A method for manufacturing a complex tungsten part based on a binder jetting technique

Abstract

The present application belongs to the field of advanced metal material preparation and research, and relates to a method for preparing a tungsten metal complex part based on a binder jetting forming technology. The specific steps of the method are as follows: first, a nano-tungsten powder is prepared into a near-spherical micron-level powder by using a spray granulation technology; then, the micron-level powder prepared is bonded into a green body with a complex shape by using a binder jetting forming technology through a water-based binder; and finally, the green body is subjected to a debinding and sectional sintering treatment, so that the tungsten metal complex part with the complex shape is obtained. The method combines the spray granulation, the binder jetting forming, the two-step sintering method and other technologies to prepare the refractory tungsten complex part, provides a train of thought for the near-net-shape manufacturing of the refractory metal, breaks through the limitation of the traditional manufacturing, and is suitable for the preparation of small-batch tungsten products with complex shapes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of advanced refractory metal material preparation, and particularly provides a method for preparing a tungsten complex part based on a binder jetting forming technology. BACKGROUND

[0002] Tungsten is widely used in aerospace, national defense, nuclear power, energy and other industries due to its high melting point, high hardness, low vapor pressure, small thermal expansion coefficient, radiation resistance and other advantages. The traditional method for manufacturing tungsten products usually adopts powder metallurgy, and the preparation is realized through processes such as pressing, sintering and deformation. However, due to the high hardness and brittleness of tungsten, machining is difficult, which limits the preparation of some complex shaped components, and the manufacturing cost is high. With the development of additive manufacturing technology, some researchers try to use laser selective melting technology to prepare tungsten products, but the technology is prone to cracking during high-temperature melting and solidification, and the organization and performance are anisotropic, and the process uses spherical powder, which has a high manufacturing cost. In order to overcome the above problems, the present application uses indirect 3D printing technology to prepare tungsten complex components, which has the advantages of fast forming speed, low production cost, uniform organization and performance, and high density. In the prior art, a method of mixing and granulating combined with laser low-temperature sintering is used to obtain a blank, and then debinding and sintering are performed. This technology uses laser point scanning forming, which has low forming efficiency and strict control of printing parameters, and the strength of the printed blank is limited. The present application uses a spray granulation method to obtain spherical powder with higher sphericity and more uniform particle size distribution; in terms of forming method, the binder jetting forming technology is used to spray the binder in a surface scanning form, which has high printing efficiency and can be printed at room temperature without thermal stress. In particular, the water-based binder and the binder in the granulated powder are further reacted to obtain a green body with high strength, and the green body size can reach 200*200*100mm.

[0003] The binder jetting forming technology uses powder laying and binder layer accumulation to prepare three-dimensional entities, and the powder has high requirements. It not only needs to have a certain fluidity to meet the powder laying condition, but also needs to be small and easy to sinter to be dense. Therefore, 5-25μm metal powder is usually used as the printing raw material. However, due to the high melting point of tungsten, which is as high as 3400℃, at least 2500℃ sintering temperature is required for ordinary micron powder and it is difficult to sinter to be dense, which is a difficulty in the preparation of refractory tungsten products by binder jetting forming. Nano powder has low bulk density, poor fluidity and easy agglomeration, and direct use in binder jetting forming has poor effect. SUMMARY

[0004] The present application discloses a method for preparing a tungsten complex part based on a binder jetting forming technology, which solves the above 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 complex tungsten metal parts based on binder spray forming technology, the specific steps of which are as follows:

[0006] S1) Spray granulation technology is used to prepare nano-tungsten powder into near-spherical micron-sized powder;

[0007] S2) The micron-sized powder prepared in S1) is used to form a green body with a complex shape by using binder spray forming technology;

[0008] S3) The green blank obtained from S2) is degreased and sintered in stages to obtain a complex tungsten metal part with a complex shape.

[0009] Furthermore, the specific steps of S1 are as follows:

[0010] S1.1) Select nano-tungsten powder of a certain particle size and add it to the prepared polyvinyl alcohol aqueous solution to obtain a slurry;

[0011] S1.2) The slurry of S1.1) is placed in a spray dryer for spray granulation to obtain near-spherical micron-sized powder.

[0012] Furthermore, the particle size of the nano-tungsten powder in S1.1) is 50-400 nm; the tungsten powder accounts for 60-80% of the slurry mass;

[0013] The process parameters for spray granulation in S1.2) are: inlet temperature set between 250-300℃, outlet temperature set between 120-140℃, atomizer speed set between 15000-24000r / min, to obtain spherical powder with a sphericity greater than 90%.

[0014] Furthermore, the specific steps of S2 are as follows:

[0015] S2.1) Prepare the water-based adhesive and set the printing parameters as needed;

[0016] S2.2) Micron-sized powder and water-based binder are added to the spray forming equipment respectively. According to the set printing parameters, the powder spreading roller spreads the powder, and the binder is sprayed and bonded according to the slice pattern of the model. The powder bed is heated and cured by ultraviolet lamp, and layers are accumulated to obtain a green body with a complex shape.

[0017] Furthermore, the printing parameters in S2.1) are: powder layer thickness 50-200μm, powder spreading speed 10-150mm / s, printing speed 100-400mm / s, binder saturation 50-80%. The green blank forming accuracy prepared by this printing process can be controlled within 0.15mm, and the green blank bending strength is not less than 5MPa.

[0018] During the powder spreading process, a powder spreading speed of less than 150 mm / s is used to compact the powder, while the powder layer thickness is set to be less than 200 μm to ensure the density of the powder spreading, and the relative density of the printed green body is greater than 30%.

[0019] Furthermore, the specific steps of S3) are as follows:

[0020] S3.1) Degreasing stage: The temperature is slowly increased to a certain level at a certain heating rate and then held at that temperature to complete the thermal degreasing.

[0021] S3.2) Sintering stage: A two-step sintering method is adopted. In the first stage, the temperature is slowly raised to T1 and held at high temperature for a short time. In the second stage, the temperature is rapidly lowered from T1 to T2 and held at low temperature for a long time. The sintering temperature T1 in the first stage is higher than the sintering temperature T2 in the second stage, and the holding time is shorter than that in the second stage.

[0022] Furthermore, in step S3.1), the heating rate is 1-3℃, and the temperature is maintained at 300℃ and 600℃ for 1-2 hours respectively during the heating process;

[0023] In the first stage of S3.2), the temperature is increased to T1 at a rate of 4-6℃ / min, where T1 is 1500-1800℃, and held for 1-2 hours. In the second stage, the temperature is decreased to T2 at a rate of 10-20℃ / min, where T2 is 1200-1400℃, and held for 10-40 hours. The sintering atmosphere is hydrogen protection. The final product has a uniform structure with a sintering density of over 90% and a grain size of less than 1μm. The sintered product has uniform dimensional shrinkage with a shrinkage rate deviation of less than 3%.

[0024] Furthermore, the aqueous adhesive contains 5-15% PVP, 2-5% isopropanol (an organic co-solvent), 0.5-5% ethylene glycol ether (a surfactant), and the remainder is deionized water. The viscosity of the adhesive is 4-15 cps, and the surface tension at room temperature is 25-40 mN / m.

[0025] Furthermore, the mass percentage of each component in the polyvinyl alcohol aqueous solution is as follows: the mass fraction of polyvinyl alcohol is 5-15%, the mass fraction of stearic acid is 1-5%, and the remainder is deionized water.

[0026] A tungsten complex part is prepared by the above method, and the shape of the tungsten complex part includes, but is not limited to, rectangle, arc, shell or grid irregular structure with a thickness greater than 1 mm; the dimensional accuracy of the prepared part can be controlled within 0.2 mm, the surface is smooth and the roughness Ra < 4 μm.

[0027] The beneficial effects of the present invention are as follows: Due to the adoption of the above technical solution, the preparation method of the present invention uses spray granulation to prepare nanoparticles into micron-sized powders, which have both the high sintering activity of nanoparticles and the good flowability of micron-sized powders. This ensures the powder spreading and printing effect, and at the same time, it can obtain high-density products under low-temperature sintering conditions.

[0028] A water-based binder was prepared, which reacted with PVA in the granulated powder to further increase the bonding strength, and the binder is green and environmentally friendly.

[0029] A two-step sintering method was used to obtain sintered products with high density, uniform structure and fine grains. The sintering density can reach more than 90% and the grain size is less than 1μm.

[0030] This invention is also a near-net-shape forming technology that enables the direct manufacturing of complex parts, solving problems such as the high hardness and brittleness of tungsten, making machining difficult, and breaking through the limitations of traditional processes on the structure of complex parts. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of a method for preparing complex tungsten metal parts based on binder spray forming technology according to the present invention. Specific implementation examples:

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 1 As shown, this invention discloses a method for preparing complex tungsten metal parts based on binder spray forming technology. The specific steps of this method are as follows:

[0034] S1) Spray granulation technology is used to prepare nano-tungsten powder into near-spherical micron-sized powder;

[0035] S2) The micron-sized powder prepared in S1) is used to form a green body with a complex shape by using binder spray forming technology;

[0036] S3) The green blank obtained from S2) is degreased and sintered in stages to obtain a complex tungsten metal part with a complex shape.

[0037] The specific steps of S1 are as follows:

[0038] S1.1) Select nano-tungsten powder of a certain particle size and add it to the prepared polyvinyl alcohol aqueous solution to obtain a slurry;

[0039] S1.2) The slurry of S1.1) is placed in a spray dryer for spray granulation to obtain near-spherical micron-sized powder.

[0040] The nano-tungsten powder in S1.1) has a particle size of 50-400 nm; the tungsten powder accounts for 60-80% of the slurry mass;

[0041] The process parameters for spray granulation in S1.2) are: inlet temperature set between 250-300℃, outlet temperature set between 120-140℃, and atomizer speed set between 15000-24000r / min.

[0042] The specific steps of S2 are as follows:

[0043] S2.1) Prepare the water-based adhesive and set the printing parameters as needed;

[0044] S2.2) Micron-sized powder and water-based binder are added to the spray forming equipment respectively. According to the set printing parameters, the powder spreading roller spreads the powder, and the binder is sprayed and bonded according to the slice pattern of the model. The powder bed is heated and cured by ultraviolet lamp, and layers are accumulated to obtain a green body with a complex shape.

[0045] The printing parameters in S2.1) are: powder layer thickness 50-200μm, powder spreading speed 10-150mm / s, printing speed 100-400mm / s, and binder saturation 50-80%.

[0046] During the powder spreading process, a powder spreading speed of less than 150 mm / s is used to compact the powder, while the powder layer thickness is set to be less than 200 μm to ensure the density of the powder spreading, and the relative density of the printed green body is greater than 30%.

[0047] The specific steps of S3 are as follows:

[0048] S3.1) Degreasing stage: Slowly heat to a certain temperature at a certain heating rate and hold at that temperature to complete thermal degreasing. According to the thermogravimetric curve of the adhesive, hold at 300℃ and 600℃ for 1-2 hours respectively during the heating process.

[0049] S3.2) Sintering stage: A two-step sintering method is adopted. In the first stage, the temperature is slowly raised to T1 and held at high temperature for a short time. In the second stage, the temperature is rapidly lowered from T1 to T2 and held at low temperature for a long time. The sintering temperature T1 in the first stage is higher than the sintering temperature T2 in the second stage, and the holding time is shorter than that in the second stage.

[0050] In S3.1), the heating rate is 1-3℃, and the temperature is maintained at 300℃ and 600℃ for 1-2 hours respectively during the heating process;

[0051] In the first stage of S3.2), the temperature is increased to T1 at a rate of 4-6℃ / min, where T1 is 1500-1800℃, and held for 1-2 hours. In the second stage, the temperature is decreased to T2 at a rate of 10-20℃ / min, where T2 is 1200-1400℃, and held for 10-40 hours. The sintering atmosphere is hydrogen protection. The final product has a uniform structure with a sintering density of over 90% and a grain size of less than 1μm. The sintered product has uniform dimensional shrinkage with a shrinkage rate deviation of less than 3%.

[0052] The aqueous adhesive contains 5-15% PVP, 2-5% isopropanol (an organic co-solvent), 0.5-5% ethylene glycol ether (a surfactant), and the remainder is deionized water. The adhesive has a viscosity of 4-15 cps and a surface tension of 25-40 mN / m at room temperature.

[0053] The mass percentages of each component in the polyvinyl alcohol aqueous solution are as follows: polyvinyl alcohol is 5-15% by mass, stearic acid is 1-5% by mass, and the remainder is deionized water.

[0054] A tungsten complex part is prepared by the above method, and the shape of the tungsten complex part includes, but is not limited to, rectangle, arc, shell or grid irregular structure with a thickness greater than 1 mm; the dimensional accuracy of the prepared part can be controlled within 0.2 mm, the surface is smooth and the roughness Ra < 4 μm.

[0055] Example 1:

[0056] Using 50nm tungsten powder as raw material, spray granulation was used to obtain granulated powder of 5-25μm.

[0057] 50nm tungsten powder was uniformly mixed with a polyvinyl alcohol aqueous solution to prepare a slurry. Spray granulation was then performed to obtain near-spherical granules with a particle size of 5-25μm. The powder was added to a binder spray molding machine and printed under process parameters of a powder layer thickness of 0.1mm, a powder spreading speed of 70mm / s, and a printing speed of 240mm / s, resulting in a green body with a complex shape. The green body was then heated and cured at 150℃ for 2 hours. Subsequently, the green body was degreased and sintered. It was slowly heated to 600℃ at a heating rate of 3℃, with holding times at 300℃ and 600℃ for 1 hour each for thermal degreasing. In the first sintering stage, the temperature was increased to 1500℃ at a heating rate of 5℃ / min and held for 1 hour. In the second stage, the temperature was decreased to 1300℃ at a cooling rate of 15℃ / min and held for 30 hours. The sintering atmosphere was hydrogen-protected. The final product was a high-density tungsten product with a complex shape, a density of 96%, and an average grain size of 0.65μm.

[0058] Example 2:

[0059] Using 200nm tungsten powder as raw material, spray granulation was used to obtain granulated powder of 5-25μm.

[0060] Tungsten powder with a particle size of 200 nm was uniformly mixed with a polyvinyl alcohol aqueous solution to prepare a slurry. The slurry was then spray-granulated to obtain near-spherical granules with a particle size of 5-25 μm. The powder was added to a binder spray molding equipment and printed under process parameters of a powder layer thickness of 0.1 mm, a powder spreading speed of 70 mm / s, and a printing speed of 240 mm / s to obtain a green body with a complex shape. The green body was then heated and cured at 150 °C for 2 hours. Subsequently, the green body was degreased and sintered. It was slowly heated to 600 °C at a heating rate of 3 °C, with holding times at 300 °C and 600 °C for 1 hour each for thermal degreasing. In the first sintering stage, the temperature was increased to 1600 °C at a heating rate of 4 °C / min and held for 1 hour. In the second stage, the temperature was decreased to 1350 °C at a cooling rate of 20 °C / min and held for 30 hours. The sintering atmosphere was hydrogen-protected. The final product was a high-density tungsten product with a complex shape, a density of 97%, and an average grain size of 0.74 μm.

[0061] Example 3:

[0062] Using 400nm tungsten powder as raw material, spray granulation was used to obtain granulated powder of 5-25μm.

[0063] Tungsten powder with a particle size of 400 nm was uniformly mixed with a polyvinyl alcohol aqueous solution to prepare a slurry. Spray granulation was then performed to obtain near-spherical granules with a particle size of 5-25 μm. The powder was added to a binder spray molding equipment and printed under process parameters of a powder layer thickness of 0.1 mm, a powder spreading speed of 70 mm / s, and a printing speed of 240 mm / s to obtain a green body with a complex shape. The green body was then heated and cured at 150 °C for 2 h. Subsequently, the green body was degreased and sintered. It was slowly heated to 600 °C at a heating rate of 2 °C, with holding times at 300 °C and 600 °C for 1 h each for thermal degreasing. In the first sintering stage, the temperature was increased to 1700 °C at a heating rate of 5 °C / min and held for 1.5 h. In the second stage, the temperature was decreased to 1400 °C at a cooling rate of 20 °C / min and held for 30 h. The sintering atmosphere was hydrogen-protected. The final product was a high-density tungsten product with a complex shape, a density of 96%, and an average grain size of 0.81 μm.

[0064] Example 4:

[0065] Using 400nm tungsten powder as raw material, spray granulation was used to obtain granulated powder of 15-53μm.

[0066] A slurry was prepared by uniformly mixing 400nm tungsten powder with a polyvinyl alcohol aqueous solution. The slurry was then spray-granulated to obtain near-spherical granules with a particle size of 15-53μm. The powder was added to a binder spray molding machine and printed under the following process parameters: a powder layer thickness of 0.13mm, a powder spreading speed of 100mm / s, and a printing speed of 360mm / s. This yielded a green body with a complex shape, which was then heated and cured at 150℃ for 2 hours. Subsequently, the green body was degreased and sintered by slowly heating it to 600℃ at a heating rate of 3℃, with thermal degreasing performed at 300℃ and 600℃ for 1 hour each. In the first stage of sintering, the temperature was increased to 1700℃ at a heating rate of 4℃ / min and held for 2 hours. In the second stage, the temperature was decreased to 1400℃ at a cooling rate of 20℃ / min and held for 40 hours. The sintering atmosphere was hydrogen protection. Finally, a high-density tungsten product with a complex shape was obtained, with a density of 94% and an average grain size of 0.93μm.

[0067] The foregoing has provided a detailed description of a method for preparing complex tungsten metal parts based on binder spray forming technology, as provided in 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 complex tungsten metal parts based on binder spray forming technology, characterized in that, The specific steps of the method are as follows: S1) Spray granulation technology is used to prepare nano-tungsten powder into near-spherical micron-sized powder; The specific steps are as follows: S1.1) Select nano-tungsten powder of a certain particle size and add it to the prepared polyvinyl alcohol aqueous solution to obtain a slurry; S1.2) The slurry of S1.1) is placed in a spray dryer for spray granulation to obtain near-spherical micron-sized powder; The nano-tungsten powder has a particle size of 50-400 nm; the tungsten powder accounts for 60-80% of the slurry mass. The process parameters for spray granulation in S1.2) are: inlet temperature set between 250-300℃, outlet temperature set between 120-140℃, atomizer speed set between 15000-24000r / min, to obtain spherical powder with a sphericity greater than 90%. S2) The micron-sized powder prepared in S1) is used to form a green body with a complex shape by using binder spray forming technology; The specific steps are as follows: S2.1) Configure the water-based adhesive and preset the printing parameters; S2.2) Micron-sized powder and water-based binder are added to the spray forming equipment respectively. According to the set printing parameters, the powder spreading roller spreads the powder, and the binder is sprayed and bonded according to the slice pattern of the model. The powder bed is heated and cured by ultraviolet lamp, and layers are accumulated to obtain a green body with a complex shape. S3) The green blank obtained from S2) is degreased and sintered in stages to obtain complex tungsten metal parts with complex shapes; The specific steps are as follows: S3.1) Degreasing stage: The temperature is slowly increased to a certain level at a certain heating rate and then held at that temperature to complete the thermal degreasing. S3.2) Sintering stage: A two-step sintering method is adopted. In the first stage, the temperature is slowly raised to T1 and held at high temperature for a short time. In the second stage, the temperature is rapidly lowered from T1 to T2 and held at low temperature for a long time. The sintering temperature T1 in the first stage is higher than the sintering temperature T2 in the second stage, and the holding time is shorter than that in the second stage. The heating rate in S3.1) is 1-3℃, and the heating process is carried out at 300℃ and 600℃ for 1-2 hours respectively. In the first stage of S3.2), the temperature is increased to T1 at a rate of 4-6℃ / min, where T1 is 1500-1800℃, and held for 1-2 hours. In the second stage, the temperature is decreased to T2 at a rate of 10-20℃ / min, where T2 is 1200-1400℃, and held for 10-40 hours. The sintering atmosphere is hydrogen protection. The final product has a sintering density of over 90%, a uniform microstructure with a grain size of less than 1μm, uniform dimensional shrinkage of the sintered product, and a shrinkage rate deviation of less than 3%.

2. The method according to claim 1, characterized in that, The printing parameters in S2.1 are: powder layer thickness 50-200μm, powder spreading speed 10-150mm / s, printing speed 100-400mm / s, and binder saturation 50-80%.

3. The method according to claim 1, characterized in that, The aqueous adhesive contains 5-15% PVP, 2-5% isopropanol (an organic co-solvent), 0.5-5% ethylene glycol ether (a surfactant), and the remainder is deionized water. The viscosity of the prepared adhesive is 4-15 cps, and the surface tension at room temperature is 25-40 mN / m.

4. The method according to claim 1, characterized in that, The mass percentages of each component in the polyvinyl alcohol aqueous solution are as follows: polyvinyl alcohol is 5-15% by mass, stearic acid is 1-5% by mass, and the remainder is deionized water.

5. A complex tungsten part, characterized in that, The tungsten complex part is prepared by the method described in any one of claims 1-4, and the shape of the tungsten complex part includes rectangular, arc-shaped, shell with a thickness greater than 1 mm and grid-shaped structure; the dimensional accuracy of the prepared part is controlled within 0.2 mm, the surface is smooth, and the roughness Ra < 4 μm.

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