Tungsten material with dual-scale heterogeneous layered structure and preparation method thereof

Abstract

The invention discloses a tungsten material with a double-scale heterogeneous layered structure. Fine crystal layers and coarse crystal layers which are periodically and alternately distributed are formed on the tungsten material in the thickness direction. The preparation method comprises the following steps: 1, carrying out cold isostatic pressing and pressureless sintering on the high-purity tungsten powder; 2, thermal deformation processing; and 3, performing two-stage heat treatment to obtain the tungsten material. According to the tungsten material with the double-scale layered heterogeneous structure, by means of synergistic deformation between different-scale crystal grains and crystal boundaries in different layers, crack initiation and propagation are effectively restrained, the problem of room-temperature brittleness of the tungsten material is solved, and the plasticity of the tungsten material is improved; according to the method, hot working deformation and two-stage heat treatment are carried out on the sintered blank prepared through powder metallurgy, so that the tungsten material forms a heterogeneous layered structure in which large-size recovery grains and small-size recrystallization and deformed fine grains at grain boundaries are alternately distributed, and the strength, toughness and ductility of the tungsten material are improved; the method is suitable for the fields of nuclear fusion reactor first walls, rocket engine nozzles, X-ray tube target materials and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of tungsten materials and their preparation, and in particular relates to a tungsten material with a double-scale heterogeneous layered structure and a preparation method thereof. Background Art

[0002] Tungsten has a high melting point (3422°C), high density (19.35g / cm 3 ) characteristics, thermal conductivity of about 174W·m⁻¹·K⁻¹, and thermal expansion coefficient as low as 4.3×10⁻ 6 With a high K⁻¹ and excellent resistance to radiation damage, these properties make tungsten a key high-temperature material with widespread applications in radiation collimators, plasma-facing materials for fusion reactors, and hypersonic aircraft components. Tungsten is an intrinsically brittle material with a high ductile-brittle transition temperature (DBTT). Recrystallization further increases the DBTT, leading to recrystallization embrittlement and susceptibility to brittle fracture under extreme service conditions. Traditionally, tungsten materials have achieved material performance improvements through powder metallurgy and hot working deformation, but their room-temperature brittleness severely limits their processing and application.

[0003] At present, the main methods to improve the room temperature brittleness of tungsten materials include alloying, grain refinement, and plastic deformation. The alloying method mainly forms a solid solution by adding elements such as Re and Ta, but it will significantly reduce the melting point and high-temperature performance of tungsten, and it is expensive. The grain refinement method is to prepare ultrafine-grained tungsten materials through powder metallurgy technology, but the fine-grained structure is prone to grain growth during the deformation process and has poor stability. The method of increasing toughness through plastic deformation is to form a preferentially oriented structure through rolling, but a single texture has limited effect on improving the toughness of the material. The above methods have the disadvantage of increasing the strength of the material and reducing its ductility, resulting in not being able to have both the "fish and the bear's paw". In order to overcome this dilemma, inspired by natural materials and building materials with heterogeneous structures, researchers have designed and constructed microscopic heterogeneous structures in metal materials to achieve a perfect combination of strength and ductility.

[0004] In recent years, heterostructured materials, as an emerging material design concept, achieve a coordinated optimization of strength and toughness by constructing microstructures with varying scales and properties within the material. Research has shown that by creating heterostructures with inhomogeneous microstructures (such as alternating hard and soft regions or grain size gradients), crack propagation paths can be deflected, significantly improving fracture energy absorption and toughness. The mutual constraints and strain gradients (heterogeneous deformation-induced plasticity and hardening) between different regions within the heterostructure can enhance the synergy between strength and ductility. To improve the ductility of tungsten, several approaches have explored heterostructure designs. For example, a dual-scale grain design with coexisting fine and coarse grains can achieve a balance between strength and ductility: the fine-grained regions provide high-strength support, while the coarse-grained regions provide sufficient dislocation glide paths, significantly enhancing the material's overall ductility. Research has found that mixing fine and coarse tungsten powders in high-density alloys can produce a dual-stage structure with both high strength and ductility during sintering. By precisely controlling the ratio and distribution of grains of different sizes, it is possible to overcome the strength-toughness trade-off inherent in single-grain structures.

[0005] Therefore, there is an urgent need for a new organizational structure design concept that can simultaneously regulate grain size and grain morphology at multiple scales and levels to improve the room temperature plasticity of pure tungsten. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned existing technologies and provide a tungsten material with a dual-scale heterogeneous layered structure. The tungsten material of the present invention forms fine-grained and coarse-grained layers that are periodically alternating along the thickness direction, resulting in a dual-scale layered heterogeneous structure. By utilizing the synergistic deformation between grains of different sizes and grain boundaries in different layers, the material effectively inhibits crack initiation and propagation, improves the room-temperature brittleness of the tungsten material, and significantly enhances its strength and ductility, thus resolving the difficulty of existing tungsten materials in achieving both strength and ductility.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a tungsten material with a dual-scale heterogeneous layered structure, characterized in that the tungsten material forms fine-grained layers and coarse-grained layers that are periodically alternating along the thickness direction, wherein the fine-grained layer is composed of equiaxed recrystallized and deformed grains with an average grain size of 5μm~10μm, and the thickness of the fine-grained layer is 5μm~10μm, and the coarse-grained layer is composed of recovered grains with an average grain size of 30μm~40μm, and the subgrain boundary structure is maintained inside the recovered grains, and 5%~10% of fine recrystallized grains and 5% of fine deformed grains are distributed at the grain boundaries, and the thickness of the coarse-grained layer is 30μm~40μm. The relative density of the tungsten material is above 98%.

[0008] The aforementioned tungsten material with a dual-scale heterogeneous layered structure is characterized by equiaxed grains in the fine-grained layer, elongated grains in the coarse-grained layer, and a distinct processing deformation orientation in the coarse-grained layer. The equiaxed grains in the fine-grained layer enhance the strength and uniform plasticity of the tungsten material, while the elongated grains in the coarse-grained layer, with their distinct processing deformation orientation, can induce grain boundary deflection and slip synergistic deformation under applied loads, effectively mitigating rapid crack propagation. The periodic alternating distribution of fine-grained and coarse-grained layers along the thickness direction allows the tungsten material to significantly improve its ductility while maintaining high strength.

[0009] The aforementioned tungsten material with a dual-scale heterogeneous layered structure is characterized by the recovery grains in the coarse-grained layer being induced by thermal deformation and heat treatment, and exhibiting a subgrain or dislocation network structure within the grains. This grain structure provides a stable dislocation source and slip coordination mechanism under applied load, significantly alleviating local stress concentration and promoting the deflection and blunting of crack propagation. Furthermore, through the alternating distribution of coarse-grained and fine-grained layers, the coarse-grained layers impart to the tungsten material excellent plastic deformation capacity and fracture toughness while maintaining high strength.

[0010] At the same time, the present invention also discloses a method for preparing the tungsten material having a dual-scale heterogeneous layered structure as described above, characterized in that the method comprises the following steps: Step 1: cold isostatically pressing high-purity tungsten powder to obtain a green body, and then pressurelessly sintering the green body in a hydrogen protective atmosphere to obtain a sintered blank; Step 2: subjecting the sintered blank in step 1 to multiple hot deformation processes to form a large deformation plastic deformation structure with high density dislocations and subgrain boundaries; Step 3: Perform a two-stage heat treatment on the sintered blank after the thermal deformation process in step 2 to obtain a dual-scale layered heterogeneous structure including a coarse-grained layer and a fine-grained layer, thereby obtaining a tungsten material.

[0011] The above-mentioned preparation method is characterized by the following: the mass purity of the high-purity tungsten powder described in step 1 is not less than 99.95%, and the particle size is less than 3μm; the pressure used in the cold isostatic pressing is 200MPa-260MPa, and the green density reaches more than 85% of the theoretical density; the heating rate of the pressureless sintering is 5℃ / min-15℃ / min, the sintering temperature is 1750℃-1950℃, and the holding time is 12h-24h, and the density of the sintered blank is more than 92%. The cold isostatic pressing pressure, the pressureless sintering heating system, the sintering temperature, and the holding time are conducive to obtaining a sintered blank with high purity, high density, and controllable initial grain size, laying the foundation for subsequent thermal deformation.

[0012] The above preparation method is characterized in that the temperature of the hot deformation processing in step 2 is 1650℃~1750℃ which is higher than the recrystallization temperature of tungsten, and the deformation rate is 0.1s -1 ~0.5s -1 Hot deformation involves multiple passes of unidirectional hot rolling, with each pass reducing by 10% to 25% and a cumulative reduction exceeding 50%. Intermittent holding is performed for 0.5 hours between each pass. By controlling the hot deformation temperature, deformation rate, pass reduction, and intermittent holding settings, combined with large deformation, a high density of dislocations and subgrain boundaries is effectively introduced, forming the foundation for a coarse-grained recovery layer and ensuring deformation uniformity and structural stability.

[0013] The above-mentioned preparation method is characterized in that the two-stage heat treatment described in step three includes: a first stage of stress relief annealing, which is maintained at a temperature of 1000°C to 1100°C for 1 hour to 2 hours, and a second stage of maintaining at a temperature of 800°C to 900°C for 10 hours to 40 hours. Through the first stage heat treatment and controlled temperature and holding time, the high stress generated by thermal deformation is safely released without inducing recrystallization. Through the second stage of low-temperature, long-term annealing heat treatment, residual stress and grain boundary energy differences are utilized to selectively induce local recrystallization at the grain boundaries of the original recovered coarse grains. These recrystallize together with the remaining deformed grains to form a fine-grained layer, while retaining most of the coarse-grained recovered structure to form a coarse-grained layer, thereby obtaining a dual-scale layered heterogeneous structure.

[0014] The above preparation method is characterized in that the first and second stages of the two-stage heat treatment in step 3 are both performed at a vacuum degree not exceeding 1×10 -3 The two-stage heat treatment is carried out under vacuum or inert atmosphere to effectively inhibit high-temperature oxidation.

[0015] The above-mentioned preparation method is characterized in that the volume fraction of the coarse-grained layer in the tungsten material described in step three is 85% to 90%, and the volume fraction of the fine-grained layer is 5% to 15%. Among them, controlling the proportion of the coarse-grained layer at 85% to 90% can ensure that the material maintains a high matrix strength and provides a stable plastic deformation orientation; controlling the proportion of the fine-grained layer at 10% to 15% can form an effective crack pinning and deflection mechanism, significantly improving room temperature ductility and fracture toughness. When the proportion of the coarse-grained layer is higher than 90%, the fine-grained layer is insufficient to play a toughening role; when it is lower than 85%, it will lead to a decrease in strength and an unstable layered structure.

[0016] Compared with the prior art, the present invention has the following advantages: 1. The tungsten material of the present invention obtains a dual-scale layered heterogeneous structure by forming fine-grained layers and coarse-grained layers that are periodically alternating along the thickness direction. The synergistic deformation between grains of different sizes and grain boundaries in different layers is utilized to effectively inhibit crack initiation and propagation, significantly improve the room temperature brittleness problem of the tungsten material, change the crack propagation path, and significantly improve the plasticity of the tungsten material.

[0017] 2. Compared with traditional equiaxed homogeneous tungsten materials, the tungsten material of the present invention has a dual-scale heterogeneous layered structure, in which the grain sizes in different layers are significantly different, manifested as fine recrystallized and deformed equiaxed grains distributed at the grain boundaries, and still retains the recovery structure characteristics after thermal deformation, forming a dual-scale grain structure. While keeping the tensile strength basically unchanged, the elongation after fracture is significantly improved, combining high strength and high ductility, improving the machinability of tungsten materials at room temperature, and expanding the application range of tungsten materials.

[0018] 3. Unlike the existing tungsten materials prepared by powder metallurgy, which have coarse grains, high brittleness, poor plasticity and are difficult to meet the stringent requirements of high strength and toughness at room temperature, the present invention adopts a process route that combines powder metallurgy with thermal deformation, and precisely designs a two-stage heat treatment process to regulate the tungsten material structure into a heterogeneous layered structure composed of large-sized recovery grains, small-sized recrystallized fine grains at grain boundaries, and fine deformed grains alternatingly distributed. This makes the tungsten material have good matching of strength and toughness, and can effectively improve the room temperature brittleness problem of pure tungsten.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of the preparation process of the tungsten material with a dual-scale heterogeneous layered structure according to the present invention.

[0021] Figure 2 This is the EBSD micromorphology and grain boundary orientation distribution diagram of the tungsten material prepared in Example 1 of the present invention.

[0022] Figure 3 This is a TEM image of the coarse-grained layer in the tungsten material prepared in Example 1 of the present invention.

[0023] Figure 4 This is a distribution diagram of the recovery, deformation and recrystallization structures in the tungsten material prepared in Example 1 of the present invention and a corresponding volume distribution statistical diagram.

[0024] Figure 5 This is a distribution diagram of the recovery, deformation and recrystallization structures in the tungsten material prepared in Example 2 of the present invention and the corresponding volume distribution statistical diagram.

[0025] Figure 6These are the engineering stress-engineering strain curves of the tungsten materials prepared in Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0026] Example 1 The tungsten material of this embodiment forms fine-grained layers and coarse-grained layers that are periodically alternating along the thickness direction, wherein the fine-grained layer is composed of equiaxed recrystallized and deformed grains with an average grain size of 5 μm, and the thickness of the fine-grained layer is 5 μm. The coarse-grained layer is composed of recovered grains with an average grain size of 30 μm. The subgrain boundary structure is maintained inside the recovered grains, and 5% of fine recrystallized grains and 5% of fine deformed grains are distributed at the grain boundaries. The thickness of the coarse-grained layer is 30 μm, and the relative density of the tungsten material is 98%.

[0027] like Figure 1 As shown, the method for preparing the tungsten material with a dual-scale heterogeneous layered structure of this embodiment includes the following steps: Step 1: Pre-treat high-purity tungsten powder with a mass purity of 99.95% and a particle size of 3 μm in a hydrogen atmosphere to remove surface oxides. Then, cold isostatic pressing is performed at a pressure of 200 MPa to obtain a green body with a density of 89% of the theoretical density. The green body is then placed in a sintering furnace with a hydrogen protective atmosphere, heated to 1750°C at a heating rate of 5°C / min, and sintered for 12 hours to obtain a sintered body with a density of 94%; Step 2: The sintered blank in step 1 is subjected to multiple passes of unidirectional hot rolling at 1650°C with a deformation rate of 0.1s -1 The reduction rate of each pass is 10%, the cumulative reduction rate is 50%, and intermittent insulation is carried out for 0.5h between adjacent passes of unidirectional hot rolling to form a large deformation plastic deformation structure with high density dislocations and subgrain boundaries; Step 3: The sintered blank after thermal deformation in step 2 is subjected to two-stage heat treatment. The first stage is stress relief annealing. 3 Pa and 1000 ° C for 1 hour. In the second stage, it is kept warm at 800 ° C for 10 hours under argon protection to obtain a double-scale layered heterogeneous structure including a coarse-grained layer and a fine-grained layer to obtain tungsten material.

[0028] According to the test, the volume fraction of the coarse-grained layer in the tungsten material prepared in this embodiment is 90%, and the volume fraction of the fine-grained layer is 10%.

[0029] The tungsten material prepared in this example was sampled for microstructural characterization, and the results were as follows: Figure 2 As shown. Figure 2It can be seen from the EBSD micromorphology that the tungsten material presents alternating fine-grained layers and coarse-grained layers along the thickness direction, and the grains in the fine-grained layers are basically equiaxed, while the grains in the coarse-grained layers are elongated along the rolling direction; further EBSD grain boundary orientation distribution results show that the coarse-grained layer has obvious processing deformation orientation.

[0030] The tungsten material prepared in this example was sampled and observed by high-resolution TEM. The results are as follows: Figure 3 As shown, the right picture is an enlarged picture of the box on the left picture. Figure 3 It can be seen that some grains in the coarse-grained layer of the tungsten material undergo a recovery process after thermal deformation and heat treatment. There is an obvious subgrain structure and network dislocation distribution inside the grains. This structure helps to provide a stable dislocation source and slip channel under the action of external load, thereby enhancing the plastic deformation ability of the tungsten material.

[0031] Figure 4 The recovery, deformation and recrystallization structure distribution diagrams and the corresponding volume distribution statistics of the tungsten material prepared in this embodiment are shown in Figure (a) for the structure distribution diagram and Figure (b) for the volume distribution statistics diagram. Figure 4 It can be seen that the microstructure of the tungsten material is mainly composed of the recovery structure of the coarse-grained layer and the recrystallization and deformation structure of the fine-grained layer; the statistical results show that the volume fraction of the coarse-grained layer is about 90%, and the volume fraction of the fine-grained layer is about 10%.

[0032] Example 2 The tungsten material of this embodiment forms fine-grained layers and coarse-grained layers that are periodically alternating along the thickness direction, wherein the fine-grained layer is composed of equiaxed recrystallized and deformed grains with an average grain size of 10 μm, and the thickness of the fine-grained layer is 10 μm. The coarse-grained layer is composed of recovered grains with an average grain size of 40 μm. The subgrain boundary structure is maintained inside the recovered grains, and 10% of fine recrystallized grains and 5% of fine deformed grains are distributed at the grain boundaries. The thickness of the coarse-grained layer is 40 μm, and the relative density of the tungsten material is 99%.

[0033] like Figure 1 As shown, the method for preparing the tungsten material with a dual-scale heterogeneous layered structure of this embodiment includes the following steps: Step 1: Pre-treat high-purity tungsten powder with a mass purity of 99.97% and a particle size of 2 μm in a hydrogen atmosphere to remove surface oxides. Then, cold isostatic pressing is performed at a pressure of 260 MPa to obtain a green body with a density of 91% of the theoretical density. The green body is then placed in a sintering furnace with a hydrogen protective atmosphere, heated to 1950°C at a heating rate of 15°C / min and sintered for 24 hours to obtain a sintered body with a density of 96%. Step 2: The sintered blank in step 1 is subjected to multiple passes of unidirectional hot rolling at 1750°C with a deformation rate of 0.5s-1 The reduction rate of each pass is 25%, the cumulative reduction rate is 75%, and intermittent insulation is carried out for 0.5h between adjacent passes of unidirectional hot rolling to form a large deformation plastic deformation structure with high density dislocations and subgrain boundaries; Step 3: The sintered blank after thermal deformation in step 2 is subjected to two-stage heat treatment. The first stage is stress relief annealing. 3 Pa and 1100 ° C for 2h. In the second stage, it is kept warm at 900 ° C for 40h under argon protection to obtain a double-scale layered heterogeneous structure including a coarse-grained layer and a fine-grained layer to obtain tungsten material.

[0034] According to the test, the volume fraction of the coarse-grained layer in the tungsten material prepared in this embodiment is 85%, and the volume fraction of the fine-grained layer is 15%.

[0035] Figure 5 The recovery, deformation and recrystallization structure distribution diagrams and the corresponding volume distribution statistics of the tungsten material prepared in this embodiment are shown in Figure (a) for the structure distribution diagram and Figure (b) for the volume distribution statistics diagram. Figure 5 It can be seen that compared with Example 1, the tissue distribution in the tungsten material prepared in this example is different, wherein the proportion of the fine-grained layer is relatively increased, and the recrystallized tissue distribution is more obvious; statistical results show that the volume fraction of the coarse-grained layer is approximately 85%, and the volume fraction of the fine-grained layer is approximately 15%.

[0036] Figure 6 The engineering stress-engineering strain curves of the tungsten materials prepared in Examples 1 and 2 of the present invention are shown in FIG. Figure 6 It can be seen that the tungsten materials prepared in Example 1 and Example 2 both have high tensile strength. Among them, the room temperature elongation of the tungsten material prepared in Example 2 is significantly higher than that in Example 1, indicating that the increase in the proportion of the fine crystal layer helps to enhance the plasticity of the tungsten material.

[0037] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A tungsten material having a dual-scale heterogeneous layered structure, characterized in that: The tungsten material forms fine-grained layers and coarse-grained layers that are periodically alternating along the thickness direction, wherein the fine-grained layer is composed of equiaxed recrystallized and deformed grains with an average grain size of 5μm~10μm, and the thickness of the fine-grained layer is 5μm~10μm, and the coarse-grained layer is composed of recovered grains with an average grain size of 30μm~40μm. The subgrain boundary structure is maintained inside the recovered grains, and 5%~10% of fine recrystallized grains and 5% of fine deformed grains are distributed at the grain boundaries. The thickness of the coarse-grained layer is 30μm~40μm, and the relative density of the tungsten material is above 98%.

2. The tungsten material having a dual-scale heterogeneous layered structure according to claim 1, characterized in that: The grains in the fine-grained layer are equiaxed, the grains in the coarse-grained layer are elongated, and the coarse-grained layer has obvious processing deformation orientation.

3. The tungsten material having a dual-scale heterogeneous layered structure according to claim 1, characterized in that: The recovered grains in the coarse-grained layer are formed by thermal deformation and heat treatment, and the interior of the grains presents a sub-grain or dislocation network structure.

4. A method for preparing a tungsten material having a dual-scale heterogeneous layered structure according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: cold isostatically pressing high-purity tungsten powder to obtain a green body, and then pressurelessly sintering the green body in a hydrogen protective atmosphere to obtain a sintered blank; Step 2: subjecting the sintered blank in step 1 to multiple hot deformation processes to form a large deformation plastic deformation structure with high density dislocations and subgrain boundaries; Step 3: Perform a two-stage heat treatment on the sintered blank after the thermal deformation process in step 2 to obtain a dual-scale layered heterogeneous structure including a coarse-grained layer and a fine-grained layer, thereby obtaining a tungsten material.

5. The preparation method according to claim 4, characterized in that The mass purity of the high-purity tungsten powder described in step 1 is not less than 99.95%, and the particle size is less than 3 μm; the pressure used in the cold isostatic pressing is 200 MPa~260 MPa, and the green density reaches more than 85% of the theoretical density; the heating rate of the pressureless sintering is 5°C / min~15°C / min, the sintering temperature is 1750°C~1950°C, the holding time is 12h~24h, and the density of the sintered blank is more than 92%.

6. The preparation method according to claim 4, characterized in that The temperature of the thermal deformation process in step 2 is 1650℃~1750℃, which is higher than the recrystallization temperature of tungsten, and the deformation rate is 0.1s -1 ~0.5s -1 The hot deformation processing adopts multiple passes of unidirectional hot rolling, with a reduction rate of 10%~25% in each pass and a cumulative reduction rate of more than 50%, and intermittent insulation for 0.5h between adjacent passes of unidirectional hot rolling.

7. The preparation method according to claim 4, characterized in that The two-stage heat treatment in step three includes: a first stage of stress relief annealing, which is kept at a temperature of 1000°C to 1100°C for 1h to 2h; and a second stage of keeping at a temperature of 800°C to 900°C for 10h to 40h.

8. The preparation method according to claim 4, characterized in that The first and second stages of the two-stage heat treatment in step 3 are both performed at a vacuum degree not exceeding 1×10 -3 Pa or argon protection.

9. The preparation method according to claim 4, characterized in that In step 3, the volume fraction of the coarse-grained layer in the tungsten material is 85% to 90%, and the volume fraction of the fine-grained layer is 5% to 15%.

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