Manufacturing method for difficult-to-sinter bodies

Abstract

A method for manufacturing a difficult-to-sinter body having a complex shape is provided. [Solution] After molding a sinter-resistant powder raw material of an inorganic substance into a cylindrical or disc shape, it is heated to sinter a sinter-resistant sintered body that can withstand machining, and then the sintered body is processed. For sinter-resistant powder that is difficult to mold, the process further includes a step of filling a tantalum container, a first heating step of heating the sinter-resistant powder together with the tantalum under normal pressure in a vacuum or inert atmosphere at a temperature below the lower of the melting points of the tantalum and the sinter-resistant powder to obtain a sinter-resistant body, and a machining step of processing the sinter-resistant body.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a difficult-to-sinter body. [Background technology]

[0002] Currently, engineering ceramic materials with high melting points, high strength, and light weight, such as boron, boron nitride, boron carbide, zirconia, and yttria, are attracting attention as lightweight and durable materials in fields such as aerospace and the automotive industry. There is a growing need for inexpensive manufacturing technologies for engineering ceramic materials with such properties.

[0003] Conventionally, when sintering a difficult-to-sinter powder (raw material powder) by atmospheric sintering, a binder is mixed with the raw material powder, and then a molded body of a predetermined shape is produced by press molding, slip casting, extrusion molding, injection molding, or the like (see Patent Documents 1 and 2).

[0004] These general molding methods are limited to shapes that can be removed from a mold, and require a mold, making them suitable for mass production, but they have the problem of being expensive when producing small lots due to the cost of the mold.

[0005] Furthermore, a method for producing complex shapes is known in which a large amount of organic binder is mixed to obtain a molded body with a hardness that can be processed. The problem with this method is that the density of the raw material powder is low due to the large amount of organic binder used, making the binder removal process difficult in a vacuum or inert gas. At the same time, the sintering shrinkage is large, which reduces the processing precision of the final sintered body, and secondary processing is required, resulting in high costs. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-330924 [Patent Document 2] Japanese Patent Application Publication No. 10-53453 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventional methods such as slip casting and extrusion molding are limited in the shapes that can be formed, making it difficult to form sintered bodies with arbitrary complex shapes. In addition, methods of processing strong molded bodies by mixing a large amount of organic binder have issues with binder removal and secondary processing.

[0008] An object of the present invention is to solve the above problems and to provide a method for producing a sintered body that has a degree of freedom in shape and that can provide a sintered body with a complex shape, which has been difficult to achieve in the past. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention proposes a method for manufacturing a difficult-to-sinter body that includes a molding step in which a difficult-to-sinter powder raw material is molded into a cylindrical or disk shape, a heating step in which the raw material after the molding step is heated and sintered, and a machining step in which the raw material is machined after the heating step to obtain the required processing strength.

[0010] Furthermore, the molding step is a step of filling a tantalum container with a raw material whose main ingredient is a sinter-resistant powder, and the heating step is a step of heating the sinter-resistant powder together with the container in a vacuum or inert atmosphere under normal pressure at a temperature below the lower of the melting points of tantalum and the sinter-resistant powder to obtain a sinter-resistant body.

[0011] The sinter-resistant powder includes any one of boron, silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina.

[0012] Furthermore, when the heating step is defined as a first heating step, the manufacturing method may include a second heating step of reheating the hard-to-sinter body processed in the machining step. The second heating step is expected to promote sintering of the sintered body, improving the properties of the sintered body.

[0013] Furthermore, the raw material containing boron as a main raw material is preferably heated in the range of 1400 to 2280° C. in the first heating step. Furthermore, the raw material containing silicon carbide as a main raw material is preferably heated to a temperature in the range of 1400 to 2680°C in the first heating step.

[0014] Moreover, the raw material containing yttria as a main raw material is preferably heated in the range of 1400 to 2400° C. in the first heating step. Furthermore, the raw material containing boron nitride as a main raw material is preferably heated in the range of 1400 to 2680° C. in the first heating step.

[0015] Furthermore, the raw material containing zirconia as a main raw material is preferably heated in the range of 1400 to 2700°C in the first heating step. Furthermore, the raw material containing boron carbide as a main raw material is preferably heated to a temperature in the range of 1400 to 2400°C in the first heating step.

[0016] Furthermore, the raw material containing tungsten carbide as a main raw material is preferably heated to a temperature in the range of 1400 to 2850°C in the first heating step. Furthermore, the raw material containing titanium nitride as a main raw material is preferably heated in the range of 1400 to 3000° C. in the first heating step.

[0017] The raw material containing titanium carbide as a main raw material is preferably heated to a temperature in the range of 1400 to 2680° C. in the first heating step. Furthermore, the raw material containing molybdenum as a main raw material is preferably heated in the range of 1400 to 2580°C in the first heating step.

[0018] Furthermore, the raw material containing tungsten as a main raw material is preferably heated to a temperature in the range of 1400 to 3000° C. in the first heating step. Moreover, the raw material containing alumina as a main raw material is preferably heated in the range of 1400 to 2050°C in the first heating step. [Effects of the Invention]

[0019] According to the present invention, it is possible to obtain complex shapes by machining, and there is a degree of freedom in the shape, making it possible to manufacture sintered bodies that can have complex shapes, which was previously difficult to achieve. [Brief explanation of the drawings]

[0020] [Figure 1] 1(a) and 1(b) are perspective views of a container according to one embodiment. [Figure 2] 10(a) and 10(b) are perspective views of a container according to another embodiment. [Figure 3] (a) and (b) are photographs of the difficult-to-sinter bodies of Examples 1 and 2, (c) is a photograph of the difficult-to-sinter body of Example 3, (d) is a photograph of the difficult-to-sinter body of Example 4, (e) is a photograph of the difficult-to-sinter body of Example 5, (f) is a photograph of the difficult-to-sinter body of Example 6, and (g) is a photograph of the difficult-to-sinter body of Example 7. [Figure 4] 1 is a photograph of the difficult-to-sinter body of Example 8. [Figure 5] 10 is a photograph of the difficult-to-sinter body of Example 9. [Figure 6] 1 is a photograph of the difficult-to-sinter body of Example 10. [Figure 7] 1 is a photograph of the difficult-to-sinter body of Example 11. [Figure 8] 1 is a photograph of the difficult-to-sinter body of Example 12. [Figure 9] 1 is a photograph of the difficult-to-sinter body of Example 13. [Figure 10] 1 is a photograph of the difficult-to-sinter body of Example 14. [Figure 11] 1 is a photograph of the difficult-to-sinter body of Example 15. [Figure 12] 1 is a photograph of the difficult-to-sinter body of Example 16. [Figure 13] 1 is a photograph of the difficult-to-sinter body of Example 17. DETAILED DESCRIPTION OF THE INVENTION

[0021] <1. Difficult to sinter powder> The sinter-resistant powder is an inorganic ceramic powder, a metal powder, or a semi-metal powder. Examples of ceramic powders include powders of silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, and alumina. These difficult-to-sinter powders are typical examples that are difficult to mold without the addition of an organic binder.

[0022] Examples of metal powders include molybdenum and tungsten powders. Examples of semi-metal powders include boron powders. The purity of the components of raw materials that mainly use these sinter-resistant powders as the sinter-resistant powder is preferably 95% or higher. It is even better if the purity of the components of raw materials that mainly use the sinter-resistant powder as the sinter-resistant powder is 99% or higher, but this is not limited thereto.

[0023] The particle size of the powder is preferably from several nm to several μm, and particularly preferably from submicron to several μm, but is not limited thereto. <2. Baking conditions for the first heating step> 2.1. Sintering temperature When the melting point of the sinter-resistant powder exceeds the melting point of tantalum (3020°C), the upper limit of the heating temperature for forming a sinter-resistant body in a vacuum or under normal pressure of an inert gas in the first heating step is lower than the melting point of tantalum.

[0024] Furthermore, when the melting point of the sinter-resistant powder is equal to or lower than the melting point of tantalum (3020°C), the upper limit of the heating temperature for forming a sinter-resistant body in a vacuum or under normal pressure of an inert gas is lower than the melting point of the sinter-resistant powder.

[0025] Furthermore, after filling a container with a hard-to-sinter powder and molding it under pressure, the sintering temperature in a vacuum or under normal pressure in an inert gas is set to a higher temperature than the sintering temperature when fired under high pressure.

[0026] Generally, for difficult-to-sinter bodies (such as zirconia), the higher the sintering temperature, the higher the density, so the sintering temperature has a large effect on density. This is because heating promotes atomic diffusion and bonding, reducing porosity and increasing the overall density of the material. This first heating step provides the necessary strength for subsequent machining.

[0027] The melting point of silicon carbide is 2700°C, which is lower than the melting point of tantalum (3020°C). The sintering temperature of silicon carbide is preferably 1100 to 2680°C. The melting point of yttria is 2425°C, which is lower than the melting point of tantalum (3020°C).The sintering temperature of yttria is preferably 1400 to 2400°C.

[0028] The melting point of boron nitride is 2700°C, which is lower than the melting point of tantalum (3020°C).The sintering temperature of boron nitride is preferably 1200 to 2680°C. The melting point of zirconia is 2715°C, which is lower than the melting point of tantalum (3020°C). The sintering temperature of zirconia is preferably 1100 to 2700°C.

[0029] The melting point of boron carbide is 2427°C, which is lower than the melting point of tantalum (3020°C).The sintering temperature of boron carbide is preferably 1400 to 2400°C. The melting point of tungsten carbide is 2870°C, which is lower than the melting point of tantalum (3020°C). The sintering temperature of tungsten carbide is preferably 1400 to 2850°C.

[0030] The melting point of titanium nitride is 2700°C, which is lower than the melting point of tantalum (3020°C).The sintering temperature of titanium nitride is preferably 1400 to 2680°C. The melting point of titanium carbide is 3160°C, which exceeds the melting point of tantalum (3020°C). The sintering temperature of titanium carbide is preferably 1000 to 3000°C.

[0031] The melting point of molybdenum is 2600°C, which is lower than the melting point of tantalum (3020°C). The sintering temperature of molybdenum is preferably 1400 to 2580°C. The melting point of tungsten is 3422° C., which exceeds the melting point of tantalum (3020° C.). The sintering temperature of tungsten is preferably 1400 to 3000° C., which is lower than the melting point of tantalum (3020° C.).

[0032] The melting point of boron is 2300°C, which is lower than the melting point of tantalum (3020°C).The sintering temperature of boron is preferably 1400 to 2280°C. The melting point of alumina is 2072°C, which is lower than the melting point of tantalum (3020°C).The sintering temperature of alumina is preferably 1100 to 2050°C.

[0033] <2.2. Retention time> The holding time in the first heating step may be determined depending on the type of sinter-resistant powder, the thickness of the sinter-resistant body, etc., and is not limited thereto, but is preferably 1 hour or more and 10 hours or less.

[0034] <2.3. Firing atmosphere> The heating atmosphere in the first heating step is generally air or an inert gas. The production method of the present invention is pressureless firing in an inert atmosphere of an inert gas such as argon, or in vacuum.

[0035] Furthermore, atmospheric sintering or vacuum sintering is generally classified into liquid phase sintering, which promotes densification by generating a liquid phase at high temperatures using additives, and solid phase sintering, which promotes densification by mass transfer between solid phases without using a liquid phase.

[0036] <3. Container> The container is formed of a metal plate, for example, a tantalum plate, or a metal foil, for example, a tantalum foil. The container may be shaped so that the sinter-resistant powder is filled into the container in the filling step, and then sealed with a lid. The container may also be shaped so that the sinter-resistant powder is filled into the container body, and then sealed with a lid box. In this case, the container body and the lid box together constitute the container. In this way, the sinter-resistant powder filled into the container is covered by the container (including the lid) by the lid box or by crushing. This step corresponds to a molding step. The container has heat resistance that can withstand the heating temperature in the heating step.

[0037] The shape of the container can be cylindrical or disk-like. Figures 1(a) and 1(b) show examples of cylindrical containers. Figure 1(a) shows a cylindrical container 10 formed by rolling tantalum foil into a cylinder. Because tantalum foil is flexible, the lower end 10a is crushed and closed as shown in Figure 1(a). In this state, hard-to-sinter powder is filled into the container 10 through the open upper end 10b, and then the upper end 10b is crushed and closed as shown in Figure 1(b).

[0038] 2(a) shows an example of a disk-shaped container 20. The disk-shaped container 20 (in this case, the container body) is formed into a box shape with a bottom by press-molding a tantalum plate, for example.

[0039] In the state shown in Figure 2(a), the hard-to-sinter powder is filled into the container 20 (container body) from the open top end, and then the container is covered with a lid box 22, which is also formed into a disk-like shape with a lid by press molding, as shown in Figure 2(b).

[0040] When the sinter-resistant powder is filled and sintered in a cylindrical or disk-shaped container 10, 20, a cylindrical or disk-shaped sinter-resistant body is obtained. In this case, the cylindrical or disk-shaped sinter-resistant body has no corners compared to a sinter-resistant body filled and sintered in a rectangular columnar or square disk-shaped container, so it can be expected that the entire body will be sintered uniformly.

[0041] <Processing process> The processing tools used in the processing step, i.e., the machining step, include cutting tools (face mills, end mills, side cutters, chamfering cutters, drills, reamers, taps, etc.), grinding tools (grinding wheels), etc.

[0042] Cutting tools are used to mill, drill, cut edges, etc. Surface grinding, cylindrical grinding, internal grinding, etc. are performed using a grinding tool. It is preferable that the hardness of the processing tools (including cutting tools, grinding tools, etc.) be higher than that of the difficult-to-sinter body. A difference in hardness of 40HRC in Rockwell hardness is preferable because it allows stable processing.

[0043] Furthermore, if the difference in hardness between the processing tool (including cutting tools, grinding tools, etc.) and the difficult-to-sinter body is 20HRC on the Rockwell hardness scale, processing is still possible. Therefore, the aforementioned hardness difference should be in the range of 20HRC to 40HRC.

[0044] This machining process allows the difficult-to-sinter body to be given a complex shape. <Sintering conditions for the second heating step> The sintering temperature, holding time, and firing atmosphere of the second heating step are the same as those described above in <2.1. Sintering temperature>, <2.2. Holding time>, and <2.3. Firing atmosphere>. The second heating step corresponds to reheating.

[0045] <Example> <Examples 1 to 7> Examples 1 to 7 will be described below.

[0046] In Examples 1 and 2, boron powder was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. After that, the upper end 10b of the container 10 was crushed, and then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 0.16 g of difficult-to-sinter bodies were obtained for Examples 1 and 2.

[0047] In Example 3, boron powder was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 5 hours. 0.27 g of the difficult-to-sinter body of Example 3 was obtained.

[0048] In Example 4, boron powder was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 10 hours. 0.49 g of the difficult-to-sinter body of Example 3 was obtained.

[0049] In Example 5, boron powder was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 1800°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 1800°C for 1 hour. 0.78 g of the difficult-to-sinter body of Example 5 was obtained.

[0050] In Example 6, boron powder was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 1600°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 1600°C for 1 hour. 1.02 g of the difficult-to-sinter body of Example 6 was obtained.

[0051] In Example 7, boron powder was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 1400°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 1400°C for 1 hour. 0.42 g of the difficult-to-sinter body of Example 7 was obtained.

[0052] The container 10 used in Examples 1 to 7 was formed to have a diameter of 6 mm by winding tantalum foil with a thickness of 50 μm around a rod with a diameter of 6 mm. The amount of boron powder filled into the container 10 depends on the length of the container in each example.

[0053] The sinter-resistant boron powder used was a commercially available product (manufactured by Nilaco Corporation, product number: B-054101, purity: 98%).

[0054] [Table 1] The hard-to-sinter bodies of Examples 1 to 7 were naturally cooled in the carbon furnace after heating was completed.

[0055] <Hard-to-sinter bodies of Examples 1 and 2> 3(a) and 3(b) are photographs of the hard-to-sinter bodies of Examples 1 and 2. In Examples 1 and 2, it was confirmed that the bodies were formed into a cylindrical shape due to sintering shrinkage that progressed from the shape filled in the container 10 by sintering.

[0056] Example 1 shown in Figure 3(a) is a photograph of the difficult-to-sinter body after holes have been drilled. Example 2 shown in Figure 3(b) is a photograph of the difficult-to-sinter body after cutting from the center to the bottom end, making it narrower than the top end.

[0057] It was confirmed that complex shapes could be formed by drilling in Example 1 and cutting in Example 2 without chipping or cracking. This shows that the hard-to-sinter bodies of Examples 1 and 2 have a hardness sufficient for machining.

[0058] A straight drill (Ishihashi Seikosha, part number D100-RS) was used to drill the holes in the example shown in Figure 3(a). In the example shown in Figure 3(b), the peripheral surface was cut using a commercially available tool, tapering from the center to one end in the longitudinal direction. This enabled the difficult-to-sinter body to be shaped into a complex shape.

[0059] <Hard-to-sinter bodies of Examples 3 and 4> 3(c) and 3(d) are photographs of the hard-to-sinter bodies of Examples 3 and 4. It was confirmed that in Examples 3 and 4, sintering shrinkage progressed from the shape filled in the container 10 by sintering, resulting in a cylindrical shape. It was also confirmed that sintering shrinkage occurred more in Example 4 than in Example 3, because the holding time was longer.

[0060] <Hard-to-sinter body of Example 5> FIG. 3(e) is a photograph of the difficult-to-sinter body of Example 5. In Example 5, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by firing, resulting in a cylindrical shape. As shown in FIG. 3(e), the lower end of the difficult-to-sinter body widens downward. This is because the lower end of the container 10 has been crushed, and the thickness of the container 10 gradually decreases toward the lower end. It was confirmed that the shape of the difficult-to-sinter body was also formed to match the shape of the tantalum container.

[0061] <Hard-to-sinter body of Example 6> FIG. 3(f) is a photograph of the difficult-to-sinter body of Example 6. It was confirmed that in Example 6, sintering shrinkage progressed from the shape filled in the container 10 by firing, resulting in a cylindrical shape. As shown in FIG. 3(f), two difficult-to-sinter bodies are photographed, but these separated into two when removed from the container 10. They tend to be slightly more embrittled than the difficult-to-sinter body of Example 5. However, when the difficult-to-sinter body of Example 6 is intended for use in pellet form (cylindrical), it is at a level that does not pose any problems when used in pellet form (cylindrical).

[0062] <Hard-to-sinter body of Example 7> FIG. 3(g) is a photograph of the difficult-to-sinter body of Example 7. It was confirmed that in Example 7, sintering shrinkage progressed from the shape filled in the container 10 by firing, resulting in a cylindrical shape. As shown in FIG. 3(g), three difficult-to-sinter bodies are photographed, but these separated into three when removed from the container 10. They tend to be slightly more embrittled than the difficult-to-sinter body of Example 6. However, when the difficult-to-sinter body of Example 7 is intended for use in pellet form (cylindrical), it is at a level that does not pose any problems when used in pellet form (cylindrical).

[0063] <Second heating step of the hard-to-sinter bodies of Examples 1 to 7> The difficult-to-sinter bodies of Examples 3 to 7 were subjected to hole drilling in the same manner as in Example 1. The difficult-to-sinter bodies of Examples 3 to 7 were not cracked or chipped by the hole drilling. This enabled the difficult-to-sinter bodies to be formed into complex shapes.

[0064] <Second heating step of the hard-to-sinter bodies of Examples 1 to 7> The hard-to-sinter body having holes drilled therein as described above was subjected to a second heating step according to <2.1. Sintering temperature>, <2.2. Holding time>, and <2.3. Firing atmosphere> as required.

[0065] By subjecting the hard-to-sinter body to the second heating step, the sintering of the hard-to-sinter body is promoted, and it is expected that the properties of the hard-to-sinter boron body will be improved. <Examples 8 to 12> Examples 8 to 12 will be described.

[0066] In Example 8, tungsten carbide was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace at a sintering temperature of 2000°C under vacuum. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 4.21 g of a difficult-to-sinter body was obtained.

[0067] The tungsten carbide used was a commercially available product (manufactured by Nilaco Corporation, product number: W-467201, purity: 99.5%). In Example 9, titanium nitride was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 1.69 g of a difficult-to-sinter body was obtained.

[0068] The titanium nitride used was a commercially available product (manufactured by Nilaco Corporation, product number: TI-457301, purity: 99%). In Example 10, titanium carbide was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 1.26 g of a difficult-to-sinter body was obtained.

[0069] The titanium carbide used was a commercially available product (manufactured by Nilaco Corporation, product number: TI-457201, purity: 98%). In Example 11, molybdenum was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were a temperature increase of 30°C per minute and a holding time of 1 hour at the sintering temperature of 2000°C. 1.78 g of a difficult-to-sinter body was obtained.

[0070] The molybdenum used was a commercially available product (manufactured by Kojundo Chemical Laboratory, product number: MOE05PB, purity: 99.9% up). In Example 12, tungsten was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a) and compressed along the longitudinal direction of the container 10. The upper end 10b of the container 10 was then crushed, and the container 10 was then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were a temperature increase of 30°C per minute and a holding time of 1 hour at the sintering temperature of 2000°C. 3.44 g of a difficult-to-sinter body was obtained.

[0071] The tungsten used was a commercially available product (manufactured by Nilaco Corporation, product number: W-464101, purity: 99.95%).

[0072] [Table 2] The hard-to-sinter bodies of Examples 8 to 12 were naturally cooled in the carbon furnace after heating was completed.

[0073] <Hard-to-sinter bodies of Examples 8 to 12> In Examples 8 to 12, one of the vertical ends of the difficult-to-sinter body is wider than the other end, which indicates that one end of the container 10 is crushed, and the thickness of the container 10 gradually decreases. This indicates that the shape of the difficult-to-sinter body is also formed to match the shape of the tantalum container.

[0074] <Hard-to-sinter bodies of Examples 8 and 9> 4 and 5 are photographs of the difficult-to-sinter tungsten carbide body of Example 8 and the difficult-to-sinter titanium nitride body of Example 9. It was confirmed that in both Examples 8 and 9, sintering shrinkage progressed from the shape filled in the container 10 by sintering to a cylindrical shape.

[0075] <Hard-to-sinter bodies of Examples 10, 11, and 12> 6, 7 and 8 are photographs of the titanium carbide body difficult to sinter in Example 10, the molybdenum body difficult to sinter in Example 11, and the tungsten body difficult to sinter in Example 12.

[0076] It was confirmed that in all of Examples 10, 11, and 12, the shape of the material packed in the container 10 by sintering progressed due to sintering shrinkage, and the material was formed into a cylindrical shape. <Cutting of Hard-to-Sinter Bodies of Examples 8 to 12> The difficult-to-sinter bodies of Examples 8 to 12 were subjected to hole drilling in the same manner as in Example 1. The difficult-to-sinter bodies of Examples 8 to 12 were not cracked or chipped by the hole drilling. This enabled the difficult-to-sinter bodies to be formed into complex shapes.

[0077] <Second heating step of hard-to-sinter bodies of Examples 8 to 12> The hard-to-sinter body having holes drilled therein as described above was subjected to a second heating step according to <2.1. Sintering temperature>, <2.2. Holding time>, and <2.3. Firing atmosphere> as required.

[0078] By subjecting the difficult-to-sinter body to the second heating step, sintering of the difficult-to-sinter body is promoted, and it is expected that the properties of the difficult-to-sinter body will be improved. <Examples 13 to 18> Examples 13 to 18 will be described.

[0079] In Example 13, silicon carbide was filled without an organic binder into a 10 mm diameter container 10 shown in FIG. 1(a), and its upper end 10b was crushed. The material was then sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 1.06 g of a difficult-to-sinter body was obtained.

[0080] The silicon carbide used was a commercially available product (manufactured by Kojundo Chemical Laboratory, product number: SII01PB, purity: 99%). In Example 14, yttria was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a), and its upper end 10b was crushed. After that, the mixture was sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 1.13 g of a difficult-to-sinter body was obtained.

[0081] The yttria used was a commercially available product (manufactured by Shin-Etsu Chemical Co., Ltd., purity: 99.9%). In Example 15, boron nitride was filled without an organic binder into a 6 mm diameter container 10 shown in Figure 1(a), and its upper end 10b was crushed. After that, it was sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 0.18 g of a difficult-to-sinter body was obtained.

[0082] The boron nitride used was a commercially available product (manufactured by Mizushima Ferroalloy Co., Ltd., GRADE, HP-2, JB). In Example 16, zirconia was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a), and its upper end 10b was crushed. After that, it was sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 1.12 g of a difficult-to-sinter body was obtained.

[0083] The zirconia used was a commercially available product (Kyoritsu Ceramic Materials Co., Ltd., product number: KZ-0Y, purity: 99.9%). In Example 17, boron carbide was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a), and its upper end 10b was crushed. After that, it was sintered in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 2000°C for 1 hour. 0.84 g of a difficult-to-sinter body was obtained.

[0084] The boron carbide used was a commercially available product (manufactured by ESK Ceramics). In Example 18, alumina was filled without an organic binder into a 6 mm diameter container 10 shown in FIG. 1(a), and its upper end 10b was crushed. The material was then fired in a carbon furnace under vacuum at a sintering temperature of 1800°C. The heating conditions were to increase the temperature at a rate of 30°C per minute and hold the sintering temperature at 1800°C for 1 hour. 0.67 g of a difficult-to-sinter body was obtained. Commercially available alumina (manufactured by Kojundo Chemical Co., Ltd., purity: 99.99%) was used.

[0085] [Table 3] The hard-to-sinter bodies of Examples 13 to 18 were naturally cooled in the carbon furnace after heating was completed.

[0086] <Hard-to-sinter bodies of Examples 13 and 14> Fig. 9 is a photograph of the silicon carbide sinter-resistant body of Example 13. Fig. 10 is a photograph of the yttria sinter-resistant body of Example 14.

[0087] It was confirmed that the hard-to-sinter bodies of Examples 13 and 14 were formed into a cylindrical shape due to sintering shrinkage that progressed from the shape filled in the container 10 by sintering. <Hard-to-sinter bodies of Examples 15, 16, 17, and 18> Fig. 11 is a photograph of the sinter-resistant boron nitride body of Example 15. Fig. 12 is a photograph of the sinter-resistant zirconia body of Example 16. Fig. 13 is a photograph of the sinter-resistant boron carbide body of Example 17. Note that a photograph of the sinter-resistant body of Example 18 is omitted.

[0088] It was confirmed that the hard-to-sinter bodies of Examples 15, 16, 17, and 18 were formed into a cylindrical shape due to sintering shrinkage that progressed from the shape filled in the container 10 by firing. The hard-to-sinter boron carbide body of Example 17 was divided into three pieces when removed from the container 10. Each divided hard-to-sinter body itself maintained its hard sintered state.

[0089] <Cutting of Hard-to-Sinter Bodies of Examples 13 to 18> The difficult-to-sinter bodies of Examples 13 to 18 were subjected to hole drilling in the same manner as in Example 1. The difficult-to-sinter bodies of Examples 13 to 18 were not cracked or chipped by the hole drilling. This enabled the difficult-to-sinter bodies to be formed into complex shapes.

[0090] <Second heating step of hard-to-sinter bodies of Examples 13 to 18> The hard-to-sinter body having holes drilled therein as described above was subjected to a second heating step according to <2.1. Sintering temperature>, <2.2. Holding time>, and <2.3. Firing atmosphere> as required.

[0091] By subjecting the difficult-to-sinter body to the second heating step, sintering of the difficult-to-sinter body is promoted, and it is expected that the properties of the difficult-to-sinter body will be improved. <Other Examples> Table 4 shows the results of an evaluation test of the hardness of difficult-to-sinter bodies obtained by sintering tungsten carbide, titanium nitride, titanium carbide, molybdenum, and tungsten in the first heating step at 1400°C, 1800°C, and 2000°C. The firing conditions for these first heating steps were the same as those in Example 1, except for the heating temperature.

[0092] The evaluation was based on whether or not drilling, as in Example 1, was possible. As a result of the processing, i.e., if there were no cracks or chips, the evaluation was given as "○", if there was partial fracture, the evaluation was given as "△", and if there was cracking, the evaluation was given as "×". The hard-to-sinter bodies that were evaluated as "○" and "△" can be cut and ground.

[0093] [Table 4] As shown in Table 4, tungsten carbide, titanium nitride, titanium carbide, molybdenum, and tungsten are all rated "○" and can be cut and ground. That is, these difficult-to-sinter bodies can be cut and ground even when heated to 1400°C and 1800°C in the first heating step. Furthermore, although evaluation tests at 1600°C have not been conducted on these difficult-to-sinter bodies, the evaluations at 1400°C and 1800°C are rated "○." Therefore, if evaluation tests were conducted at 1600°C, it can be assumed that the evaluation would also be "○."

[0094] Table 5 shows the results of an evaluation test of the hardness of difficult-to-sinter bodies obtained by firing silicon carbide, yttria, boron nitride, zirconia, boron carbide, and alumina at 1400°C, 1600°C, 1800°C, and 2000°C in the first heating step. The firing conditions for these first heating steps were the same as those in Example 1, except for the heating temperature. The evaluation method was the same as in the other examples described above.

[0095] It should be noted that evaluation tests at 1600°C were not conducted on yttria, boron nitride, and zirconia.

[0096] [Table 5] As shown in Table 5, silicon carbide and alumina were evaluated as "○" or "△" at 1400°C, 1600°C, 1800°C and 2000°C, and can be cut and ground.

[0097] Boron carbide is rated as "Good" or "Good" at 1400°C, 1600°C, and 1800°C, and can be cut and ground. Boron carbide has not been evaluated at 2000°C.

[0098] Furthermore, yttria, boron nitride, and zirconia were evaluated as "good" at 1400°C, 1800°C, and 2000°C, and are therefore suitable for cutting and grinding. Although evaluation tests at 1600°C have not been conducted on yttria, boron nitride, and zirconia, they have been rated as "Good" at 1400°C and 1800°C. Therefore, if evaluation tests were conducted at 1600°C, it can be assumed that they would also be rated as "Good."

[0099] Therefore, the hard-to-sinter bodies of the other embodiments described above can be subjected to various processes in the machining process, and can also be subjected to the second heating process. This embodiment can be implemented with the following modifications: This embodiment and the following modifications can be implemented in combination with each other within the scope of technical compatibility.

[0100] In the above embodiment, the container is filled with an organic binder-free, sinter-resistant material in the molding process, but a sinter-resistant material mixed with a small amount of organic binder may also be used. · Tungsten carbide and titanium carbide, which are difficult to sinter, can be used as superhard materials.

[0101] · Difficult-to-sinter titanium nitride can be used, for example, as anti-corrosion coatings, medical implants, and surgical tools. · Molybdenum, which is difficult to sinter, can be used as tools or electronic substrates.

[0102] · Tungsten, which is difficult to sinter, can be used as armor and shielding material. ·Silicon carbide, which is difficult to sinter, can be used in the semiconductor and aerospace industries. -Yttria's hard-to-sinter body can be used in lasers and high-temperature superconductors.

[0103] · Boron nitride, which is difficult to sinter, can be used as a mold release agent and lubricant. Difficult-to-sinter zirconia can be used as a piezoelectric element or biomaterial. · Boron carbide, which is difficult to sinter, can be used as a shielding material and bulletproof material. [Explanation of symbols]

[0104] 10...Container 20…Container

Claims

1. A method for manufacturing a difficult-to-sinter body, comprising: a molding step in which a raw material, which is an inorganic, difficult-to-sinter powder, is molded into a cylindrical or disc shape; a heating step in which the raw material after the molding step is heated and fired without combustion synthesis; and a machining step in which the raw material is machined after obtaining the required processing strength in the heating step.

2. The molding step is a step of filling a tantalum container with a sinter-resistant powder, 2. The method for producing a difficult-to-sinter body according to claim 1, wherein the heating step is a step of obtaining a difficult-to-sinter body by heating the difficult-to-sinter powder together with the container at a temperature below the lower melting point of tantalum and the difficult-to-sinter powder in a vacuum or in an inert atmosphere under normal pressure.

3. 3. The method for producing a difficult-to-sinter body according to claim 1 or 2, wherein the difficult-to-sinter powder contains any one of boron, silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina.

4. The method for producing a difficult-to-sinter body according to claim 3, further comprising a second heating step of reheating the difficult-to-sinter body processed in the machining step, when the heating step is defined as a first heating step.

5. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing boron as a main raw material is heated in the range of 1400 to 2280 ° C. in the first heating step.

6. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing silicon carbide as a main raw material is heated in the range of 1400 to 2680 ° C. in the first heating step.

7. 5. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing yttria as a main raw material is heated to a temperature in the range of 1400 to 2400°C in the first heating step.

8. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing boron nitride as a main raw material is heated in the range of 1400 to 2680 ° C. in the first heating step.

9. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing zirconia as a main raw material is heated in the range of 1400 to 2700 ° C. in the first heating step.

10. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing boron carbide as a main raw material is heated in the range of 1400 to 2400 ° C. in the first heating step.

11. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing tungsten carbide as a main raw material is heated in the range of 1400 to 2850 ° C. in the first heating step.

12. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing titanium nitride as a main raw material is heated to a temperature in the range of 1400 to 2680°C in the first heating step.

13. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing titanium carbide as a main raw material is heated to a temperature in the range of 1400 to 3000°C in the first heating step.

14. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing molybdenum as a main raw material is heated to a temperature in the range of 1400 to 2580°C in the first heating step.

15. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing tungsten as a main raw material is heated to a range of 1400 to 3000 ° C. in the first heating step.

16. The method for producing a difficult-to-sinter body according to claim 4, wherein the raw material containing alumina as a main raw material is heated in the range of 1400 to 2050 ° C. in the first heating step.

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