Preparation method of high specific gravity tungsten alloy with gradient heterostructure

Abstract

The application discloses a preparation method of high-specific-gravity tungsten alloy with gradient heterogeneous structure, and aims to solve the problem that traditional homogeneous tungsten alloy bullet cores cannot simultaneously consider high hardness of a surface layer and high toughness of a core part, and the preparation steps are as follows: preparing core mixed powder A and surface layer / transition layer mixed powder B; adopting a double-direction gradient powder filling of a detachable center core sleeve, filling the core powder A first, then filling the annular area powder B, and forming a natural composition transition zone through micro-vibration after removing the core sleeve; after cold pressing forming at 200-400 MPa, two-stage gradient reaction sintering is carried out, so that WC hard phases are generated in situ in the surface layer, and the core part is densified, thereby forming the gradient heterogeneous structure which continuously transits from the surface to the inside. The method discards noble metals, is compatible with existing powder metallurgy production lines in process, and is controllable in cost, and can build the continuous gradient of high-hardness wear resistance of the surface layer and high-density high-toughness of the core part in the millimeter-level small-diameter bullet core.

Description

Technical Field

[0001] This invention relates to the field of armor-piercing projectile technology, specifically to a method for preparing a high-density tungsten alloy with a gradient heterostructure. Background Technology

[0002] Traditional armor-piercing projectile core materials are mainly tungsten-based high-density alloys (such as W-Ni-Fe or W-Ni-Cu) or depleted uranium alloys. The former is prone to insufficient resistance to high-temperature plastic deformation during high-speed penetration, and also suffers from adiabatic shear instability, forming a "mushroom head" shape, leading to passivation, severe wear during target engagement, and reduced penetration capability; the latter poses a risk of radioactive contamination. To balance high hardness and high toughness, researchers have proposed composite materials and coatings, but for projectile cores with diameters as small as approximately 10 mm, macroscopic composites suffer from weak interfacial bonding, complex processes, and high costs. In particular, the introduction of precious metals such as rhenium and tantalum for toughening is prohibitively expensive.

[0003] Powder metallurgy is a mature process for preparing tungsten alloy bullet cores, but traditional homogeneous materials cannot resolve the contradiction between surface softening and core brittleness. Therefore, there is an urgent need for innovative materials and processes that are compatible with existing powder metallurgy production lines, cost-controllable, and capable of constructing continuous performance gradients within a small size. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide a method for preparing high-density tungsten alloy with a gradient heterostructure. This method achieves a continuous transition at the millimeter scale from high surface hardness, wear resistance, and ablation resistance to high density, high toughness, and shear instability resistance in the core, which significantly improves the penetration efficiency and stability of composite armor and can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-density tungsten alloy with a gradient heterostructure, wherein the high-density tungsten alloy, in the sintered state, has a surface region, a transition region, and a core region sequentially arranged radially from the surface to the core. The method for preparing the high-density tungsten alloy includes the following steps: S1. Raw material powder preparation: The raw material powder includes core mixed powder A and surface / transition layer mixed powder B; S2, Two-way gradient powder loading: Powder loading is performed using a sleeve with a removable central core sleeve. The powder loading sequence is as follows: a. Fill the core cavity of the central core sleeve with core mixing powder A and smooth it out; b. Keeping the central core sleeve stationary, slowly and evenly pour the surface / transition layer mixed powder B into the annular cavity between the central core sleeve and the outer sleeve; c. Remove the central core sleeve, and then gently vibrate the mold to allow the two powders to interpenetrate at the interface at the micron level, forming a natural component transition zone rather than a sharp interface, thereby obtaining a powder preform with a radial component gradient. S3. Cold pressing: The filled powder preform is subjected to bidirectional pressing at a pressure of 200-400 MPa to obtain a cylindrical green body with a density of 60%-70% of the theoretical density. S4. Gradient reaction sintering: The green body is sintered in two stages under vacuum or hydrogen protection. The first stage, namely carbon diffusion and pre-sintering: the temperature is increased to 1200-1250℃ at 5-10℃ / min and held for 30-60 minutes. During this stage, carbon in graphite diffuses to the low-carbon core, establishing a stable carbon concentration gradient in the green body. At the same time, the powder particles undergo preliminary solid-phase sintering to form sufficient strength. The second stage, namely liquid phase sintering and carbide formation: continue to heat to 1350-1450℃ and hold for 60-120 minutes; S5. Heat treatment: The sintered billet is held at 1100-1300℃ in a vacuum furnace for 0.5-1 h and then cooled in the furnace to obtain a graded functional material billet.

[0006] As a preferred embodiment of the present invention, in S1, the core mixed powder A comprises: 90-95 wt% coarse spherical tungsten powder with a particle size of 20-40 μm, 5-10 wt% carbonyl iron powder and / or carbonyl nickel powder with a particle size of 3-8 μm; and the carbon content of the core mixed powder A is <0.02 wt%.

[0007] As a preferred embodiment of the present invention, in S1, the composition of the surface / transition layer mixed powder B includes: 60-70 wt% of fine irregular tungsten powder with a particle size of 3-10 μm, 28-38 wt% of pre-alloyed low alloy steel powder with a particle size of 10-20 μm, 1.0-2.0 wt% of flake graphite powder with a particle size <20 μm, and the carbon content of the surface / transition layer mixed powder B is 1.5-2.5 wt%.

[0008] As a preferred technical solution of the present invention, in the first stage of S4, carbon in the graphite diffuses into the low-carbon core, establishing a stable carbon concentration gradient in the green body, while the powder particles undergo preliminary solid-phase sintering to form sufficient strength.

[0009] As a preferred embodiment of the present invention, in the second stage of S4: In the high-carbon surface zone: carbon is fully dissolved in the molten steel and reacts with tungsten and iron to form fine spherical carbides mainly composed of WC in situ, which are dispersed in the solidified steel matrix. In the low-carbon core region: there is virtually no carbide formation, and the coarse tungsten particles are encapsulated by the molten iron-nickel binder phase, achieving complete densification; In the transition zone: A continuous microstructure transition is achieved from the surface composite material to the core high-tungsten alloy.

[0010] As a preferred technical solution of the present invention, in step c of S2, the core region of the powder preform is core mixed powder A, the surface region is surface / transition layer mixed powder B, and the transition region is a mixture of core mixed powder A and surface / transition layer mixed powder B.

[0011] Compared with the prior art, the beneficial effects of the present invention are: 1. The high-density tungsten alloy preparation method with gradient heterostructure of the present invention has excellent performance gradient: it realizes a continuous transition from high surface hardness, wear resistance, and ablation resistance to high density, high toughness, and shear instability resistance in the core at the millimeter scale, which significantly improves the penetration efficiency and stability of composite armor.

[0012] 2. The high-density tungsten alloy preparation method with gradient heterostructure exemplified by the present invention has excellent economic advantages: it uses all conventional metal powders and graphite, eliminates all precious metals, the raw material cost is close to that of traditional tungsten alloys, the core process is improved powder metallurgy, the equipment has strong inheritance, and the cost of mass production is controllable.

[0013] 3. The high-density tungsten alloy preparation method with gradient heterostructure of the present invention has perfect size adaptability: through gradient powder loading design and diffusion reaction formed at the microscale, it is not limited by the small diameter of the core, and is particularly suitable for cores with diameters of 30-125mm.

[0014] 4. The high-density tungsten alloy preparation method with gradient heterostructure of the present invention has good machinability: the surface layer is a steel matrix containing a hard phase, rather than a pure brittle ceramic, and can be precision cut with conventional cemented carbide tools to obtain a high-precision aerodynamic shape.

[0015] 5. The high-density tungsten alloy preparation method with gradient heterostructure exemplified by the present invention has strong process controllability: by precisely controlling the ratio of the two powders, the graphite content, the sintering temperature and time, the required gradient performance curve can be flexibly designed and reproduced. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the mold structure for gradient powder loading according to the present invention; Figure 2 The image shows the fracture morphology of the material in Example 1. Figure 3 Fracture morphology diagrams of the materials for comparison; Figure 4 The high-temperature compressive stress-strain curves of the materials in Example 1 and the comparative example at 1200℃ are shown. Figure 5 The friction and wear curve at 1000℃ is shown in Example 1. Figure 6 The high-temperature friction and wear curves at 1000℃ are used as a comparative example. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see Figure 1-6 This invention provides a technical solution: a method for preparing a high-density tungsten alloy with a gradient heterostructure. In the sintered state, the high-density tungsten alloy, from the surface to the core, sequentially comprises a surface region, a transition region, and a core region along the radial direction. The method for preparing this high-density tungsten alloy includes the following steps: S1. Raw material powder preparation: The raw material powder includes core mixed powder A and surface / transition layer mixed powder B; S2, Two-way gradient powder loading: Powder loading is performed using a sleeve with a removable central core sleeve. The powder loading sequence is as follows: a. Fill the core cavity of the central core sleeve with core mixing powder A and smooth it out; b. Keeping the central core sleeve stationary, slowly and evenly pour the surface / transition layer mixed powder B into the annular cavity between the central core sleeve and the outer sleeve; c. Remove the central core sleeve, and then gently vibrate the mold to allow the two powders to interpenetrate at the interface at the micron level, forming a natural component transition zone rather than a sharp interface, thereby obtaining a powder preform with a radial component gradient. S3. Cold pressing: The filled powder preform is subjected to bidirectional pressing at a pressure of 200-400 MPa to obtain a cylindrical green body with a density of 60%-70% of the theoretical density. S4. Gradient reaction sintering: The green body is sintered in two stages under vacuum or hydrogen protection. The first stage, namely carbon diffusion and pre-sintering: the temperature is increased to 1200-1250℃ at 5-10℃ / min and held for 30-60 minutes. During this stage, carbon in graphite diffuses to the low-carbon core, establishing a stable carbon concentration gradient in the green body. At the same time, the powder particles undergo preliminary solid-phase sintering to form sufficient strength. The second stage, namely liquid phase sintering and carbide formation: continue to heat to 1350-1450℃ and hold for 60-120 minutes; S5. Heat treatment: The sintered billet is held at 1100-1300℃ in a vacuum furnace for 0.5-1 h and then cooled in the furnace to obtain a graded functional material billet.

[0019] Furthermore, in S1, the composition of the core mixed powder A includes: 90-95 wt% coarse spherical tungsten powder with a particle size of 20-40 μm, 5-10 wt% carbonyl iron powder and / or carbonyl nickel powder with a particle size of 3-8 μm; the carbon content of the core mixed powder A is <0.02 wt%.

[0020] Furthermore, in S1, the composition of the surface / transition layer mixed powder B includes: 60-70 wt% fine irregular tungsten powder with a particle size of 3-10 μm, 28-38 wt% pre-alloyed low alloy steel powder with a particle size of 10-20 μm, 1.0-2.0 wt% flake graphite powder with a particle size <20 μm, and the carbon content of the surface / transition layer mixed powder B is 1.5-2.5 wt%.

[0021] Furthermore, in the first stage of S4, carbon in the graphite diffuses into the low-carbon core, establishing a stable carbon concentration gradient within the green body, while the powder particles undergo preliminary solid-phase sintering to form sufficient strength.

[0022] Furthermore, in the second phase of S4, in which: In the high-carbon surface zone: carbon is fully dissolved in the molten steel and reacts with tungsten and iron to form fine spherical carbides mainly composed of WC in situ, which are dispersed in the solidified steel matrix. In the low-carbon core region: there is virtually no carbide formation, and the coarse tungsten particles are encapsulated by the molten iron-nickel binder phase, achieving complete densification; In the transition zone: A continuous microstructure transition is achieved from the surface composite material to the core high-tungsten alloy.

[0023] Further, in step c of S2, the core region of the powder preform is core mixed powder A, the surface region is surface / transition layer mixed powder B, and the transition region is a mixture of core mixed powder A and surface / transition layer mixed powder B.

[0024] Example 1: As Figure 2 , Figure 4 and Figure 5 As shown, a 10mm diameter armor-piercing projectile core is prepared based on the above technical solution, with the following differences: Core Mixed Powder A: 93wt% spherical tungsten powder (D50=30μm), 7wt% carbonyl nickel powder (D50=5μm); Surface / transition layer mixed powder B: 65wt% fine tungsten powder (D50=6μm), 33.5wt% Fe-2Ni-1Co steel powder (D50=15μm), 1.5wt% flake graphite powder.

[0025] Powder loading: The powder is loaded using the above-mentioned bidirectional gradient powder loading method, and the pressing pressure is 300MPa to obtain a green body with a diameter of 13mm x length-to-diameter ratio of L / D≈10. Sintering: Under vacuum, the temperature is increased to 1230℃ at 8℃ / min and held for 45 minutes; then the temperature is increased to 1400℃ and held for 90 minutes, and then cooled in the furnace. Machining: The outer diameter of the sintered billet is turned to Φ10.00mm and a pointed arc shape is machined.

[0026] Performance testing: The cross-sectional metallographic structure shows a clear gradient structure; the surface layer has a hardness of 860 HV within a depth of 0.8mm, and the core has a hardness of 320 HV; the overall density is 18.1 g / cm³; ballistic tests show that its penetration depth into a homogeneous steel target is about 18% higher than that of a traditional tungsten alloy projectile core of the same size, and the projectile maintains a more complete cone shape after penetration, showing a clear self-sharpening trend.

[0027] Example 2: The difference from Example 1 is that the surface hardness is adjusted, that is, the graphite content in the surface / transition layer mixed powder B is increased to 2.0wt%, while other conditions remain unchanged; after sintering, the surface hardness (within 0.5mm) is increased to HV920, but the transition layer becomes slightly brittle, which is suitable for surface-hardened armor targets.

[0028] Comparative example: such as Figure 3 , Figure 4 and Figure 6 As shown, a single-component tungsten alloy powder (93W-4.9Ni-2.1Fe) was sintered using the same process. The metallographic structure showed a homogeneous structure with no gradient; the overall hardness was HV230 and the density was 17.3 g / cm³.

[0029] Figure 2 and Figure 3 The difference between the two lies in their grain size: Figure 2 The grain size is small and uniform, and there are certain dimples; Figure 3 The grain size is large (the tungsten grains are large), and there is obvious brittle fracture.

[0030] Figure 2 and Figure 3 The red arrows represent tungsten particles, and the yellow arrows represent the γ-(Ni, Fe) phase; among them, Figure 2 Each tiny tungsten particle is uniformly coated with γ-(Ni, Fe); Figure 3 Uneven coating affects plasticity and toughness.

[0031] Figure 4 These are the high-temperature compressive stress-strain curves of Example 1 and the comparative example. It can be clearly seen that the high-temperature resistance to plastic deformation of the material in Example 1 is significantly improved.

[0032] Figure 5 and Figure 6 In comparison, it is evident that there is a significant difference in the amount of wear between Example 1 and the comparative example; specifically: Figure 5 and Figure 6 Positive values ​​for the vertical axis “wear depth” represent surface protrusions or measurement noise, while negative values ​​represent material removal (actual wear amount). Figure 6 Peaks exceeding 20 μm in the mid-wavelength are located in the non-wear region and are positive; therefore, they cannot be used as a basis for wear analysis. However, within the wear region... Figure 6 (Comparative example) The maximum negative depth is approximately -20 μm. Figure 5 (Example 1) is approximately -10 μm, and Figure 5 The overall fluctuation is smaller; therefore, under the same experimental conditions (maximum pressure 5J, wear time 6-8 hours), Example 1 ( Figure 5 The wear of the sample was significantly less than that of the control sample ( ). Figure 6 (i.e., Example 1 is more wear-resistant).

[0033] This invention achieves a continuous transition at the millimeter scale from high surface hardness, wear resistance, and ablation resistance to high density, high toughness, and shear instability resistance in the core, significantly improving the penetration efficiency and stability against composite armor.

[0034] All parts not disclosed in this invention are prior art, and their specific structures, materials, and working principles will not be described in detail. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-density tungsten alloy with a gradient heterostructure, characterized in that: The high-density tungsten alloy, in its sintered state, consists of a surface region, a transition region, and a core region in the radial direction from the surface to the core. The preparation method of this high-density tungsten alloy includes the following steps: S1. Raw material powder preparation: The raw material powder includes core mixed powder A and surface / transition layer mixed powder B; S2, Two-way gradient powder loading: Powder loading is performed using a sleeve with a removable central core sleeve. The powder loading sequence is as follows: a. Fill the core cavity of the central core sleeve with core mixing powder A and smooth it out; b. Keeping the central core sleeve stationary, slowly and evenly pour the surface / transition layer mixed powder B into the annular cavity between the central core sleeve and the outer sleeve; c. Remove the central core sleeve, and then gently vibrate the mold to allow the two powders to interpenetrate at the interface at the micron level, forming a natural component transition zone rather than a sharp interface, thereby obtaining a powder preform with a radial component gradient. S3. Cold pressing: The filled powder preform is subjected to bidirectional pressing at a pressure of 200-400 MPa to obtain a cylindrical green body with a density of 60%-70% of the theoretical density. S4. Gradient reaction sintering: The green body is sintered in two stages under vacuum or hydrogen protection. The first stage, namely carbon diffusion and pre-sintering: the temperature is increased to 1200-1250℃ at 5-10℃ / min and held for 30-60 minutes. During this stage, carbon in graphite diffuses to the low-carbon core, establishing a stable carbon concentration gradient in the green body. At the same time, the powder particles undergo preliminary solid-phase sintering to form sufficient strength. The second stage, namely liquid phase sintering and carbide formation: continue to heat to 1350-1450℃ and hold for 60-120 minutes; S5. Heat treatment: The sintered billet is held at 1100-1300℃ in a vacuum furnace for 0.5-1 h and then cooled in the furnace to obtain a graded functional material billet.

2. The method for preparing a high-density tungsten alloy with a gradient heterostructure according to claim 1, characterized in that: In S1, the core mixed powder A consists of: 90-95 wt% coarse spherical tungsten powder with a particle size of 20-40 μm, and 5-10 wt% carbonyl iron powder and / or carbonyl nickel powder with a particle size of 3-8 μm; the carbon content of core mixed powder A is <0.02 wt%.

3. The method for preparing a high-density tungsten alloy with a gradient heterostructure according to claim 1, characterized in that: In S1, the composition of the surface / transition layer mixed powder B includes: 60-70 wt% of fine irregular tungsten powder with a particle size of 3-10 μm, 28-38 wt% of pre-alloyed low alloy steel powder with a particle size of 10-20 μm, 1.0-2.0 wt% of flake graphite powder with a particle size of <20 μm, and the carbon content of the surface / transition layer mixed powder B is 1.5-2.5 wt%.

4. The method for preparing a high-density tungsten alloy with a gradient heterostructure according to claim 1, characterized in that: In the first stage of S4, carbon in the graphite diffuses into the low-carbon core, establishing a stable carbon concentration gradient within the green body. Simultaneously, the powder particles undergo preliminary solid-phase sintering, forming sufficient strength.

5. The method for preparing a high-density tungsten alloy with a gradient heterostructure according to claim 1, characterized in that: The second phase in S4, in which: In the high-carbon surface zone: carbon is fully dissolved in the molten steel and reacts with tungsten and iron to form fine spherical carbides mainly composed of WC in situ, which are dispersed in the solidified steel matrix. In the low-carbon core region: there is virtually no carbide formation, and the coarse tungsten particles are encapsulated by the molten iron-nickel binder phase, achieving complete densification; In the transition zone: A continuous microstructure transition is achieved from the surface composite material to the core high-tungsten alloy.

6. The method for preparing a high-density tungsten alloy with a gradient heterostructure according to claim 1, characterized in that: In step c of S2, the core region of the powder preform is core mixed powder A, the surface region is surface / transition layer mixed powder B, and the transition region is a mixture of core mixed powder A and surface / transition layer mixed powder B.

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