High-strength and corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa and preparation method

Abstract

The present invention relates to a high-strength and corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 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, 47 < a < 58, 13 ≤ b ≤ 15, 22 < c ≤ 25, 2 ≤ d ≤ 3, 4 ≤ e ≤ 6, 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, and R = 8.314 J / (mol*K). The high-strength and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1900 MPa has good corrosion resistance, a tensile strength ≥ 1900 MPa, reduces the preparation 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 corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa and a preparation method thereof. Background Art

[0002] Medium-entropy alloys are developed on the basis of high-entropy alloys, containing two to four main elements, with a mixing entropy of 1R - 1.5R, easily forming a simple solid solution and having a lower stacking fault energy. Medium-entropy alloys are an inevitable product of the "performance-oriented" development of high-entropy alloys towards alloy design, compatible with excellent performance and relatively low cost. However, for both high-entropy and medium-entropy alloys, researchers have been trying to continuously optimize the alloy properties, especially for mechanical properties, that is, to improve the strength-ductility matching of the alloy. Co-Cr-Ni alloys are typical representatives of medium-entropy alloys. Researchers have obtained Co-Cr-Ni medium-entropy alloys with heterogeneous structures by controlling the alloy microstructure, grain size, and FCC-L12 nano-precipitation behavior through cryogenic cold rolling at 77K combined with heat treatment processes. This alloy has a strength as high as 2.2 GPa and an elongation of 13% at the same time (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). According to reports, after hot working and 47h aging treatment, the yield strength, tensile strength, and elongation of the Fe-Ni-Al-Ti medium-entropy alloy reached 868 MPa, 1830 MPa, and 12% respectively. In this alloy, precipitation strengthening, martensitic phase transformation during the deformation process, and transformation-induced plasticity are the internal mechanisms for the improvement of the strength and ductility of the alloy (Yang Y., Chen T.Y., Tan L.Z. et al. Bifunctional nanoprecipitates strengthen and ductilize a medium-entropy alloy. Nature, 2021, 595:245–249). Currently, in the research and development of high-strength and ultra-high-strength high-entropy alloys / medium-entropy alloys, high-density dispersed nano-precipitates are considered to be able to effectively improve the alloy strength without sacrificing plasticity, and have been widely applied and achieved many breakthrough results. However, the current research and development system focuses on the FeCoNi system, FeCoNiCr system, and FeNiCr system, which generally contain a large amount of Co or Ni, with a high cost, greatly limiting their large-scale application. In addition, most medium / high-entropy alloy composition systems contain a certain amount of Cr element and should have good corrosion resistance. However, most studies only focus on their mechanical properties. Corrosion performance is directly related to the service life of materials. Studying the comprehensive properties such as mechanical properties and corrosion resistance of high-performance materials can establish the corresponding relationship between service performance and the environment, providing data support for the service reliability of materials.

[0003] Based on this, a high-strength iron-based corrosion-resistant medium-entropy alloy with a lower cost and a tensile strength ≥ 1900 MPa is developed, which also has good corrosion resistance. At the same time, the preparation method of this alloy is economical, safe and reliable, and is suitable for large-scale production. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-strength corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa level and a preparation method, so as to obtain a high-strength corrosion-resistant iron-based medium-entropy alloy with a lower cost and a tensile strength ≥ 1900 MPa, which also has good corrosion resistance. The preparation method of this medium-entropy alloy is economical, safe and reliable.

[0005] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0006] A high-strength corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa level, and the chemical composition of this medium-entropy alloy by weight percentage is:

[0007] Fe a%; Cr b%; Ni c%; Al d%; Ti e%; Mo f%; Cu g%; P i%; S j%; where, 47 < a < 58, 13 ≤ b ≤ 15, 22 < c ≤ 25, 2 ≤ d ≤ 3, 4 ≤ e ≤ 6, 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).

[0008] The purity of the metal raw materials of Fe, Cr, Ni, Al, Ti, Mo, and Cu is all ≥ 99.95 wt.%.

[0009] In the high-strength corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1900 MPa level, the Ni element can stabilize the FCC structure, ensure that the alloy exists stably in the FCC structure at room temperature, and is beneficial to the large-deformation plastic processing of the alloy. The Cr element is the key element for the corrosion resistance of the alloy, and the Mo element can further improve the corrosion resistance of the alloy. The addition of Al and Ti elements is beneficial to the formation of precipitation phases with Fe and Ni elements. During the preparation process of the alloy, large-deformation cold rolling can effectively break the grains and provide more nucleation sites for the precipitation phases. Medium-temperature aging can promote the precipitation of the precipitation phases while restricting their growth, and at the same time inhibit the grain growth and relieve the internal stress. The combined action of fine-grain strengthening, precipitation strengthening and dislocation strengthening strengthens the FeCrNiAlTi-based medium-entropy alloy.

[0010] A preparation method of a high-strength corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa level, which uses a magnetic levitation vacuum induction furnace for smelting, plastic processing and forming after homogenizing the sample, and then obtains the medium-entropy alloy through aging treatment. The specific steps are as follows:

[0011] 1) Prepare raw materials: Weigh and proportion the constituent elements of the medium-entropy alloy according to the stated weight percentages.

[0012] 2) Melting: The magnetic levitation vacuum induction melting is carried out under the protection of argon with a purity of more than 99.99%. The argon filling pressure is -60 kPa to -65 kPa, the melting current is 200 A to 300 A, and it is turned over and remelted more than 3 times. Each melting time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained.

[0013] 3) Homogenization treatment: The ingot is subjected to homogenization treatment at 1100 °C to 1200 °C for 2 h to 12 h.

[0014] 4) Rolling forming: It is formed by hot rolling and cold rolling in sequence.

[0015] 5) Aging treatment: The rolled sample is aged at 500 °C to 700 °C for 2 h to 12 h to obtain a high-strength and corrosion-resistant medium-entropy alloy.

[0016] In step 4), after the ingot is held at 1100 °C to 1200 °C for 2 h to 12 h, it is directly hot rolled. The starting rolling temperature is 1150 °C to 1200 °C, the final rolling temperature is not lower than 980 °C, the total hot rolling deformation is 50% to 60%, and it is water cooled after rolling. Then the sample is solution treated at 1050 °C to 1150 °C for 1 h, and then cold rolled. The total cold rolling deformation is 80% to 85%.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] The high-strength and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1900 MPa grade has good corrosion resistance, the tensile strength ≥ 1900 MPa, 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 suitable for large-scale production at the same time.

[0019] This medium-entropy alloy can be used to prepare cold-rolled thin plates 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., and has a very broad development prospect and high industrial development potential. Description of the Drawings

[0020] Figure 1 It is the SEM diagram of the medium-entropy alloy of Example 1.

[0021] Figure 2 It is the room temperature stress-strain curve of the medium-entropy alloy of Example 1 to Example 5. Detailed Embodiments

[0022] The present invention will be described in detail below in conjunction with the accompanying drawings of the specification. However, it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0023] The chemical composition of the medium-entropy alloy in the embodiment is shown in Table 1.

[0024] Table 1 Chemical composition of the medium-entropy alloy in each embodiment (unit: wt.%)

[0025]

[0026] Example 1

[0027] A preparation method of a 1900 MPa grade high-strength and corrosion-resistant iron-based medium-entropy alloy, comprising the following steps:

[0028] (1) Prepare raw materials: Use a magnetic levitation vacuum induction furnace to melt the alloy. The weight of the alloy is 1 kg. Weigh and mix the alloying elements of Fe, Cr, Ni, Al, Ti, and Mo according to the weight percentages shown in Table 1 for use during melting. The element purity is ≥99.95%.

[0029] (2) Melting: Magnetic levitation vacuum induction melting is carried out under the protection of high-purity argon (99.99%). The argon filling pressure is -60 kPa, the melting current is 200 A - 300 A, the primary melting time is 5 - 7 min. To ensure uniform composition, at least turn over and remelt repeatedly 3 times to finally obtain an ingot with uniform composition.

[0030] (3) Homogenization treatment: The ingot is subjected to homogenization treatment by holding at 1100 °C - 1200 °C for 2 h - 12 h.

[0031] (4) Rolling forming: After homogenization, the ingot is directly hot-rolled. The starting rolling temperature is 1150 °C - 1200 °C, the final rolling temperature is not lower than 980 °C, the total hot-rolling deformation is 50% - 60%, and it is water-cooled after rolling. Then the sample is solution-treated by holding at 1050 °C - 1150 °C for 1 h, and then cold-rolled. The total cold-rolling deformation is 80% - 85%.

[0032] (5) Aging treatment: The rolled sample is aged at 550 °C - 600 °C for 2 h - 8 h to obtain a high-strength and corrosion-resistant medium-entropy alloy Alloy 1, and tensile samples, metallographic specimens, and electrochemical specimens are taken by wire cutting.

[0033] (7) Microstructure observation and mechanical property testing: The surface of the sample was polished with 500#, 800#, 1200#, and 2000# sandpapers, and the surface was polished with 2.5 μm polishing solution for metallographic microstructure characterization. The alloy etchant was CuCl2:HCl:HNO3:H2O = 1 g:50 ml:25 ml:150 ml. A small amount of etchant was dipped with absorbent cotton and wiped on the surface of the specimen for 60 ± 10 s, and then washed with water and alcohol and dried. The alloy microstructure is as Figure 1 shown. The mechanical property testing was carried out according to GB / T 228.1-2021, and the stress-strain curve is as Figure 2 shown in Alloy 1 in Figure 1 . It can be seen from the Figure 2 SEM image of the alloy that the alloy shows a typical strip-like morphology after cold rolling, and there are fine precipitation phases formed on the matrix. It can be seen from

[0034] that the tensile strength of alloy Alloy 1 is 1990 MPa. 2 The working area of is exposed to 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 the medium-entropy alloy Alloy 1, 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 the current density of 1 mA / cm 2 . The test result shows that alloy Alloy 1 shows a passivation phenomenon in 1 mol / L NaCl solution, with an obvious passivation zone, and the pitting potential is -0.08 V SCE , having good corrosion resistance.

[0035] Example 2

[0036] A preparation method of a high-strength and corrosion-resistant medium-entropy alloy with a tensile strength of 1900 MPa level, comprising the following steps:

[0037] (1) Prepare raw materials: Use a magnetic levitation melting furnace for melting. The alloy weight is 1 kg. Fe, Cr, Ni, Al, Ti, Mo and Cu elements are weighed and proportioned according to weight percentage for use in melting. The element purity is ≥99.95%.

[0038] (2) Alloy melting in a magnetic levitation melting furnace: Alloy melting is carried out under the protection of high-purity argon (99.99%) at a pressure of -60 kPa. To ensure uniform composition, the alloy is flipped and melted repeatedly at least three times. The melting current is 200A to 300A. The melting time per melting is 5 to 7 minutes, and an ingot with uniform composition is finally obtained.

[0039] (3) Homogenization treatment: homogenize the ingot by keeping it at 1100℃~1200℃ for 2h~12h.

[0040] (4) Rolling: After homogenization, the ingot is directly hot rolled with a starting rolling temperature of 1150℃ to 1180℃ and a final rolling temperature of not less than 980℃. The total deformation of the hot rolling is 50% to 60%, and the sample is water-cooled after rolling. The sample is then kept at 1050℃ to 1150℃ for 1 hour for solution treatment, and then cold rolled with a total deformation of 80% to 85%.

[0041] (5) Aging treatment: The rolled sample was kept at 550℃~600℃ for 2h~8h for aging treatment to obtain high-strength and corrosion-resistant medium-entropy alloy Alloy 2, and tensile samples and electrochemical samples were obtained by wire cutting.

[0042] (7) Mechanical properties test: Mechanical properties test is carried out according to GB / T 228.1-2021. The stress-strain curve is as follows: Figure 2 As shown in the figure, Alloy 2 has a tensile strength of 2000 MPa.

[0043] (8) Electrochemical test: The pitting potential of the alloy in 1 mol / L NaCl solution was tested using a potentiodynamic polarization curve. First, an electrochemical sample was prepared. A wire was welded to one side of the sample. The side with the weld point was then sealed with epoxy resin, leaving a 10×10 mm 2 The working area is in contact with the solution. The sample was polished in stages with 400#, 800#, 1500# and 2000# sandpaper. A standard three-electrode system was used, with the working electrode being the medium entropy alloy Alloy 2, the saturated calomel electrode (SCE) being the reference electrode, and the auxiliary electrode being a platinum sheet. The test was performed on an electrochemical workstation. The electrolyte in the experiment was 1 mol / L NaCl solution. Before the test, the sample was placed at -1.3V SCEThe cathode was polarized negatively 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. Subsequently, the potentiodynamic polarization curve was measured at a scanning rate of 0.33 mV / s from -0.5 V OCP to 1 mA / cm 2 current density corresponding potential. The test results showed that Alloy 2 exhibited passivation in 1 mol / L NaCl solution, with an obvious passivation zone, and the pitting potential was -0.05 V SCE , indicating good corrosion resistance.

[0044] Example 3

[0045] A preparation method of a 1900 MPa grade high-strength corrosion-resistant iron-based medium-entropy alloy, comprising the following steps:

[0046] (1) Prepare raw materials: Use a magnetic levitation melting furnace for melting. The weight of the alloy is 1 kg. Weigh and mix the elements Fe, Cr, Ni, Al, Ti, Mo and Cu according to the weight percentages shown in Table 1 for use during melting. The element purity is ≥99.95%.

[0047] (2) Melting the alloy in a magnetic levitation melting furnace: The alloy melting is carried out under the protection of high-purity argon (99.99%), the argon filling pressure is -60 kPa, and the melting current is 200 A - 300 A. The primary melting time is 5 - 7 min. To ensure uniform composition, at least turn over and remelt repeatedly for 3 times to finally obtain an ingot with uniform composition.

[0048] (3) Homogenization treatment: The ingot is subjected to homogenization treatment at 1100 °C - 1200 °C for 2 h - 12 h.

[0049] (4) Rolling forming: After homogenization, the ingot is directly hot-rolled. The starting rolling temperature is 1150 °C - 1180 °C, the final rolling temperature is not lower than 980 °C, and the total hot rolling deformation is 50% - 60%. After rolling, it is water-cooled. Then the sample is solution-treated at 1050 °C - 1150 °C for 1 h, and then cold-rolled. The total cold rolling deformation is 80% - 85%.

[0050] (5) Aging treatment: The rolled sample is aged at 550 °C - 600 °C for 2 h - 8 h to obtain the high-strength corrosion-resistant medium-entropy alloy Alloy 3, and tensile samples and electrochemical samples are taken by wire cutting.

[0051] (6) Mechanical property testing: Mechanical property testing is carried out according to GB / T 228.1-2021, and the stress-strain curve is as Figure 2 shown in Alloy 3. As can be seen from the figure, the tensile strength of Alloy 3 is 2044 MPa.

[0052] (7) Electrochemical testing: The pitting potential of the alloy in 1 mol / L NaCl solution was tested using a potentiodynamic polarization curve. First, electrochemical specimens were prepared. Wires were welded to one side of the specimens, and then the side with the solder joints was sealed with epoxy resin, exposing a working area of 10×10 mm 2 . The samples were polished step by step with 400#, 800#, 1500# and 2000# sandpapers. A standard three-electrode system was 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 tests were carried out on an electrochemical workstation. The electrolyte in the experiment was 1 mol / L NaCl solution. Before the test, the specimens were 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 stabilize the state. Then, the potentiodynamic polarization curve was measured at a scanning rate of 0.33 mV / s, scanning from -0.5V OCP to the potential corresponding to a current density of 1 mA / cm 2 . The test results showed that the alloy Alloy 3 exhibited a passivation phenomenon in 1 mol / L NaCl solution, with an obvious passivation zone, and the pitting potential was 0.01V SCE , indicating good corrosion resistance.

[0053] Example 4

[0054] A preparation method of a 1900 MPa grade high-strength corrosion-resistant iron-based medium-entropy alloy, comprising the following steps:

[0055] (1) Preparation of raw materials: Melting was carried out using a magnetic levitation melting furnace. The weight of the alloy was 1 kg. The elements Fe, Cr, Ni, Al, Ti, Mo and Cu were weighed and proportioned according to the weight percentages shown in Table 1 for use during melting, and the element purity was ≥99.95%.

[0056] (2) Melting the alloy in a magnetic levitation melting furnace: The alloy melting was carried out under the protection of high-purity argon (99.99%), the argon filling pressure was -60 kPa, and the melting current was 200 A - 300 A. The primary melting time was 5 - 7 min. To ensure uniform composition, at least 3 times of turning over and repeated melting were carried out, and finally an ingot with uniform composition was obtained.

[0057] (3) Homogenization treatment: The ingot was homogenized at 1100°C - 1200°C for 2 h - 12 h.

[0058] (4) Rolling and forming: After homogenization, the ingot is directly hot-rolled. The starting rolling temperature is 1150°C - 1180°C, the final rolling temperature is not lower than 980°C, the total hot-rolling deformation is 50% - 60%, and water cooling is carried out after rolling. Then, the sample is solution-treated at 1050°C - 1150°C for 1 h, and then cold-rolled. The total cold-rolling deformation is 80% - 85%.

[0059] (5) Aging treatment: The rolled sample is aged at 600°C for 4 h to obtain the high-strength and corrosion-resistant medium-entropy alloy Alloy 4, and tensile samples and electrochemical samples are taken by wire cutting.

[0060] (6) Mechanical property testing: Mechanical property testing is carried out according to GB / T 228.1 - 2021, and the stress-strain curve is as Figure 2 shown in Alloy 4. As can be seen from the figure, the tensile strength of alloy Alloy 4 is 1967 MPa.

[0061] (7) Electrochemical testing: The pitting potential of the alloy in 1 mol / L NaCl solution is tested by potentiodynamic polarization curves. First, electrochemical samples are prepared. Wires are welded to one side of the sample, and then the side with the solder joint is sealed with epoxy resin, exposing a working area of 10×10 mm 2 to contact the solution. The samples are 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 4, the saturated calomel electrode (SCE) as the reference electrode, and the auxiliary electrode being a platinum sheet. The test is carried out on an electrochemical workstation. The electrolyte in the experiment is 1 mol / L NaCl solution. Before the test, the sample is 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) 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 result shows that alloy Alloy 4 shows a passivation phenomenon in 1 mol / L NaCl solution, with an obvious passivation zone, and the pitting potential is 0.02 V SCE , having good corrosion resistance.

[0062] Example 5

[0063] A preparation method of a 1900 MPa grade high-strength and corrosion-resistant iron-based medium-entropy alloy, comprising the following steps:

[0064] (1) Preparation of raw materials: Melting is carried out using a magnetic levitation melting furnace. The weight of the alloy is 1 kg. The elements Fe, Cr, Ni, Al, Ti, Mo, and Cu are weighed and proportioned according to the weight percentages shown in Table 1 for use during melting. The element purity is ≥99.95%.

[0065] (2) Melting the alloy in a magnetic levitation melting furnace: The alloy melting is carried out under the protection of high-purity argon (99.99%). The argon filling pressure is -60 kPa, and the melting current is 200 A - 300 A. The primary melting time is 5 - 7 min. To ensure uniform composition, it is turned over and remelted at least 3 times repeatedly, and finally an ingot with uniform composition is obtained.

[0066] (3) Homogenization treatment: The ingot is subjected to homogenization treatment at 1100°C - 1200°C for 2 h - 12 h.

[0067] (4) Rolling into shape: After homogenization, the ingot is directly hot-rolled. The starting rolling temperature is 1150°C - 1180°C, the final rolling temperature is not lower than 980°C, and the total hot-rolling deformation is 60%. It is water-cooled after rolling. Then the sample is solution-treated at 1050°C - 1150°C for 1 h, and then cold-rolled. The total cold-rolling deformation is 85%.

[0068] (5) Aging treatment: The rolled sample is aged at 550°C - 600°C for 4 h to obtain a high-strength and corrosion-resistant medium-entropy alloy Alloy 5, and tensile samples and electrochemical specimens are taken by wire cutting.

[0069] (6) Mechanical property testing: Mechanical property testing is carried out according to GB / T 228.1 - 2021, and the stress-strain curve is as Figure 2 shown in Alloy 5. As can be seen from the figure, the tensile strength of alloy Alloy 5 is 1929 MPa.

[0070] (7) Electrochemical testing: The pitting potential of the alloy in 1 mol / L NaCl solution is tested using a potentiodynamic polarization curve. 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. A standard three-electrode system is used, with the working electrode being the medium-entropy alloy Alloy 5, the saturated calomel electrode (SCE) as the reference electrode, and the auxiliary electrode being a platinum sheet. The test is carried out on an electrochemical workstation. The electrolyte in the experiment is 1 mol / L NaCl solution. Before the test, the specimen is at -1.3 V SCEThe lower 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, scanning from -0.5 V OCP to 1 mA / cm 2 of the potential corresponding to the current density. The test results showed that Alloy 5 exhibited passivation in 1 mol / L NaCl solution, with an obvious passivation zone, and the pitting potential was 0.05 V SCE , indicating good corrosion resistance.

Claims

1. A high-strength and corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 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 47 < a < 58, 13 ≤ b ≤ 15, 22 < c ≤ 25, 2 ≤ d ≤ 3, 4 ≤ e ≤ 6, 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, and R = 8.314 J / (mol*K); The tensile strength of the medium-entropy alloy is ≥1900 MPa; The preparation method of the high-strength corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa level is smelted by a magnetic levitation vacuum induction furnace, plastically processed and formed after homogenizing the sample, and then the medium-entropy alloy is obtained through aging treatment. The specific steps are as follows: 1) Prepare raw materials: Weigh and mix the constituent elements of the medium-entropy alloy according to the weight percentages described. 2) Melting: Magnetic levitation vacuum induction melting is carried out under the protection of argon with a content of more than 99.99%. The argon filling pressure is -60 kPa to -65 kPa, the melting current is 200 A to 300 A, and it is turned over and remelted more than 3 times. The melting time for each time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained. 3) Homogenization treatment: The ingot is homogenized at 1100°C to 1200°C for 2 h to 12 h. 4) Rolling and forming: It is formed by hot rolling and cold rolling in sequence. 5) Aging treatment: The rolled and formed sample is aged at 500°C to 700°C for 2 h to 12 h to obtain a high-strength corrosion-resistant medium-entropy alloy.

2. The high-strength and corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 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 ≥99.95 wt.%.

3. The preparation method of a high-strength and corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa according to claim 1 or 2, characterized in that, Smelted by a magnetic levitation vacuum induction furnace, plastically processed and formed after homogenizing the sample, and then the medium-entropy alloy is obtained through aging treatment. The specific steps are as follows: 1) Prepare raw materials: Weigh and mix the constituent elements of the medium-entropy alloy according to the weight percentages described. 2) Melting: Magnetic levitation vacuum induction melting is carried out under the protection of argon with a content of more than 99.99%. The argon filling pressure is -60 kPa to -65 kPa, the melting current is 200 A to 300 A, and it is turned over and remelted more than 3 times. The melting time for each time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained. 3) Homogenization treatment: The ingot is homogenized at 1100°C to 1200°C for 2 h to 12 h. 4) Rolling and forming: It is formed by hot rolling and cold rolling in sequence. 5) Aging treatment: The rolled and formed sample is aged at 500°C to 700°C for 2 h to 12 h to obtain a high-strength corrosion-resistant medium-entropy alloy.

4. The preparation method of a high-strength and corrosion-resistant iron-based medium-entropy alloy with a tensile strength of 1900 MPa according to claim 3, characterized in that, In step 4), the ingot is directly hot-rolled after being held at 1100°C to 1200°C for 2 h to 12 h. The starting rolling temperature is 1150°C to 1200°C, the final rolling temperature is not lower than 980°C, the total hot-rolling deformation is 50% to 60%, and water cooling is carried out after rolling. Then, the sample is solution-treated by holding at 1050°C to 1150°C for 1 h, and then cold-rolled with a total cold-rolling deformation of 80% to 85%.

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