Novel high-toughness CoAlFeVCr high-entropy alloy and preparation method thereof

Abstract

The invention relates to the technical field of high-entropy alloys, in particular to a novel high-toughness CoAlFeVCr high-entropy alloy and a preparation method thereof. A CoAlFeCr high-entropy alloy system is not reported yet, and a method for better optimizing the strength and plasticity matching property of the CoAlFeCr high-entropy alloy system is not reported yet. The invention provides a novel high-toughness CoAlFeVCr high-entropy alloy and a preparation method thereof, the chemical formula is Co68Al16.5 Fe8.2 V4.8 Cr2.5, the microstructure of a high-entropy alloy system is composed of an FCC phase and a B2 phase, the atomic ratio of Co is as high as 68%, the heat resistance of the alloy is effectively guaranteed, the structure morphology of the alloy is regulated and controlled by changing the content of Al and Fe elements, a near-eutectic structure is formed, and the alloy has good toughness. The alloy has high strength on the premise of good plasticity, and good balance between the strength and the plasticity of the alloy is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of high entropy alloys, and in particular to a novel high-strength and high-toughness CoAlFeVCr high entropy alloy and a preparation method thereof. Background Art

[0002] High entropy alloys (HEAs) exhibit excellent comprehensive performance due to their unique multi-principal element design and high entropy effect. However, existing HEAs systems generally face two core contradictions:

[0003] Imbalance between strength and ductility: Alloy systems with both high strength and high ductility are scarce. Most high-strength HEAs require post-processing techniques such as cold rolling and heat treatment to induce phase transformation or nano-precipitation. While this process can increase strength, it is often accompanied by a significant decrease in ductility (e.g., elongation <10%), limiting their application in load-bearing structural components.

[0004] Heat-resistant HEAs, represented by CoAlFeCr, outperform traditional stainless steel in the medium- to high-temperature range of 700–900°C due to the oxidation resistance and high-entropy solid solution stability imparted by the Al element. However, their further application is still subject to the following limitations:

[0005] Solid solution strengthening ceiling: The lattice distortion strength has reached a bottleneck under the existing composition, and there is limited room for improvement in high-temperature strength;

[0006] Plasticity restriction: High Al / Cr content easily induces the precipitation of brittle B2 phase or σ phase, resulting in deterioration of room temperature and high temperature plasticity;

[0007] Structural instability: When the temperature is above 900℃ and the steel is in service for a long time, the coarsening of the precipitate phase and the growth of the grains lead to performance degradation.

[0008] Although research has shown that Co can enhance the heat resistance of HEAs, simply optimizing matrix composition cannot overcome the bottleneck of achieving strong-ductility synergy and ultra-high-temperature performance. Currently, the strategy of enhancing solid solution strengthening by inducing lattice distortion through elements with large atomic radius has not been systematically explored in the CoAlFeCr system. In particular, there is a lack of effective methods for simultaneously optimizing the room-temperature strong-ductility match and high-temperature performance through atomic-scale distortion manipulation. Summary of the Invention

[0009] The problem in the prior art is that the CoAlFeCr high entropy alloy system has not been reported, and the method for optimizing its strength and plasticity matching has not been reported. The present invention provides a new high-strength and tough CoAlFeVCr high entropy alloy with the chemical formula Co 68 Al x Fe 24.7-x V 4.8 Cr 2.5, x = 16.5-18. The purpose is to adjust the content of Al and Fe elements to adjust the microstructure of the high entropy alloy, optimize the mechanical properties, and obtain a high entropy alloy with both plasticity and strength.

[0010] Preferably, x=16.5.

[0011] Preferably, x=17.

[0012] Preferably, x=18.

[0013] Preferably, the purity of each metal element raw material used in the preparation process of CoAlFeVCr high entropy alloy is ≥99.95%.

[0014] Preferably, each metal element raw material needs to be polished, cleaned to remove surface oxides and impurities, and dried before use.

[0015] Preferably, the polishing method is sandpaper polishing.

[0016] Preferably, the cleaning method is ultrasonic cleaning, and the cleaning time is not less than 10 minutes.

[0017] Preferably, the preparation method of the novel high-strength and high-toughness CoAlFeVCr high-entropy alloy comprises the following steps:

[0018] (1) The cleaned raw materials are weighed and proportioned, and then the prepared metal raw materials are placed in a crucible of a smelting furnace in the order of the melting point of the metal raw materials from low to high, and the Ti block is placed in another crucible. The Ti block is added to remove residual oxygen; then the furnace body is vacuumed, and arc melting is carried out under the protection of argon gas at a vacuum degree of no more than 0.001MPa. The melting process is carried out under electromagnetic stirring, and the alloy raw materials are completely melted to form an alloy by adjusting the melting current; after the melting is completed, it is cast into a water-cooled copper crucible to obtain a 10×10×70mm 3 high entropy alloy plates.

[0019] (2) The alloy plate obtained in step (1) is turned over and the arc melting step in step (1) is repeated twice to obtain the target product.

[0020] In the step (1), the smelting current is 200-500A, and the smelting time is 2-8 minutes each time.

[0021] The present invention has the following beneficial effects:

[0022] The present invention provides a new type of high-strength and high-toughness Co 68 Al x Fe 24.7-x V 4.8Cr 2.5 (x = 16.5, 17, 18at%) high entropy alloys are used to enrich the high entropy alloy system. The high entropy alloy has excellent mechanical properties and a good balance between strength and plasticity. As the Al content increases and the Fe content decreases, the high entropy alloy in the present invention has a eutectic-hypereutectic microstructure transition;

[0023] The microstructure of the high-entropy alloy system in the present invention consists of two phases, FCC phase and B2 phase. By changing the content of Al and Fe elements, the microstructure of the alloy is regulated to form a near-eutectic structure, which makes the alloy have high strength under the premise of good plasticity, and achieves a good balance between alloy strength and plasticity.

[0024] The alloy of the present invention has excellent mechanical properties, wherein Co 68 Al 16.5 Fe 8.2 V 4.8 Cr 2.5 The high-entropy alloy has the best mechanical properties, with a yield strength of 761 MPa, an ultimate compressive strength of 2178 MPa, and a fracture strain of 21.9%;

[0025] The alloy preparation method of the present invention has simple process, is safe and reliable, and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The Co prepared in Examples 1, 2 and 3 of the present invention are 68 Al x Fe 24.7-x V 4.8 Cr 2.5 XRD patterns of (x=16.5, 17, 18 at%) high entropy alloys.

[0027] Figure 2 The Co prepared in Examples 1, 2 and 3 of the present invention are 68 Al x Fe 24.7-x V 4.8 Cr 2.5 SEM images of Co 68 Al 16.5 Fe 8.2 V 4.8 Cr 2.5 SEM image of high entropy alloy, Figure 2 (b) is Co 68 Al 17 Fe 7.7 V 4.8 Cr 2.5 SEM image of high entropy alloy, Figure 2 (c) is Co68 Al 18 Fe 6.7 V 4.8 Cr 2.5 SEM image of high entropy alloy.

[0028] Figure 3 The Co prepared in Examples 1-3 of the present invention 68 Al x Fe 24.7-x V 4.8 Cr 2.5 Room temperature compression performance test diagram of high entropy alloy. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.

[0030] The purity of the metal elements Co, Al, Fe, V, and Cr used in the present invention is ≥99.95%;

[0031] Example 1

[0032] Co 68 Al 16.5 Fe 8.2 V 4.8 Cr 2.5 The preparation method of (denoted as Al-16.5) is as follows:

[0033] Step 1: Use 600# SiC sandpaper to remove impurities and oxides on the surface of metal elements Co, Al, Fe, V, and Cr, then use acetone ultrasonic oscillation to clean twice, clean the surface impurities and dry it for later use;

[0034] Step 2: The raw materials in step 1 are weighed and proportioned, and then the prepared metal raw materials are placed in a crucible of a smelting furnace in the order of the melting point of the metal raw materials from low to high, and the Ti block is placed in another crucible. The Ti block is added to remove residual oxygen; then the furnace body is vacuumed, and arc melting is carried out under argon protection at a vacuum degree of no more than 0.001MPa. The smelting process is carried out under electromagnetic stirring, and the alloy raw materials are completely melted to form an alloy by adjusting the smelting current; after the smelting is completed, it is cast into a water-cooled copper crucible to obtain a 10×10×70mm 3 high entropy alloy plates.

[0035] Step 3: Turn the alloy plate obtained in step 2 over and repeat the arc melting steps in step 2 twice to obtain Co 68 Al 16.5 Fe 8.2 V 4.8Cr 2.5 High entropy alloy.

[0036] In the step 2, the smelting current is 200A, and each smelting time is 8 minutes.

[0037] Example 2 is the same as Example 1, except that the metal element raw material in Example 2 is Co 68 Al 17 Fe 7.7 V 4.8 Cr 2.5 The atomic ratio of Al-17 was converted into a mass ratio for weighing. The obtained high entropy alloy was designated as Al-17.

[0038] Example 3 is the same as Example 1, except that in Example 2, the metal element raw material is Co 68 Al 18 Fe 6.7 V 4.8 Cr 2.5 The atomic ratio of the alloy was converted into a mass ratio for weighing. The obtained high entropy alloy was designated as Al-18.

[0039] Alloy structure and mechanical properties testing:

[0040] 1. Phase Analysis

[0041] Phase analysis was performed on the high entropy alloys prepared in Examples 1-3. Specifically, X-ray diffraction (XRD, Bruker AXS D8 Advance) was used to analyze the crystal structure with a scanning range of 20°-100° and a scanning rate of 5° per minute. The sample surface was polished using standard mechanical polishing before testing. Specific XRD test results are shown in the attached manual. Figure 1 As shown in the figure, it can be seen that Al-16.5, Al-17 and Al-18 high entropy alloys all have FCC / L12 phase and BCC / B2 phase, and all three high entropy alloys have a dual-phase structure.

[0042] 2. Microstructure Characterization

[0043] The microstructure of the high entropy alloys prepared in Examples 1-3 was characterized by using a field emission scanning electron microscope (SEM, FEIQuanta 250F). Figure 2 As shown, Figure 2 (a) is Co 68 Al 16.5 Fe 8.2 V 4.8 Cr 2.5 SEM images of Figure 2 (b) is Co 68 Al17 Fe 7.7 V 4.8 Cr 2.5 SEM image of high entropy alloy, Figure 2 (c) is Co 68 Al 18 Fe 6.7 V 4.8 Cr 2.5 SEM image of high entropy alloy. The test results show that with the increase of Al content, the alloy microstructure changes from eutectic high entropy alloy to hypereutectic high entropy alloy. 68 Al 16.5 Fe 8.2 V 4.8 Cr 2.5 It is a eutectic structure, Co 68 Al 17 Fe 7.7 V 4.8 Cr 2.5 and Co 68 Al 18 Fe 6.7 V 4.8 Cr 2.5 Both are hypereutectic structures

[0044] 3. Room temperature compression mechanical properties test

[0045] The high entropy alloys prepared in Examples 1-3 were subjected to room temperature compression mechanical property tests. Specifically, a floor-standing test machine was used at room temperature to test the mechanical properties of the high entropy alloys prepared in Examples 1-3. -4 s -1 The uniaxial compression test was carried out three times at a strain rate of 1000 to confirm the reproducibility. The compression results are shown in the attached manual. Figure 3 As shown. The results show that the yield strength, ultimate compressive strength and fracture strain of the Al-16.5 eutectic high entropy alloy are ~761MPa, ~2178MPa and ~21.9%, respectively, which are better than the performance of Al-17 or Al-18 high entropy alloys, confirming that the eutectic high entropy alloy with an alternating lamellar structure has a better strength-plasticity balance. With the increase of Al content, the yield strength of the Al-17 high entropy alloy decreases to 566MPa, the ultimate compressive strength decreases to 1505MPa, and the fracture strain remains almost unchanged. When the Al content increases to x=18at%, the strength of the Al-18 high entropy alloy decreases significantly, and its yield strength and ultimate compressive strength decrease to 403MPa and 1050MPa, respectively, and the fracture strain also decreases to 10.6%. In summary, the Al-16.5 eutectic high entropy alloy obtained in Example 1 has more excellent ultimate compressive strength and plasticity.

[0046] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A new type of high-strength and high-toughness CoAlFeVCr high-entropy alloy, characterized in that: The chemical formula is Co 68 Al x Fe 24.7-x V 4.8 Cr 2.5 , x=16.5-18.

2. A novel high-strength and high-toughness CoAlFeVCr high-entropy alloy according to claim 1, characterized in that: The purity of each metal element raw material used in the preparation process of CoAlFeVCr high entropy alloy is ≥99.95%.

3. A novel high-strength and high-toughness CoAlFeVCr high-entropy alloy according to claim 2, characterized in that: Each metal element raw material must be polished, cleaned to remove surface oxides and impurities, and dried before use.

4. A novel high-strength and high-toughness CoAlFeVCr high-entropy alloy according to claim 3, characterized in that: The polishing method is sandpaper polishing.

5. A novel high-strength and high-toughness CoAlFeVCr high-entropy alloy according to claim 3, characterized in that: The cleaning method is ultrasonic cleaning, and the cleaning time is not less than 10 minutes.

6. A novel high-strength and high-toughness CoAlFeVCr high-entropy alloy according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (1) The cleaned raw materials are weighed and proportioned, and then the prepared metal raw materials are placed in a crucible of a smelting furnace in the order of the melting point of the metal raw materials from low to high, and the Ti block is placed in another crucible. The Ti block is added to remove residual oxygen; then the furnace body is vacuumed, and arc melting is carried out under the protection of argon gas at a vacuum degree of no more than 0.001MPa. The melting process is carried out under electromagnetic stirring, and the alloy raw materials are completely melted to form an alloy by adjusting the melting current; after the melting is completed, it is cast into a water-cooled copper crucible to obtain a 10×10×70mm 3 high entropy alloy plates. (2) The alloy plate obtained in step (1) is turned over and the arc melting step in step (1) is repeated twice to obtain the target product.

7. A novel high-strength and high-toughness CoAlFeVCr high-entropy alloy according to claim 6, characterized in that: The smelting current is 200-500A, and each smelting time is 2-8 minutes.

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