Forming method for reducing defects of large-size molybdenum target

Abstract

The invention relates to a forming method for reducing defects of a large-size molybdenum target in the technical field of target material processing and forming, which comprises the following steps of: performing pre-compression forming and compression forming in the compression forming process of molybdenum powder; the pre-compression molding is axial compression molding, and the compression molding is cold isostatic pressing molding. By using the pre-pressing method, the problems of uniformity of a formed body and excessive number of cavities are effectively improved, the number of target material defects, the total defect area and the defect occurrence frequency are finally reduced, the production yield is greatly improved, meanwhile, the size of a pre-pressed and formed plain blank is more standard, the machining amount is effectively reduced, the machining time and cutting excess materials are saved, and the production cost is reduced. And the production cost is reduced to a certain extent.

Description

Technical Field

[0001] This invention relates to the field of target material processing and forming technology, specifically a forming method for reducing defects in large-size molybdenum targets. Background Technology

[0002] In previous large-size molybdenum target molding processes, molybdenum powder was directly filled into the mold after mixing. However, due to limitations in the size and technology of current cold isostatic pressing equipment, large-size molybdenum targets were molded using rectangular molds with longer sides. In actual filling, the mold was placed with the longer side vertical. Therefore, during the filling process, due to gravity, the molybdenum powder in the mold would be loose at the top and tight at the bottom. At the same time, due to the limitations of this processing technology, a powder vibration device could not be used, resulting in poor flowability of the molybdenum powder. As a result, in actual production, problems such as poor and uneven filling of molybdenum powder frequently occurred, leading to a large number of defects and a large defect area in the sintered target blank. This situation greatly affected product quality and production yield, and increased production costs. Therefore, under the limitations of existing technology and equipment, achieving high-quality filling and molding of molybdenum targets is an important problem currently faced. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a molding method for reducing defects in large-size molybdenum targets. The method involves pre-compressing molybdenum powder, with the pre-compressing mold positioned horizontally along its long side. This significantly reduces the impact of gravity on powder filling, while also ensuring homogeneous filling of the molybdenum powder. This method substantially improves the uniformity of molybdenum powder filling, reduces the number and area of ​​defects in the target preform, and ultimately enhances product quality and yield.

[0004] To achieve the above-mentioned technical effects, the present invention provides a molding method for reducing defects in large-size molybdenum targets, wherein pre-pressing molding and pressing molding are performed during the pressing molding process of the molybdenum powder; The pre-pressing is axial pressing, and the pressing is cold isostatic pressing.

[0005] As a preferred embodiment of the present invention, the pressure of the axial compression molding is 10,000-20,000 Pa per square centimeter.

[0006] As a preferred technical solution of the present invention, the holding time of the axial compression molding requires that the holding time increase by 0.2-0.5s for every 1cm increase in powder filling thickness.

[0007] As a preferred technical solution of the present invention, the number of venting times in the axial compression molding is required to increase by 1 for every 10cm increase in powder filling thickness.

[0008] As a preferred technical solution of the present invention, a release agent needs to be applied to the surface of the mold before axial compression molding to ensure demolding.

[0009] As a preferred embodiment of the present invention, the pressure of the cold isostatic pressing is 220-260 MPa.

[0010] As a preferred embodiment of the present invention, the holding time of the cold isostatic pressing is 500-1000s.

[0011] In addition, to protect the preform from water ingress, a waterproof material with low oxygen and low moisture permeability is used to package the preform before cold isostatic pressing.

[0012] The beneficial effects of this invention are: the molybdenum target blank prepared by this invention has better uniformity, fewer defects, smaller total defect area, and fewer defects, which improves the quality and production yield of large-size molybdenum targets. At the same time, it ensures the dimensional specifications of the molded body, which is beneficial to the size and shape of the product after hot rolling, reduces the amount of cutting material, and achieves the effect of cost reduction. Attached Figure Description

[0013] Figure 1 These are ultrasonic flaw detection images of the large-size molybdenum target material after rolling in Embodiment 1 of the present invention; Figure 2 These are ultrasonic flaw detection images of large-size molybdenum targets after cold rolling in Embodiment 2 of the present invention; Figure 3 These are ultrasonic flaw detection images of the large-size molybdenum target material finished product in Embodiment 3 of the present invention; Figure 4 These are ultrasonic flaw detection images of the large-size molybdenum target material finished product in Embodiment 4 of the present invention; Figure 5 These are ultrasonic flaw detection images of the large-size molybdenum target material finished product in Comparative Example 1 of this invention. Detailed Implementation

[0014] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0015] In both the examples and comparative examples, the powder filling thickness is 20cm and the axial compression area is 50-80cm*100-150cm. The number and area of ​​defects are calculated only for defects that are too large and have a certain impact on product quality.

[0016] Example 1 Step 1: Apply an appropriate amount of release agent to the surface of the axial compression mold; Step 2: Fill the axial compression mold with powder and use a tool to level it; Step 3: Start the axial pressing equipment to press, with an axial pressure of >1500 tons (>10000Pa), a holding time of 2-5 seconds, and venting twice to press and shape; Step 4: Demolding. After demolding, the surface of the target blank is powdery and chipped, and a large number of fine cracks appear in the middle of the target blank. The shrinkage rate is about 33%. The strength is poor during handling and it is easy to break. Step 5: Package the target preform using a waterproof material with low oxygen and low moisture permeability; Step 6: Place the sample in a cold isostatic pressing apparatus and pressurize it. The pressing parameters are 200-220 MPa, the holding time is 500-800 s, and the shrinkage rate of the molded target blank is about 49%. Step 7: Sinter the target blank into shape, with a density >9.90 g / cm³ after sintering. 3 ; Step 8: Hot-roll the sintered target blank to its original dimensions before processing. The density of the hot-rolled target blank should be >10.18 g / cm³. 3 ; Step 9: Perform ultrasonic testing on the hot-rolled target blank to detect the number and area of ​​internal defects. The final number of defects was 18, with a total defect area of ​​24 mm. 2 The flaw detection results are as follows Figure 1 As shown.

[0017] Example 2 Step 1: Apply an appropriate amount of release agent to the surface of the axial compression mold; Step 2: Fill the axial compression mold with powder and use a tool to level it; Step 3: Start the axial pressing equipment to press, with an axial pressure of >2000 tons (>15000Pa), a holding time of 4 seconds, and venting twice to press and form the shape; Step 4: Demolding. After demolding, the surface of the target blank is powdery, the corners are chipped, and there are fine cracks in the middle of the target blank. The shrinkage rate is about 34%. The strength is not good during handling and it is easy to break. Step 5: Package the target preform using a waterproof material with low oxygen and low moisture permeability; Step 6: Place the sample in a cold isostatic pressing apparatus and pressurize it. The pressing parameters are 220-240 MPa, the holding time is 600-800 s, and the shrinkage rate of the molded target blank is about 50%. Step 7: Sinter the target blank into shape; the density after sintering is 9.96 g / cm³. 3 ; Step 8: Hot-roll the sintered target blank to its original dimensions before processing. The density of the hot-rolled target blank should be >10.18 g / cm³. 3 ; Step 9: Perform ultrasonic testing on the hot-rolled target blank to detect the number and area of ​​internal defects. The final number of defects was 17, with a total defect area of ​​21 mm. 2 The flaw detection results are as follows Figure 2 As shown.

[0018] Example 3 Step 1: Apply an appropriate amount of release agent to the surface of the axial compression mold; Step 2: Fill the axial compression mold with powder and use a tool to level it; Step 3: Start the axial pressing equipment to press, with an axial pressure of >2700 tons (>20000Pa), a holding time of 6-10 seconds, and venting twice to press and shape; Step 4: Demolding. After demolding, the surface of the target blank has slight powdering, no chipping, no visible cracks, shrinkage rate of about 38%, strength meets requirements during handling, and the target blank has good density. Step 5: Package the target preform using a waterproof material with low oxygen and low moisture permeability; Step 6: Place the sample in a cold isostatic pressing apparatus and pressurize it. The pressing parameters are 220-240 MPa, the holding time is 600-800 s, and the shrinkage rate of the molded target blank is about 50%. Step 7: Sinter the target blank into shape; the density after sintering is 10.02 g / cm³. 3 ; Step 8: Hot-roll the sintered target blank to its original dimensions before processing. The density of the hot-rolled target blank should be >10.18 g / cm³. 3 ; Step 9: Perform ultrasonic testing on the hot-rolled target blank to detect the number and area of ​​internal defects. The final number of defects was 3, with a total defect area of ​​3 mm. 2 The flaw detection results are as follows Figure 3 As shown.

[0019] Example 4 Step 1: Apply an appropriate amount of release agent to the surface of the axial compression mold; Step 2: Fill the axial compression mold with powder and use a tool to level it; Step 3: Start the axial pressing equipment to press, with an axial pressure of >2700 tons (>20000Pa), a holding time of 8 seconds, and venting twice to press and form the shape; Step 4: Demolding. After demolding, the surface of the target blank has slight powdering, no chipping, no visible cracks, shrinkage rate of about 38%, strength meets requirements during handling, and the target blank has good density. Step 5: Package the target preform using a waterproof material with low oxygen and low moisture permeability; Step 6: Place the sample in a cold isostatic pressing apparatus and pressurize it. The pressing parameters are 240-260 MPa, the holding time is 800-1000 s, and the shrinkage rate of the molded target blank is about 51%. Step 7: Sinter the target blank into shape; the density after sintering is 10.13 g / cm³. 3 ; Step 8: Hot-roll the sintered target blank to its original dimensions before processing. The density of the hot-rolled target blank should be >10.18 g / cm³.3 ; Step 9: Perform ultrasonic testing on the hot-rolled target blank to detect the number and area of ​​internal defects. The final number of defects was 0, and the maximum defect area was 0 mm. 2 The flaw detection results are as follows Figure 4 As shown.

[0020] Comparative Example 1 Step 1: Fill the cold isostatic pressing mold with molybdenum powder; Step 2: Place the sample in a cold isostatic pressing apparatus and pressurize it. The pressing parameters are 240-260 MPa, the holding time is 800-1000 s, and the shrinkage rate of the molded target blank is about 50%. Step 3: Sinter the target blank into shape; the density after sintering is 9.95 g / cm³. 3 ; Step 4: Hot-roll the sintered target blank to the original dimensions before processing. The density of the hot-rolled target blank should be >10.18 g / cm³. 3 ; Step 5: Perform ultrasonic testing on the hot-rolled target blank to detect the number and area of ​​internal defects. The final number of defects was 29, with a total defect area of ​​31 mm. 2 The flaw detection results are as follows Figure 5 As shown.

[0021] Comparative Example 2 Step 1: Apply an appropriate amount of release agent to the surface of the axial compression mold; Step 2: Fill the axial compression mold with powder and use a tool to level it; Step 3: Start the axial pressing equipment to press, with an axial pressure of >500 tons (>5000Pa), a holding time of 2-6 seconds, and venting twice to press and shape; Step 4: Demolding. After demolding, the target blank is not in good condition and cannot be formed, so it cannot proceed to the next process.

[0022] Comparative Example 3 Step 1: Apply an appropriate amount of release agent to the surface of the axial compression mold; Step 2: Fill the axial compression mold with powder and use a tool to level it; Step 3: Start the axial pressing equipment to press, with an axial pressure of >3500 tons (>25000Pa), a holding time of 6-10 seconds, and venting twice to press and shape; Step 4: Demolding. After demolding, the target blank separates into layers and fails to form well, making it unable to proceed to the next process.

[0023] The final product results of Examples 1-4 and Comparative Examples 1-3 were statistically analyzed, and the results are shown in Table 1 (process parameter table) and Table 2 (product data table).

[0024] Table 1 Process Parameters Table 2 Product Data Sheet Based on the data in Tables 1 and 2, it can be concluded that this invention effectively reduces the number of defects present in large-size molybdenum targets. Pre-pressing reduces internal cavity defects within the target material and promotes gas removal. Optimal process conditions improve the density of the preform and the sintering density of the target material, reducing defect residue and providing room for improvement in subsequent processes. Therefore, it significantly improves product yield and quality. Actual test results also show that while targets without pre-pressing meet density requirements, they have more internal defects and larger areas of defects, which is a drawback of traditional molding processes. This invention effectively overcomes the shortcomings of traditional processes, improves product quality and yield, and achieves the beneficial effects of cost reduction and efficiency improvement.

[0025] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A forming method for reducing defects in large size molybdenum targets, characterized by: The molybdenum powder is subjected to pre-pressing and pressing during the pressing process; The pre-pressing is axial pressing, and the pressing is cold isostatic pressing.

2. The method of claim 1, wherein: The pressure of the axial pressing is 10000-20000 Pa.

3. The method of claim 1, wherein: The pressure holding time of the axial pressing is required to be increased by 0.2-0.5 s for each 1 cm increase in the powder filling thickness.

4. The method of claim 1, wherein: The number of exhaust times of the axial pressing is required to be increased by 1 for each 10 cm increase in the powder filling thickness.

5. The method of claim 1, wherein: A release agent is applied on the surface of the mold before axial pressing to ensure release.

6. The method of claim 1, wherein: The pressure of the cold isostatic pressing is 220-260 mpa.

7. The method of claim 1, wherein: The pressure holding time of the cold isostatic pressing is 500-1000 s.

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