Method for manufacturing a green compact and a sintered compact

Abstract

To provide a method of producing a green compact and a method of manufacturing a sintered body, capable of reducing variations in components of a Ti-Al based green compact or sintered body.SOLUTION: A method of producing a green compact according to the present invention produces a green compact containing titanium, aluminum and other metal elements. The method includes the steps of: preparing a material powder including a titanium powder, an aluminum powder and a master alloy powder containing aluminum and the other metal elements; charging the material powder in a resin mold; and subjecting the mold charged with the material powder to cold isotropic pressurization. The other metal elements in the master alloy powder have a content equal to or higher than a content of aluminum on a mass basis. The master alloy powder is a pulverized powder, and the aluminum powder has an average aspect ratio of 1.38 or greater and 3.00 or smaller.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a green compact containing titanium, aluminum and other metal elements, and a method for producing a sintered compact. [Background technology]

[0002] Titanium alloys have been considered for use in various components due to certain excellent properties such as fatigue resistance, corrosion resistance, light weight and high specific strength. However, the production of titanium alloy products generally requires a number of processes, such as melting by electron beam melting or vacuum arc melting, casting, and in some cases further forging, rolling, heat treatment, machining, welding, etc., which increases the manufacturing cost. Due to such high costs, it is difficult to say that the range of applications of titanium alloys has been sufficiently expanded.

[0003] Under these circumstances, in recent years, a powder metallurgy method has been attracting attention as a so-called near-net shape method, in which a raw material powder containing titanium and alloying elements is filled into a resin mold and the mold filled with the raw material powder is subjected to cold isostatic pressing to obtain a green compact of a predetermined shape. In powder metallurgy, after cold isostatic pressing, sintering and / or hot isostatic pressing may be performed as necessary to form a sintered body and increase the density.

[0004] An example of this type of technology is described in Patent Document 1. Patent Document 1 discloses "a method for producing a metal powder compact having a recess, the method including a step of cold isostatically pressing raw material powder filled into a resin mold in a state in which a resin core material having a shape corresponding to the recess is positioned in the resin mold at a location corresponding to the recess." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2021 / 060363 Summary of the Invention [Problem to be solved by the invention]

[0006] Titanium alloys include, for example, Ti-Al alloys containing aluminum and other metal elements such as vanadium or iron. One example is the Ti-6Al-4V alloy, which contains vanadium as the other metal element. When producing a Ti-Al compact or sintered compact, it is possible to use a raw material powder containing titanium powder and a master alloy powder containing aluminum and other metal elements.

[0007] Here, the above-mentioned master alloy powders containing more aluminum than other metal elements by mass are relatively expensive and difficult to obtain consistently on the market. Therefore, in the production of Ti-Al-based green compacts or sintered compacts, it is preferable to use a master alloy powder in which the content of other metal elements is equal to or greater than the content of aluminum, from the viewpoints of reducing costs and realizing stable production. In this case, depending on the composition of the green compact or sintered compact to be produced, the raw material powder may further contain aluminum powder in addition to the titanium powder and the master alloy powder described above.

[0008] It was discovered that when ordinary aluminum powder is used, the raw powder becomes unevenly distributed within the mold when it is filled into the mold, resulting in variations in the composition or components of the green compact or sintered compact, impairing homogeneity.

[0009] An object of the present invention is to provide a method for producing a Ti-Al based green compact or sintered compact, which can suppress variations in the components of the green compact or sintered compact, and a method for producing a sintered compact. [Means for solving the problem]

[0010] As a result of extensive research, the inventors have found that by using at least the master alloy powder as a pulverized powder and further using aluminum powder with an average aspect ratio of 1.38 or more and 3.00 or less, it is possible to suppress the uneven distribution of particles in the raw material powder within the mold.

[0011] Conventional aluminum powders are often spherical in shape, produced by atomization or the like. If such aluminum powder is mixed with titanium powder and a master alloy powder that is not a pulverized powder to produce a raw powder, the aluminum powder, which is spherical and has a smaller specific gravity than the titanium powder and master alloy powder, tends to flow easily within the raw powder, causing uneven distribution.

[0012] In contrast, if at least the master alloy powder is pulverized and an aluminum powder having an aspect ratio within the above range is used, the flow of the aluminum powder in the raw material powder is suppressed, and it is thought that the occurrence of uneven distribution in the raw material powder is reduced, making it possible to obtain a Ti-Al-based green compact or sintered compact with a uniform composition.

[0013] The method for producing a powder compact of the present invention is a method for producing a powder compact containing titanium, aluminum, and other metal elements, and includes the steps of preparing a raw material powder containing titanium powder, aluminum powder, and a master alloy powder containing aluminum and the other metal elements, filling the raw material powder into a resin mold, and cold isostatic pressing the mold filled with the raw material powder, wherein the content of the other metal elements in the master alloy powder is equal to or greater than the content of aluminum on a mass basis, the master alloy powder is a pulverized powder, and the average aspect ratio of the aluminum powder is 1.38 or more and 3.00 or less.

[0014] The titanium powder is preferably a crushed powder.

[0015] The raw material powder preferably satisfies at least one condition selected from the group consisting of the following (1) to (4). (1) The average particle size D50 of the titanium powder is 20 μm or more and 80 μm or less. (2) The average particle size D50 of the master alloy powder is 10 μm or more and 80 μm or less. (3) The particle size of 90% or more of the aluminum powder by mass is in the range of 20 μm or more and 90 μm or less. (4) The average circularity of the aluminum powder is 0.60 or more and 0.75 or less.

[0016] The aluminum powder is preferably produced by cutting foil or by press-molding powder.

[0017] The mold may be made of a thermoplastic resin having a Shore D hardness of 30 or more and 120 or less.

[0018] The mold may be a mold produced using a three-dimensional modeling device.

[0019] The method for producing a sintered body of the present invention includes a step of heating and sintering a powder compact produced by any of the above-described methods for producing a powder compact. [Effects of the Invention]

[0020] According to the present invention, variations in the components of Ti-Al based compacts or sintered bodies can be suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described in detail. A method for producing a powder compact according to one embodiment of the present invention produces a powder compact containing titanium, aluminum, and other metal elements, i.e., a so-called Ti-Al-based powder compact. This method includes the steps of preparing a raw material powder containing titanium powder, aluminum powder, and a master alloy powder containing aluminum and other metal elements, filling a resin mold with the raw material powder, and cold isostatic pressing the mold filled with the raw material powder. Furthermore, a method for producing a sintered body according to one embodiment includes the step of heating and sintering the powder compact produced by the method for producing a powder compact, such as by sintering and / or hot isostatic pressing.

[0022] The raw material powder is obtained by mixing titanium powder, aluminum powder, and master alloy powder. The master alloy powder has a mass content of other metal elements equal to or greater than the aluminum content. Such master alloy powder is relatively inexpensive and can be obtained reliably. However, since the mass content of other metal elements in the master alloy powder is equal to or greater than the aluminum content, when attempting to produce a Ti-Al-based compact or sintered body having a higher aluminum content than the other metal elements, such as a Ti-6Al-4V alloy, it may be necessary to add aluminum powder in addition to the titanium powder and master alloy powder, as in this embodiment, to adjust the composition to the desired one.

[0023] Here, aluminum powder has a smaller specific gravity than titanium powder and is generally smaller than master alloy powder. In particular, when such aluminum powder is mixed with raw powder together with titanium powder and master alloy powder and then filled into a mold, it tends to flow and become unevenly distributed within the raw powder within the mold. The uneven distribution of aluminum powder within the raw powder within the mold leads to variations in composition in the green compact obtained by subsequent cold isostatic pressing and in the sintered compact obtained after sintering and / or hot isostatic pressing.

[0024] In contrast, in this embodiment, at least the master alloy powder is a pulverized powder, and the average aspect ratio of the aluminum powder is set to 1.38 or more and 3.00 or less. By using aluminum powder with a relatively large aspect ratio in combination with pulverized master alloy powder, uneven distribution of the aluminum powder is effectively suppressed even when the raw material powder is filled into a mold and then tapped. As a result, a Ti-Al-based green compact or sintered compact with excellent homogeneity of the metal elements can be obtained.

[0025] (Raw material powder) The raw material powder is obtained by mixing titanium powder, aluminum powder, and master alloy powder containing aluminum and other metal elements. The raw material powder may further contain other master alloy powders, alloy element powders, etc.

[0026] By using such raw material powders, it is possible to produce titanium alloy green compacts and sintered compacts made of, for example, Ti-5Al-1Fe, Ti-5Al-2Fe, Ti-6Al-4V, Ti-3Al-2.5V, etc. Note that the numbers before the element symbols of the alloying elements indicate the content (mass%). For example, "Ti-6Al-4V" means a titanium alloy containing 6 mass% Al and 4 mass% V.

[0027] Although titanium powder may inevitably contain impurities, it primarily contains titanium, and the titanium content is preferably 99% by mass or more. Specific examples of titanium powder include hydrogenated / dehydrogenated titanium powder (so-called HDH powder) obtained by hydrogenating and pulverizing sponge titanium, etc., followed by dehydrogenation, and hydrogenated titanium powder that is not dehydrogenated after the pulverization. Titanium powder may contain hydrogen at 5% by mass or less. When titanium powder contains hydrogen, it can be dehydrogenated before sintering the green compact, or dehydrogenation and sintering can be performed simultaneously in a single heat treatment. Furthermore, the hydrogen can be removed during the heating process for sintering.

[0028] The master alloy powder contains aluminum and other metal elements. Here, the other metal elements may be, for example, at least one selected from the group consisting of vanadium and iron. The master alloy powder typically contains aluminum and vanadium, or aluminum and iron, but is not limited thereto.

[0029] The master alloy powder has a mass content of other metal elements equal to or greater than the mass content of aluminum. Master alloy powders with a higher aluminum content than the mass of other metal elements can be difficult to obtain or produce, making them difficult to prepare consistently. For example, the master alloy powder may have an aluminum content of 15% by mass or more and 50% by mass or less, preferably 40% by mass or more and 50% by mass or less, and a mass content of other metal elements of 50% by mass or more and 85% by mass or less, preferably 50% by mass or more and 60% by mass or less.

[0030] Of the titanium powder and master alloy powder described above, at least the master alloy powder is a pulverized powder. The particles of the pulverized powder are often polyhedral. By using the pulverized master alloy powder, combined with the relatively large aspect ratio of the aluminum powder, as described below, uneven distribution of each powder in the raw powder in the mold is effectively suppressed. The titanium powder may be composed of spherical particles produced by a method other than pulverization, but preferably, the titanium powder is also a pulverized powder. A pulverized powder is a powder produced by pulverizing a lump or the like. For example, the aforementioned HDH titanium powder and titanium hydride powder are examples of pulverized titanium powder. The pulverized master alloy powder may be produced by pulverizing an ingot.

[0031] The aluminum powder is mainly composed of aluminum, and the aluminum content is preferably 99% by mass or more. The aluminum powder may contain impurities, but the impurity content is preferably less than 1% by mass.

[0032] The aluminum powder has an average aspect ratio (also referred to as the "average aspect ratio") of 1.38 or more and 3.00 or less. If the average aspect ratio of the aluminum powder is less than 1.38, there is a concern that uneven distribution of each powder may not be sufficiently suppressed when the raw material powder is filled into a mold. On the other hand, if the average aspect ratio of the aluminum powder exceeds 3.00, there is a risk that the effect of suppressing uneven distribution of the alloy component powder may not be fully exerted. From this perspective, the average aspect ratio of the aluminum powder is preferably 1.40 or more and 2.00 or less, more preferably 1.42 or more and 1.50 or less. In such aluminum powder, each particle often has a flake shape, such as a scale shape.

[0033] The average aspect ratio of aluminum powder is determined as follows. First, a particle shape image analyzer PITA-04 (manufactured by Seishin Enterprise Co., Ltd.) is used to obtain a projected image of aluminum powder particles dispersed in isopropyl alcohol (IPA) as a dispersion medium. The pump speed at this time can be set to 2000 Hz. Then, on the image, the maximum length between two points on the outline of the projected image is measured as the major axis L, and the minimum length in the direction perpendicular to the major axis is measured as the minor axis d. The aspect ratio of the aluminum powder particles is calculated as L / d by dividing the major axis L by the minor axis d. The aspect ratio (L / d) is calculated for approximately 10,000 aluminum powder particles, and the average value is taken as the average aspect ratio.

[0034] The average circularity of the aluminum powder may be, for example, 0.60 or more and 0.75 or less. The circularity is the ratio of the perimeter of a circle with an area equal to the area of the projected image of a particle measured using an electron microscope to the perimeter of the projected image of the particle. The average circularity is calculated by 4πA / P, where P is the perimeter of the projected image of the particle and A is the projected area. 2 The average circularity is calculated by pouring particles into a cell together with a carrier liquid, taking images of a large number of particles with a CCD camera, and calculating the circularity (4πA / P) for each particle from approximately 10,000 individual particle images. 2 ) is calculated and the average value of the circularity of each particle is obtained.

[0035] As the aluminum powder described above, commercially available products can be purchased and used. Aluminum powder can be produced, for example, by finely cutting a relatively thin aluminum foil, or by flattening aluminum powder produced by an atomization method or the like through press processing. Aluminum powder produced simply by an atomization method such as gas atomization or water atomization tends to be substantially spherical and have an average aspect ratio outside the above-mentioned range. However, the aluminum powder is not limited to a specific production method as long as the average aspect ratio is within the specified range.

[0036] The average particle size D50 of the titanium powder is preferably 20 μm or more and 80 μm or less. If the average particle size D50 of the titanium powder is 20 μm or more, it is expected that an increase in the oxygen content can be reduced, and if it is 80 μm or less, it is expected that a decrease in packing density can be suppressed. The average particle size D50 of the master alloy powder is preferably 10 μm or more and 80 μm or less. If the average particle size D50 of the master alloy powder is 10 μm or more, it is possible to reduce the increase in oxygen content and to suppress the occurrence of uneven distribution due to extreme particle size differences, and if it is 80 μm or less, it is thought that it is possible to prevent local concentration of components due to insufficient diffusion of coarse particles. It is also preferable that 90% or more of the aluminum powder has a particle size of 20 μm or more and 90 μm or less by mass. When the particle size of the aluminum powder is 20 μm or more, it is thought that the effect of suppressing uneven distribution of alloying components can be exerted, and when it is 90 μm or less, it is thought that local concentration of components due to insufficient diffusion of coarse particles can be suppressed.

[0037] The average particle size D50 refers to the particle size D50 (median diameter) of the particle size distribution (volume basis) obtained by the laser diffraction scattering method. The particle size refers to the size of the openings of a "metal mesh sieve" as specified in JIS Z8801-1:2006. A particle size in the range of 20 μm or more and 90 μm or less means that the particles pass through a 20 μm opening sieve and are undersized on a 90 μm opening sieve. If 90% or more of the particles pass through a 20 μm opening sieve and are undersized on a 90 μm opening sieve, the particle size is considered to be "in the range of 20 μm or more and 90 μm or less."

[0038] (mold) The mold into which the raw material powder is filled has an internal space having a shape corresponding to the outer shape of the green compact or sintered body to be finally produced. When producing a green compact or sintered body having a recess such as a through-hole, a core or a core having a shape corresponding to the recess may be placed in the mold before or after filling the mold with the raw material powder. The shapes of the mold and core can be changed as appropriate depending on the shape of the green compact or sintered body.

[0039] The raw material powder can be filled into the mold through the opening of the mold by tapping, etc. After the raw material powder is filled, the opening of the mold is closed and cold isostatic pressing, which will be described later, is carried out.

[0040] In this embodiment, at least the master alloy powder is made into a pulverized powder, and the average aspect ratio of the aluminum powder is set to 1.38 or more and 3.00 or less, so that when the raw material powder is filled into the mold, the uneven distribution of each powder in the raw material powder within the mold is effectively suppressed.

[0041] Here, a mold made of resin is used. More specifically, the mold is preferably made of a thermoplastic resin, and particularly preferably made of an acrylic resin, an acrylic resin containing an elastomer, a polylactic acid (PLA) resin, or the like.

[0042] To ensure the required strength and maintain its shape even when filled with raw material powder, the mold is preferably made of a thermoplastic resin having a Shore D hardness of 30 or more and 120 or less, or may be made of a thermoplastic resin having a Shore D hardness of 30 or more and 85 or less. The Shore D hardness can be measured by a test method conforming to JIS K7215-1986. From the same viewpoint, the thickness of the resin mold is preferably 0.5 mm or more and 2.0 mm or less.

[0043] Resin molds can be produced by various methods, but are preferably produced using a three-dimensional modeling device (a so-called 3D printer). This allows molds of various shapes to be easily produced. The modeling method of the three-dimensional modeling device is not particularly limited, and may be, for example, a stereolithography method, an inkjet method, an inkjet powder lamination method, a powder sintering lamination method, a fused deposition modeling method, or a powder bonding method.

[0044] (cold isostatic pressing) After the raw material powder is filled into the mold, the mold is subjected to cold isostatic pressing (CIP). More specifically, the mold filled with the raw material powder is placed inside a cold isostatic pressing device, where the raw material powder inside the mold is compressed by isostatically pressing the mold from the outside. By cold isostatic pressing, the raw material powder in the molding space of the mold is compressed and compacted into a green compact.

[0045] The pressure applied to the mold during cold isostatic pressing is, for example, 300 MPa or more, preferably 400 MPa or more, and more preferably 450 MPa or more. A pressure of 300 MPa or more sufficiently compresses the raw material powder, making it easier to obtain a green compact with the desired shape precision. The pressure may be, for example, 600 MPa or less, typically 500 MPa or less. The holding time at such a pressure may be, for example, 0.5 to 30 minutes.

[0046] In cold isostatic pressing, the mold is isostatically (hydrostatically) pressed by the surrounding fluid. Therefore, cold isostatic pressing allows the use of molds of various shapes. In addition, since the resin mold deforms appropriately when subjected to the isostatic pressure of the fluid, green compacts of various shapes can be produced.

[0047] (heat sintering) When producing a sintered body, a step of heating the green compact after cold isostatic pressing to sinter the particles that make up the green compact is included, thereby producing a sintered body.

[0048] In this step, the powder compact can be heated without pressure at a temperature of, for example, 1200°C to 1300°C for 1 hour to 12 hours. Alternatively, the powder compact can be subjected to hot isostatic pressing (HIP), for example, by applying an isostatic pressure of about 100 MPa to 200 MPa using a pressure medium such as argon gas at a temperature of, for example, 800°C to 1000°C for 30 minutes to 150 minutes.

[0049] Whether pressureless heating or hot isostatic pressing is performed, sintering of the green compact proceeds by exposing it to a relatively high temperature. When hot isostatic pressing is performed, the pores remaining in the material are crushed and densified by applying gas pressure in a temperature range where the material's deformation resistance is low. Both pressureless heating and hot isostatic pressing may be performed. When both pressureless heating and hot isostatic pressing are performed, the order is not particularly important, but for example, pressureless heating can be performed first, followed by hot isostatic pressing. [Example]

[0050] Next, the methods for producing a green compact and a sintered compact according to the present invention were experimentally carried out, and the effects thereof were confirmed. The following description will be given, however, for the purpose of illustration only and is not intended to be limiting.

[0051] Raw material powders containing titanium powder, aluminum powder, and master alloy powder containing aluminum and vanadium shown in Tables 1 and 2 were filled into a resin mold, and the mold was subjected to cold isostatic pressing to produce a green compact. The green compact was then removed from the mold, heated under vacuum without pressure, and then further subjected to hot isostatic pressing to produce a sintered body.

[0052] In Examples 1 to 12, as shown in Table 2, aluminum powders in Table 1 having an average aspect ratio of 1.45 (the shape of this aluminum powder is sometimes expressed as flaky) were used, and pulverized powders were used from the master alloy powders in Table 1. In Comparative Examples 1 to 36, aluminum powders having an average aspect ratio of 1.09 were used, and / or atomized powders were used as the master alloy powders. That is, in Comparative Examples 1 to 36, at least one of the aluminum powders and the master alloy powders was atomized powder. Note that 90% or more by mass of the flaky aluminum powders were in the range of 20 μm or more and 90 μm or less.

[0053] The mold described above was 1.0 mm thick, had internal dimensions of φ20 mm × 120 mm, was made of PLA (polylactic acid), and had a Shore D hardness of 30 or more and 85 or less. Cold isostatic pressing (hydrostatic pressing) was performed at a pressure of 490 MPa for 1 minute. The end face of the green compact obtained in the mold after cold isostatic pressing, facing the opening filled with the raw material powder, is referred to as Top, and the end face facing the bottom is referred to as Bottom. In the subsequent heat sintering process, the green compact was heated to 1200°C without pressure and held at that temperature for 480 minutes. This was followed by hot isostatic pressing at 900°C and 178 MPa for 120 minutes. This resulted in a sintered rod-shaped compact approximately φ15 mm × 100 mm.

[0054] In all of Examples 1 to 12 and Comparative Examples 1 to 36, the relative density of the green compact after cold isostatic pressing was 88% or more, and the relative density after heating without pressure was 95% or more. Furthermore, the relative density of the sintered body obtained after hot isostatic pressing was 100%. The relative density is calculated by dividing the measured density of the sintered body by the theoretical density and expressing this as a percentage. In obtaining the measured density of the sintered body, the volume of the sintered body was determined by Archimedes' method. The theoretical density for Ti-6Al-4V was 4.43 g / cm. 3 , and 4.48 g / cm for Ti-3Al-2.5V. 3 It was decided.

[0055] To confirm the homogeneity of the sintered body's components, samples measuring approximately 15 mm in diameter and 10 mm in length were cut from three locations: T, approximately 10 mm from the top of the sintered body; B, approximately 10 mm from the bottom; and M, the center between T and B. Each sample was then embedded in resin and polished in a cross section perpendicular to the longitudinal direction of the sintered body. X-ray fluorescence analysis (XRF) was then performed to examine the aluminum and vanadium contents. For this analysis, the X-ray irradiation area was approximately 10 mm in diameter. The maximum and minimum differences between the analytical values for the aluminum and vanadium contents at T, M, and B were calculated, and the maximum difference divided by the minimum difference was used as the homogeneity index (maximum difference / minimum difference). The results are shown in Table 2. The smaller the homogeneity index, the more homogeneous the sample. A homogeneity index of 1.10 or less was considered acceptable, and a homogeneity index of 1.04 or less was considered excellent.

[0056] [Table 1]

[0057] [Table 2]

[0058] The results in Table 2 show that the homogeneity index of the sintered bodies was sufficiently small in all of Examples 1 to 12. This is thought to be because the master alloy powder of the raw material powder was a pulverized powder and the average aspect ratio of the aluminum powder was relatively large, which prevented the raw material powder from becoming uneven when it was filled into the mold.

[0059] On the other hand, in Comparative Examples 1 to 36, the master alloy powder was not a pulverized powder and / or the average aspect ratio of the aluminum powder was small, so the homogeneity index of at least one of the aluminum content and the vanadium content was large.

[0060] From the above, it has been found that the present invention can suppress variations in the components of Ti-Al based green compacts or sintered compacts.

Claims

1. A method for producing a powder compact containing titanium, aluminum, and other metal elements, comprising: preparing raw material powders including titanium powder, aluminum powder, and master alloy powder containing aluminum and the other metal elements; a step of filling the raw material powder into a resin mold; cold isostatic pressing the mold filled with the raw material powder; Including, a content of the other metal element in the master alloy powder that is equal to or greater than the content of aluminum by mass, the master alloy powder being a pulverized powder, and the aluminum powder having an average aspect ratio of 1.38 or more and 3.00 or less.

2. The method for producing a green compact according to claim 1, wherein the titanium powder is a pulverized powder.

3. 3. The method for producing a powder compact according to claim 1, wherein the raw material powder satisfies at least one condition selected from the group consisting of the following (1) to (4): (1) The average particle size D50 of the titanium powder is 20 μm or more and 80 μm or less. (2) The average particle size D50 of the master alloy powder is 10 μm or more and 80 μm or less. (3) The particle size of 90% or more of the aluminum powder by mass is in the range of 20 μm or more and 90 μm or less. (4) The aluminum powder has an average circularity of 0.60 or more and 0.75 or less.

4. The method for producing a powder compact according to any one of claims 1 to 3, wherein the aluminum powder is produced by cutting a foil or by press-molding a powder.

5. 5. The method for producing a powder compact according to claim 1, wherein the mold is made of a thermoplastic resin having a Shore D hardness of 30 or more and 120 or less.

6. The method for producing a powder compact according to any one of claims 1 to 5, wherein the mold is produced using a three-dimensional modeling device.

7. A method for producing a sintered body, comprising the step of heating and sintering a powder compact produced by the method for producing a powder compact according to any one of claims 1 to 6.

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