A method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance and the titanium alloy

Abstract

This invention discloses a method and titanium alloy for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance. The method includes designing a porous structure based on a three-period minimal curved surface, forming it using 3D printing to obtain a porous, fine-grained titanium alloy, and then sequentially performing electromagnetic pulse vibration powder filling and hot isostatic pressing with a cladding design to obtain a mixed-grain structure with controllable coarse and fine grain size, content, and spatial distribution. The titanium alloy is a Ti-6.5Al-2Zr-1Mo-1V aerospace alloy. This invention solves the technical bottleneck of unstable component performance caused by the randomness and inability to quantitatively control the coarse and fine grain distribution in traditional methods. The obtained alloy exhibits higher strength-plasticity matching and fatigue resistance compared to coarse-grained or fine-grained structures of the same composition, which is of great significance to promoting the development of my country's aerospace industry.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material technology, specifically relating to a method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance, and the titanium alloy itself. Background Technology

[0002] Addressing the urgent need for lightweight structures in the aerospace field, countries worldwide have made "lightweight, high-strength materials + optimized structural design" a central theme of advanced manufacturing development in this century. Titanium alloys, with their lightweight, high strength, toughness, high damage tolerance, and high corrosion resistance, have become a hot topic of research and concern for both scientific and industrial communities. With the rapid development of the aerospace industry, the requirements for the mechanical properties of titanium alloy components are constantly increasing. However, the strength of titanium alloys is still far lower than that of high-strength steel. Further improving the strength of titanium alloys to enable them to partially replace high-strength structural steel in aerospace applications could reduce the weight of aerospace-related service components by 10%. Therefore, developing high-performance titanium alloy materials is of great significance to promoting the development of my country's aerospace industry.

[0003] In recent years, fine-grained / ultra-fine-grained titanium alloys have attracted widespread attention from researchers due to their high tensile strength. However, after achieving smaller grain sizes, the high density of grain boundaries within the microstructure hinders dislocation slip, resulting in a very limited dislocation storage capacity in fine-grained / ultra-fine-grained titanium alloys. This leads to stress concentration, causing a significant reduction in plasticity while achieving high strength. Overcoming the bottleneck of achieving both high strength and plasticity in fine-grained titanium alloys remains a challenge.

[0004] Mixed-grain alloys possess both micron / submicron scale fine grains and tens of micron scale coarse grains, exhibiting a significant characteristic of high strength while maintaining high plasticity, thus attracting widespread attention from scholars both domestically and internationally. However, current research primarily focuses on preparing coarse- and fine-grained structures using powder metallurgy combined with large plastic deformation / heat treatment. While this traditional method is simple, the grain size and distribution are random and cannot be quantitatively controlled. In mixed-grain structures, the grain size and volume distribution of the fine-grained regions significantly influence their mechanical properties. Non-uniform deformation in the coarse- and fine-grained regions easily leads to stress concentration and unstable component performance. The size, volume fraction, and spatial distribution of the fine grains are difficult to control accurately, resulting in large fatigue data dispersion and poor repeatability. This poses serious, even catastrophic, risks to the service life of critical components in aerospace and other industries, becoming a major bottleneck restricting the development of mixed-grain structure components.

[0005] Therefore, how to effectively prepare precisely controllable coarse-grained titanium alloys to improve their strength, plasticity, and fatigue performance is of great significance to promoting the development of my country's aerospace industry. However, there are currently no relevant literature reports, especially on the precise and controllable coarse-grained structure control method and fatigue performance improvement of aerospace titanium alloys. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0010] A porous titanium alloy structure model with corresponding porosity is designed based on a three-period minimum surface function.

[0011] After drying, titanium alloy powder is evenly spread on the substrate, heated, and then 3D printed according to the designed porous structure model to obtain a 3D printed porous structure titanium alloy.

[0012] Porous titanium alloys are filled with powder by electromagnetic pulse vibration. After the powder is uniformly filled into the pores of the porous structure, it is encapsulated to form an encapsulation structure.

[0013] The cladding structure is formed by hot isostatic pressing, thus obtaining a titanium alloy with a coarse-grained and fine-grained microstructure.

[0014] As a preferred embodiment of the method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in this invention, the porous structure model of the titanium alloy includes one of the following: a P-surface type structure, a D-surface type structure, and a G-surface type structure based on a three-period minimum surface.

[0015] The three periodic minimum surface functions are expressed as follows:

[0016]

[0017]

[0018]

[0019] in, This represents the structure function for the P-surface type. This represents the structure function for the D-surface type. The G-surface type structure is represented by x, y, and z, which represent the coordinates in three directions within the structural space coordinate system. t is a constant. By adjusting the design parameter t, porous structural unit models with different porosities, pore sizes, and pore types can be obtained.

[0020] As a preferred embodiment of the method for precisely controlling the coarse and fine grain structure of titanium alloy to simultaneously improve fatigue performance as described in this invention, the titanium alloy powder is Ti-6.5Al-2Zr-1Mo-1V alloy powder with a medium particle size of 27-32μm and a spherical shape, and the substrate is Ti-6Al-4V alloy.

[0021] As a preferred embodiment of the method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in this invention, the Ti-6.5Al-2Zr-1Mo-1V alloy powder comprises Ti, Al, Mo, Zr, V, and O elements, wherein the atomic ratio of each element is: Al: 6.33wt%, Mo: 1.29wt%, Zr: 1.97wt%, V: 1.65wt%, O: 0.089wt%, with the balance being Ti.

[0022] As a preferred embodiment of the method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in this invention, wherein: the 3D printing process involves a laser power of 150-250W and a laser scanning speed of 800-1200mm / s.

[0023] As a preferred embodiment of the method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in this invention, the laser scanning method is a 67° Z-shaped scan with a scanning interval of 0.12 mm and a scanning layer thickness of 0.03 mm.

[0024] As a preferred embodiment of the method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in this invention, wherein: the encapsulation temperature of the encapsulation sleeve is 500-600℃, and the vacuum degree is 10. -3 Pa.

[0025] As a preferred embodiment of the method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in this invention, the hot isostatic pressing sintering temperature is 700-900℃, the pressure is 100-150MPa, and the holding time is 1-3h.

[0026] Another objective of this invention is to provide a titanium alloy that has both coarse and fine grain structure and beneficial fatigue properties.

[0027] Another objective of this invention is to provide an application of a titanium alloy with both coarse and fine grain structure and beneficial fatigue properties in the manufacture of titanium alloy components for aerospace applications.

[0028] Beneficial effects of this invention:

[0029] (1) This invention utilizes the advantages of 3D printing in the precise structural design and controllable preparation of porous materials, which can accurately and quickly generate complex shapes that are difficult to prepare by traditional manufacturing processes. It can precisely control the geometric parameters such as pore size, pore shape and pore distribution of porous alloys, and the prepared material has a uniform pore structure.

[0030] (2) This invention utilizes the high-speed solidification process of 3D printing to form a controllable fine-grained structure at the submicron level. Based on the 3D printed porous structure, the powder is filled into the pores of the porous structure by vibration filling and electromagnetic pulse compaction. Then, hot isostatic pressing is performed to obtain coarse grains with adjustable size.

[0031] (3) The present invention can effectively close defects such as micropores left in the 3D printing process by controlling the hot isostatic pressing process, and can also eliminate the strong texture formed in the 3D printing process to ensure isotropy.

[0032] (4) In the mixed crystal structure obtained by the present invention, the fine crystal region can not only be controlled by the 3D printing forming process, but also by the design of porous structure pores, pore size and pore shape structure features. The fine crystal content and distribution area can be quantitatively controlled by changing the porous structure features, so as to achieve quantitative control of the spatial distribution and quantity distribution of coarse and fine crystal regions.

[0033] (5) In the coarse-grained alloy of the present invention, during plastic deformation, plastic deformation preferentially occurs in the coarse-grained layer, while in the coarse-grained... The slip in the directional direction is initiated because the yield strength of fine grains is higher than that of coarse grains, making it difficult for strain in the coarse grains to be transmitted to the fine grains, resulting in... Dislocations accumulate at the grain boundaries between coarse and fine grains. When dislocations accumulate to a certain extent, they generate normal stress, which activates dislocation sources in fine-grained layers or in coarse-grained layers.<c+a> Other deformation mechanisms such as slip or twinning.<c+a> Slip and twinning have compared to Slipping to a higher critical shear stress<c+a> The initiation of slip systems and twins can significantly improve the strength, ductility, and fatigue properties of alloys. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0035] Figure 1 This is a schematic diagram illustrating the design concept of the porous structure of the present invention.

[0036] Figure 2 This is a schematic diagram illustrating the fabrication process of the porous structure of this invention.

[0037] Figure 3 This is a flowchart illustrating the preparation process of the coarse and fine crystal structures of this invention.

[0038] Figure 4 The image shows a SEM image and particle size distribution characteristics of the Ti-6.5Al-2Zr-1Mo-1V alloy powder of Example 1 of this invention.

[0039] Figure 5 This is a microstructure diagram of the material obtained in Example 1 of the present invention.

[0040] Figure 6 The curves show the comparison of the mechanical properties of the titanium alloys prepared in Example 1 of the present invention with those of Comparative Examples 1 and 2. Detailed Implementation

[0041] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0042] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0043] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0044] Reference Figure 1 The design process for the porous structure based on the three-period minimal surface design of this invention is as follows:

[0045] A porous titanium alloy structure with corresponding porosity is designed based on a three-period minimum surface function. The three-period minimum surface function of the corresponding structure is input into Mathmod to generate the three-dimensional mesh surface required for the unit cell of the porous structure. The point cloud file in .obj format is exported. Then, the point cloud file is imported into the ScanTo3D plugin in SolidWorks. The "Mesh Processing Wizard" and "Surface Processing Wizard" are used to convert the mesh surface into a solid surface. After generating the solid surface, it is imported into Magics for scaling, arraying, and Boolean operations to obtain the porous structure model with the required structural features.

[0046] The 3D printing equipment used in this invention is BLT-S210.

[0047] Unless otherwise specified, all raw materials used in this invention are commercially available in the field.

[0048] The fatigue performance determination in this invention refers to the national standard GB / T15248-2008, the method for axial constant amplitude low-cycle fatigue test of metallic materials, using sinusoidal loading with a loading frequency of 10 Hz.

[0049] Example 1

[0050] Reference Figures 2-5This invention provides a method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance, specifically as follows:

[0051] 1) A Primitive porous structure model with a porosity of 70±3% was designed based on a three-period minimum surface function;

[0052] 2) Take Ti-6.5Al-2Zr-1Mo-1V alloy powder with a medium particle size of 31μm, such as... Figure 3 As shown, the composition is: Al: 6.33wt%, Mo: 1.29wt%, Zr: 1.97wt%, V: 1.65wt%, O: 0.089wt%, with the balance being Ti. The above powder was placed in a vacuum drying oven and dried at a temperature of 323K for 8 hours.

[0053] 3) After the titanium alloy powder is dried, it is placed in the powder feeding cylinder of the 3D printing equipment and spread evenly on the Ti-6Al-4V substrate. The height of the substrate is adjusted so that the distance between it and the high-speed steel scraper is 0.02μm. Then the substrate is heated to 373K and argon gas is introduced to make the oxygen content in the equipment less than 100ppm.

[0054] 4) The porous structure model was 3D printed according to the design. The laser power of the 3D printing was 200W, the scanning speed was 1000mm / s, the scanning spacing was 0.12mm, the scanning layer thickness was 0.03mm, and the scanning method was a Z-shaped scanning with a 67° rotation layer by layer to obtain a 3D printed porous titanium alloy structure.

[0055] 5) The obtained 3D-printed porous titanium alloy structure was subjected to electromagnetic pulse vibration powder filling to uniformly fill the porous structure pores. Subsequently, it was encapsulated with a stainless steel sleeve to obtain the sleeve structure. The encapsulation temperature was 600℃ and the vacuum degree was 10. -3 Pa;

[0056] 6) The above-mentioned cladding structure is sintered in HIP400 hot isostatic pressing at a temperature of 800℃, a pressure of 120MPa, and a time of 2h to obtain a titanium alloy with a coarse-fine grain structure.

[0057] Figure 5 EBSD analysis was performed on the alloy obtained in this embodiment. The results showed that the coarse-grained titanium alloy had a coarse grain size of 45±5μm and a coarse grain content of 70±3%, and a fine grain size of 10±3μm and a fine grain content of 30±3%.

[0058] Comparative Example 1

[0059] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses only 3D printing to prepare a fully fine-grained structure, and the same 3D printing process as Example 1 is used for forming. Specifically:

[0060] 1) A Primitive porous structure model with a porosity of 70±3% was designed based on a three-period minimum surface function;

[0061] 2) Take Ti-6.5Al-2Zr-1Mo-1V alloy powder with a medium particle size of 31μm, such as... Figure 3 As shown, the composition is: Al: 6.33wt%, Mo: 1.29wt%, Zr: 1.97wt%, V: 1.65wt%, O: 0.089wt%, with the balance being Ti. The above powder was placed in a vacuum drying oven and dried at a temperature of 323K for 8 hours.

[0062] 3) After the titanium alloy powder is dried, it is placed in the powder feeding cylinder of the 3D printing equipment and spread evenly on the Ti-6Al-4V substrate. The height of the substrate is adjusted so that the distance between it and the high-speed steel scraper is 0.02μm. Then the substrate is heated to 373K and argon gas is introduced to make the oxygen content in the equipment less than 100ppm.

[0063] 4) The porous structure model was 3D printed according to the design. The laser power of the 3D printing was 200W, the scanning speed was 1000mm / s, the scanning spacing was 0.12mm, the scanning layer thickness was 0.03mm, and the scanning method was a Z-shaped scanning with a 67° rotation layer by layer to obtain a 3D printed porous titanium alloy structure.

[0064] The obtained titanium alloy has a fine-grained structure with a grain size of 10±3μm and a fine grain content of 100%.

[0065] Comparative Example 2

[0066] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 is a fully coarse-grained structure prepared solely by hot isostatic pressing (HIP), and the same hot isostatic pressing process as in Example 1 is used for forming, specifically:

[0067] Take Ti-6.5Al-2Zr-1Mo-1V alloy powder with a medium particle size of 31μm, such as... Figure 3 As shown, the composition is: Al: 6.33wt%, Mo: 1.29wt%, Zr: 1.97wt%, V: 1.65wt%, O: 0.089wt%, with the balance being Ti. The above powder was placed in a vacuum drying oven and dried at a temperature of 323K for 8 hours.

[0068] Alloy powder was loaded into a cladding structure, compacted by vibration, and then sintered in a HIP400 hot isostatic pressing (HIP400) at a temperature of 800℃, a pressure of 120MPa, and a time of 2 hours to obtain a titanium alloy with a coarse-fine grain structure.

[0069] Figure 5 EBSD analysis was performed on the alloy obtained in this embodiment. The results showed that the coarse-grained titanium alloy had a coarse grain size of 45±5μm and a coarse grain content of 70±3%, and a fine grain size of 10±3μm and a fine grain content of 30±3%.

[0070] The obtained structure is a coarse-grained structure with a coarse grain size of 45±5μm and a coarse grain content of 100%.

[0071] Figure 6 The fatigue performance of the samples obtained in Example 1, Comparative Example 1, and Comparative Example 2 was analyzed. The results showed that the fatigue strength and fatigue life of the coarse-grained and fine-grained titanium alloys obtained in Example 1 were significantly better than those of coarse-grained and fine-grained titanium alloys of the same composition.

[0072] Compared to Example 1, the alloy in Comparative Example 1 has a microstructure entirely composed of fine grains. While its fatigue strength is comparable to that of Example 1, its fatigue life is reduced. This is because after obtaining smaller grain sizes, the titanium alloy exhibits a higher density of grain boundaries within the microstructure, hindering dislocation slip. Consequently, the fine-grained / ultra-fine-grained titanium alloy has a very limited capacity for dislocation storage, making it prone to stress concentration. While achieving high strength, this leads to a significant reduction in plasticity and a lack of coordinated deformation characteristic of coarse grains, thus resulting in a decreased fatigue life for the fine-grained titanium alloy.

[0073] Compared to Example 1, the microstructure of the alloy in Comparative Example 2 is entirely coarse-grained, resulting in reduced fatigue strength, while the fatigue life is comparable to that of Example 1. This is because the grain boundaries of the coarse-grained titanium alloy reduce the resistance to dislocation movement during plastic deformation, leading to a decrease in the alloy's resistance to plastic deformation. Consequently, the alloy yields under lower stress, resulting in reduced fatigue strength of the coarse-grained titanium alloy.

[0074] Example 2

[0075] The difference between this embodiment and Embodiment 1 is that the porosity of the designed porous structure is different. The porosity of the designed Primitive porous structure is adjusted to 60±3%, while the other process parameters are the same as those in Embodiment 1.

[0076] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 10±3 μm, accounting for 40±3% of the total content, while the coarse grain size was 45±5 μm, accounting for 60±3% of the total content.

[0077] Compared to Example 1, the porosity of the porous structure is reduced by 10%, resulting in a 10% increase in fine grain content. The grain size of coarse and fine grains does not change significantly. The increased fine grain content leads to improved fatigue strength of the coarse and fine grain structure alloy under this characteristic, and the fatigue life of the alloy is comparable to that of Example 1.

[0078] Example 3

[0079] The difference between this embodiment and Embodiment 1 is that the porosity of the designed porous structure is different. The porosity of the designed Primitive porous structure is adjusted to 50±3%, while the other process parameters are the same as those in Embodiment 1.

[0080] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 10±3 μm, accounting for 50±3% of the total content, while the coarse grain size was 45±5 μm, accounting for 50±3% of the total content.

[0081] Compared to Example 1, the porosity of the porous structure is reduced by 20%, resulting in a 20% increase in fine grain content. The grain size of coarse and fine grains does not change significantly. The increased fine grain content leads to an improvement in the fatigue strength of the coarse and fine grain structure alloy under this characteristic compared to Example 1 and Example 2, while the alloy fatigue life is comparable to that of Example 1.

[0082] Example 4

[0083] The difference between this embodiment and Embodiment 1 is that the porosity of the designed porous structure is different. The porosity of the designed Primitive porous structure is adjusted to 40±3%, while the other process parameters are the same as those in Embodiment 1.

[0084] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 10±3 μm, accounting for 60±3% of the total content, while the coarse grain size was 45±5 μm, accounting for 40±3% of the total content.

[0085] Compared to Example 1, the porosity of the porous structure is reduced by 30%, resulting in a 30% increase in fine grain content. The grain size of coarse and fine grains does not change significantly. The increased fine grain content leads to an improvement in the fatigue strength of the coarse and fine grain structure alloy under this characteristic compared to Examples 1, 2, and 3, while the alloy fatigue life is comparable to that of Example 1.

[0086] Example 5

[0087] The difference between this embodiment and Embodiment 1 is that the porosity of the designed porous structure is different. The porosity of the designed Primitive porous structure is adjusted to 30±3%, while the other process parameters are the same as those in Embodiment 1.

[0088] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 10±3 μm, accounting for 70±3%, and the coarse grain size was 45±5 μm, accounting for 30±3%.

[0089] Compared to Example 1, the porosity of the porous structure is reduced by 40%, resulting in a 40% increase in fine grain content. The grain size of coarse and fine grains does not change significantly. The increased fine grain content leads to an improvement in the fatigue strength of the coarse and fine grain structure alloy under this characteristic compared to Examples 1, 2, 3, and 4, while the alloy fatigue life is comparable to that of Example 1.

[0090] As can be seen from Examples 1 to 5, the present invention utilizes the advantages of 3D printing in the precise structural design and controllable preparation of porous materials, and can accurately and quickly generate complex shapes that are difficult to prepare by traditional manufacturing processes. It can precisely control the geometric parameters such as pore size, pore shape and pore distribution of porous alloys, and can quantitatively control the content and distribution area of ​​fine grains by changing the porous structure characteristics, thereby achieving quantitative regulation of the spatial and quantitative distribution of coarse and fine grain regions.

[0091] Example 6

[0092] The difference between this embodiment and Embodiment 1 is that the 3D printing process is different. The laser power for 3D printing is adjusted to 250W, while the other process parameters are the same as in Embodiment 1.

[0093] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 15±3 μm with a content of 30±3%; the coarse grain size was 45±5 μm with a content of 70±3%.

[0094] Compared to Example 1, the increased laser power in 3D printing leads to higher energy density and larger fine-grained structure size, while the porosity of the porous structure remains unchanged and the coarse-fine grain content does not change significantly. The increased fine-grained size results in a 4-5% decrease in fatigue strength of the alloy under this characteristic compared to Example 1 (parallel experiments), while the fatigue life of the alloy is comparable to that of Example 1.

[0095] Example 7

[0096] The difference between this embodiment and Embodiment 1 is that the 3D printing process is different. The scanning speed of the 3D printing is adjusted to 800mm / s, while the other process parameters are the same as those in Embodiment 1.

[0097] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 16±3 μm and the fine grain content was 30±3%; the coarse grain size was 47±5 μm and the coarse grain content was 70±3%.

[0098] EBSD analysis of the alloy prepared under these conditions showed that, compared with Example 1, the reduced scanning speed of 3D printing led to an increase in 3D printing energy density and an increase in the size of the fine-grained structure. However, the porosity of the porous structure did not change, and the content of coarse and fine grains did not change significantly. The increased size of the fine grains resulted in a 5-6% decrease in the fatigue strength of the alloy under these conditions compared with Example 1, while the fatigue life of the alloy was comparable to that of Example 1.

[0099] Furthermore, as the energy density of 3D printing decreases, the resulting grain size decreases, and the density of grain boundaries within the microstructure increases, hindering dislocation slip. This results in a very limited capacity for dislocation storage in fine-grained / ultra-fine-grained titanium alloys, making them prone to stress concentration. While achieving high strength, this leads to a significant reduction in plasticity and a lack of coordinated deformation with coarse grains, thus reducing the fatigue life of fine-grained titanium alloys. Therefore, when selecting parameters for 3D printing, it is necessary to choose appropriate printing conditions.

[0100] Example 8

[0101] The difference between this embodiment and Embodiment 1 is that the hot isostatic pressing process is different. The hot isostatic pressing temperature is adjusted to 900℃, the hot isostatic pressing pressure is 120MPa, and the holding time is 2h.

[0102] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 18±3 μm and the fine grain content was 30±3%; the coarse grain size was 50±5 μm and the coarse grain content was 70±3%.

[0103] Compared to Example 1, the hot isostatic pressing (HIP) temperature is increased, which leads to grain growth during the HIP process. The grown grains include fine grains formed during 3D printing and coarse grains formed during HIP. The content of coarse and fine grains does not change significantly. The increase in size leads to a 5-6% decrease in the fatigue strength of the alloy under this characteristic. The fatigue life of the alloy is comparable to that of Example 1.

[0104] Example 9

[0105] The difference between this embodiment and Embodiment 1 is that the hot isostatic pressing process is different. The hot isostatic pressing temperature is adjusted to 800℃, the hot isostatic pressing pressure is 120MPa, and the holding time is 3h.

[0106] EBSD analysis of the alloy prepared under these conditions showed that the fine grain size was 20±3 μm and the fine grain content was 30±3%; the coarse grain size was 53±5 μm and the coarse grain content was 70±3%.

[0107] Compared to Example 1, the extended hot isostatic pressing (HIP) holding time leads to grain growth during HIP. The grown grains include fine grains formed during 3D printing and coarse grains formed during HIP. The content of fine and coarse grains does not change significantly. The increased size results in a 6-7% decrease in the fatigue strength of the alloy under this characteristic compared to Example 1, while the fatigue life of the alloy is comparable to that of Example 1.

[0108] Furthermore, when the hot isostatic pressing temperature decreases or the holding time is shortened, the coarse grain sintering during the hot isostatic pressing process becomes incomplete, resulting in a smaller grain size and a higher density of grain boundaries within the microstructure. This hinders dislocation slip, leading to a very limited capacity for dislocation storage in fine-grained / ultra-fine-grained titanium alloys. Stress concentration is prone to occur, and while achieving high strength, this results in a significant reduction in plasticity. The lack of coordinated deformation from coarse grains leads to a decrease in the fatigue life of fine-grained titanium alloys.

[0109] In summary, this invention discloses a method for controlling the coarse-grained structure and improving the fatigue performance of aerospace titanium alloys. The method includes designing a porous structure based on a three-period minimal surface, forming it using 3D printing to obtain a porous, fine-grained titanium alloy, and then sequentially performing electromagnetic pulse vibration powder filling and hot isostatic pressing with a cladding design to obtain a mixed-grained structure with controllable coarse-grained size, content, and spatial distribution. The titanium alloy is a Ti-6.5Al-2Zr-1Mo-1V aerospace alloy. This invention solves the technical bottleneck of unstable component performance caused by the randomness and inability to quantitatively control the coarse-grained distribution in traditional methods. The obtained alloy exhibits higher strength-plasticity matching and fatigue resistance compared to coarse-grained or fine-grained structures of the same composition, which is of great significance to promoting the development of my country's aerospace industry.

[0110] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance, characterized in that: include, A porous titanium alloy structure model with corresponding porosity is designed based on a three-period minimum surface function. After drying, titanium alloy powder is evenly spread on the substrate, heated, and then 3D printed according to the designed porous structure model to obtain a 3D printed porous structure titanium alloy. The 3D printing process involves a laser power of 150–250W, a laser scanning speed of 800–1200 mm / s, a 67° Z-shaped scanning method, a scanning spacing of 0.12 mm, and a scanning layer thickness of 0.03 mm. Porous titanium alloys are filled with powder by electromagnetic pulse vibration. After the powder is uniformly filled into the pores of the porous structure, it is encapsulated to form an encapsulation structure. The cladding structure is formed by hot isostatic pressing sintering, thus obtaining a titanium alloy with a coarse and fine grain structure; The hot isostatic pressing sintering temperature is 700–900℃, the pressure is 100–150MPa, and the holding time is 1–3h.

2. The method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in claim 1, characterized in that: The porous structure model of the titanium alloy includes one of the following: P-surface type structure, D-surface type structure, and G-surface type structure based on a three-period minimum surface.

3. The method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in claim 1, characterized in that: The titanium alloy powder is Ti-6.5Al-2Zr-1Mo-1V alloy powder with a medium particle size of 27-32μm and a spherical shape. The substrate is Ti-6Al-4V alloy.

4. The method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in claim 3, characterized in that: The Ti-6.5Al-2Zr-1Mo-1V alloy powder comprises Ti, Al, Mo, Zr, V, and O elements, wherein the atomic ratio of each element is: Al: 6.33wt%, Mo: 1.29wt%, Zr: 1.97wt%, V: 1.65wt%, O: 0.089wt%, with the balance being Ti.

5. The method for precisely controlling the coarse and fine grain structure of titanium alloys to simultaneously improve fatigue performance as described in claim 1, characterized in that: The encapsulation temperature of the casing is 500–600°C, and the vacuum degree is 10. -3 Pa.

6. The titanium alloy prepared by the method described in any one of claims 1 to 5 for simultaneously improving fatigue performance by precisely controlling the coarse and fine grain structure of the titanium alloy.

7. The application of the titanium alloy as described in claim 6 in the manufacture of titanium alloy components for aerospace applications.

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