Direct aging treatment process of SLM molded Ti-6Al-4V alloy and product thereof

Abstract

The invention relates to the technical field of additive manufacturing, in particular to a direct aging treatment process of an SLM molded Ti-6Al-4V alloy and a product thereof, and the direct aging treatment process comprises the following steps: firstly, manufacturing a Ti-6Al-4V alloy sample by adopting an SLM technology, and then putting the SLM molded Ti-6Al-4V alloy sample into a vacuum heat treatment furnace for direct aging treatment, and finally, taking out the sample after furnace cooling or air cooling. According to the method, through direct aging treatment, a natural alpha'martensite structure in the Ti-6Al-4V alloy formed through SLM is decomposed into an alpha + beta double-phase structure, the front solid solution-quenching process in traditional solid solution aging treatment is not needed, and the purposes of optimizing structure uniformity and improving plasticity are achieved. The aging treatment cost and the quenching risk of the SLM titanium alloy are reduced, and the plasticity of the SLM titanium alloy can be remarkably improved while high strength is kept. The method is simple in process, low in cost and suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically to a direct aging process for SLM-formed Ti-6Al-4V alloy and its products. Background Technology

[0002] Selective Laser Melting (SLM) is an advanced additive manufacturing technology that rapidly produces metal parts with complex shapes by melting metal powder layer by layer using a high-energy laser. Ti-6Al-4V alloy, a widely used titanium alloy, has attracted significant attention in aerospace, medical, and marine fields due to its excellent comprehensive properties. SLM technology provides a new approach to manufacturing Ti-6Al-4V alloy, enabling rapid prototyping and high-performance fabrication of complex structures. Ti-6Al-4V alloy prepared by SLM technology exhibits superior hardness and strength compared to the traditional rolled state. Although its impact toughness is slightly lower, it still possesses promising application prospects. Its high degree of design freedom and rapid prototyping capability give it significant advantages in high-performance applications such as aerospace and marine equipment, including satellite sensor brackets and large military UAV optoelectronic pods. These applications place higher demands on the performance of SLM-formed Ti-6Al-4V alloys, and the performance of titanium alloys is closely related to their microstructure. Therefore, controlling the microstructure of Ti-6Al-4V alloy through heat treatment is a key means to optimize its performance.

[0003] Common heat treatment methods for SLM-formed Ti-6Al-4V alloys include conventional annealing, hot isostatic pressing, and solution aging. Solution aging is a crucial heat treatment process for SLM-manufactured Ti-6Al-4V alloys, primarily consisting of two stages: solution treatment and aging. Solution treatment is typically performed at temperatures between 900℃ and 950℃, followed by rapid cooling (e.g., water quenching) to fully dissolve the solute elements in the alloy into the matrix, forming a homogeneous solid solution. The subsequent aging treatment is carried out at approximately 550℃, with a holding time generally ranging from 4 to 8 hours, improving the alloy's mechanical properties by precipitating an α+β dual-phase structure.

[0004] Solution aging treatment can effectively improve the microstructure of Ti-6Al-4V alloys and significantly enhance their performance. However, this process also has some limitations. On the one hand, high-temperature solution treatment may lead to grain coarsening, thereby reducing the strength and toughness of the material; on the other hand, it requires a quenching process, which is complex, carries the risk of cracking or deformation, and is costly. SLM technology can generate α′ martensite phase when manufacturing Ti-6Al-4V alloys. However, there is currently no technology that directly utilizes the α′ martensite phase generated by SLM technology to replace traditional solution treatment. Specific challenges include: the α′ martensite phase generated in the SLM process of Ti-6Al-4V alloys is difficult to directly decompose into the ideal α+β dual-phase structure at lower temperatures, and the thermal stress generated during SLM cannot be effectively eliminated; higher heat treatment temperatures may lead to microstructure coarsening, affecting alloy strength; traditionally, omitting high-temperature solution treatment usually results in a decrease in material plasticity, and there is currently no method to achieve improved plasticity while omitting solution treatment.

[0005] Therefore, how to effectively utilize the α′ martensite phase generated by SLM technology without traditional solution quenching, and optimize the microstructure of the alloy through direct aging treatment to simultaneously improve strength and plasticity, has become an urgent technical problem to be solved. Summary of the Invention

[0006] To achieve one of the above objectives, this invention provides a direct aging treatment process and product for SLM-printed Ti-6Al-4V alloy. This invention improves the alloy's microstructure by optimizing heat treatment parameters, thereby significantly enhancing its plasticity while maintaining high strength. Compared to traditional solution aging methods, direct aging utilizes the α′ martensite phase generated in the Ti-6Al-4V alloy during SLM forming, eliminating the need for a pre-treatment solution quenching process. This greatly reduces the risk of deformation and cracking in complex SLM-printed parts, while also simplifying the process and lowering aging treatment costs. The technical solution of this invention is implemented as follows:

[0007] In a first aspect, the present invention provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, comprising the following steps:

[0008] S1. Using titanium alloy powder as raw material, SLM molding is used to obtain shaped alloy samples;

[0009] S2. Place the SLM-formed titanium alloy sample, either as a whole plate or separated, into a vacuum heat treatment furnace for direct aging treatment.

[0010] S3. After aging, the titanium alloy sample is cooled in the furnace or air-cooled to room temperature and then taken out to obtain the SLM titanium alloy sample after direct aging treatment.

[0011] More preferably, the chemical composition of the Ti-6Al-4V alloy powder consists of the following components by mass percentage: Al 5.50-6.75%, V 3.5-4.5%, Fe≤0.3%, O≤0.15%, C≤0.08%, N≤0.05%, H≤0.015%, with the balance being Ti, wherein the sum of the mass percentages of each component is 100%.

[0012] More preferably, the particle size of the Ti-6Al-4V alloy powder is 15–53 μm.

[0013] Preferably, the SLM process parameters in step S1 are: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0014] More preferably, the SLM-formed Ti-6Al-4V alloy sample obtained in step S1 has a widely distributed α′ martensite structure before direct aging.

[0015] Preferably, the aging treatment temperature in step S2 is 560–650°C.

[0016] Preferably, the aging time in step S2 is matched with the aging temperature, and the aging time range is 4-8 hours.

[0017] Preferably, by adjusting the aging temperature and aging time of the direct aging process, the thermal stress in the sample is eliminated, while the degree of decomposition of the α′ martensite phase and the morphology and size of the α+β dual-phase structure of the SLM-formed Ti-6Al-4V alloy are controlled, which significantly improves the strength-plasticity matching, thermal stability and creep resistance of the SLM-formed Ti-6Al-4V alloy.

[0018] More preferably, the SLM-formed Ti-6Al-4V alloy after direct aging treatment in step S2 has a microstructure containing α+β dual-phase structures of various shapes and sizes, such as short rods, long strips and lamellar structures.

[0019] Further preferably, the most preferred morphology of the α+β biphase structure is a strip shape with an aspect ratio of 1:(6-10), a width of about 1 to 2 μm, and a length of about 6 to 12 μm.

[0020] More preferably, the Ti-6Al-4V alloy in the preferred form and size has high strength and good plasticity, and also has a high yield strength ratio of about 0.93.

[0021] Preferably, in step S3, furnace cooling or air cooling is used after the aging process is completed.

[0022] In a second aspect, the present invention provides an SLM-formed Ti-6Al-4V alloy obtained by the direct aging process of the first aspect.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] (1) Compared with the existing SLM forming Ti-6Al-4V alloy solution aging process, the direct aging process proposed in this invention omits the high-temperature solution and quenching steps and directly performs aging treatment at a lower temperature, which significantly simplifies the process flow and reduces quenching risk, energy consumption and cost.

[0025] (2) In terms of microstructure, direct aging treatment can effectively decompose α′ martensite and form a mixed structure of α+β dual phase and single β phase. At the same time, intergranular α phase is generated between the grain boundaries of the original β grains, which reduces the anisotropy of the mechanical properties of the sample.

[0026] (3) The evolution of the microstructure significantly improves the plasticity of the alloy while maintaining high strength. Direct aging treatment achieves a balance between strength and plasticity by optimizing the microstructure, providing a more efficient and economical way to optimize the performance of Ti-6Al-4V titanium alloys manufactured by SLM. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0028] Figure 1 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Example 1 of this invention;

[0029] Figure 2 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Example 2 of the present invention;

[0030] Figure 3 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Example 3 of the present invention;

[0031] Figure 4 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Example 4 of this invention;

[0032] Figure 5 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Comparative Example 1 of this invention;

[0033] Figure 6 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Comparative Example 2 of this invention;

[0034] Figure 7 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Comparative Example 3 of this invention;

[0035] Figure 8 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to direct aging treatment in Comparative Example 4 of this invention;

[0036] Figure 9 This is a SEM microstructure of the SLM-formed Ti-6Al-4V alloy subjected to conventional solution aging treatment in Comparative Example 5 of this invention.

[0037] Figure 10 This is a high-magnification (20,000x) SEM microstructure of the SLM-formed Ti-6Al-4V alloy that underwent direct aging treatment in Example 4 of this invention, followed by phase inversion treatment.

[0038] Figure 11 This is a high-magnification (20,000x) SEM microstructure of the SLM-formed Ti-6Al-4V alloy that underwent direct aging treatment in Comparative Example 1 of this invention, after inversion treatment.

[0039] Figure 12 This is a high-magnification (20,000x) SEM microstructure of the SLM-formed Ti-6Al-4V alloy that underwent direct aging treatment in Comparative Example 4 of this invention, after inversion treatment.

[0040] Figure 13 This is a SEM microstructure image of an SLM-formed Ti-6Al-4V alloy sample before direct aging according to the present invention. Detailed Implementation

[0041] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0042] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0043] In this document, the terms “containing,” “comprising,” or “including” are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0044] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0045] It should be noted that during the direct aging process, α′ martensite decomposes and spheroidizes to form the equiaxed α phase in the α+β dual-phase microstructure. By controlling the SLM parameters in the early stage and adjusting the aging temperature and time of the direct aging treatment, the uniform decomposition of α′ martensite into equiaxed α phases with uniform size and distribution can be controlled. This avoids the decrease in plasticity caused by insufficiently decomposed α′ martensite phase and the decrease in strength caused by coarse β phase, thus ensuring both the strength and plasticity of the SLM Ti-6Al-4V alloy.

[0046] The α′ martensitic transformation of the original β phase is a diffusionless transformation, while the decomposition of α′ martensite is a diffusion-type transformation. In the SLM Ti-6Al-4V alloy, the α′ martensite phase undergoes two steps during its decomposition into α + β phases: α′→α + αHME and αHME→β. The αHME phase is a transitional phase with a crystal structure similar to the α / α′ phase but a chemical composition similar to the β phase. The presence of the αHME phase corroborates the formation of isometric α phase and interstitial β phases in the α + β dual-phase structure. Because the α′ martensite phase is in a metastable state, its crystal energy is high, exhibiting a spontaneous tendency to transform to lower energy levels. Atomic diffusion during the α′ martensite phase decomposition process is against the concentration gradient, a typical uphill diffusion. Its main driving force is not the atomic concentration gradient but the chemical potential gradient, and Fick's law does not apply. Here, atomic diffusion capability should be related to atomic kinetic energy; the formula describing the relationship between the average kinetic energy of particles and temperature is:

[0047]

[0048] in: <E k > represents the average kinetic energy of the particle; k B It is the Boltzmann constant (1.380649 × 10⁻⁶). -23J / K); T is temperature, in Kelvin (K).

[0049] Equation (1) shows that the average kinetic energy of particles is proportional to the absolute temperature. As the temperature increases, the average kinetic energy of atoms also increases, and the thermal motion of particles becomes more intense. This means that the diffusion rate of atoms will increase significantly. High temperature provides atoms with higher kinetic energy, enabling more atoms to obtain enough energy to overcome the activation energy barrier and thus move in the solid solution. In addition, the increase in temperature usually increases the vacancy concentration in the crystal, providing more space for atomic migration. When the temperature increases and the diffusion conditions of V and Fe atoms in the α′ martensite phase are met, due to the non-uniformity of thermal energy distribution, there will be local fluctuations in atomic concentration, forming V and Fe atom concentration depressions. Equation (2) is the Maxwell-Boltzmann distribution, which reveals that the atomic thermal motion velocity at a certain temperature follows a probability distribution.

[0050]

[0051] Where: f(v) is the probability density function of a particle with velocity v; m is the mass of the particle; k B It is the Boltzmann constant (approximately 1.38 × 10⁻⁶). -23 J / K); T is absolute temperature, in Kelvin (K); v is the particle velocity.

[0052] The α′ martensite phase is a supersaturated, non-equilibrium hexagonal α phase. When the atomic concentration in a small region of the α′ martensite phase meets the conditions for α phase formation, the α′ martensite phase in that region preferentially transforms into the α phase. This can be considered as the uniform nucleation of the α phase within the α′ martensite phase. If the nucleation radius of the α phase is greater than a critical value, it can exist stably and grow spontaneously. The growth of the α phase further promotes the diffusion of V and Fe atoms outward from the α phase until the growth of the α phase is hindered. There are two possibilities for the growth of the α phase being hindered: one is that the growing α phase encounters other growing α phases and stops growing; the other is that the concentration of diffused V and Fe atoms reaches a critical value, causing the outer α′ martensite phase to transform into an interstitial β phase that surrounds the α phase, thus stopping the growth of the α phase.

[0053] During the direct aging process of this invention, the α′ martensite in the Ti-6Al-4V alloy decomposes into an α+β dual-phase structure. The α phase has a hexagonal close-packed structure (HCP), and the β phase has a body-centered cubic structure (BCC), representing the two phase structures of titanium. Its specific microstructure consists of elongated α+β dual-phase mixed structures and interspersed granular or needle-like independent β phases. Within the elongated α+β dual-phase mixed structure, the α phases are equiaxed and tightly stacked, while the β phases are distributed in the gaps between the equiaxed α phases.

[0054] Meanwhile, the decomposition of α′ martensite into elongated α+β dual-phase structures, distributed within the matrix, hinders dislocation movement, thereby increasing the alloy's strength. However, these longer elongated structures are detrimental to the alloy's plasticity because stress concentration at the tips of these structures under external force easily leads to crack initiation. Once formed, the cracks propagate rapidly along the laths. During tension, the high stress at the tips of the elongated α+β dual-phase structures can cause microcracks beyond the local strength limit, which propagate rapidly along the lath direction under the guidance of the dual-phase structure, reducing the material's plastic deformation capacity. To achieve a balance between the alloy's strength and plasticity, the dimensions of the α+β dual-phase structure after direct aging treatment must be controlled, especially to prevent excessive aspect ratio. Specific methods to achieve this include precise control of the alloy's composition, meticulous optimization of SLM (selective laser melting) parameters, and reasonable determination of the temperature and time for direct aging treatment.

[0055] The precipitation of the α phase is usually accompanied by the redistribution of alloying elements. For example, elements such as vanadium (V) and aluminum (Al) are enriched in the α and β phases, further enhancing the strengthening effect. In addition, independent β phases with various morphologies are generated at the boundaries of the α+β dual-phase structure. Due to their numerous BCC slip planes, these phases exhibit better plasticity than the α phase with its HCP structure. Therefore, both the independent β phases at the boundaries of the α+β dual-phase structure and the interstitial β phases within the α+β dual-phase structure can improve the plasticity of the Ti-6Al-4V alloy during deformation. In short, during aging, the small-sized equiaxed α phases that decompose from α′ martensite contribute to the strength of the material, while the interstitial β phases and independent β phases contribute to the toughness.

[0056] Furthermore, under different direct aging processes of this invention, the strength and plasticity of the SLM-formed Ti-6Al-4V alloy exhibit distinct trends with temperature changes. As the aging temperature increases, the tensile strength and yield strength of the alloy generally decrease, while the elongation at break increases significantly. This change is mainly attributed to the evolution of the microstructure: at lower aging temperatures, the α′ martensite decomposes less, resulting in smaller and more uniformly distributed α+β dual-phase structures, which help maintain high strength. However, as the aging temperature increases, the α+β dual-phase structure gradually coarsens, and the size of the independent β phase in the interstitial spaces increases, leading to a decrease in the alloy's strength. Simultaneously, the β phase exhibits better plasticity than the α phase, and its increased content significantly improves the alloy's plasticity. Moreover, the formation and growth of the α phase at grain boundaries blurs the original β grain boundaries, reducing the material's anisotropy and further enhancing plasticity. Therefore, direct aging treatment achieves a balance between strength and plasticity by controlling the morphology and size of the microstructure, providing an effective way to optimize the performance of the SLM-formed Ti-6Al-4V alloy.

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the protection scope of the present invention.

[0058] Example 1

[0059] This embodiment provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0060] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0061] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 560℃ and the aging time was 8h.

[0062] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 1 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0063] from Figure 1 As can be seen from this direct aging process, most of the α′ martensite in the sample of Example 1 was decomposed, and strip-shaped α+β biphase structure and β phase particles were observed.

[0064] Example 2

[0065] This embodiment provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0066] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0067] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 600℃ and the aging time was 8h.

[0068] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 2 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0069] from Figure 2 It can be seen that under this direct aging process, the α′ martensite structure of the sample is completely decomposed, and its α+β biphase structure is coarsened to a certain extent. More widely distributed β phase particles were found on the boundary of these α+β biphase structures.

[0070] Example 3

[0071] This embodiment provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0072] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0073] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 600℃ and the aging time was 4h.

[0074] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 3 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0075] from Figure 3 As can be seen from this direct aging process, due to the shorter heat treatment time compared to Example 2, the α′ martensite structure in the sample was not completely decomposed, and more concentrated β phase clusters were also observed.

[0076] Example 4

[0077] This embodiment provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0078] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0079] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 650℃ and the aging time was 4h.

[0080] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 4 As shown, the high-magnification (20000x) SEM microstructure image is as follows. Figure 10 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0081] from Figure 4 As can be seen, under this direct aging process, the α+β dual-phase microstructure of the sample did not further coarsen, while the degree of α′ martensite decomposition was comparable to that of Example 2. This explains why it maintained its tensile strength while possessing a high elongation at break. Figure 10 As can be seen from the data, the equiaxed α phase in its α+β dual-phase structure is uniform in size and distribution, and there are no non-equiaxed α phases or coarse β phases. Therefore, it has both high strength and good plasticity.

[0082] Comparative Example 1

[0083] This comparative example provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0084] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0085] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 450℃ and the aging time was 8h.

[0086] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 5 As shown, the high-magnification (20000x) SEM microstructure image is as follows. Figure 11 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0087] from Figure 5 As can be seen from this direct aging process, the sample microstructure exhibits a mountain-like distribution of β-structure, and some needle-like, light-colored microstructure appears in the background, which is incompletely decomposed α′ martensite. From Figure 11 It can be seen that at 450℃, the α' martensite structure failed to completely decompose into equiaxed α phase, the α phase was partially spheroidized, and the β phase content was low, resulting in extremely poor plasticity of this group of samples.

[0088] Comparative Example 2

[0089] This comparative example provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0090] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0091] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 500℃ and the aging time was 8h.

[0092] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 6 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0093] from Figure 6 It can be seen that under this direct aging process, the sample's microstructure is somewhat coarsened, which may be due to the merging of α′ phases with similar orientations. A dominant orientation similar to that of the sample in Example 1 can be observed, but the dispersion of the β phase is significantly higher, and β phase particles are widely distributed at the boundaries of the strip-shaped α+β biphase microstructure.

[0094] Comparative Example 3

[0095] This comparative example provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0096] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0097] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 650℃ and the aging time was 8h.

[0098] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 7 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0099] from Figure 7 As can be seen, under this direct aging process, the α+β biphase microstructure of the sample further coarsens, with the morphology changing from needle-like to short rod-like. This may be due to the merging of similarly oriented α′ martensite phases. Granular β phases were also observed, but the β phase particles in Comparative Example 3 sample were larger. Furthermore, needle-like β phases were also found, and these needle-like and granular β phases were distributed at the boundaries of the α+β biphase microstructure.

[0100] Comparative Example 4

[0101] This comparative example provides a direct aging treatment process for SLM-formed Ti-6Al-4V alloy, including the following steps:

[0102] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0103] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to direct aging treatment. Vacuum aging treatment was performed on some samples using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and maintained for a certain aging time. The aging temperature was 730℃ and the aging time was 4h.

[0104] (3) After aging, the titanium alloy sample was cooled in the furnace or air-cooled to room temperature before being removed, resulting in an SLM titanium alloy sample that had undergone direct aging treatment. The microstructure of the obtained sample is as follows: Figure 8 As shown, the high-magnification (20000x) SEM microstructure image is as follows. Figure 12 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0105] from Figure 8 It can be seen that under this direct aging process, the α+β dual-phase structure of the sample further merged and coarsened, exhibiting short rod-like and lamellar shapes. The size of the β phase also further increased, and the morphology of the β phase changed from granular to needle-like. From Figure 12 The samples show a uniformly distributed equiaxed α phase, but a coarse β phase appears between the α+β two-phase structures. During loading, the large, flat phase interfaces cause stress concentration at the interfaces, leading to cracks and resulting in poor strength in this group of samples.

[0106] Comparative Example 5

[0107] This comparative example provides a solution aging process for a conventional Ti-6Al-4V alloy, including the following steps:

[0108] (1) Ti-6Al-4V alloy samples were manufactured using an M290 SLM additive manufacturing equipment equipped with a 400W fiber laser manufactured by EOS Corporation. The raw material was gas-atomized Ti-6Al-4V alloy spherical powder produced by Ningbo Zhongyuan Company. The powder particle size was 50μm, and the powder composition was Al: 6%, V: 4%, Fe: 0.1%, O: 0.1%, C: 0.01%, N: 0.01%, H: 0.01%, with the balance being Ti. The optimized SLM process parameters were: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

[0109] (2) The SLM-formed Ti-6Al-4V alloy samples obtained in step (1) were subjected to high-temperature solution treatment. A portion of the samples were treated using a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm. The high-temperature treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), then the sample was heated to the solution temperature and held for a certain solution time. The treatment temperature was 950℃ and the holding time was 1h. After the holding time was reached, the Ti-6Al-4V titanium alloy was taken out and water-cooled at 20℃ for 30s.

[0110] (3) The SLM-formed Ti-6Al-4V alloy samples obtained in step (2) were subjected to aging treatment. Similarly, a VHT40 / 16-MO vacuum heat treatment furnace manufactured by Nabertherm was used to perform vacuum aging treatment on some samples. Vacuum aging treatment involved evacuating the heat treatment furnace to a vacuum level (less than 3 × 10⁻⁶). -5 mbar), and then the sample was heated to the aging temperature and held for a certain aging time. The aging temperature was 550℃ and the aging time was 8h.

[0111] (4) After aging, the titanium alloy sample is cooled in the furnace or air-cooled to room temperature before being removed to obtain the solution-aged SLM titanium alloy sample. The microstructure of the obtained sample is as follows: Figure 9 As shown, the details of the mechanical properties of the samples are shown in Table 1.

[0112] from Figure 9 It can be seen that under this direct aging process, the α′ martensite phase generated during quenching is decomposed, forming a long strip-shaped α+β dual-phase structure with a large aspect ratio.

[0113] Table 1 shows the mechanical property test results of the Ti-6Al-4V alloys in Examples 1-4 and Comparative Examples 1-5 of the present invention. The test method was room temperature metal tensile test, and the test process complied with the provisions of GB / T 228.1-2010.

[0114] Table 1. Test results of mechanical properties of the Ti-6Al-4V alloy prepared in this invention.

[0115]

[0116] As can be seen from the microstructure diagrams and the test results in Table 1, the tensile properties of the Ti-6Al-4V alloy manufactured by SLM are mainly affected by internal defects and the content and morphology of α′, αHME, α, and β phases. The untreated sample contains a large amount of acicular α′ martensite, which exhibits high strength but poor plasticity. After direct aging treatment, the grain size and morphology of the sample remained essentially unchanged, showing no risk of grain coarsening compared to solution aging treatment. During the aging process, the original α′ martensite gradually decomposes, forming a mixed structure of α+β dual-phase and single β phase. With increasing aging temperature, the α phase gradually coarsens, leading to a decrease in alloy strength, while the size and quantity of the β phase increase. Since the β phase has better plasticity than the α phase, its increased content helps improve the alloy's plasticity, manifested as a significant increase in elongation at break. Due to the lower aging temperature in Comparative Example 1, the α′ martensite was not fully decomposed, and the stress generated during the SLM process was not completely removed, resulting in the worst plasticity among all examples. The aging temperature of Example 1 was increased by 100°C compared to Comparative Example 1, and the elongation at break was increased by nearly 50% compared to Comparative Example 1, reaching a usable level. Comparative Example 4 had a higher aging temperature, resulting in more severe microstructure coarsening and the elimination of twinned structures generated during the aging process. Its strength was significantly lower than that of Example 4, while its plasticity was almost not improved.

[0117] Therefore, the reasonable temperature range for direct aging treatment of Ti-6Al-4V alloy manufactured by SLM should be 560-650℃. Comparative Example 5 adopted the traditional solution aging process, and its sample had lower strength and plasticity than the samples treated by direct aging (such as Examples 1-3). This can be attributed to the grain coarsening during the solution treatment stage and the non-uniformity of quenching during the quenching stage.

[0118] In summary, this invention optimizes the microstructure and mechanical properties of SLM-manufactured Ti-6Al-4V titanium alloys through direct aging treatment. During direct aging, the original α′ martensite structure decomposes into a mixed structure of α+β dual-phase and single β phase. With increasing aging temperature, the α+β dual-phase structure gradually coarsens, and the size and quantity of the β phase increase. Since the β phase has better plasticity than the α phase, its increased content significantly improves the alloy's plasticity, manifested as an increase in elongation at break. Simultaneously, the formation of the α phase at grain boundaries blurs the original β grain boundaries, reducing the material's anisotropy and further optimizing mechanical properties. However, excessively high aging temperatures lead to coarsening of the α+β dual-phase structure, eliminating the twinned structure generated during aging, and producing coarse β phases, resulting in a decrease in alloy strength. Overall, direct aging treatment achieves an effective balance between strength and plasticity by controlling the morphology and size of the microstructure, providing a simple and efficient method for performance optimization of SLM-manufactured Ti-6Al-4V titanium alloys.

[0119] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A direct aging treatment process for SLM-formed Ti-6Al-4V alloy, characterized in that, Includes the following steps: S1. Using titanium alloy powder as raw material, SLM forming was used to obtain a shaped Ti-6Al-4V alloy sample; S2. Place the SLM-formed Ti-6Al-4V alloy sample, either as a whole plate or separated, into a vacuum heat treatment furnace for direct aging treatment. S3. After aging, the titanium alloy sample is cooled in the furnace or air-cooled to room temperature and then taken out to obtain the SLM titanium alloy sample after direct aging treatment.

2. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 1, characterized in that, The chemical composition of the titanium alloy powder in step S1 includes the following components by mass percentage: Al: 5.50-6.75%, V: 3.5-4.5%, Fe≤0.3%, O≤0.15%, C≤0.08%, N≤0.05%, H≤0.015%, with the balance being Ti, wherein the sum of the mass percentages of each component is 100%.

3. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 1, characterized in that, The process parameters of SLM in step S1 are as follows: laser power 280W, scanning speed 1300mm / s, scanning spacing 120μm, strip width 10mm, overlap width 120μm, layer thickness 40μm, spot diameter 100μm, rotation angle 67°, and preheating temperature 80℃.

4. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 3, characterized in that, The microstructure of the Ti-6Al-4V alloy sample formed under the specified process parameters contains α′ martensite.

5. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 1, characterized in that, The aging treatment temperature in step S2 is 560–650°C.

6. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 1, characterized in that, The effective time in step S2 is 4 to 8 hours.

7. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 1, characterized in that, The SLM-formed Ti-6Al-4V alloy obtained in step S3 has a microstructure containing an α+β dual-phase structure.

8. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 7, characterized in that, The α+β biphase structure is elongated, with an aspect ratio of 1:(6-10).

9. The direct aging treatment process for SLM-formed Ti-6Al-4V alloy according to claim 8, characterized in that, The width of the strip is 1 to 2 μm and the length is 6 to 12 μm.

10. An SLM-formed Ti-6Al-4V alloy obtained by the direct aging process as described in any one of claims 1-9.

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