Method for refining face-centered cubic high-entropy alloy grains

Abstract

The invention belongs to the field of metal material preparation, and particularly relates to a face-centered cubic high-entropy alloy grain refinement method. Comprising the following steps: (1) high-entropy alloy ingot preparation and solution treatment; (2) rolling the high-entropy alloy to obtain a plate; and (3) carrying out heat treatment processes at different temperatures and for different times, and controlling recrystallization and grain growth processes to realize grain size regulation and control. According to the method, the grain size of the high-entropy alloy can be regulated and controlled through low-cost and simple operation, and preparation of the ultra-fine grain high-entropy alloy is achieved. According to different use requirements of the high-entropy alloy, proper parameters are selected, the production process becomes simpler, more convenient, more economical and more efficient, and meanwhile guidance is provided for grain refinement of the face-centered cubic high-entropy alloy.

Description

Technical Field

[0001] The present invention belongs to the field of metal material preparation, and particularly relates to a method for refining grains of a face-centered cubic high-entropy alloy. Background Art

[0002] In recent years, with the rapid development of fields such as aerospace, marine vessels, and cryogenic industries, the performance requirements for materials have become increasingly high. The traditional single-principal-element alloy system has reached its limit in terms of composition design, microstructural regulation, and mechanical property optimization, and thus can no longer meet the increasingly demanding engineering service requirements. The multi-principal-element-based high-entropy alloys developed in recent years have rapidly attracted wide attention from material researchers due to their large composition design space, adjustable microstructures, and excellent properties. In particular, some single-phase FCC-structured high-entropy alloys exhibit many promising properties, such as high lattice friction stress, simultaneously improved strength and elongation at low temperatures, outstanding fracture toughness, high fatigue crack growth resistance, outstanding radiation resistance, and high corrosion resistance.

[0003] CrCoNi and VCoNi medium-entropy alloys are currently the two medium-entropy alloys with the best mechanical properties reported for single-phase FCC. The former exhibits a low stacking fault energy. At room temperature and during tensile deformation, in addition to the dislocation deformation mechanism, it can also induce high-density twins and even phase transformation. The multiple deformation mechanisms cooperate with each other, so high work-hardening ability can be obtained, ultimately leading to high tensile strength and excellent elongation. The CrCoNi medium-entropy alloy exhibits a single-phase FCC structure during annealing in a wide temperature range. Based on this, further composition regulation is carried out to maintain the single-phase FCC structure of the alloy. As V completely replaces Cr, the lattice distortion effect is further enhanced, and the stacking fault energy increases. The FCC single-phase VCoNi medium-entropy alloy can obtain a yield strength at the gigapascal level even in fine grains; at the same time, by forming a high-density Taylor lattice dislocation substructure, this alloy even exhibits a higher work-hardening ability than CrCoNi, thus achieving a good combination of high strength and plasticity at room temperature. However, due to the addition of a high content of V, the temperature range of the FCC single-phase region is significantly narrowed. Even during heat treatment at 900 °C, this alloy still contains 20% by volume of the L12 phase, and the phase stability is severely reduced, so it is difficult to further optimize the performance. Replacing half of the Cr with V improves the stability of the FCC structure, can lower the heat treatment temperature of the alloy to a lower temperature; at the same time, it can avoid the precipitation of brittle intermetallic compounds to a greater extent, enabling the alloy to maintain a solid solution structure during annealing in a relatively wide temperature range.

[0004] Compared with traditional alloy systems, due to their lattice distortion effect, medium / high entropy alloys exhibit higher lattice friction stress and Hall-Petch slope. Based on this, since the sensitivity of yield strength to grain size is also increased, refining the grain size is an effective strengthening method. However, preparing a fine-grained structure often involves very complex and difficult-to-scale-up industrial production processes, such as high-pressure torsion (HPT), liquid helium quenching, and can only be obtained by annealing for a short time in a very narrow temperature range. From a practical application perspective, these severe plastic deformation processes involved are difficult to industrialize, and the narrow annealing temperature / time window also brings inconvenience to the actual processing technology. Therefore, it is urgent to study a method to control the grain size of high entropy alloys by reasonable chemical composition regulation, reducing the recrystallization kinetics of the material, and thus using a simple process. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for refining the grains of a face-centered cubic high entropy alloy. By selecting appropriate high entropy alloy compositions, increasing the diffusion activation energy of the alloy, and through simple cold rolling and controlling the heat treatment time and temperature, the unique sluggish diffusion effect of the high entropy alloy is utilized to slow down the grain growth process of the high entropy alloy, realizing the grain refinement of the high entropy alloy, and then obtaining a single-phase face-centered cubic fine-grained fully recrystallized structure with excellent mechanical properties.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: A method for refining the grains of a face-centered cubic high entropy alloy, comprising the following steps:

[0007] Step (1): Prepare a V 0.5 Cr 0.5 CoNi high entropy alloy ingot by levitation melting and perform solution treatment;

[0008] Step (2): Multi-pass continuous cold rolling: Cold roll the solution-treated V 0.5 Cr 0.5 CoNi high entropy alloy ingot to obtain a high entropy alloy sheet;

[0009] Step (3): Heat treatment process: Heat treat the high entropy alloy sheet at 850 °C to 900 °C for 2 min to 10 min, and then water cool after completion to control the recrystallization process and grain growth process to achieve grain size control.

[0010] Further, in step (1), the temperature during solution treatment is 1150 °C, the time is 2 h, and then water cooling is carried out.

[0011] Further, in step (2), the deformation amount of each cold rolling is 0.1 mm - 0.2 mm, the total deformation amount of the final rolled sample is 90%, and the thickness after rolling is 1.5 mm.

[0012] Compared with the prior art, the present invention has the following remarkable advantages:

[0013] Compared with other methods for grain refinement of high-entropy alloys, the method of the present invention is simple to use and easy to operate. The deformation process it contains is only cold rolling. By adopting different annealing times and annealing temperatures, the grain size of the high-entropy alloy can be regulated. According to different usage requirements of the high-entropy alloy, selecting appropriate processing parameters to prepare a high-entropy alloy with fine grains plays a very important role in obtaining a high-entropy alloy with a strength-ductility balance.

[0014] The grain growth behavior of high-entropy alloys is related to the dislocation movement during the annealing process. The greater the resistance to dislocation movement, the slower the process of recrystallized grain growth. A lower stacking fault energy and a larger lattice misfit degree will increase the fluctuation of the lattice point potential energy, making the lattice friction force very large, hindering the dislocation movement and grain boundary migration during recrystallization, and thus reducing the diffusion rate. The slow diffusion rate is the main factor for the slow recrystallization kinetics of high-entropy alloys.

[0015] V 0.5 Cr 0.5 Compared with traditional alloys, CoNi high-entropy alloys have a lower activation energy and a larger grain misfit degree. Therefore, the recrystallization kinetics is slower, the grain growth process is easier to control, and the potential for grain refinement is greater. At the same time, the prepared high-entropy alloy has a uniform grain size and strong economic adaptability. Through multiple experimental attempts, it is found that an ultrafine grain structure can be obtained by annealing at a certain temperature. Designing a high-entropy alloy with slow recrystallization kinetics through composition regulation provides a new idea for the preparation of face-centered cubic fine-grained high-entropy alloys. Description of the Drawings

[0016] Figure 1 EBSD map of the microstructure of the ultrafine-grained V 0.5 Cr 0.5 CoNi alloy prepared in Example 1.

[0017] Figure 2 EBSD map of the microstructure of the fine-grained V 0.5 Cr 0.5 CoNi alloy prepared in Example 2.

[0018] Figure 3 EBSD map of the microstructure of the fine-grained V 0.5 Cr 0.5 CoNi alloy prepared in Example 3.

[0019] Figure 4 EBSD map of the microstructure of the coarse-grained V 0.5 Cr 0.5 CoNi alloy prepared in Example 4. Detailed Description of the Invention

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] Levitation melting V 0.5 Cr 0.5 The CoNi high-entropy alloy ingot is specifically: using high-purity V, Cr, Co, and Ni as raw materials and proportioning according to the atomic ratio. Before melting, wipe the inside of the copper crucible with alcohol to keep the copper crucible free of impurities. Then place the high-melting-point elements at the bottom of the crucible and the low-melting-point elements at the upper position to avoid the premature melting of the low-melting-point elements and the inability to form a stable melting zone. After loading, turn on the mechanical pump to evacuate, and then turn on the molecular pump to pump high vacuum. When the vacuum reading is lower than 10 -3 Pa, stop evacuating and fill with argon for protection. Before starting the melting, turn on the high-pressure water equipment to avoid damaging the copper crucible due to high temperature, and then carry out the melting of the alloy, repeating the melting five times.

[0022] Example 1

[0023] Subject the melted V 0.5 Cr 0.5 CoNi alloy ingot to solution treatment, with a solution temperature of 1150 °C and a holding time of 2 h. Then carry out cold rolling, with a deformation amount of 0.1 mm - 0.2 mm each time, and the total deformation amount of the final rolled sample is 90%, and the thickness after rolling is 1.5 mm. Cut the specimen from the processed sheet, select an annealing temperature of 850 °C and a holding time of 2 min, and then take out the specimen and cool it in water to obtain a fully recrystallized structure. Observe the electron backscatter diffraction pattern of the microstructure on the RD-TD plane. The EBSD pattern is as Figure 1 shown. Statistically obtain that the grain size of the fully recrystallized V 0.5 Cr 0.5 CoNi alloy is 0.9 μm.

[0024] Example 2

[0025] Subject the melted V 0.5 Cr 0.5The CoNi alloy ingot was solution-treated at a solution temperature of 1150 °C for 2 h. Then cold rolling was carried out, with a deformation amount of 0.1 mm - 0.2 mm each time, and the total deformation amount of the final rolled sample was 90%, and the thickness after rolling was 1.5 mm. The specimen was cut from the processed plate, the annealing temperature was selected as 900 °C, the holding time was 10 min, and then the specimen was taken out and cooled in water to obtain a fully recrystallized structure. Observe the electron backscatter diffraction pattern of the microstructure on the RD-TD plane. The EBSD pattern is as shown in Figure 2 shown. It was statistically obtained that the grain size of the V 0.5 Cr 0.5 CoNi alloy after full recrystallization was 2.3 μm.

[0026] Example 3

[0027] The melted V 0.5 Cr 0.5 CoNi alloy ingot was solution-treated at a solution temperature of 1150 °C for 2 h. Then cold rolling was carried out, with a deformation amount of 0.1 mm - 0.2 mm each time, and the total deformation amount of the final rolled sample was 90%, and the thickness after rolling was 1.5 mm. The specimen was cut from the processed plate, the annealing temperature was selected as 1000 °C, the holding time was 10 min, and then the specimen was taken out and cooled in water to obtain a fully recrystallized structure. Observe the electron backscatter diffraction pattern of the microstructure on the RD-TD plane. The EBSD pattern is as shown in Figure 3 shown. It was statistically obtained that the grain size of the V 0.5 Cr 0.5 CoNi alloy after full recrystallization was 7.1 μm, and the grains grew and were larger in size.

[0028] Example 4

[0029] The melted V 0.5 Cr 0.5 CoNi alloy ingot was solution-treated at a solution temperature of 1150 °C for 2 h. Then cold rolling was carried out, with a deformation amount of 0.1 mm - 0.2 mm each time, and the total deformation amount of the final rolled sample was 90%, and the thickness after rolling was 1.5 mm. The specimen was cut from the processed plate, the annealing temperature was selected as 1100 °C, the holding time was 10 min, and then the specimen was taken out and cooled in water to obtain a fully recrystallized structure. Observe the electron backscatter diffraction pattern of the microstructure on the RD-TD plane. The EBSD pattern is as shown in Figure 4 shown. It was statistically obtained that the grain size of the V 0.5 Cr 0.5 CoNi alloy after full recrystallization was 20 μm, and the grains grew and were larger in size.

Claims

1. A method for refining the grains of a face-centered cubic high-entropy alloy, characterized in that It includes the following steps: Step (1): Prepare a V 0.5 Cr 0.5 CoNi high-entropy alloy ingot by levitation melting and perform solution treatment; Step (2) Cold-roll the solution-treated V 0.5 Cr 0.5 CoNi high-entropy alloy ingot to obtain a high-entropy alloy sheet; In step (3), the high-entropy alloy sheet is heat-treated at 850°C to 900°C for 2 min to 10 min, and then water-cooled after completion to control the recrystallization process and grain growth process to achieve grain size control.

2. The method according to claim 1, characterized in that, In step (1), the solution treatment temperature is 1150°C and the time is 2 h, followed by water cooling.

3. The method according to claim 1, wherein In step (2), during cold rolling, the deformation amount each time is 0.1 mm - 0.2 mm, and the total deformation amount is 90%.

4. The method according to claim 1, wherein In step (2), the thickness after rolling is 1.5 mm.

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