Preparation method of co-cr-ni medium entropy alloy with heterogeneous grain structure with synchronous improvement of strength and plasticity
The heterogeneous grain structure CoCrNi medium-entropy alloy was prepared by a 'cold rolling-intermediate annealing-cold rolling-annealing' process, which solved the problem of insufficient strength and plasticity of medium- and high-entropy alloys, and achieved simultaneous improvement of strength and plasticity, significantly enhancing the comprehensive mechanical properties of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FUJIAN UNIV OF TECH
- Filing Date
- 2024-01-08
- Publication Date
- 2026-07-21
AI Technical Summary
Existing face-centered cubic high-entropy alloys have shortcomings in terms of strength and plasticity, which seriously limits their development and application as structural materials.
By employing a 'cold rolling-intermediate annealing-cold rolling-annealing' process and rationally designing rolling and heat treatment parameters, a heterogeneous grain structure CoCrNi medium-entropy alloy with simultaneously improved strength and plasticity was prepared.
It achieves simultaneous improvement in strength and plasticity, with tensile strength of 1135-1169 MPa, elongation of 38.9-40.3%, and strength-ductility product of 44.35-47.11 GPa·%, exhibiting excellent comprehensive mechanical properties.
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Figure CN117845116B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of medium-entropy alloy technology, specifically relating to a method for preparing a CoCrNi medium-entropy alloy with a heterogeneous grain structure that simultaneously improves strength and plasticity. Background Technology
[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0003] With the development of industries such as aerospace, automotive, and shipbuilding, the demand for high-performance materials is becoming increasingly urgent. Medium-high entropy alloys, as a new type of structural material, possess unique microstructures and excellent comprehensive mechanical properties, such as high strength, high plasticity, resistance to friction and wear, corrosion resistance, and high-temperature resistance. They have shown great application potential in aerospace, automotive, and shipbuilding fields, attracting increasing attention from researchers. In recent years, among many medium-high entropy alloys with face-centered cubic structures, CoCrNi medium-high entropy alloys have shown good toughness at both room temperature and low temperatures, attracting widespread attention. It is worth noting that face-centered cubic medium-high entropy alloys typically have good plasticity but low strength, severely limiting their development and application as structural materials. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a heterogeneous grain structure CoCrNi medium-entropy alloy with simultaneously improved strength and plasticity. This invention, through the rational design of rolling and heat treatment process parameters and the adoption of a "cold rolling-intermediate annealing-cold rolling-annealing" process, prepares a heterogeneous grain structure CoCrNi medium-entropy alloy with simultaneously improved strength and plasticity.
[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:
[0006] In a first aspect, the present invention provides a method for preparing a CoCrNi medium-entropy alloy with a heterogeneous grain structure that simultaneously improves strength and plasticity. The CoCrNi medium-entropy alloy has the following atomic percentage composition: Co: 33.3%-33.4%, Ni: 33.3%-33.4%, Cr: 33.3%-33.4%; the method includes the following steps:
[0007] S1. Smelt Ni, Co and Cr metal particles to obtain alloy ingots, and cut the alloy ingots into blocks after homogenization;
[0008] S2. The block obtained in step S1 is subjected to multiple cold rolling passes. The sample obtained after cold rolling is annealed at 700-900℃ and then water quenched.
[0009] S3. The sample obtained in step S2 is subjected to multiple cold rolling passes. The sample obtained after cold rolling is annealed at 700℃ and then water quenched to obtain a CoCrNi medium entropy alloy with heterogeneous grain structure that improves both strength and plasticity.
[0010] Preferably, in step S1, during the smelting process, Ni, Co, and Cr metal particles are mixed and smelted in order of increasing melting point, and the smelting is carried out no less than five times.
[0011] Preferably, in step S1, the homogenization temperature is 1090-1110℃ and the time is 5.9-6.1h.
[0012] Preferably, in step S1, the cutting includes wire electrical discharge machining (EDM).
[0013] Preferably, in step S2, the rolling deformation of the multi-pass cold rolling is 59%-61%.
[0014] Preferably, in step S2, the annealing holding time is 29-31 min.
[0015] Preferably, in step S3, the rolling deformation of the multi-pass cold rolling is 74%-76%.
[0016] Preferably, in step S3, the annealing holding time is 29-31 min.
[0017] In a second aspect, the present invention provides a CoCrNi medium-entropy alloy with a heterogeneous grain structure that simultaneously improves strength and plasticity, obtained by the preparation method described in the first aspect.
[0018] Preferably, the tensile strength of the CoCrNi medium-entropy alloy with a heterogeneous grain structure that simultaneously improves strength and plasticity is 1135–1169 MPa, the elongation is 38.9–40.3%, and the strength-ductility product is 44.35–47.11 GPa·s.
[0019] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:
[0020] This invention, through the rational design of rolling and heat treatment process parameters and the adoption of a "cold rolling-intermediate annealing-cold rolling-annealing" process, prepares a non-uniform microstructure (heterogeneous grain structure) CoCrNi medium-entropy alloy with a grain size ranging from 0.36 μm to 5.34 μm and simultaneously improved strength and plasticity. During deformation, the heterogeneous interface generates geometrically necessary dislocations to accommodate the incompatibility of deformation, resulting in heterogeneous deformation-induced strengthening and hardening, significantly enhancing the alloy's work hardening capability, and ultimately achieving a simultaneous improvement in strength and plasticity.
[0021] The heterogeneous grain structure CoCrNi medium-entropy alloy of this invention effectively combines strength and ductility, exhibiting excellent comprehensive mechanical properties. Its tensile strength is 1135–1169 MPa, elongation is 38.9–40.3%, and strength-ductility product is 44.35–47.11 GPa·%. Attached Figure Description
[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0023] Figure 1 This is a schematic diagram of the preparation method of the CoCrNi medium-entropy alloy with heterogeneous grain structure that simultaneously improves strength and plasticity in this invention.
[0024] Figure 2 This is a schematic diagram of a tensile specimen from a CoCrNi medium-entropy alloy with a heterogeneous grain structure, taken in an embodiment of the present invention. (Unit: mm)
[0025] Figure 3 Electron backscattering diffraction (EBSD) patterns of the heterograin structure CoCrNi medium-entropy alloys of Comparative Example 1(a), Example 1(b), Example 2(c) and Example 3(d);
[0026] Figure 4 The X-ray diffraction patterns of the heterogeneous grain structure CoCrNi medium-entropy alloys of Comparative Example 1, Example 1, Example 2 and Example 3 before stretching are shown.
[0027] Figure 5 The X-ray diffraction patterns of the heterogeneous grain structure CoCrNi medium-entropy alloys of Comparative Example 1, Example 1, Example 2 and Example 3 after stretching are shown.
[0028] Figure 6 The engineering stress-strain curves of the heterogeneous grain structure CoCrNi medium-entropy alloys of Comparative Example 1, Example 1, Example 2 and Example 3 are shown.
[0029] Figure 7 The loading-unloading-reloading (LUR) tensile test results are shown for the heterogeneous grain structure CoCrNi medium-entropy alloys of Comparative Example 1 and Example 1.
[0030] Figure 8 For the reason Figure 7 The HDI stress diagram obtained from the load-unload-reload (LUR) tensile test results. Detailed Implementation
[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.
[0032] A schematic flowchart illustrating the preparation method of a heterogeneous grain structure CoCrNi medium-entropy alloy with simultaneously improved strength and plasticity in this embodiment of the invention is shown below. Figure 1 As shown, the "cold rolling-intermediate annealing-cold rolling-annealing" process of the present invention is represented by the temperature change of the sample.
[0033] In this embodiment of the invention, the heterogeneous grain structure CoCrNi medium-entropy alloy sample is processed into a size as shown in the figure. Figure 2 The tensile specimen shown was polished with sandpaper and then subjected to a tensile test at a tensile speed of 0.6 mm / min until it broke. The entire process was automatically controlled by a computer program.
[0034] In this embodiment of the invention, the EBSD sample was first polished with sandpaper, and then polished using an electrolytic polishing machine. The polishing solution was a mixture of 77 ml of alcohol and 23 ml of perchloric acid. The polishing voltage was 30 V, and the polishing time was 30 s. After polishing, the sample was rinsed with alcohol and dried. The accelerating voltage used in the EBSD test was 15 kV, the scan step size was 0.1 μm, and the acquired data was processed using HKLChannel 5 software.
[0035] In this embodiment of the invention, before conducting the XRD experiment, the sample surface is first polished with sandpaper, and then the polished sample is polished with an electrolytic polishing machine. The polishing solution is a mixture of 77 ml alcohol and 23 ml perchloric acid, the polishing voltage is 30 V, the polishing time is 30 s, and after polishing, the sample is rinsed with alcohol and dried.
[0036] Comparative Example 1
[0037] (1) Using Co, Cr, and Ni metal particles (purity 99.98%) as raw materials, based on their atomic percentages of chemical composition: Co: 33.4%, Ni: 33.3%, Cr: 33.3%, the corresponding metal particles were weighed, ultrasonically cleaned in anhydrous ethanol, and dried with cold air. Then, in order of increasing melting point, Ni, Co, and Cr metal particles were sequentially placed into the copper mold crucible of the electric arc melting furnace. Each sample was melted at least five times to ensure the homogeneity of the composition, and finally, an alloy ingot was obtained. The alloy ingot was homogenized at 1100℃ for 6 hours, and finally, the homogenized alloy was cut into blocks of 25mm × 13mm × 10mm by wire electrical discharge machining.
[0038] (2) The sample obtained in step (1) was rolled from 10 mm to 1 mm thickness using a laboratory-grade twin-roll cold rolling mill through multiple passes (rolling deformation was 90%). The cold-rolled sample was then held at 700℃ for 30 min, followed immediately by water quenching. The heterogeneous grain structure CoCrNi medium-entropy alloy was labeled as sample 700. The electron backscattering diffraction results of this sample are as follows: Figure 3 As shown in (a), the X-ray diffraction results before and after stretching are as follows: Figure 4 and Figure 5 As shown. By Figure 3 (a) and Figure 4 It can be seen that the heat-treated sample consists of a single austenite (γ) phase with a grain size ranging from 0.36 μm to 4.29 μm. According to... Figure 5 It can be seen that no phase transformation occurred in the specimen during the tensile deformation process, and the specimen still consists of a single austenite (γ) phase after stretching. The engineering stress-strain curve of the specimen is shown below. Figure 6 As shown, its yield strength is 984 MPa, tensile strength is 1100 MPa, elongation is 28.1%, and strength-ductility product is 30.91 GPa·%.
[0039] Example 1
[0040] (1) Using Co, Cr, and Ni metal particles (purity 99.98%) as raw materials, based on their atomic percentages of chemical composition: Co: 33.4%, Ni: 33.3%, Cr: 33.3%, the corresponding metal particles were weighed, ultrasonically cleaned in anhydrous ethanol, and dried with cold air. Then, in order of increasing melting point, Ni, Co, and Cr metal particles were placed into the copper mold crucible of the electric arc melting furnace. Each sample was melted at least five times to ensure the homogeneity of the composition, and finally, an alloy ingot was obtained. The alloy ingot was homogenized at 1100℃ for 6 hours, and finally, the homogenized alloy was cut into blocks of 25mm × 13mm × 10mm by wire electrical discharge machining.
[0041] (2) The specimens obtained in step (1) were rolled from 10 mm to 4 mm in thickness using a laboratory-grade twin-roll cold rolling mill through multiple passes (rolling deformation was 60%). The cold-rolled specimens were then subjected to annealing at 700 °C for 30 min, followed by immediate water quenching. For ease of description, the specimens were labeled as 700# specimens according to the annealing temperature.
[0042] (3) The 700# sample obtained in step (2) was subjected to multiple cold rolling passes, from 4 mm to 1 mm thickness (rolling deformation of 75%). The cold-rolled sample was held at 700℃ for 30 min, followed immediately by water quenching. The water-quenched heterogeneous grain structure CoCrNi medium-entropy alloy was labeled as the 700-700 sample. The electron backscattering diffraction results of this sample are as follows: Figure 3As shown in (b) above, the X-ray diffraction results before and after stretching are as follows: Figure 4 and Figure 5 As shown. By Figure 3 (b) and Figure 4 It can be seen that the heat-treated sample consists of a single austenite (γ) phase with a grain size ranging from 0.36 μm to 3.43 μm. According to... Figure 5 It can be seen that no phase transformation occurred in the specimen during the tensile deformation process, and the specimen still consists of a single austenite (γ) phase after stretching. The engineering stress-strain curve of the specimen is shown below. Figure 6 As shown, its yield strength is 1023 MPa, tensile strength is 1169 MPa, elongation is 40.3%, and strength-ductility product is 47.11 GPa·s.
[0043] Example 2
[0044] (1) Using Co, Cr, and Ni metal particles (purity 99.98%) as raw materials, based on their atomic percentages of chemical composition: Co: 33.4%, Ni: 33.3%, Cr: 33.3%, the corresponding metal particles were weighed, ultrasonically cleaned in anhydrous ethanol, and dried with cold air. Then, in order of increasing melting point, Ni, Co, and Cr metal particles were sequentially placed into the copper mold crucible of the electric arc melting furnace. Each sample was melted at least five times to ensure the homogeneity of the composition, and finally, an alloy ingot was obtained. The alloy ingot was homogenized at 1100℃ for 6 hours, and finally, the homogenized alloy was cut into blocks of 25mm × 13mm × 10mm by wire electrical discharge machining.
[0045] (2) The sample obtained in step (1) was rolled from 10 mm to 4 mm thickness using a laboratory-grade twin-roll cold rolling mill through multiple passes (rolling deformation was 60%). The cold-rolled sample was then held at 800 °C for 30 min and immediately quenched in water. For ease of description, the sample was marked as 800# sample according to the annealing temperature.
[0046] (3) The 800# sample obtained in step (2) was subjected to multiple cold rolling passes, from 4 mm to 1 mm thickness (rolling deformation of 75%). All cold-rolled samples were held at 800℃ for 30 min, followed immediately by water quenching. The water-quenched heterogeneous grain structure CoCrNi medium-entropy alloys were labeled as 800-700 samples. The electron backscattering diffraction results of these samples are as follows: Figure 3 As shown in (c), the X-ray diffraction results before and after stretching are as follows: Figure 4 and Figure 5 As shown. By Figure 3 (c) and Figure 4 It can be seen that the heat-treated sample consists of a single austenite (γ) phase with a grain size ranging from 0.36 μm to 3.70 μm. According to... Figure 5It can be seen that no phase transformation occurred in the specimen during the tensile deformation process, and the specimen still consists of a single austenite (γ) phase after stretching. The engineering stress-strain curve of the specimen is shown below. Figure 6 As shown, its yield strength is 906 MPa, tensile strength is 1140 MPa, elongation is 38.9%, and strength-ductility product is 44.35 GPa·s.
[0047] Example 3
[0048] (1) Using Co, Cr, and Ni metal particles (purity 99.98%) as raw materials, based on their atomic percentages of chemical composition: Co: 33.4%, Ni: 33.3%, Cr: 33.3%, the corresponding metal particles were weighed, ultrasonically cleaned in ethanol, and dried with cold air. Then, in order of increasing melting point, Ni, Co, and Cr metal particles were sequentially placed into the copper mold crucible of the electric arc melting furnace. Each sample was melted at least five times to ensure the homogeneity of the composition, and finally, an alloy ingot was obtained. The alloy ingot was homogenized at 1100℃ for 6 hours, and finally, the homogenized alloy was cut into blocks of 25mm × 13mm × 10mm by wire electrical discharge machining.
[0049] (2) The specimens obtained in step (1) were rolled from 10 mm to 4 mm thickness using a laboratory-grade twin-roll cold rolling mill through multiple passes (rolling deformation was 60%). The cold-rolled specimens were then subjected to 900°C for 30 min and immediately water quenched. For ease of description, the specimens were marked as 900# specimens according to the annealing temperature.
[0050] (3) The 900# sample obtained in step (2) was subjected to multiple cold rolling passes, from 4 mm to 1 mm thickness (rolling deformation of 75%). The cold-rolled sample was held at 900℃ for 30 min, followed immediately by water quenching. The water-quenched heterogeneous grain structure CoCrNi medium-entropy alloy was labeled as the 900-700 sample. The electron backscattering diffraction results of this sample are as follows: Figure 3 As shown in (d) in the figure, the X-ray diffraction results before and after stretching are as follows: Figure 4 and Figure 5 As shown. By Figure 3 (d) and Figure 4 It can be seen that the heat-treated sample consists of a single austenite (γ) phase with a grain size ranging from 0.36 μm to 5.34 μm. According to... Figure 5 It can be seen that no phase transformation occurred in the specimen during the tensile deformation process, and the specimen still consists of a single austenite (γ) phase after stretching. The engineering stress-strain curve of the specimen is shown below. Figure 6 As shown, its yield strength is 847 MPa, tensile strength is 1135 MPa, elongation is 39.1%, and strength-ductility product is 44.38 GPa·s.
[0051] As shown in Table 1, the heterogeneous grain structure CoCrNi medium-entropy alloy obtained by "cold rolling-annealing" in Comparative Example 1 exhibits superior yield strength and tensile strength, but poor elongation and strength-ductility product, failing to achieve simultaneous improvement in strength and ductility. In contrast, the heterogeneous grain structure CoCrNi medium-entropy alloys obtained in Examples 1-3 simultaneously possess excellent strength and ductility. This invention primarily designs a back stress strengthening mechanism, such as... Figure 7 and Figure 8 As shown, the HDI stress in Example 1 is significantly improved compared to that in Prior Artwork 1. This strengthening mechanism can enhance the alloy's strength and plasticity. The "cold rolling-intermediate annealing-cold rolling-annealing" process (corresponding to 700-700) can increase the alloy's back stress, thereby improving its strength and plasticity. The EBSD diagram shows the cross-scale grain heterogeneous CoCrNi alloy prepared in this invention, composed of ultrafine grains (250 nm to 1 μm) and micron-sized grains (1 μm to 5 μm). Obtaining a cross-scale heterogeneous grain structure can further improve the mechanical properties of high-entropy alloys. This is attributed to the fact that the cross-scale heterogeneous structure can fully utilize the heterogeneous deformation-induced hardening mechanism, enhancing the material's work hardening capability. Simultaneously, the high strength of the cross-scale heterogeneous material induces other deformation mechanisms in the alloy, such as stacking faults and twinning, further enhancing the material's work hardening capability. Ultimately, the cross-scale grain heterogeneous material achieves a perfect combination of high strength and high plasticity.
[0052] Table 1 Mechanical properties of CoCrNi medium-entropy alloys with heterogeneous grain structure
[0053]
[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., 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 CoCrNi medium-entropy alloy with a heterogeneous grain structure that simultaneously improves strength and plasticity, characterized in that, The CoCrNi medium-entropy alloy has the following atomic percentage composition: Co: 33.3%-33.4%, Ni: 33.3%-33.4%, Cr: 33.3%-33.4%; including the following steps: S1. Ni, Co, and Cr metal particles are melted to obtain an alloy ingot. The alloy ingot is then homogenized and cut into blocks. In step S1, the homogenization temperature is 1090-1110 ℃ and the time is 5.9-6.1 h. S2. The block obtained in step S1 is subjected to multiple cold rolling passes. The sample obtained after cold rolling is annealed at 700-900 ℃ and then water quenched. In step S2, the rolling deformation of multiple cold rolling passes is 59%-61%. In step S2, the annealing holding time is 29-31 min. S3. The sample obtained in step S2 is subjected to multiple cold rolling passes. The sample obtained after cold rolling is annealed at 700 ℃ and then water quenched to obtain a CoCrNi medium-entropy alloy with a heterogeneous grain structure that simultaneously improves strength and plasticity. In step S3, the rolling deformation of the multiple cold rolling passes is 74%-76%. In step S3, the annealing holding time is 29-31 min. The resulting grain size is 0.36μm~5.34μm. The tensile strength of the CoCrNi medium-entropy alloy with a heterograin structure that simultaneously improves strength and plasticity is 1135~1169MPa, the elongation is 38.9~40.3%, and the strength-ductility product is 44.35~47.11 GPa•.
2. The preparation method according to claim 1, characterized in that, In step S1, during the smelting process, Ni, Co, and Cr metal particles are mixed and smelted in order of increasing melting point, and the smelting is carried out no less than five times.
3. The preparation method according to claim 1, characterized in that, In step S1, the cutting includes wire electrical discharge machining (EDM).
4. A CoCrNi medium-entropy alloy with a heterogeneous grain structure that simultaneously improves strength and plasticity, characterized in that... Obtained by the preparation method described in any one of claims 1-3.