A method for manufacturing a high-strength and high-ductility titanium alloy by defect-free selective laser melting

Abstract

This invention relates to the field of metal additive manufacturing technology, specifically a method for preparing high-strength and high-toughness titanium alloys by defect-free selective laser melting forming, comprising the following steps: S1: Raw material preparation: using Ti-6Al-4V as a substrate, and Ti-6Al-4V atomized spherical powder as raw material, the powder particles being spherical; S2: Powder pretreatment: drying the powder, cooling it, and then screening out the dried powder within a preset particle size range, adding it to the printing powder hopper; S3: Selective laser melting forming: using a selective laser melting 3D printing device for laser printing to obtain the formed part; S4: Post-printing treatment: stress-relief annealing is performed on the formed part and the substrate together, then the formed part is separated from the substrate, and the formed part is subjected to subsequent heat treatment; This method solves the problems of numerous metallurgical defects, high residual stress, and difficulty in achieving both strength and plasticity in existing selective laser melting forming of Ti-6Al-4V titanium alloys.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing technology, specifically a method for preparing high-strength and high-toughness titanium alloys by defect-free selective laser melting. Background Technology

[0002] The rapid development of high-end manufacturing fields such as aerospace, biomedicine, and marine engineering has placed increasingly stringent demands on the comprehensive mechanical properties of key load-bearing structural components. Ti-6Al-4V (TC4) titanium alloy, due to its excellent specific strength, good corrosion resistance, and outstanding biocompatibility, has become an indispensable core material in these fields. In particular, as component geometry evolves towards greater complexity and lighter weight, traditional forging and casting processes face technical bottlenecks such as long processing cycles, low material utilization, and even inability to form complex components with lattice structures and thin-walled flow channels. Selective Laser Melting (SLM), with its high design freedom and near-net-shape forming capabilities, has opened up new avenues for manufacturing high-performance complex titanium alloy components. This technology selectively melts powder layers using a high-energy laser beam, directly producing dense metal parts with mechanical properties superior to castings and even approaching those of forgings. Therefore, achieving defect-free, high-strength, and high-toughness TC4 alloy laser additive manufacturing is of significant strategic importance for promoting the lightweighting and performance improvement of high-end equipment.

[0003] While SLM technology has shown great potential in forming complex titanium alloy components, its layer-by-layer melting and solidification process has also led to several metallurgical defects, becoming a major bottleneck restricting the widespread industrial application of TC4 alloy. During SLM forming, the extremely high temperature gradient and complex molten pool flow behavior easily lead to porosity, incomplete fusion defects, and harmful residual stress. Porosity often originates from residual gas in the original powder or the turbulence of the molten pool entraining protective gas; while incomplete fusion defects are usually related to insufficient process energy input or improper overlap ratio, forming sharp microcrack initiation sources. More critically, although the rapid solidification conditions unique to the SLM process can refine grains, they also easily lead to the formation of non-equilibrium acicular martensite α' phase. This brittle phase, while possessing high strength, has extremely poor plasticity, often making it difficult for the formed parts to meet high toughness requirements without complex post-processing. Currently, conventional SLM-formed TC4 parts generally suffer from problems such as large density fluctuations, low plasticity, and significant anisotropy. How to simultaneously improve strength and plasticity, that is, to achieve a high strength-toughness match, remains a key scientific problem that needs to be solved in this field.

[0004] Therefore, it is necessary to invent a defect-free selective laser melting method for preparing high-strength and high-toughness titanium alloys to solve the above problems. Summary of the Invention

[0005] In order to solve the problems of numerous metallurgical defects, high residual stress, and difficulty in achieving both strength and plasticity in the existing selective laser melting forming of Ti-6Al-4V titanium alloys, this invention provides a defect-free selective laser melting forming method for preparing high-strength and high-toughness titanium alloys.

[0006] This invention is achieved using the following technical solution: A method for preparing high-strength and high-toughness titanium alloys by defect-free selective laser melting includes the following steps: S1: Raw material preparation: Using Ti-6Al-4V as the substrate, Ti-6Al-4V gas-atomized spherical powder is used as the raw material, and the powder particles are spherical or near-spherical; S2: Powder pretreatment: The Ti-6Al-4V atomized spherical powder is dried, cooled, and then the dried powder within the preset particle size range is screened and added to the printing powder hopper of the selective laser melting 3D printing equipment. S3: Selective Laser Melting Forming: Laser printing is performed using a selective laser melting 3D printing device. After the substrate is mounted and leveled, under a protective atmosphere, the dry powder is pushed from the printing powder hopper onto the substrate using a scraper to form a powder layer. The laser beam is controlled to selectively melt the current powder layer. The above powder laying and laser melting process is repeated until the part is formed, resulting in a shaped part. The laser printing process parameters are: laser power of 100-200 W, scanning speed of 1100-1400 mm / s, single-layer powder thickness of 30 μm, scanning spacing of 90 μm, and scanning direction rotation angle of 45-90°. S4: Post-printing processing: The formed part and the substrate are subjected to stress-relief annealing together, and then the formed part is separated from the substrate. The formed part is then subjected to subsequent heat treatment, including solution treatment and aging treatment, to obtain the defect-free selective laser melting formed high-strength and tough titanium alloy.

[0007] Furthermore, in step S2, the parameters for the drying process are: drying temperature of 150-250℃ and drying time of 2-4 h.

[0008] Furthermore, in step S2, the preset particle size range is 15-53 μm.

[0009] Furthermore, in step S3, the protective atmosphere is argon, and the oxygen content in the molding chamber of the selective laser melting 3D printing equipment is less than 0.3 ppm.

[0010] Furthermore, in step S3, the scraper is a metal scraper made of Ti-6Al-4V.

[0011] Furthermore, in step S3, before starting printing, the number of printing layers is set to 3, and a single sintering is performed first before printing begins.

[0012] Furthermore, in step S4, the parameters for stress-relief annealing are: temperature 400-550℃, time 2-3 h.

[0013] Furthermore, in step S4, the parameters for the solution treatment are: temperature 950-980℃, time 5-10 min.

[0014] Furthermore, in step S4, the parameters for the aging process are: temperature 500-600℃, time 1-3 h.

[0015] A defect-free selective laser melting forming high-strength and high-toughness titanium alloy is prepared by the method described in this invention.

[0016] This invention provides a method for preparing high-strength and high-toughness titanium alloys by defect-free selective laser melting, which has the following advantages compared with the prior art: Firstly, it achieves a high strength-toughness balance. Through the synergistic regulation of the entire chain—"powder pretreatment—printing strategy optimization—segmented multi-stage heat treatment"—this invention effectively eliminates metallurgical defects such as porosity and incomplete fusion, as well as residual stress in SLM-formed Ti-6Al-4V titanium alloy. It also regulates the non-equilibrium acicular martensite α' phase into a dual-state or basketweave structure composed of fine lamellar α phase and residual β phase, resulting in a tensile strength of 1323 MPa and an elongation of up to 26.7%, solving the technical problem of achieving both strength and plasticity in existing technologies.

[0017] Secondly, it boasts high material utilization and is environmentally friendly. The powder used in this invention can be reused after sieving, reducing material waste and waste by-products, and lowering manufacturing costs. At the same time, it adopts sustainable material recycling methods, reducing dependence on limited resources and aligning with the development direction of green manufacturing.

[0018] Thirdly, it offers high manufacturing efficiency and design freedom. This invention employs selective laser melting technology, enabling the integrated molding and rapid manufacturing of high-precision and complex parts, shortening the product manufacturing cycle, and providing new technical support for the lightweighting and performance improvement of high-end equipment. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the processing dimensions of the tensile specimen of the present invention.

[0020] Figure 2 This is a scanning electron microscope image of the Ti-6Al-4V atomized spherical powder before 3D printing in Embodiment 1 of the present invention.

[0021] Figure 3 This is a scanning electron microscope image of the microstructure of the high-strength and tough titanium alloy 3D printed after segmented multi-stage heat treatment in Embodiment 1 of the present invention. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] The selective laser melting 3D printing equipment described in this invention is model BLT-S210. Example 1

[0024] A method for preparing high-strength and high-toughness titanium alloys by defect-free selective laser melting includes the following steps: S1: Raw material preparation: Using Ti-6Al-4V as the substrate, Ti-6Al-4V gas-atomized spherical powder is used as the raw material. The powder particles are spherical or nearly spherical, without obvious hollow powder or agglomerated powder.

[0025] S2: Powder pretreatment: The Ti-6Al-4V atomized spherical powder is placed in a drying oven for drying at 200℃ for 2 hours. After drying, it is cooled to room temperature in the oven. After cooling, the dried powder with a particle size range of 15-53 μm is screened out and immediately added to the printing powder hopper of the selective laser melting 3D printing equipment.

[0026] The present invention dries the Ti-6Al-4V atomized spherical powder before printing, which can effectively reduce the defects of pores and keyholes caused by moisture evaporation during the printing process.

[0027] S3: Selective Laser Melting Forming: Laser printing is performed using a selective laser melting 3D printing device. After the substrate is mounted and leveled, a Ti-6Al-4V metal scraper is inserted, and the substrate is preheated to 150°C. The fan of the 3D printing device is turned on to purge the forming chamber with argon gas, ensuring that the oxygen content in the forming chamber is below 0.3 ppm. Then, under an argon atmosphere, the dry powder is pushed from the printing powder hopper onto the substrate by the scraper to form a powder layer. The 3D CAD model of the part to be printed is sliced ​​layer by layer (i.e., sliced), generating motion control codes for the laser scanning paths of each layer. According to the motion control codes, the device controls the laser beam to selectively melt the current powder layer layer by layer with a power of 160 W, a scanning speed of 1300 mm / s, a scanning interval of 90 μm, and a scanning direction rotation angle of 65°. After each layer is completed, the forming cylinder descends by one layer thickness, with a single layer powder thickness of 30 μm. The powder laying and melting process is repeated until the part is formed, resulting in a shaped part.

[0028] It is important to note that before starting printing, the number of printing layers should be set to 3. A single sintering should be performed first before starting printing to preheat the substrate and establish a stable molten pool environment.

[0029] S4: Post-printing processing: After printing, the substrate and the formed part are cooled to below 50°C under argon protection, and then removed. The formed part and the substrate are placed together in a heat treatment furnace for stress-relief annealing. The parameters for stress-relief annealing are: temperature 500°C, time 2 h, and then cooled to room temperature in the furnace. Then, the formed part is separated from the substrate using a wire cutting device, and the formed part is placed in a heat treatment furnace for subsequent heat treatment, which includes solution treatment and aging treatment. The parameters for solution treatment are: temperature 950°C, time 5 min, and then water quenched to room temperature; the parameters for aging treatment are: temperature 500°C, time 3 h, and then air-cooled to room temperature. After the subsequent heat treatment, the defect-free selective laser melting formed high-strength and tough titanium alloy is obtained. Example 2

[0030] The difference between this embodiment and Embodiment 1 is as follows: In step S3, the laser beam is controlled to selectively melt the current powder layer layer by layer with a power of 100 W, a scanning speed of 1300 mm / s, a scanning interval of 90 μm, and a scanning direction rotation angle of 45°. In step S4, the parameters for the stress-relief annealing are: temperature 400℃, time 3 h, followed by furnace cooling to room temperature; the parameters for the solution treatment are: temperature 950℃, time 5 min, followed by water quenching to room temperature; the parameters for the aging treatment are: temperature 500℃, time 2 h, followed by air cooling to room temperature. The remaining raw material amounts, preparation steps, and process parameters are the same as in Embodiment 1, resulting in a defect-free selective laser melting forming high-strength and tough titanium alloy. Example 3

[0031] The difference between this embodiment and Embodiment 1 is as follows: In step S3, the laser beam is controlled to selectively melt the current powder layer layer by layer with a power of 200 W, a scanning speed of 1100 mm / s, a scanning interval of 90 μm, and a scanning direction rotation angle of 90°. In step S4, the parameters for the stress-relief annealing are: temperature 550℃, time 2 h, followed by furnace cooling to room temperature; the parameters for the solution treatment are: temperature 950℃, time 5 min, followed by water quenching to room temperature; the parameters for the aging treatment are: temperature 600℃, time 2 h, followed by air cooling to room temperature. The remaining raw material amounts, preparation steps, and process parameters are the same as in Embodiment 1, resulting in a defect-free selective laser melting forming high-strength and tough titanium alloy. Example 4

[0032] The difference between this embodiment and Embodiment 1 is as follows: In step S3, the laser beam is controlled to selectively melt the current powder layer layer by layer with a power of 150 W, a scanning speed of 1400 mm / s, a scanning interval of 90 μm, and a scanning direction rotation angle of 65°. In step S4, the parameters for the stress-relief annealing are: temperature 500℃, time 1 h, followed by furnace cooling to room temperature; the parameters for the solution treatment are: temperature 950℃, time 5 min, followed by water quenching to room temperature; the parameters for the aging treatment are: temperature 600℃, time 1 h, followed by air cooling to room temperature. The remaining raw material amounts, preparation steps, and process parameters are the same as in Embodiment 1, resulting in a defect-free selective laser melting forming high-strength and tough titanium alloy. Example 5

[0033] The difference between this embodiment and Embodiment 1 is as follows: In step S3, the laser beam is controlled to selectively melt the current powder layer layer by layer with a power of 150 W, a scanning speed of 1200 mm / s, a scanning interval of 90 μm, and a scanning direction rotation angle of 90°. In step S4, the parameters for the stress-relief annealing are: temperature 450℃, time 2 h, followed by furnace cooling to room temperature; the parameters for the solution treatment are: temperature 950℃, time 5 min, followed by water quenching to room temperature; the parameters for the aging treatment are: temperature 500℃, time 2 h, followed by air cooling to room temperature. The remaining raw material amounts, preparation steps, and process parameters are the same as in Embodiment 1, resulting in a defect-free selective laser melting forming high-strength and tough titanium alloy.

[0034] To verify the mechanical properties of the titanium alloy prepared in this invention, specimens for tensile testing were prepared simultaneously using the same process conditions as in the above embodiments. Figure 1 As shown, the tensile specimen is a plate-shaped specimen with a rectangular cross-section. The total length L of the specimen is... tThe sample is 52 mm long and 2.5 mm thick. Both ends are clamping ends, with a clamping end width B of 8 mm and a clamping end length A of 11.07 mm. The middle section is a parallel section with a length L. c The width of the parallel section is 4 mm, and the clamping end and the parallel section are connected by an arc with a radius R of 10.05 mm.

[0035] The specimens prepared in Examples 1-5 above were subjected to tensile tests at room temperature. The mechanical properties after SLM forming (before heat treatment) and after heat treatment were tested respectively. The results are shown in Table 1 and Table 2.

[0036] Table 1 Tensile test results of selected area laser melting specimens

[0037] Table 2 Tensile test results of the specimens after heat treatment

[0038] A comparison of Tables 1 and 2 shows that while untreated SLM-formed parts possess a certain strength, their plasticity is poor, with elongation generally ranging from 10% to 21%. However, after the segmented multi-stage heat treatment of this invention, an excellent balance of high strength and toughness is achieved. In particular, Example 1 exhibits a tensile strength of 1323 MPa and an elongation as high as 26.7%. This demonstrates that the synergistic effect of powder pretreatment, optimized printing strategy, and segmented multi-stage heat treatment effectively eliminates metallurgical defects and regulates microstructure, thereby obtaining titanium alloy parts that possess both high strength and high plasticity.

[0039] Figure 2 The image shows the scanning electron microscope (SEM) morphology of Ti-6Al-4V atomized spherical powder before 3D printing. The powder particles are spherical or nearly spherical, with no obvious hollow powder or aggregated powder.

[0040] Figure 3 The image shows a scanning electron microscope (SEM) image of the microstructure of a 3D-printed sample after segmented multi-stage heat treatment. The microstructure is a dual-state or basketweave structure composed of fine lamellar α phase and residual β phase.

[0041] This invention addresses the technical challenges of numerous metallurgical defects, high residual stress, and the difficulty in simultaneously achieving strength and plasticity during selective laser melting (SLM) forming of Ti-6Al-4V titanium alloys. It proposes a systematic solution encompassing the entire chain from powder pretreatment to printing strategy optimization and segmented multi-stage heat treatment. First, before forming, the Ti-6Al-4V atomized spherical powder is dried to remove adsorbed moisture from the powder particle surface, effectively reducing porosity and keyhole defects caused by moisture evaporation during printing. Simultaneously, by screening spherical powder with a particle size range of 15-53 μm, the uniformity of powder spreading and loose packing density are improved, reducing the formation of incomplete fusion defects at the source. Second, based on the goals of defect control and microstructure refinement, the laser printing strategy is systematically optimized. By precisely controlling laser power, scanning speed, scanning spacing, and scanning direction rotation angle, a stable thermodynamic environment for the molten pool is constructed, suppressing the initiation of porosity and cracks, and achieving preliminary control over the solidification microstructure, providing a good microstructure foundation for subsequent heat treatment. Finally, a segmented multi-stage heat treatment process was designed and improved to address the non-equilibrium brittle martensite present in the SLM state microstructure. By precisely controlling the phase transformation process, the acicular α' phase was fully decomposed to form a biphase or basket structure composed of fine lamellar α phase and residual β phase, thus restoring the plasticity of the material while retaining the fine grain strengthening effect.

[0042] Through the synergistic effect of the above-mentioned powder pretreatment, process parameter optimization and segmented heat treatment, the present invention achieves effective elimination of internal defects and fine tailoring of microstructure in Ti-6Al-4V titanium alloy components, and finally obtains excellent mechanical properties that combine high strength and high plasticity.

[0043] In practice, the substrate and squeegee must be replaced before each printing to ensure the flatness of the substrate. After each printing, the excess Ti-6Al-4V atomized spherical powder can be reused after being sieved.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-strength and high-toughness titanium alloys by defect-free selective laser melting, characterized in that, Includes the following steps: S1: Raw material preparation: Using Ti-6Al-4V as the substrate, Ti-6Al-4V gas-atomized spherical powder is used as the raw material, and the powder particles are spherical or near-spherical; S2: Powder pretreatment: The Ti-6Al-4V atomized spherical powder is dried, cooled, and then the dried powder within the preset particle size range is screened and added to the printing powder hopper of the selective laser melting 3D printing equipment. S3: Selective Laser Melting Forming: Laser printing is performed using a selective laser melting 3D printing device. After the substrate is mounted and leveled, under a protective atmosphere, the dry powder is pushed from the printing powder hopper onto the substrate using a scraper to form a powder layer. The laser beam is controlled to selectively melt the current powder layer. The above powder laying and laser melting process is repeated until the part is formed, resulting in a shaped part. The laser printing process parameters are: laser power of 100-200 W, scanning speed of 1100-1400 mm / s, single-layer powder thickness of 30 μm, scanning spacing of 90 μm, and scanning direction rotation angle of 45-90°. S4: Post-printing processing: The formed part and the substrate are subjected to stress-relief annealing together, and then the formed part is separated from the substrate. The formed part is then subjected to subsequent heat treatment, including solution treatment and aging treatment, to obtain the defect-free selective laser melting formed high-strength and tough titanium alloy.

2. The method for preparing a defect-free selective laser melting forming high-strength and high-toughness titanium alloy according to claim 1, characterized in that, In step S2, the parameters for the drying process are: drying temperature of 150-250℃ and drying time of 2-4 h.

3. The method for preparing a defect-free selective laser melting forming high-strength and high-toughness titanium alloy according to claim 1, characterized in that, In step S2, the preset particle size range is 15-53 μm.

4. The method for preparing a defect-free selective laser melting forming high-strength and high-toughness titanium alloy according to claim 1, characterized in that, In step S3, the protective atmosphere is argon, and the oxygen content in the molding chamber of the selective laser melting 3D printing equipment is less than 0.3 ppm.

5. The method for preparing a defect-free selective laser melting forming high-strength and high-toughness titanium alloy according to claim 1, characterized in that, In step S3, the scraper is a metal scraper made of Ti-6Al-4V.

6. The method for preparing a defect-free selective laser melting forming high-strength and high-toughness titanium alloy according to claim 1, characterized in that, In step S3, before starting printing, the number of printing layers is set to 3, and a single sintering is performed first before printing begins.

7. The method for preparing a defect-free selective laser melting forming high-strength and high-toughness titanium alloy according to claim 1, characterized in that, In step S4, the parameters for stress-relief annealing are: temperature 400-550℃, time 2-3 h.

8. The method for preparing a defect-free selective laser melting forming high-strength and high-toughness titanium alloy according to claim 1, characterized in that, In step S4, the parameters for the solution treatment are: temperature 950-980℃, time 5-10 min.

9. The method for preparing a high-strength and high-toughness titanium alloy by defect-free selective laser melting according to claim 1, characterized in that, In step S4, the parameters for the aging process are: temperature 500-600℃, time 1-3 h.

10. A defect-free selective laser melting forming high-strength and tough titanium alloy, prepared by the method for preparing a defect-free selective laser melting forming high-strength and tough titanium alloy as described in any one of claims 1-9.

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