JP2014135442A - Method for manufacturing permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a permanent magnet capable of achieving high utilizing efficiency of an evaporation material.SOLUTION: In a processing chamber 70, at least two sheets of tabular evaporation material RM containing at least one kind selected from Dy, Tb, and Ho, are arranged facing each other with a distance and a plurality of iron-boron-rare earth based sintered magnets S are arranged between evaporation materials. Under reduced pressure, the processing chamber is heated to heat sintered magnets at a predetermined temperature and to evaporate the evaporation material, at least one kind selected from vaporized Dy, Tb and Ho, is attached to the surface of the sintered magnet by adjusting the amount of supply, and at least one kind selected from attached Dy, Tb and Ho, is dispersed in the grain boundaries and/or grain boundary phase of the sintered magnet. Each of sintered magnets is supported by a support member 81 having a plurality of openings to allow at least one kind selected from vaporized Dy, Tb and Ho to pass therethrough, and the proportion of the total area of each openings to an area of a surface which is opposed to evaporation materials of the support member, is equal to or more than 40%.

Description

  In the present invention, at least one selected from Dy, Tb, and Ho is diffused into the grain boundary and / or the grain boundary phase of an iron-boron-rare earth sintered magnet, thereby dramatically increasing the coercive force. The present invention relates to a method for producing a high-performance permanent magnet having

  Conventionally, a method for producing a permanent magnet having a remarkably high coercive force by diffusing at least one selected from Dy, Tb, and Ho into a crystal grain boundary and / or a grain boundary phase of a sintered magnet, For example, it is known from Patent Document 1. In this, a rectangular parallelepiped sintered magnet and a plate-like evaporation material (bulk body) containing at least one selected from Dy, Tb and Ho are placed in a processing chamber partitioned into a fixed space. Deploy. In this case, the two evaporating materials are arranged opposite to each other with a gap therebetween, and a support member having a plurality of openings is provided in the space between the evaporating materials, and the main surfaces of the evaporating materials are parallel to each other. A plurality of sintered magnets are juxtaposed at intervals. Then, by heating the inside of the processing chamber and heating the evaporation material and the sintered magnet body to 700 ° C. or more and 1000 ° C. or less, at least one selected from Dy, Tb, and Ho is applied to the surface of the sintered magnet body. While supplying, diffuse in the inside (vacuum steam treatment).

  Here, evaporating materials such as Dy, Tb, and Ho are scarce in resources, and there is a possibility that stable supply cannot be expected. How to increase the ratio of the total increase in each sintered magnet to the decrease in the evaporation material in the vacuum vapor treatment is also important for cost reduction. Therefore, the present inventors have conducted extensive research and, as in the conventional example described above, when manufacturing a permanent magnet by repeatedly performing vacuum vapor treatment, the aperture ratio of the support member that supports each sintered magnet (the above-mentioned ratio of the support member). It was found that the ratio of the total area of each opening to the area of the surface facing the evaporating material is important for increasing the efficiency of using the evaporating material.

International Publication No. 2007/102391

  This invention is made | formed based on the said knowledge, and makes it the subject to provide the manufacturing method of the permanent magnet which can achieve the high use efficiency of evaporation material.

  In order to solve the above-mentioned problem, in the method for producing a permanent magnet of the present invention, at least two plate-like evaporation materials containing at least one selected from Dy, Tb and Ho are disposed in a processing chamber. Arranged facing each other with a space between them, a plurality of iron-boron-rare earth sintered magnets are arranged between the evaporation materials, and the sintered magnet is heated to a predetermined temperature by heating the processing chamber under reduced pressure. At the same time, the evaporation material is evaporated, and at least one selected from the evaporated Dy, Tb, and Ho is deposited by adjusting the supply amount to the sintered magnet surface, and the deposited Dy, Tb, and Ho At least one selected from the above is diffused into the grain boundaries and / or grain boundary phases of the sintered magnet. At this time, each of the sintered magnets is supported by a support member having a plurality of openings that allow passage of at least one selected from the evaporated Dy, Tb, and Ho, and the evaporation of the support member is performed. The ratio of the total area of each opening to the area of the surface facing the material is 40% or more.

  According to the present invention, the ratio of the sum of the areas of the facing surfaces of the respective sintered magnets to the evaporation material relative to the sum of the areas of the facing surfaces of the evaporation material to the sintered magnet, If the distance between the opposite surfaces of the support members is appropriately set within a predetermined range, each of the sintered magnets can be used to reduce the amount of evaporation material in one vacuum vapor treatment by setting the opening ratio of the support member to 40% or more. It was confirmed that the ratio of the total increase in the amount can be increased to 75% or more. Here, when the ratio (opening ratio) is less than 40%, the use efficiency of the evaporation material is extremely lowered. When the sintered magnet or the evaporation material is heated to perform the vacuum vapor treatment, the support member is also heated to a temperature of about 900 ° C. For this reason, even if heating and cooling of the support member are repeated, the upper limit of the ratio is set so that the support member does not thermally deform. For example, when the support member is made of Mo, the aperture ratio is 95% or less. Then, it was confirmed that even if the vacuum steam treatment is repeated, the heat deformation is not so great as to affect the improvement of the magnetic characteristics.

  In the present invention, the ratio of the total area of the facing surfaces of the sintered magnets to the evaporation material to the total area of the facing surfaces of the evaporation materials to the sintered magnet is set in the range of 20% to 120%. Is preferred. When the above ratio is less than 20%, the efficiency of use of the evaporation material is extremely reduced, and when the above ratio exceeds 120%, a portion where the evaporated material does not adhere to the sintered magnet surface occurs. The crystal grain boundary and / or the crystal grain boundary phase cannot be diffused, and unevenness between the high coercive force portion and the low coercive force portion occurs, which may impair the squareness of the demagnetization curve. In this case, it was confirmed that the use efficiency of the evaporating material does not depend on the thickness of the evaporating material. In the present invention, when the sintered magnet and the evaporation material face each other, for example, when the sintered magnet is viewed from the evaporation material, not only when both faces each other, but from the outline of the evaporation material. This includes cases where some or all of the sintered magnet protrudes outside.

  Further, in the present invention, if the distance between the facing surface of the evaporating material and the facing surface of each sintered magnet is set in the range of 0.1 mm to 5 mm, the evaporating material in one vacuum vapor treatment is surely achieved. The ratio of the total increase in each sintered magnet to the decrease in the amount can be 75% or more. Here, when the said space | interval is shorter than 0.1 mm, fusion | melting with the spacer member which isolate | separates between a sintered magnet and the said sintered magnet generate | occur | produces, and mass-productivity is impaired. Moreover, when the said space | interval becomes longer than 5 mm, the number of the sintered magnets which can perform one vacuum steam process will decrease, and mass-productivity will be impaired. In this case, the interval between the evaporation materials is preferably 7 mm or less.

  Furthermore, in the present invention, it is housed in a vacuum furnace connected to a vacuum evacuation means so as to be freely put in and out, and is composed of a box part whose upper part is opened and a lid part that is detachably attached to the opening surface of this box part. The processing chamber may be defined by a box that is formed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The perspective view explaining stacking | stacking of the evaporation material and sintered magnet to a process box. The schematic plan view of the mounting part as a supporting member. The expanded sectional view which expands and shows the principal part of loading of the evaporation material of FIG. 1, and a sintered magnet. The graph explaining the procedure of a vacuum steam process. The graph of the experimental result which confirms the effect of this invention.

  Hereinafter, with reference to the drawings, the evaporation material RM contains Dy which is a heavy rare earth element, Dy is evaporated, and the evaporated Dy atoms are attached to the surface of the sintered magnet S formed in a predetermined shape. An embodiment in which a high-performance permanent magnet is manufactured by simultaneously performing a series of treatments (vacuum vapor treatment) for diffusing into crystal grain boundaries and / or grain boundary phases of a sintered magnet will be described. In the following, terms indicating directions such as “up” and “down” are based on FIG.

  The sintered magnet S as the starting material is produced as follows, for example. That is, industrial pure iron, metallic neodymium, and low carbon ferroboron are blended and dissolved using a vacuum induction furnace so that Fe, Nd, and B have a predetermined composition ratio, and then quenched by a rapid cooling method such as a strip casting method. First, an alloy raw material of 0.05 to 0.5 mm is prepared. Alternatively, an alloy raw material having a thickness of about 5 to 10 mm may be produced by a centrifugal casting method, and Dy, Tb, Co, Cu, Nb, Zr, Al, Ga, or the like may be added during blending. . The total content of rare earth elements is increased to more than 28.5%, and an ingot that does not produce α iron is obtained.

  Next, the produced alloy raw material is coarsely pulverized by a known hydrogen pulverization step, and then finely pulverized in a nitrogen gas atmosphere by a jet mill fine pulverization step to obtain an alloy raw material powder having an average particle diameter of 3 to 10 μm. This alloy raw material powder is compression molded into a predetermined shape in a magnetic field using a known compression molding machine. And the molded object taken out from the compression molding machine is stored in a sintering furnace (not shown), and is obtained by sintering (sintering process) at a predetermined temperature (for example, 1050 ° C.) for a predetermined time in a vacuum. As the sintered magnet S, the smaller the oxygen content, the faster the diffusion rate of Dy atoms into the crystal grain boundary and / or the grain boundary phase, so the oxygen content of the sintered magnet S itself is preferably 3000 ppm or less. May be 2000 ppm or less, more preferably 1000 ppm or less. The sintered magnet S thus obtained is subjected to vacuum vapor treatment. A vacuum steam processing apparatus that performs this vacuum steam processing will be described below with reference to FIG.

As shown in FIG. 1, the vacuum vapor processing apparatus 1 is a heat treatment that can be held at a reduced pressure to a predetermined pressure (for example, 1 × 10 ⁻⁵ Pa) via a vacuum exhaust means 2 such as a turbo molecular pump, a cryopump, or a diffusion pump. It has a furnace 3. In the heat treatment furnace 3, there is provided a heating means 4 composed of a heat insulating material 41 surrounding a processing box, which will be described later, and a heating element 42 arranged inside the heat insulating material 41. The heat insulating material 41 is made of, for example, Mo, and the heating element 42 is composed of an electric heater having a Mo filament (not shown). The filament is energized from a power source (not shown), and is a resistance heating type heat insulating material. The space 5 surrounded by 41 and in which the processing box is installed can be heated. In this space 5, for example, a table 6 made of Mo is provided, and at least one processing box 7 can be placed thereon.

2 to 4, the processing box 7 includes a rectangular parallelepiped box portion 71 whose upper surface is opened and a lid portion 72 that is detachably attached to the upper surface of the opened box portion 71. A flange 72a bent downward is formed on the outer peripheral edge of the lid portion 72 over the entire circumference. When the lid portion 72 is attached to the upper surface of the box portion 71, the flange 72a is fitted to the outer wall of the box portion 71. Thus (in this case, a vacuum seal such as a metal seal is not provided), and a processing chamber 70 isolated from the heat treatment furnace 3 is defined. Then, when the vacuum evacuation unit 2 is operated to depressurize the heat treatment furnace 3 to a predetermined pressure (for example, 1 × 10 ⁻⁵ Pa), the processing chamber 70 has a higher pressure than the heat treatment furnace 3 (for example, 5 × 10 ⁻⁴ Pa). ) Until the pressure is reduced. Thereby, the inside of the processing chamber 70 can be appropriately set to a predetermined pressure without requiring an additional evacuation unit.

  In the box portion 71 of the processing box 7, the sintered magnet S and the plate-like evaporation material RM are stacked up and down with the spacer member 8 interposed therebetween so that they are not in contact with each other. The spacer members 8 are juxtaposed so that a plurality of the sintered magnets S are not in contact with each other and parallel to the main surface of the evaporation material RM (upper surface RM1 and lower surface RM2 which are plate surfaces in FIG. 4). And a plate-like support portion 82 that extends in the vertical direction on both sides in the longitudinal direction (left and right direction in FIG. 1) of the mounting portion 81. And the mounting part 81 comprises the support member of this embodiment which has several opening which accept | permits passage of the evaporated Dy atom, supporting each sintered magnet S, respectively.

  As shown in FIG. 3, the mounting portion 81 of the spacer member 8 is configured by assembling a plurality of wire rods 81a (for example, φ0.1 to 10 mm) in a lattice shape, and a space surrounded by each wire rod 81a is opened. 81b. In this case, when the sintered magnet S and the evaporating material RM are stacked one above the other, the support portion 82 is respectively disposed on the outer peripheral edge portions of the upper surface RM1 and the lower surface RM2 of the evaporating material RM located immediately above or directly below the support portion 82. The area of the mounting portion 81 is set so as to abut. And the ratio (opening ratio) of the total area of each opening with respect to the area of opposing surface RM1, RM2 with respect to the evaporation material RM of the mounting part 81 is 40% or more.

  In the embodiment described above, the area of the mounting portion 81 is set as described above, but is larger than the areas of the opposing surfaces RM1 and RM2 of the evaporation material RM, that is, for example, the sintered magnet S is viewed from the evaporation material RM. The area of the mounting portion 81 is set so that a part or all of the outermost sintered magnets S positioned outside the outline of the evaporating material RM can be protruded and installed. Even in such a case, the total area of the opening 81b may be the above ratio. The shape of the opening 81b is not limited to a rectangle, and may be a circle or a polygon. Further, in FIG. 3, the wire 81a located on the outer periphery of the mounting portion 81 is assembled with a narrow pitch so that the area of the opening 81b is relatively small. It may be reinforced by making the wire diameter larger than that (not shown) or by providing a rib on the outer peripheral edge of the mounting portion 81. Further, the mounting portion 81 as the support member is not limited to this as long as it allows passage of evaporated metal atoms, and for example, so-called expanded metal can be used.

  Here, when the ratio is less than 40%, the use efficiency of the evaporation material RM is extremely reduced. Note that when the sintered magnet S and the evaporation material RM are heated in order to perform the vacuum vapor treatment, the mounting portion 81 is also heated to a temperature of about 900 ° C. For this reason, even if heating and cooling of the mounting part 81 are repeated, the upper limit of the ratio is set so that the mounting part 81 does not thermally deform. For example, when the mounting part 81 is made of Mo, If the ratio is 95% or less, even if the vacuum vapor treatment is repeated, the thermal deformation does not occur to such an extent that it affects the improvement of the magnetic properties.

The processing box 7 and the spacer member 8 are made of Mo, for example, W, V, Nb, Ta, or alloys thereof (including rare earth-added Mo alloys, Ti-added Mo alloys, etc.), CaO, Y ₂ O ₃ Alternatively, it can be made of a rare earth oxide or formed by depositing these materials as a lining film on the surface of another heat insulating material. Thereby, it can prevent that the reaction product is formed on the surface by reacting with the evaporation material RM.

  Further, the distances D1, D2 between the upper surface RM1 and the lower surface RM2 of the evaporation material RM and the opposing surfaces S1, S2 of each sintered magnet S are set to be equal in the range of 0.1 mm to 5 mm, The distance D3 between the upper surface RM1 and the lower surface RM2 of the evaporation material RM is set to be 7 mm or less. Thereby, the evaporated Dy atoms are ideally supplied, the magnetization and coercive force are further improved or recovered, and a high-performance magnet that does not impair the squareness of the demagnetization curve can be obtained with high productivity. If the distances D1 and D2 are shorter than 0.1 mm, fusion between the sintered magnet S and the spacer member 8 that separates the sintered magnets S from each other occurs, and mass productivity is impaired. In addition, when the distances D1 and D2 are longer than 5 mm, the number of sintered magnets that can be subjected to a single vacuum vapor treatment is reduced and mass productivity is impaired. In addition, the form of the support part 82 is not limited to the above, For example, the said space | interval D1-D3 is suitably adjusted using the jig for height adjustment (not shown) which consists of a solid cylinder made from Mo, for example. In such a case, the area of the mounting portion 81 of the spacer member 8 can be set larger than the areas of the upper surface RM1 and the lower surface RM2 of the evaporation material RM (in this case, evaporation) When the sintered magnet S is viewed from the material RM, part or all of the sintered magnet S protrudes outward from the outline of the evaporation material RM).

  As the evaporation material RM, Tb and Ho can be used in addition to Dy which greatly improves the magnetocrystalline anisotropy of the main phase. Further, a further coercive force such as Nd, Pr, Al, Cu and Ga is added to these. An alloy containing a metal to be increased (a mass ratio of Dy and Tb of 50% or more) can be used. And after mix | blending each said metal with a predetermined | prescribed mixing ratio, for example, after melt | dissolving with an arc melting furnace, it forms in the plate shape of predetermined thickness. When stacking on the processing box 7, first, a plate-like evaporation material RM is installed on the bottom surface of the box portion 71, and a spacer member 8 on which a plurality of sintered magnets S are placed is placed thereon. Then, another evaporation material RM is installed so as to be supported by the upper end of the support portion 82. In this way, the evaporating material RM and the spacers 8 on which a plurality of sintered magnets S are juxtaposed are alternately stacked in a hierarchical manner up to the upper end of the processing box 7. Note that the evaporating material RM can be omitted because the lid 72 is located close to the uppermost spacer 8.

  Further, the ratio of the total area of the opposing surfaces S1, S2 of each sintered magnet S to the total area of the opposing surfaces R1, R2 of the evaporation material RM is set in a range of 20% to 120%. Accordingly, the distances D1 and D2 between the upper surface RM1 and the lower surface RM2 of the evaporation material RM and the facing surfaces S1 and S2 of the sintered magnets S and the opening ratio of the mounting portion 81 are set as described above. Together, the number of sintered magnets S accommodated in one processing box 7 can be increased (increase in loading capacity) to increase mass productivity, and the spacer member 8 (on the same plane) can be improved. By forming a so-called sandwich structure in which the upper and lower sides of the sintered magnets S arranged side by side are sandwiched between plate-like evaporation materials RM, the evaporation materials RM are positioned in the vicinity of all the sintered magnets S in the processing chamber 70, and the evaporation materials RM. When evaporated Dy is evaporated, the evaporated Dy atoms are supplied to and adhered to the surface of each sintered magnet S. As a result, the ratio of the total increase in each sintered magnet S to the decrease in the evaporation material RM in one vacuum vapor treatment can be 75% or more. If the ratio is less than 20%, the use efficiency of the evaporation material RM is extremely reduced. If the ratio exceeds 120%, a portion where the evaporated material does not adhere to the surface of the sintered magnet S is generated. However, it cannot be diffused to all the crystal grain boundaries and / or crystal grain boundary phases, and unevenness occurs between the high coercive force portion and the low coercive force portion, which may impair the squareness of the demagnetization curve.

  Further, as described above, when the evaporation material RM is evaporated in a state where the evaporation material RM and the sintered magnet S are stacked in a sandwich structure in the processing box 7, the influence of the straightness of the evaporated Dy atoms is strongly affected. There is a risk of receiving it. That is, among the sintered magnets S juxtaposed on the mounting portion 81, the Dy atoms are likely to locally adhere to the opposing surfaces S1, S2 facing the evaporation material RM, while the spacer member 8 of each sintered magnet S. It is difficult for Dy atoms to be supplied to the shadowed portion of the wire 81 on the contact surface. For this reason, when the above-described vacuum vapor treatment is performed, the obtained permanent magnet has locally a portion having a high coercive force and a portion having a low coercive force, and as a result, the squareness of the demagnetization curve may be impaired. . For this reason, the inert gas introducing means 9 is provided in the vacuum chamber 3.

  The inert gas introduction means 9 has a gas introduction pipe 91 that communicates with the space 5 surrounded by the heat insulating material 41, and the gas introduction pipe 91 communicates with a gas source of an inert gas (not shown) via a mass flow controller 92. Yes. During the vacuum vapor treatment, an inert gas such as He, Ar, Ne, or Kr is introduced in a constant amount. The introduction amount of the inert gas may be changed during the vacuum vapor treatment (initially, the introduction amount of the inert gas is increased and then decreased or the introduction amount of the inert gas is decreased initially, Then increase or repeat these). The inert gas may be introduced, for example, after the evaporation material RM starts evaporation or after reaching the set heating temperature, and may be introduced during the set vacuum vapor treatment or for a predetermined time before and after the set vacuum vapor processing. In addition, when the inert gas is introduced, a valve 21 whose degree of opening and closing can be adjusted is provided in the exhaust pipe leading to the vacuum exhaust means 2 so that the partial pressure of the inert gas in the heat treatment furnace 3 can be adjusted. preferable.

  As a result, the inert gas introduced into the space 5 is also introduced into the processing box 7. At this time, since the mean free path of Dy atoms is short, the Dy atoms evaporated in the processing box 7 by the inert gas are reduced. The amount of metal atoms that diffuse and adhere directly to the surface of the sintered magnet S is reduced and supplied to the surface of the sintered magnet S from a plurality of directions. For this reason, even when the interval between the sintered magnet S and the evaporation material RM is narrow (for example, 5 mm or less), the evaporated Dy atoms wrap around and adhere to the shadowed portion of the wire constituting the spacer member 8. . As a result, problems such as excessive diffusion of Dy atoms in the crystal grains and reduction of the maximum energy product and residual magnetic flux density do not occur. And it can suppress that a part with a high coercive force and a low part exist locally, and can prevent that the squareness of a demagnetization curve is impaired.

  Below, with reference to FIG. 4, the manufacturing method of the permanent magnet of this embodiment performed through each process of a temperature rising process, a steam processing process, and an annealing process is demonstrated concretely. First, as described above, the plurality of sintered magnets S and the plate-like evaporation material RM are alternately stacked via the spacer member 8 and both are stacked on the box portion 71. And after attaching the cover part 72 to the upper surface which the box part 71 opened, the processing box 7 was installed on the table 6 in the space 5 surrounded by the heating means 4 in the heat treatment furnace 3 (see FIG. 1). Start the heating process.

In the temperature raising step, the heat treatment furnace 3 is evacuated and depressurized through the vacuum evacuation means 2 until it reaches a predetermined pressure (for example, 1 × 10 ⁻⁴ Pa). At this time, the processing chamber 70 is evacuated to a pressure higher than that of the heat treatment furnace 3. When the heat treatment furnace 3 reaches a predetermined pressure, the processing unit 70 is heated by operating the heating means 4. In this state, the pressure in the vacuum chamber 3 and the processing chamber 70 is substantially constant. Further, the pressure in the processing chamber 70 is maintained at 0.1 Pa or less, preferably 10 ⁻² Pa or less, more preferably 10 ⁻⁴ Pa or less by keeping the exhaust speed of the vacuum exhaust means 2 constant (FIG. 4). (Refer to part A). In this case, for example, the pressure may increase due to the gas released from the sintered magnet S, but about 70% of the time until the inert gas is introduced may be included in the pressure range as described below. Thereby, impurities such as oxygen are hardly taken into the sintered magnet S, and the magnetization and coercive force can be further improved or recovered.

  When the temperature in the processing chamber 70 reaches a predetermined temperature, the evaporation material RM is heated to substantially the same temperature as the processing chamber 70 to start evaporation, and a Dy vapor atmosphere is formed in the processing chamber 70. At this time, before reaching the evaporation temperature, an inert gas of 1 to 100 kPa may be introduced to suppress evaporation of Dy. Then, after the evaporation starts, when the temperature in the processing chamber 70 reaches a predetermined temperature, the opening of the valve 21 is adjusted to adjust the pressure of the inert gas in the heat treatment furnace 3. As a result, the inert gas is also introduced into the processing box 7, and the metal atoms evaporated in the processing chamber 70 are diffused by the inert gas. When the evaporating material RM starts to evaporate, the sintered magnet S and the evaporating material RM are arranged so as not to contact each other. Therefore, the molten evaporating material RM is the sintered magnet S in which the surface Nd-rich phase is dissolved. It does not adhere directly to. And it transfers to the steam processing process hold | maintained for a predetermined time at substantially constant temperature.

  In the steam treatment step, the surface of each sintered magnet S in which Dy atoms in the Dy vapor atmosphere diffused in the treatment box 7 are heated to approximately the same temperature as Dy from a plurality of directions by direct or repeated collisions. The permanent magnet M is obtained by supplying and adhering to the whole, and the adhering Dy is diffused to the crystal grain boundary and / or crystal grain boundary phase of the sintered magnet S. Here, when the Dy atoms in the Dy vapor atmosphere are supplied to the surface of the sintered magnet S so that the Dy layer (thin film) is formed, the Dy adhered and deposited on the surface of the sintered magnet S is formed. When recrystallized, the surface of the permanent magnet is remarkably deteriorated (surface roughness is deteriorated), and Dy deposited and deposited on the surface of the sintered magnet S heated to substantially the same temperature during processing is dissolved. Thus, it excessively diffuses in the grain boundary in the region close to the surface of the sintered magnet S, and the magnetic properties cannot be effectively improved or recovered. That is, once the Dy thin film is formed on the surface of the sintered magnet S, the average composition of the surface of the sintered magnet S adjacent to the thin film becomes a Dy rich composition, and when the Dy rich composition is reached, the liquidus temperature decreases, The surface of the sintered magnet S is melted (that is, the main phase is melted and the amount of the liquid phase is increased). As a result, the vicinity of the surface of the sintered magnet S melts and collapses, and the unevenness increases. In addition, Dy excessively penetrates into the crystal grains together with a large amount of liquid phase, and the maximum energy product and the residual magnetic flux density showing the magnetic characteristics are further lowered.

Therefore, in order to control the evaporation amount of Dy, the heating means 4 is controlled so that the temperature in the processing chamber 70 is set in a range of 800 ° C. to 1050 ° C., preferably 850 ° C. to 950 ° C. (for example, processing When the room temperature is 900 ° C. to 1000 ° C., the saturated vapor pressure of Dy is about 1 × 10 ⁻² to 1 × 10 ⁻¹ Pa). When the temperature in the processing chamber 70 (and thus the heating temperature of the sintered magnet S) is lower than 800 ° C., the diffusion rate of Dy atoms adhering to the surface of the sintered magnet S and / or the grain boundary layer Therefore, before the thin film is formed on the surface of the sintered magnet S, it cannot be diffused to the crystal grain boundary and / or the grain boundary phase of the sintered magnet to be uniformly distributed. On the other hand, at a temperature exceeding 1050 ° C., the vapor pressure of Dy becomes high, and there is a possibility that Dy atoms in the vapor atmosphere are excessively supplied to the surface of the sintered magnet S. Further, there is a possibility that Dy diffuses into the crystal grains, and when Dy diffuses into the crystal grains, the magnetization in the crystal grains is greatly reduced, so that the maximum energy product and the residual magnetic flux density are further lowered.

  At the same time, the degree of opening and closing of the valve 21 was changed so that the partial pressure of the inert gas introduced into the heat treatment furnace 3 was in the range of 1 kPa to 30 kPa. If it is lower than 1 kPa, Dy atoms adhere locally to the sintered magnet S due to the influence of the strong straightness of Dy, and the squareness of the demagnetization curve is impaired. On the other hand, if it exceeds 30 kPa, evaporation of Dy is suppressed by the inert gas, Dy atoms are not efficiently supplied to the surface of the sintered magnet S, and the processing time becomes excessively long. As a result, while controlling the amount of evaporation of the evaporation material RM, Dy atoms are diffused in the processing box by introducing an inert gas, thereby suppressing the amount of Dy atoms supplied to the sintered magnet S and its surface. The combination of attaching Dy atoms to the whole and increasing the diffusion rate by heating the sintered magnet S within a predetermined temperature range allows the Dy atoms attached to the surface of the sintered magnet S to be sintered. Before being deposited on the surface of the magnet S and forming a Dy layer (thin film), it can be efficiently diffused to the crystal grain boundaries and / or crystal grain boundary phases of the sintered magnet S to be evenly distributed.

As a result, the surface of the permanent magnet is prevented from deteriorating, and excessive diffusion of Dy into the grain boundary in the region close to the surface of the sintered magnet is suppressed, so that the Dy rich phase ( Dy is diffused only in the vicinity of the surface of the crystal grains, so that the magnetization and the coercive force are effectively improved or recovered. In addition, the processing chamber 70 is evacuated to 10 ⁻⁴ Pa, maintained at a predetermined pressure even in the temperature raising step, and then subjected to vacuum vapor treatment while introducing an inert gas, whereby oxygen or the like is applied to the surface of the permanent magnet. The oxygen content of the permanent magnet obtained by the vacuum vapor treatment is substantially the same as that of the sintered magnet S before the vacuum vapor treatment, and in addition, the productivity that does not require finishing is required. It becomes a high-performance permanent magnet M excellent in.

  The time for adjusting the amount of Dy atoms supplied to the surface of the sintered magnet S is set in the range of 4 to 100 hours. If the time is shorter than 4 hours, metal atoms cannot be efficiently diffused into the crystal grain boundaries and / or crystal grain boundary phases of the sintered magnet S, and the squareness of the demagnetization curve is impaired. On the other hand, if it exceeds 100 hours, metal atoms enter the crystal grains near the surface of the sintered magnet S, and a portion having a high coercive force and a portion having a low coercive force are locally generated. Is damaged. Finally, when the above processing is performed for a predetermined time, the process proceeds to the annealing step. In the annealing step, the operation of the heating means 4 is stopped and the introduction of the inert gas by the gas introduction means is temporarily stopped. Subsequently, an inert gas is introduced again (100 kPa), and evaporation of the evaporation material RM is stopped. Thereby, evaporation of Dy stops and the supply stops. Note that the evaporation may be stopped by increasing only the introduction amount without stopping the introduction of the inert gas. Then, the temperature in the processing chamber 70 is temporarily lowered to 500 ° C., for example. Subsequently, the heating means 4 is operated again, the temperature in the processing chamber 70 is set in the range of 450 ° C. to 650 ° C., and heat treatment is performed to further improve or recover the coercive force. And it cools to substantially room temperature and takes out the processing box 7 from the heat processing furnace 3. FIG.

  Next, in order to confirm the effect of the above-mentioned present invention, the following experiment was conducted. In this experiment, the vacuum steam processing apparatus 1 shown in FIG. 1 was used, and the next sintered magnet S was subjected to vacuum steam processing to obtain a permanent magnet. The sintered magnet S is made of industrial pure iron, metallic neodymium, low carbon ferroboron, electrolytic cobalt, pure copper, and the blending composition (wt%) is 25Nd-7Pr-1B-0.05Cu-0.05Ga-0. Then, vacuum induction melting was performed so as to obtain .05Zr-Bal Fe, and a flaky ingot having a thickness of about 0.3 mm was obtained by a strip casting method. Next, it was roughly pulverized by a hydrogen pulverization step, and then finely pulverized by, for example, a jet mill pulverization step to obtain an alloy raw material powder. The alloy raw material powder is obtained using a transverse magnetic field compression molding apparatus having a known structure, and then sintered in a vacuum sintering furnace at a temperature of 1050 ° C. for 2 hours to obtain a sintered magnet S. It was. Then, the sintered magnet was processed into a shape of 2 × 40 × 40 mm by wire cutting, and then finished to have a surface roughness of 10 μm or less, and then the surface was etched with dilute nitric acid. At this time, the average magnetic characteristics of the sintered magnet S were 47.1 MGOe, the residual magnetic flux density was 14.2 kG, and the coercive force was 11.4 kOe (measured by a BH curve tracer).

Next, using the vacuum vapor processing apparatus 1 shown in FIG. 1, vacuum vapor treatment was performed on the sintered magnets S produced as described above (10 pieces each). In this case, as the evaporating material RM, Dy (99%) formed so that the thickness of the evaporating material RM is 1 mm and the areas of the facing surfaces RM1 and RM2 are each 22500 mm ² is used. Was loaded on a Mo processing box 7 with a spacer member 8 interposed. In this case, the spacer member 8 was formed so that the distance D3 between the upper surface RM1 and the lower surface RM2 of the evaporation material RM was 4 mm. The conditions of the vacuum steam treatment are as follows: after the pressure in the heat treatment furnace 3 reaches 10 ⁻⁴ Pa, the heating means 4 is operated, the temperature in the treatment chamber 70 is set to 950 ° C., and the treatment time is set to 3 hours. Processed. The sintered magnet S installed on the mounting table 81 has a ratio of the total area of the opposing surfaces RM1 and RM2 of the evaporation material RM and the opposing surfaces S1 and S2 of the sintered magnets S to 60%. The ratio of the total area of each opening (opening ratio) to the area of the facing surfaces RM1, RM2 of the mounting portion 81 facing the evaporation material RM is set to 35%, 43%, 53%, and 75%. did.

  According to the above experiment, when the aperture ratio was 35%, the holding force could be increased to 18.4 kOe, but when the permanent magnet was obtained under the above conditions, the evaporation material in one vacuum vapor treatment The ratio of the total increase of each sintered magnet with respect to the weight loss (Dy use efficiency%) was 39%. On the other hand, when the aperture ratio exceeds 40%, a Dy use efficiency of about 70% can be achieved, and when the aperture ratio is 75%, the Dy use efficiency can be increased to about 95%. Also in this case, the coercive force (18.4 kOe) could be increased as described above.

  Next, the aperture ratio is set to 53%, and the ratio of the total area of the opposed surfaces S1, S2 of each sintered magnet S to the area of the opposed surfaces R1, R2 of the evaporation material RM is 15%, 18%, 30%, The vacuum steam treatment was performed under the same conditions as set forth above at 40%, 60% and 80%, respectively.

  FIG. 6 shows the results when measuring the ratio of the total increase in each sintered magnet (Dy usage efficiency%) to the decrease in evaporation material in a single vacuum vapor treatment when a permanent magnet was obtained under the above conditions. Show. According to this, when the ratio of the sum of the areas of the opposing surfaces RM1 and RM2 of the evaporation material RM and the areas of the opposing surfaces S1 and S2 of each sintered magnet S exceeds 18%, the use efficiency of Dy is 75% or more. It can be confirmed that In this case, the average magnetic properties of the permanent magnets were a maximum energy product of 47.8 MGOe, a residual magnetic flux density of 14.1 kG, a coercive force of 18.2 kOe, and the coercive force was effectively enhanced. However, if the ratio of the area of the opposing surfaces RM1 and RM2 of the evaporation material RM and the area of the opposing surfaces S1 and S2 of each sintered magnet S exceeds 75%, the coercive force becomes 15.0 kOe, and the use of Dy Although the efficiency can be increased, it has been found that the magnetic properties cannot be improved effectively.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said thing. In the said embodiment, although demonstrated using the thing using the spacer member 8 comprised by assembling the several wire 81 in a grid | lattice form, it is not limited to this, Opening ratio and evaporation material RM The ratio of the total area of the opposing surfaces S1, S2 of each sintered magnet S to the area of the opposing surfaces R1, R2, the distance between the evaporation materials RM, and the distance between the evaporation material RM and the sintered magnet S are set as described above. Any form is possible as long as it is possible. Further, when the sintered magnet S placed on the spacer member 8 is stored in the processing box 7, a mesh-like protective frame (see FIG. (Not shown) may be provided.

  Moreover, in the said embodiment, although what used Dy as an evaporation material RM was demonstrated as an example, it is using Tb and Ho with low vapor pressure in the heating temperature range of the sintered magnet S which can make an optimal diffusion rate quick. it can. For example, when Tb is used, the processing chamber 70 may be heated in the range of 900 ° C. to 1150 ° C. At a temperature lower than 900 ° C., the vapor pressure that can supply Tb atoms to the surface of the sintered magnet S is not reached. On the other hand, at a temperature exceeding 1150 ° C., Tb is excessively diffused in the crystal grains, thereby reducing the maximum energy product and the residual magnetic flux density.

  Furthermore, although the said embodiment demonstrated what attached the cover part 72 to the upper surface of the box part 71, and comprised the process box 7, it is isolated from the heat processing furnace 3, and it accompanies decompressing the heat processing furnace 3. For example, after the evaporation material RM and the sintered magnet S are stored in the box portion 71, the upper surface opening thereof is made of, for example, a thin film made of Mo. You may make it cover.

  DESCRIPTION OF SYMBOLS 1 ... Vacuum vapor processing apparatus, 2 ... Vacuum exhaust means, 3 ... Vacuum chamber, 4 ... Heating means, 7 ... Processing box, 71 ... Box part, 72 ... Cover part, 8 ... Spacer member, 81 ... Mounting part, 82 DESCRIPTION OF SYMBOLS ... Support part, 10 ... Gas introduction pipe (gas introduction means), 11 ... Valve, S ... Sintered magnet, RM ... Evaporation material.

Claims (4)

In the processing chamber, at least two plate-shaped evaporation materials containing at least one selected from Dy, Tb, and Ho are arranged to face each other with a space therebetween, and iron − is provided between the evaporation materials. A plurality of boron-rare earth-based sintered magnets are arranged, the processing chamber is heated under reduced pressure to heat the sintered magnet to a predetermined temperature, and the evaporation material is evaporated. In the evaporated Dy, Tb and Ho At least one selected from among the attached Dy, Tb and Ho is attached to the surface of the sintered magnet by adjusting the supply amount to the surface of the sintered magnet. Or in the method of producing a permanent magnet that diffuses into the grain boundary phase,
Each of the sintered magnets is supported by a support member having a plurality of openings that allow passage of at least one selected from the evaporated Dy, Tb, and Ho. A method of manufacturing a permanent magnet, wherein the ratio of the total area of each opening to the area of the opposing surface is 40% or more.   The ratio of the sum of the areas of the facing surfaces of the sintered magnets facing the evaporation material to the sum of the areas of the facing surfaces of the evaporation materials facing the sintered magnet is set in a range of 20% to 120%. Item 10. A method for producing a permanent magnet according to Item 1.   The method for manufacturing a permanent magnet according to claim 1 or 2, wherein a distance between the facing surface of the evaporation material and the facing surface of each sintered magnet is set in a range of 0.1 mm to 5 mm. The processing is performed by a box body that is housed in a vacuum furnace connected to an evacuation means so as to be freely inserted and removed, and that is composed of a box portion that is open at the top and a lid portion that is detachably attached to the opening surface of the box portion. The method for manufacturing a permanent magnet according to any one of claims 1 to 3, wherein the chamber is defined.

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