High-toughness cobalt-based high-entropy alloy and preparation method and application thereof

Abstract

The invention provides a high-toughness cobalt-based high-entropy alloy and a preparation method and application thereof, and belongs to the technical field of high-entropy alloys. The high-toughness cobalt-based high-entropy alloy provided by the invention comprises the following elements in atomic percent: 44 to 47 percent of Co, 28 to 31 percent of Cr, 7 to 8 percent of Fe, 7 to 8 percent of Ni, 7 to 8 percent of Mn and 1.3 to 1.8 percent of X, x comprises at least one of Ti, Zr and Hf. According to the invention, at least one of Ti, Zr and Hf is added on the basis of the cobalt-based high-entropy alloy to form the high-entropy alloy with fcc (face-centered cubic) and hcp (close-packed hexagonal) structures, so that the strength and toughness of the cobalt-based high-entropy alloy are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high entropy alloys, and in particular relates to a high-strength and tough cobalt-based high entropy alloy and a preparation method and application thereof. Background Art

[0002] Cobalt-based high-entropy alloys (HEAs) offer superior strength, hardness, and high-temperature resistance compared to traditional alloys, and are widely used in various fields. CoCrFeNiMn is a commonly used HEAs in the prior art, but its strength and toughness still need to be further improved.

[0003] Therefore, how to further improve the strength and toughness of cobalt-based high-entropy alloys has become a difficult problem in this field. Summary of the Invention

[0004] The present invention aims to provide a high-strength and tough cobalt-based high-entropy alloy and its preparation method and application. The high-strength and tough cobalt-based high-entropy alloy provided by the present invention has higher strength and toughness.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a high-strength and tough cobalt-based high-entropy alloy, which comprises the following elements, calculated in atomic percentage: Co 44-47%, Cr 28-31%, Fe 7-8%, Ni 7-8%, Mn 7-8% and X 1.3-1.8%; X comprises at least one of Ti, Zr and Hf.

[0007] Preferably, the following elements are included in atomic percentage: Co 45-47%, Cr 29-31%, Fe 7-8%, Ni 7-8%, Mn 7-8% and X 1.4-1.6%.

[0008] Preferably, the high-strength and tough cobalt-based high-entropy alloy includes an fcc phase and an hcp phase and a C14-Laves phase distributed at the interface between the fcc phase and the hcp phase.

[0009] The present invention also provides a method for preparing the high-strength and tough cobalt-based high-entropy alloy described in the above technical solution, comprising the following steps:

[0010] (1) melting the alloy raw materials and then cooling them to obtain alloy ingots;

[0011] (2) The alloy ingot obtained in step (1) is homogenized to obtain a high-strength and tough cobalt-based high-entropy alloy.

[0012] Preferably, the smelting temperature in step (1) is 1500-1600° C., and the smelting time is 15-25 minutes.

[0013] Preferably, the temperature of the homogenization treatment in step (2) is 1180-1220° C., and the time of the homogenization treatment is 1.8-2.2 h.

[0014] Preferably, the heating rate to the homogenization temperature is 7-9° C. / min.

[0015] Preferably, the uniform post-treatment in step (2) further includes cryogenic treatment.

[0016] Preferably, the cryogenic treatment is performed 1 to 3 times, the temperature of each cryogenic treatment is -200 to -190° C., and the time of each cryogenic treatment is 2 to 4 minutes.

[0017] The present invention also provides applications of the high-strength and tough cobalt-based high-entropy alloy described in the above technical solution or the high-strength and tough cobalt-based high-entropy alloy prepared by the preparation method described in the above technical solution in the fields of aerospace and marine engineering.

[0018] The present invention provides a high-strength and tough cobalt-based high-entropy alloy comprising, in atomic percentage, the following elements: 44-47% Co, 28-31% Cr, 7-8% Fe, 7-8% Ni, 7-8% Mn, and 1.3-1.8% X; X comprises at least one of Ti, Zr, and Hf. The present invention adds at least one of Ti, Zr, and Hf to the cobalt-based high-entropy alloy to form a high-entropy alloy with both fcc (face-centered cubic) and hcp (hexagonal close-packed) structures. A nanoscale C14-Laves phase reinforcement structure is formed at the interface between the fcc and hcp phases, resulting in the cobalt-based high-entropy alloy having excellent strength and toughness. Results from the examples show that the high-strength and tough cobalt-based high-entropy alloy provided by the present invention has a room-temperature compressive strength of ≥1500 MPa and an elongation at break of ≥60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a thermodynamic simulation diagram of the high-strength and tough cobalt-based high-entropy alloy in Example 1;

[0020] Figure 2 This is a thermodynamic simulation diagram of the high-strength and tough cobalt-based high-entropy alloy in Example 3;

[0021] Figure 3 EBSD phase diagrams of the homogenized alloys in Examples 1 to 3, XRD diagrams of the homogenized alloys and the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, and the homogenized alloys and ASME standard materials in Comparative Example 2;

[0022] Figure 4ECCI microstructure morphology of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2 after corrosion, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1 and the ASME standard material in Comparative Example 2, and the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1 and the ASME standard material in Comparative Example 2 after corrosion;

[0023] Figure 5 The open circuit potential test graphs of the homogenized alloys in Examples 1-3 and Comparative Examples 1-2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1-3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2 in a 3.5 wt% NaCl aqueous solution (1 atm, room temperature);

[0024] Figure 6 Nyquist plots of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2 after open circuit potential testing in a 3.5 wt% NaCl aqueous solution (1 atm, room temperature);

[0025] Figure 7 2D polarization curves of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2 after 1 h open circuit potential (OCP) testing in a 3.5 wt% NaCl aqueous solution (1 atm, room temperature);

[0026] Figure 8 2D cyclic polarization curves of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2 after 1 h open circuit potential (OCP) testing in a 3.5 wt% NaCl aqueous solution (1 atm, room temperature);

[0027] Figure 9 Polarization curves of the homogenized alloy in Comparative Example 1 at different NaCl aqueous solution concentrations (0.001 mol / L, 0.005 mol / L, 0.200 mol / L, 0.584 mol / L, 1.000 mol / L);

[0028] Figure 10 Polarization curves of the homogenized alloy in Example 1 at different NaCl aqueous solution concentrations (0.001 mol / L, 0.005 mol / L, 0.200 mol / L, 0.584 mol / L, 1.000 mol / L);

[0029] Figure 11 Polarization curves of the homogenized alloy in Example 2 at different NaCl aqueous solution concentrations (0.001 mol / L, 0.005 mol / L, 0.200 mol / L, 0.584 mol / L, 1.000 mol / L);

[0030] Figure 12 Polarization curves of the homogenized alloy in Example 3 at different NaCl aqueous solution concentrations (0.001 mol / L, 0.005 mol / L, 0.200 mol / L, 0.584 mol / L, 1.000 mol / L);

[0031] Figure 13 Polarization curves of the homogenized alloy in Comparative Example 2 at different NaCl aqueous solution concentrations (0.001 mol / L, 0.005 mol / L, 0.200 mol / L, 0.584 mol / L, 1.000 mol / L);

[0032] Figure 14 Critical pitting temperature (CPT) test curves of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2 at different given anode potentials in a 1 mol / L NaCl aqueous solution;

[0033] Figure 15 The oxidation weight gain curves of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, the cobalt-based high-entropy alloy of Comparative Example 1, and the ASME standard material of Comparative Example 2 at different oxidation times at 600°C are shown;

[0034] Figure 16 The oxidation weight gain curves of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, the cobalt-based high-entropy alloy of Comparative Example 1, and the ASME standard material of Comparative Example 2 at different oxidation times at 800°C are shown;

[0035] Figure 17 The oxidation weight gain curves of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, the cobalt-based high-entropy alloy of Comparative Example 1, and the ASME standard material of Comparative Example 2 at 1000°C and different oxidation times are shown;

[0036] Figure 18 The thickness of the oxide layer of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, the cobalt-based high-entropy alloy of Comparative Example 1, and the ASME standard material of Comparative Example 2 after oxidation at different temperatures (600°C, 800°C, 1000°C) for 100 hours;

[0037] Figure 19 Elemental composition diagram of the oxide layer of high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3 after oxidation at different temperatures (600°C, 800°C, 1000°C) for 100h;

[0038] Figure 20The SEM images of the alloy surface layers of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, the cobalt-based high-entropy alloy of Comparative Example 1, and the ASME standard material of Comparative Example 2 after oxidation at 600°C, 800°C, and 1000°C for 100h, respectively;

[0039] Figure 21 The Vickers hardness of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2;

[0040] Figure 22 Graphs showing engineering stress-strain curves of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2. DETAILED DESCRIPTION

[0041] The present invention provides a high-strength and tough cobalt-based high-entropy alloy, which comprises the following elements, calculated in atomic percentage: Co 44-47%, Cr 28-31%, Fe 7-8%, Ni 7-8%, Mn 7-8% and X 1.3-1.8%; X comprises at least one of Ti, Zr and Hf.

[0042] The high-strength and tough cobalt-based high-entropy alloy provided by the present invention comprises 44-47% Co in atomic percentage. As an embodiment, the atomic percentage of Co in the high-strength and tough cobalt-based high-entropy alloy may specifically be 44%, 45%, 46%, or 47%. In the present invention, the Co is a matrix element, providing the basis for the fcc phase structure and improving the high-temperature strength of the high-strength and tough cobalt-based high-entropy alloy.

[0043] The high-strength and tough cobalt-based high-entropy alloy provided by the present invention further comprises 28 to 31% Cr in atomic percentage. As an embodiment, the atomic percentage of Cr in the high-strength and tough cobalt-based high-entropy alloy may specifically be 28%, 29%, 30%, or 31%. In the present invention, the Cr promotes the formation of a passivation film (Cr2O3) and inhibits the precipitation of σ phase. The present invention controls the atomic percentage of Cr within the above range, which can further improve the strength and toughness of the high-strength and tough cobalt-based high-entropy alloy.

[0044] The high-strength and tough cobalt-based high-entropy alloy provided by the present invention further comprises 7-8% Fe in atomic percentage. As an embodiment, the atomic percentage of Fe in the high-strength and tough cobalt-based high-entropy alloy may specifically be 7%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, or 8%. In the present invention, the Fe can improve the strength and thermal stability of the high-strength and tough cobalt-based high-entropy alloy while reducing the cost.

[0045] In terms of atomic percentage, the high-strength and tough cobalt-based high-entropy alloy provided by the present invention also includes 7-8% Ni. As an embodiment, the atomic percentage of Ni in the high-strength and tough cobalt-based high-entropy alloy can be specifically 7%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9% or 8%. In the present invention, the Ni has a unique fcc configuration, can form a stable austenite phase, and has excellent corrosion resistance, high temperature resistance and other properties. At the same time, the addition of Ni can also significantly reduce the solubility of Fe and Cr, thereby improving the stability of the passivation film.

[0046] In terms of atomic percentage, the high-strength and tough cobalt-based high-entropy alloy provided by the present invention also includes 7-8% Mn. As an embodiment, the atomic percentage of Mn in the high-strength and tough cobalt-based high-entropy alloy can be specifically 7%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9% or 8%. In the present invention, the Mn can regulate the stability between phases in the high-strength and tough cobalt-based high-entropy alloy and promote the transformation of dislocations. In addition, the addition of Mn can also reduce the transformation temperature and phase transformation speed of martensite, making the structure of the high-strength and tough cobalt-based high-entropy alloy more uniform and delicate, thereby improving the strength and toughness of the high-strength and tough cobalt-based high-entropy alloy.

[0047] In terms of atomic percentage, the high-strength and tough cobalt-based high-entropy alloy provided by the present invention further comprises X1.3-1.8%. As an embodiment, the atomic percentage of X in the high-strength and tough cobalt-based high-entropy alloy can be specifically 1.3%, 1.4%, 1.5%, 1.6%, 1.7% or 1.8%.

[0048] In the present invention, the X comprises at least one of Ti, Zr, and Hf. In the present invention, the Ti can refine the grains and inhibit the coarsening of the C14-Laves phase; the Zr and Hf induce the hcp martensitic phase transformation, thereby improving the strength and toughness of the high-strength and tough cobalt-based high-entropy alloy.

[0049] In the present invention, the high-strength and tough cobalt-based high-entropy alloy includes an fcc phase, an hcp phase, and a C14-Laves phase distributed at the interface between the fcc phase and the hcp phase.

[0050] The present invention adds at least one of Ti, Zr and Hf to a cobalt-based high-entropy alloy to form a high-entropy alloy with fcc (face-centered cubic) and hcp (hexagonal close-packed) structures, controls the composition of the high-strength and tough cobalt-based high-entropy alloy, and improves the strength and toughness of the high-strength and tough cobalt-based high-entropy alloy.

[0051] The high-strength and tough cobalt-based high-entropy alloy provided by the present invention has excellent mechanical properties, with a room temperature compressive strength of ≥1500 MPa and an elongation at break of ≥60%.

[0052] The present invention also provides a method for preparing the high-strength and tough cobalt-based high-entropy alloy described in the above technical solution, comprising the following steps:

[0053] (1) melting the alloy raw materials and then cooling them to obtain alloy ingots;

[0054] (2) The alloy ingot obtained in step (1) is homogenized to obtain a high-strength and tough cobalt-based high-entropy alloy.

[0055] The present invention melts the alloy raw material and then cools it to obtain the alloy ingot.

[0056] In the present invention, the alloy raw material is preferably a metal raw material with a purity of ≥99.9%. The present invention has no special limitation on the amount of the alloy raw material, which can be determined according to the composition of the high-strength and tough cobalt-based high-entropy alloy.

[0057] In the present invention, the smelting temperature is preferably 1500-1600° C. As an embodiment, the smelting temperature may be specifically 1500° C., 1510° C., 1520° C., 1530° C., 1540° C., 1550° C., 1560° C., 1570° C., 1580° C., 1590° C. or 1600° C.

[0058] In the present invention, the smelting time is preferably 15 to 25 minutes. As an embodiment, the smelting time can be specifically 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes or 25 minutes.

[0059] In the present invention, the smelting is preferably carried out under argon protection.

[0060] As an embodiment, the smelting is carried out in a vacuum induction furnace. The present invention has no particular limitation on the type of the vacuum induction furnace, and commercially available equipment familiar to those skilled in the art can be used.

[0061] In the present invention, the cooling is preferably furnace cooling.

[0062] After obtaining the alloy ingot, the present invention performs a homogenization treatment on the alloy ingot to obtain a high-strength and tough cobalt-based high-entropy alloy.

[0063] In the present invention, the homogenization temperature is preferably 1180-1220°C, more preferably 1200°C; the homogenization time is preferably 1.8-2.2 hours, more preferably 2 hours; and the heating rate to the homogenization temperature is preferably 7-9°C / min, more preferably 8°C / min. By controlling the homogenization temperature and time within the above ranges, the present invention can further eliminate segregation, improve alloy composition homogenization, and thereby enhance the strength and toughness of the high-strength and tough cobalt-based high-entropy alloy.

[0064] As an embodiment, the present invention seals the alloy ingot in a vacuum quartz tube for homogenization. The present invention has no particular limitation on the sealing operation, and any sealing technical solution well known to those skilled in the art can be used.

[0065] After the homogenization treatment is completed, the present invention preferably performs water quenching on the homogenization product to obtain a homogenization alloy, and then performs deep cryogenic treatment on the homogenization alloy to obtain a high-strength and tough cobalt-based high-entropy alloy.

[0066] The present invention has no special limitation on the water quenching operation, and the water quenching technical solution well known to those skilled in the art can be adopted.

[0067] In the present invention, the number of times of the cryogenic treatment is preferably 1 to 3 times, more preferably 2 to 3 times, and even more preferably 3 times.

[0068] In the present invention, the temperature of each cryogenic treatment is preferably -200 to -190°C, more preferably -196°C; the time of each cryogenic treatment is preferably 2 to 4 minutes, more preferably 3 minutes.

[0069] As an embodiment, the cryogenic treatment is performed in liquid nitrogen.

[0070] When the cryogenic treatment is performed 2 to 3 times, the present invention preferably restores the product after the previous cryogenic treatment to room temperature before performing the next cryogenic treatment.

[0071] The present invention has no particular limitation on the operation of returning the alloy to room temperature. The alloy may be left at room temperature until the temperature returns to room temperature.

[0072] After the cryogenic treatment is completed, the present invention preferably restores the cryogenically treated product to room temperature to obtain a high-strength and tough cobalt-based high-entropy alloy.

[0073] The present invention has no particular limitation on the operation of returning the alloy to room temperature. The alloy may be left at room temperature until the temperature returns to room temperature.

[0074] In the present invention, the cryogenic treatment induces hcp martensitic transformation and refines the C14-Laves phase grain size. The present invention controls the cryogenic treatment parameters within the above range, which can further improve the strength and toughness of the high-strength and tough cobalt-based high-entropy alloy.

[0075] The present invention regulates the phase composition of a high-strength and tough cobalt-based high-entropy alloy through homogenization treatment and cryogenic treatment, thereby improving the strength and toughness of the high-strength and tough cobalt-based high-entropy alloy.

[0076] The present invention also provides applications of the high-strength and tough cobalt-based high-entropy alloy described in the above technical solution or the high-strength and tough cobalt-based high-entropy alloy prepared by the preparation method described in the above technical solution in the fields of aerospace and marine engineering.

[0077] The high-strength and tough cobalt-based high-entropy alloy provided by the present invention has both high strength and high plasticity, as well as good corrosion resistance and high-temperature oxidation resistance, and is suitable for harsh service environments such as aerospace high-temperature components and marine engineering equipment.

[0078] The present invention has no special limitation on the operation of the application, and the application technical solutions well known to those skilled in the art can be adopted.

[0079] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0080] Example 1

[0081] A high-strength and tough cobalt-based high-entropy alloy composed, by atomic percentage, of the following elements: Co 46%, Cr 30%, Fe 7.5%, Ni 7.5%, Mn 7.5% and Ti 1.5%;

[0082] The preparation method of the high-strength and tough cobalt-based high-entropy alloy is as follows: (1) using a metal raw material with a purity of 99.9%, weighing it according to atomic percentage, and melting it in a vacuum induction furnace under argon protection at a melting temperature of 1550° C. and a melting time of 20 minutes. After the melting is completed, the alloy ingot is cooled in the furnace to obtain;

[0083] (2) sealing the alloy ingot obtained in step (1) in a vacuum quartz tube, heating the temperature to 1200° C. at a heating rate of 8° C. / min, performing a homogenization treatment for 2 h, and water quenching to obtain a homogenized alloy;

[0084] (3) The homogenized alloy obtained in step (2) was immersed in liquid nitrogen (-196°C) and subjected to cryogenic treatment. The number of cryogenic treatments was 3 times, and the time of each cryogenic treatment was 3 minutes. After each cryogenic treatment, the alloy was allowed to stand at room temperature to return to room temperature before the next cryogenic treatment was carried out to obtain a high-strength and tough cobalt-based high-entropy alloy, which was recorded as CanT1.

[0085] Example 2

[0086] A high-strength and tough cobalt-based high-entropy alloy composed, by atomic percentage, of the following elements: Co 46%, Cr 30%, Fe 7.5%, Ni 7.5%, Mn 7.5% and Zr 1.5%;

[0087] The preparation method of the high-strength and tough cobalt-based high-entropy alloy is the same as that of Example 1, and a high-strength and tough cobalt-based high-entropy alloy is obtained, which is recorded as CanT2.

[0088] Example 3

[0089] A high-strength and tough cobalt-based high-entropy alloy composed, by atomic percentage, of the following elements: Co 46%, Cr 30%, Fe 7.5%, Ni 7.5%, Mn 7.5% and Hf 1.5%;

[0090] The preparation method of the high-strength and tough cobalt-based high-entropy alloy is the same as that of Example 1, and a high-strength and tough cobalt-based high-entropy alloy is obtained, which is recorded as CanT3.

[0091] Comparative Example 1

[0092] A cobalt-based high entropy alloy, composed of the following elements in atomic percentage: Co 47.5%, Cr 30%, Fe 7.5%, Ni 7.5% and Mn 7.5%;

[0093] The preparation method of the cobalt-based high entropy alloy is the same as that in Example 1 to obtain a cobalt-based high entropy alloy, which is recorded as CanT0.

[0094] Comparative Example 2

[0095] ASME standard material (Inconel 718), prepared in the same manner as in Example 1, is designated as R1.

[0096] Thermo-Calc software and TCNI11 database were used to perform thermodynamic simulation on the high-strength and tough cobalt-based high-entropy alloys in Example 1 and Example 3, and the calculated isoconcentration cross-sections of the high-strength and tough cobalt-based high-entropy alloys ( Figure 1 and Figure 2 The calculated molar percentages of each equilibrium phase at different temperatures ( Figure 1 and Figure 2 The small pictures in Figures 1-2 As shown. Figures 1-2 As can be seen in the thermodynamic isoconcentration cross-section of the Co-Cr-Fe-Ni-Mn-Ti / Hf system, trace additions of Ti and Hf promote the formation of the C14-Laves phase. Thermodynamic calculations predict that the designed CanT1 and CanT3 alloys may form the C14-Laves phase due to its stability over a wide temperature range. Compared to the alloying effect of Ti, Hf has a stronger stabilizing effect on the C14-Laves phase. In the current Ti-doped alloy system, the C14-Laves phase may precipitate when the Ti content exceeds 3.4 at.%.

[0097] The EBSD phase diagrams of the homogenized alloys in Examples 1 to 3, the XRD patterns of the homogenized alloys and the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, and the homogenized alloys and ASME standard materials in Comparative Example 2 are shown in FIG. Figure 3 As shown, CanT1(hs) represents the homogenized alloy in Example 1, CanT2(hs) represents the homogenized alloy in Example 2, CanT3(hs) represents the homogenized alloy in Example 3, CanT1(cs) represents the high-strength and tough cobalt-based high-entropy alloy in Example 1, CanT2(cs) represents the high-strength and tough cobalt-based high-entropy alloy in Example 2, CanT3(cs) represents the high-strength and tough cobalt-based high-entropy alloy in Example 3, R1(hs) represents the homogenized alloy in Comparative Example 2, and R1(cs) represents the ASME standard material in Comparative Example 2. Figure 3 It can be seen that the volume fraction of the fcc phase in the homogenized alloy of Example 1 is 91.4%, the volume fraction of the hcp phase is 5.08%, and the volume fraction of the C14-Laves phase is 1.36%; the volume fraction of the fcc phase in the homogenized alloy of Example 2 is 67.3%, the volume fraction of the hcp phase is 27.2%, and the volume fraction of the C14-Laves phase is 5.11%; the volume fraction of the fcc phase in the homogenized alloy of Example 3 is 83.1%, the volume fraction of the hcp phase is 10.2%, and the volume fraction of the C14-Laves phase is 4.37%; the addition of Ti / Zr / Hf alloying elements helps to improve the stability of the C14-Laves phase.

[0098] The ECCI microstructure morphology of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2 is shown in FIG. Figure 4 (a1) to (a5), ECCI microstructure morphology of the alloys after homogenization treatment (immersion in 3.5 wt.% NaCl aqueous solution for 2 h) in Examples 1 to 3 and Comparative Examples 1 to 2 are shown in FIG. Figure 4 (c1) to (c5), ECCI microstructure morphology of high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, cobalt-based high-entropy alloy of Comparative Example 1 and ASME standard material of Comparative Example 2 are shown as follows Figure 4(b1) to (b5), ECCI microstructure morphology of high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, cobalt-based high-entropy alloy of Comparative Example 1, and ASME standard material of Comparative Example 2 after corrosion (immersion in 3.5 wt.% NaCl aqueous solution for 2 h) as shown in FIG. Figure 4 (d1)~(d5). Figure 4 It can be seen that in CanT1(hs), CanT2(hs) and CanT3(hs) alloys, the C14-Laves phase precipitates in the form of eutectic structure.

[0099] XRD, ECCI, and EBSD characterizations show that the microstructures of the CanT1(hs), CanT2(hs), and CanT3(hs) alloys consist of three phases (fcc+hcp+C14-Laves), with the C14-Laves phase accounting for a very small proportion. EBSD phase diagrams show that Ti has a weaker stabilizing effect on the formation of the C14-Laves phase than alloying elements Zr and Hf. The above characterization results are consistent with the thermodynamic calculation results of the present invention. After cryogenic treatment, finer lamellar hcp martensite is formed in the alloy, while the C14-Laves phase still maintains an extremely low content (especially in the CanT2 alloy).

[0100] The open circuit potential (OCP) of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2 in a 3.5wt% NaCl aqueous solution (1atm, room temperature) was tested for 1200s, a sampling interval of 2s, a potential range of -1.5V to 1.5V, an EIS initial potential measured by open circuit, a high-frequency test upper limit of 1000kHz, a low frequency of 0.01Hz, an amplitude of 5mV, and a standing time of 2s after frequency switching. The open circuit potential (OCP) test results of the alloy are shown as follows: Figure 5 As shown in the Nyquist plot of the alloy after OCP test, Figure 6 shown.

[0101] from Figures 5-6 It can be seen that the capacitance arc radius of the alloy sample with the addition of Ti element becomes larger and the corrosion resistance is significantly improved.

[0102] The 2D polarization curves of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2 after 1 h open circuit potential (OCP) test in 3.5 wt% NaCl aqueous solution (1 atm, room temperature) are shown in FIG. Figure 7 As shown, the 2D cyclic polarization curve is as follows Figure 8The polarization curve test potential range is -2V to 2V, the scanning frequency is 10mV / s, and the sensitivity is 1e-1A / V. Figures 7-8 It can be seen that the corrosion current density of the high-strength and tough cobalt-based high-entropy alloy in Example 1 in 3.5wt% NaCl aqueous solution is 6.6×10 -7 A / cm 2 The corrosion current density of the high-strength and tough cobalt-based high-entropy alloy in 3.5 wt% NaCl aqueous solution is 10.1×10 -7 A / cm 2 The corrosion current density of the high-strength and tough cobalt-based high-entropy alloy in 3.5 wt% NaCl aqueous solution is 9.4×10 -7 A / cm 2 The capacitive arc radius of the alloy sample with the addition of Ti element becomes larger and the corrosion resistance is significantly improved.

[0103] The polarization curves of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2 at different NaCl aqueous solution concentrations (0.001 mol / L, 0.005 mol / L, 0.200 mol / L, 0.584 mol / L, 1.000 mol / L) are shown as follows: Figures 9-13 As shown, Figures 9-13 The small figure in the figure is the empirical formula E obtained by fitting the experimental data. b =E b0 +k·lnc Cl- (where E b is the breakdown potential, c Cl- Critical pitting temperature (CPT) test curves of the homogenized alloys in 1 mol / L NaCl aqueous solution at different given anode potentials in Examples 1 to 3 and Comparative Examples 1 to 2 are shown in FIG. Figure 14 As shown. Based on the stainless steel CPT standard test method, the polarization current density is set to 100 μA·cm -2 The corresponding temperature is defined as the CPT value. Figures 9-14 It can be seen that the critical pitting temperature of the homogenized alloy at a constant potential of 800 mV in Example 1 is 58.6°C, the critical pitting temperature of the homogenized alloy at a constant potential of 50 mV in Example 2 is 14.1°C, the critical pitting temperature of the homogenized alloy at a constant potential of 100 mV in Example 3 is 45.9°C, the critical pitting temperature of the homogenized alloy at a constant potential of 750 mV in Comparative Example 1 is 31.0°C, and the critical pitting temperature of the homogenized alloy at a constant potential of 750 mV in Comparative Example 2 is 57.4°C. The CPT experimental curve of the CanT1(hs) alloy shows the most stable passivation state. Even when an anodic potential of 800 mV is applied (constant potential control), its critical pitting temperature is still significantly higher than that under other conditions.

[0104] The oxidation weight gain curves of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, the cobalt-based high-entropy alloy of Comparative Example 1, and the ASME standard material of Comparative Example 2 at different oxidation times at 600°C, 800°C, and 1000°C are shown as follows: Figures 15-17 As shown, the thickness of the oxide layer of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3, the cobalt-based high-entropy alloy of Comparative Example 1, and the ASME standard material of Comparative Example 2 after oxidation at different temperatures (600°C, 800°C, 1000°C) for 100 hours is as follows: Figure 18 As shown in Figure 2, the elemental composition of the oxide layer of the high-strength and tough cobalt-based high-entropy alloys of Examples 1 to 3 after oxidation at different temperatures (600°C, 800°C, 1000°C) for 100h is as follows: Figure 19 As shown. Figures 15-19 It can be seen that for Zr / Hf doped alloys, their high temperature weight gain rate is significantly higher than that of other alloys.

[0105] The SEM images of the alloy surface after oxidation at 600℃, 800℃ and 1000℃ for 100h are as follows: Figure 20 As shown. Figure 20 As can be seen in the figure, more oxide particles formed on the surfaces of CanT2 and CanT3, and their particle size was larger than that of the other alloys. After 100 hours of high-temperature oxidation, Cr / Co / Mn composite oxides formed on the surfaces of the CanT0-CanT3 alloys at different experimental temperatures. As the temperature increased from 600°C to 1000°C, the manganese oxide content increased significantly.

[0106] The Vickers hardness of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2, the high-strength and tough cobalt-based high-entropy alloys in Examples 1 to 3, the cobalt-based high-entropy alloy in Comparative Example 1, and the ASME standard material in Comparative Example 2 is as follows: Figure 21 As shown, the engineering stress-strain curves of the homogenized alloys in Examples 1 to 3 and Comparative Examples 1 to 2 are as follows: Figure 22 As shown. Figures 21-22 It can be seen that the Vickers hardness of the homogenized alloy in Comparative Example 1 is 318HV 0.05 , the Vickers hardness of the cobalt-based high entropy alloy of comparative example 1 is 398HV 0.05 The Vickers hardness of the homogenized alloy in Example 1 is 294HV 0.05 The Vickers hardness of the high-strength and tough cobalt-based high-entropy alloy in Example 1 is 304HV 0.05 The Vickers hardness of the homogenized alloy in Example 2 is 384HV 0.05 The Vickers hardness of the high-strength and tough cobalt-based high-entropy alloy in Example 2 is 422 HV 0.05 The Vickers hardness of the homogenized alloy in Example 3 is 365HV 0.05The Vickers hardness of the high-strength and tough cobalt-based high-entropy alloy in Example 3 is 388 HV 0.05 The Vickers hardness of the homogenized alloy in Comparative Example 2 is 329HV 0.05 , the Vickers hardness of the ASME standard material of the comparative example 2 is 343HV 0.05 Compared to the homogenized alloy, the hardness of the cryogenically treated alloy is significantly increased due to the formation of a higher volume fraction of martensite during the cryogenic process. However, due to the formation of a small amount of C14-Laves phase in the CanT1(hs), CanT2(hs), and CanT3(hs) alloys, their deformation behaviors may exhibit differences. The pinning effect of the brittle second phase (i.e., the C14-Laves phase in the present invention) exacerbates the alloy's tendency to brittle fracture, resulting in lower engineering strains in the CanT2 and CanT3 alloys than in the CanT1 alloy. Titanium doping significantly increases the stress and strain levels of the alloys, reaching 1568 MPa and 69.3%, respectively. The engineering stress and strain values for CanT0 are 1180 MPa and 46.46%, respectively; for CanT2, 1550 MPa and 51.26%, respectively; and for CanT3, 1524 MPa and 47.96%, respectively.

[0107] In summary, the high-strength and tough cobalt-based high-entropy alloy provided by the present invention has higher strength and toughness.

[0108] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A high-strength and tough cobalt-based high-entropy alloy, comprising the following elements, calculated in atomic percentage: Co 44-47%, Cr 28-31%, Fe 7-8%, Ni 7-8%, Mn 7-8% and X 1.3-1.8%; wherein X comprises at least one of Ti, Zr and Hf.

2. The high-strength and tough cobalt-based high-entropy alloy according to claim 1, characterized in that: Calculated by atomic percentage, the following elements are included: Co 45-47%, Cr 29-31%, Fe 7-8%, Ni 7-8%, Mn 7-8% and X 1.4-1.6%.

3. The high-strength and tough cobalt-based high-entropy alloy according to claim 1 or 2, characterized in that: The high-strength and tough cobalt-based high-entropy alloy includes an fcc phase, an hcp phase, and a C14-Laves phase distributed at the interface between the fcc phase and the hcp phase.

4. The method for preparing the high-strength and tough cobalt-based high-entropy alloy according to any one of claims 1 to 3, comprising the following steps: (1) melting the alloy raw materials and then cooling them to obtain alloy ingots; (2) The alloy ingot obtained in step (1) is homogenized to obtain a high-strength and tough cobalt-based high-entropy alloy.

5. The preparation method according to claim 4, characterized in that The smelting temperature in step (1) is 1500-1600° C., and the smelting time is 15-25 minutes.

6. The preparation method according to claim 4, characterized in that The temperature of the homogenization treatment in step (2) is 1180-1220° C., and the time of the homogenization treatment is 1.8-2.2 hours.

7. The preparation method according to claim 6, characterized in that The heating rate for heating to the homogenization temperature is 7-9°C / min.

8. The preparation method according to claim 4, characterized in that The uniform post-treatment in step (2) also includes cryogenic treatment.

9. The preparation method according to claim 8, characterized in that The number of deep freezing treatments is 1 to 3 times, the temperature of each deep freezing treatment is -200 to -190° C., and the time of each deep freezing treatment is 2 to 4 minutes.

10. Application of the high-strength and tough cobalt-based high-entropy alloy according to any one of claims 1 to 3 or the high-strength and tough cobalt-based high-entropy alloy prepared by the preparation method according to any one of claims 4 to 9 in the fields of aerospace and marine engineering.

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