Lightweight high-strength ni-co-based single-crystal high-entropy alloy and preparation method thereof

Abstract

This invention discloses a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method. The chemical composition of this single-crystal high-entropy alloy includes eight elements: Ni, Co, Cr, Al, Ti, Mo, W, and Hf. The atomic percentages of each element are: Ni 45-55 at%, Co 15-20 at%, Cr 9-12 at%, Al 9-12 at%, Ti 4-8 at%, Mo 1-2 at%, W 0-1 at%, and Hf 0-0.1 at%. The preparation method includes the following steps: obtaining the liquidus temperature through simulation calculation and the eutectic dissolution temperature through melting point testing; sequentially placing the elemental elements Ni, Co, Cr, Ti, Mo, and W into a crucible in a vacuum induction melting furnace and casting them into a master alloy ingot; and preparing a grain with a specific orientation using the Bridgeman high-speed solidification method and the seed crystal method. <001> A single-crystal high-entropy alloy test rod was prepared; the single-crystal high-entropy alloy test rod was subjected to solution treatment, first-stage aging, and second-stage aging in sequence to obtain a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy. The single-crystal high-entropy alloy prepared by this invention has a low density and excellent room-temperature and high-temperature mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of single-crystal high-entropy alloy materials and preparation technology, specifically relating to a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method. Background Technology

[0002] As is well known, high-entropy alloys refer to novel alloy systems with four or more components, each with equal or nearly equal atomic ratios. Extensive research has been conducted on high-entropy alloys in areas such as directional solidification, and their compositional design holds immense potential, capable of meeting the requirements of lightweight, high-strength, and high-temperature resistant single-crystal turbine blades. Traditional single-crystal superalloys, using Fe, Co, Ni, and other elements as the main matrix elements, incorporate more than ten strengthening elements to eliminate grain boundary effects, resulting in alloys with superior high-temperature mechanical properties and creep resistance. However, their development has reached a bottleneck. Building upon single-crystal superalloys, a new type of single-crystal high-entropy alloy can be defined as an alloy composed of four or more elements, conforming to the characteristics of a single-crystal structure, and satisfying thermodynamic and kinetic conditions during single-crystal formation, with a mixing entropy greater than 1.38R.

[0003] There are two main development directions for existing single-crystal high-entropy alloys: one is the single-crystalization of high-entropy alloys, such as CoCrFeMnNi, AlCoCrFeNi, or transition metal systems, but progress has not been made in their performance research; the other is the high-entropyization of single-crystal superalloys, mainly Ni-Co-based and Co-Ni-based superalloys. This direction has seen extensive research in both microstructure and properties, and some progress has been made. Although researchers have been attempting to develop various alloys that surpass existing single-crystal superalloys and are suitable for high-temperature applications in recent years, the actual results have fallen short of production needs.

[0004] The invention patent with publication number CN117070825A discloses a single-crystal high-entropy alloy with excellent high-temperature mechanical properties and its preparation method. The alloy's chemical composition, by atomic percentage, is: Co 35-40%, Cr 5-7%, Mo 4-6%, Al 9-11%, Ta 2-4%, Ti 3-4%, 16%≤Al+Ti+Ta≤17%, and the remainder Ni. The preparation method includes the following steps: repeatedly melting the raw materials in a crucible of a non-consumable arc melting furnace to obtain a single-crystal high-entropy alloy master alloy button ingot; placing the elemental materials into the crucible and stacking them in order of increasing melting point, while electromagnetically stirring during the melting process; cutting the button ingot into metal rods, polishing them, and then ultrasonically cleaning them to obtain the single-crystal high-entropy alloy master material; using the Bridgeman liquid metal crystal growth technique to prepare the single-crystal high-entropy alloy master material into a single-crystal alloy; and using the seed crystal method to prepare the single-crystal high-entropy alloy, with the seed crystal orientation being... <001> During directional solidification, the casting temperature was 1540℃, the holding time was 1 hour, and the pulling rate was 100 μm / s. The single-crystal alloy was then subjected to solution treatment and aging treatment to obtain a single-crystal high-entropy alloy. This technical solution focuses on the high-temperature mechanical properties of the single-crystal high-entropy alloy, but neglects the room-temperature mechanical properties of the alloy.

[0005] Currently, to address the issues of unbalanced room temperature and high temperature properties and the inability to simultaneously achieve both strength and plasticity in single-crystal high-entropy alloys, efforts are being made to improve their mechanical properties through alloy composition design, heat treatment system optimization, and casting process improvement, thereby promoting the high-temperature application of single-crystal high-entropy alloys. Therefore, there is an urgent need to develop a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method to meet the requirement of balancing room temperature and high temperature properties of single-crystal high-entropy alloys. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy. The chemical composition of the single-crystal high-entropy alloy includes eight elements: Ni, Co, Cr, Al, Ti, Mo, W, and Hf. The atomic percentages of each element are as follows: Ni 45-55 at%, Co 15-20 at%, Cr 9-12 at%, Al 9-12 at%, Ti 4-8 at%, Mo 1-2 at%, W 0-1 at%, and Hf 0-0.1 at%, with the sum of the atomic percentages of each element being 100%.

[0007] Preferably, the mixing entropy ΔS of the single-crystal high-entropy alloy is... mix ≥1.386R, the formula for calculating the entropy of mixture is: In the formula,

[0008] ΔS mix —The mixing entropy of a single-crystal high-entropy alloy, J / (mol·K);

[0009] R—gas constant, R = 8.314 J / (mol·K);

[0010] i—any element among Ni, Co, Cr, Al, Ti, Mo, W, and Hf;

[0011] n—the sum of all elements in a single-crystal high-entropy alloy;

[0012] x i —Atomic percentage of element i in single-crystal high-entropy alloys, %.

[0013] In any of the above embodiments, it is preferred that the grain orientation of the single-crystal high-entropy alloy is as follows: <001> The dendrite spacing is 350-430 μm, the volume fraction of loose material is 0-0.2%, and the γ′ microstructure consists of square primary γ′ microstructure and granular secondary γ′ microstructure. The size of the primary γ′ microstructure is 350-500 nm, and the size of the secondary γ′ microstructure is 10-30 nm. The volume fraction of the primary γ′ microstructure is 65-70%, and the volume fraction of the secondary γ′ microstructure is 3-7%. The density of the single-crystal high-entropy alloy is less than 8.0 g / cm³. 3 .

[0014] This invention also provides a method for preparing a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy, used to prepare the lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy described in any of the above-mentioned methods, comprising the following steps in sequence:

[0015] Step 1: Using JMatPro, Thermo-Calc, or Pandat software, perform thermodynamic calculations and simulations according to the composition design ratio of the single-crystal high-entropy alloy to obtain the liquidus temperature parameters; obtain the eutectic dissolution temperature parameters through DSC melting point testing;

[0016] Step 2: Weigh out the elemental elements Ni, Co, Cr, Al, Ti, Mo, W, and Hf with a purity of 99.5% or higher according to the composition design of the single-crystal high-entropy alloy.

[0017] Step 3: Place the elemental elements Ni, Co, Cr, Ti, Mo, and W into the crucible of the vacuum induction melting furnace according to the design order, evacuate to a certain vacuum level, and then heat and melt; when the temperature rises to the refining temperature, add the elemental elements Al and Hf, and perform electromagnetic stirring. After refining is completed, cast into a single crystal high-entropy alloy master alloy ingot.

[0018] Step 4: Prepare grains with the following orientation using the high-speed solidification Bridgeman method and seed crystal method. <001> The process for producing single-crystal high-entropy alloy test bars involves first placing the single-crystal high-entropy alloy master alloy ingot into a vacuum melting single-crystal directional solidification furnace, evacuating it to a certain vacuum level, and then heating and melting it. Next, it is refined at a certain temperature. After refining, the temperature is lowered to the casting temperature. Finally, it is cast at a certain pulling rate to obtain the as-cast single-crystal high-entropy alloy.

[0019] Step 5: Place the as-cast single-crystal high-entropy alloy into a heat treatment furnace for solution treatment to obtain a solution-treated single-crystal high-entropy alloy; Step 6: Place the solution-treated single-crystal high-entropy alloy into a heat treatment furnace for first-stage aging treatment to obtain a first-stage aged single-crystal high-entropy alloy.

[0020] Step 7: Place the first-stage aged single-crystal high-entropy alloy into a heat treatment furnace for second-stage aging treatment to obtain the final heat-treated single-crystal high-entropy alloy, which is a lightweight and high-strength Ni-Co based single-crystal high-entropy alloy.

[0021] Preferably, in step one, the liquidus temperature parameters include the casting temperature and the shell insulation temperature, and the eutectic dissolution temperature parameters include the solution treatment temperature, the first-stage aging treatment temperature, and the second-stage aging treatment temperature.

[0022] In any of the above schemes, preferably, in step three, the order in which the elemental substances are placed into the crucible from bottom to top is as follows: the first layer is a mixture of 50% Ni and 50% Co, the second layer is a mixture of Mo and W, the third layer is a mixture of Cr and Ti, and the fourth layer is a mixture of 50% Ni and 50% Co; the vacuum degree does not exceed 10. -1 Pa, heating power of 20-50kW, refining temperature of 1500-1600℃, refining time of 10-30min.

[0023] Preferably, in any of the above schemes, the vacuum degree in step four does not exceed 10. -2 Pa, heating power of 20-50kW, refining temperature of 1490-1560℃, refining time of 10-20min, casting temperature of 1470-1540℃, shell insulation temperature of 1450-1520℃, and drawing speed of 2-6mm / min.

[0024] In any of the above schemes, the preferred embodiment is that, in step five, the solution treatment process is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 2-4 bar, and the furnace pressure is 70-110 Pa, while the heat treatment furnace is heated to 1160-1240℃; then, the cast single-crystal high-entropy alloy is placed into the heat treatment furnace and held at that temperature for 10-14 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0025] In any of the above schemes, the preferred embodiment is that, in step six, the process of the first-stage aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 2-4 bar, and the furnace pressure is 70-110 Pa, while the heat treatment furnace is heated to 1060-1100℃; then, the solid solution-state single-crystal high-entropy alloy is placed into the heat treatment furnace and held for 1-5 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0026] In any of the above schemes, the preferred embodiment is that, in step seven, the process of the secondary aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 2-4 bar, and the furnace pressure is 70-110 Pa, while the heat treatment furnace is heated to 840-860℃; then, the single-crystal high-entropy alloy in the primary aging state is placed into the heat treatment furnace and held for 22-26 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0027] The vacuum induction melting furnace, vacuum melting single-crystal directional solidification furnace, heat treatment furnace, and other equipment used in this invention can be existing equipment, and there are no special requirements for the models. Throughout the entire preparation process of the single-crystal high-entropy alloy, the proportions of each element, the order in which each element is placed in the crucible, the casting process parameters, the shell insulation parameters, the solution treatment regime, the first-stage aging treatment regime, and the second-stage aging treatment regime are all crucial. Only by synergistically applying these parameters can the technical effects expected by this invention be achieved.

[0028] This invention comprehensively considers the influence of various elements on the mechanical properties of room temperature and high temperature alloys when designing the alloy composition, as detailed below:

[0029] Ni: A matrix element, providing the FCC structural stability, toughness, and ductility of single-crystal high-entropy alloy matrices at high temperatures. Ni has a low diffusion rate, supporting low-rate thermally activated creep. Ni can also provide Ni elements in the γˊ phase, such as Ni3Al.

[0030] Co is the second matrix element, which can expand the FCC region, increase the dissolution temperature and microstructure stability of the γˊ phase, reduce the stacking fault energy of the matrix, cause solid solution strengthening, and reduce the solubility of elements such as Al and Ti in the matrix, thereby increasing the volume fraction of the γˊ phase.

[0031] Cr: It is an antioxidant element. Generally, the higher the Cr content, the better the alloy's heat corrosion resistance and oxidation resistance. Cr can also play a certain role in solid solution strengthening, thereby increasing its strength.

[0032] Al is a γˊ forming element, which changes the solubility of each element, increases the reverse boundary energy of γˊ, strengthens the cutting enhancement mechanism, increases the absolute value of mismatch, and causes an enhancement of the coherent strain field around γˊ.

[0033] Ti is a γˊ forming element that can promote the formation of strengthening precipitates Ni3(Al,Ti) and Ni3Ti, and also affects mismatch degree and hardness.

[0034] Mo is a solid solution strengthening element that can significantly enhance the lattice constant and yield strength of solid solutions, increase the long-range elastic stress field, increase the resistance to dislocation movement, and reduce stacking fault energy.

[0035] W is a solid solution strengthening element that can cause significant lattice expansion, prevent dislocation movement, enhance yield strength, and also increase the reverse boundary energy in the alloy, thus significantly improving the high-temperature strength of the alloy.

[0036] Hf: It is a grain boundary strengthening element that can improve mid-temperature strength and plasticity, while providing good fluidity and enhancing the castability of the alloy.

[0037] The present invention relates to a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method, which has the following beneficial effects:

[0038] (1) In designing the composition ratio of the single-crystal high-entropy alloy, the present invention takes into account the influence of density, and the density of the prepared single-crystal high-entropy alloy is approximately 7.7-8.0 g / cm³. 3 It has a density significantly lower than that of existing single-crystal superalloys (approximately 8.9 g / cm³). 3 ).

[0039] (2) The single-crystal high-entropy alloy prepared by this invention has excellent room temperature mechanical properties and high temperature mechanical properties: at room temperature, the tensile strength of the alloy reaches more than 1150 MPa and the elongation reaches more than 28%; at 760℃, the tensile strength of the alloy reaches more than 1120 MPa and the elongation reaches more than 30%; at 980℃, the tensile strength of the alloy reaches more than 650 MPa and the elongation reaches more than 30%; the comprehensive tensile properties meet the standard of second-generation nickel-based single-crystal high-temperature alloy DD6, and have great application potential.

[0040] (3) The single-crystal high-entropy alloy of the present invention does not contain rare and precious elements such as Re and Ru. Compared with traditional single-crystal high-temperature alloys, it has advantages in operation and cost, and can effectively carry out the engineering application of the alloy.

[0041] (4) No Fe element was added to the single crystal high entropy alloy of the present invention. Instead, a small amount of Hf element was added, which can improve the casting performance of the alloy and avoid a large number of structural defects such as porosity. At the same time, by adding more Cr and Al elements, the oxidation resistance of the alloy is guaranteed. Attached Figure Description

[0042] Figure 1This is a photograph of the dendritic structure of a cast single-crystal high-entropy alloy in a preferred embodiment of the lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method according to the present invention;

[0043] Figure 2 for Figure 1 Micrograph of the final heat-treated single-crystal high-entropy alloy in the embodiment shown;

[0044] Figure 3 This is a photograph of the dendritic structure of a cast single-crystal high-entropy alloy in another preferred embodiment of the lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method according to the present invention;

[0045] Figure 4 for Figure 3 Micrograph of the single-crystal high-entropy alloy in the final heat-treated state in the illustrated embodiment. Detailed Implementation

[0046] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0047] Example 1:

[0048] According to a preferred embodiment of the lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy of the present invention, the chemical composition of the single-crystal high-entropy alloy includes eight elements: Ni, Co, Cr, Al, Ti, Mo, W, and Hf. The atomic percentages of each element are: Ni 52 at%, Co 18 at%, Cr 11 at%, Al 11 at%, Ti 6 at%, Mo 1.5 at%, W 0.4 at%, and Hf 0.1 at%, with the sum of the atomic percentages of each element being 100%.

[0049] The mixed entropy ΔS of the single-crystal high-entropy alloy mix ≥1.386R, the formula for calculating the entropy of mixture is: In the formula,

[0050] ΔS mix —The mixing entropy of a single-crystal high-entropy alloy, J / (mol·K);

[0051] R—gas constant, R = 8.314 J / (mol·K);

[0052] i—any element among Ni, Co, Cr, Al, Ti, Mo, W, and Hf;

[0053] n—the sum of all elements in a single-crystal high-entropy alloy;

[0054] x i —Atomic percentage of element i in single-crystal high-entropy alloys, %.

[0055] The grain orientation of the single-crystal high-entropy alloy is as follows: <001> The dendrite spacing is 378 μm, the volume fraction of loose material is 0.06%, and the γˊ microstructure consists of square primary γˊ microstructure and granular secondary γˊ microstructure. The size of the primary γˊ microstructure is 385 nm, and the size of the secondary γˊ microstructure is 15 nm. The volume fraction of the primary γˊ microstructure is 67.32%, and the volume fraction of the secondary γˊ microstructure is 3.05%. The density of the single-crystal high-entropy alloy is 7.87 g / cm³. 3 .

[0056] This embodiment also provides a method for preparing a lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy, which includes the following steps in sequence:

[0057] Step 1: Using JMatPro, Thermo-Calc, or Pandat software, perform thermodynamic calculations and simulations according to the composition design ratio of the single-crystal high-entropy alloy to obtain the liquidus temperature parameters; obtain the eutectic dissolution temperature parameters through DSC melting point testing;

[0058] Step 2: Weigh out the elemental elements Ni, Co, Cr, Al, Ti, Mo, W, and Hf with a purity of 99.5% or higher according to the composition design of the single-crystal high-entropy alloy.

[0059] Step 3: Place the elemental elements Ni, Co, Cr, Ti, Mo, and W into the crucible of the vacuum induction melting furnace according to the design order, evacuate to a certain vacuum level, and then heat and melt; when the temperature rises to the refining temperature, add the elemental elements Al and Hf, and perform electromagnetic stirring. After refining is completed, cast into a single crystal high-entropy alloy master alloy ingot.

[0060] Step 4: Prepare grains with the following orientation using the high-speed solidification Bridgeman method and seed crystal method. <001> The process for producing single-crystal high-entropy alloy test bars involves first placing the single-crystal high-entropy alloy master alloy ingot into a vacuum melting single-crystal directional solidification furnace, evacuating it to a certain vacuum level, and then heating and melting it. Next, it is refined at a certain temperature. After refining, the temperature is lowered to the casting temperature. Finally, it is cast at a certain pulling rate to obtain the as-cast single-crystal high-entropy alloy.

[0061] Step 5: Place the as-cast single-crystal high-entropy alloy into a heat treatment furnace for solution treatment to obtain a solution-treated single-crystal high-entropy alloy; Step 6: Place the solution-treated single-crystal high-entropy alloy into a heat treatment furnace for first-stage aging treatment to obtain a first-stage aged single-crystal high-entropy alloy.

[0062] Step 7: Place the first-stage aged single-crystal high-entropy alloy into a heat treatment furnace for second-stage aging treatment to obtain the final heat-treated single-crystal high-entropy alloy, which is a lightweight and high-strength Ni-Co based single-crystal high-entropy alloy.

[0063] In step one, the liquidus temperature parameters include the casting temperature and the shell insulation temperature, and the eutectic dissolution temperature parameters include the solution treatment temperature, the first-stage aging treatment temperature, and the second-stage aging treatment temperature.

[0064] In step three, the elemental substances are placed into the crucible in the following order from bottom to top: the first layer is a mixture of 50% Ni and 50% Co; the second layer is a mixture of Mo and W; the third layer is a mixture of Cr and Ti; and the fourth layer is a mixture of 50% Ni and 50% Co. The vacuum level is 10. -1 Pa, heating power of 35kW, refining temperature of 1550℃, refining time of 20min.

[0065] In step four, the vacuum level is 10. -2 Pa, heating power of 35kW, refining temperature of 1525℃, refining time of 15min, casting temperature of 1505℃, shell insulation temperature of 1485℃, and drawing speed of 4mm / min.

[0066] In step five, the solution treatment process is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 3 bar and an internal pressure of 90 Pa, while the heat treatment furnace is heated to 1200°C; then, the cast single-crystal high-entropy alloy is placed into the heat treatment furnace and held at that temperature for 12 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0067] In step six, the process of the first-stage aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 3 bar and an internal pressure of 90 Pa, while the heat treatment furnace is heated to 1080°C; then, the solid solution-state single-crystal high-entropy alloy is placed into the heat treatment furnace and held for 3 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0068] In step seven, the process of the secondary aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 3 bar and an internal pressure of 90 Pa, while the heat treatment furnace is heated to 850°C; then, the single-crystal high-entropy alloy in the primary aging state is placed into the heat treatment furnace and held for 24 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0069] In this embodiment, the dendritic structure of the cast single-crystal high-entropy alloy is as follows: Figure 1 As shown, the microstructure of the final heat-treated single-crystal high-entropy alloy is as follows: Figure 2 As shown in Table 1, the alloy microstructure is a γ+γ′ dual-phase structure. The specific microstructure parameters are shown in Table 1, the specific tensile properties are shown in Table 2, and the specific oxidation resistance properties are shown in Table 3.

[0070] Table 1. Microstructure parameters of single-crystal high-entropy alloys

[0071]

[0072] Table 2 Mechanical property data of single-crystal high-entropy alloys

[0073] temperature Yield strength (MPa) Tensile strength (MPa) Elongation (%) Reduction of area (%) room temperature 1001 1167 28.9 24.3 760℃ 964 1131 32.8 44.7 980℃ 485 674 33.1 45.0 DD6 - Room temperature 930 970 16.0 19.5 DD6-760℃ 935 1100 8.0 12.0

[0074] Table 3. Oxidation resistance data of single-crystal high-entropy alloys

[0075] Temperature (°C) <![CDATA[Oxidation rate (g / m 2 ·h)]]> <![CDATA[Amount of scale loss (g / m 2 )]]> Antioxidant properties 1050 0.011 0.831 Fully antioxidant grade 1100 0.013 3.781 Antioxidant grade

[0076] The vacuum induction melting furnace, vacuum melting single-crystal directional solidification furnace, and heat treatment furnace used in this embodiment can be any existing equipment; no special requirements are placed on the model. Throughout the entire preparation process of the single-crystal high-entropy alloy, the proportions of each element, the order of placement of each element in the crucible, the casting process parameters, the shell insulation parameters, the solution treatment regime, the first-stage aging treatment regime, and the second-stage aging treatment regime are all crucial. Only by synergistically applying these parameters can the expected technical effect of this embodiment be achieved.

[0077] In this embodiment, the influence of various elements on the mechanical properties of room temperature and high temperature alloys is comprehensively considered when designing the alloy composition. The specific analysis is as follows: (1) Ni is a matrix element, which provides the FCC structure stability, toughness and ductility of the single crystal high entropy alloy matrix at high temperature; Ni has a low diffusion rate, which supports low-rate thermal activation creep; Ni can also provide Ni elements in the γˊ phase such as Ni3Al. (2) Co is a second matrix element, which can expand the FCC region, improve the dissolution temperature and structural stability of the γˊ phase, reduce the stacking fault energy of the matrix, cause solid solution strengthening, and reduce the solubility of elements such as Al and Ti in the matrix, thereby increasing the volume fraction of the γˊ phase. (3) Cr is an antioxidant element. Generally, the higher the Cr content, the better the heat corrosion resistance and oxidation resistance of the alloy; Cr can also play a certain solid solution strengthening effect and enhance a certain strength. (4) Al is a γˊ forming element, which changes the solubility of each element, increases the reverse boundary energy of γˊ, strengthens the cutting strengthening mechanism, increases the absolute value of mismatch, and causes the coherent strain field around γˊ to be enhanced. (5) Ti is a γˊ forming element, which can promote the formation of strengthening precipitates Ni3(Al,Ti) and Ni3Ti, and also affect misfit degree and hardness. (6) Mo is a solid solution strengthening element, which can significantly enhance the lattice constant of the solid solution and enhance the yield strength, increase the long-range elastic stress field, increase the resistance to dislocation movement, and reduce stacking fault energy. (7) W is a solid solution strengthening element, which can cause significant lattice expansion, prevent dislocation movement, enhance yield strength, and also increase the reverse boundary energy in the alloy, significantly improving the high-temperature strength of the alloy. (8) Hf is a grain boundary strengthening element, which can improve the mid-temperature strength and plasticity, while providing better fluidity and enhancing the castability of the alloy.

[0078] The lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method in this embodiment have the following beneficial effects: (1) The influence of density was considered when designing the composition ratio of the single-crystal high-entropy alloy, and the density of the prepared single-crystal high-entropy alloy is about 7.7-8.0 g / cm³. 3 (1) The density is significantly lower than that of existing single-crystal high-temperature alloys. (2) The prepared single-crystal high-entropy alloy has excellent room temperature mechanical properties and high temperature mechanical properties. Its comprehensive tensile properties meet the standard of second-generation nickel-based single-crystal high-temperature alloy DD6, and it has great application potential. (3) No Fe element is added to the single-crystal high-entropy alloy. Instead, a small amount of Hf element is added, which can improve the casting performance of the alloy and avoid a large number of porosity and other structural defects. At the same time, by adding more Cr and Al elements, the oxidation resistance of the alloy is guaranteed.

[0079] Example 2:

[0080] According to another preferred embodiment of the lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method of the present invention, its composition design, process flow, equipment used, technical principles, and beneficial effects are basically the same as those of Embodiment 1, except that:

[0081] The chemical composition of the single-crystal high-entropy alloy includes eight elements: Ni, Co, Cr, Al, Ti, Mo, W, and Hf. The atomic percentages of each element are as follows: Ni 45 at%, Co 20 at%, Cr 12 at%, Al 12 at%, Ti 8 at%, Mo 1.9 at%, W 1 at%, and Hf 0.1 at%, with the sum of the atomic percentages of each element being 100%.

[0082] The grain orientation of the single-crystal high-entropy alloy is as follows: <001> The dendrite spacing is 394 μm, the volume fraction of loose material is 0.08%, and the γ′ microstructure consists of square primary γ′ microstructure and granular secondary γ′ microstructure. The size of the primary γ′ microstructure is 352 nm, and the size of the secondary γ′ microstructure is 24 nm. The volume fraction of the primary γ′ microstructure is 68.94%, and the volume fraction of the secondary γ′ microstructure is 6.84%. The density of the single-crystal high-entropy alloy is 7.93 g / cm³. 3 .

[0083] In step one, the liquidus temperature parameters include the casting temperature and the shell insulation temperature, and the eutectic dissolution temperature parameters include the solution treatment temperature, the first-stage aging treatment temperature, and the second-stage aging treatment temperature.

[0084] In step three, the elemental substances are placed into the crucible in the following order from bottom to top: the first layer is a mixture of 50% Ni and 50% Co; the second layer is a mixture of Mo and W; the third layer is a mixture of Cr and Ti; and the fourth layer is a mixture of 50% Ni and 50% Co. The vacuum level is 10. -1 Pa, heating power of 20kW, refining temperature of 1500℃, refining time of 10min.

[0085] In step four, the vacuum level is 10. -2 Pa, heating power of 20kW, refining temperature of 1490℃, refining time of 10min, casting temperature of 1470℃, shell insulation temperature of 1450℃, and drawing speed of 2mm / min.

[0086] In step five, the process of solution treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 2 bar and an internal pressure of 70 Pa, while the heat treatment furnace is heated to 1160°C; then, the cast single-crystal high-entropy alloy is placed into the heat treatment furnace and held at that temperature for 10 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0087] In step six, the process of the first-stage aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 2 bar and an internal pressure of 70 Pa, while the heat treatment furnace is heated to 1060°C; then, the solid solution-state single-crystal high-entropy alloy is placed into the heat treatment furnace and held for 1 hour; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0088] In step seven, the process of the secondary aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 2 bar and a furnace pressure of 70 Pa, while the heat treatment furnace is heated to 840°C; then, the single-crystal high-entropy alloy in the primary aging state is placed into the heat treatment furnace and held for 22 hours; finally, the alloy is taken out of the heat treatment furnace and air-cooled.

[0089] In this embodiment, the dendritic structure of the cast single-crystal high-entropy alloy is as follows: Figure 3 As shown, the microstructure of the final heat-treated single-crystal high-entropy alloy is as follows: Figure 4 As shown in Table 4, the alloy microstructure is a γ+γ′ dual-phase structure. The specific microstructure parameters are shown in Table 4, the specific tensile properties are shown in Table 5, and the specific oxidation resistance properties are shown in Table 6.

[0090] Table 4 Microstructure parameters of single-crystal high-entropy alloys

[0091]

[0092] Table 5 Mechanical property data of single-crystal high-entropy alloys

[0093] temperature Yield strength (MPa) Tensile strength (MPa) Elongation (%) Reduction of area (%) room temperature 1010 1165 29.1 23.5 760℃ 972 1129 33.1 43.8 980℃ 490 697 33.6 42.1

[0094] Table 6. Oxidation resistance data of single-crystal high-entropy alloys

[0095] Temperature (°C) <![CDATA[Oxidation rate (g / m 2 ·h)]]> <![CDATA[Amount of mill scale peeling off (g / m 2 )]]> Antioxidant properties 1050 0.010 0.786 Fully antioxidant grade 1100 0.015 4.243 Antioxidant grade

[0096] Example 3:

[0097] According to another preferred embodiment of the lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method of the present invention, its composition design, process flow, equipment used, technical principles, and beneficial effects are basically the same as those of Embodiment 1, except that:

[0098] The chemical composition of the single-crystal high-entropy alloy includes eight elements: Ni, Co, Cr, Al, Ti, Mo, W, and Hf. The atomic percentages of each element are as follows: Ni 55 at%, Co 18 at%, Cr 10 at%, Al 10 at%, Ti 4 at%, Mo 1.9 at%, W 1 at%, and Hf 0.1 at%, with the sum of the atomic percentages of each element being 100%.

[0099] The grain orientation of the single-crystal high-entropy alloy is as follows: <001> The dendrite spacing is 388 μm, the loose volume fraction is 0.07%, and the γ′ microstructure consists of square primary γ′ microstructure and granular secondary γ′ microstructure. The size of the primary γ′ microstructure is 379 nm, and the size of the secondary γ′ microstructure is 18 nm. The volume fraction of the primary γ′ microstructure is 69.11%, and the volume fraction of the secondary γ′ microstructure is 5.21%. The density of the single-crystal high-entropy alloy is 7.72 g / cm³. 3 .

[0100] In step one, the liquidus temperature parameters include the casting temperature and the shell insulation temperature, and the eutectic dissolution temperature parameters include the solution treatment temperature, the first-stage aging treatment temperature, and the second-stage aging treatment temperature.

[0101] In step three, the elemental substances are placed into the crucible in the following order from bottom to top: the first layer is a mixture of 50% Ni and 50% Co; the second layer is a mixture of Mo and W; the third layer is a mixture of Cr and Ti; and the fourth layer is a mixture of 50% Ni and 50% Co. The vacuum level is 10. -1 Pa, heating power of 50kW, refining temperature of 1600℃, refining time of 30min.

[0102] In step four, the vacuum level is 10. -2 Pa, heating power of 50kW, refining temperature of 1560℃, refining time of 20min, casting temperature of 1540℃, shell insulation temperature of 1520℃, and drawing speed of 6mm / min.

[0103] In step five, the solution treatment process is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 4 bar and an internal pressure of 110 Pa, while the heat treatment furnace is heated to 1240°C; then, the cast single-crystal high-entropy alloy is placed into the heat treatment furnace and held at that temperature for 14 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0104] In step six, the process of the first-stage aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 4 bar and an internal pressure of 110 Pa, while the heat treatment furnace is heated to 1100°C; then, the solid solution-state single-crystal high-entropy alloy is placed into the heat treatment furnace and held for 5 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0105] In step seven, the process of the secondary aging treatment is as follows: first, argon gas is introduced into the heat treatment furnace at a pressure of 4 bar and an internal pressure of 110 Pa, while the heat treatment furnace is heated to 860°C; then, the single-crystal high-entropy alloy in the primary aging state is placed into the heat treatment furnace and held for 26 hours; finally, the alloy is removed from the heat treatment furnace and air-cooled.

[0106] In this embodiment, the alloy microstructure is a γ+γ′ dual-phase structure. The specific microstructure parameters are shown in Table 7, the specific tensile properties are shown in Table 8, and the specific oxidation resistance properties are shown in Table 9.

[0107] Table 7 Microstructure parameters of single-crystal high-entropy alloys

[0108]

[0109] Table 8 Mechanical property data of single-crystal high-entropy alloys

[0110] temperature Yield strength (MPa) Tensile strength (MPa) Elongation (%) Reduction of area (%) room temperature 1002 1158 28.3 24.1 760℃ 969 1127 32.6 44.5 980℃ 508 711 33.8 39.5

[0111] Table 9. Oxidation resistance data of single-crystal high-entropy alloys

[0112] Temperature (°C) <![CDATA[Oxidation rate (g / m 2 ·h)]]> <![CDATA[Amount of mill scale peeling (g / m 2 )]]> Antioxidant properties 1050 0.011 0.794 Fully antioxidant grade 1100 0.015 3.992 Antioxidant grade

[0113] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive experimentation. For each parameter and the combinations thereof, the inventors have recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here.

[0114] Those skilled in the art will readily understand that the lightweight, high-strength Ni-Co-based single-crystal high-entropy alloy and its preparation method of the present invention include any combination of the inventive content and specific embodiments described in the above specification and the parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lightweight high-strength Ni-Co-based single-crystal high-entropy alloy, characterized in that: The chemical composition of the single crystal high-entropy alloy includes eight elements of Ni, Co, Cr, Al, Ti, Mo, W, and Hf, and the atomic percentage of each element is 45-55 at% for Ni, 15-20 at% for Co, 9-12 at% for Cr, 9-12 at% for Al, 4-8 at% for Ti, 1-2 at% for Mo, 0-1 at% for W, and 0-0.1 at% for Hf, and the sum of the atomic percentages of the elements is 100%. The single crystal high-entropy alloy has a grain orientation of <001>, a dendrite spacing of 350-430 mu m, a loose volume fraction of 0-0.2%, and a gamma prime structure composed of square primary gamma prime structures and granular secondary gamma prime structures, wherein the size of the primary gamma prime structures is 350-500 nm, the size of the secondary gamma prime structures is 10-30 nm, the volume fraction of the primary gamma prime structures is 65-70%, and the volume fraction of the secondary gamma prime structures is 3-7%, and the density of the single crystal high-entropy alloy is less than 8.0 g / cm 3 .

2. The lightweight high-strength Ni-Co-based single-crystal high-entropy alloy according to claim 1, characterized in that: The mixing entropy ΔS of the single-crystal high-entropy alloy mix ≥ 1.386R, the calculation formula of the mixing entropy is In the formula, ΔS mix - the mixing entropy of the single-crystal high-entropy alloy, J / (mol·K); R is a gas constant, R = 8.314 J / (mol·K); i is any of Ni, Co, Cr, Al, Ti, Mo, W, and Hf; n is the sum of all elements in the single crystal high-entropy alloy; x i - atomic percentage of i element in single-crystal high-entropy alloy, %.

3. A method for preparing a lightweight high-strength Ni-Co-based single-crystal high-entropy alloy, characterized in that: The method for preparing the lightweight high-strength Ni-Co-based single crystal high-entropy alloy of claim 1 or 2 comprises the following steps in order, Step one: using JMatPro, Thermo-Calc, or Pandat software, thermodynamic calculation simulation is performed according to the composition design and proportioning of the single crystal high-entropy alloy to obtain liquidus temperature parameters; eutectic dissolution temperature parameters are obtained through DSC melting point testing; Step two: according to the composition design and proportioning of the single crystal high-entropy alloy, elemental Ni, Co, Cr, Al, Ti, Mo, W, and Hf with a purity of more than 99.5% are weighed for standby; Step three: according to the design order, elemental Ni, Co, Cr, Ti, Mo, and W are placed in the crucible of a vacuum induction melting furnace, vacuum is extracted to a certain vacuum degree, and then heating and melting are performed; when the temperature rises to the refining temperature, elemental Al and Hf are added, and electromagnetic stirring is performed, and after the refining is completed, the single crystal high-entropy alloy master alloy ingot is poured; Step four: a single crystal high-entropy alloy test rod with a grain orientation of <001> is prepared by using a high-speed solidification Bridgeman method and a seed crystal method, that is, the single crystal high-entropy alloy master alloy ingot is first placed in a vacuum melting single crystal directional solidification furnace, vacuum is extracted to a certain vacuum degree, and then heating and melting are performed; then refining is performed at a certain temperature, and after the refining is completed, the temperature is lowered to the pouring temperature; finally, pouring is performed at a certain pulling rate to obtain a cast single crystal high-entropy alloy; Step five: the cast single crystal high-entropy alloy is placed in a heat treatment furnace for solid solution treatment to obtain a solid solution state single crystal high-entropy alloy; Step six: the solid solution state single crystal high-entropy alloy is placed in a heat treatment furnace for primary aging treatment to obtain a primary aging state single crystal high-entropy alloy; Step seven: the primary aging state single crystal high-entropy alloy is placed in a heat treatment furnace for secondary aging treatment to obtain a final heat treatment state single crystal high-entropy alloy, that is, a lightweight high-strength Ni-Co-based single crystal high-entropy alloy.

4. The method of claim 3, wherein the method further comprises: In step one, the liquidus temperature parameters include the pouring temperature and the mold shell holding temperature, and the eutectic dissolution temperature parameters include the solid solution treatment temperature, the primary aging treatment temperature, and the secondary aging treatment temperature.

5. The method of claim 4, wherein the method further comprises: In step three, the order of the elemental substances from bottom to top in the crucible is as follows: the first layer is a mixture of 50% Ni and 50% Co, the second layer is a mixture of Mo and W, the third layer is a mixture of Cr and Ti, and the fourth layer is a mixture of 50% Ni and 50% Co; the vacuum degree is not more than 10 -1 Pa, the heating power is 20-50 kW, the refining temperature is 1500-1600℃, and the refining time is 10-30 min.

6. The method of claim 5, wherein the method further comprises: The vacuum degree in the fourth step is not more than 10 -2 Pa, the heating power is 20-50 kW, the refining temperature is 1490-1560℃, the refining time is 10-20 min, the pouring temperature is 1470-1540℃, the shell temperature is 1450-1520℃, and the pulling rate is 2-6 mm / min.

7. The method of claim 6, wherein the method further comprises: In step five, the process system of the solid solution treatment is that, first, the heat treatment furnace is filled with argon, the filling pressure is 2-4 bar, the furnace pressure is 70-110 Pa, and the heat treatment furnace is heated to 1160-1240℃; then the as-cast single crystal high-entropy alloy is put into the heat treatment furnace, and the heat preservation time is 10-14 h; finally, the alloy is taken out from the heat treatment furnace and air cooled.

8. The method of claim 7, wherein the method further comprises: In step six, the process system of the first aging treatment is that, first, the heat treatment furnace is filled with argon, the filling pressure is 2-4 bar, the furnace pressure is 70-110 Pa, and the heat treatment furnace is heated to 1060-1100℃; then the solid solution state single crystal high-entropy alloy is put into the heat treatment furnace, and the heat preservation time is 1-5 h; finally, the alloy is taken out from the heat treatment furnace and air cooled.

9. The method of claim 8, wherein the method further comprises: In step seven, the process system of the second aging treatment is that, first, the heat treatment furnace is filled with argon, the filling pressure is 2-4 bar, the furnace pressure is 70-110 Pa, and the heat treatment furnace is heated to 840-860℃; then the first aging state single crystal high-entropy alloy is put into the heat treatment furnace, and the heat preservation time is 22-26 h; finally, the alloy is taken out from the heat treatment furnace and air cooled.

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