High-toughness and high-temperature-resistant as-cast eutectic high-entropy alloy and preparation method thereof

Abstract

The invention discloses a high-toughness and high-temperature-resistant as-cast eutectic high-entropy alloy and a preparation method thereof. The high-toughness and high-temperature-resistant eutectic high-entropy alloy is mainly prepared by mixing an aluminum elementary substance, a cobalt elementary substance, an iron elementary substance, a nickel elementary substance and a cobalt-tantalum eutectic alloy and repeatedly smelting the aluminum elementary substance, the cobalt elementary substance, the iron elementary substance and the cobalt-tantalum eutectic alloy. The method comprises the following steps: smelting and pouring aluminum, cobalt, iron and nickel elementary substances and eutectic alloy to prepare a plurality of block cast ingots, placing the block cast ingots in commercial directional solidification equipment, carrying out drawing and cooling solidification treatment to obtain a sample, cutting the sample, and carrying out vacuum drying to obtain the aluminum-cobalt-iron-nickel alloy. Through room temperature tensile test, high temperature tensile test, scanning electron microscopy and transmission electron microscopy equipment, the cross-temperature zone mechanical property and microstructure of the sample are tested in sequence. According to the method, the solid solution strengthening effect and the precipitation strengthening effect are enhanced by regulating and controlling the morphological characteristics and element distribution of the dendrite structure in the microstructure, so that the room-temperature and high-temperature mechanical properties of the as-cast high-entropy alloy are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of high-entropy alloy technology, and in particular relates to the composition design and preparation process of a high-strength, high-toughness, and high-temperature resistant cast eutectic high-entropy alloy. Background Technology

[0002] Tantalum is widely used in nickel-based superalloys primarily due to its unique physical and chemical properties. Firstly, tantalum has a melting point close to 2980℃, and its addition to nickel-based superalloys typically significantly improves the alloy's strength and creep resistance, making it ideal for extreme environments with high temperatures and pressures, such as aerospace, gas turbine blades, and nuclear reactors. Furthermore, tantalum exhibits excellent corrosion resistance, especially under acidic and high-temperature oxidizing conditions. This has led to the widespread application of tantalum alloys in chemical and marine engineering fields, effectively extending material lifespan and reducing maintenance costs. Simultaneously, the addition of tantalum to nickel-based superalloys also improves the alloy's toughness and plasticity, reduces brittleness, and enhances its impact resistance, thereby ensuring its reliability during high-temperature service.

[0003] High-entropy alloys have attracted widespread attention from materials scientists due to their excellent comprehensive mechanical properties. Taking AlFeCoNi series eutectic high-entropy alloys as an example, although they exhibit good mechanical properties at both room temperature and high temperature, further optimization is still needed. Drawing on the alloying design concept of tantalum in nickel-based superalloys and combining it with the directional solidification process commonly used in the preparation of nickel-based single crystal materials, new ideas and guidance can be provided to improve the comprehensive mechanical properties of eutectic high-entropy alloys, broadening the application prospects of these materials in harsh high-temperature applications.

[0004] For example, patent CN 120082786 A designed an AlCoCrNiNb-based high-entropy alloy with good oxidation resistance and its preparation method. By controlling the Nb content, the alloy exhibits good microstructure stability and high-temperature oxidation resistance. However, when the Nb content is too high, the alloy still faces a series of problems such as element segregation and oxidation spalling, leading to microstructure inhomogeneity. Therefore, reasonable control of multiphase distribution characteristics is particularly important for improving the comprehensive mechanical properties of eutectic high-entropy alloys under room temperature and high temperature conditions. In addition, patent CN120249776A proposed adding different proportions of Mo, Nb, Ti, and V to an AlCrMoNbNiTiV seven-element high-entropy alloy, and obtaining a lightweight, high-strength, high-temperature resistant high-entropy alloy with multiphase synergistic strengthening through a series of solid solution and aging treatments. However, the preparation process of these materials involves a variety of complex element ratios and complicated preparation procedures, and may form a variety of hard and brittle intermetallic compounds in the microstructure, thus adversely affecting the overall performance of the high-entropy alloy. Summary of the Invention

[0005] This invention introduces tantalum (Ta) elements of varying amounts to replace aluminum (Al) elements in the eutectic high-entropy alloy matrix, and combines this with directional solidification technology to achieve rapid solidification, thereby obtaining a novel eutectic high-entropy alloy with high strength, high toughness, and high-temperature resistance.

[0006] This invention improves the overall mechanical properties of the alloy under both room temperature and high temperature conditions by controlling the morphology and elemental distribution of dendrites in the as-cast microstructure, as well as the average size and antiphase boundary energy of the nano-precipitates in the as-cast microstructure. This has significant practical implications and broad development prospects.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: I. A high-strength, high-toughness, and high-temperature-resistant cast eutectic high-entropy alloy: The high-strength, high-toughness, and high-temperature-resistant eutectic high-entropy alloy is mainly prepared by mixing elemental aluminum, cobalt, iron, nickel, and a cobalt-tantalum eutectic alloy (Co-21at.%Ta) and repeatedly smelting them. The mass / molar ratio of elemental aluminum, cobalt, iron, nickel, and the cobalt-tantalum eutectic alloy is as follows: (Here, Al is used as an example). 18 Ta1Fe 20 Co 20 Ni 41 For example, the mass / molar ratio of aluminum, cobalt, iron, nickel, and cobalt-tantalum (Co-21at.%Ta) eutectic alloy is 9.05:9.27:20.80:44.82:16.05; The atomic percentages of aluminum are 16.5% to 18.5%, cobalt is 18% to 22%, iron is 18% to 22%, nickel is 37% to 45%, and tantalum is 0.5% to 2.5%.

[0008] The total cobalt content here is 18-22 at.%, including all cobalt in elemental form and in the cobalt-tantalum eutectic alloy. Ta is first added using a Co-Ta master alloy with appropriate proportions. Co has good miscibility with FeNi, allowing it to form a single phase. Finally, the remaining Co is added as elemental.

[0009] The high-strength, high-toughness, and high-temperature resistant eutectic high-entropy alloy is prepared by mixing only aluminum, cobalt, iron, nickel and cobalt-tantalum eutectic alloy raw materials and repeatedly melting them. One of its components is set as follows: aluminum atoms account for 18% of the total number of atoms, tantalum atoms account for 1% of the total number of atoms, iron atoms account for 20% of the total number of atoms, cobalt atoms account for 20% of the total number of atoms, and nickel atoms account for 41% of the total number of atoms. The eutectic high-entropy alloy is Al.18 Ta1Fe 20 Co 20 Ni 41 ; Another composition setting is as follows: aluminum atom percentage 17%, tantalum atom percentage 2%, iron atom percentage 20%, cobalt atom percentage 20%, and nickel atom percentage 41%, wherein the eutectic high-entropy alloy is Al. 17 Ta2Fe 20 Co 20 Ni 41 .

[0010] When the total atomic percentage of Ta is 2 at.%, the alloy's plasticity decreases significantly by approximately 50%. Further addition of Ta will have a detrimental effect on mechanical properties. The above two examples illustrate the role of Ta in enhancing various mechanical properties.

[0011] II. A method for rapid directional solidification preparation of a high-strength, high-toughness, and high-temperature-resistant eutectic high-entropy alloy, the method comprising the following steps: Step S1: Prepare several bulk ingots by melting and casting aluminum, cobalt, iron, nickel and Co-21at.%Ta eutectic alloy; 21at.%Ta is the eutectic point of the Co-Ta binary alloy phase diagram. The material designed based on this content has the highest utilization rate, better alloy fluidity, and can effectively avoid element segregation.

[0012] Step S2: Place the above-mentioned block ingot and round crucible tube into a commercial directional solidification device, and perform drawing and cooling solidification at a fast rate of 100 μm / s to obtain a eutectic high-entropy alloy sample.

[0013] Specifically, after cutting the sample obtained in step S2, the mechanical properties and microstructure of the sample across temperature ranges are analyzed sequentially using room temperature tensile tests, high temperature tensile tests, scanning electron microscopy, and transmission electron microscopy.

[0014] Step S1 specifically involves: Step S1.1: First, aluminum, iron, cobalt, nickel and Co-21at.%Ta eutectic alloy are placed in an induction melting furnace and repeatedly melted under vacuum for at least 6 times, and finally cast to obtain alloy ingots. In this invention, the Ta content is mainly in the range of 0.5-2.5 at%, and the corresponding Al element is in the range of 18.5-16.5 at.%. Al and Ta are elements that promote the formation of BCC, and the sum of their addition is controlled to be 19 at.%.

[0015] Step S1.2: Transfer the arc-melted alloy ingot to a muffle furnace for high-vacuum homogenization treatment, and heat it to 1250℃ with the furnace and hold it for 12 h; the purpose is to promote full diffusion of elements, avoid compositional segregation, and obtain a eutectic high-entropy alloy raw material with uniform composition.

[0016] Step S1.3: The casting alloy ingot obtained in step S1.2 is subjected to wire cutting, mechanical grinding, ultrasonic cleaning and constant temperature drying to obtain eutectic high-entropy alloy raw materials for directional solidification. Step S1.4: The eutectic high-entropy alloy raw material obtained in step S1.3 is processed by wire cutting into several small block ingots with a volume of approximately 1 cm3.

[0017] Ta (tantalum) has a high melting point of only about 2980 °C, which differs significantly from the melting points of other elements. Therefore, directly adding tantalum metal for the first time can lead to severe tantalum segregation and element loss due to burning. To address this, this invention first mixes Fe, Co, and Ni, then adds a Co-21at.%Ta eutectic alloy, and finally adds a suitable amount of low-melting-point aluminum. Ultimately, the alloy is prepared through repeated melting and casting processes.

[0018] Step S1.1 includes: After placing the crucible containing the alloy raw material into the vacuum system, the vacuum system is activated to evacuate the air from the system. Then, argon gas is introduced as a protective gas. Whenever the vacuum level drops below 5 × 10⁻⁶, the pressure is maintained. -4 At Pa, argon gas is introduced as a protective gas; the vacuum atmosphere conditions of the crucible are as follows: vacuum degree higher than 5 × 10⁻⁶. -4 Pa.

[0019] Step S2 specifically involves: Step S2.1: Start the heating system and heat the several block ingots obtained in step S1 to 1550 ~ 1650℃ and hold them at that temperature for 40 ~ 60 min. Step S2.2: After the heat preservation stage of step S3.1 is completed, start the directional solidification pulling motion system and pull several block ingots heated in the crucible at a pulling speed of 90 ~ 110 μm / s to cool and solidify at the same time. After cooling, take out the sample.

[0020] Preferably, the heating temperature in step S2.1 is 1600℃, the holding time in step S2.1 is 50 min, and the pulling speed in step S2.2 is 100 μm / s.

[0021] Step S3 specifically involves: Step S3.1: Select the middle position of the sample obtained in step S3 and cut a tensile sample. Use a universal testing machine and extensometer to measure the tensile sample of the eutectic high-entropy alloy prepared by directional solidification, so as to obtain the yield strength, tensile strength and elongation of the tensile sample under room temperature conditions and high temperature conditions of 600℃ and 800℃. Repeat the measurement of the sample under the same conditions 4 times and use the calculated average value of the mechanical properties to obtain reliable quantitative results. Taking the 600℃ test conditions as an example, the tensile specimen is first heated to the target temperature in a vacuum furnace, and then held at that temperature for 5 minutes after it stabilizes. Throughout the entire heating and holding process, a thermocouple is used to fit tightly against the center of the gauge length of the tensile specimen to ensure the stability of the sample temperature.

[0022] Step S3.2: Cut a flat sample from the middle position of the sample obtained in step S3 along the direction of directional solidification, and perform mechanical grinding and polishing in sequence. Observe the interior of the flat sample by scanning electron microscopy to obtain the morphology and elemental distribution characteristics of the dendritic structure inside the flat sample. Step S3.3: Cut a flat sample from the middle of the sample obtained in step S3 along the direction of directional solidification, and perform mechanical grinding and polishing in sequence. Then, use focused ion beam cutting technology to cut the two-phase structure containing face-centered cubic (FCC) and body-centered cubic (BCC) phases. Observe the rich high-density nano-precipitates inside the face-centered cubic (FCC) phase through transmission electron microscopy. Specifically, high-precision microstructure analysis is carried out using aberration-corrected electron microscopy to obtain the average diameter and atomic arrangement characteristics of the high-density nano-precipitates, including morphology, average size, and atomic site distribution characteristics.

[0023] This invention involves first melting elemental aluminum, cobalt, iron, and nickel, along with a cobalt-tantalum eutectic alloy, and then rapidly directionally solidifying the alloy at a relatively fast pulling rate of 100 μm / s. This process is achieved through the synthesis of Al... 19 Fe 20 Co 20 Ni 41 Al was successfully prepared by adding different amounts of Ta to replace Al based on the alloy composition. 18 Ta1Fe 20 Co 20 Ni 41 (Hereafter referred to as Al) 18 Ta1) and Al 17 Ta2Fe 20 Co 20 Ni 41 (Hereafter referred to as Al) 17 Ta2) is a eutectic high-entropy alloy with two components.

[0024] This invention significantly improves the room temperature and high temperature mechanical properties of as-cast high-entropy alloys by controlling the morphology and elemental distribution of the dendritic structure in the microstructure to enhance the solid solution strengthening effect and precipitation strengthening effect.

[0025] The beneficial effects of this invention are: This invention, based on rapid pull-out directional solidification technology, aims to optimize the comprehensive mechanical properties of as-cast eutectic high-entropy alloys under both room temperature and high temperature conditions by replacing aluminum with tantalum. The addition of tantalum not only effectively dissolves within the face-centered cubic (FCC) and body-centered cubic (BCC) dual-phase microstructures but also modulates the morphology of the dendritic branches, thereby achieving better mechanical properties in the alloy.

[0026] 1. This invention successfully prepared Al using a rapid directional solidification process. 18 Ta1Fe 20 Co 20 Ni 41 And Al 17 Ta2Fe 20 Co 20 Ni 41 Two types of eutectic high-entropy alloys. With Al 19 Fe 20 Co 20 Ni 41 In alloy comparison, these two new compositions significantly optimized the overall mechanical properties of the eutectic high-entropy alloy under both room temperature and high temperature conditions, while maintaining excellent ductility and toughness. This indicates that the addition of tantalum can greatly improve the balance between the alloy's strength and ductility, making it more advantageous in practical applications.

[0027] 2. This invention proposes to successfully control the microstructure and elemental content of dendritic branches by replacing aluminum with different amounts of tantalum under the same directional solidification process conditions. Tantalum atoms effectively occupy aluminum sites in the nano-precipitates within the FCC phase, significantly enhancing the antiphase interface energy of the precipitates. This structural optimization not only enhances the precipitation strengthening effect but also helps explain the essential mechanism of the excellent mechanical properties of eutectic high-entropy alloys, providing efficient guidance for the multi-field application of as-cast eutectic high-entropy alloys. Attached Figure Description

[0028] Figure 1 The figures show the engineering stress-engineering strain curves of the rapidly directional solidification alloy samples of Examples 1, 2 and Comparative Example 1 under room temperature testing conditions. Figure 2 The diagram shows the engineering stress-engineering strain curves of the rapidly directional solidification alloy samples of Example 1, Example 2 and Comparative Example 1 under vacuum testing conditions at 600℃. Figure 3The diagram shows the engineering stress-engineering strain curves of the rapidly directional solidification alloy samples of Example 1, Example 2 and Comparative Example 1 under vacuum testing conditions at 800°C. Figure 4 The results of scanning electron microscopy (SEM) analysis of the longitudinal sections of the rapidly oriented solidified samples of Examples 1, 2 and Comparative Example 1 are presented. Figure 4 a, 4c, and 4e represent Al... 19 Al 18 Ta1 and Al 17 Electron backscattering image of the dendritic structure in the longitudinal section of the Ta2 sample, while Figure 4 b, 4d, and 4f respectively demonstrate Al 19 Al 18 Ta1 and Al 17 Elemental distribution characteristics in the microstructure of the longitudinal section of Ta2 sample; Figure 5 The results of transmission electron microscopy (TEM) analysis of the longitudinal sections of the rapidly oriented solidified samples of Examples 1, 2 and Comparative Example 1 are presented. Figure 5 a, 5c, and 5e represent Al respectively. 19 Al 18 Ta1 and Al 17 The distribution characteristics of high-density nano-precipitates within the FCC phase in the Ta2 sample, and Figure 5 b, 5d, and 5f are respectively Al 19 Al 18 Ta1 and Al 17 Atomic image and elemental distribution diagram of nano-precipitates within the FCC phase in the longitudinal section of Ta2 sample. Detailed Implementation

[0029] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] The embodiments of the present invention are as follows: Example 1 This embodiment introduces a high-strength, tough, and high-temperature resistant Al... 18 Ta1Fe 20 Co 20 Ni 41 The composition and directional solidification preparation method of eutectic high-entropy alloys are as follows: (1) First, high-purity elemental aluminum, elemental iron, elemental cobalt, elemental nickel and cobalt-tantalum eutectic alloy are placed in a vacuum arc melting furnace and repeatedly melted and cast. The melting is repeated at least 6 times to ensure the uniformity and purity of the alloy composition. (2) The cast ingots obtained by casting are subjected to high vacuum homogenization treatment at 1250°C for 12 hours in a muffle furnace. The purpose is to eliminate casting defects and compositional segregation, thereby obtaining a eutectic high-entropy alloy ingot with uniform composition. (3) The ingot obtained in step (2) is sequentially subjected to wire cutting, mechanical grinding, ultrasonic cleaning and constant temperature drying to finally obtain high-entropy alloy raw material, which will be used to prepare Al under directional solidification conditions. 18 Ta1Fe 20 Co 20 Ni 41 alloy; (4) Then, take the Al obtained in step (3) 18 Ta1Fe 20 Co 20 Ni 41 The alloy raw material was wire-cut into several pieces with a volume of approximately 1 cm. 3 The block ingots are placed inside the crucible tube of the commonly used directional solidification equipment. (5) Start the vacuum system in sequence: vacuum gauge, mechanical pump and molecular pump. Wait until the vacuum gauge reading is below 5 × 10⁻⁶. -4 When Pa, turn off the vacuum gauge and quickly connect high-purity argon gas as a protective gas to complete the vacuum preparation work before directional solidification. (6) Start the heating system to heat the high-entropy alloy raw materials in the crucible to 1600℃ and maintain it for 50 min; (7) After the heat preservation process is completed, start the pull-out motion control unit at the bottom of the directional solidification device. During the pull-out process, the crucible and melt gradually move towards the bottom gallium-indium liquid alloy tank. After the melt comes into contact with the liquid metal, it gradually cools down until the alloy melt is completely solidified.

[0031] (8) In this embodiment, the constant pulling rate is set to 100 μm / s. After the crucible and melt have completely cooled, the gas is released, the furnace lid is opened, and the eutectic high-entropy alloy sample is taken out; (9) Cut tensile specimens from the middle of the ingot and use a universal testing machine and video extensometer to measure the yield strength, tensile strength and elongation of the eutectic high-entropy alloy sample prepared by directional solidification at room temperature. The sample was measured 4 times under the same test conditions to calculate the average value of the mechanical properties. (10) Similarly, tensile specimens were cut from the middle of the ingot. The yield strength, tensile strength and elongation of the specimens were measured at 600℃ using a universal testing machine and a video extensometer. The specimens were measured 4 times to calculate the average value. (11) Cut tensile specimens again from the middle of the ingot, and use a universal testing machine and video extensometer to measure the yield strength, tensile strength and elongation of the specimens at 800℃. The specimens were measured 4 times to calculate the average value. (12) Cut the alloy ingot sample flat along the direction of directional solidification, cut the sample from the middle of the ingot, and then perform mechanical grinding and vibration polishing in sequence. Perform scanning electron microscopy analysis to observe the morphological characteristics and element distribution of the eutectic structure inside the sample. (13) Similarly, the alloy ingot sample was cut flat along the direction of directional solidification. Samples were cut from the longitudinal section and cross section of the middle of the ingot and mechanically ground and vibratory polished. Then, the two-phase region (including FCC and BCC phases) was cut by focused ion beam cutting and high-precision microstructure analysis was performed using aberration-corrected electron microscope to observe the morphology, number density and atomic occupancy characteristics of the high-density nano-precipitates inside the FCC phase.

[0032] Example 2 This embodiment introduces a high-strength, tough, and high-temperature resistant Al... 17 Ta2Fe 20 Co 20 Ni 41 The composition and directional solidification preparation method of eutectic high-entropy alloys are as follows: (1) First, high-purity elemental aluminum, elemental iron, elemental cobalt, elemental nickel and cobalt-tantalum eutectic alloy are placed in a vacuum arc melting furnace and repeatedly melted and cast. The melting is repeated at least 6 times to ensure the uniformity and purity of the alloy composition. (2) The cast ingots obtained by casting are subjected to high vacuum homogenization treatment at 1250°C for 12 hours in a muffle furnace. The purpose is to eliminate casting defects and compositional segregation, thereby obtaining a eutectic high-entropy alloy ingot with uniform composition. (3) The ingot obtained in step (2) is sequentially subjected to wire cutting, mechanical grinding, ultrasonic cleaning and constant temperature drying to finally obtain high-entropy alloy raw material, which will be used to prepare Al under directional solidification conditions. 17 Ta2Fe 20 Co 20 Ni 41 alloy; (4) Then, take the Al obtained in step (3) 17 Ta2Fe 20 Co 20 Ni 41The alloy raw material was wire-cut into several pieces with a volume of approximately 1 cm. 3 The block ingots are placed inside the crucible tube of the commonly used directional solidification equipment. (5) Start the vacuum system in sequence: vacuum gauge, mechanical pump and molecular pump. Wait until the vacuum gauge reading is below 5 × 10⁻⁶. -4 When Pa, turn off the vacuum gauge and quickly connect high-purity argon gas as a protective gas to complete the vacuum preparation work before directional solidification. (6) Start the heating system to heat the high-entropy alloy raw materials in the crucible to 1600℃ and maintain it for 50 min; (7) After the heat preservation process is completed, start the pull-out motion control unit at the bottom of the directional solidification device. During the pull-out process, the crucible and melt gradually move towards the bottom gallium-indium liquid alloy tank. After the melt comes into contact with the liquid metal, it gradually cools down until the alloy melt is completely solidified.

[0033] (8) In this embodiment, the constant pulling rate is set to 100 μm / s. After the crucible and melt have completely cooled, the gas is released, the furnace lid is opened, and the eutectic high-entropy alloy sample is taken out; (9) Cut tensile specimens from the middle of the ingot and use a universal testing machine and video extensometer to measure the yield strength, tensile strength and elongation of the eutectic high-entropy alloy sample prepared by directional solidification at room temperature. The sample was measured 4 times under the same test conditions to calculate the average value of the mechanical properties. (10) Similarly, tensile specimens were cut from the middle of the ingot. The yield strength, tensile strength and elongation of the specimens were measured at 600℃ using a universal testing machine and a video extensometer. The specimens were measured 4 times to calculate the average value. (11) Cut tensile specimens again from the middle of the ingot, and use a universal testing machine and video extensometer to measure the yield strength, tensile strength and elongation of the specimens at 800℃. The specimens were measured 4 times to calculate the average value. (12) Cut the alloy ingot sample flat along the direction of directional solidification, cut the sample from the middle of the ingot, and then perform mechanical grinding and vibration polishing in sequence. Perform scanning electron microscopy analysis to observe the morphological characteristics and element distribution of the eutectic structure inside the sample. (13) Similarly, the alloy ingot sample was cut flat along the direction of directional solidification. Samples were cut from the longitudinal section and cross section of the middle of the ingot and mechanically ground and vibratory polished. Then, the two-phase region (including FCC and BCC phases) was cut by focused ion beam cutting and high-precision microstructure analysis was performed using aberration-corrected electron microscope to observe the morphology, number density and atomic occupancy characteristics of the high-density nano-precipitates inside the FCC phase.

[0034] Comparative Example 1 This embodiment introduces an Al without Ta element addition. 19 Fe 20 Co 20 Ni 41 The composition and directional solidification preparation method of eutectic high-entropy alloys are as follows: (1) First, high-purity elemental aluminum, elemental iron, elemental cobalt and elemental nickel are placed in a vacuum arc melting furnace and repeatedly melted and cast. The melting is repeated at least 6 times to ensure the uniformity and purity of the alloy composition. (2) The cast ingots obtained by casting are subjected to high vacuum homogenization treatment at 1250℃ for 12 h in a muffle furnace. The purpose is to eliminate casting defects and compositional segregation, thereby obtaining a eutectic high-entropy alloy ingot with uniform composition. (3) The ingot obtained in step (2) is sequentially subjected to wire cutting, mechanical grinding, ultrasonic cleaning and constant temperature drying to finally obtain high-entropy alloy raw material, which will be used to prepare Al under directional solidification conditions. 19 Fe 20 Co 20 Ni 41 alloy; (4) Then, take the Al obtained in step (3) 19 Fe 20 Co 20 Ni 41 The alloy raw material was wire-cut into several pieces with a volume of approximately 1 cm. 3 The block ingots are placed inside the crucible tube of the commonly used directional solidification equipment. (5) Start the vacuum system in sequence: vacuum gauge, mechanical pump and molecular pump. Wait until the vacuum gauge reading is below 5 × 10⁻⁶. -4 When Pa, turn off the vacuum gauge and quickly connect high-purity argon gas as a protective gas to complete the vacuum preparation work before directional solidification. (6) Start the heating system to heat the high-entropy alloy raw materials in the crucible to 1600℃ and maintain it for 50 min; (7) After the heat preservation process is completed, start the pull-out motion control unit at the bottom of the directional solidification device. During the pull-out process, the crucible and melt gradually move towards the bottom gallium-indium liquid alloy tank. After the melt comes into contact with the liquid metal, it gradually cools down until the alloy melt is completely solidified.

[0035] (8) In this embodiment, the constant pulling rate is set to 100 μm / s. After the crucible and melt have completely cooled, the gas is released, the furnace lid is opened, and the eutectic high-entropy alloy sample is taken out; (9) Cut tensile specimens from the middle of the ingot and use a universal testing machine and video extensometer to measure the yield strength, tensile strength and elongation of the eutectic high-entropy alloy sample prepared by directional solidification at room temperature. The sample was measured 4 times under the same test conditions to calculate the average value of the mechanical properties. (10) Similarly, tensile specimens were cut from the middle of the ingot. The yield strength, tensile strength and elongation of the specimens were measured at 600℃ using a universal testing machine and a video extensometer. The specimens were measured 4 times to calculate the average value. (11) Cut tensile specimens again from the middle of the ingot, and use a universal testing machine and video extensometer to measure the yield strength, tensile strength and elongation of the specimens at 800℃. The specimens were measured 4 times to calculate the average value. (12) Cut the alloy ingot sample flat along the direction of directional solidification, cut the sample from the middle of the ingot, and then perform mechanical grinding and vibration polishing in sequence. Perform scanning electron microscopy analysis to observe the morphological characteristics and element distribution of the eutectic structure inside the sample. (13) Similarly, the alloy ingot sample was cut flat along the direction of directional solidification. Samples were cut from the longitudinal section and cross section of the middle of the ingot and mechanically ground and vibratory polished. Then, the two-phase region (including FCC and BCC phases) was cut by focused ion beam cutting and high-precision microstructure analysis was performed using aberration-corrected electron microscope to observe the morphology, number density and atomic occupancy characteristics of the high-density nano-precipitates inside the FCC phase.

[0036] Using the directional solidification and rapid drawing methods of Examples 1, 2, and Comparative Example 1, we cut samples from the dense eutectic region at the center of the longitudinal section of the alloy ingot and performed room temperature tensile tests, high temperature tensile tests (600℃ and 800℃), scanning electron microscopy, and transmission electron microscopy. Detailed microstructure analysis results can be found in [link to relevant documentation]. Figures 1 to 5 .

[0037] Figure 1 The engineering stress-strain curves of the rapidly directional solidified samples of Examples 1, 2, and Comparative Example 1 at room temperature are shown. Table 1 summarizes the average yield strength, tensile strength, and uniform elongation of Examples 1, 2, and Comparative Example 1 at room temperature. The results show that when 1 at.% of Ta is added to replace Al, Al... 18 The yield strength of the Ta1 alloy significantly increased from 826.3 MPa to 1033.2 MPa, and the tensile strength increased from 1308.3 MPa to 1519.5 MPa, representing increases of 25.0% and 9.4%, respectively. Compared with Al... 19 Compared to the alloy's uniform elongation of 22.4%, Al... 18The Ta1 alloy still maintains an excellent ductility and toughness of 17.3%.

[0038] Further observation revealed that when 2 at.% of Ta elements were added to replace Al elements, Al... 17 The yield strength of the Ta2 eutectic high-entropy alloy was further increased to 1170.3 MPa, and the tensile strength was significantly increased to 1631.8 MPa, representing increases of 41.6% and 24.7% respectively compared to Comparative Example 1. Compared to Example 1, Example 2 still maintained a good uniform elongation (10.1%), achieving an ideal balance between strength and plasticity at room temperature.

[0039] Table 1. Average yield strength, tensile strength, and elongation of as-cast eutectic high-entropy alloys at room temperature. Figure 2 The engineering stress-strain curves of the rapidly directional solidified samples of Examples 1, 2, and Comparative Example 1 under vacuum holding conditions at 600℃ are shown. Table 2 summarizes the average yield strength, tensile strength, and uniform elongation of Examples 1, 2, and Comparative Example 1 under vacuum holding conditions at 600℃. The results show that when 1 at.% of Ta is added to replace Al, Al... 18 The high-temperature yield strength of the Ta1 eutectic high-entropy alloy at 600℃ was significantly improved, increasing from 572.0 MPa to 666.7 MPa, and the high-temperature tensile strength increased from 915.9 MPa to 1078.9 MPa, representing increases of 16.6% and 17.8%, respectively. After adding 2 at.% Ta to replace Al, the Al... 17 The high-temperature yield strength of Ta2 eutectic high-entropy alloy at 600℃ was further increased to 756.3 MPa, and the high-temperature tensile strength reached 1058.2 MPa, representing increases of 32.2% and 15.5%, respectively.

[0040] Compared to the tensile strength of the three materials at room temperature, Al 17 Ta2, Al 18 Ta1 and Al 19 The tensile strength of the alloys decreased by 35.2%, 28.9%, and 30.0%, respectively. Despite the addition of 1 at.% and 2 at.% Ta to replace Al, the high-temperature elongation at 600℃ remained at 25.2% and 17.6%, respectively, demonstrating excellent high-temperature ductility and toughness.

[0041] Table 2. Average yield strength, tensile strength, and elongation of as-cast eutectic high-entropy alloys under vacuum heating at 600℃. Figure 3The engineering stress-strain curves of the rapidly directional solidified samples of Examples 1, 2, and Comparative Example 1 under vacuum conditions at 800°C are shown. Table 3 summarizes the average yield strength, tensile strength, and uniform elongation of Examples 1, 2, and Comparative Example 1 under vacuum conditions at 800°C. The results show that when 1 at.% of Ta is added to replace Al, Al... 18 The high-temperature yield strength of the Ta1 eutectic high-entropy alloy at 800℃ significantly increased from 373.4 MPa to 583.8 MPa, and the high-temperature tensile strength increased from 402.4 MPa to 628.4 MPa, representing increases of 56.3% and 56.2%, respectively. After replacing Al with 2 at.% Ta, Al... 17 The high-temperature yield strength of the Ta2 eutectic high-entropy alloy reaches 420.6 MPa at 800℃, and the high-temperature tensile strength can reach 452.3 MPa, both of which are higher than those of the matrix alloy without Ta.

[0042] Compared to its tensile strength at room temperature, Al 17 Ta2, Al 18 Ta1 and Al 19 The tensile strength of the alloy at 800℃ decreased by 72.3%, 58.6%, and 69.2%, respectively, indicating that adding 1 at.% Ta can effectively slow down the decrease in strength at high temperatures. With continuous addition of Ta, the elongation at 800℃ gradually decreased from 27.0% to 12.6% and 5.2%, showing a continuous decrease in high-temperature ductility and toughness. The high-temperature mechanical test results at different temperatures demonstrate that adding Ta can stably improve the high-temperature mechanical properties of the alloy, and 1 at.% is determined to be the ideal amount of Ta to add.

[0043] Table 3. Average yield strength, tensile strength, and elongation of as-cast eutectic high-entropy alloys under vacuum heating at 800℃. Figure 4 Scanning electron microscopy (SEM) analysis results along the longitudinal section of the ingots in Examples 1, 2, and Comparative Example 1 are presented. Table 4 summarizes the specific chemical composition of the biphase structures in the microstructures of Examples 1, 2, and Comparative Example 1. Figure 4 It can be observed that, in Comparative Example 1 (Al) 19 longitudinal section structure () Figure 4In a) and 4b), the dendritic trunk structure is mainly composed of alternating fine micron-sized lamellae. The light-colored FCC phase lamellae are rich in 24.6 at.% Fe, 23.3 at.% Co and 39.0 at.% Ni, while the dark gray BCC phase is richer in 39.9 at.% Ni and 28.7 at.% Al.

[0044] When adding 1 at.% of the Ta element to replace the Al element ( Figure 4 c and 4d), Example 1 (Al) 18 The dendritic branches of the Ta1 eutectic high-entropy alloy transform into a single-layer FCC phase structure, with Ta content in the FCC and BCC phases being 0.89 at.% and 0.52 at.%, respectively. Furthermore, when 2 at.% of Ta is added to replace Al (… Figure 4 e and 4f), Example 2 (Al) 17 The dendritic branches of the Ta2 eutectic high-entropy alloy transform into a single-layer BCC phase structure, with Ta content in the FCC and BCC phases being 1.54 at.% and 1.11 at.%, respectively. The microstructure characterization above shows that with increasing Ta addition, the morphology of the dendritic lamellae layer undergoes a significant change, while the Ta content in the FCC and BCC phases increases significantly, resulting in a stronger solid solution strengthening effect.

[0045] Table 4 Al 17 Ta2, Al 18 Ta1 and Al 19 The specific chemical composition (at.%) of the alloy's dual-phase microstructure. Figure 5 The results of transmission electron microscopy analysis along the longitudinal section of the ingots in Examples 1, 2, and 1 (Comparative Example 1) are presented. Figure 5 It can be observed that, in Comparative Example 1 (Al) 19 longitudinal section structure () Figure 5 In 5a and 5b), a high density of spherical nanoscale Ni3Al precipitates exists within the FCC phase layer. These precipitates exhibit a coherent orientation with the FCC phase matrix, and the average diameter of the particles is 13.6 nm. The precipitates observed in the atomically high-resolution microstructure exhibit a typical L12 structure.

[0046] When adding 1 at.% of the Ta element to replace the Al element ( Figure 5 c and 5d), Example 1 (Al) 18The average diameter of the spherical nanoscale Ni3(Al,Ta) precipitates inside Ta1 increased to 22.3 nm. In the atomically high-resolution microstructure, bright white Ta atoms with larger atomic numbers and radii were observed, occupying Al sites in the Ni3Al structure. This effectively enhanced the resistance to dislocation movement of the precipitates, thereby improving the precipitation strengthening effect. Furthermore, when 2 at.% of Ta replaced Al, (… Figure 5 e and 5f), Example 2 (Al) 17 The average diameter of the spherical nanoscale Ni3(Al,Ta) precipitates within Ta2 was further increased to 44.7 nm. In the atomically high-resolution microstructure, the number density of bright white Ta atoms was significantly increased, further enhancing the precipitation strengthening effect.

[0047] This invention employs a directional solidification method with a rapid pulling rate of 100 μm / s, combined with a Ta alloying design concept, to successfully prepare Al by replacing Al with 1 at.% and 2 at.% Ta, respectively. 18 Ta1Fe 20 Co 20 Ni 41 And Al 17 Ta2Fe 20 Co 20 Ni 41 As-cast eutectic high-entropy alloys. These alloys significantly improve the overall mechanical properties of metallic materials at both room temperature and high temperature conditions, and significantly expand the service life range of the alloys. The fundamental reasons for controlling the comprehensive mechanical properties across temperatures of as-cast eutectic high-entropy alloys prepared by directional solidification by adding Ta include the following aspects: 1. Solid solution strengthening effect: The Ta element added in the initial structure exists primarily as solid-solution atoms within both phases of the FCC and BCC matrices. Because the average radius and atomic number of Ta atoms are significantly larger than those of other constituent elements, the resulting lattice distortion effectively enhances the solid-solution strengthening effect.

[0048] 2. Precipitation reinforcement effect: Ta (Ta) can replace Al sublattice sites in the Ni3Al coherent nanoprecipitates with an L12 crystal structure, promoting the formation of Ni3(Al, Ta) nanoprecipitates. On the one hand, with the increase of Ta content, the volume fraction of the precipitates within the FCC phase increases significantly while maintaining a uniformly dispersed distribution, more effectively pinning the dislocation slip process. On the other hand, Ta significantly increases the anti-domain boundary energy of the nanoprecipitates, thus requiring a greater external force to induce dislocations to cut through the nanoprecipitates, thereby hindering the slip and propagation of dislocation lines and further enhancing the precipitation strengthening effect of the material.

[0049] 3. High-temperature thermal stability: As a high-melting-point refractory element, Ta significantly improves the high-temperature thermal stability of the FCC and BCC dual-phase alloys, effectively suppressing the coarsening and high-temperature softening processes of the two-phase structure, thus enabling the material to maintain superior microstructural stability at high temperatures. Therefore, this effectively optimizes the high-temperature mechanical properties of the alloy, which is crucial for designing high-performance materials that can operate across multiple temperature ranges.

[0050] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can still make various improvements and adjustments without departing from the principles of the present invention. These improvements and adjustments should all be considered within the scope of protection of the present invention.

Claims

1. A high-strength, high-toughness, high-temperature resistant cast eutectic high-entropy alloy, characterized in that: The high-strength, high-toughness, and high-temperature-resistant eutectic high-entropy alloy is mainly prepared by mixing aluminum, cobalt, iron, nickel, and a cobalt-tantalum eutectic alloy through repeated melting. The mass / molar ratio of aluminum, cobalt, iron, nickel, and the cobalt-tantalum eutectic alloy is as follows: (Here, Al is used as an example). 18 Ta1Fe 20 Co 20 Ni 41 For example, the mass / molar ratio of aluminum, cobalt, iron, nickel, and cobalt-tantalum eutectic alloy is 9.05:9.27:20.80:44.82:16.

05.

2. The high-strength and high-toughness eutectic high-entropy alloy according to claim 1, characterized in that: in, The atomic percentages of aluminum are 16.5% to 18.5%, cobalt is 18% to 22%, iron is 18% to 22%, nickel is 37% to 45%, and tantalum is 0.5% to 2.5%.

3. The high-strength and high-toughness eutectic high-entropy alloy according to claim 1, characterized in that: The high-strength, high-toughness, and high-temperature resistant eutectic high-entropy alloy is prepared by mixing only aluminum, cobalt, iron, nickel and cobalt-tantalum eutectic alloy raw materials and repeatedly melting them. One of its components is set as follows: aluminum atoms account for 18% of the total number of atoms, tantalum atoms account for 1% of the total number of atoms, iron atoms account for 20% of the total number of atoms, cobalt atoms account for 20% of the total number of atoms, and nickel atoms account for 41% of the total number of atoms. The eutectic high-entropy alloy is Al. 18 Ta1Fe 20 Co 20 Ni 41 ; Another composition setting is as follows: aluminum atom percentage 17%, tantalum atom percentage 2%, iron atom percentage 20%, cobalt atom percentage 20%, and nickel atom percentage 41%, wherein the eutectic high-entropy alloy is Al. 17 Ta2Fe 20 Co 20 Ni 41 .

4. A method for rapid directional solidification preparation of a high-strength, high-toughness, and high-temperature-resistant eutectic high-entropy alloy as described in any one of claims 1-3, characterized in that, The method includes the following steps: Step S1: Prepare several block ingots by melting and casting aluminum, cobalt, iron, nickel and eutectic alloys; Step S2: Place the above-mentioned block ingot in a commercial directional solidification equipment and perform pulling and cooling solidification treatment to obtain a sample.

5. The method for directional solidification preparation of a high-strength, high-toughness, and high-temperature resistant eutectic high-entropy alloy according to claim 4, characterized in that, Step S1 specifically involves: Step S1.1: First, aluminum, iron, cobalt, nickel and Co-21at.%Ta eutectic alloy are placed in a melting furnace for repeated vacuum melting, and finally cast to obtain alloy ingots. Step S1.2: Transfer the molten alloy ingot into the muffle furnace, heat it to 1250℃ with the furnace, and hold it for 12 hours; Step S1.3: The alloy ingot obtained in step S1.2 is subjected to wire cutting, mechanical grinding, ultrasonic cleaning and drying to obtain eutectic high-entropy alloy raw material; Step S1.4: Process the eutectic high-entropy alloy raw material obtained in step S1.3 into several block ingots.

6. The method for directional solidification preparation of a high-strength, high-toughness, and high-temperature resistant eutectic high-entropy alloy according to claim 5, characterized in that, Step S1.1 includes: After placing the crucible containing the alloy raw material into the vacuum system, the vacuum system is activated to evacuate the air from the system. Then, argon gas is introduced as a protective gas. The vacuum atmosphere conditions for the crucible are as follows: vacuum degree higher than 5 × 10⁻⁶. -4 Pa.

7. The method for directional solidification preparation of a high-strength, high-toughness, and high-temperature resistant eutectic high-entropy alloy according to claim 4, characterized in that, Step S2 specifically involves: Step S2.1: Start the heating system. First, heat the several block ingots obtained in step S1 to 1550 ~ 1650 ℃ and hold them at that temperature for 40 ~ 60 min. After the heat preservation stage in step S2.2 and step S3.1 is completed, the directional solidification pulling motion system is started, and several block ingots heated in the crucible are pulled at a pulling speed of 90 ~ 110 μm / s to cool and solidify at the same time. After cooling, the sample is taken out.

8. The method for directional solidification preparation of a high-strength, high-toughness, and high-temperature resistant eutectic high-entropy alloy according to claim 7, characterized in that: The heating temperature in step S2.1 is 1600℃, the holding time in step S2.1 is 50 min, and the pulling speed in step S2.2 is 100 μm / s.

9. The method for directional solidification preparation of a high-strength, high-toughness, and high-temperature resistant eutectic high-entropy alloy according to claim 4, characterized in that, Step S3 specifically involves: Step S3.1: Select the sample obtained in step S3 and cut a tensile sample. Use a universal testing machine and an extensometer to measure the tensile sample, thereby obtaining the yield strength, tensile strength and elongation of the tensile sample under room temperature conditions and high temperature conditions of 600℃ and 800℃. Repeat the measurement to calculate the average value. Step S3.2: Cut a flat sample from the sample obtained in step S3 along the directional solidification direction, and perform mechanical grinding and polishing in sequence. Observe the interior of the flat sample by scanning electron microscopy to obtain the morphology and elemental distribution characteristics of the dendritic structure inside the flat sample. Step S3.3: Cut the sample obtained in step S3 along the direction of directional solidification to make it flat, and then perform mechanical grinding and polishing treatment in sequence. Subsequently, observe the nano-precipitated phase inside the face-centered cubic phase by transmission electron microscopy to obtain the average diameter and atomic arrangement characteristics of the nano-precipitated phase.

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