A metal material of body-centered cubic structure and a method for producing the same

Abstract

The application relates to a body-centered cubic structure metal material and a preparation method thereof, and relates to the technical field of metal material strengthening. The main technical scheme is as follows: the deformation characteristics of the body-centered cubic structure metal material include dislocations; the preparation method comprises the following steps: annealing treatment is conducted on a body-centered cubic structure metal piece to obtain an annealed metal piece; small-angle cyclic reciprocating torsional deformation treatment is conducted on the annealed metal piece to obtain the body-centered cubic structure metal material; and the temperature of the small-angle cyclic reciprocating torsional deformation treatment is-196 to-50 DEG C. The application is mainly used for improving the strength and plasticity of the body-centered cubic structure metal material, and good strength-plasticity matching is realized.

Description

Technical Field

[0001] This invention relates to the field of metal material strengthening technology, and in particular to a body-centered cubic metal material and its preparation method. Background Technology

[0002] With the development of advanced technologies and new fields, higher demands are being placed on the performance of metallic materials under harsh environments. Body-centered cubic (BCC) metallic materials have been widely used in production and daily life since the Iron Age. They possess excellent performance over a wide temperature range and under high strain conditions, exhibiting wear resistance and corrosion resistance. Therefore, they are widely used in extreme service environments such as deep space exploration, cryogenic superconductivity, and gas industry, serving as structural components in critical equipment such as nuclear reactors, rockets, satellites, and aero engines. Consequently, BCC metallic materials have been widely used and continue to attract attention. To ensure their safety and reliability during service, higher requirements are being placed on their strength and ductility; therefore, strengthening BCC materials has always been an important theme in the development of new structural materials.

[0003] Plastic deformation is a commonly used method to improve the strength of metals, and the introduced new interfaces can effectively block dislocation movement. For face-centered cubic (FCC) metals, high strength and elongation can be achieved through the interaction of stacking faults, deformation twins, and dislocations, activating abundant slip systems and generating continuous work hardening capabilities. Unlike FCC metals, body-centered cubic (BCC) metals typically have fewer activated slip systems and higher stacking fault energies, resulting in insufficient dislocation interactions required for coordinated deformation and lower work hardening capabilities. Conventional plastic deformation methods, while increasing strength, often come with significant plasticity loss. Severe plastic deformation (SPD), developed in recent years, is an effective method to improve material strength. Common methods include cold forging, isochannel extrusion, and high-pressure torsion. However, these methods all have inherent technical limitations, such as limited sample size and poor uniformity, inevitably worsening the material's plasticity while increasing strength.

[0004] In summary, there is an urgent need for a method to improve the strength and ductility of metal materials with body-centered cubic (BCC) structures. Summary of the Invention

[0005] In view of this, the present invention provides a body-centered cubic structure metal material and its preparation method, the main purpose of which is to improve the strength and plasticity of the body-centered cubic structure metal material.

[0006] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0007] On one hand, embodiments of the present invention provide a method for preparing a body-centered cubic (BCC) metallic material, wherein the deformation characteristics of the BCC metallic material include dislocations; wherein the preparation method includes the following steps:

[0008] Annealing is performed on a body-centered cubic metal part to obtain an annealed metal part.

[0009] The annealed metal part is subjected to a small-angle cyclic torsional deformation treatment to obtain a body-centered cubic metal material; wherein the temperature of the small-angle cyclic torsional deformation treatment is -196~-50℃.

[0010] Preferably, the temperature for the small-angle cyclic torsional deformation treatment is the liquid nitrogen temperature.

[0011] Preferably, the small-angle cyclic reciprocating torsional deformation process is as follows: After clamping and fixing one end of the annealed metal part, a force is applied to rotate the other end of the annealed metal part around the central axis of the annealed metal part. First, rotate clockwise by an angle θ from the initial position, then rotate counterclockwise by an angle θ back to the initial position, continue to rotate counterclockwise by an angle θ, then rotate clockwise by an angle θ back to the initial position, so that the annealed metal part completes one reciprocating torsion, which is one cycle of torsion; then the annealed metal part starts the next reciprocating rotation process from the initial position, and so on, until the required number of cycles of torsion is reached; wherein, θ takes a fixed value in each cycle of reciprocating torsion deformation process.

[0012] Preferably, in the step of the small-angle cyclic torsional deformation treatment: the angle θ of each rotation of the annealed metal part is the torsional angle amplitude, wherein,

[0013] θ is 1°~40°, the torsion rate is 100~10000° / min, and the number of cyclic torsion cycles N is 2~500;

[0014] Preferred,

[0015] 7500%≥θπd / 360°L – σ y / 2G ≥ 0.05%;

[0016] 0.1%≤4Nθπd / 180°L - 4Nσ y / G≤7500%;

[0017] Where N is the number of cyclic torsion cycles; d is the diameter of the deformation zone of the metal rod; L is the axial length of the deformation zone of the metal rod; σ y G is the yield strength of the metal bar; G is the shear modulus of the metal bar.

[0018] Preferably, during the small-angle cyclic torsional deformation process: the annealed metal part is placed in a cavity at -196~-50℃ and subjected to small-angle cyclic torsional deformation.

[0019] Preferably, the cavity is a liquid nitrogen cavity.

[0020] Preferably, before the small-angle cyclic torsional deformation treatment, the annealed metal part needs to be treated as follows:

[0021] The annealed metal part is placed in an environment of -196~-50℃ for cooling;

[0022] Preferably, the cooling time is 10-20 minutes;

[0023] Preferably, the annealed metal part is cooled in a liquid nitrogen environment.

[0024] Preferably, the metal part with the body-centered cubic structure is a rod; preferably, the axial length L of the rod is greater than 1 mm and the diameter d is greater than 0.5 mm.

[0025] On the other hand, embodiments of the present invention also provide a method for preparing the body-centered cubic structured metallic material as described in any of the above claims, wherein...

[0026] The annealing temperature is 950-1150℃, and the annealing time is 1-2 hours; and / or

[0027] The body-centered cubic metal parts have undergone forging, drawing and other processes in the early stage, resulting in significant deformation. After annealing, the annealed metal parts have a grain size of approximately 50-100 micrometers, with no obvious deformation inside the grains.

[0028] Preferably, the yield strength of the body-centered cubic metal material is 1.3 to 1.5 times that of the annealed metal part;

[0029] The surface hardness of the body-centered cubic metal material is 1.5 to 2 times that of the annealed metal part.

[0030] In another aspect, embodiments of the present invention provide a body-centered cubic (BCC) metallic material, wherein the surface of the BCC metallic material has an equiaxed dislocation cell structure and / or subgrain boundaries; wherein the dislocation cell structure refers to a three-dimensional equiaxed cell morphology characterized by dislocations self-organizing; the subgrain boundaries are substructures developed from dislocation cells; wherein the orientation difference of the subgrain boundaries is greater than the orientation difference of the dislocation cell structure; and the interface clarity of the subgrain boundaries is greater than the interface clarity of the dislocation cell structure.

[0031] The subsurface of the body-centered cubic metallic material has a dislocation wall structure; wherein, the dislocation wall structure refers to the self-organized arrangement of dislocations into a two-dimensional spatial wall-like morphology.

[0032] The core of the body-centered cubic metallic material has an isolated dislocation structure; wherein the isolated dislocation structure exhibits a random, isolated linear morphology.

[0033] Wherein, the body-centered cubic metal material is prepared by any of the above-described methods for preparing body-centered cubic metal materials;

[0034] Preferably, the dislocation structure size of the body-centered cubic metallic material exhibits a gradient increasing trend from the surface to the interior;

[0035] Preferably, the dislocation density of the body-centered cubic metallic material decreases in a gradient from the surface to the interior.

[0036] Preferably, the diameter of the dislocation cells in the body-centered cubic metallic material is 40~800 nm;

[0037] Preferably, the spacing between the dislocation walls in the dislocation wall structure is 200~1200nm;

[0038] Preferably, in the core of the body-centered cubic metallic material, the density of the solitary dislocation structure is as follows: 10 13 ~10 16 root / m 2 .

[0039] Compared with the prior art, the body-centered cubic metallic material and its preparation method of the present invention have at least the following beneficial effects:

[0040] This invention provides a method for preparing a body-centered cubic (BCC) structured metallic material, comprising the following steps: annealing a BCC structured metallic part to obtain an annealed metallic part; subjecting the annealed metallic part to a small-angle cyclic torsional deformation treatment to obtain a BCC structured metallic material; wherein the temperature of the small-angle cyclic torsional deformation treatment is -196 to -50°C. It should be noted that, due to the typically low number of activated slip systems and high stacking fault energy in BCC structured metallic materials, the dislocation interactions required for coordinated deformation are insufficient, resulting in low work hardening capacity. Using conventional process parameters for small-angle cyclic torsional deformation treatment of BCC structured metallic materials cannot improve strength and plasticity. The inventors of this invention have conducted extensive research and innovation on the small-angle cyclic torsional deformation treatment of body-centered cubic (BCC) structure metallic materials. Under low-temperature conditions, small-angle cyclic torsional deformation treatment was applied to annealed BCC structure metallic parts, ultimately introducing a gradient-distributed dislocation substructure into the original grain structure of the BCC. A spatial gradient distribution of dislocation density is observed from the surface to the core. Specifically, the surface layer has a dislocation cell structure; the subsurface layer has a dislocation wall structure; and the core has an isolated dislocation structure. This dislocation structure enables the BCC structure metallic material to simultaneously achieve high strength and good plasticity, realizing the efficient preparation of a material with a good balance of strength and plasticity.

[0041] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the processing technology for low-temperature, small-angle cyclic torsional deformation proposed in an embodiment of the present invention.

[0043] Figure 2 The image shown is a backscattered electron micrograph of the surface to core microstructure obtained by twisting an annealed pure tantalum rod sample for 200 cycles under a torsion angle amplitude of 6°, as described in Example 1.

[0044] Figure 3 This is a microstructure diagram of the surface to core of an annealed pure tantalum rod sample obtained after being twisted 200 times under a torsion angle amplitude of 16°, as shown in Example 2. Figure 3 (a) is an EBSD crystallographic IPF orientation image; (b) is a grain boundary distribution map; and (c) is a backscattered electron scanning micrograph.

[0045] Figure 4In Example 2, the microstructure of the annealed pure tantalum rod sample after being twisted for 200 cycles at different depths under the condition of a torsion angle amplitude of 16° is shown in the transmission electron microscope images. (a) Core isolated dislocations; (b) Dislocation wall structure at a distance of about 1.5 mm from the surface; (c) Equiaxed dislocation cell structure at a distance of 800 μm from the surface; (d) Subgrain boundary at a distance of 50 μm from the surface.

[0046] Figure 5 The image shows the surface-to-core microstructure of an annealed pure tantalum rod sample obtained after 200 twists under a torsion angle amplitude of 16°, as shown in Comparative Example 2. Figure 5 (a) is an EBSD crystallographic IPF orientation image; (b) is a grain boundary distribution map; and (c) is a backscattered electron scanning micrograph.

[0047] Figure 6 The diagram shows the distribution of microhardness of pure tantalum rod samples as a function of depth from the surface after low-temperature, small-angle cyclic torsional deformation treatment in Examples 1 and 2.

[0048] Figure 7 The stress-strain curves of the pure tantalum rod samples after low-temperature, small-angle cyclic torsional deformation treatment are shown in Examples 1 and 2.

[0049] Figure 8 The stress-strain curves of the pure iron bar sample in the annealed state and after low-temperature, small-angle cyclic torsional deformation treatment are shown in Example 3. Detailed Implementation

[0050] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0051] For face-centered cubic (FCC) metallic materials, previous techniques significantly improved their mechanical properties through small-angle cyclic torsional deformation. However, body-centered cubic (BCC) metallic materials typically have fewer activated slip systems and higher stacking fault energies, resulting in insufficient dislocation interactions required for coordinated deformation and lower work hardening capacity. Under the previous process parameters, small-angle cyclic torsional deformation of BCC metallic materials suffers from problems such as easy dislocation recovery and low dislocation density.

[0052] Therefore, the inventors of this invention have conducted extensive research and innovation on the small-angle cyclic torsional deformation treatment of metal materials with body-centered cubic (BCC) structures, proposing a small-angle cyclic torsional deformation treatment suitable for BCC structure metal materials, thereby improving the strength and plasticity of BCC structure metal materials. The main solution of this invention is as follows:

[0053] On one hand, embodiments of the present invention provide a method for preparing a body-centered cubic (BCC) metallic material, wherein the deformation characteristics of the BCC metallic material include dislocations; wherein the preparation method includes the following steps: annealing a BCC metallic part to obtain an annealed metallic part; subjecting the annealed metallic part to a small-angle cyclic torsional deformation treatment to obtain a BCC metallic material; wherein the temperature of the small-angle cyclic torsional deformation treatment is -196 to -50°C, preferably the liquid nitrogen temperature.

[0054] It should be noted that, in order to achieve the temperature of -196~-50℃ (preferably liquid nitrogen temperature) for the small-angle cyclic torsional deformation treatment, this application employs the following design:

[0055] (1) See Figure 1 As shown, the annealed metal part 1 is placed in an environment of -196 to -50°C, such as in cavity 2; preferably a liquid nitrogen cavity, see [reference]. Figure 1 As shown, a small-angle cyclic torsional deformation process is performed.

[0056] (2) After immersing the annealed metal parts in liquid nitrogen, wrap them with heat insulation material and perform small-angle cyclic torsion deformation treatment; during the small-angle cyclic torsion deformation treatment, the annealed metal parts are placed in the liquid nitrogen chamber to maintain low temperature.

[0057] Preferably, before the small-angle cyclic torsional deformation treatment, the annealed metal part needs to be treated as follows: the annealed metal part is placed in an environment of -196~-50℃ (preferably in a liquid nitrogen environment) for cooling so that the annealed metal part is uniformly cooled to the target torsion temperature; wherein, the cooling time is 10~20min.

[0058] Preferably, the small-angle cyclic reciprocating torsional deformation process is as follows: After clamping and fixing one end of the annealed metal part, a force is applied to rotate the other end of the annealed metal part around the central axis of the annealed metal part. First, rotate clockwise by an angle θ from the initial position, then rotate counterclockwise by an angle θ back to the initial position, continue to rotate counterclockwise by an angle θ, then rotate clockwise by an angle θ back to the initial position, so that the annealed metal part completes one reciprocating torsion, which is one cycle of torsion; then the annealed metal part starts the next reciprocating rotation process from the initial position, and so on, until the required number of cycles of torsion is reached; wherein, θ takes a fixed value in each cycle of reciprocating torsion deformation process.

[0059] Preferably, the angle θ of each rotation of the annealed metal part is the torsional angle amplitude, where θ is 1°~40°; the torsional rate is 100~10000° / min, and the number of cyclic torsional cycles N is 2~500.

[0060] Preferably, 7500% ≥ θπd / 360°L – σ y / 2G ≥ 0.05%;

[0061] 0.1%≤4Nθπd / 180°L - 4Nσ y / G≤7500%;

[0062] Where N is the number of cyclic torsion cycles; d is the diameter of the deformation zone of the metal rod; L is the axial length of the deformation zone of the metal rod; σ y G is the yield strength of the metal bar; G is the shear modulus of the metal bar.

[0063] Preferably, the metal part with a body-centered cubic structure is a bar or tube; preferably, the axial length L of the bar is greater than 1 mm and the diameter d is greater than 0.5 mm.

[0064] In this embodiment of the invention, by subjecting the annealed metal part to small-angle cyclic torsional deformation under the above-mentioned temperature conditions, a gradient-distributed dislocation substructure is introduced into the original grain structure of the body-centered cubic metal material, resulting in a spatial gradient distribution of dislocation density from the surface to the core. The final structure is as follows: the surface layer of the body-centered cubic (BCC) metallic material (the surface layer refers to a location less than 1.5 mm from the surface) has an equiaxed dislocation cell structure (here, "equiaxed dislocation cell structure" refers to an interface around the dislocation cell with approximately equal lengths, close to a perfect circle) and / or a subgrain boundary structure; wherein, the dislocation cell structure refers to the self-organized arrangement of dislocations into a three-dimensional equiaxed cell morphology; the subgrain boundary refers to the further development of the dislocation cell into a substructure with a larger orientation difference and a clearer interface; the subsurface layer of the BCC metallic material (the subsurface layer refers to a location 1.5~2 mm from the surface) has a dislocation wall structure; wherein, the dislocation wall structure refers to the self-organized arrangement of dislocations into a two-dimensional wall morphology; the core of the BCC metallic material has an isolated dislocation structure; wherein, the isolated dislocation structure exhibits a random, isolated linear morphology. The refinement of the spatial structure gradient leads to an increase in material strength, while the spatial strain gradient distribution maintains considerable plasticity.

[0065] It should also be noted that: body-centered cubic metallic materials include pure Ta, pure Fe, pure Nb, pure V and other body-centered cubic metals and their alloys, as well as some high-entropy alloys with body-centered cubic structures such as Ti, Zr, Hf, Nb, etc.

[0066] 1. The method of the present invention involves subjecting an annealed body-centered cubic metal part to cyclic torsional deformation at a small torsional angle (<30°) using a torsion device under low-temperature conditions. This results in a gradient distribution of shear plastic strain from the surface to the core of the body-centered cubic metal material. Because the single torsional angle is small, the strain and stress are relatively small, and there is no significant change in the surface morphology and shape of the sample. However, by changing the number of torsional cycles, the cumulative plastic strain can be increased.

[0067] 2. The method of the present invention places the annealed metal part with a body-centered cubic structure in a low-temperature environment (e.g., liquid nitrogen) for torsional deformation. The overall temperature of the material is -196 to -50°C. At low temperatures, the Zener-Hollomon (Z) parameter during the deformation process is increased. This refines the microstructure by increasing the shear stress during dislocation slip. Simultaneously, the thermally activated recovery process, such as dislocation annihilation and grain boundary migration, can be effectively delayed, which is beneficial for effectively improving the material's strength. Furthermore, the deformation temperature is closely related to the deformation mode and structural refinement. Under low-temperature conditions, more slip systems can be activated, promoting multi-system slip and improving the material's plasticity.

[0068] 3. Unlike traditional methods of surface plasticity (e.g., surface nano-sizing) to obtain nanocrystalline structures on the sample surface, this invention introduces a gradient-distributed dislocation structure on the surface and interior of a body-centered cubic metal material through cyclic torsional plastic deformation, while retaining the original coarse-grained structure. This results in the body-centered cubic metal material after cyclic torsion having uniform plasticity and elongation at break comparable to the original structure, while also having high yield strength and tensile strength, exhibiting a good balance between strength and plasticity.

[0069] 4. The method of this invention can ensure low temperature throughout the entire process of cyclic torsional deformation. Its advantages include lower requirements for equipment and sample size. Traditional low-temperature deformation requires an incubator, which involves complex equipment and strict requirements on sample size. This invention, based on conventional torsional equipment, can achieve torsional deformation at liquid nitrogen temperature with significant cooling speed and effect. The processing time for a single sample is only a few minutes, resulting in high processing efficiency, low surface roughness, and less restriction on sample size by equipment. It can process samples of different sizes, which is of great significance for equipment lightweighting and energy conservation and emission reduction, and has broad application prospects in industry.

[0070] The following specific experimental examples further illustrate this point:

[0071] Example 1

[0072] This embodiment involves subjecting an annealed tantalum body-centered cubic structure metal material (bar) with an average grain size of approximately 50 micrometers to a small-angle cyclic torsional deformation process. This process introduces a gradient-distributed dislocation structure from the surface inwards, resulting in a body-centered cubic structure metal material. The annealing temperature is 950-1150℃, and the time is 2 hours.

[0073] The bar has an axial length of 12 mm, a diameter of 4.5 mm, a torsion angle amplitude of 6°, a torsion rate of 7200° / min, 200 torsion cycles, and a torsion temperature of 77 K (-196 °C). Wherein, θπd / 360°L – σ y / 2G=0.018, 4Nθπd / 180°L - 4Nσ y / G=14.1.

[0074] See Figure 2 As shown, after the annealed metal material (rod) with pure tantalum body-centered cubic structure obtained in this embodiment is subjected to low-temperature reciprocating torsion treatment, a gradient distribution of deformation substructures is formed from the surface to the core in the obtained body-centered cubic metal material (the surface layer has an equiaxed dislocation cell structure, the subsurface layer has a dislocation wall structure, and the core has an isolated dislocation structure). The original grain size remains unchanged, and it can be seen that the deformation gradient from the surface to the core decreases.

[0075] See Figure 6 As shown, in the body-centered cubic structure metal material obtained in this embodiment, the hardness is distributed in a gradient from the surface to the core, decreasing from 2.1 GPa at the surface to 1.6 GPa at the core.

[0076] See Figure 7 As shown, the yield strength of the body-centered cubic metal material obtained in this embodiment is 323 MPa, the tensile strength is 402 MPa, and the uniform elongation is 22%.

[0077] Example 2

[0078] This embodiment involves subjecting an annealed tantalum body-centered cubic structure metal material (bar) with an average grain size of approximately 50 micrometers to a small-angle cyclic torsional deformation process. This process introduces a gradient-distributed dislocation structure from the surface inwards, resulting in a body-centered cubic structure metal material. The annealing temperature is 950-1150℃, and the time is 2 hours.

[0079] The difference between this embodiment and Embodiment 1 lies in the torsion process parameters. The torsion process parameters in this embodiment are as follows: torsion angle amplitude is 16°, torsion rate is 3600° / min, and torsion cycles are 200.

[0080] Where, θπd / 360°L – σ y / 2G=0.050, 4Nθπd / 180°L - 4Nσ y / G=40.

[0081] See Figure 3 As shown, in this embodiment, after the annealed metal material (rod) with pure tantalum body-centered cubic structure is subjected to low-temperature reciprocating torsion treatment, a gradient distribution of deformed substructures is formed from the surface to the core in the resulting body-centered cubic metal material. The morphology, size orientation, and original large-angle grain boundaries of the original grains remain unchanged, while the density of small-angle interfaces gradually decreases from the surface to the core.

[0082] See Figure 4 As shown, the core of the body-centered cubic metal material is a lone dislocation structure, with a dislocation wall structure at a distance of 1.5 mm from the surface. As the strain increases, an equiaxed dislocation cell structure is formed at a distance of 800 μm from the surface, and a subgrain boundary with a clearer interface is formed at a distance of 50 μm from the surface in the outermost layer.

[0083] See Figure 6 As shown, in the body-centered cubic structure metal material obtained in this embodiment, the hardness is distributed in a gradient from the surface to the core, decreasing from 2.5 GPa at the surface to 1.5 GPa at the core.

[0084] See Figure 7As shown, the yield strength of the body-centered cubic metal material obtained in this embodiment is 345 MPa, the tensile strength is 416 MPa, and the uniform elongation is 22%.

[0085] Example 3

[0086] This embodiment involves subjecting a pure iron body-centered cubic structure annealed metal material (bar) with an average grain size of approximately 117 micrometers to small-angle cyclic torsional deformation treatment. This introduces a gradient-distributed dislocation structure from the surface inwards, resulting in a body-centered cubic structure metal material. The annealing temperature is 950°C, and the time is 1.5 hours.

[0087] The difference between this embodiment and Embodiment 1 lies in the torsion process parameters. The torsion process parameters in this embodiment are as follows: torsion angle amplitude is 16°, torsion rate is 3600° / min, and torsion cycles are 200.

[0088] Where, θπd / 360°L – σ y / 2G=0.051, 4Nθπd / 180°L - 4Nσ y / G=41.

[0089] See Figure 8 As shown, the body-centered cubic pure iron obtained in this embodiment has a yield strength of 253 MPa, a tensile strength of 274 MPa, and a uniform elongation of 9%.

[0090] Comparative Example 1

[0091] Comparative Example 1 involves subjecting an annealed metal rod with a pure tantalum body-centered cubic structure and an average grain size of approximately 50 micrometers to a small-angle cyclic torsional deformation treatment. The difference between Comparative Example 1 and Example 1 is that the small-angle cyclic torsional deformation treatment in Comparative Example 1 is performed at room temperature.

[0092] See Figure 7 As shown, the yield strength of the body-centered cubic metallic material obtained in this comparative example is 316 MPa, the tensile strength is 355 MPa, and the uniform elongation is 18%.

[0093] Comparative Example 2

[0094] Comparative Example 2 involves subjecting an annealed metal rod with a pure tantalum body-centered cubic structure and an average grain size of approximately 50 micrometers to a small-angle cyclic torsional deformation treatment. The difference between Comparative Example 2 and Example 2 is that the small-angle cyclic torsional deformation treatment in Comparative Example 1 was performed at room temperature.

[0095] See Figure 5As shown, after the annealed metal material (rod) of pure tantalum body-centered cubic structure in this comparative example is subjected to room temperature reciprocating torsion treatment, a gradient distribution of deformed substructures is formed from the surface to the core in the resulting body-centered cubic metal material. However, compared with Example 2, its small-angle grain boundary density is significantly reduced, and the deformed layer is also significantly reduced.

[0096] See Figure 7 As shown, the yield strength of the body-centered cubic metal material obtained in this comparative example is 368 MPa, the tensile strength is 409 MPa, and the uniform elongation is 9%.

[0097] Comparative Example 3

[0098] Suveen N et al. from Texas A&M University used equal channel angular extrusion technology to prepare pure tantalum with severe plastic deformation. The deformed pure tantalum can be obtained through multiple extrusions. Its room temperature tensile properties show that the yield strength of pure tantalum is 380 MPa, but its uniform elongation is less than 5%. Its poor plasticity seriously limits its practical application.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a body-centered cubic metallic material, characterized in that, The deformation characteristics of the body-centered cubic metallic material include dislocations; wherein, the preparation method includes the following steps: Annealing is performed on a body-centered cubic metal part to obtain an annealed metal part. The annealed metal part is subjected to a small-angle cyclic torsional deformation treatment to obtain a body-centered cubic metal material; wherein the temperature of the small-angle cyclic torsional deformation treatment is -196~-50℃.

2. The body-centered cubic metallic material according to claim 1, characterized in that, The temperature for the small-angle cyclic torsional deformation treatment is the liquid nitrogen temperature.

3. The method for preparing a body-centered cubic metallic material according to claim 1 or 2, characterized in that, The small-angle cyclic torsional deformation treatment is as follows: After clamping and fixing one end of the annealed metal part, a force is applied to rotate the other end of the annealed metal part around the central axis of the annealed metal part. First, rotate clockwise by an angle θ from the initial position, then rotate counterclockwise by an angle θ back to the initial position, continue to rotate counterclockwise by an angle θ, then rotate clockwise by an angle θ back to the initial position, so that the annealed metal part completes one reciprocating twist, which is one cycle of twisting. Then, the annealed metal part starts the next reciprocating rotation process from the initial position, and so on, until the required number of cycles of twisting is reached. During each cycle of reciprocating twisting deformation processing, θ takes a fixed value.

4. The method for preparing the body-centered cubic metallic material according to claim 3, characterized in that, In the step of the small-angle cyclic torsional deformation treatment: The angle θ of each rotation of the annealed metal part is the torsional angle amplitude, where, θ is 1°~40°, the torsion rate is 100~10000° / min, and the number of cyclic torsion cycles N is 2~500; Preferably, 7500%≥θπd / 360°L – σ y / 2G ≥ 0.05%; 0.1%≤4Nθπd / 180°L - 4Nσ y / G≤7500%; Where N is the number of cyclic torsion cycles; d is the diameter of the deformation zone of the metal rod; L is the axial length of the deformation zone of the metal rod; σ y G is the yield strength of the metal bar; G is the shear modulus of the metal bar.

5. The method for preparing a body-centered cubic metallic material according to claim 3 or 4, characterized in that, During the small-angle cyclic torsional deformation process: the annealed metal part is placed in a cavity at -196~-50℃ and subjected to small-angle cyclic torsional deformation. Preferably, the cavity is a liquid nitrogen cavity.

6. The method for preparing a body-centered cubic metallic material according to any one of claims 3-5, characterized in that, Before the small-angle cyclic torsional deformation treatment, the annealed metal part needs to be treated as follows: The annealed metal part is placed in an environment of -196~-50℃ for cooling; Preferably, the cooling time is 10-20 minutes; Preferably, the annealed metal part is cooled in a liquid nitrogen environment.

7. The method for preparing a body-centered cubic metallic material according to any one of claims 1-6, characterized in that, The metal component with the body-centered cubic structure is a rod. Preferably, the axial length L of the rod is greater than 1 mm, and the diameter d is greater than 0.5 mm.

8. The method for preparing a body-centered cubic metallic material according to any one of claims 1-7, characterized in that, The annealing temperature is 950-1150℃, and the annealing time is 1-2 hours; and / or The body-centered cubic metal parts have undergone forging, drawing and other processes in the early stage, resulting in significant deformation. After annealing, the annealed metal parts have a grain size of approximately 50-100 micrometers, with no obvious deformation inside the grains.

9. The method for preparing a body-centered cubic metallic material according to any one of claims 1-8, characterized in that, The yield strength of the body-centered cubic metallic material is 1.3 to 1.5 times that of the annealed metallic part; The surface hardness of the body-centered cubic metal material is 1.5 to 2 times that of the annealed metal part.

10. A body-centered cubic metallic material, characterized in that, The surface of the body-centered cubic metallic material has an equiaxed dislocation cell structure and / or subgrain boundaries; wherein, the dislocation cell structure refers to the self-organized arrangement of dislocations into a three-dimensional equiaxed cell morphology; the subgrain boundary is a substructure developed from the dislocation cell; wherein, the orientation difference of the subgrain boundary is greater than the orientation difference of the dislocation cell structure; and the interface clarity of the subgrain boundary is greater than the interface clarity of the dislocation cell structure. The subsurface of the body-centered cubic metallic material has a dislocation wall structure; wherein, the dislocation wall structure refers to the self-organized arrangement of dislocations into a two-dimensional spatial wall-like morphology. The core of the body-centered cubic metallic material has an isolated dislocation structure; wherein the isolated dislocation structure exhibits a random, isolated linear morphology. The body-centered cubic metal material is prepared by the preparation method of the body-centered cubic metal material according to any one of claims 1-9; Preferably, the dislocation structure size of the body-centered cubic metallic material exhibits a gradient increasing trend from the surface to the interior; Preferably, the dislocation density of the body-centered cubic metallic material decreases in a gradient from the surface to the interior. Preferably, the diameter of the dislocation cells in the body-centered cubic metallic material is 40~800 nm; Preferably, the spacing between the dislocation walls in the dislocation wall structure is 200~1200nm; Preferably, in the core of the body-centered cubic metallic material, the density of the solitary dislocation structure is as follows: 10 13 ~10 16 root / m 2 .

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