A high-hardness seven-element high-entropy alloy and a preparation method thereof

Abstract

The application provides a high-hardness seven-element high-entropy alloy and a preparation method thereof, and the high-hardness seven-element high-entropy alloy satisfies the following general formula according to atomic percentages: (CoCrFeNi) a (Al x Mo y W z ) b ; wherein a+b=100, a is 20at.%-46at.%, and b is 54at.%-80at.%; x, y, and z respectively represent atomic relative coefficients of Al, Mo, and W in Al x Mo y W z , and y=z; x is 1.0-2.4, and the values of y and z are both 0.7-1.5; the high-hardness seven-element high-entropy alloy is prepared by accurately setting the atomic percentage ranges of the matrix and the strengthening elements, and reasonably matching the atomic relative coefficients of Al and equal amounts of Mo and W, so that the content of the strengthening phase is sufficient, and the solid solution strengthening and ordered phase strengthening effects are fully exerted, thereby significantly improving the hardness and high-temperature stability of the alloy.

Description

Technical Field

[0001] This invention relates to the field of high-entropy alloy materials technology, and in particular to a high-hardness heptagonal high-entropy alloy with Co-Cr-Fe-Ni-Al-Mo-W and its preparation method. This high-hardness heptagonal high-entropy alloy can be used to manufacture components with extremely high requirements for wear resistance, compressive strength and high-temperature stability. Background Technology

[0002] High-entropy alloys, with their high-entropy effect, significant lattice distortion, slow diffusion effect, and "cocktail" effect, possess superior comprehensive properties compared to traditional alloys, including high strength, high hardness, excellent wear resistance, and high-temperature stability, making them a research hotspot in the field of new materials. Currently, while the mainstream 3d transition metal high-entropy alloys exhibit good plasticity, their hardness and strength levels are insufficient to meet the demands of extreme service environments.

[0003] To improve alloy hardness, existing techniques typically involve introducing aluminum (Al) to form a hard BCC (body-centered cubic) / B2 ordered phase, or adding high-melting-point elements such as molybdenum (Mo) and tungsten (W) for solid solution strengthening. However, related research has significant shortcomings. Most studies focus on single elements like Al or Mo / W, lacking a systematic study of the synergistic effects and proportions of Al and (Mo+W) composite strengthening elements, thus failing to achieve an optimal balance between hardness and toughness in complex multiphase structures.

[0004] Furthermore, Mo and W have high melting points of 2623℃ and 3422℃, respectively. Adding large quantities can easily lead to compositional segregation and unmelted particles due to the significant differences in melting points between the components, severely affecting alloy homogeneity and performance stability. Traditional smelting processes are insufficient for the homogeneous preparation of alloys containing such high-melting-point elements. Simultaneously, existing high-entropy alloys suffer from hardness limitations. How to overcome these hardness limits through systematic compositional design and controllable processes while maintaining certain machinability is a critical issue that urgently needs to be addressed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art by providing a high-hardness seven-element high-entropy alloy and its preparation method. This alloy achieves the synergy of multiple strengthening mechanisms (solid solution strengthening, ordered phase strengthening, and fine grain strengthening) through a unique composition range design and targeted melting process, thereby obtaining hardness performance far exceeding that of conventional high-entropy alloys.

[0006] Firstly, this invention provides a high-hardness seven-element high-entropy alloy, which satisfies the following general formula according to atomic percentage: (CoCrFeNi) a (Al x Mo y W z ) b ; Where a + b = 100, a takes values ​​from 20 at.% to 46 at.%, and b takes values ​​from 54 at.% to 80 at.%; x, y, and z represent Al, Mo, and W respectively in Al x Mo y W z The atomic relative coefficients are given, and y=z; x takes values ​​from 1.0 to 2.4, and y and z both take values ​​from 0.7 to 1.5.

[0007] Specifically, this invention utilizes precise design (CoCrFeNi) a (Al x Mo y W z ) b The seven-element high-entropy alloy composition system rationally limits the atomic percentage range of matrix elements and strengthening elements, and strictly controls the atomic ratio of Mo and W to 1:1. On the one hand, it can rely on Al to effectively induce the formation of hard BCC / B2 ordered phases in the alloy. At the same time, it can rely on the high-melting-point elements of Mo and W to produce significant synergistic solid solution strengthening and lattice distortion strengthening effects, greatly improving the hardness and high-temperature stability of the alloy and breaking through the performance bottleneck of existing similar alloys. On the other hand, this composition design can alleviate the problem of compositional segregation and unmelted particles caused by the large addition of high-melting-point elements, improve the uniformity of alloy structure and performance reproducibility, and avoid excessive embrittlement of the alloy while achieving ultra-high hardness. It effectively balances hardness, high-temperature stability and certain plasticity and machinability, and solves the technical problem that traditional high-entropy alloys cannot balance strength, toughness and structural uniformity in extreme environments.

[0008] Furthermore, a value of 20 at.% to 46 at.% ensures that the CoCrFeNi matrix provides the alloy with basic structural stability and a certain degree of plasticity, while avoiding an excessive matrix proportion that weakens the strengthening effect. It also prevents problems such as alloy embrittlement and coarse microstructure caused by excessive strengthening elements, thus balancing the mechanical properties and preparation feasibility of the alloy. A value of 54 at.% to 80 at.% introduces sufficient Al, Mo, and W strengthening elements, fully leveraging phase strengthening and solid solution strengthening effects, significantly improving the alloy's hardness, strength, and high-temperature stability. Moreover, this upper limit can effectively control the risks of smelting segregation and unmelted particles caused by high-melting-point elements, ensuring the microstructure. Uniformity; the range of x values ​​can effectively induce the formation of hard BCC / B2 ordered phases in the alloy to achieve phase strengthening and improve the alloy hardness. At the same time, it avoids insufficient strengthening due to too low Al content or brittleness and uncontrolled phase structure due to too high Al content, thus achieving a reasonable balance between hardness and toughness. Controlling y and z within the range of 0.7 to 1.5 can ensure sufficient Mo and W content, giving full play to the strong solid solution strengthening and lattice distortion strengthening effect brought by high melting point atoms, significantly improving the alloy hardness and high temperature stability. It can also avoid insufficient strengthening effect due to too low content, while preventing melting problems such as excessive melting point difference, unmelted particles, and compositional segregation caused by too high content, thus ensuring uniform microstructure.

[0009] Preferably, the value of a in the high-hardness heptagonal high-entropy alloy is 28 at.% to 46 at.%.

[0010] Specifically, the atomic ratio range of the aforementioned matrix element group CoCrFeNi can ensure sufficient strengthening effect to obtain high hardness, while avoiding problems such as excessive brittleness and smelting segregation, thus achieving the optimal balance between hardness, plasticity and microstructure uniformity.

[0011] Preferably, the general formula of the high-hardness heptagonal high-entropy alloy is selected from (CoCrFeNi). 46 (Al 1.5 Mo 0.7 W 0.7 ) 54 (CoCrFeNi) 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 (CoCrFeNi) 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 One of them.

[0012] Specifically, high-strength balanced type (CoCrFeNi) 46 (Al 1.5 Mo 0.7 W 0.7 )54 While ensuring high hardness, the alloy also possesses superior melting processability and microstructure uniformity, effectively reducing unmelted and segregation problems caused by high-melting-point elements, and can serve as a performance benchmark for this type of alloy system; while the two extreme strengthening compositions (CoCrFeNi) 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 With (CoCrFeNi) 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 All of them increase the total amount of strengthening elements to 72 at.%, and by finely controlling the atomic ratio of Al to Mo and W, they respectively focus on achieving stronger solid solution strengthening by relying on the refractory metals of Mo and W and on relying on Al to induce the generation of more hard BCC / B2 ordered phases. This can fully explore the hardness limit of the alloy system and meet the differentiated requirements for the comprehensive performance of high-entropy alloys under different service scenarios.

[0013] Preferably, the general formula of the high-hardness heptagonal high-entropy alloy is (CoCrFeNi). 46 (Al 1.5 Mo 0.7 W 0.7 ) 54 At that time, its average hardness after Mo-W pre-alloying, 10 melting cycles, and homogenization annealing was 82.0 HRA (Rockwell A Hardness scale); when the general formula of the high-hardness heptagonal high-entropy alloy is (CoCrFeNi). 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 At that time, its average hardness after Mo-W pre-alloying and at least 15 remeltings was 88.0 HRA; when the general formula of the high-hardness heptagonal high-entropy alloy is (CoCrFeNi). 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 At that time, its average hardness after Mo-W pre-alloying and at least 15 remeltings was 84.0 HRA.

[0014] Specifically, all three preferred alloys of this invention achieve ultra-high hardness through reasonable processes, among which the balanced alloy (CoCrFeNi) 46 (Al 1.5 Mo 0.7 W 0.7 ) 54The hardness reaches 82.0 HRA, balancing processability and performance; the other two extreme-strength alloys reach 88.0 HRA and 84.0 HRA respectively, significantly breaking through the existing upper limit of alloy hardness and meeting the high hardness requirements under different working conditions.

[0015] Secondly, the present invention also provides a method for preparing any of the above-mentioned high-hardness seven-element high-entropy alloys, comprising the following steps: S10, weigh out Co, Cr, Fe, Ni, Al, Mo and W, according to the general chemical formula (CoCrFeNi). a (Al x Mo y W z ) b The ingredients are prepared according to the stoichiometric ratio; S20, Mo and W are placed separately in a vacuum melting equipment, melted under an inert atmosphere and repeatedly remelted 3 to 4 times to obtain Mo-W binary master alloy ingot; S30: After crushing the Mo-W binary intermediate alloy ingot, it is mixed with the weighed Co, Cr, Fe, Ni and Al and placed in the crucible of the melting furnace. It is then melted under an inert atmosphere and repeatedly turned and remelted at least 8 times to obtain a seven-element alloy ingot. S40 is obtained by homogenizing and annealing a seven-element alloy ingot in a vacuum or inert atmosphere at 1100–1200°C for 20–30 hours to obtain a high-hardness seven-element high-entropy alloy.

[0016] Specifically, step S10 involves distributing materials according to the design, ensuring the precise proportion of alloying elements and achieving the desired strengthening effect. Step S20 involves remelting Mo and W to prepare a pre-alloy, which reduces the difficulty of melting high-melting-point elements and minimizes unmelted inclusions and component segregation. Step S30 involves multiple remelting cycles to ensure thorough mixing and diffusion of the components, significantly improving the uniformity of the alloy composition and microstructure. Step S40 involves high-temperature, long-term homogenization annealing, which further eliminates as-cast segregation and internal stress, stabilizes the phase structure, and results in higher alloy hardness and more stable and reliable performance.

[0017] Furthermore, for formulations with high Mo and W content (total Mo+W atomic percentage > 20%), pre-alloying in step S2 is necessary.

[0018] Preferably, in step S10, the purity of Co, Cr, Fe, Ni, Al, Mo and W is not less than 99.9 wt.%, and none of them contain Cu and Mn.

[0019] Specifically, step S10 uses high-purity elemental metal raw materials with a purity of not less than 99.9 wt.%, and strictly controls the absence of Cu and Mn impurities. This not only reduces the introduction of impurities from the source and ensures precise control of the alloy composition, but also avoids the problems of harmful segregation and weakening of strengthening effect caused by Cu and Mn.

[0020] Preferably, in step S10, a + b = 100, where a takes a value of 20 at.% to 46 at.% and b takes a value of 54 at.% to 80 at.%; x, y, and z represent Al, Mo, and W in Al, respectively. x Mo y W z The atomic relative coefficients are given, and y=z; x takes values ​​from 1.0 to 2.4, and y and z both take values ​​from 0.7 to 1.5.

[0021] Specifically, this step precisely limits the atomic percentage range of the matrix and strengthening elements, and reasonably sets the atomic relative coefficients of Al, Mo, and W, making the coefficients of Mo and W equal. This ensures sufficient strengthening phase content to achieve significant solid solution strengthening and ordered phase strengthening, greatly improving the alloy hardness, while also providing reasonable space for composition control. At the same time, it avoids segregation, unmelted material, and embrittlement problems caused by improper proportions of high-melting-point elements, so that the alloy achieves the optimal balance in terms of hardness, toughness, and microstructure uniformity.

[0022] Preferably, in step S20, the vacuum melting equipment is a vacuum arc melting furnace or a vacuum suspension melting furnace; when using vacuum arc melting, the vacuum degree of the furnace cavity is not higher than 5×10⁻⁶. -4 The furnace pressure is 0.05–0.08 MPa when inert gas is introduced, and the melting current is 1000–2000 A; when vacuum suspension melting is used, the vacuum degree of the furnace cavity is not higher than 1 × 10⁻⁶ MPa. -4 Pa, smelting power is 10-15kW.

[0023] Specifically, this step involves selecting a vacuum arc melting furnace or a vacuum suspension melting furnace and strictly matching the high vacuum degree, inert atmosphere pressure, melting current and power parameters of the corresponding furnace type. This allows for the full melting and uniform alloying of Mo and W in a low-oxygen, pollution-free environment, effectively avoiding raw material oxidation, gas absorption and impurity contamination, while ensuring sufficient melting energy to completely melt high-melting-point elements and reduce unmelted inclusions.

[0024] Preferably, in step S30, the crushed Mo-W binary master alloy ingot, Co, Cr, Fe and Ni are first placed together into the crucible of the smelting furnace, and then Al is placed on top of the crucible of the smelting furnace.

[0025] Specifically, placing low-melting-point Al in the upper part of the melting furnace crucible can utilize its characteristic of melting first to promote melt formation and flow, assist high-melting-point components to fully melt and mix evenly, effectively reduce the overall melting difficulty, reduce unmelted particles and component segregation, and at the same time avoid Al burning due to prolonged high-temperature melting, ensuring accurate alloy composition and uniform structure.

[0026] Preferably, in step S30, if the total mass of Al, Mo and W is greater than or equal to 70% of the total mass of Co, Cr, Fe, Ni, Al, Mo and W, then the number of times the remelting is repeated is not less than 15 times.

[0027] Specifically, when the total proportion of strengthening elements Al, Mo, and W is ≥70%, the number of remelting cycles is increased to no less than 15 times. This can effectively solve the problem of easy segregation and difficulty in mixing of high-content refractory elements, ensure sufficient diffusion and homogenization of the melt, reduce compositional fluctuations and unmelted defects, and make the alloy structure more uniform, harder and more stable.

[0028] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a high-hardness seven-element high-entropy alloy and its preparation method. The aforementioned high-hardness seven-element high-entropy alloy satisfies the following general formula based on atomic percentage: (CoCrFeNi) a (Al x Mo y W z ) b Where a + b = 100, a takes values ​​from 20 at.% to 46 at.%, and b takes values ​​from 54 at.% to 80 at.%; x, y, and z represent Al, Mo, and W in Al, respectively. x Mo y W z The atomic relative coefficients in the matrix are y=z; x takes values ​​of 1.0 to 2.4, and y and z both take values ​​of 0.7 to 1.5. The above-mentioned high-hardness seven-element high-entropy alloy, by precisely setting the atomic percentage range of the matrix and strengthening elements and reasonably matching the atomic relative coefficients of Al and equal amounts of Mo and W, ensures that the content of the strengthening phase is sufficient and the effects of solid solution strengthening and ordered phase strengthening are fully exerted, thereby significantly improving the alloy hardness and high-temperature stability. This avoids the problems of compositional segregation, unmelted particles and alloy embrittlement caused by improper ratio of high-melting-point elements, and ultimately achieves synergistic optimization of strengthening effect, microstructure uniformity and preparation processability. Attached Figure Description

[0029] Figure 1 A flowchart illustrating the preparation method of a high-hardness heptagonal high-entropy alloy provided in an embodiment of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] To address the aforementioned shortcomings in existing technologies, this invention first provides a high-hardness seven-element high-entropy alloy and its preparation method. The aforementioned high-hardness seven-element high-entropy alloy satisfies the following general formula according to atomic percentage: (CoCrFeNi) a (Al x Mo y W z ) b ; Where a + b = 100, a takes values ​​from 20 at.% to 46 at.%, and b takes values ​​from 54 at.% to 80 at.%; x, y, and z represent Al, Mo, and W respectively in Al x Mo y W z The atomic relative coefficients are given, and y=z; x takes values ​​from 1.0 to 2.4, and y and z both take values ​​from 0.7 to 1.5.

[0032] Accordingly, the present invention also provides a method for preparing a high-hardness heptagonal high-entropy alloy, such as... Figure 1 As shown, it includes the following steps: S10, weigh out Co, Cr, Fe, Ni, Al, Mo and W, according to the general chemical formula (CoCrFeNi). a (Al x Mo y W z ) b The ingredients are prepared according to the stoichiometric ratio; S20, Mo and W are placed separately in a vacuum melting equipment, melted under an inert atmosphere and repeatedly remelted 3 to 4 times to obtain Mo-W binary master alloy ingot; S30: After crushing the Mo-W binary intermediate alloy ingot, it is mixed with the weighed Co, Cr, Fe, Ni and Al and placed in the crucible of the melting furnace. It is then melted under an inert atmosphere and repeatedly turned and remelted at least 8 times to obtain a seven-element alloy ingot. S40 is obtained by homogenizing and annealing a seven-element alloy ingot in a vacuum or inert atmosphere at 1100–1200°C for 20–30 hours to obtain a high-hardness seven-element high-entropy alloy.

[0033] Specifically, this study innovatively proposes a high-hardness seven-element high-entropy alloy and its preparation method. This high-hardness seven-element high-entropy alloy achieves ultra-high hardness by precisely controlling the atomic ratio of the matrix and strengthening elements, and rationally matching the atomic relative coefficients of Al, Mo, and W while keeping Mo and W in equal amounts. This not only fully utilizes the strengthening effects of solid solution and ordered phase to achieve ultra-high hardness, but also effectively improves the problems of easy segregation and difficult melting of high-melting-point elements. At the same time, with the help of a special preparation process, the alloy composition uniformity and performance stability are significantly improved, effectively making up for the shortcomings of existing high-entropy alloys in terms of hardness improvement and microstructure homogenization.

[0034] The technical solution of the present invention will now be further described with reference to specific embodiments.

[0035] Example 1 (High-strength Balanced Type): Example 1 provides a high-hardness seven-element high-entropy alloy and its preparation method. The high-hardness seven-element high-entropy alloy is (CoCrFeNi). 46 (Al 1.5 Mo 0.7 W 0.7 ) 54 Its preparation method includes the following steps: Step (1) Raw material weighing and pretreatment: according to (CoCrFeNi) 46 (Al 1.5 Mo 0.7 W 0.7 ) 54 The atomic ratio of each metal element in the sample is determined by weighing out 40g of each metal element raw material with a purity of not less than 99.9 wt.%.

[0036] Step (2) Mo-W pre-alloying: All weighed Mo and W metals are placed separately in a vacuum arc melting furnace and melted under N2 protection, and repeatedly turned and remelted 4 times to produce a Mo-W binary master alloy ingot with uniform composition; wherein, the vacuum degree of the vacuum arc melting furnace is 3×10 -4 Pa, N2 is introduced until the pressure inside the furnace is 0.05MPa, and the smelting current is 2000A.

[0037] Step (3) Main alloy smelting: The Mo-W binary master alloy ingot is crushed, and then the crushed Mo-W binary master alloy ingot, Co, Cr, Fe and Ni are put into the crucible of the smelting furnace. Then Al is placed on the top of the crucible of the smelting furnace. Under the protection of high-purity N2 atmosphere, a high current of 2000A is used for smelting, and the ingot is repeatedly turned and remelted 10 times to obtain a seven-element alloy ingot with uniform composition.

[0038] Step (4) Homogenization treatment: The obtained heptagonal alloy ingot was homogenized and annealed at 1200°C for 24 hours in a N2 atmosphere to obtain (CoCrFeNi). 46 (Al 1.5 Mo 0.7 W 0.7 ) 54 Its average hardness was measured to be 82.0 HRA.

[0039] Example 2 (Ultimate Enhancement Type A): Example 2 provides a high-hardness seven-element high-entropy alloy and its preparation method. The high-hardness seven-element high-entropy alloy is (CoCrFeNi). 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 Its preparation method includes the following steps: Step (1) Raw material weighing and pretreatment: according to (CoCrFeNi) 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 The atomic ratio of each metal element in the sample is determined by weighing out the raw materials of each metal element with a purity of not less than 99.9 wt.%, and the total mass is 40 g.

[0040] Step (2) Mo-W pre-alloying: All weighed Mo and W metals are placed separately in a vacuum arc melting furnace and melted under N2 protection, and repeatedly turned and remelted 4 times to produce a Mo-W binary master alloy ingot with uniform composition; wherein, the vacuum degree of the vacuum arc melting furnace is 3×10 -4 Pa, N2 is introduced until the pressure inside the furnace is 0.05MPa, and the smelting current is 2000A.

[0041] Step (3) Main alloy smelting: The Mo-W binary master alloy ingot is crushed, and then the crushed Mo-W binary master alloy ingot, Co, Cr, Fe and Ni are put into the crucible of the smelting furnace. Then Al is placed on the top of the crucible of the smelting furnace. Under the protection of high-purity N2 atmosphere, a high current of 2000A is used for smelting, and the ingot is repeatedly turned and remelted 15 times to obtain a seven-element alloy ingot with uniform composition.

[0042] Step (4) Homogenization treatment: The obtained heptagonal alloy ingot was homogenized and annealed at 1200°C for 24 hours in a N2 atmosphere to obtain (CoCrFeNi). 28 (Al 1.8 Mo 1.2 W 1.2 ) 72Its average hardness was measured to be 88.0 HRA, exhibiting the highest hardness performance.

[0043] Example 3 (Ultimate Enhancement Type B): Example 3 provides a high-hardness seven-element high-entropy alloy and its preparation method. The high-hardness seven-element high-entropy alloy is (CoCrFeNi). 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 Its preparation method includes the following steps: Step (1) Raw material weighing and pretreatment: according to (CoCrFeNi) 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 The atomic ratio of each metal element in the sample is determined by weighing out the raw materials of each metal element with a purity of not less than 99.9 wt.%, and the total mass is 40 g.

[0044] Step (2) Mo-W pre-alloying: All weighed Mo and W metals are placed separately in a vacuum arc melting furnace and melted under N2 protection, and repeatedly turned and remelted 4 times to produce a Mo-W binary master alloy ingot with uniform composition; wherein, the vacuum degree of the vacuum arc melting furnace is 3×10 -4 Pa, N2 is introduced until the pressure inside the furnace is 0.05MPa, and the smelting current is 2000A.

[0045] Step (3) Main alloy smelting: The Mo-W binary master alloy ingot is crushed, and then the crushed Mo-W binary master alloy ingot, Co, Cr, Fe and Ni are put into the crucible of the smelting furnace. Then Al is placed on the top of the crucible of the smelting furnace. Under the protection of high-purity N2 atmosphere, a high current of 2000A is used for smelting, and the ingot is repeatedly turned and remelted 15 times to obtain a seven-element alloy ingot with uniform composition.

[0046] Step (4) Homogenization treatment: The obtained heptagonal alloy ingot was homogenized and annealed at 1200°C for 24 hours in a N2 atmosphere to obtain (CoCrFeNi). 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 The average hardness was measured to be 84.0 HRA, indicating that the high Al-induced B2 ordered phase has a significant strengthening effect.

[0047] Comparative Example 1 (without pre-alloying): Comparative Example 1 provides a seven-element high-entropy alloy and its preparation method, wherein the seven-element high-entropy alloy is (CoCrFeNi). 28(Al 1.8 Mo 1.2 W 1.2 ) 72 Its preparation method includes the following steps: Step (1) Raw material weighing and pretreatment: according to (CoCrFeNi) 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 The atomic ratio of each metal element in the sample is determined by weighing out the raw materials of each metal element with a purity of not less than 99.9 wt.%, and the total mass is 40 g.

[0048] Step (2) Alloy smelting: Weighed Mo, W, Co, Cr, Fe and Ni are placed together in the smelting furnace crucible, and Al is placed on the top of the smelting furnace crucible; under the protection of high-purity N2 atmosphere, a high current of 2000A is used for smelting, and the mixture is repeatedly turned and remelted 15 times to obtain a seven-element alloy ingot with uniform composition.

[0049] Step (3) Homogenization treatment: The obtained heptagonal alloy ingot was homogenized and annealed at 1200°C for 24 hours in a N2 atmosphere to obtain (CoCrFeNi). 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 Its hardness test values ​​are highly discrete and the average value is only 70.5 HRA, indicating a serious deterioration in performance.

[0050] Comparative Example 2 (Traditional Quaternary Alloy): Comparative Example 1 provides a quaternary high-entropy alloy and its preparation method. The quaternary high-entropy alloy is a CoCrFeNi alloy, and its preparation method includes the following steps: Step (1) Raw material weighing and pretreatment: Weigh each metal element raw material with a purity of not less than 99.9 wt.% according to the atomic ratio of each metal element in the CoCrFeNi alloy, and the total mass is 40g.

[0051] Step (2) Alloy smelting: Weighed Co, Cr, Fe and Ni are placed together in the crucible of the smelting furnace. Under the protection of high-purity N2 atmosphere, a high current of 2000A is used for smelting, and the mixture is repeatedly turned and remelted 15 times to obtain a quaternary alloy ingot with uniform composition.

[0052] Step (3) Homogenization treatment: The obtained quaternary alloy ingot was homogenized and annealed at 1200°C for 24 hours in N2 atmosphere to obtain CoCrFeNi alloy. Its hardness test value is highly discrete and the average hardness value is only 55.5HRA, which is much lower than the high hardness seven-element high entropy alloy prepared in this invention.

[0053] Comparative Example 3 (containing Cu, an unfavorable element): Comparative Example 3 provides an octagonal high-entropy alloy and its preparation method, wherein the octagonal high-entropy alloy is (CoCrFeNiCu). 50 (Al 1.0 Mo 0.7 W 0.7 ) 50 Its preparation method includes the following steps: Step (1) Raw material weighing and pretreatment: according to (CoCrFeNiCu) 50 (Al 1.0 Mo 0.7 W 0.7 ) 50 The atomic ratio of each metal element in the sample is determined by weighing out 40g of each metal element raw material with a purity of not less than 99.9 wt.%.

[0054] Step (2) Mo-W pre-alloying: All weighed Mo and W metals are placed separately in a vacuum arc melting furnace and melted under N2 protection, and repeatedly turned and remelted 4 times to produce a Mo-W binary master alloy ingot with uniform composition; wherein, the vacuum degree of the vacuum arc melting furnace is 3×10 -4 Pa, N2 is introduced until the pressure inside the furnace is 0.05MPa, and the smelting current is 2000A.

[0055] Step (3) Main alloy smelting: The Mo-W binary master alloy ingot is crushed, and then the crushed Mo-W binary master alloy ingot, Cu, Co, Cr, Fe and Ni are put into the crucible of the smelting furnace. Then Al is placed on the top of the crucible of the smelting furnace. Under the protection of high-purity N2 atmosphere, a high current of 2000A is used for smelting, and the ingot is repeatedly turned and remelted 10 times to obtain an octagonal alloy ingot with uniform composition.

[0056] Step (4) Homogenization treatment: The obtained octagonal alloy ingot was homogenized and annealed at 1200°C for 24 hours in a N2 atmosphere to obtain (CoCrFeNiCu). 50 (Al 1.0 Mo 0.7 W 0.7 ) 50 ; For (CoCrFeNiCu) 50 (Al 1.0 Mo 0.7 W 0.7 ) 50 Microscopic characterization revealed that the soft Cu-rich phase was distributed in a continuous network at the grain boundaries, significantly reducing the overall hardness of the alloy to 73.0 HRA, and inducing early brittle fracture at the grain boundaries under compressive load.

[0057] As can be seen from the comparison results of Examples 1-3 and Comparative Examples 1-3 above, the present invention achieves its effect through reasonable design (CoCrFeNi). a (Al x Mo y W z ) b The proposed composition system, combined with Mo-W pre-alloying, graded control of the number of remelting cycles, and high-temperature homogenization annealing, fully leverages the strengthening effects of solid solution and B2 ordered phases, resulting in a significant increase in alloy hardness and a uniform, dense microstructure. The optimal composition hardness reaches 88.0 HRA. Omitting the pre-alloying step leads to uneven melting and a substantial decrease in hardness. Traditional CoCrFeNi quaternary alloys lack effective strengthening elements, resulting in significantly lower hardness. Introducing Cu elements forms continuous soft phases at grain boundaries, not only reducing hardness but also easily inducing brittle fracture at grain boundaries. The above examples and comparative data demonstrate that the composition system proposed in this invention, combined with specific preparation processes, particularly pre-alloying and high-frequency remelting, is key to obtaining high-entropy alloys with ultra-high hardness and uniform composition.

[0058] Overall, compared with existing technologies, the above-conceived technical solutions can achieve the following beneficial effects: (1) Scientific system of composition design: This invention breaks through the traditional design idea of ​​single variable regulation, and constructs (CoCrFeNi) a (Al x Mo y W z ) b The composition model, which systematically controls the ratio (a / b) of matrix phase elements and strengthening phase elements, as well as the ratio (x / (y+z)) of Al and (Mo+W) within the strengthening group, enables precise design of alloy composition and predictable control of performance, laying a reliable compositional foundation for the preparation of ultra-high hardness high-entropy alloys.

[0059] (2) Original process to overcome key problems: In response to the common industry problem that high Mo and W content high entropy alloys are prone to insufficient melting and uneven composition, this invention innovatively adopts "Mo-W pre-alloying" as a necessary pre-process, and combined with a high-number remelting process, fundamentally ensuring the uniformity of the microstructure of the alloy under high strengthening element content, so that the high performance composition design can be stably realized.

[0060] (3) Excellent material properties: The alloy prepared by the present invention, especially the extreme strengthening type, has a hardness that is significantly better than that of conventional CoCrFeNi-based high entropy alloys. The hardness of some components can reach HRA80 or even higher. The alloy matrix itself achieves ultra-high hardness without relying on surface coating or composite strengthening.

[0061] (4) Broad engineering application prospects: This series of high-hardness and high-entropy alloys can be widely used in the manufacture of key components with extremely high requirements for material wear resistance, compressive strength and high temperature stability, including high-performance cutting tools, wear-resistant bearings, key components of turbine blades and wear-resistant liners for heavy equipment.

[0062] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0063] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-hardness heptagonal high-entropy alloy, characterized in that, The high-hardness heptagonal high-entropy alloy satisfies the following general formula according to atomic percentage: (CoCrFeNi) a (Al x Mo y W z ) b ; Where a + b = 100, a takes values ​​from 20 at.% to 46 at.%, and b takes values ​​from 54 at.% to 80 at.%; x, y, and z represent Al, Mo, and W respectively in Al x Mo y W z The atomic relative coefficients are given, and y=z; x takes values ​​from 1.0 to 2.4, and y and z both take values ​​from 0.7 to 1.

5.

2. The high-hardness heptagonal high-entropy alloy according to claim 1, characterized in that, In the high-hardness seven-element high-entropy alloy, the value of 'a' ranges from 28 at.% to 46 at.%.

3. The high-hardness seven-element high-entropy alloy according to claim 2, characterized in that, The general formula of the high-hardness heptagonal high-entropy alloy is selected from (CoCrFeNi). 46 (Al 1.5 Mo 0.7 W 0.7 ) 54 (CoCrFeNi) 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 (CoCrFeNi) 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 One of them.

4. The high-hardness seven-element high-entropy alloy according to claim 3, characterized in that, When the general formula of the high-hardness heptagonal high-entropy alloy is (CoCrFeNi) 46 (Al 1.5 Mo 0.7 W 0.7 ) 54 At that time, its average hardness after Mo-W pre-alloying, 10 melting cycles, and homogenization annealing was 82.0 HRA; when the general formula of the high-hardness heptagonal high-entropy alloy is (CoCrFeNi). 28 (Al 1.8 Mo 1.2 W 1.2 ) 72 When the Mo-W pre-alloying process is completed and the alloy undergoes at least 15 melting cycles, its average hardness is 88.0 HRA; and when the general formula of the high-hardness heptagonal high-entropy alloy is (CoCrFeNi). 28 (Al 2.4 Mo 0.8 W 0.8 ) 72 At that time, its average hardness after Mo-W pre-alloying and at least 15 remeltings was 84.0 HRA.

5. A method for preparing a high-hardness heptagonal high-entropy alloy according to any one of claims 1 to 4, characterized in that, Includes the following steps: S10, weigh out Co, Cr, Fe, Ni, Al, Mo and W, according to the general chemical formula (CoCrFeNi). a (Al x Mo y W z ) b The ingredients are prepared according to the stoichiometric ratio; S20, Mo and W are placed separately in a vacuum melting equipment, melted under an inert atmosphere and repeatedly remelted 3 to 4 times to obtain Mo-W binary master alloy ingot; S30, after crushing the Mo-W binary intermediate alloy ingot, it is mixed with the weighed Co, Cr, Fe, Ni and Al and placed in the crucible of the melting furnace. It is then melted under an inert atmosphere and repeatedly turned and remelted at least 8 times to obtain a seven-element alloy ingot. S40, the seven-element alloy ingot is subjected to homogenization annealing treatment at 1100-1200°C for 20-30 hours in a vacuum or inert atmosphere to obtain the high-hardness seven-element high-entropy alloy.

6. The method for preparing the high-hardness seven-element high-entropy alloy according to claim 5, characterized in that, In step S10, the purity of Co, Cr, Fe, Ni, Al, Mo and W is not less than 99.9 wt.%, and none of them contain Cu and Mn.

7. The method for preparing the high-hardness heptagonal high-entropy alloy according to claim 6, characterized in that, In step S10, a + b = 100, where a ranges from 20 at.% to 46 at.% and b ranges from 54 at.% to 80 at.%; x, y, and z represent Al, Mo, and W in Al, respectively. x Mo y W z The atomic relative coefficients are given, and y=z; x takes values ​​from 1.0 to 2.4, and y and z both take values ​​from 0.7 to 1.

5.

8. The method for preparing the high-hardness seven-element high-entropy alloy according to claim 5, characterized in that, In step S20, the vacuum melting equipment is a vacuum arc melting furnace or a vacuum suspension melting furnace; when using vacuum arc melting, the vacuum degree of the furnace cavity is not higher than 5×10⁻⁶. -4 The furnace pressure is 0.05–0.08 MPa when inert gas is introduced, and the melting current is 1000–2000 A; when vacuum suspension melting is used, the vacuum degree of the furnace cavity is not higher than 1 × 10⁻⁶ MPa. -4 Pa, smelting power is 10-15kW.

9. The method for preparing a high-hardness seven-element high-entropy alloy according to claim 5, characterized in that, In step S30, the crushed Mo-W binary intermediate alloy ingot, Co, Cr, Fe and Ni are first placed into the crucible of the smelting furnace, and then Al is placed on the upper part of the crucible of the smelting furnace.

10. The method for preparing the high-hardness heptagonal high-entropy alloy according to claim 5, characterized in that, In step S30, if the total mass of Al, Mo, and W is greater than or equal to 70% of the total mass of Co, Cr, Fe, Ni, Al, Mo, and W, then the number of times the material is repeatedly turned over and remelted shall not be less than 15 times.

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