Method for simultaneously improving strength and plasticity of entropy alloy in FeCrNi

Abstract

The invention relates to the technical field of metal materials, in particular to a method for simultaneously improving strength and plasticity of entropy alloy in FeCrNi, the chemical component of the alloy is expressed as FeCrNiNx, x is more than or equal to 0 and less than or equal to 0.1, and x is the molar percentage of elements; doping N in a form of adding CrN particles; the preparation method comprises the following steps: weighing raw materials, and preparing a FeCrNi series medium-entropy alloy by adopting an electric arc melting method; after homogenization treatment, 70% cold rolling deformation is conducted, and water quenching is conducted after annealing; after proper thermal mechanical treatment, compared with an as-cast equimolar FeCrNi medium-entropy alloy, the yield strength of the alloy is improved by 3.12 times, and the ductility is improved by 9%; according to the method, the strength and plasticity of the entropy alloy in FeCrNi can be improved at the same time through nitrogen doping and partial recrystallization after cold rolling.

Description

Technical Field

[0001] The invention relates to the technical field of metal materials, in particular to a method for simultaneously improving the strength and plasticity of a FeCrNi medium entropy alloy. Background Art

[0002] With the rapid development of science and technology, the traditional alloy design concept based on a single element has gradually shown its limitations and is unable to meet the continuous demand for high-performance materials. Multi-principal medium / high entropy alloys (M / HEAs) as a new type of alloy system have attracted widespread attention in the field of materials science. Medium / high entropy alloys are composed of multiple main elements, usually have a simple crystal structure (such as face-centered cubic FCC, body-centered cubic BCC or hexagonal close-packed HCP), and exhibit excellent mechanical properties, corrosion resistance and thermal stability.

[0003] Among the numerous medium / high entropy alloys, cobalt-free FeCrNi medium entropy alloy (MEA) with a single face-centered cubic (FCC) structure has attracted much attention due to its high performance and low cost. Studies have shown that FeCrNi alloy has higher strength and strain hardening ability than CoCrFeMnNi high entropy alloy, and has better corrosion resistance than 304 stainless steel (SS). Therefore, FeCrNi alloy has great application potential in industrial fields such as automobile, aerospace, and nuclear energy.

[0004] However, as a face-centered cubic structure, the strength of FeCrNi medium-entropy alloy is still relatively low, which limits its application as a structural material in engineering. In order to improve the strength of FeCrNi alloy without significantly reducing its plasticity, researchers have conducted a lot of exploration. Studies have shown that the mechanical properties of medium-entropy alloys can be significantly improved by doping with nitrogen (N). Therefore, a method for simultaneously improving the strength and plasticity of FeCrNi medium-entropy alloys is proposed to address the above problems. Summary of the invention

[0005] The object of the present invention is to provide a method for simultaneously improving the strength and plasticity of FeCrNi medium entropy alloys, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for simultaneously improving the strength and plasticity of a FeCrNi medium entropy alloy, wherein the chemical composition of the medium entropy alloy is FeCrNiNx, wherein 0≤x≤0.1, x is the molar percentage of nitrogen, and nitrogen is doped by adding CrN particles; the method comprises the following steps:

[0008] S1. Alloy preparation: accurately weighing Cr, Fe, Ni and CrN raw materials according to the molar percentage of the medium entropy alloy, and preparing FeCrNiNx medium entropy alloy by arc melting process;

[0009] S2: homogenization treatment: the alloy prepared in step S1 is subjected to homogenization annealing treatment at 1100° C. for 10 hours to obtain a bulk alloy with uniform composition;

[0010] S3: cutting and grinding: cutting the bulk alloy obtained in step S2 into a cuboid by electrospark machining, and grinding, polishing, cleaning and cold-air drying the six sides;

[0011] S4: cold rolling deformation: cold rolling the alloy after the treatment in step S3 to reduce the total thickness of the alloy by 70%;

[0012] Annealing treatment: anneal the cold-rolled alloy at 750°C-900°C for 0.5-1 hour, and then quench with water to obtain a FeCrNiNx medium-entropy alloy with synergistically improved strength and plasticity.

[0013] Preferably, in step S1, the purity of the Cr, Fe, Ni and CrN particles is greater than or equal to 99.9%, and before arc melting, the Cr, Fe, Ni and CrN particles are ultrasonically cleaned in acetone and ethanol solutions in sequence.

[0014] Preferably, the arc melting process in step S1 is carried out under inert gas protection, and specifically comprises the following steps:

[0015] Before melting, the furnace chamber was purged with high-purity argon gas three times to evacuate the furnace chamber to a vacuum of 1×10 -4 Pa, high-purity argon is introduced as protective gas;

[0016] The weighed raw materials are placed in a copper mold crucible in order from low to high melting points. The ingot is remelted at least five times to maintain a uniform composition, and then cooled in the copper crucible to obtain an alloy ingot.

[0017] Preferably, the size of the rectangular parallelepiped sample in step S3 is 4 mm×15 mm×25 mm.

[0018] Preferably, in step S4, the initial thickness of the cold rolling is 4 mm, the rolling reduction is 70%, and the remaining thickness is 1.2 mm.

[0019] Preferably, the annealing temperature in step S5 is 750° C.-900° C., the annealing time is 0.5-1 hour, and the annealing is followed by quenching with water.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] Improve strength and plasticity at the same time:

[0022] Through nitrogen doping and cold rolling + annealing treatment (also known as thermomechanical treatment), the strength and plasticity of FeCrNi medium entropy alloys have been significantly improved; for example, FeCrNiN annealed at 800℃ for 0.5 hours 0.1 The yield strength of the alloy reaches 563MPa, which is 3.12 times higher than that of the cast FeCrNi medium entropy alloy; the elongation is 43.3%, which is 9% higher than that of the cast FeCrNi medium entropy alloy;

[0023] Cost-effectiveness:

[0024] The present invention does not add high-cost metal elements such as molybdenum, but only uses simple nitrogen doping to significantly reduce the manufacturing cost of the alloy; compared with complex alloy preparation methods such as spark plasma sintering (SPS) and hot pressing sintering (HPS), the arc melting method is simple to operate and low in cost;

[0025] Simple process:

[0026] The process of cold rolling + annealing treatment is simple and easy to operate, which is conducive to large-scale promotion and application. This method can effectively control the microstructure of the alloy by adjusting the cold rolling and annealing process parameters, thereby achieving a synergistic improvement in strength and plasticity.

[0027] Excellent mechanical properties:

[0028] It can be seen from the experimental data of Examples 1-10 that the FeCrNi medium entropy alloy after appropriate nitrogen doping and thermomechanical treatment has significantly improved yield strength, tensile strength and elongation; for example, compared with Comparative Example 2 (cast FeCrNi), Example 2 has improved strength and plasticity, with a yield strength of 467.07 MPa, a tensile strength of 782.76 MPa, and an elongation of 48.82%;

[0029] Broad application prospects:

[0030] The FeCrNi medium entropy alloy provided by the present invention has excellent mechanical properties and corrosion resistance, is suitable for industrial fields such as automobiles, aerospace, and nuclear energy, and has broad application prospects;

[0031] Microstructure regulation:

[0032] Through nitrogen doping and thermomechanical treatment, the microstructure of the alloy has been effectively regulated, forming an inhomogeneous grain structure in which cold-rolled structure, recovery structure and recrystallized structure coexist. This inhomogeneous structure will produce additional heterogeneous deformation-induced strengthening during the deformation process, and the grains of different sizes and properties will deform in coordination with each other, so that the alloy can withstand external forces more effectively, improve strength and maintain good plasticity.

[0033] In summary, the present invention successfully achieves the simultaneous improvement of strength and plasticity of FeCrNi medium-entropy alloy through the combined improvement of material composition and processing technology, which has significant technical advantages and economic value. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with specific implementation methods.

[0036] Example:

[0037] This embodiment provides a technical solution:

[0038] A method for simultaneously improving the strength and plasticity of a FeCrNi medium entropy alloy, wherein the chemical composition of the medium entropy alloy is FeCrNiNx, wherein 0≤x≤0.1, x is the molar percentage of nitrogen, and nitrogen is doped by adding CrN particles; the method comprises the following steps:

[0039] S1. Alloy preparation: accurately weighing Cr, Fe, Ni and CrN raw materials according to the molar percentage of the medium entropy alloy, and preparing FeCrNiNx medium entropy alloy by arc melting process;

[0040] S2: homogenization treatment: the alloy prepared in step S1 is subjected to homogenization annealing treatment at 1100° C. for 10 hours to obtain a bulk alloy with uniform composition;

[0041] S3: cutting and grinding: cutting the bulk alloy obtained in step S2 into a cuboid by electrospark machining, and grinding, polishing, cleaning and cold-air drying the six sides;

[0042] S4: cold rolling deformation: cold rolling the alloy after the treatment in step S3 to reduce the total thickness of the alloy by 70%;

[0043] Annealing treatment: anneal the cold-rolled alloy at 750°C-900°C for 0.5-1 hour, and then quench with water to obtain a FeCrNiNx medium-entropy alloy with synergistically improved strength and plasticity.

[0044] Furthermore, in step S1, the purity of the Cr, Fe, Ni and CrN particles is greater than or equal to 99.9%, and before arc melting, the Cr, Fe, Ni and CrN particles are ultrasonically cleaned in acetone and ethanol solutions in sequence.

[0045] Further, the arc melting process in step S1 is carried out under inert gas protection, and specifically includes the following steps:

[0046] Before melting, the furnace chamber was purged with high-purity argon gas three times to evacuate the furnace chamber to a vacuum of 1×10 -4 Pa, high-purity argon is introduced as protective gas;

[0047] The weighed raw materials are placed in a copper mold crucible in order from low to high melting points. The ingot is remelted at least five times to maintain a uniform composition, and then cooled in the copper crucible to obtain an alloy ingot.

[0048] Furthermore, in step S3, the size of the rectangular parallelepiped sample is 4 mm×15 mm×25 mm.

[0049] Furthermore, in step S4, the initial thickness of the cold rolling is 4 mm, the rolling reduction is 70%, and the remaining thickness is 1.2 mm.

[0050] Furthermore, in step S5, the annealing temperature is 750° C.-900° C., the annealing time is 0.5-1 hour, and the annealing is followed by quenching with water.

[0051] In order to more clearly illustrate the method provided by the present invention, it is described in detail through the following examples.

[0052] Example 1

[0053] Alloy preparation:

[0054] Commercially available Fe, Cr, Ni, and CrN particles (purity: 99.9%) were used as raw materials;

[0055] The raw materials were ultrasonically cleaned in acetone and ethanol solutions in sequence;

[0056] Weigh the raw materials (33.25 g of Fe, 27.87 g of Cr, 34.95 g of Ni, 3.93 g of CrN);

[0057] According to the melting point, the weighed raw materials are placed in a copper mold crucible from bottom to top;

[0058] Prior to melting, the furnace chamber was purged three times with high-purity argon;

[0059] The vacuum pressure of the furnace chamber was pumped down to 1×10 -4 Pa, and then high-purity argon is introduced as the protective gas;

[0060] The ingots were melted by arc melting for a minimum of five repetitions to maintain a homogeneous composition and then cooled in a copper crucible;

[0061] Homogenization treatment:

[0062] Homogenization annealing (HOA) was applied to the ingot in a heat treatment furnace at 1100°C for 10 h;

[0063] The HOA samples were cut into 4 mm × 15 mm × 25 mm cuboids by electrospark machining;

[0064] The six sides of the cuboid sample were ground, polished, cleaned, and dried with cold air;

[0065] Cold rolling deformation:

[0066] The alloy treated in step S3 is cold rolled, with an initial thickness of 4 mm, a rolling reduction of 70%, and a residual thickness of 1.2 mm;

[0067] Annealing treatment:

[0068] The cold rolled alloy was annealed at 750°C for 0.5 h and subsequently quenched in water.

[0069] Example 2

[0070] The difference from Example 1 is that the cold-rolled alloy is annealed at 850° C. for 0.5 hour and then quenched with water. The other preparation processes are the same.

[0071] Example 3

[0072] The difference from Example 1 is as follows: the raw materials are weighed (33.39 g of Fe, 29.54 g of Cr, 35.10 g of Ni, and 1.97 g of CrN), and the other preparation processes are the same.

[0073] Example 4

[0074] The difference from Example 3 is that the annealing is performed at 800° C. for 0.5 hour, and the other preparation processes are the same.

[0075] Example 5

[0076] The difference from Example 3 is that the annealing is performed at 850° C. for 0.5 hour, and the other preparation processes are the same.

[0077] Example 6

[0078] The difference from Example 1 is that the raw materials are weighed (33.53 g of Fe, 31.22 g of Cr, and 35.24 g of Ni), and the other preparation processes are the same.

[0079] Example 7

[0080] The difference from Example 6 is that the annealing is performed at 800° C. for 0.5 hour, and the other preparation processes are the same.

[0081] Example 8

[0082] The difference from Example 6 is that the annealing is performed at 850° C. for 0.5 hour, and the other preparation processes are the same.

[0083] Example 9

[0084] The difference from Example 6 is that the annealing is performed at 900° C. for 0.5 hour, and the other preparation processes are the same.

[0085] Example 10

[0086] The difference from Example 6 is that the annealing is performed at 800° C. for 1 hour, and the other preparation processes are the same.

[0087] Comparative Example 1

[0088] The difference from Example 1 is that after the homogenization treatment, the cold rolling + annealing treatment is not performed.

[0089] Comparative Example 2

[0090] The difference from Example 6 is that after the homogenization treatment, the cold rolling + annealing treatment is not performed.

[0091] Experimental Results

[0092] The strength and plasticity indexes of FeCrNi alloy were measured by electronic universal tensile testing machine.

[0093] As shown in Table 1.

[0094] serial number Yield strength (MPa) Tensile strength(MPa) Elongation(%) Example 1 974.80 1005.94 11.08 Example 2 467.07 782.76 48.82 Example 3 742.83 801.84 7.65 Example 4 565.10 790.07 27.65 Example 5 369.66 634.43 31.04 Example 6 784.98 866.91 9.31 Example 7 586.09 763.76 18.18 Example 8 432.05 698.23 24.11 Example 9 421.3 669.02 32.80 Example 10 576.8 778.32 20.01 Comparative Example 1 218.95 495.48 62.42 Comparative Example 2 136.64 279.53 39.73

[0095] Table 1

[0096] in conclusion:

[0097] From the experimental data of Comparative Examples 1 and 2 in Table 1, it is found that if only nitrogen doping is performed, the plasticity of the alloy increases greatly, and although the strength increases, the increase is relatively small.

[0098] Comparing the data of Example 1 with that of Comparative Example 1, the yield strength of the alloy doped with 0.1 mol of nitrogen and annealed at 750° C. for 0.5 hour was increased by 6.1 times compared with the basic alloy FeCrNi without cold rolling and annealing, but the elongation was reduced by 72%.

[0099] Comparing the data of Example 2 with that of Comparative Example 2, the yield strength of the alloy doped with 0.1 mol of nitrogen and annealed at 850° C. for 0.5 hour increased by 2.4 times and the elongation increased by 23% compared with the basic alloy FeCrNi without cold rolling and annealing.

[0100] Comparing the data of Example 4 with that of Comparative Example 2, the yield strength of the alloy doped with 0.05 mol of nitrogen and annealed at 800° C. for 0.5 hour increased by 3.1 times and the elongation decreased by 30% compared with the basic alloy FeCrNi without cold rolling and annealing.

[0101] Comparing the data of Example 5 with that of Comparative Example 2, the yield strength of the alloy doped with 0.05 mol of nitrogen and annealed at 850° C. for 0.5 hour increased by 1.7 times and the elongation decreased by 22% compared with the basic alloy FeCrNi without cold rolling and annealing.

[0102] From the experimental data of Examples 6-9 and Comparative Example 2, it is found that when no nitrogen is doped and only cold rolling + annealing treatment is performed, the strength decreases and the plasticity increases as the annealing temperature increases. For example, when the FeCrNi medium entropy alloy without nitrogen is annealed at 850°C for 0.5 hours, the yield strength is increased by 2.2 times compared with the cast FeCrNi medium entropy alloy, while the elongation is reduced by 40%.

[0103] From the data comparison of Example 7 and Example 9, it is found that the annealing temperature is 800°C. After annealing for 1 hour, compared with annealing for 0.5 hour, the yield strength is only reduced by 1.6%, the tensile strength is slightly increased, but the elongation is increased by 10%.

[0104] From the data in Table 1, it can be concluded that only when the appropriate content of nitrogen is doped and the appropriate cold rolling + annealing process parameters are controlled at the same time, can the effect of simultaneously improving the yield strength and plasticity of the FeCrNi medium entropy alloy be achieved.

[0105] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for simultaneously improving the strength and plasticity of FeCrNi medium entropy alloys, characterized in that: The chemical composition of the medium entropy alloy is FeCrNiNx, wherein 0≤x≤0.1, x is the molar percentage of nitrogen, and the nitrogen element is doped by adding CrN particles; the method comprises the following steps: S1. Alloy preparation: accurately weighing Cr, Fe, Ni and CrN raw materials according to the molar percentage of the medium entropy alloy, and preparing FeCrNiNx medium entropy alloy by arc melting process; S2: homogenization treatment: the alloy prepared in step S1 is subjected to homogenization annealing treatment at 1100° C. for 10 hours to obtain a bulk alloy with uniform composition; S3: cutting and grinding: cutting the bulk alloy obtained in step S2 into a cuboid by electrospark machining, and grinding, polishing, cleaning and cold-air drying the six sides; S4: cold rolling deformation: cold rolling the alloy after the treatment in step S3 to reduce the total thickness of the alloy by 70%; Annealing treatment: anneal the cold-rolled alloy at 750°C-900°C for 0.5-1 hour, and then quench with water to obtain a FeCrNiNx medium-entropy alloy with synergistically improved strength and plasticity.

2. The method for simultaneously improving the strength and plasticity of FeCrNi medium entropy alloy according to claim 1, characterized in that: In step S1, the purity of the Cr, Fe, Ni and CrN particles is greater than or equal to 99.9%, and before arc melting, the Cr, Fe, Ni and CrN particles are ultrasonically cleaned in acetone and ethanol solutions in turn.

3. The method for simultaneously improving the strength and plasticity of FeCrNi medium entropy alloy according to claim 1, characterized in that: The arc melting process in step S1 is carried out under the protection of an inert gas, and specifically comprises the following steps: Before melting, the furnace chamber was purged with high-purity argon gas three times to evacuate the furnace chamber to a vacuum of 1×10 -4 Pa, high-purity argon is introduced as protective gas; The weighed raw materials are placed in a copper mold crucible in order from low to high melting points. The ingot is remelted at least five times to maintain a uniform composition, and then cooled in the copper crucible to obtain an alloy ingot.

4. The method for simultaneously improving the strength and plasticity of FeCrNi medium entropy alloy according to claim 1, characterized in that: The size of the rectangular parallelepiped sample in step S3 is 4 mm×15 mm×25 mm.

5. The method for simultaneously improving the strength and plasticity of FeCrNi medium entropy alloy according to claim 1, characterized in that: The initial thickness of the cold rolling in step S4 is 4 mm, the rolling reduction is 70%, and the remaining thickness is 1.2 mm.

6. The method for simultaneously improving the strength and plasticity of FeCrNi medium entropy alloy according to claim 1, characterized in that: The annealing treatment temperature in step S5 is 750° C.-900° C., the annealing time is 0.5-1 hour, and the annealing is followed by quenching with water.