Molybdenum alloy, rotating anode for x-ray tube, x-ray tube, and melting crucible

Abstract

A molybdenum alloy according to the present embodiment comprises at least one carbide from among titanium carbide, hafnium carbide, zirconium carbide, and tantalum carbide, with the remainder being molybdenum and unavoidable impurities. The molybdenum alloy includes 0.5 to 20.0 wt% of carbides. Furthermore, in the molybdenum alloy, 4,000 pcs / mm2 or more of carbide particles are present. In the molybdenum alloy, a D50 particle size of the carbide particles is preferably, for example, 0.2 to 5.0 μm. In the molybdenum alloy, a D10 particle size of the carbide particles is preferably, for example, 0.1 μm to 1.0 μm, and a D90 particle size is preferably, for example, 1.0 to 10.0 μm.

Description

Molybdenum alloy, rotating anode for X-ray tube, X-ray tube, and molten crucible

[0001] The embodiments relate to a molybdenum alloy with excellent strength. The embodiments also relate to a rotating anode for an X-ray tube, an X-ray tube, and a molten crucible using the molybdenum alloy.

[0002] Conventionally, molybdenum (Mo) alloys have included TZM (Ti-Zr-Mo) alloy, which consists of 0.5 wt% titanium (Ti), 0.07 wt% zirconium (Zr), 0.05 wt% carbon (C), and the remainder molybdenum, and MHC alloy, which contains approximately 1.0 to 1.3 wt% hafnium in addition to molybdenum. TZM alloys and MHC alloys exhibit excellent high-temperature strength due to the high melting point of their main component, molybdenum. Taking advantage of this property, these molybdenum alloys are used in fields requiring high-temperature strength, such as rotating anodes for industrial and medical X-ray tubes (sometimes referred to as "rotating anode" or "anode" in this specification) and crucibles used for melting metals.

[0003] The rotating anode for an X-ray tube generates X-rays when electron beams emitted from the cathode collide with the electron beam irradiation surface. The heat generated when the electron beams collide with the electron beam irradiation surface causes the anode temperature to rise. High temperatures at the anode can lead to problems such as a shortened lifespan of the device due to deterioration of the anode material, unstable X-ray output leading to a decrease in image quality, and ultimately affecting the safety of the device. Therefore, to prevent localized heating of the anode and promote heat dispersion to suppress temperature rise, the anode, i.e., the electron beam irradiation surface, is rotated at high speed during operation to move the focal point on the thermionic electron beam irradiation surface.

[0004] To suppress vibrations of the X-ray tube caused by the high-speed rotation of the rotating anode during operation, an appropriate rotation speed of the rotating anode is set. To suppress vibrations of the X-ray tube, the anode material must be of high strength. As a high-strength anode, for example, in Japanese Patent No. 5238259 (Patent Document 1), a highly hard molybdenum alloy has been developed in which the aspect ratio of the contained carbides is 2 or more. Because this molybdenum alloy has high hardness, it does not crack and provides an X-ray tube in which discharge phenomena are suppressed.

[0005] Furthermore, Japanese Patent No. 5984846 (Patent Document 2) discloses a rotating anode for an X-ray tube having a structure in which at least a portion of the focal orbital formed of tungsten or a tungsten-based alloy and the support formed of a molybdenum-based alloy is either not recrystallized or partially recrystallized. This rotating anode for an X-ray tube consists of a focal orbital and a support having high hardness.

[0006] Patent No. 5238259 Patent No. 5984846

[0007] X-ray tubes are used in various X-ray inspection devices, including X-ray CT (Computed Tomography) systems. An X-ray tube works by rotating a rotating anode, which has an electron beam irradiation surface, with a shaft (rotation axis) attached to it. The rotating anode rotates at a high speed of approximately 6,000 to 10,000 rpm while irradiating the anode with an electron beam, thereby detecting the X-rays generated from the electron beam irradiation surface. Most of the energy of the electron beam emitted from the cathode is stored as thermal energy in the anode target. In recent years, there has been a demand for higher output and higher resolution X-ray inspection devices.

[0008] To generate high-power X-rays in an X-ray tube, a large amount of energy is concentrated on the target, and this energy is converted into heat, causing the target temperature to rise. Furthermore, to achieve high resolution, the focal point of the X-rays needs to be smaller. The smaller the focal point, the higher the energy density concentrated on the target, which may lead to localized temperature increases. As mentioned above, achieving high power and high resolution in X-ray inspection equipment tends to cause the target temperature to rise even more, so it is necessary to rotate the anode at high speed to effectively dissipate heat.

[0009] Furthermore, to increase the heat capacity and improve heat dissipation efficiency, anodes tend to become larger in order to prevent the anode temperature from rising due to the heat generation and heat accumulation mentioned above. On the other hand, high-speed rotation of the anode can cause the X-ray tube to vibrate. When the X-ray tube vibrates, it is expected that the focus of the X-ray will shift, the image quality will deteriorate due to the effects of vibration noise, and the product life of the X-ray tube will be reduced due to wear of the parts involved in rotation. In addition, as the anode becomes larger in order to achieve higher output and higher resolution in X-ray inspection equipment, the load on the anode during high-speed rotation will increase, and the risk of vibration will increase. For this reason, higher-strength molybdenum alloys are required to suppress X-ray tube vibration.

[0010] Similar to X-ray inspection equipment, molten crucibles used for melting metals and other materials also experienced problems such as cracks and fissures during processing, and cracks caused by stress resulting from thermal expansion of the material during the melting process. These problems stemmed from the low strength of conventional molybdenum alloys.

[0011] The problem that this invention aims to solve is to provide a high-strength molybdenum alloy, and a rotating anode for an X-ray tube, an X-ray tube, and a molten crucible using the same.

[0012] The molybdenum alloy of this embodiment consists of at least one carbide from titanium carbide, hafnium carbide, zirconium carbide, and tantalum carbide, the remainder being molybdenum, and unavoidable impurities. The molybdenum alloy contains 0.5 wt% to 20.0 wt% of carbides. Furthermore, the molybdenum alloy has a carbide particle density of 4000 pcs / mm ２ There are more than this number.

[0013] In the molybdenum alloy, the particle size of the carbide particles D50 is preferably, for example, 0.2 μm or more and 5.0 μm or less. In the molybdenum alloy, the particle size of the carbide particles D10 is preferably, for example, 0.1 μm or more and 1.0 μm or less, and the particle size of D90 is preferably, for example, 1.0 μm or more and 10.0 μm or less. Furthermore, in the molybdenum alloy, the particle size of the molybdenum crystal grains D50 is preferably, for example, 100 μm or less. Furthermore, in the molybdenum alloy, the three-point bending strength at room temperature is preferably, for example, 900 MPa or more. Here, since the particle sizes of the carbide particles and molybdenum crystal grains in the molybdenum alloy are distributed in a nearly symmetrical manner, the particle size of D50 may be considered equal to the average particle size.

[0014] Such molybdenum alloys are suitable for rotating anodes in X-ray tubes.

[0015] Furthermore, the rotating anode for the X-ray tube of the embodiment may have a structure in which graphite is in contact with the back side of the molybdenum alloy of the embodiment by a brazing material. In addition, the molybdenum alloy is suitable for large rotating anodes for X-ray tubes with a diameter of 100 mm or more, and even more so for large rotating anodes for X-ray tubes with a diameter of 200 mm or more.

[0016] Furthermore, the rotating anode for the X-ray tube of the embodiment may have a structure in which, for example, at least one of the metals W, Mo, Nb, Ta, Re, Ti, Zr, and C, or an alloy layer mainly composed of at least one of the metals W, Mo, Nb, Ta, Re, Ti, Zr, and C, is provided on the electron beam irradiation surface of the molybdenum alloy of the embodiment. Alternatively, the rotating anode for the X-ray tube of the embodiment may have a structure in which an oxide film is provided on the surface of the molybdenum alloy of the embodiment other than the electron beam irradiation surface. Such a rotating anode for the X-ray tube is suitable for X-ray tubes.

[0017] Furthermore, the molybdenum alloy of this embodiment is also suitable for use as a molten crucible.

[0018] A cross-sectional view showing an example of the microstructure of a molybdenum alloy according to the embodiment. A cross-sectional view showing a first example of a rotating anode for an X-ray tube according to the embodiment. A cross-sectional view showing a second example of a rotating anode for an X-ray tube according to the embodiment. A schematic diagram showing an example of the configuration of an X-ray tube equipped with a rotating anode for an X-ray tube according to the embodiment. Embodiment

[0019] The embodiments of the molybdenum alloy, the rotating anode for the X-ray tube, the X-ray tube, and the molten crucible will be described in detail below with reference to the drawings.

[0020] The molybdenum alloy of this embodiment consists of at least one carbide from titanium carbide, hafnium carbide, zirconium carbide, and tantalum carbide, the remainder being molybdenum, and unavoidable impurities. The molybdenum alloy contains 0.5 wt% to 20.0 wt% of carbides. Furthermore, the molybdenum alloy has a carbide particle density of 4000 pcs / mm ２ There are more than this number.

[0021] For example, the molybdenum alloy of the embodiment contains 0.5 wt% to 20.0 wt% of at least one carbide, such as titanium carbide (TiC), hafnium carbide (HfC), zirconium carbide (ZrC), and tantalum carbide (TaC). When one or more of these carbides are used in the molybdenum alloy of the embodiment, the total content is 0.5 wt% to 20.0 wt%. Furthermore, if the carbide content in the molybdenum alloy is less than 0.5 wt%, the effect of the addition is small. On the other hand, if the carbide content exceeds 20.0 wt%, cracks are more likely to occur during manufacturing processes such as forging. Also, increasing the amount of carbides in the molybdenum alloy may increase manufacturing costs. In the molybdenum alloy of the embodiment, the carbide content is preferably, for example, 1.0 wt% to 15 wt%, and more preferably 2.0 wt% to 13.0 wt%.

[0022] Figure 1 shows a cross-sectional view illustrating an example of the cross-sectional structure of the molybdenum alloy according to the embodiment. In Figure 1, reference numeral 1 denotes carbide particles (black region) present at the grain boundaries of molybdenum crystal grains, and reference numeral 3 denotes the molybdenum alloy. The molybdenum alloy 3 consists of carbide particles 1, molybdenum crystal grains (not shown), and unavoidable impurities (not shown), etc. The aspect ratio of the carbide particles 1 in the molybdenum alloy 3 is, for example, less than 2.00. In the molybdenum alloy 3, the aspect ratio of the carbide particles 1 is preferably, for example, 1.50 or less, and more preferably 1.30 or less.

[0023] Carbide particles 1 are present in the molybdenum alloy 3 at a concentration of 4000 pcs / mm ２ The above amounts are present. Carbide particles 1 are present at the grain boundaries between molybdenum crystal grains in the molybdenum alloy 3. The presence of carbide particles 1 at the grain boundaries of the molybdenum crystal grains suppresses the growth of the molybdenum crystal grains through the pinning effect of the carbides, thereby improving the strength. Furthermore, if many small carbide particles 1 are dispersed, it is possible to further suppress the grain growth of the molybdenum crystal grains, making it possible to further improve the strength of the material.

[0024] The upper limit of the dispersion state of carbide particles 1 within the molybdenum alloy 3 is not particularly limited, but for example, 40,000 pcs / mm ２ Preferably, the dispersion of carbide particles 1 is, for example, 40,000 pcs / mm ２ If the amount exceeds a certain level, it may inhibit the sintering process and reduce the strength of molybdenum alloy 3.

[0025] The D50 particle size of the carbide particles 1 of the molybdenum alloy 3 is, for example, 0.2 μm or more and 5.0 μm or less. Preferably, the D50 particle size of the carbide particles 1 is 0.5 μm or more and 3.0 μm or less. Also, the D50 particle size of the molybdenum crystal grains of the molybdenum alloy 3 is, for example, 100 μm or less. Preferably, the D50 particle size of the molybdenum crystal grains is 70 μm or less, and more preferably 50 μm or more.

[0026] The particle size of D10 of the carbide particles 1 of the molybdenum alloy 3 is, for example, 0.1 μm or more and 1.0 μm or less. Preferably, the particle size of D10 of the carbide particles 1 is 0.2 μm or more and 0.8 μm or less.

[0027] The D90 particle size of the carbide particles 1 of the molybdenum alloy 3 is, for example, 1.0 μm or more and 10.0 μm or less. Preferably, the D90 particle size of the carbide particles 1 is 1.5 μm or more and 7 μm or less. The dispersion state of the carbide particles 1 is measured, for example, by image analysis from images taken with an optical microscope. The D50 particle size (or average particle size) of the carbide particles 1 and the D50 particle size (or average particle size) of the molybdenum crystal grains are determined by binarizing the image, measuring the particle size of the carbide particles 1 from the black image of the carbide, and measuring the particle size of the molybdenum crystal grains from the white matrix structure. The major axis length X and minor axis length Y of the carbide particles 1 in the black image of the binarized image are measured, and the aspect ratio (X / Y) of the carbide particles 1 is calculated. Furthermore, the dispersion state of the carbide particles 1 may be obtained by identifying the carbides in a broad elemental distribution using EPMA (Electron Probe Microanalyzer), mapping them, and then measuring the number of carbide particles 1 per unit area. Alternatively, the aspect ratio (X / Y) of the carbide particles 1 can be calculated by measuring the long axis length X and short axis length Y from the image obtained by EPMA. Observation using EPMA allows for the identification and mapping of carbides in a broad elemental distribution using, for example, a 1000x field of view (spot diameter 1 μm or less, CuKα rays).

[0028] Such a molybdenum alloy 3 can achieve excellent strength, for example, a three-point bending strength of 900 MPa or more at room temperature. This molybdenum alloy 3 with excellent three-point bending strength at room temperature is suitable for components requiring mechanical strength, such as rotating anodes for X-ray tubes and molten crucibles.

[0029] For X-ray tube rotating anodes using molybdenum alloy 3, graphite may be bonded to the molybdenum alloy with brazing material in order to reduce weight.

[0030] The rotating anode for an X-ray tube in the embodiment has a structure in which a shaft (rotation axis) is joined to a molybdenum alloy 3 and is rotatable. An example of such a rotating anode for an X-ray tube is shown in FIGS. 2 to 3. FIGS. 2 to 3 are cross-sectional views each including the rotation axis of the anode. In FIGS. 2 to 3, reference numeral 3 denotes the molybdenum alloy of the embodiment, reference numeral 4 denotes an electron beam irradiation surface that receives electrons and emits X-rays, reference numeral 5 denotes a shaft, and reference numeral 10 denotes the rotating anode for an X-ray tube of the embodiment.

[0031] Since the molybdenum alloy 3 of the embodiment has high strength and thus has a high effect of suppressing vibration due to high-speed rotation, it is also suitable for a rotating anode 10 for an X-ray tube having a diameter of 100 mm or more. Further, it is also suitable for a rotating anode 10 for an X-ray tube having a diameter of 200 mm or more.

[0032] In the rotating anode 10 for an X-ray tube, the material of the electron beam irradiation surface 4 is at least one metal of W, Mo, Nb, Ta, Re, Ti, Zr, C or an alloy mainly composed of at least one of W, Mo, Nb, Ta, Re, Ti, Zr, C. Examples of such an alloy include a Re-W alloy.

[0033] An oxide film may be provided on the surface of the molybdenum alloy 3. As the oxide film, aluminum oxide (for example, Al ２ O ３ ), titanium oxide (for example, TiO ２ ), zirconium oxide (for example, ZrO ２ ), silicon oxide (for example, SiO ２ ) or a mixture thereof is preferable. Also, the oxide film may be a single layer or a multilayer. Further, examples of the method for forming the oxide film include a spraying method, a CVD method (chemical vapor deposition method), a PVD method (physical vapor deposition method, sputtering method). By providing the oxide film, the gas emission amount of the rotating anode 10 for an X-ray tube can be reduced.

[0034] Furthermore, in order to reduce the weight of the rotating anode 10 for the X-ray tube, a portion of the molybdenum alloy 3 may be replaced with graphite. Figure 3 shows an example of a rotating anode 10 for an X-ray tube in which a portion of the molybdenum alloy 3 is replaced with graphite. Reference numeral 6 denotes graphite. The graphite 6 is placed on the back side of the molybdenum alloy 3 (opposite the front side to which the electron beam is irradiated) and is bonded to the molybdenum alloy 3 via a bonding layer, for example, a metal. As shown in Figure 3, by replacing a portion of the molybdenum alloy 3 with graphite 6 in the anode 10, the overall weight can be reduced compared to the anode 10 shown in Figure 2, even if the volume is the same.

[0035] The X-ray tube 20 (shown in Figure 4) using the rotating anode 10 for X-ray tubes described above has suppressed vibrations during operation. Therefore, it can be applied to X-ray inspection equipment in various fields, such as X-ray CT scanners. In particular, since the strength of the rotating anode 10 for X-ray tubes has been improved, it is suitable for X-ray tubes 20 that achieve large size, high output, and high resolution.

[0036] Furthermore, due to its high strength, it is also suitable for use in crucibles used for melting metals and other materials. In particular, even when applied to large crucibles with a diameter (maximum outer diameter) of 100 mm or more, it reduces the frequency of damage and cracking caused by external forces, demonstrating excellent durability.

[0037] Next, the manufacturing method for molybdenum alloy 3 will be described. While there are no particular limitations on the manufacturing method for molybdenum alloy 3, the following are preferred methods.

[0038] First, as raw material powder, molybdenum powder containing inevitable impurities and at least one carbide powder of titanium carbide, hafnium carbide, zirconium carbide, tantalum carbide are prepared and mixed using a ball mill or the like. The molybdenum powder may contain, for example, 5 ppm or more and 100 ppm or less of iron (Fe) as inevitable impurities. Also, the iron as inevitable impurities is, for example, 5 ppm or more and 30 ppm or less. Further, the molybdenum powder may contain, for example, 5 ppm or more and 40 ppm or less of nickel (Ni) as inevitable impurities. The nickel as inevitable impurities is, for example, 5 ppm or more and 20 ppm or less. Also, the molybdenum powder may contain 5 ppm or more and 30 ppm or less of potassium (K) as inevitable impurities. The potassium as inevitable impurities is, for example, 5 ppm or more and 20 ppm or less. The total of iron, nickel, and potassium as inevitable impurities is, for example, 15 ppm or more and 100 ppm or less. Also, the total of the inevitable impurities of the molybdenum powder is, for example, 15 ppm or more and 60 ppm or less.

[0039] The particle size of the D50 of the molybdenum powder is, for example, 5 μm or more and 30 μm or less.

[0040] The carbide powder is selected from at least one of, for example, titanium carbide, hafnium carbide, zirconium carbide, tantalum carbide, and niobium carbide, and the total amount of the carbide powder is selected to be 0.5 wt% or more and 20.0 wt% or less in the mixed powder. The carbide powder is, for example, 1.0 wt% or more and 15.0 wt% or less in the mixed powder. Also, for example, it is 2.0 wt% or more and 13.0 wt% or less. The D50 particle size of the carbide powder is 10.0 μm or less, preferably 8.0 μm or less. The D50 particle size of the carbide powder is preferably, for example, 0.2 μm or more and 8.0 μm or less, and more preferably 0.5 μm or more and 5.0 μm or less. Also, the D50 particle size of the carbide powder is, for example, smaller than the D50 particle size of the molybdenum powder. When the D50 particle size of the carbide powder is smaller than the D50 particle size of the molybdenum powder, the carbide is likely to be uniformly dispersed in the grain boundary phase of molybdenum. The ratio of the D50 particle size of the carbide powder to the D50 particle size of the molybdenum powder is, for example, 0.01 or more and 0.8 or less. More preferably, the ratio is 0.1 or more and 0.8 or less. Here, since the particle sizes of the molybdenum powder and the carbide powder each have a substantially symmetric distribution, the D50 particle size may be regarded as equal to the average particle size.

[0041] Next, the mixed raw material powder is die-formed at a pressure of 200 MPa or more to obtain a formed body. The molding pressure is preferably 200 MPa or more and 500 MPa or less. If the molding pressure is less than 200 MPa, the density of the formed body is insufficient, making it difficult to obtain a high-density sintered body. On the other hand, if it exceeds 500 MPa, cracks are likely to occur in the formed body, which is not preferable. The formed body is subjected to CIP (Cold Isostatic Pressing) treatment or degreasing treatment as necessary.

[0042] Next, the sintering of the formed body is performed by a sintering process. At this time, as the sintering atmosphere, it is desirable to perform the sintering at a sintering temperature of 1900 °C or more and 2100 °C or less in an inert gas or a reducing atmosphere. Examples of the inert gas include nitrogen, argon, krypton, etc. The reducing atmosphere is, for example, a hydrogen atmosphere.

[0043] The sintering time is, for example, 5 to 20 hours. If the sintering temperature is below 1900°C, diffusion will not proceed sufficiently, and sintering will not be possible. Also, if sintering is performed at a temperature higher than 2100°C, the carbides and molybdenum will react, and the carbide particles will not be able to exist as small particles at the grain boundaries of the molybdenum crystal grains, thus failing to improve the strength of molybdenum alloy 3.

[0044] Furthermore, if a metal layer or alloy layer containing W or the like is used on the electron beam irradiation surface 4, the anode 10 may be manufactured by molding and sintering it together with the molybdenum alloy 3 body, or the anode 10 may be manufactured by first manufacturing a sintered body of molybdenum alloy 3 and then integrating it. In addition, if necessary, an oxide film may be provided on the surface of the molybdenum alloy 3.

[0045] Furthermore, after the anode 10 is completed, a degassing treatment may be performed on the anode 10 as necessary. The degassing treatment is performed at a temperature of 1400°C to 1800°C. －３ The process can be carried out at a pressure of Pa or less for approximately 2 to 7 hours. After fabricating the anode 10, the shaft 5 is joined to the anode 10 and mounted on the X-ray tube body to complete the X-ray tube 20 shown in Figure 4.

[0046] Figure 4 is a schematic diagram showing the configuration of an X-ray tube equipped with an anode 10. In Figure 4, the same reference numerals are used for components that are the same as those shown in Figures 2 and 3, and their descriptions are omitted.

[0047] Figure 4 shows an X-ray tube 20 equipped with an anode 10. The X-ray tube 20 is used in X-ray inspection equipment. For example, X-ray inspection equipment includes inspection equipment in the medical field (general X-ray imaging equipment, mammography equipment, X-ray CT equipment, X-ray therapy equipment, etc.) and inspection equipment in the scientific and industrial fields (for example, X-ray diffraction equipment, X-ray fluorescence analyzers, non-destructive testing equipment, material inspection equipment such as thickness inspection equipment, airport baggage inspection equipment, etc.). The X-ray tube 20 has an X-ray tube container 7. The X-ray tube container 7 is a container made of glass, metal, or the like, with the inside kept under vacuum. The X-ray tube container 7 houses the shaft 5, the cathode 8, and the anode 10.

[0048] The cathode 8 has a filament formed of a metal such as tungsten or nickel, for example, in the shape of a fine wire. The cathode 8 is connected to an X-ray high-voltage device (not shown) via a cable or the like. The cathode 8 generates heat and emits an electron beam when it receives a cathode voltage and filament current from the X-ray high-voltage device.

[0049] The electron beam emitted from the cathode 8 collides with the focal point F of the electron beam irradiation surface 4 of the anode 10 due to the action of the tube voltage. The electron beam irradiation surface 4 of the anode 10 generates X-rays upon impact with the electron beam at the focal point F. By rotating the anode 10 around the rotation axis D, the X-ray tube 20 generates X-rays while shifting the focal point F on the electron beam irradiation surface 4.

[0050] Bearings (not shown) are connected to both ends of the shaft 5. A stator coil 9 is mounted on the outside of the X-ray tube container 7 so as to surround the shaft 5. The stator coil 9 is housed in the X-ray tube 20. The stator coil 9 is connected to a shaft drive power supply (not shown) and receives power from the shaft drive power supply to rotate the shaft 5 according to the principle of electromagnetic induction. The anode 10 rotates around the rotation axis D in conjunction with the rotation of the shaft 5.

[0051] The molten crucible can also be manufactured using the same sintering method as described above for the anode 10. Furthermore, an oxide coating may be applied to the surface of the molybdenum alloy 3 as needed.

[0052] (Example) Molybdenum powder with a D50 particle size of 15 μm was mixed with carbide powder (at least one of TiC, HfC, ZrC, and TaC powders) with a D50 particle size of 1.0 μm in the amounts shown in Table 1, and mixed in a ball mill. Next, the mixed powder was molded in a mold at a pressure of 300 MPa to obtain a molded body.

[0053] Next, the molded body was sintered in a hydrogen atmosphere at a temperature between 1900°C and 2100°C as shown in Table 1. The shape of the sintered body was standardized to a cylindrical shape with a base diameter of 40 mm and a height of 500 mm. The obtained sintered body was then processed by forging until it became a cylindrical shape with a base diameter of 50 mm and a height of 50 mm to obtain molybdenum alloy 3 according to the example.

[0054] (Comparative Examples) In Comparative Example 1, a molybdenum alloy was produced in the same manner as in Example 2, except that the sintering temperature was changed. In Comparative Example 2, a molybdenum alloy was produced in the same manner as in Example 2, except that the particle size of D50 in the mixed HfC powder was 14 μm.

[0055] The particle sizes of the carbide particles 1 and molybdenum crystal grains of the molybdenum alloy 3 in each example were measured by image analysis from images of the cross-sectional structure taken with an optical microscope. The measurement results for the particle size of the carbide particles 1 are shown in Table 2, and the measurement results for the particle size of the molybdenum crystal grains are shown in Table 3. Specifically, the obtained cross-sectional structure images were binarized, and the particle size of the carbide particles 1 was measured from the carbide, which is the black image, and the particle size of the molybdenum crystal grains was measured from the structure of the white matrix. Similarly, the particle size of the carbide particles and the particle size of the molybdenum crystal grains were measured for the molybdenum alloy in the comparative example.

[0056] Furthermore, the cross-sectional structure of molybdenum crystal grains was observed for the examples and comparative examples, and the aspect ratio of the carbide particles was investigated. Specifically, the obtained cross-sectional images were binarized, and the major axis length X and minor axis length Y of carbide particle 1 were measured from the carbide, which was represented by the black image. Then, the aspect ratio (X / Y) based on the major axis length X and minor axis length Y of the carbide particle was determined. Specifically, the aspect ratio of the carbide particle is the average value (average aspect ratio) of multiple aspect ratios corresponding to each of the multiple carbide particles observed.

[0057] Next, a rectangular parallelepiped specimen measuring 3 mm × 4 mm × 40 mm was cut from a cylindrical molybdenum alloy with a base diameter of 50 mm and a height of 50 mm, and the three-point bending strength of the specimen was measured. The three-point bending strength of the specimen was measured at room temperature, under atmospheric conditions, with a support distance of 30 mm and a test speed of 0.5 mm / min. The measurement results of the three-point bending strength are shown in Table 3.

[0058]

[0059]

[0060]

[0061] As shown in Table 1, the number of carbide particles in molybdenum alloy 3 is 4000 pcs / mm２ If the above conditions are met, the three-point bending strength at room temperature is high, exceeding 900 MPa, as shown in Table 3, demonstrating excellent properties.

[0062] (Applicable to rotating anode 10 for X-ray tube) In Example 13, a molybdenum alloy was produced in the same manner as in Example 1, except that the particle size of D50 of the carbide powder (HfC powder) mixed with the same molybdenum powder as in Example 1 was 0.8 μm (1.0 μm in Example 1). On the other hand, in Comparative Example 3, a molybdenum alloy was produced in the same manner as in Comparative Example 1, except that the particle size of D50 of the HfC powder mixed with the same molybdenum powder as in Comparative Example 1 was 0.8 μm (1.0 μm in Comparative Example 1). In other words, the sintering temperature differs between Example 13 and Comparative Example 3.

[0063] This section describes an example in which the molybdenum alloy 3 according to Example 13 and the molybdenum alloy according to Comparative Example 3 were used in a rotating anode 10 for an X-ray tube. An anode 10 with a diameter of 100 mm was manufactured using the molybdenum alloy 3 according to Example 13, a shaft (rotating axis) was attached to the anode 10, and the X-ray tube 20 was fabricated by assembling it into the X-ray tube body. The anode 10 of the X-ray tube 20 was rotated at a rotation speed of 8000 rpm, and the vibration defects of the X-ray tube 20 were measured with a vibration meter. The vibration defects were similarly measured in an X-ray tube incorporating a 100 mm diameter anode using the molybdenum alloy according to Comparative Example 3. Comparing these results, it was confirmed that the vibration defects were suppressed in the X-ray tube of Example 13.

[0064] In other words, in the anode 10 using the molybdenum alloy 3 according to this embodiment, vibration defects can be suppressed even in an X-ray tube 20 incorporating a large anode 10 with a diameter of 100 mm or more, due to the high strength of the molybdenum alloy 3. Therefore, when this X-ray tube is applied to X-ray inspection equipment in various fields, it is possible to provide an X-ray tube that achieves high output and high resolution.

[0065] (Application to a molten crucible) Next, an example of using the molybdenum alloy 3 according to Example 13 and the molybdenum alloy according to Comparative Example 3 in a molten crucible will be described. Molybdenum powder with a D50 particle size of 15 μm is mixed with 0.5 wt% of HfC powder, which is a carbide powder with a D50 particle size of 0.8 μm, in a ball mill.

[0066] Next, a crucible-shaped molded body was produced by CIP molding at a pressure of 200 MPa. Then, the crucible-shaped molded body was placed in a carbon crucible, and a sintering process was carried out at 2000°C in an inert gas atmosphere to produce a molten crucible using the molybdenum alloy 3 according to Example 13. The sintering time was in the range of 5 to 20 hours.

[0067] Except for performing the sintering process at 2200°C instead of 2000°C, a molten crucible using the molybdenum alloy according to Comparative Example 3 was prepared in the same manner as in Example 13. Both the molten crucible using molybdenum alloy 3 according to Example 13 and the molten crucible using molybdenum alloy according to Comparative Example 3 had a wall thickness of 10 mm, a height of 50 mm, and an outer diameter of 100 mm. Since the molten crucible according to Example 13 has higher three-point bending strength than the molten crucible according to Comparative Example 3, the molten crucible of the embodiment exhibits superior durability by reducing the frequency of damage and cracking caused by external forces.

[0068]

[0069] According to at least one embodiment described above, it is possible to provide a high-strength molybdenum alloy 3, a rotating anode 10 for an X-ray tube using the same, an X-ray tube, and a molten crucible. Furthermore, according to at least one embodiment described above, even if the molybdenum alloy 3 is used in the rotating anode 10 for an X-ray tube equipped in a high-power, high-resolution X-ray inspection device, it is possible to suppress vibrations of the X-ray tube caused by the high-speed rotation of the rotating anode 10, thereby realizing the performance of a high-power, high-resolution X-ray inspection device. Moreover, according to at least one embodiment described above, it is possible to provide a high-strength molybdenum alloy 3 that suppresses the occurrence of cracks and other damage during the manufacturing process and melting process of the molten crucible.

[0070] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. Consists of at least one carbide from titanium carbide, hafnium carbide, zirconium carbide, and tantalum carbide, with the remainder being molybdenum and unavoidable impurities, containing 0.5 wt% to 20.0 wt% of the carbide, and the carbide particle size of the carbide is 4000 pcs / mm ２ The above are examples of molybdenum alloys.

2. The molybdenum alloy according to claim 1, wherein the particle size of the D50 of the carbide particles is 0.2 μm or more and 5.0 μm or less.

3. The molybdenum alloy according to claim 1 or 2, wherein the particle size of the D50 molybdenum crystal grains of the remaining molybdenum is 100 μm or less.

4. The molybdenum alloy according to claim 1 or 2, wherein the particle size of the D10 of the carbide particles is 0.1 μm or more and 1.0 μm or less.

5. The molybdenum alloy according to claim 1 or 2, wherein the particle size of the D90 of the carbide particles is 1.0 μm or more and 10.0 μm or less.

6. The molybdenum alloy according to claim 1 or 2, wherein the three-point bending strength at room temperature is 900 MPa or more.

7. A rotating anode for an X-ray tube using the molybdenum alloy according to claim 1 or 2.

8. A rotating anode for an X-ray tube, wherein graphite is bonded to the back side of the molybdenum alloy according to claim 1 or 2 using a brazing material.

9. The rotating anode for an X-ray tube according to claim 7, wherein the diameter is 100 mm or more.

10. The rotating anode for an X-ray tube according to claim 7, wherein the electron beam irradiation surface of the molybdenum alloy is provided with a layer of at least one metal from W, Mo, Nb, Ta, Re, Ti, Zr, and C, or an alloy layer mainly composed of at least one of W, Mo, Nb, Ta, Re, Ti, Zr, and C.

11. The rotating anode for an X-ray tube according to claim 7, wherein an oxide film is provided on the surface of the molybdenum alloy other than the electron beam irradiation surface.

12. An X-ray tube using the rotating anode for an X-ray tube as described in claim 7.

13. A molten crucible using the molybdenum alloy described in claim 1.

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