Preparation method of spherical tungsten alloy powder for 3D printing

Abstract

The invention provides a preparation method of spherical tungsten alloy powder for 3D printing, and belongs to the technical field of metal additive manufacturing. According to the method, fine-particle tungsten powder and tungsten oxide powder are mixed to serve as a composite tungsten source, the volatilization-deposition characteristic in the tungsten oxide hydrogen reduction process is utilized, wet hydrogen reduction is conducted on spray-dried precursor aggregates, and the purpose of auxiliary sintering is achieved. The reduced tungsten alloy intermediate powder inherits the spray-dried spherical morphology, the cohesion strength is remarkably improved, meanwhile, loose and porous structures are kept in particles, the stability of the plasma spheroidizing powder feeding process can be effectively guaranteed, heat is easier to absorb and transfer in a plasma torch, energy consumption can be reduced in actual production, and the production efficiency is improved. And higher spheroidizing efficiency and spheroidizing rate are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of metal additive manufacturing, and specifically relates to a method for preparing spherical tungsten alloy powder for 3D printing. Background Art

[0002] The refractory metal tungsten and its alloys have excellent properties such as high melting point, high hardness, high high-temperature strength, high elastic modulus, low thermal expansion coefficient, good conductivity and corrosion resistance. They are widely used in cutting-edge fields such as aerospace, national defense and military industry, nuclear industry, medical equipment, and electronics. Powder metallurgy is the most commonly used method for preparing tungsten alloys. However, due to the high brittleness of tungsten alloys at room temperature, some parts with complex structural features such as thin walls, curved surfaces, and porous structures are difficult to prepare by conventional powder metallurgy, which limits the wider application of tungsten alloy materials in the industrial field. Compared with traditional powder metallurgy methods, 3D printing has unique technical advantages such as high material utilization, high manufacturing flexibility, small processing allowance, few structural design constraints, near-net forming of complex structural parts, and rapid response to structural design changes. It has become one of the current hot spots in the preparation and production of tungsten alloy materials.

[0003] Powder bed fusion and direct energy deposition are the two most commonly used 3D printing technologies for tungsten alloy additive manufacturing. The morphology and particle size of the raw powder are important factors affecting the performance of 3D printed tungsten alloy parts. Compared with irregular powders, spherical powders have a higher energy absorption rate, which is conducive to the formation of continuous scanning trajectories and the densification of formed parts. Whether it is powder bed fusion or direct energy deposition, the raw powder must meet the requirements of high sphericity, good fluidity, high bulk density, small particle size and narrow particle size distribution. With the increasing demand for complex and precise structure tungsten alloy parts in the medical equipment, electronic information and other industries, and the urgent requirements for rapid prototyping of high-performance tungsten alloy parts in the fields of aerospace, weaponry and equipment, spherical powder as a core material has become the greatest value of tungsten alloy 3D printing additive manufacturing.

[0004] Laser 3D printing powder generally requires spherical powder with a particle size range of 5 to 250 μm. The existing technology usually uses various molten metal atomization methods to produce spherical powders that meet the particle size requirements of 3D printing, but this type of method is mainly used to produce low-melting-point metal and alloy powders, such as copper powder, aluminum powder, nickel powder and stainless steel powder, etc., but it is powerless for metals, alloys and ceramics with high melting points. In the existing technology, radio frequency plasma spheroidization is used to spheroidize high-melting-point metals and alloys. However, plasma spheroidization requires the preparation of precursor particles with certain fluidity, uniformity and agglomeration to ensure the plasma spheroidization effect. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing spherical tungsten alloy powder for laser 3D printing, which has good sphericity and fluidity, high density and uniform distribution of alloy components, in response to the above needs.

[0006] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions: A method for preparing spherical tungsten alloy powder for 3D printing, comprising the following steps: Step 1: According to the designed proportion of the tungsten alloy, the tungsten source powder composed of fine-grained tungsten powder and tungsten oxide powder, the alloy element powder, the solvent, the dispersant, and the binder are ball-milled and mixed to prepare a stable slurry with a solid content of 50% to 85%. The slurry is spray-dried and spheroidized by a centrifugal spray drying device; Step 2: Use the multi-temperature zone tubular reduction furnace equipment commonly used in industrial production to perform wet hydrogen reduction assisted sintering treatment on the spheroidized granulated powder obtained in step 1. The reduction adopts the following two processes: A) Wet hydrogen-dry hydrogen isothermal reduction: The reduction process is divided into two stages, humidified hydrogen and dry hydrogen are introduced respectively, the reduction temperature is 750~880℃, the hydrogen dew point of the first stage is -15~20℃, the flow rate is 10~25m / min, and the reduction time is 20~40min. The hydrogen dew point of the second stage is ≤-50℃, the flow rate is 30~50m / min, and the reduction time is 30~80min. This process is suitable for the rapid development of tungsten alloy powders with different compositions.

[0007] B) Staged temperature rise wet hydrogen reduction: The reduction process adopts staged temperature rise, and humidified hydrogen is introduced. The first stage reduction temperature is 700-860℃, the reaction time is 20-50min, and the second stage reduction temperature is 890-1100℃, the reaction time is 30-70min; the hydrogen dew point is -40--10℃, the hydrogen flow rate is 30-55m / min, which is suitable for continuous production.

[0008] Step 3: The reduced intermediate powder is subjected to plasma spheroidization treatment, and tungsten alloy powder suitable for laser 3D printing is obtained after classification.

[0009] Furthermore, in step one, the fine particle tungsten powder has an average particle size of 0.1 to 5 μm, the tungsten oxide powder is selected from one of yellow tungsten, purple tungsten and blue tungsten, has an average particle size of 0.02 to 2 μm, and the mass ratio of tungsten powder to tungsten oxide is 4:1 to 10:1.

[0010] Furthermore, in step 1, the alloying element is one or more transition metal elements, and the average particle size of the alloying element single substance powder is 0.2 to 10 μm.

[0011] Furthermore, the method is also applicable to molybdenum alloy powder. When preparing molybdenum alloy powder, it is only necessary to replace the molybdenum source with fine-grained molybdenum powder and molybdenum oxide powder in the same particle size range.

[0012] The solvent in step 1 of the present invention can be anhydrous ethanol or other ball milling solvents conventional in the art, the dispersant and binder can be polyethylene glycol, polyethylene, polypropylene, polyvinyl alcohol or polytetrafluoroethylene conventional in the art, and the classification can be conventional screening or air flow classification.

[0013] Technical effects and advantages of the present invention: (1) The present invention adopts wet grinding and mixing to prepare the spray drying slurry, which can effectively solve the component segregation and agglomeration problems caused by the density and size differences of the raw material powder, realize the uniform mixing and dispersed distribution of the alloy components, and ensure the composition uniformity and organizational uniformity of the plasma spheroidized tungsten alloy powder.

[0014] (2) By adjusting the spray drying parameters such as slurry concentration, tungsten source ratio, centrifugal atomization nozzle speed, etc., the particle size of tungsten alloy precursor can be flexibly controlled. The spherical tungsten alloy powder products after spheroidization can be widely used in various near-net-shape manufacturing technologies such as laser powder bed melting, laser stereo forming, electron beam powder bed melting, and injection molding.

[0015] (3) The present invention mixes fine-grained tungsten powder and tungsten oxide powder as a composite tungsten source, and utilizes the volatilization-deposition characteristics of tungsten oxide during the wet hydrogen reduction process. The spray-dried precursor pellets can be subjected to wet hydrogen reduction to achieve the sintering purpose, which can effectively maintain the spherical morphology of the spray-dried powder particles. At the same time, the cohesive strength of the tungsten alloy pellets can be significantly improved. The obtained intermediate powder has good fluidity and is not easy to break, which can effectively ensure the stability of the plasma spheroidization powder feeding process.

[0016] (4) The tungsten alloy pellet intermediate powder obtained by wet hydrogen reduction assisted sintering is looser, more porous and has a higher specific surface area than the pellets obtained by direct sintering of conventional metal powders due to the addition of tungsten oxide. It is easier to absorb and transfer heat in the plasma torch, with a low temperature gradient in the pellets and high energy utilization. In actual production, it can reduce energy consumption and obtain higher spheroidization efficiency and spheroidization rate.

[0017] (5) Molybdenum oxide and tungsten oxide have similar volatilization-deposition characteristics during wet hydrogen reduction. The preparation method of the present invention is also applicable to the preparation of molybdenum alloys. It is only necessary to replace the molybdenum source with fine-grained molybdenum powder and molybdenum oxide powder with the same particle size range. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 5~25 μm spherical tungsten powder for 3D printing prepared in Example 1 (a low magnification; b high magnification); Figure 2 15~53 μm 97W-2Ni-Fe powder for 3D printing prepared in Example 2 (a low magnification; b high magnification); Figure 3 53-105 μm spherical W-50Mo powder for 3D printing prepared in Example 3 (a low magnification SEM of intermediate powder after reduction; b high magnification SEM of intermediate powder after reduction; c low magnification SEM of spherical W-50Mo powder; d high magnification SEM of spherical W-50Mo powder); Figure 4 Comparative Example 1: Morphology of 5-25 μm spherical tungsten powder for 3D printing prepared without tungsten oxide addition; Figure 5 Comparative Example 2: Morphology of 5~25 μm spherical tungsten powder for 3D printing prepared by non-wet hydrogen reduction assisted sintering. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example 1: Preparation of 5~25 μm spherical tungsten powder for 3D printing.

[0021] According to the mass ratio of tungsten to tungsten trioxide of 4:1, 2kg of W powder with an average particle size of 0.5μm and 0.5kg of tungsten trioxide with an average particle size of 0.02μm were ball-milled and mixed with 37.5g of polyethylene glycol and 1071g of anhydrous ethanol to form a stable slurry with a solid content of 70%. The precursor powder was spray-dried and granulated by a centrifugal spray drying device. The spray drying process was as follows: the inlet air temperature was 180℃ and the atomizer speed was 18000 rpm. In a multi-temperature zone tubular reduction furnace, the precursor powder was reduced by a wet hydrogen-dry hydrogen isothermal reduction process. The reduction process was as follows: first, under a humidified hydrogen atmosphere, the reduction was carried out at 850℃ for 30min, the hydrogen dew point was -10℃, and the flow rate was 15m / min; then, under a dry hydrogen atmosphere, the reduction was carried out at 850℃ for 60min, the hydrogen dew point was -60℃, and the flow rate was 40m / min. The reduced intermediate powder was treated by plasma spheroidization, and 5~25 μm spherical tungsten powder for 3D printing was obtained after classification. The plasma spheroidization process is as follows: powder feeding rate 37.5g / min, power 40KW, side gas 1 (argon) 52slpm, center gas (argon) 19.5slpm, side gas 2 (hydrogen) 10slpm, carrier gas (argon) 4.5slpm, pressure 15psi. The morphology and performance of 5~25 μm spherical tungsten powder for 3D printing are as follows Figure 1 And as shown in Table 1.

[0022] Table 1 Performance of 5~25 μm spherical tungsten powder for 3D printing Powder ingredients <![CDATA[Density (g / cm 3 )]]> <![CDATA[Bulk density (g / cm 3 )]]> Fluidity(s / 50g) Oxygen content Particle size distribution W 19.11 9.92 9.7 0.0181% <![CDATA[D 10 =7.2 µmD 50 =15.9 µmD 90 =22.1 µm]]>

[0023] Example 2: Preparation of 15~53 μm spherical tungsten-nickel-iron powder for 3D printing.

[0024] According to the mass ratio of tungsten to tungsten trioxide of 5:1, 2kg of W powder with an average particle size of 0.5μm, 0.4kg of tungsten trioxide with an average particle size of 0.02μm, 48g of nickel powder with an average particle size of 1μm and 24g of iron powder were ball-milled with 47.8g of polyethylene glycol and 1287g of anhydrous ethanol to prepare a stable slurry with a solid content of 65%. The precursor powder was spray-dried and granulated by a centrifugal spray drying device. The spray drying process was as follows: the inlet air temperature was 170℃ and the atomizer speed was 15000 rpm. In the multi-temperature zone tubular reduction furnace equipment, the precursor powder was reduced by a staged heating wet hydrogen reduction process. The reduction process was as follows: in a humidified hydrogen atmosphere, reduction at 800℃ for 30 min, reduction at 1050℃ for 60 min, hydrogen dew point of -20℃, and flow rate of 50m / min. The reduced intermediate powder was treated by plasma spheroidization, and 15~53 μm spherical 97W-2Ni-Fe powder for 3D printing was obtained after classification. The plasma spheroidization process is: powder feeding rate 50g / min, power 40KW, side gas 1 (argon) 52slpm, center gas (argon) 19.5slpm, side gas 2 (hydrogen) 8slpm, carrier gas (argon) 4.5slpm, pressure 15psi. The morphology and performance of 97W-2Ni-Fe powder for 15~53 μm 3D printing are as follows Figure 2 And as shown in Table 2.

[0025] Table 2 Properties of 97W-2Ni-Fe powder for 15~53 μm 3D printing Powder ingredients <![CDATA[Density (g / cm 3 )]]> <![CDATA[Bulk density (g / cm 3 )]]> Fluidity(s / 50g) Oxygen content Particle size distribution 97W-2Ni-Fe 18.23 9.11 10.34 0.0446% <![CDATA[D 10 =19.2 µmD 50 =37.8 µmD 90 =46.6 µm]]>

[0026] Example 3: Preparation of 53~105 μm spherical tungsten and molybdenum powders for 3D printing.

[0027] According to the mass ratio of molybdenum to molybdenum oxide of 4:1, 1.2 kg of Mo powder with an average particle size of 0.5 μm, 0.3 kg of molybdenum oxide with an average particle size of 0.1 μm, and 1.4 kg of W powder with an average particle size of 1 μm were ball-milled and mixed with 58 g of polyethylene glycol and 1243 g of anhydrous ethanol to form a stable slurry with a solid content of 70%. The precursor powder was spray-dried and granulated by a centrifugal spray drying device. The spray drying process was as follows: the inlet air temperature was 160 ° C and the atomizer speed was 10000 rpm. In the multi-temperature zone tubular reduction furnace equipment, the precursor powder was reduced by a staged heating wet hydrogen reduction process. The reduction process was as follows: in a humidified hydrogen atmosphere, reduction at 850 ° C for 30 min, reduction at 1050 ° C for 60 min, hydrogen dew point -30 ° C, and flow rate 50 m / min. The reduced intermediate powder was treated by plasma spheroidization, and 53~105 μm spherical W-50Mo powder for 3D printing was obtained after classification. The plasma spheroidization process is: powder feeding rate 50g / min, power 40KW, side gas 1 (argon) 52slpm, center gas (argon) 19.5slpm, side gas 2 (hydrogen) 9slpm, carrier gas (argon) 4.5slpm, pressure 15psi. The morphology and performance of 53~105 μm spherical W-50Mo powder for 3D printing are as follows Figure 3 As shown in Table 3, Figure 3 (a) and (b) are intermediate powders obtained by reduction sintering. Figure 3 (c) and (d) are spherical tungsten-molybdenum powders for 3D printing obtained after plasma spheroidization.

[0028] Table 3 Performance of 53~105 μm spherical W-50Mo powder for 3D printing Powder ingredients <![CDATA[Density (g / cm 3 )]]> <![CDATA[Bulk density (g / cm 3 )]]> Fluidity(s / 50g) Oxygen content Particle size distribution W-50wt.%Mo 13.21 6.93 10.22 0.0242% <![CDATA[D 10 =58.4 µmD 50 =82.6 µmD 90 =99.1 µm]]>

[0029] Comparative Example 1: Preparation of 5~25 μm spherical tungsten powder for 3D printing without tungsten oxide addition.

[0030] According to the mass ratio of tungsten to tungsten trioxide of 4:1, 2kg of W powder with an average particle size of 0.5μm and 0.5kg of tungsten trioxide with an average particle size of 0.02μm were ball-milled and mixed with 37.5g of polyethylene glycol and 1071g of anhydrous ethanol to form a stable slurry with a solid content of 70%. The precursor powder was spray-dried and granulated by a centrifugal spray drying device. The spray drying process was as follows: the inlet air temperature was 180℃ and the atomizer speed was 18000 rpm. In a multi-temperature zone tubular reduction furnace, the precursor powder was reduced by a wet hydrogen-dry hydrogen isothermal reduction process. The reduction process was as follows: first, under a humidified hydrogen atmosphere, the reduction was carried out at 850℃ for 30min, the hydrogen dew point was -10℃, and the flow rate was 15m / min; then, under a dry hydrogen atmosphere, the reduction was carried out at 850℃ for 60min, the hydrogen dew point was -60℃, and the flow rate was 40m / min. The reduced intermediate powder was treated by plasma spheroidization, and 5~25 μm spherical tungsten powder for 3D printing was obtained after classification. The plasma spheroidization process is as follows: powder feeding rate 37.5g / min, power 40KW, side gas 1 (argon) 52slpm, center gas (argon) 19.5slpm, side gas 2 (hydrogen) 10slpm, carrier gas (argon) 4.5slpm, pressure 15psi. The morphology and performance of 5~25 μm spherical tungsten powder for 3D printing are as follows Figure 4 And as shown in Table 4.

[0031] Table 4 Properties of 5~25 μm spherical tungsten powder for 3D printing prepared without tungsten oxide addition Powder ingredients <![CDATA[Density (g / cm 3 )]]> <![CDATA[Bulk density (g / cm 3 )]]> Fluidity(s / 50g) Oxygen content Particle size distribution W 17.34 7.42 14.8 0.0461% <![CDATA[D 10 =9.2 µmD 50 =18.7 µmD 90 =29.3 µm]]> Compared with Example 1, Comparative Example 1 does not add tungsten oxide to prepare spherical tungsten powder for 3D printing. The strength of the intermediate powder agglomerates obtained in the reduction sintering process is low. During the plasma spheroidization process, the agglomerate shape cannot be maintained and is broken into fine W particles. Subsequently, the agglomerates are bonded into irregular W clusters during the spheroidization process, which seriously damages the performance of the powder.

[0032] Comparative Example 2: Preparation of 5~25 μm spherical tungsten powder for 3D printing without wet hydrogen reduction assisted sintering.

[0033] According to the mass ratio of tungsten to tungsten trioxide of 4:1, 2kg of W powder with an average particle size of 0.5μm and 0.5kg of tungsten trioxide with an average particle size of 0.02μm were ball-milled and mixed with 37.5g of polyethylene glycol and 1071g of anhydrous ethanol to form a stable slurry with a solid content of 70%. The precursor powder was spray-dried and granulated by a centrifugal spray drying device. The spray drying process was as follows: the air inlet temperature was 180℃ and the atomizer speed was 18000 rpm. In a multi-temperature zone tubular reduction furnace, the precursor powder was reduced by a dry hydrogen isothermal reduction process. The reduction process was as follows: in a dry hydrogen atmosphere, reduction at 850℃ for 90min, hydrogen dew point -60℃, and flow rate 40m / min. The reduced intermediate powder was treated by plasma spheroidization, and 5~25 μm spherical tungsten powder for 3D printing was obtained after classification. The plasma spheroidization process is as follows: powder feeding rate is 37.5 g / min, power is 40KW, side gas 1 (argon) is 52 slpm, center gas (argon) is 19.5 slpm, side gas 2 (hydrogen) is 10 slpm, carrier gas (argon) is 4.5 slpm, and pressure is 15psi. The morphology and properties of 5~25 μm spherical tungsten powder for 3D printing are shown in Figure 5 and Table 5.

[0034] Table 5 5~25 μm spherical tungsten powder for 3D printing prepared by non-wet hydrogen reduction assisted sintering Powder ingredients <![CDATA[Density (g / cm 3 )]]> <![CDATA[Bulk density (g / cm 3 )]]> Fluidity(s / 50g) Oxygen content Particle size distribution W 16.91 7.12 15.3 0.0857% <![CDATA[D 10 =8.2 µmD 50 =16.9µmD 90 =24.6 µm]]> Compared with Example 1, in Comparative Example 2, the precursor powder is obtained by isothermal reduction spray drying with dry hydrogen. The volatilization and deposition effect of tungsten oxide in a dry hydrogen atmosphere is not significant. The cohesive strength of the intermediate powder agglomerates after reduction is broken into fine W particles during the plasma spheroidization process. Subsequently, the fine W particles are bonded into irregular clusters during the spheroidization process, which seriously damages the performance of the powder.

[0035] The above describes in detail the preferred implementation of this patent, but this patent is not limited to the above implementation. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of this patent.

Claims

1. A method for preparing spherical tungsten alloy powder for 3D printing, characterized in that: The following steps are involved: Step 1: According to the designed proportion of the tungsten alloy composition, the tungsten source powder composed of fine-grained tungsten powder and tungsten oxide powder, the alloy element powder, the solvent and the binder are ball-milled and mixed to prepare a stable slurry with a solid content of 50% to 85%. The slurry is spray-dried and spheroidized by a centrifugal spray drying device to obtain a precursor powder; Step 2: using a multi-temperature zone tubular reduction furnace to perform wet hydrogen reduction assisted sintering on the spherical granulated powder obtained in step 1; Step 3: The reduced intermediate powder is subjected to plasma spheroidization treatment, and tungsten alloy powder suitable for 3D printing is obtained after classification.

2. The method for preparing spherical tungsten alloy powder for 3D printing according to claim 1, characterized in that: In step 1, the fine particle tungsten powder has an average particle size of 0.1 to 5 μm, the tungsten oxide powder is selected from one of yellow tungsten, purple tungsten and blue tungsten, has an average particle size of 0.02 to 2 μm, and the mass ratio of tungsten powder to tungsten oxide is 4:1 to 10:

1.

3. The method for preparing spherical tungsten alloy powder for 3D printing according to claim 1, characterized in that: In step 1, the alloying element is one or more transition metal elements, and the average particle size of the alloying element single substance powder is 0.2 to 10 μm.

4. The method for preparing spherical tungsten alloy powder for 3D printing according to claim 1, characterized in that: In step 1, the ball milling mixing also includes a dispersant.

5. The method for preparing spherical tungsten alloy powder for 3D printing according to claim 1, characterized in that: In step 2, wet hydrogen-dry hydrogen isothermal reduction is used: The reduction process is divided into two stages, humidified hydrogen and dry hydrogen are introduced respectively, and the reduction temperature is 750-880°C. In the first stage, the hydrogen dew point is -15-20°C, the flow rate is 10-25m / min, and the reduction time is 20-40min; in the second stage, the hydrogen dew point is ≤-50°C, the flow rate is 30-50m / min, and the reduction time is 30-80min.

6. The method for preparing spherical tungsten alloy powder for 3D printing according to claim 1, characterized in that: In step 2, wet hydrogen reduction is performed by step-wise heating: The reduction process adopts staged temperature increase, and humidified hydrogen is introduced. The first stage reduction temperature is 700-860°C, the reaction time is 20-50min, and the second stage reduction temperature is 890-1100°C, the reaction time is 30-70min; the hydrogen dew point is -40--10°C, and the hydrogen flow rate is 30-55m / min.

7. A method for preparing spherical molybdenum alloy powder for 3D printing, characterized in that: The preparation method according to any one of claims 1 to 6 is adopted, and the tungsten source powder is replaced by molybdenum source powder, and the molybdenum source powder adopts fine-grained molybdenum powder and molybdenum oxide powder.

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