Rod-shaped metal material and tubular metal material, and preparation methods therefor

Abstract

The present invention relates to the technical field of the strengthening of metal materials. Disclosed are a rod-shaped metal material and a tubular metal material, and preparation methods therefor. A main technical solution used is as follows: the average grain size of the rod-shaped metal material is greater than 1 μm, but smaller than 200 μm, and the metal material involves a metal material with dislocations as a main deformation characteristic, wherein, in the rod-shaped metal material, a gradient dislocation structure is present from the surface layer to the core layer; and the surface layer of the rod-shaped metal material has a dislocation cell structure, the subsurface layer thereof has a dislocation wall structure, and the core portion thereof has an isolated and dispersed dislocation structure. Different types of dislocation structure characteristics are introduced from the surface to the interior without changing the grain dimension structure characteristics, e.g., the original grain morphology and size, of the metal material, and therefore the metal material achieves both high strength and good plasticity, and realizes a good match between the strength and the plasticity.

Description

Rod-shaped metal material, tubular metal material and preparation method thereof

[0001] This disclosure claims priority to the Chinese patent application filed with the China Patent Office on September 13, 2023, with application number 202311179260.5 and invention name “A rod-shaped metal material, a tubular metal material and a preparation method thereof”, the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0002] The present invention relates to the technical field of metal material strengthening, in particular to a rod-shaped metal material, a tubular metal material and a preparation method thereof. Background Art

[0003] At present, the development of high-performance metal materials with both high strength and excellent plasticity is a hot topic in the frontier research of advanced materials with fierce competition among countries around the world. Looking back at the history of material development over the past nearly 100 years, a series of technologies have been developed to strengthen metal materials by regulating the composition, microstructure and internal defects of the materials, such as solid solution strengthening, deformation strengthening, dispersion strengthening and other strengthening strategies. These traditional strengthening strategies can significantly improve the strength of metal materials; however, their plasticity and other properties (such as fracture toughness, etc.) are almost lost, and it is difficult to have both comprehensive properties. The poor plasticity of high-strength structural materials has become a major scientific problem that seriously restricts their engineering applications. In order to meet the challenges faced by the new generation of materials and achieve a revolutionary improvement in material performance, it is urgent to develop new material design and strengthening and toughening principles.

[0004] Furthermore, traditional strengthening strategies often emphasize the introduction of uniformly distributed, high-density defects (e.g., point defects, line defects, surface defects, and volume defects), while paying little attention to the spatial distribution of defects. In recent years, the design concept of multi-scale spatial construction, inspired by nature, has been gradually applied to engineering materials design. By designing and manipulating spatial gradients in grain size, high-angle grain boundaries, and twinning, materials scientists have achieved exemplary gradient-structured structures with excellent performance. For example, surface mechanical grinding has enabled the first-ever creation of a surface gradient nanostructure (GNG) layer with a thickness of hundreds of microns on the surface of a pure Cu rod. From the surface to the interior, the grain size continuously increases from the nanoscale to the micrometer scale. Room-temperature tensile tests demonstrate that the overall yield strength of the GNG Cu can be increased to twice that of coarse-grained Cu. Furthermore, constrained by the coarse grains in the core, the gradient nanostructured surface layer remains intact and crack-free even at tensile true strains up to 100%. This is primarily due to the coarse-grained matrix's restraint on strain localization in the GNG surface layer and the unique mechanically driven grain growth mechanism. However, the limited thickness of the surface nanocrystal layer and its intrinsic mechanical instability in the gradient nanocrystal structure obtained by this technology limit further improvement of its strength.

[0005] In fact, the plastic deformation of most metal materials is usually coordinated through the multiplication of full dislocations, twinning, shearing, or phase transformation. Dislocations are often considered the fundamental carriers of plastic deformation, strengthening the material by interacting with other structural defects (such as grain boundaries, twin boundaries, and phase boundaries). During large plastic deformation, they form small-angle dislocation boundaries that evolve into large-angle grain boundaries, achieving grain refinement. Due to their short-range stress field effects, the strengthening effect of dislocations themselves is limited. Currently, there are few reports on dislocation control methods and strengthening behaviors based on the most common deformation characteristics.

[0006] Summary of the Invention

[0007] In view of this, the present invention provides a rod-shaped metal material, a tubular metal material and a preparation method thereof, the main purpose of which is to significantly improve the strength of the metal material by introducing a special spatial gradient distribution dislocation structure into the metal material, and to ensure the uniform plasticity and fracture elongation of the metal material.

[0008] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0009] On the one hand, an embodiment of the present invention provides a rod-shaped metal material, wherein the average grain size in the rod-shaped metal material is greater than 1 μm and less than 200 μm, and the metal material is a metal material with dislocation as a deformation characteristic; wherein, in the rod-shaped metal material, a gradient dislocation structure is presented from the surface layer to the core layer; wherein,

[0010] The surface layer of the rod-shaped metal material has a dislocation cell structure; wherein the dislocation cell structure refers to: dislocations self-organized and arranged into a three-dimensional cellular or network morphology;

[0011] The subsurface layer of the rod-shaped metal material has a dislocation wall structure; wherein the dislocation wall structure refers to: dislocations self-organized and arranged into a two-dimensional wall-like morphology feature;

[0012] The core of the rod-shaped metal material has a solitary dislocation structure; wherein the solitary dislocation structure has a random, isolated linear morphology.

[0013] Preferably, the size of the dislocation structure of the rod-shaped metal material increases gradually from the surface to the inside; and the dislocation density of the rod-shaped metal material decreases gradually from the surface to the inside.

[0014] Preferably, the wall thickness of the dislocation cells in the dislocation cell structure is 5 to 80 nm and the diameter is 20 to 700 nm.

[0015] Preferably, the dislocation wall in the dislocation wall structure has a wall thickness of 10 to 100 nm and a spacing of 200 to 1000 nm.

[0016] Preferably, in the core of the rod-shaped material, the density of the solitary dislocation structure is as follows: 10 13 ~10 16 root / m 2 (The number of dislocations per unit area).

[0017] Preferably, the rod-shaped metal material is a dog-bone rod that is thick at both ends and thin in the middle; or the rod-shaped metal material is a rod of constant diameter.

[0018] On the other hand, the method for preparing the rod-shaped metal material according to any one of the above-mentioned aspects of the present invention comprises the following steps:

[0019] The metal rod is subjected to a small-angle cyclic reciprocating torsion deformation process under set conditions to introduce a gradient-distributed dislocation structure from the surface to the inside, thereby obtaining the rod-shaped metal material; wherein,

[0020] The small-angle cyclic torsion deformation treatment refers to: fixing one end of the metal bar and applying force to rotate the other end of the metal bar around its central axis, first rotating the metal bar clockwise by an angle θ from the initial position, and then rotating the metal bar counterclockwise by an angle θ back to the initial position, so that the metal bar completes one reciprocating rotation, which is considered a cyclic torsion cycle; then the metal bar starts the next reciprocating rotation process from the initial position, and repeats this cycle until the desired cyclic torsion cycle is reached; wherein, θ takes a fixed value during each cyclic reciprocating torsion deformation treatment process;

[0021] In the small-angle cyclic reciprocating torsional deformation treatment under the set conditions: the angle θ of each rotation of the metal bar is the torsion angle amplitude, the number of cyclic torsion cycles is N, the diameter of the metal bar is d, and the length of the metal bar is L, then the following conditions must be met: πθd / 360°L≥0.02 and πNθd / 180°L≥25.

[0022] Preferably, the length L of the metal rod is greater than 1 mm, the diameter d is greater than 0.5 mm, the torsion angle amplitude θ is greater than 7.2L / πd degrees, and the number of cyclic torsion cycles is N≥4500°L / πθd; preferably, if the length of the metal rod is 12 mm±1 mm and the diameter is 4.5 mm±1 mm, the torsion angle amplitude is 20°±1°, the number of torsion cycles is greater than 191 cycles, the torsion rate is between 10 and 10,000° / min, and the torsion temperature is 25°C±2°C.

[0023] Preferably, the yield strength of the rod-shaped metal material is 2 to 5 times that of the metal bar; the uniform plasticity of the rod-shaped metal material is 0.7 to 1.3 times that of the metal bar; and the elongation at break of the rod-shaped metal material is 0.8 to 1.5 times that of the metal bar.

[0024] In another aspect, an embodiment of the present invention provides a tubular metal material, wherein the average grain size in the tubular metal material is greater than 1 μm and less than 200 μm, and the metal material is a metal material characterized by dislocation deformation; wherein the dislocation structure in the tubular metal material is any one of a first dislocation structure, a second dislocation structure, and a third dislocation structure;

[0025] Wherein, the first dislocation structure includes a dislocation cell structure, a dislocation wall structure, and a solitary dislocation structure sequentially arranged along the first direction;

[0026] Wherein, the second dislocation structure includes a dislocation cell structure and a dislocation wall structure arranged in sequence along the first direction;

[0027] Wherein, the third dislocation structure is a dislocation cell structure;

[0028] The first direction is from the outer wall of the tube to the inner wall of the tube, and the first direction is perpendicular to the tube wall.

[0029] Preferably, the tubular metal material has an axial length greater than 1 mm, a diameter greater than 0.5 mm, and a wall thickness greater than 0.2 mm. Further preferably, the tubular metal material has a wall thickness of 0.2 to 2.5 mm.

[0030] Preferably, the tubular metal material is made from any of the rod-shaped metal materials described above.

[0031] Preferably, the rod-shaped metal material is formed into a tubular metal material by using an electro-corrosion combined with a perforation process. Preferably, the rod-shaped metal material is treated with electro-corrosion of a copper tube using an electro-spark punching machine to obtain a through-hole of a first diameter in the rod-shaped metal material; then, an electro-spark cutting process is performed to expand the hole to obtain a tubular metal material with a set wall thickness; further preferably, the first diameter is 0.3 to 2 mm; further preferably, the electro-corrosion process parameters are as follows: a pulse current is selected, with a peak current of 0.1-20 A and a pulse of 2-500 μs; and water cooling is selected to maintain the temperature of the metal material at 20°C ± 2°C.

[0032] Preferably, the rod-shaped metal material is prepared by the following method: the metal rod is subjected to a small-angle cyclic reciprocating torsional deformation treatment under set conditions to introduce a gradient-distributed dislocation structure from the surface to the inside, thereby obtaining the rod-shaped metal material; wherein the yield strength of the tubular metal material is 2 to 5 times that of the metal rod; wherein the uniform plasticity of the tubular metal material is 0.7 to 1.3 times that of the metal rod; and the elongation at break of the tubular metal material is 0.8 to 1.5 times that of the metal rod.

[0033] Compared with the prior art, the rod-shaped metal material, tubular metal material and preparation method thereof of the present invention have at least the following beneficial effects:

[0034] On the one hand, the present invention provides a rod-shaped metal material, which mainly introduces gradient-distributed dislocation cells, dislocation walls and isolated dislocation structures from the surface to the core of the rod-shaped metal material while retaining the original average grain size of the metal material basically unchanged, and the dislocation density and dislocation structure size gradually increase with depth. It should be noted here that the twinning, second phase and other organizational structural characteristics introduced by existing traditional structural materials are mainly based on alloying metallurgical strategies, that is, they rely on the addition of various alloying elements in the periodic table to obtain them. However, the strategy of the present invention is to achieve strength improvement only by regulating the dislocation configuration, density and spatial distribution without changing the material composition. In the current situation of increasingly severe resource shortages and serious environmental pollution, this is not only conducive to reducing the use of alloys, but also more conducive to reducing dependence on scarce resources.

[0035] The gradient dislocation structure strategy proposed in this paper significantly improves the yield strength and tensile strength of the material while maintaining comparable uniform plasticity and improved elongation at break to the original structure. Its strength-plasticity match is significantly better than reported in the literature for materials with the same composition using uniform or gradient structures. This is in stark contrast to traditional structural strategies such as nanocrystals and secondary relative mechanical properties, which significantly improve material strength but significantly reduce its plasticity. This significantly overcomes the dilemma of traditional structural strategies that often result in a strong-plastic inversion.

[0036] Furthermore, in order to introduce the aforementioned "dislocation cells, dislocation walls, and isolated dislocation structures" into a rod-shaped metal material, the present invention proposes that: the metal material is a metal material characterized by dislocation deformation, and the average grain size of the metal material is greater than 1μm and less than 200μm. On this basis, the metal rod is subjected to a small-angle cyclic reciprocating torsion deformation treatment under set conditions, and the set processing conditions are controlled to obtain the aforementioned gradient dislocation structure that can significantly improve the strength and plasticity of the metal rod-shaped material. The set processing conditions are as follows: πθd / 360°L≥0.02 and πNθd / 180°L≥25; wherein the angle θ of each rotation of the metal rod is the torsion angle amplitude, the number of cyclic torsion cycles is N, the diameter of the metal rod is d, and the length of the metal rod is L.

[0037] Here, the small-angle cyclic reciprocating torsional deformation treatment proposed by the present invention is to perform reciprocating torsional deformation treatment on metal bars using a torsional device. Its advantage is that the equipment requirements are low, while the equipment used in traditional severe plastic deformation and surface mechanical deformation processes is relatively complex, and it is necessary to use a carbide tool head with special geometric dimensions to grind or roll the metal surface. In addition, the time it takes for the present invention to process a single sample is about tens of seconds to a few minutes, and the processing efficiency is high. In addition, the technology of the present invention has small restrictions on the diameter and length of the processed sample, and its axial length L is greater than 1 mm and the diameter d is greater than 0.5 mm, and the macroscopic shape and surface roughness of the sample do not change before and after the reciprocating torsional deformation treatment. It has broad prospects for industrial application.

[0038] On the other hand, the present invention proposes a tubular metal material, which is mainly made by using electro-corrosion combined with a perforation process to make the above-mentioned rod-shaped metal material into a tubular metal material; here, the dislocation structure on the tubular metal material is any one of the first dislocation structure, the second dislocation structure, and the third dislocation structure depending on the wall thickness. Among them, the first dislocation structure includes a dislocation cell structure, a dislocation wall structure, and a solitary dislocation structure arranged in sequence along the first direction. Among them, the second dislocation structure includes a dislocation cell structure and a dislocation wall structure arranged in sequence along the first direction. The third dislocation structure is a dislocation cell structure. Here, the present invention introduces a special gradient dislocation structure into the tubular material, so that the tubular metal material has excellent strength and plasticity (compared with the original metal rod, the yield strength of the tubular metal material can be increased by more than 2.6 times; the plasticity is equivalent or slightly improved), achieving a good match between strength and plasticity.

[0039] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 illustrates the proposed strategy for introducing a gradient dislocation structure into a metal material to improve its mechanical properties. While the original grain structure of the metal material remains uniform from the surface to the core of the rod-shaped sample, the dislocation structure characteristics (e.g., dislocation morphology, size, and density) gradually increase with depth.

[0041] FIG2 is an Al2O3 electrode with a diameter of 4.5 mm and a length of 12 mm in the embodiment. 0.1Electron backscatter diffraction imaging images of the cross-sectional microstructure obtained by scanning electron microscopy after the CoCrFeNi high-entropy alloy rod sample was twisted 200 times under the condition of a torsion angle amplitude of 20°; among them: (a, c) and (b, d) respectively represent the spatial distribution characteristics of the grains (morphology, size, orientation) within 1.2 mm from the sample surface (a, c) and the core (b, d) and the three internal interface structures (large-angle grain boundaries, small-angle grain boundaries, twin boundaries).

[0042] FIG3 is an Al2O3 tube with a diameter of 4.5 mm and a length of 12 mm in the embodiment. 0.1 The gradient dislocation structure of a CoCrFeNi high-entropy alloy rod sample after 200 cycles of torsion at a torsion angle amplitude of 20°. Figures a, b, and c show typical transmission electron micrographs of the surface, 0.7 mm from the surface, and the core, respectively. These images reveal distinct structural features of dislocation cells, dislocation walls, and isolated dislocations at different depths. Figure d shows the size statistics of the dislocation cells at the surface and the dislocation walls at a depth of 0.7 mm.

[0043] Figure 4 shows the bulk gradient dislocation structure Al in the embodiment. 0.1 Vickers hardness distribution of the surface and core of a CoCrFeNi high-entropy alloy rod sample. For comparison, a Vickers hardness plot of a fine-grained structure (grain size 46 μm) before reciprocating torsional deformation is also included. Samples #1, #2, and #3 correspond to the hardness distributions of tubular samples with varying thicknesses.

[0044] Figure 5 shows a typical hollow tubular Al 0.1 CoCrFeNi high-entropy alloy samples. (a) and (c) X-ray 3D morphologies of sample #1 (0.45 mm thick) and sample #3 (1.75 mm thick), respectively. (b) and (d) cross-sectional morphologies through the center of the corresponding tubular samples, respectively.

[0045] FIG6 is a block gradient dislocation structure Al after cyclic torsional deformation process in the embodiment. 0.1 The uniaxial tensile engineering stress-strain curves of CoCrFeNi high entropy alloy samples and corresponding hollow tube samples #1-#3. For comparison, the figure also includes Al with the same chemical composition but no dislocation structure characteristics. 0.1 Tensile results of the coarse-grained (grain size of 560 μm) and fine-grained (grain size of 46 μm) structures of CoCrFeNi. DETAILED DESCRIPTION

[0046] To further illustrate the technical means and effects employed by the present invention to achieve its intended objectives, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention is provided in conjunction with the accompanying drawings and preferred embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0047] The purpose of the present invention is to introduce a special gradient dislocation structure concept into metal materials, and experimental verification has been obtained. The introduced special gradient dislocation structure can not only significantly improve the strength of the metal material, but also maintain uniform plasticity and better fracture elongation comparable to the original structure.

[0048] The main scheme of the present invention is as follows:

[0049] On the one hand, an embodiment of the present invention provides a rod-shaped metal material, wherein the average grain size in the rod-shaped metal material is greater than 1 μm and less than 200 μm, and the metal material is a metal material with dislocation as the main deformation feature; wherein, in the rod-shaped metal material, a gradient dislocation structure is presented from the surface layer to the core layer; wherein, the surface layer of the rod-shaped metal material has a dislocation cell structure; wherein, the dislocation cell structure refers to: dislocations self-organize and arrange into spatial three-dimensional cellular morphology characteristics (see the blue box in Figure a in Figure 3); the sub-surface layer of the rod-shaped metal material has a dislocation wall structure; wherein, the dislocation wall structure refers to: dislocations self-organize and arrange into spatial two-dimensional wall-like morphology characteristics (see the blue box in Figure b in Figure 3); the core of the rod-shaped metal material has a solitary dislocation structure; wherein, the solitary dislocation structure has an isolated linear morphology (see the blue box in Figure c in Figure 3).

[0050] Regarding the above solution, it should be noted that the present invention is mainly aimed at specific metal materials (the specific material refers to a metal material with an average grain size greater than 1μm and less than 200μm, and a metal material with dislocation as the main deformation characteristic), and introduces the above-mentioned "gradient dislocation structure from the surface to the core layer". Preferably, the above-mentioned specific metal materials can be the following metal materials: Cu, Cu-Zn, Cu-Al, Cu alloy, 304 stainless steel, 316 stainless steel, 321 stainless steel, stainless steel, Al 0.1 CoCrFeNi high entropy alloy, etc., but not limited thereto.

[0051] On the other hand, an embodiment of the present invention further provides a method for preparing the above-mentioned rod-shaped metal material, which is mainly as follows: a metal rod is subjected to a small-angle cyclic reciprocating torsional deformation treatment under set conditions to introduce a gradient-distributed dislocation structure from the surface to the inside, thereby obtaining a rod-shaped metal material; wherein the small-angle cyclic torsional deformation treatment comprises: fixing one end of the metal rod and applying a force to rotate the other end of the metal rod about its central axis, first rotating clockwise by an angle θ from an initial position, and then rotating counterclockwise by an angle θ back to the initial position, so that the metal rod completes one reciprocating rotation, which is considered as a cyclic torsional cycle; then the metal rod is caused to start the next reciprocating rotation process from the initial position, and this cycle is repeated until the desired cyclic torsional cycle is reached; wherein θ takes a fixed value during each cyclic reciprocating torsional deformation treatment process;

[0052] It should be noted that in order to introduce the aforementioned "gradient dislocation structure from the surface to the core" into the aforementioned metal rod (a metal material with a grain size greater than 1 μm and less than 200 μm, and a metal material with dislocation as the primary deformation characteristic), the following conditions must be met during the small-angle cyclic torsional deformation process:

[0053] The angle θ of each rotation of the metal bar is the torsion angular amplitude. The number of cyclic torsion cycles is N, the diameter of the metal bar is d, and the length of the metal bar is L. The following conditions must be met: πθd / 360°L ≥ 0.02 and πNθd / 180°L ≥ 25. It should be noted that only this lower limit is required; there is no upper limit. As long as the metal bar's deformation during rotation is characterized by dislocations and cracks are not generated, the larger the πNθd / 180°L, the better the structural evolution characteristics.

[0054] After the reciprocating torsion treatment, a gradient distribution of scaled dislocation cells, dislocation walls, and isolated dislocations was introduced into the rod-shaped metal material, while retaining the original crystal structure. Accordingly, the microhardness increased continuously from 2.2 GPa in the core to 3.7 GPa at the surface.

[0055] On the other hand, an embodiment of the present invention provides a tubular metal material; wherein, the above-mentioned rod-shaped metal material is subjected to an electro-corrosion combined with a perforation process to prepare the tubular metal material.

[0056] Here, according to the size of the perforation, the dislocation structure in the tubular metal material is any one of the first dislocation structure, the second dislocation structure, and the third dislocation structure; wherein the first dislocation structure includes a dislocation cell structure, a dislocation wall structure, and an isolated dislocation structure arranged in sequence along a first direction; wherein the second dislocation structure includes a dislocation cell structure and a dislocation wall structure arranged in sequence along the first direction; wherein the third dislocation structure is a dislocation cell structure; wherein the first direction is the direction from the outer wall of the tube to the inner wall of the tube, and the first direction is perpendicular to the tube wall.

[0057] The tubular metal material has an axial length L greater than 1 mm, a diameter d greater than 0.5 mm, and a wall thickness greater than 0.2 mm.

[0058] One preparation process for tubular metal materials is as follows: Using an EDM perforator, copper tubes with inner and outer diameters of 0.2mm and 0.5mm are used to electro-etch metal rods to produce holes of 0.3-2mm. The electro-etching parameters are pulsed current with a peak current of 0.1-20A and a pulse of 2-500μs. Pure water cooling is used to maintain the metal temperature at 20°C. Subsequently, the rods containing the 0.3-2mm through-holes are expanded by EDM cutting using a wire-cutting machine to produce dog-bone tubular samples with varying wall thicknesses.

[0059] It should be noted that compared to the original metal material before processing (i.e., metal bar), the yield strength of the rod-shaped metal material is 2-5 times higher, while its uniform plasticity and elongation at break are slightly lower than those of the metal bar. The yield strength of the tubular metal material is increased by more than 2.6 times, while its uniform plasticity is comparable to that of the metal bar, while its elongation at break is significantly better than that of the metal bar, achieving a good match between strength and plasticity.

[0060] The present invention is further described below by means of specific embodiments:

[0061] The following embodiments of the present invention target specific metal rods (having an average grain size greater than 1 μm and less than 200 μm, and characterized by dislocations as the primary deformation characteristic) by introducing the aforementioned "gradient dislocation structure from the surface to the core" to produce a rod-shaped metal material. The rod-shaped metal material is then further processed into a tubular metal material. The dimensions of the metal rod are an axial length (L) greater than 1 mm and a diameter (d) greater than 0.5 mm. The wall thickness of the tubular metal material ranges from 0.45 mm to 1.75 mm.

[0062] Example 1

[0063] In this embodiment, the average grain size of the single-phase face-centered cubic structure Al 0.1The CoCrFeNi high entropy alloy rod (i.e., the original fine-grained alloy rod) is subjected to a small-angle cyclic reciprocating torsion deformation treatment under set conditions to introduce a gradient-dislocation structure from the surface to the inside to obtain a rod-shaped metal material.

[0064] Among them, Al 0.1 The diameter of the CoCrFeNi high-entropy alloy rod is 4.5 mm, the length is 12 mm, the torsion angle amplitude is 20 degrees, the torsion rate is 1700° / min, the torsion cycle is 200 cycles, the torsion time is about 140 seconds, and the torsion temperature is room temperature 20°C.

[0065] Here, the above parameters satisfy: πθd / 360°L≥0.02 and πNθd / 180°L≥25.

[0066] The structural characterization and performance characterization are as follows:

[0067] (1) After the original alloy rod is subjected to reciprocating torsion treatment, the morphology, size orientation, and original large-angle grain boundaries and twin boundaries of the original grains remain unchanged. However, the obtained rod-shaped metal material introduces a gradient distribution of small-angle interfaces from the surface to the inside (see Figure 1), which is a gradient distribution of dislocation structures. Among them, the surface layer is composed of dislocation cells of hundreds of nanometers with an average diameter of 200nm; the subsurface layer (0.7mm depth) is a dislocation wall structure with an average dislocation wall spacing of 340nm; and the core of the sample is mainly composed of isolated dislocation structures (see Figure 2). Correspondingly, the microhardness increases continuously from 2.2GPa in the core to 3.7GPa at the surface.

[0068] (2) As shown in FIG3 , the dislocation cell structure refers to: dislocations self-organize and arrange into a spatial three-dimensional cellular morphology (see the box in FIG3 a); the sub-surface of the rod-shaped material has a dislocation wall structure; wherein, the dislocation wall structure refers to: dislocations self-organize and arrange into a spatial two-dimensional wall-like morphology (see the box in FIG3 b); the core of the rod-shaped material has a solitary dislocation structure; wherein, the solitary dislocation structure has an isolated linear morphology (see the box in FIG3 c).

[0069] (3) As the depth from the surface increases, the dislocation configuration, size, and density in the material show a gradient change trend, forming a gradient-distributed dislocation structure (see Figure 2). Due to the existence of the gradient dislocation structure, the microhardness of the rod-shaped metal material gradually decreases from 3.7 GPa to 2.2 GPa as the depth from the material surface increases, also showing a gradient change characteristic, which is significantly higher than that of the coarse-grained alloy rod (1.7 GPa), as shown in Figure 4.

[0070] (4) In this embodiment, the obtained rod-shaped metal material was subjected to a uniaxial tensile test at room temperature. The engineering stress-strain curve is shown in FIG6 . Its uniaxial tensile yield strength is 539 MPa and its tensile strength is 689 MPa, which are approximately 2.91 times and 1.15 times those of the original fine-grained alloy rod; its uniform elongation is 43% and its elongation at break is 71%, which are slightly lower than those of the original fine-grained alloy rod.

[0071] Example 2

[0072] The gradient dislocation structure distribution is characterized by gradually decreasing density from the surface to the core. In order to further highlight the mechanical performance advantages of the high-density dislocation structure, in this embodiment, the center of the rod-shaped metal material (e.g., the rod-shaped metal material prepared by the process of Example 1) is corroded to remove the central area with the lowest hardness of 1 mm in diameter at the core, thereby obtaining a gradient dislocation structure hollow tube #1 sample (i.e., 1# tubular metal material) with a wall thickness of 1.75 mm, as shown in a and b of Figure 5.

[0073] As the depth from the surface increases, the structure and hardness characteristics of the tubular material also show a gradient trend, forming a gradient-distributed dislocation structure (see Figure 2). Basically the same as Example 1, the surface of the tubular metal material obtained in this example still has a dislocation cell structure with an average size of 200 nm, and its hardness reaches 3.7 GPa. However, the core or inner wall of the tube is structurally characterized by isolated dislocations, which corresponds to a higher hardness (2.4 GPa).

[0074] In this embodiment, the gradient dislocation structure hollow tube #1 sample was subjected to a uniaxial tensile test at room temperature. The engineering stress-strain curve is shown in FIG6 . Its uniaxial tensile yield strength was 556 MPa and its tensile strength was 661 MPa, which were approximately 3.01 times and 1.16 times those of the original fine-grained alloy rod. Its uniform elongation was 46% and its elongation at break was 66%.

[0075] Example 3

[0076] In this example, a rod-shaped metal material (e.g., the rod-shaped metal material prepared by the process of Example 1) was subjected to center etching to remove the core area with a diameter of 3 mm and the lowest hardness, thereby obtaining a hollow tube sample #2 with a gradient dislocation structure (i.e., tubular metal material #2) with a wall thickness of 0.75 mm.

[0077] As the depth from the surface increases, the structure and hardness characteristics of the tubular material also show a gradient trend, forming a gradient-distributed dislocation structure (see Figure 2). Basically the same as Examples 1 and 2, the outermost surface still has a dislocation cell structure with an average size of 200 nm and a hardness of up to 3.7 GPa; however, the core or inner wall of the tube is characterized by dislocation wall dislocations, which corresponds to a higher hardness (2.9 GPa).

[0078] In this embodiment, the gradient dislocation structure hollow tube #2 sample was subjected to a uniaxial tensile test at room temperature. The engineering stress-strain curve is shown in FIG6 . Its uniaxial tensile yield strength was 604 MPa and its tensile strength was 735 MPa, which were approximately 3.26 times and 1.23 times those of the original alloy bar. Its uniform elongation was 58% and its elongation at break was 89%.

[0079] Example 4

[0080] In this example, a rod-shaped metal material (e.g., a rod-shaped metal material prepared by the process of Example 1) is subjected to center corrosion to remove the central region of the core with a diameter of 3.6 mm where the hardness is the lowest, thereby obtaining a hollow tube #3 sample (i.e., 3# tubular metal material) with a gradient dislocation structure and a wall thickness of 0.45 mm, as shown in c and d in FIG5 .

[0081] As the depth from the surface increases, the structure and hardness characteristics of the tubular material also show a gradient trend, forming a gradient-distributed dislocation structure (see Figure 2). Basically the same as in Examples 1-3, the outermost surface still has a dislocation cell structure with an average size of 200 nm and a hardness of up to 3.7 GPa; however, the core or inner wall of the tube also has a structure of dislocation cells, corresponding to a hardness of 3.1 GPa.

[0082] In this embodiment, the gradient dislocation structure hollow tube #3 sample was subjected to a uniaxial tensile test at room temperature. The engineering stress-strain curve is shown in FIG6 . Its uniaxial tensile yield strength was 676 MPa and its tensile strength was 789 MPa, which were approximately 3.65 times and 1.32 times those of the original fine-grained alloy rod. Its uniform elongation was 52% and its elongation at break was 80%.

[0083] Comparative Example 1

[0084] Normal annealed Al 0.1 CoCrFeNi high entropy alloy (average grain size of about 46 μm, such as the original fine-grained alloy rod in Example 1) was stretched at room temperature, with a yield strength of 185 MPa, a tensile strength of 599 MPa, a uniform elongation of 55%, and an elongation at break of 65%, as shown in Figure 6. Annealed Al 0.1 A CoCrFeNi high-entropy alloy sample (average grain size of approximately 560 μm, i.e., a coarse-grained alloy rod) exhibited a yield strength of 138 MPa, a tensile strength of 545 MPa, a uniform elongation of 63%, and an elongation at break of 76% under room temperature tension. These results indicate that the original structures (the fine-grained and coarse-grained alloy rods) exhibit good tensile ductility but exhibit lower yield and tensile strengths.

[0085] Comparative Example 2

[0086] TG Nieh of the University of Hong Kong and MW Chen of Johns Hopkins University in the United States used low temperature (-196 ° C) rolling combined with 500 ° C / 1 hour annealing technology to prepare nanocrystalline Al with an average grain size of 100 nm. 0.1 Tensile tests on the CoCrFeNi high-entropy alloy sample showed that the yield strength and tensile strength of the Al0.1CoCrFeNi sample were as high as 1540MPa and 1670MPa, respectively, but the uniform elongation was only 5% and the elongation at break was 5%.

[0087] Comparative Example 3

[0088] S. Gangireddy et al. from the University of North Texas in the United States used room temperature rolling technology to prepare severely deformed Al2O3 containing high-density dislocations. 0.1 Tensile tests on CoCrFeNi high-entropy alloy samples showed that the yield strength and tensile strength of the sample were 750 MPa and 780 MPa respectively, but the uniform elongation was only 4% and the elongation at break was 14%.

[0089] Comparative Example 4

[0090] ZHWang et al. from Taiyuan University of Technology used high-speed dynamic torsion technology to prepare gradient nanostructured Al with grain and twin size gradients. 0.1 Tensile tests on a CoCrFeNi high-entropy alloy sample showed a yield strength of 590 MPa and a tensile strength of 730 MPa, but the uniform elongation was only 8.4% and the elongation at break was less than 15%. The poor plasticity of severely deformed metals severely limits their practical applications.

[0091] Comparative Example 5

[0092] K. Alagarsamy et al. from the University of North Texas in the United States prepared fine-grained Al with an average grain size of 50 microns by combining room temperature rolling and subsequent 1000℃, 24-hour annealing. 0.1 CoCrFeNi high entropy alloy sample. Tensile tests show that the sample has a uniform elongation of up to 50% and 75%, but its yield strength and tensile strength are 210MPa and 570MPa respectively.

[0093] Comparative Example 6

[0094] Comparative Example 6 is Example 3 in Patent No. ZL201911044516.5, which is a coarse-grained Al with a grain size of 560 microns. 0.1The diameter of the CoCrFeNi high entropy alloy sample is 4.5mm (the length of the sample involved is 25mm), the torsion angle amplitude is 15 degrees, and the torsion cycle is 200 cycles. According to the known parameters, πθd / 360°L=0.023 and πNθd / 180°L=9.4 are calculated. Obviously, the strain conditions required for the formation of gradient dislocation results in this application are not satisfied, which are πθd / 360°L≥0.02 and πNθd / 180°L≥25. Therefore, the uniaxial tensile yield strength (427MPa), tensile strength (556MPa) and elongation at break (7.5%) of the sample prepared in Comparative Example 6 are significantly lower than those of the Al alloy with gradient dislocation structure prepared under the conditions of this application. 0.1 CoCrFeNi high entropy alloy (and, since Comparative Example 6 does not adopt the conceptual strategy of the present invention, the dislocation structure of the sample prepared therefrom is also far different from that of the present invention).

[0095] By comparing with the above results, it is found that the special gradient dislocation structure concept proposed in the present invention, that is, without changing the original grain structure characteristics of the metal material, introduces gradient distribution dislocation structure characteristics (dislocation cells, dislocation walls, isolated dislocations) from the surface to the inside. By applying a small-angle cyclic reciprocating torsion deformation that meets the set conditions to the metal sample, the controllable preparation of this structural feature can be achieved, and the original grain structure is retained. The yield strength of the metal material after the cyclic reciprocating torsion process is increased by more than 1.9 times, and its uniform plasticity and elongation at break are slightly lower than those of the original structure. In particular, by removing the lower dislocation density area in the core through subsequent corrosion and cutting processes, the yield strength of the obtained high-density gradient dislocation structure tubular sample can be increased by more than 2.6 times, and its uniform plasticity is equivalent to that of the fine-grained structure, while the elongation at break is significantly better than that of the fine-grained structure, achieving a good match between strength and plasticity.

[0096] In addition, it should be noted that the above embodiments of the present invention are only Al 0.1 The CoCrFeNi high entropy alloy is used as an example for illustration, but is not limited to this metal material. In principle, any metal material that meets the requirements of "grain size greater than 1 μm and less than 200 μm, and the metal material is a metal material with dislocation as the deformation characteristic" is applicable to the solution of the present invention.

[0097] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiment based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A rod-shaped metal material, characterized in that: The average grain size of the rod-shaped metal material is greater than 1 μm and less than 200 μm, and the metal material is a metal material with dislocation as a deformation feature; wherein, in the rod-shaped metal material, a spatial gradient distribution of dislocation structure is presented from the surface layer to the core layer; The surface layer of the rod-shaped metal material has a dislocation cell structure; wherein the dislocation cell structure refers to: dislocations are self-organized and arranged into a spatial three-dimensional cellular or network morphology feature; The sub-surface of the rod-shaped metal material has a dislocation wall structure; wherein the dislocation wall structure refers to: dislocations are self-organized and arranged into a spatial two-dimensional wall-like morphology feature; The core of the rod-shaped metal material has a lone dislocation structure; wherein the lone dislocation structure has a random, isolated linear morphology.

2. The rod-shaped metal material according to claim 1, characterized in that: The size of the dislocation structure of the rod-shaped metal material increases gradually from the surface to the inside; and / or The dislocation density of the rod-shaped metal material decreases gradually from the surface to the inside; and / or The wall thickness of the dislocation cell in the dislocation cell structure is 5 to 80 nm and the diameter is 20 to 700 nm; and / or The dislocation wall in the dislocation wall structure has a wall thickness of 10 to 100 nm and a spacing of 200 to 1000 nm; and / or In the core of the rod-like material, the density of the solitary dislocation structure is as follows: 10 13 ~10 16 Root / m 2 .

3. The rod-shaped metal material according to claim 1 or 2, characterized in that: The rod-shaped metal material is a dog-bone rod or a rod of equal diameter that is thick at both ends and thin in the middle.

4. The method for preparing a rod-shaped metal material according to any one of claims 1 to 3, characterized in that: It includes the following steps: The metal rod is subjected to a small-angle cyclic reciprocating torsion deformation treatment under set conditions to introduce a gradient-distributed dislocation structure from the surface to the inside to obtain the rod-shaped metal material; wherein, The small-angle cyclic torsion deformation treatment refers to: fixing one end of the metal bar and applying force to rotate the other end of the metal bar around its central axis, first rotating clockwise from the initial position by an angle θ, then rotating counterclockwise by an angle θ back to the initial position, so that the metal bar completes a reciprocating rotation, which is regarded as a cyclic torsion cycle; then the metal bar starts the next reciprocating rotation process from the initial position, and the cycle is repeated until the required cyclic torsion cycle is reached; wherein, θ takes a fixed value in each cyclic reciprocating torsion deformation treatment process; In the small-angle cyclic reciprocating torsion deformation process under the set conditions: the angle θ of each rotation of the metal bar is the torsion angle amplitude, the number of cyclic torsion cycles is N, the diameter of the metal bar is d, and the length of the metal bar is L, then the following conditions must be met: πθd / 360°L≥0.02 and πNθd / 180°L≥25.

5. The method for preparing a rod-shaped metal material according to claim 4, characterized in that: The length L of the metal bar is greater than 1 mm, the diameter d is greater than 0.5 mm, the torsion angle amplitude θ is greater than 7.2L / πd degrees, and the cyclic torsion frequency is N≥4500°L / πθd; Preferably, if the length of the metal rod is 12 mm ± 1 mm and the diameter is 4.5 mm ± 1 mm, the torsion angle amplitude is 20° ± 1°, the torsion cycles are greater than 190 cycles, the torsion rate is between 10 and 10000° / min, and the torsion temperature is 25°C ± 2°C.

6. The method for preparing a rod-shaped metal material according to claim 4, characterized in that: The yield strength of the rod-shaped metal material is 2 to 5 times that of the metal bar; the uniform plasticity of the rod-shaped metal material is 0.7 to 1.3 times that of the metal bar; and the elongation at break of the rod-shaped metal material is 0.8 to 1.5 times that of the metal bar.

7. A tubular metal material, characterized in that: The average grain size of the tubular metal material is greater than 1 μm and less than 200 μm, and the metal material is a metal material with dislocation as a deformation feature; wherein the dislocation structure in the tubular metal material is any one of the first dislocation structure, the second dislocation structure, and the third dislocation structure; Wherein, the first dislocation structure includes a dislocation cell structure, a dislocation wall structure, and a solitary dislocation structure arranged in sequence along the first direction; Wherein, the second dislocation structure includes a dislocation cell structure and a dislocation wall structure arranged in sequence along the first direction; Wherein, the third dislocation structure is a dislocation cell structure; Wherein, the first direction is the direction from the outer wall of the tube to the inner wall of the tube, and the first direction is perpendicular to the tube wall; Preferably, the tubular metal material has an axial length greater than 1 mm and a diameter greater than 0.5 mm. Wall thickness greater than 0.2mm; Further preferably, the wall thickness of the tubular metal material is 0.2-2.5 mm.

8. The method for preparing a tubular metal material according to claim 7, characterized in that: The tubular metal material is made from the rod-shaped metal material according to any one of claims 1 to 3.

9. The method for preparing a tubular metal material according to claim 8, characterized in that: The rod-shaped metal material is made into a tubular metal material by using an electro-corrosion combined with a perforation process; Preferably, based on an electric spark perforator, the rod-shaped metal material is treated by electro-corrosion of a copper tube to obtain a through hole of a first diameter in the rod-shaped metal material; then, an electric spark cutting process is performed to expand the hole to obtain a tubular metal material with a set wall thickness; Further preferably, the first wall thickness is 0.3 to 2 mm; Further preferably, the electro-corrosion treatment parameters are as follows: a pulse current with a peak current of 0.1 to 20 A and a pulse of 2 to 500 μs is selected, and water cooling is selected to maintain the temperature of the metal material at 20°C ± 2°C.

10. The method for preparing a tubular metal material according to claim 9, characterized in that: The rod-shaped metal material is prepared by the following method: subjecting the metal rod to a small-angle cyclic reciprocating torsion deformation treatment under set conditions to introduce a gradient-distributed dislocation structure from the surface to the inside, thereby obtaining the rod-shaped metal material; Wherein, the yield strength of the tubular metal material is 2 to 5 times that of the metal bar; Wherein, the uniform plasticity of the tubular metal material is 0.7 to 1.3 times that of the metal bar; The elongation at break of the tubular metal material is 0.8 to 1.5 times that of the metal rod.

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