High-tensile-strength tungsten powder, its preparation method and application

Abstract

This invention relates to the field of metal powder preparation technology, and discloses a high-pressure compact strength tungsten powder, its preparation method, and its applications. Using ammonium paratungstate as raw material, a purple tungsten oxide precursor is prepared by nitrogen calcination. Then, a unique multi-temperature gradient reduction process is employed. Under the synergistic effect of low-temperature nucleation, medium-temperature high-flow-rate gas-induced growth, and high-temperature curing and shaping, a tungsten powder coarse material with abundant micro-burrs and a porous framework is constructed. Finally, the finished product is obtained through air-jet milling, shaping, and passivation. The prepared tungsten powder has a Fisher particle size of 2.8–3.8 μm, a bulk density of 2.5–3.0 g / cm³, a specific surface area of ​​0.40–0.60 m² / g, and a compact strength of 11.5–12.70 MPa at 200 MPa pressure, significantly superior to conventional tungsten powder. This tungsten powder possesses high purity, high mechanical interlocking force, and good processing fluidity, greatly reducing the molding difficulty and breakage rate of irregularly shaped or thin-walled tungsten products.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, and more specifically, to a high-pressure billet strength tungsten powder, its preparation method, and its application. Background Technology

[0002] Tungsten, a typical refractory metal, is widely used in core fields such as national defense, aerospace, electronics, and nuclear industry due to its high melting point (3410℃), high density (19.3 g / cm³), low coefficient of thermal expansion, and excellent high-temperature strength and corrosion resistance. In practical industrial applications, high-purity tungsten powder is mainly used in powder metallurgy to prepare various high-performance structural components and functional materials, such as high-purity sputtering targets for semiconductor chip manufacturing, heat shields and heating elements in high-temperature furnaces, heat sinks for high-power electronic devices, and high-density alloy components such as armor-piercing projectile cores. Furthermore, tungsten powder is also a key raw material for the production of cemented carbide, and its quality directly determines the final service life and machining accuracy of cutting tools, drilling tools, and wear-resistant parts. With the upgrading of high-end manufacturing, the market has placed higher demands on the complexity of tungsten product shapes and dimensional accuracy.

[0003] However, with the increasing demand from modern industry for more complex and thinner-walled tungsten products, traditional tungsten powder faces severe challenges in the forming and processing stages. In powder metallurgy, the strength of the pressed blank is a key indicator determining whether the green blank can be completely demolded, handled, and subsequently machined without breakage. When using existing commercially available high-purity tungsten powder to press irregularly shaped parts, components with large aspect ratios, or thin-walled structures, insufficient green blank strength easily leads to defects such as edge chipping, corner chipping, cracking, or even overall collapse, severely limiting the yield and production efficiency of high-end tungsten products. Although adding organic forming agents such as paraffin wax and rubber can temporarily improve strength, this not only increases the cost and time of subsequent degreasing processes but also easily results in carbon and oxygen residues, thus deteriorating the purity and performance of the final product. Therefore, developing a high-purity tungsten powder that can achieve high-pressure blank strength through its own morphological characteristics without additives has become a pressing technical bottleneck for the industry. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a high-pressure tungsten powder with high strength, its preparation method and application, solving the technical problems of low strength of existing high-purity tungsten powder compacts, easy breakage of green blanks and low yield of molded products.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for preparing high-strength tungsten powder from high-pressure billets, comprising the following steps: Preparation of S1 precursor: High-purity ammonium paratungstate was placed in a calcination furnace and calcined at a temperature of 600-680°C under a nitrogen atmosphere to obtain a high-purity tungsten oxide precursor. S2 Multi-Temperature Gradient Reduction: The high-purity tungsten oxide precursor is loaded onto a boat and pushed into a multi-tube reduction furnace. Under a reducing atmosphere with a hydrogen flow rate of 3.0-3.5 m³ / h, it is sequentially reduced through a low-temperature nucleation zone, a medium-temperature growth zone, and a high-temperature shaping zone with a temperature range of 550-950℃ to obtain tungsten powder coarse material. S3 Airflow milling and shaping: The tungsten powder coarse material is fed into an airflow mill. Under the conditions of a milling pressure of 0.45~0.65MPa and a classifying wheel speed of 2250~3000r / min, the powder particles are driven by high-speed airflow to collide, shape and classify, and high-pressure billet strength tungsten powder is collected.

[0007] In a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, the calcination temperature of the precursor is 640°C.

[0008] In a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, the hydrogen flow rate is 3.3 m³ / h.

[0009] In a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, the reduction temperature of the low-temperature nucleation zone is set to 600°C, and the effective residence time of the material is 30-35 min.

[0010] In a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, the reduction temperature of the intermediate-temperature growth zone is set to 790°C, and the effective residence time of the material is 40-45 min.

[0011] In a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, the reduction temperature of the high-temperature shaping zone is set to 920°C, and the effective residence time of the material is 20-25 min.

[0012] In a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, the pulverizing pressure is 0.5-0.55 MPa.

[0013] In a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, the speed of the classifying wheel is 2500~2750 r / min.

[0014] As a preferred embodiment of the method for preparing high-pressure billet strength tungsten powder according to the present invention, after the high-pressure billet strength tungsten powder is prepared, it needs to be passivated for 12 to 24 hours under a nitrogen atmosphere with an oxygen volume content of 0.1% to 0.5%.

[0015] The present invention also provides a high-pressure compact strength tungsten powder, prepared by the above method, wherein: the tungsten powder has a Fisher particle size of 2.8~3.8μm, a loose packing density of 2.5~3.0g / cm³, a specific surface area of ​​0.40~0.60m² / g, and a compact strength of 11.5~12.70MPa under a pressure of 200MPa.

[0016] The beneficial effects of this invention are as follows: By employing a fully physical field synergistic control technology combining purple tungsten framework genetics, unsteady gradient reduction, and airflow micro-pruning, this invention successfully constructs a microstructure with rich mechanical interlocking structures while ensuring high purity, thus solving the pain points of traditional modification processes that easily introduce impurities and have unstable frameworks. In particular, the innovative high-temperature curing and airflow shaping processes effectively lock the fragile primary dendrites and improve powder processability, increasing the compact strength of the final product to 11.5~12.70 MPa. At the same time, it also has suitable bulk density and particle size distribution, significantly improving the yield of irregularly shaped and difficult-to-form tungsten products, making it suitable for large-scale industrial production. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The figure shows the experimental results for optimizing the flow rate of reduced hydrogen gas.

[0019] Figure 2 The figure shows the results of the screening experiment for the low-temperature nucleation region.

[0020] Figure 3 The figure shows the results of the screening experiment for the temperature of the high-temperature curing zone.

[0021] Figure 4 The diagrams show the process parameters for the fluidized bed air jet mill shaping process, including the spatial surface diagram (top left) and contour map (top right) of the compact strength test results, and the spatial surface diagram (bottom left) and contour map (bottom right) of the loose packing density test results.

[0022] Figure 5 This is a flowchart illustrating the preparation process of high-pressure billet strength tungsten powder. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "example" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The appearance of an embodiment in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments.

[0026] Example 1 This embodiment provides a performance comparison and screening experiment of tungsten powders with different micromorphologies to explore the specific influence of tungsten powder micromorphology on the strength of the compact and to determine the target morphology parameters of the preparation process. First, three commercially available high-purity tungsten powders with different micromorphologies (purity ≥99.95%) were purchased from the market as experimental samples and labeled as Sample A (regular polyhedron), Sample B (regular sphere), and Sample C (irregular coral-like shape).

[0027] First, the microstructure was verified by scanning electron microscopy. Among them, the particles of sample A have a regular polyhedral structure, complete crystal development, smooth surface, good dispersion between particles, and no obvious agglomeration; the particles of sample B are highly regular spherical or near-spherical, with extremely smooth surface and no sharp edges; the particles of sample C have an irregular coral-like or chain-like structure, rough surface and obvious micropores.

[0028] Then, physical performance tests and compact strength verification were performed on the three samples. The Fisher particle size (FSSS) was determined according to GB / T3249 standard; the loose density was determined according to GB / T1479 standard; the compact strength was tested by pressing 5.0g of tungsten powder into a 20×5×5mm long green billet in a steel mold under a pressure of 200MPa, and then performing a three-point bending test, recording the maximum load at fracture and calculating the compact strength.

[0029] The test results are as follows: Sample B, while exhibiting good flowability (high loose density), suffers from extremely low compact strength due to the lack of mechanical interlocking points between particles, leading to easy relative sliding under pressure and failing to meet high-strength molding requirements. Sample C, on the other hand, possesses high compact strength, attributed to the strong mechanical interlocking effect generated during pressing by its rough surface and complex dendritic structure. Its lower loose density indicates the presence of abundant irregular pores within the compact. These results suggest that tungsten powder with a rough surface, coral-like or porous aggregate microstructure is crucial for achieving high compact strength. Subsequent experiments will use this morphology as a target to screen for the optimal process for preparing high-performance tungsten powder.

[0030] Example 2 This embodiment provides a screening experiment for tungsten powder preparation processes based on different technical routes, in order to explore the actual performance of the current mainstream preparation processes that can produce irregular micromorphologies in terms of high-pressure billet strength index, thereby selecting the basic process route with the greatest modification potential.

[0031] The selected process and its specific preparation steps are as follows: Vapor phase deposition: Vapor phase reduction deposition is performed using tungsten hexafluoride (WF6) at 600°C in a hydrogen atmosphere. Vapor phase growth exhibits excellent anisotropy and can obtain ultrafine tungsten powder with dendritic or needle-like structures; Doping-induced reduction method: A trace amount of potassium nitrate and aluminum nitrate solution is added to ammonium paratungstate raw material via wet doping, followed by calcination and hydrogen reduction. The pinning effect of impurity elements at grain boundaries hinders the spheroidization growth of grains, inducing the formation of irregular polyhedral structures. Mechanical ball milling method: Commercially available ordinary tungsten powder (Fishellseau particle size approximately 3.5μm) is selected as raw material and placed in a planetary ball mill. High-energy ball milling is performed for 2 hours using carbide grinding balls under argon protection. The particles are broken by strong mechanical impact, artificially creating fragmented morphologies with sharp edges. Plasma spheroidization: Ordinary tungsten powder is fed into an RF plasma torch, where the particles melt and spheroidize on the surface at an instantaneous high temperature, followed by rapid cooling. Although this process is typically used to prepare spherical powders, by adjusting the powder feed rate and power, a modified powder with a molten surface but maintaining a certain degree of irregularity can be obtained. This can be used to compare and study the effect of surface smoothness on the strength of the compact. High-temperature reduction method: Tungsten oxide is placed in a single-tube reduction furnace and reduced at high temperature under a conventional dry hydrogen atmosphere to prepare tungsten powder. This is a basic industrial process because tungsten oxide has a needle-like / rod-like structure, and its reduction can give the product a certain needle-like / rod-like microstructure.

[0032] The Fisher particle size of the sample was determined by the air permeability method to determine whether the powder was in the medium particle size range (2.5~4.5μm) suitable for pressing. The specific surface area of ​​the sample was then determined by the low temperature nitrogen adsorption method to quantify the microscopic surface roughness and microcrack structure of the powder. The loose packing density can be used as a macroscopic physical indicator to reflect the packing behavior and interlocking potential between powder particles. The compact strength is a direct quantitative indicator of the bonding ability and structural stability of powder particles under cold pressing conditions.

[0033] The test results are as follows: Among the various methods, doping-induced compaction, while possessing the best compaction strength, introduces impurities that increase the uncertainty of subsequent processing, and is therefore excluded. The next-best method, vapor deposition, is unsuitable for compaction due to its excessively fine particle size. While high-temperature reduction does not match the performance of commercially available powders, it has no significant drawbacks. Mechanical ball milling offers performance similar to high-temperature reduction, but it detects impurities such as Fe and Ni, and causes severe powder work hardening. Therefore, high-temperature reduction is chosen as the target process for subsequent process improvement experiments.

[0034] Example 3 Reference Figure 1 ~ Figure 3 This is the third embodiment of the present invention, which aims to systematically screen and optimize the process parameters for tungsten powder preparation in order to select the process parameters with the optimal high-pressure billet strength.

[0035] 3.1 Screening of tungsten oxide precursor preparation processes Tungsten oxide, as the direct precursor of tungsten powder, often exhibits significant hereditary effects in its initial microstructural characteristics (such as porosity, crystal morphology, and aggregation mode), directly determining the morphological potential of subsequently reduced tungsten powder. Since current tungsten oxide production uses high-purity ammonium paratungstate as a precursor, this experiment selected five representative tungsten oxide preparation methods for comparative testing to determine the most suitable precursor process for industrial-scale preparation of high-strength tungsten powder. All methods used were based on the same batch of high-purity ammonium paratungstate.

[0036] Sol-gel method: A tungstate solution is first prepared using ammonium paratungstate, then acidified to form a sol, which is then aged, dried, and calcined. This method can obtain nanoscale mesoporous structures.

[0037] Solid-phase calcination method: Ammonium paratungstate crystals are placed directly in a rotary furnace, and tungsten oxide is prepared by in-situ pore formation by utilizing the escape effect of ammonia and water vapor during its thermal decomposition. Spray pyrolysis: Ammonium paratungstate solution is atomized and sprayed into a high-temperature zone for instantaneous decomposition. The resulting tungsten oxide has a hollow spherical shell structure.

[0038] Hydrothermal synthesis: Growth occurs via reaction in an aqueous solution environment within a high-pressure autoclave. The resulting material possesses specific nanowire or flower-like structures.

[0039] Precipitation method: Tungstic acid is directly precipitated by adding acid to a tungstate solution, and then tungsten oxide is prepared by washing and calcination.

[0040] After the reaction is complete, tungsten powder is prepared using the precursor product as raw material. The reduced tungsten powder sample is subjected to a full set of performance tests, including Fisher particle size, loose packing density, specific surface area and compact strength, in order to screen out the optimal process.

[0041] The test results are as follows: Among them, the hydrothermal synthesis method has high strength but extremely low yield and complex process, which makes it difficult to meet the needs of industrial mass production and has no practical application value. Therefore, the solid-phase calcination method with excellent comprehensive performance is selected as the best precursor preparation process.

[0042] 3.2 Effect of calcination temperature on the reduction properties of precursors After establishing the solid-state calcination method as the basic approach, the calcination temperature becomes the most critical variable determining the microstructure and phase composition of the precursor. The thermal decomposition of ammonium paratungstate is a complex, multi-stage reaction process involving dehydration, deammoniation, and lattice rearrangement. Under a nitrogen protective atmosphere, with increasing temperature, ammonium paratungstate undergoes a continuous phase transition from ammonium paratungstate to various non-stoichiometric tungsten oxides (such as hexagonal, triclinic, monoclinic, and various suboxides). The mixed phases generated at different temperature ranges exhibit significant differences in their inherent crystal habits (such as needle-like, plate-like, or blocky structures) and pore structures, inheriting these differences to the final reduced tungsten powder.

[0043] The starting point was selected as 450℃, the lowest temperature at which the initial thermal decomposition rate of ammonium paratungstate meets the requirements of industrial production, and the ending point was 750℃, where the grains coarsen significantly and the phase tends to reach thermodynamic stability. Within this range, an experimental group was set up every 50℃, for a total of 7 temperature points (450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃).

[0044] Precursors prepared at different calcination temperatures were reduced to tungsten powder. Subsequently, a full range of performance tests were performed on the reduced tungsten powder samples, including Fisher particle size, bulk density, specific surface area, and compact strength, to screen for the optimal calcination temperature.

[0045] The test results are as follows: At temperatures exceeding 700℃, significant coarsening and densification of the crystals severely disrupt the loose structure conducive to interlocking, leading to a precipitous drop in the compact strength. By performing a quadratic polynomial fitting analysis on the experimental data, a response surface model of temperature and compact strength was constructed, calculating the theoretical optimal calcination temperature to be 639.3℃, corresponding to a theoretical peak compact strength of 9.69 MPa. Considering the temperature control accuracy of industrial rotary kilns (typically ±10℃) and the convenience of production operations, 640℃, the temperature closest to the theoretical peak, was ultimately selected as the preferred process parameter for precursor calcination.

[0046] 3.3 Optimization of reducing hydrogen flow rate (construction of unsteady flow field) After identifying the optimal precursor, the gas-phase kinetics during the reduction process become the next key variable affecting the microstructure of tungsten powder. Conventional reduction processes typically aim for a stable laminar flow atmosphere (flow rate of approximately 1.5~2.0 m³ / h) to obtain regular and dense crystals. Excessive gas flow rate can delay the spheroidization trend of grains, generate shear disturbances on the surface of the growing crystals, and induce the formation of more microscopic defects and burr structures. This microstructural "defect process," which needs to be avoided in conventional processes, has a significant effect on improving the strength of high-pressure tungsten powder billets.

[0047] Starting with a flow rate significantly higher than the conventional 2.5 m³ / h, and with an estimated flow field disruption threshold of 4.5 m³ / h as the endpoint, 11 experimental groups were established with an increment of 0.2 m³ / h. In addition to continuing to use Fisher particle size, specific surface area, and compact strength as the basic evaluation dimensions, it is also necessary to use oxygen content detection to determine whether excessive flow rate may lead to insufficient reduction as a judgment indicator.

[0048] Test results are as follows Figure 1 As shown, the oxygen content significantly increased after the flow rate exceeded 3.7 m³ / h, indicating that the excessive airflow carried away a large amount of reaction heat, leading to incomplete reduction. Furthermore, while the particle size decreased and the specific surface area increased, the strength decreased. This suggests that although excessive airflow can create more microstructures, the resulting skeletal fracture and structural damage outweigh the strength gain from the increased microstructure. This negative impact could no longer be mitigated, ultimately manifesting as a decrease in strength on a macroscopic scale. Therefore, 3.3 m³ / h, where the compact strength is optimal, was ultimately selected as the optimal process point.

[0049] 3.4 Parameter Optimization of Reduction Process After establishing the optimal precursor and gas-phase kinetic conditions, the reduction reaction becomes the decisive factor in regulating the microstructure of tungsten powder. The crystal formation process follows classical crystallization kinetics and can be divided into two core stages: nucleation and growth. First, driven by supersaturation (provided by the reducing atmosphere), new phase clusters overcome surface energy barriers to form stable nuclei. The rate of this stage determines the number and initial distribution of the final product's grains. Subsequently, reactant atoms migrate to the nucleus surface via gas-phase diffusion and accumulate in an ordered manner according to a specific crystallographic orientation, causing the nuclei to grow into macroscopic crystals. Considering the practical application requirements of powder metallurgy, conventional processes introduce an additional solidification stage after the aforementioned basic thermodynamic process. This stage aims to utilize a high-temperature sintering mechanism to heat-treat the grown primary framework, eliminating lattice stress and strengthening the interparticle bonding necks.

[0050] 3.4.1 Screening of temperatures in the low-temperature nucleation region Nucleation temperature is the foundation of the entire reduction process. If the temperature is too low, the reduction reaction lacks kinetic energy, resulting in ineffective nucleation. If the temperature is too high, the reaction instantly enters an explosive nucleation mode, leading to an excessive number of tiny nuclei. In subsequent growth stages, the numerous and dispersed binding sites prevent the formation of a robust framework, ultimately resulting in an excessively fine and dense product. Only a suitable nucleation density can provide sufficient space and material source for subsequent intermediate-temperature growth.

[0051] Based on thermodynamic calculations and industrial experience, the effective temperature range for the conversion of tungsten oxide to metallic tungsten nuclei covers 500℃ to 700℃. To accurately capture the optimal nucleation point, 11 parallel experiments were conducted within this range at 20℃ gradients. The nucleation state was evaluated by measuring the oxygen content of the intermediate product. The oxygen content of the precursor (purple tungsten) used in this experiment was found to be approximately 19.7%. According to classical theories in powder metallurgy, the optimal nucleation precursor is not a pure metallic tungsten nucleus, but rather a metastable state in which purple tungsten transitions to brown tungsten (WO2, theoretical oxygen content 14.14%) with trace amounts of metallic nuclei generated. At this point, the system produces sufficient crystallization centers (nuclei) through appropriate reduction while retaining the oxide framework (material) to support subsequent growth. Calculations show that the oxygen content window corresponding to this optimal nucleus-material ratio should be controlled between 14.5% and 16.0%.

[0052] Test results are as follows Figure 2 As shown, the temperature range corresponding to the target window is 592~628℃. Considering that lower temperatures are more conducive to refining crystal nuclei and preventing premature sintering of the skeleton, 600℃ was finally selected as the optimal process temperature for the low-temperature nucleation region.

[0053] 3.4.2 Screening of temperatures in the mesophilic growth zone During the intermediate-temperature growth stage, the reduction reaction rate accelerates significantly, and tungsten atoms migrate rapidly to the surface of the formed crystal nuclei under the drive of the hydrogen gas flow. Too low a temperature results in insufficient atomic mobility, making it difficult to form complex dendritic structures; while too high a temperature leads to excessively rapid surface diffusion, tending to fill lattice defects and form regular polyhedra (spheroidization effect), resulting in decreased surface roughness. This stage, combined with a high-flow-rate hydrogen gas of 3.3 m³ / h, most effectively utilizes the strong gas flow shearing effect, introducing the maximum amount of microscopic defects and burrs while simultaneously promoting rapid crystal growth, thus maximizing morphological complexity.

[0054] The nucleation product after processing in the low-temperature nucleation zone at 600℃ was selected as the raw material. An optimized hydrogen flow rate of 3.3 m³ / h was maintained. The temperature range of 700℃ to 900℃ was used as the investigation range, and a gradient of 20℃ was set to form 11 growth groups in the experiment.

[0055] The specific surface area was used as the primary indicator to measure the abundance of burr / dendritic growth, while the compact strength was tested to verify its macroscopic effect.

[0056] The test results are shown in the table below: Among them, after fitting calculation, (786.5℃, 10.98MPa) is the optimal process point. Considering industrialization, 790℃ is finally selected as the optimal process point.

[0057] During testing, the data stability of samples taken at 780℃ and 800℃ was poor. For the same batch of samples, the measured compact strength decreased by 0.3~0.5MPa with the delay in sampling sequence, and the dispersion of repeated tests was significantly greater than that of other temperature ranges. This indicates that although abundant burr structures with great interlocking potential grow at this temperature, these nascent skeletons are extremely fragile with weak microscopic bonding, making it difficult to maintain their structural integrity for a long time. This demonstrates the necessity of introducing a high-temperature curing process for locking in conventional process designs.

[0058] Example 3.4.3 Screening of High-Temperature Curing Zone Temperature Given the high potential and low stability of the primary dendritic framework prepared during the intermediate-temperature growth stage, the introduction of the high-temperature curing zone is particularly crucial. This stage aims to induce initial neck sintering at the particle contact points through controlled high-temperature heat treatment, thereby fixing the fragile microscopic burrs onto the main framework. This sacrifices extremely small initial morphological abundance in exchange for long-term stability of macroscopic mechanical properties.

[0059] The nucleation temperature was fixed at 600℃, the growth temperature at 790℃, and the hydrogen flow rate at 3.3 m³ / h. A high-temperature curing zone was connected in series after the growth zone, with a temperature range of 800~1000℃, and 11 experimental groups were established with a temperature gradient of 20℃. Fresh tungsten powder samples prepared in each group were uniformly placed in a clean air environment with constant temperature and humidity (25℃, 40%RH) for open storage to simulate the transfer and storage scenarios in actual industrial production. Starting from the moment of furnace exit (0h) as the baseline, samples were taken every 2 hours until the 10th hour, for a total of 6 time points. The compact strength of the samples at each time point was tested to evaluate their resistance to aging degradation.

[0060] Experimental results are as follows Figure 3 As shown, through comprehensive analysis of the initial strength and the attenuation range, 920℃ was ultimately determined as the optimal process parameter point.

[0061] 3.5 Optimization of reduction reaction time After determining the multi-temperature gradient (600℃ / 790℃ / 920℃) and high-flow gas (3.3m³ / h), there are differences between actual production and laboratory testing. As the reaction time increases, the degree of reduction gradually becomes more complete, and the crystal morphology evolves from a metastable state to a steady state. The performance of the final product will stabilize at a theoretical plateau value. In order to obtain the best experimental data, the previous reaction time was set to a supersaturated value to ensure the sufficiency of the reaction. In actual production, it is necessary to balance production efficiency and product performance to set the residence time of the material in the furnace (i.e., the pusher speed) parameter.

[0062] By continuously shortening the reaction time, it was finally determined that the low-temperature nucleation time should be controlled at 30-35 minutes, the medium-temperature growth time should be 40-45 minutes, and the high-temperature solidification time should be controlled at 20-25 minutes.

[0063] Through multiple rounds of orthogonal screening and refined control, the physical properties of the tungsten powder coarse material prepared under this optimal process window have been fully solidified and upgraded: in addition to the compact strength, which is the explicit optimization target and stabilized at 10.62 MPa, the other accompanying properties have also reached an ideal state due to the synergistic effect of the process. The Fisher particle size has converged to 3.38 μm, which not only avoids agglomeration caused by excessive fineness but also ensures good compaction and filling properties; the loose density is controlled at 2.92 g / cm³, reflecting the fluffy characteristics of the microstructure; the specific surface area is maintained at a high level of 0.45 m² / g, confirming the existence of abundant burr structure; and the oxygen content is at a sub-oxidized state of 1250 ppm.

[0064] Example 4 Reference Figure 4This is the fourth embodiment of the present invention, which aims to systematically screen and optimize the parameters of the tungsten powder crushing and shaping process. Although the tungsten powder coarse material prepared by the gradient reduction process has an ideal framework structure at the microscopic level, it still contains a large number of soft agglomerates caused by van der Waals forces and abnormal dendrites with excessive aspect ratios at the macroscopic level. If these defects are not treated, they will lead to poor powder flowability (inability to automatically fill the mold) and uneven distribution of pressed density. Although traditional mechanical ball milling or disc milling processes can deagglomerate, the strong impact of the media often flattens the precious microstructure and introduces metallic impurities. Finally, it was decided to use a fluidized bed air jet mill, which has no media contamination and whose crushing mechanism is based on particle self-collision, for shaping treatment, so as to achieve precise trimming of the microstructure rather than destructive crushing.

[0065] Using conventional parameter ranges, the crushing pressure is 0.4~0.8MPa and the classifying wheel speed is 1000~4000rpm. Nine test points are set at equal intervals to provide the optimal process parameters for testing the compact strength and loose packing density.

[0066] Test results are as follows Figure 4 As shown, the closest point to the extreme value of the compacted strength is (0.55, 2500), while the closest point to the loose density is (0.50, 2750). Considering large-scale industrial production, the crushing pressure of 0.45~0.65 MPa and the classifying wheel speed of 2250~3000 rpm were finally selected as optional parameters.

[0067] Example 5 Reference Figure 5 This is the fifth embodiment, representing a percentage. This embodiment provides a method for preparing high-pressure billet strength tungsten powder based on optimized parameters throughout the entire process. This method integrates the optimal precursor and gradient reduction process determined in Example 3, as well as the optimized airflow shaping parameters in Example 4, aiming to verify the synergistic effect of the process chain and the comprehensive performance of the final product. The specific preparation steps are as follows: High-purity ammonium paratungstate was selected as the starting material and placed in a dynamic rotary calcination furnace. Under a pure nitrogen protective atmosphere, the calcination temperature was precisely set to 640℃, utilizing the thermal decomposition characteristics of ammonium paratungstate to generate a purple tungsten oxide precursor with a needle-like / rod-like crystal structure in situ.

[0068] The prepared tungsten precursor was loaded into a stainless steel boat (500g / boat) and pushed into a 15-tube multi-tube reduction furnace. The reducing atmosphere was dry hydrogen with a dew point of -40℃, and the hydrogen flow rate was set to 3.3m³ / h to create a strong convective unsteady flow field.

[0069] The reduction process passes through three functional temperature zones in sequence: Low-temperature nucleation zone: The temperature is set at 600℃ and the effective residence time is controlled at 35min to initiate gentle nucleation and prevent explosive metallization; Medium-temperature growth zone: The temperature is set at 790℃ and the effective residence time is controlled at 45min. High-flow-rate airflow is used to induce non-equilibrium irregular growth of crystals to maximize the burr structure. High-temperature curing zone: The temperature is set at 920℃ and the effective residence time is controlled at 25min. The nascent skeleton is subjected to rapid heat treatment to eliminate internal stress and strengthen the bonding neck.

[0070] Coarse tungsten powder is fed into a fluidized bed air jet mill. Using high-purity nitrogen as the working fluid, the grinding pressure is set to 0.55 MPa and the classifier speed is set to 2500 r / min. The high-speed airflow drives the particles to self-collide in the center of the grinding chamber, precisely breaking up soft agglomerates and trimming excessively long dendrites, while preserving the edges of the core framework.

[0071] After shaping, the tungsten powder is left to stand and passivate for 18 hours in a nitrogen atmosphere with an oxygen volume content of 0.3% to form an extremely thin and uniform oxide protective layer on the particle surface, preventing activity decay during subsequent processing.

[0072] The final product prepared by the above process was subjected to a full set of physical and mechanical property tests, and the results were: Fisher particle size 3.15μm, loose packing density 2.75g / cm³, specific surface area 0.52m² / g, oxygen content 1350ppm, tungsten purity >99.95%, and compact strength 12.68MPa.

[0073] In summary, this invention utilizes a fully physical field-based synergistic control technology combining purple tungsten framework genetics, unsteady gradient reduction, and airflow micro-pruning to successfully construct a microstructure with rich mechanical interlocking structures while ensuring high purity. This addresses the pain points of traditional modification processes, such as the easy introduction of impurities and framework instability. In particular, the innovative high-temperature curing and airflow shaping processes effectively lock in fragile primary dendrites and improve powder processability, increasing the compact strength of the final product to 11.5~12.70 MPa. Simultaneously, it achieves suitable bulk density and particle size distribution, significantly improving the yield of irregularly shaped and difficult-to-form tungsten products, making it suitable for large-scale industrial production.

[0074] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-pressure billet strength tungsten powder, characterized in that, Includes the following steps: Preparation of S1 precursor: High-purity ammonium paratungstate was placed in a calcination furnace and calcined at a temperature of 600-680°C under a nitrogen atmosphere to obtain a high-purity tungsten oxide precursor. S2 Multi-Temperature Gradient Reduction: The high-purity tungsten oxide precursor is loaded onto a boat and pushed into a multi-tube reduction furnace. Under a reducing atmosphere with a hydrogen flow rate of 3.0-3.5 m³ / h, it is sequentially reduced through a low-temperature nucleation zone, a medium-temperature growth zone, and a high-temperature shaping zone with a temperature range of 550-950℃ to obtain tungsten powder coarse material. S3 Airflow milling and shaping: The tungsten powder coarse material is fed into an airflow mill. Under the conditions of a milling pressure of 0.45~0.65MPa and a classifying wheel speed of 2250~3000r / min, the powder particles are driven by high-speed airflow to collide, shape and classify, and high-pressure billet strength tungsten powder is collected.

2. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, The calcination temperature of the precursor is 640℃.

3. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, The hydrogen flow rate is 3.3 m³ / h.

4. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, The reduction temperature of the low-temperature nucleation zone is set to 600℃, and the effective residence time of the material is 30-35 minutes.

5. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, The reduction temperature of the intermediate temperature growth zone is set at 790℃, and the effective residence time of the material is 40-45 min.

6. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, The reduction temperature in the high-temperature shaping zone is set at 920°C, and the effective residence time of the material is 20–25 min.

7. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, The crushing pressure is 0.5~0.55MPa.

8. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, The speed of the grading wheel is 2500~2750 r / min.

9. The method for preparing high-pressure billet strength tungsten powder according to claim 1, characterized in that, After the high-pressure billet strength tungsten powder is prepared, it needs to be left to stand and passivate for 12 to 24 hours in a nitrogen atmosphere with an oxygen volume content of 0.1% to 0.5%.

10. A high-pressure billet strength tungsten powder, characterized in that, The tungsten powder is prepared by the method according to any one of claims 1 to 9, wherein the tungsten powder has a Fisher particle size of 2.8 to 3.8 μm, a loose packing density of 2.5 to 3.0 g / cm³, a specific surface area of ​​0.40 to 0.60 m² / g, and a compact strength of 11.5 to 12.70 MPa under a pressure of 200 MPa.

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