High-strength high-plasticity heterostructure FeNiCoAlTa high-entropy alloy and preparation method thereof

Abstract

The invention relates to the technical field of high-entropy alloy preparation, in particular to a high-strength high-plasticity heterostructure FeNiCoAlTa high-entropy alloy and a preparation method thereof.The high-entropy alloy is prepared from, by atomic percent, 31%-32% of Fe elementary substance particles, 30% of Ni elementary substance particles, 26% of Co elementary substance particles, 9% of Al elementary substance particles and 3%-4% of Ta elementary substance particles. The Fe-Ni-Co-Al-Ta-based single-phase FCC high-entropy alloy is subjected to precise component regulation and control and process optimization, a high-density coherent L12 nano precipitated phase is constructed in a matrix, and a heterostructure with bimodal grain distribution is formed, so that the strength and plasticity are synergistically improved under the condition that the phase structure is kept stable.

Description

Technical Field

[0001] This invention relates to the field of high-entropy alloy preparation technology, specifically to a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy and its preparation method. Background Technology

[0002] High-entropy alloys, as a novel metallic material system based on the multi-principal element design concept, exhibit potential advantages over traditional alloy systems in terms of mechanical properties, thermal stability, and functional characteristics due to their comprehensive features such as high-entropy effect, lattice distortion effect, and slow diffusion effect. In recent years, they have become a key research direction in advanced structural materials. Among them, high-entropy alloys with face-centered cubic (FCC) crystal structures have high research value in related application fields due to their good plasticity, fracture toughness, and low-temperature ductility. However, similar to other FCC structural metallic materials, FCC high-entropy alloys generally suffer from low yield strength at room temperature, making it difficult to meet the high strength requirements of some load-bearing components, thus limiting their further application in engineering fields.

[0003] To enhance the strength of FCC high-entropy alloys, various strengthening approaches have been developed. Firstly, strengthening is achieved by introducing a certain volume fraction of a second phase (such as B2 or Laves phase) into the FCC matrix, utilizing a multiphase microstructure. Secondly, precipitation strengthening is achieved through trace element alloying and aging treatment, precipitating nanoscale, coherent L12 ordered phases within the matrix. Furthermore, heterogeneous structure design strategies proposed in recent years (including constructing bimodal or multimodal grain structures) have also been proven to effectively improve the yield strength and work hardening capacity of materials through back stress strengthening. These techniques have improved the mechanical properties of FCC high-entropy alloys to varying degrees.

[0004] Nevertheless, existing technologies still have limitations in simultaneously improving strength, plasticity, and microstructural stability. For multiphase high-entropy alloys relying on second-phase strengthening, the stability of phase boundaries under complex loads and the long-term microstructural stability remain uncertain. For single-phase FCC alloy systems primarily strengthened by L12 precipitation, maintaining sufficient plasticity while achieving higher yield strength remains a pressing research challenge. Therefore, developing an alloy system and preparation process capable of achieving high strength, high plasticity, and excellent microstructural stability, while ensuring the FCC matrix retains its single-phase structure and avoiding phase transformations during deformation, is of great significance. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy and its preparation method.

[0006] This invention is achieved through the following technical solution: A high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy, by atomic percentage, has the following solid particle composition: 31%–32% Fe elemental particles, 30% Ni elemental particles, 26% Co elemental particles, 9% Al elemental particles, and 3%–4% Ta elemental particles; the high-entropy alloy has a yield strength of 953–1369 MPa, a tensile strength of 1252–1798 MPa, and an elongation of 13%–25%.

[0007] A method for preparing a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy, comprising: S1, Smelting: Prepare Fe, Ni, Co, Al, and Ta according to the proportions, and perform high-vacuum non-consumable arc melting to obtain the master alloy ingot; S2, Casting: The master alloy ingot is melted under vacuum and argon protection, and after complete melting, it is cast and cooled to obtain a cast high-entropy alloy ingot. S3, Homogenization: The cast high-entropy alloy ingot is subjected to homogenization annealing under vacuum, and then water quenched to room temperature to obtain a homogenized high-entropy alloy with uniform structure and elimination of dendritic segregation. S4, Cold rolling: Cold rolling a homogenized high-entropy alloy to obtain a cold-rolled sheet; S5, recrystallization annealing: The cold-rolled sheet is heated to the first holding temperature and held for a period of time, and then water-quenched and cooled to room temperature to obtain an annealed alloy sample. S6, Aging treatment: The annealed alloy sample is heated to the second holding temperature and held for a period of time, and then water-quenched to room temperature to obtain a high-entropy alloy with a heterostructure.

[0008] Preferably, in S1, the smelting process is as follows: Fe, Ni, Co, Al, and Ta elements are stacked from bottom to top in order of increasing melting point into a water-cooled copper crucible in a high-vacuum non-consumable arc melting furnace. Then, a vacuum is drawn until the vacuum level inside the melting furnace reaches 2.5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced as a protective gas; then alloying and smelting are carried out, with a smelting current of 20~500A. During the smelting process, electromagnetic stirring is used to homogenize the alloy. After cooling, an alloy ingot is obtained. The alloy ingot is flipped and smelted repeatedly to obtain a master alloy ingot.

[0009] Preferably, in S1, during melting, the actual temperature of the circulating water is 22-24℃, the distance between the arc-igniting needle and the solid particles is 2mm, the gas pressure during melting is controlled to be <0.05MPa, the arc-igniting current during arc melting is 20A, the melting current is 300-350A, the melting temperature is >2000℃, the melting time is 2-3 minutes, and the number of melting cycles is [not specified]. 8 times.

[0010] Preferably, in S2, the vacuum degree during melting is 2.5 × 10⁻⁶. -3 Pa, heating current is 300~350A, temperature is 1600℃.

[0011] Preferably, in S3, during the homogenization annealing process, the vacuum degree is 1×10⁻⁶. -3 Below Pa, the temperature is 1250℃, the heating rate is 10℃ / min, and the holding time is 5~8h.

[0012] Preferably, in S4, the surface of the homogenized high-entropy alloy is polished with sandpaper before cold rolling; during cold rolling, the reduction in each rolling pass is 5%, and the total deformation is 80%~90%.

[0013] Preferably, in S5, the first heat preservation temperature is 1050℃ and the heat preservation time is 0.5h.

[0014] Preferably, in S6, the second heat preservation temperature is 700℃, and the heat preservation time is 1~3h.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy. Through precise compositional control and process optimization of Fe-Ni-Co-Al-Ta based single-phase FCC high-entropy alloy, a high-density, coherent L12 nano-precipitates are constructed in the matrix, forming a heterostructure with a bimodal grain distribution. This achieves a synergistic improvement in strength and plasticity while maintaining phase structure stability. Room temperature tensile tests show that the yield strength of this heterostructure high-entropy alloy is 953–1369 MPa, the tensile strength is 1252–1798 MPa, and the elongation is 13%–25%.

[0016] This invention discloses a method for preparing a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy. Through a specific thermomechanical treatment process, a heterostructure is constructed, consisting of a high-density coherent nano-L12 precipitate and bimodal grains, while maintaining a completely face-centered cubic (FCC) single-phase matrix. This heterostructure originates from the synergistic effect of multi-scale microstructure evolution under compositional design and process control. The formation mechanism is as follows: During cold rolling, deformation bands with high dislocation density form within the alloy, leading to uneven energy storage distribution. Subsequently, during recrystallization annealing, these high-energy storage regions preferentially nucleate. Simultaneously, Ta atoms with low solubility diffuse and agglomerate towards locations with higher defect (such as dislocations and subgrain boundaries) density under thermal activation, forming fine Ta-rich particles. Due to the extremely high defect density within the deformation bands, the nucleation density of Ta-rich particles in this region is significantly greater than in the relatively uniformly deformed regions. These dispersed Ta-rich particles, through a strong Zener pinning effect, can suppress grain boundary migration in their respective regions, thereby stabilizing the grain size at a fine scale (approximately 1 micrometer). In regions with lower initial deformation and less Ta-rich particle segregation, grain boundary pinning weakens, allowing some grains to grow abnormally and form coarse grain rows. Therefore, the non-uniform deformation introduced by cold rolling, combined with the selective segregation and precipitation of Ta atoms, ultimately constructs a unique heterostructure with spatially striped distribution, bimodal grain size, and Ta-rich particles dispersed in a fine-grained matrix through differentiated grain boundary pinning strength.

[0017] Furthermore, aging treatment uniformly precipitates high-density, nanoscale L12 strengthening phases within the FCC matrix (including both coarse and fine grains), providing the alloy with extremely high yield strength through strong ordered strengthening and coherent strain effects. Simultaneously, the heterogeneous structure composed of bimodal grains induces a significant strain gradient at the soft / hard grain interface during deformation, promoting the accumulation of geometrically necessary dislocations and thus generating continuous back stress strengthening (this mechanism was confirmed by cyclic loading-unloading experiments), significantly improving the alloy's work hardening ability and uniform plasticity.

[0018] Furthermore, the selection of the first holding temperature, holding time, quenching, and cooling method during recrystallization annealing is to obtain an initial microstructure dominated by fully recrystallized equiaxed crystals, in which a structural prototype of fine-grained and potentially coarse-grained regions has been formed, providing a uniform FCC matrix for subsequent aging precipitation.

[0019] Furthermore, the selection of the second holding temperature, holding time, quenching, and cooling method during aging treatment is to enable the alloy matrix to uniformly precipitate high-density, nanoscale coherent L12 ordered strengthening phases within the already formed recrystallized grains. At the same time, by controlling the holding time, the size and distribution of the precipitated phases can be optimized, ultimately obtaining a composite strengthening structure composed of high-density L12 precipitates and bimodal grains, thereby achieving a synergy of high strength and high plasticity. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a method for preparing a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to the present invention. Figure 2 The XRD patterns are of the FeNiCoAlTa-based high-entropy alloys with heterostructures in Example 2 and Comparative Example 2 of this invention. Figure 3 This is a SEM image of the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention; Figure 4 This is a statistical diagram of the grain size of the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention; Figure 5 The FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention before deformation ( =0%) and its stretching ( EBSD plot (=22%); Figure 6 The TEM characterization results are shown for the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention. Figure 7 The results are TEM characterizations of the FeNiCoAlTa-based high-entropy alloy with a heterostructure after room temperature stretching in Example 2 of this invention. Figure 8 The figures show the room temperature tensile engineering stress-engineering strain curves of FeNiCoAlTa-based high-entropy alloys with heterostructures in Examples 1-3 and Comparative Examples 1-3 of this invention. Figure 9 The results of room temperature cyclic loading-unloading tensile testing of the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention; Figure 10 This paper compares the room temperature tensile properties of the FeNiCoAlTa-based high-entropy alloy with a heterostructure (labeled "This work" in the figure) in Example 2 of this invention with those of various previously reported FCC-based high-entropy alloys. Detailed Implementation

[0021] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0022] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0023] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0024] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0025] This invention discloses a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy. The solid particle composition of the high-entropy alloy, by atomic percentage, is as follows: Fe elemental particles 31%–32%, Ni elemental particles 30%, Co elemental particles 26%, Al elemental particles 9%, and Ta elemental particles 3%–4%.

[0026] This invention also discloses a method for preparing a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy, comprising: S1, Smelting: Prepare Fe, Ni, Co, Al, and Ta according to the proportions, and perform high-vacuum non-consumable arc melting to obtain the master alloy ingot.

[0027] Specifically: Fe, Ni, Co, Al, and Ta elements are stacked from bottom to top in order of increasing melting point in a water-cooled copper crucible of a high-vacuum non-consumable arc furnace. Then, a vacuum is drawn until the vacuum level inside the furnace reaches 2.5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced as a protective gas; then alloying and smelting are carried out, with a smelting current of 20~500A. During the smelting process, electromagnetic stirring is used to homogenize the alloy. After cooling, an alloy ingot is obtained. The alloy ingot is flipped and smelted repeatedly to obtain a master alloy ingot.

[0028] During smelting, the actual temperature of the circulating water is 22-24℃, the distance between the arc-igniting needle and the solid particles is 2mm, the gas pressure is controlled to be <0.05MPa, the arc-igniting current is 20A, the smelting current is 300-350A, the smelting temperature is >2000℃, the smelting time is 2-3 minutes, and the number of smelting cycles is [not specified]. 8 times.

[0029] S2, Casting: The master alloy ingot is melted under vacuum and argon protection. After complete melting, it is cast and cooled to obtain a cast high-entropy alloy ingot. The vacuum degree during melting is 2.5 × 10⁻⁶. -3 Pa, heating current is 300~350A, temperature is 1600℃.

[0030] Specifically, the master alloy ingot is placed in a high-vacuum electric arc melting-tilting casting system, and the furnace cavity is evacuated until the vacuum degree reaches 2.5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced; under argon protection, melting is carried out with a heating current of 300-350A to heat the master alloy ingot to 1600℃. After the master alloy ingot is completely melted, the alloy liquid is poured into a copper mold and cooled to obtain a cast high-entropy alloy ingot.

[0031] S3, Homogenization: The as-cast high-entropy alloy ingot is subjected to homogenization annealing under vacuum, followed by water quenching to room temperature, to obtain a homogenized high-entropy alloy with uniform microstructure and eliminated dendritic segregation. The vacuum degree during the homogenization annealing process is 1×10⁻⁶. -3 Below Pa, the temperature is 1250℃, the heating rate is 10℃ / min, and the holding time is 5~8h.

[0032] Specifically, the as-cast high-entropy alloy ingot is sealed in a quartz glass tube, and the vacuum level of the glass tube is evacuated to 1×10⁻⁶. -3 Below Pa, the tubes are sealed using a hydrogen flame. After sealing, they are placed in a KSL-1400 box furnace for homogenization annealing at 1250℃. The heating rate is 10℃ / min, and the holding time is 5-8h. Then, the tubes are water-quenched to room temperature to obtain a homogenized high-entropy alloy with uniform microstructure and eliminated dendrite segregation.

[0033] Furthermore, the preferred heat preservation time is 6 hours.

[0034] S4, Cold Rolling: The homogenized high-entropy alloy is cold rolled to obtain a cold-rolled sheet. Before cold rolling, the surface of the sample is polished with 400#, 800#, and 1200# sandpaper to homogenize the high-entropy alloy. Then, cold rolling is performed, with a reduction of 5% for each rolling and a total deformation of 80%~90%.

[0035] Furthermore, a total cold rolling deformation of 85% is preferred, which introduces a high dislocation density and strain band, providing a non-uniform nucleation basis for subsequent recrystallization to form a heterogeneous structure.

[0036] S5, Recrystallization Annealing: The cold-rolled sheet is heated to the first holding temperature and held for 0.5 hours, then water-quenched to room temperature to obtain the annealed alloy sample. The first holding temperature is 1050℃ and the holding time is 0.5 hours.

[0037] Specifically, the cold-rolled sheet was placed in a KSL-1200 box furnace and held at that temperature for a period of time, then water-quenched to room temperature to obtain an annealed alloy sample. The holding temperature was 1050℃ and the holding time was 0.5h. Quenching was selected as the cooling method to obtain an initial microstructure dominated by fully recrystallized equiaxed crystals, in which the structural prototypes of fine-grained and potentially coarse-grained regions had already formed, providing a uniform FCC matrix for subsequent aging precipitation.

[0038] S6, Aging Treatment: The annealed alloy sample is heated to the second holding temperature and held therefore, followed by water quenching and cooling to room temperature to obtain a high-entropy alloy with a heterostructure. The second holding temperature is 700℃, and the holding time is 1~3h.

[0039] Specifically, the annealed alloy sample is placed in a KSL-1100 box furnace, held at that temperature for a period of time, and then water-quenched to room temperature to obtain a high-entropy alloy with a heterogeneous structure. Preferably, the second holding temperature is 700℃, the holding time is 1-3 hours, and water quenching is selected to allow high-density, nanoscale coherent L12 ordered strengthening phases to precipitate uniformly within the already formed recrystallized grains of the alloy matrix. At the same time, by controlling the holding time, the size and distribution of the precipitated phases can be optimized, ultimately obtaining a composite strengthening structure composed of high-density L12 precipitates and bimodal grains, thereby achieving a synergy of high strength and high plasticity.

[0040] Room temperature tensile test Flat, dog-bone-shaped specimens (10mm × 2mm × 1.5mm) were cut from a high-entropy alloy with a heterogeneous structure, and the surface of the specimens was successively polished with 400#, 800#, 1200#, and 2000# sandpaper until smooth. The test was performed according to the national standard "Metallic Materials - Tensile Testing - Part 1: Test at Room Temperature" (GB / T 228.1). In 2021, the static tensile mechanical properties of the alloy were tested using an electronic universal testing machine at a fixed strain rate of 0.72 mm / min. The average values ​​of yield strength, tensile strength and elongation at break were taken from three samples with the same treatment.

[0041] Experiments showed that the high-strength, high-plasticity heterostructure FeNiCoAlTa-based high-entropy alloy prepared had a yield strength of 953 MPa to 1369 MPa, a tensile strength of 1252 MPa to 1798 MPa, and an elongation of 13% to 25%.

[0042] Room temperature cyclic tensile test Flat, dog-bone-shaped specimens (10mm × 2mm × 1.5mm) were cut from a high-entropy alloy with a heterogeneous structure, and the surface of the specimens was successively polished with 400#, 800#, 1200#, and 2000# sandpaper until smooth. A universal testing machine was used to perform cyclic tensile tests on the samples, including loading-unloading-reloading, to further analyze the evolution of back stress. During the test, a 1×10⁻⁶ g / L ... -3 s -1 The strain rate was stretched to 1.2% strain, then unloaded to 50 N via load control mode, and then at the same strain increment (2%) and strain rate (1×10⁻⁶). -3 s -1 Reload to the next unload strain, and cycle through load-unload until 15.2% strain.

[0043] Example 1 A high-strength, high-ductility heterostructure high-entropy alloy with the chemical formula Fe 31 Ni 30 Co 26 Al9Ta4 is prepared by the following steps: S1, according to atomic percentage, 31% Fe, 30% Ni, 26% Co, 9% Al, and 4% Ta metal particles are stacked from bottom to top in order of increasing melting point into a water-cooled copper crucible in a high-vacuum non-consumable arc melting furnace. Then, a vacuum is drawn until the vacuum level inside the furnace reaches 2.5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced as a protective gas; then alloying and melting are carried out with a melting current of 350A. During the melting process, electromagnetic stirring is used to homogenize the alloy. After cooling, an alloy ingot is obtained. The alloy ingot is flipped and the melting is repeated multiple times to obtain a master alloy ingot.

[0044] S2, place the master alloy ingot in a high-vacuum electric arc melting-tilting casting system, evacuate the furnace cavity, and wait until the vacuum reaches 2.5 × 10⁻⁶. -3 Pa, high-purity argon gas was introduced, the melting current was 350A, and electromagnetic stirring was carried out during the alloy melting process. After repeated remelting 8 times, the alloy was cooled in a water-cooled copper crucible to obtain a 10x10x50mm cast high-entropy alloy ingot.

[0045] S3, place the as-cast high-entropy alloy ingot into a quartz glass tube, and evacuate the vacuum level of the glass tube to 1 × 10⁻⁶. -3Below Pa, the tube was sealed using a hydrogen flame, held at 1250 degrees Celsius for 6 hours in a KSL-1400 box furnace, and then water-quenched to room temperature to obtain a homogenized high-entropy alloy.

[0046] S4. The homogenized high-entropy alloy is polished with 400#, 800# and 1200# sandpaper. After polishing, it is cold rolled at room temperature. The reduction amount of each pass is 5% of the current thickness of the sample until the total reduction amount is 85%, and the cold-rolled alloy sheet is obtained.

[0047] S5. The cold-rolled alloy sheet was subjected to recrystallization annealing at 1050℃ for 30 minutes, and then water-quenched to room temperature to obtain the annealed alloy sample.

[0048] S6. The annealed alloy sample was aged at 700℃ for 1 hour, and then water-quenched to room temperature to obtain Fe with a heterostructure. 31 Ni 30 Co 26 Al9Ta4 high-entropy alloy.

[0049] Example 2 A high-strength, high-ductility heterostructure high-entropy alloy with the chemical formula Fe 31 Ni 30 Co 26 The preparation method of Al9Ta4 is the same as that in Example 1, except for the aging time in S6; S6. The annealed alloy sample was aged at 700℃ for 3 hours, followed by water quenching to room temperature to obtain a heterostructured Fe. 31 Ni 30 Co 26 Al9Ta4 high-entropy alloy.

[0050] Figure 2 The images show the XRD patterns of the FeNiCoAlTa-based high-entropy alloys with heterostructures in Example 2 and Comparative Example 2 of this invention. Figure 1 As can be seen from the data, the alloys in Example 2 and Comparative Example 2 are both single-phase FCC structures, and no other diffraction peaks are observed.

[0051] Figure 3 This is a SEM image of the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention. Figure 3As can be seen in the image, several abnormally large coarse grains (10-60 micrometers in size) are visible, surrounded by a matrix composed of numerous fine recrystallized grains (approximately 1 micrometer in size) and medium-sized grains (approximately 6-7 micrometers in size). The three types are distributed in an almost layered alternating manner. In addition, fine, diffusely distributed Ta-rich particles can be observed in the matrix, especially in the fine-grained regions.

[0052] Figure 4 This is a grain size statistical diagram of the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention. Figure 4 The grain size distribution exhibits a distinct bimodal characteristic, indicating the presence of two dominant grain size groups in the microstructure. A first, sharper peak appears at approximately 1.4 micrometers, corresponding to the fine-grained region; a second, broader peak appears at approximately 6 micrometers, corresponding to the medium-sized grain region. This bimodal distribution is a direct result of the non-uniform grain growth during recrystallization and the differentiated pinning effect of second-phase particles (such as Ta-rich particles) on grain boundary migration, manifesting as a heterogeneous grain structure in the alloy.

[0053] Figure 5 The FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention before deformation ( =0%) and its stretching ( =22%) of the EBSD plot, from Figure 5 As can be seen in (a~c), the inverse pole figure (IPF) before stretching clearly shows a heterogeneous grain morphology composed of coarse and fine grains. All grains are equiaxed, and the corresponding nucleus average orientation difference (KAM) diagram shows a uniform blue distribution with low values ​​(close to 0°), indicating that the material has an extremely low dislocation density in the initial state and is in a fully recrystallized state.

[0054] After stretching and deformation, such as Figure 5 (d~f) In the IPF diagram, the grains are significantly elongated and exhibit an orientation gradient. The overall KAM value increases significantly after deformation, with high-value regions generally appearing around the grain boundaries. The distribution of KAM values ​​is directly related to the density of geometrically necessary dislocations. The general increase in KAM values ​​at grain boundaries indicates that during plastic deformation, geometrically necessary dislocations accumulate in large quantities near the grain boundaries to coordinate the deformation inhomogeneity between grains, thereby forming a significant local orientation gradient and internal stress field.

[0055] Figure 6 The TEM characterization results of the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention show the microstructure of the nanoscale precipitated phase. Figure 6(a) Dark-field images clearly show that nanoscale precipitates are uniformly and densely distributed in the face-centered cubic (FCC) matrix, with a statistical average size of about 10 nanometers. Figure 6 (b, c) High-resolution transmission electron microscopy (HRTEM) images and their corresponding selected area electron diffraction (SAED) pattern analysis (inset showing the diffraction spots of L12 and FCC) jointly confirm that the nanophase is an L12-type ordered structure and maintains a coherent relationship with the FCC matrix. Based on image analysis, the volume fraction of this coherent L12 precipitate is estimated to be as high as approximately 50%–55%. This high-content, high-density, coherent nano-L12 ordered phase is the key strengthening phase that endows the alloy with ultra-high strength.

[0056] Figure 7 The TEM characterization results of the FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention after room temperature stretching show that the dislocation slip mode is dominated by planar slip, with a large number of dislocations concentrated along specific slip planes, forming clear slip bands. High-resolution TEM observation further confirms this. <111> The slip traces were observed in the direction of the slip, and stacking faults were observed in multiple regions. These features collectively indicate that plane slip of dislocations and the formation of stacking faults are the main mechanisms for coordinating strain during plastic deformation of materials.

[0057] Figure 8 The figures show room temperature tensile stress-strain curves of FeNiCoAlTa-based high-entropy alloys with heterostructures in Examples 1-3 and Comparative Examples 1-3 of this invention. In the examples, 1h, 3h, and 5h represent Examples 1-3, respectively, and in the comparative examples, 1h, 3h, and 5h represent Comparative Examples 1-3, respectively. The high-entropy alloys provided by this invention exhibit high yield strength, tensile strength, and elongation at break.

[0058] Figure 9 The results of room temperature cyclic loading-unloading tensile testing of a FeNiCoAlTa-based high-entropy alloy with a heterostructure in Example 2 of this invention are shown below. Figure 9 As can be seen from the cyclic tensile curve in (a), the stress-strain curve of the alloy exhibits a significant hysteresis loop during plastic deformation, and the loop width continues to increase with the increase of true strain. This reveals the accumulation of internal stress caused by the accumulation of geometrically necessary dislocations. Figure 9 (b) is a magnified view of a portion of the image. Figure 9 (c) Quantitative analysis of back stress and effective stress shows that the back stress remains at a high level (about 1050-1100 MPa) throughout the tensile process, confirming that the back stress strengthening contributed by the accumulation of geometrically necessary dislocations is one of the key mechanisms for the alloy to achieve a high work hardening rate.

[0059] Figure 10This section compares the room-temperature tensile properties of the FeNiCoAlTa-based high-entropy alloy with a heterostructure (labeled "This work" in the figure) in Example 2 of this invention with those of various previously reported FCC-based high-entropy alloys. Figure 10 As can be seen from the graph, the data point representing the alloy of this invention is located in the upper right corner of the performance graph. Its performance parameters (yield strength of about 1300 MPa, tensile strength of about 1800 MPa, and elongation of about 22%) intuitively demonstrate that the alloy with high-density nano-L12 precipitates and bimodal grain heterostructure designed in this invention effectively synergizes multiple strengthening mechanisms, thereby achieving a significant breakthrough in the classic strength-plasticity trade-off relationship.

[0060] Example 3 A high-strength, high-ductility heterostructure high-entropy alloy with the chemical formula Fe 31 Ni 30 Co 26 Al9Ta4; The alloy preparation method described herein is the same as in Example 1, except for the aging time in S6. S6. The annealed alloy sample was aged at 700℃ for 5 hours, followed by water quenching to room temperature to obtain a heterostructured Fe alloy. 31 Ni 30 Co 26 Al9Ta4 high-entropy alloy.

[0061] Comparative Example 1 A high-strength, high-plasticity FCC-based high-entropy alloy, with the chemical formula Fe. 32 Ni 30 Co 26 Al9Ta3; The alloy preparation method includes the following steps: S1, according to atomic percentage, 32% Fe, 30% Ni, 26% Co, 9% Al, and 3% Ta metal particles are stacked from bottom to top in order of increasing melting point into a water-cooled copper crucible in a high-vacuum non-consumable arc melting furnace. Then, a vacuum is drawn until the vacuum level inside the furnace reaches 2.5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced as a protective gas; then alloying and melting are carried out with a melting current of 350A. During the melting process, electromagnetic stirring is used to homogenize the alloy. After cooling, an alloy ingot is obtained. The alloy ingot is flipped and the melting is repeated multiple times to obtain a master alloy ingot.

[0062] S2, place the master alloy ingot in a high-vacuum electric arc melting-tilting casting system, evacuate the furnace cavity, and wait until the vacuum reaches 2.5 × 10⁻⁶. -3Pa, high-purity argon gas was introduced, the melting current was 350A, and electromagnetic stirring was carried out during the alloy melting process. After repeated remelting 8 times, the alloy sample was cooled in a water-cooled copper crucible to obtain a 10x10x50mm as-cast alloy sample.

[0063] S3. The cast alloy rod is placed in a quartz glass tube, the vacuum degree of the glass tube is evacuated to below 1× 10-3 Pa, the tube is sealed with a hydrogen flame, and then held in a KSL-1400 box furnace at a temperature of 1250 degrees for 6 hours. After water quenching and cooling to room temperature, a homogenized alloy is obtained.

[0064] S4. The homogenized alloy is polished with 400#, 800# and 1200# sandpaper. After polishing, it is cold rolled at room temperature. The reduction amount of each pass is 5% of the current thickness of the sample until the total reduction amount is 85%, and the cold rolled alloy sheet is obtained.

[0065] S5. The cold-rolled alloy sheet was annealed at 1050℃ for 30 minutes and then water-quenched to room temperature to obtain the annealed alloy sample.

[0066] S6. The annealed alloy sample was subjected to aging treatment at 700℃ for 1 hour, followed by water quenching to room temperature to obtain high-strength and high-plasticity FCC-based Fe. 32 Ni 30 Co 26 Al9Ta3 high-entropy alloy.

[0067] Comparative Example 2 A high-strength, high-plasticity FCC-based high-entropy alloy, with the chemical formula Fe. 32 Ni 30 Co 26 Al9Ta3; Except for the aging time in S6, the alloy preparation method described herein is the same as that in Comparative Example 1. S6. The annealed alloy sample was subjected to aging treatment at 700℃ for 3 hours, followed by water quenching to room temperature to obtain high-strength and high-plasticity FCC-based Fe. 32 Ni 30 Co 26 Al9Ta3 high-entropy alloy.

[0068] Comparative Example 3 A high-strength, high-plasticity FCC-based high-entropy alloy, with the chemical formula Fe. 32 Ni 30 Co 26 Al9Ta3; Except for the aging time in S6, the alloy preparation method described herein is the same as that in Comparative Example 1. S6. The annealed alloy sample was aged at 700℃ for 5 hours, followed by water quenching to room temperature to obtain high-strength, high-plasticity FCC-based Fe. 32 Ni 30 Co 26 Al9Ta3 high-entropy alloy.

[0069] Table 1. Room temperature tensile properties of the high-entropy alloys obtained in the examples and comparative examples.

[0070] This invention provides a FeNiCoAlTa-based high-entropy alloy with excellent strength-ductility matching. Through a specific thermomechanical processing technique, this alloy, while completely maintaining a face-centered cubic (FCC) single-phase matrix, constructs a heterostructure consisting of a high-density coherent nano-L12 precipitate phase and bimodal grains. Taking Example 2 as an example, the volume fraction of the L12 ordered phase in this alloy is approximately 50-55%, with an average size of approximately 10 nm, exhibiting a diffuse distribution and high-density coherence with the matrix. This type of nanoscale ordered phase provides a foundation for ultra-high yield strength through significant ordered strengthening and coherent strain strengthening effects, achieving a room-temperature yield strength of approximately 1302 MPa. Simultaneously, the significant strain incompatibility induced by the bimodal grains during deformation promotes the accumulation of geometrically necessary dislocations at the interface, generating a back stress as high as 1050-1100 MPa. This back stress provides sustained work hardening capability, enabling the alloy to achieve high tensile strength (1798 MPa) while maintaining a 22% elongation at break.

[0071] Furthermore, the plastic deformation of the alloy during tensile deformation was mainly dominated by dislocation plane slip, and no phase transformation behavior was observed. The microstructure maintained a stable coexistence of the FCC single-phase matrix and the nano-L12 precipitate throughout the loading process, indicating that the alloy system has excellent microstructure stability and structural reliability during deformation.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy, characterized in that, Based on atomic percentage, the solid particle composition of this high-entropy alloy is as follows: Fe elemental particles 31%–32%, Ni elemental particles 30%, Co elemental particles 26%, Al elemental particles 9%, and Ta elemental particles 3%–4%.

2. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 1, characterized in that, The high-entropy alloy has a yield strength of 953–1369 MPa, a tensile strength of 1252–1798 MPa, and an elongation of 13%–25%.

3. A method for preparing a high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy as described in any one of claims 1 to 2, characterized in that, include: S1, Smelting: Prepare Fe, Ni, Co, Al, and Ta according to the proportions, and perform high-vacuum non-consumable arc melting to obtain the master alloy ingot; S2, Casting: The master alloy ingot is melted under vacuum and argon protection, and after complete melting, it is cast and cooled to obtain a cast high-entropy alloy ingot. S3, Homogenization: The cast high-entropy alloy ingot is subjected to homogenization annealing under vacuum, and then water quenched to room temperature to obtain a homogenized high-entropy alloy. S4, Cold rolling: Cold rolling a homogenized high-entropy alloy to obtain a cold-rolled sheet; S5, recrystallization annealing: The cold-rolled sheet is heated to the first holding temperature and held for a period of time, and then water-quenched and cooled to room temperature to obtain an annealed alloy sample. S6, Aging treatment: The annealed alloy sample is heated to the second holding temperature and held for a period of time, and then water-quenched to room temperature to obtain a high-entropy alloy with a heterostructure.

4. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 3, characterized in that, In S1, the smelting process is as follows: Fe, Ni, Co, Al, and Ta elements are stacked from bottom to top in order of increasing melting point into a water-cooled copper crucible in a high-vacuum non-consumable arc melting furnace. Then, a vacuum is drawn until the vacuum level inside the furnace reaches 2.5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced as a protective gas; then alloying and smelting are carried out, with a smelting current of 20~500A. During the smelting process, electromagnetic stirring is used to homogenize the alloy. After cooling, an alloy ingot is obtained. The alloy ingot is flipped and smelted repeatedly to obtain a master alloy ingot.

5. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 4, characterized in that, In S1, during melting, the actual temperature of the circulating water is 22-24℃, the distance between the arc-igniting needle and the solid particles is 2mm, the gas pressure during melting is controlled to be <0.05MPa, the arc-igniting current during arc melting is 20A, the melting current is 300-350A, the melting temperature is >2000℃, the melting time is 2-3 minutes, and the number of melting cycles is [not specified]. 8 times.

6. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 4, characterized in that, In S2, the vacuum degree during melting is 2.5 × 10⁻⁶. -3 Pa, heating current is 300~350A, temperature is 1600℃.

7. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 3, characterized in that, In S3, during the homogenization annealing process, the vacuum degree is 1×10⁻⁶. -3 Below Pa, the temperature is 1250℃, the heating rate is 10℃ / min, and the holding time is 5~8h.

8. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 3, characterized in that, In S4, the surface of the homogenized high-entropy alloy is polished with sandpaper before cold rolling; during cold rolling, the reduction in each rolling pass is 5%, and the total deformation is 80%~90%.

9. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 3, characterized in that, In S5, the first insulation temperature is 1050℃ and the insulation time is 0.5h.

10. The method for preparing the high-strength, high-plasticity heterostructure FeNiCoAlTa high-entropy alloy according to claim 3, characterized in that, In S6, the second insulation temperature is 700℃, and the insulation time is 1~3h.

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