Preparation method of high-purity dense dysprosium ingot

Abstract

The application discloses a preparation method of high-purity dense dysprosium ingot, and belongs to the technical field of sputtering target material preparation. The preparation method comprises the following steps: transferring dysprosium melt from a vacuum atmosphere to an argon atmosphere within 10-15 s, performing differential pressure casting, electromagnetic solidification, gradient cooling and demolding annealing. The method combines vacuum smelting and differential pressure casting, and increases electromagnetic stirring special treatment in the casting process, so that the raw material ingot for Dy target material with high density and low oxygen content can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of sputtering target preparation technology, and relates to a method for preparing high-purity dense dysprosium ingots. Background Technology

[0002] Dysprosium (Dy) is a rare earth metal element with a high melting point (1412℃) and boiling point (2652℃). Currently, Dy targets are obtained by direct vacuum induction melting followed by conventional casting or argon-protected casting, and then processing after rolling deformation. This method is only suitable for planar targets and suffers from problems such as difficulty in completely removing oxygen / nitrides during the melting process, high ingot shrinkage and density (<90%), and coarse grains and low purity (oxygen content >500ppm) in the target material. Alternatively, planar or rotating targets can be directly obtained by gravity casting followed by processing, but this method results in excessively large grains and casting defects such as shrinkage cavities and porosity on the surface and core. Targets can also be prepared by powder metallurgy through hot isostatic pressing, but this method is costly and the size of the finished target is limited, limiting its application.

[0003] Optimizing the casting process is of great significance for improving the casting defects of high-purity Dy targets. Zhang Yongjian (Influence of conical hot top on internal defects and microstructure of high-purity Dy target ingots [J], Special Casting and Nonferrous Alloys, 2025, 45(3): 475-480) disclosed that reasonable control of solidification sequence can effectively reduce ingot defects. However, Dy, as a heavy rare earth element, has the characteristics of low heat capacity and low thermal conductivity. It solidifies quickly and is prone to forming a large temperature gradient during solidification, which leads to excessively fast solidification around the casting and on the surface. An isolated liquid phase region is formed in the center, which cannot be fed back during subsequent solidification, resulting in casting defects. Using a conical hot top can significantly improve the internal defects of high-purity Dy ingots, but it still cannot solve the problem of low density of Dy ingots. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing high-purity, dense dysprosium ingots. By combining vacuum melting with differential pressure casting and adding a special electromagnetic stirring treatment during the casting process, raw material ingots for Dy targets with high density and low oxygen content can be obtained.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a high-purity dense dysprosium ingot, comprising the following steps: dysprosium melt is transferred from a vacuum atmosphere to an argon atmosphere within 10-15s, then filled by differential pressure casting, electromagnetic solidification, gradient cooling, and demolding annealing.

[0006] In some embodiments, the temperature of the dysprosium melt is 1535-1625°C, preferably 1550-1600°C.

[0007] The dysprosium melt described in this invention is prepared by vacuum melting of Dy ingots.

[0008] Preferably, the method for preparing the dysprosium melt is as follows: Dy ingots are subjected to (1-5)×10⁻⁶... -3 Vacuum melting at Pa.

[0009] More preferably, the vacuum melting conditions are: heating to 800-850℃ at a heating rate of 80-100℃ and holding for 10-20 minutes; heating to 1535-1625℃ at a heating rate of 50-80℃ and holding for refining for 5-10 minutes.

[0010] More preferably, before the heat preservation and refining, a refining agent and a deoxidizer are added under electromagnetic stirring.

[0011] More preferably, the electromagnetic stirring is performed at a frequency of 3-10 Hz for 15-30 minutes.

[0012] More preferably, the amount of the refining agent added is 0.2%-0.5% of the mass of the Dy ingot.

[0013] More preferably, the amount of deoxidizer added is 0.05%-0.1% of the mass of Dy ingot.

[0014] In some embodiments, the pressure of the argon atmosphere is 0.8-1.2 MPa.

[0015] In some embodiments, the casting temperature of the differential pressure casting is 1485-1575°C, preferably 1500-1550°C.

[0016] Preferably, the mold is preheated to 300-350°C before the differential pressure casting process.

[0017] In some embodiments, the electromagnetic solidification is as follows: after filling, an alternating magnetic field is applied for electromagnetic stirring, and high-purity argon gas is introduced into the mold shell for pressurization, so that the pressure is maintained at 2.5-3.5 MPa for 0-4 minutes after filling, and the pressurization stage is from 4 to 8 minutes, with a pressurization rate of 0.1-0.2 MPa / min, so that the pressure in the mold shell increases to 2.9-4.3 MPa. After the pressurization is completed, the pressure is maintained for 10-15 minutes until solidification is completed.

[0018] Preferably, the frequency of the alternating magnetic field is 20-50Hz and the field strength is 0.1-0.3T.

[0019] In some implementations, the gradient cooling is as follows: the mold is divided into three cooling zones in the height direction: bottom, middle, and top. Water cooling starts from the bottom zone, forming a cooling sequence from bottom to top. After filling is completed, the bottom heating is turned off, and the bottom temperature of the ingot is reduced to 1250-1300°C. The middle heating is turned off, and the middle temperature of the ingot is reduced to 1280-1330°C. The top heating is turned off, and the water cooling channel is closed, allowing the ingot to naturally cool down to 300-350°C within the mold.

[0020] In some implementations, the demolding annealing is performed by demolding the ingot after the ingot temperature drops to 300-350°C, followed by vacuum annealing to eliminate casting stress.

[0021] Preferably, the vacuum annealing is performed at a temperature of 800-850℃ for 3-5 hours.

[0022] The beneficial effects of this invention are as follows: (1) This invention combines vacuum melting and differential pressure casting, and adds a special electromagnetic stirring treatment during the casting process to obtain Dy target material ingots with high density and low oxygen content.

[0023] (2) Experiments have shown that the relative density of the Dy ingot prepared by the present invention is not less than 95%, the density is high, the oxygen content is not more than 100 pm, the nitrogen content is not more than 50 ppm, and the purity is also improved. The Dy target material prepared by using the Dy ingot does not crack during the sputtering coating process. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention.

[0026] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] Unless otherwise specified, all raw materials used are commercially available products, and their sources are not specifically limited. Unless otherwise specified, all operations are performed at room temperature (20-25°C). The vacuum melting crucible is a ceramic crucible lined with tantalum foil (Y₂O₃-ZrO₂), with a tantalum foil thickness of 0.2-0.3 mm and an oxygen permeability of <10%. -10 g / cm 2 •s, for example, the refining agent is a rare earth refining agent purchased from Zhenjiang Ningyuan Metallurgical Materials Co., Ltd., and the deoxidizer is a rare earth deoxidizer purchased from Henan Bosen Metallurgical Refractory Co., Ltd.

[0028] Implementation Case 1: S1. Vacuum Melting: After cleaning and drying the surface of the Dy ingot, place it in a ceramic crucible lined with tantalum foil, and evacuate it to a vacuum of 3×10⁻⁶ using a molecular pump. -3 Pa, the temperature is raised to 850℃ at a heating rate of 80℃ / min, held for 10min for degassing, and then raised to 1550℃ at a rate of 50℃ / min. 0.2wt% refining agent is added, and electromagnetic stirring is performed at a frequency of 10Hz for 15min to remove nitrogen and slag. Then 0.1wt% deoxidizer is added, and vacuum refining is carried out at 1550℃ for 10min to obtain Dy melt; S2. Differential Pressure Transfer: When the temperature of the Dy melt drops to 1500℃, the transfer operation is performed. The vacuum melting chamber and the differential pressure casting chamber are connected through a high-temperature resistant transfer channel. The Dy melt flows from the vacuum melting chamber into the differential pressure casting chamber through the transfer channel. The differential pressure casting chamber is pre-filled with high-purity argon gas to replace the air in the differential pressure casting chamber and form an argon atmosphere (pressure 0.8MPa). The transfer time of the Dy melt is 10s to reduce the oxidation of the Dy melt during the transfer process.

[0029] S3. Differential pressure casting + electromagnetic solidification: Preheat the casting mold to 350℃, start casting and filling at 1500℃. After filling, apply an alternating magnetic field with a frequency of 50Hz and a field strength of 0.1T for electromagnetic stirring, and fill the mold shell with high-purity argon gas for pressurization. Maintain the pressure at 2.5MPa for 0-4min after filling, and increase the pressure at a rate of 0.2MPa / min for 4-8min, so that the pressure inside the mold shell increases to 3.3MPa. After pressurization, maintain this pressure for 15min until solidification is complete.

[0030] S4. Gradient Cooling: The mold is divided into three cooling zones in the height direction: bottom, middle, and top. Water cooling starts from the bottom zone, forming a cooling sequence from bottom to top. After filling is completed, the bottom heating is turned off, and the bottom temperature of the ingot is reduced to 1250℃. The middle heating is turned off, and the middle temperature of the ingot is reduced to 1280℃. The top heating is turned off, and the water cooling channel is closed, allowing the ingot to naturally cool down to 300℃ in the mold.

[0031] S5. Demolding and Annealing: After the ingot temperature drops to 300℃, the ingot is demolded and then vacuum annealed at 800℃ for 5 hours to eliminate casting stress.

[0032] S6. Processing finished ingots: In a processing chamber protected by argon gas, the ingots are turned and peeled to the required dimensions. During the processing, anhydrous oil-based cutting fluid is used for cooling.

[0033] Implementation Case 2: S1. Vacuum Melting: After cleaning and drying the surface of the Dy ingot, place it in a ceramic crucible lined with tantalum foil, and evacuate it to a vacuum of 1×10⁻⁶ using a molecular pump. -3 Pa, the temperature is raised to 800℃ at a heating rate of 100℃ / min, held for 20min for degassing, and then raised to 1600℃ at a rate of 80℃ / min. 0.5wt% refining agent is added, and electromagnetic stirring is performed at a frequency of 3Hz for 30min to remove nitrogen and slag. Then 0.05wt% deoxidizer is added, and vacuum refining is carried out at 1600℃ for 5min to obtain Dy melt; S2. Differential Pressure Transfer: When the temperature of the Dy melt drops to 1550℃, the transfer operation is carried out. The vacuum melting chamber and the differential pressure casting chamber are connected through a high-temperature resistant transfer channel. The Dy melt flows from the vacuum melting chamber into the differential pressure casting chamber through the transfer channel. The differential pressure casting chamber is pre-filled with high-purity argon gas to replace the air in the differential pressure casting chamber and form an argon atmosphere (1.2MPa). The transfer time of the Dy melt is 15s to reduce the oxidation of the Dy melt during the transfer process.

[0034] S3. Differential pressure casting + electromagnetic solidification: Preheat the casting mold to 300℃, start casting and filling at 1550℃. After filling, apply an alternating magnetic field with a frequency of 20Hz and a field strength of 0.3T for electromagnetic stirring, and fill the mold shell with high-purity argon gas for pressurization. Maintain the pressure at 3.5MPa for 0-4 minutes after filling, and increase the pressure at a rate of 0.1MPa / min for 4-8 minutes, increasing the pressure inside the shell to 3.9MPa. After pressurization, maintain this pressure for 10 minutes until solidification is complete.

[0035] S4. Gradient Cooling: The mold is divided into three cooling zones in the height direction: bottom, middle, and top. Water cooling starts from the bottom zone, forming a cooling sequence from bottom to top. After filling is completed, the bottom heating is turned off, and the bottom temperature of the ingot is reduced to 1300℃. The middle heating is turned off, and the middle temperature of the ingot is reduced to 1330℃. The top heating is turned off, and the water cooling channel is closed, allowing the ingot to naturally cool down to 350℃ in the mold.

[0036] S5. Demolding and Annealing: After the ingot temperature drops to 350℃, the ingot is demolded. After demolding, the ingot is vacuum annealed at 850℃ for 3 hours to eliminate casting stress.

[0037] S6. Processing finished ingots: In a processing chamber protected by argon gas, the ingots are machined and peeled to the required dimensions. During the processing, lubricating oil is used to cool them down.

[0038] Comparison Case 1: S1. Vacuum Melting: After cleaning and drying the surface of the Dy ingot, place it in an alumina crucible and use a molecular pump to create a vacuum of ≤3×10⁻⁶. - 2 Pa, the power is increased by 5kw every 20 minutes until the temperature rises to 1500℃, and Dy melt is obtained; S2. Gravity casting: The casting mold is preheated to 450℃, and the casting and filling process begins. The casting temperature is 1460℃. The Dy melt is poured into the mold through a tilting ladle. Argon gas is used for protection during the casting process. The Dy melt solidifies and feeds back under its own gravity. It is then naturally cooled to 200℃ for demolding. S3. Processing finished ingots: In a processing chamber protected by argon gas, the ingots are turned and peeled to the required dimensions. During the processing, anhydrous oil-based cutting fluid or lubricating oil is used to cool them down.

[0039] Comparison Case 2: The only differences between this comparative case and Implementation Case 1 are: the parameters for electromagnetic solidification and the parameters for gradient cooling are different.

[0040] Specifically: The electromagnetic solidification process involves electromagnetic stirring at a frequency of 35 kHz after filling, and pressurization by filling the mold housing with high-purity argon gas. The pressure is maintained at 2.0 MPa for 0-4 minutes after filling, and then increased at a rate of 0.2 MPa / min for 4-8 minutes, raising the pressure inside the mold housing to 4.5 MPa. This pressure is maintained for 15 minutes after the pressurization is completed, until solidification is finished.

[0041] The gradient cooling process involves reducing the bottom temperature of the ingot to 1350°C, shutting off the middle heating, reducing the middle temperature of the ingot to 1370°C, shutting off the top heating, closing the water cooling channel, and allowing the ingot to naturally cool to 300°C within the mold.

[0042] The rest are the same as in Implementation Case 1.

[0043] Comparison Case 3: The only differences between this comparative case and Implementation Case 1 are: the parameters for electromagnetic solidification and the parameters for gradient cooling are different.

[0044] Specifically: The electromagnetic solidification process involves applying an alternating magnetic field with a frequency of 50 Hz and a field strength of 0.1 T after filling the mold. Simultaneously, high-purity argon gas is introduced into the mold housing for pressurization, maintaining a pressure of 3.5 MPa for 0-5 minutes after filling. From 5-10 minutes, a pressurization phase is initiated at a rate of 0.5 MPa / min, increasing the pressure inside the mold housing to 4.3 MPa. This pressure is then maintained for 15 minutes after pressurization, until solidification is complete.

[0045] The gradient cooling process involves reducing the bottom temperature of the ingot to 1250°C, shutting off the middle heating, reducing the middle temperature of the ingot to 1290°C, shutting off the top heating, closing the water cooling channel, and allowing the ingot to naturally cool to 300°C within the mold.

[0046] The rest are the same as in Implementation Case 1.

[0047] Comparison Case 4: The only difference between this comparative case and Implementation Case 1 is that the transfer time of the Dy melt and the vacuum melting method of the Dy melt are different.

[0048] Specifically: The vacuum melting process involves cleaning and drying the surface of the Dy ingot, placing it in a ceramic crucible lined with tantalum foil, and then evacuating it to a vacuum of 3 × 10⁻⁶ using a molecular pump. -3 Pa, the temperature is raised to 850℃ at a heating rate of 70℃ / min, held for 10min for degassing, and then raised to 1550℃ at a rate of 100℃ / min. 0.2wt% refining agent is added, and electromagnetic stirring is performed at a frequency of 35kHz for 5min to remove nitrogen and slag. Then 0.1wt% deoxidizer is added, and vacuum refining is carried out at 1550℃ for 10min to obtain Dy melt.

[0049] The differential pressure transfer: the transfer time of the Dy melt is 18s.

[0050] The rest are the same as in Implementation Case 1.

[0051] The performance of the dysprosium ingots prepared in the implementation case and the comparative case was tested, and the results are shown in Table 1.

[0052] The specific testing methods are as follows: 1. Oxygen content / Nitrogen content The oxygen and nitrogen analyzer heats the sample to over 3000°C, releasing oxygen and nitrogen elements from the material in an inert gas environment. The oxygen content is then detected using the principle of infrared light absorption, and the nitrogen content is determined using a thermal conductivity detector.

[0053] 2. Relative density The theoretical basis of the displacement method is Archimedes' principle: an object immersed in a liquid will displace an amount of liquid equal to its volume. The volume difference V2-V1 can be used to accurately determine the object's volume, which can then be combined with its mass to calculate the density. Relative density is the percentage of the actual measured density to the theoretical density.

[0054] Table 1

[0055] The results show that the dysprosium (Dy) ingots prepared in Embodiments 1 and 2 of this invention have a relative density of not less than 95%, high density, oxygen content not exceeding 100 pm, nitrogen content not exceeding 50 ppm, and improved purity. The Dy target material prepared using the Dy ingots does not crack during the sputtering coating process.

[0056] Comparing Implementation Case 1 with Comparative Cases 2-4, it can be seen that parameters such as electromagnetic solidification, gradient cooling, transfer time of Dy melt, and vacuum melting method of Dy melt all have a significant impact on the performance of Dy ingots.

[0057] The above description, in conjunction with specific embodiments, further illustrates the present invention. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions to the details and form of the technical solutions of the present invention can be made without departing from the spirit and scope of the invention, and all such modifications and substitutions fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-purity, dense dysprosium ingot, characterized in that, The process includes the following steps: the dysprosium melt is transferred from a vacuum atmosphere to an argon atmosphere within 10-15 seconds, then filled by pressure differential casting, electromagnetic solidification, gradient cooling, and demolding annealing; The dysprosium melt is prepared by vacuum melting of Dy ingots. The specific preparation method is as follows: Dy ingots are melted in a process of (1-5)×10⁻⁶ mm. -3 Vacuum melting at Pa, wherein the vacuum melting conditions are as follows: heating to 800-850℃ at a heating rate of 80-100℃ and holding at that temperature for 10-20 minutes; heating to 1535-1625℃ at a heating rate of 50-80℃, adding refining agent and deoxidizer under electromagnetic stirring, and holding at that temperature for 5-10 minutes; wherein the electromagnetic stirring is: electromagnetic stirring at a frequency of 3-10Hz for 15-30 minutes; The electromagnetic solidification process involves: applying an alternating magnetic field for electromagnetic stirring after filling and filling the mold shell with high-purity argon gas for pressurization, maintaining a pressure of 2.5-3.5 MPa for 0-4 minutes after filling, and a pressurization phase for 4-8 minutes at a rate of 0.1-0.2 MPa / min, increasing the pressure inside the mold shell to 2.9-4.3 MPa. After pressurization, this pressure is maintained for 10-15 minutes. The gradient cooling process involves: shutting off bottom heating, reducing the bottom temperature of the ingot to 1250-1300℃; shutting off middle heating, reducing the middle temperature of the ingot to 1280-1330℃; shutting off top heating; and shutting off the water cooling channel, allowing the ingot to naturally cool to 300-350℃ within the mold.

2. The preparation method according to claim 1, characterized in that, The pressure of the argon atmosphere is 0.8-1.2 MPa.

3. The preparation method according to claim 1, characterized in that, The mold is divided into three cooling zones in the height direction: bottom, middle and top. Water cooling starts from the bottom zone, forming a cooling sequence from bottom to top.

4. The preparation method according to claim 1, characterized in that, The frequency of the alternating magnetic field is 20-50Hz, and the field strength is 0.1-0.3T.

5. The preparation method according to claim 1, characterized in that, The heat preservation and refining time is 5-10 minutes.

6. The preparation method according to claim 5, characterized in that, The amount of the refining agent added is 0.2%-0.5% of the mass of Dy ingots; the amount of the deoxidizer added is 0.05%-0.1% of the mass of Dy ingots.

7. The preparation method according to claim 1, characterized in that, The casting temperature for differential pressure casting is 1485-1575℃.

8. The preparation method according to claim 7, characterized in that, Before the differential pressure casting process, the mold is preheated to 300-350°C.

9. The preparation method according to claim 1, characterized in that, The demolding annealing process involves demolding the ingot after its temperature drops to 300-350℃, followed by vacuum annealing of the demolded ingot.

10. The preparation method according to claim 9, characterized in that, The vacuum annealing is performed at a temperature of 800-850℃ for 3-5 hours.

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