High-strength, high-ductility and corrosion-resistant FeCrNiAlTi medium-entropy alloy with a tensile strength of 1500 MPa and its preparation method

Abstract

The present invention relates to a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1500 MPa and a preparation method thereof. The chemical composition by weight percentage is as follows: Fe a%; Cr b%; Ni c%; Al d%; Ti e%; Mo f%; Cu g%; P i%; S j%; wherein, 58 < a < 66, 11 ≤ b < 13, 18 ≤ c ≤ 20, 2 ≤ d ≤ 3, 2 ≤ e ≤ 3, 1 ≤ f ≤ 2, 0 ≤ g ≤ 1, i ≤ 0.001, j ≤ 0.001, and a + b + c + d + e + f + g + i + j = 100; the mixing entropy is 1R to 1.5R, where R = 8.314 J / (mol*K). The medium-entropy alloy prepared by the method of the present invention has good corrosion resistance, a tensile strength ≥ 1500 MPa, an elongation after fracture ≥ 12%, reduces the cost, and is beneficial to industrial production.

Description

Technical Field

[0001] The present invention belongs to the field of medium-entropy alloys, and relates to a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1500 MPa and a preparation method thereof. Background Art

[0002] High-entropy alloys are one of the important developments in the field of materials in the past decade or so. They are multi-principal-element metallic materials with configurational entropy as the core design index. They have structural characteristics different from those of traditional metals, so they have unique deformation mechanisms and mechanical property characteristics. In addition, due to their variety, they bring opportunities to the field of material development, attracting extensive research by domestic and foreign research scholars, especially the mechanical properties are the research focus. After more than a decade of research, the design of high-entropy alloys has gradually developed towards alloying "performance-oriented". The composition ratio can be non-equiatomic ratio, and at the same time, the existence of second phases such as precipitated phases or intermetallic compounds is tolerated. Medium-entropy alloys are developed on this basis.

[0003] For both medium-entropy alloys and high-entropy alloys, researchers improve the strength and plasticity of alloys by changing the elemental composition, microstructure and structure of the alloys, and using various strengthening methods such as grain refinement and precipitation. Among them, high-density dispersed nano-precipitates can effectively improve the alloy strength without sacrificing plasticity, and are applied to the development of high-strength medium / high-entropy alloys. Patent Publication No. CN108193088A discloses a precipitation-strengthened AlCrFeNiV system high-entropy alloy and its preparation method. The atomic stoichiometric ratios of the components in the high-entropy alloy are Al 0.30-0.60, Cr 0.20-0.89, Fe 0.60-1.20, Ni 1.50-3.50, and V 0.10-0.30, and it is prepared by a melting and forming process and a thermomechanical treatment process. By regulating the content of each element and optimizing the synthesis process, this invention obtains a modulated structure with coherent two phases of disordered FCC and ordered L12, and the grains are fine, significantly improving the strength of the high-entropy alloy. Its yield strength exceeds 1200 MPa, and its tensile strength exceeds 1300 MPa. In the prior art, researchers (Yang T, Zhao Y L, Tong Y, et al, Multicomponent intermetallic nanoparticles and superb mechanical behaviors of complex alloys. Science, 2018, 362:933-937.) used traditional thermodynamics methods for composition screening and microstructure control, controllably prepared ductile multi-component intermetallic nanoparticles in the (FeCoNi)86Al7Ti7 alloy, and controlled the order-disorder phase transformation and elemental partitioning to achieve the strengthening and toughening of the alloy, making the tensile strength of the alloy as high as 1.5 GPa while maintaining a post-elongation rate of up to 50%. Literature reports (Du, X.H., Li, W.P., Chang, H.T. et al. Dual heterogeneous structures lead to ultrahigh strength and uniform ductility in a Co-Cr-Ni medium-entropy alloy. Nat Commun, 2020, 11:2390.) adopted cryogenic large-deformation cold rolling to introduce a dual-phase heterogeneous structure in the Co-Cr-Ni medium-entropy alloy combined with precipitation strengthening to effectively improve the strength of the alloy, making the strength of the alloy as high as 2.2 GPa while maintaining excellent elongation performance of 13%.

[0004] The currently disclosed ultra-high strength medium / high entropy alloys have good strength-ductility matching, which is superior to the properties of traditional materials. However, most of them contain a large amount of Ni and Co elements. The high cost and the difficult-to-scale-up process routes such as cryogenic cold rolling seriously restrict their potential for commercial application. At the same time, although the reported high strength medium / high entropy alloys have excellent mechanical properties, their corrosion resistance has not been considered or evaluated. Scholars generally believe that medium / high entropy alloys with excellent mechanical properties may be applied to harsh conditions or even extreme service environments, so it is very necessary to evaluate their corrosion resistance. Summary of the Invention

[0005] The object of the present invention is to provide a high strength, high plasticity and corrosion resistant FeCrNiAlTi-based medium entropy alloy with a tensile strength of 1500 MPa level and its preparation method, so as to obtain a high strength and high plasticity medium entropy alloy with a tensile strength ≥ 1500 MPa and an elongation after fracture ≥ 12% at a lower cost, and with good corrosion resistance. The preparation method of this medium entropy alloy is economical, safe and reliable.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] A high strength, high plasticity and corrosion resistant FeCrNiAlTi-based medium entropy alloy with a tensile strength of 1500 MPa level, and the chemical composition of this medium entropy alloy by weight percentage is:

[0008] Fe a%; Cr b%; Ni c%; Al d%; Ti e%; Mo f%; Cu g%; P i%; S j%; wherein, 58 < a < 66, 11 ≤ b < 13, 18 ≤ c ≤ 20, 2 ≤ d ≤ 3, 2 ≤ e ≤ 3, 1 ≤ f ≤ 2, 0 ≤ g ≤ 1, i ≤ 0.001, j ≤ 0.001, a + b + c + d + e + f + g + i + j = 100; the mixing entropy is 1R - 1.5R, R = 8.314 J / (mol*K).

[0009] The purity of the metal raw materials of Fe, Cr, Ni, Al, Ti, Mo, and Cu is all ≥ 99.9 wt.%.

[0010] The addition of Ni in the FeCrNiAlTi medium-entropy alloy mainly stabilizes the FCC structure, making the stable structure of the alloy at room temperature the FCC structure, ensuring the cold-working plastic deformation ability and the plasticity of the alloy. The addition of Cr and Mo elements mainly ensures that the alloy has a certain corrosion resistance, and at the same time can form σ-phase and χ-phase rich in Cr and Mo elements. The main purpose of adding Al and Ti elements is to promote the formation of B2-phase rich in Ni and Al elements. After homogenization of the alloy, large-deformation cold rolling can provide more nucleation points for the precipitated phases. The medium-temperature aging process ensures the precipitation of the precipitated phases while restricting the growth of the precipitated phases. The nano-precipitates distributed dispersedly can play a significant precipitation strengthening role, while the soft FCC matrix can effectively slow down the crack formation and crack propagation. The soft matrix and the hard second phases such as σ-phase, χ-phase and B2-phase work together to make the alloy achieve excellent strength-ductility matching performance.

[0011] A preparation method of a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi medium-entropy alloy with a tensile strength of 1500 MPa grade. Using an electric arc furnace for melting, after homogenizing the sample, plastic processing and forming are carried out, and then the medium-entropy alloy is obtained after aging treatment; specifically, it includes the following steps:

[0012] 1) Prepare raw materials: Weigh and mix the constituent elements of the medium-entropy alloy according to the described weight percentages.

[0013] 2) Electric arc furnace melting: It is carried out under the protection of argon with a content of more than 99.99%. The melting current is 350 - 450 A, and the ingot is turned over and remelted at least 4 times. The melting time for each time is 60 ± 20 s, and finally an ingot with uniform composition is obtained.

[0014] 3) Homogenization treatment: The ingot is homogenized at 1000℃ - 1200℃ for 2 h - 12 h and then quenched and water-cooled.

[0015] 4) Cold rolling forming

[0016] 5) Aging treatment: The rolled sample is aged at 500℃ - 700℃ for 2 h - 12 h and then water-cooled to obtain the high-strength, high-ductility and corrosion-resistant medium-entropy alloy.

[0017] In the described cold rolling forming, the total cold rolling deformation amount is 80% - 85%.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] The high-strength, high-ductility and corrosion-resistant FeCrNiAlTi medium-entropy alloy with a tensile strength of 1500 MPa grade has good corrosion resistance, the tensile strength ≥ 1500 MPa, the elongation after fracture ≥ 12%, does not contain high-cost elements such as Co, and saves Ni, reducing the preparation cost, which is beneficial to industrial production; the preparation method of the present invention is economical, safe and reliable, and is also applicable to large-scale production.

[0020] This medium-entropy alloy can be used to prepare cold-rolled thin sheets and cold-drawn wires, with both high strength and corrosion resistance, and can be applied to fields such as national defense and military industry, cross-sea bridges, etc. It has a very broad development prospect and high industrial development potential. Description of the Drawings

[0021] Figure 1 SEM microstructural image of the medium-entropy alloy Alloy 1 in Example 1 Figure 1 。

[0022] Figure 2 SEM microstructural image of the medium-entropy alloy Alloy 1 in Example 1 Figure 2 。

[0023] Figure 3 TEM image of the medium-entropy alloy Alloy 2 in Example 2.

[0024] Figure 4 Room temperature stress-strain curves of the medium-entropy alloys Alloy 1 - Alloy 5 in Examples 1 - 5.

[0025] Figure 5 Polarization curves of the medium-entropy alloys Alloy 1 - Alloy 3 in Examples 1 - 3 in 1mol / L NaCl solution. Detailed Embodiments

[0026] The present invention will be described in detail below with reference to the accompanying drawings of the specification, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0027] The chemical composition of the medium-entropy alloy in the embodiment is shown in Table 1. [[ID=#36]]

[0028] Table 1 Chemical composition of the medium-entropy alloy in each embodiment (unit: wt.%)

[0029]

[0030]

[0031] Example 1

[0032] A preparation method of a high-strength and corrosion-resistant medium-entropy alloy with a tensile strength of 1500 MPa level, comprising the following steps:

[0033] (1) Prepare raw materials: Using an electric arc furnace for melting, the weight of the alloy is 60 g. Weigh and mix the elements Fe, Cr, Ni, Al, Ti, and Cu according to the weight percentages shown in Table 1 for use during melting, and the element purity is ≥99.95%.

[0034] (2) Arc furnace melting of the alloy: The alloy melting is carried out under the protection of high-purity argon. The melting current is 350 A - 400 A, and the melting time is 60 ± 10 s. To ensure uniform composition, the ingot is turned over and remelted 4 times, and finally an ingot with uniform composition is obtained.

[0035] (3) Homogenization treatment: The ingot is put into a box-type resistance furnace and kept at 1100 °C - 1200 °C for 2 h - 12 h for homogenization treatment, and water cooling is adopted.

[0036] (5) Rolling forming: The samples after homogenization treatment are cold-rolled, and the total cold rolling deformation is 80% - 85% to obtain alloy thin plates.

[0037] (6) Aging treatment: The samples after rolling forming are aged at 550 °C for 4 h to obtain a high-strength and corrosion-resistant medium-entropy alloy (Alloy 1), and tensile samples and metallographic samples are obtained by wire cutting.

[0038] (7) Microstructure observation and mechanical property testing:

[0039] The surface of the samples is polished with 500#, 800#, 1200#, and 2000# sandpapers, and the surface is polished with 2.5 μm polishing solution for metallographic microstructure characterization. The alloy etchant is CuCl2:HCl:HNO3:H2O = 1 g:50 ml:25 ml:150 ml. Dip a cotton ball in the alloy etchant and wipe it on the surface of the specimen for 60 ± 5 s, then wash it with water and alcohol and dry it. The alloy microstructure is as Figure 1 shown. The mechanical property testing is carried out according to GB / T 228.1-2021, and the stress-strain curve is as Figure 3 shown. It can be seen from Figure 1 that the alloy microstructure consists of two phases, and there are dispersed fine precipitates formed on the matrix. It can be seen from Figure 3 that the yield strength, tensile strength and elongation of alloy Alloy1 are 1278 MPa, 1592 MPa and 17.5% respectively, and the strength-plasticity match is good.

[0040] (8) Electrochemical testing: The pitting potential of the medium-entropy alloy Alloy1 in 1 mol / L NaCl solution is tested by potentiodynamic polarization curves. First, prepare the electrochemical specimens. Weld the wire to one side of the specimen, and then seal the side with the solder joint with epoxy resin, exposing a working area of 10×10 mm 2 to contact with the solution. The samples are ground successively with 400#, 800#, 1500# and 2000# sandpapers. A standard three-electrode system is adopted, with the working electrode being Alloy1 alloy, the saturated calomel electrode (SCE) as the reference electrode, and the auxiliary electrode being a platinum sheet, and the test is carried out on an electrochemical workstation. The electrolyte in the experiment is 1 mol / L NaCl solution. Before the test, the specimens are at -1.3 VSCE The cathode was polarized for 180 s to remove the oxide film formed in air, and then the open circuit potential (OCP) was recorded for 7200 s to stabilize the state. Then, the potentiodynamic polarization curve was measured at a scanning rate of 0.33 mV / s from -0.5 V OCP scanned to 1 mA / cm 2 corresponding to the current density potential. The test results are as Figure 4 shown. In the test results, the high-entropy alloy Alloy1 showed a passivation phenomenon in 1 mol / L NaCl solution, and the pitting potential was -0.05 V SCE , showing good corrosion resistance.

[0041] Example 2

[0042] A preparation method of a high-strength and corrosion-resistant medium-entropy alloy with a tensile strength of 1500 MPa level, comprising the following steps:

[0043] (1) Prepare raw materials: Use an electric arc furnace for melting. The weight of the alloy is 60 g. Weigh and mix the elements Fe, Cr, Ni, Al, Ti, and Cu according to the weight percentages shown in Table 1 for use during melting. The element purity is ≥99.95%.

[0044] (2) Electric arc furnace melting of the alloy: The alloy melting is carried out under the protection of high-purity argon. The melting current is 350 A - 450 A, and the primary melting time is 60 ± 20 s. To ensure uniform composition, turn it over and melt it repeatedly 4 times. Finally, an ingot with uniform composition is obtained.

[0045] (3) Homogenization treatment: Put the ingot into a box-type resistance furnace and keep it at 1100 °C - 1200 °C for 2 h - 8 h for homogenization treatment, and use water cooling for cooling.

[0046] (5) Rolling forming: Cold-roll the homogenized sample, and the cold-rolling deformation is 80% - 85% to obtain an alloy thin plate by rolling forming.

[0047] (6) Aging treatment: Keep the rolled sample at 600 °C for 2 h - 12 h for aging treatment to obtain a high-strength and corrosion-resistant medium-entropy alloy (Alloy 2), and use wire cutting to take tensile samples and metallographic samples.

[0048] (7) TEM microstructure observation and mechanical property testing: Prepare TEM samples by ion thinning method. The TEM diagram of the alloy microstructure is as Figure 2 shown. According to GB / T 228.1 - 2021, mechanical property testing is carried out, and the stress-strain curve is as Figure 3 shown. It can be seen from Figure 2 that there are short rod-shaped precipitation phases formed in the alloy. Figure 3The results show that the yield strength, tensile strength and elongation of the alloy are 1364 MPa, 1597 MPa and 15% respectively, and the strength and plasticity are well matched.

[0049] (8) Electrochemical test: The pitting potential of the medium-entropy alloy Alloy 2 in 1 mol / L NaCl solution was measured by potentiodynamic polarization curve. First, prepare the electrochemical specimen, weld the wire to one side of the specimen, then seal the side with the solder joint with epoxy resin, and expose a working area of 10×10 mm 2 to contact with the solution. The samples were polished step by step with 400#, 800#, 1500# and 2000# sandpapers. A standard three-electrode system was used, with the working electrode being the Alloy 2 alloy, the saturated calomel electrode (SCE) as the reference electrode, and the auxiliary electrode being a platinum sheet. The test was carried out on an electrochemical workstation. The electrolyte in the experiment was 1 mol / L NaCl solution. Before the test, the specimen was cathodically polarized at -1.3 V SCE for 180 s to remove the oxide film formed in the air, and then the open-circuit potential (OCP) was recorded for 7200 s to make the state stable. Then, the potentiodynamic polarization curve was measured at a scanning rate of 0.33 mV / s, scanning from -0.5 V OCP to the potential corresponding to a current density of 1 mA / cm 2 . The test results are as Figure 4 shown. The medium-entropy alloy Alloy 2 shows a passivation phenomenon in 1 mol / L NaCl solution, and the pitting potential is 0.24 V SCE , and the passive current density is 1.58 μA, indicating that Alloy 2 has good corrosion resistance in 1 mol / L NaCl solution.

[0050] Example 3

[0051] A preparation method of a 1500 MPa grade high-strength and corrosion-resistant medium-entropy alloy, comprising the following steps:

[0052] (1) Prepare raw materials: Use an electric arc furnace for melting, with an alloy weight of 60 g. Weigh and mix the Fe, Cr, Ni, Al, Ti, Mo and Cu elements according to the weight percentages shown in Table 1 for use during melting, and the element purity is ≥99.95%.

[0053] (2) Electric arc furnace melting of the alloy: The alloy melting is carried out under the protection of high-purity argon. The melting current is 350 - 450 A, and the primary melting time is 60 ± 20 s. To ensure uniform composition, turn it over and melt it repeatedly 4 times. Finally, an ingot with uniform composition is obtained.

[0054] (3) Homogenization treatment: Put the ingot into a box-type resistance furnace and keep it at 1100 °C - 1200 °C for 2 h - 8 h for homogenization treatment, and use water cooling for cooling.

[0055] (4) Rolling and forming: Cold-roll the homogenized sample with a cold rolling deformation of 80% - 85% to obtain an alloy sheet with a thickness of 1.5 mm.

[0056] (5) Aging treatment: After aging the specimen at 600 °C for 4 h - 8 h, a medium-entropy alloy (Alloy 3) is obtained. Tensile specimens and electrochemical specimens are taken from the rolled sample by wire cutting.

[0057] (6) Mechanical property and electrochemical property testing:

[0058] The mechanical property testing is carried out according to GB / T 228.1 - 2021. The test results are as Figure 3 shown. The yield strength, tensile strength and elongation of Alloy 3 are 1322 MPa, 1576 MPa and 14% respectively, and the strength-ductility match is good.

[0059] Electrochemical testing: The corrosion resistance of the medium-entropy alloy is tested electrochemically. First, prepare the electrochemical specimen. Weld the wire to one side of the specimen, and then seal the side with the solder joint with epoxy resin, leaving a working area of 10×10 mm 2 to contact the solution. The sample is polished step by step with 400#, 800#, 1500# and 2000# sandpapers. A standard three-electrode system is adopted, with the working electrode being the medium-entropy alloy Alloy 3, the saturated calomel electrode (SCE) as the reference electrode, and the auxiliary electrode being a platinum sheet. The evaluation is carried out on an electrochemical workstation. The electrolyte in the experiment is 1 mol / L NaCl solution. Before the test, the specimen is cathodically polarized at -1.3 V SCE for 180 s to remove the oxide film formed by air, and then the open circuit potential (OCP) is recorded for 7200 s to make the state stable. Then, the potentiodynamic polarization curve is measured at a scanning rate of 0.33 mV / s, scanning from -0.5 V OCP to the potential corresponding to a current density of 1 mA / cm 2 . The test results are as Figure 4 shown. The medium-entropy alloy Alloy 3 shows a passivation phenomenon in 1 mol / L NaCl solution, and the pitting potential is 0.19 V SCE , and the passive current density is 1.6 μA, indicating that Alloy 3 has good corrosion resistance in 1 mol / L NaCl solution.

[0060] Example 4

[0061] A preparation method of a high-strength and corrosion-resistant medium-entropy alloy with a tensile strength of 1500 MPa level, comprising the following steps:

[0062] (1) Prepare raw materials: Using an electric arc furnace for melting, with an alloy weight of 60 g, weigh and proportion the elements Fe, Cr, Ni, Al, Ti, and Cu according to the weight percentages shown in Table 1 for use during melting, and the element purity is ≥99.95%.

[0063] (2) Electric arc furnace melting of the alloy: The alloy melting is carried out under the protection of high-purity argon. The melting current is 350 A - 400 A, and the melting time is 60 ± 10 s. To ensure uniform composition, turn it over and melt it repeatedly 4 times to finally obtain an ingot with uniform composition.

[0064] (3) Homogenization treatment: Put the ingot into a box-type resistance furnace and keep it at 1100 °C - 1200 °C for 2 h - 12 h for homogenization treatment, and use water cooling for cooling.

[0065] (5) Rolling into shape: Cold roll the sample after homogenization treatment. The total cold rolling deformation is 80% - 85% to obtain an alloy thin plate.

[0066] (6) Aging treatment: Carry out aging treatment on the rolled sample at 550 °C - 600 °C for 4 h to obtain a high-strength and corrosion-resistant medium-entropy alloy (Alloy 4), and use wire cutting to obtain tensile samples and electrochemical test samples.

[0067] (7) Mechanical property and corrosion resistance tests:

[0068] Carry out mechanical property tests according to GB / T 228.1 - 2021, and the test results are as Figure 3 shown. The yield strength, tensile strength, and elongation of alloy Alloy 4 are 1323 MPa, 1599 MPa, and 16% respectively, and the strength-plasticity matching is good.

[0069] Use the potentiodynamic polarization curve to test the pitting potential of the medium-entropy alloy Alloy 4 in 1 mol / L NaCl solution. First, prepare the electrochemical specimen. Weld the wire to one side of the specimen, and then seal the side with the solder joint with epoxy resin, exposing a working area of 10×10 mm 2 to contact the solution. The sample is polished step by step with 400#, 800#, 1500#, and 2000# sandpapers. Use a standard three-electrode system. The working electrode is the Alloy 4 alloy, the saturated calomel electrode (SCE) is the reference electrode, and the auxiliary electrode is a platinum sheet for testing on an electrochemical workstation. The electrolyte in the experiment is 1 mol / L NaCl solution. Before the test, cathodically polarize the specimen at -1.3 V SCE for 180 s to remove the oxide film formed in the air, and then record the open circuit potential (OCP) for 7200 s to make the state stable. Then measure the potentiodynamic polarization curve at a scanning rate of 0.33 mV / s, scanning from -0.5 V OCP to 1 mA / cm2 The potential corresponding to the current density. The test result shows that the medium-entropy alloy Alloy 4 exhibits passivation in 1 mol / L NaCl solution, and the pitting potential is 0.05 V. SCE It has good corrosion resistance.

[0070] Example 5

[0071] A preparation method of a high-strength and corrosion-resistant medium-entropy alloy with a tensile strength of 1500 MPa level includes the following steps:

[0072] (1) Prepare raw materials: Use an electric arc furnace for melting. The weight of the alloy is 60 g. Weigh and mix the elements Fe, Cr, Ni, Al, Ti, and Cu according to the weight percentages shown in Table 1 for use during melting. The element purity is ≥99.95%.

[0073] (2) Melt the alloy in an electric arc furnace: The alloy melting is carried out under the protection of high-purity argon. The melting current is 350 A - 400 A, and the melting time is 60 ± 10 s. To ensure uniform composition, turn it over and melt it repeatedly 4 times to finally obtain an ingot with uniform composition.

[0074] (3) Homogenization treatment: Put the ingot into a box-type resistance furnace and keep it at 1100 °C - 1200 °C for 2 h - 12 h for homogenization treatment, and use water cooling for cooling.

[0075] (5) Roll forming: Cold roll the sample after homogenization treatment. The total cold rolling deformation is 80% - 85% to obtain an alloy thin plate by roll forming.

[0076] (6) Aging treatment: Keep the roll-formed sample at 600 °C - 700 °C for 4 h for aging treatment to obtain a high-strength and corrosion-resistant medium-entropy alloy (Alloy 5), and use wire cutting to obtain tensile samples and metallographic samples.

[0077] (7) Mechanical property and corrosion resistance tests:

[0078] Conduct mechanical property tests according to GB / T 228.1 - 2021. The test results show that the yield strength, tensile strength, and elongation of the alloy are 1030 MPa, 1526 MPa, and 13.5% respectively, and the strength-plasticity match is good.

[0079] Use the potentiodynamic polarization curve to test the pitting potential of the medium-entropy alloy Alloy 5 in 1 mol / L NaCl solution. First, prepare an electrochemical specimen, weld the wire to one side of the specimen, and then seal the side with the solder joint with epoxy resin, exposing 10 × 10 mm 2The working area is in contact with the solution. The sample was polished step by step with 400#, 800#, 1500# and 2000# sandpapers. A standard three-electrode system was adopted, with the working electrode being Alloy 5 alloy, the saturated calomel electrode (SCE) as the reference electrode, and the auxiliary electrode being a platinum sheet, and the tests were carried out on an electrochemical workstation. The electrolyte in the experiment was 1 mol / L NaCl solution. Before the test, the specimen was cathodically polarized at -1.3V SCE for 180 s to remove the oxide film formed in the air, and then the open circuit potential (OCP) was recorded for 7200 s to make the state stable. Then the potentiodynamic polarization curve was measured at a scanning rate of 0.33 mV / s, from -0.5V OCP scanning to the potential corresponding to the current density of 1 mA / cm 2 . The test results show that the medium entropy alloy Alloy 5 shows a passivation phenomenon in 1 mol / L NaCl solution, and the pitting potential is 0.07V SCE , having good corrosion resistance.

Claims

1. A high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1500 MPa, characterized in that, The chemical composition of the medium-entropy alloy by weight percentage is as follows: Fe a%; Cr b%; Ni c%; Al d%; Ti e%; Mo f%; Cu g%; P i%; S j%; where 58 < a < 66, 11 ≤ b < 13, 18 ≤ c ≤ 20, 2 ≤ d ≤ 3, 2 ≤ e ≤ 3, 1 ≤ f ≤ 2, 0 ≤ g ≤ 1, i ≤ 0.001, j ≤ 0.001, and a + b + c + d + e + f + g + i + j = 100; the mixing entropy is 1R~1.5R, and R = 8.314 J / (mol*K); The alloy structure of the medium-entropy alloy consists of two phases, and there are dispersed fine precipitates formed on the matrix; The tensile strength of the medium-entropy alloy is ≥1500 MPa, and the elongation after fracture is ≥12%; The preparation method of the high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1500 MPa level uses an electric arc furnace for melting. After homogenizing the sample, plastic processing is carried out for forming, and then the medium-entropy alloy is obtained after aging treatment; specifically, it includes the following steps: 1) Prepare raw materials: Weigh and mix the constituent elements of the medium-entropy alloy according to the stated weight percentages; 2) Electric arc furnace melting: It is carried out under the protection of argon with a content of more than 99.99%. The melting current is 350~450 A, and the ingot is repeatedly melted at least 4 times with the surface turned over. The melting time for each pass is 60 ± 20 s, and finally an ingot with uniform composition is obtained; 3) Homogenization treatment: The ingot is subjected to homogenization treatment at 1000°C~1200°C for 2 h~12 h and then quenched and water-cooled; 4) Cold rolling forming 5) Aging treatment: The rolled sample is aged at 500°C~700°C for 2 h~12 h and then water-cooled to obtain the high-strength, high-ductility and corrosion-resistant medium-entropy alloy.

2. A high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1500 MPa according to claim 1, characterized in that, The purity of the metal raw materials of Fe, Cr, Ni, Al, Ti, Mo, and Cu is ≥99.9 wt.%.

3. The preparation method of a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1500 MPa according to claim 1 or 2, characterized in that, Using an electric arc furnace for melting, after homogenizing the sample, plastic processing is carried out for forming, and then the medium-entropy alloy is obtained after aging treatment; specifically, it includes the following steps: 1) Prepare raw materials: Weigh and mix the constituent elements of the medium-entropy alloy according to the stated weight percentages; 2) Electric arc furnace melting: It is carried out under the protection of argon with a content of more than 99.99%. The melting current is 350~450 A, and the ingot is repeatedly melted at least 4 times with the surface turned over. The melting time for each pass is 60 ± 20 s, and finally an ingot with uniform composition is obtained; 3) Homogenization treatment: The ingot is subjected to homogenization treatment at 1000°C~1200°C for 2 h~12 h and then quenched and water-cooled; 4) Cold rolling forming 5) Aging treatment: The rolled sample is aged at 500°C~700°C for 2 h~12 h and then water-cooled to obtain the high-strength, high-ductility and corrosion-resistant medium-entropy alloy.

4. The preparation method of a high-strength and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1500 MPa according to claim 3, characterized in that, In the cold rolling forming, the total cold rolling deformation is 80%~85%.

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