High-strength, high-ductility and corrosion-resistant FeCrNiAlTi medium-entropy alloy with a tensile strength of 1600 MPa and 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 1600 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, 53 < a < 62, 13 ≤ b ≤ 15, 20 < c ≤ 22, 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). This medium-entropy alloy has good corrosion resistance, a tensile strength ≥ 1600 MPa, an elongation after fracture ≥ 10%, reduces the preparation cost, and is conducive to industrial production.

Description

Technical Field

[0001] The present invention belongs to the field of medium-entropy alloys, and particularly relates to a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 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, and are prone to form simple solid solutions. 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 regulating the alloy microstructure, grain size, and FCC-L12 nano-precipitation behavior through cryogenic cold rolling at 77K combined with heat treatment processes. The strength of this alloy is as high as 2.2 GPa, and it also has an elongation of 13% (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). It is reported that 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 used and achieved many breakthrough results. However, the current research and development system focuses on alloy systems such as FeCoNi, FeCoNiCr, and FeNiCr, which generally contain a large amount of Co or Ni, resulting in high costs, 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. The comprehensive performance research on the 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 corrosion-resistant medium-entropy alloy with a lower cost, a tensile strength ≥ 1600 MPa, and an elongation after fracture ≥ 10% 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 object of the present invention is to provide a high-strength and high-ductility corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 MPa and a preparation method thereof, so as to obtain a high-strength corrosion-resistant medium-entropy alloy with a lower cost, a tensile strength ≥ 1600 MPa, and an elongation after fracture ≥ 10%, and also has good corrosion resistance. The preparation method of this medium-entropy alloy is economical, safe and reliable.

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

[0006] A high-strength and high-ductility corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 MPa, 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%; wherein, 53 < a < 62, 13 ≤ b ≤ 15, 20 < c ≤ 22, 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).

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

[0009] On the one hand, the addition of Ni in the FeCrNiAlTi medium-entropy alloy stabilizes the FCC structure, enabling the alloy to form a stable FCC structure at room temperature, ensuring the cold-working plastic deformation ability and plasticity of the alloy. On the other hand, as the main element for forming the precipitation phase, different Ni contents affect the element composition, morphology, and distribution of the precipitation phase. The addition of Cr and Mo elements mainly ensures that the alloy has certain corrosion resistance and can also 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 the B2 phase rich in Ni and Al elements. After homogenization, hot rolling of the alloy will break the grains and, at the same time, be accompanied by dynamic recovery and recrystallization to obtain fine grains. Large-deformation cold rolling can provide more nucleation sites for the precipitation phase and induce the formation of the precipitation phase. The medium-temperature aging process ensures the precipitation of the precipitation phase while restricting the growth of the precipitation phase. The dispersed nano-precipitation can exert a significant precipitation strengthening effect, and the soft FCC matrix can effectively slow down crack formation and crack propagation. The combined action of the soft matrix and the hard second phases such as σ-phase, χ-phase, and B2 phase enables the alloy to achieve excellent strength-ductility matching performance.

[0010] A preparation method of a high-strength, high-ductility, and corrosion-resistant FeCrNiAlTi medium-entropy alloy with a tensile strength of 1600 MPa grade. It is smelted by a magnetic levitation vacuum induction furnace, plastically processed and formed after homogenizing the sample, and then a medium-entropy alloy is obtained 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 specified weight percentages for use in magnetic levitation vacuum induction furnace melting.

[0012] 2) Melting: 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 repeatedly melted more than 3 times, with each melting time being 5 to 7 minutes, finally obtaining an ingot with uniform composition.

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

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

[0015] 5) Aging treatment: The sample formed by rolling is aged at 550 °C to 650 °C for 2 h to 8 h to obtain a high-strength and corrosion-resistant medium-entropy alloy. Different aging processes can obtain different strength-ductility matches.

[0016] In step 4), the homogenized ingot is directly hot-rolled. The starting rolling temperature is 1100°C to 1180°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 ± 10°C for 1 h to 3 h, and then cold-rolled. The total cold-rolling deformation is 80% to 85%.

[0017] In step 4), the homogenized ingot is directly cold-rolled into shape, and the total cold-rolling deformation is 80% to 85%.

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

[0019] The high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 MPa grade has good corrosion resistance, a tensile strength ≥ 1600 MPa and an elongation after fracture ≥ 10%. It does not contain high-cost elements such as Co, saves Ni, reduces the preparation cost, and is conducive to industrial production. The preparation method of the present invention is economical, safe and reliable, and is also suitable for large-scale production.

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

[0021] Figure 1 It is a SEM micrograph of the microstructure of the medium-entropy alloy of Example 1.

[0022] Figure 2 It is a TEM micrograph of the microstructure of the medium-entropy alloy of Example 1.

[0023] Figure 3 It is the room-temperature stress-strain curve of the medium-entropy alloys of Examples 1 to 4.

[0024] Figure 4 It is the polarization curve of the medium-entropy alloys Alloy 1 and Alloy 2 of Examples 1 and 2 in 1 mol / L NaCl solution. Detailed Embodiments

[0025] 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.

[0026] The chemical composition of the medium-entropy alloy in the embodiment is shown in Table 1.

[0027] Table 1 Chemical composition of the medium-entropy alloy in each embodiment (unit: wt.%)

[0028]

[0029]

[0030] Example 1

[0031] Preparation method of high-strength, high-ductility and corrosion-resistant Fe-Cr-Ni-Al-Ti medium-entropy alloy with tensile strength of 1600 MPa level, comprising the following steps:

[0032] (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, and Ti according to the weight percentages shown in Table 1 for use during melting. The element purity is ≥99.95%.

[0033] (2) Melting: Magnetic levitation vacuum induction melting is carried out under the protection of high-purity argon (content 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 melted repeatedly more than 3 times. Each melting time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained;

[0034] (3) Homogenization treatment: Heat the ingot to 1100 °C to 1200 °C in a box-type resistance furnace and hold for 2 h to 12 h for homogenization treatment.

[0035] (4) Rolling forming. After the ingot is homogenized at 1200 °C for 2 h, it is directly hot-rolled. The starting rolling temperature is 1100 °C to 1180 °C, the final rolling temperature is not lower than 980 °C, the hot-rolling deformation amount is 60%, and it is water-cooled after rolling. Then the sample is solution-treated at 1050 °C for 1 h, and then cold-rolled. The cold-rolling deformation amount is 85% to obtain an alloy sheet.

[0036] (5) Aging treatment. The roll-formed sample is aged at 550 °C for 2 h to 4 h to obtain a high-strength and corrosion-resistant medium-entropy alloy (Alloy 1), and tensile samples and metallographic samples are taken by wire cutting.

[0037] (7) Microstructure observation and mechanical property testing: Polish the surface of the sample with 500#, 800#, 1200#, and 2000# sandpaper, and polish the surface with a 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 small amount of etchant with absorbent cotton and wipe it on the surface of the specimen for 60 ± 10 s, and wash and dry it with water and alcohol. At the same time, prepare TEM samples by ion thinning method. The alloy SEM image and TEM image are as Figure 1 Figure 2 shown. Mechanical property testing is carried out according to GB / T228.1-2021, and the stress-strain curve is as Figure 3 shown. From Figure 1The SEM and TEM images of the alloy show that there are a large number of spherical precipitates on the matrix of the alloy microstructure, with sizes ranging from a dozen to dozens of nanometers, and the precipitation strengthening effect is obvious. From Figure 3 it can be seen that the yield strength, tensile strength and elongation of the alloy are 1427 MPa, 1673 MPa and 19% respectively, and the strength-plasticity match is good.

[0038] (8) Electrochemical test: The pitting potential of the alloy in 1 mol / L NaCl solution was measured 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, leaving a working area of 10×10 mm 2 to contact the solution. The samples were polished successively with 400#, 800#, 1500# and 2000# sandpapers. A standard three-electrode system was used, 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 a current density of 1 mA / cm 2 . The test results are as Figure 4 shown. The alloy Alloy 1 shows a passivation phenomenon in 1 mol / L NaCl solution, and the pitting potential is -0.02 V SCE , with good corrosion resistance.

[0039] Example 2

[0040] A preparation method of a high-strength and corrosion-resistant Fe-Cr-Ni-Al-Ti series medium-entropy alloy with a tensile strength of 1600 MPa level, comprising the following steps:

[0041] (1) Prepare raw materials: Use a magnetic levitation melting furnace for melting. The weight of the alloy is 1 kg. Weigh and mix the Fe, Cr, Ni, Al, Ti, Cu and C elements according to the weight percentages shown in Table 1 for use during melting. The element purity is ≥99.95%.

[0042] (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 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 min, and finally an ingot with uniform composition is obtained;

[0043] (3) Homogenization treatment: The ingot is heated to 1100 °C - 1200 °C in a box-type resistance furnace and held for 2 h - 12 h for homogenization treatment.

[0044] (4) Rolling forming. After the ingot is homogenized at 1200 °C for 2 h, it is directly cold-rolled, and the cold-rolling deformation is 80% - 85% to obtain an alloy thin plate.

[0045] (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 2), and tensile samples and metallographic samples are taken by wire cutting.

[0046] (6) Testing of mechanical properties and corrosion resistance:

[0047] The mechanical properties are tested according to GB / T 228.1 - 2021, and the test results are as Figure 2 shown. The yield strength, tensile strength and elongation of the alloy are 1417 MPa, 1603 MPa and 15.9% respectively, and the strength-plasticity match is good.

[0048] The pitting potential of the medium-entropy alloy Alloy 2 in 1 mol / L NaCl solution is tested by potentiodynamic polarization curves. First, an electrochemical specimen is prepared. The wire is welded to one side of the specimen, and then the side with the solder joint is sealed with epoxy resin, exposing a working area of 10×10 mm 2 to contact with 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 Alloy 2 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 specimen 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 results are as Figure 3 shown. The medium-entropy alloy Alloy 2 shows a passivation phenomenon in 1 mol / L NaCl solution, and the pitting potential is -0.13 V SCE , having good corrosion resistance.

[0049] Example 3

[0050] A preparation method of a high-strength and corrosion-resistant Fe-Cr-Ni-Al-Ti series medium-entropy alloy with a tensile strength of 1600 MPa level, comprising the following steps:

[0051] (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%.

[0052] (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 to -65 kPa, the melting current is 200 A to 300 A, and it is turned over and melted repeatedly more than 3 times. Each melting time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained.

[0053] (3) Homogenization treatment: Heat the ingot to 1100 °C to 1200 °C in a box-type resistance furnace and hold for 2 h to 12 h for homogenization treatment.

[0054] (4) Rolling forming. After the ingot is homogenized at 1200 °C for 2 h, it is directly hot-rolled. The starting rolling temperature is 1100 °C to 1180 °C, the final rolling temperature is not lower than 980 °C, the hot-rolling deformation is 60%, and it is water-cooled after rolling. Then the sample is solution-treated by holding at 1050 °C for 1 h, and then cold-rolled. The cold-rolling deformation is 85%.

[0055] (5) Aging treatment. The rolled sample is aged at 600 °C for 2 h to 4 h to obtain the high-strength and corrosion-resistant medium-entropy alloy Alloy 3, and tensile samples and metallographic samples are taken by wire cutting.

[0056] (6) Mechanical property and corrosion resistance tests:

[0057] According to GB / T 228.1-2021, mechanical property tests are carried out. The test results are as Figure 3 shown. The yield strength, tensile strength, and elongation of the alloy are 1384 MPa, 1617 MPa, and 12% respectively, and the strength and plasticity match well.

[0058] Use the potentiodynamic polarization curve to test the pitting potential of the medium-entropy alloy Alloy 3 in 1 mol / L NaCl solution. First, prepare the electrochemical sample. Weld the wire to one side of the sample, 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# sandpaper. A standard three-electrode system is adopted. The working electrode is the Alloy 3 alloy, the saturated calomel electrode (SCE) is the reference electrode, and the auxiliary electrode is 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 at -1.3 V 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. 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 current density corresponding potential. The test results showed that Alloy 3 alloy exhibited passivation behavior in 1 mol / L NaCl solution, and the pitting potential was -0.2 V SCE , and the passive current density was relatively low at 1 μA / cm 2 , indicating that the alloy had good corrosion resistance.

[0059] Example 4

[0060] A preparation method of a high-strength and corrosion-resistant Fe-Cr-Ni-Al-Ti medium-entropy alloy with a tensile strength of 1600 MPa grade, comprising the following steps:

[0061] (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 ≥99.9%.

[0062] (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 to -65 kPa, the melting current is 200 A to 300 A, and it is turned over and melted repeatedly more than 3 times. The melting time for each time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained;

[0063] (3) Homogenization treatment: Heat the ingot to 1100 °C to 1200 °C in a box-type resistance furnace and hold for 2 h to 12 h for homogenization treatment.

[0064] (4) Rolling forming. After the ingot is homogenized at 1200 °C for 2 h, it is directly cold-rolled, and the cold rolling deformation is 80% to 85%.

[0065] (5) Aging treatment. The rolled sample is aged at 550 °C to 600 °C for 2 h to 4 h to obtain a high-strength and corrosion-resistant medium-entropy alloy Alloy 4, and tensile samples and metallographic samples are taken by wire cutting.

[0066] (6) Mechanical property and corrosion resistance tests:

[0067] According to GB / T 228.1-2021, the mechanical properties are tested, and the test results are as Figure 3 shown. The yield strength, tensile strength and elongation of the alloy are 1375 MPa, 1682 MPa and 13.5% respectively, and the strength-plasticity matching is good.

[0068] The pitting potential of the medium-entropy alloy Alloy 4 in 1 mol / L NaCl solution was tested using a potentiodynamic polarization curve. First, an electrochemical specimen was prepared. A wire was welded to one side of the specimen, and then the side with the solder joint was sealed with epoxy resin, exposing a working area of 10×10 mm 2 to contact the solution. The sample was 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 4 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 -1.3V 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 medium-entropy alloy Alloy 4 exhibited a passivation phenomenon in 1 mol / L NaCl solution, with a pitting potential of 0.01V SCE , and a passive current density of 1 μA, indicating that the alloy has good corrosion resistance.

[0069] Example 5

[0070] A preparation method of a high-strength corrosion-resistant Fe-Cr-Ni-Al-Ti series medium-entropy alloy with a tensile strength of 1600 MPa class, comprising the following steps:

[0071] (1) Prepare raw materials: Use a magnetic levitation melting furnace for melting. The weight of the alloy is 1 kg. 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. The element purity is ≥99.9%.

[0072] (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 to -65 kPa, the melting current is 200 A to 300 A, and it is turned over and melted repeatedly more than 3 times. Each melting time is 5 to 7 min, and finally an ingot with uniform composition is obtained;

[0073] (3) Homogenization treatment: The ingot is homogenized in a box-type resistance furnace by heating to 1100°C to 1200°C and holding for 2 h to 12 h.

[0074] (4) Rolling forming. After homogenization of the ingot at 1200 °C for 2 h, it is directly hot-rolled. The starting rolling temperature is 1100 °C - 1180 °C, the final rolling temperature is not lower than 980 °C, the hot-rolling deformation is 60%, and water cooling is carried out after rolling. Then the sample is solution-treated at 1050 °C for 1 h, and then cold-rolled with a cold-rolling deformation of 85%.

[0075] (5) Aging treatment. The rolled sample is aged at 600 °C for 2 h - 4 h to obtain the high-strength and corrosion-resistant medium-entropy alloy Alloy 4, and tensile samples and metallographic samples are taken by wire cutting.

[0076] (6) Mechanical property and corrosion resistance tests:

[0077] Mechanical property tests are carried out according to GB / T 228.1-2021. The test results show that the yield strength, tensile strength and elongation of alloy Alloy 5 are 1463 MPa, 1631 MPa and 13.5% respectively, and the strength-plasticity match is good.

[0078] The pitting potential of the medium-entropy alloy Alloy 5 in 1 mol / L NaCl solution is measured by potentiodynamic polarization curves. First, electrochemical specimens are prepared. The wire is welded to one side of the specimen, and then the side with the solder joint is sealed with epoxy resin, exposing a working area of 10×10 mm 2 to contact with 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 Alloy 5 alloy, 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 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 results show that the medium-entropy alloy Alloy 5 shows a passivation phenomenon in 1 mol / L NaCl solution, the pitting potential is -0.03 V SCE , and the passive current density is 0.25 μA, showing good corrosion resistance.

Claims

1. A high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 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 53 < a < 62, 13 ≤ b ≤ 15, 20 < c ≤ 22, 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, and R = 8.314 J / (mol*K); The tensile strength of the medium-entropy alloy is ≥1600 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 1600 MPa class uses a magnetic levitation vacuum induction furnace for smelting. After homogenizing the sample, plastic processing is carried out for forming, and then aging treatment is performed to obtain the medium-entropy alloy. It specifically includes the following steps: 1) Prepare raw materials: Weigh and proportion the constituent elements of the medium-entropy alloy according to the stated weight percentages for use during melting in the magnetic levitation vacuum induction furnace; 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 repeatedly melted on the reverse side more than 3 times. Each melting time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained; 3) Homogenization treatment: The ingot is subjected to homogenization treatment at 1100°C to 1200°C for 2 h to 12 h; 4) Rolling forming: It is formed by hot rolling and cold rolling in sequence, or directly by cold rolling; 5) Aging treatment: The rolled sample is aged at 550°C to 650°C for 2 h to 8 h to obtain a high-strength 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 1600 MPa, characterized in that, The purity of the metal raw materials of Fe, Cr, Ni, Al, Ti, Mo, and Cu is all ≥99.95 wt.%.

3. The preparation method of a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 MPa according to claim 1 or 2, characterized in that Using a magnetic levitation vacuum induction furnace for smelting, after homogenizing the sample, plastic processing is carried out for forming, and then aging treatment is performed to obtain the medium-entropy alloy. It specifically includes the following steps: 1) Prepare raw materials: Weigh and proportion the constituent elements of the medium-entropy alloy according to the stated weight percentages for use during melting in the magnetic levitation vacuum induction furnace; 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 repeatedly melted on the reverse side more than 3 times. Each melting time is 5 to 7 minutes, and finally an ingot with uniform composition is obtained; 3) Homogenization treatment: The ingot is subjected to homogenization treatment at 1100°C to 1200°C for 2 h to 12 h; 4) Rolling forming: It is formed by hot rolling and cold rolling in sequence, or directly by cold rolling; 5) Aging treatment: The rolled sample is aged at 550°C to 650°C for 2 h to 8 h to obtain a high-strength and corrosion-resistant medium-entropy alloy.

4. The preparation method of a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 MPa according to claim 3, characterized in that In step 4), the homogenized ingot is directly hot-rolled. The starting rolling temperature is 1100°C to 1180°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 at 1050 ± 10°C for 1 h to 3 h, and then cold-rolled. The total cold-rolling deformation is 80% to 85%.

5. The preparation method of a high-strength, high-ductility and corrosion-resistant FeCrNiAlTi-based medium-entropy alloy with a tensile strength of 1600 MPa according to claim 3, characterized in that, In step 4), the homogenized ingot is directly cold-rolled into shape, and the total cold-rolling deformation is 80% to 85%.

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