High-strength medium-entropy alloy and preparation method thereof

Abstract

The invention discloses a high-strength medium-entropy alloy and a preparation method thereof. The molecular formula of the high-strength medium-entropy alloy is (CrCoNi) 100-xAlx, x ranges from 0 to 12 and is not 0, and the preparation method of the high-strength medium-entropy alloy comprises the steps that raw material metal is smelted, and an alloy ingot is obtained; and the alloy ingot is subjected to homogenization heat treatment under the vacuum condition and then subjected to hot forging treatment, an obtained forged plate is subjected to aging heat treatment, and the high-strength medium-entropy alloy is obtained. According to the preparation method, the content and the size of the precipitated phase of the intermetallic compound of the medium-entropy alloy can be controlled at the same time, and the medium-entropy alloy which is high in strength, high in speed and excellent in comprehensive mechanical property is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal alloy materials, and in particular relates to a medium-entropy alloy and a preparation method thereof. Background Art

[0002] Multi-principal alloys are composed of multiple (greater than or equal to 3) main constituent elements. According to the configuration entropy value criterion, they can be divided into high entropy alloys and medium entropy alloys. Medium entropy alloys, referred to as MEA, are composed of 3-4 main elements, with element contents ranging from 5% to 35%, atomic radius differences less than 15%, and mixing entropy values ​​between 1R and 1.5R. Medium entropy alloys exhibit a series of special properties different from traditional alloys, including high entropy effect, atomic hysteresis diffusion effect, lattice distortion effect, and cocktail effect.

[0003] Currently, a major challenge facing multi-principal alloys is that when increasing their strength, it is often difficult to avoid a decrease in plasticity and obtain high toughness. However, many fields, such as energy and power, aerospace, and shipbuilding industries, have an urgent need for high-strength and high-toughness metal structural materials.

[0004] To solve the above problems, some improvements have been made to the existing medium entropy alloys. For example, the addition of Al to the CrCoNi-based medium entropy alloy can form a BCC structured intermetallic compound phase precipitation phenomenon, which can enhance the comprehensive mechanical properties of the medium entropy alloy, including plasticity. Controlling the content and size of the BCC structured intermetallic compound phase precipitation is the basis for preparing such high-strength and tough medium entropy alloys.

[0005] The existing technical methods for regulating the content and size of BCC structured intermetallic compound precipitates in medium-entropy alloys mainly regulate the chemical composition and heat treatment process parameters. For example, increasing the W content increases the content of BCC structured intermetallic compound precipitates, but this method increases the cost and cannot effectively regulate the size and distribution of the precipitates, limiting the further improvement of its mechanical properties; or lowering the temperature of the heat treatment process to obtain a fine-sized BCC structured intermetallic compound precipitate, but the content of the precipitate will be reduced, also limiting the improvement of the mechanical properties of the medium-entropy alloy.

[0006] Therefore, the prior art still urgently needs a preparation method for a medium-entropy alloy with simple process, low cost, and the ability to simultaneously control the content and size of the BCC structure intermetallic compound precipitation phase of the medium-entropy alloy to obtain excellent comprehensive mechanical properties. Summary of the invention

[0007] In order to solve the problems of the prior art, the purpose of the present invention is to propose a preparation method for a medium-entropy alloy with simple process, low cost, and the ability to simultaneously control the content and size of the BCC structure intermetallic compound precipitation phase of the medium-entropy alloy to obtain a medium-entropy alloy with excellent comprehensive mechanical properties and to obtain a medium-entropy alloy with high strength and high plasticity under impact conditions.

[0008] The technical solution of the present invention is as follows:

[0009] A high-strength medium-entropy alloy with the molecular formula (CrCoNi) 100-x Al x , where x is 0-12 and not 0.

[0010] A method for preparing a high-strength medium-entropy alloy comprises the following steps:

[0011] (1) Weighing raw metals required for high-strength medium-entropy alloy according to element ratio;

[0012] (2) arranging and mixing the raw metals in order of melting point from low to high, then smelting them several times, and obtaining alloy ingots after cooling;

[0013] (3) subjecting the alloy ingot to homogenization heat treatment under vacuum conditions to obtain a homogenized alloy block;

[0014] (4) subjecting the homogenized alloy block to hot forging to obtain a forged plate;

[0015] (5) Subjecting the forged plate to aging heat treatment to obtain the high-strength medium-entropy alloy.

[0016] According to some preferred embodiments of the present invention, the preparation method further comprises: ultrasonically cleaning the raw metal and drying it before performing step (2).

[0017] According to some preferred embodiments of the present invention, the preparation method further comprises: subjecting the forged plate to mechanical grinding and / or surface contamination treatment and / or cutting before performing step (5).

[0018] According to some preferred embodiments of the present invention, the preparation method further comprises: casting the alloy melt obtained by the several smelting processes, and then cooling the alloy melt to obtain the alloy ingot.

[0019] According to some preferred embodiments of the present invention, the smelting is performed 3-5 times, each time for 15-25 minutes, in a vacuum suspension smelting furnace; the smelting current of the vacuum suspension smelting furnace is set to 230-250A.

[0020] According to some preferred embodiments of the present invention, the homogenization heat treatment comprises: subjecting the alloy ingot to a heat preservation treatment, and then subjecting the alloy ingot to a quenching cooling; the temperature of the heat preservation treatment is 1200° C., and the time is 12 hours.

[0021] According to some preferred embodiments of the present invention, the heating temperature of the hot forging treatment is 1000° C., and the forging deformation is 30-50%, more preferably 50%.

[0022] According to some preferred embodiments of the present invention, the aging heat treatment is performed at a temperature of 900° C. and for 30 minutes.

[0023] The high-strength medium-entropy alloy prepared by the present invention adopts a second-phase strengthening mechanism, that is, the strength and hardness of the alloy are improved by introducing discontinuous second-phase particles into the alloy matrix. These second-phase particles are usually precipitated by adding specific elements during the alloying process or by a heat treatment process, and they play a role in hindering the movement of dislocations in the alloy matrix. When the alloy is subjected to external force, the dislocations meet the second-phase particles during the movement. Since the hardness and elastic modulus of the second-phase particles are usually different from those of the matrix, it is difficult for the dislocations to easily pass through these particles, so more energy is needed to overcome the obstacles, resulting in an increase in the deformation resistance of the alloy, and a significant increase in strength and hardness. This strengthening method is widely used in a variety of alloy systems and is an effective method for improving the mechanical properties of materials.

[0024] The preparation method of the present invention can effectively increase the dislocation density of the medium-entropy alloy by specifically controlling the deformation amount when the alloy ingot is forged and deformed, providing more nucleation sites for the precipitate phase, and the subsequent aging heat treatment can simultaneously regulate the size and content of the precipitate phase of the medium-entropy alloy, thereby improving the mechanical properties of the medium-entropy alloy.

[0025] The preparation method of the invention is simple and easy to implement; the raw material elements used are all non-toxic substances and are easy to obtain; the preparation process is safe and environmentally friendly, and has high economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the EDS element distribution diagram of Example 1 of the present invention after aging heat treatment;

[0027] Figure 2 This is a SEM photo of the microstructure of Example 1 of the present invention after aging heat treatment;

[0028] Figure 3 This is the XRD diagram of Example 1 of the present invention after aging heat treatment;

[0029] Figure 4 EBSD grain size distribution diagram (a) and phase distribution diagram (b) of Example 1 of the present invention after aging heat treatment;

[0030] Figure 5 It is a curve diagram of the dynamic mechanical properties of the entropy alloy in Example 1 of the present invention and the entropy alloy in Comparative Example 1. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with the embodiments and drawings, but it should be understood that the embodiments and drawings are only used to exemplify the present invention and do not constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention.

[0032] Unless otherwise specified, the methods or operations used in the following examples and comparative examples are conventional methods or operations in the art.

[0033] Example 1

[0034] High strength medium entropy alloy (CoCrNi) was prepared by the following steps 88 Al 12 :

[0035] (1) Accurately weigh according to the element ratio (CoCrNi) 88 Al 12 The required raw metal, accurate to 0.1mg;

[0036] (2) ultrasonically cleaning the weighed raw metal in ethanol and vacuum drying to obtain a cleaned raw material;

[0037] (3) placing the cleaned raw materials into a crucible in order of melting point from low to high, placing the crucible in a magnetic suspension induction melting furnace, and performing 4 smeltings under inert atmosphere conditions at a current of 240 A, each smelting for 20 min, and casting the raw materials into a copper mold to obtain a cast alloy ingot;

[0038] (4) subjecting the alloy ingot to homogenization heat treatment, keeping the temperature at 1200° C. for 12 h, and quenching and cooling in water to obtain alloy ingot A, which was then cut into sheets with a thickness of 10 mm by wire cutting;

[0039] (5) The sheet material is hot forged at 1100° C. with a deformation of 50%, and multiple pressing passes are performed. The pressing amount of a single forging is 0.5 mm. The forging is stopped when the final thickness becomes 5 mm, thereby obtaining an alloy ingot B;

[0040] (6) The alloy ingot B is subjected to aging heat treatment at 900° C. for 30 min, and quenched in water to obtain the high-strength medium-entropy alloy.

[0041] In the above steps, the EDS element distribution diagram of Example 1 after aging heat treatment is as shown in the attached figure. Figure 1 The microstructure morphology is shown in the attached Figure 2 As shown in the attached XRD diagram Figure 3 As shown in the attached figure, the EBSD grain size distribution diagram (a) and phase distribution diagram (b) are shown in the attached figure. Figure 4 shown.

[0042] It can be seen that the high-strength medium-entropy alloy obtained in Example 1 presents an obvious two-phase structure, the intensity of its fcc structure characteristic peak is significantly higher than the intensity of the bcc structure characteristic peak, Co, Cr, Ni, and Al elements are evenly distributed in the matrix of the fcc structure, while Ni and Al elements are enriched in the second phase; its grain orientation is randomly distributed, and the second phase particles are evenly distributed in the matrix.

[0043] Comparative Example 1

[0044] High strength medium entropy alloy (CoCrNi) was prepared by the following steps 97 Al 3 :

[0045] (1) Accurate weighing (CoCrNi) 97 Al 3 The required raw metals are accurate to 0.1 mg. The mass of each metal is calculated based on the alloy composition to ensure that the ratio of Co, Cr, Ni and Al is accurate.

[0046] (2) Place the weighed raw metal in ethanol for ultrasonic cleaning for 10-15 minutes to remove surface oil, oxides and other impurities. After cleaning, place the raw metal in a vacuum drying oven at 60-80°C for 2-3 hours to ensure that the raw material is completely dry to avoid adverse effects of moisture in the subsequent smelting process.

[0047] (3) The cleaned and dried raw metals are placed in a quartz crucible in the order of melting point from low to high. The crucible is placed in a magnetic levitation induction melting furnace and smelted under argon protection. The smelting current is controlled to 220A, and smelting is performed three times, each smelting time is 15 minutes. After the smelting is completed, the molten alloy is cast into a copper mold and rapidly cooled to obtain a cast alloy ingot with an equiaxed crystal structure.

[0048] (4) The cast alloy ingot is placed in a high temperature furnace and kept at 1000°C for 24 hours for homogenization heat treatment to eliminate component segregation and make the alloy composition more uniform. After the heat treatment is completed, the alloy ingot is quickly cooled by quenching in water to obtain alloy ingot A. Subsequently, the alloy ingot A is cut into sheet materials with a thickness of 8 mm by wire cutting for subsequent processing.

[0049] (5) The sheet material is subjected to room temperature rolling. During the rolling process, the total deformation is controlled to be 50%, and multiple passes are used. The pressing amount of a single rolling is 0.4 mm. When the material thickness finally becomes 4 mm, the rolling is stopped to obtain the alloy ingot B. During the rolling process, attention should be paid to uniform pressure to avoid local stress concentration, and the surface oxide scale should be cleaned in time to prevent it from affecting subsequent processing.

[0050] (6) The alloy ingot B is heated to 900°C, kept at this temperature for 30 minutes, subjected to aging heat treatment, and then rapidly cooled by quenching in water to obtain the final medium entropy alloy (CoCrNi). 97 Al 3 .

[0051] The medium entropy alloys obtained in Example 1 and Comparative Example 1 were subjected to impact mechanical properties tests. The test method was as follows: a dynamic impact test was performed on a Hopkinson bar at room temperature with a strain rate of 6000 / s. The test results are shown in FIG. Figure 5 As shown, it can be seen that (CoCrNi) 88 Al 12 The yield strength of the medium entropy alloy is 1.2GPa, and the ultimate impact strength is 1.7GPa, which is significantly higher than (CoCrNi) 97 Al 3 Medium entropy alloy.

[0052] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high-strength medium-entropy alloy, characterized in that: Its molecular formula is (CrCoNi) 100-x Al x , where x is 0-12 and not 0.

2. A method for preparing a high-strength medium-entropy alloy, characterized in that: It includes the following steps: (1) Weighing raw metals required for high-strength medium-entropy alloy according to element ratio; (2) arranging and mixing the raw metals in order of melting point from low to high, then smelting them several times, and obtaining alloy ingots after cooling; (3) subjecting the alloy ingot to homogenization heat treatment under vacuum conditions to obtain a homogenized alloy block; (4) subjecting the homogenized alloy block to hot forging to obtain a forged plate; (5) Subjecting the forged plate to aging heat treatment to obtain the high-strength medium-entropy alloy.

3. The preparation method according to claim 2, characterized in that: The method further comprises: ultrasonically cleaning and drying the raw metal, and then performing step (2).

4. The preparation method according to claim 2, characterized in that: It also includes: performing mechanical grinding and / or surface contamination treatment and / or cutting on the forged plate before performing step (5).

5. The preparation method according to claim 2, characterized in that: The method further comprises: casting the alloy melt obtained by smelting for several times, and then cooling the alloy melt to obtain the alloy ingot.

6. The preparation method according to claim 2, characterized in that: The smelting is performed 3-5 times, each time for 15-25 minutes, in a vacuum suspension smelting furnace; the smelting current of the vacuum suspension smelting furnace is set to 230-250A.

7. The preparation method according to claim 2, characterized in that: The homogenization heat treatment comprises: subjecting the alloy ingot to a heat preservation treatment, and then subjecting the alloy ingot to a quenching cooling treatment; the temperature of the heat preservation treatment is 1200° C., and the time is 12 hours.

8. The preparation method according to claim 2, characterized in that: The heating temperature of the hot forging treatment is 1000° C., and the forging deformation is 30-50%.

9. The preparation method according to claim 2, characterized in that: The temperature of the aging heat treatment is 900° C. and the time is 30 minutes.

10. The preparation method according to claim 2, characterized in that: The high strength medium entropy alloy is (CrCoNi) 88 Al 12 .

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