Method for preparing self-sharpening fine-grain tungsten alloy through flash sintering and product

Abstract

The invention relates to a method for preparing self-sharpening fine-grain tungsten alloy through flash sintering and a product, and the method comprises the following steps: filling high-specific-gravity tungsten alloy powder into an insulating mold, and inserting electrodes at two ends to seal the mold; pulse current and sintering pressure parameters are preset according to the powder components; afterwards, pulse current is applied to the powder through an electrode according to set parameters, meanwhile, corresponding pressure is applied, the powder is rapidly heated through Joule heat, and rapid sintering is achieved. According to the method, the problems of low sintering efficiency, high cost and long technological process of the traditional tungsten alloy are solved by virtue of the rapid Joule heat temperature rise characteristic of flash sintering. And by means of the ultra-fast sintering process, sintering of the high-specific-gravity tungsten alloy can be completed in the air atmosphere, complete densification of the material can be effectively guaranteed through pressure assistance in the process, growth of tungsten grains can be effectively restrained through fast sintering, and finally fast preparation of the fine-grain tungsten alloy with the self-sharpening performance is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of powder preparation, and particularly relates to a method for preparing fine-grained tungsten alloy with self-sharpening by flash sintering and a product. BACKGROUND

[0002] Tungsten-nickel-iron alloy, as a two-phase alloy, has high density, high strength, high hardness, good plasticity and mechanical processing performance, and is widely used in national defense industry and civil industry. After adding Co and Cr elements in its system, the hardness and strength can be further improved by using high-entropy alloy as the adhesive phase. In civil industry, the alloy has high density and can be used for balance weight. Due to its high melting point, good electrical conductivity, high temperature strength and wear resistance, it is widely used in electric heating heat treatment, such as electric upsetting material, electric riveting rivet material, electric spark electrode material, welding material, high-voltage electrical switch contact material and heat shield, etc. In addition, due to its low vapor point, it is also used to manufacture ignition tubes of rocket engines. Due to its better X-ray absorption capacity than lead, it can be applied to defense and shielding of various X-rays, such as X-ray shielding materials in medical industry and shell materials of spacecraft. In addition, it can also be applied to radiators, watch industry rotors, special golf clubs, magnetrons and plasma-facing materials in fusion reactors. In national defense industry, the alloy is used in bullets, cannonballs and other weapons and equipment, and is widely used in the core material of armor-piercing bullets, and is expected to replace depleted uranium alloy to become a new generation of armor-piercing bullet material.

[0003] For armor-piercing bullet material, whether it has self-sharpening is an important evaluation standard. During the penetration process of depleted uranium alloy bullet head, the edge of the bullet head will peel off layer by layer under the action of shear force, so that the bullet head always maintains a sharp geometric shape to maintain the continuous stress concentration between the bullet head and the target interface, which can effectively improve the penetration depth, i.e. the "self-sharpening effect". The core of self-sharpening lies in the formation of adiabatic shear band and the fracture failure induced thereby. A large number of studies have found that fine-grained tungsten-nickel-iron alloy can help to improve the sensitivity of tungsten-nickel-iron alloy to adiabatic shear band, thereby improving its self-sharpening.

[0004] When tungsten alloy is sintered by traditional high-temperature sintering method, the sintering temperature is high, and the sintering time is as long as several tens of hours, which is time-consuming and energy-consuming. In this process, the tungsten grain size grows significantly. At present, a number of studies have been carried out on the optimization and development of new sintering processes. Some studies have successfully achieved good control of grain size. However, controlling the grain size often means more stringent preparation conditions, more complex preparation process and sacrifice of some mechanical properties.

[0005] The prior art CN102139371B discloses a tungsten alloy target material preparation method using variable pressure and plasma-direct current double mode sintering technology, which can prepare high-density (>99.98% TD), large-size and uniform structure target materials, and has the advantages of high energy efficiency, small mold loss and the like. However, this process has problems such as long sintering time, limited grain size control, complex process, high energy consumption, etc., and is not suitable for dynamic performance optimization, especially in the application of armor-piercing bullets which require "self-sharpening effect" structural materials.

[0006] The prior art CN117821820A discloses a tungsten-nickel-iron alloy preparation method with self-sharpening, which introduces high dislocation density structure into conventional tungsten-nickel-iron alloy through multi-stage swaging and intermediate annealing, thereby improving the adiabatic shear sensitivity and realizing the "self-sharpening effect" during penetration. However, this process has problems such as complex process, high energy consumption, long cycle, etc., and needs to go through multiple processes such as pretreatment, multi-stage swaging, intermediate annealing and surface processing; its grain size control ability is limited, the tungsten particles after swaging are ellipsoidal with a long axis of 50-100 μm; and it is easy to introduce surface cracks, uneven structure and other processing defects, which reduces the mechanical performance of the material under conventional processing.

[0007] The prior art CN120041735A discloses a fine-grained tungsten-nickel-iron composite material and a low-temperature sintering preparation method thereof. The method introduces low-melting-point Sn element as a sintering aid and Y2O3 as a grain growth inhibitor, uses carbon thermal reduction + hydrogen reduction to prepare W-Ni-Fe composite powder, and then obtains fine-grained structure through wet grinding, mold pressing, debinding, pre-sintering and low-temperature liquid phase sintering (1200-1300°C), thereby improving the strength, hardness and plasticity of the material. However, this process still belongs to the traditional powder metallurgy route, and even the process is more complex and the cycle is longer, which needs to go through multiple steps of reduction, mixing, debinding and segmented sintering, with a total time consumption of several hours to several tens of hours, and the cost is also high.

[0008] The prior art CN113523273B discloses a sintering method for rapidly preparing ultra-fine-grained pure tungsten material under multi-field coupling. Under the assistance of ultra-high pressure, ultra-fine-grained pure tungsten can be prepared within minutes. However, it is only suitable for pure tungsten system and has no requirement for the purity of tungsten powder. When sintering W-Ni-Fe and other multi-phase alloys in tungsten powder, it cannot guarantee the uniformity of two-phase distribution, and it does not involve the study of dynamic mechanical properties and adiabatic shear behavior, and it is not suitable for the preparation of tungsten alloys with self-sharpening effect.

[0009] Therefore, the above-mentioned existing processes have problems such as more complex process, longer cycle, multiple steps of reduction, mixing, debinding and segmented sintering, total time consumption of several hours to several tens of hours, and high cost. SUMMARY

[0010] In order to overcome the above problems existing in the prior art, the present application provides a method for flash sintering to prepare fine-grained tungsten alloy with self-sharpening and a product, which are used to solve the above problems existing in the prior art.

[0011] The method for flash sintering to prepare fine-grained tungsten alloy with self-sharpening comprises the following steps: S1. Placing high specific gravity tungsten alloy powder in an insulating mold, inserting two end electrodes into the mold to close the insulating mold; S2. According to the specific content ratio of the powder, pre-setting pulse current and sintering pressure parameters in sections; S3. Applying pulse current to the powder through the electrodes according to the pre-set pulse current parameters, and applying pressure to the two end electrodes according to the sintering pressure parameters, so that the powder is rapidly heated under the action of its own Joule heat, and the sintering process is rapidly completed to control the grain growth and achieve fine crystallization, thereby obtaining fine-grained tungsten alloy with self-sharpening.

[0012] According to the above-mentioned aspects and any possible implementation manner, further provided is an implementation manner, wherein the powder in S1 is uniformly mixed by mechanical alloying or spray drying method.

[0013] According to the above-mentioned aspects and any possible implementation manner, further provided is an implementation manner, wherein the pulse current parameters comprise pulse voltage, pulse current, pulse frequency and power-on time.

[0014] According to the above-mentioned aspects and any possible implementation manner, further provided is an implementation manner, wherein the powder in S1 is ternary alloy W-Ni-Fe or alloy powder added with one or several of Co, Cr and Mn on the basis of the ternary alloy.

[0015] According to the above-mentioned aspects and any possible implementation manner, further provided is an implementation manner, wherein in S2, according to the specific content ratio of the powder, pulse current and sintering pressure parameters are pre-set in sections, specifically: When the content of alloy tungsten is in the range of (75, 90]wt.%, the pre-set pulse voltage is 10-36V, the pulse current density is 1000-4000A / cm 2 , the sintering pressure is 30-300MPa, the pulse frequency is 5000-50000Hz, and the power-on sintering time is 30-1000s; When the content of alloy tungsten is in the range of (90, 97]wt.%, the pre-set pulse voltage is 5-36V, the pulse current density is 1500-4000A / cm 2 , the sintering pressure is 30-400MPa, the pulse frequency is 5000-50000Hz, and the power-on sintering time is 30-800s.

[0016] In addition to the aspects described above and any possible implementations, a further implementation is provided in which, when the alloy tungsten content is 93%, the Ni content is 4.9%, and the Fe content is 2.1%, the pulse voltage is preset to 12V and the pulse current density is 2800A / cm². 2 The pulse frequency is 10000Hz, the duration is 60s, and the sintering pressure is 60MPa.

[0017] In addition to the aspects and any possible implementations described above, a further implementation is provided in which, when the alloy tungsten content is 90%, the Ni content is 5.5%, the Fe content is 2.5%, and the Co and Cr contents are both 1%, the pulse voltage is preset to 17V and the pulse current density is 2700A / cm². 2 The pulse frequency is 10000Hz, the duration is 70s, and the sintering pressure is 50MPa.

[0018] In addition to the aspects and any possible implementations described above, a further implementation is provided in which, when the alloy tungsten content is 75%, the Ni content is 17.5%, and the Fe content is 7.5%, the pulse voltage is preset to 24V and the pulse current density is 1500A / cm. 2 The pulse frequency is 20000Hz, the duration is 100s, and the sintering pressure is 100MPa.

[0019] The present invention also provides a self-sharpening fine-grained tungsten alloy, which is prepared by the method described above. The tungsten alloy is composed of a uniformly distributed W phase and a γ-(Ni,Fe) phase with a grain size of less than 6 micrometers.

[0020] Beneficial effects of the present invention This invention discloses a method for preparing self-sharpening fine-grained tungsten alloys by flash sintering, comprising the following steps: placing high-density tungsten alloy powder in an insulating mold, inserting electrodes at both ends into the mold and sealing the mold; pre-setting pulse current and sintering pressure parameters in segments according to the specific content ratio of the powder; applying pulse current to the powder through the electrodes according to the pre-set pulse current parameters, while simultaneously applying pressure to the electrodes at both ends according to the sintering pressure parameters, thereby rapidly raising the Joule temperature of the powder and quickly completing the sintering. Compared with existing technologies, this invention utilizes the rapid Joule heating during flash sintering to solve the problems of low sintering efficiency, high production cost, and long process flow of tungsten alloys. Furthermore, pressure assistance effectively ensures complete densification, while rapid sintering effectively inhibits the growth of tungsten grains, enabling the rapid preparation of self-sharpening fine-grained tungsten alloys. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the mold structure of the present invention; Figure 2 SEM image of fine-grained 93W-4.9Ni-2.1Fe material prepared in Example 1 of the present application; Figure 3 SEM image of fine-grained 90W-5.5Ni-2.5Fe-Co-Cr material prepared in Example 2 of the present application; Figure 4 SEM image of fine-grained 90W-5.5Ni-2.5Fe-Co-Cr material prepared in Example 2 of the present application at 4000s -1 Schematic diagram of adiabatic shear band formed in the material and cracks caused by the adiabatic shear band under high strain rate compression test; Figure 5 SEM image of fine-grained 90W-5.5Ni-2.5Fe-Co-Cr material prepared in Example 2 of the present application at 4000s -1 Schematic diagram of a large number of adiabatic shear bands formed in the material edge under shear deformation and significant recrystallization phenomenon caused by adiabatic temperature rise in the material under high strain rate compression test; Figure 6 Flow chart of the method of the present application. DETAILED DESCRIPTION

[0022] In order to better understand the technical solutions of the present application, the present application includes but is not limited to the specific embodiments described below, and similar technologies and methods should be considered as falling within the scope of the present application. In order to make the technical problems, technical solutions and advantages of the present application more clear, the following will be described in detail with reference to the drawings and specific embodiments.

[0023] It should be clear that the embodiments described in the present application are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0024] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0025] Flash sintering, as an advanced alloy preparation technology, stands out among numerous sintering techniques due to its low sintering temperature and short sintering time. Utilizing high current and pressure assistance, it rapidly sintersects by using Joule heat generated by the current flowing through the tungsten framework, effectively suppressing grain growth and promoting the uniform distribution of the two-phase microstructure in the tungsten-nickel-iron alloy system. It holds promise for producing tungsten alloy products that combine high performance and fine grains. In today's increasingly severe energy and environmental challenges, the low energy consumption and high efficiency of flash sintering are also undeniable advantages.

[0026] This invention employs flash sintering technology to provide a method for preparing fine-grained tungsten alloys with self-sharpening properties by flash sintering, such as... Figure 6 As shown, it includes the following steps: S1. Place the high-density tungsten alloy powder in an insulating mold, insert the electrodes at both ends into the mold, and seal the insulating mold. S2. Based on the specific content ratio of the powder, pre-set the pulse current and sintering pressure parameters in stages; S3. A pulsed current is applied to the powder through the electrodes according to pre-set pulsed current parameters. Simultaneously, pressure is applied to the electrodes at both ends according to sintering pressure parameters, causing the powder to rapidly heat up under its own Joule heating, quickly completing the sintering process to control grain growth and achieve fine grain refinement, resulting in a fine-grained tungsten alloy with self-sharpening properties. This process achieves both rapid sintering and grain refinement by controlling grain growth, ultimately yielding a fine-grained tungsten alloy with self-sharpening properties.

[0027] like Figure 1 As shown, this invention is carried out in an insulating mold. The alloy powder is placed in the inner hole of the ceramic mold 1, and a circuit is formed by connecting the tungsten electrode 2 and the copper conductive plate 3 to an external pulse power supply. Pressure is provided by a pressure pump 4, which is conducted to the powder through the tungsten electrode 2, while ensuring a tight bond between the components. The fixture and support component 5 serves as a support structure, configured as an inverted L-shape with the short side on top and the long side on the bottom. The tungsten electrode 2, the copper conductive plate 3, and the pressure pump 4 are placed on the long side. The insulating quartz plate 6 serves as insulation and is placed between the inner wall of the short side of the support component 5 and the negative electrode plate of the copper conductive plate 3 to ensure that the current does not flow through the external components to form a circuit. The sintering process is completed in the cavity formed by the tungsten electrode 2 and the insulating mold 1. The sintering process includes: particle rearrangement, tungsten framework establishment, liquid phase generation and densification. The Joule heat generated between the particles in the sintering neck is used as the main heat source to rapidly and uniformly raise the temperature of the powder to the melting temperature of the binder phase elements. Densification is completed by filling the pores with the liquid phase. The sintered product has a uniform two-phase distribution and a grain size much smaller than that of conventional sintering, which is more conducive to the occurrence of the "self-sharpening effect".

[0028] Further, the powder in S1 is mixed uniformly by mechanical alloying or spray drying method. In this process, the alloy powder of one or several of Co, Cr, Mn added on the basis of Ni and Fe element powder is important for the grain refinement and uniform distribution, and the distribution of each element in the mixed powder is greatly retained after sintering. The target condition to be reached for powder mixing is that the W particles of large particles are surrounded by fine particles of the remaining element powder.

[0029] Further, the pulse current parameters include pulse voltage, pulse current, pulse frequency and power-on time.

[0030] Further, the powder in S1 is a ternary alloy W-Ni-Fe or an alloy powder of one or several of Co, Cr, Mn added on the basis of the ternary alloy, wherein the addition of Co element can improve the strength of γ-(Ni, Fe) phase, and Cr / Mn element can be used as a strong oxidizing agent to preferentially react with the residual oxygen in the powder pores, avoiding the reaction of O element with W-Ni-Fe composition to generate a brittle phase.

[0031] Further, in S2, according to the specific content ratio of the powder, the pulse current and sintering pressure parameters are pre-set in sections, specifically: When the alloy tungsten content is in (75, 90]wt.%, the pulse voltage is pre-set to 10-36V, the pulse current density is 1000-4000A / cm 2 , the sintering pressure is 30-300MPa, preferably 30-100MPa and 100-300MPa, the pulse frequency is 5000-50000Hz, and the power-on sintering time is 30-1000s; When the alloy tungsten content is in (90, 97]wt.%, the pulse voltage is pre-set to 5-36V, the pulse current density is 1500-4000A / cm2, the sintering pressure is 30-400MPa, the pulse frequency is 5000-50000Hz, and the power-on sintering time is 30-800s.

[0032] When the alloy tungsten content is less than 75%, the powder skeleton may not be built, and is no longer suitable for the method described in the application. The method of the application provides Joule heat for the tungsten skeleton, and the remaining elements have insufficient effect on sintering to cause too much change in the sintering parameters.

[0033] Further, when the alloy tungsten content is 93%, the Ni content is 4.9% and the Fe content is 2.1%, the pulse voltage is pre-set to 12V, the pulse current density is 2800A / cm 2 , the pulse frequency is 10000Hz, the duration is 60s, and the sintering pressure is 60MPa.

[0034] Furthermore, when the alloy contains 90% tungsten, 5.5% Ni, 2.5% Fe, and 1% Co and Cr respectively, the pulse voltage is preset to 17V and the pulse current density to 2700A / cm². 2 The pulse frequency is 10000Hz, the duration is 70s, and the sintering pressure is 50MPa.

[0035] Furthermore, when the alloy contains 75% tungsten, 17.5% Ni, and 7.5% Fe, the pulse voltage is preset to 24V and the pulse current density to 1500A / cm². 2 The pulse frequency is 10000Hz, the duration is 100s, and the sintering pressure is 100MPa.

[0036] As an embodiment of the present invention, the present invention also provides a fine-grained tungsten alloy with self-sharpening properties, wherein the tungsten alloy is composed of a uniformly distributed W phase and a γ-(Ni,Fe) phase with a grain size of less than 6 micrometers. Compared with W-Ni-Fe alloys prepared by conventional methods, the product of the present invention has increased sensitivity to adiabatic shear bands, exhibiting adiabatic shear bands and initiating fracture at lower strain rates and deformations. The W particles in the adiabatic shear bands contain dislocation cells and / or subgrains.

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0038] Example 1 In this embodiment, the fine-grained tungsten-nickel-iron alloy uses W as the hard phase and Ni and Fe as the binder phases. The alloy powder, by mass percentage, consists of: Ni 4.9%, Fe 2.1%, with the balance being W and unavoidable impurities. The W content can be as high as 93%. In the powder, the particle size of Ni and Fe is less than 5 μm to ensure that the powder particles are sufficiently refined and uniformly distributed during mixing, and the particle size of W is less than 3 μm to ensure the fine grain structure of the sintered product. The powder is uniformly mixed using a planetary ball mill. An insulating ceramic mold with a diameter of 12 mm is used, with an outer steel mold for support. The sintering process includes the following steps: S1: Load the powder into the ceramic mold and insert the electrodes at both ends into the sealed powder; S2: Set the initial pulse voltage, pulse current, and pulse frequency according to the elemental ratio of the powder; the pulse voltage is 12V, and the pulse current density is 2800A / cm³. 2 The pulse frequency was 10000Hz, the duration was 60s, the sintering pressure was 60MPa, and the sintering atmosphere was atmospheric.

[0039] S3: Start the power supply and apply an electric field to the powder through the positive and negative electrodes to start sintering. The pressure remains constant during the sintering process. S4: After sintering densification is completed, the sample is cooled to room temperature with the furnace and demolded.

[0040] As Figure 2 shown is an SEM image of the fine-grained 93W-4.9Ni-2.1Fe material prepared in this embodiment. The sintered 93W-4.9Ni-2.1Fe sample of Example 1 was tested by the Archimedes drainage method, and the calculation result showed that the sintered W-Ni-Fe alloy of Example 1 had a density of 98%, a sample hardness of 474.3±9.3HV, and an average grain size of 4μm.

[0041] The sample was characterized by high-speed compression using a Hopkinson bar experiment. At a lower 4000s -1 strain rate and a smaller 40% deformation, significant adiabatic shear fracture occurred. The conventional 93W-4.9Ni-2.1Fe alloy only exhibited adiabatic shear fracture at a strain rate of 6000s -1 and a deformation of 60%. The yield strength of the present application under a 4000s -1 strain rate loading was 2200MPa, which was 30% higher than that of the conventional tungsten-nickel-iron material.

[0042] Example 2 The fine-grained tungsten-nickel-iron alloy of this embodiment uses W as a hard phase, Ni, Fe and Co as a binder phase, Cr as a deoxidizer, and Cr2O3 generated by the reaction of Cr and O elements as a dispersion strengthening particle. The alloy powder consists of the following components in mass percentage: Ni 5.5%, Fe 2.5%, Co 1%, Cr 1%, and the balance of W and unavoidable impurities. The content of W can be as high as 90%. In the powder, the particle size of Ni, Fe, Cr and Co is less than 5μm to ensure that the powder particles can be fully refined and uniformly distributed during the mixing process. The particle size of W is less than 3μm to ensure the fine-grained sintering product. The powder is mixed uniformly by a planetary ball mill, an insulation ceramic mold with a diameter of 12mm, and a steel mold as a support. The specific sintering includes the following steps: S1: The powder is loaded into the ceramic mold, and the electrodes at both ends are inserted to seal the powder. S2: According to the element proportion of the powder, the initial pulse voltage, pulse current and pulse frequency are set. The pulse voltage is 17V, the pulse current density is 2700A / cm 2 , the pulse frequency is 10000Hz, the duration is 70s, the sintering pressure is 50MPa, and the sintering atmosphere is atmospheric air.

[0043] S3: Start the power supply and apply an electric field to the powder through the positive and negative electrodes to start sintering. The sintering process maintains a constant pressure. S4: After sintering densification is completed, the sample is cooled to room temperature with the furnace and demolded.

[0044] Figure 3 SEM images of fine-grained 90W-5.5Ni-2.5Fe-Co-Cr material prepared in the present embodiment are shown; the sintered tungsten-nickel-iron alloy of Example 2 was tested by the Archimedes drainage method, and the calculation result shows that the density of the sintered 90W-5.5Ni-2.5Fe-Co-Cr of Example 2 is 98.6%. The hardness of the sample is 501.4±11.2HV, and the average grain size is 3.1μm.

[0045] The oxygen content of the mixed powder before sintering and the sintered sample was analyzed by an oxygen-nitrogen-hydrogen analyzer, and the result shows that the oxygen content of the powder is 0.262±0.006%, and the oxygen content of the sintered sample is 0.287±0.005%.

[0046] As shown in Figure 4 and Figure 5 , the sintered tungsten-nickel-iron alloy of Example 2 was characterized by high-speed compression using a Hopkinson bar, and at a lower 4000s -1 strain rate and a smaller 35% deformation, significant adiabatic shear fracture occurred, while the conventional 90W-7Ni-3Fe alloy only appeared adiabatic shear fracture at a strain rate of 6000s -1 and a deformation of 60%. The strain rate sensitivity analysis shows that in the high-speed dynamic compression behavior, the strain rate sensitivity factor of the material is 0.2787, which is 12 times that in the static compression behavior, and the strain rate sensitivity factor is 0.0229. In the conventional 90W-7Ni-3Fe material, the strain rate sensitivity factor in the dynamic compression is only 4 times that in the static state, and the large increase in the strain rate sensitivity factor indicates that the strain rate hardening effect of the material is prominent, which is beneficial to the formation of the adiabatic shear band. The yield strength of the powder is 2400MPa under the loading of 4000s -1 strain rate, which is 40% higher than that of the conventional tungsten-nickel-iron material.

[0047] Example 3 The fine-grained tungsten-nickel-iron alloy of the present embodiment uses W as the hard phase and Ni and Fe as the binder phase. The alloy powder consists of the following components in mass percentage: Ni 17.5%, Fe 7.5%, and the balance of W and unavoidable impurities, wherein the content of W can be as high as 75%. In the powder, the particle size of Ni and Fe is less than 5μm to ensure that the powder particles can be fully refined and uniformly distributed during the mixing process, and the particle size of W is less than 3μm to ensure the fine-graining of the sintered product. The powder is mixed uniformly by a planetary ball mill, and an insulating ceramic mold with a diameter of 12mm is used as the support, and a steel mold is used as the support. The specific sintering includes the following steps: S1: The powder is loaded into the ceramic mold, and the two end electrodes are inserted to seal the powder; S2: According to the element proportion of the powder, set the initial pulse voltage, pulse current and pulse frequency; the pulse voltage is 24V, the pulse current density is 1500A / cm 2 , the pulse frequency is 20000Hz, the duration is 100s, and the sintering pressure is 100MPa.

[0048] S3: Start the power supply, and apply an electric field to the powder through the positive and negative electrodes to start sintering, and keep the pressure constant during the sintering process; S4: After sintering densification is completed, the sample is cooled to room temperature and demolded.

[0049] The oxygen content of the mixed powder before sintering and the sintered sample is analyzed by an oxygen-nitrogen-hydrogen analyzer, and the results show that the oxygen content of the powder is 0.254±0.006%, and the oxygen content of the sintered sample is 0.295±0.006%.

[0050] The sintered tungsten-nickel-iron sample of Example 3 is tested by the Archimedes drainage method, and the calculation result shows that the density of 75W-17.5Ni-7.5Fe sintered in Example 3 is 98.5%. The hardness of the sample is 434±13.6HV, and the average grain size is 4.3μm.

[0051] Example 4 The fine-grained tungsten-nickel-iron alloy of this embodiment takes W as the hard phase and Ni and Fe as the binder phase; the alloy powder consists of the following components in mass percentage: Ni 4.9%, Fe 2.1%, and the balance of W and unavoidable impurities, and the content of W can be as high as 93%. In the powder, the particle size of Ni and Fe is less than 5μm to ensure that the powder particles can be fully refined and uniformly distributed during the mixing process, and the particle size of W is less than 3μm to ensure the fine-graining of the sintered product. The powder is mixed uniformly by a planetary ball mill, an insulating ceramic mold with a diameter of 30mm is used as the support, and a steel mold is used as the support; the specific sintering includes the following steps: S1: Put the powder into the ceramic mold, and insert the electrodes into the closed powder; S2: According to the element proportion of the powder, set the initial pulse voltage, pulse current and pulse frequency; the pulse voltage is 16V, the pulse current is 1600A / cm 2 , the pulse frequency is 10000Hz, the duration is 600s, the sintering pressure is 200MPa, and the sintering atmosphere is atmospheric atmosphere.

[0052] S3: Start the power supply, and apply an electric field to the powder through the positive and negative electrodes to start sintering, and keep the pressure constant during the sintering process; S4: After sintering densification is completed, the sample is cooled to room temperature and demolded.

[0053] The sintered W-Ni-Fe sample of Example 1 was tested by Archimedes drainage method, and the calculation result shows that the sintered W-Ni-Fe alloy of Example 1 has a density of 98.1%, a hardness of 471.3±6.7HV, and an average grain size of 4.3μm.

[0054] From the above examples, it can be seen that the present application sets the corresponding initial pulse voltage, pulse current, pulse frequency, sintering time and sintering pressure according to the difference of the powder composition; during the sintering process, the pressure applied between the two electrodes is kept constant until the sintering is completed. The method of the present application can guarantee fine grain and high performance of the sintered tungsten alloy product, and has unique advantages in the production of "self-sharpening" high specific gravity tungsten alloy.

[0055] The above description shows and describes several preferred embodiments of the present application, but as previously described, it should be understood that the present application is not limited to the forms disclosed herein, should not be considered as excluding other embodiments, and can be used in various other combinations, modifications and environments, and can be modified within the scope of the application described herein, by the above teaching or related technical or knowledge. The modifications and changes made by those skilled in the art without departing from the spirit and scope of the present application shall fall within the scope of protection of the appended claims of the present application.

Claims

1. A method for preparing a fine-grained tungsten alloy with self-sharpening properties by flash sintering, characterized in that, Includes the following steps: S1. Place the high-density tungsten alloy powder in an insulating mold, insert the electrodes at both ends into the mold, and seal the insulating mold. S2. Based on the specific content ratio of the powder, pre-set the pulse current and sintering pressure parameters in stages; S3. Apply pulse current to the powder through the electrodes according to the preset pulse current parameters; at the same time, apply pressure to the electrodes at both ends according to the sintering pressure parameters, so that the powder can be heated rapidly by its own Joule heat.

2. The method according to claim 1, characterized in that, The powder in S1 is mixed evenly by mechanical alloying or spray drying.

3. The method according to claim 1, characterized in that, The atmosphere in which the mold is located, i.e. the sintering atmosphere, can be a vacuum, an inert gas atmosphere, or an atmospheric atmosphere.

4. The method according to claim 1, characterized in that, The pulse current parameters include pulse voltage, current density, pulse frequency, and energizing time, wherein the current density is greater than 1000 A / cm². 2 The pulse frequency is greater than 5000Hz and the energizing time is less than 1000s to achieve flash Joule thermal sintering and obtain a fine-grained tungsten alloy with self-sharpening properties.

5. The method according to claim 3, characterized in that, The powder in S1 is a ternary alloy W-Ni-Fe or an alloy powder with one or more of Co, Cr, and Mn added to the ternary alloy.

6. The method according to claim 4, characterized in that, In step S2, pulse current and sintering pressure parameters are pre-set in segments according to the specific content ratio of the powder, specifically as follows: When the tungsten content of the alloy is between (75, 90) wt.%, the pulse voltage is preset to 10~36V and the pulse current density is preset to 1000~4000A / cm. 2 The sintering pressure is 30-300MPa, the pulse frequency is 5000~50000Hz, and the sintering time is 30-1000s. When the tungsten content of the alloy is between (90, 97) wt.%, the pulse voltage is preset to 5~36V and the pulse current density is 1500~4000A / cm. 2 The sintering pressure is 30-400MPa, the pulse frequency is 5000~50000Hz, and the sintering time is 30-800s.

7. The method according to claim 5, characterized in that, When the alloy contains 93% tungsten, 4.9% Ni, and 2.1% Fe, the preset pulse voltage is 12V and the pulse current density is 2800A / cm². 2 The pulse frequency is 10000Hz, the duration is 60s, and the sintering pressure is 60MPa.

8. The method according to claim 5, characterized in that, When the alloy contains 90% tungsten, 5.5% Ni, 2.5% Fe, and 1% Co and Cr respectively, the preset pulse voltage is 17V and the pulse current density is 2700A / cm². 2 The pulse frequency is 10000Hz, the duration is 70s, and the sintering pressure is 50MPa.

9. The method according to claim 5, characterized in that, When the alloy contains 75% tungsten, 17.5% Ni, and 7.5% Fe, the preset pulse voltage is 24V and the pulse current density is 1500A / cm². 2 The pulse frequency is 10000Hz, the duration is 100s, and the sintering pressure is 100MPa.

10. A fine-grained tungsten alloy with self-sharpening properties, characterized in that, The self-sharpening fine-grained tungsten alloy is prepared by the method described in any one of claims 1-9, and the tungsten alloy is composed of a uniformly distributed W phase and a γ-(Ni,Fe) phase with a grain size of less than 6 micrometers.

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