Laser powder bed molten high-strength and high-plasticity TA15 titanium alloy and preparation method and application thereof

Abstract

The invention provides a laser powder bed molten high-strength and high-plasticity TA15 titanium alloy and a preparation method and application thereof. TA15 titanium alloy powder is molten through a laser powder bed to prepare the titanium alloy, the organization structure of the TA15 titanium alloy comprises primary beta grains and a martensite multi-scale heterostructure, the average length-diameter ratio of the primary beta grains is smaller than or equal to 3.8, the martensite multi-scale heterostructure comprises large martensite grains and small martensite grains, and the average length-diameter ratio of the large martensite grains is smaller than or equal to 3.8. The large martensite grains are martensite grains with the grain size larger than or equal to 2.5 micrometers, the small martensite grains are martensite grains with the grain size smaller than 2.5 micrometers, the average length-diameter ratio of the large martensite grains is smaller than or equal to 5.8, and the average length-diameter ratio of the small martensite grains is larger than or equal to 3.5. The titanium alloy shows high-strength and high-plasticity performance and excellent work hardening capacity under the condition that heat treatment is not needed, the application requirements for forming and high mechanical performance of titanium alloy of a complex shape structure can be met, and particularly the application requirements for aerospace, weapon armor, ocean and the like are met.

Description

Technical Field

[0001] This invention belongs to the field of laser powder bed melting technology, specifically relating to a laser powder bed melting method for high-strength and high-plasticity TA15 titanium alloy and its application. Background Technology

[0002] Titanium alloys have wide applications in aerospace, medical, and marine fields. Traditional machining methods struggle to manufacture components with a wide variety of complex shapes. Laser powder bed melting, as a core additive manufacturing technology, overcomes the limitations of traditional machining, enabling the production of products in almost any shape. However, the extremely high cooling rate (10⁻⁶ m / s) during laser powder bed melting presents significant challenges. 5 ~10 7 The microstructure of near-α type (e.g., TA15) and α+β type titanium alloys (e.g., TC4) formed by high temperatures (℃ / s) typically consists of coarse columnar primary β grains and acicular martensitic α′ structures. Their mechanical properties are generally characterized by high tensile strength (>1200 MPa), but low plasticity, with elongation typically below 10%. Most titanium alloys in the current technology have an elongation of 6-8%. Low plasticity can lead to cracking during the forming process of aerospace and weapon armor components, especially large-sized meter-scale components, as well as a rapid decrease in strength after heat treatment. Low work hardening capacity results in poor energy absorption during service, all of which limit the practical application of titanium alloys in aerospace, weapon armor, and other service environments. Furthermore, lightweight structures (e.g., lightweight cellular structures) are crucial for weight reduction and performance improvement in aerospace and other fields. Under a given design load, high strength and high plasticity mean increased design freedom and the ability to minimize design weight while maintaining load-bearing capacity to meet design requirements. Therefore, manufacturing high-strength, high-plasticity titanium alloys is essential for their application in aerospace, weapon armor, and other fields.

[0003] In its untreated state, titanium alloys exhibit a microstructure consisting of columnar primary β grains and lamellar martensite of varying sizes. While heat treatment can decompose the non-equilibrium martensite structure into equilibrium α+β, significantly improving plasticity, it also leads to a marked decrease in strength. Although compositional modification of titanium alloys can improve their plasticity, it may result in a significant reduction in strength. For example, introducing pure Mo powder into TC4 powder can significantly improve the plasticity of the titanium alloy obtained by laser powder bed melting, from 7.3% to 20.1%, but the strength decreases significantly, from 1267 MPa to 919 MPa. Maintaining tensile strength >1300 MPa while achieving an elongation of 10% is a technical challenge in this field. Even after achieving 10% plasticity, further improving plasticity by 1% without significantly reducing strength presents technical difficulties.

[0004] High strength or high ductility alone cannot meet application requirements. Current technologies for modifying materials to achieve high strength may sacrifice high ductility, while pursuing high ductility may result in a loss of strength. It is difficult to achieve excellent comprehensive performance in both areas simultaneously. High-end applications such as aerospace, weaponry, automotive, medical, consumer electronics, and marine engineering demand both high performance and high ductility. Furthermore, high strength and high ductility are crucial for the lightweight structural design (e.g., lightweight cellular structures) and weight reduction of laser powder bed fusion components, allowing for greater design possibilities and weight reduction while meeting design load requirements. Therefore, there is an urgent need to develop titanium alloys that simultaneously possess high strength and high ductility, and to research efficient preparation methods that retain high strength in the printed state while improving ductility. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a laser powder bed melting high-strength and high-plasticity TA15 titanium alloy, its preparation method, and its application. By controlling the primary β grains and the multi-scale heterogeneous structure of martensite, a printed high-strength and high-plasticity TA15 titanium alloy is prepared, which meets the requirements of high-strength and high-plasticity mechanical properties and lightweight structure reduction of titanium alloys with complex shapes without heat treatment.

[0006] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows: On one hand, this invention provides a high-strength, high-plasticity TA15 titanium alloy obtained by laser powder bed melting. This TA15 titanium alloy exhibits a heterogeneous reinforcement effect. The microstructure of the TA15 titanium alloy includes primary β grains and a multi-scale heterogeneous martensitic structure. The primary β grains have an average aspect ratio ≤3.8, for example, aspect ratios of 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, or smaller. The aspect ratio is defined as the ratio of the longer side to the shorter side; therefore, an aspect ratio ≥1. Due to the small aspect ratio, primary β grains with an average aspect ratio ≤3.8 are considered equiaxed or near-equiaxed structures. These equiaxed or near-equiaxed primary β grains differ from the coarse columnar primary β grains found in existing titanium alloys. The multi-scale heterogeneous martensitic structure includes large martensitic grains and small martensitic grains. The large martensitic grains have a grain size ≥2.5 mm. The martensite grains are defined as having a grain size of <2.5 μm, where the grain size is the equivalent diameter of a circle. The large-sized martensite grains have an average aspect ratio ≤5.8, for example, an aspect ratio of 5.8, 5.7, 5.6, 5.5, 5.4, 5.3, 5.2, 5.1, 5.0 or smaller. The small-sized martensite grains have an average aspect ratio ≥3.5, for example, an aspect ratio of 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1 or larger.

[0007] Conventional titanium alloys consist of columnar primary β grains and lamellar martensite of varying sizes. Existing technologies struggle to simultaneously achieve high strength and high plasticity. This paper addresses this by controlling the coarse columnar primary β grains to be equiaxed or near-equiaxed, while simultaneously regulating the martensite to a multi-scale heterogeneous martensite structure with varying aspect ratios. This allows TA15 titanium alloy to possess comprehensive mechanical properties of high strength and high plasticity. Excessively large aspect ratios (>3.8) in the primary β grains tend to develop into columnar structures, hindering strength and plasticity. Controlling the average aspect ratio of large martensite to ≤5.8 promotes equiaxed development, while controlling the average aspect ratio of small martensite to ≥3.5 encourages lamellar development. Through size control, a multi-scale heterogeneous structure of martensite with varying sizes can be achieved. Compared to conventional structures, this heterogeneous structure can induce heterogeneous deformation strengthening, enhancing the strength-plasticity synergy and thus achieving both high strength and high plasticity.

[0008] Without heat treatment, the TA15 titanium alloy exhibits a tensile strength ≥1300 MPa, a yield strength ≥1100 MPa, an elongation ≥12%, and a work hardening capacity ≥200 MPa. Work hardening capacity, also known as strain hardening capacity, refers to the intrinsic property of a metallic material where its strength and hardness significantly increase with the amount of deformation during plastic deformation. Work hardening capacity is measured by subtracting the yield strength from the tensile strength.

[0009] More preferably, the TA15 titanium alloy has a tensile strength ≥1330 MPa, a yield strength ≥1120 MPa, an elongation ≥12.5%, and a work hardening capacity ≥210 MPa. Existing laser powder bed fused printing titanium alloy TA15 exhibits a tensile strength as high as 1300 MPa, but typically has an elongation of less than 10%. Heat treatment can improve plasticity, but the strength will decrease. This invention can retain the high strength of the printed state while improving plasticity without heat treatment, thus optimizing performance without heat treatment.

[0010] The titanium alloy material is widely applicable to various fields with high requirements for material mechanical properties and design and manufacturing flexibility, including but not limited to aerospace, medical, automotive, consumer electronics, marine engineering, and weaponry. For example, preferably in the aerospace field, the titanium alloy can be used to manufacture components such as intermediate casings, nozzles, and blades for aircraft engines; in the medical field, it is suitable for load-bearing implants such as hip joints; in the automotive field, it can be used for high-strength lightweight connecting rods and valve components; in the weaponry field, it is suitable for bulletproof liners; in the consumer electronics field, it is suitable for the mid-frame, hinges, and internal support structures of smartphones and laptops; and in the marine engineering field, it can be used for pressure-resistant shells for deep-sea probes.

[0011] It should be noted that the above application scenarios are merely illustrative examples and are not intended to limit the scope of application of this invention. Based on the high strength and high plasticity of the titanium alloy of this invention, it is also suitable for other fields requiring additive manufacturing of titanium alloys, especially those with high strength and high plasticity requirements.

[0012] On the other hand, the present invention also provides a method for preparing high-strength and high-plasticity TA15 titanium alloy by laser powder bed melting. This method is a preparation method for TA15 titanium alloy with heterogeneous reinforcement effect. The preparation steps include: generating a forming file from a three-dimensional model using model processing software and process software; importing the forming file into a laser powder bed melting device; placing TA15 powder raw material into the laser powder bed melting device; and forming the TA15 titanium alloy layer by layer according to the slicing path and process parameters of the three-dimensional model. The scanning line energy density is 125~170 J / m, and the scanning volume energy density is 35~48 J / mm². 3 The laser process parameters include a laser power of 160~280 W, a scanning speed of 1000~1400 mm / s, a scanning spacing of 90~120 μm, and a powder layer thickness of 20~50 μm. The scanning line energy density is calculated as laser power / scanning speed, and the scanning volume energy density is calculated as laser power / (scanning speed × scanning spacing × layer thickness). The scanning line energy density can be adjusted by the laser power and scanning speed, and the scanning volume energy density can be adjusted by the laser power, scanning speed, scanning spacing, and powder layer thickness.

[0013] Laser powder bed melting technology for preparing titanium alloys involves the interaction between laser and powder, encompassing complex melting and solidification processes. These processes are characterized by rapid cooling and cyclic heating, making microstructure control challenging. Current techniques typically focus on the volumetric energy density, neglecting the scanline energy density, and particularly lack research on the effect of matching these two factors on microstructure and properties. Furthermore, the conventional range of volumetric energy density in existing technologies is 60–100 J / mm². 3 This invention creatively employs the synergistic control of scanning volume energy density and scanning line energy density, and unlike the conventional scanning volume energy density range, this invention selects a scanning volume energy density of 35~48 J / mm². 3 By controlling the laser power, scanning speed, scanning spacing, powder layer thickness, and the specific selection of scanning line energy density and scanning volume energy density, heat accumulation and cooling rate can be affected, thereby obtaining specific heterogeneous reinforced tissues.

[0014] Furthermore, a strip printing strategy is adopted, with a strip width of 4~10 mm and a strip overlap spacing of -0.06~0.01 mm (negative numbers indicate overlapping overlap lines, and positive numbers indicate gaps in the overlap lines). The laser scanning method adopts a "Zig-Zag" zigzag scanning pattern.

[0015] Furthermore, the titanium alloy powder has a particle size range of 15~53 μm, wherein the titanium alloy powder D10 has a particle size of 15~25 μm, D50 has a particle size of 30~40 μm, and D90 has a particle size of 40~60 μm.

[0016] Furthermore, the laser powder bed melting is carried out under argon protection, and the oxygen content in the forming chamber is controlled below 1000 ppm.

[0017] Compared with the prior art, the beneficial effects of this invention are: 1. Preparation of titanium alloys with specific microstructures. For laser powder bed melting TA15 titanium alloys, unlike simply controlling the primary β grains or martensite structure, this invention simultaneously controls both primary β grains and martensite structures, achieving a unique microstructure of "equiaxed or near-equiaxed primary β grains + multi-scale heterogeneous martensite with a specific aspect ratio combination." This is significantly different from conventional titanium alloy microstructures. By controlling the average aspect ratio of the primary β grains to ≤3.8, an equiaxed or near-equiaxed structure is formed. Compared to conventional coarse columnar primary β grains, this is more conducive to the development of strength and plasticity. While controlling the primary β grains, a multi-scale heterogeneous martensite structure with a specific aspect ratio combination is obtained. Utilizing the heterogeneous deformation-induced strengthening effect generated by the heterogeneous structure, the strength is significantly improved, and the heterogeneous deformation-induced strengthening effect synergistically increases the elongation of the material, achieving synergistic optimization of strength and plasticity. This results in high strength and high plasticity while maintaining excellent work hardening ability.

[0018] 2. Overcoming the challenge of the strength-plasticity inversion, achieving "dual high" performance without heat treatment while maintaining excellent work hardening ability. In existing technologies, while TA15 titanium alloy prepared by laser powder bed melting possesses a tensile strength as high as 1300 MPa, its elongation is typically below 10%, resulting in poor plasticity. Subsequent heat treatment can improve plasticity, but inevitably leads to a decrease in strength. This invention, through innovative microstructure control, prepares a titanium alloy with a specific microstructure. This structure, without any heat treatment, simultaneously retains the high strength of the printed state and significantly improves plasticity. In some embodiments of this invention, the elongation of the printed titanium alloy TA15 is increased from the typical 6-8% level to 12% and above, while maintaining high tensile strength (≥1300 MPa), high yield strength (≥1100 MPa), and excellent work hardening ability (≥200 MPa). In the preferred embodiment, excellent comprehensive properties of 1354 MPa tensile strength, 1139 MPa yield strength, 13.0% elongation, and 215 MPa work hardening capacity are achieved, successfully overcoming the technical challenge of simultaneously achieving strength, plasticity, and work hardening capacity in existing technologies. This performance level can meet the "dual high" requirements of high strength and high plasticity for materials in high-end fields, and can help additive manufacturing titanium alloys be better applied in aerospace, weapon armor, and other fields, such as the preparation of intermediate casings for aero engines, aero engine nozzles, and aero engine blades.

[0019] 3. Solving component forming challenges, simplifying the process, and improving component forming reliability: The titanium alloy of this invention possesses high plasticity in the printed state, significantly reducing the risk of cracking due to residual stress in complex-shaped components during additive manufacturing. This greatly improves the forming reliability and success rate of large, complex meter-scale structural components such as intermediate casings and nozzles for aero-engines. Due to its excellent printed performance, heat treatment steps can be omitted in some applications, which not only significantly shortens the production cycle but also significantly reduces energy consumption and equipment investment costs, resulting in significant economic benefits.

[0020] 4. An additive manufacturing process with specific matching process parameters: This invention specifically develops an additive manufacturing process method that matches the target microstructure. Unlike existing technologies that typically focus only on a single energy density, such as the volumetric energy density, this invention innovatively and precisely controls both the scan line energy density and the volumetric energy density simultaneously, ensuring that they are within a specific matching range. Furthermore, the conventional range for volumetric energy density in existing technologies is 60~100 J / mm². 3 The present invention uses a scanning volume energy density of 35~48 J / mm². 3By controlling the laser power, scanning speed, scanning spacing, powder layer thickness, and specifically selecting the scanning line energy density and scanning volume energy density, heat accumulation and cooling rate are influenced, thereby obtaining a specific microstructure. The process parameter adjustments of this invention are not conventional adjustments in the art, but rather specific process parameter selections to obtain a specific structure. Through a unique process window of synergistic control of line energy density and volume energy density, the aforementioned novel heterogeneous microstructure was successfully formed, thereby achieving a breakthrough improvement in material properties. The selection of process parameters has unexpected technical effects. Given that the microstructure and properties of the product prepared by this invention are significantly different from those of the prior art, priority is given to protecting the titanium alloy product with this specific microstructure. Furthermore, protection is further claimed for the additive manufacturing method for achieving this specific microstructure. Attached Figure Description

[0021] Figure 1a IPF image of large-size martensite extraction using EBSD for printed TA15 titanium alloy prepared in Example 1; Figure 1b The EBSD large-size martensitic grain aspect ratio of the printed TA15 titanium alloy prepared in Example 1; Figure 2a IPF image of small-sized martensite extracted using EBSD on printed TA15 titanium alloy prepared in Example 1; Figure 2b The small-size martensitic aspect ratio of the printed TA15 titanium alloy EBSD prepared in Example 1; Figure 3a Low-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared in Example 1; Figure 3b Here is a high-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared in Example 1; Figure 4a IPF image of EBSD large-size martensite extracted from printed TA15 titanium alloy prepared for Comparative Example 1; Figure 4b The aspect ratio of large-sized martensitic grains in EBSD printed TA15 titanium alloy was prepared as a comparative example 1. Figure 5a IPF image of small-sized martensite extracted using EBSD method for printed TA15 titanium alloy prepared as Comparative Example 1; Figure 5b The small-size martensitic aspect ratio of the printed TA15 titanium alloy EBSD prepared for Comparative Example 1; Figure 6a Low-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared for Comparative Example 1. Figure 6bHigh-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared for Comparative Example 1. Figure 7 This is a comparative schematic diagram of the microstructure of the printed TA15 titanium alloy prepared in Example 1 and Comparative Example 1; Figure 8 This is a comparison chart showing the performance of the printed TA15 titanium alloy of Example 1 and Comparative Example 1, and related titanium alloys in the prior art. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0023] Example 1 A 3D model of the titanium alloy was drawn using 3D drawing software. The 3D model was then used to generate a formable file in model processing software and process software. The file was imported into a laser powder bed melting equipment. TA15 titanium alloy powder raw material was placed into the laser powder bed melting equipment. The laser powder bed melting equipment formed the TA15 titanium alloy layer by layer according to the slicing path and process parameters of the 3D model.

[0024] The forming process parameters were set as follows: laser power 200 W, scanning speed 1200 mm / s, scanning spacing 120 μm, and powder layer thickness 30 μm. The oxygen content in the forming chamber was maintained below 1000 ppm. A strip strategy was adopted, with a strip width of 5 mm and a strip overlap spacing of 0.01 mm. The scanning line energy density was 166.7 J / m, and the scanning volume energy density was 46.3 J / mm². 3 The scanning method is "Zig-Zag" zigzag scanning with 67° interlayer rotation. After the laser powder bed is melted, TA15 titanium alloy is obtained.

[0025] Example 2 A 3D model of the titanium alloy was drawn using 3D drawing software. The 3D model was then used to generate a formable file in model processing software and process software. The file was imported into a laser powder bed melting equipment. TA15 titanium alloy powder raw material was placed into the laser powder bed melting equipment. The laser powder bed melting equipment formed the TA15 titanium alloy layer by layer according to the slicing path and process parameters of the 3D model.

[0026] The forming process parameters were set as follows: laser power 180 W, scanning speed 1400 mm / s, scanning spacing 90 μm, and powder layer thickness 30 μm. The oxygen content in the forming chamber was maintained below 1000 ppm. A strip strategy was adopted, with a strip width of 5 mm and a strip overlap spacing of 0.01 mm. The scanning line energy density was 128.6 J / m, and the scanning volume energy density was 47.6 J / mm². 3 The scanning method is "Zig-Zag" zigzag scanning with 67° interlayer rotation. After the laser powder bed is melted, TA15 titanium alloy is obtained.

[0027] Example 3 A 3D model of the titanium alloy was drawn using 3D drawing software. The 3D model was then used to generate a formable file in model processing software and process software. The file was imported into a laser powder bed melting equipment. TA15 titanium alloy powder raw material was placed into the laser powder bed melting equipment. The laser powder bed melting equipment formed the TA15 titanium alloy layer by layer according to the slicing path and process parameters of the 3D model.

[0028] The forming process parameters were set as follows: laser power 180 W, scanning speed 1300 mm / s, scanning spacing 120 μm, and powder layer thickness 30 μm. The oxygen content in the forming chamber was maintained below 1000 ppm. A strip strategy was adopted, with a strip width of 5 mm and a strip overlap spacing of 0.01 mm. The scanning line energy density was 138.5 J / m, and the scanning volume energy density was 38.5 J / mm². 3 The scanning method is "Zig-Zag" zigzag scanning with 67° interlayer rotation. After the laser powder bed is melted, TA15 titanium alloy is obtained.

[0029] Example 4 A 3D model of the titanium alloy was drawn using 3D drawing software. The 3D model was then used to generate a formable file in model processing software and process software. The file was imported into a laser powder bed melting equipment. TA15 titanium alloy powder raw material was placed into the laser powder bed melting equipment. The laser powder bed melting equipment formed the TA15 titanium alloy layer by layer according to the slicing path and process parameters of the 3D model.

[0030] The forming process parameters were set as follows: laser power 200 W, scanning speed 1300 mm / s, scanning spacing 120 μm, and powder layer thickness 30 μm. The oxygen content in the forming chamber was maintained below 1000 ppm. A strip strategy was adopted, with a strip width of 5 mm and a strip overlap spacing of 0.01 mm. The scanning line energy density was 153.8 J / m, and the scanning volume energy density was 42.7 J / mm². 3 The scanning method is "Zig-Zag" zigzag scanning with 67° interlayer rotation. After the laser powder bed is melted, TA15 titanium alloy is obtained.

[0031] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is the laser process parameters; all other conditions remain unchanged. Specifically, the laser power is 200 W, the scanning speed is 1500 mm / s, the scanning spacing is 65 μm, and the powder layer thickness is 30 μm. The scanning line energy density is 133.3 J / m, and the scanning volume energy density is 68.4 J / mm². 3 Compared to Example 1, while keeping the laser power and powder layer thickness constant, the scanning line energy density and scanning volume energy density were adjusted by changing the scanning speed and scanning spacing.

[0032] Test methods, technical effects, and analysis of Examples 1 to 4 and Comparative Example 1: Test methods: After preparing TA15 titanium alloys in Examples 1 to 4 and Comparative Example 1, the printed titanium alloys were subjected to microstructure and mechanical property tests. The microstructure test was performed using EBSD analysis. Large and small martensite grains were extracted using EBSD analysis software according to a grain size threshold of 2.5 μm. The extracted EBSD images of large and small martensite were analyzed using software to display the aspect ratio distribution and automatically calculate the average aspect ratio. The grain size was the equivalent diameter of a circle.

[0033] Technical Effects: In Examples 1 to 4, the printed TA15 titanium alloys all meet the following requirements: primary β grain aspect ratio ≤ 3.8, average aspect ratio in large-size martensite ≤ 5.8, and average aspect ratio in small-size martensite ≥ 3.5. Tensile strength ≥ 1300 MPa, yield strength ≥ 1100 MPa, work hardening capacity ≥ 200 MPa, and elongation ≥ 12%. Work hardening capacity is measured by subtracting yield strength from tensile strength. Figure 1a The image shows the EBSD large-size martensite extraction IPF image of the printed TA15 titanium alloy prepared in Example 1. Figure 1b The EBSD large-size martensitic grain aspect ratio of the printed TA15 titanium alloy prepared in Example 1. Figure 2a The image shows the EBSD small-size martensite extraction IPF image of the printed TA15 titanium alloy prepared in Example 1. Figure 2b The small-size martensitic aspect ratio of the TA15 titanium alloy EBSD prepared in Example 1. Figure 3a This is a low-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared in Example 1. Figure 3bThis is a high-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared in Example 1. Microstructure and mechanical property tests show that, in the preferred Example 1, the primary β grains of the printed titanium alloy have an aspect ratio of 3.58, the large-size martensite has an average aspect ratio of 5.64, and the small-size martensite has an average aspect ratio of 3.71. The SEM morphology of the tensile fracture surface shows obvious dimples, a tensile strength of 1354 MPa, a yield strength of 1139 MPa, a work hardening capacity of 215 MPa, and an elongation of 13.0%.

[0034] Figure 4a The IPF image of the large-size martensite extraction on EBSD of the printed TA15 titanium alloy prepared for Comparative Example 1 is shown. Figure 4b The aspect ratio of large-sized martensitic grains in EBSD printed TA15 titanium alloy was prepared as a comparative example 1. Figure 5a The EBSD small-sized martensite extraction IPF image of the printed TA15 titanium alloy prepared in Comparative Example 1 is shown. Figure 5b The small-sized martensitic aspect ratio of the printed TA15 titanium alloy EBSD prepared for Comparative Example 1. Figure 6a This is a low-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared in Comparative Example 1. Figure 6b The image shows a high-magnification SEM image of the tensile fracture surface of the printed TA15 titanium alloy prepared for Comparative Example 1. Microstructure and mechanical property tests indicate that the primary β grains in the printed titanium alloy of Comparative Example 1 have an aspect ratio of 4.33, the large-size martensite has an average aspect ratio of 6.78, and the small-size martensite has an average aspect ratio of 3.33. The SEM morphology of the tensile fracture surface shows obvious quasi-cleavage planes (step gradient structure), indicating brittle fracture. The tensile strength is 1351 MPa, the yield strength is 1169 MPa, the work hardening capacity is 182 MPa, and the elongation is 8.5%. In Comparative Example 1, although the strength is very high, the plasticity is poor.

[0035] Table 1 lists the superior mechanical properties of the titanium alloys in Example 1 and Comparative Example 1. Comparative Example 1 cannot achieve both high strength and high plasticity; while achieving high strength, its plasticity is only 8.5%. The printed titanium alloys in Examples 1 to 4 maintain high tensile strength (≥1300 MPa), yield strength (≥1100 MPa), elongation (≥12%), and excellent work hardening ability (≥200 MPa). In the superior Example 1, excellent comprehensive properties of tensile strength 1354 MPa, yield strength 1139 MPa, elongation 13.0%, and work hardening ability 215 MPa are achieved.

[0036] Table 1 Comparison of mechanical properties between Example 1 and Comparative Example 1

[0037] Figure 7This is a schematic diagram comparing the microstructures of Example 1 and Comparative Example 1, revealing the multi-scale microstructural evolution of primary β grains and martensite of different sizes in Comparative Example 1 and Example 1 under controlled scan line energy and scan volume energy density. In Comparative Example 1, the primary β grains are columnar, with large-sized martensite exhibiting lamellar development and small-sized martensite showing an equiaxed development trend. In Example 1, the microstructure of the titanium alloy evolved from columnar primary β grains in Comparative Example 1 to equiaxed or near-equiaxed primary β grains. In Example 1, large-sized martensite exhibits an equiaxed development trend, while small-sized martensite shows a layered structure development trend. In Example 1, a tensile strength of 1354 MPa, a yield strength of 1139 MPa, an elongation of 13.0%, and a work hardening capacity of 215 were achieved. The excellent comprehensive performance of TA15 lies in the mechanism of simultaneously controlling the primary β grains and martensite structure. By controlling the formation of equiaxed or near-equiaxed structures of primary β grains and controlling the aspect ratio of martensite of different sizes, heterogeneous structures of martensite of different sizes can be achieved. This heterogeneous structure can form heterogeneous deformation-induced strengthening, which helps to enhance the synergistic effect of strength and plasticity. It can meet the dual requirements of "high strength and high plasticity" for high-end applications. At the same time, the excellent work hardening ability improves the energy absorption capacity of titanium alloys during service.

[0038] like Figure 8 This is a comparison chart of the properties of Example 1 of the present invention, Comparative Example 1, and existing titanium alloy literature. Figure 8 It can be seen that in the field of laser powder bed fusion forming of titanium alloys, high strength may mean sacrificing high plasticity, and pursuing high plasticity may result in a loss of high strength. In existing technologies, the elongation of titanium alloys is typically less than 10% when achieving high strength. Even if the elongation reaches 10%, achieving high strength is difficult; further increases after reaching this value are very challenging, representing a bottleneck that conventional technologies struggle to achieve. Furthermore, maintaining strength while achieving 10% plasticity, even with a 1% increase in plasticity, presents technical difficulties. Figure 8 Further, it becomes clear that existing technologies (including Comparative Example 1 of this invention) consistently face the core technical bottleneck of a strength-plasticity inversion. While both Comparative Example 1 and Example 1 achieve tensile strength ≥1300 MPa, the elongation of Comparative Example 1 and the elongation of printed Ti-6Al-4V and TA15 alloys in the literature are generally <10%, exhibiting brittle characteristics. In contrast, the strength drops to <1200 MPa when an elongation of ~13% is achieved in existing technologies. This invention achieves a breakthrough by simultaneously realizing a high strength of 1354 MPa and a high elongation of 13% in the printed state, with its data points significantly deviating from and surpassing the previous high strength. Figure 8The existing technical data shows a negative correlation trend between strength and plasticity. This synergistic achievement of "high strength and high plasticity" is due to the innovative microstructure of "equiaxed or near-equiaxed β grains + multi-scale heterogeneous martensite", which simultaneously improves strength and plasticity through a heterogeneous deformation-induced strengthening mechanism.

[0039] This invention solves the existing problem of balancing strength and plasticity, achieving a synergistic improvement in performance. It significantly exceeds the conventional understanding and general level of the printed performance of TA15 titanium alloy in laser powder bed fusion forming. This invention is expected to solve the cracking risk caused by insufficient plasticity in the printed state of large aerospace components (especially meter-sized components). The technical effects of achieving high strength, high plasticity and excellent work hardening ability in titanium alloys are not improvements that can be easily achieved in this field, but rather technical effects that are difficult to expect in this field. It has outstanding substantive characteristics and significant progress, and has very promising industrial application value in high-end application fields.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength, high-plasticity TA15 titanium alloy obtained by laser powder bed melting, characterized in that, The microstructure of the TA15 titanium alloy includes primary β grains and a multi-scale heterostructure of martensite. The primary β grains have an average aspect ratio of ≤3.

8. The multi-scale heterostructure of martensite includes large martensite grains and small martensite grains. The large martensite grains are martensite grains with a grain size ≥2.5 μm, and the small martensite grains are martensite grains with a grain size <2.5 μm. The average aspect ratio of the large martensite grains is ≤5.8, and the average aspect ratio of the small martensite grains is ≥3.

5.

2. The TA15 titanium alloy according to claim 1, characterized in that, The TA15 titanium alloy is in a laser powder bed fusion printing state and does not require heat treatment.

3. The TA15 titanium alloy according to any one of claims 1 to 2, characterized in that, The TA15 titanium alloy has a tensile strength ≥1300 MPa, a yield strength ≥1100 MPa, an elongation ≥12%, and a work hardening capacity ≥200 MPa.

4. A method for preparing TA15 titanium alloy as described in any one of claims 1 to 3, characterized in that, The process includes the following steps: generating a forming file from the 3D model using model processing software and process software; importing the forming file into a laser powder bed melting device; placing TA15 titanium alloy powder raw material into the laser powder bed melting device; and using the laser powder bed melting device to form the TA15 titanium alloy layer by layer according to the slicing path and process parameters of the 3D model. The process parameters include a scanning line energy density of 125~170 J / m and a scanning volume energy density of 35~48 J / mm². 3 The laser power is 160~280 W, the scanning speed is 1000~1400 mm / s, the scanning spacing is 90~120 μm, and the powder layer thickness is 20~50 μm.

5. The method for preparing TA15 titanium alloy according to claim 4, characterized in that, Strip printing is employed, with a strip width of 4~10 mm and a strip overlap spacing of -0.06~0.01 mm. The laser scanning method uses a "Zig-Zag" zigzag scanning pattern.

6. The method for preparing TA15 titanium alloy according to claim 4, characterized in that, The TA15 titanium alloy powder has a D10 particle size of 15~25 μm, a D50 particle size of 30~40 μm, and a D90 particle size of 40~60 μm.

7. The application of a TA15 titanium alloy as described in any one of claims 1 to 3 or a titanium alloy prepared by the preparation method as described in any one of claims 4 to 6 in the fields of aerospace, medical, automotive, consumer electronics, shipbuilding and marine, and weaponry and armor.

8. The application according to claim 7, characterized in that, Used in the preparation of intermediate casings, nozzles, and blades for aero engines.

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