A nickel-based superalloy with a γ+γ'' dual-phase structure and its preparation method

Abstract

This invention provides a nickel-based superalloy with a γ+γ'' dual-phase microstructure and its preparation method. Based on a Nb–Ni–W ternary system, without the addition of other elements, the atomic percentages are: Nb: 14–20 at%; Ni: 75–81 at%; W: 1–6 at% (summing 100%). Through phase diagram calculations and atomic percentage conversion, a stable γ+γ'' dual-phase microstructure is directly formed during the solidification process of the alloy melting and as-cast sample. fcc(Ni) acts as the γ matrix phase, with the γ'' phase, i.e., the Ni₃Nb strengthening phase, precipitating internally, without the precipitation of harmful phases such as the Laves phase. The preparation method does not involve solution treatment or aging treatment; it only requires arc melting under a high-purity argon atmosphere followed by cooling to complete the preparation. This invention features a simple composition system, a significantly simplified process, and yields a uniform and stable microstructure.

Description

Technical Field

[0001] This invention belongs to the field of nickel-based superalloy technology, specifically relating to a nickel-based superalloy based on the Nb–Ni–W ternary system, which has a γ+γ'' dual-phase structure calculated by the CALPHAD method, and has no solid solution or aging process, as well as its preparation method. Background Technology

[0002] In recent years, nickel-based superalloys have become key and ideal materials in high-temperature service systems such as aero-engines, gas turbines, and nuclear power equipment due to their excellent high-temperature stability, high high-temperature strength, and good microstructure balance. The γ''-Ni3Nb phase has a typical intermetallic compound structure. Because it maintains a coherent relationship with the γ matrix, has high interfacial matching, and a low high-temperature coarsening rate, it can provide a significant precipitation strengthening effect per unit volume, greatly improving the alloy's high-temperature yield strength and creep resistance. Simultaneously, Nb can stabilize the strengthening phase structure and inhibit harmful phase transformations, resulting in higher structural stability of the γ+γ'' dual-phase alloy under high-temperature service environments. W has a significant solid solution strengthening effect in nickel-based alloys, effectively improving matrix strength and reducing element diffusion rates; therefore, these alloys have outstanding application potential in the field of high-temperature structural materials.

[0003] Ni is a typical austenitic matrix element, often used as the core matrix of high-temperature alloys due to its excellent high-temperature stability, lack of solid-state phase transformation, and strong oxidation resistance. In recent years, some researchers have used the Ni–Nb binary system to conduct research on γ'' strengthened alloys. However, the high-temperature strength and microstructural stability of a simple binary system are insufficient. Therefore, there are few reports on the use of ternary composites of Ni, Nb, and W to prepare γ+γ'' dual-phase high-temperature alloys with high strength, high stability, and no harmful phases for high-temperature load-bearing components. Furthermore, no publicly available technology proposes a complete alloy design and preparation scheme under this ternary system with precisely defined Nb: 14–20 at%; Ni: 75–81 at%; W: 1–6 at%; without other added elements; and without solid solution and aging. Summary of the Invention

[0004] To address the shortcomings of existing γ'' strengthened nickel-based superalloys, such as complex composition, reliance on solution treatment and aging heat treatment, easy precipitation of harmful phases, and long process flow, this invention provides a nickel-based superalloy with a γ+γ'' dual-phase structure and its preparation method. This achieves a Nb–Ni–W ternary system without adding any other elements; the preparation process does not include solution treatment or aging treatment; and the cost is low, with a simple process to obtain a stable strengthened structure.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A nickel-based superalloy with a γ+γ'' dual-phase microstructure is provided. Based on the calculated liquidus projection diagram of the Nb–Ni–W ternary system, a suitable alloy composition is selected. The preferred composition is: Nb: 14–20 at%; Ni: 75–81 at%; W: 1–6 at%; the sum of the atomic percentages of the three is 100%. Exceeding this range will easily lead to the precipitation of harmful phases such as bcc(Nb,W) and Nb7Ni6, failing to achieve the microstructure objective of this invention. The volume fraction of the γ'' strengthening phase in conventional nickel-based superalloys is typically 15%–25%.

[0007] Furthermore, according to the above alloy composition ratio, high-purity Ni, Nb, and W raw materials are used for batching.

[0008] Furthermore, when melting in an electric arc furnace, the furnace must first be evacuated before high-purity argon gas is introduced to prevent oxidation of the sample during the melting process.

[0009] Furthermore, the alloy is subjected to a flipping and remelting process at least six times to ensure sample uniformity.

[0010] Furthermore, after melting, the alloy is cooled to room temperature using circulating water to directly obtain a nickel-based superalloy with a γ+γ'' dual-phase structure.

[0011] The microstructure and composition of the alloy were tested according to the following method:

[0012] The alloy sample was ground and polished, and its smooth surface was electrolytically etched. The microstructure was observed by scanning electron microscopy (SEM), and the phase composition was identified by X-ray diffraction (XRD). The alloy was determined to be a complete γ+γ'' dual-phase microstructure with no Laves phase or other TCP harmful phases precipitated.

[0013] In summary, the present invention has the following beneficial effects:

[0014] This invention successfully designed and prepared a ternary nickel-based superalloy composed solely of Ni, Nb, and W. Testing showed that the alloy exhibits a complete γ+γ'' dual-phase structure without the precipitation of any brittle or harmful phases. Through precise compositional control, using only arc melting and solidification, Nb was fully formed into a Ni3Nb-type γ'' strengthening phase, while W provided solid solution strengthening and structural stabilization, resulting in a γ+γ'' dual-phase alloy with high strength, no segregation, and no impurities. SEM and XRD analysis revealed a continuous γ-phase matrix, with the γ'' phase forming a dense, coherent strengthening network within the matrix, exhibiting pure phase composition and good interface matching. Quantitative metallographic analysis indicated that the area fraction of the γ'' phase in this experimental nickel-based superalloy was approximately 55±2%. Based on the principles of metallographic observation, the area fraction and volume fraction are approximately equal; therefore, the volume fraction of the γ'' phase could reach 55±2%.

[0015] In summary, the composition design and preparation method for γ+γ'' dual-phase nickel-based superalloys proposed in this invention contributes to the development and improvement of next-generation superalloys. Therefore, the nickel-based superalloys with γ+γ'' dual-phase structure prepared by the method of this invention have very good market application prospects and industrial production value. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below.

[0017] Figure 1 This is a schematic diagram of a ternary alloy design method provided by the present invention.

[0018] Figure 2 This is a SEM image of the alloy microstructure obtained in Example 1 of the present invention.

[0019] Figure 3 This is a SEM image of the alloy microstructure obtained in Comparative Example 1 of this invention.

[0020] Figure 4 This is a SEM image of the alloy microstructure obtained in Comparative Example 2 of this invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific comparative examples and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. In the description of the present invention, it should be noted that the percentages, process parameters, and microstructure descriptions appearing in the text are all key information related to the technical solution of the present invention, which facilitates quick understanding and repeated implementation by those skilled in the art; however, these specific details are not intended to limit the scope of protection of the present invention.

[0022] For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the concept and principles of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0023] For ease of description and consistent comparison, unless otherwise specified, all percentages of the components involved in the embodiments and comparative examples in this specification are atomic percentages (at%). Example 1

[0024] This embodiment has a nickel-based superalloy with a γ+γ'' dual-phase structure, and its atomic percentages are: Nb 14.1%, Ni 80.6%, W 5.3%, with the remaining unavoidable impurities content ≤0.1%.

[0025] The preparation process is as follows:

[0026] The first step is to mix and pre-treat high-purity Ni, Nb, and W raw materials according to the specified proportions; the second step is to carry out arc melting in a high-purity argon atmosphere; the third step is to flip the alloy melt 8 times and remelt it; the fourth step is to cool it to room temperature using a circulating water cooling method.

[0027] The tissue testing process is as follows:

[0028] The first step is to grind and polish the obtained alloy sample; the second step is to perform electrolytic etching in a solution of nitric acid: hydrochloric acid: water = 1:1:1, at a voltage of 5V for 5 seconds; the third step is to characterize the microstructure and determine the composition using SEM / EDS and XRD.

[0029] Testing revealed that the obtained alloy exhibited uniform composition and no significant dendritic segregation, with a single γ+γ'' dual-phase structure. Its high-temperature mechanical properties and microstructure stability met the application requirements. CALPHAD phase diagram calculations verified that only a γ+γ'' dual-phase structure formed within this compositional range. Comparative Example 1

[0030] The atomic percentages of this comparative alloy are: Nb 28.4%, Ni 67.9%, W 3.7%. The Nb content of this sample significantly exceeds the composition range defined in this invention, and the content of other unavoidable impurities is ≤0.1%.

[0031] The preparation process is as follows:

[0032] The first step is to mix and pre-treat high-purity Ni, Nb, and W raw materials according to the specified proportions; the second step is to carry out arc melting in a high-purity argon atmosphere; the third step is to flip the alloy melt 8 times and remelt it; the fourth step is to cool it to room temperature using a circulating water cooling method.

[0033] Upon testing, it was found that the composition exceeded the scope of protection of this invention, and the alloy contained γ'' phase, Nb7Ni6 phase, and bcc(Nb,W) phase. Among them, the Nb7Ni6 phase is a brittle and harmful phase. The alloy has a complex structure, brittle phase precipitation, and poor structural stability, and cannot form the single γ+γ'' dual-phase structure required by this invention. Therefore, the composition and process are not within the scope of protection of this invention and do not belong to the nickel-based high-temperature alloy with γ+γ'' dual-phase structure described in this invention. Comparative Example 2

[0034] The atomic percentages of this comparative alloy are: Nb 6.8%, Ni 80.0%, W 13.2%. The W element content of this sample exceeds the composition range defined in this invention, and the content of other unavoidable impurities is ≤0.1%.

[0035] The preparation process is as follows:

[0036] The first step is to clean and dry high-purity Ni, Nb, and W raw materials according to the above-mentioned proportions and set them aside. The second step is to carry out arc melting in a high-purity argon atmosphere. The third step is to flip the alloy melt 8 times and remelt it. The fourth step is to cool it to room temperature using a circulating water cooling method to obtain the target alloy.

[0037] Upon testing, it was found that because the composition was outside the range defined in this invention, a large amount of bcc(Nb,W) phase precipitated in the alloy microstructure, such as... Figure 4 It is difficult to precipitate a sufficient volume fraction of γ''-Ni3Nb reinforcing phase, and it is impossible to form a stable γ+γ'' dual-phase coupled structure; therefore, it does not belong to the nickel-based superalloys containing γ+γ'' dual-phase structure protected by this invention.

[0038] The test results from the above embodiments show that:

[0039] The nickel-based superalloy with γ+γ'' dual-phase structure proposed in this invention and its preparation method have a pure and stable γ+γ'' dual-phase structure without the precipitation of harmful phases, which provides a good foundation for the subsequent engineering application and industrial production of this alloy.

Claims

1. A nickel-based superalloy with a γ+γ'' dual-phase structure, characterized in that, The alloy is based on the Nb–Ni–W ternary system and does not contain any other elements; and by calculating the atomic percentage, the possible content ranges of each element are obtained: Nb: 14–20 at%; Ni: 75–81 at%; W: 1–6 at%; the sum of the three atomic percentages is 100%.

2. The nickel-based superalloy according to claim 1, characterized in that, Through extensive experiments and tests, the optimal ranges for the content of each element were obtained: Nb: 14–20 at%; Ni: 75–81 at%; W: 1–6 at%; the sum of the percentages of the three atoms is 100%.

3. The nickel-based superalloy according to claim 1, characterized in that, The alloy has a γ+γ'' dual-phase structure in the range of room temperature to service temperature, wherein the γ phase is the fcc(Ni) matrix phase and the γ'' phase is the intermetallic compound Ni3Nb phase; no TCP brittle and harmful phases such as Laves phase are precipitated in the alloy structure.

4. The nickel-based superalloy with a γ+γ'' dual-phase structure according to claim 1, characterized in that, The γ'' phase precipitates in the γ matrix in a blocky morphology, and the alloy structure is uniform with no obvious dendritic segregation or banded distribution of composition.

5. A method for preparing a nickel-based superalloy with a γ+γ'' dual-phase structure, used to prepare the nickel-based superalloy satisfying the conditions of claim 2, characterized in that, The entire preparation process does not include solution treatment or any aging treatment.

6. The alloy composition ratio according to claim 2, characterized in that, The raw materials are precisely formulated using pure metals of Nb, Ni, and W with a purity of not less than 99.9 wt%.

7. The preparation method according to claim 5, characterized in that, The metal raw material prepared according to claim 6 is placed in an electric arc melting furnace and melted under high-purity argon conditions. After the raw material is completely melted, it is turned over and remelted 6 to 8 times.

8. The smelting method according to claim 7, characterized in that, After the obtained ingot is cooled to room temperature, a nickel-based superalloy with a stable γ+γ'' dual-phase structure is directly obtained.

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