NiCoCrFeMo high-entropy alloy and preparation method thereof

Abstract

The invention relates to a NiCoCrFeMo high-entropy alloy and a preparation method thereof, and the high-entropy alloy comprises the following elements in percentage by mass: 23.5-27.5% of Ni; 18.5% to 22.5% of Co; 17.5% to 23.5% of Cr; 18.0 to 22.0 percent of Fe (ferrum); a preparation method of the steel comprises the following steps that S1, raw materials are prepared; s2, raw material smelting; s3, heat treatment: at the first stage, heating the cast ingot to 870-930 DEG C, and keeping the temperature; in the second stage, the cast ingot is heated to 990-1030 DEG C for heat preservation; in the third stage, the cast ingot is heated to 1270-1340 DEG C, and heat preservation is conducted; in the first stage, the annealing temperature range ranges from 720 DEG C to 770 DEG C, and in the second stage, the annealing temperature ranges from 720 DEG C to 770 DEG C; and in the second stage, the annealing temperature range is 1065-1170 DEG C. The method has the advantages that composition segregation structures are reduced, an ultra-fine grain structure is obtained, and the comprehensive mechanical property of the alloy is improved.

Description

Technical Field

[0001] This invention relates to the field of alloy manufacturing, and in particular to a NiCoCrFeMo high-entropy alloy and its preparation method. Background Technology

[0002] High-entropy alloys are a new type of alloy formed by combining multiple pure metallic elements. Unlike traditional alloys such as steel and aluminum alloys, which use a single main alloy with trace elements, high-entropy alloys have limitations in mechanical properties and high-temperature resistance. Through diversified composition design, high-entropy alloys overcome the design limitations of traditional alloys and exhibit superior performance in specialized properties.

[0003] Currently, the mainstream high-entropy alloy is the AlCoCeFeNi high-entropy alloy, which uses Al as a lightweight element to reduce the alloy's density. However, during the manufacturing and testing of this type of high-entropy alloy, it was found that Al and Ni easily form ordered intermetallic compounds, preferentially enriching at grain boundaries and forming grain boundary segregation layers. The resulting segregated structure affects the uniformity of the microstructure, which is reflected in the macroscopic properties. Tests showed that the alloy's Mohs hardness was around 2.70, and its tensile strength and yield strength at high temperatures did not meet the standards.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a NiCoCrFeMo high-entropy alloy and its preparation method.

[0006] A NiCoCrFeMo high-entropy alloy comprising the following elements by mass percentage: Ni, 23.5-27.5%; Co, 18.5-22.5%; Cr, 17.5-23.5%; Fe, 18.0-22.0%; Mo, 14.5-15.5%.

[0007] A method for preparing a NiCoCrFeMo high-entropy alloy includes the following steps: Step S1: Prepare the raw materials; Step S2, raw material smelting: First, Ni, Co and Fe raw materials are put into an electric arc furnace, and then Cr and Mo are added for smelting. The smelting temperature range is 1633~1660℃. Then the power is turned off and solidification is obtained to obtain an ingot. Then the smelting is repeated with the same parameters and the ingot is obtained after cooling. Step S3, heat treatment: First stage: Heat the ingot to 870~930℃ and hold it at that temperature; Second stage: Heat the ingot to 990~1030℃ and hold it at that temperature; The third stage: the ingot is heated to 1270~1340℃ and held at that temperature, and finally cooled to room temperature to obtain the material billet; Step S4, Deformation: The billet is first heated to 480±20℃, then upset, and then drawn to the initial size, with a single deformation amount of 15~25%; Step S5, Plasticizing Annealing: First stage: Annealing temperature range 720~770℃; Second stage: Annealing temperature range 1065~1170℃ Furthermore, in step S1, the purity of the Ni metal raw material is 99.9%, the purity of the Co metal raw material is 99.9%, the purity of the Cr metal raw material is 99.9%, the purity of the Fe metal raw material is 99.9%, and the purity of the Mo metal raw material is 99.95%.

[0008] Furthermore, in step S2, the electric arc furnace is evacuated, and then argon gas with a concentration of 99.9% is introduced into it.

[0009] Furthermore, in step S2, the melting process is repeated 4 to 6 times.

[0010] Furthermore, in the first stage of step S3, the heat preservation time ranges from 5 to 8 hours, and the heating rate is 110 to 140°C / h.

[0011] Furthermore, in the second stage of step S3, the heat preservation time ranges from 5 to 8 hours, and the heating rate is 90 to 100℃ / h.

[0012] Furthermore, in the third stage of step S3, the heat preservation time ranges from 12 to 16 hours, and the heating rate is 120 to 150 °C / h.

[0013] Furthermore, in the first stage of step S5, the annealing holding time is 20-30 minutes.

[0014] Furthermore, in the second stage of step S5, the annealing and holding time is 3~8 hours.

[0015] Advantages of this invention: 1. Using the elemental combination of NiCoCrFeMo, a reinforced phase structure composed of FCC and BCC phases is formed. Al is not used to avoid local segregation caused by the segregation layer formed by Al. Multiple melting processes are used to eliminate compositional segregation of raw materials and improve the uniformity of raw materials. Then, a multi-stage heat treatment process is used to induce slip of metal atoms and generate multiple dislocations in the structure, reducing microsegregation in the as-cast structure, optimizing the distribution of FCC and BCC phases, and improving the uniformity of the structure. After that, low-temperature deformation is performed to induce secondary slip and improve the fracture resistance of the structure. Finally, annealing is performed to release the internal stress accumulated in the structure. The precipitates in the previous heat treatment dissolve to obtain an ultrafine grain structure and improve the comprehensive mechanical properties of the alloy.

[0016] 2. Strictly control the purity of raw materials and repeatedly melt them in an argon-protected environment to avoid oxidation of metal elements, avoid introducing impurities, and ensure the purity of the structure.

[0017] 3. Multi-stage heat treatment is adopted, and the heat treatment window and holding time are strictly controlled. In the first stage, the ingot is preheated, and it takes time for heat to be conducted from the outside to the core. Atomic diffusion gradually begins, reducing the temperature difference between the inside and outside. Then, the temperature is accelerated to dissolve the harmful phases present in the as-cast structure, and the atomic diffusion is accelerated. The BCC phase diffuses from the dendrites to the grain, reducing the segregation of the layout. In the final high-temperature zone, atomic diffusion is maximized to form a uniform crystal structure, ensuring that the final structure is a pure FCC and BCC dual-phase structure, reducing abnormal grain growth caused by sudden temperature rise.

[0018] 4. Low-temperature deformation is employed, which causes dislocations to accumulate at grain boundaries, hindering grain boundary slip, increasing the material's hardness, yield strength, and tensile strength. Furthermore, deformation twins appear in the microstructure during the deformation process, improving the toughness of the crystal structure.

[0019] 5. Annealing is used to decompose the residual harmful phases and coarse grains that have precipitated, further eliminating component segregation, improving the grain size of the microstructure, reducing brittle harmful phases, balancing the toughness and brittleness of the material, and eliminating the internal stress accumulated during deformation during the process, reducing grain boundary microcracks caused by stress concentration.

[0020] 6. Ni is the main element for phase stabilization. Co works synergistically with Ni. Co can replace Ni at the center of the cubic lattice, resulting in lattice distortion and an increase in dislocations, which hinders grain boundary sliding and can form a more stable FCC phase. Introducing Fe, Ni and Co have good compatibility and participate in the formation of the FCC phase. Cr is mainly a promoting element for the formation of the BCC phase and also has good corrosion resistance. Mo has higher solubility in the BCC phase and plays a strengthening role by being dispersed in it. However, controlling the proportion of Mo can avoid excessive precipitation of brittle and harmful phases, ultimately resulting in an alloy material with excellent comprehensive performance. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the steps of a method for preparing a NiCoCrFeMo high-entropy alloy.

[0022] Figure 2 The image shown is a metallographic image of the product in Example 1.

[0023] Figure 3 The image shown is a metallographic image of the product in Example 2.

[0024] Figure 4 The image shown is a metallographic image of the product in Example 3. Detailed Implementation

[0025] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0026] Example 1: A NiCoCrFeMo high-entropy alloy comprising the following elements by mass percentage: Ni, 25%; Co, 20%; Cr, 20%; Fe, 20%; Mo, 15%.

[0027] Its preparation method, such as Figure 1 As shown, it includes the following steps: Step S1: Prepare the raw materials. The weights of each raw material are as follows: Ni, 300 kg; Co, 240 kg; Cr, 240 kg; Fe, 240 kg; Mo, 180 kg. The purity of the Ni metal raw material is 99.9%, the purity of the Co metal raw material is 99.9%, the purity of the Cr metal raw material is 99.9%, the purity of the Fe metal raw material is 99.9%, and the purity of the Mo metal raw material is 99.95%.

[0028] Step S2, raw material melting: First, a vacuum is drawn into the electric arc furnace, then argon gas (99.9% concentration) is introduced to prevent oxygen from entering the furnace and contaminating the alloy with metal oxides during melting. Ni, Co, and Fe raw materials are then added to the electric arc furnace. After the raw materials melt, Cr and Mo are added, and melting continues at a temperature of 1640℃ for 4 hours. Power is then cut off for solidification. The same process parameters are then repeated four times, followed by cooling to obtain an ingot.

[0029] Step S3, heat treatment: First stage: The ingot is placed in the furnace, and argon gas is filled into the furnace as a protective gas. The ingot is heated to 870℃ and held for 6 hours. The heating rate is 120℃ / h.

[0030] Second stage: Heat the ingot to 990℃ and hold for 5 hours, with a heating rate of 90℃ / h.

[0031] The third stage involves heating the ingot to 1270℃ and holding it for 12 hours at a rate of 120℃ / hour. Finally, the ingot is cooled to room temperature using oil cooling to obtain a rough billet. The billet dimensions are 420mm × 420mm × 850mm.

[0032] Step S4, Deformation: The billet is first heated to 480℃, then upset to a height of 722.5mm, with a deformation of (850-722.5) / 850=15%, and then drawn to the initial size. The above deformation process is repeated with the same process parameters, and the number of deformation firings is controlled within 3 times. In this embodiment, the number of deformation firings is 2.

[0033] Step S5, Plasticizing Annealing: First stage: Annealing temperature range 720℃, annealing holding time 20min.

[0034] Second stage: Annealing temperature range 1065℃, annealing holding time 3h. Finally, the material is air-cooled to room temperature, and product samples are taken for testing.

[0035] Example 2: A NiCoCrFeMo high-entropy alloy comprising the following elements by mass percentage: Ni, 26%; Co, 18.5%; Cr, 23%; Fe, 18%; Mo, 14.5%.

[0036] Its preparation method, such as Figure 1 As shown, it includes the following steps: Step S1: Prepare the raw materials. The weights of each raw material are as follows: Ni, 312 kg; Co, 222 kg; Cr, 276 kg; Fe, 216 kg; Mo, 174 kg. The purity of the Ni, Co, Cr, and Fe metal raw materials is 99.9%, 99.9%, and 99.95%, respectively.

[0037] Step S2, raw material melting: First, a vacuum is drawn into the electric arc furnace, then argon gas (99.9% concentration) is introduced to prevent oxygen from entering the furnace and contaminating the alloy with metal oxides during melting. Ni, Co, and Fe raw materials are then added to the electric arc furnace. After the raw materials melt, Cr and Mo are added, and melting continues at 1650℃ for 4 hours. Power is then cut off for solidification. The same process parameters are then repeated five times, followed by cooling to obtain an ingot.

[0038] Step S3, heat treatment: First stage: The ingot is placed in the furnace, and argon gas is filled into the furnace as a protective gas. The ingot is heated to 910℃ and held for 7 hours. The heating rate is 130℃ / h.

[0039] Second stage: Heat the ingot to 1005℃ and hold for 5 hours, with a heating rate of 100℃ / h.

[0040] The third stage: The ingot is heated to 1305℃ and held for 15 hours at a heating rate of 140℃ / h. Finally, it is cooled to room temperature by oil cooling to obtain a rough billet. The billet dimensions are 420mm×420mm×850mm.

[0041] The billet is first heated to 480℃, then upset to a height of 680mm, with a deformation of (850-680) / 850=20%, and then drawn to the initial size. The above deformation process is repeated with the same process parameters, and the number of deformation firings is controlled within 3 times. In this embodiment, the number of deformation firings is 2.

[0042] Step S5, Plasticizing Annealing: First stage: Annealing temperature range 750℃, annealing holding time 20min.

[0043] Second stage: Annealing temperature range 1065℃, annealing holding time 6h. Finally, the material is air-cooled to room temperature, and product samples are taken for testing.

[0044] Example 3: A NiCoCrFeMo high-entropy alloy comprising the following elements by mass percentage: Ni, 23.5%; Co, 22.5%; Cr, 17.5%; Fe, 21.5%; Mo, 15%.

[0045] Its preparation method, such as Figure 1 As shown, it includes the following steps: Step S1: Prepare the raw materials. The weights of each raw material are as follows: Ni, 282 kg; Co, 270 kg; Cr, 210 kg; Fe, 258 kg; Mo, 180 kg. The purity of the Ni metal raw material is 99.9%, the purity of the Co metal raw material is 99.9%, the purity of the Cr metal raw material is 99.9%, the purity of the Fe metal raw material is 99.9%, and the purity of the Mo metal raw material is 99.95%.

[0046] Step S2, raw material melting: First, a vacuum is drawn into the electric arc furnace, then argon gas (99.9% concentration) is introduced to prevent oxygen from entering the furnace and contaminating the alloy with metal oxides during melting. Ni, Co, and Fe raw materials are then added to the electric arc furnace. After the raw materials melt, Cr and Mo are added, and melting continues at a temperature of 1660℃ for 4 hours. Power is then cut off for solidification. The same process parameters are then repeated six times, followed by cooling to obtain an ingot.

[0047] Step S3, heat treatment: First stage: The ingot is placed in the furnace, and argon gas is filled into the furnace as a protective gas. The ingot is heated to 925℃ and held for 8 hours. The heating rate is 140℃ / h.

[0048] Second stage: Heat the ingot to 1030℃ and hold for 8 hours, with a heating rate of 100℃ / h.

[0049] The third stage involves heating the ingot to 1330℃ and holding it for 16 hours at a rate of 130℃ / hour. Finally, the ingot is cooled to room temperature using oil cooling to obtain a rough billet. The billet dimensions are 420mm × 420mm × 850mm.

[0050] The billet is first heated to 480℃, then upset to a height of 637.5mm, with a deformation of (850-637.5) / 850=25%, and then drawn to the initial size. The above deformation process is repeated with the same process parameters, and the number of deformation tests is controlled within 3 times. In this embodiment, the number of deformation tests is 3.

[0051] Step S5, Plasticizing Annealing: First stage: Annealing temperature range 770℃, annealing holding time 30min.

[0052] Second stage: Annealing temperature range 1070℃, annealing holding time 8h. Finally, the material is air-cooled to room temperature, and product samples are taken for testing.

[0053] Comprehensive mechanical performance testing: Samples: Three-dimensional samples were taken from the products made in Examples 1 to 3.

[0054] The test results are shown in Table 1.

[0055] Table 1 project Tensile strength (MPa) Yield strength (MPa) Elongation (%) Hardness (HV) Example 1 812 / 804 / 811 667 / 674 / 669 35 716 Example 2 798 / 803 / 797 656 / 663 / 658 37 691 Example 3 806 / 810 / 807 673 / 688 / 684 38 735 standard ≥700 ≥550 ≥20 ≥600 in conclusion: Tensile strength: Exceeds the standard by approximately 110 MPa, and the maximum difference in triaxial tensile strength is less than 15 MPa, demonstrating that the microstructure has good uniformity.

[0056] Yield strength: Exceeds the standard by approximately 100 MPa, and the maximum difference in triaxial yield strength is less than 20 MPa, demonstrating that the microstructure has good uniformity.

[0057] Elongation: Exceeds the standard by about twice, and the material has good toughness.

[0058] Hardness: Exceeds the standard by approximately 90 HV.

[0059] Metallographic testing of products: Magnification: 20μm.

[0060] Example 1: As Figure 2 As shown, the crystal structure has a grain size of grade 5, with no coarse or mixed grain structures, no structural defects such as cracks or pitting, and no segregation structure.

[0061] Example 2: As Figure 3 As shown, the crystal structure has a grain size of grade 5, with no coarse or mixed grain structures, no structural defects such as cracks or pitting, and no segregation structure.

[0062] Example 3: As Figure 4 As shown, the crystal structure has a grain size of grade 5, with no coarse or mixed grain structures, no structural defects such as cracks or pitting, and no segregation structure.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A NiCoCrFeMo high-entropy alloy, characterized in that, Including elements counted by mass percentage: Ni, 23.5~27.5%; Co, 18.5~22.5%; Cr, 17.5~23.5%; Fe, 18.0~22.0%; Mo, 14.5~15.5%.

2. A method for preparing the NiCoCrFeMo high-entropy alloy according to claim 1, characterized in that, Includes the following steps: Step S1: Prepare the raw materials; Step S2, raw material smelting: First, Ni, Co and Fe raw materials are put into an electric arc furnace, and then Cr and Mo are added for smelting. The smelting temperature range is 1633~1660℃. Then the power is turned off and solidification is obtained to obtain an ingot. Then the smelting is repeated with the same parameters and the ingot is obtained after cooling. Step S3, heat treatment: First stage: Heat the ingot to 870~930℃ and hold it at that temperature; Second stage: Heat the ingot to 990~1030℃ and hold it at that temperature; The third stage: the ingot is heated to 1270~1340℃ and held at that temperature, and finally cooled to room temperature to obtain the material billet; Step S4, Deformation: The billet is first heated to 480±20℃, then upset, and then drawn to the initial size, with a single deformation amount of 15~25%; Step S5, Plasticizing Annealing: First stage: Annealing temperature range 720~770℃; Second stage: Annealing temperature range 1065~1170℃.

3. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 2, characterized in that: In step S1, the purity of Ni metal raw material is 99.9%, the purity of Co metal raw material is 99.9%, the purity of Cr metal raw material is 99.9%, the purity of Fe metal raw material is 99.9%, and the purity of Mo metal raw material is 99.95%.

4. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 2, characterized in that: In step S2, the electric arc furnace is evacuated, and then argon gas with a concentration of 99.9% is introduced into it.

5. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 4, characterized in that: In step S2, the melting process is repeated 4 to 6 times.

6. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 2, characterized in that: In the first stage of step S3, the heat preservation time ranges from 5 to 8 hours, and the heating rate is 110 to 140℃ / h.

7. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 2, characterized in that: In the second stage of step S3, the heat preservation time ranges from 5 to 8 hours, and the heating rate is 90 to 100℃ / h.

8. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 2, characterized in that: In the third stage of step S3, the heat preservation time ranges from 12 to 16 hours, and the heating rate is 120 to 150 °C / h.

9. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 2, characterized in that: In the first stage of step S5, the annealing holding time is 20~30 minutes.

10. The method for preparing the NiCoCrFeMo high-entropy alloy according to claim 2, characterized in that: In the second stage of step S5, the annealing holding time is 3~8 hours.

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