Method for producing porous tungsten articles

Abstract

The application belongs to the field of metal powder forming, and provides a preparation method of a porous tungsten product. The preparation method of the porous tungsten product comprises the following steps: S1, preparing a porous tungsten framework by using tungsten powder as raw material; S2, performing first heat treatment on the porous tungsten framework and metal M, so that the metal M is converted into a molten metal liquid and infiltrates into the tungsten framework to obtain a tungsten-M composite material, the metal M is lead, tin or bismuth; S3, performing mechanical processing on the tungsten-M composite material to obtain a formed product; and S4, performing second heat treatment on the formed product under vacuum conditions to evaporate the metal M and remove the metal M in the formed product, thereby obtaining the porous tungsten product. The prepared porous tungsten product has almost no residual infiltrated metal, does not affect the microstructure of the tungsten framework, and can reduce the operation and maintenance costs of vacuum equipment.

Description

Technical Field

[0001] This application relates to the field of metal powder forming, and specifically, provides a method for preparing porous tungsten parts. Background Technology

[0002] Porous tungsten is a powder metallurgy tungsten product containing numerous pores. Due to its high melting point, excellent electron emission performance, high specific surface area, high mechanical strength, good chemical stability, and high thermal conductivity, it has become an ideal substrate for diffusion cathodes. Diffusion cathodes typically consist of porous tungsten and active materials (such as barium aluminate) doped within its porous structure. The porous structure of the tungsten material provides storage sites and reaction contact surfaces for the active materials, as well as diffusion channels for their migration. Tungsten's high melting point and good chemical stability ensure stable operation of the cathode at high temperatures, while its high thermal conductivity facilitates rapid heat conduction, maintaining the cathode's operating temperature. These properties collectively make porous tungsten play a crucial role in diffusion cathodes, widely used in vacuum electronic devices, microwave tubes, and other fields.

[0003] As a core component of diffused cathodes, the performance of porous tungsten directly affects the output performance and lifespan of microwave sources. The fabrication of porous tungsten materials typically involves sintering tungsten blanks to form porous sintered blanks. However, due to the brittle nature of tungsten, these blanks cannot be directly machined, such as by turning. Therefore, a copper infiltration method is usually employed to improve machinability. This involves filling the pores of the tungsten framework with molten copper, followed by cooling to obtain machinable tungsten-copper (W-Cu) material. This W-Cu material is then machined into shapes of the required size, and the copper is removed using vacuum or chemical methods to obtain the final porous tungsten material. Currently, the copper infiltration method for fabricating porous tungsten negatively impacts its performance. Chemical copper removal methods have several drawbacks, including incomplete removal, damage to the pore structure, and excessive time consumption. Residual copper can distort parameters such as porosity and pore size in porous tungsten, and high levels of residual copper can also affect the electron emission capability of the cathode, reducing emission current density and emission efficiency. Strong acid reagents (such as nitric acid) used in the copper removal process can easily damage the tungsten matrix, resulting in surface roughness, structural damage, and reduced strength. Furthermore, chemical copper removal mainly involves immersing the shaped porous tungsten in nitric acid, which has a long corrosion cycle, typically requiring several days.

[0004] Therefore, it is necessary to develop new methods for preparing porous tungsten. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing porous tungsten parts. Compared with vacuum copper removal processes, the preparation method of this application can reduce the operation and maintenance costs of vacuum equipment, and the prepared porous tungsten parts have almost no molten metal residue, which does not affect the microstructure of the porous tungsten framework.

[0006] The method for preparing porous tungsten parts provided in this application includes:

[0007] S1: A porous tungsten framework was prepared using tungsten powder as raw material;

[0008] S2: The metal M is subjected to a first heat treatment with the porous tungsten framework to convert the metal M into a molten metal liquid and penetrate into the porous tungsten framework to obtain a tungsten-M composite material, wherein the metal M is lead, tin or bismuth;

[0009] S3: The tungsten-M composite material is machined to obtain a molded product;

[0010] S4: The molded product is subjected to a second heat treatment under vacuum conditions to evaporate the metal M to remove the metal M from the molded product, thereby producing a porous tungsten part.

[0011] In the preparation method of this application, metal M (i.e., lead, tin, or bismuth) is used as a flocculant to infiltrate the porous tungsten framework prepared from tungsten powder. This improves the brittleness of tungsten and makes the resulting tungsten-M composite material (i.e., W-Pb, W-Sn, or W-Bi composite material) machinable. Furthermore, metal M has a lower boiling point than copper, which allows for effective removal of metal M from the machinable tungsten-M composite material at lower vacuum levels and temperatures, reducing the operation and maintenance costs of vacuum equipment. In addition, the porous tungsten part prepared in this application maintains essentially the same pore characteristics as the porous tungsten framework before processing. The residual content of infiltrated metal M in the porous tungsten part is less than 0.01 wt.%, and the linear deformation of the external dimensions is less than 0.1%, which has virtually no impact on the application performance of the porous tungsten part.

[0012] In some embodiments of this application, the tungsten powder has a Fisher particle size of 3–10 μm. This reduces the possibility of closed pores forming during sintering due to excessively small tungsten powder particles, while also avoiding excessively large pore size and brittleness in the sintered blank caused by excessively large tungsten powder particles.

[0013] In some embodiments of this application, the average porosity of the porous tungsten framework is 10% to 30%.

[0014] In some embodiments of this application, step S1, the method for preparing a porous tungsten framework using tungsten powder as a raw material, includes:

[0015] S1-1: Press tungsten powder into a compact shape to obtain a powder compact;

[0016] S1-2: The powder compact is sintered to produce a porous tungsten skeleton.

[0017] Furthermore, the pressing method is cold isostatic pressing. Cold isostatic pressing can produce powder compacts with higher density and more uniform distribution, improve the shrinkage uniformity of the powder compacts during sintering, and obtain porous tungsten skeletons with higher dimensional accuracy.

[0018] Furthermore, the pressure of the cold isostatic pressing is 180-250 MPa, and the holding time is 50-200 s.

[0019] Furthermore, the sintering is carried out in a hydrogen atmosphere at a temperature T of 1800–2200°C for a time t of 3–12 hours. This one-step high-temperature sintering method is beneficial for forming a dense porous structure.

[0020] In some embodiments of this application, the ratio of the volume of metal M to the pore volume of the porous tungsten framework is (1.1-2):1. Compared to the pore volume of the porous tungsten framework, controlling the amount of metal M to be slightly excessive can ensure that the pores of the tungsten framework are filled with molten metal, avoiding chipping and other issues during subsequent processing.

[0021] In some embodiments of this application, the lead is a lead ingot with a chemical composition content of not less than 99.9%.

[0022] In some embodiments of this application, the tin is a tin ingot with a chemical composition content of not less than 99.9%.

[0023] In some embodiments of this application, the bismuth is a bismuth ingot with a chemical composition content of not less than 99.9%.

[0024] In some embodiments of this application, the metal M is lead or tin, and the temperature T1 of the first heat treatment is 600–1550°C.

[0025] In some embodiments of this application, the metal M is bismuth, and the temperature T1 of the first heat treatment is 600–1200°C.

[0026] In some embodiments of this application, in the first heat treatment, the holding time at the temperature T1 of the first heat treatment is t1, which is 0.5 to 5 hours.

[0027] In some embodiments of this application, the first heat treatment is performed in the presence of a protective atmosphere, and the protective atmosphere includes at least one of hydrogen and argon.

[0028] In some embodiments of this application, the first heat treatment process includes: raising the temperature to the first heat treatment temperature T1 at a rate of 5 to 10 °C / min.

[0029] In some embodiments of this application, the temperature T2 of the second heat treatment is ≤1550℃ and the vacuum degree is ≤10Pa, preferably 0.01~10Pa.

[0030] In some embodiments of this application, in the second heat treatment, the holding time t2 at temperature T2 is 1 to 5 hours.

[0031] In some embodiments of this application, the metal M is lead or tin, and the temperature T2 of the second heat treatment is 1350–1550°C.

[0032] In some embodiments of this application, the metal M is bismuth, and the temperature T2 of the second heat treatment is 900–1550 °C.

[0033] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0034] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein:

[0035] Figure 1 SEM image showing the fracture morphology of the porous tungsten framework of Example 1;

[0036] Figure 2 , Figure 3 The images shown are, in sequence, metallographic images of the W-Pb composite material of Example 1 and SEM images of the fracture morphology of the porous tungsten part.

[0037] Figure 4 , Figure 5 The images shown are, in sequence, metallographic images of the W-Sn composite material of Example 2 and SEM images of the fracture morphology of the porous tungsten part;

[0038] Figure 6 , Figure 7 The images shown are, in sequence, metallographic images of the W-Bi composite material of Example 3 and SEM images of the fracture morphology of the porous tungsten part. Detailed Implementation

[0039] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0040] The "scope" disclosed in this application is defined in the form of a lower limit and / or an upper limit, whereby a given scope is defined by selecting a lower limit and / or an upper limit. This type of scope may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined scope, and any lower limit can be combined with other lower limits to form an undefined scope, similarly, any upper limit can be combined with any other upper limit to form an undefined scope. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value, or with other lower or upper limits, to form an undefined scope.

[0041] It should be noted that in this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0043] The porous structure of the tungsten framework is mainly due to the incomplete densification of tungsten powder blanks after high-temperature sintering. Its physical characteristics are difficult to change after high-temperature sintering, exhibiting high hardness and brittleness, making it difficult to machine. The traditional solution is to first infiltrate metallic copper into the pores of the tungsten framework to create a tungsten-copper composite material, then machine it to the specified shape and size before chemically or vacuum-removing the copper to obtain the porous tungsten part. However, as mentioned above, chemical copper removal is ineffective, affecting the purity of the porous tungsten, and residual copper occupying the pores affects the emission performance and service life of the porous tungsten. Vacuum heat treatment for copper removal requires a high vacuum level (100 kJ / L). -3 Only with a pressure of Pa or even higher and a temperature can copper be removed more thoroughly. This places very high demands on the vacuum equipment and will significantly increase the operating and maintenance costs of the equipment.

[0044] To address the above problems, this application provides a method for preparing porous tungsten parts, which includes the following steps S1 to S4:

[0045] S1: A porous tungsten framework was prepared using tungsten powder as raw material;

[0046] S2: The metal M is subjected to a first heat treatment with the porous tungsten framework to convert the metal M into a molten metal liquid and penetrate into the porous tungsten framework to obtain a tungsten-M composite material, wherein the metal M is lead, tin or bismuth;

[0047] S3: The tungsten-M composite material is machined to obtain a molded product;

[0048] S4: The molded product is subjected to a second heat treatment under vacuum conditions to evaporate the metal M to remove the metal M from the molded product, thereby producing a porous tungsten part.

[0049] In the method of this application, the metal M used is lead, tin, or bismuth, which has a lower boiling point than copper. This allows the vacuum removal of metal M to be carried out at a lower vacuum level and temperature. In other words, the metal vapor formed during the removal of metal M is more easily detached from the porous tungsten framework, avoiding the problems of excessive copper residue after processing and forming caused by using copper as a flux, or excessive wear and tear on vacuum equipment caused by vacuum copper removal. Furthermore, this application removes metal M through vacuum heat treatment, eliminating the need for chemical reagents such as nitric acid, thus preventing corrosion of the porous tungsten parts.

[0050] In step S1, to further meet the application requirements of porous tungsten for high-lifetime diffusion cathodes, the tungsten powder preferably has a Fisher particle size of 3–10 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. According to some embodiments, the average porosity of the porous tungsten framework is 10%–30%.

[0051] In step S1, tungsten powder can be prepared into a powder compact by means of, but not limited to, injection molding or compression molding, and then the compact can be sintered to form the porous tungsten framework. Furthermore, the compression molding method can be die molding, extrusion molding, static pressing, or hot static pressing.

[0052] According to some specific implementation methods, the methods for preparing porous tungsten frameworks using tungsten powder as raw material include:

[0053] S1-1: Press tungsten powder into a compact shape to obtain a powder compact;

[0054] S1-2: The powder compact is sintered to produce a porous tungsten skeleton.

[0055] In step S1-1, the preferred pressing method is cold isostatic pressing. Cold isostatic pressing not only simplifies the process but also yields powder compacts with higher density and uniform distribution, improving the dimensional accuracy of the porous tungsten framework. The cold isostatic pressing operation may include, for example, loading tungsten powder into an elastic mold, placing it in a high-pressure container, and using a high-pressure pump to press liquid into the container. Utilizing the uniform pressure transmission properties of the liquid, the tungsten powder within the elastic mold is uniformly compressed. The elastic mold can be a rubber mold or a resin mold, and the high-pressure container can be, for example, a steel sealed container.

[0056] In step S1-1, the pressure of the cold isostatic pressing is typically 180–250 MPa, such as 180 MPa, 190 MPa, 195 MPa, 200 MPa, 205 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 245 MPa, 250 MPa, etc. The holding time is typically 50–200 s, such as 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 150 s, 170 s, 180 s, 185 s, 190 s, 200 s, etc.

[0057] In step S1-1, the formed powder compact can be of various shapes, such as, but not limited to, cylinders, cubes (including cuboids and rectangular prisms). The diameter of the cylinder can be 20–60 mm, for example, 20 mm, 40 mm, 50 mm, 60 mm, etc., and the height can be 30–100 mm, such as 30 mm, 60 mm, 70 mm, 80 mm, 85 mm, 90 mm, etc. The dimensions of the cube can be expressed as a×b×c, where a and b can be the same or different, and are independently 20–500 mm, for example, 20 mm, 50 mm, 70 mm, 80 mm, 100 mm, 110 mm, 130 mm, 140 mm, 150 mm, 300 mm, 500 mm, etc., and c can be 15–500 mm, for example, 15 mm, 20 mm, 50 mm, 100 mm, 110 mm, 130 mm, 140 mm, 150 mm, 180 mm, 200 mm, 400 mm, 500 mm, etc. As some specific examples, the specifications of the powder compact can be 110 mm × 130 mm × 180 mm, 110 mm × 140 mm × 200 mm.

[0058] In steps S1-2, sintering causes the powder compact to shrink, forming a sintered compact with a dense but porous structure (i.e., the porous tungsten framework). The sintering temperature can be selected based on the desired porosity; generally, the porosity of the porous tungsten framework decreases with increasing sintering temperature. Furthermore, too low a sintering temperature may prevent the formation of a dense structure and affect strength; too high a sintering temperature may result in excessively high density of the sintered compact, failing to achieve the target porosity. According to some embodiments, the sintering temperature T is 1800–2200°C, for example, 1800°C, 1900°C, 1950°C, 2000°C, 2050°C, 2100°C, 2150°C, 2200°C, etc. Additionally, the sintering time t can be 3–12 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, etc. The sintering can be carried out in the presence of a hydrogen atmosphere. For example, sintering can be performed in a medium-frequency induction furnace.

[0059] According to this application, in step S2, the porous tungsten framework and the metal M are subjected to a first heat treatment together, which enables the molten metal formed by the heating of the metal M to penetrate into the porous structure of the tungsten framework by capillary force, thereby forming a tungsten-M composite material.

[0060] In some embodiments, the metal M is lead. The lead may be selected from lead ingots conforming to GB / T 469-2023. The chemical composition content of lead is preferably not less than 99.9%, for example, selected from lead ingots with grades Pb99.99, Pb99.994, and Pb99.996.

[0061] In some embodiments, the metal M is tin. The tin may be selected from tin ingots conforming to GB / T 728-2020. The chemical composition content of the tin is preferably not less than 99.9%.

[0062] In some embodiments, the metal M is bismuth. Bismuth may be selected from bismuth ingots conforming to GB / T 915-2010. The bismuth chemical composition content is preferably not less than 99.9%.

[0063] In step S2, the amount of metal M can be determined based on the pore volume of the tungsten framework, and generally increases with the increase of the pore volume of the tungsten framework. According to some embodiments, the ratio of the volumetric amount of metal M to the pore volume of the porous tungsten framework is (1.1–2) : 100, for example, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.4:1, 1.5:1, 1.7:1, etc. In this way, while ensuring that metal M fills the pores of the tungsten framework, the production cost is minimized as much as possible.

[0064] In step S2, the mass of metal M can be calculated and weighed based on its volume. Specifically, the mass of metal M satisfies the following formula: m = ρ × V × C, where,

[0065] m represents the mass of metal M, in grams;

[0066] ρ represents the density of metal M: when metal M is lead, ρ is 11.34 g / cm³. 3 When metal M is tin, ρ is 7.28 g / cm³. 3 When metal M is bismuth, ρ is 9.78 g / cm³. 3 ;

[0067] V represents the pore volume of the porous tungsten framework, in cm³. 3 ;

[0068] C represents the ratio of the volume of metal M to the pore volume of the porous tungsten framework, which is 1.1 to 2.

[0069] In this application, pore volume = tungsten framework volume × average porosity. Three locations on the sample (e.g., both ends, the middle) are taken, and the average porosity is calculated from these three porosity values. The porosity of a single sample is calculated as (1 - sample density / theoretical density) × 100%, where the theoretical density is taken as the density of tungsten, 19.35 g / cm³. 3 The sample density can be calculated with reference to "GB T 5163-2006 Determination of density, oil content and porosity of permeable sintered metal materials (excluding cemented carbide)".

[0070] In step S2, the temperature T1 of the first heat treatment can be selected according to the type of metal M. When metal M is bismuth or lead, the temperature T1 of the first heat treatment can satisfy the formula: T m <T1<T b When metal M is tin, the temperature T1 of the first heat treatment can satisfy the formula: T m <T1<T, where T m T represents the melting point of metal M. b T represents the boiling point of metal M, and T represents the sintering temperature.

[0071] According to some specific implementation methods, the metal M is bismuth, and the temperature T1 of the first heat treatment is 600 to 1200°C, such as 600°C, 700°C, 770°C, 800°C, 900°C, 950°C, 1000°C, 1100°C, 1200°C, etc.

[0072] According to some specific implementation methods, the metal M is tin, and the temperature T1 of the first heat treatment is 600 to 1550°C, such as 600°C, 700°C, 770°C, 800°C, 900°C, 950°C, 1000°C, 1100°C, 1200°C, 1500°C, 1550°C, etc.

[0073] According to some specific implementation methods, the metal M is lead, and the temperature T1 of the first heat treatment is 600 to 1550°C, such as 600°C, 650°C, 700°C, 800°C, 900°C, 950°C, 1000°C, 1100°C, 1200°C, 1500°C, 1550°C, etc.

[0074] In step S2, the first heat treatment process may include: raising the temperature to the first heat treatment temperature T1 at a rate of 5 to 10 °C / min.

[0075] In step S2, the duration of the first heat treatment can be selected based on the pore volume of the porous tungsten framework, and typically increases with increasing pore volume. According to some embodiments, the holding time t1 at the first heat treatment temperature T1 is 0.5–5 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 5 hours, etc. Preferably, the holding time t1 at temperature T1 is 0.5–2 hours.

[0076] In step S2, the first heat treatment can be performed in the presence of a protective atmosphere. This protective atmosphere may include at least one of hydrogen and argon. As some examples, the first heat treatment can be performed in an atmosphere furnace.

[0077] According to this application, in step S3, by machining the tungsten-M composite material, the precision and roughness of the product can be controlled to obtain molded articles that meet the usage requirements. For example, the tungsten-M composite material can be machined into molded articles of various specifications that can meet the requirements of diffusion cathode applications. The machining methods include, but are not limited to, one or more of the following operations: turning, cutting, internal grinding, external grinding, wire cutting, etc. In addition, the specific operations of machining are well known in the art and will not be described in detail here.

[0078] According to this application, in step S4, by heat-treating the molded product under vacuum conditions, the metal M filling the pores of the porous tungsten framework can be volatilized at a temperature below its boiling point, resulting in a porous tungsten part with almost no metal M residue.

[0079] In some embodiments, the temperature T2 of the second heat treatment is ≤1550℃, for example, 1000~1550℃; and the vacuum degree is ≤10Pa. In particular, compared with the traditional vacuum copper removal process, the metal M used in this application can be efficiently removed at a lower vacuum degree, thereby reducing equipment operation and maintenance costs. Therefore, the vacuum degree in the second heat treatment is preferably 0.01~10Pa, for example, 0.01Pa, 0.5Pa, 1Pa, 2Pa, 5Pa, 6Pa, 8Pa, 10Pa, etc.

[0080] In step S4, the temperature T2 of the second heat treatment can also be selected according to the type of metal M. Preferably, the temperature T2 of the second heat treatment satisfies the formula: T2 < T b And T2 < T.

[0081] According to some specific implementation methods, the metal M is bismuth, and the temperature T2 of the second heat treatment is 900 to 1550°C, such as 900°C, 920°C, 950°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1540°C, 1550°C, etc.

[0082] According to some specific implementation methods, the metal M is tin, and the temperature T2 of the second heat treatment is 1350 to 1550°C, such as 1350°C, 1370°C, 1400°C, 1450°C, 1500°C, 1550°C, etc.

[0083] According to some specific implementation methods, the metal M is lead, and the temperature T2 of the second heat treatment is 1350 to 1550°C, such as 1350°C, 1370°C, 1400°C, 1450°C, 1500°C, 1550°C, etc.

[0084] In step S4, during vacuum heat treatment, the holding time t2 at the second heat treatment temperature T2 can be 1 to 5 hours, for example, 1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 5 hours, etc.

[0085] In step S4, as some specific examples, the second heat treatment process may include: controlling the vacuum degree to 0.01 to 10 Pa, and under this vacuum condition, first raising the temperature to T at a rate of 5 to 10 °C / min. 20 Then, raise the temperature to T2 at a rate of 1–5℃ / min and hold it at that temperature, where 200℃ ≤ T2 - T 20 ≤500℃, T is preferred 20 The temperature is 900–1000℃. Optionally, after the second heat treatment, the product is further cooled to T at a rate of 1–5℃ / min. 21 Then, it is allowed to cool naturally to room temperature in the furnace, 100℃≤T 20 -T 21 ≤300℃.

[0086] In step S4, the second heat treatment can be carried out in a vacuum furnace. The boiling point of the metal M used is lower than that of copper, and it is easier to evaporate under vacuum conditions, thereby enabling the effective recovery of the metal M.

[0087] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0088] In the following embodiments, the bismuth ingots used are Bi99.95, the lead ingots are Pb99.994, and the tin ingots are Sn99.9.

[0089] Example 1

[0090] (1) Press molding: Tungsten powder with a Fisher particle size of 8μm is loaded into a rubber mold (the inner cavity size of the mold is 110mm×150mm×400mm), mechanically vibrated, and then the mold containing tungsten powder is locked and placed in a cold isostatic press for cold isostatic pressing treatment. The pressure is controlled at 200MPa and held for 180s. After depressurization, the mold is demolded to obtain a powder compact of 110mm×130mm×180mm.

[0091] (2) High-temperature sintering: The powder compact is placed in a medium-frequency induction furnace and sintered in a hydrogen atmosphere at a temperature of 1950℃ and held for 6 hours to obtain a porous tungsten skeleton.

[0092] (3) Lead infiltration: The tungsten skeleton and lead ingot are placed in an alumina ceramic crucible (the volume ratio of the lead ingot to the tungsten skeleton hole is 1.2), and sent to an atmosphere furnace. The temperature is raised to 700℃ at 10℃ / min in a hydrogen atmosphere, held for 1.5h, and then cooled to room temperature with the furnace to obtain the W-Pb composite material.

[0093] (4) Machining: W-Pb composite material is processed by wire cutting and centerless external cylindrical grinding to obtain molded products that meet the target dimensions.

[0094] (5) Vacuum lead removal: The molded product is placed in an alumina ceramic crucible and sent to a vacuum heating furnace. The vacuum degree inside the furnace is controlled at 1 Pa. The temperature is increased to 1000℃ at 10℃ / min, then increased to 1500℃ at 5℃ / min and held for 2 hours. Then the temperature is decreased to 800℃ at 5℃ / min and then naturally cooled to room temperature to obtain a porous tungsten part.

[0095] Example 2

[0096] (1) Press molding: Tungsten powder with a Fisher particle size of 8μm is loaded into a rubber mold (the inner cavity size of the mold is 110mm×150mm×400mm), mechanically vibrated, and then the mold containing tungsten powder is locked and placed in a cold isostatic press for cold isostatic pressing treatment. The pressure is controlled at 200MPa and held for 180s. After depressurization, the mold is demolded to obtain a powder compact of 110mm×130mm×180mm.

[0097] (2) High-temperature sintering: The powder compact is placed in a medium-frequency atmosphere furnace and sintered in a hydrogen atmosphere at a temperature of 1950℃ and held for 6 hours to obtain a porous tungsten skeleton.

[0098] (3) Tin infiltration: The tungsten skeleton and tin ingot are placed in an alumina ceramic crucible (the volume ratio of the tin ingot to the tungsten skeleton hole is 1.2), and sent to an atmosphere furnace. The temperature is raised to 700℃ at 10℃ / min in a hydrogen atmosphere, held for 1.5h, and then cooled to room temperature with the furnace to obtain the W-Sn composite material.

[0099] (4) Machining: W-Sn composite material is processed by wire cutting and centerless external cylindrical grinding to obtain molded products that meet the target dimensions.

[0100] (5) Vacuum detinning: The molded product is placed in an alumina ceramic crucible and sent to a vacuum heating furnace. The vacuum degree in the furnace is controlled to be 1 Pa. The temperature is increased to 1000℃ at 10℃ / min, then increased to 1500℃ at 5℃ / min and held for 2 hours. Then the temperature is decreased to 700℃ at 5℃ / min and then naturally cooled to room temperature to obtain a porous tungsten part.

[0101] Example 3

[0102] (1) Press molding: Tungsten powder with a Fisher particle size of 8μm is loaded into a rubber mold (the inner cavity size of the mold is 110mm×150mm×400mm), mechanically vibrated, and then the mold containing tungsten powder is locked and placed in a cold isostatic press for cold isostatic pressing treatment. The pressure is controlled at 200MPa and held for 180s. After depressurization, the mold is demolded to obtain a powder compact of 110mm×130mm×180mm.

[0103] (2) High-temperature sintering: The powder compact is placed in a medium-frequency atmosphere furnace and sintered in a hydrogen atmosphere at a temperature of 1950℃ and held for 6 hours to obtain a porous tungsten skeleton.

[0104] (3) Bismuth infiltration: The tungsten skeleton and bismuth ingot are placed in an alumina ceramic crucible (the volume ratio of the bismuth ingot to the tungsten skeleton pores is 1.2), and sent to an atmosphere furnace. The temperature is increased to 950℃ at 10℃ / min in a hydrogen atmosphere, held for 1.5h, and then cooled to room temperature with the furnace to obtain the W-Bi composite material.

[0105] (4) Machining: W-Bi composite material is processed by wire cutting and centerless external cylindrical grinding to obtain molded products that meet the target dimensions.

[0106] (5) Vacuum removal of bismuth: The product is placed in an alumina ceramic crucible and sent to a vacuum heating furnace. The vacuum degree inside the furnace is controlled at 1 Pa. The temperature is increased to 1000℃ at 10℃ / min, then increased to 1500℃ at 5℃ / min and held for 2 hours. Then the temperature is decreased to 700℃ at 5℃ / min and then naturally cooled to room temperature to obtain a porous tungsten part.

[0107] Example 4

[0108] (1) Press molding: Tungsten powder with a Fisher particle size of 6.5μm is loaded into a rubber mold (mold inner cavity size is 110mm×150mm×400mm), mechanically vibrated, and then the mold containing tungsten powder is locked and placed in a cold isostatic press for cold isostatic pressing treatment. The pressure is controlled at 210MPa and held for 160s. After depressurization, the mold is demolded to obtain a powder compact of 110mm×140mm×180mm.

[0109] (2) High-temperature sintering: The powder compact is placed in a medium-frequency atmosphere furnace and sintered in a hydrogen atmosphere at a temperature of 1850℃ and held for 5 hours to obtain a porous tungsten skeleton.

[0110] (3) Lead infiltration: Tungsten skeleton and lead ingot are added to alumina ceramic crucible (the volume ratio of lead ingot to tungsten skeleton hole is 1.5), sent to atmosphere furnace, heated to 1200℃ in hydrogen atmosphere at 10℃ / min, held for 2h, and cooled to room temperature with furnace to obtain W-Pb composite material.

[0111] (4) Machining: W-Pb composite material is processed by wire cutting and centerless external cylindrical grinding to obtain molded products that meet the target dimensions.

[0112] (5) Vacuum lead removal: The molded product is placed in an alumina ceramic crucible and sent to a medium-frequency atmosphere furnace. The vacuum degree inside the furnace is controlled at 5Pa. The temperature is increased to 900℃ at 10℃ / min, then increased to 1400℃ at 5℃ / min and held for 3h. Then the temperature is decreased to 800℃ at 5℃ / min and then naturally cooled to room temperature to obtain a porous tungsten part.

[0113] Examples 5-7

[0114] Porous tungsten parts were prepared according to the method of Example 4, except that the type of metal M and the operating conditions of the first or second heat treatment were adjusted as shown in Table 1.

[0115] Comparative Example 1

[0116] Porous tungsten parts were prepared according to the method in Example 1, except that copper was used instead of lead in steps (3) to (5). The specific operations are as follows.

[0117] (3) Copper infiltration: The porous tungsten skeleton and copper block (the volume ratio of the copper block to the pores of the tungsten skeleton is 1.5) are placed in an alumina ceramic crucible and sent to an atmosphere furnace. The temperature is raised to 1500℃ at 10℃ / min under a hydrogen atmosphere and held for 1.5h. The furnace is then cooled to room temperature to obtain the W-Cu composite material.

[0118] (4) Machining: The W-Cu composite material is processed by wire cutting and centerless external cylindrical grinding to obtain molded products that meet the target dimensions;

[0119] (5) Chemical copper removal: Immerse the molded product in a nitric acid solution (HNO3 concentration of 48wt.%) and change the solution continuously until the solution no longer turns blue.

[0120] Comparative Example 2

[0121] Porous tungsten parts were prepared according to the method in Example 1, except that copper was used instead of lead in steps (3) to (5). The specific operations are as follows.

[0122] (3) Copper infiltration: The porous tungsten skeleton and copper block (the volume ratio of the copper block to the pores of the tungsten skeleton is 1.5) are placed in an alumina ceramic crucible and sent to an atmosphere furnace. The temperature is raised to 1500℃ at 10℃ / min under a hydrogen atmosphere and held for 1.5h. The furnace is then cooled to room temperature to obtain the W-Cu composite material.

[0123] (4) Machining: The W-Cu composite material is processed by wire cutting and centerless external cylindrical grinding to obtain molded products that meet the target dimensions;

[0124] (5) Vacuum copper removal: The molded product is placed in an alumina ceramic crucible and sent to a vacuum heating furnace. The vacuum degree inside the furnace is controlled at 1 Pa. The temperature is raised to 1500℃ at 10℃ / min and held for 5 hours. Then the temperature is lowered to 800℃ at 5℃ / min and then naturally cooled to room temperature to obtain a porous tungsten part.

[0125] The melting metals, their dosages, and main operating conditions used in the above embodiments and comparative examples are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] Note: Comparative Example 1 is a chemical method for copper removal.

[0130] Test case

[0131] The test examples are used to illustrate the average porosity, closed-pore ratio, and residual infiltrated metal content of the porous tungsten prepared in the above embodiments and comparative examples.

[0132] 1. Average porosity

[0133] The porosity of three different locations on the sample was measured, and the average porosity was calculated. The porosity of a single sample was calculated as (1 - sample density / theoretical density) × 100%, where the theoretical density was taken as tungsten's density of 19.35 g / cm³. 3The sample density is referenced to GB / T 5163-2006 "Determination of density, oil content and porosity of permeable sintered metal materials (excluding cemented carbide)".

[0134] 2. Residual amount of infiltrated metal

[0135] The test method for residual infiltrated metal is in accordance with GB / T 19502-2023 "General Rules for Glow Discharge Emission Spectroscopy Methods for Surface Chemical Analysis".

[0136] 3. Linear deformation of external dimensions

[0137] At room temperature, using a 5mm long sample as the test sample, the length change rate of the metal-infiltrated sample and the sample after metal removal was measured. The test method was in accordance with GB / T 1958-2017 "Geometric Tolerance Inspection and Verification of Product Geometric Specifications (GPS)" and the absolute value was taken.

[0138] 4. Closed-pore ratio

[0139] The closed-cell rate of the finished product is measured. The closed-cell rate of a single sample is calculated as (1 - true density of the sample / theoretical density) × 100%, where the theoretical density is taken as tungsten density, which is 19.35 g / cm³. 3 The true density of the sample was determined with reference to GB / T 40401-2021 Measurement of Skeleton Density by Gas Volume Replacement Method.

[0140] The test results are shown in Table 2.

[0141] Table 2

[0142]

[0143] Figures 1-3 The images show SEM images of the fracture morphology of the tungsten framework prepared in Example 1 before lead infiltration, metallographic images after lead infiltration, and SEM images of the fracture morphology of the product after lead removal (i.e., the porous tungsten part). Figures 1-3 It can be seen that after lead infiltration, the porous tungsten framework loses its pore structure, indicating that lead has fully penetrated into the pore structure of the tungsten framework. After lead removal treatment, the lead is removed from the pore structure, ultimately revealing the porous structure of the tungsten again. Combined with... Figures 4-7 It is known that the molten tin and molten bismuth formed by heating and melting can fully penetrate into and fill the pores of the tungsten skeleton to form composite materials. Furthermore, after machining, vacuum heating treatment can completely remove the tin and bismuth from the pores.

[0144] As shown in Tables 1 and 2, in Examples 1-7, after infiltrating and removing metal M from the porous tungsten framework, the porosity and closed-pore ratio of the tungsten remained essentially unchanged. Furthermore, after vacuum heat treatment to remove metal M, almost no infiltrated metal residue remained. In contrast, in Comparative Examples 1-2, after copper infiltration and removal from the porous tungsten, the copper residue was excessively high, affecting the porosity of the porous tungsten and leading to a significant increase in the closed-pore ratio. Additionally, because the boiling point of copper is much higher than that of metal M, the temperature required for copper removal is much higher than that of metal M. Moreover, chemical copper removal (Comparative Example 1) caused corrosion of the porous tungsten, altering its pore structure and resulting in a very high copper residue. Vacuum and high-temperature copper removal (Comparative Example 2) were too inefficient, failing to effectively remove copper in a short time.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a porous tungsten part, characterized in that, The preparation method includes: S1: A porous tungsten framework was prepared using tungsten powder as raw material; S2: The metal M and the porous tungsten framework are subjected to a first heat treatment to convert the metal M into a molten metal liquid and penetrate into the porous tungsten framework to obtain a tungsten-M composite material. S3: The tungsten-M composite material is machined to obtain a molded product; S4: The molded product is subjected to a second heat treatment under vacuum conditions to evaporate the metal M in the molded product and remove the metal M in the molded product, thereby producing a porous tungsten part. In step S1, the method for preparing a porous tungsten framework using tungsten powder as raw material includes: S1-1: Press tungsten powder into a compact shape to obtain a powder compact; S1-2: Sinter the powder compact to obtain a porous tungsten framework; The pressing method is cold isostatic pressing, and the pressure of cold isostatic pressing is 180~250MPa, and the holding time is 50~200s; The sintering is carried out in a hydrogen atmosphere, the sintering temperature T is 1800~2200℃, and the sintering time t is 3~12h. In step S2, the metal M is lead or tin, and the temperature T1 of the first heat treatment is 600~1550℃; or The metal M is bismuth, and the temperature T1 of the first heat treatment is 600~1200℃.

2. The preparation method according to claim 1, characterized in that, The tungsten powder has a Fisher particle size of 3~10μm.

3. The preparation method according to claim 1 or 2, characterized in that, The average porosity of the porous tungsten framework is 10%~30%.

4. The preparation method according to claim 1 or 2, characterized in that, The ratio of the volume of the metal M to the pore volume of the porous tungsten framework is (1.1~2):

1.

5. The preparation method according to claim 1 or 2, characterized in that, The lead is a lead ingot with a chemical composition content of not less than 99.9%; the tin is a tin ingot with a chemical composition content of not less than 99.9%; and the bismuth is a bismuth ingot with a chemical composition content of not less than 99.9%.

6. The preparation method according to claim 1 or 2, characterized in that, In the first heat treatment, the holding time at the temperature T1 of the first heat treatment is 0.5~5h.

7. The preparation method according to claim 1 or 2, characterized in that, The first heat treatment is carried out in the presence of a protective atmosphere, which includes at least one of hydrogen and argon.

8. The preparation method according to claim 1 or 2, characterized in that, The first heat treatment process includes: raising the temperature to the first heat treatment temperature T1 at a rate of 5~10℃ / min.

9. The preparation method according to claim 1 or 2, characterized in that, The temperature of the second heat treatment is T2 ≤ 1550℃, and the vacuum degree is ≤ 10Pa.

10. The preparation method according to claim 9, characterized in that, The vacuum degree of the second heat treatment is 0.01~10 Pa.

11. The preparation method according to claim 9, characterized in that, The second heat treatment is performed at a temperature T2 for a holding time t2 of 1 to 5 hours.

12. The preparation method according to claim 9, characterized in that, The metal M is lead or tin, and the temperature T2 of the second heat treatment is 1350~1550℃; or The metal M is bismuth, and the temperature T2 of the second heat treatment is 900~1550℃.

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