A high-entropy alloy and a preparation method thereof

Abstract

The application discloses a kind of high-entropy alloy and preparation method thereof, belong to additive manufacturing technical field.The application is by CoCrFeMnNi high-entropy alloy powder and rare earth oxide particles are mixed, obtain composite powder, wherein rare earth oxide particles have core-shell structure, its inner layer is nano La2O3 Particle, nano Ni is coated on the outside of La2O3, the overall size of rare earth oxide particles with core-shell structure is less than 100nm;And the obtained composite powder is prepared high-entropy alloy using laser selective melting processing.The preparation method in the application is by preparing nano size rare earth oxide with core-shell structure as the reinforcing phase of high-entropy alloy, simplifies the mixing operation of nano size reinforcing phase and high-entropy alloy matrix powder doping, and can play the role of reinforcing plasticizing.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more specifically, to a high-entropy alloy and its preparation method. Background Technology

[0002] Multi-component high-entropy alloys break away from traditional alloy design concepts, possessing four unique effects: a thermodynamic high-entropy effect, a kinetic hysteresis diffusion effect, a lattice distortion effect in the microstructure, and a "cocktail" effect in performance. These effects endow them with excellent mechanical properties, corrosion resistance, radiation resistance, and high-temperature oxidation resistance, making them promising new structural materials for extreme environments such as aerospace, nuclear industry, and polar research. However, high-entropy alloys prepared using traditional processes such as casting, mechanical alloying, and powder metallurgy often suffer from limitations in shape and size, coarse grains, and compositional segregation, restricting their widespread application. With the development of alloy manufacturing technology, selective laser melting (SLM) for high-entropy alloys has become one of the most widely used additive manufacturing technologies due to its ability to manufacture high-precision and high-performance metal parts and its short design and production cycle. It has also become a new green approach for preparing high-entropy alloys.

[0003] In the process of preparing high-entropy alloys using selective laser melting (SLM), modifying the alloy powder matrix by adding reinforcing phases is one of the hot research topics in this field. When the size of rare earth oxide particles used as reinforcing phases reaches the nanoscale, the strength and plasticity of the resulting composite material do not change synchronously when the reinforcing phase and the high-entropy alloy matrix powder are mixed using traditional mechanical methods. Specifically, the strength improvement of the material is limited while the plasticity decreases significantly.

[0004] A search revealed Chinese patent application number 202210713202.5, which discloses a high-entropy alloy composite material for additive manufacturing, its preparation method, and its application. The method involves uniformly mixing nano-reinforcing phase powder and deionized water using ultrasonic vibration to obtain a suspension. The mass ratio of the nano-reinforcing phase powder to the volume of deionized water is (1-20 mg): 1 ml. The suspension and high-entropy alloy powder are then uniformly mixed under an ammonia atmosphere at a temperature of 500-800°C, followed by drying under vacuum to obtain the nanoparticle-reinforced high-entropy alloy composite material. While this application improves the strength of the composite material, suppresses thermal cracking, reduces defects, and improves the uniformity of the alloy microstructure, simultaneously enhancing both strength and toughness, the mixing method of the nano-reinforcing phase powder and the high-entropy alloy powder is relatively complex. Summary of the Invention

[0005] 1. Technical problems to be solved

[0006] To address the relatively complex technical problem of limited strength improvement and significant decrease in plasticity of high-entropy alloy matrix powder with nanoparticle reinforcing phases, this invention provides a high-entropy alloy and its preparation method. In this preparation method, nano-sized rare earth oxides with core-shell structures are prepared as the reinforcing phase of the high-entropy alloy, which can simultaneously improve the plasticity and strength of the high-entropy alloy.

[0007] 2. Technical Solution

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0009] The first aspect of this invention provides a method for preparing a high-entropy alloy, comprising: mixing CoCrFeMnNi matrix high-entropy alloy powder and rare earth oxide particles with a core-shell structure to obtain a composite powder, and preparing a high-entropy alloy by selective laser melting of the obtained composite powder; wherein the rare earth oxide particles have a core-shell structure, the inner layer of which is nano-La2O3 particles, and nano-Ni particles are coated on the outside of the La2O3 particles, and the overall size of the rare earth oxide particles is less than 100 nm.

[0010] It should be noted that high-entropy alloy powders with different compositions have different requirements for laser energy density during SLM preparation, which can affect the microstructure and properties of the SLM-prepared samples, and even lead to the inability to prepare samples. Therefore, the selection and preparation of powders are particularly critical. To address this, the inventors conducted extensive experimental research and ultimately selected CoCrFeMnNi as the matrix powder and La2O3@Ni with a core-shell structure as the reinforcing phase to prepare samples that meet the requirements of this invention.

[0011] More importantly, when the inventors studied rare earth oxide particles as a reinforcing phase in CoCrFeMnNi-based high-entropy alloy powder, they found that when the size of the rare earth oxide particles as the reinforcing phase reached the nanoscale, the strength and plasticity of the resulting composite material prepared by traditional mechanical mixing of the reinforcing phase and the high-entropy alloy matrix powder did not change synchronously. The plasticity decreased significantly, meaning the composite material exhibited poor plasticity and limited strength improvement. To solve these technical problems, the inventors added a shell structure to the outer surface of the nano-La2O3 particles and limited the overall size of the rare earth oxide particles with the added shell structure to within 100 nm. By using simple mechanical mixing of these nano-sized rare earth oxide particles with the high-entropy alloy matrix powder, the strength and plasticity of the resulting composite material were simultaneously improved. Compared to direct doping with nano-La2O3 particles, its plasticity was significantly improved. The specific mechanism is as follows: On the one hand, the nanoparticles act as heterogeneous nucleation cores during the SLM forming process, promoting the transformation of columnar crystals into equiaxed crystals. On the other hand, the La2O3 in the nanoparticles maintains a coherent relationship with Ni, and after SLM forming, the La2O3@Ni nanoparticles can maintain a coherent relationship with the high-entropy alloy matrix, thereby playing a role in strengthening and toughening.

[0012] Furthermore, the study found that as the size of the reinforcing phase decreases, especially when the size of the doped rare earth oxide particles reaches the nanoscale, the reinforcing phase is prone to segregation, leading to compositional segregation. By coating nano-Ni particles around nano-La2O3 particles, on the one hand, the Ni shell, being one of the components of the high-entropy alloy, can reduce the density difference between the nanoparticles and the high-entropy alloy, preventing the nanoparticles from floating in the liquid during the SLM process and causing compositional segregation. This improves the dispersion distribution of the rare earth oxide and high-entropy alloy matrix powders, thus simplifying the mixing process. On the other hand, nano-Ni particles possess good toughness and strength. Simultaneously, Ni has the optimal mixing enthalpy with La compared to other elements in the high-entropy alloy matrix, allowing Ni and La2O3 to better combine and form a core-shell structure.

[0013] Furthermore, the inner layer of the rare earth oxide shell has a size of less than 50 nm, and the thickness of the nano-Ni coating layer is 5 to 50 nm.

[0014] It should be further explained that if the outer nano-Ni coating layer is too thick, it will not be conducive to improving plasticity and toughness; conversely, if the coating layer is too thin, it will result in incomplete encapsulation of the inner layer.

[0015] Furthermore, the mass ratio of the CoCrFeMnNi powder to the rare earth oxide particles with a core-shell structure is 100:(0.5-2). Increasing the mass proportion of rare earth oxide particles improves the mechanical properties of the prepared high-entropy alloy within a certain range. However, with the increase of the reinforcing phase addition, oxide particle segregation occurs during laser selective melting, which is detrimental to the improvement of high-entropy alloy performance. Therefore, the preferred doping mass ratio is 100:(0.5-2).

[0016] Furthermore, the specific preparation method of rare earth oxide particles is as follows: Step 1, La(OH)3 nanoparticles are prepared by liquid-phase precipitation; Step 2, La(OH)3@Ni(OH)3 nanoparticle core-shell precursor powder is prepared by chemical reaction induction; Step 3, core-shell structured La2O3@Ni nanoparticles are obtained by calcination reduction method.

[0017] Furthermore, the preparation of La(OH)3@Ni(OH)3 nanoparticle core-shell precursor powder via chemical reaction induction specifically includes the following process parameters: Under ultrasonic treatment and stirring conditions, NiCl3 solution is added to the La(OH)3 suspension at a rate of 2-3 ml / min, wherein the molar ratio of Ni to La is 8-15%. During the addition of NiCl3 to the La(OH)3 suspension, if the addition rate is too fast, the nano-Ni will agglomerate; conversely, if the dropping rate is too slow, the nano-La will agglomerate. If the molar ratio of Ni to La is too low, the coating will be incomplete; if the molar ratio is too high, the outer layer will be too thick.

[0018] Furthermore, the CoCrFeMnNi high-entropy alloy powder and rare earth oxide particles with a core-shell structure are mixed, specifically by mechanical mixing at a mixing speed of 40–60 r / min and a mixing time of 8–10 h. By optimizing the mechanical mixing process parameters and adopting low-speed mechanical mixing, the original structure of the powder particles can be maintained. Furthermore, by optimizing the mixing time, a uniformly mixed La2O3@Ni / CoCrFeMnNi powder is obtained.

[0019] Furthermore, the composition of the CoCrFeMnNi powder is as follows: the molar fraction of Fe is 18-22%, the molar fraction of Co is 18-22%, the molar fraction of Ni is 18-22%, the molar fraction of Cr is 18-22%, the molar fraction of Mn is 18-22%, and the size of the CoCrFeMnNi powder is 15-53 μm.

[0020] Furthermore, the specific parameters for the laser selective melting process are as follows: laser power is controlled at 250W–350W, scanning speed at 600mm / s–1000mm / s, scanning interval at 0.05–0.2mm, powder layer thickness at 0.03–0.1mm, and adjacent layers are rotated 60–70° during sample preparation. Through the optimized design of the above-mentioned laser selective melting process parameters, high-density samples can be prepared. If the laser power is too high or the scanning speed is too low, the powder will completely melt during the preparation process, the molten pool will evaporate, and even sample collapse may occur. If the laser power is too low or the scanning speed is too high, insufficient energy will prevent the powder from completely melting, reducing the width and depth of the molten pool and decreasing the relative density of the sample.

[0021] It should be noted that this invention employs selective laser melting (SLM) technology for preparation. Firstly, compared to laser cladding, SLM does not involve coating the material surface for strengthening; instead, it directly prepares the sample, allowing for the direct production of the desired sample and parts with more complex shapes. Furthermore, comparing the microstructure of the prepared coating and the sample, the microstructure produced by SLM exhibits finer grains and optimized performance. Secondly, compared to traditional forging methods, samples prepared using SLM possess higher microhardness and tensile strength, resulting in higher surface quality, finer dimensions, and greater suitability for automated mechanical applications.

[0022] Furthermore, during the laser selective melting preparation process, the powder supply for the first 30 layers of the sample preparation is increased by 2-3 times compared to the subsequent layers. This ensures that the powder at the bottom layer covers the substrate, making the sample and the substrate more firmly bonded during the preparation process and preventing the bottom of the prepared sample from collapsing.

[0023] Furthermore, before the laser selective melting preparation begins, the forming cavity is evacuated, and argon is used as the protective gas throughout the process.

[0024] Furthermore, this includes preheating the substrate of the printed sample to 70–90°C before performing selective laser melting. By preheating the substrate of the printed sample, the temperature gradient between the underlying powder and the substrate is reduced, thereby reducing internal defects at the contact points between the formed sample and the substrate.

[0025] A second aspect of the present invention provides a high-entropy alloy prepared according to any of the above-mentioned preparation methods.

[0026] Furthermore, the high-entropy alloy has a tensile strength ≥936MPa, a yield strength ≥795MPa, and a strain ≥18.3%.

[0027] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0028] (1) This invention optimizes the structure of rare earth oxide particles by wrapping nano-sized Ni nanoparticles on the outside of rare earth oxide particles to form rare earth oxide particles with a core-shell structure. The overall size of the rare earth oxide particles is less than 100 nm. The rare earth oxide particles are mechanically mixed with a high-entropy alloy powder matrix, and the resulting composite powder is used to prepare the high-entropy alloy. The strength and plasticity of the high-entropy alloy are improved simultaneously.

[0029] (2) By optimizing the structure of the rare earth oxide particles, the present invention can reduce the density difference between the nanoparticles and the high entropy alloy by wrapping the rare earth oxide particles with nano-sized Ni nanoparticles. This eliminates the need for a mixing medium, simplifies the mixing process of rare earth oxide particles and the nano-sized Ni nanoparticles wrapped around them, and significantly improves the uniformity of the mixed powder. Attached Figure Description

[0030] Figure 1 The images show the morphology of the composite powders prepared in Comparative Example 1 and Example 1 of this invention.

[0031] Figure 2 The microstructure morphology of Comparative Example 1, Comparative Example 2, and the samples prepared in Example 1 are shown.

[0032] Figure 3 The stress-strain curves are shown for Comparative Examples 1 and 2 of the present invention and for the samples prepared in Example 1. Detailed Implementation

[0033] To further understand the content of the present invention, the present invention will be described in detail with reference to embodiments and comparative examples.

[0034] Example 1

[0035] This embodiment provides a method for preparing a high-entropy alloy, the method of which is as follows:

[0036] I. Preparation of La2O3@Ni nanoparticles, as detailed below:

[0037] (1) At room temperature, the crystal form control agent PEG400 was added to the La(NO3)3 solution, and then 0.01mol / L NaOH solution was added dropwise to adjust the pH of the mixed solution to about 10. The resulting precipitate was centrifuged and washed multiple times to obtain La(OH)3 precipitate.

[0038] (2) Using the La(OH)3 precipitate obtained in step 1, a La(OH)3 suspension was prepared. Under ultrasonic treatment and stirring conditions, a certain amount of NiCl3 solution was added dropwise and uniformly to the La(OH)3 suspension prepared in step 1 at a rate of 3 ml / min. The molar ratio of Ni element to La element used was 15%. Then, 0.01 mol / L NaOH solution was added dropwise to allow the precipitated Ni(OH)3 to nucleate and grow heterogeneously on the surface of La(OH)3 and coat the outside of La(OH)3. The precipitate was centrifuged and washed multiple times, and finally dried to obtain La(OH)3@Ni(OH)3 core-shell precursor powder.

[0039] (3) Calcine at 110°C in air for 1 hour to completely remove carbon impurities such as dispersant and ethanol cleaning agent; then reduce at 450°C in hydrogen atmosphere for a certain time and cool to room temperature to obtain rare earth oxide particles with core-shell structure, denoted as La2O3@Ni nanoparticles.

[0040] The La2O3@Ni nanoparticles prepared in this embodiment have an inner layer size of less than 50 nm and a nano-Ni coating thickness of 5–50 nm.

[0041] II. Preparation of Composite Powder

[0042] CoCrFeMnNi powder, a high-entropy alloy matrix, and La2O3@Ni nanoparticles, used as reinforcing phase, were mechanically mixed. The mechanical mixing process parameters were: mixing speed 50 r / min, mixing time 9 h, and the mass ratio of La2O3@Ni particles to CoCrFeMnNi powder was 1:100.

[0043] The specific composition of the CoCrFeMnNi powder used is as follows: Fe molar fraction 22%, Co molar fraction 20%, Ni molar fraction 18%, Cr molar fraction 22%, Mn molar fraction 18%, with the sum of the mass percentages of each component being 100%. The size of the CoCrFeMnNi powder is 15–53 μm. The size of the La2O3@Ni nanoparticles used is less than 100 nm. The morphology of the prepared composite powder is as follows: Figure 1 As shown in (b).

[0044] III. Sample preparation using selective laser melting

[0045] High-entropy alloy samples were prepared using laser selective melting technology, with uniformly mixed composite powder as the printing material. The process included the following steps:

[0046] (1) Before the sample preparation begins, the printed sample substrate is preheated at 80°C.

[0047] (2) During the laser selective melting process, the forming chamber is evacuated and argon is used as the protective gas throughout the process. The laser power is controlled at 350W, the scanning speed is 600mm / s, the scanning interval is 0.07mm, the powder layer thickness is 0.05mm, and the interlayer scanning strategy is to rotate 67° for preparation. In the sample preparation process, the amount of powder used in the first 30 layers is increased to twice that of the subsequent layers.

[0048] The sample prepared in this embodiment is designated as La2O3@Ni / CoCrFeMnNi sample. The sample has no obvious defects, high surface precision, tensile strength of 1046MPa, yield strength of 871MPa, and strain of 19.8%.

[0049] Comparative Example 1

[0050] This comparative example provides a method for preparing a high-entropy alloy, which differs from Example 1 in that no reinforcing phase is added; that is, the composite powder used as the printing material is only CoCrFeMnNi powder, and the morphology of the composite powder is as follows. Figure 1 As shown in (a); the rest of the operations are basically the same.

[0051] The sample prepared in this comparative example is denoted as CoCrFeMnNi sample.

[0052] Comparative Example 2

[0053] This comparative example provides a method for preparing a high-entropy alloy. The difference between this method and Example 1 is that the reinforcing phase used is La2O3 nanoparticles with a size of less than 100 nm. That is, the powder used as the printing material is only a composite powder of CoCrFeMnNi and La2O3 nanoparticles. The rest of the operations are basically the same.

[0054] The sample prepared in this comparative example is denoted as the La2O3 / CoCrFeMnNi sample.

[0055] Comparative Example 3

[0056] This comparative example provides a method for preparing a high-entropy alloy. The difference from Example 1 is that the reinforcing phase used is La2O3@Ni with a core-shell structure, which is formed by coating multiple nano-La2O3 particles with nano-Ni and has an overall size of 15-53 μm, which is roughly the same as the size of the high-entropy alloy matrix powder. The micron-sized core-shell structured La2O3@Ni nanoparticles are mechanically mixed with the high-entropy alloy matrix powder, and the rest of the operations are basically the same.

[0057] The sample prepared in this comparative example is denoted as U-La2O3@Ni / CoCrFeMnNi sample.

[0058] Comparative Example 4

[0059] This comparative example provides a method for preparing a high-entropy alloy. The difference between this method and Example 1 is that the reinforcing phase used is a rare earth oxide La2O3 particle with a core-shell structure, the overall size of which is greater than 100 nm. Specifically, the rare earth oxide La2O3 particle is 200-300 nm. The rest of the operations are basically the same.

[0060] The sample prepared in this comparative example is denoted as L-La2O3@Ni / CoCrFeMnNi sample.

[0061] Performance testing

[0062] The samples prepared in Example 1 and Comparative Examples 1-2 were analyzed and tested as follows:

[0063] (1) High-entropy alloys from Examples 1 and 1-2 were taken respectively, and samples were prepared using SLM technology. The samples were polished and etched with a etching solution (sulfuric acid). The microstructure was observed, and the results are as follows: Figure 2 As shown, the microstructure of the SLM-prepared samples mainly consists of cellular and columnar crystals. Compared to the CoCrFeMnNi sample, the columnar crystals in the La2O3 / CoCrFeMnNi and La2O3@Ni / CoCrFeMnNi samples are significantly reduced, while the equiaxed crystals are significantly increased. Compared to the La2O3@Ni / CoCrFeMnNi sample, the equiaxed crystals are more pronounced in the latter, and the core-shell structure and high-entropy alloys tend to form a coherent structure.

[0064] (2) Stress-strain properties of laser selectively melted CoCrFeMnNi and laser selectively melted La2O3@Ni / CoCrFeMnNi samples were tested, and the results are as follows: Figure 3 As shown. Combined with Figure 3 It can be seen that by adding core-shell structured La2O3@Ni nanoparticles, the mechanical properties of the La2O3@Ni / CoCrFeMnNi sample prepared in Example 1 are significantly enhanced.

[0065] Specifically, by adding core-shell structured La2O3@Ni nanoparticles, the mechanical properties of the prepared samples were significantly improved. Compared with the CoCrFeMnNi sample, the yield strength and tensile strength increased by 74% and 69%, respectively. Compared with the CoCrFeMnNi sample, the yield strength and tensile strength of the La2O3 / CoCrFeMnNi sample increased by 57% and 42%, respectively, but the strain coefficient decreased from 20.1% to 9.8%. Addressing the challenge of matching high strength and high ductility and toughness in face-centered cubic high-entropy alloys, core-shell structured rare earth oxide nanoparticles were introduced as a reinforcing phase. These nanoparticles can be dispersed in the high-entropy alloy matrix and form a coherent relationship with the matrix; they can also act as heterogeneous nucleation cores during SLM forming, promoting the transformation of columnar crystals to equiaxed crystals, thereby enhancing and plasticizing the alloy.

[0066] Example 2

[0067] This embodiment provides a method for preparing a high-entropy alloy, the method of which is as follows:

[0068] I. Preparation of La2O3@Ni nanoparticles, as detailed below:

[0069] (1) At room temperature, the crystal form control agent PEG400 was added to the La(NO3)3 solution, and then 0.01mol / L NaOH solution was added dropwise to adjust the pH of the mixed solution to about 10. The resulting precipitate was centrifuged and washed multiple times to obtain La(OH)3 precipitate. La(OH)3 suspension was prepared using the obtained La(OH)3 precipitate.

[0070] (2) Under ultrasonic treatment and stirring conditions, a certain amount of NiCl3 solution was added dropwise and uniformly to the La(OH)3 suspension prepared in step 1 at a rate of 2 ml / min, wherein the molar ratio of La element to Ni element used was 10%. Then, 0.01 mol / L NaOH solution was added dropwise to allow the precipitated Ni(OH)3 to nucleate and grow heterogeneously on the surface of La(OH)3 and coat the outside of La(OH)3. The precipitate was centrifuged and washed multiple times, and finally dried to obtain La(OH)3@Ni(OH)3 core-shell precursor powder.

[0071] (3) Calcination was carried out in air at 110°C for 1 hour to completely remove impurities such as dispersant and ethanol cleaning agent carbon. Then, high-temperature reduction was carried out in hydrogen atmosphere at 450°C for a certain time, and then cooled to room temperature to obtain rare earth oxide particles with core-shell structure, denoted as La2O3@Ni nanoparticles.

[0072] The La2O3@Ni nanoparticles prepared in this embodiment have an inner layer size of less than 50 nm and a nano-Ni coating thickness of 5–50 nm.

[0073] II. Preparation of Composite Powder

[0074] CoCrFeMnNi powder, a high-entropy alloy matrix, and La2O3@Ni nanoparticles, used as reinforcing phase, were mechanically mixed. The mechanical mixing process parameters were: mixing speed 40 r / min, mixing time 10 h, and the mass ratio of La2O3@Ni particles to CoCrFeMnNi powder was 2:100.

[0075] The specific composition of the CoCrFeMnNi powder used is as follows: Fe molar fraction is 18%, Co molar fraction is 22%, Ni molar fraction is 20%, Cr molar fraction is 18%, Mn molar fraction is 22%, the sum of the mass percentages of each component is 100%, and the size of the CoCrFeMnNi powder is 15-53 μm; the size of the La2O3@Ni nanoparticles used is less than 100 nm.

[0076] III. Sample preparation using selective laser melting

[0077] High-entropy alloy samples were prepared using laser selective melting technology, with uniformly mixed composite powder as the printing material. The process included the following steps:

[0078] (1) Before the sample preparation begins, the printed sample substrate is preheated at 70°C.

[0079] (2) During the laser selective melting process, the forming chamber is evacuated and argon is used as the protective gas throughout the process. The laser power is controlled at 250W, the scanning speed is 700mm / s, the scanning interval is 0.05mm, the powder layer thickness is 0.1mm, and the interlayer scanning strategy is to rotate 67° for preparation. In the sample preparation process, the amount of powder used in the first 30 layers is increased to twice that of the subsequent layers.

[0080] The sample prepared in this embodiment has no obvious defects, high surface precision, tensile strength of 1121 MPa, yield strength of 950 MPa, and strain of 18.3%.

[0081] Example 3

[0082] This embodiment provides a method for preparing a high-entropy alloy, the method of which is as follows:

[0083] I. Preparation of La2O3@Ni nanoparticles, as detailed below:

[0084] (1) At room temperature, the crystal form control agent PEG400 was added to the La(NO3)3 solution, and then 0.01mol / L NaOH solution was added dropwise to adjust the pH of the mixed solution to about 10. The resulting precipitate was centrifuged and washed multiple times to obtain La(OH)3 precipitate.

[0085] (2) Under ultrasonic treatment and stirring conditions, a certain amount of NiCl3 solution was added dropwise and uniformly to the prepared La(OH)3 suspension at a rate of 3 ml / min, wherein the molar ratio of La element to Ni element used was 8%. Then, 0.01 mol / L NaOH solution was added dropwise to allow the precipitated Ni(OH)3 to nucleate and grow heterogeneously on the surface of La(OH)3 and coat the outside of La(OH)3. The precipitate was centrifuged and washed multiple times, and finally dried to obtain La(OH)3@Ni(OH)3 core-shell precursor powder.

[0086] (3) Calcination was carried out at 110°C in air for 1 hour to completely remove carbon impurities such as dispersant and ethanol cleaning agent. Then, high-temperature reduction was carried out at 450°C in hydrogen atmosphere for a certain time, and then cooled to room temperature to obtain rare earth oxide particles with core-shell structure, denoted as La2O3@Ni nanoparticles.

[0087] The La2O3@Ni nanoparticles prepared in this embodiment have an inner layer size of less than 50 nm and a nano-Ni coating thickness of 5–50 nm.

[0088] II. Preparation of Composite Powder

[0089] CoCrFeMnNi powder, a high-entropy alloy matrix, and La2O3@Ni nanoparticles, used as reinforcing phase, were mechanically mixed. The mechanical mixing process parameters were: mixing speed 60 r / min, mixing time 8 h, and the mass ratio of La2O3@Ni particles to CoCrFeMnNi powder was 0.5:100.

[0090] The specific composition of the CoCrFeMnNi powder used is as follows: Fe molar fraction is 20%, Co molar fraction is 18%, Ni molar fraction is 22%, Cr molar fraction is 20%, Mn molar fraction is 20%, the sum of the mass percentages of each component is 100%, and the size of the CoCrFeMnNi powder is 15-53 μm; the size of the La2O3@Ni nanoparticles used is less than 100 nm.

[0091] III. Sample preparation using selective laser melting

[0092] High-entropy alloy samples were prepared using laser selective melting technology, with uniformly mixed composite powder as the printing material. The process included the following steps:

[0093] (1) Before the sample preparation begins, the printed sample substrate is preheated at 70°C.

[0094] (2) During the laser selective melting process, the forming chamber is evacuated and argon is used as the protective gas throughout the process. The laser power is controlled at 300W, the scanning speed is 800mm / s, the scanning interval is 0.15mm, the powder layer thickness is 0.03mm, and the interlayer scanning strategy is to rotate 67° for preparation. In the sample preparation process, the amount of powder used in the first 30 layers is increased to 3 times that of the subsequent layers.

[0095] The sample prepared in this embodiment has no obvious defects, high surface precision, tensile strength of 936 MPa, yield strength of 795 MPa, and strain of 20%.

Claims

1. A method for preparing a high-entropy alloy, characterized in that, include: CoCrFeMnNi high-entropy alloy powder and rare earth oxide particles are mixed to obtain composite powder; The resulting composite powder was subjected to selective laser melting to prepare a high-entropy alloy. Among them, rare earth oxide particles have a core-shell structure, with nano-La2O3 particles as the inner layer and nano-Ni coating the outside of La2O3. The overall size of the rare earth oxide particles is less than 100nm.

2. The method for preparing the high-entropy alloy according to claim 1, characterized in that, The inner layer of the rare earth oxide shell has a size of less than 50 nm, and the thickness of the nano-Ni coating layer is 5~50 nm.

3. The method for preparing the high-entropy alloy according to claim 1, characterized in that, The mass ratio of the CoCrFeMnNi powder to the rare earth oxide particles with a core-shell structure is 100:(0.5~2).

4. The method for preparing the high-entropy alloy according to any one of claims 1-3, characterized in that, The specific method for preparing the rare earth oxide particles is as follows: Step 1: La(OH)3 nanoparticles were prepared by liquid-phase precipitation. Step 2: Prepare La(OH)3@Ni(OH)3 nanoparticle core-shell precursor powder through chemical reaction induction; Step 3: Core-shell structured La2O3@Ni nanoparticles are obtained by calcination reduction method.

5. The method for preparing the high-entropy alloy according to claim 4, characterized in that, The preparation of La(OH)3@Ni(OH)3 nanoparticle core-shell precursor powder by chemical reaction induction includes the following process parameters: under ultrasonic treatment and stirring conditions, NiCl3 solution is added to La(OH)3 suspension at a rate of 2~3 ml / min, wherein the molar ratio of Ni element to La element is 8~15%.

6. The method for preparing the high-entropy alloy according to claim 4, characterized in that, The CoCrFeMnNi high-entropy alloy powder and rare earth oxide particles with core-shell structure are mixed, specifically by mechanical mixing at a mixing speed of 40~60 r / min and a mixing time of 8~10 h.

7. The method for preparing the high-entropy alloy according to claim 4, characterized in that, The CoCrFeMnNi powder has the following composition: Fe molar fraction of 18-22%, Co molar fraction of 18-22%, Ni molar fraction of 18-22%, Cr molar fraction of 18-22%, and Mn molar fraction of 18-22%. The CoCrFeMnNi powder size is 15-53µm.

8. The method for preparing the high-entropy alloy according to claim 4, characterized in that, The specific parameters for the laser selective melting process are as follows: the laser power is controlled at 250W~350W, the scanning speed is 600mm / s~1000mm / s, the scanning interval is 0.05~0.15mm, the powder layer thickness is 0.03~0.1mm, and the sample is prepared by rotating adjacent layers by 60~70°. And / or may also include preheating the substrate of the printed sample to 70-90°C before performing laser selective melting.

9. A high-entropy alloy, characterized in that, It is prepared according to any one of claims 1-8.

10. The high-entropy alloy according to claim 9, characterized in that, The high-entropy alloy has a tensile strength ≥936MPa, a yield strength ≥795MPa, and a strain ≥18.3%.

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