A method for preparing laser formed high-strength titanium alloy based on mixed alloy powder

Abstract

The application discloses a kind of preparation methods of laser forming high-strength titanium alloy based on mixed alloy powder, to solve the problem such as high dependence of high-strength titanium alloy manufacturing on custom powder, poor strength and plasticity matching.The application determines metastable beta titanium alloy and duplex titanium alloy powder ratio based on multidimensional theory; by laser forming, the volume energy density is controlled to be 50-90J / mm 3 In-situ alloying is realized; by two-stage heat treatment, solid solution at 780-900 DEG C and aging at 400-600 DEG C, the heterogeneous structure of large-size primary alpha phase cluster and fine secondary alpha phase interweaving is constructed.The application significantly reduces the preparation cost, and realizes the high coordination of strength and plasticity.

Description

Technical Field

[0001] This invention relates to the fields of laser additive manufacturing technology and titanium alloy materials technology, and in particular to a method for preparing high-strength titanium alloys by laser forming based on mixed alloy powders. Background Technology

[0002] Titanium alloys, with their low density, high specific strength, excellent corrosion resistance, and good biocompatibility, have become indispensable key strategic materials in aerospace, marine engineering, energy and chemical engineering, and high-end biomedical fields. In recent years, laser additive manufacturing technology, especially laser selective melting and laser directional energy deposition technology, has broken through the physical limitations of traditional casting and forging processes in the preparation of complex thin-walled components and integral integrated structures, thanks to its significant advantages of high forming freedom, extremely fast cooling rate, and ability to achieve near-net-shape forming. This has greatly promoted the structural-functional integration of high-performance titanium alloy components.

[0003] However, despite the enormous potential of laser additive manufacturing technology in titanium alloy forming, the preparation of high-strength titanium alloys still faces numerous challenges in practical engineering applications. From the perspective of fundamental material design logic, existing high-strength titanium alloy composition designs often have significant limitations, typically relying excessively on a single metastable β-titanium alloy design theory for composition control. This single-dimensional design model often lacks sufficient predictive accuracy and matching depth when dealing with the complex thermophysical interactions during laser printing. Because the laser forming process involves extremely high cooling rates and cyclic thermal shocks, the elemental distribution within the molten pool, solid-state phase transformation kinetics, and non-equilibrium solidification microstructure evolution mechanisms are extremely complex. A single compositional design theory cannot achieve a precise match between elemental proportions and the formation of a two-phase microstructure during subsequent heat treatment. This directly leads to insufficient microstructural stability of the alloy under service conditions, making it difficult to construct a heterogeneous microstructure that simultaneously balances high dislocation resistance and high variable hysteresis at the microscopic level. Consequently, the material exhibits a significant imbalance between strength and plasticity in macroscopic properties; that is, to obtain extremely high tensile strength, critical elongation indicators must often be sacrificed, resulting in limited reliability of components under complex operating conditions.

[0004] At the raw material preparation level, existing technological approaches also face an irreconcilable conflict between cost and efficiency. Currently, high-strength titanium alloy powders for additive manufacturing heavily rely on customized pre-alloying powder preparation processes, such as vacuum induction melting gas atomization or plasma rotating electrode methods. While these processes can ensure macroscopic uniformity of composition, their production processes are cumbersome, powder preparation costs are high, and raw material acquisition cycles are extremely long. For novel alloys in the research and development stage, every minute adjustment to the composition means the need for small-batch, high-cost customized melting and powder spraying again. This "one composition, one powder" model severely restricts the efficiency of new material development and iteration. At the same time, although using commercially available mature powders for physical mixing is a potential cost-reduction and efficiency-enhancing solution, in practice, how to ensure that mixed powders of different compositions and densities achieve atomic-level uniform fusion under the action of a high-energy laser beam, and avoid local stress concentration or performance fluctuations caused by uneven mixing, has always been a deep-seated problem that plagues engineers in the field.

[0005] The more critical technical bottleneck lies in the fact that laser-formed titanium alloys, having undergone intense thermal stress cycling, often retain significant anisotropic structures and residual stresses within their interiors. Existing post-processing techniques often lack targeted control methods for this unique initial microstructure. Traditional one-step annealing or simple single-stage aging treatments easily lead to excessively fine and uniform precipitate distribution, or induce the formation of coarse needle-like structures, making it difficult to construct a heterogeneous synergistic strengthening system within the matrix, where large-sized primary phases and fine secondary phases intertwine. This uniformity at the microstructure level results in a lack of effective energy dissipation mechanisms during crack propagation, leading to a severe deficiency in ductility reserve while maintaining high strength.

[0006] In summary, how to achieve the scale gradient distribution and heterogeneous synergy of primary and secondary phases in the microstructure of high-strength titanium alloys, under the premise of ensuring low-cost raw material supply, and through multi-dimensional and precise composition design theory guidance combined with efficient laser forming and directional microstructure control technology, in order to overcome the inherent contradiction between strength and plasticity, has become an urgent technical problem to be solved in the fields of laser additive manufacturing and advanced metal materials. Summary of the Invention

[0007] The purpose of this invention is to propose a laser forming method for preparing high-strength titanium alloys based on mixed alloy powders, in order to overcome the technical problems existing in the additive manufacturing process of high-strength titanium alloys, such as the single dimension of composition design theory, high dependence on customized pre-alloyed powders, long raw material preparation cycle and high cost, and mismatch between the uniformity of the microstructure and the strength and plasticity of the formed components.

[0008] To achieve the above objectives, this invention proposes a method for preparing high-strength titanium alloys by laser forming based on mixed alloy powders, characterized by comprising the following steps: Step 1, Composition Design and Element Ratio Determination: The composition of the target alloy is calculated based on the multidimensional metastable β-titanium alloy design theory; The design theory includes phase transition mechanism-guided design based on valence electron concentration e / a, and design incorporating the β stability coefficient K. β The two-phase ratio control, β-phase stability control based on molybdenum equivalent [Mo]eq, and strength-toughness matching design based on d-electron theory Bo-Md diagram were achieved. By adjusting the mixing ratio, the e / a value of the mixed alloy was made between 4.0 and 4.15, the [Mo]eq value was made between 10.5 and 13.5, and the alloy composition point was located in the metastable β region of the Bo-Md diagram. Step 2, Mixed Powder Preparation: Commercial metastable β-titanium alloy powder and commercial duplex titanium alloy powder are selected as raw materials, wherein the mass fraction of metastable β-titanium alloy powder is 30% to 60%, and the remainder is duplex titanium alloy powder; the weighed powders are placed in a mechanical powder mixer for mixing, and the mixing process is carried out in an inert gas protection environment. After mixing, vacuum drying is performed. Step 3, Laser Printing: Using laser additive manufacturing equipment, the sample is formed on the pre-treated and preheated substrate; Step 4, two-stage heat treatment control: The titanium alloy sample after laser forming is subjected to a two-stage heat treatment of solution and aging; the first stage is solution treatment, in which the sample is heated to 780℃~900℃, held for 0.5h~2h and then air-cooled to room temperature, so as to construct a non-uniformly clustered primary α phase in the microstructure. The second stage is aging treatment, in which the sample is heated to 400℃~600℃, kept at that temperature for 3h~9h, and then air-cooled to room temperature to induce the precipitation of fine secondary α phase in the β matrix.

[0009] Furthermore, the stability of the β phase is controlled based on the molybdenum equivalent [Mo]eq: the molybdenum equivalent of the mixed alloy is calculated according to the formula [Mo]eq=[Mo]+0.2[Ta]+0.28[Nb]+0.4[W]+0.67[V]+1.25[Cr]+1.25[Ni]+1.7[Mn]+2.5[Fe](wt%), ensuring that the β phase remains stable during heat treatment and providing a high-quality parent phase for the uniform precipitation of the secondary α phase; the symbols of each element in the formula represent the mass percentage of that element in the mixed system; through the synergistic limitation of the valence electron concentration e / a and the molybdenum equivalent [Mo]eq, it is ensured that the initial microstructure of the alloy after laser forming is a supersaturated metastable β single-phase microstructure.

[0010] Furthermore, in step one, the Bo-Md diagram is controlled by calculating the average bond order Bo and the average d-electron orbital hybridization parameter Md of the mixed alloy. BoBo is used to characterize the bonding strength of covalent bonds between alloy atoms, and Md is used to characterize the interaction between electronegativity and atomic radius of alloy elements. By positioning the composition point in the metastable β region of the Bo-Md diagram, a thermodynamic basis is provided for the precipitation kinetics of heterogeneous structures in the subsequent step four.

[0011] Furthermore, in step two, the metastable β titanium alloy powder uses TB9 alloy powder, and the duplex titanium alloy powder uses TC4 alloy powder.

[0012] Furthermore, in step two, the particle diameter distribution range of both metastable β titanium alloy powder and dual-phase titanium alloy powder is controlled within 30μm to 210μm.

[0013] Furthermore, in step two, the mechanical powder mixer adopts a three-dimensional oscillating powder mixer, with the mixing speed set to 60 r / min to 240 r / min and the mixing time to 10 min to 40 min; the ambient vacuum degree during the mixing process is better than 10 Pa or high-purity argon is introduced to control the increase in oxygen content in the mixed powder to within 0.08 wt.%; the specific process of vacuum drying is as follows: drying at 80℃ to 100℃ for 4 h to 8 h to remove the moisture adsorbed on the powder surface.

[0014] Furthermore, in step three, the oxygen content in the printing chamber is controlled to decrease to below 0.1%, the laser power is set to 200W–500W, the laser scanning speed to 900mm / s–1300mm / s, the powder layer thickness to 0.08mm–0.07mm, the scanning spacing to 0.09mm–0.16mm, and the volumetric energy density to 50J / mm². 3 ~90J / mm 3 This allows the mixed powder to be alloyed in situ within the laser melting pool, and then cooled to room temperature with the furnace after forming. This parameter range can balance forming efficiency and billet density, avoiding defects such as pores and cracks.

[0015] Furthermore, the substrate is made of TC4 titanium alloy sheet. Before printing, the substrate surface is sandblasted to remove oxide scale and ultrasonically cleaned with anhydrous ethanol. Then, the substrate is preheated using the equipment's built-in heating system to reduce thermal stress and crack generation during the molding process.

[0016] Furthermore, in step four, the heating rate of the solution treatment is controlled at 5℃ / min to 15℃ / min; the temperature of the solution treatment is set in the upper region of the α+β two-phase region. By holding the temperature in this range, the primary α phase preferentially nucleates and grows in the solute-depleted region formed by in-situ alloying. The primary α phase ultimately exhibits a non-uniform clustered distribution in the microstructure, and its volume fraction is controlled at 15% to 35%, with the size range of a single primary α phase being 2μm to 10μm.

[0017] Furthermore, in step four, the heating rate of the aging treatment is controlled at 5℃ / min to 15℃ / min; by holding at 400℃ to 600℃ for 3h to 9h, the residual supersaturated metastable β matrix undergoes desolvation and decomposition, precipitating needle-like or plate-like secondary α phases, with the thickness of the secondary α phase controlled between 100nm and 1000nm; the high-strength titanium alloy obtained after the two-stage heat treatment has a microstructure composed of a bimodal heterostructure consisting of large-sized primary α phase clusters, fine secondary α phases, and residual β matrix. The room temperature tensile strength of this alloy is not less than 1350MPa, and the elongation is not less than 6%.

[0018] Compared with the prior art, the advantages of the present invention are: 1. The component design possesses a high degree of scientific rigor and synergy. This invention abandons the traditional single-dimensional component design approach, utilizing e / a and K... β The design theory was deeply cross-validated across four dimensions: [Mo]eq, Bo-Md, and [Mo-Md]. This multi-dimensional design paradigm can not only accurately predict the phase transformation path of the alloy in the extreme non-equilibrium solidification process of laser additive manufacturing, but also reserve a precise control window for the microstructure evolution during subsequent heat treatment. Through the design at the electronic structure level, the chemical homogeneity and thermodynamic stability of the mixed powder after in-situ alloying in the molten pool were ensured, providing solid theoretical support for the development of high-performance titanium alloys.

[0019] 2. This invention achieves efficient raw material supply and low cost. It cleverly utilizes two commercially available titanium alloy powders (such as TB9 and TC4) as precursors, replacing the expensive and time-consuming customized pre-alloying powder preparation process with physical mixing. This method significantly accelerates the iteration speed of new titanium alloy composition development and reduces experimental and production costs. Simultaneously, the powder particle size distribution and mixing process defined by this invention ensure smooth powder spreading and melting stability of the mixed system in additive manufacturing equipment, solving the technical challenge of segregation of powders with different compositions.

[0020] 3. A heterogeneous microstructure with superior mechanical properties was constructed. The core technological contribution of this invention lies in inducing a bimodal heterogeneous microstructure within the titanium alloy through precise control of laser printing parameters and a two-stage heat treatment process. The critical solution treatment described in step four can directionally cultivate large-sized primary α phases in a clustered distribution. These phase regions can effectively disperse stress concentration during tensile deformation, significantly improving the material's plasticity reserve through a multi-stage deformation-induced mechanism. The subsequent low-temperature long-term aging treatment precipitates nanoscale secondary α phases densely in the metastable β matrix, producing a significant precipitation strengthening effect. Thus, the material maintains ultra-high strength while still possessing good fracture toughness and ductility, successfully overcoming the technical bottleneck of the incompatibility between strength and plasticity in titanium alloys.

[0021] 4. The process flow exhibits strong engineering operability and repeatability. The laser printing parameter range and heat treatment temperature gradient involved in this invention have been precisely optimized, making it compatible with various mainstream metal additive manufacturing equipment. The entire preparation process does not involve complex special equipment, has clear parameter boundaries, and is easy to implement on an industrial scale. It has a significant promoting effect on the low-cost, high-performance manufacturing of large, complex, and high-strength titanium alloy structural components in the aerospace field. Attached Figure Description

[0022] Figure 1 The tensile strength diagrams are for Example 1, Comparative Example 1, and Comparative Example 2. Figure 2 Low-magnification microstructure of the titanium alloy part in the heat-treated state provided in Example 1; Figure 3 High-magnification microstructure of the titanium alloy part in the heat-treated state provided in Example 1; Figure 4 XRD results of the microstructure of the titanium alloy part in the heat-treated state provided in Example 1; Figure 5 Low-magnification microstructure of the titanium alloy part in the heat-treated state provided for Comparative Example 1; Figure 6 High-magnification microstructure of the titanium alloy part in the heat-treated state provided for Comparative Example 1. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0024] Example 1 This embodiment includes the following steps: The design of mixed powder ratios was carried out using the metastable β-titanium alloy design theory. First, based on the phase transition mechanism guided by the valence electron concentration e / a, the weighted values ​​of the number of valence electrons and atomic fractions of each element in TB9 and TC4 powders were calculated, and the e / a value was determined to be 4.05. Secondly, the atomic fraction ratio of α-stable elements and β-stable elements is quantified by the β stability coefficient to obtain K. β The value is 2.4; then, according to the formula: [Mo]eq=[Mo]+0.2[Ta]+0.28[Nb]+0.4[W]+0.67[V]+1.25[Cr]+1.25[Ni]+1.7[Mn]+2.5[Fe](wt%) The molybdenum equivalent of the hybrid alloy was calculated to ensure that [Mo]eq was greater than 10.5. Finally, the bond order Bo was calculated to be 2.4 and the d-electron orbital hybridization parameter Md was calculated to be 2.3 using the d-electron theory Bo-Md diagram, thus completing the composition design.

[0025] Commercially available metastable β-titanium alloy TB9 powder and duplex titanium alloy TC4 powder were selected as raw materials. TB9 powder consisted of spherical particles with good sphericity and a particle size range of 30–210 μm, accounting for 50%–60% of the total mixed powder by mass. TC4 powder also consisted of spherical particles with good sphericity and a particle size range of 30–210 μm, accounting for 40%–50% of the total mixed powder by mass.

[0026] Table 1

[0027] The two types of titanium alloy powders were added to a planetary mixer, and the mixer speed was set to 150 r / min for 25 min for mechanical mixing.

[0028] After the powder is mixed, the mixed powder is collected by a powder collector and placed in a vacuum drying oven at 80°C for 6 hours. Then it is sealed and stored for later use. Dry storage avoids the powder absorbing moisture and affecting the density of subsequent laser forming.

[0029] Titanium alloy laser printing was performed using the EOS-290 laser printing equipment. First, the surface of the TC4 titanium alloy substrate and the inside of the printing chamber were cleaned with anhydrous ethanol to remove impurities and oxide layers. Then, the substrate was mounted and fixed on the worktable.

[0030] The dried mixed powder is placed into the powder supply hopper of the equipment. The working distance between the scraper and the substrate is adjusted to 0.1 mm. The heights of the powder supply hopper and the powder collection hopper are adjusted to ensure uniform powder layer thickness. The specific process of vacuum drying is as follows: drying at 100℃ for 8 hours to remove moisture adsorbed on the powder surface.

[0031] High-purity argon gas is introduced into the printing chamber and continuously ventilated until the oxygen content in the chamber drops below 0.08% to prevent the titanium alloy from oxidizing during the high-temperature forming process.

[0032] Start the substrate preheating program, raise the substrate temperature to 100°C and hold for 10 minutes to reduce the accumulation of thermal stress during the molding process.

[0033] Start the laser printing program and set the printing parameters as follows: laser power 350W, toner lift height 0.05mm, overlap 0.12mm, scanning speed 1100mm / s, energy density 70J / mm². 3 The titanium alloy billet is printed according to the preset three-dimensional model.

[0034] After printing is completed, the titanium alloy sample is removed after cooling to room temperature along with the substrate, resulting in a printed titanium alloy sample. An electrical discharge machining (EDM) machine is then used to separate the sample from the substrate.

[0035] The printed sample was treated using a two-stage heat treatment process: First, the heat treatment furnace was heated to 820°C. After the temperature stabilized, the sample was placed in the furnace and kept at that temperature for 1 hour. Then, the sample was taken out and air-cooled to room temperature. Next, the heat treatment furnace was heated to 600°C. The cooled sample was placed back into the furnace and kept at that temperature for 6 hours. Finally, it was air-cooled to room temperature.

[0036] The heating rate of the solution treatment was controlled at 10℃ / min; the temperature of the solution treatment was set in the upper region of the α+β two-phase region. By holding the temperature in this range, the primary α phase preferentially nucleates and grows in the solute-depleted region formed by in-situ alloying. The primary α phase eventually exhibits a non-uniform clustered distribution in the microstructure, and its volume fraction is controlled at 25%, with the size of a single primary α phase being 6μm.

[0037] The aging treatment heating rate was controlled at 10℃ / min; by holding at 600℃ for 9h, the residual supersaturated metastable β matrix underwent desolvation and precipitation, resulting in needle-like or plate-like secondary α phases, the thickness of which was controlled at 600nm; the high-strength titanium alloy obtained after the two-stage heat treatment had a microstructure consisting of a bimodal heterostructure composed of large primary α phase clusters, fine secondary α phases, and residual β matrix.

[0038] After heat treatment, a high-strength titanium alloy specimen was obtained. The specimen was clamped on a CNC lathe and machined into a rod-shaped tensile specimen according to the ASTM-E8M standard, ensuring that the surface roughness Ra of the specimen was ≤0.8μm. Finally, room temperature tensile mechanical property tests were performed on a universal testing machine, and the stress-strain curve and related performance data were recorded according to the standard requirements.

[0039] Comparative Example 1: This comparative example includes the following steps: The only difference between this comparative example and Example 1 is the heat treatment regime. All other process steps, including the selection, particle size, and mixing ratio of TB9 and TC4 powders, mixing speed and time, substrate treatment for laser printing, oxygen content control, laser power, scanning speed, and other parameters, are completely consistent with Example 1.

[0040] After printing, the titanium alloy billet is subjected to a single-stage aging treatment. The heat treatment process of this comparative example is as follows: First, the heat treatment furnace is heated to 550°C. After the temperature stabilizes, the sample is placed in the furnace and kept at that temperature for 7 hours. Then, the sample is taken out and air-cooled to room temperature.

[0041] After heat treatment, a titanium alloy specimen for Comparative Example 1 was obtained. The specimen was clamped on a CNC lathe and machined into a rod-shaped tensile specimen according to the ASTM-E8M standard, ensuring that the surface roughness Ra of the specimen was ≤0.8μm. Finally, room temperature tensile mechanical properties were tested on a universal testing machine, and the stress-strain curve and related performance data were recorded according to the standard requirements.

[0042] Comparative Example 2: This comparative example includes the following steps: The comparative printing process steps, including the selection of TB9 and TC4 powders, particle size, mixing ratio, powder mixing speed and time, substrate treatment for laser printing, oxygen content control, laser power, scanning speed, and all other parameters are completely consistent with those in Example 1.

[0043] After printing, a titanium alloy specimen for Comparative Example 2 was obtained. The specimen was clamped on a CNC lathe and machined into a rod-shaped tensile specimen according to the ASTM-E8M standard, ensuring that the surface roughness Ra of the specimen was ≤0.8μm. Finally, room temperature tensile mechanical property tests were performed on a universal testing machine, and the stress-strain curve and related performance data were recorded according to the standard requirements.

[0044] The high-strength titanium alloy sample prepared in Example 1 was compared with the titanium alloy parts prepared in Comparative Examples 1 and 2. The results are shown in Table 2.

[0045] Table 2 Sample tensile strength elongation Example 1 1360Mpa 7.5% Comparative Example 1 1560Mpa 3.5% Comparative Example 2 875Mpa 14.5%

[0046] Figure 1 These are tensile strength diagrams of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention. Figure 1 It can be seen that Comparative Example 1, which underwent a single aging process, has higher strength, while Comparative Example 2 in the printed state has a higher elongation than Example 1 but lower tensile strength, making it unusable in practice.

[0047] Example 1 employs a two-stage heat treatment process: critical solution treatment followed by aging at 600°C. Figure 2This is a low-magnification microstructure image of the high-strength titanium alloy sample prepared in Example 1 of this invention. Figure 3 This is a high-magnification microstructure image of the high-strength titanium alloy sample prepared in Example 1 of this invention. Figure 2 Figure 3 It can be seen that by controlling the precipitation of primary α phases of 2–10 μm at the critical solution temperature, some of the primary α phases are distributed in clusters. After aging, secondary α phases of 100–1000 nm are uniformly distributed, forming a heterogeneous structure with synergistic strengthening of two phases. Therefore, it meets the performance requirements of tensile strength >1350 MPa and elongation >6%. Figure 4 This is the XRD characterization image of the high-strength titanium alloy sample prepared in Example 1 of this invention. Figure 4 It is evident that in the printed state of Example 1, only a single β-structure is formed, providing a high-quality parent phase for subsequent heat treatment and two-phase control. This highlights the innovation of the design and preparation process of this invention.

[0048] Comparative Example 1 only underwent aging treatment at 550℃ while extending the aging time. Figure 5 This is a low-magnification microstructure image of the titanium alloy sample prepared in Comparative Example 1 of this invention. Figure 6 This is a high-magnification microstructure image of the titanium alloy sample prepared in Comparative Example 1 of this invention. Due to the lack of a critical solid solution step, the size and distribution of the primary α phase cannot be controlled. The secondary α phase is too fine due to the low aging temperature. While the strength is significantly improved, the plasticity is significantly deteriorated. Moreover, a single aging heat treatment is not enough to eliminate the internal defects remaining in the printed state, resulting in insufficient plasticity. This proves that critical solid solution is the core step to achieve two-phase control.

[0049] Comparative Example 2 is in the printed state. Since it has not undergone heat treatment control, the internal thermal stress and micro-pore defects remaining during the printing process cannot be eliminated, resulting in significantly insufficient strength, which is far below the actual engineering requirements for high-strength titanium alloys and cannot meet the practical application. This confirms that the two-stage heat treatment process of the present invention is the key to improving the strength of titanium alloys and achieving a synergistic match between strength and plasticity.

[0050] This invention combines four design methods to rapidly develop and prepare new titanium alloys with low cost based on existing commercial titanium alloy powders. After two-stage heat treatment, a biphase heterogeneous structure is accurately obtained, effectively producing a high-strength titanium alloy with good strength and plasticity.

[0051] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A method for preparing high-strength titanium alloys by laser forming based on mixed alloy powders, characterized in that, Includes the following steps: Step 1, Composition Design and Element Ratio Determination: The composition of the target alloy is calculated based on the multidimensional metastable β-titanium alloy design theory; The design theory includes phase transition mechanism-guided design based on valence electron concentration e / a, combined with the β stability coefficient K. β The two-phase ratio control, β-phase stability control based on molybdenum equivalent [Mo]eq, and strength-toughness matching design based on d-electron theory Bo-Md diagram were achieved. By adjusting the mixing ratio, the e / a value of the mixed alloy was made between 4.0 and 4.15, the [Mo]eq value was made between 10.5 and 13.5, and the alloy composition point was located in the metastable β region of the Bo-Md diagram. Step 2, Mixed Powder Preparation: Commercial metastable β-titanium alloy powder and commercial duplex titanium alloy powder are selected as raw materials, wherein the mass fraction of metastable β-titanium alloy powder is 30% to 60%, and the remainder is duplex titanium alloy powder; the weighed powders are placed in a mechanical powder mixer for mixing, and the mixing process is carried out in an inert gas protection environment. After mixing, vacuum drying is performed. Step 3, Laser Printing: Using laser additive manufacturing equipment, the sample is formed on the pre-treated and preheated substrate; Step 4, two-stage heat treatment control: The titanium alloy sample after laser forming is subjected to a two-stage heat treatment of solution and aging; the first stage is solution treatment, in which the sample is heated to 780℃~900℃, held for 0.5h~2h and then air-cooled to room temperature, so as to construct a non-uniformly clustered primary α phase in the microstructure. The second stage is aging treatment, in which the sample is heated to 400℃~600℃, kept at that temperature for 3h~9h, and then air-cooled to room temperature to induce the precipitation of fine secondary α phase in the β matrix.

2. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, Stability control of the β phase based on molybdenum equivalent [Mo]eq: The molybdenum equivalent of the mixed alloy is calculated according to the formula [Mo]eq=[Mo]+0.2[Ta]+0.28[Nb]+0.4[W]+0.67[V]+1.25[Cr]+1.25[Ni]+1.7[Mn]+2.5[Fe](wt%) to ensure that the β phase remains stable during heat treatment, providing a high-quality parent phase for the uniform precipitation of the secondary α phase; the symbols of each element in the formula represent the mass percentage of that element in the mixed system; by synergistically limiting the valence electron concentration e / a and the molybdenum equivalent [Mo]eq, it is ensured that the initial microstructure of the alloy after laser forming is a supersaturated metastable β single-phase microstructure.

3. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, In step one, the Bo-Md diagram manipulation is achieved by calculating the average bond order Bo and the average d-electron orbital hybridization parameter Md of the mixed alloy. BoBo is used to characterize the bonding strength of covalent bonds between alloy atoms, and Md is used to characterize the interaction between electronegativity and atomic radius of alloy elements. By positioning the composition point in the metastable β region of the Bo-Md diagram, a thermodynamic basis is provided for the precipitation kinetics of heterogeneous structures in the subsequent step four.

4. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, In step two, the metastable β titanium alloy powder is TB9 alloy powder, and the dual-phase titanium alloy powder is TC4 alloy powder.

5. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, In step two, the particle diameter distribution range of both the metastable β titanium alloy powder and the dual-phase titanium alloy powder is controlled within 30μm to 210μm.

6. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, In step two, the mechanical powder mixer is a three-dimensional oscillating powder mixer, with the mixing speed set to 60 r / min to 240 r / min and the mixing time to 10 min to 40 min. The ambient vacuum degree during the mixing process is better than 10 Pa or high-purity argon is introduced to control the increase in oxygen content in the mixed powder to within 0.08%. The specific process of the vacuum drying treatment is as follows: drying at 80℃ to 100℃ for 4 h to 8 h to remove the moisture adsorbed on the powder surface.

7. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, In step three, the oxygen content in the printing chamber is controlled to decrease to below 0.1%, the laser power is set to 200W–500W, the laser scanning speed to 900mm / s–1300mm / s, the powder layer thickness to 0.08mm–0.07mm, the scanning interval to 0.09mm–0.16mm, and the volumetric energy density to 50J / mm². 3 ~90J / mm 3 This allows the mixed powder to be alloyed in situ within the laser melting pool, and then cooled to room temperature with the furnace after forming. This parameter range can balance forming efficiency and billet density, avoiding defects such as pores and cracks.

8. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, The substrate is made of TC4 titanium alloy sheet. Before printing, the substrate surface is sandblasted to remove oxide scale and ultrasonically cleaned with anhydrous ethanol. Then, the substrate is preheated using the equipment's built-in heating system to reduce thermal stress and cracking during the molding process.

9. The method for preparing high-strength titanium alloy by laser forming based on mixed alloy powder according to claim 1, characterized in that, In step four, the heating rate of the solution treatment is controlled at 5℃ / min to 15℃ / min; the temperature of the solution treatment is set in the upper region of the α+β two-phase region. By holding the temperature in this range, the primary α phase preferentially nucleates and grows in the solute-depleted region formed by in-situ alloying. The primary α phase finally formed exhibits a non-uniform clustered distribution in the microstructure, and its volume fraction is controlled at 15% to 35%. The size range of a single primary α phase is 2μm to 10μm.

10. The method for preparing high-strength titanium alloys by laser forming based on mixed alloy powders according to any one of claims 1 or 9, characterized in that, In step four, the heating rate of the aging treatment is controlled at 5℃ / min to 15℃ / min; by holding at 400℃ to 600℃ for 3h to 9h, the residual supersaturated metastable β matrix undergoes desolvation and decomposition, precipitating needle-like or plate-like secondary α phases, the thickness of which is controlled between 100nm and 1000nm; the high-strength titanium alloy obtained after the two-stage heat treatment has a microstructure composed of a bimodal heterostructure consisting of large primary α phase clusters, fine secondary α phases, and residual β matrix, and the room temperature tensile strength of the alloy is not less than 1350MPa and the elongation is not less than 6%.

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