Additive manufacturing method for high-toughness CoCrNiAl eutectic high-entropy alloy

Abstract

The invention belongs to the technical field of high-entropy alloys, and particularly relates to a high-toughness CoCrNiAl series eutectic high-entropy alloy additive manufacturing method. Aiming at the condition that traditional additive manufacturing metal materials are insufficient in strength and toughness, the invention provides the principle that in-situ refining of an additive manufacturing structure is realized through a fine and uniform B2 phase capable of being sheared by utilizing the characteristic of rapid solidification of additive manufacturing, so that the strength and toughness are comprehensively improved. Based on the principle, the general formula of the eutectic high-entropy alloy is CoaCrbNicAld, a is larger than or equal to 29 and smaller than or equal to 35, b is larger than or equal to 18 and smaller than or equal to 23, c is larger than or equal to 27 and smaller than or equal to 35, d is larger than or equal to 13 and smaller than or equal to 19, and a + b + c + d = 100. The eutectic high-entropy alloy prepared through the laser powder bed melting technology achieves high strength, high ductility and high fracture toughness under the condition that subsequent heat treatment is not needed. The design principle of the invention can also be popularized to other eutectic high-entropy alloy systems.

Description

A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys Technical Field

[0001] This invention belongs to the field of high-entropy alloy technology, specifically relating to an additive manufacturing method for a high-strength and high-toughness CoCrNiAl eutectic high-entropy alloy. Background Technology

[0002] Additive manufacturing technology enables the rapid and precise fabrication of complex-shaped parts, offering high material utilization and reducing assembly processes and connectors. Furthermore, extremely high cooling rates can create fine, uniform metastable microstructures, minimizing compositional segregation. Through path planning and parameter control, it is possible to achieve functionally graded materials or the customization of anisotropic properties, enabling the synthesis of novel alloys that are difficult to synthesize using traditional methods. Like traditional alloys, their mechanical properties follow classical dislocation theory, and improvements in mechanical properties depend on the introduction of new strengthening mechanisms.

[0003] Eutectic high-entropy alloys, as a novel class of metallic materials, exhibit excellent mechanical properties due to their heterogeneous structure, where the soft phase provides plasticity and the hard phase enhances strength. Furthermore, the inherent high fluidity of eutectic alloys makes them highly suitable for additive manufacturing. However, while the introduction of bulk heterogeneous B2 phases can induce significant deformation-induced hardening in the early stages of deformation, it can lead to severe stress concentration and fracture in the later stages because dislocations can only bypass the bulk precipitates. Therefore, utilizing the rapid solidification characteristics of additive manufacturing to prepare metastable ultrafine-structured eutectic high-entropy alloys, and achieving a shift in dislocation movement mechanism from bypassing to shearing, may be an effective means to improve the mechanical properties of additive-manufactured metallic materials. Summary of the Invention

[0004] To improve the mechanical properties of additively manufactured alloys, this invention aims to provide a method for additive manufacturing high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys. By utilizing the rapid cooling characteristic during additive manufacturing, in-situ refinement of the additive manufacturing microstructure is achieved. The equiaxed grains of the FCC matrix are in-situ subdivided into cellular structures with diameters of several hundred nanometers by a B2 phase framework, and for the first time, bulk stacking fault shear precipitates are observed at room temperature. The prepared printed alloy exhibits extremely high strength and fracture toughness.

[0005] The technical solution adopted in this invention is as follows: A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys, with the general formula Co... a Cr b Ni c Al dIn the chemical expression, a, b, c, and d represent the molar percentages of the corresponding elements, where: 29≤a≤35, 18≤b≤23, 27≤c≤35, 13≤d≤19, and a+b+c+d=100.

[0006] The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys, wherein the eutectic high-entropy alloys include, but are not limited to, CoCrNiAl eutectic high-entropy alloys.

[0007] The additive manufacturing method for the high-strength and high-toughness CoCrNiAl eutectic high-entropy alloy includes the following steps: (1) Vacuum drying the CoCrNiAl eutectic high-entropy alloy powder at a temperature of 80-100℃ for 2-4 hours, with a vacuum degree ≤ 10. -2 Pa, remove moisture from the surface of eutectic high-entropy alloy powder; (2) draw the shape of the printed part using three-dimensional modeling software and then import it into the 3D printing equipment; (3) print on a horizontally placed substrate. The 3D printing parameters are: laser power 200-300 W, scanning speed 800-1200 mm / s, scanning spacing 70-110 μm; powder layer thickness 40 μm, spot diameter 80 μm, scanning direction “Z” shaped cycle, printing direction vertically upward; (4) after printing, use wire cutting method to separate the component from the substrate to obtain the final product.

[0008] In the additive manufacturing method of the high strength and toughness CoCrNiAl eutectic high entropy alloy, in step (1), the particle size of the CoCrNiAl eutectic high entropy alloy powder is 15-53 μm.

[0009] In the additive manufacturing method of the high strength and toughness CoCrNiAl eutectic high entropy alloy, in step (3), the substrate is 304 stainless steel, and the substrate is polished, cleaned and dried in sequence before use.

[0010] In the additive manufacturing method of the high strength and toughness CoCrNiAl eutectic high entropy alloy, step (3) uses powder spreading method for printing, and the powder is spread to fill the printing chamber before printing.

[0011] In the additive manufacturing method of the high strength and toughness CoCrNiAl eutectic high entropy alloy, in step (3), the printing chamber is preheated to 200 ℃ before printing.

[0012] In the additive manufacturing method of the high strength and toughness CoCrNiAl eutectic high entropy alloy, the protective gas in step (3) is high-purity argon.

[0013] The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys produced by this method yields eutectic high-entropy alloys with a room temperature yield strength exceeding 1300 MPa, a tensile strength exceeding 1500 MPa, a total elongation of 29%, and a fracture toughness K0.05. Ⅰc More than 200 MPa·m 0.5 .

[0014] To address the insufficient strength and toughness of traditional additively manufactured metallic materials, this invention proposes a principle that leverages the rapid solidification characteristic of additive manufacturing to achieve in-situ refinement of the additive manufacturing microstructure through the formation of fine, uniform, shearable B2 phases, thereby comprehensively improving both strength and toughness. The eutectic high-entropy alloy prepared using laser powder bed melting technology achieves high strength, high ductility, and high fracture toughness without the need for subsequent heat treatment. The design principles of this invention can also be extended to other eutectic high-entropy alloy systems, and the processing technology is simple, which is beneficial for industrial production.

[0015] The design principle and beneficial effects of this invention are as follows: 1. Design Principle: This invention proposes an additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys. Additive manufacturing alloys inherently possess advantages such as high forming efficiency and fast cooling rate, but inevitably produce defects such as porosity, incomplete fusion, and residual stress. Eutectic high-entropy alloys, on the other hand, not only have excellent mechanical properties but also good casting fluidity. The extremely fast molten pool cooling rate in additive manufacturing can suppress element diffusion and segregation tendencies, which is beneficial for obtaining a microstructure with uniform composition and no macroscopic segregation.

[0016] The strengthening effect of eutectic high-entropy alloys prepared by traditional methods originates from the heterogeneous deformation-induced strengthening effect brought about by the bulk heterogeneous B2 phase. However, while such bulk precipitates are beneficial for improving the overall yield strength in the early stage of deformation, severe stress pile-up occurs in the later stage of deformation because dislocations can only bypass the bulk precipitates, which seriously affects the alloy's plasticity. Compared to the bypass mechanism, the shearing mechanism generates less stress concentration and has a smaller impact on plasticity. The shearing mechanism usually occurs when the precipitate size is small and the degree of coherence is high. Therefore, rapid cooling during the additive manufacturing process to generate fine and uniform B2 precipitates, promoting the transformation of dislocation interaction from bypass to shearing, will be an effective way to improve the mechanical properties of additively manufactured eutectic high-entropy alloys.

[0017] 2. Beneficial Effects: This invention aims to provide an additive manufacturing method for high-strength and fracture-toughness CoCrNiAl eutectic high-entropy alloys. Through rapid solidification during the additive manufacturing process, in-situ refinement of the microstructure is successfully achieved. FCC grains are subdivided into cellular structures with diameters of several hundred nanometers by the B2 phase framework. Furthermore, a stacking fault shearing mechanism at room temperature was observed for the first time during the stretching process. The ultrafine cellular structure results in ultra-high yield strength, while the shearing mechanism significantly improves toughness. This method eliminates the need for subsequent heat treatment and can directly produce high-strength and high-toughness additive manufacturing metal materials. The process is simple, lower in cost, safe, and reliable, and has broad engineering application prospects. Attached Figure Description

[0018] Figure 1 is a schematic diagram of the 3D printing strategy and sampling direction of the present invention.

[0019] Figure 2 is a physical image of the block sample prepared according to the present invention.

[0020] Figure 3 shows the microstructure characterization of the additively manufactured eutectic high-entropy alloy prepared in this invention.

[0021] Figure 4 shows the room temperature tensile engineering stress-strain curves of the eutectic high-entropy alloy prepared in this invention. In the figure, the horizontal axis represents engineering strain (%), and the vertical axis represents engineering stress (MPa).

[0022] Figure 5 shows the crack propagation resistance (J-integral) curve of the eutectic high-entropy alloy prepared in this invention.

[0023] Figure 6 shows the transmission characterization results at a tensile strain of 9%.

[0024] Figure 7 shows a physical image of the sample prepared at a printing angle of 45°. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 instances that are improved or modified by those skilled in the art are within the scope of protection of the present invention. It should be understood that the embodiments of the present invention are only used to illustrate the technical effects of the present invention, and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the methods used in the embodiments are conventional methods.

[0026] Example 1: In this example, a high-strength and high-toughness CoCrNiAl eutectic high-entropy alloy additive manufacturing method is described. CoCrNiAl eutectic high-entropy alloy powder with a particle size of 15-53 μm is selected, and its composition has the following atomic percentages of metals: Co 33%, Cr 20%, Ni 30%, Al 17%, which can be represented as Co... 33 Cr 20 Ni 30 Al 17 The CoCrNiAl eutectic high-entropy alloy powder is prepared according to the following steps: Step 1: Before use, the CoCrNiAl eutectic high-entropy alloy powder is vacuum dried at a temperature of 100℃ for 2 hours, with a vacuum degree ≤ 10. -2 Pa removes moisture from the surface of eutectic high-entropy alloy powder.

[0027] Step 2: Use a 304 stainless steel plate as the substrate. Before use, polish, clean and dry the surface of the substrate at 60°C for 1 hour.

[0028] Step 3: Draw the shape of the printed part using 3D modeling, and then import it into the EOS M 290 3D printer; the protective gas is high-purity argon, and the powder-spreading method is used for printing, with powder filling the printing chamber before printing. The printing chamber is preheated to 200℃ before printing.

[0029] Step 4: 3D print on a horizontally placed substrate. The printing parameters are: laser power 260 W, scanning speed 1050 mm / s, scanning spacing 80 μm; powder layer thickness 40 μm, spot diameter 80 μm, scanning direction "Z" shaped cycle, and printing direction vertically upward.

[0030] Step 5: After printing, use wire cutting to cut the two sizes of 8×8×43 mm. 3 and 34×31×14 mm 3 Separate the block component from the substrate to obtain a high-strength and high-toughness CoCrNiAl eutectic high-entropy alloy; Step 6: Perform a room temperature tensile test on an Instron 8862 fatigue testing machine equipped with a video extensometer, with a tensile rate of 0.36 mm / min.

[0031] Step 7: Conduct room temperature elastoplastic fracture toughness tests on an Instron 8801 fatigue testing machine to obtain the relationship between crack propagation resistance (J-integral) and crack propagation length, using the formula... The fracture toughness value is obtained, where .

[0032] Figure 1 shows a schematic diagram of the printing strategy used in this invention. As shown in Figure 2, the alloy prepared by this invention has a neat surface and no obvious defects were observed. The additive manufacturing eutectic high-entropy alloy printed structure prepared by this invention is a uniform cellular structure as shown in Figure 3. The diameter is about 300 to 600 nanometers and the cell wall thickness of the B2 phase is about 30 to 70 nanometers, as measured by ImageJ software. The tensile test results are shown in Figure 4. The tensile test method is described in reference [1]. The yield strength, tensile strength and total elongation along the scanning direction (LD direction) are 1317 MPa, 1536 MPa and 29.6%, respectively, showing excellent strong and ductile properties. As shown in Figure 5, the fracture toughness test method is described in reference [2] QYL Liu, Z. Wang, Jon Ell, MX Huang, Robert O. Ritchie, Making ultrastrong steel tough by grain-boundary delamination, Science 368 (2020) 1347–1352. The fracture toughness along the scanning direction (LD direction) reached 200 MPa·m. 0.5 The eutectic high-entropy alloy prepared by additive manufacturing exhibits excellent comprehensive mechanical properties. As shown in Figure 6, the transmission characterization method is described in reference [1] ZQ Wang, XT Li, ZJ Zhang, ZF Zhang, High Specific Strength Eutectic High‐Entropy Alloy: Collaborative Effects of TRIP, TWIP, and Nanoprecipitation, Advanced Science 12 (2025) 202501703. The eutectic high-entropy alloy prepared by this invention showed significant stacking fault shearing B2 phase phenomenon when the tensile strain was 9%, and the shearing mechanism effectively improved the toughness of the prepared alloy. This invention provides a way for the design and preparation of high-strength and high-toughness additive manufacturing structural metal materials, which is applicable to CoCrNiAl system eutectic high-entropy alloys, and also applicable to other systems of eutectic high-entropy alloys.

[0033] The results demonstrate that, addressing the insufficient strength and toughness of traditional additive manufacturing of eutectic high-entropy alloys, this invention proposes an additive manufacturing method for a CoCrNiAl eutectic high-entropy alloy reinforced with shearable B2 phase. The in-situ refined microstructure effectively improves strength, while the shearable B2 phase enhances toughness, overcoming the traditional strength-toughness inverse relationship in metals. This method produces an additively manufactured eutectic high-entropy alloy possessing both high strength and high toughness. The design principles of this invention can also be extended to other eutectic high-entropy alloy systems, and it eliminates the need for subsequent heat treatment, simplifying the processing and facilitating industrial production.

[0034] Example 2: A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys. The process and conditions are the same as in Example 1, except that the laser power is 250 W and the scanning speed is 827 mm / s.

[0035] Example 3: A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys. The process and conditions are the same as in Example 1, except that the laser power is 250 W, the scanning speed is 827 mm / s, and the scanning spacing is 100 μm.

[0036] Example 4: A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys. The process and conditions are the same as in Example 1, except that the laser power is 291 W, the scanning speed is 885 mm / s, and the scanning spacing is 90 μm.

[0037] Example 5: A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys. The process and conditions are the same as in Example 1, except that the scanning speed is 885 mm / s and the scanning spacing is 90 μm.

[0038] Example 6: A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys. The process and conditions are the same as in Example 1, except that the laser power is 250 W, the scanning speed is 1000 mm / s, and the scanning spacing is 90 μm.

[0039] The relative densities of the additive manufacturing high-entropy alloys obtained in Performance Test Examples 1-6 are shown in Table 1. The relative densities of all alloys are above 99%, indicating that the alloys prepared within this process range have fewer defects and higher density.

[0040] Table 1 Relative density of additively manufactured high-entropy alloys

[0041] Comparative Example 1 describes an additive manufacturing method for a high-strength and high-toughness CoCrNiAl eutectic high-entropy alloy. The process and conditions are the same as in Example 1, except that the printing direction is at 45° to the horizontal plane. As shown in Figure 7, obvious cracks appear in the results, indicating that the sample obtained with a printing direction of 90° has better quality.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for additive manufacturing of high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys, characterized in that, High-strength and high-toughness CoCrNiAl eutectic high-entropy alloys were prepared by laser powder bed melting technology using CoCrNiAl eutectic high-entropy alloy powder. The general formula of the eutectic high-entropy alloy is Co. a Cr b Ni c Al d In the chemical expression, a, b, c, and d represent the molar percentages of the corresponding elements, where: 29≤a≤35, 18≤b≤23, 27≤c≤35, 13≤d≤19, and a+b+c+d=100.

2. The additive manufacturing method for CoCrNiAl eutectic high-entropy alloys according to claim 1, characterized in that, Eutectic high-entropy alloys include, but are not limited to, CoCrNiAl-based eutectic high-entropy alloys.

3. The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys according to claim 1, characterized in that, The process includes the following steps: (1) Vacuum drying of the CoCrNiAl eutectic high-entropy alloy powder at a temperature of 80-100℃ for 2-4 hours, with a vacuum degree ≤ 10. -2 Pa, remove moisture from the surface of eutectic high-entropy alloy powder; (2) draw the shape of the printed part by three-dimensional modeling and then import it into the 3D printing equipment; (3) 3D print the component on a horizontally placed substrate; the 3D printing parameters are: laser power 200-300W, scanning speed 800-1200mm / s, scanning spacing 70-110μm; powder layer thickness 40μm, spot diameter 80μm, scanning direction "Z" shaped cycle, printing direction vertically upward; (4) after printing, the component is separated from the substrate by wire cutting method, and the result is obtained.

4. The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys according to claim 3, characterized in that, In step (1), the particle size of the CoCrNiAl eutectic high-entropy alloy powder is 15-53 μm.

5. The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys according to claim 4, characterized in that, In step (3), the substrate is made of 304 stainless steel. Before use, the substrate is polished, cleaned and dried in sequence.

6. The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys according to claim 5, characterized in that, In step (3), the printing chamber is preheated to 200 ℃ before printing.

7. The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys according to claim 5, characterized in that, In step (3), the powder spreading method is used for printing, and the powder is spread to fill the printing chamber before printing.

8. The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys according to claim 6, characterized in that, In step (3), the protective gas used in the 3D printing process is high-purity argon.

9. The additive manufacturing method for high-strength and high-toughness CoCrNiAl eutectic high-entropy alloys according to claim 7, characterized in that, In step (4), the obtained printed additive eutectic high-entropy alloy has a room temperature yield strength exceeding 1300 MPa, a tensile strength exceeding 1500 MPa, a total elongation of 29%, and a fracture toughness K0.

05. Ⅰc More than 200 MPa·m 0.5 .

Images