Low-oxygen WRe / TZM metal target disc for bulb tube of CT machine and preparation method thereof

Abstract

The invention provides a low-oxygen WRe / TZM metal target disc for a bulb tube of a CT machine and a preparation method of the low-oxygen WRe / TZM metal target disc. The method comprises the following steps that S1, WRe alloy powder is weighed and dried, and a TZM alloy plate blank is cleaned and dried; (S2) the WRe alloy powder and the TZM alloy plate blank are loaded into gradient molds correspondingly, and pre-pressing forming is conducted; s3) putting the gradient mold filled with the pre-pressed and formed blank into a furnace chamber of an SPS sintering furnace, vacuumizing to be below 6Pa, and sintering to obtain a WRe / TZM composite sintered blank; and S4) carrying out machining to obtain the WRe / TZM metal target disc. The metal target disc has the advantages of being high in density, uniform in structure distribution, low in content of impurities such as gas, high in molybdenum alloy matrix strength, good in machining performance, high in heat dissipation capacity, good in thermal shock resistance and the like, and the interface achieves good metallurgical bonding.

Description

Technical Field

[0001] The invention relates to the field of rotating anode target disks, and in particular to a low-oxygen WRe / TZM metal target disk for a CT machine tube and a preparation method thereof. Background Art

[0002] The tube is one of the core components of the CT machine, and the target disc is a key component of the tube. At present, the mainstream target discs on the market are mainly composed of a three-layer structure of WRe / TZM / graphite. Its working principle is that during operation, the rotating anode target disc rotates at high speed, and the high-speed electrons emitted by the cathode bombard the target surface to generate X-rays. Therefore, the density, uniform composition, mechanical properties, heat dissipation performance and interface bonding strength of the rotating anode target disc are key factors that determine the service life of the target disc.

[0003] WRe alloy is an alloy composed of W and Re. W has a high melting point, high high temperature strength, good heat dissipation performance, and high atomic number. It can stimulate strong X-rays under electron bombardment, but W has a notch sensitivity effect, which easily leads to the expansion and deepening of cracks, thereby causing the target disc matrix to peel off. The recrystallization temperature of Re is 500℃ higher than that of W, and Re does not have a ductile-brittle transition temperature. Therefore, the addition of Re can significantly improve the room temperature brittleness of W, reduce the ductile-brittle transition temperature, and enhance the mechanical properties of W in a certain high temperature area. Therefore, WRe alloy is selected as the target surface of the anode target disc. Due to the large difference in the melting points of WRe alloy and TZM alloy, it is very difficult to sinter and densify WRe alloy and TZM alloy at the same time.

[0004] The metal target is in a high vacuum and high-speed rotating working state, which requires it to have a high recrystallization temperature, good toughness and high-temperature performance.

[0005] At present, the main methods for preparing metal target disks are the following two process routes: (1) Powder metallurgy + forging, which is also the mainstream preparation process for foreign products. Its main characteristics are large investment and complex process control. At present, large-scale metal target disks have not yet been mass-produced in China. Due to poor forging process control, local stress concentration is easy to cause cracking, and the grain structure has obvious grain orientation and other problems; (2) Powder metallurgy + hot isostatic pressing technology. In the actual preparation process, the uniformity of large-size metal target disks needs to be improved, and the grains of the molybdenum alloy layer are relatively coarse; according to market feedback, metal target disks have problems such as large outgassing and easy cracking on the target surface during use, which leads to failure of the CT tube; in addition, there are problems such as large equipment investment and long preparation process cycle, which are also the main reasons restricting the application of this process.

[0006] Therefore, a simple and efficient method for manufacturing low-oxygen WRe / TZM metal targets for CT tubes needs to be explored. Summary of the invention

[0007] Technical issues

[0008] The inventor of the present invention found in research that the presence of impurity elements affects the performance of the target disc. In order to solve the shortcomings of the prior art and achieve high performance and efficient manufacturing of WRe / TZM metal target discs, the present invention proposes a low-oxygen WRe / TZM metal target disc for CT machine tubes and a preparation method thereof.

[0009] Technical Solution

[0010] According to one aspect of the present invention, a method for preparing a low-oxygen WRe / TZM metal target for a CT machine tube is provided, which comprises the following steps:

[0011] S1: Weigh the WRe alloy powder required for the anode target, place it in a tray, put it in a vacuum drying oven, and dry the powder; wash the TZM alloy slab, and put it in a vacuum drying oven for drying;

[0012] S2: taking out the dried WRe alloy powder and TZM alloy slab, respectively loading them into gradient molds, placing the WRe alloy powder in a mold cavity portion with a relatively thin wall thickness of the gradient mold, and placing the TZM alloy slab in a mold cavity portion with a relatively thick wall thickness of the gradient mold, and pre-pressing and forming;

[0013] S3: sending the gradient mold containing the pre-pressed blank into the SPS sintering furnace chamber, evacuating the vacuum to below 6 Pa, and sintering to obtain a WRe / TZM composite sintered blank;

[0014] S4: Mechanically process the WRe / TZM composite sintered blank to obtain a WRe / TZM metal target.

[0015] Preferably, in step S1, a hydrochloric acid aqueous solution with a mass fraction of 2% to 15% is used to clean the TZM alloy slab in an ultrasonic cleaning machine to remove impurities on the surface of the metal target disk, and then the slab is cleaned with deionized water and then dehydrated with anhydrous ethanol.

[0016] Preferably, the content of Re in the WRe alloy powder is 3 wt % to 15 wt %, more preferably 10 wt %.

[0017] Preferably, in step S2, the gradient mold is a graphite mold having a shape of two cylinders combined, wherein the inner diameters of the two cylinders are the same, the outer diameters are different, and the inner holes of the two cylinders are aligned to form a through-hole cavity in the mold. That is, the inner cavity of the mold is cylindrical, but different parts of the mold have different wall thicknesses. The WRe alloy powder is placed in a portion of the mold with a relatively thin wall thickness, which belongs to the high temperature zone; the TZM alloy plate is located in a portion of the mold with a relatively thick wall thickness, which belongs to the low temperature zone.

[0018] Preferably, the difference in wall thickness between the cavity portion having a relatively thinner wall thickness and the cavity portion having a relatively thicker wall thickness is 5-50 mm.

[0019] Preferably, the SPS sintering furnace in step S3 is a JPX400 type SPS production line equipment.

[0020] Preferably, the sintering process in step S3 is:

[0021] Axial pressure: 10~50MPa;

[0022] Heating rate: 10~60℃ / min;

[0023] Sintering temperature: 1500~1750℃; Holding time: 10~60min;

[0024] Cooling method: gradient cooling; cooling rate: 10-30℃ / min, cooling to 1000℃, and then cooling with the furnace.

[0025] More preferably, the sintering process in step S3 is:

[0026] Axial pressure: adopting a gradient pressurization method, when the temperature is from room temperature to the first temperature, the pressure is 10-25 MPa; when the temperature is higher than the first temperature, the pressure is greater than 25 MPa, wherein the first temperature is any temperature between 1100 and 1200°C;

[0027] Gradient heating: adopting the gradient heating method, when the room temperature reaches the first temperature, the heating rate is 30-60℃ / min, and when it is higher than the first temperature, the heating rate is more than 10℃ / min and less than 30℃ / min.

[0028] Preferably, the outer diameter of the WRe / TZM metal anode target for CT machine is 140-190 mm.

[0029] Preferably, the mechanical processing of the WRe / TZM composite body in step S4 is carried out according to the target plate model and drawings.

[0030] Preferably, the surface roughness Ra of the target surface WRe alloy is lower than 0.8, the surface has no processing cracks and defects, and presents a uniform metallic luster; the surface roughness Ra of the TZM alloy is lower than 1.6, and there are no processing cracks and defects.

[0031] According to a second aspect of the present invention, a low-oxygen WRe / TZM metal target disk for a CT machine tube is provided, which is prepared by the preparation method of the low-oxygen WRe / TZM metal target disk for a CT machine tube according to the present invention.

[0032] Preferably, the oxygen content of the TZM alloy in the WRe / TZM metal target disk is less than 200 ppm.

[0033] Preferably, the density of the WRe layer of the WRe / TZM metal target is 18.50 g / cm 3 above.

[0034] Preferably, the density of the TZM alloy in the WRe / TZM metal target is 10.05 g / cm 3 above.

[0035] Preferably, the joint shear strength of WRe / TZM is greater than 180 MPa.

[0036] Preferably, the tensile strength of the TZM alloy in the WRe / TZM metal target is greater than 400 MPa.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. Compared with the prior art, the present invention uses SPS sintering technology to manufacture large-size anode target discs, which has the advantages of short sintering time, one-time forming of metal target discs, low energy consumption, simple operation / process, high efficiency, etc., which can greatly reduce the production cycle and cost.

[0039] 2. Compared with the prior art, the present invention adopts the sintering process of tungsten-rhenium powder + TZM alloy slab, which reduces the risk of impurities introduced into the TZM alloy during the molding and sintering processes, improves the purity of the TZM alloy material, and thus ensures the high quality and efficient production of the metal target plate.

[0040] 3. The low-oxygen WRe / TZM metal target for CT and tube manufactured by the present invention has the advantages of high density, uniform tissue distribution, good metallurgical bonding at the interface, low content of impurities such as gas, high strength of the molybdenum alloy matrix, good processing performance, strong heat dissipation capacity and good thermal shock resistance.

[0041] 4. The WRe layer density of the low-oxygen WRe / TZM metal target for CT and tube manufactured by the present invention can reach 18.50 g / cm 3 Above, the density of TZM alloy can reach 10.05g / cm 3 Above; the shear strength of WRe / TZM joint is greater than 180MPa, the oxygen content of TZM alloy is less than 200ppm, and the tensile strength of TZM alloy is greater than 400MPa. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with embodiments. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0043] The spark plasma sintering furnace used in the following examples is a JPX-400 series spark plasma sintering system produced by Sinter Land Co., Ltd. of Japan, and its current type is a direct current pulse current with a pulse sequence of 40:7. (The following sintering temperatures are based on the high temperature zone temperature)

[0044] The density test is the Archimedean drainage method;

[0045] The oxygen content test is conducted by inert gas fusion infrared absorption method-thermal conductivity method, GB / T4325.23-2013;

[0046] The tensile strength test is the metal material tensile laboratory temperature test method GB / T 228.1-2010.

[0047] Example 1

[0048] In this embodiment, a W-10Re / TZM metal target disk with a diameter of Φ140 mm is manufactured, and the specific steps are as follows:

[0049] (1) Calculate the required W-10Re alloy according to the volume and density of the target plate, weigh the corresponding powder and put it in a tray, clean the TZM alloy slab in an ultrasonic cleaner using a 5% hydrochloric acid aqueous solution, then use deionized water for ultrasonic cleaning, and finally use alcohol for ultrasonic cleaning and blow dry; then, put the tungsten-rhenium powder and TZM plate into a vacuum drying oven, evacuate and heat to dry, and take out after cooling to room temperature;

[0050] (2) The dried W-10Re powder is loaded into the thin-walled cavity at the top of the gradient mold, and the dried TZM alloy plate is loaded into the thick-walled cavity at the bottom of the gradient mold (wherein the difference in wall thickness between the thin-walled cavity and the thick-walled cavity is 35 mm), and pre-pressing is performed. The graphite pressing head is placed in the graphite mold, and the outer periphery of the graphite mold is wrapped with 2 to 3 layers of carbon felt. The graphite mold is then transported into the SPS sintering furnace by a transport trolley to ensure the symmetry of the upper and lower graphite pads. Pressurization is performed and vacuum is evacuated to below 6 Pa to start sintering.

[0051] (3) According to factors such as the diameter of the metal target and the axial thickness, the specific sintering process is:

[0052] Axial pressure: Gradient pressure (from room temperature to 1200°C, the pressure is 10MPa; above 1200°C, up to 1650°C, the pressure is 30MPa);

[0053] Heating rate: 40℃ / min from room temperature to 1200℃, 20℃ / min above 1200℃ to 1650℃;

[0054] Sintering temperature: 1650℃;

[0055] Insulation time: 30min;

[0056] Cooling rate: 20°C / min, cooling to 1000°C, then cooling to room temperature with the furnace and taking out to obtain W-10Re / TZM sintered blank.

[0057] (4) The W-10Re / TZM sintered blank is processed according to the requirements of the drawing. The roughness Ra of the W-10Re alloy target surface is less than 0.8, and the surface roughness Ra of the TZM alloy is less than 1.6, so as to obtain a machined metal target disk with uniform surface metallic gloss and no defects.

[0058] The metal target was subjected to a dissection destructive test. The densities of the W-10Re alloy and TZM alloy of the metal target were 18.60 g / cm 3 and 10.09 g / cm 3 The shear strength of the WRe / TZM joint is 195MPa, the oxygen content of the TZM alloy is 60ppm, and the room temperature tensile strength of the TZM alloy is 433MPa.

[0059] Example 2

[0060] In this embodiment, a W-10Re / TZM metal target disk with a diameter of Φ140 mm is manufactured, and the specific steps are as follows:

[0061] (1) Calculate the required W-10Re alloy according to the volume and density of the target plate, weigh the corresponding powder and put it in a tray, clean the TZM alloy slab in an ultrasonic cleaner using a 5% hydrochloric acid aqueous solution, then use deionized water for ultrasonic cleaning, and finally use alcohol for ultrasonic cleaning and blow dry; then, put the tungsten-rhenium powder and TZM plate into a vacuum drying oven, evacuate and heat to dry, and take out after cooling to room temperature;

[0062] (2) The dried W-10Re powder is loaded into the thin-wall layer cavity at the upper part of the gradient mold, and the dried TZM alloy plate is loaded into the cavity at the lower part of the gradient mold (wherein the difference in wall thickness between the thin-wall cavity and the thick-wall cavity is 35 mm), and pre-pressing is performed. The graphite pressing head is placed in the graphite mold, and the outer periphery of the graphite mold is wrapped with 2 to 3 layers of carbon felt. The graphite mold is then transported into the SPS sintering furnace by a transport trolley to ensure the symmetry of the upper and lower graphite pads. Pressurization is performed and vacuum is evacuated to below 6 Pa to start sintering.

[0063] (3) According to factors such as the diameter of the metal target and the axial thickness, select a suitable sintering process. The specific sintering process is:

[0064] Axial pressure: Gradient pressure (from room temperature to 1100°C, the pressure is 10MPa; above 1100°C, up to 1600°C, the pressure is 30MPa);

[0065] Heating rate: 40℃ / min from room temperature to 1100℃, 20℃ / min above 1100℃ to 1600℃;

[0066] Sintering temperature: 1600℃;

[0067] Insulation time: 20min;

[0068] Cooling rate: 20°C / min, cooling to 1000°C, then cooling to room temperature with the furnace and taking out to obtain W-10Re / TZM sintered blank.

[0069] (4) The W-10Re / TZM sintered blank is processed according to the requirements of the drawing. The roughness Ra of the W-10Re alloy target surface is less than 0.8, and the surface roughness Ra of the TZM alloy is less than 1.6, so as to obtain a machined metal target disk with uniform surface metallic gloss and no defects.

[0070] The densities of the W-10Re alloy and TZM alloy of the metal target are 18.58 g / cm 3 and 10.08 g / cm 3 The shear strength of the WRe / TZM joint is 186MPa, the oxygen content of the TZM alloy is 57ppm, and the room temperature tensile strength of the TZM alloy is 428MPa.

[0071] Example 3

[0072] In this embodiment, a W-10Re / TZM metal target disk with a diameter of Φ140 mm is manufactured, and the specific steps are as follows:

[0073] (1) Calculate the required W-10Re alloy according to the volume and density of the target plate, weigh the corresponding powder and put it in a tray, clean the TZM alloy slab in an ultrasonic cleaner using a 5% hydrochloric acid aqueous solution, then use deionized water for ultrasonic cleaning, and finally use alcohol for ultrasonic cleaning and blow dry; then, put the tungsten-rhenium powder and TZM plate into a vacuum drying oven, evacuate and heat to dry, and take out after cooling to room temperature;

[0074] (2) The dried W-10Re powder is loaded into the thin-walled cavity at the top of the gradient mold, and the dried TZM alloy plate is loaded into the thick-walled cavity at the bottom of the gradient mold (wherein the difference in wall thickness between the thin-walled cavity and the thick-walled cavity is 35 mm), and pre-pressing is performed. The graphite pressing head is placed in the graphite mold, and the outer periphery of the graphite mold is wrapped with 2 to 3 layers of carbon felt. The graphite mold is then transported into the SPS sintering furnace by a transport trolley to ensure the symmetry of the upper and lower graphite pads. Pressurization is performed and vacuum is evacuated to below 6 Pa to start sintering.

[0075] (3) According to factors such as the diameter of the metal target and the axial thickness, select a suitable sintering process. The specific sintering process is:

[0076] Axial pressure: Gradient pressure (from room temperature to 1200°C, the pressure is 10MPa; above 1200°C, up to 1700°C, the pressure is 30MPa);

[0077] Heating rate: 40℃ / min from room temperature to 1200℃, 20℃ / min above 1200℃ to 1700℃;

[0078] Sintering temperature: 1700℃;

[0079] Insulation time: 20min;

[0080] Cooling rate: 20°C / min, cooling to 1000°C, then cooling to room temperature with the furnace and taking out to obtain W-10Re / TZM sintered blank.

[0081] (4) The W-10Re / TZM sintered blank is processed according to the requirements of the drawing. The roughness Ra of the W-10Re alloy target surface is less than 0.8, and the surface roughness Ra of the TZM alloy is less than 1.6, so as to obtain a machined metal target disk with uniform surface metallic gloss and no defects.

[0082] The densities of the W-10Re alloy and TZM alloy of the metal target are 18.74 g / cm 3 and 10.15g / cm 3 , the shear strength of WRe / TZM joint is 210MPa, the oxygen content of TZM alloy is 36ppm, and the room temperature tensile strength of TZM alloy is 430MPa.

[0083] Table 1: Properties of the metal targets obtained in Examples 1 to 3 and commercially available samples

[0084]

[0085]

[0086] Table 1 shows some performance parameters of W-10Re / TZM metal target disks prepared according to Examples 1 to 3 of the present invention and common commercially available products of the same type and specifications. Among them, Product 1, Product 2 and Product 3 are all commercially available W-10Re / TZM metal target disks, and their specifications are exactly the same as those of the products obtained in the examples. It can be seen from the data in Table 1 that the oxygen content of the TZM alloy of the metal target disk according to the present invention is much lower than that of commercially available products, and at the same time, the tungsten-rhenium alloy density, the TZM alloy density, and the room temperature tensile strength performance of the TZM alloy are more balanced.

Claims

1. A method for preparing a low-oxygen WRe / TZM metal target for a CT tube, comprising the following steps: S1: Weigh the WRe alloy powder required for the anode target, place it in a tray, put it in a vacuum drying oven, and dry the powder; wash the TZM alloy slab, and put it in a vacuum drying oven for drying; S2: taking out the dried WRe alloy powder and TZM alloy slab, respectively loading them into gradient molds, placing the WRe alloy powder in a mold cavity portion with a relatively thin wall thickness of the gradient mold, and placing the TZM alloy slab in a mold cavity portion with a relatively thick wall thickness of the gradient mold, and pre-pressing and forming; S3: sending the gradient mold containing the pre-pressed blank into the SPS sintering furnace chamber, evacuating the vacuum to below 6 Pa, and sintering to obtain a WRe / TZM composite sintered blank; S4: Mechanically process the WRe / TZM composite sintered blank to obtain a WRe / TZM metal target.

2. The method for preparing a low-oxygen WRe / TZM metal target for a CT tube according to claim 1, wherein: In step S1, the TZM alloy slab is cleaned in an ultrasonic cleaning machine using a hydrochloric acid aqueous solution with a mass fraction of 2% to 15%, then cleaned with deionized water, and then dehydrated with anhydrous ethanol; and / or The content of Re in the WRe alloy powder is 3 wt % to 15 wt %.

3. The method for preparing a low-oxygen WRe / TZM metal target for a CT tube according to claim 1 or 2, wherein: In step S2, the gradient mold is a graphite mold having a shape of two cylinders combined, wherein the two cylinders have the same inner diameter and different outer diameters, and the inner holes of the two cylinders are aligned to form a through-hole cavity in the mold.

4. The method for preparing a low-oxygen WRe / TZM metal target for a CT tube according to any one of claims 1 to 3, wherein: The difference in wall thickness between the cavity portion having a relatively thin wall thickness and the cavity portion having a relatively thick wall thickness is 5 to 50 mm.

5. The method for preparing a low-oxygen WRe / TZM metal target for a CT tube according to any one of claims 1 to 4, wherein: The sintering process in step S3 is: Axial pressure: 10~50MPa; Heating rate: 10~60℃ / min; Sintering temperature: 1500~1750℃; Holding time: 10~60min; Cooling method: gradient cooling; cooling rate: 10-30℃ / min, cooling to 1000℃, and then cooling with the furnace.

6. The method for preparing a low-oxygen WRe / TZM metal target for a CT tube according to claim 5, wherein: The sintering process in step S3 is: Axial pressure: adopting a gradient pressurization method, when the temperature is from room temperature to the first temperature, the pressure is 10-25 MPa; when the temperature is higher than the first temperature, the pressure is greater than 25 MPa, wherein the first temperature is any temperature between 1100 and 1200°C; Gradient heating: adopting the gradient heating method, when the room temperature reaches the first temperature, the heating rate is 30-60℃ / min, and when it is higher than the first temperature, the heating rate is more than 10℃ / min and less than 30℃ / min.

7. The method for preparing a low-oxygen WRe / TZM metal target for a CT tube according to any one of claims 1 to 6, wherein: The outer diameter of the WRe / TZM metal anode target is 140-190 mm; and / or The surface roughness Ra of the target surface WRe alloy is lower than 0.8, with no processing cracks or defects on the surface, showing a uniform metallic luster; the surface roughness Ra of the TZM alloy is lower than 1.6, with no processing cracks or defects.

8. A low-oxygen WRe / TZM metal target plate for a CT tube, which is prepared by the preparation method of the low-oxygen WRe / TZM metal target plate for a CT tube according to any one of claims 1 to 6.

9. The low oxygen WRe / TZM metal target for CT tube according to claim 8, wherein: The oxygen content of the TZM alloy in the WRe / TZM metal target disk is lower than 200 ppm, preferably lower than 100 ppm, and more preferably lower than 80 ppm.

10. The low oxygen WRe / TZM metal target for CT tube according to claim 8 or 9, wherein: The density of the WRe layer of the WRe / TZM metal target is 18.50 g / cm 3 above; and / or The density of TZM alloy in WRe / TZM metal target is 10.05g / cm 3 above; and / or The shear strength of the WRe / TZM joint is greater than 180 MPa; and / or The tensile strength of the TZM alloy in the WRe / TZM metal target is greater than 400MPa.

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