A niobium-silicon alloy powder for powder metallurgy and its preparation method

Abstract

This invention discloses a niobium-silicon alloy powder for powder metallurgy and its preparation method. The preparation method involves: firstly, preparing a main alloy raw material and performing a first melting to obtain a main alloy ingot; then, preparing a micro-alloying raw material and performing a second melting together with the main alloy ingot to obtain a niobium-silicon alloy melt; after the melt is homogeneous, heating it to the casting temperature and casting it to obtain a niobium-silicon alloy ingot; heat-treating the niobium-silicon alloy ingot and then processing it to obtain a niobium-silicon alloy electrode rod; placing the niobium-silicon alloy electrode rod in a PREP (Preheating Electrode Processing) device, first preheating the niobium-silicon alloy electrode rod with plasma, and then pulverizing the niobium-silicon alloy electrode rod with plasma to obtain the niobium-silicon alloy powder for powder metallurgy. The niobium-silicon alloy powder prepared by this invention has high sphericity, low powder impurity content, and low hollow powder content, which is beneficial to improving the formability and mechanical properties of niobium-silicon alloy powder products.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, and relates to a niobium-silicon alloy powder for powder metallurgy and its preparation method. Background Technology

[0002] High-temperature alloys play a crucial role in industrial manufacturing, including aviation, aerospace, nuclear power systems, and civilian gas turbines. Currently, nickel-based high-temperature alloys are among the most widely used, with a maximum withstand temperature of 1039℃. However, with the rapid development of industrial construction and science and technology, the demand for metallic materials capable of operating in a higher temperature range (1093–1370℃) is becoming increasingly urgent.

[0003] Niobium-based alloys, due to their high melting point, good ductility, thermal conductivity, high strength and specific strength, and lightweight properties, have become the most promising ultra-high temperature structural materials to replace nickel-based superalloys. However, niobium-based alloys undergo severe oxidation in air above 600°C, making them unsuitable for use in unprotected environments. The oxidation resistance of niobium-based alloys has been improved through alloying methods, specifically by adding elements such as Ti, Al, and Si. Niobium-aluminum and niobium-silicon alloys are two typical examples of niobium-based alloys, with niobium-silicon alloys exhibiting higher high-temperature strength and greater application potential.

[0004] Niobium-silicon alloys can be prepared using various methods, including arc melting, investment casting, and powder metallurgy. Among these, powder metallurgy is an effective process that can refine the grain size and improve the properties of the material. It avoids defects such as compositional segregation and inconsistent microstructure that occur during ingot metallurgy, and can also eliminate porosity and shrinkage cavities in the material, improving its density and strength. Furthermore, powder metallurgy can directly produce near-net-shape products, avoiding losses and costs in subsequent processing.

[0005] However, the key to obtaining high-performance powder metallurgy niobium-silicon alloy materials lies in breaking through the preparation technology of high-quality niobium-silicon alloy powder, providing a reliable material basis for the powder metallurgy process of niobium-silicon alloy, thereby improving the overall performance of powder metallurgy niobium-silicon alloy parts.

[0006] However, existing technologies only produce niobium-silicon alloy powder prepared by gas atomization. Since both niobium and silicon have high melting points, gas atomization cannot produce high-quality niobium-silicon alloy powder with high sphericity and high fluidity, which cannot meet the needs of powder metallurgy. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the first objective of the present invention is to provide a method for preparing niobium-silicon alloy powder for powder metallurgy with high purity, high sphericity, high fluidity, and low oxygen content.

[0008] The second objective of this invention is to provide niobium-silicon alloy powder for powder metallurgy prepared by the above-described preparation method.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] This invention discloses a method for preparing niobium-silicon alloy powder for powder metallurgy. First, main alloy raw materials are prepared and smelted for the first time to obtain a main alloy ingot. Then, microalloying raw materials are prepared and smelted together with the main alloy ingot for the second time to obtain a niobium-silicon alloy melt. After the niobium-silicon alloy melt is homogeneous, it is heated to the casting temperature and cast to obtain a niobium-silicon alloy ingot. The niobium-silicon alloy ingot is heat-treated and then processed to obtain a niobium-silicon alloy electrode rod. The niobium-silicon alloy electrode rod is placed in a PREP (Preheating Electrode Processing) device, preheated with plasma, and then powdered with plasma to obtain niobium-silicon alloy powder for powder metallurgy.

[0011] The preparation method of this invention involves first melting to obtain a main alloy ingot, and then melting the micro-alloying raw material together with the main alloy ingot. The inventors discovered that by using the above method, a niobium-silicon alloy ingot with uniform composition can be obtained. The niobium-silicon alloy ingot is then heat-treated to improve its toughness and processing performance. This not only avoids potential breakage problems during the ingot processing into electrode rods and results in high surface quality of the processed niobium-silicon alloy ingot, but also, in conjunction with the preheating treatment of the niobium-silicon alloy electrode rod, allows the electrode rod to uniformly melt at its end under the action of plasma during the powder preparation process. The atomized droplets are then ejected from the end of the niobium-silicon alloy rod under centrifugal force, forming fine droplets that rapidly cool into spherical particles, resulting in high-purity, high-sphericity, high-flowability, and low-oxygen-content niobium-silicon powder for powder metallurgy.

[0012] In this invention, the composition of the niobium-silicon alloy powder is not limited, and the niobium-silicon alloys commonly used in the prior art are all suitable for the preparation method of this invention.

[0013] In a preferred embodiment, the niobium-silicon alloy powder for powder metallurgy has the following composition by atomic percentage: Nb 40-60%; Si 15-20%; Ti 15-25%; Al 2-4%; Cr 2-4%; Re 0.2-0.5%; La 0.5-1%. Compared to conventional NbSi alloys, this preferred composition adds a small amount of the rare and precious metal rhenium and the rare earth element lanthanum. Rhenium can increase the volume fraction of the NbSi phase and reduce the volume fraction of silicides, thereby improving the fracture toughness of the niobium-silicon based alloy. Lanthanum, as a rare earth active element, can enhance the adhesion between the oxide and the matrix, thereby significantly improving its oxidation resistance.

[0014] In a preferred embodiment, the main alloying raw material refers to a raw material containing ≥15% by mass of metallic elements in niobium-silicon alloy powder for powder metallurgy, and the microalloying raw material refers to a raw material containing <5% by mass of metallic elements in niobium-silicon alloy powder for powder metallurgy.

[0015] In a preferred embodiment, both the main alloying material and the microalloying material are metals with a purity of ≥99.9%.

[0016] In a further preferred embodiment, the main alloying raw material is selected from Nb particles, Si particles, and Ti particles with a purity ≥ 99.9%, and the microalloying raw material is selected from sponge titanium, aluminum briquettes, rhenium particles, and lanthanum particles with a purity ≥ 99.9%.

[0017] In actual operation, each raw material is first prepared according to atomic percentage, then the raw materials are immersed in alcohol for ultrasonic treatment, and after being fully dried, they are degassed under vacuum.

[0018] In a preferred embodiment, both the first and second melting processes employ cold crucible suspension melting. The inventors have discovered that cold crucible suspension melting reduces the contact between the material and the crucible container in the high-temperature molten state, thereby avoiding the introduction of high-temperature reaction impurities. Cold crucible suspension melting also facilitates the homogenization of alloying elements, resulting in ingots with uniform compositional distribution and performance stability.

[0019] In a preferred embodiment, the temperature of the first melting is 2100–2200°C.

[0020] In a further preferred embodiment, the first melting process is as follows: the main alloy raw material is placed in a melting furnace, a vacuum is first drawn to ≤0.2Pa, and then an argon protective atmosphere is introduced to make the pressure inside the melting furnace reach above 0.8MPa. The temperature is then raised to 2100-2200℃ at a power of 10-15kW / min and held for 10-15min for melting. Electromagnetic stirring is applied during the melting process. After the melting is completed, the temperature is lowered to form an ingot, and then the ingot is turned over and heated again for melting to obtain the main alloy ingot.

[0021] In actual operation, when evacuating, a mechanical pump is first used to evacuate the melting furnace to a vacuum level of less than 5 Pa. Then, a diffusion pump is used to continue evacuating the melting furnace to ≤0.2 Pa. Then, an argon protective atmosphere is introduced to make the pressure inside the melting furnace reach more than 0.8 MPa. The melting power is gradually increased to raise the temperature, allowing the raw materials to melt fully. An automatic electromagnetic stirrer is used to continuously stir and mix the melt evenly. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again in a crucible to ensure that the alloy ingot has a uniform composition.

[0022] In a preferred embodiment, the temperature of the second melting is 2100–2200°C.

[0023] In a further preferred embodiment, the second melting process is as follows: the microalloyed raw material and the main alloy ingot are placed in a melting furnace, the vacuum is first drawn to ≤0.2Pa, and then argon gas is introduced to create a protective atmosphere so that the pressure inside the melting furnace reaches above 0.8MPa. The temperature is then raised to 2100-2200℃ at a power of 10-15kW / min and held for 10-15min for melting. Electromagnetic stirring is applied during the melting process. After the melting is completed, the ingot is cooled to form an ingot, and then the ingot is turned over and heated again for melting to obtain the main alloy ingot.

[0024] In actual operation, after the melting is completed and the ingot is taken out, all the slits of the copper crucible are cleaned to prevent the solidified shell from excessively wetting the slits during the next melting.

[0025] In a preferred embodiment, the casting process involves heating the niobium-silicon alloy melt to 2250–2400°C, preferably 2300–2400°C, and then casting it into a mold to obtain a niobium-silicon alloy ingot.

[0026] In a further preferred embodiment, the mold is made of graphite.

[0027] The inventors discovered that niobium-silicon alloy melt has poor fluidity. If the niobium-silicon alloy melt is directly cast, the melt near the mold surface cools down quickly to the solidification temperature and solidifies into a shell. The metal melt is difficult to replenish in time, resulting in a hollow ingot. However, this invention increases the casting temperature to improve the fluidity of the melt and allow for timely replenishment, thereby obtaining a dense and solid niobium-silicon alloy ingot.

[0028] In a preferred embodiment, the heat treatment temperature is 1350℃~1450℃, and the heat treatment time is 30~50h. In this invention, by heat-treating the niobium-silicon alloy ingot obtained from casting at the above temperature, within this temperature range, the Nb3Si phase transforms into the Nbss phase, thereby reducing the Nb3Si phase and increasing the Nbss phase. The increase of the Nbss phase can improve the impact toughness of the niobium-silicon alloy and improve the brittleness problem of the electrode rod.

[0029] In actual operation, the niobium-silicon alloy ingot obtained after heat treatment is precision machined. The riser of the annealed niobium-silicon alloy ingot is first removed, and then the niobium-silicon alloy electrode rod is obtained by wire cutting.

[0030] In a preferred embodiment, the niobium-silicon alloy electrode rod has a diameter of 50–100 mm and a length of 500–700 mm.

[0031] In a preferred embodiment, the niobium-silicon alloy electrode rod is placed in a plasma rotating electrode atomization (PREP) device, and the PREP device is first evacuated to 10... -3 Pa~10 -1Pa, then a protective atmosphere is introduced, and then plasma is used to preheat the niobium-silicon alloy electrode rod. Then plasma is used to pulverize the niobium-silicon alloy electrode rod to obtain niobium-silicon alloy powder for powder metallurgy.

[0032] In a preferred embodiment, when preheating the niobium-silicon alloy electrode rod with plasma, the plasma current is 100–150 A, and the rotation speed of the niobium-silicon alloy electrode rod is 5000–10000 r / min. Preheating under these conditions can further improve brittleness and prevent powder splattering. Of course, the current should not be too high, as this will cause the electrode rod to melt, while a low current will result in poor preheating effect.

[0033] In the preferred embodiment, when using plasma to pulverize the niobium-silicon alloy electrode rod, the plasma current is 1000-2000A; the rotational speed of the niobium-silicon alloy electrode rod is 5000r / min to 20000r / min; and the feed rate is 1 to 3mm / s.

[0034] In the powder preparation process, plasma is used to heat the end of the niobium-silicon alloy electrode rod, causing the end of the electrode rod to melt uniformly. The atomized droplets are thrown out from the end of the niobium-silicon alloy rod under the action of centrifugal force, forming fine droplets and rapidly cooling into spherical particles, thus obtaining niobium-silicon powder with high sphericity and high purity for powder metallurgy.

[0035] The present invention also provides niobium-silicon alloy powder for powder metallurgy prepared by the above preparation method.

[0036] The niobium-silicon powder used in powder metallurgy has a hollow powder ratio of <0.1%, a sphericity of >95%, and a tap density of >4.3 g / cm³. 3 Oxygen content <800ppm, average particle size 50μm~200μm.

[0037] The advantages of this invention over the prior art are:

[0038] (1) This invention prepares ingots through two cold crucible suspension melting and one casting process, improves the plasticity of niobium-silicon alloy ingots through heat treatment, processes the smelted ingots into electrode rods through precision machining, and prepares spherical niobium-silicon alloy powders through plasma rotating electrode method, thereby obtaining niobium-silicon alloy powders suitable for powder metallurgy with uniform particle size distribution, high sphericity of powder particles, and an average sphericity ≥90%, which improves the utilization rate of powders and reduces production costs.

[0039] (2) The niobium-silicon alloy powder prepared by this invention has low impurity content, with oxygen content ≤800ppm, carbon content ≤150ppm, and nitrogen content ≤200ppm. The formed parts obtained by powder metallurgy have uniform and dense structure, high dimensional accuracy, and excellent mechanical properties.

[0040] The niobium-silicon alloy prepared by the method of this invention has uniform composition, fine microstructure, and excellent performance, meeting the application requirements in the aerospace field.

[0041] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Attached Figure Description

[0042] Figure 1 This is a scanning electron microscope image of niobium-silicon powder for powder metallurgy prepared in Example 1 of the present invention; Figure 1 (a) is a macroscopic photograph of the powder. Figure 1 (b) is a microscopic photograph of the powder. As shown in the figure, the powder has high sphericity and no impurities.

[0043] Figure 2 This is a cross-sectional scanning photograph of the niobium-silicon powder for powder metallurgy prepared in Example 1 of the present invention; as shown in the figure, the powder is dense inside.

[0044] Figure 3 The above are the energy dispersive spectroscopy (EDS) surface scan analysis results of the niobium-silicon powder for powder metallurgy prepared in Example 1 of this invention. Figure 3 The upper left image shows the cross-sectional morphology of the powder and a schematic diagram of the surface scan area, which shows that the composition is relatively uniformly distributed.

[0045] Figure 4 This is a flowchart of the present invention. Detailed Implementation

[0046] Example 1

[0047] This invention discloses a metal powder for niobium-silicon alloy powder metallurgy, which is implemented according to the following steps:

[0048] Step 1: Prepare and charge the raw materials for suspension melting in a cooling crucible. The alloy composition is: Nb 55.0%, Si 16%, Ti 24%, Al 2%, Cr 2%, Re 0.5%, and La 0.5%. Weigh high-purity (purity greater than 99.9%) commercial Nb, Si, Ti, Al, and Cr particles according to atomic percentage. Immerse the raw materials in alcohol and sonicate for 10 minutes. After thorough drying, degas them under vacuum. First, add the Nb, Si, and Ti particles to the furnace using a D80 crucible. Use a mechanical pump to evacuate the furnace to a vacuum level of less than 5 Pa, then use a diffusion pump to continue evacuating the furnace to 0.2 Pa.

[0049] Step 2: First melting: Argon gas is introduced to protect the atmosphere. When the pressure inside the furnace reaches 0.8MPa, the melting power is gradually increased at a rate of 10-15kW / min to raise the temperature. The melting temperature is 2200℃ and the power is 100KW. The raw materials are fully melted and stirred continuously. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again using a D80 crucible to ensure that the alloy ingot has a uniform composition.

[0050] Step 3: Second melting: Cr and Al granular materials are added to a D120 crucible, and after vacuuming to 0.2 Pa, argon protective gas is introduced. When the pressure reaches 0.8 MPa, the temperature is raised again to 2200℃. When the power reaches 100KW, the ingot is melted for 10 minutes to form an ingot. The temperature is raised again and the ingot is turned over and melted again in a D120 crucible. After the melting is completed, the temperature is raised again and the ingot is cast using a graphite mold at a casting temperature of 2400℃.

[0051] Step 4: Ingot heat treatment: After the niobium-silicon alloy ingot has completely cooled, place it in a heat treatment furnace; heat the heat treatment furnace to 1450℃ and hold it for 50 hours; after the holding period, cool it with the furnace.

[0052] Step 5: Precision machining to prepare electrode rods: Remove the riser from the annealed niobium-silicon alloy ingot; obtain niobium-silicon alloy electrode rods by wire cutting, with a diameter of 50 mm and a length of 500 mm.

[0053] Step Six: Preheating the Niobium-Silicon Alloy Electrode Rod in the PREP Equipment: Place the obtained niobium-silicon alloy electrode rod in the plasma rotating electrode atomization equipment, and evacuate the reaction chamber to 10°C. -3 Pa~10 -1 Pa, inert gas was introduced into the reaction chamber, the plasma current was set to 150A and the electrode rod rotation speed was set to 5000r / min, and the niobium-silicon alloy electrode rod end was uniformly preheated by plasma.

[0054] Step 7: PREP preparation of niobium-silicon alloy powder: Adjust the plasma current to 1000A, the electrode rod rotation speed to 5000r / min, and the feed speed to 3mm / s; use plasma to heat the end of the niobium-silicon alloy electrode rod, so that the end of the electrode rod melts uniformly. The atomized droplets are thrown out from the end of the niobium-silicon alloy rod under the action of centrifugal force, forming fine droplets and rapidly cooling into spherical particles, thus obtaining niobium-silicon powder for powder metallurgy with high sphericity and high purity.

[0055] Scanning electron microscope (SEM) image of the niobium-silicon alloy powder prepared using Example 1 is shown below. Figure 1 As shown. By Figure 1It can be seen that the prepared niobium-silicon alloy powder mostly has good sphericity, with powder diameters ranging from 75 to 200 μm and an average particle size of 98 μm. SEM images of the niobium-silicon powder particle profile prepared in Example 1 are shown below. Figure 2 As shown. By Figure 2 It can be seen that the powder is dense internally, without any hollow areas. The energy dispersive spectroscopy (EDS) results of the niobium-silicon alloy powder prepared using this method are as follows: Figure 3 As shown. By Figure 3 As can be seen, the chemical composition of the powder is uniformly distributed, and its specific performance data is as follows:

[0056] The hollow powder content of the niobium-silicon alloy powder is 0.08%;

[0057] The sphericity of the niobium-silicon alloy powder is 94%.

[0058] The tap density of the niobium-silicon alloy powder is 4.32 g / cm³.

[0059] The oxygen content of the niobium-silicon alloy powder is 580 ppm;

[0060] The average particle size of the niobium-silicon alloy powder is 98 μm.

[0061] Example 2 (Failure: No temperature rise during casting process)

[0062] This invention discloses a metal powder for niobium-silicon alloy powder metallurgy, which is implemented according to the following steps:

[0063] Step 1: Prepare and charge the raw materials for suspension melting in a cooling crucible. The alloy composition is: Nb 55.0%, Si 16%, Ti 24%, Al 2%, Cr 2%, Re 0.5%, and La 0.5%. Weigh high-purity (purity greater than 99.9%) commercial Nb, Si, Ti, Al, and Cr particles according to atomic percentage. Immerse the raw materials in alcohol and sonicate for 10 minutes. After thorough drying, degas them under vacuum. First, add the Nb, Si, and Ti particles to the furnace using a D80 crucible. Use a mechanical pump to evacuate the furnace to a vacuum level of less than 5 Pa, then use a diffusion pump to continue evacuating the furnace to 0.2 Pa.

[0064] Step 2: First melting: Argon gas is introduced to protect the atmosphere. When the pressure inside the furnace reaches 0.8MPa, the melting power is gradually increased at a rate of 10-15kW / min to raise the temperature. The melting temperature is 2200℃ and the power is 100KW. The raw materials are fully melted and stirred continuously. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again using a D80 crucible to ensure that the alloy ingot has a uniform composition.

[0065] Step 3: Second melting: Cr and Al granular materials are added to a D120 crucible, and after vacuuming to 0.2 Pa, argon protective gas is introduced. When the pressure reaches 0.8 MPa, the temperature is raised to 2200℃ again. When the power reaches 100KW, melting is carried out for 10 minutes to generate an ingot. The ingot is then turned over and melted again in a D120 crucible without raising the temperature. After melting, the ingot is cast using a graphite mold at a casting temperature of 2200℃. The resulting ingot is hollow inside and cannot be used for subsequent powdering processes.

[0066] Example 3 (Failure: Ingot without heat treatment process)

[0067] This invention discloses a metal powder for niobium-silicon alloy powder metallurgy, which is implemented according to the following steps:

[0068] Step 1: Prepare the raw materials and charge for suspension melting in a cooling crucible. The alloy composition is: Nb 55.0%, Si 16%, Ti 24%, Al 2%, Cr 2%, Re 0.5%, and La 0.5%. Weigh high-purity (purity greater than 99.9%) commercial Nb, Si, Ti, Al, and Cr particles according to atomic percentage. Immerse the raw materials in alcohol and sonicate for 10 minutes. After thorough drying, degas them under vacuum. First, add the Nb, Si, and Ti particles to the furnace using a D80 crucible. Use a mechanical pump to evacuate the furnace to a vacuum level of less than 5 Pa, then use a diffusion pump to continue evacuating the furnace to 0.2 Pa.

[0069] Step 2: First melting: Argon gas is introduced to protect the atmosphere. When the pressure inside the furnace reaches 0.8MPa, the melting power is gradually increased at a rate of 10-15kW / min to raise the temperature. The melting temperature is 2200℃ and the power is 100KW. The raw materials are fully melted and stirred continuously. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again using a D80 crucible to ensure that the alloy ingot has a uniform composition.

[0070] Step 3: Second melting: Cr and Al granular materials are put into a D120 crucible, and after the vacuum is evacuated to 0.2 Pa, argon protective gas is introduced. When the pressure reaches 0.8 MPa, the temperature is raised to 2200℃ again. When the power reaches 100KW, the ingot is melted for 10 minutes to form an ingot. The temperature is raised again and the ingot is turned over and melted again in a D120 crucible. After the melting is completed, the ingot is cast using a graphite mold at a casting temperature of 2400℃.

[0071] Step 4: Precision machining to prepare electrode rods: Remove the riser from the annealed niobium-silicon alloy ingot; obtain niobium-silicon alloy electrode rods by wire cutting, with a diameter of 50 mm and a length of 500 mm.

[0072] Step 5: Preheating the niobium-silicon alloy electrode rod in the PREP equipment: Place the obtained niobium-silicon alloy electrode rod in the plasma rotating electrode atomization equipment, and evacuate the reaction chamber to 10°C. -3 Pa~10 -1 Pa, inert gas was introduced into the reaction chamber, the plasma current was set to 150A and the electrode rod rotation speed was set to 5000r / min, and the niobium-silicon alloy electrode rod end was uniformly preheated by plasma.

[0073] Step 6: PREP preparation of niobium-silicon alloy powder: Adjust the plasma current to 500A, the electrode rod rotation speed to 25000r / min, and the feed speed to 3mm / s; use plasma to heat the end of the niobium-silicon alloy electrode rod to melt the end of the electrode rod. Since no heat treatment was performed to improve brittleness, the electrode rod broke during the rotation process, and powder could not be obtained.

[0074] Example 4 (Failure: No preheating step)

[0075] This invention discloses a metal powder for niobium-silicon alloy powder metallurgy, which is implemented according to the following steps:

[0076] Step 1: Prepare and charge the raw materials for suspension melting in a cooling crucible. The alloy composition is: Nb 55.0%, Si 16%, Ti 24%, Al 2%, Cr 2%, Re 0.5%, and La 0.5%. Weigh high-purity (purity greater than 99.9%) commercial Nb, Si, Ti, Al, and Cr particles according to atomic percentage. Immerse the raw materials in alcohol and sonicate for 10 minutes. After thorough drying, degas them under vacuum. First, add the Nb, Si, and Ti particles to the furnace using a D80 crucible. Use a mechanical pump to evacuate the furnace to a vacuum level of less than 5 Pa, then use a diffusion pump to continue evacuating the furnace to 0.2 Pa.

[0077] Step 2: First melting: Argon gas is introduced to protect the atmosphere. When the pressure inside the furnace reaches 0.8MPa, the melting power is gradually increased at a rate of 10-15kW / min to raise the temperature. The melting temperature is 2200℃ and the power is 100KW. The raw materials are fully melted and stirred continuously. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again using a D80 crucible to ensure that the alloy ingot has a uniform composition.

[0078] Step 3: Second melting: Cr and Al granular materials are put into a D120 crucible, and after the vacuum is evacuated to 0.2 Pa, argon protective gas is introduced. When the pressure reaches 0.8 MPa, the temperature is raised to 2200℃ again. When the power reaches 100KW, the ingot is melted for 10 minutes to form an ingot. The temperature is raised again and the ingot is turned over and melted again in a D120 crucible. After the melting is completed, the ingot is cast using a graphite mold at a casting temperature of 2400℃.

[0079] Step 4: Ingot heat treatment: After the niobium-silicon alloy ingot has completely cooled, place it in a heat treatment furnace; heat the heat treatment furnace to 1450℃ and hold it for 50 hours; after the holding period, cool it with the furnace.

[0080] Step 5: Precision machining to prepare electrode rods: Remove the riser from the annealed niobium-silicon alloy ingot; obtain niobium-silicon alloy electrode rods by wire cutting, with a diameter of 50 mm and a length of 500 mm.

[0081] Step 6: PREP preparation of niobium-silicon alloy powder: Adjust the plasma current to 1000A, the electrode rod rotation speed to 5000r / min, and the feed speed to 3mm / s; use plasma to heat the end of the niobium-silicon alloy electrode rod. Due to the lack of electrode rod preheating treatment, the electrode rod cracked during rotation and could not produce powder.

[0082] Example 5 (Failure: Rotation speed outside protection range)

[0083] This invention discloses a metal powder for niobium-silicon alloy powder metallurgy, which is implemented according to the following steps:

[0084] Step 1: Prepare and charge the raw materials for suspension melting in a cooling crucible. The alloy composition is: Nb 55.0%, Si 16%, Ti 24%, Al 2%, Cr 2%, Re 0.5%, and La 0.5%. Weigh high-purity (purity greater than 99.9%) commercial Nb, Si, Ti, Al, and Cr particles according to atomic percentage. Immerse the raw materials in alcohol and sonicate for 10 minutes. After thorough drying, degas them under vacuum. First, add the Nb, Si, and Ti particles to the furnace using a D80 crucible. Use a mechanical pump to evacuate the furnace to a vacuum level of less than 5 Pa, then use a diffusion pump to continue evacuating the furnace to 0.2 Pa.

[0085] Step 2: First melting: Argon gas is introduced to protect the atmosphere. When the pressure inside the furnace reaches 0.8MPa, the melting power is gradually increased at a rate of 10-15kW / min to raise the temperature. The melting temperature is 2200℃ and the power is 100KW. The raw materials are fully melted and stirred continuously. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again using a D80 crucible to ensure that the alloy ingot has a uniform composition.

[0086] Step 3: Second melting: Cr and Al granular materials are put into a D120 crucible, and after the vacuum is evacuated to 0.2 Pa, argon protective gas is introduced. When the pressure reaches 0.8 MPa, the temperature is raised to 2200℃ again. When the power reaches 100KW, the ingot is melted for 10 minutes to form an ingot. The temperature is raised again and the ingot is turned over and melted again in a D120 crucible. After the melting is completed, the ingot is cast using a graphite mold at a casting temperature of 2400℃.

[0087] Step 4: Ingot heat treatment: After the niobium-silicon alloy ingot has completely cooled, place it in a heat treatment furnace; heat the heat treatment furnace to 1450℃ and hold it for 50 hours; after the holding period, cool it with the furnace.

[0088] Step 5: Precision machining to prepare electrode rods: Remove the riser from the annealed niobium-silicon alloy ingot; obtain niobium-silicon alloy electrode rods by wire cutting, with a diameter of 50 mm and a length of 500 mm.

[0089] Step Six: Preheating the Niobium-Silicon Alloy Electrode Rod in the PREP Equipment: Place the obtained niobium-silicon alloy electrode rod in the plasma rotating electrode atomization equipment, and evacuate the reaction chamber to 10°C. -3 Pa~10 -1 Pa, inert gas was introduced into the reaction chamber, the plasma current was set to 150A and the electrode rod rotation speed was set to 5000r / min, and the niobium-silicon alloy electrode rod end was uniformly preheated by plasma.

[0090] Step 7: PREP preparation of niobium-silicon alloy powder: Adjust the plasma current to 500A, the electrode rod rotation speed to 25000r / min, and the feed speed to 3mm / s; use plasma to heat the end of the niobium-silicon alloy electrode rod to make the end of the electrode rod melt uniformly.

[0091] Because the electrode rod rotates at too high a speed (beyond the scope of protection of this invention), it breaks during rotation due to excessive speed, making it impossible to obtain powder.

[0092] Example 6

[0093] This invention discloses a metal powder for niobium-silicon alloy powder metallurgy, which is implemented according to the following steps:

[0094] Step 1: Prepare and charge the raw materials for suspension melting in a cooling crucible. The alloy composition is: Nb 55.0%, Si 16%, Ti 24%, Al 2%, Cr 2%, Re 0.5%, and La 0.5%. Weigh high-purity (purity greater than 99.9%) commercial Nb, Si, Ti, Al, and Cr particles according to atomic percentage. Immerse the raw materials in alcohol and sonicate for 10 minutes. After thorough drying, degas them under vacuum. First, add the Nb, Si, and Ti particles to the furnace using a D80 crucible. Use a mechanical pump to evacuate the furnace to a vacuum level of less than 5 Pa, then use a diffusion pump to continue evacuating the furnace to 0.2 Pa.

[0095] Step 2: First melting: Argon gas is introduced to protect the atmosphere. When the pressure inside the furnace reaches 0.8MPa, the melting power is gradually increased at a rate of 10-15kW / min to raise the temperature. The melting temperature is 2200℃ and the power is 100KW. The raw materials are fully melted and stirred continuously. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again using a D80 crucible to ensure that the alloy ingot has a uniform composition.

[0096] Step 3: Second melting: Cr and Al granular materials are put into a D120 crucible, and after the vacuum is evacuated to 0.2 Pa, argon protective gas is introduced. When the pressure reaches 0.8 MPa, the temperature is raised to 2200℃ again. When the power reaches 100KW, the ingot is melted for 10 minutes to form an ingot. The temperature is raised again and the ingot is turned over and melted again in a D120 crucible. After the melting is completed, the ingot is cast using a graphite mold at a casting temperature of 2400℃.

[0097] Step 4: Ingot heat treatment: After the niobium-silicon alloy ingot has completely cooled, place it in a heat treatment furnace; heat the heat treatment furnace to 1450℃ and hold it for 50 hours; after the holding period, cool it with the furnace.

[0098] Step 5: Precision machining to prepare electrode rods: Remove the riser from the annealed niobium-silicon alloy ingot; obtain niobium-silicon alloy electrode rods by wire cutting, with a diameter of 50 mm and a length of 500 mm.

[0099] Step Six: Preheating the Niobium-Silicon Alloy Electrode Rod in the PREP Equipment: Place the obtained niobium-silicon alloy electrode rod in the plasma rotating electrode atomization equipment, and evacuate the reaction chamber to 10°C. -3 Pa~10 -1 Pa, inert gas was introduced into the reaction chamber, the plasma current was set to 150A and the electrode rod rotation speed was set to 5000r / min, and the niobium-silicon alloy electrode rod end was uniformly preheated by plasma.

[0100] Step 7: PREP preparation of niobium-silicon alloy powder: Adjust the plasma current to 2000A, the electrode rod rotation speed to 20000r / min, and the feed speed to 3mm / s; use plasma to heat the end of the niobium-silicon alloy electrode rod, so that the end of the electrode rod melts uniformly, and the atomized droplets are thrown out from the end of the niobium-silicon alloy rod under the action of centrifugal force, forming fine droplets and rapidly cooling into spherical particles, to obtain niobium-silicon powder for powder metallurgy with high sphericity and high purity;

[0101] The hollow powder content of the niobium-silicon alloy powder is 0.04%.

[0102] The sphericity of the niobium-silicon alloy powder is 96%.

[0103] The tap value of the niobium-silicon alloy powder is 4.38 g / cm.

[0104] The oxygen content of the niobium-silicon alloy powder is 520 ppm;

[0105] The average particle size of the niobium-silicon alloy powder is 51 μm.

[0106] Example 7 (Failure: Current not within protection range)

[0107] This invention discloses a metal powder for niobium-silicon alloy powder metallurgy, which is implemented according to the following steps:

[0108] Step 1: Prepare the raw materials and charge for suspension melting in a cooling crucible. The alloy composition is: Nb 55.0%, Si 16%, Ti 24%, Al 2%, Cr 2%, Re 0.5%, and La 0.5%. Weigh high-purity (purity greater than 99.9%) commercial Nb, Si, Ti, Al, and Cr particles according to atomic percentage. Immerse the raw materials in alcohol and sonicate for 10 minutes. After thorough drying, degas them under vacuum. First, add the Nb, Si, and Ti particles to the furnace using a D80 crucible. Use a mechanical pump to evacuate the furnace to a vacuum level of less than 5 Pa, then use a diffusion pump to continue evacuating the furnace to 0.2 Pa.

[0109] Step 2: First melting: Argon gas is introduced to protect the atmosphere. When the pressure inside the furnace reaches 0.8MPa, the melting power is gradually increased at a rate of 10-15kW / min to raise the temperature. The melting temperature is 2200℃ and the power is 100KW. The raw materials are fully melted and stirred continuously. After holding the temperature for ten minutes to form an ingot, the temperature is raised again at the aforementioned rate. The ingot is then turned over and melted again using a D80 crucible to ensure that the alloy ingot has a uniform composition.

[0110] Step 3: Second melting: Cr and Al granular materials are put into a D120 crucible, and after the vacuum is evacuated to 0.2 Pa, argon protective gas is introduced. When the pressure reaches 0.8 MPa, the temperature is raised to 2200℃ again. When the power reaches 100KW, the ingot is melted for 10 minutes to form an ingot. The temperature is raised again and the ingot is turned over and melted again in a D120 crucible. After the melting is completed, the ingot is cast using a graphite mold at a casting temperature of 2400℃.

[0111] Step 4: Ingot heat treatment: After the niobium-silicon alloy ingot has completely cooled, place it in a heat treatment furnace; heat the heat treatment furnace to 1450℃ and hold it for 50 hours; after the holding period, cool it with the furnace.

[0112] Step 5: Precision machining to prepare electrode rods: Remove the riser from the annealed niobium-silicon alloy ingot; obtain niobium-silicon alloy electrode rods by wire cutting, with a diameter of 50 mm and a length of 500 mm.

[0113] Step Six: Preheating the Niobium-Silicon Alloy Electrode Rod in the PREP Equipment: Place the obtained niobium-silicon alloy electrode rod in the plasma rotating electrode atomization equipment, and evacuate the reaction chamber to 10°C. -3 Pa~10 -1 Pa, inert gas was introduced into the reaction chamber, the plasma current was set to 150A and the electrode rod rotation speed was set to 5000r / min, and the niobium-silicon alloy electrode rod end was uniformly preheated by plasma.

[0114] Step 7: PREP preparation of niobium-silicon alloy powder: Adjust the plasma current to 2500A, the electrode rod rotation speed to 20000r / min, and the feed speed to 3mm / s; use plasma to heat the end of the niobium-silicon alloy electrode rod, so that the end of the electrode rod melts uniformly, and the atomized droplets are thrown out from the end of the niobium-silicon alloy rod under the action of centrifugal force, forming fine droplets and rapidly cooling into spherical particles to obtain niobium-silicon powder;

[0115] The hollow powder content of the niobium-silicon alloy powder is 5%.

[0116] The sphericity of the niobium-silicon alloy powder is 78%.

[0117] The tap density of the niobium-silicon alloy powder is 4.14 g / cm³.

[0118] The oxygen content of the niobium-silicon alloy powder is 620 ppm;

[0119] The average particle size of the niobium-silicon alloy powder is 158 μm.

[0120] Because the current is too high (exceeding the protection scope of this invention), the atomized droplets are too large and cannot form a spherical shape during the ejection process, resulting in a low rate of hollow powder and low sphericity, which cannot meet production requirements.

Claims

1. A method for preparing niobium-silicon alloy powder for powder metallurgy, characterized in that: First, the main alloy raw materials are prepared and smelted for the first time to obtain the main alloy ingot. Then, the micro-alloying raw materials are prepared and smelted together with the main alloy ingot for the second time to obtain the niobium-silicon alloy melt. After the niobium-silicon alloy melt is homogeneous, it is heated to the casting temperature and cast to obtain the niobium-silicon alloy ingot. The niobium-silicon alloy ingot is heat-treated and then processed to obtain the niobium-silicon alloy electrode rod. The niobium-silicon alloy electrode rod is placed in the PREP equipment. First, the niobium-silicon alloy electrode rod is preheated with plasma, and then the niobium-silicon alloy electrode rod is powdered with plasma to obtain the niobium-silicon alloy powder for powder metallurgy. The main alloying raw material refers to the raw material containing metal elements with a mass fraction of ≥15% in niobium-silicon alloy powder for powder metallurgy, and the microalloying raw material refers to the raw material containing metal elements with a mass fraction of <5% in niobium-silicon alloy powder for powder metallurgy. The casting process involves heating the niobium-silicon alloy melt to 2250–2400°C and then casting it into a mold to obtain a niobium-silicon alloy ingot. The heat treatment temperature is 1350℃~1450℃, and the heat treatment time is 30~50h; When plasma is used to preheat niobium-silicon alloy electrode rods, the plasma current is 100-150A; when plasma is used to pulverize niobium-silicon alloy electrode rods, the plasma current is 1000-2000A. The niobium-silicon alloy powder for powder metallurgy has the following composition by atomic percentage: Nb 40-60%; Si 15-20%; Ti 15-25%; Al 2-4%; Cr 2-4%; Re 0.2-0.5%; La 0.5-1%.

2. The method for preparing niobium-silicon alloy powder for powder metallurgy according to claim 1, characterized in that: Both the first and second melting processes were carried out using cold crucible suspension melting. The temperature of the first melting is 2100-2200℃, and the temperature of the second melting is 2100-2200℃.

3. The method for preparing niobium-silicon alloy powder for powder metallurgy according to claim 2, characterized in that: The first melting process is as follows: the main alloy raw material is placed in the melting furnace, the vacuum is first drawn to ≤0.2Pa, and then argon gas is introduced to protect the atmosphere so that the pressure inside the melting furnace reaches above 0.8MPa. The temperature is then raised to 2100-2200℃ at a power of 10-15kW / min and held for 10-15min for melting. Electromagnetic stirring is applied during the melting process. After the melting is completed, the temperature is lowered to form an ingot, and then the ingot is turned over and heated again for melting to obtain the main alloy ingot. The second melting process is as follows: the microalloyed raw materials and the main alloy ingot are placed in a melting furnace. First, a vacuum is drawn to ≤0.2Pa, and then an argon protective atmosphere is introduced to make the pressure inside the melting furnace reach more than 0.8MPa. Then, the temperature is raised to 2100-2200℃ at a power of 10-15kW / min and held for 10-15min for melting. During the melting, electromagnetic stirring is applied. After the melting is completed, the temperature is lowered to form an ingot, and then the ingot is turned over and heated again for melting to obtain the main alloy ingot.

4. The method for preparing niobium-silicon alloy powder for powder metallurgy according to claim 1, characterized in that: The niobium-silicon alloy electrode rod has a diameter of 50-100 mm and a length of 500-700 mm.

5. The method for preparing niobium-silicon alloy powder for powder metallurgy according to claim 1, characterized in that: Place the niobium-silicon alloy electrode rod in the PREEP equipment and first evacuate the PREEP equipment to 10. -3 Pa~10 -1 Pa, then a protective atmosphere is introduced, and then plasma is used to preheat the niobium-silicon alloy electrode rod. Then plasma is used to pulverize the niobium-silicon alloy electrode rod to obtain niobium-silicon alloy powder for powder metallurgy.

6. The method for preparing niobium-silicon alloy powder for powder metallurgy according to claim 5, characterized in that: When plasma is used to preheat the niobium-silicon alloy electrode rod, the rotation speed of the niobium-silicon alloy electrode rod is 5000-10000 r / min. When using plasma to pulverize niobium-silicon alloy electrode rods, the rotation speed of the niobium-silicon alloy electrode rods is 5000 r / min to 20000 r / min, and the feed rate is 1 to 3 mm / s.

7. Niobium-silicon alloy powder for powder metallurgy prepared by the preparation method according to any one of claims 1-6.

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