Coated high-specific-gravity tungsten alloy and preparation method thereof

Abstract

The invention discloses a coated high-specific-gravity tungsten alloy and a preparation method thereof. The preparation method of the coated high-specific-gravity tungsten alloy comprises the following steps that pure tungsten powder and nickel-based intermediate alloy powder are placed in a W-shaped double-cone mixer to be mixed for 5-30 min, mixed powder is obtained, and the mass ratio of the pure tungsten powder to the nickel-based intermediate alloy powder is (4-49): 1; then the mixed powder is placed in radio frequency plasma spheroidizing equipment to be subjected to spheroidizing treatment, the power of the radio frequency plasma spheroidizing equipment is 50-120 Kw, the carrier gas flow is 2-15 L / min, the rotating speed of a powder feeder is 5-35 r / min, the mixed powder is heated, the pure tungsten powder in the mixed powder is in a molten state, and the nickel-based intermediate alloy powder in the mixed powder is in a gasified state; and synchronous cooling is kept, so that the nickel-based intermediate alloy powder is condensed and coats the surface of the spheroidized pure tungsten powder, and the coated high-specific-gravity tungsten alloy is formed. Through the preparation method provided by the invention, the problems of powder agglomeration and non-uniform powder components are effectively avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy material preparation, and in particular relates to a coated high-density tungsten alloy and a preparation method thereof. Background Art

[0002] High specific gravity tungsten alloy is a two-phase alloy composed of tungsten particles (mass fraction is 80%-98%) and a bonding phase. The bonding phase is generally composed of two or more elements such as nickel, iron, copper, cobalt, and manganese. Its density can be as high as 16.5-18.8g / cm 3 High-density tungsten alloys have a wide range of applications in defense industry and civilian industry, including aerospace, weapons, automobiles, energy, and medical treatment.

[0003] The preparation of traditional high-density tungsten alloys requires powder metallurgy methods such as powder mixing, pressing, sintering and post-processing. At present, compression molding can only press green billets with simple and neat shapes and small sizes. For parts with complex shapes, various forming problems such as uneven green billet density and inability to demold will occur. Although the use of additive manufacturing methods (such as powder mixing or ball milling) can solve the problem of complex parts being unable to demold, there are serious powder agglomeration and uneven powder composition, which seriously affect the uniformity of tungsten alloy preparation. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a coated high-density tungsten alloy and a preparation method thereof, aiming to solve the technical problems of serious powder agglomeration and uneven powder composition in the current high-density tungsten alloy additive manufacturing process.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a coated high-density tungsten alloy, comprising the following steps:

[0006] Mixing treatment: placing pure tungsten powder and nickel-based master alloy powder in a W-type double cone mixer and mixing for 5-30 minutes to obtain a mixed powder, wherein the mass ratio of the pure tungsten powder to the nickel-based master alloy powder is (4-49):1;

[0007] Spheroidization and coating treatment: The mixed powder is placed in a radio frequency plasma spheroidization device for spheroidization treatment. The power of the radio frequency plasma spheroidization device is 50-120Kw, the carrier gas flow rate is 2-15L / min, and the powder feeder speed is 5-35r / min. The mixed powder is heated so that the pure tungsten powder in the mixed powder is in a molten state and the nickel-based master alloy powder is in a gasified state; synchronous cooling is maintained so that the nickel-based master alloy powder is condensed and coated on the surface of the spheroidized pure tungsten powder to form a coated high-density tungsten alloy.

[0008] Furthermore, the laser particle size distribution of the nickel-based master alloy powder is D90 ≤35μm.

[0009] Furthermore, the nickel-based master alloy powder is any one of nickel-copper master alloy powder, nickel-iron master alloy powder, nickel-chromium master alloy powder, nickel-molybdenum master alloy powder, and nickel-cobalt master alloy powder.

[0010] Furthermore, the nickel content in the nickel-based master alloy is 50%-90%.

[0011] Furthermore, the pure tungsten powder has a Fisher particle size of 4-12 μm.

[0012] Furthermore, in the spheroidization and coating treatment step: the system pressure of the radio frequency plasma spheroidization equipment is 100-150Kpa, the inner ring gas flow rate is 30-100L / min, the outer ring gas flow rate is 60-200L / min, and the side gas flow rate is 60-200L / min.

[0013] Furthermore, the inner ring gas, the outer ring gas, the side gas and the carrier gas are all argon.

[0014] Furthermore, the frequency of the W-shaped double-cone mixer is 15-75 Hz.

[0015] Furthermore, the purity of the pure tungsten powder is 99%-99.9%.

[0016] The present application also discloses a coated high-density tungsten alloy, which is prepared by the coated high-density tungsten alloy preparation method as described above.

[0017] The beneficial effects of the present invention are as follows: compared with the prior art, the coated high-density tungsten alloy and the preparation method thereof in the present invention effectively ensure uniform mixing of pure tungsten powder and nickel-based master alloy powder by placing pure tungsten powder and nickel-based master alloy powder in a W-type double cone mixer and stirring for 5-30 minutes; by placing the uniformly mixed powder in a radio frequency plasma spheroidizing device, controlling the power, carrier gas flow rate, and powder feeder speed and other parameters of the radio frequency plasma spheroidizing device, and based on the higher melting point characteristic of pure tungsten powder relative to nickel-based master alloy powder, during the heating process of the mixed powder, the pure tungsten powder is ensured to be in a molten state, while the nickel-based master alloy powder is in a gasified state; then, synchronous cooling is maintained, and the pure tungsten powder is The nickel-based master alloy powder is condensed into spherical droplets under the action of its own surface tension to form crystal nucleus sites for cooling and solidification, which improves the nucleation rate during the solidification process and makes the nickel-based master alloy powder evenly condense on the surface of the spheroidized tungsten powder, avoiding powder agglomeration; through the gasification treatment of the nickel-based master alloy powder, it can ensure the synchronous gasification and volatilization of the higher melting point component and the lower melting point component of the nickel-based master alloy powder during the gasification process, avoiding the uneven composition caused by the pre-gasification and volatilization of the lower melting point component in the master alloy at high temperature and the retention of the higher melting point component, ensuring the uniform composition of the tungsten-based alloy powder, and effectively ensuring the small composition fluctuation and high organizational uniformity of the parts obtained by subsequent 3D printing.

[0018] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0020] Figure 1 A flow chart of a method for preparing a coated high-density tungsten alloy according to an embodiment of the present invention;

[0021] Figure 2 This is a SEM scan of the spherical heavy tungsten alloy powder coated with nickel-iron alloy in the present invention;

[0022] Figure 3 This is the distribution diagram of each element of the spherical heavy tungsten alloy powder coated with nickel-iron alloy analyzed by the EDS energy spectrometer of the present invention. DETAILED DESCRIPTION

[0023] like Figure 1 As shown, this embodiment proposes a coated high-density tungsten alloy and a preparation method thereof, comprising the following steps:

[0024] S01: Mixing treatment: placing pure tungsten powder and nickel-based master alloy powder in a W-type double cone mixer and mixing for 5-30 minutes to obtain a mixed powder, wherein the mass ratio of the pure tungsten powder to the nickel-based master alloy powder is (4-49):1;

[0025] S02: Spheroidization and coating treatment: Place the mixed powder in a radio frequency plasma spheroidization device for spheroidization treatment. The power of the radio frequency plasma spheroidization device is 50-120Kw, the carrier gas flow rate is 2-15L / min, and the powder feeder speed is 5-35r / min. The mixed powder is heated so that the pure tungsten powder in the mixed powder is in a molten state and the nickel-based master alloy powder is in a gasified state; synchronous cooling is maintained so that the nickel-based master alloy powder is condensed and coated on the surface of the spheroidized pure tungsten powder to form a coated high-density tungsten alloy.

[0026] In the present application, pure tungsten powder and nickel-based master alloy powder are placed in a W-type double cone mixer and stirred for 5-30 minutes to effectively ensure that the pure tungsten powder and the nickel-based master alloy powder are evenly mixed; the evenly mixed powder is placed in a radio frequency plasma spheroidizing device, the power, carrier gas flow rate, and powder feeder speed of the radio frequency plasma spheroidizing device are controlled, and based on the higher melting point characteristics of pure tungsten powder relative to nickel-based master alloy powder, the mixed powder is ensured to be in a molten state and the nickel-based master alloy powder in a gasified state during heating; then synchronous cooling is maintained, and the pure tungsten powder is condensed into spherical droplets under the action of its own surface tension. The nickel-based master alloy powder is cooled and solidified to form crystal nucleus sites, which improves the nucleation rate during the solidification process and makes the nickel-based master alloy powder evenly condense on the surface of the spheroidized tungsten powder, avoiding powder agglomeration. Through the gasification treatment of the nickel-based master alloy powder, the higher melting point component and the lower melting point component of the nickel-based master alloy powder can be ensured to be vaporized and volatilized synchronously during the gasification process, avoiding the uneven composition caused by the lower melting point component in the master alloy being vaporized and volatilized at high temperature in advance and the higher melting point component being retained, ensuring the uniform composition of the tungsten-based alloy powder, and effectively ensuring the small composition fluctuation and high organizational uniformity of the parts obtained by subsequent 3D printing.

[0027] Preferably, the mixing time in the mixing step is 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc. Of course, according to actual conditions and specific needs, the mixing time can also be set to other ranges, which is not the only limitation here.

[0028] Preferably, the mass ratio of pure tungsten powder to nickel-based master alloy powder in the mixing treatment step can be 4:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 49:1, etc., and can be adjusted accordingly according to actual conditions.

[0029] Preferably, the raw material purity of the pure tungsten powder is 99%-99.9%. By selecting tungsten powder with higher purity, on the one hand, the melting point of the pure tungsten powder is effectively guaranteed to be higher than the melting point of the nickel-based master alloy powder, and on the other hand, the composition of the spheroidized tungsten powder coated with the nickel-based master alloy powder is uniform, and at the same time, the influence of impurities in the tungsten powder with lower purity on the nucleation rate of the tungsten powder is avoided.

[0030] The pure tungsten powder has a Fischer-Tropsch particle size of 4-12 μm. Specifically, the pure tungsten powder may have a Fischer-Tropsch particle size of 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, etc. By controlling the particle size of the pure tungsten powder, the coarse grain structure of the subsequent additively manufactured tungsten-based alloy is avoided, which affects the performance of the subsequent products.

[0031] Preferably, the power of the radio frequency plasma spheroidization equipment is 60Kw, 70Kw, 80Kw, 90Kw, 100Kw, 110Kw, 120Kw, etc. The specific power selected can be based on the time required for the reaction, which is not limited here.

[0032] Preferably, the frequency of the W-type double cone mixer is 15-75 Hz. Specifically, the frequency can be 50 Hz, 55 Hz, 60 Hz, 65 Hz, 70 Hz, 75 Hz, etc. By controlling the frequency of the W-type double cone mixer, the high-speed rotating stirring blades can break up the agglomerated materials, so that the materials are quickly mixed in the cylinder to achieve a uniform effect.

[0033] Preferably, the laser particle size distribution of the nickel-based master alloy powder is D 90 ≤35μm. By limiting the laser particle size distribution distance of the nickel-based master alloy powder, it is effectively avoided that the nickel-based master alloy powder is too coarse to affect the gasification effect, thereby affecting the subsequent coating effect of high-density tungsten alloy.

[0034] In the present application, the nickel-based master alloy powder is any one of nickel-copper master alloy powder, nickel-iron master alloy powder, nickel-chromium master alloy powder, nickel-molybdenum master alloy powder, and nickel-cobalt master alloy powder. By selecting nickel alloys, on the one hand, nickel has a high surface tension and is easy to spheroidize. On the other hand, after spheroidization, the nickel-based alloy powder has high sphericity, good fluidity and powder spreading performance, which is beneficial to the subsequent 3D printing process.

[0035] In the present application, nickel-iron, nickel-copper, nickel-molybdenum, nickel-chromium, nickel-cobalt and other binding phase components are made into an intermediate alloy and coated on the tungsten alloy spheroidized powder, which can ensure the synchronous vaporization and volatilization of the higher melting point component and the lower melting point component in the intermediate alloy during the gasification process, avoiding the composition unevenness caused by the lower melting point component in the nickel-based intermediate alloy being pre-vaporized and volatilized at high temperature while retaining the higher melting point component, thereby ensuring the composition uniformity of the formed coated tungsten-based alloy spherical powder, and also avoiding the formation of brittle phase due to component segregation caused by gasification, effectively ensuring the formability of tungsten alloy in additive manufacturing.

[0036] Preferably, the nickel content in the nickel-based master alloy is 50%-90%. Specifically, the nickel content can be 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., which is not limited here.

[0037] Furthermore, in the spheroidization and coating treatment step: the system pressure of the radio frequency plasma spheroidization equipment is 100-150Kpa, the inner ring gas flow rate is 30-100L / min, the outer ring gas flow rate is 60-200L / min, and the side gas flow rate is 60-200L / min. By adjusting the flow rate of the side gas, the temperature field of the plasma can be accurately controlled, which is beneficial to the control of the spheroidization effect and the heating rate of the powder particles; by adjusting the flow rate of the inner ring gas, the distribution of the powder particles in the high-temperature flow field can be affected; by controlling the system pressure, it is ensured that under a certain pressure, the powder particles quickly absorb heat and melt in the plasma, and cool and solidify into spherical powder under the action of surface tension. Through the coordinated cooperation of the above parameters, it can be better ensured that the vaporized nickel alloy is coated on the spheroidized tungsten powder, so that a coated high-density tungsten alloy with good powder uniformity and high composition uniformity can be obtained.

[0038] Preferably, the inner ring gas, the outer ring gas, the side gas and the carrier gas are all argon. By selecting argon, a stable inert environment can be provided for the powder during the spheroidization process to prevent metal oxidation.

[0039] The present application also provides a coated high-density tungsten alloy, which is prepared by the coated high-density tungsten alloy preparation method as described above, which will not be described in detail here.

[0040] In order to better demonstrate that the coated high-density tungsten alloy prepared by the present invention has good composition uniformity, a comparative analysis is now conducted through the following examples:

[0041] Embodiment 1

[0042] Weigh 45 kg of tungsten powder with a purity of 99.5% and a Fisher particle size of 9 μm, and weigh 5 kg of nickel-iron master alloy powder, in which the content ratio of nickel to iron is 7:3. 90=29.45μm, then the weighed tungsten powder raw material and nickel-iron intermediate alloy powder are placed in a W-type double-cone high-efficiency mixer for preliminary powder mixing, the frequency of the W-type double-cone high-efficiency mixer is controlled to be 35Hz, and the mixing time is 15min; then, 50Kg of the evenly mixed mixed powder is placed in a powder feeder, and the RF plasma spheroidization equipment is set to operate with an inner ring gas flow rate of 53L / min, an outer ring gas flow rate of 85L / min, a side gas flow rate of 105L / min, a carrier gas flow rate of 8L / min, a powder feeder speed of 13r / min, a system pressure of 130Kpa, and an equipment heating power of 85Kw.

[0043] Figure 2 : is a SEM scanning image of the nickel-iron alloy-coated spherical heavy tungsten alloy powder formed by the above preparation method; Figure 3 (a) is the distribution diagram of tungsten measured by EDS spectrometer; Figure 3 (b) is the distribution diagram of nickel element measured by EDS spectrometer; Figure 3 (c) is the distribution diagram of iron element measured by EDS spectrometer.

[0044] Embodiment 2

[0045] Weigh 45 kg of tungsten powder with a purity of 99.5% and a Fisher particle size of 11 μm, and weigh 5 kg of nickel-copper master alloy powder, in which the content ratio of nickel to copper is 1:1. 90 =32.84μm, then the weighed tungsten powder raw material and nickel-iron intermediate alloy powder are placed in a W-type double-cone high-efficiency mixer for preliminary powder mixing, the frequency of the W-type double-cone high-efficiency mixer is controlled to be 50Hz, and the mixing time is 5min; then, 50Kg of the evenly mixed mixed powder is placed in a powder feeder, and the RF plasma spheroidization equipment is set to operate with an inner ring gas flow rate of 67L / min, an outer ring gas flow rate of 103L / min, a side gas flow rate of 120L / min, a carrier gas flow rate of 6L / min, a powder feeder speed of 18r / min, a system pressure of 120Kpa, and an equipment heating power of 73Kw.

[0046] Embodiment 3

[0047] Weigh 45 kg of tungsten powder with a purity of 99.5% and a Fisher particle size of 12 μm, and weigh 5 kg of nickel-iron master alloy powder, in which the content ratio of nickel to iron is 5:4. 90=31.48μm, then the weighed tungsten powder raw material and nickel-iron intermediate alloy powder are placed in a W-type double-cone high-efficiency mixer for preliminary powder mixing, the frequency of the W-type double-cone high-efficiency mixer is controlled to be 28Hz, and the mixing time is 20min; then, 50Kg of the evenly mixed mixed powder is placed in a powder feeder, and the RF plasma spheroidization equipment is set to run with an inner ring gas flow rate of 75L / min, an outer ring gas flow rate of 150L / min, a side gas flow rate of 145L / min, a carrier gas flow rate of 13L / min, a powder feeder speed of 20r / min, a system pressure of 115Kpa, and an equipment heating power of 65Kw.

[0048] Comparative Example

[0049] Weigh the purity of 99.5%, D 90 =45Kg of spherical tungsten powder raw material with a diameter of 35.86μm, and 7Kg of carbonyl nickel powder and 3Kg of carbonyl iron powder are weighed at the same time. The average Fisher particle size of the spherical tungsten powder, carbonyl nickel powder and carbonyl iron powder is less than 5μm. Then the weighed tungsten powder raw material and nickel-iron intermediate alloy powder are placed in a W-type double-cone high-efficiency mixer for preliminary mixing of the powders. The frequency of the W-type double-cone high-efficiency mixer is controlled to 35Hz, and the mixing time is 48h.

[0050] Referring to the requirements for chemical composition detection of tungsten alloy powder in 4.1 of GB / T 41338-2022 Tungsten and Tungsten Alloy Powders for Additive Manufacturing, the chemical composition of Examples 1, 2, 3 and the comparative example was tested, and the composition test results were compared with the designed composition values ​​as follows:

[0051] Sample name Composition design value ICP component measured value (W is the balance) Embodiment 1 W-90%; Ni-7%; Fe-3% Ni-7.0525%; Fe-3.1758%; W-89.7717% Embodiment 2 W-90%; Ni-5%; Cu-5% Ni-5.0468%; Cu-5.0126%; W-89.9406% Embodiment 3 W-91%; Ni-5%; Fe-4% Ni-5.1006%; Fe-4.0325%; W-90.8669% Comparative Example W-90%; Ni-7%; Fe-3% Ni-5.4625%; Fe-6.4569%; W-88.0806%

[0052] The results of ICP detection in Examples 1 to 3 show that the chemical composition of the coated high-density tungsten alloy spherical powder obtained by the preparation method of the present application is almost the same as the chemical composition of the designed composition value, and the composition deviation can be controlled within 0.2%. The ICP test results in the comparative example show that the actual chemical composition of the tungsten alloy powder prepared by the ball milling mixing method has a large deviation from the designed composition value, which will cause the tungsten alloy obtained by additive manufacturing to have poor formability and uneven bulk composition. Therefore, compared with the ball milling mixing powder making technology, the present application has more advantages in powder composition uniformity, avoiding the tungsten alloy brittle phase formed by the traditional method to affect the mechanical properties of the bulk material, and can also greatly shorten the preparation time and improve the preparation efficiency. In addition, the solid parts obtained by additive manufacturing of the high-density tungsten alloy powder of the present application also have the characteristics of uniform composition, which is beneficial to obtain tungsten alloy solid parts with high performance.

[0053] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing a coated high-density tungsten alloy, characterized in that: The steps include: Mixing treatment: placing pure tungsten powder and nickel-based master alloy powder in a W-type double cone mixer and mixing for 5-30 minutes to obtain a mixed powder, wherein the mass ratio of the pure tungsten powder to the nickel-based master alloy powder is (4-49):1; Spheroidization and coating treatment: The mixed powder is placed in a radio frequency plasma spheroidization device for spheroidization treatment. The power of the radio frequency plasma spheroidization device is 50-120Kw, the carrier gas flow rate is 2-15L / min, and the powder feeder speed is 5-35r / min. The mixed powder is heated so that the pure tungsten powder in the mixed powder is in a molten state and the nickel-based master alloy powder is in a gasified state; synchronous cooling is maintained so that the nickel-based master alloy powder is condensed and coated on the surface of the spheroidized pure tungsten powder to form a coated high-density tungsten alloy.

2. The method for preparing a coated high-density tungsten alloy according to claim 1, characterized in that: The laser particle size distribution of the nickel-based master alloy powder is D 90 ≤35μm.

3. The method for preparing a coated high-density tungsten alloy according to claim 1, characterized in that: The nickel-based master alloy powder is any one of nickel-copper master alloy powder, nickel-iron master alloy powder, nickel-chromium master alloy powder, nickel-molybdenum master alloy powder and nickel-cobalt master alloy powder.

4. The method for preparing a coated high-density tungsten alloy according to claim 3, characterized in that: The nickel content in the nickel-based master alloy is 50%-90%.

5. The method for preparing a coated high-density tungsten alloy according to claim 1, characterized in that: The pure tungsten powder has a Fisher particle size of 4-12 μm.

6. The method for preparing a coated high-density tungsten alloy according to claim 1, characterized in that: In the spheroidization and coating treatment step: the system pressure of the radio frequency plasma spheroidization equipment is 100-150Kpa, the inner ring gas flow rate is 30-100L / min, the outer ring gas flow rate is 60-200L / min, and the side gas flow rate is 60-200L / min.

7. The method for preparing a coated high-density tungsten alloy according to claim 6, characterized in that: The inner ring gas, the outer ring gas, the side gas and the carrier gas are all argon gas.

8. The method for preparing a coated high-density tungsten alloy according to claim 1, characterized in that: The frequency of the W-type double-cone mixer is 15-75 Hz.

9. The method for preparing a coated high-density tungsten alloy according to claim 1, characterized in that: The purity of the pure tungsten powder is 99%-99.9%.

10. A coated high-density tungsten alloy, wherein the coated high-density tungsten alloy is prepared by the method for preparing a coated high-density tungsten alloy according to any one of claims 1 to 9.

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