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

Abstract

The present invention relates to a rod-shaped metal material, a tubular metal material and a preparation method thereof, and relates to the technical field of metal material strengthening. The main technical scheme adopted is: 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, the sub-surface layer has a dislocation wall structure, and the core has a solitary dislocation structure. Under the premise of not changing the original grain morphology, size and other grain scale structural characteristics of the metal material, the present invention introduces different types of dislocation structural characteristics from the surface to the inside, so that the metal material simultaneously obtains high strength and good plasticity, and achieves a good match between strength and plasticity.

Description

Technical Field

[0001] The 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

[0002] 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 in 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 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 issue 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 principles.

[0003] In addition, traditional strengthening strategies often emphasize the introduction of uniformly distributed high-density defects (such as point defects, line defects, surface defects and body defects), while paying little attention to the spatial distribution of defects. In recent years, the design concept of multi-scale spatial construction has been gradually applied to the design of engineering materials by learning from nature. Materials scientists have obtained typical gradient construction structures with excellent performance by designing and regulating the spatial gradient changes of grain size, large-angle grain boundaries and twins. For example, the surface gradient nanostructure layer (GNG) with a thickness of up to hundreds of microns can be obtained on the surface of pure Cu rods for the first time using surface mechanical grinding technology. From the surface to the inside, the grain size increases continuously from the nanoscale gradient to the micron scale. Room temperature tensile tests show that the overall yield strength of GNG Cu can be increased to twice that of coarse-grained Cu. At the same time, under the constraint of coarse grains in the core, the gradient nanostructured surface layer remains intact without cracks when the tensile true strain is as high as 100%, which is mainly due to the restriction of the coarse-grained matrix on the localization of strain on 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 the further improvement of its strength.

[0004] In fact, the plastic deformation of most metal materials is usually coordinated based on the multiplication movement, twinning, shearing or phase transformation of all dislocations. Among them, dislocations are often regarded as the basic carriers of plastic deformation, which strengthen the material by interacting with other structural defects (such as grain boundaries, twin boundaries, phase boundaries, etc.); during large plastic deformation, they evolve into large-angle grain boundaries by forming small-angle dislocation boundaries, achieving fine grain strengthening. Due to its short-range stress field effect, the strengthening effect of dislocations themselves is limited. At present, there are few reports on dislocation control methods and strengthening behaviors based on the most common deformation characteristics. Summary of the invention

[0005] 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 and ensure the uniform plasticity and elongation at fracture of the metal material by introducing a special dislocation structure with a spatial gradient distribution into the metal material.

[0006] In order to achieve the above object, the present invention mainly provides the following technical solutions:

[0007] 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 feature; wherein, in the rod-shaped metal material, a gradient dislocation structure is presented from the surface layer to the core layer; wherein,

[0008] 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;

[0009] 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;

[0010] The core of the rod-shaped metal material has a lone dislocation structure; wherein the lone dislocation structure has a random, isolated linear morphology.

[0011] Preferably, the dislocation structure size 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.

[0012] 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.

[0013] 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.

[0014] Preferably, in the core of the rod-shaped material, the density of the solitary dislocation structure is as follows: 1013 ~10 16 Root / m 2 (The number of dislocations per unit area).

[0015] 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 equal diameter.

[0016] On the other hand, the method for preparing the rod-shaped metal material according to any one of the above-mentioned embodiments of the present invention comprises the following steps:

[0017] 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,

[0018] 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;

[0019] In the small-angle cyclic reciprocating torsion 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.

[0020] 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 10000° / min, and the torsion temperature is 25°C±2°C.

[0021] 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.

[0022] 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 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;

[0023] 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;

[0024] Wherein, the second dislocation structure includes a dislocation cell structure and a dislocation wall structure arranged in sequence along the first direction;

[0025] Wherein, the third dislocation structure is a dislocation cell structure;

[0026] 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.

[0027] Preferably, the axial length of the tubular metal material is greater than 1 mm, the diameter is greater than 0.5 mm, and the wall thickness is greater than 0.2 mm. Further preferably, the wall thickness of the tubular metal material is 0.2 to 2.5 mm.

[0028] Preferably, the tubular metal material is made from any of the rod-shaped metal materials described above.

[0029] Preferably, 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 electro-spark perforator, the rod-shaped metal material is electro-corroded by a copper tube to obtain a through hole of a first diameter in the rod-shaped metal material; then, an expansion electro-spark cutting process is performed 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 processing parameters are as follows: a pulse current is selected, the peak current is 0.1-20A, the pulse is 2-500μs, and water cooling is selected to maintain the temperature of the metal material at 20℃±2℃.

[0030] Preferably, the rod-shaped metal material is prepared by the following method: subjecting the metal rod 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 to obtain 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.

[0031] 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:

[0032] 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 organizational structure characteristics such as twins and second phases introduced by existing traditional structural materials are mainly based on alloying metallurgical strategies, that is, they are obtained by relying on the addition of various alloying elements in the periodic table. 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.

[0033] Here, the gradient dislocation structure strategy proposed in the present invention can significantly improve the yield strength and tensile strength of the material, and maintain the uniform plasticity and better elongation at break comparable to the original structure, and its strength-plasticity matching is significantly better than the uniform or gradient structure materials with the same composition reported in the literature. This is completely different from the situation of traditional structural strategies such as nanocrystals and second relative mechanical properties (significantly improving material strength but significantly reducing material plasticity), and significantly breaks through the dilemma of traditional structural strategies often causing strong plasticity inversion.

[0034] Furthermore, in order to introduce the above-mentioned "dislocation cells, dislocation walls and isolated dislocation structures" into the rod-shaped metal material, the present invention proposes that: the metal material is a metal material with dislocation as a deformation feature, 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 above-mentioned gradient dislocation structure that can significantly improve the strength and plasticity of the metal rod-shaped material. Among them, 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.

[0035] Here, the small-angle cyclic reciprocating torsional deformation treatment proposed by the present invention is to use a torsional device to perform a reciprocating torsional deformation treatment on a metal bar. Its advantage is that the equipment requirements are low, while the equipment used in the 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 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 1mm and the diameter d is greater than 0.5mm, and the macroscopic shape and surface roughness of the sample before and after the reciprocating torsional deformation treatment do not change. It has broad prospects for industrial application.

[0036] On the other hand, the present invention proposes a tubular metal material, which is mainly made of the above-mentioned rod-shaped metal material by using electro-corrosion combined with a perforation process; 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 according to the different wall thicknesses. 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.

[0037] 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 in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the strategy proposed by the present invention for introducing a gradient dislocation structure into a metal material to improve the mechanical properties of the material. The original grain structure characteristics of the metal material are evenly distributed from the surface to the core of the rod-shaped sample without changing, while the dislocation structure characteristics (such as dislocation morphology, size, and density) gradually increase with depth.

[0039] Figure 2 The Al2O3 in the embodiment has a diameter of 4.5 mm and a length of 12 mm. 0.1Electron backscatter diffraction imaging images of the cross-sectional microstructure obtained by scanning electron microscope after the CoCrFeNi high-entropy alloy rod sample was twisted for 200 cycles at 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).

[0040] Figure 3 In the embodiment, the Al 0.1 The gradient dislocation structure of the CoCrFeNi high entropy alloy rod sample after 200 cycles of twisting at a torsion angle amplitude of 20°. Figures a, b, and c are typical transmission electron micrographs corresponding to the surface layer, 0.7 mm depth from the surface layer, and the core, respectively, showing different dislocation cells, dislocation walls, and isolated dislocation structure characteristics at different depths. Figure d is the size statistics of the corresponding dislocation cells at the surface layer and the dislocation wall at a depth of 0.7 mm.

[0041] Figure 4 The bulk gradient dislocation structure Al in the embodiment 0.1 Vickers hardness distribution diagram of the surface and core of CoCrFeNi high entropy alloy rod sample. For comparison, the Vickers hardness diagram of the fine-grained structure (grain size of 46μm) before reciprocating torsion deformation treatment is also included in the figure. #1, #2 and #3 correspond to the hardness distribution diagrams of tubular samples with different thicknesses.

[0042] Figure 5 A typical hollow tubular Al 0.1 CoCrFeNi high entropy alloy samples. a and c are the X-ray 3D morphologies of sample #1 with a wall thickness of 0.45 mm and sample #3 with a wall thickness of 1.75 mm, respectively. b and d are the cross-sectional morphologies of the corresponding tubular samples through the center, respectively.

[0043] Figure 6 The block gradient dislocation structure Al after cyclic torsion deformation process in the embodiment 0.1 The uniaxial tensile engineering stress-strain curves of CoCrFeNi high entropy alloy samples and corresponding #1-#3 hollow tube samples. For comparison, Al with the same chemical composition but without dislocation structure characteristics is also included in the figure. 0.1 Tensile results of CoCrFeNi coarse-grained (grain size 560 μm) and fine-grained (grain size 46 μm) structures. DETAILED DESCRIPTION

[0044] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention application are described in detail below in conjunction with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0045] The purpose of the present invention is to introduce a special gradient dislocation structure concept into a metal material, and experimental verification has been obtained that 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.

[0046] The main scheme of the present invention is as follows:

[0047] 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 are self-organized and arranged into a spatial three-dimensional cellular morphology feature (see, for example Figure 3 The subsurface of the rod-shaped metal material has a dislocation wall structure; the dislocation wall structure refers to: the dislocations are self-organized into a two-dimensional wall-like morphology (see Figure 3 The core of the rod-shaped metal material has a solitary dislocation structure; the solitary dislocation structure has an isolated linear morphology (see Figure 3 (shown in the blue box in Figure c).

[0048] It should be noted that the present invention is mainly aimed at specific metal materials (the specific material refers to: the average grain size is greater than 1μm and less than 200μm, and the metal material is a metal material with dislocation as the main deformation feature), and introduces the above-mentioned "gradient dislocation structure from the surface layer 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.

[0049] 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: subjecting a 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 a rod-shaped metal material; wherein the small-angle cyclic reciprocating torsion deformation treatment refers to: fixing one end of the metal rod, and applying force to rotate the other end of the metal rod around its central axis, first rotating clockwise from an initial position by an angle θ, and then rotating counterclockwise by an angle θ back to the initial position, so that the metal rod completes one reciprocating rotation, which is regarded as a cyclic torsion cycle; then the metal rod is caused to perform the next reciprocating rotation process from the initial position, and the cycle is repeated until the required cyclic torsion cycle is reached; wherein, in each cyclic reciprocating torsion deformation treatment process, θ takes a fixed value;

[0050] It should be noted that in order to introduce the above-mentioned "gradient dislocation structure from the surface to the core layer" into the above-mentioned metal rod (the grain size is greater than 1μm and less than 200μm, and the metal material is a metal material with dislocation as the main deformation feature), the following conditions must be met during the small-angle cyclic reciprocating torsion deformation process:

[0051] 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. It should be noted here that only the lower limit needs to be met, and the upper limit is not limited. As long as the metal bar is deformed with dislocation as the characteristic during the rotation and no cracks are generated, the larger the πNθd / 180°L, the better the structural evolution characteristics.

[0052] After the reciprocating torsion treatment, the rod-shaped metal material is introduced with gradient distribution of scale dislocation cells, dislocation walls and isolated dislocation structures from the surface to the inside, and the original crystal structure is retained. Correspondingly, the microhardness increases continuously from 2.2GPa in the core to 3.7GPa on the surface.

[0053] 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 electro-corrosion combined with a perforation process to prepare a tubular metal material.

[0054] 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 a solitary 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.

[0055] Wherein, 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.

[0056] Among them, one preparation process of tubular metal materials is as follows: Based on the EDM perforator, copper tubes with inner and outer diameters of 0.2mm and 0.5mm are used to electro-corrode the rod metal material to obtain 0.3-2mm holes. The electro-corrosion parameters are pulse current, peak current 0.1-20A, pulse 2-500μs, pure water cooling, and the temperature of the metal material is maintained at 20°C. Subsequently, the rods with 0.3-2mm through holes are expanded by EDM cutting using a slow wire-feeding device to obtain dog-bone tube samples with different wall thicknesses.

[0057] It should be noted that: compared with the original metal material before processing (i.e., metal bar), the yield strength of the rod-shaped metal material is increased by 2-5 times, and 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, and its uniform plasticity is equivalent 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.

[0058] The present invention is further described below by specific embodiments:

[0059] The following embodiments of the present invention are directed to a specific metal rod (the average grain size is greater than 1 μm and less than 200 μm, and the metal material is a metal material with dislocation as the main deformation characteristic), and the above-mentioned "gradient dislocation structure from the surface layer to the core layer" is introduced to obtain a rod-shaped metal material; the rod-shaped metal material is further prepared into a tubular metal material. Among them, the size of the metal rod is 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 is between 0.45 mm and 1.75 mm.

[0060] Example 1

[0061] In this embodiment, the average grain size of the single-phase face-centered cubic structure Al 0.1The CoCrFeNi high entropy alloy rod (ie, 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.

[0062] 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.

[0063] Here, the above parameters satisfy: πθd / 360°L≥0.02 and πNθd / 180°L≥25.

[0064] After structural characterization and performance characterization, the details are as follows:

[0065] (1) After the original alloy rod is subjected to reciprocating torsion treatment, the morphology, size orientation, original large-angle grain boundaries and twin boundaries of the original grains remain unchanged, but a gradient distribution of small-angle interfaces is introduced from the surface to the inside of the obtained rod-shaped metal material (see Figure 1 ), that is, a gradient-distributed dislocation structure, in which the surface layer is a hundred-nanometer-scale dislocation cell 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 a solitary dislocation structure (see Figure 2 ). Correspondingly, the microhardness increases continuously from 2.2 GPa in the core to 3.7 GPa on the surface.

[0066] (2) See Figure 3 As shown in the figure, the dislocation cell structure refers to the self-organization of dislocations into a three-dimensional cellular morphology (see Figure 3 The subsurface of the rod-shaped material has a dislocation wall structure; the dislocation wall structure refers to: the dislocations are self-organized into a two-dimensional wall-like morphology (see Figure 3 The core of the rod-shaped material has a solitary dislocation structure; wherein the solitary dislocation structure has an isolated linear morphology (see Figure 3 (shown in the box in Figure c).

[0067] (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 distribution of dislocation structures (see Figure 2 Due to the existence of gradient dislocation structure, as the depth from the material surface increases, the microhardness of the rod-shaped metal material gradually decreases from 3.7 GPa to 2.2 GPa, also showing the characteristics of gradient change, which is significantly higher than that of the coarse-grained alloy rod (1.7 GPa). Figure 4shown.

[0068] (4) In this embodiment, the obtained rod-shaped metal material is subjected to a uniaxial tensile test at room temperature, and the engineering stress-strain curve is as follows: Figure 6 As shown, its uniaxial tensile yield strength is 539MPa and its tensile strength is 689MPa, which are approximately 2.91 times and 1.15 times 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.

[0069] Example 2

[0070] The gradient dislocation structure distribution gradually decreases from the surface to the core. In order to further highlight the mechanical property advantages of the high-density dislocation structure, this embodiment performs central corrosion on a rod-shaped metal material (e.g., a rod-shaped metal material prepared by the process of Example 1) to remove the central area with the smallest hardness of 1 mm in diameter of the core, and obtains a gradient dislocation structure hollow tube #1 sample (i.e., 1# tubular metal material) with a wall thickness of 1.75 mm. Figure 5 As shown in a and b.

[0071] As the depth from the surface increases, the structure and hardness characteristics of the tubular material also show a gradient change trend, forming a gradient distribution of dislocation structures (see Figure 2 As shown in the figure, the tubular metal material obtained in this embodiment is basically the same as in Example 1. The outermost surface of the tubular metal material obtained in this embodiment is still a dislocation cell structure with an average size of 200 nm, and its hardness value is as high as 3.7 GPa; however, the structural feature of the core or the inner wall of the tube is a solitary dislocation, but it corresponds to a higher hardness (2.4 GPa).

[0072] 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 FIG. Figure 6 As shown, its uniaxial tensile yield strength is 556MPa and its tensile strength is 661MPa, which are approximately 3.01 times and 1.16 times of the original fine-grained alloy rod; its uniform elongation is 46% and its elongation at break is 66%.

[0073] Example 3

[0074] In this embodiment, the rod-shaped metal material (e.g., the rod-shaped metal material prepared by the process of Example 1) is subjected to central corrosion to remove the central region with the smallest hardness of the core 3 mm in diameter, and a gradient dislocation structure hollow tube #2 sample (i.e., 2# tubular metal material) with a wall thickness of 0.75 mm is obtained.

[0075] As the depth from the surface increases, the structure and hardness characteristics of the tubular material also show a gradient change trend, forming a gradient distribution of dislocation structures (see Figure 2As shown). It is basically the same as Examples 1 and 2, the outermost surface is still a dislocation cell structure with an average size of 200 nm, and its hardness value is as high as 3.7 GPa; but the structural feature of its core or the inner wall of the tube is dislocation wall dislocation, but it corresponds to a higher hardness (2.9 GPa).

[0076] 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 FIG. Figure 6 As shown, its uniaxial tensile yield strength is 604MPa and its tensile strength is 735MPa, which are approximately 3.26 times and 1.23 times of the original alloy rod; its uniform elongation is 58% and its elongation at break is 89%.

[0077] Example 4

[0078] 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 center area with the smallest hardness of 3.6 mm in diameter of the core, and a gradient dislocation structure hollow tube #3 sample (i.e., 3# tubular metal material) with a wall thickness of 0.45 mm is obtained. Figure 5 c and d in.

[0079] As the depth from the surface increases, the structure and hardness characteristics of the tubular material also show a gradient change trend, forming a gradient distribution of dislocation structures (see Figure 2 As shown in the figure, it is basically the same as Example 1-3, the outermost surface is still a dislocation cell structure with an average size of 200nm, and its hardness value is as high as 3.7GPa; but the structure of its core or the inner wall of the tube is also a dislocation cell, and the corresponding hardness is 3.1GPa.

[0080] 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 FIG. Figure 6 As shown, its uniaxial tensile yield strength is 676MPa and its tensile strength is 789MPa, which are approximately 3.65 times and 1.32 times of the original fine-grained alloy rod; its uniform elongation is 52% and its elongation at break is 80%.

[0081] Comparative Example 1

[0082] Normal annealed Al 0.1 CoCrFeNi high entropy alloy (average grain size of about 46 μm, such as the original fine-grained alloy rod of 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 a fracture elongation of 65%. Figure 6 Annealed Al 0.1CoCrFeNi high entropy alloy sample (average grain size of about 560μm, i.e. coarse-grained alloy rod) was stretched at room temperature, yield strength of 138MPa, tensile strength of 545MPa, uniform elongation of 63%, and elongation at break of 76%. These results show that the original structure (original fine-grained alloy rod, coarse-grained alloy rod) has good tensile plasticity, but its yield strength and tensile strength are low.

[0083] Comparative Example 2

[0084] 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 100nm. 0.1 CoCrFeNi high entropy alloy sample. Tensile tests show that the yield strength and tensile strength of the Al0.1CoCrFeNi sample are as high as 1540MPa and 1670MPa respectively, but the uniform elongation is only 5% and the elongation at break is 5%.

[0085] Comparative Example 3

[0086] 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 CoCrFeNi high entropy alloy sample. Tensile test shows that the yield strength and tensile strength of the sample are 750MPa and 780MPa respectively, but the uniform elongation is only 4% and the elongation at break is 14%.

[0087] Comparative Example 4

[0088] ZH Wang 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 CoCrFeNi high entropy alloy sample. Tensile tests show that the yield strength of the sample is 590MPa and the tensile strength is 730MPa, but the uniform elongation is only 8.4%, the elongation at break is less than 15%, and the poor plasticity of severely deformed metals seriously limits its practical application.

[0089] Comparative Example 5

[0090] K. Alagarsamy et al. from the University of North Texas in the United States combined room temperature rolling with subsequent 1000℃, 24-hour annealing to produce fine-grained Al with an average grain size of 50 microns. 0.1 CoCrFeNi high entropy alloy sample. The tensile test shows that the uniform elongation of the sample is as high as 50% and 75%, but its yield strength and tensile strength are 210MPa and 570MPa respectively.

[0091] Comparative Example 6

[0092] Comparative Example 6 is Example 3 in Patent No. ZL201911044516.5, which is a coarse-grained Al with a grain size of 560 μm. 0.1 The 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, πNθd / 180°L=9.4 are calculated, which obviously does not meet the strain conditions for the formation of gradient dislocation results in this application, which follow 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 Al2O3 with gradient dislocation structure prepared under the conditions of this application. 0.1 CoCrFeNi high entropy alloy (and, since Comparative Example 6 did 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).

[0093] By comparing with the above results, it is found that the special gradient dislocation structure concept proposed in the present invention, that is, while not changing the original grain structure characteristics of the metal material, introduces gradient distribution of 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 the structural characteristics can be achieved, and the original grain structure is retained. The yield strength of the metal material treated by 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 the fine-grained structure, while the elongation at break is significantly better than the fine-grained structure, achieving a good match between strength and plasticity.

[0094] 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 it is not limited to this metal material. In principle, any metal material that satisfies the requirement of "grain size greater than 1 μm and less than 200 μm, and the metal material is a metal material with dislocation as deformation characteristic" is applicable to the scheme of the present invention.

[0095] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls 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; The metal rod is subjected to a small-angle cyclic reciprocating torsion deformation treatment under set conditions to introduce a dislocation structure with a gradient distribution from the surface to the inside, thereby obtaining a rod-shaped metal material; after the reciprocating torsion treatment, dislocation cells, dislocation walls and isolated dislocation structures with a gradient distribution from the surface to the inside are introduced into the rod-shaped metal material; Among them, 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.

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 5-80 nm and the diameter is 20-700 nm; and / or The dislocation wall in the dislocation wall structure has a wall thickness of 10-100 nm and a spacing of 200-1000 nm; and / or In the core of the rod-shaped metal material, the density of the isolated 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 reciprocating 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, and then rotating counterclockwise by an angle θ back to the initial position, so that the metal bar completes one 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 repeats this cycle until the required cyclic torsion cycle is reached; wherein, θ takes a fixed value during each cyclic reciprocating torsion deformation treatment process.

5. The method for preparing a rod-shaped metal material according to claim 4, characterized in that: 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.

6. The method for preparing a rod-shaped metal material according to claim 5, characterized in that: 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 cycle is greater than 190 cycles, the torsion rate is between 10 and 10000 ° / min, and the torsion temperature is 25 ℃ ± 2 ℃.

7. 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.

8. 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; Wherein, the tubular metal material is prepared from the rod-shaped metal material according to any one of claims 1-3.

9. The tubular metal material according to claim 8, characterized in that: 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.

10. The tubular metal material according to claim 9, characterized in that: The wall thickness of the tubular metal material is 0.2 to 2.5 mm.

11. 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 utilizing an electric corrosion combined with a perforation process.

12. The method for preparing a tubular metal material according to claim 11, characterized in that: Based on an electric spark perforator, the rod-shaped metal material is treated by copper tube electrocorrosion to obtain a through hole of a first diameter in the rod-shaped metal material; then, hole expansion electric spark cutting is performed to obtain a tubular metal material with a set wall thickness.

13. The method for preparing a tubular metal material according to claim 12, characterized in that: The set wall thickness is 0.3~2 mm.

14. The method for preparing a tubular metal material according to claim 12, characterized in that: The parameters of the electro-corrosion treatment are as follows: a pulse current with a peak current of 0.1~20A and a pulse of 2~500μs is selected, and water cooling is selected to maintain the temperature of the metal material at 20℃±2℃.

15. The method for preparing a tubular metal material according to claim 8, 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; 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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