Molybdenum composite material processed product for vacuum and high-temperature device and method for manufacturing molybdenum composite material processed product for vacuum and high-temperature device

Abstract

Provided are a molybdenum composite material processed product and a method for manufacturing a molybdenum composite material processed product, which are made of a material having good durability for use at high temperatures and in a vacuum and good workability, and in particular, when used as a bolt, there are no problems such as galling after use, and which are excellent in terms of production cost and production efficiency. 【Solution means】 A molybdenum composite material processed product obtained by processing a sintered body of a mixed powder of molybdenum powder and carbide powder, wherein the carbide contains at least one of Zr carbide and Hf carbide in an amount of 2 to 10% by mass, and the Vickers hardness is 200 to 300 HV.

Description

Technical Field

[0001] The present invention relates to For vacuum and high-temperature equipment a processed product of a molybdenum composite material and For vacuum and high-temperature equipment a method for manufacturing a processed product of a molybdenum composite material.

Background Art

[0002] Conventionally, molybdenum has been used for parts used in parts exposed to high temperatures. For example, bolts and nuts made of molybdenum are used for fixing units in the high-temperature part (about 1500°C) of an ion implantation apparatus. The bolts and nuts for fixing this unit need to be removed during equipment maintenance about 2 to 4 times a month, but there is a problem that the screw part is damaged each time it is removed. Here, "be damaged" refers to a phenomenon where the screw part does not move at all whether it is loosened or tightened. As a result, measures such as breaking the bolt are required, and there is a problem that the bolt and the unit to which the bolt is attached need to be replaced.

[0003] Such problems are common in equipment that becomes vacuum and high temperature. For example, molybdenum bolts are also used in a vacuum furnace, but after use of the vacuum furnace, the bolts cannot be removed and must be broken off, which has become a major problem.

[0004] On the other hand, regarding molybdenum alloys that are heat-resistant metals in this way, Patent Documents 1, 2, etc. are known. Patent Document 1 discloses a material obtained by adding carbides of Ti, Zr, Hf, etc. to molybdenum and a manufacturing method thereof. Patent Document 3 describes that when the dispersion state of particles such as carbides deteriorates, the strength becomes insufficient, but the powder mixing method and the index of dispersibility are not specified, and information for obtaining good dispersibility of carbide particles in the molybdenum composite material of the present invention is not presented.

[0005] In addition, Patent Document 2 discloses a material obtained by adding titanium carbide, hafnium carbide, zirconium carbide, and tantalum carbide to molybdenum. Patent Document 2 describes that as a powder mixing method, Mo powder and carbide powders such as TiC are prepared and mixed using a ball mill or the like, but no index of dispersibility is specified.

[0006] In any case, according to Patent Documents 1 and 2, for molybdenum alloys, the dispersibility between molybdenum powder and additive particles and the sintered state seem to be problems. However, the emergence of a molybdenum composite material with excellent target heat resistance and durability and also excellent in terms of production cost and production efficiency has been desired.

[0007] However, it has been grasped that the durability such as heat resistance, workability, and strength of the obtained material varies greatly depending on various combinations of conditions such as material conditions such as the particle size of the raw material powder, conditions for crushing and pulverizing the raw material powder, mixing conditions, sintering conditions, and molding conditions. In particular, the dispersibility of the powder of the molybdenum composite material is greatly related to durability, but it has been difficult to grasp what is optimal depending on the combination with the mixing conditions even if the particle size distribution of the raw material or the hardness of the powder changes slightly. It has also been found that the environment during mixing, especially the temperature, etc. also greatly affects the dispersion state.

[0008] Therefore, as a result of examining various molybdenum composite materials, it was invented that a molybdenum composite material with good durability can be grasped by paying attention to the average area of the Voronoi division of the molybdenum composite material, and a patent was obtained previously (Patent Document 3).

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, the galling problem of the bolts and nuts used in the above-mentioned high-temperature parts is not simply solved by using a high-hardness composite material. It is necessary to select a material with good durability for use at high temperatures and in a vacuum and good workability.

[0011] Therefore, an object of the present invention is to provide a molybdenum composite material processed product and a method for manufacturing a molybdenum composite material processed product, which are excellent in durability for use at high temperatures and in a vacuum, have no problems such as galling after use when used as bolts, and are also excellent in terms of production cost and production efficiency.

Means for Solving the Problems

[0012] To achieve the above object, a first aspect of the present invention is a molybdenum composite material processed product obtained by processing a sintered body of a mixed powder containing molybdenum powder and carbide powder, wherein the carbide contains at least one of Zr carbide and Hf carbide in an amount of 2 to 10% by mass, and the Vickers hardness is 200 to 300 HV.

[0013] A second aspect of the present invention is the molybdenum composite material processed product according to the above aspect, wherein the processed product is at least one of a bolt and a nut.

[0014] A third aspect of the present invention is the molybdenum composite material processed product according to the above aspect, wherein the processed product is a combination of a bolt and a nut.

[0015] A fourth aspect of the present invention is that the average area of the Voronoi division of the sintered body is 80 μm 2 or less, and the standard deviation / mean value, which is the coefficient of variation of the area of the Voronoi division, is 1.8 or less, in the molybdenum composite material processed product according to the above aspect.

[0016] The fifth aspect of the present invention is that the average area of the Voronoi division of the sintered body is 80 μm 2 or less, and when the coefficient of variation of the area of the Voronoi division is defined as the standard deviation / mean value, it is in the molybdenum composite material processed product according to the above aspect, where 1.8 < coefficient of variation ≤ 3.5.

[0017] The sixth aspect of the present invention is that the average area of the Voronoi division of the sintered body is 80 μm 2 < average area ≤ 100 μm 2 and the standard deviation / mean value, which is the coefficient of variation of the area of the Voronoi division, is 1.8 or less, in the molybdenum composite material processed product according to the above aspect.

[0018] The seventh aspect of the present invention is in the molybdenum composite material processed product according to the above aspect, which is a processed product of a sintered body obtained by hot pressing the mixed powder obtained by crushing, pulverizing, and mixing the molybdenum powder and the carbide powder.

[0019] The eighth aspect of the present invention includes a step of preparing a molybdenum powder and a carbide powder composed of at least one of Zr carbide and Hf carbide in a predetermined ratio, a step of crushing, pulverizing, and mixing the molybdenum powder and the carbide powder to obtain a mixed powder, and sintering the mixed powder to obtain a sintered body mainly composed of molybdenum and containing at least one of Zr carbide and Hf carbide in the range of 2 to 10% by mass, and having a Vickers hardness of 200 to 300 HV, and a step of forming and processing the sintered body into a predetermined shape to obtain a processed product, which is a method for manufacturing a molybdenum composite material processed product.

[0020] The ninth aspect of the present invention is in the method for manufacturing a molybdenum composite material processed product according to the above aspect, where the processed product is at least one of a bolt and a nut.

[0021] The tenth aspect of the present invention is in the method for manufacturing a molybdenum composite material processed product according to the above aspect, where the processed product is a combination of a bolt and a nut.

[0022] In the 11th aspect of the present invention, 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, and the method for manufacturing a molybdenum composite material processed product described in the above aspect.

[0023] In the 12th aspect of the present invention, the molybdenum powder has an average particle size D obtained by the laser diffraction / scattering method Ave of 2.5 to 4.0 μm and a median diameter D50 of 2.0 to 3.5 μm, and the carbide powder has an average particle size D Ave of 1.5 to 3.0 μm and a median diameter D50 of 1.0 to 2.5 μm, and the method for manufacturing a molybdenum composite material processed product described in the above aspect.

[0024] In the 13th aspect of the present invention, the average particle size D of the mixed powder Ave is 1.5 to 3.5 μm and the median diameter D50 is 1.0 to 3.0 μm, and the method for manufacturing a molybdenum composite material processed product described in the above aspect.

[0025] In the 14th aspect of the present invention, the step of crushing and pulverizing and mixing the molybdenum powder and the carbide powder is carried out by a rod mill, and the method for manufacturing a molybdenum composite material processed product described in the above aspect.

Advantages of the Invention

[0026] According to the present invention, it is possible to provide a molybdenum composite material processed product excellent in heat resistance and durability and also excellent in terms of production cost and production efficiency, and a method for manufacturing a molybdenum composite material processed product.

Embodiments for Carrying Out the Invention

[0027] The molybdenum composite material of the present invention is a sintered body containing 2 to 10% by mass of a carbide powder composed of at least one of Zr carbide and Hf carbide and molybdenum powder.

[0028] The molybdenum composite material processed product of the present invention is manufactured by processing a sintered body manufactured using molybdenum powder and carbide powder as raw materials.

[0029] Here, although it was also considered to use Ti carbide in addition to Zr carbide or Hf carbide as the carbide powder, Zr carbide or Hf carbide is suitable for the following reasons.

[0030] First, when a part of Ti carbide is oxidized during sintering, processing, or use, it becomes titanium oxide that is likely to sublime, and in particular, heating in a vacuum can cause impurities in the atmosphere.

[0031] That is, since the vapor pressure of Ti carbide is 100 to 100,000 times greater than that of Zr carbide, when a part of it is oxidized during production by adding Ti carbide, Ti oxide is released into the vacuum while the parts are being used under vacuum heating, for example, which may cause impurities in products manufactured in a vacuum furnace. In addition, since the additive for strengthening molybdenum is lost, for example, if bolts are repeatedly used in a vacuum furnace, there is a risk that the strength will decrease.

[0032] Also, when comparing the Vickers hardness of the sintered body, when using Zr carbide, even if the addition amount to molybdenum powder is large, the Vickers hardness of the sintered body does not increase as much as that of Ti carbide. For example, there is an advantage that the workability of the thread of the bolt is not reduced.

[0033] Although Hf carbide can be expected to have a similar heat resistance improvement effect as compared with Zr carbide, the material price is much higher than that of Zr carbide, which is a negative point in that it leads to an increase in the cost of the product.

[0034] As the molybdenum powder used as the raw material, it is preferable to use a powder with an average particle size D Ave of 2.5 to 4.0 μm and a median diameter D50 of 2.0 to 3.5 μm.

[0035] Also, as the carbide powder used as the raw material, it is preferable to use a powder with an average particle size D Ave of 1.5 to 3.0 μm and a median diameter D50 of 1.0 to 2.5 μm.

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

[0037] The average particle size D of the obtained mixed powder Ave is preferably 1.5 to 3.5 μm, and the median diameter D50 is preferably 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 a desired mixed powder can be obtained, but it is preferably carried out by 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, there is a method of obtaining a sintered body by a hot isostatic pressing method (HIP). However, HIP is more costly than HP and is a method that is preferably avoided if possible. In the present invention, a sintered body having a relative density of 98% or more can be obtained by the HP method.

[0041] Also, the hardness of the sintered body is Vickers hardness (HV), 200 or more, preferably 220 or more, and 300 or less, preferably 260 or less.

[0042] In the present invention, in the molybdenum composite material, the addition amount of the carbide, which is at least one of Zr carbide and Hf carbide, is closely related to the heat resistance, durability, and hardness of the molybdenum composite material. If the addition amount of the carbide is within a predetermined range, it has all the heat resistance, durability, and hardness required for molybdenum composite material processed products.

[0043] Here, the predetermined dispersion characteristics are not particularly limited. As one method for obtaining a sintered body having the desired heat resistance, durability, and hardness of the molybdenum composite material, as an easily implementable method, the average area of the Voronoi division is 80 μm2 The condition that the coefficient of variation of the area of the Voronoi division, which is the standard deviation / average value, is 1.8 or less may be added.

[0044] The physical property evaluation of the molybdenum composite material of the present invention was carried out as follows.

[0045] (Hardness) A test piece with a width of 10 mm, a length of 40 mm, and a thickness of about 0.5 mm was cut out from the material to be evaluated for physical properties. After polishing the surface, the hardness was measured by the Vickers hardness test defined in JIS Z 2244. As the measuring instrument, a micro Vickers hardness tester "HM-200" manufactured by Mitutoyo was used.

[0046] The molybdenum composite material of the present invention is excellent in heat resistance strength and heat resistance hardness as described above, but it is impossible to grasp whether the dispersion state of carbides in the molybdenum composite material is optimal.

[0047] Also, even if the current heat resistance strength and heat resistance hardness are within the desired range, if the dispersion state cannot be grasped, there may be unevenness in heat resistance strength and heat resistance hardness.

[0048] Furthermore, even if the current dispersion state is optimal, due to differences in the particle size distribution state of the raw material powder, etc., even if the crushing, pulverizing, and mixing conditions are the same, the dispersion state of carbides in the sintered body may change, and it is impossible to always grasp that the dispersion state is good and there is no unevenness in the current heat resistance strength and heat resistance hardness.

[0049] As described above, the good dispersion state of carbides in the molybdenum composite material of the present invention can be grasped by the fact that the average area of the Voronoi division is 80 μm 2 or less, and the coefficient of variation of the area of the Voronoi division, which is the standard deviation / average value, is 1.8 or less.

[0050] This dispersibility was grasped as follows. (Dispersibility) After cutting the non-deformed part at the end after the above bending strength test and polishing the cross-section, three SEM images were taken at 2 mm intervals in the horizontal direction near the center in the thickness direction using the electron microscope "TM4000Plus" manufactured by Hitachi High-Technologies Corporation. For the taken SEM images, the positions of carbide particles were first recognized from the difference in contrast using the image analysis software "Image-J". Subsequently, using the "Voronoi" function of "Image-J", the image was divided by a straight line where points equidistant from the boundary between the two closest particles were aggregated. That is, each divided region (Voronoi region) contains one carbide particle. The area of the Voronoi region becomes smaller where carbide particles are densely present, and the area of the Voronoi region becomes larger where carbide particles are sparsely present. 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 obtain 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.

[0051] (Meaning of the average area of the Voronoi region) The smaller the average area of the Voronoi region obtained by the above method, the denser the carbide particles are present in the entire molybdenum composite material. Also, since the average area of this Voronoi region is essentially the same as the value obtained by dividing the area of the entire SEM image 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, although the concentration of the total number of carbide particles in the molybdenum composite material can be determined by the average area of the Voronoi region or the number of carbide particles contained in a cross-section of a certain area, the local density variation of the carbide particles cannot be defined.

[0052] (Importance of the coefficient of variation) It has been found that the variation in the density of carbide particles, in other words, the dispersibility of carbide particles, has a significant impact on the physical properties of molybdenum alloys. That is, in a material where carbide particles are dispersed in a molybdenum base material to enhance heat resistance, what is important is not so much the addition amount of carbide particles but rather how uniformly the carbide particles are dispersed. If there are many locations where carbide particles are not present locally even after adding carbide particles, recrystallization of molybdenum due to heating progresses in that part, resulting in local coarsening of molybdenum crystal grains and the inability to obtain high heat resistance for the entire composite material. Therefore, it has been found that the coefficient of variation of the area of the Voronoi region can be used as an index for the variation in the density of carbide particles, and it can well explain the heat resistance of the molybdenum composite material. That is, the smaller this coefficient of variation, the more uniformly the carbide particles are dispersed.

[0053] From the above considerations, it is preferable that the average area of the Voronoi region of carbide particles is 80 μm 2 or less, and its coefficient of variation is 1.8 or less.

[0054] Here, a small coefficient of variation means that carbide particles are uniformly present, and the heat resistance is high. However, to obtain this, it is necessary to spend a long time on powder mixing. When the use temperature is relatively low, even if the coefficient of variation exceeds 1.8, sufficient performance can be exhibited, so the powder mixing time can be shortened to reduce the manufacturing cost. However, if the carbide particles are too unevenly present, local Mo crystal grain growth occurs and it becomes brittle, so the coefficient of variation needs to be 3.5 or less.

[0055] From the above considerations, it is also preferable for processed products such as bolts and nuts that the average area of the Voronoi division of the sintered body is 80 μm 2 or less, and when the coefficient of variation of the area of the Voronoi division is defined as the standard deviation / mean value, 1.8 < coefficient of variation ≤ 3.5.

[0056] Also, a small average area means that carbide particles are densely present, and the heat resistance is high, but the hardness also increases. When the hardness of the mating part of the screw is low, when the average area is 80 μm2 In some cases, a material with a lower hardness exceeding [a certain value] may be preferred. To ensure heat resistance, the average area should be 100 μm 2 or less.

[0057] Therefore, when the average area of the Voronoi division of the sintered body is 80 μm 2 <average area ≤ 100 μm 2 and the coefficient of variation of the area of the Voronoi division, which is standard deviation / average value, is 1.8 or less, it can also be preferably used as processed products such as bolts and nuts.

[0058] When the average area of the Voronoi region of the carbide particles is 100 μm 2 , preferably 80 μm 2 exceeds this value, overall, the recrystallization of molybdenum cannot be sufficiently suppressed, the crystal grains of molybdenum become coarser, and the heat resistance decreases. Also, when the coefficient of variation exceeds 3.5, preferably exceeds 1.8, there are parts where carbide particles are sparse, and locally, grain coarsening due to recrystallization of molybdenum occurs, resulting in a decrease in heat resistance.

[0059] In particular, in this way, the dispersibility of the carbide particles in the molybdenum composite material can be confirmed by grasping the average area and the coefficient of variation of the Voronoi region of the carbide particles, and it has been confirmed that it is possible to relatively easily grasp that the heat resistance is good and the bending strength after heating is good. Therefore, even if the particle size distribution of the raw material or the hardness of the powder changes slightly, and the dispersion state changes due to the combination with the mixing conditions, or is greatly affected by the environment during mixing, especially the temperature, etc., it can be grasped by the average area and the coefficient of variation of the Voronoi region of the carbide particles.

[0060] Hereinafter, a manufacturing method according to an embodiment for manufacturing the molybdenum composite material of the present invention will be described.

[0061] The molybdenum composite material of the present invention is composed of molybdenum powder with an average particle size D Ave obtained by the laser diffraction / scattering method being 2.5 - 4.0 μm and a median diameter D50 being 2.0 - 3.5 μm, and an average particle size D AveCarbide powders (titanium carbide, zirconium carbide, hafnium carbide) with an average particle diameter D of 1.5 to 3.0 μm and a median diameter D50 of 1.0 to 2.5 μm are put into a molybdenum pot at a predetermined ratio, and a molybdenum rod is inserted and the pot is rotated for 1 to 24 hours by a rotary stand to crush, grind and mix the powders (rod mill), and the average particle diameter D of the mixed powder Ave is reduced to 1.5 to 3.5 μm and the median diameter D50 is reduced to 1.0 to 3.0 μm, and then hot pressing (HP) is performed at a temperature of 1400 °C or higher and 1800 °C or lower to obtain the molybdenum composite material of the present invention. And by processing the sintered body into a desired shape, a molybdenum composite material molded product, which is a product made of the molybdenum composite material of the present invention, can be manufactured.

[0062] (Point 1 of the manufacturing method: raw materials and molybdenum powder particle size after RM) The manufacturing method of the molybdenum composite material of the present invention uses molybdenum powder with an average particle diameter D Ave obtained by the laser diffraction / scattering method 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 as raw materials, and by RM, the average particle diameter D of the molybdenum powder Ave is reduced to 1.5 to 3.5 μm and the median diameter D50 is reduced to 1.0 to 3.0 μm, which is the first point. If the average particle diameter of the raw material molybdenum powder is too large, it is difficult for carbide particles to be uniformly dispersed by RM, and if it is too small, the raw material molybdenum powder aggregates and it is difficult for carbide particles to be uniformly dispersed, so it is necessary to set it within a predetermined range. Also, if the average particle diameter of the molybdenum powder after RM is too large, the sintering temperature will be high and a sintered body with a predetermined density cannot be obtained, and if it is too small, the density will increase rapidly during HP and pores will be trapped and a sintered body with a predetermined density cannot be obtained, so it is necessary to set it within a predetermined range.

[0063] (Point 2 of the manufacturing method: raw carbide powder particle size) Also, the manufacturing method of the molybdenum composite material of the present invention uses molybdenum powder with an average particle diameter D AveThe second point is to use carbide powder with an average 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 as the raw material. If the average particle size of the raw material carbide powder is large, the average particle size of the carbide powder after RM will remain large. Even if carbide particles are uniformly dispersed in molybdenum, the brittleness derived from the carbide will lead to a decrease in the strength of the entire composite material. In addition, the number of carbide particles decreases, so that the recrystallization inhibition effect of molybdenum cannot be sufficiently obtained, and the strength of the entire composite material also decreases due to the coarsening of molybdenum crystal grains locally. On the other hand, if the average particle size of the raw material carbide powder is small, the average particle size of the carbide powder after RM will become too small, and the carbide particles will aggregate and will not be uniformly dispersed. Therefore, it is necessary to set it within a predetermined range.

[0064] (Point 3 of the manufacturing method: Rod mill and conditions) Moreover, using the above-mentioned molybdenum powder and carbide powder as raw materials, while pulverizing and crushing the coarse particles in which the primary particles of the powder are aggregated by RM, mixing the molybdenum powder and the carbide powder is the third point. In order to perform crushing and pulverization efficiently, it is desirable that the rotational speed be 0.55 to 0.8 times the critical rotational speed [rpm] given by 42.3 / √D when the diameter of the container is D [m]. Note that RM may be replaced with other known methods as long as it is a method that can crush and pulverize the powder while mixing at the same time. That is, a mixing method using a pulverization medium other than a rod, for example, it may be replaced with a ball mill, the rotation method of the pot may be a method using other devices, for example, a planetary ball mill may be used, or a method using energy other than the kinetic energy of the pulverization medium as the pulverization energy, for example, a jet mill after mixing the raw material molybdenum powder and carbide powder may be adopted. As a judgment material for selecting from several mixing methods and determining the conditions of the mixing method, it is desirable to prepare a small sample obtained by sintering a small amount of the mixed powder and confirm whether appropriate dispersibility is obtained using the above-described method for evaluating the dispersibility of carbide particles.

[0065] The reason for setting the RM process to 1 to 24 hours is that if it is less than 1 hour, the effect of improving the dispersibility of carbide particles by crushing, grinding, and mixing cannot be obtained, and if it exceeds 24 hours, it is difficult to obtain further effects of crushing, grinding, and mixing, leading to a deterioration in production efficiency.

[0066] (Hot pressing conditions) In the HP process, a sintered body having a relative density of 95% or more is produced. The HP temperature for producing such a sintered body is preferably 1400°C or higher and 1800°C or lower. If the HP temperature is too low, the relative density will be low and the strength of the composite material will decrease. If it is too high, the crystal growth of molybdenum will progress and the strength of the alloy will decrease.

[0067] The molybdenum composite material processed product of the present invention, particularly a bolt or a component of a bolt and nut assembly, is a processed product of a molybdenum composite material which is a sintered body of a mixed powder mainly composed of molybdenum powder and carbide powder which is at least one of Zr carbide and Hf carbide, contains 2 to 10% by mass of carbide which is at least one of Zr carbide and Hf carbide, and has a Vickers hardness of 200 to 300 HV.

[0068] Such a molybdenum composite material processed product of the present invention is excellent in durability against use at high temperatures and in a vacuum. When used as a bolt, there are no problems such as galling after use, and it is also excellent in terms of production cost and production efficiency. Specific examples will be shown below for more specific explanation.

[0069] The present invention will be further described below with specific examples. (Examples) In the example, 4% by weight of Zr carbide powder was added to molybdenum powder, and a mixed powder obtained by crushing, grinding, and mixing for 1 to 24 hours with a rod mill was hot pressed at 1750°C to obtain a sintered body, from which M4 bolts and nuts, and M4 parts with M4 screw holes were processed.

[0070] More specifically, the average particle size D obtained by the laser diffraction / scattering method AveMolybdenum powder with a particle size of 2.5 to 4.0 μm and a median diameter D50 of 2.0 to 3.5 μm, and Zr carbide powder (zirconium carbide) with an average particle size D Ave of 1.5 to 3.0 μm and a median diameter D50 of 1.0 to 2.5 μm are put into a molybdenum pot at a predetermined ratio, a molybdenum rod is inserted, and the pot is rotated for 1 to 24 hours on a rotary stand to crush, grind, and mix the powder (rod mill). The average particle size D Ave of the mixed powder is reduced to 1.5 to 3.5 μm and the median diameter D50 is reduced to 1.0 to 3.0 μm, and then hot-pressed (HP) at a temperature of 1750 °C to form a sintered body. The sintered body is processed into M4 bolts and nuts, and M4 parts with M4 threaded holes to obtain the molybdenum composite material molded product of the present invention.

[0071] (Comparative Example) In the comparative example, commercially available pure Mo bolts and nuts, and a commercially available pure Mo plate with an M4 threaded hole processed into an M4 part with a threaded hole were used.

[0072] (Test Example) With the M4 bolt attached to the M4 nut or the M4 part with a threaded hole, vacuum heating was carried out under vacuum at 1800 °C or 1500 °C for 8 hours, then the bolt was removed, the state of the processed product was observed, and the maximum torque when loosening the bolt was measured. The results are shown in Tables 1 and 2.

[0073] Note that the vacuum heating conditions in this test example simulate the usage environment of parts in ion implantation devices and vacuum furnaces.

[0074] In Test Examples 1 and 2 where both the male and female parts were the processed products of the present invention, although the vacuum heating temperature was as high as 1800 °C, there was no galling, the maximum loosening torque was 1 Nm, and there was no breakage. Of course, there were no problems in Test Examples 5 and 6 with the same processed products and a vacuum heating temperature of 1500 °C.

[0075] Also, in Test Examples 3 and 4 where only the male parts are the processed products of the present invention, the female parts are made of molybdenum, and the vacuum heating temperature is 1500 °C, there is no galling of the bolts which are male parts, the maximum loosening torque is 1 Nm, and there is no breakage.

[0076] On the other hand, in Test Examples 11 and 12 where only the male parts are the processed products of the present invention, the female parts are made of molybdenum, and the vacuum heating temperature is 1800 °C, galling occurred on the bolts which are male parts, the maximum loosening torque became 4 - 5 Nm, and breakage occurred. This breakage is considered to be mainly due to the deformation on the female part side of pure molybdenum. Therefore, it was found that the bolts which are the processed products of the present invention cannot withstand a vacuum heating temperature of 1800 °C if the nuts are not also the processed products of the present invention, and galling occurs due to breakage on the nut side.

[0077] Also, in Test Examples 13 and 14 where only the female parts are the processed products of the present invention and the male parts are made of molybdenum, and the vacuum heating temperature is 1800 °C, galling occurred on the bolts which are male parts, the maximum loosening torque became 3 - 4 Nm, and breakage of the bolts occurred. This breakage is such that the pure molybdenum bolts are broken and galling occurs, but the nuts which are the processed products of the present invention are intact and are presumed to be functioning as nuts.

[0078] In Test Examples 15 - 18 where both the male and female parts are made of molybdenum, it was confirmed that breakage occurs not only at a vacuum heating temperature of 1800 °C but also at 1500 °C.

[0079]

Table 1

[0080]

Table 2

Claims

1. A molybdenum composite material processed product for a vacuum and high-temperature device, which is obtained by processing a sintered body of a mixed powder containing molybdenum powder and carbide powder, which is at least one of a bolt and a nut, and the sintered body contains at least one of Zr carbide and Hf carbide as a carbide in an amount of 2 to 10% by mass, has a Vickers hardness of 200 to 300 HV, and the sintered body has an average area of Voronoi division with the carbide powder as the mother point of 80 μm² or less, and a standard deviation / mean value, which is the coefficient of variation of the area of Voronoi division, of 1.8 or less, or the average area of Voronoi division with the carbide powder as the mother point is 80 μm² or less, and when the coefficient of variation of the area of Voronoi division is the standard deviation / mean value, 1.8 < coefficient of variation ≤ 3.5, or the average area of Voronoi division with the carbide powder as the mother point is 80 μm² < average area ≤ 100 μm², and a standard deviation / mean value, which is the coefficient of variation of the area of Voronoi division, of 1.8 or less. A molybdenum composite material processed product for a vacuum and high-temperature device.

2. The molybdenum composite material processed product for a vacuum and high-temperature device according to Claim 1, wherein the processed product is a combination of a bolt and a nut.

3. The molybdenum composite material processed product for a vacuum and high-temperature device according to Claim 1, which is a processed product of a sintered body obtained by crushing, pulverizing, and mixing the molybdenum powder and the carbide powder and then hot-pressing the mixed powder.

4. A method for manufacturing a molybdenum composite material processed product for a vacuum and high-temperature device, which is a vacuum and high-temperature durable molybdenum composite material processed product that is at least one of a bolt and a nut, comprising: a step of preparing molybdenum powder and carbide powder composed of at least one of Zr carbide and Hf carbide in a predetermined ratio; a step of crushing, pulverizing, and mixing the molybdenum powder and the carbide powder to obtain a mixed powder; Sintering the mixed powder to obtain a sintered body mainly composed of molybdenum and containing at least one of Zr carbide and Hf carbide in the range of 2 to 10% by mass, having a Vickers hardness of 200 to 300 HV, and the average area of Voronoi division with the carbide powder as the mother point being 80 μm² or less, and the coefficient of variation of the area of Voronoi division, which is the standard deviation / average value, being 1.8 or less, or the average area of Voronoi division with the carbide powder as the mother point being 80 μm² or less, and when the coefficient of variation of the area of Voronoi division is the standard deviation / average value, 1.8 < coefficient of variation ≤ 3.5, or the average area of Voronoi division with the carbide powder as the mother point being 80 μm² < average area ≤ 100 μm², and the standard deviation / average value, which is the coefficient of variation of the area of Voronoi division, being 1.8 or less, to obtain a sintered body; Forming and processing the sintered body into a predetermined shape which is at least one of a bolt and a nut to obtain a vacuum high-temperature durable molybdenum composite material processed product; A method for manufacturing a molybdenum composite material processed product for a vacuum and high-temperature device, comprising the above steps.

5. The method for manufacturing a molybdenum composite material processed product for a vacuum and high-temperature device according to claim 4, wherein the processed product is a combination of a bolt and a nut.

6. The method for manufacturing a molybdenum composite material processed product for a vacuum and high-temperature device according to claim 5, 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.

7. The molybdenum powder has an average particle size D obtained by the laser diffraction / scattering method Ａｖｅ of 2.5 to 4.0 μm and a median diameter D50 of 2.0 to 3.5 μm, and the carbide powder has an average particle size D Ａｖｅ of 1.5 to 3.0 μm and a median diameter D50 of 1.0 to 2.5 μm. The method for manufacturing a molybdenum composite material processed product for a vacuum and high-temperature device according to claim 6.

8. The average particle diameter D of the mixed powder Ａｖｅ is 1.5 to 3.5 μm, and the median diameter D50 is 1.0 to 3.0 μm. The method for manufacturing a molybdenum composite material processed product for a vacuum and high-temperature device according to claim 7.

9. The method for manufacturing a molybdenum composite material processed product for a vacuum and high-temperature device according to claim 4, wherein the step of crushing, pulverizing, and mixing the molybdenum powder and the carbide powder is carried out by a rod mill.

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