A method for producing a porous structure of tungsten metal

Abstract

The present application belongs to the field of additive manufacturing technology research, and particularly provides a preparation method of a porous tungsten structure. The method uses high-purity micron tungsten powder prepared by a hydrogen reduction method as raw material, obtains near-spherical powder with uniform particle size distribution through airflow mill classification treatment, uses an epoxy resin binder to spray form the powder into a green body, and after heat debinding, uses a sectional sintering method to sinter, thereby obtaining a porous tungsten structure with uniform and small pores. The porosity of the porous tungsten structure is 10-50%, and the pore size is less than 1 μm. The present application has the advantages of low cost, fast speed, no need for support, and less cracking, etc. The present application provides a new idea for the preparation of porous tungsten complex parts.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology research, and specifically provides a method for preparing porous tungsten metal structures. Background Technology

[0002] Tungsten, as the refractory metal with the highest melting point, possesses excellent high-temperature performance, low vapor pressure, and corrosion resistance, making it widely used in defense and military industries, aerospace, energy, and electronics and information industries, occupying an important position in the national economy. It also has significant applications in industrial and nuclear power sectors. Tungsten has shown promising prospects as a high-temperature material in nuclear fusion reactors; for example, high-current-density porous cathodes are one important application of porous tungsten. Currently, the most widely used diffusion cathodes are prepared by impregnating porous tungsten with aluminate of metallic barium. The pores within the porous tungsten serve as storage and transport channels for emission materials. Certain requirements are placed on the size, shape, uniformity of pore distribution, and porosity of these pores. Pore characteristics significantly influence the storage, activation, and transport of materials within the tungsten matrix. Therefore, preparing high-quality porous tungsten matrices is a key technology for achieving uniform electron emission from the cathode.

[0003] Traditionally, porous tungsten is prepared using powder sintering, where a pore-forming agent is added to tungsten powder, followed by pressing and sintering to obtain a porous structure. However, this method struggles to control the uniformity of pores and requires machining to produce complex parts. Due to tungsten's high hardness and brittleness, traditional machining methods are extremely difficult for preparing complex porous tungsten components. 3D printing, a popular emerging manufacturing technology, can directly form complex parts, offering significant advantages for small-batch, customized production. Currently, metal 3D printing technologies mainly include laser forming, electron beam forming, and binder jet forming. Because tungsten has a high melting point and high brittleness, laser or electron beam forming can easily cause severe deformation and cracking during melting and solidification, limiting its application. Binder jet forming, an indirect 3D printing technology, involves layer-by-layer powder spreading and bonding at room temperature to obtain a green body, followed by debinding and sintering to obtain the desired product. The prepared samples have uniform microstructure and properties, without anisotropy or cracking issues. This process is particularly suitable for preparing porous structures of refractory metals. Summary of the Invention

[0004] This invention discloses a method for preparing a porous structure of metallic tungsten, which solves the above-mentioned technical problems and other technical problems in the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for preparing a porous tungsten metal structure. The method uses high-purity micron-sized tungsten powder prepared by hydrogen reduction as raw material, and obtains near-spherical powder with uniform particle size distribution by air jet milling. The powder is then spray-formed into a green body using epoxy resin binder, and after thermal debinding, it is sintered by segmented sintering to obtain a porous tungsten metal structure with uniform fine pores.

[0006] Furthermore, the preparation method specifically includes the following steps:

[0007] S1) Tungsten powder obtained by hydrogen reduction is subjected to air jet milling. The frequency of air jet milling is set, nitrogen is introduced as the grinding medium, and the powder is graded under a certain grinding pressure to obtain near-spherical powder with narrow particle size distribution and good flowability.

[0008] S2) Weigh out the adhesive, solvent, curing agent and toughening agent in a certain proportion, mix them evenly, stir and filter to obtain epoxy resin adhesive;

[0009] S3) Set the powder spreading, inkjet, and printing parameters, and perform powder spreading and bonding to form the part; after printing, move the powder bed containing the part to the oven for heating and curing, and clean the powder around the part after curing to obtain the green blank;

[0010] S4) First, the binder is removed by hot degreasing, and then sintering is carried out by segmented sintering under a protective atmosphere to obtain a porous tungsten metal structure with a porosity of 10-50%, a pore size of less than 1μm, and a pore size variance of less than 0.2.

[0011] Furthermore, the tungsten powder has a particle size of 1-10 μm and a purity of 99.9% or higher.

[0012] Furthermore, the specific steps of S1) are as follows:

[0013] S1.1) First, turn on the air jet mill, fill it with nitrogen gas with a purity greater than 99.9% as the grinding medium, adjust the grinding pressure to 0.5-0.7 MPa, and add tungsten powder;

[0014] S1.2) Based on the powder particle size requirements, first set the sorting wheel frequency to a maximum of 150-200HZ to disperse the powder, and then gradually reduce the sorting wheel frequency to 100-20HZ. The processing time is 2-4h, and tungsten powder is collected in batches to obtain powder with coarse, medium and fine narrow particle size distribution. Select the powder with the medium particle size as the printing powder.

[0015] Further, in S2), the mass fraction of the adhesive is 10-30%, the mass fraction of the curing agent is 4-8%, the mass fraction of the toughening agent is 0.5-3%, and the remainder is solvent; the viscosity of the adhesive is 3-15 cps.

[0016] Furthermore, the adhesive is epoxy resin; the curing agent is m-phenylenediamine or imidazole curing agent; the toughening agent is polyamide resin; and the solvent is dimethylformamide or butyl glycidyl ether.

[0017] Furthermore, the printing parameters in S3) are: powder layer thickness 0.05-0.2mm, powder spreading speed 15-120mm / s, printing speed 100-400mm / s, adhesive saturation 50-80%; curing temperature 150-200℃, and heat preservation time 1-3h.

[0018] Furthermore, the specific steps of S4 are as follows:

[0019] S4.1) Thermal degreasing process: Heat from room temperature to 300℃ at a heating rate of 1-3℃ / min and hold for 1 hour, then continue heating to 600-700℃ and hold for 1-2 hours to remove the adhesive completely.

[0020] S4.2) Under a protective atmosphere, the temperature is raised to T1 for low-temperature sintering and then held at that temperature;

[0021] S4.3) Increase the sintering temperature to T2 and hold for a period of time to complete dense sintering.

[0022] Furthermore, in S4.2), the heating rate is 1-3℃ / min, the value of T1 is 600℃-700℃, and the holding time is 1-2h;

[0023] The value of S4.3)T2 is 1400-2000℃, and the heat is maintained for 1-3 hours.

[0024] Furthermore, the protective atmosphere is hydrogen.

[0025] This invention aims to provide a method for preparing porous tungsten parts using binder jetting technology. The core of the invention lies in the preparation of porous tungsten products through powder pretreatment combined with 3D printing and segmented sintering techniques, resulting in parts with uniform pore size, stable performance, flexible design, and no need for machining. To obtain a uniform porous structure, this invention specifically employs a segmented sintering process. First, a pre-coarsening treatment is performed, involving slow heating at a low temperature and prolonged holding. During the slow heating, sintering necks gradually form between powder particles. This low-temperature, long-term holding sintering method homogenizes the microstructure, controls grain boundary migration, and prevents abnormal grain growth, which could lead to large grains engulfing small grains and causing microstructure inhomogeneity, resulting in uneven pore size or distribution. The second step uses rapid heating at a high temperature and short holding time to further densify the tungsten, meeting the requirements for porosity and pore size. This sintering process can obtain a uniform and fine pore structure.

[0026] The beneficial effects of this invention are:

[0027] (1) Powder with narrow particle size distribution, good flowability, good dispersion and near-spherical shape can be obtained by air jet milling. The optimization of powder characteristics can significantly improve the powder spreading quality. Compared with spherical powder, the near-spherical powder prepared by this method greatly reduces the raw material cost.

[0028] (2) Prepare epoxy resin adhesive with high bonding strength, simple degreasing process with no carbon residue, and high printing precision;

[0029] (3) The binder spraying process adopts a layer-by-layer powder spreading and bonding process, which ensures the uniform distribution of green body pores. It is particularly suitable for the preparation of porous structures. The product pores can be controlled by adjusting the powder particle size and sintering process.

[0030] (4) A segmented sintering method is adopted. First, a pre-coarsening treatment is carried out to make the pore size uniform. Then, the sintering temperature is further increased to improve the density and meet the requirements of porosity and pore size. This sintering process can obtain uniform and fine pores; such as obtaining porous tungsten products with a porosity of 10-50%, a pore size of less than 1μm, and a pore size variance of less than 0.2.

[0031] (5) Compared with other 3D printing technologies, the use of binder spraying to prepare porous tungsten structures has advantages such as low cost, high speed, no need for support, and less susceptibility to cracking. This invention provides a new approach for the preparation of complex parts with porous tungsten structures. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating a method for preparing a porous tungsten structure according to the present invention.

[0033] Figure 2 The image shows the effect of powder spreading and binder spraying during the printing process in the preparation method of this invention.

[0034] Figure 3 This is a macroscopic morphology diagram of the molded part of Example 1 prepared using the preparation method of the present invention.

[0035] Figure 4 This is a macroscopic morphology diagram of the molded part of Example 2 prepared using the preparation method of the present invention. Detailed implementation method:

[0036] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0037] This invention provides a method for preparing a porous tungsten structure. The method uses high-purity micron-sized tungsten powder prepared by hydrogen reduction as raw material. The powder is then graded by air jet milling to obtain a near-spherical particle size distribution. The powder is then formed into a green body using an epoxy resin binder. After thermal debinding, the green body is sintered using a segmented sintering method to obtain a porous tungsten structure with uniform and fine pores.

[0038] like Figure 1 As shown, the present invention discloses a method for preparing a porous tungsten metal structure, the method specifically comprising the following steps:

[0039] S1) Tungsten powder obtained by hydrogen reduction is subjected to air jet milling. The frequency of air jet milling is set, nitrogen is introduced as the grinding medium, and the powder is graded under a certain grinding pressure to obtain near-spherical powder with narrow particle size distribution and good flowability.

[0040] S2) Weigh out the adhesive, solvent, curing agent and toughening agent in a certain proportion, mix them evenly, stir and filter to obtain epoxy resin adhesive;

[0041] S3) Set the powder spreading, inkjet, and printing parameters, and perform powder spreading and bonding to form the part; after printing, move the powder bed containing the part to the oven for heating and curing, and clean the powder around the part after curing to obtain the green blank;

[0042] S4) First, the binder is removed by hot degreasing, and then sintering is carried out by segmented sintering under a protective atmosphere to obtain a porous tungsten metal structure with a porosity of 10-50%, a pore size of less than 1μm, and a pore size variance of less than 0.2.

[0043] The tungsten powder is selected with a Fisher particle size of 1-10 μm and a purity of 99.9% or higher.

[0044] The specific steps of S1) are as follows:

[0045] S1.1) First, turn on the air jet mill, fill it with nitrogen gas with a purity greater than 99.9% as the grinding medium, adjust the grinding pressure to 0.5-0.7 MPa, and add tungsten powder;

[0046] S1.2) Based on the powder particle size requirements, first set the sorting wheel frequency to a maximum of 150-200HZ to disperse the powder, and then gradually reduce the sorting wheel frequency to 100-20HZ. The processing time is 2-4h, and tungsten powder is collected in batches to obtain powder with coarse, medium and fine narrow particle size distribution. Select the powder with the medium particle size as the printing powder.

[0047] The adhesive in S2) has a mass fraction of 10-30%, a curing agent mass fraction of 4-8%, a toughening agent mass fraction of 0.5-3%, and the remainder is solvent; the viscosity of the adhesive is 3-15 cps.

[0048] The adhesive is epoxy resin; the curing agent is m-phenylenediamine or imidazole curing agent; the toughening agent is polyamide resin; and the solvent is dimethylformamide or butyl glycidyl ether.

[0049] The printing parameters in S3) are: powder layer thickness 0.05-0.2mm, powder spreading speed 15-120mm / s, printing speed 100-400mm / s, adhesive saturation 50-80%; curing temperature 150-200℃, and heat preservation time 1-3h.

[0050] The specific steps of S4 are as follows:

[0051] S4.1) Thermal degreasing process: Heat from room temperature to 300℃ at a heating rate of 1-3℃ / min and hold for 1 hour, then continue heating to 600-700℃ and hold for 1-2 hours to remove the adhesive completely.

[0052] S4.2) Under a protective atmosphere, the temperature is raised to T1 for low-temperature sintering and then held at that temperature;

[0053] S4.3) Increase the sintering temperature to T2 and hold for a period of time to complete dense sintering.

[0054] The heating rate in S4.2) is 1-3℃ / min, the value of T1 is 600℃-700℃, and the holding time is 1-2h;

[0055] The value of S4.3)T2 is 1400-2000℃, and the heat is maintained for 1-3 hours.

[0056] The protective atmosphere is hydrogen.

[0057] Example 1

[0058] Tungsten powder with a Fisher particle size of 1μm was used and subjected to air jet milling with nitrogen as the grinding medium at a pressure of 0.7MPa. The sorting wheel frequency was set to 150Hz to break up powder agglomerates. The sorting wheel frequency was then reduced to 100Hz, 70Hz, and 20Hz, collecting powder sequentially. Near-spherical powder with a particle size distribution of 1.22-3.46μm was selected for printing at a sorting wheel frequency of 70Hz. The powder was added to a binder jet forming equipment with the following printing parameters: powder layer thickness of 0.1mm, powder spreading speed of 30mm / s, printing speed of 240mm / s, and binder saturation of 60%. Powder was spread layer by layer until printing was complete. The formed area was heated and cured at 180℃ for 1-3 hours, depending on the part size. After curing, the powder around the part was removed, and the blank was removed. The degreasing and sintering process involves heating from room temperature to 300℃ at a rate of 1℃ / min and holding for 1 hour, followed by further heating to 600℃ and holding for 1 hour. Sintering continues with two steps: first, pre-coarsening sintering at 900℃ for 4 hours to ensure pore uniformity; second, densification sintering at 1500℃ for 2 hours to adjust porosity and pore size. Hydrogen gas is used for atmosphere protection during sintering. Finally, the furnace is cooled to room temperature, resulting in a porous tungsten product with a porosity of 20%, an average pore size of 0.51 micrometers, and a pore size variance of less than 0.2. Figure 2 As shown.

[0059] Example 2

[0060] Tungsten powder with a Fisher particle size of 3μm was used and subjected to an air jet mill with nitrogen as the grinding medium at a pressure of 0.7MPa. The sorting wheel frequency was set to 150Hz to break up powder agglomerates. The sorting wheel frequency was then reduced to 100Hz, 70Hz, and 20Hz, collecting powder sequentially. Near-spherical powder with a particle size distribution of 2.24-4.51μm was selected for printing at a sorting wheel frequency of 70Hz. The powder was added to a binder jet forming equipment with the following printing parameters: powder layer thickness of 0.1mm, powder spreading speed of 50mm / s, printing speed of 240mm / s, and binder saturation of 60%. Powder was spread layer by layer until printing was complete. The formed area was heated and cured at 180℃ for 1-3 hours, depending on the part size. After curing, the powder around the part was removed, and the blank was removed. The degreasing and sintering process involved heating from room temperature to 300℃ at a rate of 3℃ / min and holding for 1 hour, followed by further heating to 600℃ and holding for 1 hour. Sintering continued with two steps: first, pre-coarsening sintering at 950℃ for 6 hours to ensure pore uniformity; second, densification sintering at 1650℃ for 2 hours to adjust porosity and pore size. Hydrogen gas was used for atmosphere protection during sintering, and the furnace was finally cooled to room temperature. The final product obtained was a porous tungsten product with a porosity of 34%, an average pore size of 0.6 micrometers, and a pore size variance of less than 0.2. Figure 3 As shown.

[0061] Example 3

[0062] Tungsten powder with a Fisher particle size of 5μm was used and subjected to an air jet mill with nitrogen as the grinding medium at a pressure of 0.7MPa. The sorting wheel frequency was set to 100Hz to break up powder agglomerates. The sorting wheel frequency was then reduced to 70Hz, 50Hz, and 20Hz, collecting powder sequentially. Near-spherical powder with a particle size distribution of 2.67-6.05μm was selected for printing at a sorting wheel frequency of 50Hz. The powder was added to a binder jet forming equipment with the following printing parameters: powder layer thickness of 0.1mm, powder spreading speed of 100mm / s, printing speed of 240mm / s, and binder saturation of 60%. Powder was spread layer by layer until printing was complete. The formed area was heated and cured at 180℃ for 1-3 hours, depending on the part size. After curing, the powder around the part was removed, and the blank was removed. The degreasing and sintering process involves heating from room temperature to 300℃ at a rate of 1.5℃ / min and holding for 1 hour, followed by further heating to 600℃ and holding for 1 hour. Sintering continues with two steps: first, pre-coarsening sintering at 1000℃ for 5 hours to ensure pore uniformity; second, densification sintering at 1700℃ for 2 hours to adjust porosity and pore size. Hydrogen gas is used for atmosphere protection during sintering, and the furnace is finally cooled to room temperature. The final product has a porosity of 30%, an average pore size of 0.64 micrometers, and a pore size variance of less than 0.2.

[0063] Example 4

[0064] Tungsten powder with a Fisher particle size of 8μm was used and subjected to an air jet mill with nitrogen as the grinding medium at a pressure of 0.7MPa. The sorting wheel frequency was set to 100Hz to break up powder agglomerates. The sorting wheel frequency was then reduced to 70Hz, 50Hz, and 20Hz, collecting powder sequentially. Near-spherical powder with a particle size distribution of 7.18-10.43μm was selected for printing at a sorting wheel frequency of 50Hz. The powder was added to a binder jet forming equipment with the following printing parameters: powder layer thickness of 0.13mm, powder spreading speed of 100mm / s, printing speed of 360mm / s, and binder saturation of 50%. Powder was spread layer by layer until printing was complete. The formed area was heated and cured at 180℃ for 1-3 hours, depending on the part size. After curing, the powder around the part was removed, and the blank was removed. The degreasing and sintering process involved heating from room temperature to 300℃ at a rate of 2.5℃ / min and holding for 1 hour, followed by further heating to 600℃ and holding for 1 hour. Sintering continued with two steps: first, pre-coarsening sintering at 1100℃ for 6 hours to ensure pore uniformity; second, densification sintering at 1800℃ for 2 hours to adjust porosity and pore size. Hydrogen gas was used for atmosphere protection during sintering, and the furnace was finally cooled to room temperature, resulting in a porous tungsten product with a porosity of 40%, an average pore size of 0.81 micrometers, and a pore size variance of less than 0.2.

[0065] The foregoing has provided a detailed description of a method for preparing a uniform porous tungsten part according to the embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and its core ideas; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0066] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0067] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0068] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0069] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for preparing a porous tungsten metal structure, characterized in that, This method uses micron-sized tungsten powder prepared by hydrogen reduction as raw material. It obtains near-spherical powder with uniform particle size distribution through air jet milling and classification. The near-spherical powder is formed into a green body using binder spray forming technology. After hot debinding, it is sintered by segmented sintering method to obtain a porous tungsten metal structure with uniform fine pores. The preparation method specifically includes the following steps: S1) The tungsten powder obtained by hydrogen reduction is subjected to air jet milling to obtain near-spherical powder; The micron-sized tungsten powder has a Fisher particle size of 1-10 μm and a purity of over 99.9%. S2) Preparation of epoxy resin adhesive; The epoxy resin adhesive comprises 10-30% by mass of the binder, 4-8% by mass of the curing agent, and 0.5-3% by mass of the toughening agent, with the remainder being solvent; the viscosity of the adhesive is 3-15 cps. The adhesive is epoxy resin; the curing agent is m-phenylenediamine or imidazole curing agent; the toughening agent is polyamide resin; the solvent is dimethylformamide or butyl glycidyl ether. S3) Add the near-spherical powder obtained in S1) and the epoxy resin binder obtained in S2) into the equipment. After setting the powder spreading, inkjet and printing parameters, perform powder spreading and bonding to form the part. After printing, move the powder bed containing the part to the oven for heating and curing. After curing, clean the powder around the part to obtain the green blank. The printing parameters are as follows: powder layer thickness 0.05-0.2mm, powder spreading speed 15-120mm / s, printing speed 100-400mm / s, adhesive saturation 50-80%; curing temperature 150-200℃, and heat preservation time 1-3h. S4) First, the binder is removed by hot degreasing, and then sintering is carried out by segmented sintering under a protective atmosphere to obtain a porous tungsten metal structure with a porosity of 10-50%, a pore size of less than 1μm, and a pore size variance of less than 0.

2.

2. The preparation method according to claim 1, characterized in that, The specific steps of S1 are as follows: S1.1) First, turn on the air jet mill, fill it with nitrogen gas with a purity greater than 99.9% as the grinding medium, adjust the grinding pressure to 0.5-0.7MPa, and add tungsten powder; S1.2) Based on the powder particle size requirements, set the sorting wheel frequency to 150HZ to disperse the powder, and then successively reduce the sorting wheel frequency to 100HZ, 70HZ, and 20HZ. The processing time is 2-4 hours. Select the powder with the middle particle size from the processed powder as the printing powder.

3. The preparation method according to claim 1, characterized in that, The specific steps of S4 are as follows: S4.1) Hot degreasing process: Heat from room temperature to 300℃ at a heating rate of 1-3℃ / min and hold for 1 hour, then continue heating to 600-700℃ and hold for 1-2 hours; S4.2) Under a protective atmosphere, the temperature is raised to T1 for low-temperature sintering and then held at that temperature; S4.3) Further increase the sintering temperature to T2 and hold it at that temperature to complete the dense sintering.

4. The preparation method according to claim 3, characterized in that, The heating rate in S4.2) is 1-3℃ / min, the value of T1 is 600℃-700℃, and the holding time is 1-2h; S4.3) The value of T2 is 1400-2000℃, and the heat is maintained for 1-3 hours.

5. The preparation method according to claim 3, characterized in that, The protective atmosphere is hydrogen.

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