Tubular metal material and method for producing the same

Abstract

The present application relates to a kind of tubular metal materials and its preparation method, wherein the average grain size of tubular metal material is greater than 1 μm, less than 200 μm, and metal material is the metal material with dislocation as deformation feature;In tubular metal material, dislocation structure presents spatial gradient distribution in the first direction;Wherein, the dislocation structure in tubular metal material includes dislocation cell and dislocation wall;Wherein, along the first direction: the content of dislocation cell gradually reduces, and the content of dislocation wall gradually increases;Wherein, the first direction is from the direction of outer wall to inner wall of tubular metal material.The present application introduces different types of dislocation structure features from outside to inside without changing the original grain morphology, size and other grain size structure characteristics of metal material, while keeping the shape and surface finish of tubular metal material, so that tubular metal material obtains high strength and good plasticity while near net forming, realizes the efficient preparation of high-performance metal pipe.

Description

Technical Field

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

[0002] Structural materials serve all sectors of the national economy, social development, national defense, and people's lives, serving as an irreplaceable cornerstone for human civilization and social progress. In particular, for transporting media such as gases, liquids (e.g., oil), and powders, metallic tubular structural materials (referred to as metal tubing) are widely used in petrochemical, construction, power, machinery, water utilities, aerospace, and nuclear power industries due to their excellent deformability, corrosion resistance, aging resistance, and good thermal conductivity. They are an indispensable class of basic materials. For example, heat exchangers, as crucial equipment in nuclear power plants, are used for the heat exchange of coolant and to prevent the leakage of radioactive media. Zirconium alloys, with their low neutron capture cross-section, effectively achieve heat transfer and protection of the coolant due to their good corrosion resistance and high-temperature stability, making them one of the preferred materials for heat exchangers and ensuring the safe operation of nuclear power plants.

[0003] Pipe manufacturing techniques typically include extrusion, hot rolling, cold rolling, and cold drawing to obtain pipes of specific diameters. Heat treatment is usually performed to facilitate further processing such as bending, flaring, and flattening during use. Most pipe samples undergo subsequent annealing to eliminate defects such as high-density grain boundaries from the deformation process and restore their deformability. However, the strength of these pipe samples is often relatively low, severely limiting their application in harsh working conditions. Due to increasingly stringent safety regulations and energy consumption in recent years, materials are continuously developing towards high-speed, heavy-duty, energy-saving, and environmentally friendly directions, placing increasingly higher demands on the strength, environmental performance, and safety reliability of metal pipes. Therefore, developing high-strength metal pipes is a challenging task.

[0004] Over the past century of materials science development, a series of techniques have been developed to strengthen metallic materials by controlling their composition, microstructure, and internal defects, such as solid solution strengthening, deformation strengthening, and dispersion strengthening. These traditional strengthening strategies can significantly improve the strength of metal pipes; however, they are primarily based on alloying metallurgy, relying on the addition of various alloying elements from the periodic table to obtain homogeneous materials with relatively uniform composition and structure. Given the increasingly severe resource shortages and environmental pollution, in order to reduce dependence on scarce resources, address the challenges facing next-generation metal pipes, and improve their strength, it is urgent to explore new preparation technologies and strengthening principles. Summary of the Invention

[0005] In view of this, the present invention provides a tubular metal material and a method for preparing the same, with the main objective of providing a novel strengthening method to significantly improve the mechanical properties of the tubular metal material.

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

[0007] On one hand, embodiments of the present invention provide a tubular metal material, wherein 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 characterized by dislocation deformation; in the tubular metal material, the dislocation structure exhibits a spatial gradient distribution in a first direction; wherein,

[0008] The dislocation structure in the tubular metal material includes dislocation cells and dislocation walls; wherein, along the first direction: the content of dislocation cells gradually decreases and the content of dislocation walls gradually increases;

[0009] Wherein, the first direction is the direction from the outer wall to the inner wall of the tubular metal material (the first direction is a straight line, preferably, the first direction is perpendicular to the tube wall);

[0010] The term "dislocation cell" refers to a three-dimensional cellular or network-like morphological feature formed by the self-organization of dislocations; the term "dislocation wall" refers to a two-dimensional wall-like morphological feature formed by the self-organization of dislocations.

[0011] Preferably, the dislocation structure of the outer wall of the tubular metal material is a dislocation cell structure or a first cell-wall hybrid dislocation structure; wherein, the first cell-wall hybrid dislocation structure refers to a hybrid dislocation structure including dislocation cells and dislocation walls, and in the hybrid dislocation structure, the volume fraction of dislocation cells is greater than 60%; the dislocation structure of the inner wall of the tubular metal material is a dislocation wall structure or a second cell-wall hybrid dislocation structure; wherein, the second cell-wall hybrid dislocation structure refers to a hybrid dislocation structure including dislocation cells and dislocation walls, and in the hybrid dislocation structure, the volume fraction of dislocation walls is greater than 60%.

[0012] Preferably, the dislocation cell has a diameter of 20–1000 nm and a wall thickness of 100–180 nm; and / or the dislocation walls have a spacing of 200–1000 nm and a wall thickness of 50–400 nm.

[0013] Preferably, the size of the dislocation structure in the tubular metal material increases gradually from the surface to the interior; and / or the dislocation density in the tubular metal material decreases gradually from the surface to the interior.

[0014] Furthermore, the method for preparing the tubular metal material described in any of the above-mentioned claims includes the following steps:

[0015] The clamping section of the metal pipe is filled with a mold (where the mold is a solid cylindrical mold);

[0016] The clamping section of the metal tube is clamped, and then the metal tube is subjected to small-angle cyclic torsional deformation under set conditions to introduce a gradient distribution of dislocation cells and dislocation wall structures from the outer wall to the inner wall of the metal tube, thereby obtaining a tubular metal material.

[0017] Preferably, the metal pipe has an axial length greater than 1 mm, an outer diameter greater than 0.3 mm, a wall thickness greater than 0.1 mm, and a wall thickness to outer diameter ratio less than 0.8.

[0018] Preferably, the small-angle cyclic reciprocating torsional deformation process includes: clamping and fixing one end of the metal pipe after filling it with a mold, and applying force to rotate the other end of the metal pipe around its central axis. First, rotate clockwise by an angle θ from the initial position, then counterclockwise by an angle θ, and return to the initial position, completing one reciprocating rotation, which is considered one cycle of torsion. Then, the metal pipe starts the next reciprocating rotation process from the initial position, repeating this cycle until the required number of cycles of torsion is reached. θ is a fixed value in each cyclic reciprocating torsional deformation process. Rotation around the central axis of the metal pipe: the tangential stress applied to the metal pipe is perpendicular to the central axis of the metal pipe and along the tangential direction parallel to the pipe wall.

[0019] Preferably, the small-angle cyclic torsional deformation treatment needs to meet the following conditions:

[0020] 20% ≥ πθd1 / 360°L ≥ 1%;

[0021] 23≥πNθd1 / 180°L≥3;

[0022] The angle θ of each rotation of the metal tube is defined as the torsional angle amplitude;

[0023] N represents the number of cyclic torsion cycles; d1 represents the outer diameter of the metal pipe; and L represents the axial length of the metal pipe.

[0024] Preferably, the small-angle cyclic torsional deformation treatment needs to meet the following conditions:

[0025] 72L / πd1 degrees ≥ θ ≥ 3.6L / πd1 degrees;

[0026] 4140°L / πθd1≥N≥540°L / πθd1;

[0027] Where L is the axial length of the metal pipe, θ is the torsional angle amplitude, N is the number of cyclic torsional cycles, and d1 is the outer diameter of the metal pipe.

[0028] Preferably, the hardness of the outer wall of the tubular metal material is 1.4 to 2.1 times that of the outer wall of the metal pipe; and / or the hardness of the inner wall of the tubular metal material is 1.2 to 1.5 times that of the inner wall of the metal pipe.

[0029] Compared with the prior art, the tubular metal material and its preparation method of the present invention have at least the following beneficial effects:

[0030] On one hand, embodiments of the present invention provide a tubular metal material, wherein 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 characterized by dislocation deformation; in the tubular metal material, the dislocation structure exhibits a spatial gradient distribution in a first direction; wherein the dislocation structure in the tubular metal material includes dislocation cells and dislocation walls; wherein, along the first direction: the content of the dislocation cells gradually decreases, and the content of the dislocation walls gradually increases; wherein, the first direction is the direction from the outer wall to the inner wall of the tubular metal material; preferably The dislocation structure of the outer wall of the tubular metal material is a dislocation cell structure or a first cell-wall mixed dislocation structure; wherein, the first cell-wall mixed dislocation structure refers to a mixed dislocation structure including dislocation cells and dislocation walls, and in the mixed dislocation structure, the volume fraction of dislocation cells is greater than 60%; the dislocation structure of the inner wall of the tubular metal material is a dislocation wall structure or a second cell-wall mixed dislocation structure; wherein, the second cell-wall mixed dislocation structure refers to a mixed dislocation structure including dislocation cells and dislocation walls, and in the mixed dislocation structure, the volume fraction of dislocation walls is greater than 60%. Regarding the tubular metallic material with the aforementioned dislocation structure of the present invention, due to the gradient distribution of dislocation structure size from small to large along the direction from the outer wall to the inner wall, it exhibits asynchronicity in plastic deformation, which differs from that of materials with uniform structures: the large-sized dislocation wall structure on the inner wall preferentially undergoes plastic deformation due to its low yield strength, while the smaller dislocation cell structure on the outer wall remains in the elastic deformation stage; as the applied stress or strain increases, plastic deformation gradually propagates and extends from the low-strength dislocation wall structure to the high-strength dislocation cell structure, thereby forming a plastic strain gradient. The plastic strain gradient generated by non-uniform deformation is influenced by additional deformation defects such as geometrically necessary dislocations; the larger the strain gradient, the higher the density of additional deformation defects. Additional deformation defects not only hinder dislocation-contributed strengthening (i.e., high-strength) but also increase dislocation storage, resulting in additional work hardening (high hardness), exhibiting good plasticity.

[0031] On the other hand, in order to achieve the dislocation structure described above in the tubular metal material, so that the hardness of the outer wall of the tubular metal material is 1.4 to 2.1 times that of the original metal tube, and the hardness of the inner wall of the tubular metal material is 1.2 to 1.5 times that of the original metal tube, the present invention performs small-angle cyclic reciprocating torsional deformation treatment on the metal tube under set conditions to obtain the tubular material with the above-mentioned excellent performance. Specifically, the set conditions need to satisfy: 72L / πd1 degrees ≥ θ ≥ 3.6L / πd1 degrees; 4140°L / πθd1 ≥ N ≥ 540°L / πθd1; where θ is the angle of rotation of the metal tube each time, defined as the torsional angle amplitude; N is the number of cyclic torsional cycles; d1 is the outer diameter of the metal tube; and L is the axial length of the metal tube. Furthermore, the axial length of the metal tube is greater than 1 mm, the outer diameter is greater than 0.3 mm, the wall thickness (d1-d2) / 2 is greater than 0.1 mm (where d2 is the inner diameter of the metal tube), and the ratio of wall thickness to outer diameter (d1-d2) / 2d1 is less than 0.8. It should be noted that to obtain dislocation cell and dislocation wall structures, the outer surface of the tube wall must first undergo plastic deformation (>1%). To maintain the roughness of the sample's outer surface, the amount of plastic deformation should not be too large, i.e., <20%, approximately 30% to 50% of the material's uniform plasticity. Additionally, to obtain a well-developed hybrid structure of dislocation cells and dislocation walls, according to research results, the cumulative plastic deformation should be at least greater than 3 and less than 23 (excessive deformation will lead to increased surface roughness). In summary, based on the above considerations, the inventors believe that the above formula must be satisfied to obtain the tubular metal material with the desired dislocation structure.

[0032] In summary, the solution of this invention achieves strength enhancement solely by controlling the dislocation configuration, density, and distribution without altering the material composition. This demonstrates that dislocations can exert the effects of alloying elements, essentially equating dislocations with alloying elements. In the context of increasingly severe resource shortages and environmental pollution, this not only helps reduce the amount of alloys used but also reduces dependence on scarce resources. Furthermore, the solution of this invention can maintain the original pipe shape and dimensions while increasing the hardness of the outer and inner walls, achieving near-net-shape forming of the pipe, effectively controlling subsequent processing costs, and enabling efficient manufacturing. This can effectively improve production efficiency, reduce production costs, and ensure the safe, reliable, and stable operation of production and daily life.

[0033] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0034] Figure 1These are scanning electron microscope (SEM) images of the cross-sectional microstructure of the pure copper hollow tube sample and the Cu-Zn alloy tube sample used in this invention. The grain size of the pure Cu sample is approximately 51 μm, and the grain size of the Cu-Zn alloy is approximately 50 μm.

[0035] Figure 2 This is a schematic diagram showing the surface roughness comparison before and after small-angle cyclic torsional deformation treatment of copper tubes with an outer diameter of 4mm (wall thickness of 1.1mm, gauge length of 12mm), copper tubes with an outer diameter of 6mm (wall thickness of 0.7mm, gauge length of 12mm), copper tubes with an outer diameter of 10mm (wall thickness of 1.1mm, gauge length of 12mm), Cu-Zn tubes with an outer diameter of 6mm (wall thickness of 0.7mm, gauge length of 12mm), and Cu-Zn tubes with an outer diameter of 10mm (wall thickness of 1.1mm, gauge length of 12mm).

[0036] Note: In Figure 2 middle: Figure 2 In the left figure, the dashed line represents the initial roughness, and the solid line represents the roughness after torsion. Figure 2 In the physical image located in the middle, each sample group is shown in two images: the top image shows the initial surface morphology, and the bottom image shows the surface morphology after twisting; additionally... Figure 2 In this context, Φ4-1 represents the copper tube with an outer diameter of 4mm in Example 1, Φ4-2 represents the copper tube with an outer diameter of 4mm in Example 2, Φ6-1 represents the copper tube with an outer diameter of 6mm in Example 1, and Φ6-2 represents the copper tube with an outer diameter of 6mm in Example 2.

[0037] Figure 3 The images are electron backscatter diffraction images of the cross-sectional microstructure obtained by scanning electron microscopy after twisting copper tubes with an outer diameter of 4 mm (wall thickness of 1.1 mm and gauge length of 12 mm), an outer diameter of 6 mm (wall thickness of 0.7 mm and gauge length of 12 mm), and an outer diameter of 10 mm (wall thickness of 1.1 mm and gauge length of 12 mm) for 150 cycles, respectively, under the conditions of torsion angle amplitudes of 5.2°, 3.5°, and 2.1° (here, the torsion angle amplitudes corresponding to the outer diameter of 4 mm copper tube are 5.2°, 6 mm copper tube are 3.5°, and 10 mm copper tube are 2.1°).

[0038] in, Figure 3Figure a shows the low-magnification macroscopic morphology of the cross-section of the tube after small-angle cyclic torsion deformation treatment. Taking a copper tube with an outer diameter of 10 mm (wall thickness of 1.1 mm and gauge length of 12 mm) that is torn 150 times under the condition of torsion angle amplitude of 2.1° as an example, the material after torsion still maintains the initial grain morphology, and the grain morphology and size have not changed.

[0039] The spatial distribution characteristics of grains (morphology and size) 100 μm from the outer wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the tubular material obtained after small-angle cyclic torsional deformation treatment of a copper tube with an outer diameter of 4 mm (wall thickness of 1.1 mm and gauge length of 12 mm) are shown in the figure. Figure 3 As shown in Figure b; the spatial distribution characteristics of grains (morphology and size) 100 μm from the inner wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the obtained tubular material are shown in Figure b. Figure 3 As shown in Figure e.

[0040] The spatial distribution characteristics of grains (morphology and size) 100 μm from the outer wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in a copper tube with an outer diameter of 6 mm (wall thickness of 0.7 mm and gauge length of 12 mm) after undergoing small-angle cyclic torsional deformation treatment are described in the following figure. Figure 3 As shown in Figure c; the spatial distribution characteristics of grains (morphology and size) 100 μm from the inner wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the obtained tubular material are shown in Figure c. Figure 3 As shown in Figure f.

[0041] The spatial distribution characteristics of grains (morphology and size) 100 μm from the outer wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in a 10 mm outer diameter copper tube (wall thickness 1.1 mm, gauge length 12 mm) after small-angle cyclic torsional deformation are described in the following figure. Figure 3 The spatial distribution characteristics of the grains (morphology and size) 100 μm from the inner wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the obtained tubular material are shown in Figure d. Figure 3 As shown in the g-graph.

[0042] Figure 4The images are electron backscatter diffraction images of the cross-sectional microstructure obtained by scanning electron microscopy after twisting copper tubes with an outer diameter of 4 mm (wall thickness of 1.1 mm, gauge length of 12 mm), an outer diameter of 6 mm (wall thickness of 0.7 mm, gauge length of 12 mm), and an outer diameter of 10 mm (wall thickness of 1.1 mm, gauge length of 12 mm) for Embodiment 2 of the present invention for 150 cycles, under the conditions of torsion angle amplitudes of 11.2°, 7.5°, and 4.5° (here, the torsion angle amplitudes corresponding to the outer diameter of 4 mm copper tubes are 11.2°, 7.5°, and 4.5°, respectively).

[0043] Among them, the spatial distribution characteristics of the grains (morphology and size) 100μm from the outer wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the tubular material obtained after small-angle cyclic torsional deformation treatment of a copper tube with an outer diameter of 4mm (wall thickness of 1.1mm and gauge length of 12mm) are shown in the figure. Figure 4 As shown in Figure a; the spatial distribution characteristics of grains (morphology and size) 100 μm from the inner wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the obtained tubular material are shown in Figure a. Figure 4 As shown in Figure d.

[0044] The spatial distribution characteristics of grains (morphology and size) 100 μm from the outer wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in a copper tube with an outer diameter of 6 mm (wall thickness of 0.7 mm and gauge length of 12 mm) after undergoing small-angle cyclic torsional deformation treatment are described in the following figure. Figure 4 As shown in Figure b; the spatial distribution characteristics of grains (morphology and size) 100 μm from the inner wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the obtained tubular material are shown in Figure b. Figure 4 As shown in Figure e.

[0045] The spatial distribution characteristics of grains (morphology and size) 100 μm from the outer wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in a 10 mm outer diameter copper tube (wall thickness 1.1 mm, gauge length 12 mm) after small-angle cyclic torsional deformation are described in the following figure. Figure 3 As shown in Figure c; the spatial distribution characteristics of grains (morphology and size) 100 μm from the inner wall and the three internal interfaces (large-angle grain boundaries, small-angle grain boundaries, and twin boundaries) in the obtained tubular material are shown in Figure c. Figure 3 As shown in Figure f.

[0046] Figure 5This is a Vickers hardness distribution diagram from the outer surface to the inner wall of the pure Cu hollow tubular material and Cu-Zn alloy hollow tubular material samples in the embodiments of the present invention.

[0047] in, Figure 5 Figure a shows the hardness distribution of copper tubes with an outer diameter of 4 mm (wall thickness of 1.1 mm, gauge length of 12 mm), an outer diameter of 6 mm (wall thickness of 0.7 mm, gauge length of 12 mm), and an outer diameter of 10 mm (wall thickness of 1.1 mm, gauge length of 12 mm) after small-angle cyclic torsional deformation treatment in Example 1. For comparison, the Vickers hardness of the copper tube before cyclic torsional deformation treatment (average grain size of 51 μm) is also included in the figure.

[0048] in, Figure 5 Figure b in the figure shows the hardness distribution of copper tubes with an outer diameter of 4 mm (wall thickness of 1.1 mm, gauge length of 12 mm), an outer diameter of 6 mm (wall thickness of 0.7 mm, gauge length of 12 mm), and an outer diameter of 10 mm (wall thickness of 1.1 mm, gauge length of 12 mm) after small-angle cyclic torsional deformation treatment in Example 2. For comparison, the Vickers hardness of the copper tube before cyclic torsional deformation treatment (average grain size of 51 μm) is also included in the figure.

[0049] in, Figure 5 Figure c in the figure shows the hardness distribution of Cu-18Zn alloy tubes with an outer diameter of 6 mm (wall thickness of 0.7 mm and gauge length of 12 mm) and Cu-18Zn alloy tubes with an outer diameter of 10 mm (wall thickness of 1.1 mm and gauge length of 12 mm) after small-angle cyclic torsional deformation treatment. For comparison, the Vickers hardness of the alloy tube (Cu-Zn alloy grain size of 50 μm) before cyclic torsional deformation treatment is also included in the figure.

[0050] Figure 6 These are characteristic images of a 321 stainless steel tube before and after undergoing a small-angle cyclic torsional deformation treatment; among them... Figure 6 Figure (a) shows the original structural features of a 321 stainless steel tube before it undergoes a small-angle cyclic torsional deformation treatment; it can be seen that the grain size is uniformly distributed. Figure 6 Figures (b) and (c) show the surface undulation height of the 321 stainless steel metal tube sample before and after the small-angle cyclic torsional deformation treatment, respectively. It can be seen that the surface undulation of the sample changes very little after the small-angle cyclic torsional deformation treatment. Figure 6 Figure (d) shows the change in surface roughness of the 321 stainless steel metal tube sample before and after small-angle cyclic torsional deformation treatment.

[0051] Figure 7 This is a typical structural image of a tubular 321 stainless steel sample with an outer diameter of 6 mm and a wall thickness of 0.7 mm in Example 4 after undergoing cyclic torsional deformation at a small angle.

[0052] in, Figure 7 Figure (a) shows the low-magnification macroscopic morphology of the cross-section of a tubular 321 stainless steel sample after small-angle cyclic torsion deformation treatment. Taking a tubular 321 stainless steel sample with an outer diameter of 6 mm (wall thickness of 0.7 mm and gauge length of 10 mm) that was torsioned 150 times under the condition of a torsion angle amplitude of 7.5° as an example, it can be seen that the material after torsion still maintains the initial grain morphology, and the grain morphology and size do not change.

[0053] The tubular 321 stainless steel sample with an outer diameter of 6 mm, a wall thickness of 0.7 mm, and a gauge length of 10 mm was subjected to 150 rotations under a torsion angle amplitude of 3.5°. The dislocation structure characteristics of the outer wall are shown in [reference needed]. Figure 7 For the dislocation structure features of the inner wall shown in Figure (b), please refer to [reference needed]. Figure 7 Figure (c) in the middle.

[0054] The tubular 321 stainless steel sample with an outer diameter of 6 mm, a wall thickness of 0.7 mm, and a gauge length of 10 mm was obtained after being torsionally rotated 150 times under a torsion angle amplitude of 7.5°. The dislocation structure characteristics of the outer wall are shown in [reference needed]. Figure 7 For the dislocation structure characteristics of the inner wall shown in Figure (d), please refer to [reference needed]. Figure 7 Figure (e) in the middle.

[0055] The tubular 321 stainless steel sample with an outer diameter of 6 mm, a wall thickness of 0.7 mm, and a gauge length of 60 mm was subjected to 150 rotations after being torsionally rotated at a torsion angle amplitude of 58.5°. The dislocation structure characteristics of the outer wall are shown in [reference needed]. Figure 7 For the dislocation structure characteristics of the inner wall shown in Figure (f), please refer to [reference needed]. Figure 7 (g) diagram.

[0056] from Figure 7 It can be seen that after being subjected to repeated torsional deformation at small angles, the size of the dislocation feature structure from the outer wall to the inner wall of the sample increases significantly, forming a gradient-dislocation structure.

[0057] Figure 8 These are typical structural images of tubular 321 stainless steel samples with outer diameters of 6mm, 8mm, and 12mm in Example 5 after undergoing cyclic torsional deformation at a small angle.

[0058] in, Figure 8Figure (a) shows the low-magnification macroscopic morphology of the cross-section of the tube after small-angle cyclic torsion deformation treatment. Taking a tubular 321 stainless steel sample with an outer diameter of 8 mm (wall thickness of 1.2 mm and gauge length of 45 mm) torsioned for 150 cycles under the condition of torsion angle amplitude of 25.3° as an example, it can be seen that the material after torsion still maintains the initial grain morphology, and the grain morphology and size do not change.

[0059] A tubular 321 stainless steel sample with an outer diameter of 6 mm, a wall thickness of 0.7 mm, and a length of 10 mm was obtained after being torn 150 times under a torsion angle amplitude of 7.5°. The dislocation structure characteristics of the outer wall are shown in [reference needed]. Figure 8 For the dislocation structure features of the inner wall shown in Figure (b), please refer to [reference needed]. Figure 8 Figure (c) in the middle.

[0060] A tubular 321 stainless steel sample with an outer diameter of 8 mm, a wall thickness of 1.2 mm, and a length of 45 mm was obtained after being torn 150 times under a torsion angle amplitude of 25.3°. The dislocation structure characteristics of the outer wall are shown in [reference needed]. Figure 8 For the dislocation structure characteristics of the inner wall shown in Figure (d), please refer to [reference needed]. Figure 8 Figure (e) in the middle.

[0061] A tubular 321 stainless steel sample with an outer diameter of 12 mm, a wall thickness of 0.9 mm, and a length of 103 mm was obtained after being torn 150 times under a torsion angle amplitude of 38.6°. The dislocation structure characteristics of the outer wall are shown in [reference needed]. Figure 8 For the dislocation structure characteristics of the inner wall shown in Figure (f), please refer to [reference needed]. Figure 8 (g) diagram.

[0062] Depend on Figure 8 It can be seen that after cyclic torsion treatment, the size of the dislocation feature structure from the outer wall to the inner wall of the sample increases significantly, forming a gradient-dislocation structure.

[0063] Figure 9 The figures show the Vickers hardness distribution of the surface and core of 321 stainless steel tubular samples with gradient dislocation structures prepared by different cyclic torsion processes in the examples. For comparison, the Vickers hardness of the coarse-grained structure (grain size of 15 μm) before annealing was also included in the figures.

[0064] in, Figure 9Figure (a) shows the Vickers hardness distribution of the surface and core of the 321 stainless steel tubular sample with a 6mm outer diameter (wall thickness of 0.7mm, gauge lengths of 1#-10mm, 2#-10mm and 3#-60mm respectively) prepared by torsion for 150 cycles under the conditions of torsion angle amplitudes of 3.5°, 7.5° and 58.5° respectively (here, the torsion angle amplitude corresponding to 1# tubular 321 stainless steel sample is 3.5°, the torsion angle amplitude corresponding to 2# tubular 321 stainless steel sample is 7.5° and the torsion angle amplitude corresponding to 3# tubular 321 stainless steel sample is 58.5°).

[0065] Figure 9 Figure (b) shows the Vickers hardness distribution of the surface and core of the 321 stainless steel tubular samples with a 6mm outer diameter (wall thickness 0.7mm, gauge length 10mm), an 8mm outer diameter (wall thickness 1.2mm, gauge length 45mm), and a 12mm outer diameter (wall thickness 0.9mm, gauge length 103mm) prepared by torsion for 150 cycles in Example 5 of the present invention. For comparison, the Vickers hardness of the coarse-grained structure (grain size of 15μm) before annealing and reciprocating torsional deformation treatment is also included in the figure. Detailed Implementation

[0066] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0067] The purpose of this invention is to provide a tubular metal material and its preparation method, primarily aimed at significantly improving the mechanical properties (e.g., hardness, strength) of the tubular metal material. To achieve the above objective, the design and technical solutions adopted in this invention are as follows:

[0068] The method for preparing tubular metallic materials proposed in this invention introduces a gradient-distributed dislocation cell-wall hybrid structure from the outer wall to the inner wall, without altering the original grain morphology, size, or other grain-scale structural characteristics of the metallic material. Specifically, the outer wall is a first-cell-wall hybrid dislocation structure dominated by dislocation cells or ultrafine dislocation cells; the dislocation cell density gradually decreases from the surface to the interior, while the dislocation wall density gradually increases; the inner wall is a second-cell-wall hybrid dislocation structure dominated by dislocation walls or dislocation walls.

[0069] For tubular metal materials: axial length (L) greater than 1 mm, outer diameter greater than 0.3 mm, wall thickness (d1-d2) / 2 greater than 0.1 mm, and the ratio of wall thickness to outer diameter (d1-d2) / 2d1 less than 0.8.

[0070] Specifically, the method for preparing the tubular metal material proposed in this invention includes the following steps:

[0071] 1) Use molds to fill the clamping section of the metal pipe.

[0072] The purpose of this step is to ensure that the tubular sample maintains its tubular shape after being subjected to clamping force. The mold is required to be a solid metal cylinder with a hardness greater than that of the tubular metal material, and its diameter should be 0.05 mm smaller than the inner wall of the tubular metal to ensure a tight fit.

[0073] 2) Clamp the clamping section of the metal tube, and then perform small-angle cyclic torsional deformation treatment on the metal tube under set conditions to introduce a gradient distribution of dislocation cells and dislocation wall structures from the outer wall to the inner wall of the metal tube, thereby obtaining a tubular metal material.

[0074] Here, the small-angle cyclic torsional deformation treatment refers to the following: the clamping section of the pipe is filled and clamped using a mold, and force is applied to rotate the other end of the pipe around its central axis. First, it rotates clockwise by an angle θ from the initial position, then counterclockwise by an angle θ back to the initial position, completing one round of rotation, i.e., one cycle of torsion. Then, the pipe starts the next round of rotation from the initial position, and so on, until the required number of cycles of torsion is reached. θ is a fixed value during each cyclic torsion deformation treatment.

[0075] In order to introduce the required gradient dislocation structure into the metal tube, small-angle cyclic torsional deformation treatment is required, satisfying the following conditions:

[0076] 20% ≥ πθd1 / 360°L ≥ 1%; 23 ≥ πNθd1 / 180°L ≥ 3; where θ is the angle of rotation of the metal pipe each time, defined as the torsional angle amplitude; N is the number of cycles of torsion; d1 is the outer diameter of the metal pipe; d2 is the inner diameter of the metal pipe; and L is the length of the metal pipe.

[0077] 72L / πd1 degrees ≥ θ ≥ 3.6L / πd1 degrees; 4140°L / πθd1 ≥ N ≥ 540°L / πθd1; wherein, the length L of the metal pipe is greater than 1mm, the wall thickness (d1-d2) / 2 is greater than 0.1mm, and the ratio of wall thickness to outer diameter (d1-d2) / 2d1 is less than 0.8; wherein, θ is the torsional angle amplitude, N is the number of cyclic torsional cycles, d1 is the outer diameter of the metal pipe, and d2 is the inner diameter of the metal pipe.

[0078] For example, if the length of the metal pipe is 10mm±1mm and the outer diameter of the metal pipe is 6mm±1mm, then the torsion angle amplitude is greater than 1.9° and less than 38.2°, the torsion rate is 10~10000° / min, and the torsion temperature is 25℃±5℃; preferably, if the torsion angle amplitude is 2°, the number of torsion cycles is greater than 143 cycles and less than 1098 cycles; preferably, if the torsion angle amplitude is 38°, the number of torsion cycles is greater than 8 cycles and less than 58 cycles.

[0079] After undergoing the reciprocating torsion treatment described above in this invention, a hybrid structure of nanoscale dislocation cells and dislocation walls with a gradient distribution from the outer wall to the inner wall is introduced into the tubular metal material, while retaining the original coarse-grained structure. Correspondingly, the microhardness increases continuously from the inner wall to the outer wall.

[0080] After being processed by the method of the present invention, the hardness of the outer wall of the tubular metal material is 1.4 to 2.1 times that of the outer wall of the metal pipe; the hardness of the inner wall of the tubular metal material is 1.2 to 1.5 times that of the inner wall of the metal pipe; at the same time, the tubular metal material maintains a surface finish and roughness comparable to that of the metal pipe.

[0081] Preferably, the tubular metal material in the present invention can be made of the following metal materials: Cu, Cu-Zn, Cu-Al, Cu alloy, 304 stainless steel, 316 stainless steel, 321 stainless steel, stainless steel, Al alloy, Al 0.1 CoCrFeNi high-entropy alloys, medium-entropy alloys, etc., but not limited to these.

[0082] The solution of the present invention has the following advantages:

[0083] 1) The novel structural strategy proposed in this invention is to introduce a gradient-distributed nanoscale dislocation cell-dislocation wall hybrid structure from the outer wall to the inner wall of the tubular sample while preserving the original grain structure of the metal material. The dislocation cell density gradually decreases with depth, the dislocation wall density gradually increases with depth, the thickness of the dislocation cell wall and the dislocation wall gradually increases with depth, and the size of the dislocation structure gradually increases with depth.

[0084] Traditional structural materials introduce microstructural features such as twins and second phases primarily based on alloying metallurgical strategies, relying on the addition of various alloying elements from the periodic table. In contrast, this invention achieves increased strength by controlling dislocation configuration, density, and distribution without altering the material composition. This demonstrates that dislocations can exert the effects of alloying elements, essentially equating dislocations with alloying elements. In the context of increasingly severe resource shortages and environmental pollution, this not only reduces the amount of alloys used but also decreases dependence on scarce resources.

[0085] 2) The solution of this invention can significantly improve the hardness of materials, especially by obtaining a small-sized outer wall surface dislocation cell structure through small-angle cyclic torsional deformation under set conditions. This increases the hardness of the pipe material by 1.4 to 2.1 times while maintaining a surface finish and roughness comparable to the original structure. The solution of this invention can improve the hardness of the outer and inner walls of the pipe while maintaining the original pipe shape and size, achieving near-net-shape forming of the pipe, effectively controlling subsequent processing costs, and enabling efficient manufacturing. It can effectively improve production efficiency, reduce production costs, and ensure the safe, reliable, and stable operation of production and daily life.

[0086] 3) The present invention utilizes a torsion device to perform reciprocating torsional deformation treatment on metal pipes. Its advantage lies in its low equipment requirements. Traditional severe plastic deformation and surface mechanical deformation processes require complex equipment and necessitate grinding or rolling of the metal surface using carbide cutting tools with specific geometric dimensions. Furthermore, the processing time for a single sample is only tens of seconds to several minutes, resulting in high processing efficiency. In addition, this invention has few limitations on the diameter and length of the processed samples; the axial length (L) can be greater than 1 mm, the outer diameter greater than 0.3 mm, the wall thickness (d1-d2) / 2 greater than 0.1 mm, and the ratio of wall thickness to outer diameter (d1-d2) / 2d1 less than 0.8. Moreover, the macroscopic shape and surface roughness of the sample remain unchanged before and after the reciprocating torsional deformation treatment. It has broad prospects for industrial application.

[0087] The present invention will be further described in detail below through specific embodiments and comparative examples:

[0088] Example 1

[0089] This embodiment describes the small-angle cyclic torsional deformation treatment of a single-phase face-centered cubic pure copper hollow tubular sample with an average grain size of 51 μm to obtain a tubular metal material. See also... Figure 1 As shown, the pure copper tubular sample has no dislocation structure characteristics inside.

[0090] In this embodiment, the outer diameters of the pure copper hollow tubular samples are 4mm (wall thickness 1.1mm, wall thickness to outer diameter ratio 0.28, gauge length 12mm), 6mm (wall thickness 0.7mm, wall thickness to outer diameter ratio 0.12, gauge length 12mm), and 10mm (wall thickness 1.1mm, wall thickness to outer diameter ratio 0.11, gauge length 12mm); the length of each sample is 10mm.

[0091] The process parameters for the small-angle cyclic torsional deformation treatment were selected as follows: torsion angle amplitude of 5.2°, 3.5°, and 2.1° (i.e., the torsion angle amplitude corresponding to a copper tube with an outer diameter of 4mm is 5.2°, the torsion angle amplitude corresponding to a copper tube with an outer diameter of 6mm is 3.5°, and the torsion angle amplitude corresponding to a copper tube with an outer diameter of 10mm is 2.1°), torsion rate of 1700° / min, torsion cycles of 150 cycles, and torsion temperature of room temperature of 20℃.

[0092] See Figure 2 As shown, after the pure copper tubular sample underwent small-angle cyclic torsional deformation treatment, the surface roughness of the outer wall of the tubular metal material obtained did not change significantly.

[0093] See Figure 3 As shown, after the pure copper tubular sample underwent small-angle cyclic torsional deformation treatment, the morphology, size, orientation, and original large-angle grain boundaries and twin boundaries remained unchanged. However, a gradient distribution of small-angle interfaces, i.e., a gradient distribution of dislocation structures, was introduced into the tubular metal material from the surface inwards. Specifically, the outer wall of the tubular metal material is a nanoscale dislocation cell-wall hybrid structure (dislocation cell volume fraction greater than 60%, accounting for the majority); the average diameter of the dislocation cells and the average spacing of the dislocation walls are 750–770 nm; the wall thickness of the dislocation cells and the wall thickness of the dislocation walls are 110–140 nm. The inner wall of the tubular metal material is a cell-wall hybrid structure with a dislocation wall volume fraction greater than 60%.

[0094] Correspondingly, after the aforementioned pure copper tubular samples underwent small-angle cyclic torsional deformation treatment, the resulting tubular metal materials exhibited a continuous gradient increase in microhardness from the inner wall to the outer wall. Specifically, for a pure copper tube with an outer diameter of 4 mm, the microhardness of the inner wall after small-angle cyclic torsional deformation treatment was 0.76 GPa, and the microhardness of the outer wall was 0.83 GPa. For a pure copper tube with an outer diameter of 6 mm, the microhardness of the inner wall was 0.79 GPa, and the microhardness of the outer wall was 0.83 GPa. For a pure copper tube with an outer diameter of 10 mm, the microhardness of the inner wall was 0.76 GPa, and the microhardness of the outer wall was 0.83 GPa.

[0095] See Figure 3 As shown, after the pure copper tubular sample underwent small-angle cyclic torsional deformation treatment, the resulting tubular metal material exhibited a gradient change trend in dislocation configuration, size, and density with increasing depth from the outer wall surface, forming a gradient-dislocation structure. For example... Figure 5 As shown in Figure (a), due to the presence of the gradient nanodislocation structure, the microhardness of the tubular metal material gradually decreases from 0.83 GPa to 0.76–0.79 GPa with increasing depth from the outer wall surface, exhibiting a gradient change characteristic, but significantly higher than the original pure copper tubular sample (0.59 GPa). After small-angle cyclic torsional deformation treatment, hollow tubular samples of different sizes obtained tubular metal materials with consistent properties. The reciprocating torsion process in this embodiment is not limited to sample size and can maintain good structural and performance stability for samples of different sizes.

[0096] Example 2

[0097] The samples used in Example 2 were the same as those in Example 1, except that the process parameters for the samples in Example 2 were as follows: The outer diameters of the pure copper hollow tubular samples were 4mm (wall thickness 1.1mm, wall thickness to outer diameter ratio 0.28, gauge length 12mm), 6mm (wall thickness 0.7mm, wall thickness to outer diameter ratio 0.12, gauge length 12mm), and 10mm (wall thickness 1.1mm, wall thickness to outer diameter ratio 0.11, gauge length 12mm). The process parameters for the small-angle cyclic torsion deformation treatment (with a length of 12mm) were selected as follows: torsion angle amplitudes of 11.2°, 7.5°, and 4.5° (that is, here, the torsion angle amplitudes corresponding to copper tubes with an outer diameter of 4mm are 11.2°, those corresponding to copper tubes with an outer diameter of 6mm are 7.5°, and those corresponding to copper tubes with an outer diameter of 10mm are 4.5°), the torsion rate is 1700° / min, the torsion cycles are 150, and the torsion temperature is room temperature of 20℃.

[0098] See Figure 2 As shown, after the pure copper tubular sample in this embodiment underwent small-angle cyclic torsional deformation treatment, the surface roughness of the outer wall of the resulting metal tubular material did not change significantly.

[0099] See Figure 4As shown, after the pure copper tubular sample in this embodiment underwent small-angle cyclic torsional deformation treatment, the resulting metal tubular material retained the original grain morphology, size, orientation, and original large-angle grain boundaries and twin boundaries. However, a gradient distribution of small-angle interfaces was introduced from the surface inwards, forming a gradient-dislocation structure. The outer wall remained a nanoscale dislocation cell-wall hybrid structure (with a dislocation cell volume fraction greater than 60%, accounting for the majority), essentially the same as in Example 1. However, the dislocation cell size and wall thickness of the outer and inner walls were smaller. The diameter of the dislocation cells and the spacing between the dislocation walls were 550–650 nm, and the wall thickness of the dislocation cells and walls was 100–120 nm. The inner wall exhibited a cell-wall hybrid structure with a dislocation wall volume fraction greater than 60%, resulting in a higher dislocation cell content compared to Example 1. Correspondingly, the microhardness was also higher, but it continued to increase in a continuous gradient from the inner wall to the outer wall. Among them, for pure copper tubes with an outer diameter of 4 mm, after small-angle cyclic torsional deformation treatment, the resulting metal tubular material has the following characteristics: the microhardness of the inner wall is 0.83 GPa and the microhardness of the outer wall is 1.10 GPa; for pure copper tubes with an outer diameter of 6 mm, after small-angle cyclic torsional deformation treatment, the resulting metal tubular material has the following characteristics: the hardness of the inner wall is 0.92 GPa and the hardness of the outer wall is 1.10 GPa; for pure copper tubes with an outer diameter of 10 mm, after small-angle cyclic torsional deformation treatment, the resulting metal tubular material has the following characteristics: the hardness of the inner wall is 0.81 GPa and the hardness of the outer wall is 1.11 GPa.

[0100] See Figure 4 As shown, in this embodiment, after the pure copper tubular sample undergoes small-angle cyclic torsional deformation treatment, the resulting tubular metal material exhibits a gradient change trend in dislocation configuration, size, and density with increasing depth from the outer wall surface, forming a gradient-dislocation structure. For example... Figure 5 As shown in Figure (b), due to the presence of the gradient nanodislocation structure, the microhardness gradually decreases from approximately 1.1 GPa to 0.8–0.9 GPa with increasing depth from the outer surface of the material, exhibiting a gradient change characteristic, but significantly higher than the original pure copper tubular sample (0.59 GPa). After small-angle cyclic torsional deformation treatment, hollow tubular samples of different sizes achieved consistent performance of the resulting tubular metal materials. The reciprocating torsion process in this embodiment is not limited to sample size and can maintain good structural and performance stability for samples of different sizes.

[0101] Example 3

[0102] This embodiment involves subjecting a single-phase face-centered cubic Cu-18Zn alloy tube with an average grain size of 50 μm to small-angle cyclic torsional deformation to obtain a tubular metal material sample with a gradient dislocation structure.

[0103] The sample size selection for Example 3 was the same as that for Example 1, with outer diameters of 6 mm (wall thickness of 0.7 mm, wall thickness to outer diameter ratio of 0.12) and 10 mm (wall thickness of 1.1 mm, wall thickness to outer diameter ratio of 0.11). The difference was that the sample in Example 3 was a Cu-Zn alloy hollow tubular sample. The process parameters selected for the outer diameters of 6 mm and 10 mm were: torsion angle amplitude of 7.5° and 4.5° (wherein, the torsion angle amplitude corresponding to the alloy tube with an outer diameter of 6 mm is 7.5°; and the torsion angle amplitude corresponding to the alloy tube with an outer diameter of 10 mm is 4.5°), torsion rate of 1700° / min, torsion cycles of 150, and torsion temperature of room temperature (20°C).

[0104] Example 3 is basically the same as Example 1 and Example 2. After the Cu-18Zn alloy hollow tubular sample in Example 3 was subjected to small-angle cyclic torsional deformation treatment, the surface roughness of the outer wall of the resulting tubular metal material sample did not change significantly (see Example 3). Figure 2 As shown, the morphology, size, orientation, and original large-angle grain boundaries and twin boundaries of the original grains remain unchanged. Gradient distribution of small-angle interfaces is also introduced from the surface to the inside, which is a gradient distribution of dislocation structure. However, the hardness value of the outermost layer of its outer wall reaches about 1.4 GPa, and the inner wall also has a correspondingly higher hardness of about 1.1 GPa.

[0105] As the depth from the outer wall surface increases, the dislocation configuration, size, and density of the Cu-18Zn alloy hollow tubular sample in Example 3, after small-angle cyclic torsional deformation treatment, exhibit a gradient change trend, forming a gradient-dislocation structure. Correspondingly, the microhardness increases continuously from the inner wall to the outer wall: for a Cu-Zn tubular sample with an outer diameter of 6 mm after small-angle cyclic torsional deformation treatment, the microhardness of the inner wall is 1.10 GPa, and the microhardness of the outer wall is 1.36 GPa. For a Cu-Zn tubular sample with an outer diameter of 10 mm after small-angle cyclic torsional deformation treatment, the microhardness of the inner wall is 1.19 GPa, and the microhardness of the outer wall is 1.45 GPa. This is significantly higher than the original Cu-18Zn alloy tubular sample (0.88 GPa). Figure 5 As shown in Figure (c).

[0106] Example 4

[0107] This embodiment describes the small-angle cyclic torsional deformation treatment of a single-phase face-centered cubic tubular 321 stainless steel sample with an average grain size of 15 μm to obtain a tubular metal material. See also... Figure 6 As shown in (a), the tubular 321 stainless steel sample has no dislocation structure inside.

[0108] In this embodiment, tubular 321 stainless steel samples (denoted as 1#, 2#, and 3#) with gauge lengths of 10mm, 10mm, and 60mm, outer diameters of 6mm, wall thicknesses of 0.7mm, and wall thickness-to-outer diameter ratios of 0.12 were subjected to small-angle cyclic torsional deformation treatment to obtain tubular metal materials.

[0109] See Figure 6 As shown in Figures (b), (c), and (d), the surface roughness of the outer wall of the tubular 321 stainless steel sample did not change significantly after undergoing small-angle cyclic torsional deformation treatment.

[0110] Among the tubular materials obtained, the hardness gradually decreased with increasing depth from the surface. Specifically: Sample 1# gradually decreased from approximately 2.3 GPa at the surface to 1.9 GPa; Sample 2# gradually decreased from approximately 2.4 GPa at the surface to 2.0 GPa; and Sample 3# gradually decreased from approximately 2.6 GPa at the surface to 2.4 GPa.

[0111] In this embodiment, the three samples underwent the same small-angle cyclic torsional deformation process. The selected process parameters were: torsion angle amplitudes of 3.5°, 7.5°, and 58.5° (i.e., the torsion angle amplitudes for sample #1 (tubular 321 stainless steel) were 3.5°, for sample #2 (tubular 321 stainless steel) were 7.5°, and for sample #3 (tubular 321 stainless steel) were 58.5°), the torsion rate was 1700° / min, the number of torsion cycles was 150, and the torsion temperature was room temperature (20°C). During torsion, the cumulative shear strain exhibits a gradient distribution with depth. With increasing depth from the surface, the structural and hardness characteristics of the resulting tubular metal material also show a gradient change trend, forming a gradient-dislocation structure (see...). Figure 7 , Figure 9 (as shown in Figure (a)).

[0112] See Figure 7 As shown, after the tubular 321 stainless steel sample of this embodiment underwent small-angle cyclic torsional deformation treatment, the resulting tubular metal material retained the original grain morphology, size, orientation, and original large-angle grain boundaries and twin boundaries. However, a gradient distribution of small-angle interfaces was introduced from the surface inwards, forming a gradient-dislocation structure. The outer wall remained a nanoscale dislocation cell-wall hybrid structure (dislocation cell volume fraction greater than 60%, accounting for the majority), essentially the same as in Example 1. However, the dislocation cell size and cell wall thickness of the outer and inner walls were smaller. The diameter of the dislocation cells and the spacing between dislocation walls were 585–665 nm; the wall thickness of the dislocation cells and the wall thickness of the dislocation walls were 80–120 nm; the inner wall was a cell-wall hybrid structure with a dislocation wall volume fraction greater than 60%. The microhardness increased continuously from the inner wall to the outer wall.

[0113] See Figure 7 As shown, in this embodiment, after the tubular 321 stainless steel sample undergoes small-angle cyclic torsional deformation treatment, the resulting tubular metal material exhibits a gradient change trend in dislocation configuration, size, and density with increasing depth from the outer wall surface, forming a gradient-dislocation structure. For example... Figure 9 As shown in Figure (a), due to the presence of the gradient nanodislocation structure, the microhardness gradually decreases with increasing depth from the outer surface of the material: sample #1 decreases from approximately 2.3 GPa at the surface to 1.9 GPa; sample #2 decreases from approximately 2.4 GPa at the surface to 2.0 GPa; and sample #3 decreases from approximately 2.6 GPa at the surface to 2.4 GPa. The hardness exhibits a gradient change, but is significantly higher than that of the original pure copper tubular sample (1.7 GPa). The reciprocating torsion process in this embodiment is not limited to the sample size and can maintain good structural and performance stability for samples of different sizes.

[0114] Since samples #1 and #2 have the same gauge length, the structure of the resulting tubular metal material after small-angle cyclic torsional deformation treatment (see...) Figure 7 The samples shown (as shown) have similar properties, with surface hardnesses of 2.30 GPa and 2.36 GPa, respectively. However, sample #3 has a larger torsional angle amplitude and a larger cumulative shear strain, resulting in a smaller surface cell size and higher hardness in the tubular metal material, with a surface hardness of 2.60 GPa.

[0115] Example 5

[0116] This embodiment describes the small-angle cyclic torsional deformation treatment of a single-phase face-centered cubic tubular 321 stainless steel sample with an average grain size of 15 μm to obtain a tubular metal material. See also... Figure 6 As shown in Figure (a), the tubular 321 stainless steel sample has no dislocation structure inside.

[0117] This embodiment describes the process of obtaining tubular metal materials by treating three 321 stainless steel samples with different lengths and outer diameters using different small-angle cyclic torsion deformation processes. The outer diameters of the three samples are 6 mm (wall thickness of 0.7 mm, wall thickness to outer diameter ratio of 0.12), 8 mm (wall thickness of 1.2 mm, wall thickness to outer diameter ratio of 0.15), and 12 mm (wall thickness of 0.9 mm, wall thickness to outer diameter ratio of 0.08), with corresponding gauge lengths of 10 mm, 45 mm, and 103 mm, respectively. Among them, tubular 321 stainless steel samples with an outer diameter of 6 mm (wall thickness of 0.7 mm and gauge length of 10 mm), tubular 321 stainless steel samples with an outer diameter of 8 mm (wall thickness of 1.2 mm and gauge length of 45 mm), and tubular 321 stainless steel samples with an outer diameter of 12 mm (wall thickness of 0.9 mm and gauge length of 103 mm) were twisted for 150 revolutions under the conditions of torsion angle amplitudes of 7.5°, 25.3°, and 38.6°, respectively (here, the torsion angle amplitudes corresponding to the tubular 321 stainless steel samples with an outer diameter of 6 mm are 7.5°, the tubular 321 stainless steel samples with an outer diameter of 8 mm are 25.3°, and the tubular 321 stainless steel samples with an outer diameter of 12 mm are 38.6°).

[0118] See Figure 6 As shown in Figures (b), (c), and (d), the surface roughness of the outer wall of the tubular 321 stainless steel sample after small-angle cyclic torsional deformation treatment did not change significantly. Furthermore, the hardness of the obtained tubular metal material gradually decreased from approximately 2.4 GPa at the surface to 1.9–2.0 GPa with increasing depth from the surface.

[0119] In this embodiment, the three samples have different outer diameters. By controlling the torsion process, the cumulative shear strain experienced by the three samples during the torsion process is made the same, ultimately resulting in similar structures and properties. See also Figure 8 As shown, the structure in this tubular material forms a gradient-dislocation structure, with the size of the outermost dislocation structure ranging from approximately 600 to 620 nm. From... Figure 9 As can be seen from Figure (b), after the three samples were treated with a small-angle cyclic torsion deformation process, they obtained extremely similar hardness gradients, with the hardness of the outermost layer being very close, approximately 2.35 GPa.

[0120] Comparative Example 1

[0121] Comparative Example 1 provides a hollow tubular sample of pure copper in a normal annealed state (with a grain size of approximately 51 μm). This sample exhibits a coarse equiaxed crystal structure and lacks internal dislocation features. Figure 1 As shown. The microhardness distribution within the cross-sectional area is uniform (0.59 GPa), as... Figure 2As shown, its surface roughness is 7–9 μm. These results indicate that the hardness of the original coarse-grained structure is significantly lower than that of the tubular metal material samples obtained in Examples 1 and 2 of this invention.

[0122] Comparative Example 2

[0123] Comparative Example 2 prepared a hollow tubular sample (grain size approximately 50 μm) of a coarse-grained Cu-18Zn alloy in a common annealed state. The sample exhibited a coarse equiaxed crystal structure with no internal dislocation features, such as... Figure 1 As shown, the microhardness distribution within the cross-section is uniform (0.88 GPa), significantly lower than that of the tubular metal material sample obtained in Example 3. Figure 2 As shown, its surface roughness is 7–9 μm.

[0124] Comparative Example 3

[0125] Comparative Example 3: Zhang Weihua et al. from the Institute of Metal Research, Chinese Academy of Sciences, used a roller-type surface nano-sizing method to nano-process IF steel, preparing a gradient microstructure with a thickness of 700 μm. The outermost grains were refined to 19 nm, and the microhardness of the outermost layer was 3.0 GPa. At a depth of approximately 50 μm from the surface, the hardness decreased to 1.5 GPa, and with increasing depth from the surface, the microhardness gradually decreased to 0.9 GPa. Although this sample achieved a very high surface hardness, this result was obtained from a solid bar; processing tubular samples would easily cause changes in the tube shape.

[0126] It should be noted that: metal tubular samples (thin tubes) are prone to shape change and instability during deformation due to their hollow structure; this invention overcomes this technical problem by applying smaller single-cycle strain and larger cumulative strain within a small range by limiting the torsion angle and the number of cycles.

[0127] Comparative Example 4

[0128] Comparative Example 4: Wang Zhenbo et al. from the Institute of Metal Research, Chinese Academy of Sciences, used heat treatment and surface mechanical rolling nano-sizing to prepare a gradient nanostructure layer with surface grains refined to 63 nm. The surface hardness was increased from 6.7 GPa of the substrate to 7.5 GPa, with a hardness increase of 11%, which is significantly lower than the embodiment of the present invention.

[0129] Comparative Example 5

[0130] Comparative Example 5 involves YJWei et al. from the Institute of Mechanics, Chinese Academy of Sciences, treating cold-rolled 304 stainless steel using a 180-degree torsional deformation process. Due to the excessively large torsional angle, it does not satisfy the requirement θ≥3.6Lπd1 in the formula described in this invention. The obtained plastic strain and πθd1 / 360°L, as well as the cumulative plastic strain πNθd1 / 180°L, are 26.2% and 26.2%, respectively, both failing to satisfy 20%≥πθd1 / 360°L≥1% and 23≥πNθd1 / 180°L≥3. The obtained structure is a mixed structure of gradient twins and martensite, rather than the gradient dislocation structure described in this patent. The microhardness of the outermost layer is 2.6 GPa, and that of the coarse-grained matrix is ​​1.9 GPa, representing a hardness increase of 36%, significantly lower than the embodiments of this invention.

[0131] Comparative Example 6

[0132] Comparative Example 6 shows that BN Mordyuk et al. from the Kurdyumov Institute of Metal Physics in Ukraine used laser shock peening to prepare a high-strength surface layer on a 321 stainless steel substrate with a hardness of 1.5 GPa. The outermost layer structure (approximately 5 μm depth) is a dislocation cell structure, and the hardness of the outermost layer is approximately 2.75 GPa. However, the hardness gradient decreases rapidly and is limited to a range of less than 20 μm in the surface layer. Moreover, this hardness was obtained in a bulk sample.

[0133] Comparative Example 7

[0134] Comparative Example 7 describes how Sadegh Pour-Ali et al. from the University of Fildosi in Mashhad, Iran, used shot peening to form α' martensite with a volume fraction of approximately 65% ​​and nanocrystals with a grain size of 53 nm on the outermost layer. This resulted in a hardness gradient of 1.2 GPa to 2.8 GPa within a 180 μm range on the surface. This method resulted in a rapid decrease in hardness gradient, which was limited to a 200 μm range on the surface. Furthermore, due to localized deformation and uneven surface deformation during shot peening, the surface roughness Ra value was relatively high, exceeding 1 μm.

[0135] Comparative Example 8

[0136] Comparative Example 8 is a study by Schuh et al. from the University of Mines Leoben in Austria, who treated a high-entropy CoCrFeMnNi alloy under high pressure torsion, refining the coarse cast grains to a size of about 50 nm and increasing the microhardness from about 1.5 GPa to 5.1 GPa.

[0137] Comparative Example 9

[0138] Comparative Example 9 is a study by Zhang et al. from Beijing University of Aeronautics and Astronautics who applied torsional fatigue treatment to 2A12-T4 aluminum alloy. Due to the small torsion angle, the study did not meet the requirement of "θ≥3.6Lπd1" as described in this invention, and thus failed to form a gradient dislocation structure inside the sample.

[0139] Comparative Example 10

[0140] Comparative Example 10 is a study conducted by Xue et al. from the University of Paris, France, who subjected D38MSV5S steel and 100C6 steel to torsional fatigue treatment at 20Hz and 35Hz. Due to the small torsional angle, the study did not meet the requirement of "θ≥3.6Lπd1" as defined in this invention, and thus failed to form a gradient dislocation structure inside the sample.

[0141] Through comparison of the results of the above embodiments and comparative examples, it was found that the solution of the present invention introduces a gradient-dislocation structure from the outer wall to the inner wall of the tubular metal material without changing the original grain structure characteristics of the metal material. By applying small-angle cyclic torsional deformation under set conditions to the metal tube, this structural feature can be controllably prepared while retaining the original coarse-grained structure. The hardness of the tubular metal material after the cyclic torsional process reaches 1.4 to 2.1 times. Compared with traditional alloying methods and severe plastic deformation processes such as high-pressure torsional deformation, dynamic plastic deformation, equal-channel angle extrusion, and cumulative rolling to improve the strength of metal tubes, the solution of the present invention can controllably adjust the internal microstructure of the metal tube while ensuring the surface roughness and smoothness, thereby achieving near-net-shape forming, effectively controlling subsequent processing costs, improving production efficiency, reducing production costs, and achieving efficient preparation. This contributes to ensuring the safe, reliable, and stable operation of production and daily life. The metal tube has fewer size limitations, controllable process parameters, and low requirements for subsequent processing, making it promising for broad industrial applications.

[0142] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A tubular metal material, characterized in that, The tubular metal material has an average grain size greater than 1 μm and less than 200 μm, and is a metal material characterized by dislocation deformation; in the tubular metal material, the dislocation structure exhibits a spatial gradient distribution in a first direction; wherein... The dislocation structure in the tubular metal material includes dislocation cells and dislocation walls; wherein, along the first direction: the content of dislocation cells gradually decreases and the content of dislocation walls gradually increases; Wherein, the first direction is the direction from the outer wall to the inner wall of the tubular metal material; The term "dislocation cell" refers to a three-dimensional cellular or network-like morphological feature formed by the self-organization of dislocations; the term "dislocation wall" refers to a two-dimensional wall-like morphological feature formed by the self-organization of dislocations. The method for preparing the tubular metal material includes the following steps: The clamping section of the metal pipe is filled using a mold; The clamping section of the metal tube is used to clamp the metal tube, and then the metal tube is subjected to small-angle cyclic torsional deformation under set conditions to introduce a gradient distribution of dislocation cells and dislocation wall structures from the outer wall to the inner wall of the metal tube, thereby obtaining a tubular metal material. The metal pipe has an axial length greater than 1 mm, an outer diameter greater than 0.3 mm, a wall thickness greater than 0.1 mm, and a wall thickness to outer diameter ratio less than 0.

8. The small-angle cyclic reciprocating torsional deformation process includes: clamping and fixing one end of a metal tube after filling it with a mold, and applying force to rotate the other end of the metal tube around its central axis. First, it rotates clockwise by an angle θ from the initial position, then counterclockwise by an angle θ, and returns to the initial position, completing one reciprocating rotation, which is considered one cycle of torsion. Then, the metal tube starts the next reciprocating rotation process from the initial position, and so on, until the required number of cycles of torsion is reached. θ is a fixed value in each cyclic reciprocating torsional deformation process. The small-angle cyclic torsional deformation process must meet the following conditions: 20%≥πθd1 / (360°L)≥1%; 23≥πNθd1 / (180°L)≥3; The angle θ of each rotation of the metal tube is defined as the torsional angle amplitude; The small-angle cyclic torsional deformation treatment must meet the following conditions: 72L / (πd1) degrees ≥ θ ≥ 3.6L / (πd1) degrees; 4140°L / (πθd1)≥N≥540°L / (πθd1); Where L is the axial length of the metal pipe, θ is the torsional angle amplitude, N is the number of cyclic torsional cycles, and d1 is the outer diameter of the metal pipe.

2. The tubular metal material according to claim 1, characterized in that, The dislocation structure of the outer wall of the tubular metal material is a dislocation cell structure or a first cell-wall hybrid dislocation structure; wherein, the first cell-wall hybrid dislocation structure refers to a hybrid dislocation structure including dislocation cells and dislocation walls, and in the hybrid dislocation structure, the volume fraction of dislocation cells is greater than 60%; The dislocation structure of the inner wall of the tubular metal material is a dislocation wall structure or a second cell-wall hybrid dislocation structure; wherein, the second cell-wall hybrid dislocation structure refers to a hybrid dislocation structure including dislocation cells and dislocation walls, and in the hybrid dislocation structure, the volume fraction of dislocation walls is greater than 60%.

3. The tubular metal material according to claim 1 or 2, characterized in that, The dislocation cell has a diameter of 20-1000 nm and a wall thickness of 100-180 nm; and / or The dislocation walls have a spacing of 200~1000nm and a wall thickness of 50~400nm; and / or The size of the dislocation structure in the tubular metal material increases in a gradient from the surface to the inside; and / or The dislocation density of the tubular metal material decreases in a gradient from the surface to the interior.

4. The tubular metal material according to claim 1, characterized in that, The hardness of the outer wall of the tubular metal material is 1.4 to 2.1 times that of the outer wall of the metal pipe.

5. The tubular metal material according to claim 1, characterized in that, The hardness of the inner wall of the tubular metal material is 1.2 to 1.5 times that of the inner wall of the metal pipe.

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