Preparation method of nickel-based medium-entropy alloy with high toughness and obtained product

Abstract

The application discloses a preparation method of a nickel-based medium-entropy alloy with high toughness and a product obtained by the method. The preparation method comprises the following steps: preparing and smelting each element into an ingot; without pre-uniformizing annealing, directly performing one-time rolling and subsequent one-time annealing on the ingot at room temperature to obtain the product. The process flow of the application is extremely simple, easy to operate and implement, the alloy is only four-component, has a single face-centered cubic structure solid solution phase, and has a heterogeneous microstructure characteristic of polycrystalline grain size. The nickel-based medium-entropy alloy has novel composition, simple structure, high strength and excellent ductility, superior comprehensive mechanical properties, and is easy to be industrialized and applied in structures.

Description

Technical Field

[0001] This invention relates to a method for preparing a medium-entropy alloy and the resulting product, specifically to a method for preparing a nickel-based medium-entropy alloy with high strength and toughness and the resulting product, belonging to the field of metallic materials and their preparation technology. Background Technology

[0002] In recent years, materials researchers have been mixing multiple elements at relatively high concentrations, creating a new type of alloy called "high-entropy alloys." This strategy contrasts sharply with traditional alloys. Due to the vast number of possible element combinations, this new alloy design concept undoubtedly provides a new direction for developing metallic materials with superior performance. Medium-entropy alloys fall between traditional alloys (low-entropy alloys) and high-entropy alloys, maintaining the outstanding performance of high-entropy alloys while reducing the number of principal elements. Their mixing entropy is closer to that of traditional alloys, resulting in better plasticity and workability.

[0003] In face-centered cubic (FCC) structures, high-entropy alloys are currently the most widely studied medium-entropy alloy systems. In FCC structures, high-entropy alloys possess a series of excellent properties, including high ductility, superior impact resistance, and unique low-temperature performance, making them ideal engineering structural materials. However, medium-entropy alloys in FCC exhibit a severe mismatch between strength and toughness. For example, pure NiFeCo medium-entropy alloys have a yield strength of only about 330 MPa at room temperature, while their elongation reaches as high as 72%. This strength-toughness contradiction severely restricts the development and application of medium-entropy alloys in FCC.

[0004] Furthermore, nickel-based medium-entropy alloys, as a promising new high-temperature alloy system, have not yet received widespread attention, and there is a lack of research and inventions regarding their microstructure and mechanical properties. Currently developed high-performance medium-entropy alloys have complex heat treatment processes. The alloys require prolonged homogenization annealing followed by rolling and annealing, often involving multiple rolling processes under different conditions and repeated annealing cycles. Secondly, rolling is not performed at room temperature but requires heating to eliminate work hardening. Simultaneously, the required annealing temperatures are high, currently reported to be typically above 1000℃, resulting in high energy consumption. Therefore, they are unsuitable for large-scale industrialization.

[0005] In summary, it is an urgent problem to develop a preparation method suitable for large-scale industrialization that can produce medium-entropy alloys with excellent mechanical properties and high strength-toughness matching. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing face-centered cubic (FCC) medium-entropy alloys, this invention provides a method for preparing a nickel-based medium-entropy alloy with high strength and toughness, as well as the resulting product. This method is simple and easy to operate. Through the effective combination of elemental composition, room temperature single rolling, and single annealing, the heterogeneous structure of multi-scale grains in the medium-entropy alloy is formed. No special equipment is required, the cost is low, the annealing temperature is low, and the resulting medium-entropy alloy has high strength and good ductility, exhibiting superior performance.

[0007] The specific technical solution of this invention is as follows:

[0008] A method for preparing a nickel-based medium-entropy alloy with high strength and toughness, wherein the medium-entropy alloy is composed of the following elements in atomic percentage: Ni: 35-43%, Fe: 27-35%, Co: 18-22%, Al: 8-12%, and the preparation method includes the following steps:

[0009] (1) Select each metal element as raw material and melt each raw material into a medium entropy alloy ingot according to the atomic percentage content.

[0010] (2) The medium-entropy alloy ingot was rolled at room temperature with a deformation of 77.5-82.5% to obtain the rolled sample;

[0011] (3) The rolled sample was annealed once to obtain a nickel-based medium-entropy alloy with high strength and toughness.

[0012] Furthermore, in the medium-entropy alloy, the atomic percentage of Ni is preferably 40%.

[0013] Furthermore, in the medium-entropy alloy, the atomic percentage of Fe is preferably 30%.

[0014] Furthermore, in the medium-entropy alloy, the atomic percentage of Co is preferably 20%.

[0015] Furthermore, in the medium-entropy alloy, the atomic percentage of Al is preferably 10%.

[0016] Furthermore, in step (1), each element is introduced in the form of its metallic element, and the purity of each metallic element is greater than 99.95 wt.%. Before use, each metal is ground to remove the oxide film on the surface of the raw material, and then placed in alcohol for ultrasonic cleaning and drying.

[0017] Furthermore, in step (1), the melting method of the medium-entropy alloy ingot can refer to the methods in the existing technology. For example, the raw materials can be placed in a vacuum induction melting furnace and the vacuum can be drawn to 1×10⁻⁶. -3The raw materials are melted at a temperature of 1500°C or higher to obtain a medium-entropy alloy ingot. Argon gas is then used as a protective gas.

[0018] Furthermore, in step (2), the entropy alloy ingot of this invention does not require pre-homogenization annealing and is directly rolled. Rolling is carried out at room temperature, and the deformation is 77.5-82.5%. That is, rolling is performed with a relative reduction of 77.5-82.5% relative to the thickness of the entropy alloy ingot. During rolling, it is best to cut the entropy alloy ingot into blocks or sheets with a thickness of 3-5 mm before rolling.

[0019] Furthermore, in step (2), a twin-roll mill is used for rolling, with the rolling direction consistent, until the deformation meets the requirements.

[0020] Furthermore, in step (3), annealing is performed under vacuum at a temperature of 600℃-700℃, such as 600℃, 650℃, or 700℃. The annealing time is generally 1-48h, such as 1h, 3h, 6h, 9h, 12h, 20h, 24h, 30h, 36h, 40h, or 48h, preferably 6h. This invention achieves a grain distribution of different sizes in the medium-entropy alloy through a single annealing process at a relatively low temperature. Surprisingly, it was found that the strength and toughness of the medium-entropy alloy were significantly improved under the polycrystalline grain size, overcoming the insufficiency of the contradiction between strength and toughness, and also overcoming the technical prejudice that medium-entropy alloys with a single fully recrystallized grain have better performance.

[0021] Preferably, in step (3), during annealing, the rolled sample is heated to the annealing temperature at a heating rate of 8-12℃ / min for annealing treatment.

[0022] Furthermore, in step (3), after annealing, the sample is water-quenched to room temperature to obtain a nickel-based medium-entropy alloy with high strength and toughness.

[0023] This invention achieves optimal combinations of different grain existence modes and grain sizes through the selection of alloying elements and process optimization, thereby forming a nickel-based medium-entropy alloy with heterogeneous microstructure features of multiple grain sizes. This medium-entropy alloy has a solid solution phase with a single face-centered cubic phase structure, and its matrix is ​​composed of refined recrystallized grains and recrystallized grains with different degrees of coarsening, thus forming a heterogeneous microstructure feature with multi-scale grains, which combines high strength and excellent ductility.

[0024] This invention designs a high-strength and high-toughness nickel-based medium-entropy alloy system, and achieves a multi-scale, heterogeneous grain structure through the effective combination of alloy composition, a single-stage rolling deformation at room temperature after melting, and a single-stage annealing treatment. Compared with the prior art, the beneficial effects of this invention are reflected in:

[0025] 1. The process of this invention is simple, easy to operate, has a low annealing temperature, requires no special equipment, has low cost, and is easy to industrialize and apply.

[0026] 2. The medium-entropy alloy obtained by this invention is a four-element alloy with few element types, novel composition, simple structure, and lower cost than existing high-entropy alloy systems. This invention employs room temperature rolling followed by medium-temperature annealing, resulting in lower energy consumption compared to traditional processes. The process is simple and eliminates the need for multiple rolling and heat treatment steps, thereby reducing preparation costs. By controlling the process, different grain structures can be obtained, resulting in nickel-based medium-entropy alloys with heterogeneous microstructures exhibiting multi-grain sizes.

[0027] 3. The ingots of this invention do not require pre-homogenization annealing. They are rolled directly at room temperature in one step, requiring only one hot annealing treatment. Compared with the existing process route of multi-step rolling and high-temperature heat treatment of alloys after homogenization, this invention has strong repeatability, low overall energy consumption, shortened process route, easy control of process parameters, low cost, and is more conducive to industrial mass production.

[0028] 4. The annealing heat treatment of this invention does not change the FCC solid solution structure of the medium entropy alloy. After annealing, the medium entropy alloy is still a single-phase FCC solid solution structure, and can obtain the heterogeneous microstructure characteristics of deformed grains and recrystallized fine and coarse grains respectively. To a certain extent, it can obtain the toughness and strength of grains of different sizes, thereby controlling the simultaneous improvement of strength and toughness.

[0029] 5. This invention can effectively obtain a microstructure in which different grains coexist by fine-tuning process parameters, thereby improving the strength and toughness of medium-entropy alloys. The resulting alloys have superior comprehensive mechanical properties, and the medium-entropy alloys possess both high strength and excellent ductility. The tensile yield strength of the nickel-based medium-entropy alloys is 1022-1300 MPa, the tensile strength is 950-1445 MPa, and the uniform elongation is 5.6-26.1%. Compared with existing medium- and high-entropy alloy systems, this invention is at an advanced level and has high engineering application value. Attached Figure Description

[0030] Figure 1 The XRD patterns are those of the medium-entropy alloys prepared in Examples 1, 4, 1, and 8 of this invention.

[0031] Figure 2 The inverse pole figures are for nickel-based medium-entropy alloys prepared in the untreated as-cast state and at annealing temperatures of 600℃, 800℃, and 1200℃. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0033] Example 1

[0034] Step (1): Preparation of medium-entropy alloy ingots: Co, Ni, Fe, and Al metal blocks with a purity ≥ 99.5 wt.% are prepared according to Ni 40 Fe 30 Co 20 Al 10 Weigh (at.%), place each metal block in a vacuum induction melting furnace, and evacuate to 1×10⁻⁶. -3 The alloy is melted under argon gas at a pressure below Pa using magnetic levitation. During the melting process, it is continuously turned and remelted at least 5 times, and then poured into a cylindrical mold with a diameter of 2 cm to cool, resulting in a medium-entropy alloy ingot.

[0035] Step (2): Rolling: Rolling the Ni prepared in step (1) 40 Fe 30 Co 20 Al 10 The medium-entropy alloy ingot is wire-cut into cuboid blocks with a thickness of 4mm. The cut cuboid blocks do not require pre-homogenization annealing and are directly rolled at room temperature using a twin-roll mill. The rolling direction is consistent until the relative reduction relative to the original thickness is 80% (i.e., the deformation is 80%), finally obtaining a 0.8mm thick plate.

[0036] Step (3): Annealing heat treatment: The plate prepared in step (2) is placed in a vacuum tube furnace and heated to 650°C with the furnace. The heating rate is 10°C per minute. The annealing heat treatment temperature is 650°C and the temperature is held for 6 hours. After annealing, the plate is quenched in water to room temperature to obtain a nickel-based medium entropy alloy with high strength and toughness.

[0037] Example 2

[0038] A nickel-based medium-entropy alloy with high strength and toughness was prepared according to the method in Example 1, except that in step (3), the annealing heat treatment holding time was 12h.

[0039] Example 3

[0040] A nickel-based medium-entropy alloy with high strength and toughness was prepared according to the method in Example 1, except that in step (3), the annealing heat treatment holding time was 24h.

[0041] Example 4

[0042] A nickel-based medium-entropy alloy with high strength and toughness was prepared according to the method in Example 1, except that in step (3), the annealing heat treatment holding time was 48h.

[0043] Example 5

[0044] A nickel-based medium-entropy alloy with high strength and toughness was prepared according to the method of Example 1, except that the annealing heat treatment temperature in step (3) was 600°C.

[0045] Example 6

[0046] A nickel-based medium-entropy alloy with high strength and toughness was prepared according to the method in Example 1, except that the annealing heat treatment temperature in step (3) was 700°C.

[0047] Example 7

[0048] A nickel-based medium-entropy alloy with high strength and toughness was prepared according to the method of Example 1, except that in step (2), rolling was carried out at room temperature with a relative reduction of 77.5% (all relative to the original height, 4 mm) to finally obtain a plate with a thickness of 0.9 mm.

[0049] Example 8

[0050] A nickel-based medium-entropy alloy with high strength and toughness was prepared according to the method of Example 1, except that in step (2), rolling was carried out at room temperature with a relative reduction of 82.5% (all relative to the original height, 4 mm) to finally obtain a plate with a thickness of 0.7 mm.

[0051] Example 9

[0052] A high-strength and high-toughness nickel-based medium-entropy alloy was prepared according to the method of Example 1, except that in step (1), Co, Ni, Fe, and Al metal blocks with a purity ≥ 99.5 wt.% were prepared according to the method of Ni 42.5 Fe 27.5 Co 22 Weigh Al8 (at.%).

[0053] Example 10

[0054] A high-strength and high-toughness nickel-based medium-entropy alloy was prepared according to the method of Example 1, except that in step (1), Co, Ni, Fe, and Al metal blocks with a purity ≥ 99.5 wt.% were prepared according to the method of Ni 37.5 Fe 32.5 Co 18 Al 12 Weigh (at.%).

[0055] Comparative Example 1

[0056] The medium entropy alloy was prepared according to the method of Example 1, except that in step (3), the annealing heat treatment temperature was 800℃.

[0057] Comparative Example 2

[0058] The medium-entropy alloy was prepared according to the method of Example 1, except that in step (3), the annealing heat treatment temperature was 1050℃.

[0059] Comparative Example 3

[0060] The medium-entropy alloy was prepared according to the method of Example 1, except that in step (3), the annealing heat treatment temperature was 1200℃.

[0061] Comparative Example 4

[0062] The medium-entropy alloy was prepared according to the method of Example 1, except that in step (2), it was rolled at room temperature with a relative reduction of 60% (all relative to the original height, 4 mm) to finally obtain a 1.6 mm plate.

[0063] Comparative Example 5

[0064] The medium-entropy alloy was prepared according to the method of Example 1, except that in step (2), it was rolled at room temperature with a relative reduction of 75% (all relative to the original height, 4 mm) to finally obtain a 1.0 mm plate.

[0065] Comparative Example 6

[0066] The medium-entropy alloy was prepared according to the method of Example 1, except that in step (1), Co, Ni, Fe, and Al metal blocks with a purity ≥ 99.5 wt.% were prepared according to the method of Ni 25 Fe 25 Co 25 Al 25 Weigh it.

[0067] Comparative Example 7

[0068] The medium-entropy alloy was prepared according to the method of Example 1, except that in step (1), Co, Ni, Fe, and Al metal blocks with a purity ≥ 99.5 wt.% were prepared according to the method of Ni 60 Fe 10 Co 10 Al 20 Weigh it.

[0069] Comparative Example 8

[0070] Step (1): Preparation of medium-entropy alloy ingot: Same as in Example 1;

[0071] Without steps (2) and (3), the resulting medium-entropy alloy exhibits a severe mismatch between strength and toughness, thus losing its practical significance.

[0072] The surfaces of the obtained medium-entropy alloy samples were cleaned for testing.

[0073] 1. XRD test: XRD test was performed on the medium-entropy alloys obtained in the above examples and comparative examples. The results showed that the medium-entropy alloys in all examples still maintained a single FCC solid solution structure. This indicates that the annealing treatment of the present invention does not change the phase structure of the medium-entropy alloy, which is beneficial to maintaining the characteristic performance advantages of the FCC medium-entropy alloy.

[0074] The XRD patterns of Examples 1, 4, Comparative Example 1, and Comparative Example 8 are as follows: Figure 1 As shown, the as-cast alloy without annealing heat treatment (Comparative Example 8) has a single FCC solid solution structure, while the alloy treated at 800℃ (Comparative Example 1) consists of an FCC solid solution structure and an in-situ generated intermetallic compound phase (cubic phase). This demonstrates that medium-temperature heat treatment below 700℃ does not alter the crystal structure of the medium-entropy alloy and is key to maintaining a single FCC solid solution structure.

[0075] 2. Grain Morphology Testing: The microstructure of the medium-entropy alloys obtained in Examples 1-5, Comparative Examples 1-3, and Comparative Example 8 was observed using electron backscatter diffraction (EBSD) analysis. Then, the percentage of different grains (deformed grains and recrystallized fine and coarse grains) in the medium-entropy alloys was statistically analyzed using OimA software based on the large and small angle grain boundaries, as shown in Table 1. The microstructure diagrams of the medium-entropy alloys obtained in Examples 5, Comparative Examples 1, 3, and 8 are shown below. Figure 2 As shown.

[0076] Table 1

[0077]

[0078] Note: Ratio 8 is not statistically significant and therefore does not appear in Table 1.

[0079] analyze Figure 2 It can be seen that the as-cast alloy (Comparative Example 8) without annealing heat treatment exhibits a single equiaxed coarse grain. After rolling heat treatment with different parameters, different grain forms were obtained, as shown in Table 1. Analysis of Table 1 shows that the alloy heat-treated at a lower temperature (700℃) has a heterogeneous microstructure characterized by a combination of deformed grains, recrystallized ultrafine grains, and recrystallized large grains. However, when the heat treatment temperature is increased to 800℃, no deformed grains are observed in the alloy (Comparative Example 1); with further increases in temperature, only fully recrystallized coarse grains are observed. Therefore, it can be concluded that the multi-scale grain distribution characteristics of the nickel-based medium-entropy alloy of the present invention benefit from a suitable medium-temperature heat treatment temperature.

[0080] 3. Room temperature tensile property test: Using an Instron testing machine, the tensile rate was 1×10⁻⁶. -3 s -1The experiment was repeated three times to obtain the yield strength, tensile strength and uniform elongation of the nickel-based medium-entropy alloy material. The statistical results are shown in Table 2 below.

[0081] Table 2

[0082]

[0083] As can be seen from Table 2, compared with the as-cast medium-entropy alloy of Comparative Example 8, the medium-entropy alloys of Examples 1-10 all have good ductility while having high yield strength, and all achieve excellent comprehensive mechanical properties of high strength and high elongation.

[0084] By comparing Examples 1, 5, and 6, and Comparative Examples 1-3, the medium-entropy alloy treated at medium temperature in this invention achieves a good balance between strength and ductility, exhibiting both good strength and ductility, and realizing high strength and toughness. This is attributed to the combination of grains of different sizes. As shown in Table 1, Examples 1, 5, and 6 at medium temperature can achieve deformed grains, achieving both subgrain boundaries and recrystallized grains, thus better controlling the simultaneous improvement of strength and toughness. In contrast, Comparative Examples 1-3 only show typical recrystallized grains. Therefore, Comparative Examples 1-3 with recrystallized structures treated at high temperature exhibit a typical contradictory relationship between strength and ductility, i.e., increased elongation but lower strength, even lower than that of the as-cast alloy, resulting in poor performance.

[0085] Furthermore, Comparative Examples 4 and 5, with lower rolling amounts, showed lower strength improvements than Example 1 under the same process conditions, and their ductility was poor because they could not achieve the combination of grains of different sizes. Meanwhile, Comparative Examples 6 and 7 altered the elemental proportions in the medium-entropy alloys. The results showed that the strength and toughness of the medium-entropy alloys in Comparative Examples 6 and 7 after medium-temperature treatment were significantly lower than those in Example 1. This indicates that the nickel-based composition of the present invention is advanced, thus resulting in better subsequent mechanical property enhancement.

[0086] The medium-entropy alloys in Examples 1-10 exhibit yield strengths exceeding 1000 MPa, consistent with the high-strength characteristics of this invention. To better study the preferred embodiments, the tensile strength × uniform elongation was calculated. Yield strength and tensile strength × uniform elongation are two characteristics that reflect the overall strength and toughness of the alloy. Among them, the tensile strength × uniform elongation of Examples 1-4 are all above 10000, representing preferred embodiments of this invention. Example 4 exhibits the best performance; its high yield strength primarily stems from the combined effect of grains of different sizes. The maximum tensile strength × uniform elongation value is related to a work hardening mechanism involving a sufficient proportion of recrystallized grains, a mechanism modulated by the synergistic deformation of recrystallized ultrafine grains and large grains.

[0087] The four-component FCC solid solution structure entropy alloy involved in this invention can achieve the goal of simultaneously improving strength and toughness. This invention has low cost, simple process, and combines high strength and ductility, exhibiting excellent comprehensive mechanical properties, thus possessing significant industrial application value.

Claims

1. A method for preparing a nickel-based medium-entropy alloy with high strength and toughness, characterized in that: The medium-entropy alloy is composed of the following elements in atomic percentage: Ni: 40%, Fe: 30%, Co: 20%, Al: 10%, and its preparation includes the following steps: (1) Select each metal element as raw material and melt each raw material into a medium entropy alloy ingot according to the atomic percentage content; (2) The medium-entropy alloy ingot was rolled at room temperature with a deformation of 80% to obtain the rolled sample; (3) The rolled sample was heated to 650°C under vacuum and held for 24-48 hours to obtain a nickel-based medium-entropy alloy with high strength and toughness.

2. The preparation method according to claim 1, characterized in that: In step (1), each element is introduced in the form of its metallic elemental form, and the purity of each metallic elemental form is greater than 99.95 wt.%.

3. The preparation method according to claim 1, characterized in that: In step (2), a twin-roll mill is used for rolling, and the rolling direction is consistent.

4. The preparation method according to claim 1 or 3, characterized in that: In step (2), the medium-entropy alloy ingot is cut into pieces with a thickness of 3-5 mm and rolled.

5. The preparation method according to claim 1, characterized in that: In step (3), after annealing, the sample is water-quenched to room temperature to obtain a nickel-based medium-entropy alloy with high strength and toughness.

6. A nickel-based medium-entropy alloy with high strength and toughness prepared by the method of any one of claims 1-5.

7. The nickel-based medium-entropy alloy according to claim 6, characterized in that: The medium-entropy alloy has a face-centered cubic solid solution phase with heterogeneous microstructure features of multi-scale grains.

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