CN114289718B - Method for efficiently preparing porous tungsten product with complicated shape nano-pores - Google Patents
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Abstract
A forming method of a porous tungsten product with a nano-pore structure belongs to the technical field of powder metallurgy. The invention relates to a forming method for preparing a complex-shape porous tungsten product design with excellent pore characteristics, uniform structure, complex shape, high dimensional accuracy and good consistency with high efficiency and low cost. Firstly, carrying out dispersion grading spheroidization on powder by adopting a combination of a fluidization dispersion technology and a radio frequency plasma spheroidization technology to obtain dispersed spherical tungsten powder with narrow particle size distribution and fine particle size; and then uniformly mixing the powder with a plastic-based binder to prepare a feed, preparing a tungsten product green body with a complex shape through powder microinjection molding, and finally preparing a porous tungsten product with a complex shape through degreasing and sintering. The invention obviously optimizes the injection molding process of raw material powder and micro powder, and the prepared porous tungsten product with the nano pore structure has uniform tissue structure, the grain size is less than or equal to 1 mu m, the aperture is 100-800 nm, the porosity is 15-35%, the pore is uniform and the connectivity is good.
Description
Technical Field
The invention belongs to the technical field of powder metallurgy, and particularly relates to a method for efficiently preparing a porous tungsten product with a complicated shape and nano-pores.
Background
The refractory metal tungsten has the characteristics of high melting point, high strength, high elastic modulus, high temperature resistance, corrosion resistance and the like, and the porous member has irreplaceable functions in the fields of electric vacuum, atomic energy, aerospace and the like, in particular to a key component of a field emission propulsion system for a spacecraft. Therefore, for precise control of the micro-ox level of the propulsion system, long service life and high reliability, the micro-nano porous tungsten member is required to have uniform pore size, uniform distribution, good connectivity, generally complex shape (gears, grooves, needles, steps, large aspect ratio, etc.), and high dimensional accuracy requirement for meeting the assembly requirement. However, because the tungsten has high hardness, large brittleness and poor processability, complex components cannot be directly prepared by mechanical processing, and the traditional process is to prepare a machinable tungsten-copper false alloy by adopting a powder metallurgy process, and then remove copper after the tungsten-copper false alloy is processed into components with required shapes. The method has complex process and low material utilization rate, and is particularly limited by the processing technology, and the porous tungsten product with fine grains, nano pore structure and micron-sized complex shape is difficult to prepare.
The powder microinjection molding is a near net molding technology which introduces the modern plastic injection molding technology into the field of powder metallurgy, and mainly comprises the steps of mixing metal powder with a binder to form a feed, then injecting and molding the feed into a green body through microinjection molding equipment, and finally degreasing and sintering to obtain the required product. The method has the advantages of capability of directly preparing products with complex high dimensional accuracy and complex shapes, excellent performance, high yield, good product consistency and the like. The powder prepared by powder spheroidizing has uniform particle size, high sphericity and difficult pollution, and the prepared porous tungsten member has uniform pore size, uniform distribution and good connectivity. Chinese patent (CN 105499574 a) discloses a method for preparing a porous tungsten product with uniform pore, which comprises dispersing high-purity tungsten powder, collecting and removing ultrafine particles (< 2 um) in the original tungsten powder, and obtaining a cathode substrate with uniform pore distribution. But the pore diameter and the grain size of the prepared product are larger, and the porous tungsten product with fine grains, nano pore structure and micron-sized complex shape can not be prepared. Chinese patent (CN 108907214 a) discloses a method for preparing tungsten-rhenium alloy powder by spray pyrolysis and hydrogen reduction, and preparing porous tungsten-rhenium alloy parts by twice jet milling treatment and selective laser melting. However, the sample which can only be prepared is generally larger, the dimensional accuracy is lower, the grain size and the porosity are in the micron level, and the porous tungsten product with the complicated shape and the nano pore structure is difficult to prepare. Chinese patent (CN 107604188A) discloses a method for preparing porous tungsten products by sintering after press forming or hot press sintering, which cannot be used for preparing porous tungsten products with complex shapes.
Therefore, the invention adopts a novel technology for efficiently preparing the porous tungsten product with the nano-pore structure in a complex shape to realize the preparation of the porous tungsten product with the nano-pore structure with uniform structure, complex shape, high dimensional accuracy and good product consistency at lower cost.
Disclosure of Invention
The invention aims to provide a forming method of a porous tungsten product with a nano-pore structure.
A forming method of a porous tungsten product with a nano pore structure uses fine-grained tungsten powder as a raw material, and adopts a combination of a fluidization and dispersion technology and a radio frequency plasma spheroidization technology to carry out dispersion and spheroidization on the powder so as to obtain dispersed spherical tungsten powder with narrow particle size distribution and fine particle size; then preparing a porous tungsten product with a nano pore structure in a complex shape through powder microinjection molding, and finally preparing the porous tungsten product with the nano pore structure in the complex shape through degreasing and sintering, wherein the preparation method comprises the following specific steps of:
1. the raw material powder is tungsten powder, the purity is more than 99.9 percent, and the granularity is less than 1 mu m;
2. the raw material powder is added into a fluidized bed, high-purity inert gas is firstly filled into the equipment from bottom to top to remove air before dispersion treatment, gas protection environment is provided for the powder, and the equipment is inflated and cleaned; after the air in the cavity of the fluidized bed is exhausted, transferring the air into a heating device, continuously introducing high-purity inert gas with stable flow in the fluidized bed treatment process, wherein the flow speed of the gas flow is 1-3L/min, the heating temperature is 100-280 ℃, and the fluidization treatment is carried out for 100-180 min at constant flow and constant temperature. After the fluidized bed dispersion treatment, removing the fluidized bed cavity from the heating device, continuously introducing high-purity inert protective gas, and stopping introducing the protective gas after cooling to room temperature in air to obtain powder after the fluidization dispersion treatment;
3. feeding the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, and performing spheroidization on the powder, wherein the powder feeding speed is 5-15 g/min, the treatment power is 5-25 kw, the powder feeding air flow is 5-10L/min, the medium air flow is 25-35L/min, the side air flow is 30-60L/min, and collecting the powder after the plasma spheroidization after cooling to obtain spheroidized powder;
4. uniformly mixing the spheroidized powder with an organic binder, and preparing a granular feed;
5. according to different application scenes of porous tungsten products with nano pore structures, the requirements on the shapes and the sizes of the products are different, and a tungsten blank with the required shapes and the sizes is formed by microinjection;
6. the microinjection molding blank is subjected to catalytic degreasing in a catalytic degreasing furnace by adopting concentrated nitric acid or concentrated oxalic acid as a catalytic medium, so as to remove part of binder;
7. and (3) under the condition that high-purity hydrogen with the purity of more than 99.9% is used as a protective atmosphere, carrying out thermal sintering treatment on the dried sample obtained in the step (6) in a tungsten wire sintering furnace to prepare the porous tungsten product with the complicated shape and the nano pore structure.
Further, the proportion of the binder in the step 4 is as follows: 80-88% of polyformaldehyde, 3-8% of low-density polyethylene, 3-10% of vinyl acetate copolymer, 2-5% of stearic acid, 2-10% of microcrystalline wax and 2-7% of polypropylene.
Further, the concentration of the concentrated nitric acid or the concentrated oxalic acid adopted in the step 6 is 86% -95%, the catalytic degreasing is carried out for 1-12 hours at the temperature of 110-150 ℃, a porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the subsequent thermal sintering process are facilitated.
Further, the thermal sintering treatment process in the step 7 is to heat up to 200 ℃ at 0.2-0.5 ℃/min, heat up to 60min at 0.5-1 ℃/min to 450 ℃, heat up to 40-90 min at 0.5-0.8 ℃/min to 550 ℃, heat up to 60min at 0.5-1 ℃/min to 650 ℃, heat up to 60min at 30-60 min, heat up to 750 ℃ at 2-3 ℃/min, heat up to 120min at 2-3 ℃/min, heat up to 950 ℃ at 2-3 ℃/min, heat up to 1000-1250 ℃ at 60-180 min at 1-3 ℃/min, heat down to 900 ℃ at 2-5 ℃/min to 700 ℃, and heat down to room temperature at 5-10 ℃/min.
Further, the grain size of the sintered porous tungsten product with the nano pore structure is less than or equal to 1 mu m, the pore diameter is 100-800 nm, the porosity is 15-35%, the pores are uniform, and the connectivity is good.
By adopting the technical scheme, the invention has the beneficial effects that: (1) From the perspective of optimizing the powder raw material, the particle size of the adopted raw material powder is smaller than 1 mu m, the particle size is small, the powder agglomeration is serious, the requirement of microinjection molding on the raw material powder cannot be met, and the porous tungsten product with the nano pore structure has a plurality of closed pores and uneven pores, so that the performance of related equipment is affected. The powder is subjected to fluidization and dispersion treatment, so that agglomeration of powder particles can be relieved, dispersion and classification can be realized, and the spherical tungsten powder particles with fine granularity, high dispersion and narrow distribution can be finally obtained by utilizing plasma spheroidization. (2) Uniformly mixing the treated powder with a plastic-based binder, and preparing a granular feed; the tungsten blank prepared by micro injection molding has higher strength and shape retention; the method adopts a sectional sintering and retarded heating mode in the thermal sintering process, which is beneficial to realizing the precise control of the porosity of the porous tungsten. (3) The powder microinjection molding is suitable for the precise manufacture of micro parts with micron-sized characteristic sizes, the subsequent processing is not needed, the material utilization rate is high, and the porous tungsten product with the final shape, the nano pore structure and the micron-sized characteristic can be directly prepared. (4) The prepared porous tungsten product with the complicated shape nano pore structure has low impurity content, uniform pores, grain size less than or equal to 1 mu m, pore diameter of 100-800 nm, porosity of 15-35%, and open pore porosity accounting for more than 95% of the total porosity.
Drawings
Figure 1 is an SEM of tungsten powder before and after processing,
figure 2 is an XRD of tungsten powder before and after treatment,
fig. 3 is a fracture SEM of the prepared porous tungsten article.
Detailed Description
Example 1
1) The raw material powder is commercial tungsten powder, the Fisher particle size is 0.8 mu m, and the purity is more than 99.9%;
2) The raw material powder is added into a fluidized bed, high-purity inert gas is firstly filled into the equipment from bottom to top to remove air before dispersion treatment, gas protection environment is provided for the powder, and the equipment is inflated and cleaned; after the air in the cavity of the fluidized bed is exhausted, the air is transferred to a heating device, high-purity inert gas with stable flow is continuously introduced in the treatment process of the fluidized bed, the flow speed of the gas flow is 3L/min, the heating temperature is 220 ℃, and the fluidization treatment is carried out for 100min at constant flow and constant temperature. After the fluidized bed dispersion treatment, the cavity of the fluidized bed is removed from the heating device, and high-purity inert shielding gas is continuously introduced, and after the cavity is cooled to room temperature in the air, the shielding gas is stopped to obtain the powder after the fluidization dispersion treatment.
3) And (3) feeding the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, and performing spheroidization on the powder, wherein the powder feeding speed is 15g/min, the treatment power is 20kw, the powder feeding air flow is 8L/min, the middle air flow is 35L/min, the side air flow is 40L/min, and collecting the powder after the plasma spheroidization after cooling to obtain the spheroidized powder.
4) Uniformly mixing the spheroidized powder with an organic binder (86% of polyformaldehyde, 4% of low-density polyethylene, 3% of vinyl acetate copolymer, 2% of stearic acid, 3% of microcrystalline wax and 2% of polypropylene) to prepare a granular feed, wherein the volume fraction of the powder in the feed is 52%;
5) Feeding the granular feed on a microinjection molding machine, and microinjection molding to obtain a tungsten blank with a required shape and size;
6) The organic binder in the tungsten blank is removed by adopting a proper process, and the degreasing process is to degrease in a catalytic degreasing furnace at 110 ℃ for 12 hours by adopting 90% concentrated nitric acid, so that a porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the thermal degreasing process are facilitated; then carrying out thermal sintering in a tubular furnace under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, heating to 200 ℃ at 0.5 ℃/min, preserving heat for 60min, heating to 450 ℃ at 1 ℃/min, preserving heat for 90min, heating to 550 ℃ at 0.8 ℃/min, preserving heat for 60min, heating to 650 ℃ at 1 ℃/min, preserving heat for 60min, heating to 750 ℃ at 3 ℃/min, preserving heat for 120min, heating to 950 ℃ at 3 ℃/min, preserving heat for 120min, heating to 1050 ℃ at 3 ℃/min, preserving heat for 180min, cooling to 900 ℃ at 5 ℃/min, cooling to 700 ℃ at 10 ℃/min, and cooling to room temperature. The finally prepared porous tungsten product with the complicated shape nano pore structure has low impurity content, uniform pores, grain size of 1.0 mu m, average pore diameter of 500nm, open porosity of 22 percent and open porosity of more than 98 percent of the total porosity.
Example 2
1) The raw material powder is commercial tungsten powder, the Fisher particle size is 0.6 mu m, and the purity is more than 99.9%;
2) The raw material powder is added into a fluidized bed, high-purity inert gas is firstly filled into the equipment from bottom to top to remove air before dispersion treatment, gas protection environment is provided for the powder, and the equipment is inflated and cleaned; after the air in the cavity of the fluidized bed is exhausted, the air is transferred to a heating device, high-purity inert gas with stable flow is continuously introduced in the treatment process of the fluidized bed, the flow speed of the gas flow is 2L/min, the heating temperature is 180 ℃, and the fluidization treatment is carried out for 120min at constant flow and constant temperature. After the fluidized bed dispersion treatment, the cavity of the fluidized bed is removed from the heating device, and high-purity inert shielding gas is continuously introduced, and after the cavity is cooled to room temperature in the air, the shielding gas is stopped to obtain the powder after the fluidization dispersion treatment.
3) And (3) feeding the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, and performing spheroidization on the powder, wherein the powder feeding speed is 10g/min, the treatment power is 15kw, the powder feeding air flow is 6L/min, the middle air flow is 30L/min, the side air flow is 35L/min, and collecting the powder after the plasma spheroidization after cooling to obtain the treated powder.
4) Uniformly mixing the spheroidized powder with an organic binder (such as polyformaldehyde 84%, low-density polyethylene 5%, vinyl acetate copolymer 3%, stearic acid 2%, microcrystalline wax 4% and polypropylene 2%), and preparing a granular feed, wherein the volume fraction of the powder in the feed is 48%;
5) Feeding the granular feed on a microinjection molding machine, and microinjection molding to obtain a tungsten blank with a required shape and size;
6) The organic binder in the tungsten blank is removed by adopting a proper process, and the degreasing process is to degrease in a catalytic degreasing furnace at 120 ℃ for 8 hours by adopting 95% concentrated nitric acid, so that a porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the thermal degreasing process are facilitated; then carrying out thermal sintering in a tubular furnace under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, heating to 200 ℃ at 0.3 ℃/min, preserving heat for 60min, heating to 450 ℃ at 0.5 ℃/min, preserving heat for 60min, heating to 550 ℃ at 0.8 ℃/min, preserving heat for 60min, heating to 650 ℃ at 1 ℃/min, preserving heat for 60min, heating to 750 ℃ at 2 ℃/min, preserving heat for 120min, heating to 950 ℃ at 3 ℃/min, preserving heat for 120min, heating to 1150 ℃ at 3 ℃/min, preserving heat for 180min, cooling to 900 ℃ at 3 ℃/min, cooling to 700 ℃ at 4 ℃/min, and cooling to room temperature at 10 ℃/min, thereby finally preparing the complex-shape nano-pore structure porous tungsten product with low impurity content, uniform pore size, average pore diameter of 450nm, open pore rate of 21 percent and open pore porosity of more than 97 percent of the total porosity.
Example 3
1) The raw material powder is commercial tungsten powder, the Fisher particle size is 0.4 mu m, and the purity is more than 99.9%;
2) The raw material powder is added into a fluidized bed, high-purity inert gas is firstly filled into the equipment from bottom to top to remove air before dispersion treatment, gas protection environment is provided for the powder, and the equipment is inflated and cleaned; after the air in the cavity of the fluidized bed is exhausted, the air is transferred to a heating device, high-purity inert gas with stable flow is continuously introduced in the treatment process of the fluidized bed, the flow speed of the gas flow is 1L/min, the heating temperature is 150 ℃, and the fluidization treatment is carried out for 180min at constant flow and constant temperature. After the fluidized bed dispersion treatment, the cavity of the fluidized bed is removed from the heating device, and high-purity inert shielding gas is continuously introduced, and after the cavity is cooled to room temperature in the air, the shielding gas is stopped to obtain the powder after the fluidization dispersion treatment.
3) And (3) feeding the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, and performing spheroidization on the powder, wherein the powder feeding speed is 5g/min, the treatment power is 10kw, the powder feeding air flow is 5L/min, the middle air flow is 25L/min, the side air flow is 30L/min, and the powder after the plasma spheroidization is cooled and then collected to obtain the treated powder.
4) Uniformly mixing the spheroidized powder with an organic binder (80% of polyformaldehyde, 3% of low-density polyethylene, 5% of vinyl acetate copolymer, 2% of stearic acid, 6% of microcrystalline wax and 4% of polypropylene) to prepare a granular feed, wherein the volume fraction of the powder in the feed is 45%;
5) Feeding the granular feed on a microinjection molding machine, and microinjection molding to obtain a tungsten blank with a required shape and size;
6) The organic binder in the tungsten blank is removed by adopting a proper process, and the degreasing process is to degrease in a catalytic degreasing furnace at 130 ℃ for 4 hours by adopting 90% of concentrated oxalic acid, so that a porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the thermal degreasing process are facilitated; then carrying out thermal sintering in a tubular furnace under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, heating to 200 ℃ at 0.2 ℃/min, preserving heat for 60min, heating to 450 ℃ at 0.5 ℃/min, preserving heat for 60min, heating to 550 ℃ at 0.5 ℃/min, preserving heat for 60min, heating to 650 ℃ at 1 ℃/min, preserving heat for 60min, heating to 750 ℃ at 2 ℃/min, preserving heat for 120min, heating to 950 ℃ at 2 ℃/min, preserving heat for 120min, heating to 1250 ℃ at 3 ℃/min, preserving heat for 180min, cooling to 900 ℃ at 3 ℃/min, cooling to 700 ℃ at 10 ℃/min, and cooling to room temperature at last, wherein the finally prepared porous tungsten product with the complicated shape nano pore structure has low impurity content, uniform pore size, grain size of 0.8 mu m, average pore diameter of 350nm, open porosity of 20 percent and open porosity of more than 96 percent of total porosity.
While the invention has been described with respect to preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention, and that any such changes and modifications as described in the above embodiments are intended to be within the scope of the invention.
Claims (3)
1. A method for preparing a porous tungsten product with a complicated shape and a nano pore structure is characterized in that fine-grained tungsten powder is used as a raw material, and the porous tungsten product with the complicated shape and the nano pore structure is prepared by adopting a method of combining a fluidization dispersion technology and a radio frequency plasma spheroidization technology to carry out dispersion grading spheroidization and microinjection forming on the powder, and the specific steps are as follows:
1) The raw material powder is fine-grained tungsten powder, the purity is more than 99.9%, and the granularity is less than 1 mu m;
2) The raw material powder is added into a fluidized bed, high-purity inert gas is firstly filled into the equipment from bottom to top to remove air before dispersion treatment, gas protection environment is provided for the powder, and the equipment is inflated and cleaned; after the air in the cavity of the fluidized bed is exhausted, transferring the air into a heating device, continuously introducing high-purity inert gas with stable flow in the fluidized bed treatment process, wherein the flow speed of the gas flow is 1-3L/min, the heating temperature is 100-280 ℃, and carrying out fluidization treatment for 100-180 min at constant flow and constant temperature; after the fluidized bed dispersion treatment, removing the fluidized bed cavity from the heating device, continuously introducing high-purity inert protective gas, and stopping introducing the protective gas after cooling to room temperature in air to obtain powder after the fluidization dispersion treatment;
3) Feeding the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, and performing spheroidization on the powder, wherein the powder feeding speed is 5-15 g/min, the treatment power is 5-25 kw, the powder feeding air flow is 5-10L/min, the medium air flow is 25-35L/min, the side air flow is 30-60L/min, and collecting the powder after the plasma spheroidization after cooling to obtain spheroidized powder;
4) Uniformly mixing the spheroidized powder with an organic binder, and preparing a granular feed;
5) According to different application scenes of porous tungsten products with nano pore structures, the requirements on the shapes and the sizes of the products are different, and a tungsten blank with the required shapes and the sizes is formed by microinjection;
6) The microinjection molding blank is subjected to catalytic degreasing in a catalytic degreasing furnace by adopting concentrated nitric acid or concentrated oxalic acid as a catalytic medium, so as to remove part of binder;
7) Under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9%, carrying out thermal sintering treatment on the dried sample obtained in the step 6) in a tungsten wire sintering furnace to prepare a porous tungsten product with a complicated shape and a nano pore structure;
the thermal sintering treatment process in the step 7) is that the temperature is raised to 200 ℃ at 0.2-0.5 ℃/min, the temperature is kept for 30-60 min, the temperature is raised to 450 ℃ at 0.5-1 ℃/min, the temperature is kept for 40-90 min, the temperature is raised to 550 ℃ at 0.5-0.8 ℃/min, the temperature is kept for 30-60 min, the temperature is raised to 650 ℃ at 0.5-1 ℃/min, the temperature is kept for 30-60 min, the temperature is raised to 750 ℃ at 2-3 ℃/min, the temperature is kept for 60-120 min, the temperature is raised to 950 ℃ at 2-3 ℃/min, the temperature is kept for 60-120 min, the temperature is raised to 1000-1250 ℃ at 1-3 ℃/min, the temperature is kept for 60-180 min, the temperature is lowered to 900 ℃ at 1-3 ℃/min, the temperature is lowered to 700 ℃ at 5-10 ℃/min, and the temperature is lowered to room temperature at 2-5 ℃/min;
the grain size of the sintered porous tungsten product with the nano pore structure is less than or equal to 1 mu m, the pore diameter is 100-800 nm, the porosity is 15-35%, the open pore porosity accounts for more than 95% of the total porosity, the pores are uniform, and the connectivity is good.
2. The method for preparing a porous tungsten article with a complicated shape and a nano pore structure according to claim 1, wherein the ratio of the organic binder in the step 4) is: 80-88% of polyformaldehyde, 3-8% of low-density polyethylene, 3-10% of vinyl acetate copolymer, 2-5% of stearic acid, 2-10% of microcrystalline wax and 2-7% of polypropylene.
3. The method for preparing the porous tungsten product with the complicated shape nano pore structure according to claim 1, wherein the concentration of the concentrated nitric acid or the concentrated oxalic acid adopted in the step 6) is 86% -95%, the catalytic degreasing is carried out for 1-12 hours at the temperature of 110-150 ℃, the porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the subsequent thermal sintering process are facilitated.
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