A titanium alloy extruded tube blank having a gradient texture and a method of making the same

Abstract

The application discloses a titanium alloy extruded pipe blank with gradient texture and a preparation method thereof. The titanium alloy extruded pipe blank with gradient texture has gradient texture characteristics in the wall thickness direction, including a surface layer region: within a depth range of 0-1.5 μm from an outer surface and / or an inner surface, a {0001} basal plane strong shear texture is formed, and the crystallographic orientation of the region has an included angle of 30°-60° with the radial direction; a core region: a wall thickness center region, the texture strength is weak, and the texture strength is randomly distributed or weak; a transition region: between the surface layer region and the core region, the texture strength changes in a gradient manner; and a maximum pole density difference of the surface layer and the core region is greater than or equal to 4. Through the gradient texture design, the surface layer of the pipe blank forms a strong shear texture, has high crack resistance, the core region keeps random texture, and provides isotropic high plastic deformation capacity. The performance zoning enables the pipe to withstand a larger deformation amount without being prone to cracking in the subsequent cold working process.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic processing technology, specifically relating to a titanium alloy extruded tube blank with gradient texture and its preparation method. Background Technology

[0002] Extrusion forming is one of the important methods for tube production. The tube blanks obtained by extrusion usually need to undergo subsequent cold working (such as cold rolling, cold drawing, spinning, etc.) to achieve the final size and performance requirements. However, traditional extruded tube blanks often fail in subsequent large deformation processing due to insufficient plasticity or the initiation of surface cracks, resulting in low yield and high production costs.

[0003] To address these issues, researchers have explored various technical approaches. For instance, heat treatment refines grains to improve plasticity, but this often fails to simultaneously improve surface crack resistance. Alternatively, surface treatment techniques (such as shot peening and laser shock peening) can introduce residual compressive stress, but these methods increase processing steps and are difficult to implement on the inner walls of pipes. In recent years, gradient-structured materials have attracted attention due to their ability to achieve performance zoning. Studies have shown that gradient grain structures (such as fine surface grains and coarse core grains) can optimize overall mechanical properties (CN202511279558.2, CN202411672298.0). However, precise control and industrial-scale preparation of gradient textures (i.e., the gradient distribution of crystallographic orientations along the thickness direction) are currently lacking effective methods. CN202511132506.2 discloses a method for controlling the texture of copper alloys through gradient temperature-controlled deformation, which can effectively reduce Brass texture content and increase Y texture content. However, this method is mainly applicable to sheet metal and relies on temperature field control.

[0004] Crystallographic texture has a significant impact on the mechanical properties of materials. Specific oriented textures (such as basal texture and shear texture) can significantly improve the crack resistance of materials, while random textures are beneficial for maintaining isotropic high plasticity. Achieving a gradient distribution of strong surface texture and random core texture in extruded tube blanks could potentially balance surface crack resistance and high core plasticity, enabling the tube to withstand greater subsequent deformation without easily cracking. However, how to precisely control this gradient texture through the extrusion process remains a pressing technical challenge in this field. Summary of the Invention

[0005] To address the technical problem of easy cracking in existing titanium alloy extruded tube blanks during subsequent large deformation processing, the primary objective of this invention is to provide a method for preparing titanium alloy extruded tube blanks with gradient texture. This method achieves a gradient texture by controlling the extrusion process to form a strong shear texture on the surface of the tube blank to suppress crack initiation, and a weak shear texture or random texture in the core to maintain high plasticity, thereby obtaining a high-performance titanium alloy extruded tube blank.

[0006] Another object of the present invention is to provide a titanium alloy extruded tube blank with gradient texture obtained by the above method.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a titanium alloy extruded tube blank with gradient texture includes the following steps:

[0009] Step 1: Determine the process parameter window through multi-scale simulation coupling

[0010] 1.1 Macroscopic finite element simulation: A thermo-mechanical coupling model was established using the Abaqus / Explicit explicit dynamics module to simulate the stress-strain distribution under different combinations of extrusion process parameters. The simulated process parameters include: extrusion ratio, extrusion temperature, and extrusion speed.

[0011] 1.2 Crystal Plasticity Finite Element Simulation: The stress-strain history data of each element obtained from the macroscopic finite element simulation are used as boundary conditions and imported into the finite element model based on the rate-dependent crystal plasticity theory to simulate the texture evolution process at different thickness locations (from the surface to the core) and obtain the pole figure.

[0012] If the pole figure shows that the surface layer forms a strong shear texture and the core maintains a random texture or a weak texture, and the maximum pole density difference between the two is ≥4, then the condition is met and the optimized process parameters are obtained; otherwise, adjust the extrusion temperature, extrusion speed, and extrusion ratio, and repeat step 1.

[0013] Step 2: Extrusion molding

[0014] Based on the optimized process parameters determined in step 1, the billet is extruded and shaped using an extrusion device to obtain an extruded tube blank with a gradient texture.

[0015] Step 3: Stress-relief annealing

[0016] The extruded tube blank obtained in step 2 is subjected to stress-relief annealing to eliminate residual stress generated during the extrusion process while retaining the deformation texture, ultimately achieving precise control of the gradient radial texture.

[0017] Preferably, in the process of establishing the thermo-coupling model in step 1, the simulated process parameters include: extrusion temperature of 500~750℃, extrusion speed of 10~25 mm / s, and extrusion ratio of 8~25.

[0018] Extrusion temperature 500~750℃: This temperature range is lower than or close to the recrystallization initiation temperature of TA16 titanium alloy (approximately 600℃). On the one hand, it can effectively suppress the occurrence of dynamic recrystallization, allowing the deformation texture to be fully preserved; on the other hand, even if limited recrystallization occurs locally, due to the low degree of thermal activation, the orientation of the recrystallized grains is still inherited from the deformed matrix, and will not significantly interfere with the original texture. Therefore, this temperature range can ensure that the material has a certain degree of hot working plasticity while maximally preserving the strong texture characteristics induced by shear deformation, providing an organizational basis for achieving precise control of gradient texture.

[0019] Extrusion speed 10~25 mm / s: The extrusion speed is controlled at 10~25 mm / s. Firstly, it allows sufficient time for grain rotation and orientation adjustment to ensure that the shear texture is fully formed. Secondly, it suppresses flow defects caused by excessive flow rate difference between the surface and the core, and ensures the continuity and uniformity of the texture gradient.

[0020] The extrusion ratio is controlled between 8 and 25. The key is to provide sufficient total deformation to activate strong shear deformation in the surface layer while avoiding excessive deformation in the core that could damage the gradient structure. Specifically, a larger extrusion ratio allows the metal to accumulate high strain as it passes through the conical die. Due to the long shear path and intense deformation in the surface layer, the grains rotate fully, forming a strong shear texture. While the core also experiences compressive deformation, the shear component is smaller, and the texture remains randomly distributed. If the extrusion ratio is too low (<8), the shear strain is insufficient, making it difficult for the surface layer to form a strong texture. If the extrusion ratio is too high (>25), the core deformation increases, the texture strength rises, the gradient characteristics weaken, and the extrusion pressure increases significantly, resulting in excessive die load. Therefore, an extrusion ratio range of 8 to 25 can achieve the optimal match between a strong surface texture and a weak core texture.

[0021] Preferably, in step 1, the optimized process parameters obtained (satisfying the maximum extreme density difference between the surface region and the core region ≥ 4) include: extrusion temperature of 600~700℃, extrusion speed of 15~20 mm / s, and extrusion ratio of 10~16.

[0022] More preferably, the optimized process parameters in step 1 include: extrusion temperature 700℃, extrusion speed 15 mm / s, and extrusion ratio 12.

[0023] Preferably, in step 2, the billet is a titanium alloy billet.

[0024] Preferably, in step 2, the extrusion device includes an extrusion cylinder, an extrusion die, and a mandrel;

[0025] The mandrel corresponding to the sizing zone is set as a conical structure, and its outer wall surface has a continuously varying taper along the extrusion direction, with a taper angle β of 10°~30°;

[0026] The extrusion die is configured as a conical structure, with its diameter gradually decreasing along the extrusion direction and a cone angle α of 30°~60°.

[0027] The mandrel cone angle β of the extrusion device is set to 10°~30°, and the extrusion cylinder cone angle α is set to 30°~60°. The difference in angles between the two is designed to subject the surface metal of the billet to strong shear stress when passing through the die: on the one hand, the large cone angle of the extrusion cylinder forces the outer surface of the billet to contract sharply radially at the inlet, generating intense frictional shear with the inner wall of the die; on the other hand, the small cone angle of the mandrel makes the flow path of the inner wall metal relatively gentle, and the difference in deformation rate between the inner and outer walls further enhances the shear gradient in the wall thickness direction. This structure increases the equivalent shear strain of the surface metal, while the core is mainly subjected to compressive deformation, providing a deformation basis for achieving a gradient distribution of strong surface texture and random core texture.

[0028] Preferably, in step 2, a layer of lubricant is applied to the surface of the billet before extrusion. The extrusion die and lubricant introduce strong shearing forces on the inner and outer surfaces of the billet, laying the foundation for the deformation of the gradient texture.

[0029] More preferably, the lubricant is a glass lubricant, specifically composed of 85-95 wt.% borosilicate glass powder and 5-15 wt.% colloidal graphite; the coating thickness of the glass lubricant is 0.1-0.3 mm. This lubricant forms a continuous glass film during extrusion, achieving boundary lubrication (friction coefficient 0.2-0.4), providing the required shear stress to the surface of the blank while completely isolating the titanium alloy from direct contact with the mold, thus preventing mold sticking and mold wear.

[0030] More preferably, the borosilicate glass powder has a softening point of 550~600℃ and a viscosity of 10 at an extrusion temperature of 600~700℃. 3 ~10 4 Pa·s.

[0031] More preferably, the borosilicate glass powder has a particle size of 10-75 μm, and the colloidal graphite has a particle size of 1-10 μm; more preferably, the borosilicate glass powder has a particle size of 20-50 μm, and the colloidal graphite has a particle size of 1-5 μm.

[0032] Preferably, the annealing process described in step 3 is carried out at a temperature of 500~580℃ and a holding time of 0.5~2 hours.

[0033] The annealing temperature is controlled at 500~580℃, lower than the recrystallization initiation temperature of TA16 titanium alloy (approximately 600℃), and held for 0.5~2 hours. This process aims to fully eliminate residual extrusion stress while avoiding recrystallization, ensuring that the deformation texture is not weakened, thereby fully preserving the gradient texture characteristics.

[0034] Preferably, the preparation method further includes, after the annealing treatment in step 3, the following steps: performing texture characterization on the annealed tube blank, and using electron backscatter diffraction technology to verify the texture gradient distribution from the surface to the core along the wall thickness direction.

[0035] The present invention also provides a titanium alloy extruded tube blank with a gradient texture.

[0036] Preferably, the titanium alloy extruded tube blank with gradient texture has gradient texture characteristics along the wall thickness direction, specifically including:

[0037] a. Surface region: Within a depth of 0 to 1.5 mm from the outer and / or inner surfaces, a strong shear texture is formed, and the crystallographic orientation of this region forms an angle of 30° to 60° with the radial direction;

[0038] b. Core region: The central region of the wall thickness, with weaker texture intensity, exhibiting random distribution or weak texture characteristics;

[0039] c. Transition region: The texture intensity changes in a gradient between the surface region and the core region; and the maximum extreme density difference between the surface region and the core region is ≥4.

[0040] The strong shear texture is characterized by the c-axis of the α-phase grains forming an angle of 30° to 60° with the radial direction (RD) of the tube blank. In the {0001} basal plane pole figure, the maximum polar density is located in an annular region with an angle of 30° to 60° with the radial direction, and the maximum polar density is ≥7.

[0041] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0042] (1) Performance zoning optimization: This invention uses gradient texture design to form a strong shear texture on the surface of the tube blank, which has high crack resistance (the Schmidt factor of a specific slip system is low, which is beneficial to suppress crack initiation); the core maintains a random texture, providing isotropic high plastic deformation capacity. This performance zoning enables the tube to withstand greater deformation during subsequent cold working without cracking.

[0043] (2) Strong process controllability: This invention establishes a quantitative relationship between process parameters, stress-strain and texture evolution by coupling macroscopic finite element simulation and crystal plasticity simulation, thereby realizing the controllable regulation of gradient texture and avoiding the high cost of traditional trial and error methods.

[0044] (3) Die design innovation: This invention sets micro-structural features in the sizing zone of the extrusion die to generate strong shear deformation in the surface metal, providing key equipment support for the realization of gradient texture.

[0045] (4) Wide range of applicable materials: The method of the present invention is applicable to a variety of metal materials, including but not limited to titanium and titanium alloys. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the extrusion device used in Embodiment 1 of the present invention, wherein: 1-extrusion cylinder, 2-mandrel, 3-extrusion pad, 4-extrusion die, 5-extrusion tube.

[0047] Figure 2 The EBSD test results of the TA16 titanium alloy extruded tube blank prepared in Example 1 of the present invention show the texture gradient distribution along the wall thickness direction; (a) surface layer; (b) core layer; different colors represent the magnitude of the extreme values ​​of the pole figure. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0049] Figure 1 The extrusion apparatus used in this embodiment 1 includes an extrusion cylinder 1, a mandrel 2, an extrusion pad 3, an extrusion die 4, and an extruded tube 5. The mandrel 2 is configured with a conical structure corresponding to the sizing zone of the extrusion die, with a cone angle β = 10° and a smooth transition on the outer wall surface; the extrusion die 4 is configured with a conical structure, with a cone angle α = 30°, and smoothly connects to the inlet end of the extrusion die; its working mechanism is as follows:

[0050] (1) Billet positioning and pressure application: The heated titanium alloy ingot is loaded into the extrusion cylinder 1, and the extrusion pad 3 is pushed forward under the action of the press, applying axial pressure to the billet. Under the constraint of the inner wall of the extrusion cylinder, the billet first undergoes upsetting deformation and fits tightly against the cylinder wall;

[0051] (2) Plastic deformation and flow: When the pressure exceeds the yield strength of the material, the metal is forced to flow in the direction of least resistance and enter the conical deformation zone of the extrusion die 4. At the same time, the conical surface at the front end of the mandrel 2 guides the metal to fill the annular gap, so that the solid billet gradually forms a hollow tubular flow state;

[0052] (3) Sizing and forming stage: When the metal flows through the annular gap between the working zone of the extrusion die 4 and the sizing section of the mandrel 2, uniform plastic deformation occurs. During this process, the outer diameter of the pipe is controlled by the die sizing zone (located at the pipe outlet), and the inner diameter is controlled by the mandrel sizing section. At the same time, stable dimensional accuracy and surface quality are obtained through friction.

[0053] (4) Pipe extrusion and cycle completion: The extruded pipe 5 after forming is continuously extruded through the die along the mandrel rod. After extrusion is completed, the press returns, the extrusion pad 3 and the mandrel 2 are reset, and the press is ready for the next extrusion cycle.

[0054] Example 1

[0055] The material used to prepare the extruded tube blank in this embodiment is TA16 titanium alloy (Ti-2Al-2.5Zr). The initial state is a drilled bar blank (diameter of 300 mm and wall thickness of 100 mm) after homogenization treatment. After heating in the α phase region, it is air-cooled to obtain an equiaxed α structure with a grain size of about 30-50 μm.

[0056] Step 1: Selection of high-shear extrusion die

[0057] To achieve strong shear deformation of TA16 titanium alloy during high-temperature extrusion, the extrusion die used in this embodiment is as follows: Figure 1 As shown;

[0058] Step 2: Determine process parameters through multi-scale simulation coupling

[0059] 2.1 Macroscopic Finite Element Simulation: An axisymmetric thermo-coupling model was established in Abaqus to simulate the stress-strain distribution under different combinations of extrusion process parameters. These parameters included the extrusion ratio, extrusion temperature, and extrusion speed. The material constitutive model adopted the Johnson-Cook model, with parameters fitted based on high-temperature compression experimental data of TA16 titanium alloy. A modified Coulomb friction model was used for contact friction, with the friction coefficient set to 0.3.

[0060] 2.2 Crystal plasticity simulation: The stress-strain history data of the unit obtained by macroscopic finite element simulation is used as the boundary condition and imported into the finite element model based on rate-related crystal plasticity theory to simulate the texture evolution at different thickness positions and obtain the pole figure. The slip system of TA16 titanium alloy considers cylindrical slip, basal slip and conical slip. The critical shear stress of each slip system is determined according to the literature data ([1] BO G, YUNCHANG X, XIAOXU H, CHENGLU L, PEIDONG W, QING L. The mechanism for an orientation dependence of grain boundary strengthening in pure titanium[J]. International Journal of Plasticity, 2022,153: 103276.; [2] YANG Zhongze. Evolution of thermally strong spiral texture and strengthening mechanism of titanium alloy with variable loading path[D]; Harbin Institute of Technology, 2022.) and high temperature compression test calibration. Under these conditions, if the simulation results (pole diagram) show that the surface layer forms a strong shear texture and the core region has a random distribution of texture, and the maximum pole density difference between the two is ≥4, then the gradient deformation requirement is met.

[0061] The specific simulation process for step 2 is as follows:

[0062] 2.1 Macroscopic Finite Element Simulation: Obtaining the Deformation History of the Entire Field

[0063] (1) Geometric model and mesh

[0064] An axisymmetric thermo-coupled model was built in ABAQUS / Explicit. The geometric model included: billet (initial dimensions converted according to the extrusion ratio), extrusion cylinder (inner wall cone angle α), extrusion die, mandrel (cone angle β), and sizing belt. The billet was modeled using eight-node hexahedral thermo-coupled elements (C3D8RT), with at least 20 element layers in the thickness direction. The die was designed as an analytical rigid body. ALE adaptive meshing technology was used to control unit distortion.

[0065] (2) Contact and friction

[0066] Contact pairs: outer surface of billet and inner wall of extrusion cylinder, inner surface of billet and outer surface of mandrel, front end of billet and entrance face of extrusion die. Penalty contact method is used, and the friction model is modified Coulomb friction. Friction coefficient settings: 0.3 for extrusion cylinder-billet, 0.3 for mandrel-billet.

[0067] (3) Material constitutive model

[0068] The high-temperature rheological behavior of titanium alloys was investigated using the Johnson-Cook constitutive model. Parameters were determined by testing the target titanium alloy at temperatures ranging from 500 to 750 °C and strain rates from 0.001 to 10 s⁻¹. -1 Isothermal hot compression test calibration within the specified range. Thermophysical parameters (thermal conductivity, specific heat capacity, inelastic heat fraction) are set according to standard procedures.

[0069] (4) Boundary conditions and loading

[0070] Initial billet temperature: 500~750℃; initial die temperature: 350℃. Extrusion speed: 10~25 mm / s (constant speed applied by the ejector pin); extrusion ratio: 8~25. Contact heat transfer coefficient: 5000 W / (m²). 2 ·K).

[0071] (5) Output and Post-processing

[0072] Output the nodal temperature, equivalent strain, and stress tensor components for each increment step. Select 5–10 material trajectory lines at equal intervals along the wall thickness direction, and extract the nodal coordinate history x of the elements on each trajectory line. l (t) and velocity vector v l (t), save as a .csv file.

[0073] 2.2 Deformation Boundary Condition Extraction (for VPSC)

[0074] Extrusion forming is a localized, incremental forming process where a strain gradient exists along the workpiece's thickness, and all components of the velocity gradient are non-zero. Based on continuum theory, the deformation history (stress-strain history data) of elements is extracted from the ABAQUS finite element model, and the velocity gradient L is calculated. F −1 , which serves as the input boundary condition for VPSC.

[0075] (1) Write a Fortran subroutine to extract the node coordinates X of each increment step of the target cell from the ABAQUS result file. I (t), velocity V I (t) and node number.

[0076] (2) Implement shape function interpolation in Python:

[0077]

[0078]

[0079] in For unit shape functions, .

[0080] (3) Output the sequence of the velocity gradient tensor L (6 independent components) at each integration point as a function of time.

[0081] 2.3 Viscoplastic Self-Consistent (VPSC) Texture Simulation

[0082] (1) VPSC model principle

[0083] VPSC treats each grain as an ellipsoidal viscoplastic inclusion embedded in a homogeneous effective medium (HEM), and solves for the stress-strain rate interaction between the grain and the HEM using the Eshelby method. A rate-dependent power-law flow rule is employed.

[0084]

[0085] in The reference shear rate is 0.001 s. -1 ), where m is the rate sensitivity index (taken as 0.02). To decompose shear stress, The critical shear stress (CRSS) is the stress that is quantified by the critical shear stress.

[0086] (2) Hardening model

[0087] Adopting the extended Voce hardening criterion:

[0088]

[0089] in For the initial CRSS, The initial hardening rate, For progressive hardening rate, This represents the cumulative shear strain.

[0090] (3) Sliding system

[0091] For α-titanium alloys (HCP structure), the following slip systems are activated: basal slip {0001} < 11 0> (3), cylindrical slip {10 0}<11 0> (3), cone surface Slip {10 1}<11 0> (6), cone surface<a+c> Slip {11 1}<11 3> (6). A total of 18 slip systems. The CRSS ratio of each slip system was calibrated by high-temperature compression test combined with EBSD trace method.

[0092] (4) Initial texture

[0093] The initial texture of the billet was measured by XRD (X-ray diffraction) or EBSD (electron backscatter diffraction), and discretized into 2000–5000 grain orientations (represented by quaternions) using MTEX ​​software, which served as input for VPSC.

[0094] (5) Applying boundary conditions

[0095] The velocity gradient sequence L(t) calculated in step 2.2 is used as the macroscopic velocity gradient boundary condition for VPSC, driving grain rotation and texture evolution step by step.

[0096] (6) Texture output and judgment

[0097] After the VPSC simulation is completed, the final texture at each thickness location (surface and core) is output, and the polar diagram of the {0001} basal plane and the maximum polar density P are calculated. max Judgment criteria:

[0098] If the maximum polar density difference between the surface layer (0-1.5 mm from the outer surface) and the core is ≥4, then the process parameters are qualified.

[0099] Otherwise, adjust the extrusion temperature, extrusion speed, and extrusion ratio, and repeat steps 2.1 to 2.3.

[0100] The optimal extrusion process obtained through the above simulation in this embodiment is: extrusion temperature 700℃, extrusion speed 15 mm / s, and extrusion ratio 12. Under this extrusion process, the maximum extreme density difference between the surface layer and the core is ≥5.

[0101] Step 3: Extrusion molding

[0102] According to the optimal process parameters (extrusion temperature 700℃, extrusion speed 15 mm / s, extrusion ratio 12), an extrusion experiment was conducted using the extrusion die described in step 1. The billet was preheated to 600℃ and held for 2 hours; the die was preheated to 350℃; a glass lubricant was coated onto the billet surface (the glass lubricant consisted of 90 wt.% borosilicate glass powder and 10 wt.% colloidal graphite, with a coating thickness of 0.2 mm; the softening point of the borosilicate glass powder was 550~600℃, and the viscosity at an extrusion temperature of 600~700℃ was 10). 3 ~10 4 (Pa·s, borosilicate glass powder particle size 20~50 μm, colloidal graphite particle size 1~5 μm); extrusion process: extrusion temperature 700℃, extrusion speed 15 mm / s, extrusion ratio 12. TA16 titanium alloy tube blanks with an outer diameter of 90 mm and a wall thickness of 20 mm were obtained by extrusion. Stable extrusion pressure was monitored during the extrusion process, indicating good lubrication and uniform flow.

[0103] Step 4: Stress-relief annealing

[0104] The TA16 titanium alloy tube blank obtained in step 3 was subjected to stress-relief annealing: heated to 550℃, held for 1.5 hours, and cooled in a vacuum furnace. This annealing process aims to eliminate residual stress generated by extrusion while preserving the deformed texture and preventing recrystallization.

[0105] Step 5: Texture Characterization

[0106] Samples were taken along the cross-section of the pipe from the outer wall to the inner wall, mechanically polished, and then electrolytically polished before EBSD testing. Test parameters: accelerating voltage 20 kV, scan step size 0.5 μm, test area covering from the outer surface to the center of the wall thickness. Test results are as follows. Figure 2 As shown:

[0107] Within a depth range of 0–1.5 mm near the outer surface, a strong shear texture is formed, with the crystallographic orientation forming an angle of 30°–60° with the radial direction, and the texture intensity (maximum polar density) is approximately 9.16; in the central region of the wall thickness (9–11 mm from the inner and outer surfaces), the texture intensity is approximately 3.57, the polar figure is diffusely distributed, and there is no obvious preferred orientation; similar texture characteristics are present near both the inner and outer surfaces, realizing the distribution of gradient texture along the wall thickness direction, with a maximum polar density difference ≥5.

[0108] The pipes obtained in step 4 were subjected to tensile mechanical property tests (GB / T228.1-2021 Metallic materials, tensile testing—Part 1: Tests at room temperature). The test results are shown in Table 1.

[0109] Table 1 Tensile mechanical properties of TA16 titanium alloy tubing

[0110]

[0111] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A titanium alloy extruded tube blank with gradient texture, characterized in that, The titanium alloy extruded tube blank with gradient texture has gradient texture characteristics along the wall thickness direction, specifically including: a. Surface region: Within a depth of 0 to 1.5 mm from the outer and / or inner surfaces, a strong shear texture is formed, and the crystallographic orientation of this region forms an angle of 30° to 60° with the radial direction; b. Core region: The central region of the wall thickness, with weaker texture intensity, exhibiting random distribution or weak texture characteristics; c. Transition region: The texture intensity changes in a gradient between the surface region and the core region; and the maximum extreme density difference between the surface region and the core region is ≥4.

2. The titanium alloy extruded tube blank with gradient texture according to claim 1, characterized in that, The strong shear texture is characterized by the c-axis of the α-phase grains forming an angle of 30° to 60° with the radial direction of the tube blank. In the {0001} basal plane pole figure, the maximum polar density is located in an annular region with an angle of 30° to 60° with the radial direction, and the maximum polar density is ≥7.

3. A method for preparing a titanium alloy extruded tube blank with gradient texture, characterized in that, Includes the following steps: Step 1: Determine the process parameter window through multi-scale simulation coupling 1.1 Macroscopic finite element simulation: A thermo-mechanical coupling model was established using the Abaqus / Explicit explicit dynamics module to simulate the stress-strain distribution under different combinations of extrusion process parameters. The simulated process parameters include: extrusion ratio, extrusion temperature, and extrusion speed. 1.2 Crystal Plasticity Finite Element Simulation: The stress-strain history data of each element obtained from the macroscopic finite element simulation are used as boundary conditions and imported into the finite element model based on the rate-dependent crystal plasticity theory to simulate the texture evolution process from the surface to the core at different thicknesses and obtain the pole figure. If the pole figure shows that the surface layer forms a strong shear texture and the core maintains a random texture or a weak texture, and the difference in pole density between the two is ≥4, then the condition is met and the optimized process parameters are obtained. Step 2: Based on the optimized process parameters determined in Step 1, the billet is extruded and shaped using an extrusion device to obtain an extruded tube blank with a gradient texture. Step 3: Perform stress-relief annealing on the extruded tube blank obtained in Step 2 to obtain the titanium alloy extruded tube blank with gradient texture.

4. The preparation method according to claim 3, characterized in that, In step 1, during the establishment of the thermo-coupling model, the simulated process parameters include: extrusion temperature of 500~750℃, extrusion speed of 10~25 mm / s, and extrusion ratio of 8~25.

5. The preparation method according to claim 3, characterized in that, In step 1, the optimized process parameters obtained include: extrusion temperature of 600~700℃, extrusion speed of 15~20 mm / s, and extrusion ratio of 10~16.

6. The preparation method according to claim 3, characterized in that, In step 2, the extrusion device includes an extrusion cylinder, an extrusion die, and a mandrel; The mandrel corresponding to the sizing zone is set as a conical structure, and its outer wall surface has a continuously varying taper along the extrusion direction, with a taper angle β of 10°~30°; The extrusion die is configured as a conical structure, with its diameter gradually decreasing along the extrusion direction and a cone angle α of 30°~60°.

7. The preparation method according to claim 3, characterized in that, In step 2, a layer of lubricant is applied to the surface of the billet before extruding it.

8. The preparation method according to claim 7, characterized in that, The lubricant is a glass lubricant, specifically composed of 85-95 wt.% borosilicate glass powder and 5-15 wt.% colloidal graphite; the coating thickness of the glass lubricant is 0.1-0.3 mm.

9. The preparation method according to claim 8, characterized in that, The borosilicate glass powder has a softening point of 550~600℃ and a viscosity of 10 at an extrusion temperature of 600~700℃. 3 ~10 4 Pa·s; the particle size of the borosilicate glass powder is 10~75 μm, and the particle size of the colloidal graphite is 1~10 μm.

10. The preparation method according to claim 3, characterized in that, The annealing process described in step 3 involves controlling the temperature at 500~580℃ and holding it at that temperature for 0.5~2 hours.

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