CoFeNi-based medium-entropy alloys simultaneously reinforced by L12 nanoparticles and dislocations and their preparation method

Abstract

The application discloses a CoFeNi-based medium-entropy alloy which is simultaneously strengthened by L12 nanoparticles and dislocations, and the composition is (CoFeNi) 100‑x‑y‑ z Ti x Al y V z Wherein, 4.0<=x<=8.0, 4.0<=y<=8.0, 4.0<=z<=8.0; the application further discloses a preparation method of the CoFeNi-based medium-entropy alloy, specifically: arc melting the raw materials, and then sequentially performing solid solution, primary cold rolling, annealing, secondary cold rolling and aging ordering treatment on the obtained medium-entropy alloy ingot, and the high-strength CoFeNi-based medium-entropy alloy is obtained. The microstructure of the high-strength CoFeNi-based medium-entropy alloy is composed of a small amount of recrystallized regions and a large amount of unrecrystallized regions, and the two regions have high-density L12 nanoparticles, which can play a role in precipitation strengthening, and the unrecrystallized regions contain high-density dislocations, which can play a role in dislocation strengthening.

Description

Technical Field

[0001] This invention belongs to the field of medium-entropy alloy preparation technology, specifically relating to a CoFeNi-based medium-entropy alloy simultaneously strengthened by L12 nanoparticles and dislocations, and also relating to a method for preparing the CoFeNi-based medium-entropy alloy. Background Technology

[0002] High-entropy alloys and medium-entropy alloys are a new type of metallic material composed of multiple main elements. They have attracted widespread attention due to their excellent properties, especially face-centered cubic (fcc) high-entropy and medium-entropy alloys, which have drawn considerable attention from researchers due to their superior elongation, good corrosion resistance, and radiation resistance. However, the strength of fcc high-entropy or medium-entropy alloys (CoCrFeNiMn, CoCrFeNi, CoFeNi, etc.) is typically low, with yield strength usually below 400 MPa, thus limiting their industrial applications.

[0003] To improve its yield strength, researchers have employed various methods, such as solid solution strengthening, grain refinement strengthening, multiphase strengthening, precipitation strengthening, and dislocation strengthening. Among these, precipitation strengthening has shown the best results, particularly the precipitation strengthening of L12 nanoparticles, for example, by adding L12 phase-forming elements Ti and Al(CoFeNi) to CoFeNi medium-entropy alloys. 86 Al7Ti7), whose yield strength increased from 200 MPa to 1050 MPa (T. Yang, Y. Zhao, Y. Tong, Z. Jiao, J. Wei, J. Cai, X. Han, D. Chen, A. Hu, J. Kai, Science 362 (2018) 933-937); L12 phase forming elements Ti and Al ((FeCoNiCr)) were added to CoCrFeNi medium entropy alloys. 94 The yield strength of Ti2Al4 increased from 165 MPa to 1005 MPa (T. Yang, Y. Zhao, Y. Tong, Z. Jiao, J. Wei, J. Cai, X. Han, D. Chen, A. Hu, J. Kai, Science 362(2018)933-937). Although the precipitation strengthening effect of these L12 nanoparticles is good, their yield strength is still not high enough. How to further improve their yield strength to tap the maximum potential of the alloy is the main problem currently encountered. Summary of the Invention

[0004] The purpose of this invention is to provide a CoFeNi-based medium-entropy alloy that is simultaneously strengthened by L12 nanoparticles and dislocations, thus solving the problem of low yield strength in existing medium-entropy alloys.

[0005] The technical solution adopted in this invention is a CoFeNi-based medium-entropy alloy simultaneously strengthened by L12 nanoparticles and dislocations, wherein the alloy composition of the medium-entropy alloy is (CoFeNi). 100-x-y-z Ti x Al y V z The composition is as follows: 4.0≤x≤8.0, 4.0≤y≤8.0, 4.0≤z≤8.0, with Co, Fe, and Ni in equal atomic percentages; the medium-entropy alloy has an fcc matrix and an L12 phase.

[0006] Another technical solution adopted in this invention is a method for preparing a CoFeNi-based medium-entropy alloy simultaneously strengthened by L12 nanoparticles and dislocations, specifically implemented according to the following steps:

[0007] Step 1: Grind, clean, and dry the raw materials Co, Fe, Ni, Ti, Al, and V;

[0008] Step 2, according to (CoFeNi) 100-x-y-z Ti x Al y V z The composition of Co, Fe, and Ni is in equal atomic percentage, with 4.0≤x≤8.0, 4.0≤y≤8.0, and 4.0≤z≤8.0. Weigh out the elemental metal raw materials of Co, Fe, Ni, Ti, Al, and V.

[0009] Step 3: The raw materials are subjected to electric arc melting to obtain (CoFeNi). 100-x-y-z Ti x Al y V z Medium-entropy alloy ingots;

[0010] Step 4: The medium-entropy alloy ingot is subjected to solution treatment, first cold rolling, annealing, second cold rolling, and aging ordering treatment in sequence to obtain CoFeNi-based medium-entropy alloy.

[0011] The invention is further characterized in that,

[0012] Step 3 specifically includes the following steps:

[0013] Step 3.1: Place the raw materials weighed in Step 2 into the water-cooled copper crucible of the vacuum arc melting furnace, close the furnace chamber, evacuate the furnace, and then fill it with argon gas as a protective gas.

[0014] Step 3.2: Arc melt the raw materials in the water-cooled copper crucible. The melting current is 425-475A. After the raw materials are completely melted, turn on the electromagnetic stirring and keep it for 5-6 minutes. After the molten metal cools into a solid state, the first ingot is obtained.

[0015] Step 3.3: Turn the initial ingot over in a water-cooled copper crucible and repeat the electric arc melting process of Step 3.2 four times to obtain a button-shaped (CoFeNi) with uniform microstructure. 100-x-y-z Ti x Al y V z Medium-entropy alloy ingots.

[0016] In step 4, during the solution treatment, the treatment temperature is 1150℃~1200℃, and the holding time is 12h-48h.

[0017] In step 4, the thinning rate of a single cold rolling operation is 60% to 80%.

[0018] In step 4, the annealing temperature is 900℃~1050℃, and the time is 3~60min; the thinning rate of the second cold rolling is 0-15%.

[0019] If the annealing temperature is higher than 980℃, it is high-temperature annealing, which requires secondary cold rolling to provide dislocations; if the annealing temperature is lower than 980℃, the thinning rate of secondary cold rolling is 0, that is, secondary cold rolling is not required.

[0020] In step 4, during the time-ordered aging process: the aging temperature is 600℃~800℃, and the aging time is 0.5~24h.

[0021] The beneficial effects of this invention are as follows: The high-strength CoFeNi-based medium-entropy alloy with simultaneous L12 nanoparticle and dislocation strengthening prepared by this invention has a microstructure composed of a small amount of recrystallized regions and a large amount of non-recrystallized regions (i.e., deformed regions, with a volume fraction of more than 80% to ensure high-density dislocations). Both regions have high-density L12 nanoparticles, which can play a precipitation strengthening role (Ti, Al, and V are L12 phase forming elements, which are conducive to the formation of L12 phase, and the lattice defects caused by cold rolling promote the precipitation of L12 nanoparticles during the later aging process). Moreover, the non-recrystallized regions (i.e., deformed regions) contain high-density dislocations, which can play a dislocation strengthening role, thereby improving the yield strength of the medium-entropy alloy. Attached Figure Description

[0022] Figure 1 The (CoFeNi) value is calculated using JMatPro software in this invention. 82 Solidification path diagram of Ti5Al5V8 medium entropy alloy;

[0023] Figure 2a The (CoFeNi) in Embodiments 1, 2, and Comparative Example 1 of this invention. 82 XRD pattern of Ti5Al5V8 medium entropy alloy;

[0024] Figure 2bThis is (CoFeNi) in Comparative Example 1 of the present invention. 82 Peak fitting diagram of (311) crystal plane diffraction peaks of Ti5Al5V8 medium entropy alloy;

[0025] Figure 2c It is (CoFeNi) in Embodiment 2 of the present invention. 82 Peak fitting diagram of (311) crystal plane diffraction peaks of Ti5Al5V8 medium entropy alloy;

[0026] Figure 2d It is (CoFeNi) in Embodiment 1 of the present invention. 82 Peak fitting diagram of (311) crystal plane diffraction peaks of Ti5Al5V8 medium entropy alloy;

[0027] Figure 3a It is (CoFeNi) in Embodiment 1 of the present invention. 82 OM diagram of Ti5Al5V8 medium entropy alloy;

[0028] Figure 3b It is (CoFeNi) in Embodiment 1 of the present invention. 82 SEM images of Ti5Al5V8 medium entropy alloy (I);

[0029] Figure 3c It is (CoFeNi) in Embodiment 1 of the present invention. 82 SEM images of Ti5Al5V8 medium entropy alloy (II);

[0030] Figure 4a It is (CoFeNi) in Embodiment 1 of the present invention. 82 KAM diagram of Ti5Al5V8 medium entropy alloy;

[0031] Figure 4b It is (CoFeNi) in Embodiment 2 of the present invention. 82 KAM diagram of Ti5Al5V8 medium entropy alloy;

[0032] Figure 4c This is (CoFeNi) in Comparative Example 1 of the present invention. 82 KAM diagram of Ti5Al5V8 medium entropy alloy;

[0033] Figure 4d It is (CoFeNi) in Embodiment 1 of the present invention. 82 KAM value of Ti5Al5V8 medium entropy alloy;

[0034] Figure 4e It is (CoFeNi) in Embodiment 2 of the present invention. 82 KAM value of Ti5Al5V8 medium entropy alloy;

[0035] Figure 4fThis is (CoFeNi) in Comparative Example 1 of the present invention. 82 KAM value of Ti5Al5V8 medium entropy alloy;

[0036] Figure 5 The three conditions described in Embodiment 1, Embodiment 2, and Comparative Example 1 of this invention (CoFeNi) are as follows. 82 Tensile stress-strain curve of Ti5Al5V8 medium-entropy alloy;

[0037] Figure 6a It is (CoFeNi) in Embodiment 2 of the present invention. 82 OM diagram of Ti5Al5V8 medium entropy alloy;

[0038] Figure 6b It is (CoFeNi) in Embodiment 2 of the present invention. 82 SEM images of Ti5Al5V8 medium entropy alloy (I);

[0039] Figure 6c It is (CoFeNi) in Embodiment 2 of the present invention. 82 SEM images of Ti5Al5V8 medium entropy alloy (II);

[0040] Figure 7a This is (CoFeNi) in Comparative Example 1 of the present invention. 82 OM diagram of Ti5Al5V8 medium entropy alloy;

[0041] Figure 7b This is (CoFeNi) in Comparative Example 1 of the present invention. 82 SEM images of Ti5Al5V8 medium entropy alloy (I);

[0042] Figure 7c This is (CoFeNi) in Comparative Example 1 of the present invention. 82 SEM images of Ti5Al5V8 medium entropy alloy (II). Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0044] This invention relates to a CoFeNi-based medium-entropy alloy simultaneously strengthened by L12 nanoparticles and dislocations. Specifically, it involves adding L12 phase-forming elements Ti, Al, and V to the CoFeNi medium-entropy alloy and designing a (CoFeNi) alloy with an fcc matrix and L12 phase using JMatPro software. 100-x-y-z Ti x Al y V z Medium entropy alloys;

[0045] The alloy composition of the medium-entropy alloy is (CoFeNi). 100-x-y-z Tix Al y V z Wherein, 4.0≤x≤8.0, 4.0≤y≤8.0, 4.0≤z≤8.0, and Co, Fe, and Ni are composed of equal atomic percentages;

[0046] The preparation method of the CoFeNi-based medium-entropy alloy simultaneously strengthened by L12 nanoparticles and dislocations according to the present invention is specifically implemented according to the following steps:

[0047] Step 1: Grind, clean, and dry the elemental metal raw materials of Co, Fe, Ni, Ti, Al, and V;

[0048] Step 2: Design (CoFeNi) according to JMatPro software. 100-x-y-z Ti x Al y V z The raw materials are composed of Co, Fe, and Ni in equal atomic percentages, with 4.0≤x≤8.0, 4.0≤y≤8.0, and 4.0≤z≤8.0. The elemental metal raw materials of Co, Fe, Ni, Ti, Al, and V are weighed according to atomic percentage.

[0049] The specific design process using JMatPro software is as follows: Select the "Nicke Based Superalloy" material module, and then follow the (CoFeNi)... 100-x-y-z Ti x Al y V z Input the composition, where Co, Fe, and Ni are composed of equal atomic percentages, 4.0≤x≤8.0, 4.0≤y≤8.0, and 4.0≤z≤8.0. Then, select "StepTemperature" in the "Thermodynamic Properties" module to perform the calculation.

[0050] Step 3: The raw materials weighed in Step 2 are subjected to electric arc melting to obtain (CoFeNi). 100-x-y-z Ti x Al y V z Medium-entropy alloy ingot casting; specifically including the following steps:

[0051] Step 3.1: Place the raw materials weighed in Step 2 into the water-cooled copper crucible of the vacuum arc melting furnace, close the furnace chamber, evacuate the furnace, and then fill it with argon gas as a protective gas.

[0052] Step 3.2: Arc melt the raw materials in the water-cooled copper crucible. The melting current is 425-475A. After the raw materials are completely melted, turn on the electromagnetic stirring and keep it for 5-6 minutes. After the molten metal cools into a solid state, the first ingot is obtained.

[0053] Step 3.3: Turn the initial ingot over in a water-cooled copper crucible and repeat the electric arc melting process of Step 3.2 four times to obtain a button-shaped (CoFeNi) with uniform microstructure. 100-x-y-z Ti x Al y V z Medium-entropy alloy ingots;

[0054] Step 4, for (CoFeNi) 100-x-y-z Ti x Al y V z The medium-entropy alloy ingot was subjected to solution treatment, first cold rolling, annealing, second cold rolling, and aging ordering treatment in sequence to obtain a CoFeNi-based medium-entropy alloy that is simultaneously strengthened by L12 nanoparticles and dislocations.

[0055] During solution treatment, the treatment temperature is 1150℃~1200℃, and the holding time is 12h-48h.

[0056] The thinning rate of a single cold rolling process is 60% to 80%;

[0057] The annealing temperature is 900℃~1050℃, and the time is 3~60min; the thinning rate of the second cold rolling is 0-15%;

[0058] If the annealing temperature exceeds 980℃, it is considered high-temperature annealing. At this temperature, the microstructure undergoes complete recrystallization, resulting in a reduced dislocation density. A second cold rolling process is required to provide dislocations, and then L-shaped structures appear during the aging process. 12 Nanoparticles play a role in simultaneous reinforcement.

[0059] If the annealing temperature is below 980℃ and recrystallization is not complete, the non-recrystallized area contains a large number of dislocations. In this case, the thinning rate of the second cold rolling is 0, meaning that the second cold rolling is not required, and the high dislocation density is maintained.

[0060] During the time-controlled aging process: the aging temperature is 600℃~800℃, and the aging time is 0.5~24h.

[0061] This invention maintains a high dislocation density during low-temperature annealing after a single cold rolling process. Subsequent aging treatment yields high-density L12 nanoparticles, achieving simultaneous strengthening of both L12 nanoparticles and dislocations. To further enhance strength, a second rolling process can be employed. The primary rolling in this invention aims to eliminate defects from the casting process, introducing dislocations to provide nucleation sites for recrystallization during subsequent high-temperature annealing. The secondary rolling primarily provides dislocations, and the subsequent aging process (low-temperature aging does not significantly eliminate dislocations) yields high-density L12 nanoparticles, thus achieving simultaneous strengthening of both L12 nanoparticles and dislocations.

[0062] Example 1

[0063] The preparation method of high-strength CoFeNi-based medium-entropy alloys simultaneously strengthened by L12 nanoparticles and dislocations includes the following steps:

[0064] Step 1: Grind, clean, and dry the elemental metal raw materials of Co, Fe, Ni, Ti, Al, and V;

[0065] Step 2: Design (CoFeNi) according to JMatPro software. 100-x-y-z Ti x Al y V z The composition is based on Co, Fe, and Ni in equal atomic percentages, with x = 5.0, y = 5.0, and z = 8.0, i.e., (CoFeNi). 82 Ti5Al5V8, weigh out the elemental metal raw materials of Co, Fe, Ni, Ti, Al and V according to atomic percentage;

[0066] The specific process of designing using JMatPro software in step 2 is as follows: Select the "Nicke Based Superalloy" material module, and then follow the (CoFeNi) design parameters. 100-x-y-z Ti x Al y V z Enter the composition, where Co, Fe, and Ni are composed of equal atomic percentages, x = 5.0, y = 5.0, z = 8.0, and then select "Step Temperature" in the "Thermodynamic Properties" module to perform the calculation.

[0067] Step 3: The raw materials weighed in Step 2 are subjected to electric arc melting to obtain (CoFeNi). 82 Ti5Al5V8 medium-entropy alloy ingot casting; specifically including the following steps:

[0068] Step 3.1: Place the raw materials weighed in Step 2 into the water-cooled copper crucible of the vacuum arc melting furnace, close the furnace chamber, evacuate the furnace, and then fill it with argon gas as a protective gas.

[0069] Step 3.2: Arc melting of the raw materials in the water-cooled copper crucible with a melting current of 450A. After the raw materials are completely melted, electromagnetic stirring is turned on and maintained for 6 minutes. After the molten metal cools into a solid state, the first ingot is obtained.

[0070] Step 3.3: Turn the initial ingot over in a water-cooled copper crucible, and repeat step 3.2 four times to obtain a button-shaped (CoFeNi) structure with uniform composition. 82 Ingots of Ti5Al5V8 medium entropy alloy.

[0071] Step 4, for (CoFeNi) 82 Ti5Al5V8 medium-entropy alloy ingots are subjected to solution treatment, primary cold rolling, low-temperature / high-temperature annealing, secondary cold rolling (cold rolling can be omitted if the previous step is low-temperature annealing), and aging ordering treatment to obtain a medium-entropy alloy that is simultaneously strengthened by L12 nanoparticles and dislocations.

[0072] In step 4, during the solution treatment process, the treatment temperature is 1150℃ and the holding time is 24h.

[0073] The thinning rate of the single cold rolling process in step 4 is 65%.

[0074] Step 4, high-temperature annealing process: temperature is 1000℃, processing time is 3 minutes.

[0075] The thinning rate of the second cold rolling in step 4 is 15% because the previous step was high-temperature annealing, which reduced the dislocation density. Therefore, a second rolling process is required to maintain a high dislocation density.

[0076] Step 4 involves an aging process with an aging temperature of 700℃ and an aging time of 1 hour.

[0077] In Embodiment 1 of this invention, JMatPro software was used to design and calculate (CoFeNi). 82 The solidification path of the Ti5Al5V8 medium entropy alloy, such as Figure 1 As shown, calculations indicate that the alloy microstructure will consist of an fcc matrix and an L12 phase. In Example 1 (CoFeNi) 82 The XRD results of the Ti5Al5V8 medium-entropy alloy are as follows: Figure 2a As shown, the diffraction peaks of the matrix fcc and L12 nanoparticles of the alloy almost overlap, and the fitting diagram of the fcc matrix and L12 nanoparticles at the (311) crystal plane by XRD analysis (as shown in the figure) Figure 2d As shown in the figure, the results indicate that the lattice constants are very close, and the two phases are highly coherent. In Example 1 (CoFeNi) 82 OM and SEM results of the Ti5Al5V8 medium-entropy alloy indicate that the microstructure consists of a small amount of recrystallized regions (R) and a large amount of non-recrystallized regions (NR, volume fraction approximately 91%), such as... Figure 3a and 3b As shown, high-density L12 nanoparticles precipitated in both the recrystallized and non-recrystallized regions, such as... Figure 3c and Figure 3a As shown. In Example 1 (CoFeNi) 82 The EBSD (Extended Entropy Map) results of the Ti5Al5V8 medium-entropy alloy show that the local orientation of the unrecrystallized region is larger, and the corresponding KAM value is also higher (2.75°). Figure 4a and 4dAs shown, the corresponding dislocation density is even higher; based on the KAM value, the dislocation density can be calculated to be ~6.29*10⁻⁶. 14 m -2 The dislocation density is relatively high. In Example 1 (CoFeNi) 82 The tensile stress-strain curve of the Ti5Al5V8 medium-entropy alloy shows that under these conditions, the alloy can achieve extremely high yield strength, reaching approximately 1500 MPa, and ultimate tensile strength, reaching 1747 MPa, while still retaining a certain degree of plasticity (approximately 16%). Figure 5 As shown. Based on analysis, it is believed that in Example 1 (CoFeNi)... 82 The high strength of the Ti5Al5V8 medium entropy alloy is mainly attributed to precipitation strengthening and dislocation strengthening by L12 nanoparticles, resulting in excellent performance.

[0078] Example 2

[0079] High-strength CoFeNi-based medium-entropy alloys simultaneously strengthened by L12 nanoparticles and dislocations, and their preparation method, including the following steps:

[0080] Step 1: Grind, clean, and dry the elemental metal raw materials of Co, Fe, Ni, Ti, Al, and V;

[0081] Step 2: Design (CoFeNi) according to JMatPro software. 100-x-y-z Ti x Al y V z The composition is based on Co, Fe, and Ni in equal atomic percentages, with x = 5.0, y = 5.0, and z = 8.0, i.e., (CoFeNi). 82 Ti5Al5V8, weigh out the elemental metal raw materials of Co, Fe, Ni, Ti, Al and V according to atomic percentage;

[0082] The specific process of designing using JMatPro software in step 2 is as follows: Select the "Nicke Based Superalloy" material module, and then follow the (CoFeNi) design parameters. 100-x-y-z Ti x Al y V z Enter the composition, where Co, Fe, and Ni are composed of equal atomic percentages, x = 5.0, y = 5.0, z = 8.0, and then select "Step Temperature" in the "Thermodynamic Properties" module to perform the calculation.

[0083] Step 3: The raw materials weighed in Step 2 are subjected to electric arc melting to obtain (CoFeNi). 82 Ti5Al5V8 medium-entropy alloy ingot casting; specifically including the following steps:

[0084] Step 3.1: Place the raw materials weighed in Step 2 into the water-cooled copper crucible of the vacuum arc melting furnace, close the furnace chamber, evacuate the furnace, and then fill it with argon gas as a protective gas.

[0085] Step 3.2: Arc melting of the raw materials in the water-cooled copper crucible with a melting current of 475A. After the raw materials are completely melted, electromagnetic stirring is turned on and maintained for 5 minutes. After the molten metal cools into a solid state, the first ingot is obtained.

[0086] Step 3.3: Turn the initial ingot over in a water-cooled copper crucible, and repeat step 3.2 four times to obtain a button-shaped (CoFeNi) structure with uniform composition. 82 Ingots of Ti5Al5V8 medium-entropy alloy.

[0087] Step 4, for (CoFeNi) 82 Ti5Al5V8 medium-entropy alloy ingots are subjected to solution treatment, primary cold rolling, low-temperature / high-temperature annealing, secondary cold rolling (cold rolling can be omitted if the previous step is low-temperature annealing), and aging ordering treatment to obtain a medium-entropy alloy that is simultaneously strengthened by L12 nanoparticles and dislocations.

[0088] In step 4, during the solution treatment process, the treatment temperature is 1150℃ and the holding time is 24h.

[0089] The thinning rate of the single cold rolling process in step 4 is 80%.

[0090] In step 4, during the low-temperature annealing process: the temperature is 900℃ and the processing time is 30 minutes.

[0091] The thinning rate of the second cold rolling in step 4 is 0 because the previous step was low-temperature annealing, which resulted in a high dislocation density. Therefore, a second rolling process is not required to maintain the high dislocation density.

[0092] In step 4, during the time-ordered aging process: the aging temperature is 700℃ and the aging time is 1 hour.

[0093] In Embodiment 2 of this invention, (CoFeNi) was designed using JMatPro software. 82 The solidification path of the Ti5Al5V8 medium entropy alloy, such as Figure 1 As shown, calculations indicate that the alloy microstructure will consist of an fcc matrix and an L12 phase. In Example 2 (CoFeNi) 82 The XRD results of the Ti5Al5V8 medium-entropy alloy are as follows: Figure 2a As shown, the diffraction peaks of the matrix fcc and L12 nanoparticles of the alloy almost overlap, and the fitting diagram of the fcc matrix and L12 nanoparticles at the (311) crystal plane by XRD analysis (as shown in the figure) Figure 2cAs shown in the figure, the results indicate that the lattice constants are very close, and the two phases are highly coherent. In Example 2 (CoFeNi) 82 OM and SEM results of the Ti5Al5V8 medium-entropy alloy indicate that the microstructure consists of a small amount of recrystallized regions (R) and a large amount of non-recrystallized regions (NR, volume fraction approximately 83%). Figure 6a and 6b As shown, high-density L12 nanoparticles precipitated in both the recrystallized and non-recrystallized regions, such as... Figure 6c and Figure 6c As shown. In Example 2 (CoFeNi) 82 The EBSD (Extended Entropy Map) results of the Ti5Al5V8 medium-entropy alloy indicate that the local orientation of the unrecrystallized region is larger, and the corresponding KAM value is also higher (2.01°). Figure 4b and 4e As shown, the corresponding dislocation density is relatively high; based on the KAM value, the dislocation density can be calculated to be ~4.60*10⁻⁶. 14 m -2 The dislocation density is relatively high. In Example 2 (CoFeNi) 82 The tensile stress-strain curve of the Ti5Al5V8 medium-entropy alloy shows that under these conditions, the alloy can achieve a high yield strength of approximately 1142 MPa and an ultimate tensile strength of 1399 MPa, while retaining a certain degree of plasticity (approximately 15%). Figure 5 As shown. Based on analysis, it is believed that in Example 2 (CoFeNi)... 82 The high strength of the Ti5Al5V8 medium entropy alloy is mainly attributed to precipitation strengthening and dislocation strengthening by L12 nanoparticles, resulting in excellent performance.

[0094] Comparative Example 1

[0095] High-strength CoFeNi-based medium-entropy alloys simultaneously strengthened by L12 nanoparticles and dislocations, and their preparation method, including the following steps:

[0096] Step 1: Grind, clean, and dry the elemental metal raw materials of Co, Fe, Ni, Ti, Al, and V;

[0097] Step 2: Design (CoFeNi) according to JMatPro software. 100-x-y-z Ti x Al y V z The composition is based on Co, Fe, and Ni in equal atomic percentages, with x = 5.0, y = 5.0, and z = 8.0, i.e., (CoFeNi). 82 Ti5Al5V8, weigh out the elemental metal raw materials of Co, Fe, Ni, Ti, Al and V according to atomic percentage;

[0098] The specific design process using JMatPro software is as follows: Select the "Nicke Based Superalloy" material module, and then follow the (CoFeNi) design process. 100-x-y-z Ti x Al y V z Enter the composition, where Co, Fe, and Ni are composed of equal atomic percentages, x = 5.0, y = 5.0, z = 8.0, and then select "Step Temperature" in the "Thermodynamic Properties" module to perform the calculation.

[0099] Step 3: The raw materials weighed in Step 2 are subjected to electric arc melting to obtain (CoFeNi). 82 Ti5Al5V8 medium-entropy alloy ingot casting; specifically including the following steps:

[0100] Step 3.1: Place the raw materials weighed in Step 2 into the water-cooled copper crucible of the vacuum arc melting furnace, close the furnace chamber, evacuate the furnace, and then fill it with argon gas as a protective gas.

[0101] Step 3.2: Arc melting of the raw materials in the water-cooled copper crucible with a melting current of 475A. After the raw materials are completely melted, electromagnetic stirring is turned on and maintained for 5 minutes. After the molten metal cools into a solid state, the first ingot is obtained.

[0102] Step 3.4: Turn the initial ingot over in a water-cooled copper crucible, and repeat step 3.2 four times to obtain a button-shaped (CoFeNi) structure with uniform composition. 82 Ingots of Ti5Al5V8 medium-entropy alloy.

[0103] Step 4, for (CoFeNi) 82 Ti5Al5V8 medium-entropy alloy ingots were subjected to solution treatment, primary cold rolling, low-temperature / high-temperature annealing, secondary cold rolling, and aging ordering treatment in sequence to obtain a medium-entropy alloy simultaneously strengthened by L12 nanoparticles and dislocations.

[0104] In step 4, during the solution treatment process, the treatment temperature is 1150℃ and the holding time is 24h.

[0105] The thinning rate of the single cold rolling process in step 4 is 80%.

[0106] Step 4, high-temperature annealing process: temperature is 1000℃, processing time is 3 minutes.

[0107] In step 4, the thinning rate of the secondary cold rolling is 0. Unlike Example 1 (which requires secondary rolling after high-temperature annealing due to the decrease in dislocation density), Comparative Example 1 did not undergo secondary rolling, resulting in a lower dislocation density and thus greatly weakening the dislocation strengthening effect.

[0108] Step 4 involves an aging process with an aging temperature of 700℃ and an aging time of 1 hour.

[0109] In Comparative Example 1 of this invention, (CoFeNi) was designed using JMatPro software. 82 The solidification path of the Ti5Al5V8 medium entropy alloy, such as Figure 1 As shown, calculations indicate that the alloy microstructure will consist of an fcc matrix and an L12 phase. (Comparative Example 1: CoFeNi) 82 The XRD results of the Ti5Al5V8 medium-entropy alloy are as follows: Figure 2a As shown, the diffraction peaks of the matrix fcc and L12 nanoparticles of the alloy almost overlap, and the fitting diagram of the fcc matrix and L12 nanoparticles at the (311) crystal plane by XRD analysis (as shown in the figure) Figure 2b As shown in the figure, the results indicate that the lattice constants are very close, and the two phases are highly coherent. (Comparative Example 1: (CoFeNi)) 82 Omnidirectional annealing (OM) results for the Ti5Al5V8 medium-entropy alloy indicate complete recrystallization after high-temperature annealing, with no unrecrystallized regions. The microstructure is a fine equiaxed grain structure, such as... Figure 7a As shown in the image. SEM results indicate that high-density L12 nanoparticles precipitated within the crystal, such as... Figure 7b and 7c As shown. In Comparative Example 1, (CoFeNi) 82 The EBSD (Extended Entropy Map) results of the Ti5Al5V8 medium-entropy alloy show that the local orientation of the unrecrystallized region is very small, and the corresponding KAM value is also very small (0.381°). Figure 4c and 4f As shown, the corresponding dislocation density is relatively high. Based on the KAM value, the dislocation density can be calculated to be ~0.5229*10. 14 m -2 Compared with Example 1 (~6.29*10) 14 m -2 Example 1 and Example 2 (~4.60*10) 14 m -2 Compared to (CoFeNi), the dislocation density is much lower. 82 The tensile stress-strain curve of the Ti5Al5V8 medium-entropy alloy shows that the alloy has a low yield strength of about 772 MPa and good plasticity (about 46%). Figure 5 As shown. Based on analysis, it is believed that in Comparative Example 1 (CoFeNi)... 82 The dislocation density in the Ti5Al5V8 medium-entropy alloy is very low, and the effect of dislocation strengthening is negligible. Therefore, in Comparative Example 1 (CoFeNi)... 82The strengthening mechanism of the Ti5Al5V8 medium entropy alloy is mainly attributed to the precipitation strengthening of L12 nanoparticles, without obvious dislocation strengthening. Therefore, the yield strength is low, which is the opposite of the high yield strength caused by dislocation strengthening in Examples 1 and 2.

[0110] Example 3

[0111] The preparation method of the CoFeNi-based medium-entropy alloy with simultaneous strengthening of L12 nanoparticles and dislocations of the present invention promotes the precipitation of L12 nanoparticles during the subsequent aging process by first cold rolling and second cold rolling, while maintaining a high dislocation density by low-temperature annealing or low-temperature aging, and finally achieves the effect of simultaneous strengthening of L12 nanoparticles and dislocations.

Claims

1. A method for preparing high-strength CoFeNi-based medium-entropy alloys simultaneously strengthened by L12 nanoparticles and dislocations, characterized in that, Includes the following steps: Step 1: Grind, clean, and dry the elemental metal raw materials of Co, Fe, Ni, Ti, Al, and V; Step 2: Design (CoFeNi) according to JMatPro software. 100-x-y-z Ti x Al y V z The composition is based on Co, Fe, and Ni in equal atomic percentages, with x = 5.0, y = 5.0, and z = 8.0, i.e., (CoFeNi). 82 Ti5Al5V8, weigh out the elemental metal raw materials of Co, Fe, Ni, Ti, Al and V according to atomic percentage; Step 3: The raw materials weighed in Step 2 are subjected to electric arc melting to obtain (CoFeNi). 82 Ti5Al5V8 medium-entropy alloy ingot casting; specifically including the following steps: Step 3.1: Place the raw materials weighed in Step 2 into the water-cooled copper crucible of the vacuum arc melting furnace, close the furnace chamber, evacuate the furnace, and then fill it with argon gas as a protective gas. Step 3.2: Arc melting of the raw materials in the water-cooled copper crucible with a melting current of 450A. After the raw materials are completely melted, electromagnetic stirring is turned on and maintained for 6 minutes. After the molten metal cools into a solid state, the first ingot is obtained. Step 3.3: Turn the initial ingot over in a water-cooled copper crucible, and repeat step 3.2 four times to obtain a button-shaped (CoFeNi) structure with uniform composition. 82 Ingots of Ti5Al5V8 medium-entropy alloy; Step 4, for (CoFeNi) 82 Ti5Al5V8 medium-entropy alloy ingots were subjected to solution treatment, first cold rolling, high-temperature annealing, second cold rolling, and aging ordering treatment in sequence to obtain a medium-entropy alloy that is simultaneously strengthened by L12 nanoparticles and dislocations. In step 4, during the solution treatment process: the treatment temperature is 1150℃ and the holding time is 24h; the thinning rate of the first cold rolling process in step 4 is 65%; in step 4, during the high-temperature annealing process: the temperature is 1000℃ and the treatment time is 3min; in step 4, during the second cold rolling process, the thinning rate is 15%; in step 4, during the aging and ordering treatment process: the aging temperature is 700℃ and the aging time is 1h. (CoFeNi) 82 The microstructure of the Ti5Al5V8 medium-entropy alloy consists of an fcc matrix and an L12 phase. The microstructure comprises a small amount of recrystallized regions and a large amount of non-recrystallized regions. High-density L12 nanoparticles are precipitated in both recrystallized and non-recrystallized regions. Based on the KAM value, the dislocation density is calculated to be 6.29 × 10⁻⁶. 14 m -2 It has a high dislocation density; its yield strength reaches 1500MPa and its ultimate tensile strength reaches 1747MPa.

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