Wide-temperature-range high-strength and high-toughness NiCoCrAlNb medium-entropy alloy and preparation method thereof

Abstract

The application discloses a wide-temperature-range high-strength and high-toughness NiCoCrAlNb medium-entropy alloy and a preparation method thereof, and belongs to the technical field of metal structural materials serving in extreme environments. The alloy mainly comprises Ni, Co, Cr, Al and Nb elements, the matrix of the alloy is a face-centered cubic structure, and L12 phases and D0 19 phases at grain boundaries are constructed in the alloy through mechanical heat treatment system regulation. The alloy maintains high yield strength and fracture elongation in a wide temperature range of-196 DEG C to 750 DEG C. The process flow of the application mainly comprises smelting, homogenization heat treatment, rolling, annealing heat treatment and aging heat treatment. The material preparation process flow is simple, mature and controllable, and provides a new material design scheme for aerospace, advanced energy equipment and other cross-temperature core structural components.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, specifically relating to a wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy and its preparation method. Background Technology

[0002] In cutting-edge industrial fields, such as hot-end components of aerospace vehicles and cryogenic-high-temperature alternating energy equipment, metallic structural materials are facing unprecedentedly harsh service conditions. These critical components frequently endure severe thermal shocks ranging from extremely low temperatures (-196°C) to extreme high temperatures (above 700°C) during actual operation, accompanied by complex and multidimensional mechanical alternating loads. This places stringent demands on the mechanical properties of materials across a wide temperature range: the materials must not only effectively resolve localized stress concentrations and overcome cleavage brittle fracture tendencies at extremely low temperatures to ensure excellent fracture toughness, but also possess strong microstructural thermal stability during high-temperature service to prevent grain boundary sliding, second-phase coarsening, and macroscopic creep softening phenomena caused by rapid atomic diffusion.

[0003] However, faced with such an extreme wide temperature range, traditional metallic structural materials often fall into the "strong-plasticity inversion" dilemma of physical metallurgy, exhibiting limitations that come at the expense of other aspects. On the one hand, materials represented by austenitic stainless steel or classic medium / high entropy alloys, while exhibiting excellent cryogenic toughness at low temperatures due to their face-centered cubic structure, show a significant decrease in yield strength when the temperature rises to the medium / high temperature range due to the lack of an effective dislocation interception mechanism, making it difficult to meet the load-bearing requirements of medium / high temperatures. On the other hand, precipitation-strengthened nickel-based superalloys, while exhibiting excellent microstructural stability and creep resistance at high temperatures due to a large number of dispersed coherent precipitates, suffer from insufficient overall low-temperature strength in extremely low-temperature environments. Some of the hard carbides precipitated in superalloys undergo severe deformation mismatch in cryogenic environments, leading to crack initiation. Summary of the Invention

[0004] To address the aforementioned technical problems, or some of them, this invention proposes a wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy and its preparation method. NiCoCrAlNb medium-entropy alloys within a certain composition range can achieve excellent mechanical properties over a wide temperature range after melting, homogenization heat treatment, rolling, annealing heat treatment, and aging heat treatment.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy, wherein the elemental composition of the NiCoCrAlNb medium-entropy alloy, by atomic percentage, is Ni: 44-48 at%, Co: 24-29 at%, Cr: 15-21 at%, Al: 2-5 at%, Nb: 2-5 at%; the wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy is characterized by a multiphase structure, including a face-centered cubic solid solution matrix, and L12 phase dispersed in the matrix and D0 phase at the grain boundaries. 19 Mutually.

[0006] Furthermore, the NiCoCrAlNb system entropy alloy is allowed to contain at least one of the following elements as a modifier: ≤ 1 at % trace amounts of V, Mo, W, Zr, B, C, La, Ce, etc.

[0007] A method for preparing a wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy, specifically including the following steps: (1) Clean the metal raw materials according to the elements of the wide temperature range high strength and toughness NiCoCrAlNb system medium entropy alloy, and then weigh the elements according to the atomic percentage; (2) The metal raw materials are smelted in a non-consumable argon protective vacuum arc furnace. After the smelting is completed, the alloy is cast into a multi-principal alloy ingot using a non-consumable vacuum arc furnace. (3) The multi-principal alloy ingot is subjected to homogenization heat treatment under argon protection and immediately water quenched; (4) Cut the core plate from the homogenized heat-treated ingot and roll it at room temperature; (5) The rolled plate is subjected to recrystallization annealing heat treatment and aging heat treatment to obtain NiCoCrAlNb medium entropy alloy.

[0008] Furthermore, in step (1), the purity of the metal raw material is ≥99.9 wt%, and the oxide scale is removed and the material is cleaned.

[0009] Furthermore, in step (2), the vacuum level inside the vacuum arc melting furnace needs to be controlled at 1×10 before melting. -4 The pressure is below Pa, and argon inert gas is introduced as a protective gas. During smelting, the titanium ingot must be smelted first to absorb the residual oxygen in the vacuum arc melting furnace, and then the raw material is smelted repeatedly at least 4 times. After smelting, the alloy is cast into a rectangular ingot with a final size of 70×10×10 mm.

[0010] Furthermore, in step (3), the ingot is sealed in a quartz tube, and the raw material is placed in the quartz tube. The vacuum degree is controlled at 1×10⁻⁶. -4After the pressure drops below Pa, a small amount of argon gas is introduced and the quartz tube is sealed. Then, the sealed ingot is subjected to homogenization heat treatment at a temperature of 1150-1250℃ for 4-24 hours.

[0011] Further, in step (4), the homogenized heat-treated ingot is cut into plates using electrical discharge wire cutting. The plates need to be cut away from the ingot riser, the central loose area and the surface oxidation area. The rolling reduction is controlled at 50%-80% to finally obtain plates with a thickness of 1mm-2mm.

[0012] Further, in step (5), the rolled plate is subjected to recrystallization annealing heat treatment at a temperature of 900-1050℃ and an annealing time of 30-90min, followed by water cooling to room temperature; then aging heat treatment is performed at a temperature of 600-800℃ and an aging time of 4-48h, followed by air cooling to room temperature.

[0013] A wide-temperature-range high-strength and high-toughness NiCoCrAlNb medium-entropy alloy is prepared according to the above-mentioned method for preparing wide-temperature-range high-strength and high-toughness NiCoCrAlNb medium-entropy alloys.

[0014] The design concept of this invention is: This invention, starting from the actual service requirements of aerospace propulsion systems and cryogenic-high temperature alternating energy equipment, controls the cold deformation of NiCoCrAlNb alloys and subsequent stepped heat treatment processes to meet the requirements of synergistic strength and toughness and microstructure thermal stability of materials under a wide temperature range (-196℃ to 750℃). It prepares a three-phase composite medium-entropy alloy that combines low-temperature fracture toughness and high-temperature softening resistance to meet the actual needs of related engineering fields for wide-temperature-range core structural components.

[0015] Compared with the prior art, the present invention exhibits the following advantages and technical effects: (1) This invention provides a wide temperature range high strength and toughness FCC-L12-D0 19 The three-phase synergistic medium-entropy alloy and its preparation method can effectively improve the problem that existing single-strength alloys cannot simultaneously achieve both cryogenic toughness at extremely low temperatures and creep resistance at high temperatures, and significantly broaden the effective service temperature range of medium-entropy alloys.

[0016] (2) The present invention adopts the process route of "cold deformation + step heat treatment", which utilizes the difference in nucleation kinetics of different phases in the alloy to disperse and precipitate coherent L12 phase in the face-centered cubic matrix to provide basic strength in the whole temperature range; at the same time, D0 with high thermal stability is constructed in situ at the grain boundaries. 19The multiphase synergy effectively suppresses grain boundary sliding and microstructure coarsening at high temperatures. This multiphase synergistic microstructure creates a deformation mechanism that adapts to a wide temperature range, significantly improving the alloy's comprehensive mechanical properties under alternating thermal stress and complex stresses, maintaining high yield strength and elongation at break across a wide temperature range from -196℃ to 750℃. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall process flow of the present invention; Figure 2 and Figure 4 The results are scanning electron microscopy (SEM) images of the medium-entropy alloy prepared in this invention, showing the alloy microstructure. Figure 3 and Figure 5 These are the transmission electron microscopy results of the medium-entropy alloy prepared in this invention. Detailed Implementation

[0018] The application and implementation of the present invention will be further illustrated below through specific embodiments: Example 1: This embodiment provides a method for preparing a low-temperature, high-strength, high-toughness, second-phase-reinforced NiCoCrAlNb medium-entropy alloy. The medium-entropy alloy has the following atomic percentages: Ni: 47 at%, Co: 28.2 at%, Cr: 18.8 at%, Al: 3 at%, Nb: 3 at%. The overall process flow is as follows: Figure 1 As shown, the specific preparation process is as follows: Step (1): Wash the elemental raw materials with anhydrous ethanol for 30 minutes and then dry them. Then weigh the elements according to atomic percentage, with each button ingot weighing about 50g. Step (2): Multi-principal alloys are smelted using a non-consumable argon-protected vacuum arc furnace. Before smelting, the vacuum level inside the vacuum arc furnace must be controlled at 1×10⁻⁶. -4 The pressure is below Pa, and argon inert gas is introduced as a protective gas. During the smelting process, the titanium ingot needs to be smelted first to absorb the residual oxygen in the vacuum arc melting furnace. The smelting is repeated 4 times and electromagnetic stirring is used to ensure uniform composition. After the smelting is completed, it is cast into a multi-principal element alloy ingot with an ingot size of 70×10×10 mm. In step (3), the ingot is sealed in a quartz tube, and the raw material is placed in the quartz tube. The vacuum degree is controlled at 1×10 -4 After the pressure drops below Pa, a small amount of argon gas is introduced and the quartz tube is sealed. Then, the sealed ingot is subjected to homogenization heat treatment at a temperature of 1200℃ for 12 hours. After homogenization heat treatment, it is immediately water quenched. Step (4): Cut the ingot into 4mm thick plates using electrical discharge wire cutting. The plates should be cut away from the ingot riser, the central loose area and the surface oxidation area. Then, roll the plates in multiple passes at room temperature with a reduction of about 75% to a thickness of 1mm. Step (5): The cold-rolled sheet is subjected to annealing heat treatment at a temperature of 950℃ for 5 minutes. After annealing, it is water-cooled and then subjected to aging heat treatment at a temperature of 700℃ for 24 hours. After aging, it is air-cooled.

[0019] The scanning electron microscope results show that the D0 of the medium-entropy alloy in this embodiment is... 19 The phase is mainly distributed at the grain boundaries, such as Figure 2 As shown, the black one is D0. 19 The alloy also contains a large number of annealed twins. Transmission electron microscopy results show that the medium-entropy alloy in this embodiment has an L12 phase, uniformly distributed within the face-centered cubic matrix phase of the alloy, such as... Figure 3 As shown. A wide-temperature-range environmental tensile test was conducted on the heat-treated alloy at a tensile rate of 1×10⁻⁶. -3 / s, the test results are shown in Table 1.

[0020] Table 1 Example 2: This embodiment provides a method for preparing a low-temperature, high-strength, and tough second-phase reinforced NiCoCrAlNb medium-entropy alloy. The medium-entropy alloy has the following atomic percentages: Ni: 47 at%, Co: 28 at%, Cr: 18 at%, Al: 3.5 at%, Nb: 3.5 at%. The specific preparation process is as follows: Step (1): Wash the elemental raw materials with anhydrous ethanol for 30 minutes and then dry them. Then weigh the elements according to atomic percentage, with each button ingot weighing about 50g. Step (2): Multi-principal alloys are smelted using a non-consumable argon-protected vacuum arc furnace. Before smelting, the vacuum level inside the vacuum arc furnace must be controlled at 1×10⁻⁶. -4 The pressure is below Pa, and argon inert gas is introduced as a protective gas. During the smelting process, the titanium ingot needs to be smelted first to absorb the residual oxygen in the vacuum arc melting furnace. The smelting is repeated 4 times and electromagnetic stirring is used to ensure uniform composition. After the smelting is completed, it is cast into a multi-principal element alloy ingot with an ingot size of 70×10×10 mm. In step (3), the ingot is sealed in a quartz tube, and the raw material is placed in the quartz tube. The vacuum degree is controlled at 1×10 -4After the pressure drops below Pa, a small amount of argon gas is introduced and the quartz tube is sealed. Then, the sealed ingot is subjected to homogenization heat treatment at a temperature of 1200℃ for 12 hours. After homogenization heat treatment, it is immediately water quenched. Step (4): Cut the ingot into 4mm thick plates using electrical discharge wire cutting. The plates should be cut away from the ingot riser, the central loose area and the surface oxidation area. Then, roll the plates in multiple passes at room temperature with a reduction of about 75% to a thickness of 1mm. Step (5): The cold-rolled sheet is subjected to annealing heat treatment at a temperature of 1050℃ for 5 minutes. After annealing, it is water-cooled and then subjected to aging heat treatment at a temperature of 700℃ for 24 hours. After aging, it is air-cooled.

[0021] Scanning electron microscopy results show that the medium-entropy alloy in this embodiment has a single-phase structure, such as... Figure 4 As shown, annealing twins also exist in the alloy. Transmission electron microscopy results show that the medium-entropy alloy in this embodiment has an L12 phase, uniformly distributed in the face-centered cubic matrix phase of the alloy, as shown... Figure 5 As shown. A wide-temperature-range environmental tensile test was conducted on the heat-treated alloy at a tensile rate of 1×10⁻⁶. -3 / s, the results are shown in Table 1. The mechanical properties at room temperature are: yield strength 978.6 MPa, tensile strength 1392.4 MPa, and elongation at break 38.2%.

[0022] The results show that this wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy can achieve synergistic strengthening effects of the two types of second phases through a reasonable mechanical heat treatment process. It achieves a high strength-ductility balance across a wide temperature range, proving the rationality and feasibility of the design principle of this invention. Its composition is simple, the processing flow is short, the internal structure is dense and uniform, and the surface is defect-free, indicating that the designed alloy has industrial transformation potential.

[0023] The above embodiments are merely several specific implementations of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A wide-temperature-range high-strength and high-toughness NiCoCrAlNb medium-entropy alloy, wherein the constituent elemental composition of the NiCoCrAlNb medium-entropy alloy, by atomic percentage, is Ni: 44-48 at%, Co: 24-29 at%, Cr: 15-21 at%, Al: 2-5 at%, Nb: 2-5 at%; the wide-temperature-range high-strength and high-toughness NiCoCrAlNb medium-entropy alloy is characterized by a multiphase structure, including a face-centered cubic solid solution matrix, and L12 phase dispersed in the matrix and D0 phase at the grain boundaries. 19 Mutually.

2. The wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy according to claim 1, characterized in that, It contains ≤ 1 at % of a regulator, wherein the regulator contains at least one of the elements V, Mo, W, Zr, B, C, La, and Ce.

3. A method for preparing a wide-temperature-range, high-strength and high-toughness NiCoCrAlNb medium-entropy alloy, characterized in that, Includes the following steps: The elements of the wide-temperature-range high-strength and high-toughness NiCoCrAlNb medium-entropy alloy according to claim 1 or 2 are used to clean the metal raw materials, and then the elements are weighed according to atomic percentage. The metal raw materials are smelted using a non-consumable argon-protected vacuum arc furnace. After smelting, the alloy is cast into a multi-principal element alloy ingot using the non-consumable vacuum arc furnace. The multi-principal alloy ingot was subjected to homogenization heat treatment under argon protection and immediately water quenched. Core plates are cut from the homogenized heat-treated ingot and rolled at room temperature; The rolled sheet was subjected to recrystallization annealing heat treatment and aging heat treatment to obtain NiCoCrAlNb medium entropy alloy.

4. The preparation method according to claim 3, characterized in that, The purity of the metal raw material is ≥99.9 wt%, and the oxide scale is removed and the material is cleaned.

5. The preparation method according to claim 3, characterized in that, Before the melting process, the vacuum level inside the vacuum arc melting furnace must be controlled at 1×10⁻⁶. -4 The pressure is below Pa, and argon inert gas is introduced as a protective gas. During smelting, the titanium ingot is first smelted to absorb the residual oxygen in the vacuum arc melting furnace, and then the raw material is smelted repeatedly at least 4 times. After smelting, the alloy is cast into a rectangular ingot with a final size of 70×10×10 mm.

6. The preparation method according to claim 3, characterized in that, The homogenization heat treatment of the multi-principal alloy ingot under argon protection includes: placing the ingot in a quartz tube, and controlling the vacuum degree at 1×10⁻⁶. -4 After the pressure drops below Pa, a small amount of argon gas is introduced and the quartz tube is sealed. Then, the sealed ingot is subjected to homogenization heat treatment at a temperature of 1150-1250℃ for 4-24 hours.

7. The preparation method according to claim 3, characterized in that, The process of cutting the core plate from the homogenized heat-treated ingot involves using an electrical discharge wire cutter to cut the homogenized heat-treated ingot into plates, avoiding the ingot riser, the central loose area, and the surface oxidation area during cutting, and controlling the rolling reduction at 50%-80% to finally obtain a 1mm-2mm thick plate.

8. The preparation method according to claim 3, characterized in that, The recrystallization annealing heat treatment is performed at an annealing temperature of 900-1050℃ for 30-90 min, followed by water cooling to room temperature; the aging heat treatment is performed at an aging temperature of 600-800℃ for 4-48 h, followed by air cooling to room temperature.

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