A low-cost fe-based medium-entropy alloy with thermal aging strengthening and a preparation method thereof

Abstract

The application discloses a low-cost Fe-based medium-entropy alloy with variable temperature aging strengthening and a preparation method thereof, and belongs to the technical field of alloys. a Ni b Cr c Al d Ti e , a=46, 23<=b<=28, 18<=c<=23, 5<=d<=6, 2<=e<=3, sequentially through vacuum induction smelting, hot forging, room temperature rolling and variable temperature aging treatment. The application is characterized in that a reasonable alloy composition is designed, and continuous variable temperature aging is adopted to replace traditional isothermal aging, so that L12 phases with high density, uniform distribution and moderate size can be precipitated. The L12 phases can effectively promote dislocations to move in a bypass mechanism, and can significantly improve the yield strength of the alloy to above 1.3 GPa, and the uniform elongation is also above 10%. The application breaks through the strength bottleneck of low-cost medium-entropy alloys, and provides a high-performance and low-cost option for engineering applications of the medium-entropy alloys in extreme environments.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of medium-entropy alloys, and particularly relates to a low-cost Fe-based medium-entropy alloy with variable-temperature aging strengthening and a preparation method thereof. BACKGROUND

[0002] High-performance structural metal materials are highly sought after in extreme application fields. However, for most metals, the improvement of strength is often at the expense of ductility, and only a small number of martensitic steels in traditional alloys can exhibit high levels of strength-ductility matching, but still face the risk of brittle-ductile transition. Limited by the interaction between the matrix element and other limited elements, the performance of traditional alloys is difficult to continuously break through, and the recently emerging medium / high-entropy alloys adopt a multi-component design strategy, opening up a broad composition design space for the research and development of new materials, and having great application prospects in the fields of aerospace, biomedicine and energy storage.

[0003] However, a major bottleneck limiting the large-scale application of medium / high-entropy alloys is the high preparation cost: the alloy matrix usually contains elements such as Fe, Co, Cr, Ni and V, and the elements such as Al, Ti, Ta, W and Mo are added to play the effect of precipitation strengthening to obtain GPa-level tensile properties, but the elements such as Co, V, Mo and Ta are relatively expensive. Developing low-cost medium / high-entropy alloys will face some new problems: (1) how to avoid the formation of harmful precipitated phases such as B2, sigma, mu, Laves and carbides in the alloy during composition design? (2) Without Co, V, Mo and Ta, can the beneficial precipitated phase L12 still increase the strength of the medium / high-entropy alloy with low matrix strength to the GPa level? Based on thermodynamic calculation, the team previously designed a low-cost Fe-based medium-entropy alloy Fe a Ni b Cr c Al d Ti e , which can selectively precipitate the beneficial L12 phase. However, the L12 phase precipitated by the conventional isothermal aging process has a small volume fraction and is unevenly distributed, or plays a role through the dislocation cutting mechanism with a small strengthening effect, and these precipitation behaviors have limited strengthening effect on the alloy (yield strength less than 1 GPa).

[0004] Therefore, under the premise of not weakening the room temperature plasticity, it is urgent to optimize the preparation process to precipitate L12 phase with high density, uniform distribution and appropriate size, and effectively improve the strength of the low-cost Fe-based medium / high-entropy alloy. SUMMARY

[0005] In view of the problem of low strength (yield strength <1 GPa) of the existing low-cost medium-entropy alloy, the application provides a method for preparing a low-cost Fe-based medium-entropy alloy with variable-temperature aging strengthening.

[0006] The technical scheme adopted by the present application is:

[0007] In a first aspect, the present application provides a low-cost Fe-based medium-entropy alloy strengthened by temperature change aging, and an atomic expression of the alloy is Fe a Ni b Cr c Al d Ti e wherein a = 46, 23 ≤ b ≤ 28, 18 ≤ c ≤ 23, 5 ≤ d ≤ 6, and 2 ≤ e ≤ 3.

[0008] In a second aspect, the present application provides a preparation method of a low-cost Fe-based medium-entropy alloy strengthened by temperature change aging, and the Fe-based medium-entropy alloy is obtained by sequentially performing vacuum induction smelting, hot forging, room temperature rolling, and temperature change aging treatment.

[0009] wherein the initial temperature of the temperature change aging is 600-650 ℃, the final temperature is 850-900 ℃, the heating rate is 2-5 ℃ / min, and the sample is taken and air-cooled after being heated to the highest temperature.

[0010] Compared with the prior art, the present application has the following advantages:

[0011] 1. Composition optimization based on thermodynamic calculation to realize selective precipitation: the chemical composition of the alloy is designed through phase diagram simulation (thermodynamic database), so that the alloy belongs to the category of high-entropy alloys (configuration entropy is between 1-1.5R) even if it only contains inexpensive metal elements Fe, Cr, Ni, Al, and Ti, and has the ability to precipitate beneficial L12 precipitates in the medium temperature range (600-900 ℃), which lays a foundation for improving the strength-plasticity matching of the alloy.

[0012] 2. Replace the traditional isothermal aging process with a dynamic temperature change aging process to precipitate high-density, uniformly distributed, and appropriately sized L12 phases.

[0013] 3. Achieve high performance in a low-cost Fe-based medium-entropy alloy system: improve the yield strength of the alloy to more than 1.3 GPa, and the uniform plasticity to more than 10%, thereby improving the engineering application potential of low-cost medium-entropy alloys.

[0014] 4. The process route is simple, and the preparation cost is also low.

[0015] The technical scheme of the present application will be further described in detail below through the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A simulated phase diagram of the high-strength low-cost Fe-based medium-entropy alloy prepared in Example 1 of the present application;

[0017] Figure 2A temperature aging process curve for Example 1 of the present application;

[0018] Figure 3 A tensile property diagram of the high-strength low-cost Fe-based medium-entropy alloy prepared in Example 1 of the present application;

[0019] Figure 4 A microstructure of the high-strength low-cost Fe-based medium-entropy alloy prepared in Example 1 of the present application;

[0020] Figure 5 A microstructure of the high-strength low-cost Fe-based medium-entropy alloy prepared in Example 2 of the present application;

[0021] Figure 6 A tensile property diagram of the high-strength low-cost Fe-based medium-entropy alloy prepared in Example 2 of the present application;

[0022] Figure 7 A tensile property diagram of the low-cost Fe-based medium-entropy alloy prepared in Comparative Example 1 of the present application;

[0023] Figure 8 A microstructure of the low-cost Fe-based medium-entropy alloy prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0024] The present application will be further described below in conjunction with specific examples.

[0025] It should be noted that the terms such as "upper", "lower", "left", "right", "intermediate" and the like cited in the present specification are merely for the convenience of clear description, and are not intended to limit the scope of implementation, and any change in relative relationship without substantial change in technical content is also regarded as the scope of implementation of the present application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the term "and / or" used herein includes any and all combinations of one or more related listed items.

[0027] Unless otherwise specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0028] As used herein, the term "about" is used to provide flexibility to a given term, measurement, or value associated with a given term, measurement, or value. The degree of flexibility of a particular variable can be readily determined by one skilled in the art.

[0029] As used herein, the term "at least one of" is intended to mean one or more of. For example, "at least one of A, B and C" means "A alone; B alone; C alone; A and B together; A and C together; B and C together; or A, B, and C together."

[0030] The present application is based on the design concept of multi-principal element alloy, the alloy material selects low-cost Fe, Cr, Ni, Al and Ti elements, optimizes the alloy composition to meet the high mixing entropy characteristics, and then ensures the formation of simple solid solution in the solidification process. Through room temperature rolling + variable temperature aging to realize microstructure control to obtain high strength and high plasticity mechanical properties. The preparation process is simple and efficient, which is conducive to large-scale industrial production.

[0031] The alloy adopts low-cost Fe, Cr, Ni, Al and Ti elements. Vacuum induction melting is beneficial to prepare large-size and uniform composition alloy ingot, hot forging treatment is beneficial to reduce casting defects and refine grains, rolling treatment changes the material into a specified thickness plate, and variable temperature aging treatment precipitates high-density, uniform distribution and appropriate size L12 phase. The finally obtained alloy has high strength and high plasticity mechanical properties, including the following steps:

[0032] Step one, select Fe, Cr, Ni, Al and Ti block raw materials with a purity of not less than 99.9%, according to the component ratio, the raw materials are cleaned by anhydrous ethanol ultrasonic cleaning and then dried, packaged according to different elements, Fe, Cr, Ni and Ti raw materials are arranged in the copper crucible according to the melting point from high to low (high melting point raw materials are at the bottom, low melting point raw materials are at the top), and Al raw materials are arranged in the middle of other raw materials;

[0033] Step two, the vacuum degree of the melting chamber cavity is extracted to less than 5x10 -3 Pa level, and the argon atmosphere is filled to not higher than 0.05 MPa. Turn on the heating power, deliver alternating current to the induction coil to promote the raw materials to heat and melt. The melting power is increased in steps: increase by 5 kw for 1 minute, and observe the melting process until all the furnace charges form a uniform flowing molten pool.

[0034] Step three, appropriately increase the melting power, so that the solution temperature is about 100 ℃ higher than the melting point of the raw material. The holding time is 30 min, and the electromagnetic field is used to stir the solution. During this period, it is necessary to stand for a moment to promote the slag to float up, and the slag produced during the melting process is transferred to the special crucible next to it with a quartz ladle;

[0035] Step four, after waiting for the complete alloying of the raw materials, tilt the furnace body to pour the metal liquid into the pre-placed water-cooled copper mold below the furnace body to obtain an alloy ingot of appropriate size;

[0036] Step five, the alloy ingot obtained in step four is forged for multiple times, a three-mound three-pulling mode is adopted, the forging temperature is 1000 DEG C, the ingot is preserved for 30 min in a high-temperature furnace before forging, and air cooling is performed after each time of forging is completed.

[0037] Step six, the forged bulk is subjected to cold rolling treatment, 2 mm per pass, and the total reduction is 70 %, to obtain a plate with a specified deformation.

[0038] Step seven, the plate is subjected to temperature aging treatment, the furnace is heated, the initial temperature of the temperature aging is 600-650 DEG C, the final temperature is 850-900 DEG C, the heating rate is 2-5 DEG C / min, and air cooling is performed immediately after the highest temperature is reached.

[0039] Further, the metal raw material selected in step one is a bulk, and the mass purity is not less than 99.9 %. The expensive metals Ta, V, Nb and the like are not used in the application, and the vacuum induction melting is used to prepare the ingot, so that the material component purity is ensured, and the preparation cost is reduced.

[0040] Further, the holding time of the induction melting in step three is 30 min, and the time is too short to reduce the alloy component uniformity, and the time is too long to cause element volatilization, alloy liquid and crucible reaction and the like.

[0041] Further, the auxiliary magnetic stirring in steps two and three is used to realize component uniformity. The application can realize material alloying by using the simplest equipment.

[0042] Further, the pouring process in step four uses a water-cooled copper mold, which can promote rapid solidification and forming of the alloy solution.

[0043] Further, the forging treatment in step five needs to be performed for three times, the temperature is guaranteed to be 1000 DEG C, the three-mound three-pulling forging mode is adopted, air cooling is performed after each time of forging is completed, and the ingot is preserved for 30 min again, and the thickness direction size is guaranteed to be 30 mm after the last time of forging. The forging mode can fully realize plastic forming and grain crushing. The application is forged at a reasonable temperature, and the forging temperature does not need to be too high, and the equipment requirement is high at a too high temperature, and the cost is increased; the forging temperature is too low, and the risk of medium-temperature brittleness is introduced.

[0044] Further, the rolling treatment in step six only needs to be performed at room temperature, the rolling is performed at a reduction of 2 mm per pass, and the total reduction is 70 %, so that the continuous grain refinement of the material can be guaranteed.

[0045] Further, the starting temperature of the temperature aging is 600-650 DEG C, the end temperature is 850-900 DEG C, the heating rate is 2-5 DEG C / min, and the sample is taken after heating to the highest temperature and air cooling. If the starting temperature is too low, the aging efficiency will be reduced, and the time will be wasted. If the starting temperature is too high, the L12 embryo cannot form in large quantities at low temperature. If the end temperature is too low, the L12 precipitated phase size is too small. If the end temperature is too high, the alloy will recrystallize completely, and the L12 phase will not be precipitated, and the alloy strength will be reduced. If the heating rate is too small, the L12 phase is coarsened, the size is too large, and the strengthening effect is reduced. If the heating rate is too large, the L12 embryo cannot form in large quantities at low temperature.

[0046] Further, the low-cost Fe-based entropy alloy has a yield strength of not less than 1.3 GPa and a uniform plasticity of more than 10%.

[0047] Example 1

[0048] The alloy composition (calculated in terms of atomic percentage) of this embodiment is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0049] The method of the temperature aging strengthening low-cost Fe-based entropy alloy of this embodiment comprises the following steps:

[0050] Step one, select Fe, Cr, Ni, Al and Ti block raw materials with a purity of not less than 99.9%, and mix them according to the component ratio. After the raw materials are ultrasonically cleaned with anhydrous ethanol, they are blown dry, packaged in different bags according to different elements, and arranged in the copper crucible according to the melting point from high to low (high melting point raw materials are at the bottom, and low melting point raw materials are at the top). The Al raw material is arranged in the middle of the other raw materials.

[0051] Step two, the cavity of the smelting chamber is vacuumed to a level of less than 5*10 -3 Pa, and filled with an argon atmosphere of not higher than 0.05 MPa. Turn on the heating power supply, and supply alternating current to the induction coil to cause the raw materials to heat and melt spontaneously. The smelting power is increased in steps: increase by 5 kw for 1 minute, and observe the smelting process until all the furnace charges form a uniform flowing molten pool.

[0052] Step three, increase the smelting power to 35 kw, and the holding time is 30 min. Use an external electromagnetic field to stir the solution, and need to stand for a moment to promote the slag to float up. Use a quartz scoop to transfer the slag produced during smelting to a special crucible next to it.

[0053] Step four, after the raw materials are completely alloyed, tilt the furnace body to pour the metal liquid into the pre-placed water-cooled copper mold below the furnace body to obtain an alloy ingot of appropriate size.

[0054] Step five, the alloy ingot obtained in step four is forged for multiple times, using a three-die three-pulling method, the forging temperature is 1000 ℃, the ingot is kept in a high-temperature furnace for 30 min before forging, and is air-cooled after each time of forging. The final forging thickness is about 30 mm, the forged blank is removed of surface residues to obtain a block material with clean surface.

[0055] Step six, the forged block is subjected to cold rolling treatment, 2 mm per pass, the total reduction is 70 %, to obtain a 9 mm thick plate.

[0056] Step seven, the plate is subjected to temperature aging treatment, the furnace is heated, the initial temperature of the temperature aging is 600 ℃, the final temperature is 900 ℃, the heating rate is 5 ℃ / min, and the plate is air-cooled immediately after being heated to 900 ℃.

[0057] The alloy composition of the embodiment is designed according to a phase diagram. Figure 1 The temperature aging process curve of the embodiment is shown in Figure 2 The Fe 46 Ni 23 Cr 23 Al6Ti2 alloy in the embodiment contains high-density, uniformly distributed and appropriately sized L12 phase Figure 4 , with an average size of 51±14 nm. The alloy after temperature aging has a quasi-static yield strength of 1405 MPa and a uniform elongation of 14.4%, Figure 3 which is much higher than that of the cold-rolled alloy. The appropriately sized L12 phase can make the dislocation bypass mechanism move, effectively improving the yield strength of the alloy. The material has excellent strength and plasticity matching, and can be further processed into various structural component materials.

[0058] Example 2

[0059] The alloy composition of the embodiment (calculated in terms of atomic percentage content) is Fe 46 Ni 28 Cr 18 Al5Ti3.

[0060] Except that the melting power in step three is 33 kw, the other steps are the same as in example 1.

[0061] The Fe 46 Ni 28 Cr 18 Al5Ti3 alloy in the embodiment contains high-density, uniformly distributed and appropriately sized L12 phase Figure 5), the average size is 49±16 nm. It is detected that the quasi-static yield strength of the alloy after the temperature aging is 1526 MPa, and the uniform elongation is 12.6% (both far more than those of the cold-rolled alloy. Figure 6

[0062] Example 3

[0063] The alloy composition of this example (calculated according to the atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0064] Except that the starting temperature of the temperature aging in step seven is changed to 650 ℃, the rest of the steps are the same as those in Example 1.

[0065] It is characterized that the Fe 46 Ni 23 Cr 23 Al6Ti2 alloy organization in this example contains high-density, uniformly distributed and appropriately sized L12 phase, the average size is 52±9 nm. It is detected that the quasi-static yield strength of the alloy after the temperature aging is 1423 MPa, and the uniform elongation is 12.7%, and the comprehensive mechanical properties are far more than those of the cold-rolled alloy.

[0066] Example 4

[0067] The alloy composition of this example (calculated according to the atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0068] Except that the ending temperature of the temperature aging in step seven is changed to 850 ℃, the rest of the steps are the same as those in Example 1.

[0069] It is characterized that the Fe 46 Ni 23 Cr 23 Al6Ti2 alloy organization in this example contains high-density, uniformly distributed and appropriately sized L12 phase, the average size is 55±17 nm. It is detected that the quasi-static yield strength of the alloy after the temperature aging is 1397 MPa, and the uniform elongation is 13.5%, and the comprehensive mechanical properties are far more than those of the cold-rolled alloy.

[0070] Example 5

[0071] The alloy composition of this example (calculated according to the atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0072] ​Except that the temperature rising rate in step seven is changed to 2 ℃ / min, the other steps are the same as those in Example 1.

[0073] The Fe in the alloy after the temperature aging in this example is characterized. 46 Ni 23 Cr 23 The Al6Ti2 alloy has a high density of L12 phases with uniform distribution and appropriate size, and the average size is 47±11 nm. The alloy after the temperature aging has a yield strength of 1455 MPa and a uniform elongation of 13.8%, and the comprehensive mechanical properties are far better than those of the cold-rolled alloy.

[0074] Comparative Example 1

[0075] The alloy composition in this example (calculated according to the atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0076] Except that the temperature aging process in step seven is changed to isothermal aging treatment (600 ℃ for 1 h and then air cooling), the other steps are the same as those in Example 1.

[0077] The Fe in the alloy after the isothermal aging in this comparative example is characterized. 46 Ni 23 Cr 23 The Al6Ti2 alloy has a high density of L12 phases with uniform distribution and appropriate size, and the average size is 47±11 nm. The alloy after the temperature aging has a yield strength of 1455 MPa and a uniform elongation of 13.8%, and the comprehensive mechanical properties are far better than those of the cold-rolled alloy. Figure 7 ), and the strength is lower than that of the cold-rolled alloy. A large number of L12 phase nuclei are formed at 600 ℃, but the L12 phase grows slowly at this temperature, and the small L12 phase can only strengthen the alloy by the dislocation cutting mechanism, which can prolong the work hardening stage and improve the plasticity, but the strengthening effect is not as good as the dislocation bypass mechanism.

[0078] Comparative Example 2

[0079] The alloy composition in this example (calculated according to the atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0080] Except that the temperature aging process in step seven is changed to isothermal aging treatment (900 ℃ for 30 min and then air cooling), the other steps are the same as those in Example 1.

[0081] The Fe in the alloy after the isothermal aging in this example is characterized. 46 Ni 23 Cr 23The Al6Ti2 alloy contains low-density, discrete distribution and size-appropriate L12 phase, with an average size of 54±16 nm. The alloy after single-step isothermal aging has a quasi-static yield strength of 987 MPa and a uniform elongation of 13.9%, and the strength is lower than that of the cold-rolled alloy. Without the low-temperature aging step, it is difficult to form a high-density L12 phase embryo.

[0082] Comparative Example 3

[0083] The alloy composition of the present comparative example (calculated in terms of atomic percentage content): Fe 50 Ni 23 Cr 17 Al7Ti3 (component deviates from the appropriate range).

[0084] Except that the smelting power is increased to 36 kw, the remaining steps are the same as in Example 1.

[0085] After characterization, the Fe 50 Ni 23 Cr 17 Al7Ti3 alloy contains high-density, uniformly distributed and size-appropriate L12 phase, with an average size of 61±15 nm, and also precipitates high-density brittle B2 phase (black precipitated phase in Figure 8 ). After detection, the quasi-static yield strength of the alloy after temperature aging is 1421 MPa, and the uniform elongation is 6.9%, and the plasticity is poor. Phase diagram analysis shows that for this composition alloy, the B2 phase is also very stable in the 600-900 ℃ interval, and a large amount of B2 brittle phase is easily precipitated during aging in this temperature interval, which weakens the room temperature plasticity of the alloy.

[0086] Comparative Example 4

[0087] The alloy composition of the present example (calculated in terms of atomic percentage content): Fe 46 Ni 23 Cr 23 Al6Ti2.

[0088] Except that the starting temperature of temperature aging in step seven is changed to 700 ℃, the remaining steps are the same as in Example 1.

[0089] After characterization, the Fe 46 Ni 23 Cr 23 Al6Ti2 alloy contains low-density, discrete distribution and size-appropriate L12 phase, with an average size of 52±8 nm. After detection, the quasi-static yield strength of the alloy after temperature aging is 967 MPa, and the uniform elongation is 14.2%, and the strength is lower than that of the cold-rolled alloy.

[0090] Comparative Example 5

[0091] The alloy composition of this example (calculated in terms of atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0092] Except that the end temperature of the temperature aging in step seven is changed to 800 ℃, the rest of the steps are the same as example 1.

[0093] After temperature aging, the Fe 46 Ni 23 Cr 23 Al6Ti2alloy organization contains a high density, uniform distribution and small size of L12 phase, the average size is 25±13nm. After testing, the quasi-static yield strength of the alloy after temperature aging is 1101MPa, and the uniform elongation is 14.5%. The small L12 phase can only strengthen the alloy by dislocation cutting mechanism, although it can prolong the work hardening stage to improve the plasticity, but the strengthening effect is not as good as the dislocation bypass mechanism.

[0094] Comparative example 6

[0095] The alloy composition of this example (calculated in terms of atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0096] Except that the end temperature of the temperature aging in step seven is changed to 950 ℃, the rest of the steps are the same as example 1.

[0097] After temperature aging, the Fe 46 Ni 23 Cr 23 Al6Ti2alloy organization does not contain L12 phase. After testing, the quasi-static yield strength of the alloy after temperature aging is 931MPa, and the uniform elongation is 10.9%, the strength is lower than that of the cold rolled alloy. The too high end temperature makes the alloy completely recrystallize, leaving only the FCC matrix.

[0098] Comparative example 7

[0099] The alloy composition of this example (calculated in terms of atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0100] Except that the temperature rising rate of the temperature aging in step seven is changed to 1 ℃ / min, the rest of the steps are the same as example 1.

[0101] After temperature aging, the Fe 46 Ni23 Cr 23 The Al6Ti2 alloy microstructure contains high density, uniformly distributed and coarse size L12 phase, with an average size of 87±23 nm. The alloy after temperature aging has a quasi-static yield strength of 1243 MPa and a uniform elongation of 12.90%. The slower heating rate prolongs the overall aging time, coarsens the L12 phase, and weakens the precipitation strengthening effect.

[0102] Comparative Example 8

[0103] The alloy composition of this example (calculated in terms of atomic percentage content) is: Fe 46 Ni 23 Cr 23 Al6Ti2.

[0104] Except that the heating rate of temperature aging in step seven is changed to 7 ℃ / min, the rest of the steps are the same as in Example 1.

[0105] Characterized, the Fe 46 Ni 23 Cr 23 The Al6Ti2 alloy microstructure contains low density, discrete distribution and fine size L12 phase, with an average size of 31±12 nm. The alloy after temperature aging has a quasi-static yield strength of 991 MPa and a uniform elongation of 13.50%, and the strength is lower than that of the cold-rolled alloy. The faster heating rate reduces the number of L12 phase nuclei at low temperature, and the L12 phase does not have time to grow. The low density of fine L12 phase has limited strengthening effect on the alloy.

[0106] The important step parameters in all examples and comparative examples and the corresponding alloy microstructure and mechanical property results are shown in Table 1 below.

[0107] Table 1

[0108]

[0109] The composition characteristics of the Fe-based entropy alloy prepared in Examples 1-2 are calculated, and the results are shown in Table 2.

[0110] Table 2 Composition characteristics of Fe-based entropy alloy

[0111]

[0112] By changing the component ratio, the configuration entropy of the three alloys is lower than the common threshold of high-entropy alloy, and belongs to the range of medium-entropy alloy. The atomic size difference δ is between 4.1-4.7%, which is smaller than the critical value (~6.5%) of forming amorphous, and is conducive to the formation of solid solution. The valence electron concentration is between face-centered cubic and body-centered cubic structure, and can be optimized by heat treatment process to control the microstructure of mixed phase. Figure 1 As shown in FIG. 1, the alloys in Example 1 and Example 2 can be controlled to have face-centered cubic matrix and L12 nanometer precipitated phase in the temperature range of 600-900 ℃. The mechanical properties of the alloys after aging ( Figure 3 and Figure 6 ) are very outstanding, and the microstructure ( Figure 4 and Figure 5 ) is a mixed structure of multiple phases coexisting.

[0113] In summary, the present application breaks through the strength bottleneck of low-cost medium-entropy alloy, and provides a high-performance and low-cost option for its engineering application in extreme environments.

[0114] The above implementation cases are only the preferred implementation cases of the present application, but the implementation manner of the present application is not limited by the above implementation cases. For example, various forms of combinations of the schemes in the examples, any changes, modifications, substitutions, combinations made without departing from the spirit and principles of the present application should be equivalent replacement ways, and are within the protection scope of the present application.

Claims

1. A low-cost Fe-based medium-entropy alloy with variable-temperature aging strengthening, characterized in that, The atomic expression for this intermediate-entropy alloy is Fe. a Ni b Cr c Al d Ti e Where a=46, 23≤b≤28, 18≤c≤23, 5≤d≤6, 2≤e≤3; The medium-entropy alloy was obtained by vacuum induction melting, hot forging, room temperature rolling and variable temperature aging treatment in sequence. The starting temperature of the variable temperature aging process is 600~650 ℃, the ending temperature is 850~900 ℃, the heating rate is 2~5 ℃ / min, and the sample is taken and air-cooled after the temperature reaches the highest temperature. The quasi-static yield strength of this medium-entropy alloy is not less than 1.3 GPa, and its uniform plasticity exceeds 10%.

2. The medium-entropy alloy as described in claim 1, characterized in that, Hot forging adopts a three-stage forging and three-stage drawing method, with a forging temperature of 1000 ℃, a holding time of 30 min before forging, and air cooling after each forging cycle.

3. The medium-entropy alloy as described in claim 1, characterized in that, During room temperature rolling, each pass is 2 mm, and the total reduction is 70%.

4. A method for preparing a medium-entropy alloy as described in any one of claims 1-3, characterized in that, The Fe-based medium-entropy alloy was obtained by sequentially performing vacuum induction melting, hot forging, room temperature rolling, and variable-temperature aging treatment. The starting temperature of the variable temperature aging process is 600~650 ℃, the ending temperature is 850~900 ℃, the heating rate is 2~5 ℃ / min, and the sample is taken and air-cooled after reaching the highest temperature.

5. The preparation method according to claim 4, characterized in that, Hot forging adopts a three-stage forging and three-stage drawing method, with a forging temperature of 1000 ℃, a holding time of 30 min before forging, and air cooling after each forging cycle.

6. The preparation method according to claim 4, characterized in that, During room temperature rolling, each pass is 2 mm, and the total reduction is 70%.

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