Manufacturing method of sintered metal powder

Abstract

To provide a method for producing a sintered body of a metal powder, which can suppress the deterioration of a quality of the sintered body, which originates in a discharge gas containing a thermal decomposition product of an organic component, by simple means.SOLUTION: The method for producing the sintered body of the metal powder includes: in a step of preparing a degreased body, arranging a first housing that encloses a molded body and covers the periphery, and a first metal material that is formed from titanium, niobium, or a mixture of titanium and niobium, between the molded body and the first housing; in a step of preparing the sintered body, arranging a second housing that covers the periphery of a degreased body, a third housing that encloses the second housing and covers the periphery, and a second metal material that is formed from titanium, niobium, or a mixture of titanium and niobium, between the second housing and the third housing; and structuring the first housing, the second housing and the third housing, from one or more materials of molybdenum, a molybdenum alloy, tungsten, a tungsten alloy and a ceramic.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for producing a sintered metal powder compact, and more particularly to a method for producing a sintered metal powder compact using a compact made from a mixture containing a metal powder and an organic component. [Background technology]

[0002] Metal injection molding (MIM) is known as one of the methods for manufacturing sintered metal powder bodies. A typical MIM process includes a molding step of producing a green body from a mixture containing metal powder and organic components, a degreasing step of producing a degreased body (brown body) by removing the organic components from the green body, and a sintering step of strongly sintering the metal powder constituting the degreased body to produce a sintered body. If necessary, a pre-sintering step is included in which the metal powder constituting the degreased body is weakly sintered to produce a calcined body, and a sintering step is adopted in which the metal powder constituting the calcined body is further strongly sintered instead of the degreased body to produce a sintered body.

[0003] Many proposals have been made regarding the heating debinding and sintering of general MIM. For example, Patent Document 1 discloses a method in which a heating furnace (graphite furnace) containing graphite as a furnace material is used to heat and debind a metal powder containing a hard-to-reduc element such as Cr (chromium), Mn (manganese) or Si (silicon) and a molded body containing an organic component, and then the molded body is placed on a setter made of ceramics and sintered under high vacuum. The ceramics contain 95% by mass or more of alumina, boron nitride or silicon carbide, which are hard to evaporate under high vacuum.

[0004] For example, Patent Document 2 discloses a method in which a molded body containing a metal powder and an organic component is placed on a ceramic setter, heated and degreased under high vacuum, and sintered under high vacuum. This ceramic is made of oxide-based ceramics that do not easily react with the metal powder, and is laminated on a base material made of graphite, hexagonal boron nitride, aluminum nitride, beryllium oxide, silicon carbide, or a composite of two or more of these that do not easily react with CO gas generated during the heating and degreasing and sintering.

[0005] For example, Patent Document 3 discloses a method in which a compact containing a metal powder and an organic component is placed on a degreasing setter, heated and degreased in the atmosphere, and the degreased body is placed on a sintering setter and sintered under a vacuum with Ar (argon) introduced. The degreasing setter is made of ceramics containing 95% by mass or more of alumina and having a porosity of 50% to 60%. The sintering setter is made of ceramics containing 99% by mass or more of alumina and having a porosity of 10% or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2-057617 [Patent Document 2] Japanese Patent Application Publication No. 4-210405 [Patent Document 3] Japanese Patent Application Publication No. 11-117005 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned MIM debinding process, when the organic components are removed by heating, the organic components are heated to a temperature at which they decompose. For example, if the main organic component is polyolefin-based, the molded body is heated to 420°C or higher, and if it is polystyrene-based, the molded body is heated to 380°C or higher. This heating causes the organic components contained in the molded body to decompose and are released into the furnace as gas containing C (carbon) and O (oxygen). Most of the gasified pyrolysis products (organic components) are discharged outside the furnace, where the pressure has increased due to heating. However, some of the gasified pyrolysis products (organic components) may adhere to and be absorbed by the debound body, or may accumulate in the furnace.

[0008] In the above-mentioned MIM, when a pre-sintering process is included, heating is performed at a lower temperature than in the sintering process, but at a high temperature at which the metal powder begins to densify through sintering. If organic components remain in the degreased body, this heating releases gases containing C and O into the furnace, and also gasifies the deposits in the furnace. At this time, some of the gasified pyrolysis products (organic components) are not discharged from the furnace to the outside, but instead adhere to and are absorbed in the pre-sintered body, or are deposited again in the furnace.

[0009] In the sintering process of MIM described above, heating is performed at a high temperature at which the sintered body made of metal powder reaches an appropriate density (relative density). This high-temperature heating gasifies the deposits in the furnace. Most of the gasified pyrolysis products (organic components) are discharged outside the furnace. However, some of the gasified pyrolysis products (organic components) may adhere to and be absorbed by the sintered body, or may accumulate in the furnace. The pyrolysis products (organic components) that adhere to and are absorbed in the sintered body react with the metal components, forming a sintered body that contains excessive carbides and oxides. Excessive carbides and oxides can cause quality deterioration of the sintered body (for example, a decrease in density and properties).

[0010] Although the problems caused by such gasified organic components (pyrolysis products) were known, no simple means for appropriately controlling the released gas had been proposed. For example, Patent Document 1 takes into consideration the evaporation of ceramic components from the setter, but does not take into consideration the control of the released gas from the compact or deposits in the furnace. For example, Patent Document 2 takes into consideration the reaction of the released gas (CO gas) from the compact with the setter and base material, but does not take into consideration the problem of the CO gas component being absorbed by the degreased body or sintered body, or the control of the released gas from deposits in the furnace. For example, Patent Document 3 takes into consideration the porosity of the setter during degreasing and sintering, but does not take into consideration the problem caused by the released gas from the compact.

[0011] The object of the present invention is to provide a method for producing a metal powder sintered body, which can suppress, by simple means, deterioration in the quality of the sintered body caused by heating the molded body, the degreased body, the calcined body, and gases released (pyrolysis products) from deposits in the furnace. [Means for solving the problem]

[0012] The inventors examined from various perspectives the behavior of gases released from the molded body, degreased body, calcined body, and deposits in the furnace when heated, and discovered that the above-mentioned problem could be solved by a simple means of unidirectional gas flow, which led to the invention.

[0013] The method for producing a metal powder sintered body according to the present invention includes a molded body producing step of producing a molded body from a mixture containing a metal powder and an organic component, a degreased body producing step of producing a degreased body by removing the organic component from the molded body by a first heating, and a sintered body producing step of sintering the metal powder constituting the degreased body by a second heating to produce a sintered body, wherein in the degreased body producing step, a first housing is disposed to contain and cover the molded body, and a first metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the molded body and the first housing, and in the sintered body producing step, a second housing is disposed to cover the degreased body, and a third housing is disposed to contain and cover the second housing, and a second metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the second housing and the third housing, and the first housing, the second housing, and the third housing are made of one or more of molybdenum, molybdenum alloy, tungsten, tungsten alloy, and ceramics.

[0014] The method for manufacturing a metal powder sintered body according to the present invention includes a calcined body preparation step in which the metal powder constituting the degreased body is sintered by a third heating which is lower than the second heating to prepare a calcined body, and in the calcined body preparation step, a fourth housing is disposed to contain and cover the degreased body, and a third metal material consisting of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the degreased body and the fourth housing, and the fourth housing is made of one or more of molybdenum, a molybdenum alloy, tungsten, a tungsten alloy, and ceramics, and in the sintered body preparation step, the calcined body can be used in place of the degreased body.

[0015] The method for producing a metal powder sintered body according to the present invention exerts particularly favorable effects when the metal powder consists of 50 mass % or more of Ti, one or more of B, C, Al, Si, V, Cr, Ni, Zr, Nb and Mo, and unavoidable impurities.

[0016] The method for producing a metal powder sintered body according to the present invention exerts particularly favorable effects when the metal powder consists of 50 mass % or more of Ni, one or more of B, C, Al, Si, Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta and W, and unavoidable impurities. Effect of the Invention

[0017] According to this invention, deterioration of the quality of the sintered body caused by gases (thermal decomposition products) emitted from the compact, degreased body, calcined body, and deposits in the furnace due to heating can be suppressed by a simple means. Therefore, this invention can contribute to stabilizing the quality of the sintered body at a relatively low cost. [Brief description of the drawings]

[0018] [Figure 1] 1A to 1C are diagrams illustrating an example of the configuration of a housing that can be applied in the degreased body producing step and the calcined body producing step, according to an embodiment of the method for producing a metal powder sintered body of the present invention. [Diagram 2]1A to 1C are diagrams illustrating an example of the configuration of a housing that can be applied in the degreased body producing step and the calcined body producing step, according to an embodiment of the method for producing a metal powder sintered body of the present invention. [Diagram 3] 1 is a diagram showing an example of a configuration of a housing that can be applied in the sintered body production process according to an embodiment of the method for producing a metal powder sintered body of the present invention. FIG. [Figure 4] 1 is a diagram showing an example of a configuration of a housing that can be applied in the sintered body production process according to an embodiment of the method for producing a metal powder sintered body of the present invention. FIG. [Diagram 5] 1 is a diagram showing an example of a configuration of a housing that can be applied in the sintered body production process according to an embodiment of the method for producing a metal powder sintered body of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the method for manufacturing a sintered metal powder body according to the present invention will be described with reference to the drawings as appropriate. Note that the method for manufacturing a sintered metal powder body according to the present invention is not limited to the contents exemplified here. The method for manufacturing a sintered metal powder body according to the present invention is defined by the claims, and it is appropriate to interpret that the method includes all modifications within the meaning and scope equivalent to the claims.

[0020] The method for producing a metal powder sintered compact according to the present invention includes the following steps (1) to (3), and if necessary, the following step (4) can be carried out before the following step (3). (1) A compact production process for producing a compact from a mixture containing a metal powder and an organic component. (2) A degreased body preparation step in which organic components are removed from the compact by first heating to prepare a degreased body. (3) A sintered body preparation process in which the metal powder constituting the degreased body is sintered by a second heating to prepare a sintered body. (4) A calcination process in which the metal powder constituting the degreased body is sintered by a third heating at a lower temperature than the second heating to produce a calcined body.

[0021] The above steps (1), (2), (4) and (3) will be described below in that order, but the present invention is not limited to the configuration in which the above step (4) is performed. In addition, the sintered body produced in the above step (3) may be subjected to a step of removing distortion or straightening, a step of machining such as cutting, grinding or polishing, a step of heat treatment such as HIP (Hot Isostatic Pressing) treatment, or a step of surface treatment such as cleaning or plating treatment, depending on the specifications such as dimensional accuracy and various characteristics.

[0022] <Molded body production process> In the present invention, in the molded body preparation process, a molded body is prepared from a mixture containing a metal powder and an organic component. In this case, in a typical MIM, an injection molding machine equipped with a mold having a cavity corresponding to the shape of the molded body is used. The molded body can be prepared by injecting a mixture plasticized by moderate heating into the cavity of the mold and cooling it. The mixture can be prepared by mixing an appropriate amount of an organic component with a metal powder, kneading sufficiently, and granulating to an appropriate size. In a typical MIM, for example, a metal powder having a median diameter (d50) of 5 μm to 50 μm in an accumulated volume distribution curve can be used. The metal powder is composed of a main element that is contained in an amount of 50 mass% or more and serves as the basis of the alloy, an additive element that is contained in a total amount of less than 50 mass% and constitutes the alloy, and unavoidable impurities, and can be selected according to the application and desired characteristics. In a typical MIM, the organic component is an organic substance containing C (carbon), such as a polymer compound (thermoplastic resin) having thermoplasticity, an oily compound (wax, wax ester), etc. By organic is intended compounds that upon heating produce CO gas (carbon monoxide) or CO2 gas (carbon dioxide).

[0023] In the present invention, the metal powder may be a Ti-based alloy powder containing Ti (titanium) as the main element, i.e., 50% by mass or more of Ti. In the present invention, when the metal powder is a Ti-based alloy powder, the additive element may be one or more of B (boron), C (carbon), Al (aluminum), Si (silicon), V (vanadium), Cr (chromium), Ni (nickel), Zr (zirconium), Nb (niobium), Mo (molybdenum), and Sn (tin). This invention has a particularly favorable effect when the metal powder is composed of 50% by mass or more of Ti, one or more of B, C, Al, Si, V, Cr, Ni, Zr, Nb, and Mo that are likely to form carbides or oxides, and unavoidable impurities. The metal powder contains one or more of the above elements that are likely to form carbides or oxides. Therefore, by applying this invention, it is possible to sufficiently suppress deterioration in the quality of the molded body, the degreased body, the calcined body, and the sintered body caused by gases released (pyrolysis products) from deposits in the furnace due to heating.

[0024] In the present invention, the metal powder may be a Ni-based alloy powder containing Ni (nickel) as the main element, i.e., 50% by mass or more of Ni. In the present invention, when the metal powder is a Ni-based alloy powder, the additive element may be one or more of B (boron), C, Al, Si, Ti, V, Cr, Mn (manganese), Fe (iron), Co (cobalt), Cu (copper), Zn (zinc), Zr, Nb, Mo, Sn, Ta (tantalum) and W (tungsten). This invention has a particularly favorable effect when the metal powder is composed of 50% by mass or more of Ni, one or more of B, C, Al, Si, Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta and W, and unavoidable impurities. The above metal powder contains one or more of the above elements that are likely to form carbides or oxides. Therefore, by applying this invention, it is possible to sufficiently suppress deterioration in the quality of the molded body, the degreased body, the calcined body, and the sintered body caused by gases released (pyrolysis products) from deposits in the furnace due to heating.

[0025] <Degreased body production process> In this invention, a degreased body preparation step is performed after the molded body preparation step. In this invention, in the degreased body preparation step, organic components are removed from the molded body by first heating to prepare a degreased body. The process of removing organic components from the molded body by first heating is called thermal degreasing. The first heating is intended to be heating at a temperature higher than the temperature at which the organic components (organic substances) contained in the molded body placed in the furnace are thermally decomposed and lower than the temperature at which the metal powder contained in the molded body begins to sinter (for example, 800°C or lower). For example, if the main organic component (organic substance) is polyolefin-based, heating is intended to be performed in the range of 420°C to 800°C, and if it is polystyrene-based, heating is intended to be performed in the range of 380°C to 800°C. By this first heating, the organic components contained in the molded body are thermally decomposed, and gases containing C (carbon) and O (oxygen) are released into the furnace. Conventionally, at this time, part of the released gas flows inside the furnace, and the gasified pyrolysis products (organic components) adhere to and are absorbed by the compact (degreased body) or accumulate on the furnace walls.

[0026] As a measure against the above-mentioned released gas, in this invention, in the degreased body production process, a first housing is placed to contain and cover the molded body, and a first metal material 11, 21 made of a titanium material, a niobium material, or a mixture of titanium material and niobium material is placed between the molded body and the first housing.

[0027] 1 and 2 show an embodiment of the method for producing a metal powder sintered body according to the present invention, illustrating an example of the configuration of a housing (first housing) that can be used in the degreased body producing step.

[0028] The green body 10 shown in FIG. 1 is made of a mixture containing a metal powder and an organic component. In a typical MIM, the green body is placed in a furnace while being placed on a jig (setter) made of ceramics such as alumina, zirconia, yttria, silicon carbide, etc. In contrast, the green body 10 shown in FIG. 1 is placed in a furnace while being placed inside a first housing 12. In this invention, the first housing is intended to be a structure that can contain the green body and cover the green body, and has a function of separating the atmosphere of the space containing the green body (internal space) from the atmosphere inside the furnace (external space) that does not contain the green body. "Containing the green body and covering the green body" refers to the case where the sides and the top of the green body are covered (a form with a lid), and does not include the case where only the sides of the green body are covered without covering the top of the green body (a form without a lid).

[0029] The first housing 12 shown in FIG. 1 is composed of a flat base plate 12a and a box-shaped case 12b. The box-shaped case 12b is composed of a flat plate portion and an annular wall portion. The molded body 10 is placed on the upper surface of the base plate 12a. The case 12b is arranged on the base plate 12a so as to cover the sides and the top of the molded body 10. The upper surface of the base plate 12a and the lower end surface of the case 12b are in contact with each other to separate the space 14 from the inside of the furnace, but are not joined by welding, brazing, or the like in order to later take out a degreased body made from the molded body 10. Therefore, a gap 13 exists between the base plate 12a and the case 12b. With this configuration, the space 14 (internal space) in the first housing 12 can be separated from the inside of the furnace (external space), while the gap 13 can connect the space 14 in the first housing 12 to the inside of the furnace.

[0030] In the case of the configuration shown in FIG. 1, the case 12b can be regarded as the first housing according to the present invention, and the base plate 12a can be composed of a refractory material (setter) suitable for the metal powder contained in the compact 10. In this case, the refractory material (setter) to be used has a small porosity, for example, 20% or less. A refractory material (setter) with a large porosity, for example, exceeding 20%, can be placed on the base plate 12a for use. Also, the powdered refractory material can be applied, spread, or sprayed onto the surface of the base plate 12a for use.

[0031] When such a first housing 12 is used in the degreased body preparation process, the pressure inside (space 14) of the first housing 12 increases when gas containing pyrolysis products (organic components) is released from the compact 10 by the first heating. By utilizing the pressure difference caused by this first heating, the released gas can be made to flow to the outside (furnace) of the first housing 12 where the pressure is relatively lower. Therefore, the flow of the released gas from the compact 10 is unidirectional from the inside (space 14) of the first housing 12 to the outside, and the released gas can be prevented from flowing back into the first housing 12 and coming into contact with the surface of the compact 10. As a result, it is possible to prevent a part of the gasified pyrolysis products (organic components) from adhering to and being absorbed by the compact 10 and the degreased body being degreased.

[0032] The first housing 12 is made of one or more of molybdenum, molybdenum alloy, tungsten, tungsten alloy, and ceramics. Molybdenum, molybdenum alloy, tungsten, tungsten alloy, and ceramics are less likely to react with gasified pyrolysis products (organic components), and are suitable for making the first housing 12. In addition, in the first heating, which is generally performed under reduced pressure and therefore has reduced heat transferability, molybdenum, molybdenum alloy, tungsten, tungsten alloy, and ceramics have a sufficiently higher thermal conductivity and a sufficiently smaller heat capacity than the ceramics constituting the above-mentioned conventional jig (setter), and are therefore advantageous for uniform heating of the inside (space 14) of the first housing 12. If the inside (space 14) of the first housing 12 is configured to be easily uniformly heated, it is advantageous for uniform heating of the molded body 10 placed inside. The first housing 12 is preferably made of molybdenum or a molybdenum alloy, which is easier to process and easier to maintain than tungsten, tungsten alloy, and ceramics. Furthermore, when the first housing 12 is made partially or entirely of ceramics, it is preferably made of ceramics with a porosity of 20% or less, which sufficiently prevents gasified pyrolysis products (organic components) from passing through the interior of the ceramics.

[0033] The molded body 20 shown in FIG. 2 is made of a mixture containing a metal powder and an organic component. The molded body 20 is placed in a furnace while being placed inside a first housing 22. The first housing 22 shown in FIG. 2 is composed of a flat base plate 22a, a flat roof plate 22b, and an annular side wall 22c. The annular side wall 22c can be easily made from a flat plate material or a pipe material. The molded body 20 is placed on the upper surface of the base plate 22a. The roof plate 22b is placed above the base plate 22a in opposition to cover the upper part of the molded body 20. The annular side wall 22c is placed between the base plate 22a and the roof plate 22b to surround the periphery of the molded body 20 and cover the sides. The upper surface of the base plate 22a and the lower end surface of the sidewall 22c are in contact with each other, and the lower surface of the roof plate 22b and the upper end surface of the sidewall 22c are in contact with each other, dividing the space 25 (internal space) from the inside of the furnace (external space), but they are not joined by welding, brazing, or the like, in order to later remove a degreased body produced from the compact 20. Therefore, a gap 23 exists between the base plate 22a and the sidewall 22c, and a gap 24 exists between the roof plate 22b and the sidewall 22c. With this configuration, the space 25 (internal space) in the first housing 22 is divided from the inside of the furnace (external space), while the gaps 23 and 24 connect the space 25 in the first housing 22 to the inside of the furnace.

[0034] In the case of the configuration shown in Fig. 2, the structure consisting of the roof plate 22b and the sidewalls 22c can be regarded as the first housing according to the present invention, and the base plate 22a can be composed of a refractory material (setter) suitable for the metal powder contained in the compact 20. In this case, the refractory material (setter) used has a low porosity, for example, 20% or less. A refractory material (setter) with a high porosity, for example, exceeding 20%, can be placed on the base plate 22a. Also, the powdered refractory material can be applied, spread, or sprayed onto the surface of the base plate 22a.

[0035] When such a first housing 22 is used, the pressure inside (space 25) of the first housing 22 increases when gas containing pyrolysis products (organic components) is released from the compact 20 by the first heating. By utilizing the pressure difference caused by this first heating, the released gas can be made to flow to the outside (furnace) of the first housing 22 where the pressure is relatively lower. Therefore, the flow of the released gas from the compact 20 is unidirectional from the inside (space 25) of the first housing 22 to the outside, and the released gas can be prevented from flowing back into the first housing 22 and coming into contact with the surface of the compact 20. As a result, it is possible to prevent a part of the gasified pyrolysis products (organic components) from adhering to and being absorbed by the compact 20 and the degreased body during degreasing.

[0036] For the same reasons as the first housing 12 shown in Fig. 1, the first housing 22 is made of one or more of molybdenum, molybdenum alloy, tungsten, tungsten alloy, and ceramics. From the viewpoint of ease of processing and maintenance, the first housing is preferably made of a flat roof plate 22b and an annular sidewall 22c that can be made of a flat plate or a pipe, as shown in Fig. 2. When the first housing 22 is made of ceramics in part or in whole, it is preferably made of ceramics with a porosity of 20% or less, so as to sufficiently prevent gasified pyrolysis products (organic components) from passing through the inside of the ceramics.

[0037] In this invention, in the degreased body preparation step, a first metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is placed between the compact and the first housing. In the configuration shown in FIG. 1, the first metal material 11 is placed between the case 12b of the first housing 12 and the compact 10, on the base plates 12a, 22a near the gap 13. In the configuration shown in FIG. 2, the first metal material 21 is placed between the sidewall 22c of the first housing 22 and the compact 20, on the base plates 22a, 22a near the gap 23, and preferably also near the gap 24. As shown in FIG. 1 and FIG. 2, if the first metal materials 11, 21 are placed near the gaps 13, 23, 24, the released gas from the compacts 10, 20 is likely to come into contact with the surfaces of the first metal materials 11, 21 when it flows from the inside (spaces 14, 25) of the first housings 12, 22 to the outside (inside the furnace).

[0038] The configuration of first housing 12 shown in Fig. 1 has gap 13 in one location on the bottom, while the configuration of first housing 22 shown in Fig. 2 has gaps 23, 24 in two locations, one on the bottom and one on the top. In the configuration of first housing 12 shown in Fig. 1 with gap 13 in one location on the bottom, the flow path of gas released from molded body 10 is limited to one location on the bottom. Therefore, the configuration of first housing 12 shown in Fig. 1, in which the first metal material only needs to be disposed in the vicinity of gap 13, is advantageous for reducing the total amount of the first metal material and improving the efficiency of gas adsorption by the first metal material.

[0039] With the above-mentioned configuration, most of the gas released from the compacts 10, 20 to the inside (spaces 14, 25) of the first housings 12, 22 comes into contact with the surface of the first metal material 11, 21. When the gasified pyrolysis products (organic components) come into contact with the surface of the first metal material 11, 21, most of them are adsorbed by the first metal material 11, 21. Therefore, it is possible to reduce the pyrolysis products (organic components) contained in the released gas inside the first housings 12, 22 (spaces 14, 25). It is also possible to reduce the pyrolysis products (organic components) contained in the released gas flowing from the inside (spaces 14, 25) of the first housings 12, 22 to the outside (inside the furnace). The reduction in the pyrolysis products (organic components) contained in the released gas can suppress the absorption of the pyrolysis products (organic components) into the compacts 10, 20 (degreased bodies 10, 20) during and after degreasing, and suppress the accumulation of the pyrolysis products (organic components) on the furnace walls.

[0040] In this invention, the first metal material is made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material. The titanium material has a strong affinity with C (carbon) and O (oxygen), and therefore can efficiently adsorb gasified pyrolysis products (organic components). For example, titanium sponge, titanium particles, titanium foil, or titanium foil pieces can be used as the titanium material. Since the titanium sponge has a large specific surface area and many adsorption sites, it can efficiently adsorb gasified pyrolysis products (organic components). Titanium sponge is easy to obtain. Niobium material is particularly advantageous for adsorbing C (carbon) because it easily produces niobium carbide. For example, niobium particles, niobium foil (niobium foil pieces) and the like can be used as the niobium material. Niobium foil (niobium foil pieces) is easy to obtain and easy to cut. Niobium foil (niobium foil pieces) containing an additive element having the ability to adsorb C, such as Zr (zirconium), can also be used. The mixture of the titanium material and the niobium material may be, for example, a mixture of titanium sponge and niobium foil.

[0041] In this invention, for example, when the organic components contained in the molded body include waxes, preferably, in the degreased body preparation step, after solvent degreasing, thermal degreasing accompanied by the first heating is performed. Solvent degreasing refers to a process in which the molded body is immersed in a solvent that dissolves waxes, and the waxes contained in the molded body are dissolved and removed to prepare a precursor of the degreased body. Thereby, in the degreased body preparation step, a precursor of the degreased body is prepared from the molded body by solvent degreasing, and the degreased body can be prepared from the precursor by thermal degreasing. The molded body (precursor of the degreased body) that has undergone solvent degreasing has reduced organic components remaining in the molded body (precursor of the degreased body) compared to a molded body that has not undergone solvent degreasing. Therefore, the organic components remaining in the molded body (precursor of the degreased body) can be smoothly and sufficiently removed by thermal degreasing.

[0042] <Preparation of calcined body> In this invention, after the above-mentioned degreased body preparation step (thermal degreasing), a calcined body preparation step is preferably performed before the sintered body preparation step described below. In this invention, in the calcined body preparation step, the metal powder constituting the degreased body is sintered by the third heating at a temperature lower than the second heating to prepare a calcined body. The second heating is the heating performed in the sintered body preparation step. The third heating is intended to be heating at a temperature equal to or higher than the temperature at which the metal powder constituting the degreased body placed in the furnace starts to sinter (for example, 700°C or higher) and to be heating such that the density after sintering is less than 90%. The process of sintering the metal powder constituting the degreased body by the third heating is called calcination (calcination). The calcined body prepared by calcination has many pores. Therefore, the calcined body has a lower density than the sintered body prepared in the above-mentioned sintered body preparation step (3), for example, less than 80%.

[0043] For example, if organic components remain in the degreased body, the organic components contained in the degreased body are pyrolyzed by the third heating, and gases containing C (carbon) and O (oxygen) are released into the furnace. In the past, the released gas flowed and came into contact with the surface of the degreased body (calcined body), so some of the gasified pyrolysis products (organic components) would adhere to and be absorbed by the degreased body (calcined body). Alternatively, the released gas flowed inside the furnace and came into contact with the surface of the furnace wall, so some of the gasified pyrolysis products (organic components) would accumulate on the furnace wall.

[0044] As a measure against the above-mentioned released gas, in the calcined body preparation step, a fourth housing is disposed to enclose and cover the degreased body, and a third metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the degreased body and the fourth housing. The fourth housing is made of one or more of molybdenum, a molybdenum alloy, tungsten, a tungsten alloy, and ceramics.

[0045] The configuration examples of the housing applicable in the degreased body preparation step shown in Figures 1 and 2 are also applicable to the calcined body preparation step. Here, Figures 1 and 2 show a configuration example of the first housing applicable in the degreased body preparation step, but by making the compacts 10 and 20 into calcined bodies 10 and 20, making the first housings 12 and 22 into fourth housings 12 and 22, and making the first metal materials 11 and 21 into third metal materials 11 and 21, it becomes a configuration example of the fourth housing and the third metal material applicable in the calcined body preparation step. Therefore, for a detailed description of the configuration examples of the fourth housing and the third metal material applicable in the calcined body preparation step, please refer to the description of the configuration examples of the first housing and the first metal material applicable in the degreased body preparation step, and will be omitted here.

[0046] When such fourth housings 12, 22 are used in the calcined body preparation step, the pressure difference caused by the third heating can be used to cause the released gas to flow to the outside (inside the furnace) of the fourth housings 12, 22 where the pressure is relatively lower, as in the degreased body preparation step. Therefore, the flow of the released gas from the degreased bodies 10, 20 is unidirectional from the inside (spaces 14, 25) of the fourth housings 12, 22 to the outside, and the released gas can be prevented from flowing back into the inside of the first housings 12, 22 and coming into contact with the surfaces of the degreased bodies 10, 20. As a result, it is possible to prevent a part of the gasified pyrolysis product (organic components) from adhering to and being absorbed by the degreased bodies 10, 20 and the calcined body during the preliminary sintering. When the fourth housings 12, 22 are partly or entirely made of ceramics, they are preferably made of ceramics with a porosity of 20% or less, so as to sufficiently prevent the gasified pyrolysis product (organic components) from passing through the inside of the ceramics.

[0047] <Sintered body manufacturing process> In this invention, the sintered body preparation step is performed after the degreased body preparation step, but if a calcined body preparation step is performed, it is performed after the calcined body preparation step. In this invention, in the sintered body preparation step, organic components are removed from the degreased body (or calcined body) by second heating to prepare a sintered body. The process of sintering metal powder by second heating is called main sintering. The second heating is intended to be heating at a temperature (e.g., 850°C or higher) at which the sintering of the metal powder constituting the degreased body (or calcined body) placed in the furnace progresses, and to be heating to a density of 90% or more after sintering. The sintered body prepared by main sintering has a dense sintered structure with almost no pores. Therefore, the sintered body has a high density, for example, 90% or more.

[0048] Here, the density of the sintered body (calcined body) is the relative density. The relative density is the ratio of the actual density to the theoretical density (actual density / theoretical density) expressed as a percentage. In other words, relative density (%) = actual density / theoretical density x 100. The actual density is the value obtained by dividing the mass of the actual body of the sintered body (calcined body) composed of metal (metal element) by the volume obtained from the dimensions of the actual body. The theoretical density is a value obtained from the blending composition of the raw materials used, assuming that the metals (metal elements) in the sintered structure of the sintered body (calcined body) exist individually and independently. When calculating the theoretical density, it is not necessary to consider metal elements that are in a small amount compared to other metal elements and whose influence on the relative density is assumed to be negligible, such as metal elements whose blending ratio to the total mass of the raw materials used is 1 mass% or less.

[0049] In the sintered body production process, for example, if pyrolysis products of organic components are deposited in the furnace, a part of the pyrolysis products deposited in the furnace is gasified again by the second heating and released into the furnace. At this time, in the past, the released gas flows and comes into contact with the surface of the degreased body (or the calcined body), so that a part of the gasified pyrolysis products (organic components) adheres to the degreased body and is eventually absorbed into the sintered body. Also, for example, if organic components remain in the degreased body, the organic components contained in the degreased body are pyrolyzed by the second heating, and gas containing C (carbon) and O (oxygen) is released into the furnace. At this time, in the past, the released gas flows and comes into contact with the surface of the degreased body, so that a part of the gasified pyrolysis products (organic components) adheres to the degreased body and is eventually absorbed into the sintered body.

[0050] As a measure against the above-mentioned released gas, in the sintered body manufacturing process, in this invention, a second housing that covers the periphery of the degreased body (or the calcined body) and a third housing that encloses and covers the periphery of the second housing are arranged, and a second metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is arranged between the second housing and the third housing. The second housing and the third housing are made of one or more of molybdenum, a molybdenum alloy, tungsten, a tungsten alloy, and ceramics. By arranging the second metal material between the second housing and the third housing, it is possible to adsorb the pyrolysis product (organic component) gasified by the second heating, as in the case of the first metal material described above. In addition, by arranging the second metal material outside the second housing, it is possible to suppress the second metal material from sublimating or floating by the second heating and adhering to and reacting with the degreased body (or the calcined body) or the sintered body during sintering.

[0051] 3, 4 and 5 show an embodiment of the method for producing a metal powder sintered body according to the present invention, and show examples of the configuration of housings (second housing, third housing) that can be used in the sintered body production process.

[0052] In Fig. 3, Fig. 4 and Fig. 5, the objects indicated by the reference numerals 30, 40 and 50 are degreased bodies or calcined bodies, respectively. The degreased bodies and calcined bodies indicated by the reference numerals 30, 40 and 50 are made of metal powder. Note that organic components may remain in the degreased bodies, but it may be considered that the calcined bodies have substantially no organic components remaining. In a typical MIM, the degreased body (or the calcined body) is placed on a jig (setter) made of ceramics and placed in a furnace. In contrast, the degreased body 30 (or the calcined body 30) shown in Fig. 3 is placed in a furnace with the second housing 32 that covers the periphery of the degreased body 30 (or the calcined body 30) and the third housing 34 that encloses and covers the second housing 32. 4 is placed in a furnace with a second housing 42 that covers the periphery of the degreased body 40 (or the calcined body 40) and a third housing 45 that encloses and covers the second housing 42. The degreased body 50 (or the calcined body 50) shown in FIG. 5 is placed in a furnace with a second housing 52 that covers the periphery of the degreased body 50 (or the calcined body 50) and a third housing 55 that encloses and covers the second housing 52.

[0053] The second housing in this invention is intended to be a structure having a function of covering the periphery of the degreased body or the calcined body. Covering the periphery of the degreased body or the calcined body includes a configuration in which the sides of the degreased body or the calcined body are covered but not the top (a configuration without a lid), and includes a configuration in which the sides and the top of the degreased body or the calcined body are covered (a configuration with a lid). The second housing 32 shown in FIG. 3 is a configuration without a lid, and is a structure that does not separate the atmosphere of the space 33 (innermost space) containing the degreased body 30 (or the calcined body 30) from the atmosphere of the space 36 (internal space) not containing the degreased body 30. The two-dot chain line shown in FIG. 3 is a schematic boundary line that separates the space 33 from the space 36.

[0054] The third housing in this invention is intended to be a structure capable of containing the degreased body or the calcined body and covering the periphery thereof, and having the function of separating the atmosphere of the space (internal space) including the degreased body or the calcined body 3 from the atmosphere inside the furnace (external space) which does not include the degreased body or the calcined body. "Containing the degreased body or the calcined body and covering the periphery thereof" refers to the case where the sides and above of the degreased body or the calcined body are covered (a form with a lid), and does not include the case where only the sides of the degreased body or the calcined body are covered without covering the above of the degreased body or the calcined body (a form without a lid).

[0055] [Configuration shown in Figure 3] 3 is a case composed of a flat bottom 32a and an annular wall 32b. The degreased body 30 (or the calcined body 30) is disposed on the upper surface of the bottom 32a of the second housing 32, and its periphery is covered by the annular wall 32b of the second housing 32. This configuration allows a space 33 (innermost space) in the second housing 32 to be separated from a space 36 (internal space) in a third housing 34 on the outside thereof on the side of the degreased body 30 (or the calcined body 30).

[0056] In the case of the configuration shown in FIG. 3, the annular wall portion 32b can be regarded as the second housing according to the present invention, and the bottom portion 32a can be made of a refractory material (setter) suitable for the metal powder contained in the degreased body 30 (or the calcined body 30). In this case, the refractory material (setter) used has a low porosity, for example, 20% or less. A refractory material (setter) with a high porosity, for example, exceeding 20%, can be placed on the bottom portion 32a. Also, the powdered refractory material can be applied, spread, or sprayed onto the surface of the bottom portion 32a.

[0057] The third housing 34 shown in FIG. 3 is composed of a flat base plate 34a and a box-shaped case 34b. The box-shaped case 34b is composed of a flat plate portion and an annular wall portion. The degreased body 30 (or the calcined body 30) is placed on the upper surface of the base plate 34a. The case 34b is arranged on the upper surface of the base plate 34a so as to cover the sides and the top of the degreased body 30 (or the calcined body 30). The upper surface of the base plate 34a and the lower end surface of the case 34b are in contact with each other to separate the space 36 (internal space) from the inside of the furnace (external space), but are not joined by welding, brazing, or the like because the sintered body will be removed later. Therefore, a gap 35 exists between the base plate 34a and the case 34b. With this configuration, the space 36 (internal space) in the third housing 34 can be separated from the inside of the furnace (external space) while the gap 35 can connect the space 36 in the third housing 34 to the inside of the furnace.

[0058] In the configuration shown in FIG. 3, the case 34b can be regarded as a third housing according to the present invention, and the base plate 34a can be made of a refractory material (setter) suitable for the metal powder contained in the degreased body 30 (or the calcined body 30). In this case, the refractory material (setter) used has a low porosity, for example, 20% or less. A refractory material (setter) with a high porosity, for example, exceeding 20%, can be placed on the base plate 34a. Also, the powdered refractory material can be applied, spread, or sprayed onto the surface of the base plate 34a.

[0059] [Configuration shown in Figure 4] The second housing 42 shown in FIG. 4 is composed of a box-shaped case 42a and a flat roof plate 42b. The box-shaped case 42a is composed of a flat bottom and an annular wall. The degreased body 40 (or the calcined body 40) is placed on the upper surface of the bottom of the case 42a. The roof plate 42b is disposed above and facing the bottom of the case 42a so as to cover the upper side of the degreased body 40 (or the calcined body 40). The upper end surface of the annular wall of the case 42a and the lower surface of the roof plate 42b are in contact with each other to separate the space 44 from the space 48 outside it, but they are not joined by welding, brazing, or the like because the sintered body will be removed later. Therefore, a gap 43 exists between the case 42a and the roof plate 42b. With this configuration, the space 44 (innermost space) inside the second housing 42 and the space 48 (internal space) outside the second housing 42 can be separated within the third housing 45, while the gap 43 can connect the space 44 and the space 48.

[0060] In the case of the configuration shown in FIG. 4, the structure formed by the annular wall of the case 42a and the roof plate 42b can be regarded as the second housing according to the present invention, and the bottom of the case 42a can be made of a refractory material (setter) suitable for the metal powder contained in the degreased body 40 (or the calcined body 40). Also, without using the roof plate 42b, the degreased body 40 (or the calcined body 40) can be covered by covering it from above with the case 42a turned upside down. In this case, the gap between the second housing and the third housing (base plate 45a) is located near the second metal material 41, and the released gas moving from the space 48 to the space 44 can easily come into contact with the second metal material 41, which is preferable. In addition, when a refractory material (setter) is used, one with a small porosity, for example, 20% or less, is used. A refractory material (setter) with a large porosity, for example, exceeding 20%, can be placed on the bottom of the case 42a and used. Also, powdered refractory material can be applied, spread or sprayed onto the surface of the bottom of the case 42a.

[0061] The third housing 45 shown in FIG. 4 is composed of a flat base plate 45a, a flat roof plate 45b, and an annular sidewall 45c. The annular sidewall 45c can be easily made from a flat plate material or a pipe material. The degreased body 40 (or the calcined body 40) is placed on the upper surface of the base plate 45a. The roof plate 45b is disposed above and facing the base plate 45a so as to cover the upper side of the degreased body 40 (or the calcined body 40). The annular sidewall 45c is disposed between the base plate 45a and the roof plate 45b so as to surround the periphery of the degreased body 40 (or the calcined body 40) and cover the sides. The upper surface of the base plate 45a and the lower end surface of the sidewall 45c are in close contact with each other, and the lower surface of the roof plate 45b and the upper end surface of the sidewall 45c are in contact with each other, dividing the space 48 (internal space) from the inside of the furnace (external space). However, they are not joined by welding, brazing, or the like, in order to take out a sintered body made from the degreased body 40 (or the calcined body 40) later. Therefore, a gap 46 exists between the base plate 45a and the sidewall 45c, and a gap 47 exists between the roof plate 45b and the sidewall 45c. With this configuration, the space 48 (internal space) in the third housing 45 is divided from the inside of the furnace (external space), while the gaps 46, 47 connect the space 48 in the third housing 45 to the inside of the furnace.

[0062] In the case of the configuration shown in FIG. 4, the structure formed by the roof plate 45b and the sidewalls 45c can be regarded as the third housing according to the present invention, and the base plate 45a can be made of a refractory material (setter) suitable for the metal powder contained in the degreased body 40 (or the calcined body 40). In this case, the refractory material (setter) used has a low porosity, for example, 20% or less. A refractory material (setter) with a high porosity, for example, exceeding 20%, can be placed on the base plate 45a. Also, the powdered refractory material can be applied, spread, or sprayed onto the surface of the base plate 45a.

[0063] [Configuration shown in Figure 5] The second housing 52 shown in FIG. 5 is composed of a box-shaped case 52a and a flat roof plate 52b. The box-shaped case 52a is composed of a flat bottom and an annular wall. The degreased body 50 (or the calcined body 50) is placed on the upper surface of the bottom of the case 52a. The roof plate 52b is disposed above and facing the bottom of the case 52a so as to cover the upper side of the degreased body 50 (or the calcined body 50). The upper end surface of the annular wall of the case 52a and the lower surface of the roof plate 52b are in contact with each other to separate the space 54 from the space 57 outside it, but are not joined by welding, brazing, or the like in order to remove the sintered body later. Therefore, a gap 53 exists between the case 52a and the roof plate 52b. With this configuration, within third housing 55, space 54 (innermost space) within second housing 52 and space 57 (internal space) outside second housing 52 can be separated, while space 54 and space 57 can be connected by gap 53.

[0064] In the case of the configuration shown in FIG. 5, the structure formed by the annular wall of the case 52a and the roof plate 52b can be regarded as the second housing according to the present invention, and the bottom of the case 52a can be made of a refractory material (setter) suitable for the metal powder contained in the degreased body 50 (or the calcined body 50). Also, without using the roof plate 52b, the degreased body 50 (or the calcined body 50) can be covered from above by the inverted case 52a. In this case, the gap between the second housing and the third housing (base plate 55a) is located near the second metal material 51, and the released gas moving from the space 57 to the space 54 can easily come into contact with the second metal material 51, which is preferable. In addition, when a refractory material (setter) is used, one with a small porosity, for example, 20% or less, is used. A refractory material (setter) with a large porosity, for example, exceeding 20%, can be placed on the bottom of the case 42a and used. Also, powdered refractory material can be applied, spread or sprayed onto the surface of the bottom of the case 42a.

[0065] The third housing 55 shown in FIG. 5 is composed of a flat base plate 55a and a box-shaped case 55b. The box-shaped case 55b is composed of a flat plate portion and an annular wall portion. The degreased body 50 (or the calcined body 50) is placed on the upper surface of the base plate 55a. The case 55b is arranged on the upper surface of the base plate 55a so as to cover the sides and the top of the degreased body 50 (or the calcined body 50). The upper surface of the base plate 55a and the lower end surface of the case 55b are in contact with each other to separate the space 57 (internal space) from the inside of the furnace (external space), but are not joined by welding, brazing, or the like because the sintered body will be removed later. Therefore, a gap 56 exists between the base plate 55a and the case 55b. With this configuration, the space 57 (internal space) in the third housing 55 can be separated from the inside of the furnace (external space) while the gap 56 can connect the space 57 in the third housing 55 to the inside of the furnace.

[0066] In the configuration shown in FIG. 5, the case 55b can be regarded as a third housing according to the present invention, and the base plate 55a can be made of a refractory material (setter) suitable for the metal powder contained in the degreased body 50 (or the calcined body 50). In this case, the refractory material (setter) used has a low porosity, for example, 20% or less. A refractory material (setter) with a high porosity, for example, exceeding 20%, can be placed on the base plate 55a. Also, the surface of the base plate 55a can be coated, spread, or sprayed with a powdered refractory material.

[0067] When the configuration shown in FIG. 3 is used, the pressure inside the third housing 34 (spaces 33, 36) increases when the gas containing the pyrolysis product (organic component) is released from the degreased body 30 by the second heating. Alternatively, when the configuration shown in FIG. 4 or FIG. 5 is used, the pressure inside the second housing 42, 52 (spaces 44, 54) increases, and the pressure inside the third housing 45, 55 (spaces 48, 57) increases when the gas containing the pyrolysis product (organic component) is released from the degreased body 40, 50 by the second heating. By utilizing the pressure difference caused by this second heating, the released gas can be made to flow to the outside of the third housing (inside the furnace) where the pressure is relatively low. Therefore, when gas is released from the degreased body, the flow of the released gas is unidirectional from the inside to the outside of the third housing, and it is possible to prevent the released gas from flowing into the inside of the third housing again and coming into contact with the surface of the degreased body. 4 or 5, the flow of gas released from the degreased bodies 40, 50 is unidirectional from the inside (spaces 48, 57) of the third housings 45, 55 to the outside, making it possible to prevent the released gas from flowing back into the third housings 45, 55 and coming into contact with the surfaces of the degreased bodies 40, 50. In this way, by using the configuration shown in Fig. 3, 4 or 5, it is possible to prevent a portion of the gasified pyrolysis products (organic components) from adhering to and being absorbed by the degreased bodies 30, 40, 50 and the sintered body during sintering.

[0068] In addition, when a sintered body is produced from a degreased body or a calcined body that does not substantially contain organic components, the degreased body or the calcined body does not release gas, so there is no increase in pressure inside the third housing due to the second heating. However, pyrolysis products (organic components) that have accumulated on the furnace wall may be gasified by the second heating, and gas containing pyrolysis products (organic components) may enter the third housing through gaps from inside the furnace (outside). To address this issue, in this invention, second metal materials 31, 41, 51 made of titanium material, niobium material, or a mixture of titanium material and niobium material are arranged between the second housing 32, 42, 52 and the third housing 34, 44, 54, as shown in Figures 3, 4 and 5.

[0069] In the configurations shown in Figures 3, 4 and 5, the second metal material 31, 41, 51 is disposed between the second housing 32, 42, 52 and the third housing 34, 45, 55, on the base plate 34a, 45a, 55a near the gap 35, 46, 56. In this manner, if the second metal material 31, 41, 51 is disposed near the gap 35, 46, 56, gas that has entered the inside (space 36, 48, 57) of the third housing 34, 45, 55 from inside the furnace (outside) through the gap 35, 46, 56 is likely to come into contact with the surface of the second metal material 31, 41, 51. When the gasified pyrolysis product (organic component) comes into contact with the surface of the second metal material 31, 41, 51, most of it is adsorbed by the second metal material 31, 41, 51. Therefore, according to the configurations shown in Figures 3, 4 and 5, the amount of pyrolysis products (organic components) contained in the gas that has entered the interior (spaces 36, 48, 57) of the third housing 34, 45, 55 is reduced, and the pyrolysis products (organic components) can be prevented from adhering to and being absorbed by the degreased body 30, 40, 50 or the sintered body during sintering.

[0070] This configuration is also effective for gas released from the degreased bodies 30, 40, and 50. In the configuration shown in FIG. 3, gas flowing from the inside (spaces 33 and 36) of the third housing 34 through the gap 35 to the outside (inside the furnace) is likely to come into contact with the surface of the second metal material 31. In the configuration shown in FIG. 4, gas flowing from the inside (space 44) of the second housing 42 through the gap 43 to the inside (space 48) of the third housing 45, and further flowing from the inside (space 48) of the third housing 45 through the gap 46 to the outside (inside the furnace) is likely to come into contact with the surface of the second metal material 41. In the configuration shown in FIG. 5, gas flowing from the inside (space 54) of the second housing 52 through the gap 53 to the inside (space 57) of the third housing 55, and further flowing from the inside (space 57) of the third housing 55 through the gap 56 to the outside (inside the furnace) is likely to come into contact with the surface of the second metal material 51. Therefore, according to the configurations shown in Figures 3, 4 and 5, the amount of pyrolysis products (organic components) contained in the gas flowing into the furnace is reduced, and the accumulation of the pyrolysis products (organic components) on the furnace walls can be suppressed.

[0071] The second housing 32 shown in Fig. 3 is advantageous over the second housings 42, 52 shown in Fig. 4 and 5 because it does not have roof plates 42b, 52b, making the structure simpler. A second housing such as the case shown in Fig. 3 can also be formed of a flat base plate and an annular sidewall. Although a gap is formed between the base plate and the sidewall, the second housing thus configured has a simple structure and is advantageous in terms of ease of processing and maintenance.

[0072] The second housings 42, 52 shown in Figures 4 and 5 are advantageous over the second housing 32 shown in Figure 3 because they have roof plates 42b, 52b, which makes it difficult for gas from the outside (inside the furnace) to enter the interior (spaces 44, 54) of the second housings 42, 52. The second housings 42, 52 shown in Figures 4 and 5 can also be configured with a flat base plate and an annular sidewall instead of the case 42a, 52a. The second housing configured in this way has a gap between the base plate and the sidewall, but has a simple structure and is advantageous in terms of ease of processing and maintenance.

[0073] The third housing 34, 55 shown in Figs. 3 and 5 has a gap 35, 56 at one location on the lower side. The third housing 45 shown in Fig. 4 has gaps 46, 47 at two locations on the lower and upper sides. With the configuration of the third housing 34, 55 shown in Figs. 3 and 5, the gap 35, 56 is limited to one location on the lower side, so that the flow path of the gas entering the inside from the inside of the furnace (outside) or the flow path of the gas released from the degreased body 30, 50 can be limited to one location on the lower side. Therefore, with the configuration of the third housing 34, 55 shown in Figs. 3 and 5, the second metal material only needs to be disposed near the gaps 35, 56, which is advantageous for reducing the total amount of the second metal material and improving the efficiency of gas adsorption by the second metal material.

[0074] In this invention, the second housing and the third housing are made of one or more of molybdenum, molybdenum alloy, tungsten, tungsten alloy, and ceramics. Molybdenum, molybdenum alloy, tungsten, tungsten alloy, and ceramics are suitable for making the second housing and the third housing because they are less likely to react with gasified pyrolysis products (organic components), have high melting points, thermal conductivity sufficiently higher than oxides, have excellent thermal stability and thermal shock resistance, and can withstand repeated heating from room temperature to about 2000°C. The second housing and the third housing are preferably made of molybdenum or a molybdenum alloy, which is easier to process and maintain than tungsten, tungsten alloy, and ceramics. In addition, when the second housing is made of a part or all of ceramics, or when the third housing is made of a part or all of ceramics, it is preferably made of ceramics with a porosity of 20% or less. This makes it possible to sufficiently prevent the gasified pyrolysis products (organic components) from passing through the inside of the ceramics. The reason for configuring the materials of the second housing and the third housing in this way is to obtain substantially the same effects as those of the first housing described above. Therefore, for detailed explanations of the materials of the second housing and the third housing applicable in the sintered body production process, please refer to the explanation of the materials of the first housing applicable in the degreased body production process, and they will not be explained here.

[0075] In this invention, as shown in Figures 3, 4 and 5, second metal materials 31, 41, 51 made of titanium material, niobium material, or a mixture of titanium material and niobium material are disposed between second housings 32, 42, 52 and third housings 34, 45, 55. The reason for configuring the second metal materials 31, 41, 51 in this manner is to obtain substantially the same effect as in the case of the first metal materials 11, 21 described above. Therefore, the explanation of the second metal material applicable in the sintered body preparation step is omitted here, and refer to the explanation of the first metal material applicable in the degreased body preparation step. In addition, when the second metal material 31, 41, 51 contains a low-melting point compound, the second housing 32, 42, 52 is arranged to separate the second metal material 31, 41, 51 from the degreased body 30, 40, 50, thereby preventing the low-melting point compound volatilized from the second metal material 31, 41, 51 heated to a high temperature (for example, 1200°C or higher) from adhering to the degreased body 30, 40, 50 (or the calcined body 30, 40, 50).

[0076] Next, experiments 1 to 8, which were conducted to confirm the effectiveness of the manufacturing method of conductive metal particles (particle groups) according to the present invention, will be described. The configurations and sintered bodies produced by the manufacturing methods used in experiments 1 and 5 are examples of the present invention. The configurations and sintered bodies produced by the manufacturing methods used in experiments 2-4 are comparative examples for experiment 1. Moreover, the configurations and sintered bodies produced by the manufacturing methods used in experiments 6-8 are comparative examples for experiment 5.

[0077] [Experiment 1] In the compact manufacturing process of experiment 1, Ni-based alloy powder equivalent to USA ASTM Alloy 713LC (C: 0.0920 mass%, O: 0.0176 mass%, median diameter d50: about 33 μm) was mixed with organic binders consisting of paraffin wax, polypropylene, polyolefin resin, and styrene resin, and kneaded to produce a compound with a Ni-based alloy powder ratio of about 65%. This compound was put into an injection molding device to produce a compact. In the injection molding, the compound injection temperature was 145°C and the injection pressure was 120 MPa. The compact was a cylindrical body (round bar) with a diameter of 8 mm and a length of 50 mm.

[0078] Ni-based alloy powder contains 50% by mass or more of Ni, C, O, Al, Ti, Cr, Zr, Nb, and Mo, which are likely to form carbides and oxides, and also contains unavoidable impurities. Depending on the production lot, impurities that may be contained include, for example, N (nitrogen), P (phosphorus), S (sulfur), as well as B, Si, V, Mn, Fe, Ta, and W.

[0079] Next, in the degreased body preparation step, the molded body was heated and degreased in the configuration shown in FIG. 1 to prepare a degreased body. At this time, as shown in FIG. 1, the molded body 10 was placed in the center of the Mo base plate 12a of the first housing 12, and the periphery of the molded body 10 was covered with the annular wall of the Mo case 12b of the first housing 12, and the upper part of the molded body 10 was covered with the bottom of the Mo case 12b. With this configuration, the first housing 12 was in a state of containing the molded body 10 and covering the periphery. Then, an appropriate amount of titanium sponge (first metal material 11) matching the size of the molded body 10 was placed between the molded body 10 and the annular wall of the case 12b of the first housing 12. The titanium sponge was placed around the molded body 10.

[0080] The heating pattern for degreasing (corresponding to the first heating) was to supply argon gas at about 5 L / min while evacuating the furnace atmosphere with a vacuum pump, then raise the temperature at about 30°C / h, and after reaching 650°C, hold it there for about 2 hours. In this way, a degreased body was produced.

[0081] Next, in the calcined body preparation step, the degreased body was calcined in the configuration shown in FIG. 1, following the degreased body preparation step, to prepare a calcined body. At this time, as shown in FIG. 1, the degreased body 10 is placed on the center of the Mo base plate 12a of the fourth housing 12, so that the periphery of the degreased body 10 is covered by the annular wall of the Mo case 12b of the fourth housing 12. Also, since the bottom of the Mo case 12b is located above the degreased body 10, the degreased body 10 is covered by the case 12b. With this configuration, the fourth housing 12 contains the degreased body 10 and covers the periphery. Also, between the degreased body 10 and the annular wall of the case 12b of the fourth housing 12, an appropriate amount of sponge titanium (third metal material 21) that matches the size of the degreased body 10 is arranged.

[0082] The heating pattern for the calcination (corresponding to the third heating) was as follows: after the heating for degreasing, the pressure inside the furnace was adjusted to about 13.3 kPa by timely exhausting while supplying argon gas, then the temperature was raised at about 150°C / h, and after reaching 1000°C, it was held there for about 2 hours. In this way, the calcined body was produced.

[0083] Next, in the sintered body preparation step, the Ni-based alloy powder constituting the calcined body was sintered in the configuration shown in FIG. 5 to prepare a sintered body. At this time, as shown in FIG. 5, the calcined body 50 was placed in the center of the bottom of the Mo case 52a of the second housing 52, so that the periphery of the calcined body 50 was covered by the annular wall of the case 52a. In addition, a Mo roof plate 52b was installed on the top of the case 52a, so that the upper part of the calcined body 50 was covered by the roof plate 52b. In addition, the second housing 52 was placed in the center of the Mo base plate 55a of the third housing 55, so that the periphery of the second housing 52 was covered by the Mo case 55b of the third housing 55. In addition, since the Ni-based alloy powder heated to a high temperature may react with the bottom of the Mo case 52a, a flat plate made of zirconia ceramics was placed between the calcined body 50 and the bottom of the case 52a. With this configuration, the third housing 55 encloses and covers the second housing 52. In addition, an appropriate amount of titanium sponge (second metal material 51) matching the size of the calcined body 50 was placed between the annular wall portion of the case 52a of the second housing 52 and the annular wall portion of the case 55b of the third housing 55. The titanium sponge was placed around the calcined body 50.

[0084] The heating pattern for sintering the Ni-based alloy powder (corresponding to the second heating) was to adjust the inside of the furnace to a vacuum of 1 Pa or less, then raise the temperature at about 260°C / h, and after reaching 1280°C, hold it there for about 3 hours. This produced a sintered body of roughly cylindrical shape (round bar) corresponding to the compact (cylinder with a diameter of 8 mm and a length of 50 mm).

[0085] [Experiment 2] In experiment 2, Ni-based alloy powder (C: 0.0037 mass%, O: 0.0198 mass%, median diameter d50: about 31 μm) was used, which was the Ni-based alloy powder used in experiment 1 with reduced C (carbon). Using this Ni-based alloy powder, a compact was produced, a degreased body was produced, and a calcined body was produced in the same manner as in experiment 1. Next, a sintered body was produced. However, the compact was a rectangular parallelepiped with a width of 20 mm, a length of 80 mm, and a thickness of 3 mm.

[0086] In the sintered body preparation process, the Ni-based alloy powder constituting the calcined body was sintered in a configuration substantially equivalent to that shown in FIG. 1 to prepare a sintered body. At this time, the calcined body was placed in the center of the Mo base plate of the outer housing (see the third housing 55 shown in FIG. 5) without using the inner housing (see the second housing 52 shown in FIG. 5) used in Experiment 1. In addition, for the same reason as in Experiment 1, a flat plate made of zirconia ceramics was placed between the calcined body and the base plate of the outer housing. With this configuration, the outer housing was in a state of containing the calcined body and covering the periphery. In addition, as in Experiment 1, a titanium sponge (second metal material) was placed around the calcined body.

[0087] The heating pattern (corresponding to the second heating) for sintering the Ni-based alloy powder was the same as in Experiment 1. As a result, a sintered body having a substantially rectangular parallelepiped shape corresponding to the compact (a rectangular parallelepiped having a width of 20 mm, a length of 80 mm, and a thickness of 3 mm) was produced.

[0088] [Experiment 3] In experiment 3, the same Ni-based alloy powder (C: 0.0037 mass%, O: 0.0198 mass%, median diameter d50: about 31 μm) as that used in experiment 2 was used. Using this Ni-based alloy powder, a compact was produced, a degreased body was produced, and a calcined body was produced, as in experiment 1. Then, a sintered body was produced. However, the compact was a rectangular parallelepiped with a width of 20 mm, a length of 80 mm, and a thickness of 3 mm, as in experiment 2.

[0089] In the sintered body preparation process, the Ni-based alloy powder constituting the calcined body was sintered in a configuration substantially equivalent to that shown in Fig. 5 to prepare a sintered body. At this time, the titanium sponge (second metal material) used in Experiment 1 was not used.

[0090] The heating pattern (corresponding to the second heating) for sintering the Ni-based alloy powder was the same as in Experiment 1. As a result, a sintered body having a substantially rectangular parallelepiped shape corresponding to the compact (a rectangular parallelepiped having a width of 20 mm, a length of 80 mm, and a thickness of 3 mm) was produced.

[0091] [Experiment 4] In experiment 4, Ni-based alloy powder equivalent to USA ASTM Alloy 718 (C: 0.0600 mass%, O: 0.0580 mass%, median diameter d50: about 15 μm) was used. Using this Ni-based alloy powder, a compact (a cylindrical body with a diameter of 8 mm and a length of 50 mm) was produced in the same manner as in experiment 1. Next, the organic binder was removed from the compact, and the Ni-based alloy powder was sintered to produce a sintered body. The calcined body production process was omitted. That is, the compact was used to produce a sintered body by successively performing heating in the degreased body production process (corresponding to the first heating), heating in the calcined body production process (corresponding to the third heating), and heating in the sintered body production process (corresponding to the second heating).

[0092] Ni-based alloy powder contains 50% by mass or more of Ni, C, O, Al, Ti, Cr, Fe, Nb, and Mo, which are likely to form carbides and oxides, and also contains unavoidable impurities. Depending on the production lot, impurities that may be contained include, for example, N, P, S, as well as B, Si, V, Mn, Fe, Zr, Ta, and W.

[0093] In the degreased body preparation process and the sintered body preparation process, the organic binder constituting the molded body was removed and the Ni-based alloy powder was sintered in a configuration substantially equivalent to that shown in FIG. 1, and a sintered body was prepared from the molded body. In this process, the molded body was turned into a degreased body by heating and degreasing, and the degreased body was turned into a sintered body through a calcined body by sintering. At this time, the molded body was placed in the center of the Mo base plate of the outer housing (see the third housing 55 shown in FIG. 5) without using the inner housing (see the second housing 52 shown in FIG. 5) used in the sintered body preparation process of Experiment 1. In addition, for the same reason as in Experiment 1, a flat plate made of zirconia ceramics was placed between the degreased body (molded body) and the base plate. With this configuration, the outer housing was in a state of containing the molded body and covering the periphery. The titanium sponge (second metal material) used in Experiment 1 was not used.

[0094] The heating pattern (corresponding to the first and second heating) for removing the organic binder and sintering the Ni-based alloy powder was as follows: heat up to about 650°C, introduce hydrogen gas and hold for about 2 hours, heat up to about 750°C at 100°C / h and hold for about 2 hours, replace hydrogen with nitrogen gas to create a furnace atmosphere, adjust the furnace pressure to about 13.3kPa by timely exhaust while supplying argon gas, heat up further at about 63°C / h, and hold for about 4 hours after reaching 1250°C. This produced a roughly cylindrical sintered body corresponding to the compact (cylinder with a diameter of 8 mm and a length of 50 mm).

[0095] [Experiment 5] In experiment 5, a Ti-based alloy powder (C: 0.0590 mass%, O: 0.0864 mass%, median diameter d50: about 36 μm) containing Al (about 29 mass%), Nb (about 18 mass%), and Fe (about 0.03 mass%) was used. Using this Ti-based alloy powder, a compact (cylinder with a diameter of 8 mm and a length of 50 mm) was produced, a degreased body was produced, a calcined body was produced, and a sintered body was produced, in the same manner as in experiment 1.

[0096] The Ti-based alloy powder contains 50% by mass or more of Ti, C, O, Al, Fe, and Nb, which tend to form carbides and oxides, as well as unavoidable impurities. Depending on the production lot, impurities that may be contained include, for example, N (nitrogen), P (phosphorus), S (sulfur), as well as B, Si, V, Cr, Ni, Zr, and Mo.

[0097] In the sintered body preparation process, the Ti-based alloy powder constituting the calcined body was sintered in a configuration substantially equivalent to that shown in Fig. 5 to prepare the sintered body. At this time, the zirconia ceramic flat plate used in Experiment 1 was not used, and the calcined body was placed directly on a Mo base plate.

[0098] The heating pattern for sintering the Ti-based alloy powder (corresponding to the second heating) was to adjust the pressure inside the furnace to about 13.3 kPa by timely exhausting while supplying argon gas, then to raise the temperature at about 145°C / h, and to hold the temperature at 1450°C for about 4 hours after it reached that temperature. This produced a roughly cylindrical sintered body corresponding to the compact (cylinder with a diameter of 8 mm and a length of 50 mm).

[0099] [Experiment 6] In experiment 6, the same Ti-based alloy powder (C: 0.0530 mass%, O: 0.0976 mass%, median diameter d50: about 41 μm) as the Ti-based alloy powder used in experiment 5 was used. Using this Ti-based alloy powder, a compact (a cylindrical body with a diameter of 8 mm and a length of 50 mm) was produced in the same manner as in experiment 1. Next, the organic binder was removed from the compact, and the Ti-based alloy powder was sintered to produce a sintered body. The calcined body production process was omitted. That is, the compact was used to produce a sintered body by successively performing heating in the degreased body production process (corresponding to the first heating), heating in the calcined body production process (corresponding to the third heating), and heating in the sintered body production process (corresponding to the second heating).

[0100] In the degreased body preparation process and the sintered body preparation process, the organic binder constituting the compact was removed and the Ni-based alloy powder was sintered in a configuration substantially equivalent to that shown in FIG. 1, and a sintered body was prepared from the compact. In this process, the compact is heated and degreased to become a degreased body, and the degreased body is sintered to become a calcined body and then a sintered body. At this time, the compact was placed in the center of the Mo base plate of the outer housing (see the third housing 55 shown in FIG. 5) without using the inner housing (see the second housing 52 shown in FIG. 5) used in the sintered body preparation process of Experiment 1. In addition, since the Ti-based alloy powder heated to a high temperature may react with the Mo base plate, a flat plate made of yttria ceramics was used between the compact and the base plate. With this configuration, the outer housing was in a state of containing the compact and covering the periphery. In addition, a titanium sponge (second metal material) was placed around the compact, as in Experiment 1.

[0101] The heating pattern (corresponding to the first and second heating) for removing the organic binder and sintering the Ti-based alloy powder was as follows: the furnace atmosphere was evacuated by a vacuum pump while supplying argon gas at about 5 L / min, then the temperature was increased at about 30°C / h, and after reaching 650°C, the temperature was held for about 2 hours, then the pressure inside the furnace was adjusted to about 13.3 kPa by timely exhaust while supplying argon gas, then the temperature was increased at about 98°C / h, and after reaching 1430°C, the temperature was held for about 8 hours. This produced a roughly cylindrical sintered body corresponding to the compact (a cylinder with a diameter of 8 mm and a length of 50 mm).

[0102] [Experiment 7] In experiment 7, a Ti-based alloy powder (C: 0.0100 mass%, O: 0.1250 mass%, median diameter d50: about 35 μm) containing Al (about 32 mass%), Nb (about 5.4 mass%), Cr (about 2.3 mass%) and Fe (about 0.05 mass%) was used. Using this Ti-based alloy powder, a compact was produced in the same manner as in experiment 1. Next, the organic binder was removed from the compact, and the Ti-based alloy powder was sintered to produce a sintered body. The calcined body production process was omitted. That is, the compact was used to produce a sintered body by successively carrying out heating in the degreased body production process (corresponding to the first heating), heating in the calcined body production process (corresponding to the third heating), and heating in the sintered body production process (corresponding to the second heating). However, the compact was a cone approximating a cone shape with a diameter of 41 mm and a height of 34 mm.

[0103] The Ti-based alloy powder contains 50% by mass or more of Ti, C, O, Al, Cr, Fe, and Nb, which tend to form carbides and oxides, as well as unavoidable impurities. Depending on the production lot, impurities that may be contained include, for example, N (nitrogen), P (phosphorus), S (sulfur), as well as B, Si, V, Ni, Zr, and Mo.

[0104] In the degreased body preparation process and the sintered body preparation process, the organic binder constituting the compact was removed and the Ti-based alloy powder was sintered in a configuration substantially equivalent to that shown in FIG. 1, and a sintered body was prepared from the compact. In this process, the compact is heated and degreased to become a degreased body, and the degreased body is sintered to become a calcined body and then a sintered body. At this time, the compact was placed in the center of the Mo base plate of the outer housing (see the third housing 55 shown in FIG. 5), and the entire periphery of the compact was covered with niobium foil. Therefore, the inner housing (see the second housing 52 shown in FIG. 5) used in the sintered body preparation process of Experiment 1 was not used. Note that, since the Ti-based alloy powder heated to a high temperature may melt the niobium foil and react with the Mo base plate, a flat plate made of yttria ceramics was used between the compact and the base plate. With this configuration, the outer housing was in a state of containing the compact covered with niobium foil and covering the periphery. In addition, as in Experiment 1, a titanium sponge (second metal material) was placed around the compact.

[0105] The heating pattern (corresponding to the first and second heating) for removing the organic binder and sintering the Ti-based alloy powder was as follows: the furnace atmosphere was evacuated by a vacuum pump while supplying argon gas at about 5 L / min, then the temperature was increased at about 30°C / h, and after reaching 650°C, the temperature was held for about 2 hours, then the pressure inside the furnace was adjusted to about 13.3 kPa by timely exhaust while supplying argon gas, then the temperature was increased at about 98°C / h, and after reaching 1430°C, the temperature was held for about 8 hours. This produced a roughly conical sintered body corresponding to the compact (a cone with a diameter of 41 mm and a height of 34 mm).

[0106] [Experiment 8] In experiment 8, the same Ti-based alloy powder (C: 0.0100 mass%, O: 0.1250 mass%, median diameter d50: about 35 μm) as the Ti-based alloy powder used in experiment 7 was used. Using this Ti-based alloy powder, a compact (a cone approximating a cone shape with a diameter of 41 mm and a height of 34 mm) was produced in the same manner as in experiment 1. Next, the organic binder was removed from the compact, and the Ti-based alloy powder was sintered to produce a sintered body. The calcined body production process was omitted. That is, the sintered body was produced by successively performing heating in the degreased body production process (corresponding to the first heating), heating in the calcined body production process (corresponding to the third heating), and heating in the sintered body production process (corresponding to the second heating) using the compact.

[0107] In the degreased body preparation process and the sintered body preparation process, the organic binder constituting the compact was removed and the Ti-based alloy powder was sintered in a configuration substantially equivalent to that shown in FIG. 1, as in Experiment 7, to prepare a sintered body from the compact. At this time, as in Experiment 7, the entire periphery of the compact was covered with niobium foil, and a flat plate made of yttria ceramics was used. With this configuration, the outer housing was enclosed in the compact covered with niobium foil and covered the periphery. The titanium sponge (second metal material) used in Experiment 7 was not used.

[0108] The heating pattern (corresponding to the first and second heating) for removing the organic binder and sintering the Ti-based alloy powder was as follows: the furnace atmosphere was evacuated by a vacuum pump while supplying argon gas at about 5 L / min, then the temperature was increased at about 30°C / h, and after reaching 650°C, the temperature was held for about 2 hours, then the pressure inside the furnace was adjusted to about 13.3 kPa by timely exhaust while supplying argon gas, then the temperature was increased at about 98°C / h, and after reaching 1430°C, the temperature was held for about 8 hours. This produced a roughly conical sintered body corresponding to the compact (a cone with a diameter of 41 mm and a height of 34 mm).

[0109] The carbon content of the metal powders used and the calcined and sintered bodies produced in the above-mentioned Experiments 1 to 8 was analyzed. A carbon / sulfur analyzer (Horiba, Ltd. EMIA-920, combustion-infrared absorption method, ASTM E1019 compliant) was used to analyze the carbon content of the metal powders, calcined bodies, and sintered bodies.

[0110] Table 1 shows the C content (mass%) of the metal powder, calcined body, and sintered body in Experiments 1 to 8, the ratio of the C content (mass%) of the calcined body to the metal powder (calcined body / metal powder), and the ratio of the C content (mass%) of the sintered body to the metal powder. "-" in Table 1 indicates that the calcined body preparation process was omitted, so analysis in the form of the calcined body could not be performed. Hereinafter, the ratio of the C content (mass%) will be referred to as "C ratio," calcined body / metal powder will be referred to as "C ratio of calcined body," and sintered body / metal powder will be referred to as "C ratio of sintered body."

[0111] [Table 1]

[0112] In addition, the O content (oxygen content) of the metal powder used and the calcined and sintered bodies produced in the above-mentioned Experiments 1 to 4 was analyzed. The O content of the metal powder, calcined and sintered bodies was analyzed using an oxygen / nitrogen analyzer (Horiba EMGA-920, inert gas fusion-infrared absorption method, ASTM E1019 compliant). Ni-based alloy powders such as Alloy 713LC and Alloy 718, which are widely used as ultra-heat-resistant materials, are susceptible to the effects of O (oxygen) because they contain many oxide-forming elements. Considering this point, an evaluation of O was performed for Experiments 1 to 4 using Ni-based alloy powders.

[0113] Table 2 shows the O amount (mass %) of the metal powder, calcined body, and sintered body in Experiments 1 to 4, the ratio of the O amount (mass %) of the calcined body to the metal powder (calcined body / metal powder), and the ratio of the O amount (mass %) of the sintered body to the metal powder. "-" in Table 1 indicates that the calcined body could not be analyzed in its form because the calcined body preparation step was omitted. Hereinafter, the ratio of the O amount will be referred to as "O ratio", calcined body / metal powder will be referred to as "O ratio of calcined body", and sintered body / metal powder will be referred to as "O ratio of sintered body".

[0114] [Table 2]

[0115] In experiment 1 (example of the present invention) using Ni-based alloy powder, the C ratio of the calcined body was 1.24 and the C ratio of the sintered body was 1.15 for metal powder with a C content of 0.0920 mass%. From this, it was found that the C content increased by 24% when the metal powder became a calcined body, and decreased by 9% when the calcined body became a sintered body, and finally the C content of the sintered body was 15% greater than that of the metal powder. In addition, for metal powder with an O content of 0.0176 mass%, the O ratio of the calcined body was 0.70 and the O ratio of the sintered body was 0.34. From this, it was found that the O content decreased by 30% when the metal powder became a calcined body, and further decreased by 36% when the calcined body became a sintered body, and finally the O content of the sintered body was 66% less than that of the metal powder.

[0116] In experiment 2 (comparative example) using Ni-based alloy powder, the C ratio of the calcined body was 10.54 and the C ratio of the sintered body was 4.49 for metal powder with a C content of 0.0037% by mass. From this, it was found that the C content increased by 954% when the metal powder became a calcined body, and decreased by 605% when the calcined body became a sintered body, and the final C content of the sintered body was 349% greater than that of the metal powder. In addition, for metal powder with an O content of 0.0198% by mass, the O ratio of the calcined body was 1.54 and the O ratio of the sintered body was 1.16. From this, it was found that the O content increased by 54% when the metal powder became a calcined body, and decreased by 38% when the calcined body became a sintered body, and the final O content of the sintered body was 16% greater than that of the metal powder.

[0117] In experiment 3 (comparative example) using Ni-based alloy powder, the C ratio of the calcined body was 10.54 and the C ratio of the sintered body was 9.73 for metal powder with a C content of 0.0037% by mass. From this, it was found that the C content increased by 954% when the metal powder became a calcined body, and decreased by 81% when the calcined body became a sintered body, and finally the C content of the sintered body was 873% more than that of the metal powder. Also, for metal powder with an O content of 0.0198% by mass, the O ratio of the calcined body was 1.54 and the O ratio of the sintered body was 2.40. From this, it was found that the O content increased by 54% when the metal powder became a calcined body, and further increased by 86% when the calcined body became a sintered body, and finally the O content of the sintered body was 140% more than that of the metal powder.

[0118] In experiment 4 (comparative example) using Ni-based alloy powder, the C ratio of the sintered body was 3.07 for metal powder with a C content of 0.0600 mass%. This shows that the C content increases by 207% when the metal powder becomes a sintered body, and the final C content of the sintered body is 207% greater than that of the metal powder. Also, the O ratio of the sintered body was 7.84 for metal powder with an O content of 0.0580 mass%. This shows that the O content increases by 684% when the metal powder becomes a sintered body, and the final O content of the sintered body is 684% greater than that of the metal powder.

[0119] In experiment 5 (example of the present invention) using a Ti-based alloy powder, the C ratio of the calcined body was 1.27 and the C ratio of the sintered body was 1.32 for a metal powder with a C content of 0.0590 mass%. This shows that the C content increases by 27% when the metal powder becomes a calcined body, and increases by 5% when the calcined body becomes a sintered body, and finally the C content of the sintered body is 32% greater than that of the metal powder.

[0120] In experiment 6 (comparative example) using Ti-based alloy powder, the C ratio of the sintered body was 1.74 for metal powder with a C content of 0.0530 mass%. This shows that the C content increases by 74% when the metal powder becomes a sintered body, and the C content of the sintered body is ultimately 74% higher than that of the metal powder.

[0121] In Experiment 7 (Comparative Example) using Ti-based alloy powder, the C ratio of the sintered body was 2.90 for metal powder with a C content of 0.0100 mass%. This shows that the C content increases by 190% when the metal powder becomes a sintered body, and the C content of the sintered body is ultimately 190% greater than that of the metal powder.

[0122] In Experiment 8 (Comparative Example) using a Ti-based alloy powder, the C ratio of the sintered body was 10.40 for a metal powder with a C content of 0.0100 mass%. This shows that the C content increases by 940% when the metal powder becomes a sintered body, and the C content of the sintered body is ultimately 940% greater than that of the metal powder.

[0123] For the sintered body made of Ni-based alloy powder, the effect of suppressing the C amount and O amount of the sintered body relative to the Ni-based alloy powder can be confirmed by comparing Experiment 1 (example of the present invention) and Experiments 2 to 4 (comparative examples) in which a sintered body made of Ni-based alloy powder was produced. Specifically, in Experiment 1 (example of the present invention), the C amount of the sintered body was +15% relative to the C amount and O amount of the Ni-based alloy powder, which was relatively small, and the O amount of the sintered body was -66%, which was significantly small. On the other hand, in Experiments 2 to 4 (comparative examples), the C amount of the sintered body was +349%, +873%, and +207%, respectively, relative to the C amount and O amount of the Ni-based alloy powder, which could not be suppressed small, and the O amount of the sintered body was +16%, +140%, and +684%, respectively, which could not be suppressed small.

[0124] As a result, in a method for producing a Ni-based alloy powder sintered body, in which a compact is produced from a mixture containing Ni-based alloy powder and organic components, the organic components are heated to remove the compact to produce a degreased body, and the Ni-based alloy powder constituting the degreased body is heated to sinter to produce a sintered body, the application of the configuration according to the present invention was able to confirm an effect of suppressing an increase in the C and O contents of the sintered body, using the C and O contents of the Ni-based alloy powder as a comparison standard.

[0125] For sintered bodies made of Ti-based alloy powder, a comparison between Experiment 5 (example of the present invention) and Experiments 6 to 8 (comparative examples) in which sintered bodies made of Ti-based alloy powder were produced confirms the effect of suppressing the C content of the sintered body relative to the Ti-based alloy powder. Specifically, in Experiment 5 (example of the present invention), the C content of the sintered body was +32% compared to the C content of the Ti-based alloy powder, which was a relatively small amount. On the other hand, in Experiments 6 to 8 (comparative examples), the C content of the sintered body was +74%, ​​+190%, and +940%, respectively, compared to the C content of the Ti-based alloy powder, which was not possible to suppress to a small amount.

[0126] As a result, in a method for producing a Ti-based alloy powder sintered body, in which a compact is produced from a mixture containing a Ti-based alloy powder and organic components, the organic components are heated to remove the compact to produce a degreased body, and the Ti-based alloy powder constituting the degreased body is heated to sinter to produce a sintered body, the application of the configuration according to the present invention was able to confirm an effect of suppressing an increase in the C content of the sintered body, using the C content of the Ti-based alloy powder as a comparison standard.

[0127] Considering the results of Experiments 1 to 8 described above, in a method for producing a metal powder sintered body, in which a compact is produced from a mixture containing a metal powder and an organic component, the organic component is removed from the compact by heating to produce a degreased body, and the metal powder constituting the degreased body is sintered by heating to produce a sintered body, the application of the configuration according to the present invention can be confirmed to have an effect of suppressing an increase in the C content and O content of the sintered body when the metal powder is used as a comparison standard.

[0128] From the above, it was found that the present invention can suppress the quality deterioration of the sintered body caused by the gas (thermal decomposition product) emitted from the compact, degreased body, calcined body, and deposits in the furnace by heating by a simple means. Therefore, the present invention is expected to contribute to the stabilization of the quality of the metal powder sintered body. [Explanation of symbols]

[0129] <Degreased body production process> <Calcined body production process> 10 Molded or degreased body 11 First metallic material or third metallic material 12 1st or 4th housing 12a Base plate 12b Case 13. Gap 14 Space <Degreased body production process> <Calcined body production process> 20 Molded or degreased body 21 First metallic material or third metallic material 22 1st or 4th housing 22a Base plate 22b Roof plate 22c sidewall 23 Gap 24 Gap 25 Space <Sintered body manufacturing process> 30 Degreased or calcined body 31 Second metal material 32 Second Housing 32a bottom 32b wall 33 Space 34 3rd Housing 34a Base plate 34b Case 35 Gap 36 Space <Sintered body manufacturing process> 40 Degreased or calcined body 41 Second metal material 42 Second Housing 42a Case 42b Roof plate 43 Gap 44 Space 45 3rd Housing 45a Base plate 45b roof plate 45c sidewall 46 Gap 47 Gap 48 Space <Sintered body manufacturing process> 50 Degreased or calcined body 51 Second metal material 52 Second Housing 52a Case 52b roof plate 53 Gap 54 Space 55 3rd Housing 55a Base plate 55b Case 56 Gap 57 Space

Claims

1. A method for producing a molded body comprising the steps of: preparing a molded body from a mixture containing metal powder consisting of 50 mass% or more of Ti, one or more of B, C, Al, Si, V, Cr, Ni, Zr, Nb, and Mo, and unavoidable impurities, and organic components; preparing a degreased body by removing the organic components from the molded body through a first heating; and preparing a sintered body by sintering the metal powder constituting the degreased body through a second heating, In the degreased body preparation step, a first housing is disposed to enclose and cover the compact, and a first metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the compact and the first housing; In the sintered body preparation step, a second housing that covers the periphery of the degreased body and a third housing that encloses and covers the periphery of the second housing are disposed, and a second metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the second housing and the third housing; A method for manufacturing a metal powder sintered body, wherein the first housing, the second housing and the third housing are made of one or more of molybdenum, a molybdenum alloy, tungsten, a tungsten alloy, and ceramics.

2. A method for producing a molded body from a mixture containing metal powder and organic components, the metal powder consisting of 50 mass% or more of Ni, one or more of B, C, Al, Si, Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta and W, and unavoidable impurities; a degreased body preparation process in which the organic components are removed from the molded body by a first heating to prepare a degreased body; and a sintered body preparation process in which the metal powder constituting the degreased body is sintered by a second heating to prepare a sintered body, In the degreased body preparation step, a first housing is disposed to enclose and cover the compact, and a first metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the compact and the first housing; In the sintered body preparation step, a second housing that covers the periphery of the degreased body and a third housing that encloses and covers the periphery of the second housing are disposed, and a second metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the second housing and the third housing; A method for manufacturing a metal powder sintered body, wherein the first housing, the second housing and the third housing are made of one or more of molybdenum, a molybdenum alloy, tungsten, a tungsten alloy, and ceramics.

3. a calcined body producing step of sintering the metal powder constituting the degreased body by a third heating at a temperature lower than the second heating to produce a calcined body; In the calcined body preparation step, a fourth housing is disposed to enclose and cover the degreased body, and a third metal material made of a titanium material, a niobium material, or a mixture of a titanium material and a niobium material is disposed between the degreased body and the fourth housing; The fourth housing is made of one or more of molybdenum, a molybdenum alloy, tungsten, a tungsten alloy, and ceramics; 3. The method for producing a metal powder sintered body according to claim 1, wherein the calcined body is used in place of the degreased body in the sintered body production step.

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