Fe and ti free high plasticity single crystal high-entropy high-temperature alloy and preparation method thereof

Abstract

The application discloses a kind of high plasticity single crystal high-entropy high-temperature alloy without Fe and Ti and a preparation method thereof.The chemical composition of the alloy includes Co, Ni, Cr, Al, Ta, Mo and W seven elements, and the atomic percentage of each element is Co 35-45at%, Ni 30-40at%, Cr 3-5at%, Al 10-13at%, Ta 1-4at%, Mo 1-3ar% and W 3-5at%.The preparation method includes the following steps: sequentially putting elemental Co, Ni, Cr, Ta, Mo and W into the crucible of vacuum induction melting furnace for heating and melting, adding elemental Al when the temperature rises to the refining temperature, and pouring into master alloy ingot;using high-speed solidification Bridgeman method and seed crystal method to prepare single crystal high-entropy high-temperature alloy test rod with <001> grain orientation;and sequentially carrying out solid solution treatment, primary aging and secondary aging on the single crystal high-entropy high-temperature alloy test rod, to obtain the high plasticity single crystal high-entropy high-temperature alloy without Fe and Ti.The single crystal high-entropy high-temperature alloy of the application has the advantages of high-entropy alloy and single crystal high-temperature alloy, and has 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 high-plasticity single-crystal high-entropy high-temperature alloy without Fe or Ti and its preparation method. Background Technology

[0002] High-entropy alloys refer to novel alloy systems with four or more components, where the atomic ratios of each component are equal or nearly equal. The mixing entropy of high-entropy alloys is greater than 1.386R, exhibiting high-entropy effects, lattice distortion effects, hysteresis diffusion effects, and the cocktail effect. The cocktail effect refers to the phenomenon where different elements, when mixed, exhibit their respective properties. These four effects endow high-entropy alloys with excellent comprehensive properties, such as high-temperature stability, oxidation resistance, and high-temperature mechanical properties. Therefore, high-entropy alloys have potential applications in high-temperature fields such as hot-end components of aero-engines.

[0003] Currently, under conditions of high temperature, high stress, and combustion gas corrosion, single-crystal superalloys are the most widely used materials for turbine blades in aero-engines. While single-crystal superalloys can avoid the problem of grain boundary softening at high temperatures and compensate for the shortcomings of traditional superalloys, such as severe segregation, poor hot workability, and difficulty in forming, further optimization and improvement of material properties are needed to meet the requirements of advanced aero-engines with a thrust-to-weight ratio of 20. The introduction of the concept of high-entropy alloys has brought about a significant turning point in the design approach of single-crystal superalloys, such as single-crystal Co... 1.5 CrFeNi 1.5 Ti 0.5 Single-crystal Al exhibits good performance at around 800℃. 0.3 CrCuFeNi2 has a tensile strength of 522 MPa and an elongation of 35%. Therefore, improving the alloy's performance through composition design and preparation process improvement is an urgent problem to be solved in the research and application of high-entropy alloys.

[0004] Patent application CN110317990A discloses a Ni-Co-Al-Cr-Fe single-crystal high-entropy superalloy and its preparation method. The alloy's chemical composition by atomic percentage is: Ni 35-40%, Co 30-35%, Al 10-13%, Cr 5-10%, Fe 5-8.5%, Ti 1-2.5%, Ta 1-3%, Mo 0.01-1%, W 0.01-1%, Re 0-1%, C 0.02-0.12%, B 0.002-0.015%, Hf 0.005-0.12%, RE 0.05-0.15%, 14%≤Al+Ti+Ta≤16%, where RE is any rare earth element among Ce, L, and Y; the preparation method includes the following steps: each element is placed in a melting furnace for melting, high-temperature refining for 15-30 minutes at a refining temperature of 1550-1650℃, and then cast into an alloy ingot; single-crystal high-entropy high-temperature alloy rods are prepared by high-speed solidification method with a pulling rate of 2-4 mm / min; the high-entropy alloy rods are solution treated at 1220-1235℃ for 4-6 hours and air-cooled to obtain a solution-treated alloy; the alloy rods are subjected to a two-stage aging treatment, first held at 1080-1100℃ for 4-6 hours, then held at 870℃ for 24 hours, and air-cooled to obtain the final heat-treated alloy rods. The single-crystal high-entropy superalloy of this technical solution contains both Fe and Ti low-melting-point phase elements. Although the tensile strength at room temperature is improved, the elongation is reduced significantly. The highest tensile strength at room temperature reaches 881 MPa, with a corresponding elongation of 40.2%.

[0005] Currently, to address the issue of high strength but low plasticity in single-crystal high-entropy alloys, it is necessary to modify the precipitated phases of the alloy by adjusting the alloy composition, heat treatment method, and casting process, thereby improving the balance between room temperature and high temperature strength and plasticity of single-crystal high-entropy alloys. Therefore, it is urgent to develop a high-plasticity single-crystal high-entropy high-temperature alloy without Fe or Ti and its preparation method, which can significantly improve the alloy plasticity while meeting the tensile strength requirements. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a Fe- and Ti-free, high-plasticity single-crystal high-entropy superalloy. The chemical composition of the single-crystal high-entropy superalloy includes seven elements: Co, Ni, Cr, Al, Ta, Mo, and W. The atomic percentages of each element are as follows: Co 35-45 at%, Ni 30-40 at%, Cr 3-5 at%, Al 10-13 at%, Ta 1-4 at%, Mo 1-3 at%, and W 3-5 at%, with the sum of the atomic percentages of each element being 100%.

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

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

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

[0010] i—any element from Co, Ni, Cr, Al, Ta, Mo, W;

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

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

[0013] Preferably, in any of the above embodiments, the single-crystal high-entropy superalloy is an L12-type strengthened FCC alloy with a microstructure of γ+γ′ dual-phase structure. The γ′ structure consists of square primary γ′ structures and strip-shaped granular secondary γ′ structures. The size of the primary γ′ structure is 400-500 nm, the size of the secondary γ′ structure is 80-120 nm, the volume fraction of the γ′ structure is 80-85%, and the grain orientation is [missing information]. <001> .

[0014] This invention also provides a method for preparing a Fe- and Ti-free, highly ductile, single-crystal, high-entropy superalloy, used to prepare the Fe- and Ti-free, highly ductile, single-crystal, high-entropy superalloy described in any of the above-mentioned methods, comprising the following steps in sequence:

[0015] Step 1: Weigh out the elemental elements Co, Ni, Cr, Al, Ta, Mo, and W with a purity of 99.5% or higher according to the designed ratio and set them aside;

[0016] Step 2: Place the elemental elements Co, Ni, Cr, Ta, Mo, and W into the crucible of the vacuum induction melting furnace in the designed order, evacuate to a certain vacuum level, and then heat and melt; when the temperature rises to the refining temperature, add the elemental element Al and perform electromagnetic stirring. After refining is completed, cast into a single crystal high-entropy high-temperature alloy master alloy ingot.

[0017] Step 3: Prepare grains with the following orientation using the high-speed solidification Bridgeman method and seed crystal method. <001> The process for obtaining a single-crystal high-entropy superalloy test bar involves first placing the single-crystal high-entropy superalloy 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 superalloy.

[0018] Step 4: Place the cast single-crystal high-entropy superalloy into a heat treatment furnace for solution treatment to obtain a solution-treated single-crystal high-entropy superalloy.

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

[0020] Step 6: Place the first-stage aged single-crystal high-entropy superalloy into a heat treatment furnace for second-stage aging treatment to obtain the final heat-treated single-crystal high-entropy superalloy, which is also a Fe-free and Ti-free high-plasticity single-crystal high-entropy superalloy.

[0021] Preferably, in step two, 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 Ta, Mo, and W; the third layer is Cr; 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.

[0022] Preferably, in any of the above schemes, the vacuum degree in step three does not exceed 10. -2 Pa, heating power of 20-50kW, refining temperature of 1470-1520℃, refining time of 10-20min, casting temperature of 1450-1500℃, and drawing speed of 2-5mm / min.

[0023] In any of the above schemes, preferably, in step four, the solution treatment process is as follows: the cast single-crystal high-entropy superalloy is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 2-4 bar, and the furnace pressure is 70-110 Pa; the temperature is increased from room temperature to 1150℃ at a heating rate of 10-15℃ / min, and held for 2-3 hours; the temperature is increased from 1150℃ to 1200℃ at a heating rate of 10-15℃ / min, and held for 2-3 hours; the temperature is increased from 1200℃ to 1250℃ at a heating rate of 10-15℃ / min, and held for 10-15 hours; the alloy is then removed from the heat treatment furnace and air-cooled.

[0024] In any of the above schemes, the preferred embodiment is that, in step five, the process of the first-stage aging treatment is as follows: the solid solution-state single-crystal high-entropy superalloy is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 2-4 bar, and the furnace pressure is 70-110 Pa; the temperature is increased from room temperature to 1100℃ at a heating rate of 10-15℃ / min, and held for 3-6 hours; the alloy is then 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 secondary aging treatment is as follows: the single-crystal high-entropy superalloy in the primary aging state is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 2-4 bar, and the furnace pressure is 70-110 Pa; the temperature is increased from room temperature to 870°C at a heating rate of 10-15°C / min, and held for 20-30 hours; the alloy is then removed from the heat treatment furnace and air-cooled.

[0026] 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 superalloy, the proportions of each element, the order of placement of each element in the crucible, the casting process 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.

[0027] This invention comprehensively considers the influence of various elements on the mechanical properties of the alloy, especially its plasticity, when designing the alloy composition. The specific analysis is as follows:

[0028] Co and Ni are the two most important basic elements for high-entropy effects in the alloy of this invention. They are the matrix elements that mainly play a role in solid solution strengthening, forming a face-centered cubic crystal structure. Ni is a traditional single-crystal high-temperature alloying element with high chemical stability, capable of dissolving a large number of alloying elements without forming harmful phases. Co has stronger resistance to hot corrosion than Ni, can reduce the solubility of Al and Ti in the matrix, precipitate more strengthening phases, increase the solid solution temperature of the γˊ strengthening phase, and reduce the precipitation of carbides between dendrites.

[0029] Cr: It mainly plays an antioxidant role and is an essential alloying element in single-crystal superalloys. It is dissolved in the matrix, causing lattice distortion, increasing the strength of the solid solution, reducing the stacking fault energy of the solid solution, and improving the alloy's creep resistance, corrosion resistance and oxidation resistance. However, excessive Cr will promote the precipitation of TCP phase and affect the stability of the alloy.

[0030] Al and Ta are primarily γ-strengthening phase-forming elements. Al is a precipitation strengthening element, increasing the volume fraction of γ-. Al produces an Al2O3 protective film on the alloy surface, improving high-temperature oxidation resistance. Ta is a sparingly soluble element, generally entering the γ-strengthening phase, promoting its precipitation, and delaying its aggregation and growth, thereby improving the high-temperature strength of the alloy. However, excessive Ta levels can lead to severe compositional segregation.

[0031] Mo and W are mainly solid solution strengthening elements and refractory elements. They mainly enter the γ matrix, which can increase the lattice constant of the crystal, reduce the mismatch of γ / γˊ, effectively suppress the coarsening of γˊ precipitates, maintain the γ / γˊ structure, thereby enabling the alloy to obtain a longer high-temperature service life and further improve high-temperature performance.

[0032] The present invention relates to a high-plasticity single-crystal high-entropy superalloy without Fe or Ti and its preparation method, which has the following beneficial effects:

[0033] (1) Compared with the existing single-crystal high-entropy alloys, the single-crystal high-entropy high-temperature alloy of the present invention removes low-melting-point phase elements such as Fe and Ti, and adds refractory elements such as Mo, Ta and W, which improves the high-temperature resistance of the alloy. At the same time, the single-crystal high-entropy high-temperature alloy of the present invention eliminates grain boundaries and has an FCC and L12 dual-phase structure. The microstructure is a γ+γˊ dual-phase structure. The γˊ structure is composed of a 400-500nm square primary γˊ structure and an 80-120nm strip nanoparticle secondary γˊ structure, which has a high γˊ strengthening phase volume fraction, low stacking fault energy and high microstructure stability.

[0034] (2) The single-crystal high-entropy high-temperature alloy of the present invention has the advantages of both high-entropy alloy and single-crystal high-temperature alloy, and has excellent room temperature and high temperature mechanical properties, especially the plasticity at room temperature is as high as 62% and the plasticity at 760°C is as high as 51%, which has the potential to work under high temperature, high stress and high corrosion conditions in aero-engine turbine blades.

[0035] (3) The single-crystal high-entropy high-temperature 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.

[0036] (4) The present invention adopts a heat treatment system of step solution treatment + first-level aging + second-level aging, which can significantly improve the uniformity of the alloy structure and make the alloy have high plasticity. Attached Figure Description

[0037] Figure 1 This is a photograph of the dendritic structure of a cast single-crystal high-entropy superalloy without Fe or Ti and its preparation method according to a preferred embodiment of the present invention.

[0038] Figure 2 for Figure 1 Micrograph of the final heat-treated single-crystal high-entropy superalloy in the illustrated embodiment;

[0039] Figure 3 for Figure 1 Tensile curves of the single-crystal high-entropy superalloy prepared in the example shown. Detailed Implementation

[0040] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0041] Example 1:

[0042] According to a preferred embodiment of the Fe- and Ti-free high-plasticity single-crystal high-entropy superalloy of the present invention, the chemical composition of the single-crystal high-entropy superalloy includes seven elements: Co, Ni, Cr, Al, Ta, Mo, and W. The atomic percentages of each element are: Co 40 at%, Ni 35 at%, Cr 4 at%, Al 12 at%, Ta 3 at%, Mo 2 at%, and W 4 at%, with the sum of the atomic percentages of each element being 100%.

[0043] The mixed entropy ΔS of the single-crystal high-entropy superalloy mix ≥1.386R, the formula for calculating the entropy of mixture is: In the formula,

[0044] ΔS mix —The mixed entropy of single-crystal high-entropy superalloys, J / (mol·K);

[0045] R—gas constant, R = 8.314 J / (mol·K);

[0046] i—any element from Co, Ni, Cr, Al, Ta, Mo, W;

[0047] n—the sum of all elements in a single-crystal high-entropy superalloy;

[0048] x i —Atomic percentage of element i in single-crystal high-entropy superalloys, %.

[0049] The single-crystal high-entropy superalloy is an L12-type strengthened FCC alloy with a microstructure of γ+γ′ dual phase. The γ′ structure consists of square primary γ′ structures and strip-shaped granular secondary γ′ structures. The size of the primary γ′ structure is 454 nm, and the size of the secondary γ′ structure is 109 nm. The volume fraction of the γ′ structure is 80.15%, and the grain orientation is as follows: <001> .

[0050] This embodiment also provides a method for preparing a Fe- and Ti-free, highly ductile, single-crystal, high-entropy superalloy, which includes the following steps in sequence:

[0051] Step 1: Weigh out the elemental elements Co, Ni, Cr, Al, Ta, Mo, and W with a purity of 99.5% or higher according to the designed ratio and set them aside;

[0052] Step 2: Place the elemental elements Co, Ni, Cr, Ta, Mo, and W into the crucible of the vacuum induction melting furnace in the designed order, evacuate to a certain vacuum level, and then heat and melt; when the temperature rises to the refining temperature, add the elemental element Al and perform electromagnetic stirring. After refining is completed, cast into a single crystal high-entropy high-temperature alloy master alloy ingot.

[0053] Step 3: Prepare grains with the following orientation using the high-speed solidification Bridgeman method and seed crystal method. <001> The process for obtaining a single-crystal high-entropy superalloy test bar involves first placing the single-crystal high-entropy superalloy 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 superalloy.

[0054] Step 4: Place the cast single-crystal high-entropy superalloy into a heat treatment furnace for solution treatment to obtain a solution-treated single-crystal high-entropy superalloy.

[0055] Step 5: Place the solid solution-treated single-crystal high-entropy superalloy into a heat treatment furnace for first-stage aging treatment to obtain a first-stage aged single-crystal high-entropy superalloy.

[0056] Step 6: Place the first-stage aged single-crystal high-entropy superalloy into a heat treatment furnace for second-stage aging treatment to obtain the final heat-treated single-crystal high-entropy superalloy, which is also a Fe-free and Ti-free high-plasticity single-crystal high-entropy superalloy.

[0057] In step two, 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 Ta, Mo, and W; the third layer is Cr; 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.

[0058] In step three, the vacuum level is 10. -2 Pa, heating power of 35kW, refining temperature of 1495℃, refining time of 15min, casting temperature of 1475℃, and drawing speed of 3.5mm / min.

[0059] In step four, the solution treatment process is as follows: the cast single-crystal high-entropy superalloy is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 3 bar, and the furnace pressure is 90 Pa; the temperature is increased from room temperature to 1150°C at a rate of 12°C / min and held for 2.5 h; the temperature is increased from 1150°C to 1200°C at a rate of 12°C / min and held for 2.5 h; the temperature is increased from 1200°C to 1250°C at a rate of 12°C / min and held for 12 h; the alloy is then removed from the heat treatment furnace and air-cooled.

[0060] In step five, the process of the first-level aging treatment is as follows: the solid solution-state single-crystal high-entropy superalloy is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 3 bar, and the furnace pressure is 90 Pa; the temperature is increased from room temperature to 1100℃ at a heating rate of 12℃ / min, and held for 4.5 h; the alloy is then removed from the heat treatment furnace and air-cooled.

[0061] In step six, the process of the secondary aging treatment is as follows: the single-crystal high-entropy high-temperature alloy in the primary aging state is placed in a heat treatment furnace, filled with argon gas at a pressure of 3 bar, and the furnace pressure is 90 Pa; the temperature is increased from room temperature to 870°C at a heating rate of 12°C / min and held for 25 hours; the alloy is then removed from the heat treatment furnace and air-cooled.

[0062] In this embodiment, the dendritic structure of the cast single-crystal high-entropy superalloy is as follows: Figure 1 As shown, the microstructure of the final heat-treated single-crystal high-entropy superalloy is as follows: Figure 2 As shown, the tensile curve of the single-crystal high-entropy superalloy is as follows. Figure 3 As shown in Table 1, the alloy microstructure is a γ+γ′ dual-phase structure. The specific microstructure parameters are shown in Table 1, and the specific tensile properties are shown in Table 2.

[0063] Table 1 Microstructure parameters of single-crystal high-entropy superalloys

[0064] Primary dendrite spacing (μm) Primary γ′ phase size (nm) Secondary γ′ phase size (nm) γ′ volume fraction (%) 352 454 109 80.15

[0065] Table 2 Mechanical property data of single-crystal high-entropy superalloys

[0066]

[0067] 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, and there are no special requirements for their models. Throughout the entire preparation process of the single-crystal high-entropy superalloy, the proportions of each element, the order in which each element is placed in the crucible, the casting process 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.

[0068] In designing the alloy composition, this embodiment comprehensively considers the influence of various elements on the mechanical properties of the alloy, especially the influence on the plasticity of the alloy. The specific analysis is as follows: (1) Co and Ni are the two most important basic elements with high entropy effect in the alloy of this invention. They are the matrix elements that mainly play the role of solid solution strengthening and form a face-centered cubic crystal structure. Ni is a traditional single-crystal high-temperature alloy element with high chemical stability. It can dissolve more alloy elements without generating harmful phases. Co has stronger resistance to hot corrosion than Ni. It can reduce the solubility of Al and Ti in the matrix, precipitate more strengthening phases, increase the solid solution temperature of the γ′ strengthening phase, and reduce the precipitation of carbides between dendrites. (2) Cr mainly plays the role of anti-oxidation. It is an essential alloy element in single-crystal high-temperature alloys. It dissolves in the matrix, causes lattice distortion, increases the strength of the solid solution, reduces the stacking fault energy of the solid solution, and improves the durability, corrosion resistance and oxidation resistance of the alloy. However, excessive Cr will promote the precipitation of TCP phase and affect the stability of the alloy. (3) Al and Ta are mainly γ′ strengthening phase forming elements. Al is a precipitation strengthening element, which increases the volume fraction of γ′. Al will produce an Al2O3 protective film on the alloy surface, which improves the high-temperature oxidation resistance. Ta is a sparingly soluble element, which generally enters the γ′ strengthening phase, promotes the precipitation of the γ′ strengthening phase, and delays the aggregation and growth of the γ′ phase, thereby improving the high-temperature strength of the alloy. However, excessive Ta will lead to severe compositional segregation. (4) Mo and W are mainly solid solution strengthening elements. They are refractory elements and mainly enter the γ matrix. They can increase the lattice constant of the crystal, reduce the mismatch of γ / γ′, effectively inhibit the coarsening of the γ′ precipitate, maintain the γ / γ′ structure, thereby enabling the alloy to obtain a longer high-temperature service life and further improve the high-temperature performance.

[0069] This embodiment of the high-plasticity single-crystal high-entropy superalloy without Fe and Ti and its preparation method has the following beneficial effects: (1) The single-crystal high-entropy superalloy removes low-melting-point phase elements such as Fe and Ti and adds refractory elements such as Mo, Ta, and W, which improves the high-temperature resistance of the alloy; at the same time, the single-crystal high-entropy superalloy eliminates grain boundaries and has an FCC and L12 dual-phase structure. The microstructure is a γ+γˊ dual-phase structure. The γˊ structure is composed of 400-500nm square primary γˊ structure and 80-120nm strip nanoparticle secondary γˊ structure, which has a high γˊ strengthening phase volume fraction, low stacking fault energy and high microstructure stability. (2) The single-crystal high-entropy superalloy has the advantages of both high-entropy alloy and single-crystal superalloy. It has excellent room temperature and high temperature mechanical properties, especially the room temperature plasticity is as high as 62% and the plasticity at 760℃ is as high as 51%, which has the potential to work under high temperature, high stress and high corrosion conditions in aero-engine turbine blades. (3) Single-crystal high-entropy superalloys do not contain rare and precious elements such as Re and Ru. Compared with traditional single-crystal superalloys, they have advantages in operation and cost, and can effectively carry out engineering applications of the alloy. (4) The heat treatment system of step solution treatment + first-stage aging + second-stage aging can significantly improve the uniformity of the alloy structure and make the alloy have high plasticity.

[0070] Example 2:

[0071] According to another preferred embodiment of the Fe- and Ti-free high-plasticity single-crystal high-entropy superalloy 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 in Embodiment 1, except that:

[0072] The chemical composition of the single-crystal high-entropy superalloy includes seven elements: Co, Ni, Cr, Al, Ta, Mo, and W. The atomic percentages of each element are: Co 35 at%, Ni 40 at%, Cr 3 at%, Al 13 at%, Ta 1 at%, Mo 3 at%, and W 5 at%, with the sum of the atomic percentages of each element being 100%. The single-crystal high-entropy superalloy is an L12-type strengthened FCC alloy with a microstructure of γ+γˊ dual-phase structure. The γˊ structure consists of square primary γˊ structures and strip-shaped granular secondary γˊ structures. The size of the primary γˊ structure is 402 nm, and the size of the secondary γˊ structure is 83 nm. The volume fraction of the γˊ structure is 82.73%, and the grain orientation is [not specified]. <001> .

[0073] In step two, 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 Ta, Mo, and W; the third layer is Cr; and the fourth layer is a mixture of 50% Ni and 50% Co. The vacuum level is 10. -1Pa, heating power of 20kW, refining temperature of 1500℃, refining time of 10min.

[0074] In step three, the vacuum level is 10. -2 Pa, heating power of 20kW, refining temperature of 1470℃, refining time of 10min, casting temperature of 1450℃, and drawing speed of 2mm / min.

[0075] In step four, the solution treatment process is as follows: the cast single-crystal high-entropy superalloy is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 2 bar, and the furnace pressure is 70 Pa; the temperature is increased from room temperature to 1150°C at a rate of 10°C / min and held for 2 hours; the temperature is increased from 1150°C to 1200°C at a rate of 10°C / min and held for 2 hours; the temperature is increased from 1200°C to 1250°C at a rate of 10°C / min and held for 10 hours; the alloy is then removed from the heat treatment furnace and air-cooled.

[0076] In step five, the process of the first-level aging treatment is as follows: the solid solution-state single-crystal high-entropy superalloy is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 2 bar, and the furnace pressure is 70 Pa; the temperature is increased from room temperature to 1100℃ at a heating rate of 10℃ / min, and held for 3 hours; the alloy is taken out of the heat treatment furnace and air-cooled.

[0077] In step six, the process of the secondary aging treatment is as follows: the single crystal high entropy high temperature alloy in the primary aging state is placed in a heat treatment furnace, filled with argon gas at a pressure of 2 bar, and the furnace pressure is 70 Pa; the temperature is increased from room temperature to 870°C at a heating rate of 10°C / min and held for 20 hours; the alloy is then removed from the heat treatment furnace and air-cooled.

[0078] The mechanical properties of the single-crystal high-entropy superalloy prepared in this embodiment are shown in Figure 3.

[0079] Table 3 Mechanical property data of single-crystal high-entropy superalloys

[0080]

[0081] Example 3:

[0082] According to another preferred embodiment of the Fe- and Ti-free high-plasticity single-crystal high-entropy superalloy 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 in Embodiment 1, except that:

[0083] The chemical composition of the single-crystal high-entropy superalloy includes seven elements: Co, Ni, Cr, Al, Ta, Mo, and W. The atomic percentages of each element are: Co 45 at%, Ni 30 at%, Cr 5 at%, Al 10 at%, Ta 4 at%, Mo 3 at%, and W 3 at%, with the sum of the atomic percentages of each element being 100%. The single-crystal high-entropy superalloy is an L12-type strengthened FCC alloy with a microstructure of γ+γ′ dual-phase structure. The γ′ structure consists of a square primary γ′ structure and a strip-shaped granular secondary γ′ structure. The size of the primary γ′ structure is 497 nm, and the size of the secondary γ′ structure is 119 nm. The volume fraction of the γ′ structure is 84.91%, and the grain orientation is... <001> .

[0084] In step two, 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 Ta, Mo, and W; the third layer is Cr; 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.

[0085] In step three, the vacuum level is 10. -2 Pa, heating power of 50kW, refining temperature of 1520℃, refining time of 20min, casting temperature of 1500℃, and drawing speed of 5mm / min.

[0086] In step four, the solution treatment process is as follows: the cast single-crystal high-entropy superalloy is placed in a heat treatment furnace, filled with argon gas at a pressure of 4 bar, and the furnace pressure is 110 Pa; the temperature is increased from room temperature to 1150°C at a rate of 15°C / min and held for 3 hours; the temperature is then increased from 1150°C to 1200°C at a rate of 15°C / min and held for 3 hours; the temperature is then increased from 1200°C to 1250°C at a rate of 15°C / min and held for 15 hours; the alloy is then removed from the heat treatment furnace and air-cooled.

[0087] In step five, the process of the first-level aging treatment is as follows: the solid solution-state single-crystal high-entropy superalloy is placed in a heat treatment furnace, argon gas is introduced, the charging pressure is 4 bar, and the furnace pressure is 110 Pa; the temperature is increased from room temperature to 1100℃ at a heating rate of 15℃ / min, and held for 6 hours; the alloy is taken out of the heat treatment furnace and air-cooled.

[0088] In step six, the process of the secondary aging treatment is as follows: the single crystal high entropy high temperature alloy in the primary aging state is placed in a heat treatment furnace, filled with argon gas at a pressure of 4 bar, and the furnace pressure is 110 Pa; the temperature is increased from room temperature to 870°C at a heating rate of 15°C / min and held for 30 hours; the alloy is then removed from the heat treatment furnace and air-cooled.

[0089] The mechanical properties of the single-crystal high-entropy superalloy prepared in this embodiment are shown in Figure 4.

[0090] Table 4 Mechanical property data of single-crystal high-entropy superalloys

[0091]

[0092] 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.

[0093] Those skilled in the art will readily understand that the Fe- and Ti-free high-plasticity single-crystal high-entropy superalloy 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. An Fe- and Ti-free, high plasticity, single-crystal, high-entropy, high-temperature alloy, characterized in that, The single crystal high-entropy superalloy includes seven elements of Co, Ni, Cr, Al, Ta, Mo and W in a chemical composition, and the atomic percentage of each element is Co 35-45at%, Ni 30-40at%, Cr 3-5at%, Al 10-13at%, Ta 1-4at%, Mo 1-3at%, and W 3-5at%, and the sum of the atomic percentages of the elements is 100%. The preparation method of the Fe-free and Ti-free high-plasticity single crystal high-entropy superalloy comprises the following steps in sequence: Step one: Co, Ni, Cr, Al, Ta, Mo and W elements with a purity of more than 99.5% are weighed according to the designed proportion; Step two: according to the design order, put the single element Co, Ni, Cr, Ta, Mo, W into the crucible of the vacuum induction melting furnace, the order from bottom to top is the mixture of 50% Ni and 50% Co in the first layer, the mixture of Ta, Mo and W in the second layer, Cr in the third layer, and the mixture of 50% Ni and 50% Co in the fourth layer, vacuumize to the vacuum degree of not more than 10 -1 Pa, then heat and melt, the heating power is 20-50 kW; when the temperature rises to the refining temperature of 1500-1600℃, add the single element Al, and conduct electromagnetic stirring, the refining time is 10-30 min, after the refining is completed, pour into single crystal high-entropy high-temperature alloy master alloy ingot; Step three: single crystal high-entropy high-temperature alloy test rods with <001> grain orientation are prepared by high-speed solidification Bridgeman method and seed crystal method, i.e. first, the single crystal high-entropy high-temperature alloy mother alloy ingot is put into a vacuum melting single crystal directional solidification furnace, the vacuum degree is not more than 10 -2 Pa, and heated and melted, the heating power is 20-50 kW; then refining is carried out at a temperature of 1470-1520℃, the refining time is 10-20 min, after the refining is completed, the temperature is reduced to the pouring temperature 1450-1500℃; finally, pouring is carried out at a pulling rate of 2-5 mm / min, and the as-cast single crystal high-entropy high-temperature alloy is obtained; Step four: the as-cast single crystal high-entropy superalloy is placed in a heat treatment furnace for solid solution treatment, the solid solution treatment process is as follows: argon is filled, the filling pressure is 2-4 bar, the furnace pressure is 70-110 Pa, the temperature is raised from room temperature to 1150 DEG C at a rate of 10-15 DEG C / min, the temperature is kept for 2-3 h, the temperature is raised to 1200 DEG C at a rate of 10-15 DEG C / min, the temperature is kept for 2-3 h, the temperature is raised to 1250 DEG C at a rate of 10-15 DEG C / min, the temperature is kept for 10-15 h, the alloy is taken out of the heat treatment furnace and air-cooled to obtain the single crystal high-entropy superalloy in a solid solution state; Step five: the single crystal high-entropy superalloy in the solid solution state is placed in a heat treatment furnace for primary aging treatment, the primary aging treatment process is as follows: argon is filled, the filling pressure is 2-4 bar, the furnace pressure is 70-110 Pa, the temperature is raised from room temperature to 1100 DEG C at a rate of 10-15 DEG C / min, the temperature is kept for 3-6 h, the alloy is taken out of the heat treatment furnace and air-cooled to obtain the single crystal high-entropy superalloy in a primary aging state; Step six: the single crystal high-entropy superalloy in the primary aging state is placed in a heat treatment furnace for secondary aging treatment, the secondary aging treatment process is as follows: argon is filled, the filling pressure is 2-4 bar, the furnace pressure is 70-110 Pa, the temperature is raised from room temperature to 870 DEG C at a rate of 10-15 DEG C / min, the temperature is kept for 20-30 h, the alloy is taken out of the heat treatment furnace and air-cooled to obtain the single crystal high-entropy superalloy in a final heat treatment state, that is, the Fe-free and Ti-free high-plasticity single crystal high-entropy superalloy.

2. The Fe- and Ti-free, high-plasticity, single-crystal, high-entropy, high- temperature alloy of claim 1, wherein, The single-crystal high-entropy high-temperature alloy has a mixing entropy The calculation formula of the mixing entropy is , wherein, - the mixing entropy of the single-crystal high-entropy high-temperature alloy, J / (mol K); - the gas constant, J / (mol K); - any of Co, Ni, Cr, Al, Ta, Mo, W; - the sum of all elements in the single-crystal high-entropy high-temperature alloy; - in single-crystal high-entropy high-temperature alloys atomic percentage of the elements, %.

3. The Fe- and Ti-free, high-plasticity, single-crystal, high-entropy, high- temperature alloy of claim 2, wherein, The single crystal high-entropy superalloy is an L12 type strengthened FCC alloy, the microstructure is a γ+γ´ dual-phase structure, the γ´ structure is composed of primary γ´ structure and secondary γ´ structure, the primary γ´ structure is a square of 400-500 nm, the secondary γ´ structure is a strip-shaped nanoparticle of 80-120 nm, the volume fraction of the γ´ structure is 80-85%, and the grain orientation is <001>.

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