Heat-resistant high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and preparation method thereof

Abstract

The application discloses a heat-resistant high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and a preparation method thereof, wherein CoCrNiB powder is prepared through gas atomization, mixed CoCrNiB powder and Ti powder are obtained, and the mixed powder is fused and formed through a laser powder bed to obtain the heat-resistant high-strength CoCrNi-based medium-entropy alloy; the heat-resistant high-strength CoCrNi-based medium-entropy alloy has a hierarchical structure, including columnar grains, a molten pool, a cellular dislocation structure and precipitates; the precipitates include in-situ generated TiB2 and Cr2B; the Cr2B is distributed at the boundaries of the cellular dislocation structure and three-way junctions; and the TiB2 is distributed at the boundaries of the cellular dislocation structure and intracellularly. The alloy cooperatively stabilizes the dislocation cell structure through in-situ generated nano precipitates and element segregation, and significantly improves the high-temperature strength and thermal stability of the L-PBF CoCrNi-based medium-entropy alloy.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing, specifically relating to a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. Background Technology

[0002] The aerospace, energy, and other fields have an increasingly urgent need for alloys with excellent strength and ductility over a wide temperature range. Medium / high entropy alloys (M / HEAs) have attracted widespread attention due to their unique design concepts and potential structural applications. Among them, single-phase face-centered cubic (FCC) CoCrNi MEAs have become one of the research hotspots in this field due to their excellent low-temperature and room-temperature strength, toughness, and ductility. However, these alloys suffer from severe thermal softening at high temperatures, making it difficult to meet the requirements of harsh thermomechanical loading environments.

[0003] Laser powder bed fusion (L-PBF) additive manufacturing technology can form dislocation cell substructures with high-density dislocation entanglements, endowing alloys with excellent mechanical properties and thermal stability. However, the current technological bottleneck is that these dislocation cell structures decompose above 600℃ and lack effective competitive strengthening mechanisms, which limits the application of alloys in a wider temperature range.

[0004] A common method to improve high-temperature strength is to introduce ceramic reinforcing particles (such as borides and carbides). These particles can effectively pin dislocations and hinder dislocation movement and recovery at high temperatures. However, particles introduced by traditional external methods have poor compatibility with the metal matrix interface, easily leading to stress concentration, resulting in interface cracking, particle delamination, or matrix damage, becoming crack initiation points and impairing material properties. In-situ alloying, which involves first decomposing / dissolving non-metallic particles in the metal matrix, and then generating a second phase through a chemical reaction, can obtain nanoparticles with better interface compatibility and more dispersed distribution. This effectively pins dislocations and grain boundaries, promotes uniform stress transmission, and inhibits interface failure, potentially improving strength while maintaining ductility.

[0005] Furthermore, based on the Gibbs-Thomson principle of interface energy reduction, elemental segregation can enhance the load-bearing capacity of individual interfaces by strengthening grain boundary binding energy, thereby reducing the probability of catastrophic interface failure in structural components. On the other hand, solute segregation and the reduced interface energy together enhance the grain boundary drag effect and weaken the Gibbs-Thomson force, slowing down the grain coarsening process driven by recrystallization and capillary action. These effects work together to significantly improve the microstructure stability of materials at high temperatures, providing structural protection for maintaining high-temperature mechanical properties. Summary of the Invention

[0006] To address the technical problem of insufficient improvement in the thermal stability and wide-temperature-range strength of alloys in existing technologies, the first objective of this invention is to provide a method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation. This invention employs laser powder bed melting technology, and the preparation method is simple, controllable, and suitable for industrial production.

[0007] The second objective of this invention is to provide a heat-resistant, high-strength CoCrNi-based medium-entropy alloy prepared by the above-described method, based on the regulation of cellular dislocation structure. The heat-resistant, high-strength CoCrNi-based medium-entropy alloy provided by this invention exhibits excellent mechanical properties and thermal stability.

[0008] The third objective of this invention is to provide an application of a heat-resistant, high-strength CoCrNi-based medium-entropy alloy prepared by the above-described preparation method, based on the regulation of cellular dislocation structure.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] This invention discloses a method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation. The method involves preparing CoCrNiB powder by gas atomization, mixing the CoCrNiB powder with Ti powder to obtain a mixed powder, and then using laser powder bed melting to form the alloy.

[0011] The heat-resistant, high-strength CoCrNi-based medium-entropy alloy comprises, by atomic percentage: Co: 25-35%; Cr: 25-35%; Ni: 25-35%; B: 1-20%; Ti: 2-10%.

[0012] The heat-resistant, high-strength CoCrNi-based medium-entropy alloy has a hierarchical structure, including columnar grains, molten pools, cellular dislocation structures, and precipitates. Ti element segregation exists at the boundaries of the cellular dislocation structures. The precipitates include in-situ generated TiB2 and Cr2B. Cr2B is distributed at the boundaries of the cellular dislocation structures and at the tri-junctions, while TiB2 is distributed at the boundaries of the cellular dislocation structures and within the cells.

[0013] The heat-resistant, high-strength CoCrNi-based medium-entropy alloy provided by this invention has TiB2 and Cr2B nanoprecipitates. Most of these nanoprecipitates are pinned to the submicron dislocation cell boundaries. Combined with the Gibbs segregation effect of Ti element at the cell boundaries, the thermal stability of the dislocation cells is significantly improved.

[0014] The heat-resistant, high-strength CoCrNi-based medium-entropy alloy of the present invention is obtained by first preparing CoCrNiB powder and mixing it with Ti powder using a gas atomization method, and then using laser powder bed melting. During the laser powder bed melting process, solute atoms such as B, Ti, and Cr are pushed to the solid-liquid interface during solidification (similar to grain boundary segregation), providing a local high-concentration environment for precipitation. Therefore, TiB2 and Cr2B nanoprecipitates are generated in situ, most of which are pinned to the submicron dislocation cell boundaries. Combined with the Gibbs segregation effect of Ti element at the cell boundaries, the thermal stability of the dislocation cells is significantly improved. Furthermore, the good wettability of the in-situ precipitated phases and the interface achieves nanoscale homogenization of the stress field, avoiding the risk of interface cracking of traditional reinforcing phases.

[0015] In this invention, the key to obtaining the microstructure of this invention lies in first preparing CoCrNiB powder through gas atomization and then mixing it with Ti powder. If CoCrNiBTi powder is prepared directly through gas atomization, TiB2 precipitate will form during the gas atomization process. However, TiB2 has a melting point of 3225 °C, which makes it difficult to melt during the subsequent L-PBF process. This will result in poor interfacial wettability and poor bonding due to the mismatch in thermal expansion coefficients with the CoCrNi matrix, thus deteriorating the material properties. Similarly, mixing CoCrNi powder with TiB2 particles will also lead to large-scale cracks in the formed sample. However, by using gas atomized CoCrNiB powder, the Cr2B phase (melting point 1890 °C) formed during gas atomization will completely melt during the L-PBF process. During solidification, the B element can react in situ with the Ti and Cr elements, thereby generating TiB2 and Cr2B nano-reinforcing phases in situ.

[0016] Preferably, the CoCrNiB powder is a spherical powder with a particle size of 15 ~ 53 μm and a purity ≥ 99.9 wt%.

[0017] Preferably, the Ti powder is a spherical powder with a particle size of 15 ~ 53 μm and a purity ≥ 99.95 wt%.

[0018] Preferably, the process of preparing CoCrNiB powder by gas atomization is as follows: pure Ni, pure Cr, pure Co, and NiB are prepared according to the designed ratio. 20 First, divide the pure Ni into two parts. Place the first part of pure Ni at the bottom, then add pure Cr on top of the first part of pure Ni. Next, add the second part of pure Ni and pure Co on top of the pure Cr. Heat the mixture, add gas for the first time, and melt to obtain a melt. Then refine the melt to obtain alloy liquid A. Then add NiB... 20 The alloy liquid A is added and melted to obtain alloy liquid B. After a second gas injection, alloy liquid B is added to the intermediate ladle for gas atomization and sieving to obtain CoCrNiB powder.

[0019] In this invention, during the preparation of CoCrNiB powder by gas atomization, a portion of the lower melting point Ni is first placed at the bottom and melts in the early stage of heating, forming a liquid metal pool at the bottom of the furnace. The liquid Ni pool can protect the refractory material at the bottom of the furnace, preventing the high melting point and high density Cr added later from directly impacting or being in contact with the high-temperature furnace bottom for a long time, thus reducing furnace lining erosion. Then, higher melting point Cr particles or blocks are added successively and immersed or sunk into the liquid Ni pool. Liquid metal is a better heat conductor than solid metal, which can more effectively transfer heat to Cr, significantly accelerating the melting process of Cr and preventing Cr from accumulating, sintering, or forming refractory lumps at the bottom of the furnace, thus overcoming the difficulty of its high melting point. The remaining Ni and Co cover the Cr blocks, providing heat for downward conduction and allowing them to fall smoothly when the Cr below melts and shrinks, preventing bridging and completing the final alloying.

[0020] In this invention, NiB 20 Alloy, referring to B in NiB 20 The mass fraction of the alloy is 20%.

[0021] Further optimization involves placing the first pure Ni in a compacted state at the bottom layer, while the middle layer of Cr and the upper layer of Ni and Co remain in a naturally stacked state.

[0022] In a further preferred embodiment, the refining temperature is 1460 ~ 1550 ℃, and the refining time is 8 ~ 12 min.

[0023] Further optimization, using NiB 20 When adding the alloy liquid A, the temperature is controlled at 1520 ~ 1540 ℃.

[0024] In a further preferred embodiment, the second gas injection is performed to a pressure of 94,500 to 95,500 Pa.

[0025] In a further preferred embodiment, the temperature of the intermediate ladle is 1280~1290 ℃, and the temperature of the alloy liquid B is 1590~1610 ℃.

[0026] In a further preferred embodiment, the pressure of the gas atomization is 2.7 ~ 3 MPa.

[0027] Further optimization involves cooling the powder for 1 to 2 hours after atomization, then collecting and sieving it in an argon atmosphere.

[0028] Preferably, the CoCrNiB powder and Ti powder are mixed in a V-type mixer at a speed of 40-60 rpm for 2-5 hours.

[0029] Preferably, the mixed powder is first dried, and then melt-formed using a laser powder bed fusion molding process. The drying temperature is 80-120°C, and the drying time is 8-12 hours. In actual operation, the drying is carried out in a vacuum drying oven.

[0030] Preferably, during the laser powder bed melting process, the laser power is controlled at 150-300 W, the scanning speed at 800-1200 mm / s, the scanning spacing at 60-120 μm, the layer thickness at 30-40 μm, and the scanning strategy is 67° interlayer rotation. Using these preferred parameters, the resulting medium-entropy alloy exhibits the best morphology and ultimately the best performance.

[0031] Preferably, the laser powder bed melting process involves placing the mixed powder in the powder supply cylinder of the printing chamber, preheating the forming cylinder substrate to 70-80°C, introducing argon gas into the printing chamber, and melting the powder layer by layer on the forming cylinder substrate with a high-energy laser beam to obtain a medium-entropy alloy formed by laser powder bed melting. The oxygen content in the printing chamber is less than 80 ppm.

[0032] Preferably, the heat-resistant, high-strength CoCrNi-based medium-entropy alloy contains the following components by atomic percentage: Co: 30-32%; Cr: 30-32%; Ni: 30-32%; B: 2-6%; Ti: 2-6%.

[0033] In a further preferred embodiment, the heat-resistant high-strength CoCrNi-based medium-entropy alloy comprises the following components by atomic percentage: Co: 30-31%; Cr: 30-31%; Ni: 30-31%; B: 4-6%; Ti: 4-6%.

[0034] Further preferred, the TiB2 distributed at the boundary and inside the cellular dislocation structure is granular with an average particle size of 40-60 nm; the Cr2B distributed at the trifle junction of the cellular dislocation structure is granular with an average particle size of 80-200 nm; the Cr2B distributed at the boundary of the cellular dislocation structure is wrapped in a quasi-continuous grid structure around the boundary of the cellular dislocation structure.

[0035] The ultra-high cooling rate of laser powder bed melting leads to nanoscale, highly dispersed precipitates. These precipitates are small in size and spacing, producing significant dispersion strengthening and precipitation strengthening effects. Nanoscale TiB2 and Cr2B particles exhibit extremely high hardness, modulus, strength, and thermal stability. Intracellular TiB2 particles effectively hinder dislocation movement, thereby improving the alloy's room temperature and high temperature strength. The dislocation cell structure of laser powder bed melting CoCrNi decomposes above 600 °C. The TiB2 and Cr2B at the cell boundaries not only prevent dislocation passage but also pin dislocations at the cell boundaries, inhibiting dislocation cell collapse and improving the alloy's thermal stability. The quasi-continuous presence of Cr2B at the cell boundaries provides strong evidence for dislocation movement and retains the activation effect of the dislocation cells on dislocation movement, promoting synergistic deformation and maintaining the alloy's good plasticity.

[0036] Preferably, the matrix of the heat-resistant, high-strength CoCrNi-based medium-entropy alloy is an FCC structure.

[0037] The present invention also provides a heat-resistant, high-strength CoCrNi-based medium-entropy alloy prepared by the above preparation method based on the cellular dislocation structure regulation.

[0038] Preferably, the heat-resistant high-strength CoCrNi-based medium-entropy alloy has a yield strength of 920-1280 MPa, a tensile strength of 1200-1540 MPa, and an elongation of 12-32% at room temperature; and a yield strength of 720-905 MPa, a tensile strength of 1000-1200 MPa, and an elongation of 20-45% at 700℃.

[0039] The beneficial effects of this invention are:

[0040] This invention achieves a breakthrough improvement in the wide-temperature-range performance of CoCrNi-based medium-entropy alloys through innovative composition design and additive manufacturing process: TiB2 and Cr2B nanoprecipitates are generated in situ during L-PBF forming. Most of these nanoprecipitates are pinned to submicron dislocation cell boundaries. Combined with the Gibbs segregation effect of Ti element at the cell boundaries, the thermal stability of dislocation cells is significantly improved. Furthermore, the good wettability of the in-situ precipitated phases and interfaces achieves nanoscale homogenization of the stress field, avoiding the risk of interface cracking of traditional reinforcing phases.

[0041] CoCrNi-based medium-entropy alloys exhibit a yield strength of 920–1280 MPa, a tensile strength of 1200–1500 MPa, and an elongation of 12–32% at room temperature; and a yield strength of 720–1030 MPa, a tensile strength of 1070–1260 MPa, and an elongation of 17–40% at 700 °C. These alloys provide a material solution with both superior performance and industrialization potential for cutting-edge equipment such as aero-engine turbine disks and guide vanes that face harsh service environments involving extreme temperatures and severe thermal cycling. Attached Figure Description

[0042] Figure 1 The image shows the metallographic diagram of the CoCrNi-based medium-entropy alloy prepared in Example 4.

[0043] Figure 2 This is a scanning electron microscope image of the CoCrNi-based medium-entropy alloy prepared in Example 4.

[0044] Figure 3 This is a transmission electron microscope (TEM) image of the CoCrNi-based medium-entropy alloy prepared in Example 4.

[0045] Figure 4 This is a transmission electron microscope (TEM) image of the CoCrNi-based medium-entropy alloy prepared in Example 4.

[0046] Figure 5 The image shows a scanning electron microscope (SEM) image of the CoCrNi-based medium-entropy alloy prepared in Example 4, aged at 700 °C for 5 h.

[0047] Figure 6 The image shows a scanning electron microscope (SEM) image of the CoCrNi medium-entropy alloy prepared in Comparative Example 1.

[0048] Figure 7 The image shows a scanning electron microscope (SEM) image of the CoCrNi medium-entropy alloy prepared in Comparative Example 1 after aging at 700 °C for 5 h.

[0049] Figure 8 The image shows the metallographic diagram of the CoCrNi-based medium-entropy alloy prepared in Comparative Example 4.

[0050] Figure 9 The image shows the metallographic image of the TiB2 / CoCrNi composite material prepared in Comparative Example 5. Detailed Implementation

[0051] To enable those skilled in the art to better understand the present invention, the following detailed description of specific embodiments, in conjunction with the accompanying drawings and examples, is provided. These embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0052] Example 1

[0053] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The steps include: Atomic ratio of Co: 32%; Cr: 32%; Ni: 32%; B: 2%; Ti: 2%. Half of the Ni is placed at the bottom, followed by pure Cr, then all Ni and Co are added. The mixture is then heated under vacuum with argon gas purging, followed by gas replenishment. The material melts rapidly. After confirming complete melting, it is refined at 1500 °C for 8 minutes. Once the alloy temperature reaches 1530 °C, NiB is added. 20 The material melted rapidly, and the temperature stabilized at 1600 ℃ after 6 minutes. Gas was added to bring the pressure to 95000 Pa, and preparations such as starting the blower were initiated. Normal atomization was then performed, with the tundish temperature at 1280 ℃ and the casting temperature at approximately 1610 ℃. The atomization pressure was 2.8 MPa. After atomization, the material was cooled for 1.5 hours, then the powder was collected and sieved. Fine powder was sieved using an air classifier under an argon atmosphere, ultimately yielding CoCrNiB powder with a particle size range of 15~53 μm as raw material. The CoCrNiB powder and spherical Ti powder were mixed in a V-type mixer at 50 rpm for 3 hours. The mixed powder was then placed in a vacuum drying oven and dried at 100 ℃ for 10 hours. The purity of the Ti powder was not less than 99.95 wt%, and the particle size was 15~53 μm. The mixed powder is placed in the powder supply cylinder of the printing chamber. The forming cylinder substrate is preheated to 70 °C, and argon gas is introduced into the printing chamber. A high-energy laser beam melts the powder layer by layer on top of the forming cylinder substrate to obtain a medium-entropy alloy formed by laser powder bed fusion. During the printing process, the oxygen content in the chamber is below 80 ppm, the laser power is 200 W, the scanning speed is 1000 mm / s, the scanning spacing is 90 μm, the layer thickness is 40 μm, and the scanning strategy is 67° interlayer rotation.

[0054] Example 2

[0055] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 1 is that the atomic ratio of the alloy is as follows: Co: 31%; Cr: 31%; Ni: 32%; B: 4%; Ti: 2%.

[0056] Example 3

[0057] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 1 is that the alloy is prepared according to the atomic ratio: Co: 31%; Cr: 31%; Ni: 30%; B: 6%; Ti: 2%.

[0058] Example 4

[0059] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 1 is that the alloy is prepared according to the atomic ratio: Co: 31%; Cr: 31%; Ni: 30%; B: 4%; Ti: 4%.

[0060] Example 5

[0061] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 1 is that the alloy is prepared according to the atomic ratio: Co: 30%; Cr: 30%; Ni: 30%; B: 4%; Ti: 6%.

[0062] Example 6

[0063] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 4 is that the laser power is 150 W and the scanning speed is 800 mm / s.

[0064] Example 7

[0065] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 4 is that the laser power is 250 W and the scanning speed is 1200 mm / s.

[0066] Comparative Example 1 (No Ti, No B)

[0067] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 1 is that the alloy is prepared according to the atomic ratio: Co: 33%; Cr: 33%; Ni: 34%.

[0068] Comparative Example 2 (without Ti)

[0069] This embodiment presents a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference from Example 1 lies in the atomic ratio of the alloy components: Co: 32%; Cr: 32%; Ni: 32%; B: 4%. Sample performance parameters are shown in Tables 1 and 2.

[0070] Comparative Example 3 (without B)

[0071] This embodiment presents a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference from Example 1 lies in the atomic ratio of the raw materials: Co: 32%; Cr: 32%; Ni: 32%; Ti: 4%. Sample performance parameters are shown in Tables 1 and 2.

[0072] Comparative Example 4

[0073] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The difference between this embodiment and Embodiment 1 is that the laser power is 300 W and the scanning speed is 800 mm / s.

[0074] Comparative Example 5

[0075] This embodiment describes a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation and its preparation method. The steps include: Atomic ratio of Co: 33%; Cr: 33%; Ni: 34%; Half of the Ni is placed at the bottom, followed by pure Cr, then all of the Ni and Co. The mixture is then heated under vacuum with argon gas, and the pressure is increased to a certain level for rapid alloying. After the alloy is completely melted, it is refined at 1500 °C for 8 min. When the temperature stabilizes at 1600 °C, the pressure is increased to 95000 Pa, and preparation work such as starting the blower is initiated. Normal atomization is performed, with the tundish temperature at 1280~1290 °C, the casting temperature at approximately 1610 °C, and the atomization pressure at 2.8 MPa. After atomization, the mixture is cooled for 1~2 h, then the powder is collected and sieved. Fine powder is sieved using an air classifier under an argon atmosphere. The final product is CoCrNi powder with a particle size range of 15~53 μm, which is used as raw material. CoCrNi powder and TiB2 powder (average size: 50 nm) were mixed in a planetary ball mill at 180 rpm for 4 h with a ball-to-powder ratio of 5:1. The mixed powder was then dried in a vacuum drying oven at 100 °C for 10 h. The mixed powder was then placed in the powder supply cylinder of a laser powder bed fusion printing chamber. The forming cylinder substrate was preheated to 70 °C, and argon gas was introduced into the printing chamber. A high-energy laser beam melted the powder layer by layer above the forming cylinder substrate, thus obtaining a medium-entropy alloy formed by laser powder bed fusion. During the printing process, the oxygen content in the chamber was below 80 ppm, the laser power was 200 W, the scanning speed was 1000 mm / s, the scanning spacing was 90 μm, the layer thickness was 40 μm, and the scanning strategy was 67° interlayer rotation.

[0076] The materials obtained in the examples and comparative examples were subjected to structural and performance tests.

[0077] Figure 1 The image shows a metallographic image of the CoCrNi-based alloy printed in Example 4. The results indicate that there are no obvious defects on the sample surface and the parameters were appropriately selected. Figure 2 The image shows a scanned image of the CoCrNi-based alloy printed in Example 4. The results indicate that the sample consists of a submicron cellular structure with a high volume fraction of precipitated phase at the boundaries of the cellular structure. Figure 3 and Figure 4The image shows a transmission electron microscope (TEM) image of the printed CoCrNi-based alloy from Example 4. Cr2B mainly exists in two forms: one is as granular particles (average size 80-200 nm) distributed at the triangular junctions of dislocation cells; the other is as a quasi-continuous grid structure enveloping the boundaries of dislocation cells. TiB2 particles are distributed both at the boundaries and inside the cellular structure, with an average particle size of 40-80 nm. Ti segregates at the boundaries of the dislocation cellular structure. Figure 5 The image shows the scanning microstructure of Example 4 after aging at 700 °C for 5 h. The cellular structure remained stable, indicating that Ti element segregation and Cr2B / TiB2 precipitation effectively pinned the cell boundaries, thus enhancing the stability of the cellular structure. Figure 7 The scanning microstructure of Comparative Example 1 after aging at 700 °C for 5 h showed that the cellular tissue decomposed. Figure 8 The metallographic image for Comparative Example 4 shows that due to inappropriate parameter selection, a large number of cracks appeared in the sample, which had a serious adverse effect on the mechanical properties. Figure 9 The metallographic image shown in Comparative Example 5 illustrates how the addition of TiB2 caused numerous cracks in the printed sample due to the significant difference in thermal expansion coefficients between TiB2 and the CoCrNi matrix.

[0078] The room temperature and high temperature tensile strength results of the printed alloys obtained in the examples and comparative examples are shown in Tables 1 and 2, indicating that the contents of Ti and B significantly improve the room temperature and high temperature strength of the samples, while still maintaining good plasticity.

[0079]

[0080]

[0081] The embodiments described are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation, characterized in that: CoCrNiB powder is prepared by gas atomization, and then mixed with Ti powder to obtain a mixed powder. The mixed powder is then melted and formed by laser powder bed melting. The heat-resistant, high-strength CoCrNi-based medium-entropy alloy comprises, by atomic percentage: Co: 25-35%; Cr: 25-35%; Ni: 25-35%; B: 1-20%; Ti: 2-10%. The heat-resistant, high-strength CoCrNi-based medium-entropy alloy has a hierarchical structure, including columnar grains, molten pools, cellular dislocation structures, and precipitates. Ti element segregation exists at the boundaries of the cellular dislocation structures. The precipitates include in-situ generated TiB2 and Cr2B. Cr2B is distributed at the boundaries and bifurcation junctions of the cellular dislocation structures, while TiB2 is distributed at the boundaries and within the cells of the cellular dislocation structures. The process of preparing CoCrNiB powder by gas atomization is as follows: pure Ni, pure Cr, pure Co, and NiB are prepared according to the designed ratio. 20 First, divide the pure Ni into two parts. Place the first part of pure Ni at the bottom, then add pure Cr on top of the first part of pure Ni. Next, add the second part of pure Ni and pure Co on top of the pure Cr. Heat the mixture, add gas for the first time, and melt to obtain a melt. Then refine the melt to obtain alloy liquid A. Then add NiB... 20 The alloy liquid A is added and melted to obtain alloy liquid B. After a second gas injection, alloy liquid B is added to the intermediate ladle for gas atomization and sieve to obtain CoCrNiB powder.

2. The method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation according to claim 1, characterized in that: The CoCrNiB powder is a spherical powder with a particle size of 15~53 μm and a purity ≥ 99.9 wt%. The Ti powder is a spherical powder with a particle size of 15 ~ 53 μm and a purity ≥ 99.95 wt%.

3. The method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation according to claim 1, characterized in that: The first pure Ni was placed in a compacted state at the bottom layer, while the middle layer of Cr and the upper layer of Ni and Co remained in a natural stacking state. The refining temperature is 1460 ~ 1550 ℃, and the refining time is 8 ~ 12 min; NiB 20 When adding the alloy liquid A, the temperature should be controlled at 1520 ~ 1540 ℃; The second gas injection was performed to bring the pressure up to 94500 ~ 95500 Pa; The temperature of the tundish is 1280 ~ 1290 ℃, and the temperature of the alloy liquid B is 1590 ~ 1610 ℃; The pressure of the atomization is 2.7 ~ 3 MPa; After atomization, the powder is cooled down for 1 to 2 hours, then collected and sieved in an argon atmosphere.

4. The method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation according to claim 1, characterized in that: The CoCrNiB powder and Ti powder are mixed in a V-type mixer at a speed of 40-60 rpm for 2-5 hours.

5. The method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation according to claim 1, characterized in that: The mixed powder is first dried, and then melted and shaped using a laser powder bed. The drying temperature is 80-120℃, and the drying time is 8-12 hours.

6. The method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation according to claim 1, characterized in that: During the laser powder bed melting process, the laser power is controlled at 150 ~ 300 W, the scanning speed at 800 ~ 1200 mm / s, the scanning spacing at 60 ~ 120 μm, the layer thickness at 30 ~ 40 μm, and the scanning strategy is 67° interlayer rotation.

7. The method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation according to claim 1, characterized in that: The laser powder bed melting process involves placing the mixed powder in the powder supply cylinder of the printing chamber, preheating the forming cylinder substrate to 70-80°C, introducing argon gas into the printing chamber, and melting the powder layer by layer on the forming cylinder substrate with a high-energy laser beam to obtain a medium-entropy alloy formed by laser powder bed melting. The oxygen content in the printing chamber is less than 80 ppm.

8. The method for preparing a heat-resistant, high-strength CoCrNi-based medium-entropy alloy based on cellular dislocation structure regulation according to claim 1, characterized in that: TiB2 distributed at the boundaries and inside the cells of the cellular dislocation structure is granular with an average particle size of 40-60 nm; Cr2B distributed at the trifles of the cellular dislocation structure is granular with an average particle size of 80-200 nm; Cr2B distributed at the boundaries of the cellular dislocation structure is wrapped in a quasi-continuous grid structure around the boundaries of the cellular dislocation structure. The matrix of the heat-resistant, high-strength CoCrNi-based medium-entropy alloy is an FCC structure.

9. A heat-resistant, high-strength CoCrNi-based medium-entropy alloy prepared by the preparation method according to any one of claims 1-8, characterized in that: The heat-resistant, high-strength CoCrNi-based medium-entropy alloy has a yield strength of 920-1280 MPa, a tensile strength of 1200-1540 MPa, and an elongation of 12-32% at room temperature; and a yield strength of 720-905 MPa, a tensile strength of 1000-1200 MPa, and an elongation of 20-45% at 700℃.

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