Nanometer precipitation strengthening high-entropy alloy and preparation method thereof

Abstract

The invention relates to a nano-precipitation strengthened high-entropy alloy and a preparation method thereof, in particular to a nano-precipitation strengthened high-entropy alloy and a preparation method thereof. The invention aims to solve the problem of strength-plasticity mutual exclusion effect of the traditional alloy. The chemical formula of the nano-reinforced high-entropy alloy is Co28Cr30Cu6Mn15Ni21, an alloy ingot is prepared by adopting a simple vacuum arc melting technology, then a high-density coherent nano precipitated phase (lattice mismatch delta = 2.2%) is introduced into an alloy matrix by accurately regulating and controlling an alloy aging heat treatment process, the strength and plasticity are synergistically improved, the yield strength reaches 433 MPa after aging is performed for 5 h at the temperature of 600 DEG C, and the tensile strength reaches 433 MPa after aging is performed for 5 h at the temperature of 600 DEG C. And compared with an as-cast state, the ductility is improved by 37%, the ductility is synchronously improved to 53%, and the strength-plasticity trade-off effect is broken through. The method is applied to the field of high-entropy alloys.

Description

Technical Field

[0001] The invention relates to a nano-precipitation strengthened high-entropy alloy and a preparation method thereof. Background Art

[0002] High-entropy alloys (HEAs) are a new class of metallic materials composed of multiple primary elements. They exhibit properties such as high entropy, severe lattice distortion, slow diffusion, and cocktail effects. In recent years, they have attracted widespread attention due to their excellent comprehensive mechanical properties, thermal stability, and corrosion resistance. The CoCrCuMnNi quinary alloy system, exhibiting good ductility and moderate strength, is considered a typical "flexible" HEA. However, significant limitations exist in improving the strength of these alloys, particularly achieving a synergistic effect between strength and plasticity without sacrificing ductility. Traditional strengthening mechanisms, such as solid solution strengthening and grain boundary strengthening, have limited effectiveness in these alloys. Therefore, the introduction of nanoscale precipitations (nanoprecipitations) as a secondary phase strengthening method has become an effective strategy for improving their overall properties. Previous studies have demonstrated that the introduction of well-sized, well-oriented nanoprecipitates (e.g., L12 structure) into an FCC matrix can significantly improve the yield strength and tensile strength of the alloy while maintaining good ductility. However, achieving this type of nanoprecipitation strengthening mechanism still faces the following technical challenges: First, traditional alloy design methods (such as high-throughput calculations and diffusion couple experiments) have difficulty accurately predicting the precipitate formation pathway in multi-component systems, often accompanied by incoherent coarse precipitates that trigger grain boundary embrittlement. Therefore, it is necessary to design a rational alloy composition to induce precipitate formation without causing severe element segregation. Second, existing nanoprecipitation-strengthened HEAs rely on complex thermomechanical treatments, requiring a controlled heat treatment regime to precisely control the nucleation and growth behavior of the precipitate. Third, the interfacial structure and compatibility between the precipitate and the matrix significantly influence the mechanical properties, requiring high coherence between the precipitate and the matrix. Therefore, it is urgent to develop a new alloy composition and process pathway that can form uniform, stable, and size-controlled nanoprecipitates in CoCrCuMnNi-based high-entropy alloys to achieve a synergistic improvement in high strength and high ductility, thereby expanding their application prospects in high-performance structural materials such as aerospace and nuclear power equipment. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem that the existing CoCrCuMnNi quinary alloy system cannot achieve strength-plastic synergy, and to propose a nano-precipitation strengthened high entropy alloy and a preparation method thereof.

[0004] The nano-precipitation strengthened high entropy alloy of the present invention is composed of 28% Co, 30% Cr, 6% Cu, 15% Mn and 21% Ni in atomic percentage, and its chemical formula is Co 28 Cr30 Cu6Mn 15 Ni 21 .

[0005] A method for preparing a nano-precipitation strengthened high entropy alloy is carried out by the following steps:

[0006] 1. Weighing metal elements in atomic percentages of 28% Co, 30% Cr, 6% Cu, 15% Mn and 21% Ni to obtain a raw material;

[0007] 2. Pre-treat the raw materials, then add the raw materials into the crucible of the melting furnace, evacuate the melting furnace and fill it with protective gas, melt it, and after cooling, obtain the button ingot sample;

[0008] 3. The button ingot sample is repeatedly melted and then cooled, ultrasonically cleaned and then aged to obtain a nano-precipitation strengthened high entropy alloy.

[0009] The alloy composition of the present invention is Co 28 Cr 30 Cu6Mn 15 Ni 21 (at.%), satisfying the following thermodynamic criteria:

[0010] Mixing entropy (>1.5R, ensuring high entropy effect)

[0011] Atomic size difference δ = 2.85% (<6.6%, suppressing amorphization)

[0012] Valence electron concentration VEC = 8.13 (close to the FCC phase stability threshold of 8.55)

[0013] Aging process of the present invention:

[0014] Temperature window: 400-600 ℃ (below 700 ℃ to avoid grain boundary coarsening and precipitation).

[0015] Time window: 1–5 hours (more than 5 hours induces Co / Cr-rich sigma phase or Cr-rich BCC phase).

[0016] Optimized parameters: 600°C × 5 hours, water quenching to retain the coherence of the nanoprecipitate phase.

[0017] The formation mechanism of the high entropy alloy nanoprecipitate phase of the present invention is as follows:

[0018] Spinodal decomposition: The Cu element undergoes spinodal decomposition during the aging process to form a Cu-rich nano-precipitate phase (λ=20nm).

[0019] Coherent interface: The lattice mismatch between the precipitate phase and the FCC matrix is ​​δ=2.2%. Calculation formula:

[0020]

[0021] Strengthening mechanism: Modulus strengthening ( ) plays a leading role, contributing to a strength increase of ~125 MPa.

[0022] Beneficial effects of the present invention:

[0023] The present invention provides a Co 28 Cr 30 Cu6Mn 15 Ni 21 A novel method for preparing nano-reinforced high-entropy alloy compositions utilizes a coordinated arc melting and aging process to introduce a coherent nano-precipitate phase into the HEAs matrix, achieving a synergistic improvement in both high strength (yield strength ≥ 400 MPa) and high ductility (elongation ≥ 50%). This high-entropy alloy exhibits excellent strength and ductility, and holds great promise for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the alloy aging process flow chart;

[0025] Figure 2 As-cast Co 28 Cr 30 Cu6Mn 15 Ni 21 Microstructure of HEA;

[0026] Figure 3 Microstructure of Co28Cr30Cu6Mn15Ni21 HEA aged for 1 hour at different temperatures; (ab) 400 ℃; (cd) 500 ℃; (ef) 600 ℃; (gh) 700 ℃; (ij) 800 ℃;

[0027] Figure 4 For Co 28 Cr 30 Cu6Mn 15 Ni 21 Microstructure of HEA after aging treatment at 600℃ for different durations: (ab) 1 hour; (cd) 2 hours; (ef) 5 hours; (gh) 8 hours; (ij) 10 hours;

[0028] Figure 5 For Co 28 Cr 30 Cu6Mn 15 Ni 21Tensile engineering stress-strain curves of HEA as-cast and after aging at 600°C for 5 and 10 hours;

[0029] Figure 6 For Co 28 Cr 30 Cu6Mn 15 Ni 21 True stress-strain curves and strain hardening rate curves of HEA in the as-cast state and after aging at 600℃ for 5 hours;

[0030] Figure 7 For Co 28 Cr 30 Cu6Mn 15 Ni 21 Yield strength and elongation of HEA after aging at 400-800°C for 1 hour;

[0031] Figure 8 For Co 28 Cr 30 Cu6Mn 15 Ni 21 Yield strength and elongation of HEA after aging at 600 °C for 1 h, 2 h, 5 h, 8 h, and 10 h;

[0032] Figure 9 Co aged at 600℃ for 5 hours 28 Cr 30 Cu6Mn 15 Ni 21 TEM characterization of HEAs. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is not limited to the specific implementation methods listed below, but also includes any combination of the specific implementation methods.

[0034] Specific embodiment 1: In this embodiment, a nano-precipitation strengthened high entropy alloy is composed of 28% Co, 30% Cr, 6% Cu, 15% Mn and 21% Ni in atomic percentage, and the chemical formula is Co 28 Cr 30 Cu6Mn 15 Ni 21 .

[0035] Specific embodiment 2: In this embodiment, a method for preparing a nano-precipitation strengthened high entropy alloy is carried out according to the following steps:

[0036] 1. Weighing metal elements in atomic percentages of 28% Co, 30% Cr, 6% Cu, 15% Mn and 21% Ni to obtain a raw material;

[0037] 2. Pre-treat the raw materials, then add the raw materials into the crucible of the arc melting furnace, evacuate the melting furnace and fill it with protective gas, melt it, and after cooling, obtain the button ingot sample;

[0038] 3. The button ingot sample is repeatedly melted and then cooled, ultrasonically cleaned and then aged to obtain a nano-precipitation strengthened high entropy alloy.

[0039] Specific embodiment 3: This embodiment differs from specific embodiment 2 in that the pretreatment in step 2 refers to cleaning with ultrasonic waves, followed by rinsing with anhydrous ethanol and drying for later use. Other aspects are the same as specific embodiment 2.

[0040] Specific embodiment 4: This embodiment differs from specific embodiment 2 or 3 in that in step 2, the raw materials are added to the crucible of the smelting furnace from bottom to top in the order of melting point from low to high.

[0041] Specific embodiment 5: This embodiment differs from the first of the specific embodiments 2 to 4 in that the mechanical pump is first turned on to evacuate to a vacuum degree of ≤30Pa, then the mechanical pump is turned off and the molecular pump is turned on to continue evacuating until the pressure is ≤5×10 - 3 Pa, turn off the molecular pump, open the vent valve, and fill the protective gas to 50 Pa. Other aspects are the same as those in the second to fourth embodiments.

[0042] Specific embodiment 6: This embodiment differs from specific embodiments 2 to 5 in that the protective gas used in step 2 is argon or helium. Other aspects are the same as specific embodiments 2 to 5.

[0043] Specific embodiment 7: This embodiment differs from specific embodiments 2 to 6 in that: in step 3, the button ingot sample is repeatedly melted and turned over 5 times. Other aspects are the same as specific embodiments 2 to 6.

[0044] Specific embodiment 8: This embodiment differs from specific embodiments 2 to 7 in that the aging step 3 is performed at 600° C. for 5 hours. Other aspects are the same as specific embodiments 2 to 7.

[0045] Specific embodiment 9: This embodiment differs from specific embodiments 2 to 8 in that the yield strength of the prepared nano-precipitation-strengthened high-entropy alloy is ≥400 MPa and the elongation is ≥50%. Other aspects are the same as specific embodiments 2 to 8.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Example 1: A method for preparing a nano-precipitation-strengthened high-entropy alloy. The preparation method is as follows:

[0048] (1) Weigh 150 g of raw materials containing 28% Co, 30% Cr, 6% Cu, 15% Mn, and 21% Ni in atomic percentage. Considering burnout and volatilization, weigh each element at 103% of the atomic ratio.

[0049] (2) Preparation of alloy mother ingot: Add the pre-treated metal raw materials into the crucible of the smelting furnace from bottom to top in the order of melting point from low to high. After closing the vacuum chamber, turn on the mechanical pump, evacuate the chamber to below 30Pa and then turn off the mechanical pump. Turn on the molecular pump and continue evacuating until the pressure is below 5×10 -3 Pa, turn off the molecular pump. Open the vent valve and introduce high-purity argon to 50Pa. After vacuuming and introducing protective gas, start alloy smelting. Before starting to smelt the alloy ingot, first melt a titanium metal ingot with a mass of 100g to consume the residual oxygen in the furnace. During the smelting process, gradually increase the power supply to completely melt the metal. After the initial smelting is completed, wait for the molten metal to solidify into a button ingot, turn the ingot over, and smelt it again. The alloy ingot needs to be repeatedly smelted and turned over five times to ensure uniform distribution of elements. Finally, the alloy ingot is obtained. After cooling for more than 20 minutes, open the vacuum chamber and take out the ingot.

[0050] (3) Aging heat treatment

[0051] The alloy button ingots were cut into dog-bone tensile specimens with gauge dimensions of 10mm × 2mm × 1.8mm and scanning specimens with dimensions of 10mm × 10mm × 5mm using wire-cut electrospark cutting technology, and then cleaned using ultrasonic waves. After cutting, the specimens were aged. The specific aging heat treatment route is as follows: Figure 1 shown.

[0052] Experimental test analysis:

[0053] Figure 2 Is cast Co 28 Cr 30 Cu6Mn 15 Ni 21 Scanning organization diagram of HEA, where Figures a and c are cast Co 28 Cr 30 Cu6Mn 15 Ni 21 The microstructure of the steel is shown in Figure 1. a is a local enlarged view of the grain boundary, c is the element distribution, and b is the mixing enthalpy between the five elements. Figure 2 The results showed clear grain boundaries, with no harmful large precipitates observed at the grain boundaries. The as-cast alloy exhibited significant element segregation. EDS analysis revealed that cobalt, chromium, and nickel were primarily concentrated in the dendrite region, while copper and manganese were enriched in the interdendritic region.

[0054] The as-cast samples were aged in a heat treatment furnace at 400-800°C for 1 hour and then water quenched. Figure 3 Shows Co 28 Cr 30 Cu6Mn 15 Ni 21 Microstructure of HEA after aging at 400-800°C for 1 hour; (ab) 400°C; (cd) 500°C; (ef) 600°C; (gh) 700°C; (ij) 800°C; the right figure is a magnified view of the box on the left.

[0055] from Figure 3 As can be seen, copper segregation was observed in all samples at different aging temperatures, similar to the situation in the as-cast alloy. At aging temperatures between 400°C and 600°C, the grain boundaries remained smooth and intact, with no large precipitates observed at the grain boundaries. However, after aging at 700°C and 800°C, harmful large precipitates were detected at the grain boundaries, leading to the selection of 600°C for aging.

[0056] The as-cast specimens were aged in a 600°C heat treatment furnace for 1, 2, 5, 8, or 10 hours and subsequently water quenched. Figure 4 Shows Co 28 Cr 30 Cu6Mn 15 Ni 21 Microstructures of HEA aged at 600°C for different times: (a-b) 1 hour; (c-d) 2 hours; (e-f) 5 hours; (e-gh) 8 hours; and (i-j) 10 hours. The right image is a magnified view of the boxed area in the left image. Copper segregation was observed in all samples at different aging times, similar to that of the as-cast alloy. For aging times of 1 to 5 hours, the grain boundaries remained smooth and intact, with no large precipitates observed at the grain boundaries. After aging for 8 and 10 hours, detrimental large precipitates were observed at the grain boundaries.

[0057] Figures 5 to 8 Shows Co 28 Cr 30 Cu6Mn 15 Ni 21The mechanical properties of HEA show that, compared to the as-cast alloy, after aging at 600°C for 5 hours, the yield strength of the alloy increased from 315 MPa to 433 MPa, a 37% increase in strength. This strengthening effect is achieved without sacrificing ductility, with the elongation increasing from 48% to 53%, effectively overcoming the strength-ductility mutual exclusion effect. The strain hardening rate peaks at 1652 MPa, significantly higher than that of the as-cast alloy (1425 MPa). When aged at 400°C to 600°C for 1 hour, the yield strength of the alloy gradually increases. After aging at 700°C for 1 hour, the yield strength reaches a peak of 412 MPa, but the ductility decreases significantly, with the elongation dropping to 36%. Similarly, when aged at 800°C, both strength and ductility decrease.

[0058] After aging at 600 °C for 8 and 10 hours, the ductility of the alloy decreases significantly. After aging at 600 °C for 10 hours, the yield strength reaches 435 MPa, while the elongation decreases to 41%.

[0059] Figure 9 Co aged at 600℃ for 5 hours 28 Cr 30 Cu6Mn 15 Ni 21 TEM results of the HEA. (a-b) Brightfield images; (c) SAED pattern from the entire area shown in (b); (d) Average spacing of the nanoprecipitates; (e-g) HRTEM image and its corresponding FFT transform, showing complete coherence between the nanoprecipitates and the matrix; (hi) The intensity distribution along the arrow in (g) shows the atomic arrangement and interplanar spacing between the two phases; (f) STEM image and its corresponding elemental distribution map. The results show that after aging at 600°C for 5 hours, the alloy undergoes spinodal decomposition, forming uniformly distributed nanoprecipitates with an FCC crystal structure. The average spacing of these nanoprecipitates is approximately 20 nm. The nanoprecipitates are completely coherent with the matrix, with a lattice mismatch (δ) of approximately 2.2%. These nanoprecipitates are rich in copper. The formation of these nanoprecipitates allows the alloy to achieve increased strength without sacrificing ductility, breaking the traditional strength-ductility trade-off.

Claims

1. A nano-precipitation strengthened high entropy alloy, characterized in that: The high entropy alloy is composed of 28% Co, 30% Cr, 6% Cu, 15% Mn and 21% Ni in atomic percentage, and has the chemical formula Co 28 Cr 30 Cu6Mn 15 Ni 21 .

2. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, wherein: The preparation method is carried out according to the following steps:

1. Weighing metal elements in atomic percentages of 28% Co, 30% Cr, 6% Cu, 15% Mn and 21% Ni to obtain a raw material; 2. Pre-treat the raw materials, then add the raw materials into the crucible of the arc melting furnace, evacuate the melting furnace and fill it with protective gas, melt it, and after cooling, obtain the button ingot sample; 3. The button ingot sample is repeatedly melted and then cooled, ultrasonically cleaned and then aged to obtain a nano-precipitation strengthened high entropy alloy.

3. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, characterized in that The pretreatment described in step 2 refers to cleaning with ultrasound, then rinsing with anhydrous ethanol, and drying for later use.

4. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, wherein In step 2, the raw materials are added to the crucible of the smelting furnace from bottom to top in the order of melting point from low to high.

5. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, characterized in that Step 2: First, turn on the mechanical pump and evacuate until the vacuum degree is ≤30Pa. Then turn off the mechanical pump and turn on the molecular pump. Continue evacuating until the pressure is ≤5×10 -3 Pa, turn off the molecular pump, open the vent valve, and fill in the protective gas to 50Pa.

6. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, characterized in that In step 2, the protective gas used is argon or helium.

7. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, characterized in that Step 3: Repeat the melting and flipping of the button ingot sample 5 times.

8. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, characterized in that Step three, aging, refers to aging at 600°C for 5 hours.

9. The method for preparing a nano-precipitation strengthened high entropy alloy according to claim 1, characterized in that The yield strength of the prepared nano-precipitation strengthened high entropy alloy is ≥400 MPa and the elongation is ≥50%.

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