High-entropy alloy and preparation method thereof

Abstract

The invention discloses a high-entropy alloy and a preparation method thereof, and belongs to the technical field of additive manufacturing. CoCrFeMnNi high-entropy alloy powder and rare earth oxide particles are mixed to obtain composite powder, the rare earth oxide particles are of core-shell structures, the inner layers of the rare earth oxide particles are nanometer La2O3 particles, the La2O3 particles are coated with nanometer Ni, and the overall size of the rare earth oxide particles of the core-shell structures is smaller than 100 nm; and the obtained composite powder is subjected to selective laser melting treatment to prepare the high-entropy alloy. According to the preparation method, the nanoscale rare earth oxide with the core-shell structure is prepared to serve as the reinforcement phase of the high-entropy alloy, the operation of doping and mixing the nanoscale reinforcement phase and the high-entropy alloy matrix powder is simplified, and the reinforcement and plasticization effects can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and more specifically, to a high-entropy alloy and a preparation method thereof. Background Art

[0002] Multi-component high-entropy alloys break the design concept of traditional alloys and have four unique effects: the high-entropy effect in thermodynamics, the sluggish diffusion effect in kinetics, the lattice distortion effect in the organizational structure, and the "cocktail" effect in performance, making them have excellent mechanical properties, corrosion resistance, radiation resistance, and high-temperature oxidation resistance, etc., and thus becoming new structural materials with application potential in extreme environments such as aerospace, nuclear industry, and polar scientific research. However, high-entropy alloys prepared by traditional processes such as casting, mechanical alloying, and powder metallurgy usually have problems such as limited shape and size, coarse grains, and composition segregation, which limit the popularization and application of high-entropy alloys. With the development of alloy manufacturing technology, the selective laser melting technology of high-entropy alloys (abbreviated as SLM) has become one of the most widely used additive manufacturing technologies because it can manufacture high-precision and high-performance metal parts and has the characteristics of a short design and production cycle, and has also become a new way for green preparation of high-entropy alloys.

[0003] In the process of preparing high-entropy alloys by selective laser melting technology, adding reinforcing phases to modify the alloy powder matrix is one of the hot research topics in this field. When the size of rare earth oxide particles as the reinforcing phase reaches the nanoscale, and the reinforcing phase and the high-entropy alloy matrix powder are mixed by traditional mechanical mixing, the changing trends of the strength and plasticity of the prepared composite material are not synchronous. Specifically, the strength improvement of the material is limited and the plasticity decreases significantly.

[0004] After retrieval, the Chinese patent application case with the application number 202210713202.5 discloses an additive manufacturing high-entropy alloy composite material, a preparation method thereof, and an application. It mixes a nano-reinforcing phase powder and deionized water evenly by ultrasonic vibration to obtain a suspension, and the mass ratio of the nano-reinforcing phase powder to the volume of deionized water is (1-20 mg): 1 ml; S2, mixes the suspension and the high-entropy alloy powder evenly in an ammonia atmosphere, the mixing temperature is 500-800 °C, and then dries it in a vacuum environment to obtain a nano-particle-reinforced high-entropy alloy composite material. Although this application case improves the strength of the composite material, inhibits hot cracking, reduces defects, and improves the uniformity of the alloy structure, making the strength and toughness of the alloy increase synchronously, 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] In view of the relatively complex technical problems that the strengthening effect of the nanoparticle reinforcement phase on the high-entropy alloy matrix powder is limited and the plasticity decreases significantly, the present invention provides a high-entropy alloy and a preparation method thereof. In this preparation method, by preparing rare-earth oxides with a core-shell structure in nanoscale as the reinforcement phase of the high-entropy alloy, the plasticity and strength of the high-entropy alloy can be improved simultaneously.

[0007] 2. Technical Solution

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

[0009] The first aspect of the present invention provides a preparation method of a high-entropy alloy, including: 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 treatment of the obtained composite powder; wherein, the rare-earth oxide particles have a core-shell structure, the inner layer is nano-La 2 O 3 particles, and nano-Ni particles are coated on the outside of La 2 O 3 , 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 the laser energy density during the SLM preparation process, which will affect the microstructure and properties of the SLM-prepared specimens, and even lead to the inability to prepare specimens. Therefore, the selection and preparation of powders are particularly crucial. In this regard, the inventor has conducted a large number of experimental studies. To prepare specimens that meet the requirements of the present invention, CoCrFeMnNi is finally selected as the matrix powder, and La 2 O 3 @Ni with a core-shell structure is used as the reinforcement phase.

[0011] More importantly, when the inventor studied rare-earth oxide particles as the reinforcement phase of CoCrFeMnNi-based high-entropy alloy powder, when the size of the rare-earth oxide particles as the reinforcement phase reached the nanoscale, and the reinforcement phase and the high-entropy alloy matrix powder were mixed by traditional mechanical methods, the change trends of the strength and plasticity of the prepared composite material were not synchronized, and the plasticity decreased significantly, that is, the plasticity of the composite material became poor and the strength improvement was limited. To solve the above technical problems, the inventor added a shell structure to the outside of the nano-La 2 O 3 particles, and limited the overall size of the rare-earth oxide with the added shell structure within 100 nm. By simply mechanically mixing the nanoscale rare-earth oxide particles with the high-entropy alloy matrix powder and using the composite powder, the strength and plasticity of the prepared composite material are improved synchronously. Compared with nano-La 2 O 3Direct doping of particles significantly improves its plasticity. The specific mechanism is as follows: on the one hand, nano-particles act as heterogeneous nucleation cores during the SLM forming process, promoting the transformation of columnar grains into equiaxed grains. On the other hand, La 2 O 3 maintains a coherent relationship with Ni, and after SLM forming, La 2 O 3 @Ni nano-particles can maintain a coherent relationship with the high-entropy alloy matrix, thus playing a role in strengthening and toughening.

[0012] Furthermore, it is found that with the decrease of the size of the reinforcement phase, especially when the size of the doped rare-earth oxide particles reaches the nanoscale, the reinforcement phase is prone to segregation, leading to composition segregation. By coating the outside of the nano-La 2 O 3 particles with nano-Ni particles, on the one hand, the Ni shell is one of the components of the high-entropy alloy, which can reduce the density difference between the nano-particles and the high-entropy alloy, avoid the floating of nano-particles in the liquid during the SLM process, resulting in composition segregation, and thus can improve the dispersion degree of rare-earth oxides and high-entropy alloy matrix powder, and further simplify the mixing process of the two; on the other hand, nano-Ni particles have good toughness and strength. At the same time, Ni has the best mixing enthalpy with La compared with other elements in the high-entropy alloy matrix, so that Ni and La 2 O 3 can better combine to form a core-shell structure.

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

[0014] It should be further noted that if the thickness of the outer nano-Ni coating layer is too large, it is not conducive to improving plasticity and toughness; on the contrary, if the thickness of the coating layer is too small, it will lead to incomplete wrapping of the inner layer.

[0015] Further, the mass ratio of the CoCrFeMnNi powder to the rare-earth oxide particles with a core-shell structure satisfies 100:(0.5 - 2). Increasing the mass ratio of rare-earth oxide particles, within a certain addition range, the mechanical properties of the prepared high-entropy alloy are improved. However, with the increase of the addition amount of the reinforcement phase, during the selective laser melting preparation process, segregation of oxide particles will occur, which is not conducive to the improvement of the properties of the high-entropy alloy. Therefore, the preferred doping mass ratio is 100:(0.5 - 2).

[0016] Further, the preparation method of the rare-earth oxide particles is specifically as follows: Step 1, prepare La(OH) 3 nano-particles by the liquid-phase precipitation method; Step 2, prepare La(OH) 3 @Ni(OH)3 Core-shell precursor powder of nanoparticles; Step 3, obtaining La with a core-shell structure by calcination reduction method 2 O 3 @Ni nanoparticles.

[0017] Furthermore, the preparation of La(OH) induced by chemical reaction 3 @Ni(OH) 3 Core-shell precursor powder of nanoparticles specifically includes the following process parameters: under ultrasonic treatment and stirring conditions, add NiCl 3 solution to the La(OH) 3 suspension at a rate of 2 - 3 ml / min, where the molar ratio of Ni element to La element used is 8 - 15%. When adding NiCl 3 to the La(OH) 3 suspension, if the addition rate is too fast, nano-Ni will agglomerate; conversely, if the dropping rate is too slow, nano-La will agglomerate. If the molar ratio of Ni element to La element is too low, the coating will be incomplete; if the molar ratio of the two is too high, the outer layer will be too thick.

[0018] Furthermore, the CoCrFeMnNi high-entropy alloy powder and the rare earth oxide particles with a core-shell structure are mixed. Specifically, mechanical powder mixing is carried out at a mixing speed of 40 - 60 r / min for a mixing time of 8 - 10 h. By optimizing the process parameters of mechanical powder mixing and using low-speed mechanical powder mixing, it is beneficial to maintain the original structure of the powder particles, and by optimizing the mixing time design, a uniformly mixed La 2 O 3 @Ni / CoCrFeMnNi powder is obtained.

[0019] Furthermore, the composition of the CoCrFeMnNi powder is: 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%, and the molar fraction of Mn is 18 - 22%. The size of the CoCrFeMnNi powder is 15 - 53 μm.

[0020] Furthermore, the specific parameters of the selective laser melting process are as follows: the laser power is controlled to be 250W - 350W, the scanning speed is 600mm / s - 1000mm / s, the scanning spacing is 0.05 - 0.2mm, the powder layer thickness is 0.03 - 0.1mm, and adjacent layers are rotated by 60 - 70° to prepare the specimen. Through the optimized design of the above specific process parameters of selective laser melting, specimens with high density can be prepared. If the laser power is too high or the scanning speed is too low, during the preparation process, the powder will be completely melted, the molten pool will evaporate, and even the specimen will collapse; if the laser power is too low or the scanning speed is too high, due to insufficient energy, the powder cannot be completely melted, the width and depth of the molten pool will decrease, and the relative density of the specimen will decrease.

[0021] It should be noted that the present invention uses the selective laser melting technology for preparation. On the one hand, compared with laser cladding treatment, the selective laser melting technology does not perform coating strengthening treatment on the material surface, but directly prepares specimens, can directly prepare the required specimens, produce parts with more complex shapes, and comparing the prepared coating with the specimen structure, the grains of the structure prepared by selective laser melting are finer and the performance is optimized. On the other hand, compared with the traditional forging preparation method, the specimens prepared by selective laser melting have higher microhardness and tensile strength, the surface quality of the prepared specimens is higher, the size is more refined, and it is more conducive to mechanical automation use.

[0022] Furthermore, during the selective laser melting preparation process, the powder supply amount for the first 30 layers of specimen preparation is increased to 2 - 3 times that of the subsequent other layers, so as to ensure that the bottom layer of powder covers the substrate, making the combination between the specimen and the substrate more stable during the preparation process and preventing the bottom of the prepared specimen from collapsing.

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

[0024] Furthermore, it also includes preheating the substrate of the printed specimen to 70 - 90°C before selective laser melting. By preheating the substrate of the printed specimen, the temperature gradient between the bottom layer of powder and the substrate is reduced, thereby reducing the internal defects at the contact position between the formed specimen and the substrate.

[0025] The second aspect of the present invention provides a high-entropy alloy prepared according to the preparation method of any one of the above.

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

[0027] Adopting the technical solution provided by the present invention, compared with the prior art, it has the following beneficial effects:

[0028] (1) The present invention optimizes the structure of nano rare earth oxide particles. By coating nano Ni nanoparticles on the outside of the rare earth oxide particles, rare earth oxide particles with a core-shell structure are formed, and their overall size is less than 100 nm. The obtained high-entropy alloy is prepared by mechanically mixing the rare earth oxide particles with a high-entropy alloy powder matrix, and the strength and plasticity of the high-entropy alloy are improved simultaneously.

[0029] (2) The present invention optimizes the structure of nano rare earth oxide particles. By coating nano Ni nanoparticles on the outside of the rare earth oxide particles, the density difference between the nanoparticles and the high-entropy alloy can be reduced, so that there is no need to rely on a mixing medium, simplifying the powder mixing process of the rare earth oxide particles and the nano Ni nanoparticles coated on the outside of the rare earth oxide particles, and significantly improving the uniformity of powder mixing. Description of the Drawings

[0030] Figure 1 Morphology of the composite powders prepared in Comparative Example 1 and Example 1 of the present invention.

[0031] Figure 2 Microstructure morphologies of the specimens prepared in Comparative Example 1, Comparative Example 2 and Example 1 of the present invention.

[0032] Figure 3 Stress-strain curve diagrams of the specimens prepared in Comparative Example 1, Comparative Example 2 and Example 1 of the present invention. Detailed Embodiments

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

[0034] Example 1

[0035] This example provides a preparation method of a high-entropy alloy, and the preparation method is as follows:

[0036] I. Preparation of La 2 O 3 @Ni nanoparticles, specifically as follows:

[0037] (1) At room temperature, add the crystal form control agent PEG400 to the La(NO 3 ) 3 solution, and then dropwise add 0.01 mol / L NaOH solution to adjust the pH value of the mixed solution to about 10. Centrifuge and wash the obtained precipitate multiple times to obtain La(OH) 3 precipitate.

[0038] (2) Use the La(OH) 3 precipitate obtained in step 1 to prepare La(OH)3 Suspension. Under ultrasonic treatment and stirring conditions, a certain amount of NiCl solution was added dropwise at a rate of 3 ml / min to the La(OH) suspension prepared in step 1 3 solution, where the molar ratio of Ni element to La element used was 15%. Then, 0.01 mol / L NaOH solution was added dropwise to cause the precipitated Ni(OH) 3 to heterogeneously nucleate and grow on the surface of La(OH), covering the outside of La(OH); the obtained precipitate was centrifuged and washed several times, and finally dried to obtain La(OH) 3 @Ni(OH) 3 core-shell precursor powder. 3 (3) Calcined at 110 °C in air atmosphere for 1 h to completely remove impurity carbon such as dispersant and ethanol cleaning agent; then high-temperature reduced in hydrogen atmosphere at 450 °C for a certain time and cooled to room temperature to obtain rare earth oxide particles with core-shell structure, denoted as La 3 O 3 @Ni nanoparticles.

[0039] (3) Calcined at 110 °C in air atmosphere for 1 h to completely remove impurity carbon such as dispersant and ethanol cleaning agent; then high-temperature reduced in hydrogen atmosphere at 450 °C for a certain time and cooled to room temperature to obtain rare earth oxide particles with core-shell structure, denoted as La 2 O 3 @Ni nanoparticles.

[0040] The La 2 O 3 @Ni nanoparticles prepared in this example have an inner layer size of less than 50 nm, and the thickness of the nano-Ni coating layer is 5 - 50 nm.

[0041] II. Preparation of composite powder

[0042] The CoCrFeMnNi powder of the high-entropy alloy matrix and the La 2 O 3 @Ni nanoparticles as the reinforcing phase were mechanically mixed. The process parameters of mechanical mixing were: mixing speed 50 r / min, mixing time 9 h, where the mass ratio of La 2 O 3 @Ni particles to CoCrFeMnNi powder was 1:100.

[0043] Among them, the specific composition of the CoCrFeMnNi powder used was: the molar fraction of Fe was 22%, the molar fraction of Co was 20%, the molar fraction of Ni was 18%, the molar fraction of Cr was 22%, the molar fraction of Mn was 18%, and the sum of the mass percentages of each component was 100%. The size of the CoCrFeMnNi powder was 15 - 53 μm; the size of the La 2 O 3 @Ni nanoparticles was less than 100 nm, and the morphology of the prepared composite powder was as shown in Figure 1 (b).

[0044] III. Preparation of Specimens by Selective Laser Melting

[0045] Using the selective laser melting technology, the uniformly mixed composite powder is used as the printing material to prepare high-entropy alloy specimens, including the following steps:

[0046] (1) Before the start of specimen preparation, preheat the printing specimen substrate at 80 °C;

[0047] (2) During the selective laser melting process, evacuate the forming chamber, use argon as the protective gas throughout the process, control the laser power at 350 W, the scanning speed at 600 mm / s, the scanning spacing at 0.07 mm, the layer thickness of powder spreading at 0.05 mm, and the interlayer scanning strategy is to prepare by rotating 67°; among them, during the specimen preparation process, increase the powder spreading amount of the first 30 layers to 2 times that of the subsequent other layers.

[0048] The specimen prepared in this example is denoted as La 2 O 3 @Ni / CoCrFeMnNi specimen. The specimen has no obvious defects and high surface accuracy. Its tensile strength is 1046 MPa, the yield strength is 871 MPa, and the strain is 19.8%.

[0049] Comparative Example 1

[0050] This comparative example provides a preparation method of high-entropy alloy. The difference from Example 1 is 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 shown in Figure 1 (a); the remaining operations are basically the same.

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

[0052] Comparative Example 2

[0053] This comparative example provides a preparation method of high-entropy alloy. The difference from Example 1 is that: the reinforcing phase used is La 2 O 3 nanoparticles with a size less than 100 nm, that is, the powder used as the printing material is only the composite powder of CoCrFeMnNi and La 2 O 3 nanoparticles; the remaining operations are basically the same.

[0054] The specimen prepared in this comparative example is denoted as La 2 O 3 / CoCrFeMnNi specimen.

[0055] Comparative Example 3

[0056] This comparative example provides a preparation method of a high-entropy alloy, which is different from Example 1 in that the reinforcing phase used is La with a core-shell structure 2 O 3 @Ni, which is formed by coating multiple nano-La 2 O 3 particles with nano-Ni, and its overall size is 15-53 μm, which is roughly the same as the size of the high-entropy alloy matrix powder. The micron-sized core-shell structured La 2 O 3 @Ni nanoparticles and the high-entropy alloy matrix powder are mechanically mixed, and the remaining operations are basically the same.

[0057] The sample prepared in this comparative example is denoted as U-La 2 O 3 @Ni / CoCrFeMnNi sample.

[0058] Comparative Example 4

[0059] This comparative example provides a preparation method of a high-entropy alloy, which is different from Example 1 in that the reinforcing phase used is rare earth oxide La with a core-shell structure 2 O 3 particles, whose overall size is greater than 100 nm. Specifically, the rare earth oxide La 2 O 3 particles are specifically 200-300 nm, and the remaining operations are basically the same.

[0060] The sample prepared in this comparative example is denoted as L-La 2 O 3 @Ni / CoCrFeMnNi sample.

[0061] Performance test

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

[0063] (1) Samples of the high-entropy alloys of Example 1 and Comparative Examples 1-2 were respectively taken, and the samples prepared by using the SLM technology were polished, and then corroded with a corrosion solution (sulfuric acid) to observe the microstructure. The results are as Figure 2 shown. It can be observed that the microstructure of the samples prepared by SLM mainly consists of cellular crystals and columnar crystals. Compared with the CoCrFeMnNi sample, the columnar crystals of the La 2 O 3 / CoCrFeMnNi and La 2 O 3 @Ni / CoCrFeMnNi samples are significantly reduced, and the equiaxed crystals are significantly increased. La 2 O 3 / CoCrFeMnNi and La 2 O 3 @Ni / CoCrFeMnNi specimens, the equiaxed grains of the latter are more significant, and the core-shell structure and high-entropy alloy are prone to form a coherent structure.

[0064] (2) Perform stress-strain property tests on the selective laser melting CoCrFeMnNi specimens and the selective laser melting La 2 O 3 @Ni / CoCrFeMnNi specimens, and the results are as Figure 3 shown. Combining Figure 3 it can be seen that by adding the core-shell structure La 2 O 3 @Ni nanoparticles, the mechanical properties of the La 2 O 3 @Ni / CoCrFeMnNi specimens prepared in Example 1 are significantly enhanced.

[0065] Specifically, by adding the core-shell structure La 2 O 3 @Ni nanoparticles, the mechanical properties of the prepared specimens are significantly improved. Compared with the CoCrFeMnNi specimens, the yield strength and tensile strength are increased by 74% and 69% respectively; the La 2 O 3 / CoCrFeMnNi specimens compared with the CoCrFeMnNi specimens, the yield strength and tensile strength are increased by 57% and 42% respectively, but the strain coefficient before and after decreases from 20.1% to 9.8%. Aiming at the matching problem of high strength and high plastic toughness of face-centered cubic structure high-entropy alloys, introducing core-shell structure rare earth oxide nanoparticles as reinforcement phases can be dispersed in the high-entropy alloy matrix and form a coherent relationship with the matrix; it can also be used as a heterogeneous nucleation core during the SLM forming process to promote the transformation of columnar grains to equiaxed grains, thus playing a role in strengthening and plasticizing.

[0066] Example 2

[0067] This example provides a preparation method of high-entropy alloy, and the preparation method is as follows:

[0068] I. Prepare La 2 O 3 @Ni nanoparticles, specifically as follows:

[0069] (1) At room temperature, add the crystal form control agent PEG400 to La(NO 3 ) 3In a solution, 0.01 mol / L NaOH solution was then added dropwise to adjust the pH value of the mixed solution to about 10. The obtained precipitate was centrifuged and washed repeatedly to obtain La(OH) 3 precipitate. Using the obtained La(OH) 3 precipitate to prepare La(OH) 3 suspension.

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

[0071] (3) Calcined at 110 °C in air atmosphere for 1 h to completely remove impurities such as dispersant and ethanol cleaning agent. Then reduced at high temperature in hydrogen atmosphere at 450 °C for a certain time and cooled to room temperature to obtain rare earth oxide particles with core-shell structure, denoted as La 2 O 3 @Ni nanoparticles.

[0072] The La 2 O 3 @Ni nanoparticles prepared in this example have an inner layer size of less than 50 nm, and the thickness of the nano-Ni coating layer is 5 - 50 nm.

[0073] II. Preparation of composite powder

[0074] The CoCrFeMnNi powder of the high-entropy alloy matrix and La 2 O 3 @Ni nanoparticles as the reinforcement phase were mechanically mixed. The process parameters of mechanical mixing were: mixing speed 40 r / min, mixing time 10 h, and the mass ratio of La 2 O 3 @Ni particles to CoCrFeMnNi powder was 2:100.

[0075] Among them, the specific composition of the CoCrFeMnNi powder used is as follows: the molar fraction of Fe is 18%, the molar fraction of Co is 22%, the molar fraction of Ni is 20%, the molar fraction of Cr is 18%, the molar fraction of Mn is 22%, and the sum of the mass percentages of each component is 100%. The size of the CoCrFeMnNi powder is 15 - 53 μm; the La 2 O 3 @Ni nanoparticles have a size of less than 100 nm.

[0076] III. Preparing specimens by selective laser melting

[0077] Using the selective laser melting technology, the uniformly mixed composite powder is used as the printing material to prepare high-entropy alloy specimens, including the following steps:

[0078] (1) Before the start of specimen preparation, the printing specimen substrate is preheated at 70 °C.

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

[0080] The specimens prepared in this example have no obvious defects, high surface accuracy, a tensile strength of 1121 MPa, a yield strength of 950 MPa, and a strain of 18.3%.

[0081] Example 3

[0082] This example provides a preparation method of a high-entropy alloy, and its preparation method is as follows:

[0083] I. Preparing La 2 O 3 @Ni nanoparticles, specifically as follows:

[0084] (1) At room temperature, the crystal shape control agent PEG400 is added to the La(NO 3 ) 3 solution, and then 0.01 mol / L NaOH solution is added dropwise to adjust the pH value of the mixed solution to about 10. The obtained precipitate is centrifuged and washed repeatedly to obtain La(OH) 3 precipitate.

[0085] (2) Under ultrasonic treatment and stirring conditions, a certain amount of NiCl is added dropwise and uniformly to the prepared La(OH) 3 suspension at a speed of 3 ml / min3 A solution in which the molar ratio of La element to Ni element used is 8%, and then 0.01 mol / L NaOH solution is added dropwise to precipitate Ni(OH) 3 heterogeneous nucleation and growth occur on the surface of La(OH) 3 and it coats on the outside of La(OH) 3 The obtained precipitate is centrifuged and washed several times, and finally dried to obtain La(OH) 3 @Ni(OH) 3 core-shell precursor powder.

[0086] (3) Calcinate at 110 °C in air atmosphere for 1 h to completely remove impurities such as dispersants and ethanol cleaning agents. Then reduce at high temperature in hydrogen atmosphere at 450 °C for a certain time and cool to room temperature to obtain rare earth oxide particles with a core-shell structure, denoted as La 2 O 3 @Ni nanoparticles.

[0087] The La 2 O 3 @Ni nanoparticles prepared in this example have an inner layer size of less than 50 nm and the thickness of the nano-Ni coating layer is 5 - 50 nm.

[0088] II. Preparation of composite powder

[0089] Mix the CoCrFeMnNi powder of the high-entropy alloy matrix and La 2 O 3 @Ni nanoparticles used as the reinforcement phase by mechanical powder mixing. The process parameters of mechanical powder mixing are: powder mixing rotation speed 60 r / min, powder mixing time 8 h, and the mass ratio of La 2 O 3 @Ni particles to CoCrFeMnNi powder is 0.5:100.

[0090] Among them, the specific composition of the CoCrFeMnNi powder used is: the molar fraction of Fe is 20%, the molar fraction of Co is 18%, the molar fraction of Ni is 22%, the molar fraction of Cr is 20%, the molar fraction of Mn is 20%, and the sum of the mass percentages of each component is 100%. The size of the CoCrFeMnNi powder is 15 - 53 μm; the size of the La 2 O 3 @Ni nanoparticles is less than 100 nm.

[0091] III. Preparation of specimens by selective laser melting

[0092] Adopt selective laser melting technology, use the uniformly mixed composite powder as the printing material to prepare high-entropy alloy specimens, including the following steps:

[0093] (1) Before the start of specimen preparation, preheat the printed specimen substrate at 70 °C.

[0094] (2) During the selective laser melting process, evacuate the forming chamber, use argon as the protective gas throughout the process, control the laser power at 300 W, the scanning speed at 800 mm / s, the scanning spacing at 0.15 mm, the layer thickness of powder spreading at 0.03 mm, and the interlayer scanning strategy is to prepare by rotating 67°; among them, during the specimen preparation process, increase the powder spreading amount of the first 30 layers to 3 times that of the subsequent other layers.

[0095] For the specimen prepared in this example, the specimen has no obvious defects, high surface accuracy, its tensile strength is 936 MPa, the yield strength is 795 MPa, and the strain is 20%.

Claims

1. A method for preparing a high entropy alloy, characterized in that: include: Mixing CoCrFeMnNi high entropy alloy powder and rare earth oxide particles to obtain composite powder; and subjecting the obtained composite powder to selective laser melting to prepare a high entropy alloy; The rare earth oxide particles have a core-shell structure, the inner layer of which is nano La2O3 particles, nano Ni is coated on the outside of La2O3, and the overall size of the rare earth oxide particles is less than 100nm.

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

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

4. The method for preparing a high entropy alloy according to any one of claims 1 to 3, characterized in that: The preparation method of the rare earth oxide particles is specifically as follows: Step 1, preparing La(OH)3 nanoparticles by liquid phase precipitation method; Step 2, preparing La(OH)3@Ni(OH)3 nanoparticle core-shell precursor powder by chemical reaction induction; Step 3, obtaining La2O3@Ni nanoparticles with core-shell structure by calcination reduction method.

5. The method for preparing a 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 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 to 3 ml / min, wherein the molar ratio of the Ni element to the La element is 8 to 15%.

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

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

8. The method for preparing a high entropy alloy according to claim 4, characterized in that: The specific parameters of the laser selective melting treatment are: controlling the laser power to 250W-350W, the scanning speed to 600mm / s-1000mm / s, the scanning spacing to 0.05-0.15mm, the powder layer thickness to 0.03-0.1mm, and rotating adjacent layers by 60-70° to prepare the sample; And / or also includes preheating the substrate of the printed sample to 70-90° C. before performing laser selective melting.

9. A high entropy alloy, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

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

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