A method for improving the yield of refractory metal powder produced by prep

Abstract

This invention discloses a method for improving the yield of refractory metal powder prepared by PREP (Preparation-Extraction Process). The method includes the following steps: 1. Machining a refractory metal blank on a lathe to obtain a bar with external threads at one end; 2. Placing the bar in a PREP device and connecting it to a mechanical shaft, evacuating it, filling it with protective gas, and then preheating it through an induction coil installed at the molten pool end of the bar; 3. Rotating the preheated bar and using plasma arc powdering, gradually increasing the rotation speed of the bar during the powdering process, and obtaining refractory metal powder after cooling. The method of this invention, by installing an induction coil at the molten pool end of the metal bar to preheat it, establishes a heat buffer zone between the molten pool and the rear end of the bar, ensuring uniform heating at the molten pool end. This significantly reduces the power supply current to the bar, reduces the wear of the carbon brushes used to supply current to the mechanical shaft, effectively increases the rotation speed of the bar, and achieves a significant increase in fine powder yield. This method is applicable to the field of metal powder preparation technology.

Description

Technical Field

[0001] This invention belongs to the field of metal powder preparation technology, and in particular relates to a method for improving the yield of refractory metal powders prepared by PREP. Background Technology

[0002] TaW and NbW alloys are rare metal alloys with high melting points, high thermal conductivity, excellent high-temperature mechanical properties, and corrosion resistance. Suitable for operation in high-temperature, evaporative cooling, and corrosive environments, they are considered crucial raw materials for next-generation aerospace structural components. They can be used to manufacture key components such as combustion chamber nozzles and throat liners for rocket engines, spacecraft, and hypersonic missiles. In recent years, the rapid development of additive manufacturing technology has made the one-piece fabrication of complex components with internal flow channel structures, such as combustion chamber nozzles and throat liners, a reality. As essential raw materials, the development of TaW and NbW alloy powders is particularly important.

[0003] Currently, for spherical TaW and NbW refractory metal powders used in additive manufacturing, the plasma rotating electrode method (PREP) and plasma spheroidization method are commonly employed. Among these methods, spherical powders prepared using plasma spheroidization are highly susceptible to contamination, resulting in powders with low purity and generally high oxygen content.

[0004] In the PREP powder preparation process, the metal rod is severely affected by the high current under high-speed rotation, and some of the heat is transferred to the mechanical shaft. The carbon brushes, powered by frictional current, are prone to rapid wear and failure under the heat transfer from the mechanical shaft, making it difficult to maintain a constant power supply. Secondly, the edges of the rod are far from the energy center, easily forming a semi-melted state, causing the rod to fold. Simultaneously, the dynamic imbalance during the melting process can cause the rod to vibrate. Under such high torque, the heat-affected mechanical shaft is more prone to warping and deformation, further preventing the rod from achieving continuous high-speed rotation, ultimately resulting in a high yield of coarse powder and a low yield of fine powder. Therefore, a method to improve the yield of refractory metal powder prepared by PREP is urgently needed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for improving the yield of refractory metal powder prepared by PREP. This method mainly involves installing an induction coil at the molten pool end of the metal bar to preheat the bar. This creates a heat buffer zone between the molten pool and the rear end of the bar, resulting in more uniform heating at the molten pool end. This significantly reduces the power supply current to the bar, reduces the wear of the friction-carrying current-carrying carbon brush to maintain a constant power supply, and effectively increases the rotational speed of the bar, thereby achieving a significant increase in the fine powder yield and solving the problem of low yield in the preparation of refractory metal powder using existing technologies.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for improving the yield of refractory metal powder prepared by PREP, characterized in that the method includes the following steps:

[0007] Step 1: Machining the refractory metal blank on a lathe to obtain a bar with external threads on one end;

[0008] Step 2: Place the bar stock obtained in Step 1 into the PREP equipment, connect it to the mechanical shaft of the PREP equipment, evacuate it and fill it with protective gas, and then preheat it through the induction coil set at the molten pool end of the bar stock.

[0009] Step 3: Rotate the preheated bar from Step 2 and use plasma arc to pulverize it, gradually increasing the bar's rotation speed during the pulverization process. After cooling, refractory metal powder is obtained.

[0010] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that the refractory metal blank in step one is made of TaW alloy or NbW alloy.

[0011] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that the diameter of the bar stock in step one is 30 mm or 50 mm.

[0012] This invention improves the yield of fine powder by controlling the diameter of the rod material, enabling high-speed rotation of the rod material under high torque during the PREP powdering process.

[0013] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that, in step two, the bar stock is connected to the mechanical shaft of the PREP equipment through a metal connecting sleeve with internal threads, and the material of the metal connecting sleeve is the same as that of the bar stock.

[0014] This invention effectively solves the problem of metal-based inclusions in the finished powder caused by the easy melting of the edges of ordinary material connecting sleeves under high current density during the PREP powder making process by using connecting sleeves of the same material.

[0015] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that the protective gas in step two is one of argon, helium, or a mixture of argon and helium.

[0016] This invention protects incompletely cooled refractory metal powders during PREP powdering by setting a protective gas, effectively reducing the adsorption of impurity gases on the powder surface and improving powder quality.

[0017] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that the heating power of the induction coil in step two is 10kW to 25kW.

[0018] This invention determines the heating power of the induction coil by combining the diameter, preheating range, preheating volume, and thermophysical parameters of the refractory metal bar. This avoids situations where the heating power is too low to achieve the preheating effect, or too high to cause the bar temperature to rise sharply, or even melt, leading to the termination of the experiment.

[0019] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that the rotation speed during the bar powder preparation process in step three is 25000 r / min to 40000 r / min.

[0020] This invention improves the linear velocity of molten metal droplets by controlling the rotation speed during the bar stock powdering process, which is beneficial for increasing the yield of fine powder.

[0021] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that the plasma arc in step three is loaded by a plasma tungsten electrode gun, and the loading current of the plasma tungsten electrode gun is 1000A to 2500A.

[0022] This invention, by setting a high-density loading current, facilitates the full melting of refractory metal bars, increases the superheat of the molten pool and the fluidity of the melt, reduces viscosity, and is more conducive to atomization and crushing.

[0023] The above-mentioned method for improving the yield of refractory metal powder prepared by PREP is characterized in that the method of gradually increasing the yield in step three is as follows: for every 10 mm of bar length consumed, the rotation speed is increased by 1000 r / min.

[0024] This invention improves the yield of fine powder by gradually increasing the rotation speed in stages. As the bar stock is gradually consumed, the weight of the bar stock becomes lighter, and the mechanical shaft load decreases, it is more conducive to increasing the bar stock rotation speed while maintaining stability.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. This invention adds an induction coil to the molten pool end of the bar stock to preheat the bar stock, thereby establishing a heat buffer zone between the molten pool and the rear end of the bar stock, making the molten pool end of the bar stock more uniformly heated, achieving matching between the power and power density generated by the bar stock current during the powder making process. The power density can be adaptively adjusted to cover the entire end face of the bar stock, effectively avoiding the bar stock turning over during PREP powder making, which would result in more coarse powder and less fine powder. Secondly, by adding the induction heating coil, the power supply current of the bar stock can be significantly reduced, and the carbon brush wear is also significantly reduced.

[0027] 2. This invention improves the yield of fine powder from refractory metal powder by gradually increasing the rotation speed of the bar stock during the powdering process, thereby achieving high-speed rotation of the bar stock. Since solid, liquid, and semi-solid substances may appear during the formation of the molten pool on the end face of the bar stock, the molten pool may experience dynamic imbalance, causing it to jump or vibrate, affecting the balance of the bar stock at high rotation speed. However, by activating the plasma arc at a relatively low rotation speed of the bar stock, a stable and gradual molten pool can be formed on the end face of the bar stock. As the molten pool grows larger, the rotation speed of the bar stock is gradually increased, allowing the molten pool to achieve dynamic balance, thus achieving relative balance of the bar stock at high rotation speed and improving the yield of fine powder.

[0028] 3. The present invention introduces a connecting sleeve of the same material, which effectively avoids the presence of metal-based inclusions in the powder prepared due to the easy melting of the edge of the ordinary material connecting sleeve under high current density during the PREP powder preparation process.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the powder preparation process for the refractory metal billet bar of the present invention.

[0031] Figure 2 This is a microscopic morphology image of the refractory metal powder obtained in Example 1 of the present invention.

[0032] Figure 3 This is a photograph of the bar stock head after the powdering process is completed in Embodiment 1 of the present invention.

[0033] Figure 4 This is a photograph of the bar stock head after the powdering process in Comparative Example 1 of this invention.

[0034] Figure 5 This is a microscopic morphology image of the refractory metal powder obtained in Example 3 of the present invention. Detailed Implementation

[0035] Example 1

[0036] The method in this embodiment includes the following steps:

[0037] Step 1: Machin the Ta10W refractory metal billet on a lathe to obtain a billet with an external thread at one end and a diameter of 30mm.

[0038] Step 2: Connect the bar obtained in Step 1 to the Ta10W connecting sleeve with internal threads, then place it in the PREP equipment and connect it to the mechanical shaft of the PREP equipment. After evacuating the vacuum system, fill it with argon gas, and then preheat it through the induction coil set at the molten pool end of the bar to form a heat buffer zone; the heating power of the induction coil is 15kW.

[0039] Step 3, as follows Figure 1 As shown, the motor is started to drive the mechanical shaft to rotate the preheated bar stock from step two. When the rotation reaches 35,000 r / min, a plasma arc is applied using a plasma tungsten electrode gun to form a molten pool at the end of the bar stock for powdering. During the powdering process, the rotation speed of the bar stock is gradually increased. The metal powder thrown out of the molten pool by the rotation of the bar stock is cooled and enters the powder collection tank to obtain spherical refractory metal powder. The loading current of the plasma tungsten electrode gun is 1500A. The method of gradually increasing the current is as follows: for every 10 mm of bar stock length consumed, the rotation speed is increased by 1000 r / min, with a maximum rotation speed of 40,000 r / min.

[0040] The microstructure of the spherical refractory metal powder obtained in this embodiment is as follows: Figure 2 As shown, the yield of fine powder with a diameter less than 53 μm was 52%, and the yield of powder with a diameter less than 150 μm was 99.5%. No metal inclusions were found after random field inspection.

[0041] The bar stock head after preparation in this embodiment is as follows: Figure 3 As shown, no edge flipping phenomenon was observed.

[0042] Comparative Example 1

[0043] This comparative method includes the following steps:

[0044] Step 1: Machin the Ta10W refractory metal billet on a lathe to obtain a billet with an external thread at one end and a diameter of 30mm.

[0045] Step 2: Connect the bar stock obtained in Step 1 to the mechanical shaft of the PREP equipment, evacuate the vacuum system, and then fill it with argon gas.

[0046] Step 3: Start the motor to make the mechanical shaft drive the preheated bar from Step 2 to rotate. When the rotation reaches 35,000 r / min, use a plasma tungsten electrode gun to apply a plasma arc to form a molten pool at the end of the bar for powdering. After cooling, spherical refractory metal powder is obtained. The loading current of the plasma tungsten electrode gun is 1500A.

[0047] The bar stock head after the preparation of this comparative example is as follows: Figure 4 As shown, a folded edge phenomenon occurs.

[0048] Example 2

[0049] The method in this embodiment includes the following steps:

[0050] Step 1: Machin the Ta10W refractory metal billet on a lathe to obtain a billet with an external thread at one end and a diameter of 30mm.

[0051] Step 2: Connect the bar obtained in Step 1 to the Ta10W connecting sleeve with internal threads, then place it in the PREP equipment and connect it to the mechanical shaft of the PREP equipment. After vacuuming, fill it with argon gas, and then preheat it through the induction coil set at the molten pool end of the bar; the heating power of the induction coil is 25kW.

[0052] Step 3: Start the motor to rotate the preheated bar stock from Step 2. Once the rotation reaches 25,000 r / min, use a tungsten electrode plasma gun to apply a plasma arc for powder preparation. The preparation process is as follows: Figure 1 As shown, the rotation speed of the rod is gradually increased during the powder preparation process, and spherical refractory metal powder is obtained after cooling; the loading current of the plasma tungsten electrode gun is 2500A, and the method of gradually increasing the speed is as follows: for every 10mm of rod length consumed, the rotation speed is increased by 1000r / min, and the maximum rotation speed is 30000r / min; the loading current of the plasma tungsten electrode gun is 2500A.

[0053] In this embodiment, the yield of fine powder with a diameter of less than 53 μm was 45%, and the yield of powder with a diameter of less than 150 μm was 99.5%. No metal inclusions were found after random field inspection. No edge flipping phenomenon was observed in the bar stock after preparation in this embodiment.

[0054] Example 3

[0055] The method in this embodiment includes the following steps:

[0056] Step 1: Machining the NbW refractory metal billet on a lathe to obtain a billet with an external thread at one end and a diameter of 30mm;

[0057] Step 2: Connect the bar obtained in Step 1 to the NbW connecting sleeve with internal threads, then place it in the PREP equipment and connect it to the mechanical shaft of the PREP equipment. After vacuuming, fill it with helium and then preheat it through the induction coil set at the molten pool end of the bar; the heating power of the induction coil is 10kW.

[0058] Step 3: Start the motor to rotate the preheated bar stock from Step 2 using the mechanical shaft. Once the rotation reaches 36,000 r / min, use a tungsten electrode plasma gun to apply a plasma arc for powder preparation. The preparation process is as follows: Figure 1 As shown, the rotation speed of the rod is gradually increased during the powder making process, and spherical refractory metal powder is obtained after cooling; the loading current of the plasma tungsten electrode gun is 1000A, and the method of gradually increasing the current is: for every 10mm of rod length consumed, the rotation speed is increased by 1000r / min, and the maximum rotation speed is 40000r / min.

[0059] The microstructure of the spherical refractory metal powder obtained in this embodiment is as follows: Figure 5As shown, the yield of fine powder with a diameter less than 53 μm was 48%, and the yield of fine powder with a diameter less than 150 μm was 99.5%. No metal inclusions were found after random field inspection. No edge flipping phenomenon was observed in the bar stock after preparation in this embodiment.

[0060] Example 4

[0061] The method in this embodiment includes the following steps:

[0062] Step 1: Machining the NbW refractory metal billet on a lathe to obtain a billet with an external thread at one end and a diameter of 50mm;

[0063] Step 2: Connect the bar obtained in Step 1 to the NbW connecting sleeve with internal threads, then place it in the PREP equipment and connect it to the mechanical shaft of the PREP equipment. After evacuation, fill it with a mixture of argon and helium gas, and then preheat it through an induction coil set at the molten pool end of the bar; the heating power of the induction coil is 20kW.

[0064] Step 3: Start the motor to rotate the preheated bar stock from Step 2. Once the rotation reaches 25,000 r / min, use a tungsten electrode plasma gun to apply a plasma arc for powder preparation. The preparation process is as follows: Figure 1 As shown, the rotation speed of the rod is gradually increased during the powder making process, and spherical refractory metal powder is obtained after cooling; the loading current of the plasma tungsten electrode gun is 2500A, and the method of gradually increasing the current is: for every 10mm of rod length consumed, the rotation speed is increased by 1000r / min, and the maximum rotation speed is 30000r / min.

[0065] In this embodiment, the yield of fine powder with a diameter of less than 53 μm was 45%, and the yield of powder with a diameter of less than 150 μm was 99.4%. No metal inclusions were found after random field inspection. No edge flipping phenomenon was observed in the bar stock after preparation in this embodiment.

[0066] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the yield of refractory metal powder prepared by PREP, characterized in that, The method includes the following steps: Step 1: Machining the refractory metal blank on a lathe to obtain a bar with external threads on one end; Step 2: Place the bar stock obtained in Step 1 into the PREP equipment, connect it to the mechanical shaft of the PREP equipment, evacuate it and fill it with protective gas, and then preheat it through the induction coil set at the molten pool end of the bar stock. Step 3: Rotate the preheated bar from Step 2 and use plasma arc to pulverize it, gradually increasing the rotation speed of the bar during the pulverization process. After cooling, refractory metal powder is obtained. The method of gradually increasing the rotation speed is as follows: for every 10mm of bar length consumed, the rotation speed is increased by 1000r / min.

2. The method for improving the yield of refractory metal powder prepared by PREP according to claim 1, characterized in that, The refractory metal blank mentioned in step one is made of TaW alloy or NbW alloy.

3. The method for improving the yield of refractory metal powder prepared by PREP according to claim 1, characterized in that, The diameter of the bar stock mentioned in step one is 30mm or 50mm.

4. The method for improving the yield of refractory metal powder prepared by PREP according to claim 1, characterized in that, In step two, the bar stock is connected to the mechanical shaft of the PREP equipment through a metal connecting sleeve with internal threads. The metal connecting sleeve is made of the same material as the bar stock.

5. The method for improving the yield of refractory metal powder prepared by PREP according to claim 1, characterized in that, The protective gas mentioned in step two is one of argon, helium, or a mixture of argon and helium.

6. The method for improving the yield of refractory metal powder prepared by PREP according to claim 1, characterized in that, The heating power of the induction coil mentioned in step two is 10kW~25kW.

7. The method for improving the yield of refractory metal powder prepared by PREP according to claim 1, characterized in that, The rotation speed during the bar stock powdering process described in step three is 25,000 r / min to 40,000 r / min.

8. The method for improving the yield of refractory metal powder prepared by PREP according to claim 1, characterized in that, In step three, the plasma arc is loaded using a tungsten plasma gun, and the loading current of the tungsten plasma gun is 1000A~2500A.

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