JP2009200179A - Manufacturing method of sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a sintered compact by which the sintered compact can be manufactured inexpensively with high mass-productivity while enhancing product functions, such as the improvement of magnetic characteristics of a sintered magnet. <P>SOLUTION: The manufacturing method of the sintered compact includes: a stage of obtaining a compact by compressing and compacting raw material powder; and a step of disposing the compact in a processing chamber to heat it, vaporizing a vaporized material disposed in the same or a different processing chamber to stick vaporized metal atoms on a compact surface, and performing liquid-phase sintering while diffusing the stuck metal atoms to grain boundaries and/or a grain boundary phase. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a sintered body, and in particular, produces high-performance permanent magnets in which Dy and Tb are diffused in the grain boundaries and / or grain boundary phases of Nd—Fe—B based sintered magnets. The present invention relates to a method for manufacturing with good quality.

  Conventionally, Nd—Fe—B sintered magnets (so-called neodymium magnets), which are sintered bodies, are mainly produced by powder metallurgy. In this method, first, Nd, Fe, and B are mixed with a predetermined composition ratio. Blend in. At that time, rare earth elements such as dysprosium (Dy) and terbium (Tb) are mixed to increase the coercive force. Then, the alloy raw material is prepared by melting and casting, for example, coarsely pulverized by, for example, a hydrogen pulverization step, and then finely pulverized by, for example, a jet mill pulverization step (pulverization step) to obtain alloy raw material powder. Next, the obtained alloy raw material powder is oriented in a magnetic field (magnetic field orientation), and compression molded in a state where a magnetic field is applied to obtain a compact. Finally, this compact is subjected to liquid phase sintering under predetermined conditions (for example, 1100 ° C.) to produce a sintered magnet (see Patent Document 1).

  By the way, among rare earth elements appropriately mixed at the time of blending, Dy and Tb have a magnetic anisotropy of 4f electrons larger than Nd, and have a negative Stevens factor like Nd, so that the main phase crystal magnetism. It is known that the anisotropy is greatly improved. However, when Dy or Tb is added at the time of producing a sintered magnet, Dy and Tb have a spin arrangement opposite to Nd in the main phase crystal lattice. Since the ferrimagnetic structure is adopted, the magnetic field strength, and hence the maximum energy product showing the magnetic characteristics, is greatly reduced.

  As a solution to such a problem, using a sintered magnet obtained by powder metallurgy, this sintered magnet and a metal evaporation material containing at least one of Dy and Tb are separated from each other and stored in a processing chamber, The processing box is heated in a vacuum atmosphere to evaporate the metal evaporation material, the evaporated metal atoms are attached to the surface of the sintered magnet, and the attached metal atoms are attached to the sintered magnet surface by a thin film made of a metal evaporation material. It has been proposed by the present applicant (International Application PCT / JP2007 / 066272) to perform a treatment (vacuum vapor treatment) for diffusing into the crystal grain boundaries and / or grain boundary phases of the sintered magnet before the sinter is formed. ).

However, if the process for obtaining a sintered magnet by liquid phase sintering as described above and the vacuum vapor treatment process for improving or recovering the magnetic properties such as coercive force are carried out by separate processing devices, the production facilities increase. In addition, since the process is performed for several hours (heating) in each step, high mass productivity cannot be achieved, and the production cost increases.
Japanese Unexamined Patent Application Publication No. 2004-6761 (for example, see the description of the prior art)

  In view of the above points, the present invention provides a method for manufacturing a sintered body that can be manufactured at a low cost with high mass productivity while enhancing product functions such as improvement of magnetic properties of a permanent magnet (sintered body). There is a particular problem.

  In order to solve the above-described problems, the method for producing a sintered body of the present invention includes a step of obtaining a molded body by compression molding raw material powder, and heating the molded body by placing the molded body in a processing chamber. The evaporation material disposed in the processing chamber is evaporated, the evaporated metal atoms are attached to the surface of the compact, and liquid phase sintering is performed while diffusing the attached metal atoms to the crystal grain boundary and / or the crystal grain boundary phase. And a process.

  According to the present invention, liquid phase sintering (sintering process) is the same as diffusing the evaporated specific metal element into the crystal grain boundary and / or crystal grain boundary phase (vacuum vapor treatment process). Since it is performed simultaneously in the processing chamber, it can be manufactured with high mass productivity and low cost while enhancing the product functions such as improvement of the magnetic characteristics of the permanent magnet (sintered body). At that time, since the compact during the liquid phase sintering is not densified, the metal atoms are easily diffused, and the treatment time can be shortened compared to the case where the metal atom diffusion treatment step is performed after the sintering step. Contributes to improving mass productivity.

  In the present invention, the raw material powder is for an Nd—Fe—B based sintered magnet, obtained by pulverizing a raw material alloy produced by a strip casting method or a centrifugal casting method, and the evaporating material. Is optimal for producing a high performance magnet if it contains at least one of Dy and Tb.

  According to this, a permanent magnet (sintered body) is obtained in which the compact is compacted by liquid phase sintering and at the same time the metal atoms of Dy and Tb are diffused into the crystal grain boundaries and crystal grain boundary phases. As a result, it has a Dy-rich phase (phase containing Dy in the range of 5 to 80%) in the crystal grain boundary or the crystal grain boundary phase, and further, Dy diffuses only near the surface of the crystal grain. A permanent magnet having effectively improved or recovered coercive force is obtained.

  In this case, when the evaporating material is evaporated, the evaporating material is prevented from adhering directly to the molded body. Therefore, when the molded body and the evaporating material are arranged in the same processing chamber, they are arranged apart from each other It is preferable to do.

  Moreover, the said molded object may be arrange | positioned and the heating temperature in a process chamber should just be set to the range of 900 to 1150 degreeC. When the temperature is lower than 900 ° C., sintering cannot be performed, and when the temperature exceeds 1150 ° C., the magnetic characteristics deteriorate due to abnormal grain growth of the magnet crystal grains.

  Furthermore, the magnetic properties of the permanent magnet may be further improved as long as it further includes a step of performing a heat treatment on the sintered body at a temperature lower than the heating temperature.

  A processing chamber in which the molded body and the evaporation material are arranged is constituted by a box, and W, Nb, V, Ta are used as spacers for separating the molded body and the evaporation material from each other in the box and the box. A material selected from yttria or an alloy thereof may be used.

  Hereinafter, a method for producing a sintered body according to an embodiment of the present invention will be described with reference to the drawings, taking as an example the case of producing a permanent magnet (Nd—Fe—B based sintered magnet). First, 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 05 mm 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. .

  Next, the produced alloy raw material is coarsely pulverized by a known hydrogen pulverization step, then finely pulverized in a nitrogen gas atmosphere by a jet mill fine pulverization step, and is a raw material powder that is polarized in a magnetic field having an average particle diameter of 3 to 10 μm. A raw material powder is obtained. And raw material powder is orientated in a magnetic field using a well-known compression molding machine, and is compression-molded to a predetermined shape. And a sintering process and a vacuum steam processing process are performed simultaneously with respect to the molded object taken out from the compression molding machine. Below, the vacuum steam processing apparatus which performs the said sintering process and a vacuum steam processing process simultaneously is demonstrated using FIG.1 and FIG.2.

The vacuum vapor processing apparatus 1 has a vacuum chamber 3 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. In the vacuum chamber 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 an electric heater having a Mo-made filament 42. The filament 42 is energized from a power source (not shown) and is heated by a resistance heating type. The space 5 in which the processing box 7 is enclosed can be heated. In this space 5, for example, a mounting table 6 made of Mo is provided, and at least one processing box 7 can be mounted.

The processing box 7 includes a rectangular parallelepiped box portion 71 whose upper surface is opened and a lid portion 72 that is detachable from 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 vacuum chamber 3 is defined. Then, a predetermined pressure of the vacuum chamber 3 by actuating the evacuating means 2 (e.g., 1 × 10 -5 ^Pa) until the depressurizing substantially semi orders of magnitude higher pressure than the process chamber 70 is a vacuum chamber 3 (e.g., 5 × 10 ^{- The} pressure is reduced to ⁴ Pa). As a result, the inside of the processing chamber 70 can be appropriately reduced to a predetermined vacuum pressure without the need for additional evacuation means. In this case, the volume of the processing chamber 70 is set so that metal atoms in the vapor atmosphere are supplied to the shaped body S from a plurality of directions directly or repeatedly in consideration of the mean free path of the evaporation material v. Yes.

  Further, a spacer 8 formed by assembling a plurality of wire rods 81 made of Mo (for example, φ0.1 to 10 mm) in a lattice shape is formed at a predetermined height position from the bottom surface of the processing box 70. A plurality of molded bodies S can be arranged side by side, and the molded body S and the evaporation material v are separated from each other in the processing chamber 70 (see FIG. 2). On the other hand, the evaporation material v is appropriately disposed on the bottom surface, side surface, top surface, or the like of the processing chamber 70 in a state of being stored directly or in the mesh-like containers 9a and 9b. This prevents the molded body S and the evaporation material v from contacting each other in the processing box 7 (the containers 9a and 9b play the same role as the spacer 8).

  Here, as the evaporating material v, Dy and Tb that greatly improve the magnetocrystalline anisotropy of the main phase, or an alloy in which these are mixed with a metal that further increases the coercive force such as Nd, Pr, Al, Cu, and Ga ( Dy or Tb mass ratio is 50% or more), and after blending the above metals at a predetermined mixing ratio, for example, after melting in an arc melting furnace, granular (φ0.1 to 10 mm) or flaky (0 0.03 to 1.00 mm).

The processing box 7 and the spacer 8 (including the container when the evaporation material v is placed in the mesh-like containers 9a and 9b) are made of W, Nb, V, Ta, yttria (Including rare earth-added Mo alloys and the like). Thereby, it can prevent reacting with evaporated Dy and Tb, adhering to the surface, and forming a reaction product. Incidentally, CaO, Y 2 _{O 3,} or either fabricated from rare earth oxide, or may be constructed of these materials from those deposited as lining film on the surface of another heat-insulating material.

Next, a method for manufacturing a permanent magnet (sintered body) will be described using the vacuum vapor processing apparatus 1 and Dy as the evaporation material v as an example. The molded bodies S and Dy produced as described above are arranged apart from each other in the box portion 71, the lid portion 72 is attached to the opened upper surface of the box portion 71, and then the heating means 4 in the vacuum chamber 3. The processing box 7 is installed on the table 6 in the space 5 surrounded by (see FIG. 1). Then, the vacuum chamber 3 is evacuated and reduced in pressure until it reaches a predetermined pressure (for example, 1 × 10 ⁻⁴ Pa) via the vacuum evacuation means 2 (the processing chamber 70 is evacuated to a pressure approximately half digit higher). ) When the vacuum chamber 3 reaches a predetermined pressure, the heating means 4 is operated to heat the processing chamber 70. At this time, the temperature of the processing chamber 70 may be increased stepwise and held at a predetermined temperature (for example, 200 ° C., 500 ° C., 800 ° C.) for a certain period of time to perform a debinding process or a degassing process. preferable.

  When the temperature in the processing chamber 70 reaches a predetermined temperature under reduced pressure, the Dy in the processing chamber 70 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. The When Dy starts to evaporate, the molded body S and Dy are arranged so as not to contact each other, so that the melted Dy does not directly adhere to the molded body S. Then, Dy atoms in the Dy vapor atmosphere diffused in the processing box 70 are supplied from a plurality of directions, directly or repeatedly, toward the substantially entire surface of the compact S heated to substantially the same temperature as Dy. Attached. Thereby, the liquid phase sintering (sintering process) and the diffusion of evaporated Dy to the crystal grain boundary and / or the crystal grain boundary phase (vacuum vapor processing process) are performed simultaneously in the same processing chamber 70. Done.

Here, in order to perform liquid phase sintering and Dy atom diffusion simultaneously, the temperature of the processing chamber 70 is set to 900 ° C. to 1150 ° C. (for example, when the processing chamber temperature is 900 ° C. to 1000 ° C., saturated steam of Dy) The pressure is set in a range of about 1 × 10 ⁻² to 1 × 10 ⁻¹ Pa). When the temperature is lower than 900 ° C., sintering cannot be performed, and when the temperature exceeds 1150 ° C., the magnetic characteristics deteriorate due to abnormal grain growth of the magnet crystal grains.

  As a result, a permanent magnet (sintered body) is obtained in which the compact S is densified by liquid phase sintering and at the same time Dy atoms are diffused into the grain boundaries and the grain boundary phases. As a result, it has a Dy-rich phase (phase containing Dy in the range of 5 to 80%) in the crystal grain boundary or the crystal grain boundary phase, and further, Dy diffuses only near the surface of the crystal grain. A permanent magnet whose coercivity is effectively improved or recovered can be obtained.

  Next, after the vacuum vapor treatment is performed for a predetermined time (for example, 0.5 to 8 hours), the operation of the heating unit 4 is stopped, and an inert gas is introduced through a gas introduction unit (not shown) (for example, 10 kPa), the evaporation of the evaporation material v is stopped. Then, after the temperature in the processing chamber 70 is temporarily lowered to, for example, 500 ° C., the heating unit 4 is operated again while stopping the introduction of the inert gas and evacuating, so that the temperature in the processing chamber 70 is increased from 450 ° C. Heat treatment is performed in order to further improve or recover the coercive force by setting the temperature within a range of 650 ° C. Finally, the processing chamber 70 is cooled, and the produced permanent magnet is taken out from the processing chamber 70 together with the processing box 7.

  In the present embodiment, the spacer 8 is described as an example of a structure in which wires are assembled in a lattice shape. However, the spacer 8 is not limited to this and is formed while allowing the passage of evaporated metal atoms. As long as the body S and the evaporating material S are separated from each other, for example, the spacer 8 (the containers 9a and 9b for storing the evaporating material v) may be formed of a so-called expanded metal regardless of the form.

  In the present embodiment, the example using Dy as the evaporation material v has been described as an example, but Tb having a low vapor pressure at the liquid phase sintering temperature can be used. In this case, the processing chamber 70 may be heated in the range of 950 ° C to 1150 ° C. When the temperature is lower than 950 ° C., Tb is not effectively supplied to the surface of the sintered magnet S, and when the temperature exceeds 1150 ° C., the magnetic characteristics deteriorate due to abnormal grain growth of the magnet grains. .

  Further, in the present embodiment, the description has been given of the case in which the lid 72 is attached to the upper surface of the box portion 71 to constitute the processing box 7, but the processing chamber 7 is isolated from the vacuum chamber 3 and the vacuum chamber 3 is decompressed. For example, after the evaporation material v and the molded body S are stored in the box portion 71, the upper surface opening is covered with, for example, a foil made of Mo. You may do it. On the other hand, for example, the processing chamber 70 may be sealed in the vacuum chamber 3 and may be configured to be maintained at a predetermined pressure independently of the vacuum chamber 3.

  In the present embodiment, the manufacture of the permanent magnet S has been described as an example. However, a specific metal element is diffused into the crystal grain boundary and / or the crystal grain boundary phase while being sintered in a liquid phase, and sintered. As long as the function of the bonded body is improved, the method for manufacturing a sintered body of the present invention can be applied. For example, SiC carbide material is mixed with silicon carbide (SiC) powder and C powder (carbon black) at a predetermined mass ratio and pulverized to obtain a raw material powder. A molded body is formed by compression molding. Next, liquid phase sintering is performed while supplying silicon by vacuum evaporation using the vacuum vapor processing apparatus 1. Thereby, since a strong binder phase of Si and SiC is formed at the crystal grain boundary, a cemented carbide material having a mechanical strength, in particular, a high toughness value can be produced.

  In Example 1, a raw material powder for an Nd—Fe—B based sintered magnet was prepared as follows, and a forming process was performed while aligning using a known automatic transverse magnetic field pressing device to prepare a compact S. Then, using the vacuum vapor processing apparatus shown in FIG. 1, liquid phase sintering and Dy diffusion were simultaneously performed on the compact to obtain a permanent magnet (sintered magnet).

  <Raw material powder> The composition is 28 (Nd + Pr) -1Co-0.1Cu-0.1Hf-0.1Ga-0.98B-bal. An ingot (alloy raw material) was prepared by centrifugal casting in a vacuum induction melting furnace using a material of Fe (average thickness is 30 mm). The ingot was pulverized with hydrogen in a hydrogen atmosphere at 1 atm for 5 hours (hydrogen pulverization step), then dehydrogenated at 600 ° C. for 5 hours and cooled.

Next, the cooled product was pulverized using a jet mill pulverizer under a pressure of 8 kg / cm ² for 1 hour (jet mill pulverization step). This obtained the raw material powder with an average particle diameter of 2.8 micrometers (FSS measured value).

<Molding Step> After filling the cavity of the press apparatus with the raw material powder, the magnetic field was oriented while applying a static magnetic field of 20 k0 e at the maximum, and compression molding was performed (molding step). The molding pressure in this case was set to 1.0 t / cm ² . And after the compression molding, a 4 k0e reverse magnetic field was applied to demagnetize. Thereafter, a molded body S formed into a rectangular parallelepiped shape having a length of 75 mm, a width (magnetic field orientation direction) of 75 mm, and a height of 50 mm was taken out of the cavity 22.

  <Sintering Step and Vacuum Vapor Treatment Step> Using the vacuum vapor treatment apparatus 1 shown in FIG. 1, the molded bodies S (four pieces each) produced as described above were accommodated in treatment boxes 7 made of different materials. . In this case, 0.5 mm flaky Dy (purity 99.5%) was used as the evaporation material v, and Dy was placed in each processing box 7 in a total amount of 10 g. In this case, Dy is disposed on the bottom surface of the processing box 7 and is stored in a mesh material made of the same material as the processing box 7 on the upper side and the side surface of the molded body S (thereby, the molded body S and Dy). Are separated from each other). Thus, the processing box in which Dy and the molded object S were set, respectively, was placed in the vacuum chamber 3 (16 boxes) together with the one not containing the evaporation material made of Dy (comparative example).

Next, the vacuum chamber 3 was evacuated, and after the pressure reached 10 ⁻⁵ Pa, the heating means 4 was operated to start heating the processing chamber 70. In this case, when the temperature in the processing chamber 70 reaches 200 ° C., 500 ° C., and 800 ° C. under a pressure of 10 ⁻⁵ Pa to 20 kPa in the temperature rising process, vacuum debinding and degassing treatment are performed for 60 minutes, respectively. Went. And the temperature of the process chamber 70 was raised to 950 degreeC (vapor pressure of 0.1 kPa of Dy), and the sintering process and the vacuum steam process process were implemented for 4 hours.

  Next, after the above process, the operation of the heating means 4 is stopped, the temperature in the processing chamber 70 is subjected to heat treatment at 800 ° C., 2 hours, 500 ° C., 3 hours, and then cooled to room temperature, and then the processing box 7 from the vacuum chamber. Was taken out.

  FIG. 3 shows the average value of the density (measured by the underwater weight method) and magnetic properties (measured by the BH curve tracer) of the magnet cut out from the central part of the permanent magnet taken out from the processing box 7 in a size of φ10 × 10 mm. It is a table | surface which shows. According to this, when the material of the processing box and the spacer is any one of Mo, W, Nb, V, Ta, and yttria, the adhesion of the molded body S to the spacer is not confirmed, and the density is about 7. It can be seen that a permanent magnet that is a dense sintered body at 5 g / cc or more is obtained, and that a high-performance magnet having a high coercive force of 17 kOe or more is obtained. When the material of the processing box or spacer is made of SUS or the like, the molded body is welded. On the other hand, when it is made of alumina or the like used in a general vacuum processing apparatus, the molded body adheres to the spacer, Moreover, it turns out that the coercive force has not been improved effectively.

  In Example 2, SiC powder having an average particle diameter of 7 μm and C powder (carbon black) were mixed in an attritor at a molar ratio of 10: 1.

Next, using a molding machine having a known structure, the mixed powder was set at 1.5 t / cm ² and compression molded to obtain a molded body.

Next, the molded body S was accommodated in a quartz processing box 7 using the vacuum vapor processing apparatus shown in FIG. In this case, 0.5 mm flakes (flakes) Si (purity 99.9%) was used as the evaporation material v, and Si was disposed on the bottom surface of each processing box 7 in a total amount of 10 g. Thus, the processing box in which Si and the compact were set was placed in the vacuum chamber 3. Then, after the vacuum chamber 3 is evacuated and the pressure reaches 10 ⁻⁵ Pa, the heating means 4 is operated to start heating the processing chamber 70, and the processing chamber 70 is heated under a pressure of 10 ⁻² Pa. Was heated to reach 1400 ° C., and a sintering process and a vacuum steam treatment process were performed for 6 hours. Finally, it was cooled to room temperature and the processing box was removed from the vacuum chamber.

  FIG. 4 is a table showing the bending strength (measured by an Instron universal testing machine) and fracture toughness value (measured by a Charpy impact test) of a sintered body (SiC) cemented carbide material taken out from the processing box, A value in the case of liquid phase sintering without adding Si metal into the processing box is also shown (comparative example). According to this, it turns out that the sintered compact obtained in Example 2 has about 5 times the bending strength, and the fracture toughness value is also about twice.

Sectional drawing which shows schematically the vacuum processing apparatus which implements the process of this invention. The perspective view which illustrates typically the accommodation of the molded object and evaporation material to a processing box. 2 is a table showing the magnetic characteristics of the permanent magnet produced in Example 1. The table | surface which shows the mechanical characteristic of the sintered compact produced in Example 2. FIG.

Explanation of symbols

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 S Molding body M Permanent magnet v Metal evaporation material

Claims (6)

A step of compression molding raw material powder to obtain a molded body;
The molded body is placed in a processing chamber and heated, and evaporation material disposed in the same or another processing chamber is evaporated, the evaporated metal atoms are attached to the surface of the molded body, and the attached metal atoms are crystallized. And a liquid phase sintering process while diffusing into the boundary and / or grain boundary phase.   2. The method for manufacturing a sintered body according to claim 1, wherein when the molded body and the evaporating material are disposed in the same processing chamber, they are disposed apart from each other.   The raw material powder is for an Nd—Fe—B based sintered magnet, obtained by pulverizing a raw material alloy produced by a strip casting method or a centrifugal casting method, and the evaporating materials include Dy and Tb. The method for producing a sintered body according to claim 1, comprising at least one of the following.   The method for producing a sintered body according to claim 3, wherein the heating temperature in the processing chamber in which the compact is disposed is set in a range of 900 ° C to 1150 ° C.   The method for producing a sintered body according to claim 3, further comprising a step of heat-treating the sintered body at a temperature lower than the heating temperature. A processing chamber in which the molded body and the evaporation material are arranged is constituted by a box, and W, Nb, V, Ta, and yttria are used as spacers for separating the molded body and the evaporation material from each other in the box and the box. Or the thing selected from these alloys is used, The manufacturing method of the sintered compact of any one of Claim 3 thru | or 4 characterized by the above-mentioned.

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