CoCrNiAl series multi-mechanism synergistically reinforced eutectic high-entropy alloy and preparation method thereof

Abstract

The invention belongs to the technical field of high-entropy alloys, and particularly relates to a CoCrNiAl series multi-mechanism synergistically strengthened eutectic high-entropy alloy and a preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high-entropy alloy. Aiming at the condition that the strength and plasticity of a traditional eutectic high-entropy alloy of a double-phase structure are insufficient, the principle that all composition phases are optimized respectively, and then the overall mechanical property is improved is put forward. Based on the principle, the general formula of the non-equal-atomic-ratio medium-entropy alloy is CoaCrbNicAld, a is larger than or equal to 29 and smaller than or equal to 35, b is larger than or equal to 18 and smaller than or equal to 23, c is larger than or equal to 27 and smaller than or equal to 35, d is larger than or equal to 13 and smaller than or equal to 19, and a + b + c + d = 100. A metal raw material with the purity being 99.5% or above is ground and cleaned and then smelted into a cast ingot in a vacuum electric arc furnace, and then the eutectic high-entropy alloy with the high toughness performance can be obtained after solid solution, cold rolling and annealing processes are conducted. The design principle can also be popularized to other double-phase alloy systems, the machining process is simple, and industrial production is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of high entropy alloys, and specifically relates to a CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy and a preparation method thereof. Background Art

[0002] Traditional alloy composition design usually takes a certain element as the main element, that is, it is at the edge of the phase diagram, which greatly limits the scope of composition design. In recent years, researchers have tried to move the composition range to the central area of ​​the phase diagram and proposed the concept of high entropy alloys, which brings more possibilities to composition design. It has been proven that high entropy alloys have great potential in the fields of strength and toughness, fatigue resistance, corrosion resistance, and radiation resistance, and are expected to become new engineering structural materials.

[0003] Like traditional solid solution alloys, high entropy alloys also follow the classical dislocation theory, with phase change, twinning, and slip as the main deformation modes. Similarly, they also face the dilemma of inverted strength and plasticity. Generally, FCC structural metals have high toughness but insufficient yield strength, and BCC structural metals have high strength but lack plasticity. Eutectic alloys can effectively combine the two phases together, with the hard phase providing strength and the soft phase bearing deformation, resulting in a relatively excellent match between strength and plasticity. Specifically in the field of high entropy alloys, a variety of eutectic high entropy alloys have been developed, but the performance is still not enough to meet engineering requirements, and there is an urgent need to develop higher performance eutectic high entropy alloys. Summary of the invention

[0004] In view of the insufficient strength and plasticity of two-phase eutectic alloys, the present invention aims to provide a CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy and a preparation method thereof, and proposes to accurately control the composition of the two phases respectively and optimize the composition of each constituent phase to improve the comprehensive mechanical properties of the eutectic high entropy alloy; after simple solid solution, rolling and annealing treatment, a high-strength and plastic eutectic high entropy alloy can be obtained.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A CoCrNiAl-based eutectic high entropy alloy with multiple mechanisms for synergistic strengthening, with the general formula Co a Cr b Ni c Al d , a, b, c, and d in the chemical expression represent the molar percentage of the corresponding elements, where: 29≤a≤35, 18≤b≤23, 27≤c≤35, 13≤d≤19, and a+b+c+d=100.

[0007] The CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy, and the eutectic high entropy alloy includes but is not limited to the CoCrNiAl series eutectic high entropy alloy.

[0008] The preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy comprises the following steps:

[0009] (1) pure metal raw materials are cast into ingots by vacuum induction melting;

[0010] (2) subjecting the ingot to a solution treatment, wherein the solution temperature is ≥1150°C and the holding time is ≥1h;

[0011] (3) cold rolling the solutionized ingot;

[0012] (4) The rolled ingot is subjected to vacuum recrystallization annealing at a temperature of 650 to 900° C. for a holding time of 10 to 60 min.

[0013] The preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy comprises the following steps: in step (1), the purity of the metal raw material is above 99.5wt%, the surface oxide scale is polished before smelting, and the material is ultrasonically cleaned for standby use; the vacuum arc furnace is filled with protective gas argon after evacuation, the sponge titanium is first melted to absorb the air in the furnace chamber, and then the Co, Cr, Ni, and Al materials are melted, the melting is repeated five times, the surface oxide scale is polished, the material is ultrasonically cleaned, and the eutectic high entropy alloy ingot is obtained after drying, and the final size of the alloy ingot is 200×90×30mm.

[0014] The preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy, in step (2), the ingot is cut into metal plates with a thickness of 10 mm using electric spark wire cutting, preferably at a temperature of 1150-1250°C and a holding time of 2-5 hours for solution treatment to ensure composition uniformity, and then water quenching is cooled to room temperature.

[0015] In the preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy, in step (3), the total pressing amount of cold rolling deformation is 60% to 70%.

[0016] In the preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy, in order to prevent cracking during rolling, the pressing amount of each pass of cold rolling deformation should be reduced as much as possible and not exceed 0.1 mm / pass.

[0017] In the preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy, preferably, the initial pressing amount is 0.05-0.1 mm / pass, and after the total pressing amount reaches 50%, the pressing amount is 0.01-0.05 mm / pass.

[0018] In the preparation method of the CoCrNiAl series multi-mechanism synergistically strengthened eutectic high entropy alloy, in step (4), after cutting a tensile specimen from the rolled plate, a vacuum recrystallization annealing treatment is performed, preferably with an annealing temperature of 810°C±10°C and a holding time of 60 minutes, followed by water quenching and cooling to room temperature.

[0019] The design principle and beneficial effects of the present invention are as follows:

[0020] 1. Design principle: The present invention proposes the principle of optimizing each component phase separately to improve the overall mechanical properties. Furthermore, the present invention designs a dual-phase alloy that combines soft and hard phases. The dual-phase alloy that combines soft and hard phases can effectively combine strength and plasticity. The soft phase bears plastic deformation, and the hard phase hinders dislocation movement and improves strength. In actual deformation, the dual-phase alloy exhibits alternating deformation of the two phases, and each component phase contributes to the overall force. Therefore, optimizing any one of the phases will improve the overall performance.

[0021] Improving the mechanical properties of metals is usually carried out by introducing deformation mechanisms. Common deformation mechanisms include introducing phase change or twinning by reducing stacking fault energy, producing dynamic refinement effect during deformation, promoting more uniform deformation, and newly generated twins or close-packed hexagonal phases can also serve as new dislocation sources and hinder dislocation movement, improve work hardening ability, and thus improve plasticity. Another method is to introduce coherent or semi-coherent nano-precipitation phases. When the volume of the precipitate phase is large, the interaction between the dislocation and the precipitate phase in the movement is carried out in a bypassing manner, and it is easy to produce plugging at the phase boundary, resulting in stress concentration; while dislocations usually cut through nano-precipitation phases with small size and coherent interface, this method does not cause stress concentration, and while improving strength, it does not cause excessive loss of plasticity. Therefore, the present invention introduces a variety of work hardening mechanisms by reducing the stacking fault energy of each constituent phase and introducing the nano-precipitation phase, improving the performance of each constituent phase, thereby bringing about an improvement in overall performance.

[0022] 2. Beneficial effects: The present invention aims to provide a design concept and preparation method for a high-strength and tough dual-phase structural alloy. By optimizing the composition of each component phase, a variety of work hardening mechanisms are introduced to effectively improve the strength and plasticity of the eutectic high-entropy alloy; and due to the addition of high Cr and Al elements in the eutectic high-entropy alloy itself, it has excellent performance in terms of lightweight, corrosion resistance, and oxidation resistance. The present invention grinds and cleans the metal raw material with a purity of more than 99.5%, melts it into an ingot in a vacuum arc furnace, and then obtains a eutectic high-entropy alloy with high strength and toughness after solid solution, cold rolling, and annealing processes. It has excellent mechanical properties, a simple preparation process, is safe and reliable, and has a wide range of engineering application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1The microstructure characterization of the eutectic high entropy alloy prepared by the present invention. The right picture is a partial enlarged picture of the left picture.

[0024] Figure 2 The tensile engineering stress-strain curve result of the eutectic high entropy alloy prepared in the present invention. In the figure, the abscissa Engineeringstrain is the engineering strain (%), and the ordinate Engineeringstress is the engineering stress (MPa).

[0025] Figure 3 This is the SEM-ECCI (electron channel contrast imaging) characterization result after tensile deformation. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other examples improved or modified by ordinary technicians in this field belong to the scope of protection of the present invention. It should be understood that the embodiments of the present invention are only used to illustrate the technical effects of the present invention, rather than to limit the scope of protection of the present invention. In the embodiments, the methods used are conventional methods unless otherwise specified.

[0027] Example 1

[0028] In this embodiment, a CoCrNiAl system multi-mechanism synergistically strengthened eutectic high entropy alloy and a preparation method thereof are selected, and a high-purity metal raw material with a purity exceeding 99.5wt% is selected, and the composition is the following atomic percentages of metal elements: Co 33%, Cr 20%, Ni 30%, Al 17%, which can be expressed as Co 33 Cr 20 Ni 30 Al 17 , prepared according to the following steps:

[0029] Step 1: Before smelting, the surface oxide scale of the material should be polished and ultrasonically cleaned for use. The vacuum arc furnace is filled with protective gas argon after evacuation. Sponge titanium should be melted first to absorb the air in the furnace chamber, and then Co, Cr, Ni, and Al materials should be melted. The smelting is repeated five times, the surface oxide scale is polished, ultrasonically cleaned, and dried to obtain a eutectic high entropy alloy ingot. The final size of the metal ingot is 200×90×30mm.

[0030] Step 2: The ingot is cut into metal plates with a thickness of 10 mm each using an electric spark wire, and solution treated at a temperature of 1200°C for 4 hours to ensure the uniformity of the composition, and then water quenched and cooled to room temperature.

[0031] Step 3: Cold rolling the metal plate at room temperature. In order to prevent cracking during rolling, the initial pressing amount shall not exceed 0.1 mm / pass (0.05-0.08 mm / pass in this embodiment). After the total pressing amount reaches 50%, the pressing amount shall not exceed 0.05 mm / pass (0.02-0.04 mm / pass in this embodiment), and the final total pressing amount shall be 70%.

[0032] Step 4: After cutting the tensile specimens from the rolled plate, vacuum recrystallization annealing treatment was performed at 810°C for 60 min, followed by water quenching and cooling to room temperature.

[0033] Step 5: Perform a room temperature tensile test on an 8862 testing machine equipped with a video extensometer, with a tensile rate of 0.36 mm / min.

[0034] like Figure 1 As shown in the figure, the novel eutectic high entropy alloy prepared by the present invention exhibits a two-level heterogeneous structure after thermomechanical processing, namely, micron-scale FCC phase and BCC phase, and nano-scale nano-precipitation phase. Figure 2 As shown in the figure, the yield strength, tensile strength and uniform elongation are 1218MPa, 1571MPa and 22.0% respectively, showing excellent strong plasticity. Figure 3 As shown, after deformation, twins, phase transformation and nano-precipitation phases can be observed simultaneously in SEM-ECCI characterization, and the synergistic effect of multiple mechanisms improves the comprehensive mechanical properties of eutectic high entropy alloys. The present invention provides a way for the design and preparation of high-strength and high-toughness dual-phase structural metal materials, which is applicable to eutectic high entropy alloys and other dual-phase structural alloy systems.

[0035] The implementation results show that in view of the insufficient strength and plasticity of the traditional two-phase eutectic high entropy alloy, the present invention proposes a design and preparation method of a multi-mechanism synergistic eutectic high entropy alloy. After optimizing the components of each component phase, multiple work hardening mechanisms such as twinning, phase transformation, and nano-precipitation phase are introduced to design and prepare a eutectic high entropy alloy with high strength and toughness. The design principle of the present invention can also be extended to other two-phase alloy systems, and the processing technology is simple, which is conducive to industrial production.

Claims

1. A CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy, characterized in that: The general formula is Co a Cr b Ni c Al d , a, b, c, and d in the chemical expression represent the molar percentage of the corresponding elements, where: 29≤a≤35, 18≤b≤23, 27≤c≤35, 13≤d≤19, and a+b+c+d=100.

2. The CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to claim 1, characterized in that: Eutectic high entropy alloys include but are not limited to CoCrNiAl eutectic high entropy alloys.

3. The method for preparing the CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to claim 1, characterized in that: The following steps are involved: (1) pure metal raw materials are cast into ingots by vacuum induction melting; (2) subjecting the ingot to a solution treatment, wherein the solution temperature is ≥1150°C and the holding time is ≥1h; (3) cold rolling the solutionized ingot; (4) The rolled ingot is subjected to vacuum recrystallization annealing at a temperature of 650 to 900° C. for a holding time of 10 to 60 min.

4. The method for preparing the CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to claim 3, characterized in that: In step (1), the purity of the metal raw material is above 99.5wt%, the surface oxide scale is polished before smelting, and the material is ultrasonically cleaned for standby use; the vacuum arc furnace is filled with protective gas argon after evacuation, the sponge titanium is first melted to absorb the air in the furnace chamber, and then the Co, Cr, Ni, and Al materials are melted, the smelting is repeated five times, the surface oxide scale is polished, the material is ultrasonically cleaned, and the eutectic high entropy alloy ingot is obtained after drying, and the final size of the alloy ingot is 200×90×30mm.

5. The method for preparing the CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to claim 4, characterized in that: In step (2), the ingot is cut into metal plates with a thickness of 10 mm using an electric spark wire, preferably subjected to solution treatment at a temperature of 1150-1250° C. for a holding time of 2-5 h to ensure composition uniformity, and then water quenched to room temperature.

6. The method for preparing the CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to claim 5, characterized in that: In step (3), the total pressing amount of cold rolling deformation is 60% to 70%.

7. The method for preparing the CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to claim 6, characterized in that: In order to prevent cracking during the rolling process, the amount of pressure in each pass of cold rolling deformation should be reduced as much as possible and not exceed 0.1mm / pass.

8. The method for preparing the CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to claim 7, characterized in that: Preferably, the initial pressing amount is 0.05-0.1 mm / pass, and after the total pressing amount reaches 50%, the pressing amount is 0.01-0.05 mm / pass.

9. The method for preparing the CoCrNiAl-based multi-mechanism synergistically strengthened eutectic high entropy alloy according to any one of claims 3 to 8, characterized in that: In step (4), after cutting the tensile specimen from the rolled plate, a vacuum recrystallization annealing treatment is performed, preferably at an annealing temperature of 810°C ± 10°C and a holding time of 60 min, followed by water quenching and cooling to room temperature.

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