A high-strength high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy and a preparation method thereof

Abstract

The application discloses a high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy and a preparation method thereof, and the alloy has multiple strengthening mechanisms through composition, process and structure design, and the yield strength of the alloy is improved by 3 times.The high-strength and high-plasticity heterogeneous structure high-entropy alloy has the characteristics that the high-entropy alloy comprises a soft phase and a hard phase, and the matrix is controlled to precipitate needle-shaped and block-shaped precipitates through a thermal mechanical treatment process, thereby forming a multi-stage and multi-phase heterogeneous structure organization, and the composition of the high-entropy alloy is CoCrNiFeAl.The high-entropy alloy has excellent yield strength, ultimate tensile strength and good fracture elongation, exhibits good strength-ductility synergy, and has a simple and feasible preparation process, and has great engineering application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-performance high-entropy alloy materials, and particularly relates to a high-strength high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy and a preparation method thereof. BACKGROUND

[0002] High-entropy alloy is a new type of high-performance metal material with broad application potential, which takes four or more elements as main elements, the composition element content ratio can be non-atomic ratio, but the maximum main element concentration is not higher than 35%, it breaks the design concept of traditional alloy single main element, opens up a huge, undeveloped alloy composition design field, and provides a large number of new alloy systems for development. High-entropy alloy has high mixing entropy effect, delayed diffusion effect, severe lattice distortion effect and cocktail effect, and thus shows a series of excellent properties different from traditional alloys, such as good comprehensive mechanical properties (strength-toughness matching), excellent damage tolerance, excellent fatigue resistance and radiation resistance, excellent friction and wear resistance and corrosion resistance.

[0003] So far, a large number of multi-main element high-entropy alloys have been reported. Simple single-phase solid solution is usually beneficial to the improvement of mechanical properties, and the element composition and ratio will affect the microstructure of the alloy. Early studies on the equal atomic ratio CoCrNi high-entropy alloy show that the nanotwin formed in the early stage of deformation of the single-phase high-entropy alloy with face-centered cubic (FCC) structure promotes the high strain hardening rate, the twin boundary not only refines the grains but also hinders the slip of dislocations and improves the ability of the alloy to store dislocations, so that the alloy has high strength and hardening rate value. However, similar to the pure metal with FCC structure, although the single-phase high-entropy alloy has high ductility, the yield strength is limited, which limits its engineering application. Therefore, how to coordinate the element composition and ratio to regulate the microstructure of the alloy and obtain a high-entropy alloy with good mechanical properties is one of the technical problems to be solved. How to make the alloy have high strength and good plastic deformation ability at the same time is the key to break through the performance inversion between strength and ductility of the alloy system. SUMMARY

[0004] In view of the good strength-toughness synergistic ability of the CoCrNiFe-based high-entropy alloy, the present application provides a heterogeneous structure high-entropy alloy and a preparation method thereof, a CoCrNiFe-based high-entropy alloy containing soft phase and hard phase and having needle-shaped and block-shaped precipitates is constructed by regulating the element composition and ratio, and a CoCrNiFeAl high-entropy alloy with multi-level heterogeneous structure is obtained through simple thermal mechanical treatment. The alloy has high yield strength and sufficient elongation > 16% for engineering use.

[0005] The present application is realized through the following technical means:

[0006] A high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy, comprising 22-25% of Co, 22-25% of Ni, 22-25% of Cr, 15-25% of Fe and 0-10% of Al in terms of atomic percentage.

[0007] Preferably, the high-entropy alloy is a dual-phase structure, namely an FCC matrix phase and a B2 reinforcing phase.

[0008] Preferably, the ultimate tensile strength, yield strength and elongation at break of the high-entropy alloy are greater than 16%.

[0009] A preparation method of a high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy, comprising the following steps:

[0010] Step 1: mixing and smelting 22-25% of Co, 22-25% of Ni, 22-25% of Cr, 15-25% of Fe and 0-10% of Al in terms of atomic percentage;

[0011] Step 2: homogenizing the alloy obtained by the mixing and smelting in step 1;

[0012] Step 3: cold rolling the alloy obtained in step 2, and immersing in liquid nitrogen after each cold rolling process until the total deformation is 65-75%;

[0013] Step 4: annealing the cold-rolled alloy above the recrystallization temperature to cause recrystallization of the cold-rolled elongated grains, and controlling the annealing time to be 10-30 min to ensure that the alloy does not completely recrystallize and retains a moderate density of dislocations.

[0014] Step 5: aging the alloy treated in step 4 for 2-16 h to obtain a CoCrNiFeAl high-entropy alloy with a multi-level heterogeneous structure.

[0015] Preferably, the alloy is smelted by a vacuum arc smelting method in step 1.

[0016] Preferably, the vacuum is first reduced to 10 Pa, and then fine vacuum is reduced to 5x10 -3 Pa, high-purity argon is introduced, the smelting induction current is 220-240 A, the alloy smelting process is accompanied by electromagnetic stirring, and the alloy sample is cooled in a water-cooled copper crucible after repeated remelting 4-6 times;

[0017] Preferably, the homogenization treatment temperature in step 2 is 1200-1240℃.

[0018] Preferably, water quenching is performed after each annealing.

[0019] Preferably, the recrystallization annealing temperature is 850-950 DEG C, and the aging treatment temperature is 600-750 DEG C.

[0020] Compared with the prior art, the application has the following beneficial technical effects:

[0021] The application provides a high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy, the alloy elements are designed based on valence electron concentration, dislocation energy, lattice mismatch degree and thermodynamic parameter calculation, and simple thermal mechanical treatment is performed, so that the CoCrNiFe-based high-entropy alloy containing a soft phase and a hard phase and having needle-shaped and block-shaped two-morphology precipitates is obtained, and the strength-ductility synergistic ability is improved. Generally, the CoCrFeNi alloy has multiple slip systems due to the crystallographic characteristics of the FCC structure, has good plastic deformation capacity, but the yield strength is limited, and is generally 250-350 MPa. Therefore, in order to improve the yield strength of the alloy and maintain good plasticity, the application introduces multiple strengthening mechanisms through composition design and microstructure control, so that the yield strength of the high-entropy alloy is improved by 3 times. The application has excellent room temperature mechanical properties, the yield strength of the CoCrNiFe alloy is improved to about 1157 MPa, the tensile strength is improved by 2 times to 1394 MPa, and more than 16 % of the tensile ductility is simultaneously achieved. Based on the above characteristics, the application has a great competitive advantage in the FCC-based high-entropy alloy, and has great engineering application prospect.

[0022] The preparation method provided by the application is simple, and excellent mechanical properties can be obtained only by simple thermal mechanical treatment. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The microstructure organization diagram of the high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy of the application is shown in the figure;

[0024] Figure 2 The tensile property comparison diagram of the high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy of the application is shown in the figure;

[0025] Figure 3 The strength and plasticity comparison diagram of the high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy of the application and other dual-phase structure high-entropy alloys is shown in the figure; DETAILED DESCRIPTION

[0026] The application will be further described in detail below with reference to the accompanying drawings, which are an explanation of the application rather than a limitation.

[0027] A high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy, comprising 22-25% of Co, 22-25% of Ni, 22-25% of Cr, 15-25% of Fe and 0-10% of Al in terms of atomic percentage (at%).

[0028] The above raw materials are high-purity metal particles with a purity of not less than 99.95%.

[0029] The CoCrNiFe-based high-entropy alloy has a dual-phase structure and a certain density of dislocations, and the dislocation density is: ρ = (3.0-5.0) × 10 14 m -2 The recrystallized grain size in the matrix is about 0.6-2 μm, and the B2 phase exhibits a blocky and acicular morphology, and the B2 phase in the FCC phase grain exhibits a nanometer acicular morphology.

[0030] The heterogeneous structure CoCrNiFe-based high-entropy alloy has a tensile strength of 1321-1394 MPa, a yield strength of 1064-1157 MPa, and an elongation of 16.17-21.6%.

[0031] The B2 reinforcing phase in the CoCrNiFe-based high-entropy alloy has a certain plastic deformation capacity, and the initial dislocation source and back stress effect promote the deformation of the B2 phase, while the B2 phase reduces the alloy stacking fault energy by redistributing the elements and locally generates a higher stress concentration, resulting in the formation of deformation twins during the deformation of the alloy.

[0032] The CoCrNiFe-based high-entropy alloy has a multi-level heterogeneous structure, on the one hand, the alloy exhibits a two-phase structure, which is a combination of soft FCC phase and hard B2 phase in mechanical properties, and the B2 phase exhibits blocky and acicular characteristics in morphology, and the B2 phase also exhibits nanometer acicular morphology in the FCC phase grain, producing a strong back stress strengthening effect.

[0033] Through composition, process and structure design, the synergistic strengthening of multiple strengthening mechanisms of the CoCrNiFe-based high-entropy alloy is achieved to realize high strength.

[0034] The preparation method of the above high-strength and high-plasticity CoCrNiFe-based heterogeneous structure high-entropy alloy comprises the following steps:

[0035] Step 1: uniformly mix 22-25% of Co, 22-25% of Ni, 22-25% of Cr, 15-25% of Fe and 0-10% of Al metal particles in terms of atomic percentage.

[0036] When the raw materials are weighed, the weight is accurate to 0.001 g, and the mixed metal particles are melted into an alloy by an arc melting method.

[0037] The melting process is first vacuumed to 10 Pa, then fine vacuumed to 5*10 -3 Pa, high-purity argon is introduced, the alloy melting process is accompanied by electromagnetic stirring, in order to ensure the uniformity of the composition, the alloy sample is cooled in a water-cooled copper crucible after repeated remelting 4-6 times.

[0038] Step 2 homogenizes the alloy at a temperature range of 1200-1240°C.

[0039] Step 3 cold-rolls the alloy sample obtained in step 2, and then immerses it in liquid nitrogen for 1-3 minutes after each cold-rolling treatment until the total deformation is 75%.

[0040] Step 4 anneals the cold-rolled alloy above the recrystallization temperature, the temperature range is 850-950°C, recrystallizes the cold-rolled elongated grains, controls the annealing time to be 10-30 minutes, and ensures that the alloy does not completely recrystallize and retains a moderate density of dislocations.

[0041] Step 5 ages the alloy treated in step 4, the aging temperature range is 600-750°C, the aging time is 2-16 hours, and a CoCrNiFeAl high-entropy alloy with a multi-level heterogeneous structure is obtained.

[0042] Example 1

[0043] A method for preparing a high-strength and high-plasticity CoCrNiFeAl heterogeneous high-entropy alloy includes the following steps:

[0044] Step 1: uniformly mix 25% Co, 25% Ni, 25% Cr, 15.5% Fe, and 9.5% Al metal particles according to the atomic percentage.

[0045] The melting process is first vacuumed to 10 Pa, then fine vacuumed to 5*10 -3 Pa, high-purity argon is introduced, the alloy melting process is accompanied by electromagnetic stirring, in order to ensure the uniformity of the composition, the alloy sample is cooled in a water-cooled copper crucible after repeated remelting 5 times.

[0046] Step 2 homogenizes the alloy sample at 1230°C.

[0047] Step 3 cold-rolls the alloy sample obtained in step 2, and then immerses it in liquid nitrogen for 1-3 minutes after each cold-rolling treatment until the total deformation is 75%.

[0048] Step 4: annealing the alloy after cold rolling at 850-950℃ to make the cold-rolled elongated grains recrystallize, and control the annealing time to be 10 min to ensure that the alloy does not completely recrystallize and retains a moderate density of dislocations.

[0049] Step 5: aging the alloy treated in step 4 at a temperature range of 600-750℃ for 4h to obtain a CoCrNiFeAl high-entropy alloy with a multi-level heterogeneous structure.

[0050] The heterogeneous high-entropy alloy has a dual-phase structure with a certain density of dislocations, and the dislocation density is: ρ = (3.0-5.0) x 10 14 m -2 The recrystallized grain size in the matrix is about 0.6-2μm, and the B2 phase appears as blocky and needle-like morphology, and the B2 phase in the matrix grain appears as nanometer needle-like morphology. This structure makes the alloy have high yield strength and good ductility. According to the requirements of GB / T228.1-2010 standard, the mechanical properties of the alloy are measured as shown in curve 1 in the figure: the tensile strength is 1394MPa, the yield strength is 1157MPa, and the elongation at break is 16.1%, and the alloy has high strength and high ductility. Figure 2

[0051] Example 2

[0052] A method for preparing a high-strength high-ductility CoCrNiFeAl heterogeneous high-entropy alloy includes the following steps:

[0053] Step 1: mix 25% Co, 25% Ni, 25% Cr, 15.5% Fe and 9.5% Al metal particles uniformly according to the atomic percentage.

[0054] During the melting process, first vacuum to 10Pa, then fine vacuum to 5x10 -3 Pa, introduce high-purity argon, the melting induction current is 220-240A, and the alloy melting process is accompanied by electromagnetic stirring. To ensure uniformity of composition, repeat remelting 5 times, then cool in a water-cooled copper crucible to obtain a cast alloy sample.

[0055] Step 2: homogenize the cast alloy sample at 1230℃.

[0056] Step 3: cold roll the alloy sample obtained in step 2, and after each cold rolling treatment, soak in liquid nitrogen until the total deformation is 75%.

[0057] Step 4: annealing the alloy after cold rolling at 850-950℃ to make the cold-rolled elongated grains recrystallize, and control the annealing time to be 10 min to ensure that the alloy does not completely recrystallize and retains a moderate density of dislocations. ​

[0058] Step 5: aging treatment of the alloy treated in step 4, aging temperature range is 600-750℃, aging time is 4h, to obtain CoCrNiFeAl high-entropy alloy with multi-level heterogeneous structure.

[0059] The heterogeneous high-entropy alloy is a dual-phase structure with a certain density of dislocations, the recrystallized grain size in the matrix is about 0.6-2μm, and the B2 phase exhibits blocky and needle-like morphology, and the B2 phase in the matrix phase grain exhibits nanometer needle-like morphology. Such structure makes the alloy have high yield strength and good ductility. According to the requirements of GB / T228.1-2010 standard, the mechanical properties of the alloy are measured as Figure 2 as shown in curve 2: the tensile strength is 1321MPa, the yield strength is 1064MPa, and the fracture elongation is 21.6%, and the alloy has excellent strength and plasticity.

[0060] Comparative Example 1

[0061] A CoCrNiFe high-entropy alloy, according to atomic percentage, includes 25-28% Ni, 25-28% Co, 25-28% Cr, and 15-17% Fe, and the preparation method is rolling annealing.

[0062] A single-phase model CoCrNiFe high-entropy alloy is prepared to obtain a recrystallized structure. In the single-phase FCC structure, the equiaxed grain size is 10μm. According to the requirements of GB / T228.1-2010 standard, the mechanical properties of the alloy are measured as Figure 2 as shown in curve 4: the tensile strength is 701MPa, the yield strength is 297MPa, and the fracture elongation is 61.4%, and the alloy has excellent plasticity but limited strength.

[0063] Comparative Example 2

[0064] The as-cast CoCrNiFeAl high-entropy alloy sample prepared in Example 1 is subjected to 1230℃ homogenization annealing, and then the alloy sample is cold-rolled, after each cold rolling treatment, it is immersed in liquid nitrogen until the total deformation is 75%, and the mechanical properties are tested.

[0065] According to the requirements of GB / T228.1-2010 standard, the mechanical properties of the alloy are measured as Figure 2 as shown in curve 3: the tensile strength is 1478MPa, the yield strength is 1200MPa, and the fracture elongation is 6.1%, and the alloy has excellent strength but limited plasticity.

[0066] Figure 1The microstructure diagram of the CoCrNiFeAl heterogeneous structure high-entropy alloy of the application is shown in the figure, and it can be seen from the figure that the alloy shows a dual-phase heterogeneous structure, has needle-shaped and block-shaped B2 phases, and there are nanometer needle-shaped B2 precipitated phases (white arrow indicates the area) in the FCC matrix phase, and the alloy has a certain density of dislocations.

[0067] Figure 2 The room temperature tensile curves and the corresponding strain hardening curves of the CoCrNiFeAl heterogeneous structure high-entropy alloy of the application, embodiment 1, embodiment 2, and comparative examples 1 and 2 are shown in the figure, wherein 1# represents embodiment 1, 2# represents embodiment 2, 3# represents comparative example 2, and 4# represents comparative example 1.

[0068] Figure 3 The strength-plasticity comparison diagram of the CoCrNiFeAl heterogeneous structure high-entropy alloy of the application and other dual-phase structure medium / high-entropy alloys is shown in the figure, and the data point represented by "This work" is the data point of the embodiment 1 (1#) of the application, and it can be seen that compared with the alloys involved in other works, it has higher ductility under the same strength and has better strength under the same ductility, indicating that the CoCrNiFeAl heterogeneous structure high-entropy alloy of the application has improved strength-ductility synergy ability and has excellent mechanical properties of high strength and high plasticity.

[0069] The application provides a high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy, the composition of the alloy elements is designed based on the valence electron concentration, the stacking fault energy, the lattice mismatch degree and the thermodynamic parameter calculation, and a simple thermal mechanical treatment is performed, so that a CoCrNiFe-based high-entropy alloy containing soft and hard phases and having needle-shaped and block-shaped precipitated phases is obtained, and the strength-ductility synergy ability is improved. Generally, the CoCrFeNi alloy has multiple slip systems due to the crystallographic characteristics of the FCC structure, has good plastic deformation ability, but the yield strength is limited, generally in the range of 250-350 MPa. Therefore, in order to improve the yield strength of the alloy and maintain good plasticity, the application introduces multiple strengthening mechanisms through composition design and microstructure control, so that the yield strength of the high-entropy alloy is increased by 3 times. The application has excellent room temperature mechanical properties, and the yield strength of the CoCrNiFe alloy is increased to about 1157 MPa, the tensile strength is increased by 2 times to about 1394 MPa, and at the same time, more than 16% of the tensile ductility is possessed.

[0070] The above content only illustrates the technical idea of the application, and cannot limit the protection scope of the application. Any modification made according to the technical idea of the application on the basis of the technical scheme falls within the protection scope of the claims of the application.

Claims

1. A high-strength and high-ductility CoCrNiFeAl heterogeneous structure high-entropy alloy, characterized in that: In a face-centered cubic structure CoCrNiFe-based high-entropy alloy, Al element is added to obtain a CoCrNiFeAl high-entropy alloy with a dual-phase heterogeneous structure of a blocky hard B2 phase and a soft FCC matrix containing nanometer needle-shaped hard B2 phase, and the composition of the high-entropy alloy includes 22-25% of Co, 22-25% of Ni, 22-25% of Cr, 15-20% of Fe and 5-10% of Al according to the atomic percentage; the preparation method of the high-entropy alloy is as follows: mixing and smelting according to the atomic percentage; homogenizing the obtained sample to obtain an alloy sample; cold rolling the obtained alloy sample; annealing the cold-rolled alloy above the recrystallization temperature to make the cold-rolled elongated grains recrystallize, and controlling the annealing time to be 10-30 min to ensure that the alloy does not completely recrystallize and retains a certain density of dislocations, ρ=(3.0-5.0)×10 14 m -2 , aging the treated alloy to obtain a CoCrNiFeAl high-entropy alloy with a multi-level heterogeneous structure, obtaining a blocky B2 phase through recrystallization heat treatment, obtaining a nanometer needle-shaped B2 phase through one-step aging treatment, and finally obtaining a multi-level dual-phase heterogeneous structure of a blocky hard B2 phase and a soft FCC matrix containing nanometer needle-shaped hard B2 phase in the CoCrNiFeAl high-entropy alloy.

2. The high-strength and high-ductility CoCrNiFeAl heterogeneous structure high-entropy alloy according to claim 1, characterized in that, The volume fraction of B2 phase in the dual-phase heterogeneous structure is 10-12%, and the recrystallized grain size of the matrix is 0.6-2 μm.

3. The high-strength and high-ductility CoCrNiFeAl heterogeneous structure high-entropy alloy according to claim 1, characterized in that The high-entropy alloy has a medium density of dislocations, p = (3.0-5.0) x 10 14 m -2 .

4. The high-strength and high-ductility CoCrNiFeAl heterogeneous structure high-entropy alloy of claim 1, wherein The yield strength is 1.06-1.16 GPa, and the elongation at break is 16-22%.

5. A method for preparing the high-strength high-ductility CoCrNiFeAl heterogeneous structure high-entropy alloy of claim 1, characterized in that, The method comprises the following steps: Step 1: mixing and smelting 22-25% of Co, 22-25% of Ni, 22-25% of Cr, 15-20% of Fe and 5-10% of Al according to the atomic percentage; Step 2: homogenizing the sample obtained in step 1 at a temperature interval of 1200-1240 ℃; Step 3: cold rolling the alloy sample obtained in step 2, and immersing in liquid nitrogen for 1-3 min after each cold rolling treatment until the total deformation amount is 65-75%; Step 4: The cold-rolled alloy is annealed above the recrystallization temperature to cause recrystallization of the cold-rolled elongated grains. The annealing time is controlled to be 10-30 min to ensure that the alloy does not completely recrystallize and retains a certain density of dislocations, ρ = (3.0-5.0) x 1014. 14 m -2 ; Step 5: aging the alloy treated in step 4 to obtain a CoCrNiFeAl high-entropy alloy with a multi-level heterogeneous structure, a blocky B2 phase is obtained through recrystallization heat treatment, a nanometer needle-shaped B2 phase is obtained through one-step aging treatment, and finally the CoCrNiFeAl high-entropy alloy obtains a multi-level dual-phase heterogeneous structure containing a blocky hard B2 phase and a soft FCC matrix containing a nanometer needle-shaped hard B2 phase.

6. The preparation method of the high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy according to claim 5, characterized in that The mixing and smelting in step 1 adopts vacuum arc smelting.

7. The preparation method of high-strength and high-plasticity CoCrNiFeAl heterogeneous structure high-entropy alloy according to claim 5, characterized in that, The melting process is vacuumed to 10 Pa first, and then fine vacuumed to 5*10 -3 Pa, high-purity argon is introduced, the inductive current is 220-240 A during the alloy melting process, electromagnetic stirring is accompanied, in order to ensure the uniformity of the composition, the cast alloy sample is obtained by repeatedly remelting 4-6 times and then cooling in a water-cooled copper crucible.

8. The method of claim 5, wherein The recrystallization annealing temperature in step 4 is 850-950 ℃.

9. The method of claim 5, wherein The aging temperature in step 5 is 600-750 ℃, and the aging time is 2-16 h.

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