A Laser Additive Manufacturing Method for Heterogeneous Medium / High Entropy Alloys Serving in a Wide Temperature Range

Abstract

A laser additive manufacturing method for a heterogeneous medium / high entropy alloy serving in a wide temperature range, which relates to a laser additive manufacturing method for an alloy. In order to solve the problems of strong plastic inversion and narrow service temperature range existing in the existing medium / high entropy alloys. Method: Take CoCrNi alloy powder and (CoCrNi) 100‑x‑y A x B y alloy powder, and dry it; Take the substrate and polish, clean and dry it; Use a laser directed energy deposition additive manufacturing device to alternately deposit the two alloy powders on the substrate to form a heterogeneous structure CoCrNi-based medium / high entropy alloy block; Carry out heat treatment. The heterogeneous structure material of the present invention has excellent wide temperature range service performance and solves the problem of strong plastic inversion at room temperature. It meets the application of CoCrNi-based medium / high entropy alloys in extremely complex environments and has broad application prospects as a rapid manufacturing method for structural components serving in complex temperature environments in fields such as national defense, aerospace, and deep space exploration.

Description

Technical Field

[0001] The present invention relates to a method for laser additive manufacturing of an alloy. Background Art

[0002] In recent years, with the rapid development of fields such as aerospace, transportation, and energy, traditional metal and alloy materials can no longer adapt to this rapid iterative trend. Medium / high entropy alloys break through the category of traditional alloy theory. Medium / high entropy alloys are composed of three or more elements mixed in equimolar ratio or near-equimolar ratio, and have many excellent properties such as high strength, high hardness, wear resistance, and corrosion resistance, and have very broad application prospects in many high-tech fields. However, generally, the disordered solid solution medium / high entropy alloy with a face-centered cubic structure has low strength, high plasticity, and excellent low-temperature fracture toughness, while the ordered medium / high metal intermetallic compound shows characteristics such as high strength, low plasticity, and high temperature resistance. This situation of mismatched strength and plasticity (inverted strength and plasticity), especially the mismatch between high and low temperature properties, greatly limits its application.

[0003] At present, when using traditional methods, processes such as gradient physical deposition, electrochemical deposition, and accumulative rolling to prepare heterogeneous materials have limitations such as small sample size and difficulty in structure or composition regulation. The discrete - accumulation characteristics of laser directed energy deposition additive manufacturing technology can not only freely design structures in multiple dimensions, but also achieve precise deposition and regulation of alloy compositions in different parts, and can be used for the integrated forming preparation of high-performance heterogeneous medium / high entropy alloy components, realizing the intelligent collaborative control of their composition, structure, and performance, thereby expanding the application of medium / high entropy alloy components in the aerospace field, polar exploration, and space complex extreme environments. Summary of the Invention

[0004] In order to solve the problems of inverted strength and plasticity and narrow service temperature range existing in existing medium / high entropy alloys, the present invention provides a method for laser additive manufacturing of a heterogeneous medium / high entropy alloy with wide temperature range service.

[0005] The method for laser additive manufacturing of a heterogeneous medium / high entropy alloy with wide temperature range service according to the present invention is carried out according to the following steps:

[0006] Step 1: Take CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powder, and dry it; take a substrate and perform grinding, cleaning, and drying;

[0007] The (CoCrNi) 100-x-y A x B yAmong them, A is Al, Ti, Mo or V, B is Al, Ti, Mo or V, A and B are different, x = 3 to 12, y = 3 to 12; when x + y ≤ 14, it is a medium-entropy alloy, and when x + y > 14, it is a high-entropy alloy;

[0008] The volume ratio of the CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powders is (1 to 2):(1 to 2);

[0009] Step two: Add the CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powders into two hoppers of a laser directed energy deposition additive manufacturing device respectively, and use the laser directed energy deposition additive manufacturing device to alternately deposit the CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powders on the substrate to obtain a CoCrNi layer and (CoCrNi) 100-x-y A x B y layer-alternated heterogeneous structure CoCrNi-based medium / high-entropy alloy bulk;

[0010] The deposition process is as follows: In an environmental chamber, evacuate before deposition starts, then introduce argon for protection. Adopt a serpentine reciprocating scanning mode, the protection gas flow rate is 2 L / min, the laser power is 950 W to 1200 W, the scanning speed is 16 mm / s to 17 mm / s, the powder feeding gas flow rate is 4 L / min, the spot diameter is 2 to 3 mm, and the overlapping rate is 40 to 60%;

[0011] Step three: After the heterogeneous structure CoCrNi-based medium / high-entropy alloy bulk cools down, take it out, cut off the substrate by wire electrical discharge machining, and heat-treat the heterogeneous structure CoCrNi-based medium / high-entropy alloy;

[0012] The heat treatment process is as follows: First, keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 1150 to 1180 °C for 2 hours, then immediately water-cool it to room temperature; then keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 600 to 650 °C for 2 hours, and finally water-cool it to room temperature.

[0013] The principle and beneficial effects of the present invention are as follows:

[0014] (1) The present invention solves the problems of the strength-ductility inversion at room temperature in medium / high-entropy alloys with a single-phase disordered solid-solution structure and the mismatch between the low-temperature and high-temperature properties of medium / high-entropy intermetallic compounds, and proposes an integrated forming method for high-performance heterogeneous medium / high-entropy alloy components by laser directed energy deposition additive manufacturing. The mechanical characteristics of the solid-solution CoCrNi alloy are that it has high plasticity and low strength at room temperature and low temperature, and its strength rapidly decreases at high temperature; while the mechanical characteristics of the intermetallic compound (CoCrNi) 100-x-y A x B y alloy are that it has high strength, high hardness and low plasticity at room temperature and low temperature, still maintains high strength at high temperature, and has a certain plasticity; due to the "soft" CoCrNi alloy and the "hard" intermetallic compound (CoCrNi) 100-x-y A x B y alloy that make up the layered material can not only generate long-range back stress strengthening in the "soft" CoCrNi alloy layer during the deformation process, making the soft layer stronger, but also inhibit the generation of necking and improve the uniform deformation ability of the entire heterogeneous structure material, thus solving the problem of strength-ductility inversion at room temperature. Similarly, the layered combination form can enable the respective excellent properties of the two components to be fully exerted within a wide temperature range, so that the entire heterogeneous structure material has excellent service performance in a wide temperature range, solving the problem of mismatch between low-temperature and high-temperature properties.

[0015] (2) The present invention can achieve the rapid deposition of medium / high-entropy alloys with various different compositions, and avoid phenomena such as cracking during the printing process of medium / high-entropy alloys through the optimal process parameters of the alloys, and can obtain heterogeneous medium / high-entropy alloys with good forming, no obvious deformation and high density;

[0016] (3) The CoCrNi-based medium / high-entropy alloy prepared by the present invention has excellent comprehensive mechanical properties at room temperature and functional characteristics for service within a wide temperature range, and exhibits excellent mechanical properties in the temperature range from -196 °C to 600 °C, which can meet the application of CoCrNi-based medium / high-entropy alloys in extremely complex environments;

[0017] (4) The heat treatment process of the present invention first holds at a high temperature of 1150 - 1180 °C to completely transform the dendritic structure formed during the additive manufacturing process into an equiaxed crystal structure. On the one hand, it eliminates the segregation of a small amount of elements between dendrites, avoids the influence of the uneven distribution of harmful intermetallic compound phases on the plasticity of the alloy, promotes the diffusion of solute elements such as A and B into the CoCrNi layer, and forms an interlayer interface with a compositional gradient change. On the other hand, it eliminates the anisotropy of mechanical properties caused by dendrites; further, holding at 600 - 650 °C promotes (CoCrNi) 100-x-y A x By Precipitation of intermediate intermetallic compounds (such as L12 phase, σ phase) and keep them stable within this temperature range. Finally, a laminated material composed of a solid-solution CoCrNi layer - intermetallic compound (CoCrNi) 100-x-y A x B y layer combination is obtained. Therefore, the multi-hopper powder feeding directional energy deposition additive manufacturing technology of the present invention combined with the post-treatment process can, on the basis of not destroying the original shape of the workpiece, with mature and simple post-treatment technology, further regulate the microstructure of the alloy through a reasonable heat treatment process, and optimize the comprehensive performance of the CoCrNi-based medium / high-entropy alloy with heterogeneous structure.

[0018] (5) By specifically regulating the composition distribution of alloys with two components, the present invention prepares a new type of composite material, enabling the heterogeneous structure material to show regular changes in composition and microstructure, demonstrating superiority in improving the mechanical properties of the material. It can not only significantly overcome the problem of the strength-ductility inversion of medium / high-entropy alloys, but also give full play to the performance advantages of the two materials, making the prepared CoCrNi-based medium / high-entropy alloy with heterogeneous structure have excellent comprehensive performance in a wide temperature range.

[0019] (6) The present invention can adjust the proportion of the two alloy components in the heterogeneous structure according to the specific service temperature and usage environment requirements of the material, effectively preventing crack generation during the additive manufacturing process, and having broad application prospects for the rapid manufacturing of structural parts serving in complex temperature environments in fields such as national defense, aerospace, and deep space exploration.

[0020] (7) On the basis of CoCrNi alloy, the present invention adds two components A and B to form (CoCrNi) 100-x-y A x B y alloy. On the one hand, it can improve the deficiencies of CoCrNi alloy at room temperature and high temperature. On the other hand, it can also reduce the usage amount of metals such as Co and Ni and reduce the weight of the entire material. Description of the Drawings

[0021] Figure 1 Schematic diagram of the CoCrNi-based medium-entropy alloy with heterogeneous structure prepared in Example 1;

[0022] Figure 2 Physical diagram of the CoCrNi-based medium-entropy alloy with heterogeneous structure prepared in Example 1;

[0023] Figure 3 SEM microstructure diagram of the printed state of the CoCrNi-based medium-entropy alloy with heterogeneous structure prepared in Example 1;

[0024] Figure 4SEM micrograph of the heat-treated heterogeneous CoCrNi-based medium-entropy alloy prepared in Example 1;

[0025] Figure 5 Phase diagram of the heat-treated heterogeneous CoCrNi-based medium-entropy alloy prepared in Example 1;

[0026] Figure 6 Engineering stress-strain curve of the heat-treated heterogeneous CoCrNi-based medium-entropy alloy prepared in Example 1. Detailed implementation manners

[0027] The technical solution of the present invention is not limited to the specific implementation manners listed below, and also includes any reasonable combination between the specific implementation manners.

[0028] Detailed implementation manner 1: The laser additive manufacturing method of the heterogeneous medium / high-entropy alloy for wide-temperature-range service is carried out according to the following steps:

[0029] Step 1: Take CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powder, and dry it; take the substrate and polish, clean and dry it;

[0030] In the (CoCrNi) 100-x-y A x B y , A is Al, Ti, Mo or V, B is Al, Ti, Mo or V, A and B are different, x = 3 to 12, y = 3 to 12; when x + y ≤ 14, it is a medium-entropy alloy, and when x + y > 14, it is a high-entropy alloy;

[0031] The volume ratio of the CoCrNi alloy powder and the (CoCrNi) 100-x-y A x B y alloy powder is (1 to 2):(1 to 2);

[0032] Step 2: Respectively add the CoCrNi alloy powder and the (CoCrNi) 100-x-y A x B y alloy powder into two bins of the laser direct energy deposition additive manufacturing equipment, and use the laser direct energy deposition additive manufacturing equipment to alternately deposit the CoCrNi alloy powder and the (CoCrNi) 100-x-y A x B y alloy powder on the substrate to obtain CoCrNi layers and (CoCrNi) 100-x-y A x B yLayer-alternated heterogeneous structure CoCrNi-based medium / high entropy alloy bulk;

[0033] The deposition process is as follows: In the environmental chamber, evacuate before deposition starts, then introduce argon for protection. Adopt a serpentine reciprocating scanning mode, with the protective gas flow rate of 2 L / min, laser power of 950 W - 1200 W, scanning speed of 16 mm / s - 17 mm / s, powder feeding gas flow rate of 4 L / min, spot diameter of 2 - 3 mm, and overlapping rate of 40 - 60%.

[0034] Step 3: After the heterogeneous structure CoCrNi-based medium / high entropy alloy bulk cools down, take it out, cut off the substrate by wire electrical discharge machining, and heat-treat the heterogeneous structure CoCrNi-based medium / high entropy alloy.

[0035] The heat treatment process is as follows: First, keep the heterogeneous structure CoCrNi-based medium / high entropy alloy at 1150 - 1180 °C for 2 hours, and then immediately water-cool it to room temperature; then keep the heterogeneous structure CoCrNi-based medium / high entropy alloy at 600 - 650 °C for 2 hours, and finally water-cool it to room temperature.

[0036] The principle and beneficial effects of this embodiment are as follows:

[0037] (1) This embodiment solves the problems of the inversion of room-temperature strength and plasticity in the medium / high entropy alloy with a single-phase disordered solid solution structure, and the mismatch of high and low-temperature properties in the medium / high entropy intermetallic compound, and proposes an integrated forming of high-performance heterogeneous medium / high entropy alloy components by laser directed energy deposition additive manufacturing. The mechanical characteristics of the solid-solution CoCrNi alloy are that at room temperature and low temperature, it has high plasticity and low strength, and the strength rapidly decreases at high temperature; while the mechanical characteristics of the intermetallic compound (CoCrNi) 100-x-y A x B y alloy are that at room temperature and low temperature, it has high strength, high hardness, and low plasticity, and still maintains high strength at high temperature and has a certain plasticity; due to the "soft" CoCrNi alloy and the "hard" intermetallic compound (CoCrNi) 100-x-y A x B y alloy that make up the layered material can not only generate long-range back stress strengthening in the "soft" CoCrNi alloy layer during the deformation process, making the soft layer stronger, but also inhibit the generation of necking, improve the uniform deformation ability of the entire heterogeneous structure material, and solve the problem of inversion of room-temperature strength and plasticity. Similarly, the layered combination form can enable the respective excellent properties of the two components to be fully exerted in a wide temperature range, so that the entire heterogeneous structure material has excellent service performance in a wide temperature range, and solves the problem of mismatch of high and low-temperature properties.

[0038] (2) This embodiment can achieve the rapid deposition of medium / high-entropy alloys with various different compositions, and avoid phenomena such as cracking during the printing process of medium / high-entropy alloys by means of the optimal process parameters of the alloys. A heterogeneous structure medium / high-entropy alloy with good forming, no obvious deformation, and high density can be obtained;

[0039] (3) The CoCrNi-based medium / high-entropy alloy prepared by this embodiment has excellent comprehensive mechanical properties at room temperature and functional characteristics for service in a wide temperature range, and exhibits excellent mechanical properties in the temperature range from -196 °C to 600 °C, which can meet the application of CoCrNi-based medium / high-entropy alloys in extremely complex environments;

[0040] (4) The heat treatment process of this embodiment first holds at a high temperature of 1150 - 1180 °C to completely transform the dendritic structure formed during the additive manufacturing process into an equiaxed crystal structure. On the one hand, it eliminates the segregation of a small amount of elements between dendrites, avoids the influence of the uneven distribution of harmful intermetallic compound phases on the plasticity of the alloy, promotes the diffusion of solute elements such as A and B into the CoCrNi layer, and forms an interlayer interface with a compositional gradient change. On the other hand, it eliminates the anisotropy of mechanical properties caused by dendrites. Further, holding at 600 - 650 °C promotes the precipitation of intermetallic compounds (such as L12 phase, σ phase) in (CoCrNi) 100-x-y A x B y and makes it stable in this temperature range. Finally, a layered material composed of a solid solution CoCrNi layer - intermetallic compound (CoCrNi) 100-x-y A x B y layers is obtained. Therefore, the multi-hopper powder feeding directed energy deposition additive manufacturing technology of this embodiment combined with the post-treatment process can further regulate the microstructure of the alloy and optimize the comprehensive performance of the heterogeneous structure CoCrNi-based medium / high-entropy alloy on the basis of not destroying the original shape of the workpiece, with mature and simple post-treatment technology, etc., through a reasonable heat treatment process.

[0041] (5) By specifically regulating the composition distribution of alloys of two compositions, this embodiment prepares a new type of composite material, enabling the heterogeneous structure material to show regular changes in composition and microstructure, demonstrating the superiority in improving the mechanical properties of the material. It can not only significantly overcome the problem of the strong plasticity inversion of medium / high-entropy alloys, but also bring out the performance advantages of the two materials respectively, making the prepared heterogeneous structure CoCrNi-based medium / high-entropy alloy have excellent comprehensive properties in a wide temperature range.

[0042] (6) In this embodiment, the proportions of the two alloy components in the heterogeneous structure can be adjusted according to the specific service temperature of the material and the requirements of the use environment, which can effectively prevent crack generation during the additive manufacturing process. It has broad application prospects for the rapid manufacturing of structural components serving in complex temperature environments in fields such as national defense, aerospace, and deep space exploration.

[0043] (7) Based on the CoCrNi alloy, two components A and B are added to form the (CoCrNi) 100-x-y A x B y alloy. On the one hand, it can improve the deficiencies of the CoCrNi alloy at room temperature and high temperature. On the other hand, it can also reduce the usage of metals such as Co and Ni and reduce the weight of the entire material.

[0044] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the particle sizes of the CoCrNi alloy powder and the (CoCrNi) 100-x-y A x B y alloy powder in Step 1 are 45 - 105 μm.

[0045] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: the drying process of the CoCrNi alloy powder and the (CoCrNi) 100-x-y A x B y alloy powder in Step 1 is: maintaining at 60 - 120 °C for 2 hours.

[0046] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: the substrate in Step 1 is 45 - steel.

[0047] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that: the cleaning of the substrate in Step 1 uses acetone.

[0048] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that: the drying process of the substrate in Step 1 is: maintaining at 60 - 120 °C for 2 hours.

[0049] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that: the thickness of the CoCrNi layer in Step 2 is 0.5 - 1 mm; the thickness of the (CoCrNi) 100-x-y A x B y layer is 0.4 - 1 mm.

[0050] Embodiment VIII: The difference between this embodiment and any one of Embodiments I to VII is that: the deposition process described in Step 2 is as follows: in an environmental chamber, evacuate the air before deposition starts, then introduce argon for protection, adopt a serpentine reciprocating scanning mode, the protective gas flow rate is 2 L / min, the laser power is 950 W, the scanning speed is 17 mm / s, the powder feeding gas flow rate is 4 L / min, the spot diameter is 2 mm, and the overlapping rate is 60%.

[0051] Embodiment IX: The difference between this embodiment and any one of Embodiments I to VIII is that: the deposition process described in Step 2 is as follows: in an environmental chamber, evacuate the air before deposition starts, then introduce argon for protection, adopt a serpentine reciprocating scanning mode, the protective gas flow rate is 2 L / min, the laser power is 1200 W, the scanning speed is 16 mm / s, the powder feeding gas flow rate is 4 L / min, the spot diameter is 3 mm, and the overlapping rate is 40%.

[0052] Embodiment X: The difference between this embodiment and any one of Embodiments I to IX is that: the heat treatment process described in Step 3 is as follows: first, keep the heterogeneous CoCrNi-based medium / high-entropy alloy at 1180 °C for 2 hours, and then immediately water-cool it to room temperature; then keep the heterogeneous CoCrNi-based medium / high-entropy alloy at 650 °C for 2 hours, and finally water-cool it to room temperature.

[0053] Example 1:

[0054] The method for laser additive manufacturing of the wide-temperature-range service heterogeneous medium / high-entropy alloy in this example is carried out according to the following steps:

[0055] Step 1: Take CoCrNi alloy powder and (CoCrNi) 82 Al9Ti9 alloy powder, and dry them; take a substrate and polish, clean, and dry it;

[0056] The volume ratio of the CoCrNi alloy powder and the (CoCrNi) 82 Al9Ti9 alloy powder is 1:1;

[0057] The particle size of the CoCrNi alloy powder and the (CoCrNi) 82 Al9Ti9 alloy powder is 45 - 105 μm; the drying process of the CoCrNi alloy powder and the (CoCrNi) 100-x-y A x B y alloy powder is: keep at 60 °C for 2 hours; the substrate is 45 steel; the cleaning of the substrate uses acetone; the drying process of the substrate is: keep at 60 °C for 2 hours;

[0058] Step 2: Mix the CoCrNi alloy powder and the (CoCrNi) 82The Al9Ti9 alloy powder was separately added into two feed bins of a laser directed energy deposition additive manufacturing device, and the CoCrNi alloy powder and (CoCrNi) 82 Al9Ti9 alloy powder were alternately deposited on the substrate to obtain a CoCrNi layer and (CoCrNi) 82 Al9Ti9 layer alternating heterogeneous structure CoCrNi-based medium / high entropy alloy bulk;

[0059] The thickness of the CoCrNi layer is 0.5 mm; (CoCrNi) 82 The thickness of the Al9Ti9 layer is 0.5 mm;

[0060] The deposition process is as follows: In the environmental chamber, evacuate before deposition starts, then introduce argon for protection. Adopt a serpentine reciprocating scanning mode, with a protective gas flow rate of 2 L / min, a laser power of 950 W, a scanning speed of 17 mm / s, a powder feeding gas flow rate of 4 L / min, a spot diameter of 2 mm, and an overlapping rate of 60%;

[0061] Step three: After the CoCrNi-based medium / high entropy alloy bulk with heterogeneous structure cools down, take it out, cut off the substrate by wire electrical discharge machining, and heat-treat the CoCrNi-based medium / high entropy alloy with heterogeneous structure;

[0062] The heat treatment process is as follows: First, keep the CoCrNi-based medium / high entropy alloy with heterogeneous structure at 1150 °C for 2 hours, then immediately water-cool it to room temperature; then keep the CoCrNi-based medium / high entropy alloy with heterogeneous structure at 600 °C for 2 hours, and finally water-cool it to room temperature.

[0063] In this embodiment, Figure 1 is a schematic diagram of preparing a heterogeneous layered medium entropy alloy by dual-feed bin powder feeding laser directed energy deposition. The CoCrNi-based medium / high entropy alloy bulk with heterogeneous structure prepared and heat-treated by the above laser additive manufacturing method, the physical diagram is as Figure 2 shown, and no warping deformation and cracking phenomena occur in the heterogeneous structure alloy bulk.

[0064] From Figure 3 the SEM microstructure diagram of the as-printed state of the heterogeneous layered medium entropy alloy shown, it can be found that along the plane where the deposition-scanning direction is located, after being corroded by aqua regia, due to the different corrosion resistance characteristics of the two-component alloys, the as-printed heterogeneous structure alloy consists of a layered structure composed of two alloys with obvious contrast in contrast, and there are no cracks and holes between layers. Among them, the gray layer is the CoCrNi alloy layer, and the bright layer is (CoCrNi) 82 Al9Ti9 alloy layer, and the microstructures of the two alloy layers are both composed of dendrites along the deposition direction.

[0065] Figure 4 The SEM micrograph of the heat-treated additively manufactured heterogeneous laminated medium-entropy alloy is shown. It can be found that after heat treatment, the two-layer alloy microstructure has changed into equiaxed grains. This is because after two-step heat treatment, the elements between the dendrites of the as-printed heterogeneous laminated alloy have diffused, the element segregation phenomenon has been eliminated, and the initial small-angle grain boundaries have disappeared, leaving only large-angle grain boundaries. This equiaxed grain microstructure can improve the anisotropy of the alloy mechanical properties caused by additive manufacturing and greatly improve the room-temperature plasticity of the heterogeneous structure alloy.

[0066] Figure 5 The phase diagram of the heat-treated additively manufactured heterogeneous laminated medium-entropy alloy is shown. Along the deposition direction, after aging treatment at 600 °C, the equilibrium phases of the adjacent two layers of the laminated medium-entropy alloy are composed of a single-phase disordered solid solution (FCC structure) and a disordered solid solution (FCC structure) + intermetallic compound (L12 phase), respectively. This shows that the laminated alloy composed of disordered solid solution and intermetallic compound in the equilibrium state can maintain a stable phase composition in the temperature range of -196 °C to 600 °C.

[0067] Figure 6 The engineering stress-strain curve of the heat-treated additively manufactured heterogeneous laminated medium-entropy alloy is shown. It can be found that the heterogeneous laminated medium-entropy alloy has excellent comprehensive mechanical properties in a wide temperature range. The tensile strength is 1555.4 MPa and the elongation is 40.5% at -196 °C; the tensile strength is 1268.2 MPa and the elongation is 38.2% at room temperature; the tensile strength is 1024.3 MPa and the elongation is 38.7% at 600 °C.

[0068] In this example, CoCrNi and (CoCrNi) 82 Al9Ti9 (at.%) medium-entropy alloy powder is used as the raw material. Using a dual-hopper coaxial powder feeding laser melting deposition equipment, each layer of medium-entropy alloy is alternately deposited on a 45 steel substrate in a serpentine reciprocating scanning printing form. Subsequently, after two-step heat treatment, solution treatment is first carried out at 1150 °C, and then aging treatment is carried out at 600 °C, so that the L12 phase ((Ni,Co)3(Al,Ti)) precipitates dispersedly at the interface between the (CoCrNi) 82 Al9Ti9 alloy layer and the two layers. Its high strength and toughness in a wide temperature range mainly come from the excellent strength and plasticity of the CoCrNi medium-entropy alloy at low temperatures (taking liquid nitrogen temperature as an example), and the high-temperature resistance (600 - 700 °C) and oxidation resistance of the L12 phase formed by the eutectoid transformation of the (CoCrNi) 82 Al9Ti9 layer.

[0069] Example 2:

[0070] The laser additive manufacturing method for the wide-temperature-range service heterogeneous medium / high-entropy alloy in this embodiment is carried out according to the following steps:

[0071] Step 1: Take CoCrNi alloy powder and (CoCrNi) 88 Mo5Ti7 alloy powder, and dry them; take a substrate and polish, clean, and dry it; the volume ratio of the CoCrNi alloy powder to the (CoCrNi) 88 Mo5Ti7 alloy powder is 1:1;

[0072] The CoCrNi alloy powder and the (CoCrNi) 88 Mo5Ti7 alloy powder has a particle size of 45 - 105 μm; the drying process of the CoCrNi alloy powder and the (CoCrNi) 88 Mo5Ti7 alloy powder is: keep at 60 °C for 2 hours; the substrate is 45 steel; the cleaning of the substrate uses acetone; the drying process of the substrate is: keep at 60 °C for 2 hours;

[0073] Step 2: Add the CoCrNi alloy powder and the (CoCrNi) 88 Mo5Ti7 alloy powder into two hoppers of the laser direct energy deposition additive manufacturing equipment respectively, and use the laser direct energy deposition additive manufacturing equipment to alternately deposit the CoCrNi alloy powder and the (CoCrNi) 88 Mo5Ti7 alloy powder on the substrate to obtain a heterogeneous structure CoCrNi-based medium / high-entropy alloy block with alternating CoCrNi layers and (CoCrNi) 88 Mo5Ti7 layers; the thickness of the CoCrNi layer is 0.8 mm; the (CoCrNi) 88 Mo5Ti7 layer has a thickness of 0.4 mm;

[0074] The deposition process is: in an environmental chamber, evacuate before deposition starts, then pass argon for protection, adopt a serpentine reciprocating scanning mode, the protective gas flow rate is 2 L / min, the laser power is 1200 W, the scanning speed is 16 mm / s, the powder feeding gas flow rate is 4 L / min, the spot diameter is 3 mm, and the overlap rate is 40%;

[0075] Step 3: After the heterogeneous structure CoCrNi-based medium / high-entropy alloy block cools down, take it out, cut off the substrate by wire electrical discharge machining, and heat-treat the heterogeneous structure CoCrNi-based medium / high-entropy alloy; the heat treatment process is: first keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 1180 °C for 2 hours, then immediately water-cool it to room temperature; then keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 650 °C for 2 hours, and finally water-cool it to room temperature.

[0076] The tensile strength of the heterogeneous laminated medium entropy alloy prepared in this embodiment is 1364.6 MPa and the elongation is 33.1% at -196 °C; the tensile strength is 1148.2 MPa and the elongation is 26.7% at room temperature; the tensile strength is 1123.1 MPa and the elongation is 17.9% at 600 °C.

Claims

1. A laser additive manufacturing method for a wide-temperature-range service heterogeneous medium / high-entropy alloy, characterized in that: The laser additive manufacturing method for wide-temperature-range service heterogeneous medium / high-entropy alloys is carried out according to the following steps: Step 1: Take CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powder, and dry it; Take the substrate and polish, clean, and dry it; The said (CoCrNi) 100-x-y A x B y wherein, A is Al, Ti, Mo or V, B is Al, Ti, Mo or V, A and B are different, x = 3 to 12, y = 3 to 12; when x + y ≤ 14, it is a medium entropy alloy, and when x + y > 14, it is a high entropy alloy; The CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y The volume ratio of the alloy powders is (1 to 2):(1 to 2); Step 2: Add CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powder into two hoppers of the laser directed energy deposition additive manufacturing equipment respectively, and use the dual-hopper coaxial powder feeding laser melting deposition equipment to alternately deposit CoCrNi alloy powder and (CoCrNi) 100-x-y A x B y alloy powder on the substrate to obtain a CoCrNi layer and (CoCrNi) 100-x-y A x B y layer-alternated heterogeneous structure CoCrNi-based medium / high entropy alloy bulk; The deposition process is as follows: In the environmental chamber, evacuate the air before deposition starts, then introduce argon for protection. Adopt a serpentine reciprocating scanning mode, with a protective gas flow rate of 2 L / min, a laser power of 950 W - 1200 W, a scanning speed of 16 mm / s - 17 mm / s, a powder feeding gas flow rate of 4 L / min, a spot diameter of 2 - 3 mm, and an overlap rate of 40 - 60%; Step 3: After the heterogeneous structure CoCrNi-based medium / high-entropy alloy block cools down, take it out, cut off the substrate by wire electrical discharge machining, and heat-treat the heterogeneous structure CoCrNi-based medium / high-entropy alloy; The heat treatment process is as follows: First, keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 1150 - 1180 °C for 2 hours, then immediately water-cool it to room temperature; then keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 600 - 650 °C for 2 hours, and finally water-cool it to room temperature.

2. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high-entropy alloy according to claim 1, wherein: The CoCrNi alloy powder described in Step 1 and (CoCrNi) 100-x-y A x B y The particle size of the alloy powder is 45 to 105 μm.

3. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high entropy alloy according to claim 1, characterized in that: The CoCrNi alloy powder described in Step 1 and (CoCrNi) 100-x-y A x B y The drying process of the alloy powder is: maintaining at 60 - 120 °C for 2 hours.

4. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high entropy alloy according to claim 1, characterized in that: The substrate described in Step 1 is 45 steel.

5. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high entropy alloy according to claim 1, characterized in that: The cleaning of the substrate described in Step 1 uses acetone.

6. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high entropy alloy according to claim 1, characterized in that: The drying process of the substrate described in Step 1 is: Keep it at 60 - 120 °C for 2 hours.

7. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high-entropy alloy according to claim 1, characterized in that: The thickness of the CoCrNi layer described in Step 2 is 0.5 - 1 mm; (CoCrNi) 100-x-y A x B y The thickness of the layer is 0.4 - 1 mm.

8. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high entropy alloy according to claim 1, wherein: The deposition process described in Step 2 is as follows: In the environmental chamber, evacuate the air before deposition starts, then introduce argon for protection. Adopt a serpentine reciprocating scanning mode, with a protective gas flow rate of 2 L / min, a laser power of 950 W, a scanning speed of 17 mm / s, a powder feeding gas flow rate of 4 L / min, a spot diameter of 2 mm, and an overlap rate of 60%.

9. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high entropy alloy according to claim 1, characterized in that: The deposition process described in Step 2 is as follows: In the environmental chamber, evacuate the air before deposition starts, then introduce argon for protection. Adopt a serpentine reciprocating scanning mode, with a protective gas flow rate of 2 L / min, a laser power of 1200 W, a scanning speed of 16 mm / s, a powder feeding gas flow rate of 4 L / min, a spot diameter of 3 mm, and an overlap rate of 40%.

10. The laser additive manufacturing method of the wide-temperature-range service heterogeneous medium / high-entropy alloy according to claim 1, characterized in that: The heat treatment process described in Step 3 is as follows: First, keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 1180 °C for 2 hours, then immediately water-cool it to room temperature; then keep the heterogeneous structure CoCrNi-based medium / high-entropy alloy at 650 °C for 2 hours, and finally water-cool it to room temperature.

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