High-strength and high-toughness NiCoCr medium-entropy alloy prepared from LPBF and preparation process of high-strength and high-toughness NiCoCr medium-entropy alloy

Abstract

The invention discloses a high-strength and high-toughness NiCoCr medium-entropy alloy prepared from LPBF and a preparation process of the high-strength and high-toughness NiCoCr medium-entropy alloy, and belongs to the technical field of metal materials and additive manufacturing. In the preparation process, NiCoCr alloy powder is prepared through supersonic gas atomization, and a Ti / Al enrichment layer is formed on the surface of the powder; then LPBF dual-energy field collaborative forming is carried out, main forming laser constructs a continuous dislocation cell skeleton, and auxiliary modulation laser induces high-density dislocation and solute nano-clusters; and finally, carrying out aging treatment at 700-800 DEG C for 1-2 hours, and directionally inducing precise nucleation of the minimum gamma'phase. According to the method, a 10nm extremely small precipitated phase which is difficult to obtain by a traditional forged NiCoCr medium-entropy alloy is prepared, the technical bottlenecks of insufficient stability of dislocation cells, disordered nucleation of a strengthening phase and unbalanced toughness in the prior art are solved, the prepared alloy has excellent strength and toughness, the process is simple and controllable, the industrialization potential is remarkable, and the method is suitable for industrial production. The method is suitable for severe service environments such as aerospace and high-end equipment.

Description

Technical Field

[0001] This invention relates to a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF and its preparation process, specifically to a NiCoCr medium-entropy alloy prepared by LPBF with dislocation cell-minimal γ′ phase synergistic reinforcement and its preparation method. It is particularly suitable for achieving synergistic optimization of alloy structure and performance through a combination of additive manufacturing and precise structural control. This invention belongs to the field of metallic materials and additive manufacturing technology. Background Technology

[0002] NiCoCr medium-entropy alloys, as face-centered cubic multi-principal element alloys, possess excellent plasticity, fracture toughness, and corrosion resistance, and have broad application prospects in high-end equipment fields such as aerospace and energy power. Laser powder bed melting (LPBF) additive manufacturing technology, based on the "discrete-stacking" forming principle, can rapidly achieve the direct manufacturing of complex structural components, and through extremely rapid solidification (10⁻⁶ m / s²), it can achieve this. 3 -10 6 The K / s effect forms a submicron-scale dislocation cellular substructure, providing a good foundation for the material's mechanical properties.

[0003] Traditional forged NiCoCr medium-entropy alloys struggle to achieve the 10 nm micro-γ′ phase, as the coarse γ′ phase, while increasing strength, severely impacts the material's toughness. However, current technologies still face significant bottlenecks in the preparation and performance control of LPBF (Limited Partial Bored Fiber) of NiCoCr medium-entropy alloys, with γ′ coarsening behavior remaining difficult to control even after aging treatment. Traditional gas-atomized powders have a uniform composition and structure with evenly distributed solute atoms, resulting in a lack of targeted reinforcement of dislocation cell walls after LPBF forming, leading to insufficient structural stability. Single laser scanning can only form the basic dislocation cell skeleton, resulting in low cell wall dislocation density and ineffective solute atom enrichment. Subsequent heat treatment easily leads to dislocation cell deformation and disordered nucleation of the strengthening phase, making precise matching of structure and strengthening phase difficult. Conventional strengthening schemes tend to cause an imbalance between strength and toughness, failing to meet the stringent requirements of high-end equipment for comprehensive material performance. Therefore, developing a preparation method that achieves dislocation cell stabilization and precise nucleation matching of the strengthening phase through innovative end-to-end processes is crucial for promoting the engineering application of NiCoCr medium-entropy alloys. Summary of the Invention

[0004] This invention addresses the technical shortcomings of existing NiCoCr medium-entropy alloys, such as insufficient dislocation cell stability, disordered nucleation of strengthening phases, and imbalance between strength and toughness. It provides a method for preparing NiCoCr medium-entropy alloys with synergistic reinforcement of dislocation cells and minimal γ′ phases using LPBF. Through a complete chain innovation of powder preparation, forming process, and heat treatment, a stable dislocation cell framework and solute cluster precursor are first constructed, and then heat treatment induces precise nucleation of the strengthening phase, achieving excellent strength and toughness of the material.

[0005] Meanwhile, this invention provides a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF, which has a dual-scale synergistic strengthening structure of dislocation cellular framework and minimal γ′ precipitates.

[0006] Meanwhile, this invention provides an application of a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF in aerospace equipment and energy power equipment.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A preparation process for a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF includes the following steps: 1. Powder Preparation: A Ti / Al enriched layer is constructed on the powder surface using supersonic gas atomization technology. This design addresses the problem of insufficient dislocation cell stability caused by traditional homogeneous powders, providing a natural compositional basis for subsequent cell wall solute enrichment and enhanced phase nucleation after molding.

[0008] 2. LPBF Dual-Energy Field Synergistic Forming: A synergistic scanning mode of "main forming laser + secondary modulation laser" is designed. The main energy field rapidly constructs a continuous dislocation cellular framework through high-energy-density scanning and forms a solute-rich band on the cell wall using ultra-high cooling rate. The secondary energy field generates a "thermal oscillation" effect through low-power, high-speed in-situ rescanning, which does not trigger secondary melting but can induce high-density geometrically necessary dislocations and nanoscale clusters of solute atoms. The dislocation cell structure is stabilized and fixed before heat treatment, and metastable nucleation precursors are pre-placed, solving the problems of structural instability and nucleation site dispersion in single laser forming.

[0009] 3. Low-temperature short-time heat treatment: No pre-solution treatment is required. The dual-energy field formed billet is directly subjected to aging treatment at 700 ℃-800 ℃ for 1-2 h. The cell wall solute enrichment zone and metastable cluster precursor formed after powder forming are used to induce precise nucleation and diffuse distribution of the minimal γ′ phase. Finally, a dual-scale synergistic strengthening structure of "dislocation cytoskeleton-minimal γ′ precipitate phase" is formed, realizing the synergistic optimization of strength and toughness.

[0010] A preparation process for a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF specifically includes the following steps: (1) Preparation of NiCoCr alloy powder: ① Raw material pretreatment: Pure metal raw materials were prepared according to atomic percentage: Ni 49.21at%, Co 24.71at%, Cr 15.10at%, Al 2.48at%, Ti 3.23at%, Mo 2.93at%, W 1.36at%, Nb 0.43at%, Ta 0.55at, and the purity of the raw materials was ≥99.95at; after removing the oxide scale from the block raw materials, they were cut into small pieces of 8-12mm, and the filamentous raw materials were cut into segments of 15-20mm. They were dried in a vacuum drying oven at 120 ℃ for 4 h.

[0011] ② Vacuum induction melting: Add the pretreated raw materials to the crucible of the vacuum induction melting furnace, and evacuate to a vacuum level of ≤5×10. -3 Argon gas was introduced to a pressure of 0.3 MPa, and the temperature was increased to 1620 °C at a rate of 40 °C / min. The temperature was held for 40 min, and the mixture was stirred every 8 min to obtain a homogeneous alloy liquid.

[0012] ③ Supersonic gas atomization initial forming: The alloy liquid is introduced into the atomization chamber through a 6 mm guide tube, using argon gas with a purity ≥99.99% as the atomization medium. The atomization pressure is 5.0-5.5 MPa, and the atomization chamber pressure is 0.6 MPa. The alloy liquid breaks down and cools to form spherical powder. The core quantitative indicator of supersonic performance is that the atomized gas flow velocity reaches Mach 2.0-2.5, corresponding to a specific gas flow velocity of 680-850 m / s.

[0013] ④ Powder grading: After cyclone separation, the powder is passed through 150 mesh and 400 mesh standard sieves in sequence to screen out 15-53 μm powder, and then dried in a vacuum drying oven at 100 ℃ for 3 h to obtain NiCoCr alloy powder.

[0014] (2) LPBF dual-energy-field synergistic shaping: ① Powder pretreatment: Dry the powder in a vacuum drying oven at 120 ℃ for 6 h.

[0015] ② Molding atmosphere control: Using EOS M100 equipment, after the printing chamber is evacuated, argon gas is introduced to maintain the oxygen content ≤30 ppm, and the substrate of the molding cylinder is preheated to 100 ℃.

[0016] ③ Master forming laser scanning: The power was set to 280 W, the speed to 850 mm / s, the scanning spacing to 60 μm, and the layer thickness to 30 μm. A 6×6 mm island scanning strategy was adopted with an overlap rate of 12% to construct a continuous dislocation cytoskeleton and capture cell wall solutes.

[0017] ④ Sub-modulated laser scanning: After the main scan of each layer is completed, in-situ rescanning is performed within 30 seconds at a power of 90 W, a speed of 1600 mm / s, and a defocusing amount of +3.5 mm to induce high-density geometrically necessary dislocations and solute nanoclusters to form a metastable precursor structure.

[0018] (3) Short-time heat treatment: The formed billet is placed in a box furnace and held at 700℃-800℃ for 1-2 h and then naturally air-cooled to room temperature to induce the formation of extremely small γ′ phase nuclei of less than 10 nm to obtain the target alloy.

[0019] Preferably, in step (2), the cooling rate of the main forming laser scanning is ≥1×10⁻⁶. 4 K / s, the sub-modulated laser scanning only generates thermal oscillations and does not cause secondary melting of the powder.

[0020] Preferably, in step (3), no presolution treatment is required, and low-temperature aging is performed directly to avoid damage to the dislocation cytoskeleton and metastable precursor structure.

[0021] The NiCoCr medium-entropy alloy (i.e., a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF) obtained by the preparation method of the present invention has a dual-scale synergistic structure of "dislocation cellular framework-minimal γ′ precipitate phase": the dislocation cellular framework is a continuous submicron-scale structure with an average size of 450-500 nm and a geometrically necessary dislocation density of ≥1.8×10⁻⁶. 11 m -2 The nanocluster precursors are 5-10 nm in size and are uniformly distributed on the cell wall, providing sites for the nucleation of the γ′ phase. The extremely small γ′ precipitates have an L12 ordered structure with an average particle size of less than 10 nm and are coherent with the γ matrix.

[0022] Application of a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF in aerospace equipment and energy power equipment.

[0023] The beneficial effects of this invention are: Compared with the prior art, the present invention has the following significant advantages: 1. This invention utilizes supersonic gas atomization technology to form a Ti / Al enriched layer on the powder surface. After forming, it directly transforms into a cell wall solute enrichment zone, which not only enhances the stability of dislocation cells, but also provides uniformly distributed high-concentration solute sites for the γ′ phase nucleus during the heat treatment stage, ensuring the uniformity and dispersion of the enhanced phase nucleus from the source.

[0024] 2. Dual energy field regulation to achieve structural stability and precursor pre-positioning: High-density geometrically essential dislocations induced by the sub-modulated laser significantly improve the structural stability of the dislocation cell wall and avoid dislocation cell recovery or deformation during heat treatment; at the same time, the solute nanocluster precursors formed provide clear orientation sites for the γ′ phase nucleus, solving the problems of disorder and coarsening of the enhanced phase nucleus in traditional processes.

[0025] 3. Precise heat treatment induces the construction of a dual-scale synergistic strengthening structure: Aging treatment only triggers the nucleation and moderate growth of the γ′ phase, without destroying the already stable dislocation cellular framework. The resulting dual-scale synergistic structure achieves a functional division of "load-nucleation-strengthening": the dislocation cellular framework ensures the coordination of toughness and deformation, the nanocluster precursors ensure uniform nucleation of the strengthening phase, and the extremely small γ′ precipitates achieve efficient strengthening at the atomic scale. This results in an alloy room temperature yield strength of approximately 1300 MPa (preferably 1284-1332 MPa), a tensile strength of approximately 1600 MPa (preferably 1571-1641 MPa), a fracture elongation ≥18% (preferably 18.1-20.4%), and a plane strain fracture toughness (KIC) of 121-135 MPa•m. 1 / 2 This achieves a simultaneous improvement in both strength and toughness.

[0026] This invention discloses a NiCoCr medium-entropy alloy prepared by LPBF with synergistic reinforcement of dislocation cell-minimal γ′ phase and its preparation process, innovatively constructing a dual-scale synergistic reinforcement structure of "dislocation cell skeleton-minimal γ′ precipitate phase". The preparation process involves preparing NiCoCr alloy powder via supersonic gas atomization, forming a Ti / Al enriched layer on the powder surface; then, LPBF dual-energy field synergistic shaping is performed, with the main forming laser constructing a continuous dislocation cell skeleton and the secondary modulated laser inducing high-density dislocations and solute nanoclusters; finally, aging treatment at 700-800 ℃ for 1-2 h is used to directionally induce precise nucleation of the minimal γ′ phase. This method produces a 10 nm miniature precipitate phase that is difficult to obtain in traditional forged NiCoCr medium-entropy alloys. It overcomes the technical bottlenecks of insufficient dislocation cell stability, disordered nucleation of strengthening phases, and imbalance between strength and toughness in existing technologies. The prepared alloy has a room temperature yield strength of approximately 1300 MPa, a tensile strength of approximately 1600 MPa, a fracture elongation ≥18%, and a plane strain fracture toughness (KIC) of 121-135 MPa•m. 1 / 2 It combines excellent strength and toughness, has a simple and controllable process, and has significant industrialization potential, making it suitable for harsh service environments such as aerospace and high-end equipment. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention, wherein (a) is an EOS M100 additive manufacturing equipment; and (bd) is a schematic diagram of the length, width and height of a NiCoCr alloy block with a printing size of 50×12×10 mm. Figure 2 The images shown are three-dimensional EBSD images of samples from this invention, wherein (a) is a three-dimensional EBSD image of sample from Example 1; and (b) is a three-dimensional EBSD image of sample from Example 2. Figure 3 High-angle annular dark field image (HAADF) of dislocation cells in samples of the present invention, wherein (a) is a high-angle annular dark field image (HAADF) of dislocation cells in sample of Example 1; and (b) is a high-angle annular dark field image (HAADF) of dislocation cells in sample of Example 2. Figure 4 The diagram shows a comparison of the strength and toughness of the alloy in Example 1 of this invention with other alloys. The strength and toughness matching is significantly better than that of steel, titanium alloy, aluminum alloy and L12 reinforced alloy. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of 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 skilled in the art without creative effort should fall within the scope of protection of the present invention. Example 1

[0029] A preparation process for a dislocation cell-minimal γ′ phase synergistically strengthened NiCoCr medium-entropy alloy prepared by LPBF, the specific steps of which are as follows: (1) Preparation of NiCoCr alloy powder: ① Raw material pretreatment: The raw materials were proportioned according to atomic percentage: Ni 49.21at%, Co 24.71at%, Cr 15.10at%, Al 2.48at%, Ti 3.23at%, Mo 2.93at%, W 1.36at%, Nb 0.43at%, Ta 0.55at, and the purity of the raw materials was ≥99.95at; the block raw materials were cut into 10 mm pieces, and the filamentous raw materials were cut into 18 mm segments, and vacuum dried at 120 ℃ for 4 h; ② Vacuum induction melting: The raw material is added to the alumina crucible of the vacuum induction melting furnace, and a vacuum of 3×10⁻⁶ is drawn. -3 Pa, argon gas was introduced to 0.3 MPa, the temperature was increased to 1620 ℃ at 40 ℃ / min, and the temperature was held for 40 min. The mixture was stirred once every 8 min to obtain a uniform alloy liquid. ③ Supersonic gas atomization initial forming: The alloy liquid is introduced into the atomization chamber through a 6 mm guide tube. The purity of the atomizing argon gas is 99.99%, the atomization pressure is 5.2 MPa, the pressure in the atomization chamber is 0.6 MPa, and the cooling rate is approximately 2.3 × 10⁻⁶. 4K / s, forming spherical powder, the core quantitative indicator of supersonic speed is that the atomized gas flow velocity reaches Mach 2.2 (Ma), which corresponds to a specific gas flow velocity of 750 m / s; ④ Powder classification: After cyclone separation, the powder is passed through 150 mesh and 400 mesh standard sieves in sequence to screen out 15-53μm powder. The powder is then vacuum dried at 100 ℃ for 3 h. The final powder sphericity is 0.95, D50=36.2μm, and the Ti / Al enrichment of the shell layer is 5.2 times that of the core layer. (2) LPBF dual-energy-field synergistic shaping: ① Powder pretreatment: Dry the powder in a vacuum drying oven at 120 ℃ for 6 h; ② Molding atmosphere control: Using EOS M100 equipment, the oxygen content in the printing chamber is 28 ppm, and the substrate of the molding cylinder is preheated to 100 ℃; ③ Main forming laser scanning: power 280 W, speed 850 mm / s, scanning spacing 60 μm, layer thickness 30 μm, 6×6mm island scanning strategy, overlap rate 12%; ④ Sub-modulated laser scanning: power 90 W, speed 1600 mm / s, defocusing amount +3.5 mm, with in-situ rescanning performed 25 s after the main scan; finally obtaining the following... Figure 1 The 50×12×10mm preform shown has a density of 99.92%, an average dislocation cell size of 478 nm, and a geometrically necessary dislocation density of 2.1×10⁻⁶. 11 m -2 Ti-Al nanocluster precursors (size 5-10 nm) are formed at the cell wall. (3) Short-time heat treatment: The formed billet is held in a box furnace at 780 °C for 2 h to induce the nucleation of the tiny γ′ phase (less than 10 nm) on the nanocluster precursor to obtain the target NiCoCr medium-entropy alloy.

[0030] like Figure 2 As shown, Figure 2 In (a), the cross section perpendicular to the construction direction is characterized by equiaxed or irregular polygonal grains. Overall, the grain orientation distribution is relatively random, and no strong single-crystal texture is formed, thus avoiding anisotropic defects.

[0031] like Figure 3 As shown, Figure 3 In (a), the grains are densely packed with a honeycomb-like network structure. This cellular structure is actually composed of high-density dislocation entanglements and solute atoms (such as Ti and Mo with large atomic radii) enriched at the cell walls. This allows deformation to be better transferred between different grains, significantly improving the toughness coordination ability, thereby enhancing the toughness of the material.

[0032] like Figure 4 As shown, the NiCoCr medium-entropy alloy obtained in this embodiment is compared with other existing alloys in terms of strength and toughness. The strength and toughness matching of this embodiment is significantly better than that of steel, titanium alloy, aluminum alloy and L12 reinforced alloy.

[0033] This embodiment demonstrates the application of a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF in aerospace equipment and energy power equipment. Example 2

[0034] The difference between this embodiment and the method of preparing a dislocation cell-minimal γ′ phase synergistically strengthened NiCoCr medium-entropy alloy prepared by LPBF and the method of preparation is that the formed billet is held at 700°C for 2 h in a box furnace during the low-temperature short-time heat treatment.

[0035] like Figure 2 As shown, Figure 2 In (b), on the cross section perpendicular to the construction direction, the grains still exhibit an irregular polygonal or approximately equiaxed distribution, thus avoiding anisotropic defects.

[0036] like Figure 3 As shown, Figure 3 In (b), a clear and continuous dislocation cell network still exists in the sample, and its spatial scale is basically consistent with that of Example 1, further confirming that the dislocation cell structure has been preserved after aging. Example 3

[0037] The only difference between this embodiment and Embodiment 1 is that: In the preparation of NiCoCr alloy powder, during raw material pretreatment, the oxide scale on the blocky raw material is removed and it is cut into 8mm pieces, and the filamentous raw material is cut into 15mm segments. During vacuum induction melting, the vacuum is increased to 5×10⁻⁶. -3 Pa. During the initial formation of supersonic gas atomization, the atomization pressure is 5.0 MPa, and the atomizing gas flow velocity reaches Mach 2.0 (Ma), corresponding to a specific gas flow velocity of 680 m / s.

[0038] When LPBF is formed using dual energy fields, the oxygen content is maintained at 30 ppm during forming atmosphere control.

[0039] For short-time heat treatment, hold at 700℃ for 1 hour. Example 4

[0040] The only difference between this embodiment and Embodiment 1 is that: In the preparation of NiCoCr alloy powder, during raw material pretreatment, the oxide scale on the blocky raw material is removed and it is cut into 12mm pieces, and the filamentous raw material is cut into 20mm segments. During vacuum induction melting, the vacuum is increased to 4×10⁻⁶. -3Pa. During the initial formation of supersonic gas atomization, the atomization pressure is 5.5 MPa, and the atomizing gas flow velocity reaches Mach 2.5 (Ma), corresponding to a specific gas flow velocity of 850 m / s.

[0041] When LPBF is formed using dual energy fields, the oxygen content is maintained at 25 ppm during forming atmosphere control.

[0042] For short-time heat treatment, hold at 800℃ for 1 hour.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that: (1) During the gas atomization forming process of powder preparation, the atomization pressure was 3.0 MPa, the atomization chamber pressure was 0.4 MPa, and the cooling rate was approximately 8 × 10⁻⁶. 3 K / s; (2) Scanning strategy: Unidirectional scanning (without island division) and no sub-modulated laser scanning steps are adopted; the final formed blank has a density of 99.2%, an average dislocation cell size of 520nm, and no obvious solute cluster precursors.

[0045] Comparative Example 2

[0046] The difference between this comparative example and Example 1 is that: Without the secondary modulation laser scanning step, the remaining forming parameters (including powder pretreatment, forming atmosphere, main forming laser parameters, etc.) are consistent with those in Example 1; the final formed blank has a density of 99.85%, an average dislocation cell size of 490 nm, and a geometrically necessary dislocation density of 8.7 × 10⁻⁶. 10 m -2 The number of Ti-Al cluster precursors at the cell wall is small and unevenly distributed (size 3-12nm).

[0047] The performance data of the above embodiments and comparative examples are shown in Table 1 below.

[0048] Table 1 Performance Table

[0049] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0050] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A preparation process for a high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF, characterized in that, Includes the following steps: Step 1: Preparation of NiCoCr alloy powder; Step 2: LPBF dual-energy-field collaborative forming to obtain the formed blank; Step 3: Perform short-time heat treatment on the formed blank.

2. The preparation process according to claim 1, characterized in that, Step one includes the following steps: S1, Raw material pretreatment: Pure metal raw materials are prepared according to atomic percentage as follows: Ni 49.21at%, Co 24.71at%, Cr 15.10at%, Al 2.48at%, Ti 3.23at%, Mo 2.93at%, W 1.36at%, Nb 0.43at%, Ta 0.55at, with a purity of ≥99.95at for all raw materials; after removing the oxide scale from the blocky raw materials, they are cut into 8-12mm pieces, and the filamentous raw materials are cut into 15-20mm segments, and dried in a vacuum drying oven at 120 ℃ for 4 h; S2, Vacuum Induction Melting: Add the pretreated raw materials to the crucible of the vacuum induction melting furnace, and evacuate to a vacuum level of ≤5×10⁻⁶. -3 Pa, argon gas was introduced to 0.3 MPa, the temperature was increased to 1620 ℃ at 40 ℃ / min, and held at that temperature for 40 min, with stirring once every 8 min during the process, to obtain a uniform alloy liquid; S3, Supersonic gas atomization initial forming: The alloy liquid is introduced into the atomization chamber through a 6 mm guide tube, and argon gas with a purity of ≥99.99% is used as the atomization medium. The atomization pressure is 5.0-5.5 MPa, the atomization chamber pressure is 0.6 MPa, and the alloy liquid is broken and cooled to form spherical powder; the atomization gas flow velocity reaches 680-850 m / s. S4, Powder grading: After cyclone separation, the powder is passed through 150-mesh and 400-mesh standard sieves to screen out 15-53 μm powder, and then dried in a vacuum drying oven at 100 ℃ for 3 h to obtain NiCoCr alloy powder.

3. The preparation process according to claim 1, characterized in that, Step two includes the following steps: S01, Pretreatment of NiCoCr alloy powder: The NiCoCr alloy powder was dried in a vacuum drying oven at 120 ℃ for 6 h; S02, Forming Atmosphere Control: After the printing chamber is evacuated, argon gas is introduced to maintain the oxygen content ≤30 ppm, and the substrate of the forming cylinder is preheated to 100 ℃; S03, master shaping laser scanning: power 280 W, speed 850 mm / s, scanning interval 60 μm, layer thickness 30 μm, 6×6 mm island scanning strategy, overlap rate 12%, constructing continuous dislocation cytoskeleton and capturing cell wall solute; S04, Sub-modulated laser scanning: After each layer of main scanning is completed, in-situ rescanning is performed within 30 s with a power of 90 W, a speed of 1600 mm / s, and a defocusing amount of +3.5 mm to induce high-density geometrically essential dislocations and solute nanoclusters to form a metastable precursor structure.

4. The preparation process according to claim 1, characterized in that, Step 3 includes the following steps: Place the formed billet into a box furnace, hold it at 700℃-800℃ for 1-2 hours, and then allow it to air cool to room temperature to obtain the target alloy.

5. The preparation process according to claim 3, characterized in that, In S03, the cooling rate of the main forming laser scanning is ≥1×10⁻⁶. 4 K / s.

6. A high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF obtained by the preparation process according to any one of claims 1-5.

7. A high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF according to claim 6, characterized in that, The alloy exhibits a dual-scale synergistic structure of dislocation cellular framework and minimal γ′ precipitates: the dislocation cellular framework is a continuous submicron-scale structure with an average size of 450-500 nm and a geometrically necessary dislocation density ≥1.8 × 10⁻⁶. 11 m -2 The cell wall is uniformly distributed with nanocluster precursors of 5-10 nm in size, providing sites for the nucleation of the γ′ phase; the minimal γ′ precipitate has an L12 ordered structure with an average particle size of less than 10 nm and is coherent with the γ matrix.

8. A high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF according to claim 6, characterized in that, The alloy has a room temperature yield strength of 1284-1332 MPa, a tensile strength of 1571-1641 MPa, a fracture elongation of 18.1-20.4%, and a plane strain fracture toughness (KIC) of 121-135 MPa•m. 1 / 2 .

9. The application of the high-strength, high-toughness NiCoCr medium-entropy alloy prepared by LPBF according to claim 6 in aerospace equipment and energy power equipment.

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