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

Abstract

The invention discloses a Fe-free Ti-free high-plasticity single-crystal high-entropy high-temperature alloy and a preparation method thereof, the alloy comprises the following chemical components in percentage by atom: 35-45 at% of Co, 30-40 at% of Ni, 3-5 at% of Cr, 10-13 at% of Al, 1-4 at% of Ta, 1-3 at% of Mo and 3-5 at% of W. The invention further discloses a preparation method of the Fe-free Ti-free high-plasticity single-crystal high-entropy high-temperature alloy. The preparation method comprises the following steps that simple substance elements Co, Ni, Cr, Ta, Mo and W are sequentially put into a crucible of a vacuum induction melting furnace to be heated and smelted, when the temperature rises to the refining temperature, the simple substance element Al is added, and a master alloy ingot is formed through pouring; a high-speed solidification Bridgeman method and a seed crystal method are adopted to prepare a crystal grain with the orientation of 1t; 001gt, 001gt; preparing a single-crystal high-entropy high-temperature alloy test bar; and sequentially carrying out solution treatment, first-stage aging and second-stage aging on the single-crystal high-entropy high-temperature alloy test bar to obtain the Fe-free and Ti-free high-plasticity single-crystal high-entropy high-temperature alloy. The single-crystal high-entropy high-temperature alloy has the advantages of a high-entropy alloy and a single-crystal high-temperature alloy at the same time, and has excellent room-temperature and high-temperature mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of single crystal high entropy alloy materials and preparation thereof, and in particular relates to a Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy and a preparation method thereof. Background Art

[0002] High entropy alloy refers to a new type of alloy system with four or more components and the atomic ratio of each component is equal or nearly equal. The mixing entropy of high entropy alloy is greater than 1.386R. It has high entropy effect, lattice distortion effect, hysteresis diffusion effect and cocktail effect. The cocktail effect is that after various elements are mixed, each element exerts its own performance. The four major effects of high entropy alloy give it excellent comprehensive properties, such as high temperature stability, oxidation resistance, high temperature mechanical properties, etc. Therefore, high entropy alloy has the potential for application in high temperature fields such as hot end components of aircraft engines.

[0003] At present, under the conditions of high temperature, high stress, gas corrosion, etc., single crystal high temperature alloys are the most widely used materials for aircraft engine turbine blades. Although single crystal high temperature alloys can avoid the problem of grain boundary softening at high temperatures, and can also make up for the shortcomings of traditional high temperature alloys such as severe segregation, poor hot working performance, and difficult forming, in order to meet the needs of advanced aircraft engines with a thrust-to-weight ratio of 20, it is necessary to further optimize and improve the performance of the material. The introduction of the concept of high entropy alloys has brought about a huge turning point in the design of single crystal high temperature alloys. For example, single crystal Co 1.5 CrFeNi 1.5 Ti 0.5 At about 800℃, single crystal Al 0.3 CrCuFeNi2 has a tensile strength of 522MPa and an elongation of 35%. Therefore, improving alloy performance through composition design and preparation process improvement is an urgent problem that needs to be solved in the research and development and application of high entropy alloys.

[0004] The invention patent with application publication number CN110317990A discloses a Ni-Co-Al-Cr-Fe system single crystal high entropy high temperature alloy and its preparation method. The chemical composition of the alloy is as follows by atomic percentage: Ni 35-40%, Co 30-35%, Al 10-13%, Cr5-10%, 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%, Hf0.005-0.12%, RE 0.05-0.15%, 14%≤Al+Ti+Ta≤16%, wherein RE is any rare earth element of Ce, L, and Y; the preparation method comprises the following steps: placing each element into a smelting furnace for smelting, high-temperature refining for 15-30 minutes, the refining temperature is 1550-1650°C, and casting into an alloy ingot; adopting a high-speed solidification method to prepare a single crystal high-entropy high-temperature alloy rod, and the pulling rate is 2-4mm / min; the high-entropy alloy rod is solution treated at 1220-1235°C for 4-6 hours, and air-cooled to obtain a solid solution alloy; the alloy rod is subjected to secondary aging treatment, firstly keeping it at 1080-1100°C for 4-6 hours, then keeping it at 870°C for 24 hours, and air-cooling to obtain the alloy rod after the final heat treatment. The single crystal high entropy high temperature alloy 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 greatly reduced. The maximum tensile strength at room temperature reaches 881 MPa, and the corresponding elongation is 40.2%.

[0005] At present, in order to address the problem of high mechanical strength and low plasticity of single crystal high entropy alloys, it is necessary to change the precipitation phase of the alloy by adjusting the alloy composition, heat treatment method, casting process, etc., so as to improve the balance between room temperature and high temperature strength and plasticity of single crystal high entropy alloys. Therefore, it is urgent to develop a Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy and its preparation method, so as to greatly improve the plasticity of the alloy while meeting the tensile strength requirements. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy. The chemical composition of the single crystal high-entropy high-temperature alloy includes seven elements: Co, Ni, Cr, Al, Ta, Mo, and W. The atomic percentage of each element is Co 35-45at%, Ni 30-40at%, Cr 3-5at%, Al 10-13at%, Ta 1-4at%, Mo1-3at%, W 3-5at%, and the sum of the atomic percentages of each element is 100%.

[0007] Preferably, the mixing entropy ΔS of the single crystal high entropy superalloy is mix≥1.386R, the formula for calculating the mixing entropy is In the formula,

[0008] ΔS mix ——Mixing entropy of single crystal high entropy superalloy, J / (mol·K);

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

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

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

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

[0013] In any of the above schemes, it is preferred that the single crystal high entropy high temperature alloy is an L12 type strengthened FCC alloy, the microstructure is a γ+γ′ two-phase structure, the γ′ structure is composed of a square primary γ′ structure and a strip-shaped granular secondary γ′ structure, the size of the primary γ′ structure is 400-500nm, the size of the secondary γ′ structure is 80-120nm, the volume fraction of the γ′ structure is 80-85%, and the grain orientation is <001> .

[0014] The present invention also provides a method for preparing an Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy, which is used to prepare any of the above-mentioned Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloys, and comprises the following steps in order:

[0015] Step 1: weigh out single element Co, Ni, Cr, Al, Ta, Mo, and W with a purity of more than 99.5% according to the designed ratio for use;

[0016] Step 2: Put the single element 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 degree, and then heat and melt; when the temperature rises to the refining temperature, add the single element Al and perform electromagnetic stirring. After the refining is completed, cast it into a single crystal high-entropy high-temperature alloy master alloy ingot;

[0017] Step 3: Use the high-speed solidification Bridgeman method and seed crystal method to prepare grain orientation <001> The single crystal high entropy superalloy test rod is prepared by first placing a single crystal high entropy superalloy master alloy ingot into a vacuum melting single crystal directional solidification furnace, evacuating to a certain vacuum degree, and heating for melting; then refining at a certain temperature, and after the refining is completed, lowering the temperature to a pouring temperature; finally, pouring at a certain pulling rate to obtain a cast single crystal high entropy superalloy;

[0018] Step 4: placing the cast single crystal high entropy superalloy into a heat treatment furnace for solution treatment to obtain a single crystal high entropy superalloy in a solid solution state;

[0019] Step 5: placing the single crystal high entropy superalloy in a solid solution state into a heat treatment furnace for primary aging treatment to obtain a single crystal high entropy superalloy in a primary aging state;

[0020] Step 6: Place the single crystal high entropy superalloy in the primary aging state into a heat treatment furnace for secondary aging treatment to obtain the single crystal high entropy superalloy in the final heat-treated state, that is, obtain a Fe-free and Ti-free high-plasticity single crystal high entropy superalloy.

[0021] Preferably, in step 2, the order of placing the single elements into the crucible from bottom to top is: 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 is 20-50kW, refining temperature is 1500-1600℃, and refining time is 10-30min.

[0022] In any of the above schemes, preferably, in step 3, the vacuum degree does not exceed 10 -2 Pa, heating power is 20-50kW, refining temperature is 1470-1520℃, refining time is 10-20min, pouring temperature is 1450-1500℃, and pulling rate is 2-5mm / min.

[0023] In any of the above schemes, it is preferred that in step four, the process system of the solid solution treatment is as follows: placing the cast single crystal high entropy high temperature alloy into a heat treatment furnace, filling it with argon, the charging pressure is 2-4 bar, and the pressure in the furnace is 70-110Pa; heating from room temperature to 1150℃ at a heating rate of 10-15℃ / min, and keeping warm for 2-3h; continuing to heating from 1150℃ to 1200℃ at a heating rate of 10-15℃ / min, and keeping warm for 2-3h; continuing to heating from 1200℃ to 1250℃ at a heating rate of 10-15℃ / min, and keeping warm for 10-15h; taking out the alloy from the heat treatment furnace and air cooling it.

[0024] In any of the above schemes, it is preferred that in step five, the process system of the primary aging treatment is to place the single crystal high-entropy high-temperature alloy in a solid solution state into a heat treatment furnace, fill it with argon, the charging pressure is 2-4 bar, and the pressure in the furnace is 70-110Pa; heat up from room temperature to 1100°C at a heating rate of 10-15°C / min, and keep warm for 3-6h; take out the alloy from the heat treatment furnace and air cool it.

[0025] In any of the above schemes, it is preferred that in step six, the process system of the secondary aging treatment is to place the single crystal high-entropy high-temperature alloy in the primary aging state into a heat treatment furnace, fill it with argon, the charging pressure is 2-4 bar, and the pressure in the furnace is 70-110Pa; heat up from room temperature to 870°C at a heating rate of 10-15°C / min, and keep warm for 20-30h; take out the alloy from the heat treatment furnace and air cool it.

[0026] The vacuum induction melting furnace, vacuum melting single crystal directional solidification furnace, heat treatment furnace and other equipment used in the present invention can be selected from existing equipment, and no special requirements are made on the model. In the entire preparation process of the single crystal high entropy high temperature alloy, the ratio of each element, the placement order of each element in the crucible, the casting process parameters, the solution treatment system, the primary aging treatment system and the secondary aging treatment system are very critical. Only when the various parameters work together can the expected technical effect of the present invention be achieved.

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

[0028] Co and Ni: are the two most important basic elements of high entropy effect in the alloy of the present invention. They are matrix elements that mainly play a role in 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 solid-dissolve more alloy elements without generating harmful phases. Co has stronger thermal corrosion resistance 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 high-temperature alloys. 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 durability, corrosion resistance and oxidation resistance of the alloy. However, too high a Cr element will promote the precipitation of the TCP phase and affect the stability of the alloy.

[0030] Al, Ta: Mainly γˊ strengthening phase forming elements, Al is a precipitation strengthening element, increasing the γˊ volume fraction. Al will produce Al2O3 protective film on the alloy surface, improving high temperature oxidation resistance. Ta is a poorly soluble element, generally enters the γˊ strengthening phase, promotes the precipitation of the γˊ strengthening phase, delays the aggregation and growth of the γˊ phase, thereby improving the high temperature strength of the alloy, but too high Ta elements will lead to serious composition segregation.

[0031] Mo, W: Mainly act as solid solution strengthening elements, refractory elements, mainly enter the γ matrix, can increase the lattice constant of the crystal, reduce the mismatch of γ / γˊ, effectively inhibit the coarsening of γˊ precipitation phase, maintain the γ / γˊ structure, so that the alloy can obtain a longer high temperature service life and further improve the high temperature performance.

[0032] The Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy and the preparation method thereof of the present invention have the following beneficial effects:

[0033] (1) Compared with the single crystal high entropy alloy in the prior art, 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, thereby improving 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, has a FCC and L12 dual-phase structure, and a microstructure of a γ+γˊ dual-phase structure. The γˊ structure is composed of a square primary γˊ structure of 400-500nm and a strip-shaped nanoparticle secondary γˊ structure of 80-120nm, and has a higher volume fraction of the γˊ strengthening phase, lower stacking fault energy, and higher organizational stability.

[0034] (2) The single crystal high entropy high temperature alloy of the present invention possesses the advantages of both high entropy alloys and single crystal high temperature alloys, and has excellent room temperature and high temperature mechanical properties, especially room temperature plasticity of up to 62%, and plasticity of up to 51% at 760°C, and has the potential to work under high temperature, high stress and high corrosion conditions of aircraft 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 engineering applications of the alloy.

[0036] (4) The present invention adopts a heat treatment system of step solution treatment + primary aging + secondary aging, which can significantly improve the structural uniformity of the alloy and make the alloy have higher plasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A dendrite structure photograph of a cast single crystal high entropy superalloy in a preferred embodiment of the Fe-free and Ti-free high plasticity single crystal high entropy superalloy and a preparation method thereof according to the present invention;

[0038] Figure 2 for Figure 1 Microstructure photograph of the single crystal high entropy superalloy in the final heat-treated state in the embodiment shown;

[0039] Figure 3 for Figure 1 The tensile curve of the single crystal high entropy superalloy prepared in the embodiment shown. DETAILED DESCRIPTION

[0040] In order to further understand the content of the present invention, the present invention will be described in detail below in conjunction with specific embodiments.

[0041] Embodiment 1:

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

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

[0044] ΔS mix ——Mixing entropy of single crystal high entropy superalloy, J / (mol·K);

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

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

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

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

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

[0050] This embodiment also provides a method for preparing an Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy, which is used to prepare the above-mentioned Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy, and includes the following steps in order:

[0051] Step 1: weigh out single element Co, Ni, Cr, Al, Ta, Mo, and W with a purity of more than 99.5% according to the designed ratio for use;

[0052] Step 2: Put the single element 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 degree, and then heat and melt; when the temperature rises to the refining temperature, add the single element Al and perform electromagnetic stirring. After the refining is completed, cast it into a single crystal high-entropy high-temperature alloy master alloy ingot;

[0053] Step 3: Use the high-speed solidification Bridgeman method and seed crystal method to prepare grain orientation <001> The single crystal high entropy superalloy test rod is prepared by first placing a single crystal high entropy superalloy master alloy ingot into a vacuum melting single crystal directional solidification furnace, evacuating to a certain vacuum degree, and heating for melting; then refining at a certain temperature, and after the refining is completed, lowering the temperature to a pouring temperature; finally, pouring at a certain pulling rate to obtain a cast single crystal high entropy superalloy;

[0054] Step 4: placing the cast single crystal high entropy superalloy into a heat treatment furnace for solution treatment to obtain a single crystal high entropy superalloy in a solid solution state;

[0055] Step 5: placing the single crystal high entropy superalloy in a solid solution state into a heat treatment furnace for primary aging treatment to obtain a single crystal high entropy superalloy in a primary aging state;

[0056] Step 6: Place the single crystal high entropy superalloy in the primary aging state into a heat treatment furnace for secondary aging treatment to obtain the single crystal high entropy superalloy in the final heat-treated state, that is, obtain a Fe-free and Ti-free high-plasticity single crystal high entropy superalloy.

[0057] In step 2, the order of placing the single elements into the crucible from bottom to top is: 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 is 10 -1 Pa, the heating power is 35kW, the refining temperature is 1550℃, and the refining time is 20min.

[0058] In step 3, the vacuum degree is 10 -2 Pa, heating power is 35kW, refining temperature is 1495℃, refining time is 15min, pouring temperature is 1475℃, and pulling rate is 3.5mm / min.

[0059] In step four, the process system of the solution treatment is as follows: placing the cast single crystal high-entropy high-temperature alloy into a heat treatment furnace, filling it with argon, the charging pressure is 3 bar, and the pressure in the furnace is 90 Pa; heating from room temperature to 1150°C at a heating rate of 12°C / min, and keeping warm for 2.5 hours; continuing to heating from 1150°C to 1200°C at a heating rate of 12°C / min, and keeping warm for 2.5 hours; continuing to heating from 1200°C to 1250°C at a heating rate of 12°C / min, and keeping warm for 12 hours; taking out the alloy from the heat treatment furnace and air cooling it.

[0060] In step five, the process system of the primary aging treatment is to place the single crystal high-entropy high-temperature alloy in a solid solution state into a heat treatment furnace, fill it with argon, the charging pressure is 3 bar, and the pressure in the furnace is 90 Pa; heat it from room temperature to 1100°C at a heating rate of 12°C / min, and keep it warm for 4.5 hours; take out the alloy from the heat treatment furnace and air cool it.

[0061] In step six, the process system of the secondary aging treatment is to place the single crystal high-entropy high-temperature alloy in the primary aging state into a heat treatment furnace, fill it with argon, the charging pressure is 3 bar, and the pressure in the furnace is 90Pa; heat it from room temperature to 870°C at a heating rate of 12°C / min, and keep it warm for 25 hours; take out the alloy from the heat treatment furnace and air cool it.

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

[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 properties data of single crystal high entropy superalloy

[0066]

[0067] The vacuum induction melting furnace, vacuum melting single crystal directional solidification furnace, heat treatment furnace and other equipment used in this embodiment can be selected from existing equipment, and no special requirements are made on the model. In the entire preparation process of the single crystal high entropy high temperature alloy, the ratio of each element, the placement order of each element in the crucible, the casting process parameters, the solution treatment system, the primary aging treatment system and the secondary aging treatment system are all very critical. Only by synergizing various parameters can the expected technical effect of this embodiment be achieved.

[0068] In designing the alloy composition, the present embodiment comprehensively considers the influence of various elements on the mechanical properties of the alloy, especially the influence on the plasticity of the alloy, and the specific analysis is as follows: (1) Co and Ni are the two most important basic elements of the high entropy effect in the alloy of the present invention, and are the matrix elements that mainly play the role of solid solution strengthening, forming a face-centered cubic crystal structure; Ni is a traditional single crystal high temperature alloy element, has high chemical stability, and can solid dissolve more alloy elements without generating harmful phases; Co has stronger thermal corrosion resistance than Ni, 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 an antioxidant role and is an essential alloy element in single crystal high temperature alloys. It is solid dissolved in the matrix, causes lattice distortion, improves 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, too high a Cr element 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 Al2O3 protective film on the alloy surface, improving the high temperature oxidation resistance. Ta is a poorly soluble element, generally entering the γ′ strengthening phase, promoting the precipitation of the γ′ strengthening phase, delaying the aggregation and growth of the γ′ phase, thereby improving the high temperature strength of the alloy. However, too high a content of Ta will lead to serious component segregation. (4) Mo and W are mainly solid solution strengthening elements and poorly soluble elements. They mainly enter the γ matrix, which can increase the lattice constant of the crystal, reduce the mismatch of γ / γˊ, effectively inhibit the coarsening of the γˊ precipitation phase, and maintain the γ / γˊ structure, so that the alloy can obtain a longer high temperature service life and further improve the high temperature performance.

[0069] The Fe-free and Ti-free high-plasticity single crystal high-entropy superalloy and its preparation method in this embodiment have 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, thereby improving the high-temperature resistance of the alloy; at the same time, the single crystal high-entropy superalloy eliminates the grain boundary, and has a FCC and L12 dual-phase structure, and the microstructure is a γ+γˊ dual-phase structure, and the γˊ structure is composed of a square primary γˊ structure of 400-500nm and a strip-shaped nanoparticle secondary γˊ structure of 80-120nm, with a high volume fraction of γˊ strengthening phase, low stacking fault energy and high organizational stability. (2) The single crystal high-entropy superalloy has the advantages of both high-entropy alloys and single crystal superalloys, and 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%, and has the potential to work under the high temperature, high stress and high corrosion conditions of aircraft engine turbine blades. (3) Single crystal high-entropy superalloys do not contain rare 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 alloys. (4) The use of a step solution + primary aging + secondary aging heat treatment system can significantly improve the uniformity of the alloy's structure and make the alloy have higher plasticity.

[0070] Embodiment 2:

[0071] According to another preferred embodiment of the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy and its preparation method of the present invention, its composition design, process flow, equipment used, technical principles, beneficial effects, etc. are basically the same as those of the first embodiment, 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 percentage of each element is 35 at% Co, 40 at% Ni, 3 at% Cr, 13 at% Al, 1 at% Ta, 3 at% Mo, and 5 at% W. The sum of the atomic percentages of each element is 100%. The single crystal high entropy superalloy is an L12 type strengthened FCC alloy. The microstructure is a γ+γˊ dual-phase structure. The γˊ structure consists of a square primary γˊ structure and a strip-shaped granular secondary γˊ structure. The size of the primary γˊ structure is 402 nm, 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 <001> .

[0073] In step 2, the order of placing the single elements into the crucible from bottom to top is: 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 is 10 -1Pa, the heating power is 20kW, the refining temperature is 1500℃, and the refining time is 10min.

[0074] In step 3, the vacuum degree is 10 -2 Pa, heating power is 20kW, refining temperature is 1470℃, refining time is 10min, pouring temperature is 1450℃, and pulling rate is 2mm / min.

[0075] In step four, the process system of the solid solution treatment is as follows: placing the cast single crystal high-entropy high-temperature alloy into a heat treatment furnace, filling it with argon, the charging pressure is 2 bar, and the pressure in the furnace is 70 Pa; heating from room temperature to 1150°C at a heating rate of 10°C / min, and keeping warm for 2 hours; continuing to heating from 1150°C to 1200°C at a heating rate of 10°C / min, and keeping warm for 2 hours; continuing to heating from 1200°C to 1250°C at a heating rate of 10°C / min, and keeping warm for 10 hours; taking out the alloy from the heat treatment furnace and air cooling it.

[0076] In step five, the process system of the primary aging treatment is to place the single crystal high-entropy high-temperature alloy in a solid solution state into a heat treatment furnace, fill it with argon, the filling pressure is 2 bar, and the pressure in the furnace is 70Pa; heat it from room temperature to 1100°C at a heating rate of 10°C / min, and keep it warm for 3 hours; take out the alloy from the heat treatment furnace and air cool it.

[0077] In step six, the process system of the secondary aging treatment is as follows: placing the single crystal high-entropy high-temperature alloy in the primary aging state into a heat treatment furnace, filling it with argon gas, the charging pressure is 2 bar, and the pressure in the furnace is 70 Pa; heating the temperature from room temperature to 870°C at a heating rate of 10°C / min, and keeping the temperature for 20 hours; taking the alloy out of the heat treatment furnace and air cooling it.

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

[0079] Table 3 Mechanical properties data of single crystal high entropy superalloy

[0080]

[0081] Embodiment three:

[0082] According to another preferred embodiment of the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy and its preparation method of the present invention, its composition design, process flow, equipment used, technical principles, beneficial effects, etc. are basically the same as those of the first embodiment, except that:

[0083] The chemical composition of the single crystal high entropy high temperature alloy includes seven elements: Co, Ni, Cr, Al, Ta, Mo, and W. The atomic percentage of each element is 45 at% Co, 30 at% Ni, 5 at% Cr, 10 at% Al, 4 at% Ta, 3 at% Mo, and 3 at% W. The sum of the atomic percentages of each element is 100%. The single crystal high entropy high temperature alloy is an L12 type strengthened FCC alloy. The microstructure is a γ+γ′ two-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, 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 2, the order of placing the single elements into the crucible from bottom to top is: 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 is 10 -1 Pa, the heating power is 50kW, the refining temperature is 1600℃, and the refining time is 30min.

[0085] In step 3, the vacuum degree is 10 -2 Pa, heating power is 50kW, refining temperature is 1520℃, refining time is 20min, pouring temperature is 1500℃, and pulling rate is 5mm / min.

[0086] In step four, the process system of the solution treatment is as follows: placing the cast single crystal high-entropy high-temperature alloy into a heat treatment furnace, filling it with argon, the charging pressure is 4 bar, and the pressure in the furnace is 110Pa; heating from room temperature to 1150°C at a heating rate of 15°C / min, and keeping warm for 3 hours; continuing to heating from 1150°C to 1200°C at a heating rate of 15°C / min, and keeping warm for 3 hours; continuing to heating from 1200°C to 1250°C at a heating rate of 15°C / min, and keeping warm for 15 hours; taking out the alloy from the heat treatment furnace and air cooling it.

[0087] In step five, the process system of the primary aging treatment is to place the single crystal high-entropy high-temperature alloy in a solid solution state into a heat treatment furnace, fill it with argon, the charging pressure is 4 bar, and the pressure in the furnace is 110Pa; heat it from room temperature to 1100°C at a heating rate of 15°C / min, and keep it warm for 6 hours; take out the alloy from the heat treatment furnace and air cool it.

[0088] In step six, the process system of the secondary aging treatment is to place the single crystal high-entropy high-temperature alloy in the primary aging state into a heat treatment furnace, fill it with argon, the charging pressure is 4 bar, and the pressure in the furnace is 110Pa; heat it from room temperature to 870°C at a heating rate of 15°C / min, and keep it warm for 30 hours; take out the alloy from the heat treatment furnace and air cool it.

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

[0090] Table 4 Mechanical properties data of single crystal high entropy superalloy

[0091]

[0092] Special note: The technical solution of the present invention involves many parameters, and the synergistic effects between the various parameters need to be comprehensively considered to obtain the beneficial effects and significant progress of the present invention. Moreover, the value ranges of the various parameters in the technical solution are obtained after a large number of experiments. For each parameter and the combination of each parameter, the inventor has recorded a large amount of experimental data. Due to space limitations, the specific experimental data will not be disclosed here.

[0093] It is not difficult for those skilled in the art to understand that the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy and its preparation method of the present invention include any combination of the invention content and specific implementation methods of the above-mentioned invention specification and the various parts shown in the drawings. Due to the limited space and to make the specification concise, the various schemes composed of these combinations are not described one by one. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A Fe-free and Ti-free high-plasticity single crystal high-entropy superalloy, characterized in that: The chemical composition of the single crystal high entropy high temperature alloy includes seven elements: Co, Ni, Cr, Al, Ta, Mo, and W. 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%. The sum of the atomic percentages of each element is 100%.

2. The Fe-free and Ti-free high-plasticity single crystal high-entropy superalloy according to claim 1, characterized in that: The mixing entropy ΔS of the single crystal high entropy superalloy mix ≥1.386R, the formula for calculating the mixing entropy is In the formula, ΔS mix ——Mixing entropy of single crystal high entropy superalloy, J / (mol·K); R——gas constant, R=8.314J / (mol·K); i——any element among Co, Ni, Cr, Al, Ta, Mo, W; n——the sum of all elements in the single crystal high entropy superalloy; x i ——Atomic percentage of element i in single crystal high entropy superalloy, %.

3. The Fe-free and Ti-free high-plasticity single crystal high-entropy superalloy according to claim 2, characterized in that: The single crystal high entropy high temperature alloy is an L12 type strengthened FCC alloy, the microstructure is a γ+γ′ dual phase structure, the γ′ structure is composed of a primary γ′ structure and a 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> .

4. A method for preparing a Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy, characterized in that: The method for preparing the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy according to any one of claims 1 to 3 comprises the following steps in chronological order: Step 1: weigh out single element Co, Ni, Cr, Al, Ta, Mo, and W with a purity of more than 99.5% according to the designed ratio for use; Step 2: Put the single element 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 degree, and then heat and melt; when the temperature rises to the refining temperature, add the single element Al and perform electromagnetic stirring. After the refining is completed, cast it into a single crystal high-entropy high-temperature alloy master alloy ingot; Step 3: Use the high-speed solidification Bridgeman method and seed crystal method to prepare grain orientation <001> The single crystal high entropy superalloy test rod is prepared by first placing a single crystal high entropy superalloy master alloy ingot into a vacuum melting single crystal directional solidification furnace, evacuating to a certain vacuum degree, and heating for melting; then refining at a certain temperature, and after the refining is completed, lowering the temperature to a pouring temperature; finally, pouring at a certain pulling rate to obtain a cast single crystal high entropy superalloy; Step 4: placing the cast single crystal high entropy superalloy into a heat treatment furnace for solution treatment to obtain a single crystal high entropy superalloy in a solid solution state; Step 5: placing the single crystal high entropy superalloy in a solid solution state into a heat treatment furnace for primary aging treatment to obtain a single crystal high entropy superalloy in a primary aging state; Step 6: Place the single crystal high entropy superalloy in the primary aging state into a heat treatment furnace for secondary aging treatment to obtain the single crystal high entropy superalloy in the final heat-treated state, that is, obtain a Fe-free and Ti-free high-plasticity single crystal high entropy superalloy.

5. The method for preparing the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy according to claim 4, characterized in that: In step 2, the order of placing the single elements into the crucible from bottom to top is: 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 is 20-50kW, refining temperature is 1500-1600℃, and refining time is 10-30min.

6. The method for preparing the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy according to claim 5, characterized in that: In step 3, the vacuum degree does not exceed 10 -2 Pa, heating power is 20-50kW, refining temperature is 1470-1520℃, refining time is 10-20min, pouring temperature is 1450-1500℃, and pulling rate is 2-5mm / min.

7. The method for preparing the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy according to claim 6, characterized in that: In step four, the process system of the solid solution treatment is as follows: placing the cast single crystal high entropy high temperature alloy into a heat treatment furnace, filling it with argon, the charging pressure is 2-4 bar, and the pressure in the furnace is 70-110Pa; heating from room temperature to 1150°C at a heating rate of 10-15°C / min, and keeping warm for 2-3h; continuing to heating from 1150°C to 1200°C at a heating rate of 10-15°C / min, and keeping warm for 2-3h; continuing to heating from 1200°C to 1250°C at a heating rate of 10-15°C / min, and keeping warm for 10-15h; taking out the alloy from the heat treatment furnace and air cooling it.

8. The method for preparing the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy according to claim 7, characterized in that: In step five, the process system of the primary aging treatment is to place the single crystal high-entropy high-temperature alloy in a solid solution state into a heat treatment furnace, fill it with argon, the charging pressure is 2-4 bar, and the pressure in the furnace is 70-110Pa; heat it from room temperature to 1100°C at a heating rate of 10-15°C / min, and keep it warm for 3-6h; take out the alloy from the heat treatment furnace and air cool it.

9. The method for preparing the Fe-free and Ti-free high-plasticity single crystal high-entropy high-temperature alloy according to claim 8, characterized in that: In step six, the process system of the secondary aging treatment is as follows: placing the single crystal high-entropy high-temperature alloy in the primary aging state into a heat treatment furnace, filling it with argon gas, the charging pressure is 2-4 bar, and the pressure in the furnace is 70-110Pa; heating from room temperature to 870°C at a heating rate of 10-15°C / min, and keeping warm for 20-30h; taking out the alloy from the heat treatment furnace and air cooling it.

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