In-situ synthesis P-phase enhanced isometric crystal Ni3Al-based intermetallic compound alloy and preparation method thereof

Abstract

The invention discloses an in-situ synthesis P phase enhanced isometric crystal Ni3Al-based intermetallic compound alloy and a preparation method thereof, and belongs to the technical field of Ni-Al series intermetallic compounds. The invention aims to solve the problem that the strength, plasticity and toughness of the existing isometric crystal Ni3Al-based intermetallic compound are obviously reduced after long-term high-temperature thermal exposure. The alloy comprises the following components in percentage by mass: 0.10 to 0.15 percent of C, 8.7 to 8.9 percent of Al, 4.9 to 5.1 percent of Cr, 2.05 to 2.25 percent of Mo, 3.05 to 3.25 percent of W, 1.50 to 1.70 percent of Ti, 1.00 to 1.15 percent of Nb, 0 to 0.016 percent of B, less than or equal to 1ppm of H, less than or equal to 20ppm of O, less than or equal to 50ppm of N and the balance of Ni and inevitable impurities. The preparation method comprises the following steps: smelting, pouring and annealing. When the isometric crystal Ni3Al-based alloy is subjected to thermal exposure at 1100 DEG C, a P phase rich in Ni, Cr, Mo and W elements is self-generated in situ near the crystal boundary of the alloy, and the isometric crystal Ni3Al-based alloy has an in-situ precipitation strengthening effect, so that the strength and high-temperature durability of the alloy are not reduced after the alloy is subjected to long-term thermal exposure at 1100 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of Ni-Al intermetallic compounds, specifically, it relates to an in-situ self-generated P phase reinforced equiaxed Ni3Al-based intermetallic compound alloy and its preparation method. Background Technology

[0002] Ni3Al is one of the Ni-Al intermetallic compound alloy systems that can be used as high-temperature structural materials. To date, commercially available equiaxed Ni3Al-based intermetallic compound alloys have not yet achieved the performance expected of these alloys, and significant industrial potential remains to be explored. This is mainly due to the grain boundary brittleness problem inherent in equiaxed Ni3Al-based intermetallic compound alloys—room-temperature hydrogen embrittlement and intermediate-temperature oxygen embrittlement at grain boundaries. The low ductility of this series of intermetallic compound alloys also poses a significant challenge to their widespread application as engineering materials. To overcome this challenge, researchers have employed a series of techniques, including alloying, single-crystal growth, and optimization. γ' Phase volume ratio and interfacial properties are used to enhance the plasticity and toughness of Ni3Al-based intermetallic compound alloys and improve their overall performance. Adding refractory elements such as Cr, Nb, Mo, and W as effective solid solution strengthening agents can not only improve the plasticity, toughness, and high-temperature mechanical properties of nickel-based superalloys, but also enhance the comprehensive mechanical properties of equiaxed Ni3Al-based intermetallic compound alloys. However, the presence of these elements may increase the risk of topologically close-packed (TCP) phase formation during high-temperature service. Traditionally, it is believed that TCP phases precipitate in nickel-based alloys during long-term high-temperature service or thermal exposure. Since TCP phase formation consumes a large amount of solid solution strengthening elements in the alloy, it negatively impacts the high-temperature performance of the alloy. Therefore, the formation of TCP phases should be avoided as much as possible during alloying design.

[0003] For equiaxed Ni3Al-based intermetallic compound alloys, especially those deviating from the stoichiometric ratio of intermetallic compounds, γ' With a high phase content, the alloy has good high-temperature strength and creep performance. However, since no effective grain boundary strengthening measures have been developed, especially when no rare and dispersed metal elements are added, the grain boundary strength is low. During the deformation process, the grains and grain boundaries are not coordinated, which leads to a significant decrease in the strength and toughness of the alloy after long-term high-temperature heat exposure. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide an in-situ self-generated P-phase reinforced equiaxed Ni3Al-based intermetallic compound alloy and its preparation method. During the heat exposure process at 1100℃, the alloy will precipitate a P-phase—a TCP phase—near the grain boundaries. The P-phase enhances the grain boundary strength, and after 2000h of heat exposure at 1100℃, it can still maintain excellent room temperature and high temperature strength, as well as good plasticity and toughness.

[0005] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide an in-situ self-generated P-phase reinforced equiaxed Ni3Al-based intermetallic compound alloy. The alloy is formed by melting, casting, and annealing. Its chemical composition, by mass percentage, is: C: 0.05%~0.20%, Al: 8.50%~9.50%, Cr: 4.50%~5.50%, Mo: 2.00%~2.50%, W: 3.00%~4.00%, Ti: 1.40%~1.90%, Nb: 0.50%~1.50%, B: ≤0.1%, H≤1ppm, O≤20ppm, N≤50ppm, with the balance being Ni and unavoidable impurities.

[0006] Further, by mass percentage, its chemical composition is: C: 0.10%~0.15%, Al: 8.7%~8.9%, Cr: 4.9%~5.1%, Mo: 2.05%~2.25%, W: 3.05%~3.25%, Ti: 1.50%~1.70%, Nb: 1.00%~1.15%, B: 0.01%~0.016%, H≤1ppm, O≤20ppm, N≤50ppm, with the balance being Ni and unavoidable impurities; Furthermore, the alloy has a room temperature tensile strength > 510 MPa, a high temperature tensile strength ≥ 100 MPa at 1100℃, and a creep rupture time ≥ 75 h at 1100℃ / 30 MPa.

[0007] Furthermore, during thermal exposure at 1100°C in an atmospheric furnace, a P phase rich in Ni, Cr, Mo, and W is spontaneously generated in situ near the alloy grain boundaries.

[0008] Furthermore, during the thermal exposure process of the alloy at 1100°C in an atmospheric furnace, the morphology of the P phase transitions from needle-like to plate-like, and finally stabilizes into a blocky shape with a length of 200nm-1200nm.

[0009] Furthermore, after being exposed to heat in an atmospheric furnace at 1100℃ for 2000h, the alloy exhibits a room temperature tensile strength >650MPa, a high-temperature tensile strength ≥120MPa at 1100℃, and a creep rupture time ≥75h at 1100℃ / 30MPa.

[0010] Another objective of this invention is to provide a method for preparing the above-mentioned in-situ self-generated P-phase reinforced equiaxed Ni3Al-based intermetallic compound alloy.

[0011] A method for preparing an in-situ self-generated P-phase reinforced equiaxed Ni3Al-based intermetallic compound alloy includes the following steps: S1: The vacuum induction melting furnace is used for melting and casting, and the vacuum degree is always kept <0.2pa; S2: After preheating to the opening period, raise the temperature of the alloy liquid to above 1480℃ and maintain it for no less than 2 minutes, and then pour it into an alloy ingot. S3: After the alloy ingot is poured, it is slowly cooled to above 1000℃, and then quickly transferred to an atmospheric furnace and held at 1000℃ for ≥24 hours, followed by furnace cooling.

[0012] Furthermore, the order in which the furnace charge is placed in the smelting furnace is as follows: all of the metal Al and metal Ni with the same atomic ratio are placed on top, other elemental metals are placed in the middle layer, and the remaining metal Ni is placed on the bottom layer.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Without adding rare and dispersed metal elements, this invention achieves a room temperature tensile strength > 510 MPa, a high temperature tensile strength ≥ 100 MPa at 1100℃, and a creep rupture time ≥ 75 h at 1100℃ / 30 MPa by rationally designing the content of Cr, Mo and W elements in the alloy.

[0014] The composition of this invention uses traditional vacuum melting and vacuum casting techniques to manufacture equiaxed Ni3Al-based intermetallic compound alloy castings. During the heat exposure process at 1100℃, a P phase rich in Ni, Cr, Mo and W elements is generated in situ near the alloy grain boundaries. After heat exposure in an atmospheric furnace at 1100℃ for 2000h, the room temperature tensile strength is >620MPa, the high temperature tensile strength at 1100℃ is ≥110 MPa, and the creep rupture time at 1100℃ / 30MPa is ≥75h.

[0015] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings.

[0016] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0017] Figure 1 The image shows the as-cast microstructure of the equiaxed Ni3Al-based intermetallic compound alloy prepared in Example 1 of this invention. (a) Metallographic image, with grain boundaries indicated by yellow arrows. (b) SEM microstructure image, the as-cast microstructure mainly includes the γ+γ′ phase and γ′ phase (γ′-matrix) within the dendrites, as well as the eutectic γ–γ′ between the dendrites. Figure 2 The images shown are scanning electron micrographs of the equiaxed Ni3Al-based intermetallic compound alloy prepared in Example 1 of this invention after thermal exposure at 1100℃ for different times: (a) 5h, (b) 10h, (c) 20h, (d) 50h, (e) 100h, (f) 200h, (g) 500h, (h) 1000h, (i) 2000h. In (a), (b), (e), (g), and (i), the insets are magnified images of the TCP precipitate phase. All TCP phases are marked with yellow arrows, and the EPMA analysis areas are marked with blue cross symbols with numbers. Figure 3 The figures show the as-cast and room-temperature and high-temperature engineering stress-strain curves of the equiaxed Ni3Al-based intermetallic compound alloy prepared in Example 1 of this invention, after heat exposure at 1100 ℃ and 2000 h, as well as the high-temperature creep rupture time-strain curves with different parameters. (a) Tensile stress-strain curve; (b) Creep rupture time-strain curves with experimental parameters of 1000 ℃ / 100 MPa, 1050 ℃ / 60 MPa, and 1100 ℃ / 30 MPa. Figure 4(a) shows the as-cast room temperature tensile fracture morphology of the equiaxed Ni3Al-based intermetallic compound alloy prepared in Example 1 of this invention. Figure 4(b) shows the room temperature tensile fracture morphology of the equiaxed Ni3Al-based intermetallic compound alloy prepared in Example 1 of this invention after heat exposure at 1100 ℃ for 2000 h. Figure 5 This is a schematic diagram of the nucleation and growth of the P phase and the evolution of the γ' matrix in the equiaxed Ni3Al-based intermetallic compound alloy of Example 1 of the present invention after heat exposure at 1100 °C. (a) Needle-shaped P phase in the γ channel after 10 h of heat exposure at 1100 °C, (b) Plate-shaped P phase in the γ' matrix and γ+γ' phase after 500 h of heat exposure at 1100 °C, (c) Blocky P phase at and near the grain boundary of the γ' matrix after 2000 h of heat exposure at 1100 °C. Detailed Implementation

[0018] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0019] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0020] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0021] In this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0022] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] Example 1: The in-situ self-generated P-phase reinforced equiaxed Ni3Al-based intermetallic compound alloy in this example is formulated with the following composition and mass percentages: C: 0.21%, Al: 8.95%, Co: 6.27%, Cr: 5.96%, Mo: 2.57%, W: 1.77%, Ti: 1.03%, Zr: 0.60%, Nb: 0.55%, B: 0.013%, with the balance being Ni and unavoidable impurity elements, including O: 0.0015%, N: 0.0007%, and H: 0.00005%. In the batching process, the loss mass of each element is added to the planned batch mass according to its burn-off rate. The burn-off rates for B are 0.25%wt, Al and Mo are 0.02%wt, Cr, Zr, W, and Co are 0.01%wt, C is 0.07%wt, and Ti is 0.1%wt. Elemental Ni, Al, C, Cr, Mo, W, Ti, and Nb with a purity of not less than 99.95% are selected as raw materials. The furnace charge must be thoroughly cleaned and dried before smelting, followed by dehydrogenation treatment to ensure the high quality of the prepared alloy.

[0024] The preparation is carried out using the following steps: The smelting equipment used was an industrial-grade three-chamber vacuum induction furnace, model ZG-005LB. The order of placement of the charge in the furnace was as follows: all metallic Al and metallic Ni with the same atomic ratio were placed on top; other elemental metals were placed in the middle layer; and the remaining metallic Ni was placed at the bottom. After preheating the alloy at 800℃ for 10 minutes to the opening stage, the temperature of the molten alloy was rapidly increased to above the liquidus line at a rate of 60℃ / s and maintained at 1500℃ to ensure the complete melting and uniformity of high-melting-point elements such as W and Nb. The refining time was 120 seconds. To minimize the residual amounts of gaseous elements such as H, O, and N, the vacuum degree was less than 1 Pa during the filling period and less than 0.2 Pa during the opening, refining, and casting periods. After refining, the molten alloy was stabilized at 1480℃ and cast within 20 seconds to obtain the alloy ingot. After casting, the alloy was cooled to above 1000℃ in the casting chamber at a rate of 0.3℃ / s. It was then removed from the casting chamber and quickly transferred to an atmospheric furnace. After being held at 1000℃ for 24 h in the atmospheric furnace, it was air-cooled to room temperature to obtain a Ni3Al-based intermetallic compound alloy with both strong plasticity and as-cast sample.

[0025] The as-cast microstructure of the equiaxed Ni3Al-based intermetallic compound alloy obtained in this embodiment is shown in the figure. Figure 1 .

[0026] Scanning electron micrographs of the equiaxed Ni3Al-based intermetallic alloy prepared in this embodiment after heat exposure at 1100℃ for different times are shown below. Figure 2TCP phase – P phase in its initial stage γ′ and γ As the heat exposure time increases, the precipitates at the phase interface change from needle-like to plate-like, and finally to block-like.

[0027] The stress-strain curves of the equiaxed Ni3Al-based intermetallic compound alloy prepared in this embodiment, both in the as-cast state and after 1100 ℃ / 2000 h heat exposure, at room temperature and high temperature, as well as the high-temperature creep rupture time-strain curves with different parameters, are shown in the figures below. Figure 3 Its mechanical properties are as follows: In this embodiment, the as-cast alloy has a room temperature tensile strength of 513 MPa and a tensile strength of 109 MPa at 1100℃.

[0028] The alloy obtained by the method in this embodiment has a room temperature tensile strength of 654 MPa and a 120 MPa tensile strength at 1100 °C after being exposed to heat for 1100 °C for 2000 h.

[0029] In this embodiment, the creep rupture time of the cast alloy at 1000℃ / 100MPa is 10.13h and the total strain is 12.61%; the creep rupture time at 1050℃ / 60MPa is 28.76h and the total strain is 40.37%; and the creep rupture time at 1100℃ / 30MPa is 76.87h and the total strain is 86.85%.

[0030] The alloy obtained by the method in this embodiment, after being exposed to heat at 1100 ℃ for 2000 h, exhibits the following characteristics: creep rupture time at 1000 ℃ for 100 MPa with a total strain of 15.58 h; creep rupture time at 1050 ℃ for 60 MPa with a total strain of 31.09 h; creep rupture time at 1100 ℃ for 30 MPa with a total strain of 78.70 h; and creep rupture time at 1100 ℃ for 30 MPa with a total strain of 50.44%. Figure 4 shows the tensile fracture morphology of the equiaxed Ni3Al-based alloy containing the P phase. It can be seen that there are obvious differences between the as-cast state and the fracture morphology after 1100 ℃ / 2000 h heat exposure. The tensile fracture morphology of the as-cast state has typical cleavage fracture characteristics, while the fracture after heat exposure has typical transgranular fracture characteristics, and the P phase distributed in the grain boundaries and grains can be seen.

[0031] Comparative Example 1: See references: Song Jinxia, ​​Xiao Chengbo, Li Shusuo, Han Yafang. Effects of long-term aging at 950℃ on the microstructure and mechanical properties of Ni3Al-based alloy IC6. Acta Metallurgica Sinica, 2002, (03): 250-254, and the High Temperature Materials Branch of the Chinese Society for Metals. Handbook of High Temperature Alloys in China (Volume 2), Beijing: China Quality Inspection Press, China Standards Press, 2012: 707-714. IC6 alloy is a directionally solidified Ni3Al-based alloy that can be used as a guide vane material for gas turbine engines operating in the range of 950℃-1100℃. The nominal alloy content by mass percentage is Ni-8.0Al-14.0Mo-0.04B. During the aging process at 950℃, the γ-NiMo phase precipitates. After aging for 500h, the high-temperature creep life of the alloy at 1100℃ / 90MPa decreases from more than 100h to 75h.

[0032] Comparative Example 2: See reference: Zhang H, Liang Y, Ru Y, et al. Effect of thermal exposure on the stress-rupture life and microstructure of a low Re-containing single crystal alloy[J]. Progress in Natural Science: Materials International, 2015, 25(01): 84-89. IC21 alloy is a new type of cast Ni3Al-based single crystal high-temperature structural material. After standard heat treatment, the alloy has a creep rupture time of 170.57h at 1100℃ / 137MPa. After aging at 1100℃ for 500h, the creep rupture time at 1100℃ / 137MPa is reduced to 48.27h.

[0033] Table 1 Figure 2 Electron probe microscopy analysis of TCP precipitates at midpoints 1 to 10 (at. %)

[0034] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. An in-situ self-generated P-phase reinforced equiaxed Ni3Al-based intermetallic compound alloy, characterized in that, The alloy, by mass percentage, is formed by melting, casting, and annealing the following components: C: 0.10%~0.15%, Al: 8.7%~8.9%, Cr: 4.9%~5.1%, Mo: 2.05%~2.25%, W: 3.05%~3.25%, Ti: 1.50%~1.70%, Nb: 1.00%~1.15%, B: 0~0.016%, H≤1ppm, O≤20ppm, N≤50ppm, with the balance being Ni and unavoidable impurities.

2. The alloy according to claim 1, characterized in that, The components, by mass percentage, are: C: 0.10%~0.15%, Al: 8.7%~8.9%, Cr: 4.9%~5.1%, Mo: 2.05%~2.25%, W: 3.05%~3.25%, Ti: 1.50%~1.70%, Nb: 1.00%~1.15%, B: 0.01%~0.016%, H≤1ppm, O≤20ppm, N≤50ppm, with the balance being Ni and unavoidable impurities.

3. The alloy according to claim 1, characterized in that, The composition by mass percentage is as follows: C: 0.21%, Al: 8.95%, Co: 6.27%, Cr: 5.96%, Mo: 2.57%, W: 1.77%, Ti: 1.03%, Zr: 0.60%, Nb: 0.55%, B: 0.013%, with the balance being Ni and unavoidable impurity elements.

4. The alloy according to claim 1, 2 or 3, characterized in that, The impurity elements include O, N, and H.

5. The alloy according to claim 1, 2 or 3, characterized in that, Tensile strength at room temperature > 510 MPa, tensile strength at 1100℃ ≥ 100 MPa, and creep rupture time at 1100℃ / 30 MPa ≥ 75 h.

6. The alloy according to claim 1, 2 or 3, characterized in that, During the heat exposure process at 1100℃, the alloy spontaneously generates a P phase rich in Ni, Cr, Mo and W near the grain boundaries.

7. The alloy according to claim 1, 2 or 3, characterized in that, During the heat exposure process at 1100℃, the morphology of the P phase in the alloy transitions from needle-like to plate-like, and finally stabilizes into a blocky shape with a length of 200nm-1200nm.

8. The alloy according to claim 1, characterized in that, After being exposed to heat in an atmospheric furnace at 1100℃ for 2000h, the tensile strength at room temperature is >620MPa, the tensile strength at 1100℃ is ≥110 MPa, and the time to breakage at 1100℃ / 30MPa is ≥75h.

9. A method for preparing the alloy according to any one of claims 1-6, characterized in that, The method described: S1: The vacuum induction melting furnace is used for melting and casting, and the vacuum degree is always kept <0.2pa; S2: After preheating to the opening period, raise the temperature of the alloy liquid to above 1480℃ and maintain it for no less than 2 minutes, and then pour it into an alloy ingot. S3: Then slowly cool to above 1000℃, then quickly transfer to an atmospheric furnace and hold at 1000℃ for ≥24h, followed by furnace cooling.

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