was treated in the same manner as in Example 1 to produce magnetic powder. This magnetic powder was blended with an EVA binder to form pellets which were then injection-molded to produce a magnet of 12mm in inner diameter, 16mm in outer diameter and 25mm in height. This magnet had anisotropy in a radial direction, and a sample of 1.5mm x 1.5mm x 1.5mm was cut out for evaluating its magnetic properties. They were Br=0.65T, bHc=4.64 kA/cm, iHc=19.36 kA/cm and (BH)max=6.8 x 10⁴TA/m . Example 8 An anisotropic resin-bonded magnet of a compression molding type having the composition of Nd₁₃DyFe 76.8 Co 2.2 B₆Ga 0.9 Ta 0.1 was prepared in the same manner as in Example 1. The magnetic properties of the magnet were Br of nearly 0.66T, bHc of nearly 4.96 kA/cm, iHc of nearly 16.8 kA/cm and (BH)max of nearly 8.16 x 10⁴TA/m. The magnet had a crystal grain size of 0.11µm. The magnet was worked to 10mm in diameter x 7mm thick and tested with respect to thermal stability. The results are shown in Fig. 2. For comparison, an anisotropic sintered Sm₂Co₁₇ magnet and an anisotropic R-Fe-B sintered magnet of the same composition were tested. It is shown that the anisotropic resin-bonded magnet of the present invention had better thermal stability than the anisotropic sintered magnets tested as comparative materials. Example 9 Example 1 was repeated except for changing the particle size of magnetic powder to prepare an anisotropic resin-bonded magnet of Nd₁₄Fe₇₉B₆Ga₁. For comparison, an anisotropic sintered magnet of Nd₁₃Dy₂Fe₇₈B₇ was used to investigate the variation of coercive force with particle size. The results are shown in Table 6. It is shown that a sintered body has a coercive force decreased by pulverization, unable to use as a material for resin-bonded magnets, while the magnet of the present invention undergoes substantially no decrease in coercive force by pulverization. Example 10 Example 1 was repeated except for changing crystal grain size by changing the upsetting temperature to prepare an anisotropic resin-bonded magnet. The results are shown in Table 7. It is shown that with an average crystal grain size of 0.01µm to 0.5µm, good magnetic properties can be achieved. Example 11 Example 1 was repeated except for changing the heat treatment time to prepare an upset sample of R-Fe-B-Ga. The results are shown in Table 8. It is shown that magnetic properties do not change as long as the heating time at 750°C is within 240 minutes. Example 12 Example 1 was repeated except for changing the heat treatment temperature with the heating time of 10 minutes to prepare an upset sample of Nd-Fe-B-Ga. The results are shown in Table 9. It is shown that with heat treatment temperature of 600-900°C, good magnetic properties can be obtained. Example 13 Example 1 was repeated except for changing the cooling method with a constant heating time of 10 minutes to prepare an upset sample of Nd-Fe-B-Ga. The results are shown in Table 10. It is shown that with the cooling rate of 1°C/sec. or more, good results are obtained. As described above in detail, the magnetic powder for anisotropic resin-bonded magnets containing Ga according to the present invention has excellent magnetizability and small irreversible loss of flux even in a relatively high temperature environment, and are useful for anisotropic resin-bonded magnets which can be magnetized after assembling.

Claims: A magnetically anisotropic magnetic powder having an average particle size of 1-1000µm, and composed of an R-TM-B-Ga-M alloy powder having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, and M, which is an optional component, represents one or more of the elements Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn. The magnetic powder of claim 1, wherein said alloy consists essentially of 11-18 atomic % of a rare earth element, 4-11 atomic % of boron, 30 atomic % or less of cobalt, 5 atomic % or less of gallium, 3 atomic % or less of the optional component, if contained, and the balance iron and inevitable impurities. The magnetic powder of claim 1 or 2, having a residual magnetic flux density of 0.8T or more in the direction of its easy magnetization axis. The magnetic powder of any of claims 1 to 3, obtainable by preparing said alloy powder by rapidly quenching a melt of the R-TM-B-Ga-M composition to form flakes which are pressed and then subjected to plastic deformation to have anisotropy and then pulverized. The magnetic powder of claim 4, obtainable by die upsetting while heating, to provide the anisotropy. The magnetic powder of any of claims 1 to 5, wherein the average ratio of the average size (c) of said crystal grains perpendicular to their C axes to the average size (a) thereof parallel to their C axes is 2 or more. A method of producing a magnetically anisotropic magnetic powder comprising the steps of rapidly quenching a melt of an R-TM-B-Ga-M alloy, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, and M, which is an optional component, represents one or more of the elements Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn, to form flakes made of an amorphous or partially crystallized R-TM-B-Ga-M alloy, pressing these flakes to have a higher density to provide a pressed powder body, subjecting it to plastic deformation while heating to form a magnetically anisotropic R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5µm, and then pulverizing it. The method of claim 7, wherein said alloy is heat-treated to increase its coercive force, before it is pulverized. The method of claim 8, wherein the alloy is heated at a temperature between 600°C and 900°C, kept at this temperature for 240 minutes, and cooled at a rate of 1°C/sec or more. The method of any of claims 7 to 9, wherein said alloy consists essentially of 11-18 atomic % of a rare earth element, 4-11 atomic % of boron, 30 atomic % or less of cobalt, 5 atomic % or less of gallium, 3 atomic % or less of the optional component, if contained, and the balance iron and inevitable impurities. A magnetically anisotropic pressed powder magnet made of magnetically anisotropic R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, and M, which is an optional component, represents one or more of the elements Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn, said magnetically anisotropic alloy having an axis of easy magnetization aligned in the same direction. A magnetically anisotropic resin-bonded magnet composed of 15-40 volume % of a resin binder and the balance R-TM-B-Ga-M alloy powder having an average crystal grain size of 0.01-0.5µm, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, and M, which is an optional component, represents one or more of the elements Nb, W, V, Ta, Mo, Si, Aℓ, Zr, Hf, P, C and Zn, said magnetically anisotropic R-TM-B-Ga-M alloy having an axis of easy magnetization aligned in the same direction. The magnet of claim 11 or 12, wherein said alloy consists essentially of 11-18 atomic % of a rare earth element, 4-11 atomic % of boron, 30 atomic % or less of cobalt, 5 atomic % or less of gallium, 3 atomic % or less of the optional component, if contained, and the balance iron and inevitable impurities. The magnet of any of claims 11 to 13, obtainable by preparing said alloy powder by rapidly quenching a melt of the R-TM-B-Ga-M composition to form flakes which are pressed and then subjected to plastic deformation to have anisotropy and then pulverized. The magnet of claim 14, obtainable by die upsetting while heating, to provide the anisotropy.

Inventors: ENDOH MINORU, IWASAKI KATSUNORI, NOZAWA YASUTO, TANIGAWA SHIGEHO, TOKUNAGA MASAAKI, ENDOH, MINORU, IWASAKI, KATSUNORI, NOZAWA, YASUTO, TANIGAWA, SHIGEHO, TOKUNAGA, MASAAKI
Applicants: HITACHI METALS LTD, HITACHI METALS, LTD.
Application year: 1987
Main classification: H01F1
IPC codes: B61C15, H01F1, C22C1