Nanometer oxide dispersion strengthened CoCrFeNi-based high-entropy alloy and preparation method thereof

Abstract

This invention belongs to the technical field of ODS high-entropy alloy preparation process, and more specifically, relates to a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy and its preparation method. The invention first prepares CoCrFeNi pre-alloyed powder using a gas atomization method, then performs high-energy ball milling with Y2O3 powder, followed by vacuum drying and spark plasma sintering to obtain the nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy. This method has advantages such as simple operation, short ball milling time, high ball milling efficiency, and high alloy powder yield. The nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy provided by this invention exhibits excellent comprehensive mechanical properties, with a yield strength of up to 1281.4 MPa, a tensile strength of up to 1379.0 MPa, and an elongation of up to 8.8%.

Description

Technical Field

[0001] This invention belongs to the field of ODS high-entropy alloy technology, and more specifically, relates to a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy and its preparation method. Background Technology

[0002] The microstructure of oxide dispersion strengthened (ODS) alloys is characterized by a large number of nano-sized oxide particles distributed within the alloy matrix. Rare earth oxide (such as Y₂O₃) dispersion strengthened alloys are a typical example of high-performance ODS alloys. These nano-oxide particles, with their high melting points and good thermal stability, effectively hinder the movement of dislocations and grain boundaries, thereby improving the material's resistance to high-temperature creep. Furthermore, the numerous interfaces formed between the nano-oxide particles and the matrix can absorb He bubbles generated during irradiation, forming He traps and significantly improving the material's radiation resistance. For example, ODS steel, as a typical oxide dispersion strengthened alloy, is considered a promising core-shell structure material due to its excellent radiation resistance and high-temperature creep resistance. However, the presence of numerous oxide particles at the grain boundaries in conventional ODS steel materials results in poor plasticity and toughness, which limits its engineering applications to some extent. Therefore, it is necessary to develop novel ODS alloy materials that combine high strength, high hardness, high plasticity, high toughness, and good machinability.

[0003] High-entropy alloys, as a novel type of metallic material, break away from the traditional design concept of alloys using one or two main metallic elements. They are a new alloy system containing at least four components, with equiatomic or near-equiatomic ratios between the components, and each component comprising 5% to 35% of the total composition. Although there are many components, the resulting high-entropy alloys have relatively simple structures, generally simple face-centered cubic or body-centered cubic solid solutions. Due to their unique composition and structural characteristics, high-entropy alloys possess a series of excellent properties, such as high strength, high toughness, high corrosion resistance, good thermal stability, and radiation resistance. However, single-phase high-entropy alloys also have significant shortcomings: high-entropy alloys with an FCC solid solution structure have excellent toughness but low yield strength; while high-entropy alloys with a BCC solid solution structure have high strength but poor plasticity. Therefore, improving their comprehensive mechanical properties is key to the widespread application of high-entropy alloys.

[0004] Introducing oxide particles is an effective method to improve the mechanical properties of high-entropy alloys. Currently, some researchers have used mechanical alloying to introduce oxide particles such as Al2O3 and Y2O3 into high-entropy alloys to enhance their strength. For example, patent document CN106435323A uses a FeCoNiCr high-entropy alloy as the matrix and a combination of Ti and Y2O3 as oxide particles. This is achieved by mixing pure Fe powder, Co powder, Ni powder, Cr powder with Ti powder and Y2O3 powder, followed by ball milling (50-80 hours), SPS sintering, and other treatments to obtain an oxide dispersion-strengthened ODS high-entropy alloy.

[0005] However, traditional mechanical alloying mostly uses pure metal powders and oxide powders of various elements as raw materials for high-energy ball milling, which usually requires more than 50 hours of milling. This prolonged milling not only leads to low powder production efficiency but also easily introduces other impurities, causing powder contamination. Simultaneously, during high-energy ball milling, phenomena such as powder cold welding and adhesion, ball sticking, or can sticking are prone to occur, which are detrimental to mechanical alloying, resulting in low milling efficiency, poor milling effect, and low powder yield. Furthermore, the resulting oxide dispersion-strengthened high-entropy alloy materials are prone to severe segregation, uneven composition, large oxide particle size, and large brittle phase size, thus affecting the mechanical properties of the high-entropy alloy. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy and its preparation method. This invention solves problems encountered in the preparation of nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloys, such as powder cold welding adhesion, ball or can adhesion, long ball milling time, low powder yield, poor ball milling effect, severe segregation, uneven composition, excessively large grain size of the CoCrFeNi matrix, easy formation of large brittle phases, and large oxide particle size and low number density.

[0007] To achieve the above objectives, this invention provides a method for preparing a CoCrFeNi-based high-entropy alloy strengthened by nano-oxide dispersion, comprising the following steps:

[0008] S1: Mix raw materials Co, Cr, Fe and Ni and perform vacuum melting and atomization to obtain CoCrFeNi pre-alloyed powder;

[0009] S2: The CoCrFeNi pre-alloyed powder and Y2O3 powder are mixed and ball-milled to obtain alloy powder;

[0010] S3: The alloy powder is subjected to vacuum drying and spark plasma sintering to obtain a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy.

[0011] Preferably, step S1 specifically involves: vacuum melting Co, Cr, Fe, and Ni into an alloy liquid, and then introducing an atomizing gas for atomization powdering to obtain CoCrFeNi pre-alloyed powder; wherein the atomizing gas is any one of inert gases with a purity of 99.999%, and the pressure of the atomizing gas is 2MPa to 8MPa.

[0012] Preferably, the atomic ratio of Co, Cr, Fe, and Ni in the CoCrFeNi pre-alloyed powder is 1:1:1:1; and the particle size of the CoCrFeNi pre-alloyed powder is 15μm to 53μm.

[0013] Preferably, step S2 specifically involves: mixing the CoCrFeNi pre-alloyed powder and the Y2O3 powder as the powder to be ball-milled, and ball-milling the powder to be ball-milled by adding a process control agent and stainless steel grinding balls under a protective atmosphere.

[0014] Preferably, in step S2, the particle size of the Y2O3 powder is 30nm to 50nm; and the purity of the Y2O3 powder is greater than 99.99%.

[0015] Preferably, in step S2, the mass ratio of the CoCrFeNi pre-alloyed powder to the Y2O3 powder is (98-99.5):1.

[0016] Preferably, in step S2, the mass ratio of the stainless steel grinding balls to the powder to be ball-milled is (8-12):1; the process control agent is anhydrous ethanol, and the amount of anhydrous ethanol added is 1.5 wt.% to 2.5 wt.% of the powder to be ball-milled; the ball milling speed is 330 r / min to 350 r / min, and the milling is stopped for 0.5 h to 1.5 h every 2 h to 4 h, with a total milling time of 25 h to 35 h.

[0017] Preferably, the stainless steel grinding balls include small grinding balls with a diameter of 4mm to 8mm and large grinding balls with a diameter of 10mm to 12mm, and the ratio of the number of small grinding balls to the number of large grinding balls is (3 to 3.5):(1 to 1.2).

[0018] Preferably, the ratio of the small grinding balls to the large grinding balls is 3:1.

[0019] Preferably, in step S3, the vacuum drying temperature is 90℃~100℃ and the time is 24h~36h; the heating rate of the discharge plasma sintering is 90℃ / min~120℃ / min, the sintering temperature is 900℃~1000℃, the sintering pressure is 40MPa~60MPa, the holding time is 5min~10min, and after cooling, a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy is obtained.

[0020] According to another aspect of the present invention, a nano-oxide dispersion-reinforced CoCrFeNi-based high-entropy alloy prepared according to the preparation method is also provided.

[0021] In general, compared with the prior art, the above-described technical solutions conceived by this invention can achieve at least the following beneficial effects:

[0022] (1) The preparation method of the nano-oxide dispersion-reinforced CoCrFeNi-based high-entropy alloy provided by this invention involves preparing CoCrFeNi pre-alloyed powder by gas atomization, followed by high-energy ball milling, vacuum drying, and spark plasma sintering with Y2O3 powder to obtain a bulk alloy, namely, the nano-oxide dispersion-reinforced CoCrFeNi-based high-entropy alloy. The nano-oxide dispersion-reinforced CoCrFeNi-based high-entropy alloy provided by this invention has excellent comprehensive mechanical properties, with a yield strength of up to 1281.4 MPa, a tensile strength of up to 1379.0 MPa, and an elongation of up to 8.8%, and is expected to be applied in high-tech fields such as aerospace, metallurgy, chemical industry, and power energy. Meanwhile, the preparation method provided by this invention has the advantages of simple operation, short ball milling time, high ball milling efficiency, and high powder yield, and can be used for large-scale production.

[0023] (2) Compared with the traditional process of ball milling pure Fe powder, Co powder, Ni powder, Cr powder and Y2O3 powder for a long time, the present invention first uses gas atomization to prepare CoCrFeNi pre-alloyed powder, and then performs high-energy ball milling and other treatments with Y2O3 powder. First, the present invention eliminates the process of solid solution of four elements Co, Cr, Fe and Ni to obtain a high-entropy alloy matrix, shortens the ball milling time, improves the ball milling efficiency, and improves the chemical homogeneity of CoCrFeNi-based high-entropy alloy. Second, it avoids phenomena such as cold welding adhesion, ball sticking or can sticking during the ball milling process, which are not conducive to mechanical alloying, thereby improving the ball milling powder yield. Third, it avoids the formation of large-size brittle phase (Cr-Fe brittle phase), effectively reduces the size and number of brittle phases in the bulk alloy, thereby improving the plasticity of the bulk alloy. Fourth, it is conducive to the mechanical alloying process during ball milling, so that Y2O3 particles can be fully dissolved in the high-entropy alloy matrix powder, avoiding severe segregation, uneven composition and large oxide particle size in the obtained bulk alloy. Specifically, the ball milling time used in this invention is 25h to 35h, and the ball milling powder yield can reach 85%. The brittle phase in the final nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy is uniformly distributed and the size can reach the nanoscale; the dispersion-strengthened phase (Y2O3 spherical particles) is uniformly distributed and the size is less than 20nm.

[0024] (3) In this invention, Y2O3 powder is directly added as Y source and O source, which can accurately control the ratio of each element to a certain extent and avoid the excessive O element forming other metal oxide particles (such as CrO2) in the matrix, resulting in the size and distribution of the dispersion strengthening phase not reaching the ideal level.

[0025] (4) By adjusting the ball milling method and rotation speed, this invention can synergistically control the powder yield, grain size of the bulk alloy matrix, brittle phase size, and distribution, number density, and size of Y2O3 spherical particles, thereby preparing a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy with high strength and certain plasticity. For example, the optimized ball milling speed of this invention is 330 r / min to 350 r / min, avoiding severe cold welding, sticking to the can, and sticking of balls caused by excessive ball milling speed, which would lead to a low powder yield of alloy powder; if the ball milling speed is too low, it may lead to insufficient mechanical alloying, resulting in uneven composition of the oxide dispersion-strengthened high-entropy alloy material, insufficient solid solution of Y and O, resulting in excessively large grain size, brittle phase size, and Y2O3 spherical particle size of the bulk alloy matrix, which would affect the mechanical properties of the high-entropy alloy. The weighted average grain size of the matrix in the nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy prepared by this invention is 700 nm to 1000 nm, the brittle phase size is 150 nm to 300 nm, and the Y₂O₃ spherical particles have a size of less than 20 nm and a number density of 4.1 × 10⁻⁶. 22 ~4.5×10 22 And they are mostly evenly distributed inside the CoCrFeNi matrix grains. Attached Figure Description

[0026] Figure 1 This is a flowchart of the preparation method of the nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy provided in the embodiments of the present invention;

[0027] Figure 2 The XRD pattern of the alloy powder prepared in Example 1 is shown below.

[0028] Figure 3 These are SEM images of the bulk alloy prepared in Example 1;

[0029] Figure 4 These are high-resolution images and FFT electron diffraction patterns of the bulk alloy prepared in Example 1, wherein content (a) is a high-resolution image of the bulk alloy prepared in Example 1, and content (b) is an FFT electron diffraction pattern of the bulk alloy prepared in Example 1.

[0030] Figure 5 The XRD pattern of the alloy powder prepared in Comparative Example 1 is shown.

[0031] Figure 6 This is a SEM image of the bulk alloy prepared in Comparative Example 1;

[0032] Figure 7 The images show the high-resolution image and FFT electron diffraction pattern of the bulk alloy prepared in Comparative Example 2. Content (a) is the high-resolution image of the bulk alloy prepared in Comparative Example 2, and content (b) is the FFT electron diffraction pattern of the bulk alloy prepared in Comparative Example 2. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] like Figure 1 As shown, this invention provides a method for preparing a CoCrFeNi-based high-entropy alloy strengthened by nano-oxide dispersion, comprising the following steps:

[0035] S1: Mix the metals Co, Cr, Fe and Ni and then perform vacuum melting and atomization to obtain CoCrFeNi pre-alloyed powder;

[0036] S2: The CoCrFeNi pre-alloyed powder and Y2O3 powder are mixed and ball-milled to obtain alloy powder;

[0037] S3: The alloy powder is subjected to vacuum drying and spark plasma sintering to obtain a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy.

[0038] In some embodiments, step S1 includes the following steps:

[0039] Ingredients:

[0040] The raw material metals Co, Cr, Fe, and Ni are formulated according to the atomic ratio of Co, Cr, Fe, and Ni in the CoCrFeNi pre-alloyed powder being 1:1:1:1.

[0041] In some embodiments, the raw materials cobalt blocks, chromium blocks, iron blocks, and nickel blocks are polished to remove surface oxide scale, ultrasonically cleaned in anhydrous ethanol, and dried to ensure the high purity of each raw material. Preferably, the purity of the cobalt blocks, chromium blocks, iron blocks, and nickel blocks used in the embodiments of the present invention is greater than 99.9%.

[0042] Preparation of CoCrFeNi pre-alloyed powder:

[0043] This application does not limit the process for preparing CoCrFeNi pre-alloyed powder. In some embodiments, the process for preparing CoCrFeNi pre-alloyed powder can be as follows: vacuum melting prepared cobalt blocks, chromium blocks, iron blocks, and nickel blocks into an alloy liquid, and then introducing atomizing gas for atomization powder preparation to obtain CoCrFeNi pre-alloyed powder.

[0044] In some embodiments, the above-mentioned process for preparing CoCrFeNi pre-alloyed powder may also be as follows: vacuum melting prepared cobalt blocks, chromium blocks, iron blocks, and nickel blocks into a CoCrFeNi high-entropy master alloy, and then vacuum melting and gas atomization treatment of the high-entropy master alloy to obtain CoCrFeNi pre-alloyed powder.

[0045] In a specific embodiment of this application, the process for preparing CoCrFeNi pre-alloyed powder is as follows: the prepared cobalt block, chromium block, iron block, and nickel block are placed in a vacuum melting furnace, a vacuum is drawn and a protective gas is introduced, vacuum induction melting is performed and the temperature is maintained for a period of time. After the powder is fully melted, atomizing gas at a certain pressure is introduced to atomize and powder the powder, thereby obtaining CoCrFeNi pre-alloyed powder.

[0046] In some embodiments, the melting overheating is 180°C to 220°C, and the holding time is 20 to 30 minutes. The purpose is to ensure that the metal block is completely melted, so that the molten metal is fully mixed and melted into an alloy liquid with qualified composition.

[0047] In some embodiments, during the atomization process described above, the atomizing gas is any one of inert gases with a purity of 99.999%, including but not limited to nitrogen and argon; the pressure of the atomizing gas is 2MPa to 8MPa, which can effectively protect the raw material metal from oxidation and effectively prevent the raw material from evaporating while ensuring that the raw material is fully melted, thereby ensuring the performance of CoCrFeNi pre-alloying.

[0048] In some embodiments, the particle size of the CoCrFeNi pre-alloyed powder is 15 μm to 53 μm.

[0049] In some embodiments, step S2 includes the following steps:

[0050] The CoCrFeNi pre-alloyed powder and Y2O3 powder were mixed in a specific ratio. The mixed powder was used as the powder to be ball-milled. A process control agent and stainless steel grinding balls were added under a protective atmosphere to ball-mill the powder.

[0051] This application uses CoCrFeNi pre-alloyed powder and Y2O3 powder as ball milling raw materials. CoCrFeNi pre-alloyed powder is a high-entropy alloy powder. Compared with pure metal powders Co, Cr, Fe, and Ni, using pre-alloyed powder can directly skip the process of mutual solid solution of the four elements Co, Cr, Fe, and Ni, greatly reducing the required ball milling time and avoiding severe cold welding due to excessive ball milling time. This greatly improves ball milling efficiency and powder yield, while also allowing Y and O elements to be better dissolved in the matrix of the high-entropy alloy powder.

[0052] In some embodiments, the purity of the Y2O3 powder is 99.99%, and the particle size is 30nm to 50nm.

[0053] In some embodiments, the mass ratio of the CoCrFeNi pre-alloyed powder to the Y2O3 powder is (98-99.5):1. When the mass ratio is too large, the amount of Y2O3 added is too high, making it difficult to fully disperse and distribute evenly during high-energy ball milling, resulting in a significant increase in the required ball milling time. Simultaneously, excessively high Y content also leads to a significant increase in the size of the formed Y2O3 and agglomeration, severely affecting the dispersion strengthening effect. When the mass ratio is too small, the amount of Y2O3 powder added is limited, and the oxide dispersion strengthening effect is not obvious.

[0054] In some embodiments, the process control agent is anhydrous ethanol. Preferably, the purity of the anhydrous ethanol is greater than 99.7%, and its addition amount is 1.5 wt.% to 2.5 wt.% of the powder to be ball-milled.

[0055] In some embodiments, the mass ratio of the stainless steel grinding balls to the powder to be ball-milled is (8-12):1.

[0056] In some embodiments, the stainless steel grinding balls are composed of a mixture of small grinding balls with a diameter of 4 mm to 8 mm and large grinding balls with a diameter of 10 mm to 12 nm; preferably, the ratio of the number of small grinding balls to the number of large grinding balls is (3 to 3.5):(1 to 1.2). More preferably, the ratio of the number of small grinding balls to the number of large grinding balls is 3:1.

[0057] This invention designs ball milling conditions based on the mass ratio and other characteristics of CoCrFeNi pre-alloyed powder and Y2O3 powder. In some embodiments, the ball milling speed is 330 r / min to 350 r / min. If the ball milling speed is too low, it becomes difficult for Y and O elements to dissolve into the high-entropy alloy matrix powder, reducing the number density and dispersion effect of Y2O3 spherical particles in the high-entropy alloy matrix, resulting in an unsatisfactory oxide dispersion strengthening effect. If the ball milling speed is too high, severe cold welding, sticking to the container, and ball sticking are easily caused during the ball milling process, leading to a low powder yield.

[0058] In some embodiments, this application employs intermittent ball milling, specifically, milling for 2-4 hours followed by a 0.5-1.5 hour pause, for a total milling time of 25-35 hours. Preferably, milling for 2.5-3.5 hours followed by a 0.5-1.5 hour pause. This is because after a period of high-energy ball milling, the powder temperature rises, making it prone to phenomena such as cold welding, ball sticking, or can sticking, which are detrimental to mechanical alloying, thus affecting milling efficiency and reducing powder yield.

[0059] In some embodiments, step S3 includes the following steps:

[0060] The above alloy powder was vacuum dried, and then the dried alloy powder was subjected to spark plasma sintering to obtain a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy.

[0061] This application does not limit the vacuum drying method, temperature, and time described above. In actual operation, a suitable vacuum drying method, temperature, and time can be selected according to specific circumstances. In some embodiments, the drying is carried out in an environment with a vacuum degree of -0.1 MPa. In some embodiments, the vacuum drying temperature is 90℃~100℃, and the time is 24h~36h. In some embodiments, the heating rate of the spark plasma sintering is 90℃ / min~120℃ / min, the sintering temperature is 900℃~1000℃, the sintering pressure is 40MPa~60MPa, the holding time is 5min~10min, and after cooling to room temperature, a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy is obtained.

[0062] The present invention also provides a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy prepared by the above preparation method.

[0063] In summary, the method for preparing a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy provided by this invention involves preparing CoCrFeNi pre-alloyed powder using a gas atomization method, followed by high-energy ball milling, vacuum drying, and spark plasma sintering with Y₂O₃ powder to obtain the nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy. This invention, by adjusting the ball milling method and rotation speed, can synergistically control other parameters to regulate the powder yield, grain size of the bulk alloy matrix, brittle phase size, and the distribution, number density, and size of Y₂O₃ spherical particles, thereby preparing a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy with both high strength and a certain degree of plasticity. The nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy obtained by this invention is expected to be applied in high-tech fields such as aerospace, metallurgy, chemical engineering, and power energy.

[0064] The above technical solution will be described in detail below with reference to specific embodiments:

[0065] Example 1

[0066] 1) Preparation of CoCrFeNi pre-alloyed powder: Cobalt blocks, chromium blocks, iron blocks and nickel blocks were prepared according to the atomic ratio of Co, Cr, Fe and Ni in CoCrFeNi pre-alloyed powder of 1:1:1:1. The purity of cobalt blocks, chromium blocks, iron blocks and nickel blocks was all above 99.9%. The prepared cobalt, chromium, iron, and nickel blocks were placed in a vacuum induction melting furnace. After evacuating to 0.1 Pa, 99.999% pure argon gas was introduced to achieve a slightly negative pressure state inside the furnace. The metal blocks were heated until they melted, and then the heating was continued until the superheat was about 200°C to ensure that the molten metal was fully mixed and homogeneous. After holding at this temperature for 20 minutes, the atomizing gas valve was opened, and 99.999% pure argon gas at a pressure of 4 MPa was introduced. The molten metal was then poured into the guide tube through an intermediate ladle for atomization. After atomization, the mixture was cooled for 1 hour, and the powder was removed. CoCrFeNi pre-alloyed powder with a particle size of 15 μm to 53 μm was screened out.

[0067] 2) Mechanical alloying of powder: The above-mentioned CoCrFeNi pre-alloyed powder was mixed with Y2O3 powder with a purity of 99.99% and a particle size of 30nm-50nm at a mass ratio of 99:1. 40g of the prepared powder, stainless steel grinding balls, and anhydrous ethanol with a purity of 99.7% or higher were loaded into the grinding jar of a planetary ball mill. After sealing the grinding jar, a vacuum was applied and argon gas was introduced as a protective gas. High-energy ball milling was then performed to prepare the alloy powder. The stainless steel grinding balls were composed of a mixture of two different diameters: 10mm and 6mm, with a small to large grinding ball ratio of 3:1. The mass of the stainless steel grinding balls was 10 times the total mass of the powder to be milled. The amount of anhydrous ethanol added was 2.0 wt.% of the total mass of the powder to be milled. The planetary ball mill rotated at 350 r / min, and the mill was stopped for 1 hour after every 3 hours of operation, for a total milling time of 30 hours.

[0068] The alloy powder was collected and weighed, and the powder yield of Example 1 was calculated to be over 75%.

[0069] 3) Vacuum drying of alloy powder: The above alloy powder is placed in a vacuum drying oven for drying at a temperature of 95℃ for 24 hours.

[0070] The alloy powder was analyzed using a Bruker D8 advance X-ray diffractometer (XRD) from Bruker GmbH, Germany. This instrument uses Cu-Kα as the X-ray source. Figure 2 As shown, the matrix of the alloy powder is a CoCrFeNi single-phase high-entropy alloy with an FCC structure.

[0071] 4) Discharge plasma sintering: The dried alloy powder is placed in a graphite mold for vacuum discharge plasma sintering. The heating rate is 100℃ / min, the sintering temperature is 950℃, the sintering pressure is kept constant at 50MPa, and after holding at that temperature for 5min, it is cooled to room temperature in the furnace to obtain a bulk alloy, which is a nano-oxide dispersion strengthened CoCrFeNi-based high-entropy alloy.

[0072] The bulk alloy was examined using a scanning electron microscope (SEM), such as... Figure 3 As shown, a small number of small-sized (150nm~300nm) and uniformly distributed σ phases (a brittle phase rich in Cr-Fe) can be observed. The weighted average grain size of the matrix in the bulk alloy is 717.4nm. The fine grain size of the matrix can improve the strength and plasticity of the bulk alloy.

[0073] The bulk alloy was examined using transmission electron microscopy (TEM), such as... Figure 4 As shown, Figure 4 Content (a) shows that spherical particles with a size of less than 10 nm are uniformly distributed in the CoCrFeNi high-entropy alloy matrix. Figure 4 Content (b) indicates that the precipitated nanospheres are Y2O3.

[0074] In the bulk alloy, spherical Y₂O₃ particles are mostly distributed within the CoCrFeNi matrix grains, with a number density of 4.5 × 10⁻⁶. 22 Spherical Y2O3 particles can enhance the strength of bulk alloys through the strengthening effect of the second phase.

[0075] The room temperature tensile properties of the bulk alloy were tested, and its yield strength was 1281.4 MPa, tensile strength was 1379.0 MPa, and elongation was 6.3%.

[0076] Example 2

[0077] 1) Preparation of CoCrFeNi pre-alloyed powder: Cobalt blocks, chromium blocks, iron blocks and nickel blocks were prepared according to the atomic ratio of Co, Cr, Fe and Ni in CoCrFeNi pre-alloyed powder of 1:1:1:1. The purity of cobalt blocks, chromium blocks, iron blocks and nickel blocks was all above 99.9%. The prepared cobalt, chromium, iron, and nickel blocks were placed in a vacuum induction melting furnace. After evacuating to 0.1 Pa, 99.999% pure argon gas was introduced to achieve a slightly negative pressure state inside the furnace. The metal blocks were heated until they melted, and then the heating was continued until the superheat was about 200°C to ensure that the molten metal was fully mixed and homogeneous. After holding at this temperature for 20 minutes, the atomizing gas valve was opened, and 99.999% pure argon gas at a pressure of 4 MPa was introduced. The molten metal was then poured into the guide tube through an intermediate ladle for atomization. After atomization, the mixture was cooled for 1 hour, and the metal powder was removed. CoCrFeNi pre-alloyed powder with a particle size of 15 μm to 53 μm was screened out.

[0078] 2) Mechanical alloying of powder: The above-mentioned CoCrFeNi pre-alloyed powder was mixed with Y2O3 powder with a purity of 99.99% and a particle size of 30nm-50nm at a mass ratio of 99:1. 40g of the prepared powder, stainless steel grinding balls, and anhydrous ethanol with a purity of 99.7% or higher were loaded into the grinding jar of a planetary ball mill. After sealing the grinding jar, a vacuum was applied and argon gas was introduced as a protective gas. High-energy ball milling was then performed to prepare the alloy powder. The stainless steel grinding balls were composed of a mixture of two different diameters: 10mm and 6mm, with a small to large grinding ball ratio of 3:1. The mass of the stainless steel grinding balls was 10 times the total mass of the powder to be milled. The amount of anhydrous ethanol added was 2.0 wt.% of the total mass of the powder to be milled. The planetary ball mill rotated at 330 r / min, and the mill was stopped for 1 hour after every 3 hours of operation, for a total milling time of 30 hours.

[0079] The alloy powder was collected and weighed, and the powder yield of Example 2 was calculated to be above 85%.

[0080] 3) Vacuum drying of alloy powder: The above alloy powder is placed in a vacuum drying oven for drying at a temperature of 95℃ for 24 hours.

[0081] The alloy powder was analyzed using a Bruker D8 advance X-ray diffractometer (XRD) from Bruker GmbH, Germany, with Cu-Kα as the X-ray source. The results showed that the matrix of the alloy powder was a single-phase high-entropy CoCrFeNi alloy with an FCC structure.

[0082] 4) Discharge plasma sintering: The dried alloy powder is placed in a graphite mold for vacuum discharge plasma sintering. The heating rate is 100℃ / min, the sintering temperature is 950℃, the sintering pressure is kept constant at 50MPa, and the furnace is cooled to room temperature after holding for 5 minutes to obtain a bulk alloy.

[0083] Transmission electron microscopy (TEM) was used to examine the bulk alloy, revealing the presence of spherical Y₂O₃ particles with sizes ranging from 15 nm to 20 nm within the CoCrFeNi high-entropy alloy matrix. The number density of these spherical Y₂O₃ particles in the bulk alloy was 4.1 × 10⁻⁶. 22 .

[0084] The room temperature tensile properties of the bulk alloy were tested, and its yield strength was 1226.8 MPa, tensile strength was 1266.1 MPa, and elongation was 8.8%.

[0085] Comparative Example 1

[0086] This comparative example uses a traditional mechanical alloying method to prepare a nano-oxide dispersion-reinforced CoCrFeNi-based high-entropy alloy. The raw materials used are pure metal powders of Co, Cr, Fe, and Ni, and Y₂O₃ powder. The specific steps are as follows:

[0087] 1) Raw material powder formulation: Co powder, Cr powder, Fe powder, Ni powder and Y2O3 powder are formulated in a mass ratio of 25.9:22.8:24.5:25.8:1. The purity of Co powder and Cr powder is above 99.5%, the purity of Fe powder and Ni powder is above 99.9%, and the purity of Y2O3 powder is above 99.99%. The particle size of Co powder, Cr powder and Fe powder is 20μm to 50μm, the particle size of Ni powder is 15μm to 53μm, and the particle size of Y2O3 powder is 30nm to 50nm.

[0088] 2) Mechanical alloying of raw material powder: 40g of prepared powder, stainless steel grinding balls, and anhydrous ethanol with a purity of 99.7% or higher were loaded into the grinding jar of a planetary ball mill. After sealing the grinding jar, a vacuum was drawn and argon gas was introduced as a protective gas. Then, high-energy ball milling was performed to prepare alloy powder. The stainless steel grinding balls were composed of a mixture of two different diameters: 10mm and 6mm, with a ratio of small to large grinding balls of 3:1. The mass of the stainless steel grinding balls was 10 times the total mass of the powder to be milled. The amount of anhydrous ethanol added was 2.0 wt.% of the total mass of the powder to be milled. The planetary ball mill rotated at 350 r / min, and the mill was stopped for 1 hour after every 3 hours of operation, for a total milling time of 30 hours.

[0089] The alloy powder was collected and weighed, and the powder yield of Comparative Example 1 was calculated to be approximately 60%, which was significantly lower than that of Example 1 and Example 2.

[0090] 3) Drying of alloy powder: The above alloy powder is placed in a vacuum drying oven for drying at a temperature of 95℃ for 24 hours.

[0091] The alloy powder was analyzed using a Bruker D8 advance X-ray diffractometer (XRD) from Bruker GmbH, Germany. This instrument uses Cu-Kα as the X-ray source. Figure 5 As shown in the XRD pattern, the matrix of the alloy powder prepared in Comparative Example 1 contains both FCC and BCC structures. This indicates that the mechanical alloying method in Comparative Example 1 is not sufficient and fails to directly transform the elemental powder into high-entropy alloy powder through ball milling.

[0092] 4) Discharge plasma sintering: The dried alloy powder is placed in a graphite mold for vacuum discharge plasma sintering. The heating rate is 100℃ / min, the sintering temperature is 950℃, the sintering pressure is kept constant at 50MPa, and the furnace is cooled to room temperature after holding for 5 minutes to obtain a bulk alloy.

[0093] The bulk alloy was examined using a scanning electron microscope (SEM), such as... Figure 6 As shown, the σ phase in the bulk alloy is relatively large, approximately 1 μm to 2 μm in size, and its distribution is uneven. Combined with... Figure 3 and Figure 6 It can be seen that the size of the σ phase in the bulk alloy prepared in Comparative Example 1 is significantly larger than that in Example 1, and the uniformity of the σ phase distribution is significantly lower than that in Example 1.

[0094] Transmission electron microscopy (TEM) was used to examine the bulk alloy, revealing the presence of spherical Y₂O₃ particles with sizes ranging from 25 nm to 35 nm within the CoCrFeNi high-entropy alloy matrix. The number density of these spherical Y₂O₃ particles in the bulk alloy was 1.1 × 10⁻⁶. 22 .

[0095] The room temperature tensile properties of the bulk alloy were tested, and its yield strength was 1157.1 MPa and tensile strength was 1165.9 MPa. However, the alloy did not exhibit a plastic deformation stage, indicating that the bulk alloy had almost no plasticity. The reason for this may be that the mechanical alloying method used in Comparative Example 1 was insufficient, resulting in uneven composition of the alloy powder obtained after ball milling. This led to an excessive amount of large-sized hard and brittle σ phases in the bulk alloy, which severely affected its plasticity.

[0096] Comparative Example 2

[0097] 1) Preparation of CoCrFeNi pre-alloyed powder: Cobalt blocks, chromium blocks, iron blocks and nickel blocks were prepared according to the atomic ratio of Co, Cr, Fe and Ni in CoCrFeNi pre-alloyed powder of 1:1:1:1. The purity of cobalt blocks, chromium blocks, iron blocks and nickel blocks was all above 99.9%. The prepared cobalt, chromium, iron, and nickel blocks were placed in a vacuum induction melting furnace. After evacuating to 0.1 Pa, 99.999% pure argon gas was introduced to achieve a slightly negative pressure state inside the furnace. The metal blocks were heated until they melted, and then the heating was continued until the superheat was about 200°C to ensure that the molten metal was fully mixed and homogeneous. After holding at this temperature for 20 minutes, the atomizing gas valve was opened, and 99.999% pure argon gas at a pressure of 4 MPa was introduced. The molten metal was then poured into the guide tube through an intermediate ladle for atomization. After atomization, the mixture was cooled for 1 hour, and the metal powder was removed. CoCrFeNi pre-alloyed powder with a particle size of 15 μm to 53 μm was screened out.

[0098] 2) Mechanical alloying of powder: The above-mentioned CoCrFeNi pre-alloyed powder was mixed with Y2O3 powder with a purity of 99.99% and a particle size of 30nm-50nm at a mass ratio of 99:1. 40g of the prepared powder, stainless steel grinding balls, and anhydrous ethanol with a purity of 99.7% or higher were loaded into the grinding jar of a planetary ball mill. After sealing the grinding jar, a vacuum was applied and argon gas was introduced as a protective gas. High-energy ball milling was then performed to prepare the alloy powder. The stainless steel grinding balls were composed of a mixture of two different diameters: 10mm and 6mm, with a small to large grinding ball ratio of 3:1. The mass of the stainless steel grinding balls was 10 times the total mass of the powder to be milled. The amount of anhydrous ethanol added was 2.0 wt.% of the total mass of the powder to be milled. The planetary ball mill operated at a speed of 300 r / min, running for 3 hours and then stopping for 1 hour, for a total milling time of 30 hours.

[0099] The alloy powder was collected and weighed, and the powder yield of Comparative Example 2 was calculated to be over 90%.

[0100] 3) Vacuum drying of alloy powder: The above alloy powder is placed in a vacuum drying oven for drying at a temperature of 95℃ for 24 hours.

[0101] The alloy powder was analyzed using a Bruker D8 advance X-ray diffractometer (XRD) from Bruker GmbH, Germany, with Cu-Kα as the X-ray source. The results showed that the matrix of the alloy powder was a single-phase CoCrFeNi high-entropy alloy with an FCC structure.

[0102] 4) Discharge plasma sintering: The dried alloy powder is placed in a graphite mold for vacuum discharge plasma sintering. The heating rate is 100℃ / min, the sintering temperature is 950℃, the sintering pressure is kept constant at 50MPa, and the furnace is cooled to room temperature after holding for 5 minutes to obtain a bulk alloy.

[0103] Scanning electron microscopy (SEM) was used to examine the bulk alloy, revealing a small number of uniformly distributed, small-sized (150 nm–300 nm) σ phases. The weighted average grain size of the bulk alloy matrix was 1.1 μm, significantly larger than that of Example 1.

[0104] The bulk alloy was examined using transmission electron microscopy (TEM), such as... Figure 7 As shown, Figure 7 Content (a) shows that spherical particles with a size of 15 nm to 25 nm are distributed in the CoCrFeNi high-entropy alloy matrix. Figure 7 Content (b) indicates that the precipitated nanoparticles are Y₂O₃. The number density of spherical Y₂O₃ particles in the bulk alloy is 1.3 × 10⁻⁶. 22 It is significantly smaller than that in Example 1.

[0105] The room temperature tensile properties of the bulk alloy were tested, and its yield strength was 841.3 MPa, tensile strength was 922.5 MPa, and elongation was 5.8%.

[0106] Compared to Example 1, the strength of the bulk alloy prepared in Comparative Example 2 was significantly reduced. The grain size and number density of the second-phase oxide particles in the bulk alloy matrix prepared at a lower rotation speed (300 r / min) were significantly different from those in Example 1, resulting in a significantly lower strength for the prepared bulk alloy compared to Example 1.

[0107] In summary, the bulk alloys obtained in Examples 1 and 2 of this application all have a yield strength greater than or equal to 1226.8 MPa, with a maximum of 1281.4 MPa; a tensile strength greater than or equal to 1266.1 MPa, with a maximum of 1379.0 MPa; and an elongation greater than or equal to 6.3%, with a maximum of 8.8%. Moreover, they exhibit a significant plastic deformation stage before fracture. The bulk alloys obtained in Examples 1 and 2 of this application have comparable strength and plasticity, and both possess excellent comprehensive mechanical properties.

[0108] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nano-oxide dispersion-reinforced CoCrFeNi-based high-entropy alloy, characterized in that, Includes the following steps: S1: Mix raw materials Co, Cr, Fe and Ni and perform vacuum melting and atomization to obtain CoCrFeNi pre-alloyed powder; S2: The CoCrFeNi pre-alloyed powder and Y2O3 powder are mixed and ball-milled to obtain alloy powder; The CoCrFeNi pre-alloyed powder has a particle size of 15μm~53μm; the Y2O3 powder has a particle size of 30nm~50nm; the mass ratio of the CoCrFeNi pre-alloyed powder to the Y2O3 powder is (98~99.5):1; The ball milling speed is 330 r / min to 350 r / min, and the milling is stopped for 0.5 h to 1.5 h every 2 h to 4 h, with a total milling time of 25 h to 35 h. S3: The alloy powder is subjected to vacuum drying and spark plasma sintering to obtain a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy.

2. The preparation method according to claim 1, characterized in that, Step S1 specifically involves: vacuum melting Co, Cr, Fe, and Ni into an alloy liquid, then introducing an atomizing gas for atomization powdering to obtain CoCrFeNi pre-alloyed powder; wherein the atomizing gas is any one of inert gases with a purity of 99.999%, and the pressure of the atomizing gas is 2MPa~8MPa.

3. The preparation method according to claim 1 or 2, characterized in that, The atomic ratio of Co, Cr, Fe, and Ni in the CoCrFeNi pre-alloyed powder is 1:1:1:

1.

4. The preparation method according to claim 1, characterized in that, Step S2 specifically involves mixing the CoCrFeNi pre-alloyed powder and the Y2O3 powder as the powder to be ball-milled, and ball-milling the powder under a protective atmosphere by adding a process control agent and stainless steel grinding balls.

5. The preparation method according to claim 1 or 4, characterized in that, In step S2, the purity of the Y2O3 powder is greater than 99.99%.

6. The preparation method according to claim 4, characterized in that, In step S2, the mass ratio of the stainless steel grinding ball to the powder to be ball-milled is (8~12):1; the process control agent is anhydrous ethanol, and the amount of anhydrous ethanol added is 1.5wt.%~2.5wt.% of the powder to be ball-milled.

7. The preparation method according to claim 6, characterized in that, The stainless steel grinding balls include small grinding balls with a diameter of 4mm to 8mm and large grinding balls with a diameter of 10mm to 12mm, with a ratio of (3 to 3.5):(1 to 1.2).

8. The preparation method according to claim 7, characterized in that, The ratio of the number of small grinding balls to the number of large grinding balls is 3:

1.

9. The preparation method according to claim 1, characterized in that, In step S3, the vacuum drying temperature is 90℃~100℃ and the time is 24h~36h; the heating rate of the discharge plasma sintering is 90℃ / min~120℃ / min, the sintering temperature is 900℃~1000℃, the sintering pressure is 40MPa~60MPa, and the holding time is 5min~10min. After cooling, a nano-oxide dispersion-strengthened CoCrFeNi-based high-entropy alloy is obtained.

10. A nano-oxide dispersion-reinforced CoCrFeNi-based high-entropy alloy prepared by the preparation method according to any one of claims 1 to 9.

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