Molybdenum composite material, molybdenum composite material molded article using the same, and method for producing molybdenum composite material

Abstract

To provide a molybdenum composite material excellent in heat resistance and durability and also excellent in production cost and production efficiency, to provide a molybdenum composite material molded article using the same, and to provide a method for producing the molybdenum composite material.SOLUTION: A molybdenum composite material comprising molybdenum as a main component and 2 to 10% by mass of at least one kind of carbides selected from carbides of Ti, carbides of Zr, and carbides of Hf, the molybdenum composite material being a sintered body of a mixed powder of a molybdenum powder and a carbides powder, wherein a mean area of Voronoi tessellation is 80 μ m2 or less, and a standard deviation-mean value, which is a coefficient of variation of the area of Voronoi tessellation, is 1.8 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a molybdenum composite material, a molybdenum composite material molded article using the same, and a method for producing the molybdenum composite material. [Background technology]

[0002] Conventionally, composite current collectors in which Cu is vapor-deposited on the surface of a substrate such as PET have been proposed as negative electrode current collectors for lithium-ion batteries, instead of copper foil.

[0003] A tungsten evaporation boat is used for Cu evaporation to produce such a composite current collector.

[0004] However, although tungsten evaporation boats have good heat resistance, they have poor durability and tend to break after just one use.

[0005] Therefore, we considered using a molybdenum alloy evaporation boat, which is based on molybdenum, which has inferior heat resistance to tungsten but excellent workability, and to which a high-melting point compound was added, but there was a problem in that it was not strong enough.

[0006] Conventionally, Patent Documents 1 to 4 are known as molybdenum alloys.

[0007] In Patent Documents 1 and 2, mechanical alloying is an essential condition for adding a transition metal carbide to molybdenum. However, this method is a high-energy mixing method that embeds carbide particles in molybdenum particles, which poses problems in terms of production cost and production efficiency.

[0008] Furthermore, Patent Document 1 employs a densification process using hot isostatic pressing (HIP), which also poses problems in terms of production cost and production efficiency.On the other hand, Patent Document 2 employs spark plasma sintering (SPS) as the sintering method, but SPS is a method for producing relatively small samples, which also makes it unsuitable for manufacturing evaporation boats. Furthermore, Patent Document 3 discloses a material in which carbides of Ti, Zr, Hf, etc. are added to molybdenum, and a method for producing the same. Patent Document 3 states that poor dispersion of carbide particles, etc., results in insufficient strength, but does not specify a powder mixing method or indicators of dispersibility, and does not provide any information on how to achieve good carbide particle dispersibility in the molybdenum composite material of the present invention. Furthermore, Patent Document 3 also uses HIP as the sintering method, which also poses problems in terms of production cost and production efficiency.

[0009] Furthermore, Patent Document 4 discloses a material in which titanium carbide, hafnium carbide, zirconium carbide, or tantalum carbide is added to molybdenum. Patent Document 4 describes a powder mixing method in which carbide powders such as Mo powder and TiC are prepared and mixed in a ball mill or the like, but does not specify an index of dispersibility.

[0010] In any case, according to Patent Documents 1 to 4, the dispersibility of the molybdenum powder and additive particles and the sintering state seem to be problems for molybdenum alloys, but there is a need for a molybdenum composite material that is excellent in the targeted heat resistance and durability, and is also excellent in terms of production cost and production efficiency. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 3271040 [Patent Document 2] Patent Publication No. 2000-129389 [Patent Document 3] Patent No. 5546880 [Patent Document 4] Patent No. 5238259 Summary of the Invention [Problem to be solved by the invention]

[0012] However, we found that the heat resistance, processability, strength, and other durability of the resulting material vary greatly depending on the combination of various conditions, such as the particle size of the raw powder, the conditions for crushing and grinding the raw powder, the mixing conditions, the sintering conditions, and the molding conditions. In particular, the dispersibility of the powder in molybdenum composite materials has a significant impact on durability, but even slight changes in the particle size distribution of the raw materials or the hardness of the powder make it difficult to determine the optimal combination with the mixing conditions. We also found that the environment during mixing, especially the temperature, has a significant impact on the dispersion state.

[0013] As a result of examining various molybdenum composite materials, the inventors discovered that molybdenum composite materials with good durability can be identified by focusing on the average area of ​​the Voronoi tessellation of the molybdenum composite material, and completed the present invention.

[0014] An object of the present invention is to provide a molybdenum composite material that is excellent in heat resistance and durability and is also excellent in terms of production cost and production efficiency, a molybdenum composite material molded article using the same, and a method for producing the molybdenum composite material. [Means for solving the problem]

[0015] In order to achieve the above object, a first aspect of the present invention is a molybdenum composite material which is a sintered body of a mixed powder of molybdenum powder and a carbide powder, the mixed powder containing molybdenum as a main component and containing 2 to 10 mass % of at least one carbide selected from the group consisting of a carbide of Ti, a carbide of Zr, and a carbide of Hf, and which has an average area of ​​Voronoi division of 80 μm or less. 2 The molybdenum composite material has a standard deviation / average value, which is the coefficient of variation of the area of ​​Voronoi division, of 1.8 or less.

[0016] A second aspect of the present invention is the molybdenum composite material according to item 1, which has a maximum bending strength of 1000 MPa or more at room temperature after heating in a vacuum at 1800°C for 8 hours, and exhibits ductile deformation behavior.

[0017] A third aspect of the present invention resides in the molybdenum composite material according to item 1, which has a Vickers hardness of 200 HV or more after heating in a vacuum at 1800° C. for 8 hours.

[0018] A fourth aspect of the present invention is the molybdenum composite material according to item 3, wherein the Vickers hardness before and after heating in a vacuum at 1800°C for 8 hours is measured, and the hardness reduction rate (%), calculated by subtracting the hardness after heating from the hardness before heating and dividing the result by the hardness before heating, is 30% or less.

[0019] A fifth aspect of the present invention resides in the molybdenum composite material according to 1, which is obtained by crushing and pulverizing the molybdenum powder and the carbide powder, mixing them, and hot pressing the mixed powder.

[0020] In a sixth aspect of the present invention, the molybdenum powder has an average particle size D obtained by a laser diffraction / scattering method. Ave The carbide powder has an average particle size D Ave 6. The molybdenum composite material according to 5, wherein the average particle diameter is 1.5 to 3.0 μm and the median diameter D50 is 1.0 to 2.5 μm.

[0021] In a seventh aspect of the present invention, the average particle size D of the mixed powder is Ave 6. The molybdenum composite material according to 5, wherein the average particle diameter is 1.5 to 3.5 μm and the median diameter D50 is 1.0 to 3.0 μm.

[0022] An eighth aspect of the present invention is a molybdenum composite material molded article obtained by molding any one of the molybdenum composite materials of 1 to 7 into a predetermined shape.

[0023] A ninth aspect of the present invention is a sintered body comprising a step of preparing a molybdenum powder and at least one carbide powder selected from a carbide powder of Ti, a carbide powder of Zr, and a carbide powder of Hf in a predetermined ratio, a step of crushing and pulverizing the molybdenum powder and the carbide powder and mixing them to obtain a mixed powder, and a step of sintering the mixed powder to obtain a sintered body mainly composed of molybdenum and containing at least one carbide selected from a carbide of Ti, a carbide of Zr, and a carbide of Hf in an amount ranging from 2 to 10 mass%, and having an average area of ​​Voronoi division of 80 μm 2 and obtaining a molybdenum composite material having a standard deviation / average value, which is the coefficient of variation of the area of ​​Voronoi division, of 1.8 or less.

[0024] A tenth aspect of the present invention is the method for producing a molybdenum composite material according to 9, wherein the step of obtaining the sintered body is carried out by hot pressing (HP) at a temperature of 1400°C or higher and 1800°C or lower.

[0025] In an eleventh aspect of the present invention, the molybdenum powder has an average particle size D obtained by a laser diffraction / scattering method. Ave The carbide powder has an average particle size D Ave 10. The method for producing a molybdenum composite material according to claim 9, wherein the average particle diameter is 1.5 to 3.0 μm and the median diameter D50 is 1.0 to 2.5 μm.

[0026] In a twelfth aspect of the present invention, the average particle size D of the mixed powder is Ave 12. The method for producing a molybdenum composite material according to 11, wherein the average particle diameter is 1.5 to 3.5 μm and the median diameter D50 is 1.0 to 3.0 μm.

[0027] A thirteenth aspect of the present invention resides in the method for producing a molybdenum composite material according to 9, wherein the step of crushing, pulverizing and mixing the molybdenum powder and the carbide powder is carried out by a rod mill.

[0028] A fourteenth aspect of the present invention resides in a method for producing a molybdenum composite material molded article, comprising molding a molybdenum composite material produced by any one of the molybdenum composite materials recited in 1 to 7 or any one of the molybdenum composite material manufacturing methods recited in 9 to 13 into a predetermined shape to obtain a molybdenum composite material molded article. [Effects of the Invention]

[0029] According to the present invention, it is possible to provide a molybdenum composite material that is excellent in heat resistance and durability and is also excellent in terms of production cost and production efficiency, a molybdenum composite material molded product using the same, and a method for producing a molybdenum composite material. [Brief explanation of the drawings]

[0030] [Figure 1] This is an example of an image in which carbide particles are identified as black particles through image processing from an electron microscope (SEM) image of a sample in which carbide particles are densely present and uniformly dispersed. [Figure 2] FIG. 2 is a diagram showing the Voronoi regions of the particles in FIG. 1 in black. [Figure 3] This is an example of an SEM image of a sample in which carbide particles are densely present but not uniformly dispersed, and the carbide particles have been identified as black particles using image processing. [Figure 4] FIG. 4 is a diagram showing Voronoi regions in black for the particles in FIG. 3. [Figure 5] This is an example of an SEM image of a sample in which carbide particles are not densely packed but are uniformly dispersed, and carbide particles have been identified as black particles through image processing. [Figure 6] The Voronoi regions for the particles in Figure 5 are shown in black. DETAILED DESCRIPTION OF THE INVENTION

[0031] The molybdenum composite material of the present invention is a sintered body mainly composed of molybdenum and containing 2 to 10 mass % of at least one carbide selected from the group consisting of Ti carbide, Zr carbide, and Hf carbide.

[0032] The molybdenum composite material of the present invention is produced using, as raw materials, molybdenum powder and at least one carbide powder selected from the group consisting of Ti carbide powder, Zr carbide powder, and Hf carbide powder.

[0033] Here, the carbide powder can be at least one selected from Ti carbide powder, Zr carbide powder, and Hf carbide powder, with Zr carbide powder being particularly preferred. The first reason is that if Ti carbide is partially oxidized during sintering, processing, or use, it becomes titanium oxide, which easily sublimes, and can become a source of atmospheric impurities, especially when heated in a vacuum. The second reason is that although Hf carbide has the same effect as Zr carbide, its material price is much higher than Zr carbide, leading to increased product costs.

[0034] The molybdenum powder used as the raw material has an average particle size D obtained by the laser diffraction / scattering method. Ave It is preferable to use powder having a particle size of 2.5 to 4.0 μm and a median diameter D50 of 2.0 to 3.5 μm.

[0035] The raw material carbide powder has an average particle size of D Ave It is preferable to use powder having a particle size of 1.5 to 3.0 μm and a median diameter D50 of 1.0 to 2.5 μm.

[0036] To obtain the molybdenum composite material of the present invention, the molybdenum powder and the carbide powder are crushed, pulverized, and mixed to obtain a mixed powder.

[0037] Average particle size D of the resulting mixed powder Ave It is preferable that the average particle diameter is 1.5 to 3.5 μm and the median diameter D50 is 1.0 to 3.0 μm.

[0038] In the present invention, the step of crushing, pulverizing, and mixing the molybdenum powder and the carbide powder is not particularly limited as long as it can obtain a desired mixed powder, but is preferably carried out using a rod mill (RM).

[0039] To obtain the molybdenum composite material of the present invention, the above-described composite material is hot pressed (HP) at a temperature of 1400°C or higher and 1800°C or lower.

[0040] Conventionally, sintered bodies have been obtained by hot isostatic pressing (HIP), but HIP is more expensive than HP and is a method that should be avoided if possible. However, in the present invention, sintered bodies with a relative density of 98% or more can be obtained by the HP method.

[0041] Furthermore, the molybdenum composite material of the present invention has good heat-resistant strength and heat-resistant hardness, i.e., it has good bending strength after heating, good hardness after heating, and the loss of hardness due to heating is small.

[0042] The bending strength after heating is 1000 MPa or more, preferably 1100 MPa or more, and in addition, it is preferable that the deformation behavior due to bending is ductile deformation rather than brittle fracture.

[0043] The hardness after heating is 200 or more, preferably 220 or more, in Vickers hardness (HV).

[0044] The hardness reduction rate (%), calculated by subtracting the hardness after heating from the hardness before heating and dividing the result by the hardness before heating, is 30% or less, and preferably 20% or less.

[0045] Here, "after heating" refers to vacuum heat treatment at 1800°C for 8 hours, taking into consideration the use as a deposition boat.

[0046] The present inventors have discovered that the dispersion state of carbides in a molybdenum composite material is closely related to the bending strength of the molybdenum composite material, and that if the dispersion state is good and the molybdenum composite material has predetermined dispersion characteristics, there will be no unevenness in bending strength or hardness.

[0047] Here, the predetermined dispersion characteristic is that the average area of ​​Voronoi division is 80 μm 2The standard deviation / average value, which is the coefficient of variation of the area of ​​the Voronoi division, is 1.8 or less, but details will be given later.

[0048] The physical properties of the molybdenum composite material of the present invention were evaluated as follows. (bending strength) From the molybdenum composite material of the present invention, a No. 3 test piece shaped as specified in JIS Z 2248 was cut out, and the bending strength was measured by the press bending method specified in JIS Z 2248. The measuring equipment used was an Imada load measurement stand "EMX-500N" combined with a three-point bending test jig "BT-500N."

[0049] (Deformation behavior) In the bending strength test, when the test piece was pressed 20 mm with a support distance of 20 mm, if it bent without breaking it was judged to be ductile, and if it broke it was judged to be brittle.

[0050] (Hardness) After use in the bending strength test, the undeformed portion of the end was cut off to prepare a test piece for hardness measurement, and the hardness was measured using the Vickers hardness tester specified in JIS Z 2244. The measuring device used was a Mitutoyo micro Vickers hardness tester "HM-200."

[0051] The molybdenum composite material of the present invention has excellent heat-resistant strength and heat-resistant hardness, but it is not clear whether the dispersion state of the carbide in the molybdenum composite material is optimal.

[0052] Furthermore, even if the current heat resistance strength and heat resistance hardness are within the desired range, if the dispersion state cannot be grasped, there is a possibility that the heat resistance strength and heat resistance hardness will be uneven.

[0053] Furthermore, even if the current dispersion state is optimal, the dispersion state of the carbide in the sintered body may change depending on the particle size distribution of the raw material powder, even if the crushing, grinding, and mixing conditions are the same, and it is not possible to always determine whether the dispersion state is good and whether the current heat-resistant strength and heat-resistant hardness are uniform.

[0054] As described above, the carbide dispersion state of the molybdenum composite material of the present invention is good when the average area of ​​Voronoi division is 80 μm or less. 2 It was found that this can be determined by the standard deviation / average value, which is the coefficient of variation of the area of ​​Voronoi division, being 1.8 or less.

[0055] This dispersibility was determined as follows. (dispersibility) After the bending strength test, the undeformed end of the specimen was cut and polished. Three SEM images were then taken at 2 mm intervals horizontally near the center of the thickness direction using a Hitachi High-Technologies Corporation electron microscope (TM4000Plus). The image analysis software (Image-J) was used to identify the location of carbide particles based on differences in contrast. Next, the image was divided using the "Voronoi" function of Image-J along a line connecting equidistant points from the boundaries of the two nearest particles. Each divided region (Voronoi region) contained one carbide particle. The area of ​​the Voronoi region was small where carbide particles were densely distributed, and large where carbide particles were sparsely distributed. The area of ​​each region divided by the "Voronoi" function was calculated using Image-J, and the sum of the areas was divided by the number of divided regions to determine the average area of ​​the Voronoi region. Furthermore, the standard deviation of the area of ​​the Voronoi region was divided by the average area to obtain the coefficient of variation of the area of ​​the Voronoi region.

[0056] Below, a method for grasping the dispersibility will be explained using a specific example of an image. Figure 1 shows an example of an image of a sample in which carbide particles are densely and uniformly dispersed, taken by scanning electron microscope (SEM), in which the carbide particles are identified as black particles through image processing. Figure 2 shows the Voronoi regions of the particles in Figure 1 in black. Two other SEM images were taken of this sample, and when the results of similar image processing were also averaged, the average area of ​​the Voronoi division was 30 μm 2 , the standard deviation of the area is 21 μm 2 The coefficient of variation, calculated by dividing the standard deviation by the average area, was 0.7. This sample corresponds to Example 7 described below.

[0057] Figure 3 shows an example of an SEM image of a sample in which carbide particles are densely present but not uniformly dispersed, in which the carbide particles are identified as black particles through image processing. Furthermore, Figure 4 shows the Voronoi regions of the particles in Figure 3 in black. Two other SEM images were taken of this sample, and the results were processed in the same way. The average area and coefficient of variation of the Voronoi division were calculated in the same way as for the sample in Figure 1. The average area of ​​the Voronoi division was 30 μm 2 The coefficient of variation of the area was 3.2. This sample corresponds to Comparative Example 15, which will be described later.

[0058] Figure 5 shows an example of an SEM image of a sample in which carbide particles are not densely distributed but are uniformly dispersed, in which carbide particles are identified as black particles through image processing. Furthermore, Figure 6 shows the Voronoi regions of the particles in Figure 5 in black. Two other SEM images were taken of this sample, and the results were processed in the same way. The average area and coefficient of variation of the Voronoi division were calculated in the same way as for the sample in Figure 1. The average area of ​​the Voronoi division was 100 μm 2 The coefficient of variation of the area was 0.8. This sample corresponds to Comparative Example 5, which will be described later.

[0059] (Meaning of the average area of ​​Voronoi regions) The smaller the average area of ​​the Voronoi regions obtained by the above method, the denser the carbide particles are in the molybdenum composite material as a whole. Furthermore, since the average area of ​​these Voronoi regions is essentially the same as the area of ​​the entire SEM image divided by the number of carbide particles contained in that image, the microstructure of the same molybdenum composite material can also be defined by the number of carbide particles contained in a cross-section of a certain area. However, while the average area of ​​the Voronoi regions and the number of carbide particles contained in a cross-section of a certain area can determine the overall concentration of carbide particles in a molybdenum composite material, they cannot define the local variation in the density of carbide particles.

[0060] (Importance of coefficient of variation) The inventors have discovered that the variation in density of carbide particles, or in other words, the dispersibility of carbide particles, has a significant impact on the physical properties of molybdenum alloys. Specifically, in materials in which carbide particles are dispersed in a molybdenum matrix to enhance heat resistance, the most important factor is the uniformity of the carbide particles, rather than the amount of carbide particles added. If carbide particles are added but there are many localized areas where no carbide particles are present, heating will promote molybdenum recrystallization in those areas, resulting in localized coarsening of molybdenum grains and resulting in poor heat resistance for the composite material as a whole. Therefore, the inventors have discovered that the heat resistance of molybdenum composite materials can be effectively explained by using the coefficient of variation of the Voronoi region area as an index of carbide particle density variation. Specifically, the smaller this coefficient of variation, the more uniformly the carbide particles are dispersed. From the above considerations, the molybdenum composite material of the present invention is characterized by the fact that the average area of ​​the Voronoi region of the carbide particles is 80 μm 2 and its coefficient of variation was specified as 1.8 or less.

[0061] The average area of ​​the Voronoi region of the carbide particles is 80 μm 2If the coefficient of variation exceeds 1.8, the recrystallization of molybdenum cannot be sufficiently suppressed overall, causing the molybdenum grains to become coarse and reducing the heat resistance. Also, if the coefficient of variation exceeds 1.8, there will be areas where the carbide particles are sparse, causing the molybdenum grains to become coarse locally due to the recrystallization of molybdenum, reducing the heat resistance.

[0062] In particular, the dispersibility of carbide particles in a molybdenum composite material can be confirmed by determining the average area and coefficient of variation of the Voronoi regions of the carbide particles, and it was confirmed that good heat resistance and good bending strength after heating can be relatively easily determined. Therefore, the average area and coefficient of variation of the Voronoi regions of the carbide particles can be used to determine whether the dispersion state changes due to even slight changes in the particle size distribution of the raw materials or the hardness of the powder in combination with the mixing conditions, or whether the dispersion state is significantly affected by the environment during mixing, particularly the temperature.

[0063] A method for producing a molybdenum composite material according to one embodiment of the present invention will be described below.

[0064] The molybdenum composite material of the present invention has an average particle size D Ave Molybdenum powder with a mean particle size D50 of 2.5 to 4.0 μm and a median diameter D50 of 2.0 to 3.5 μm. Ave Carbide powders (titanium carbide, zirconium carbide, hafnium carbide) with a mean particle size of 1.5 to 3.0 μm and a median diameter D50 of 1.0 to 2.5 μm are placed in a molybdenum pot in a predetermined ratio, and a molybdenum rod is placed inside. The pot is rotated on a rotating stand for 1 to 24 hours to crush, pulverize, and mix (rod mill) the powders to obtain the average particle size D of the mixed powder. Ave The molybdenum composite material of the present invention is obtained by reducing the surface roughness to 1.5 to 3.5 μm and the median diameter D50 to 1.0 to 3.0 μm, and then hot pressing (HP) at a temperature of 1400° C. to 1800° C. The sintered body is then processed into a desired shape to produce a molybdenum composite material molded article, which is a product made from the molybdenum composite material of the present invention.

[0065] (Manufacturing method point 1: Raw materials and molybdenum powder particle size after RM) The method for producing the molybdenum composite material of the present invention is to use a molybdenum compound having an average particle diameter D obtained by a laser diffraction / scattering method. Ave The molybdenum powder having a mean particle size D50 of 2.5 to 4.0 μm, preferably 2.8 to 3.7 μm and a median diameter D50 of 2.0 to 3.5 μm, preferably 2.2 to 3.3 μm is used as a raw material, and the molybdenum powder is subjected to RM to obtain an average particle size D Ave The first key point is to reduce the average particle size of the raw molybdenum powder to 1.5 to 3.5 μm and the median diameter D50 to 1.0 to 3.0 μm. If the average particle size of the raw molybdenum powder is too large, it becomes difficult to uniformly disperse the carbide particles during RM. If it is too small, the raw molybdenum powder aggregates, making it difficult to uniformly disperse the carbide particles. Therefore, it is necessary to keep these within a specific range. Furthermore, if the average particle size of the molybdenum powder after RM is too large, the sintering temperature becomes too high, making it impossible to obtain a sintered body with the required density. If it is too small, the density rises sharply during HP, trapping pores and preventing the production of a sintered body with the required density. Therefore, it is necessary to keep these within a specific range.

[0066] (Manufacturing method point 2: particle size of raw carbide powder) Furthermore, the method for producing a molybdenum composite material of the present invention is characterized in that the average particle diameter D Ave The second key point is to use carbide powder as the raw material, which has a mean particle size of 1.5 to 3.0 μm, preferably 1.8 to 2.7 μm, and a median diameter D50 of 1.0 to 2.5 μm, preferably 1.3 to 2.2 μm. If the mean particle size of the raw carbide powder is large, the mean particle size of the carbide powder after RM will also remain large. Even if the carbide particles are uniformly dispersed in the molybdenum, the brittleness inherent in the carbide will lead to a decrease in the strength of the overall composite material. In addition, the reduction in the number of carbide particles will not fully inhibit the recrystallization of molybdenum, and the local coarsening of molybdenum grains will also reduce the strength of the overall composite material. Furthermore, if the mean particle size of the raw carbide powder is small, the mean particle size of the carbide powder after RM will also be too small, causing the carbide particles to aggregate and become less uniformly dispersed. Therefore, it is necessary to keep these within a specified range.

[0067] (Manufacturing method point 3: Rod mill and conditions) The third key point is to use the molybdenum powder and carbide powder as raw materials, and to mix them while crushing and grinding the coarse particles formed by agglomeration of primary particles using an RM. For efficient crushing and grinding, the rotation speed should be 0.55 to 0.8 times the critical rotation speed (rpm) given by 42.3 / √D, where D is the diameter of the container (m). The RM may be replaced with other known methods that can simultaneously crush and grind the powder. For example, mixing methods using grinding media other than rods, such as a ball mill, may be used. Other devices, such as a planetary ball mill, may be used for rotating the pot. Alternatively, methods using a grinding energy other than the kinetic energy of the grinding media, such as a jet mill, may be used after mixing the raw molybdenum powder and carbide powder. As a basis for selecting from among the many mixing methods and determining the conditions of the mixing method, it is desirable to prepare a small sample by sintering a small amount of the mixed powder and confirm whether appropriate dispersibility has been obtained using the above-mentioned method for evaluating the dispersibility of carbide particles.

[0068] The reason for limiting the RM process to 1 to 24 hours is that if the process is carried out for less than 1 hour, the effect of improving the dispersibility of the carbide particles through crushing, grinding, and mixing cannot be obtained, and if the process is carried out for more than 24 hours, it is difficult to obtain the further effects of crushing, grinding, and mixing, resulting in a deterioration in production efficiency.

[0069] (Hot pressing conditions) The HP process produces sintered bodies with a relative density of 95% or higher. The HP temperature for producing sintered bodies with such properties is preferably 1400°C to 1800°C. If the HP temperature is too low, the relative density will be low and the strength of the composite material will decrease, while if the HP temperature is too high, the crystal growth of molybdenum will proceed, reducing the strength of the alloy.

[0070] (Compared to existing technology) Prior art techniques for producing molybdenum-added transition metal carbides include powder mixing using mechanical alloying (see, for example, Japanese Patent No. 3271040 and JP 2000-129389 A). However, high-energy mixing methods that embed carbide particles in molybdenum particles are not necessary to achieve the dispersibility of carbide particles in the molybdenum composite material of the present invention. Mechanical alloying is unsuitable for producing the molybdenum composite material of the present invention because of the labor and cost involved, as well as the small amount of powder that can be processed per batch, which increases production costs and reduces production efficiency.

[0071] Furthermore, conventionally, a sintering method has been adopted in which densification is achieved by hot isostatic pressing (HIP) (Patent No. 3271040), but HIP is more expensive than HP and is therefore a technique that should be avoided when producing heat-resistant products that are consumables, such as evaporation boats.In the present invention, HP can be used to obtain sintered bodies with a relative density of 98% or more, so HIP is unsuitable and HP is the preferred method.

[0072] Furthermore, spark plasma sintering (SPS) has been used as a sintering method in the past (Japanese Patent Laid-Open No. 2000-129389), but SPS is a method for producing relatively small samples and is not suitable for producing heat-resistant products such as evaporation boats. HP is suitable as a method for producing the molybdenum composite material of the present invention.

[0073] Patent No. 5546880 discloses a material containing molybdenum doped with carbides of Ti, Zr, and Hf, and a manufacturing method for the material. While the patent notes that poor particle dispersion of carbides results in insufficient strength, it does not explicitly describe the powder mixing method or dispersibility indicators, nor does it provide information on achieving good carbide particle dispersion in the molybdenum composite material of the present invention. Furthermore, while the patent uses HIP as the sintering method, HIP is more expensive than HP and should be avoided when producing heat-resistant products such as evaporation boats, which are consumables. The patent also states that "the relative density of sintered bodies obtained by conventional powder sintering methods is approximately 90%," suggesting that HIP was employed to obtain high-density sintered bodies. However, HP can produce sintered bodies with a relative density of 98% or higher in the present invention, making HIP unsuitable and HP preferable.

[0074] The technology disclosed in Japanese Patent No. 5238259 discloses a material in which titanium carbide, hafnium carbide, zirconium carbide, or tantalum carbide is added to molybdenum. The patent describes a powder mixing method as follows: "Mo powder and carbide powders such as TiC are prepared as raw material powders and mixed in a ball mill or the like. The Mo powder preferably has an average particle size of 5 μm or less, and the carbide powder preferably has an average particle size of 2 μm or less, more preferably (the average particle size of the Mo powder > the average particle size of the carbide powder), and even more preferably (the average particle size of the Mo powder > 3 (the average particle size of the carbide powder)). The smaller the average particle size of the carbide powder is than the average particle size of the Mo powder, the easier it is for the carbide to be uniformly dispersed in the grain boundary phase of Mo." However, the patent does not specify an index of dispersibility, and does not fully disclose information on obtaining the molybdenum composite material of the present invention. Furthermore, the patent specifies that the aspect ratio of the carbide particles must be at least 2 and less than 20, and states that sintering at 1900°C or higher, or rolling or forging is suitable for achieving such an aspect ratio. However, in the production of the molybdenum composite material of the present invention, sintering at 1900°C or higher is excessive and promotes grain growth of molybdenum, so is unsuitable. Furthermore, rolling or forging may cause anisotropy in strength, making it unsuitable for heat-resistant products such as vapor deposition boards.

[0075] The present invention will be further described below with reference to specific examples.

[0076] Tables 1 and 2 list examples that are within the scope of the claims of this patent, as well as comparative examples that demonstrate the effectiveness of this patent.

[0077] In Examples 1 to 16, molybdenum powder and carbide powder were weighed so as to achieve the additive concentrations within the range claimed in the present patent, and then crushed, pulverized, and mixed in a rod mill for 1 to 24 hours to obtain mixed powders. These mixed powders were then hot pressed at 1750°C to obtain sintered bodies. Test pieces were cut out from these sintered bodies and subjected to various measurements, and the dispersibility was found to be within the range claimed in the present patent.

[0078] In Comparative Examples 1 to 10, molybdenum powder and carbide powder were weighed out so as to have addition concentrations outside the range of the present invention, and then the mixed powders were crushed, pulverized, and mixed in a rod mill for 1 to 24 hours. The mixed powders were then hot pressed at 1750°C to obtain sintered bodies, from which test pieces were cut out and subjected to various measurements.

[0079] In Comparative Examples 11 to 16, molybdenum powder and carbide powder were weighed to have addition concentrations within the range of the present invention, and then mixed in a tumbler mixer for 1 to 24 hours or in a rod mill for less than 1 hour. The mixed powder was then hot pressed at 1750°C to obtain a sintered body, from which test pieces were cut out and subjected to various measurements.

[0080] Comparative Examples 17 and 18 show the results of various measurements on commercially available pure molybdenum plate material and molybdenum plate material containing lanthanum oxide, respectively. From the results in Tables 1 and 2, the inventors determined that the sintered body is mainly composed of molybdenum and contains at least one carbide selected from Ti carbide, Zr carbide, and Hf carbide in the range of 2 to 10 mass %, and that the average area of ​​Voronoi division is 80 μm 2The inventors have come to the understanding that if a molybdenum composite material has a standard deviation / average value, which is the coefficient of variation of the area of ​​the Voronoi division, of 1.8 or less, it will have superior strength and hardness after heating and a smaller change in hardness than conventional commercially available pure molybdenum sheets and molybdenum sheets containing lanthanum oxide, and will satisfy the strength and hardness after heating required for heat-resistant applications such as evaporation boats.

[0081] [Table 1]

[0082] [Table 2]

Claims

1. A molybdenum composite material comprising a sintered body of a mixed powder of molybdenum powder and a carbide powder, the molybdenum composite material containing molybdenum as a main component and containing 2 to 10 mass % of at least one carbide selected from the group consisting of a carbide of Ti, a carbide of Zr, and a carbide of Hf, The average area of ​​Voronoi division is 80 μm ２ and the standard deviation / average value, which is the coefficient of variation of the area of ​​Voronoi division, is 1.8 or less. Molybdenum composites.

2. 2. The molybdenum composite material according to claim 1, which has a maximum bending strength of 1000 MPa or more at room temperature after heating in a vacuum at 1800°C for 8 hours, and exhibits ductile deformation behavior.

3. 2. The molybdenum composite material according to claim 1, which has a Vickers hardness of 200 HV or more after heating in a vacuum at 1800°C for 8 hours.

4. 4. The molybdenum composite material according to claim 3, wherein the Vickers hardness before and after heating in a vacuum at 1800°C for 8 hours is measured, and the hardness reduction rate (%) obtained by subtracting the hardness after heating from the hardness before heating and dividing the result by the hardness before heating is 30% or less.

5. 2. The molybdenum composite material according to claim 1, wherein the molybdenum powder and the carbide powder are crushed and pulverized, mixed, and the resulting mixed powder is hot-pressed.

6. The molybdenum powder has an average particle size D obtained by a laser diffraction / scattering method. Ａｖｅ The carbide powder has an average particle size D Ａｖｅ The molybdenum composite material according to claim 5, wherein the average particle diameter (D50) is 1.5 to 3.0 μm and the median diameter (D50) is 1.0 to 2.5 μm.

7. The average particle size D of the mixed powder Ａｖｅ The molybdenum composite material according to claim 5, wherein the average particle diameter (D50) is 1.5 to 3.5 μm and the median diameter (D50) is 1.0 to 3.0 μm.

8. A molybdenum composite material molded article obtained by molding the molybdenum composite material according to any one of claims 1 to 7 into a predetermined shape.

9. a step of preparing a molybdenum powder and at least one carbide powder selected from a Ti carbide powder, a Zr carbide powder, and a Hf carbide powder in a predetermined ratio; a step of crushing and pulverizing the molybdenum powder and the carbide powder, and mixing them to obtain a mixed powder; The mixed powder is sintered to produce a sintered body mainly containing molybdenum and containing at least one carbide selected from the group consisting of Ti carbide, Zr carbide, and Hf carbide in an amount of 2 to 10 mass %, and the average area of ​​Voronoi division is 80 μm ２ a step of obtaining a molybdenum composite material having a standard deviation / average value, which is the coefficient of variation of the area of ​​Voronoi tessellation, of 1.8 or less; and a method for producing a molybdenum composite material comprising:

10. The method for producing a molybdenum composite material according to claim 9, wherein the step of obtaining the sintered body is carried out by hot pressing (HP) at a temperature of 1400°C or higher and 1800°C or lower.

11. The molybdenum powder has an average particle size D obtained by a laser diffraction / scattering method. Ａｖｅ The carbide powder has an average particle size D Ａｖｅ The method for producing a molybdenum composite material according to claim 9, wherein the average particle diameter (D50) is 1.5 to 3.0 μm and the median diameter (D50) is 1.0 to 2.5 μm.

12. The average particle size D of the mixed powder Ａｖｅ The method for producing a molybdenum composite material according to claim 11, wherein the average particle diameter (D50) is 1.5 to 3.5 μm and the median diameter (D50) is 1.0 to 3.0 μm.

13. The method for producing a molybdenum composite material according to claim 9, wherein the step of crushing, pulverizing and mixing the molybdenum powder and the carbide powder is carried out using a rod mill.

14. A method for producing a molybdenum composite material molded article, comprising molding the molybdenum composite material according to any one of claims 1 to 7 or the molybdenum composite material produced by the method for producing a molybdenum composite material according to any one of claims 9 to 13 into a predetermined shape to obtain a molybdenum composite material molded article.

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