Ni3Al-based single crystal alloy and preparation method and application thereof

Abstract

This invention provides a Ni3Al-based single-crystal alloy, its preparation method, and its applications, belonging to the field of alloy technology. The Ni3Al-based single-crystal alloy provided by this invention, by mass percentage, comprises Re 1.2–2.8%, Ru 0–2.2%, Mo 5–9%, Al 4–8%, Ta 1–5%, Cr 1–4%, B 0.002–0.005%, with the balance being Ni. This invention controls the amounts of Mo, Re, Al, Ta, Cr, and B within the above-mentioned ranges, achieving a synergistic effect that reduces the density of the Ni3Al-based single-crystal alloy, resulting in a lightweight Ni3Al-based single-crystal alloy with lower cost, good microstructural stability, and excellent high-temperature performance, capable of meeting the ultra-high temperature (1200℃) requirements of future advanced aero-engines.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy, in particular to a Ni3Al-based single crystal alloy and a preparation method and application thereof. BACKGROUND

[0002] High-temperature alloy has good high-temperature strength, oxidation resistance and corrosion resistance, and excellent machining performance, and is widely used in key hot end components of an aero-engine, such as a combustion chamber, a turbine disc, a turbine blade and the like. According to statistics, the use amount of high-temperature alloy in an aero-engine accounts for 40-60%. At present, the aero-engine with a thrust-to-weight ratio of 8-10 levels, the turbine inlet temperature is 1500-1800K, and the temperature bearing capacity of the turbine blade made of Ni-based single crystal high-temperature alloy is 1050-1100℃, the use temperature has reached 80-90% of the melting point of the alloy, which is close to the limit of the temperature bearing capacity of the Ni-based high-temperature alloy.

[0003] With the thrust-to-weight ratio of advanced aero-engines reaching 10-15, the turbine inlet temperature approaches 2000K, and the use temperature of the high-temperature structural material for the turbine blade needs to reach 1150℃, or even 1200℃. The traditional Ni-based high-temperature alloy cannot meet the use requirements of key hot end components of future advanced aero-engines. The intermetallic compound Ni3Al has excellent high-temperature performance, specific strength and specific stiffness, its melting point is 1390℃, the density is 7.5g / cm 3 , the Young's modulus is 178.7GPa, and with the increase of temperature, Ni3Al has an abnormal temperature yield relationship, that is, with the increase of temperature, the yield strength of the alloy also gradually increases. Ni3Al has been widely concerned by domestic and foreign material scholars due to its excellent high-temperature characteristics, and a series of Ni3Al-based alloys have been developed for use as hot end key components of advanced aero-space engines, such as turbine guide vane blades or working blade materials.

[0004] The alloying of single-crystal alloys has undergone decades of development, and currently, the common practice is to improve the creep resistance of alloys by adding large amounts of refractory metal elements such as W, Ta, Re, and Ru. Among them, solid solution strengthening elements, represented by Re, significantly improve the creep life of single-crystal alloys. Second-generation and third-generation single-crystal alloys, represented by CMSX-4, N5, PWA1484, CMSX-10, N6, and TMS-80, have Re contents as high as 3wt.% and 6wt.%, respectively, which not only increases the cost of the alloys but also greatly increases their density. In addition, existing low-generation single-crystal alloys are used at temperatures below 1100℃. When second-generation and third-generation single-crystal alloys, represented by CMSX-4 and N6, are used for long-term service above 1100℃, the γ′ phase exhibits low high-temperature thermal stability, severe coarsening and merging of the γ and γ′ phases, and significant microstructural degradation. In high-generation single-crystal alloys, such as MC-NG, more Re was introduced to increase the service temperature to 1150℃. However, this significantly promoted the precipitation of the TCP phase and reduced the microstructure stability of the alloy. Therefore, high-generation single-crystal alloys have attempted to suppress the precipitation of the TCP phase by adding Ru to change the solute partition coefficient of the TCP phase-forming element in the two phases (γ phase and γ′ phase), but the effect has not been significant so far. Summary of the Invention

[0005] The purpose of this invention is to provide a Ni3Al-based single crystal alloy, its preparation method, and its application. The Ni3Al-based single crystal alloy provided by this invention is a low-cost, low-density, and high-temperature-resistant alloy.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a Ni3Al-based single-crystal alloy, comprising, by mass percentage: Re 1.2–2.8%, Ru 0–2.2%, Mo 5–9%, Al 4–8%, Ta 1–5%, Cr 1–4%, B 0.002–0.005%, with the balance being Ni.

[0008] Preferably, it comprises Re 1.9–2.1%, Ru 1.5–1.9%, Mo 5.8–7.9%, Al 6–7.5%, Ta 2.5–3.8%, Cr 2–3%, B 0.003–0.004%, with the balance being Ni.

[0009] Preferably, the Ni3Al-based single crystal alloy includes a Ni3Al phase; at room temperature, the volume percentage of the Ni3Al phase in the Ni3Al-based single crystal alloy is ≥75%; at service temperature, the volume percentage of the Ni3Al phase in the Ni3Al-based single crystal alloy is ≥65%.

[0010] This invention provides a method for preparing the Ni3Al-based single-crystal alloy described above, comprising the following steps:

[0011] Single crystal rods were prepared according to the elemental composition of the Ni3Al-based single crystal alloy.

[0012] The single crystal rod was subjected to solution treatment and aging treatment in sequence to obtain the Ni3Al-based single crystal alloy.

[0013] Preferably, the solution treatment temperature is 1300–1345°C, and the solution treatment time is 16–30 h.

[0014] Preferably, the solution treatment is any one of (1) to (3):

[0015] (1) Hold at 1300℃ for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 8 hours, raise the temperature to 1335℃ and hold for 4 to 12 hours;

[0016] (2) Hold at 1300℃ for 2 hours, raise the temperature to 1305℃ and hold for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 4 hours, raise the temperature to 1335℃ and hold for 2-10 hours, raise the temperature to 1340℃ and hold for 2-4 hours;

[0017] (3) Keep warm at 1305℃ for 2 hours, raise the temperature to 1310℃ and keep warm for 2 hours, raise the temperature to 1315℃ and keep warm for 2 hours, raise the temperature to 1320℃ and keep warm for 2 hours, raise the temperature to 1325℃ and keep warm for 2 hours, raise the temperature to 1330℃ and keep warm for 2 hours, raise the temperature to 1335℃ and keep warm for 4 hours, raise the temperature to 1340℃ and keep warm for 2 to 10 hours, raise the temperature to 1345℃ and keep warm for 2 to 4 hours.

[0018] Preferably, the aging treatment temperature is 850–1060°C, and the aging treatment time is 32–42 hours.

[0019] Preferably, the aging treatment includes sequential high-temperature aging treatment and low-temperature aging treatment; the high-temperature aging treatment is performed at a temperature of 1020–1060°C for a holding time of 1.5–2.5 h; the low-temperature aging treatment is performed at a temperature of 850–890°C for a holding time of 31–33 h.

[0020] Preferably, the single crystal rod is prepared by the seed crystal method.

[0021] This invention provides the application of the Ni3Al-based single crystal alloy described in the above technical solution or the Ni3Al-based single crystal alloy prepared by the preparation method described in the above technical solution in aero engines.

[0022] This invention provides a Ni3Al-based single-crystal alloy, comprising, by mass percentage: Re 1.2–2.8%, Ru 0–2.2%, Mo 5–9%, Al 4–8%, Ta 1–5%, Cr 1–4%, B 0.002–0.005%, with the balance being Ni. By controlling the amounts of Mo, Re, Al, Ta, Cr, and B within the aforementioned ranges, this invention achieves a synergistic effect, reducing the density of the Ni3Al-based single-crystal alloy. This results in a lightweight Ni3Al-based single-crystal alloy with lower cost, better microstructural stability, and excellent high-temperature performance, meeting the ultra-high temperature requirements of future advanced aero-engines at 1200℃.

[0023] This invention provides a method for preparing the Ni3Al-based single-crystal alloy, comprising the following steps: preparing a single-crystal rod according to the elemental composition of the Ni3Al-based single-crystal alloy; subjecting the single-crystal rod to solution treatment and aging treatment sequentially to obtain the Ni3Al-based single-crystal alloy. The method provided by this invention is simple to operate, and the prepared Ni3Al-based single-crystal alloy exhibits good microstructural stability and excellent high-temperature performance.

[0024] Furthermore, the present invention performs solid solution treatment on single crystal rods under specific conditions, which can effectively control the microstructure of Ni3Al-based single crystal alloys and greatly improve the solid solution effect and solid solution efficiency.

[0025] Furthermore, the present invention performs aging treatment under specific conditions, which helps to ensure that the size of the strengthening phase γ′ of the final Ni3Al-based single crystal alloy is appropriate and the cubicity is good. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the heat treatment process used in this invention.

[0027] Figure 2 This is a physical image of the orientation single crystal rod

[001] in an embodiment of the present invention;

[0028] Figure 3 The above is a DSC temperature rise curve in an embodiment of the present invention;

[0029] Figure 4 This is a test diagram of the initial melting test in an embodiment of the present invention;

[0030] Figure 5 These are SEM images of the solution-treated alloys obtained after solution treatment in Examples 1-4 of this invention;

[0031] Figure 6 These are the EDS line scan spectra of the solution-treated alloys obtained after solution treatment in Examples 1 to 4 of this invention;

[0032] Figure 7 The image shows a SEM image of the Ni3Al-based single-crystal alloy prepared in Example 3.

[0033] Figure 8 SEM images of the Ni3Al-based single crystal alloy prepared in Example 3 after being kept at 1200℃ for 250h, 500h, 800h, and 1000h, respectively.

[0034] Figure 9 This is a SEM image of the second-generation nickel-based single-crystal superalloy DD5 after being held at 1100℃ for 500h. Detailed Implementation

[0035] This invention provides a Ni3Al-based single-crystal alloy, comprising, by mass percentage: Re 1.2–2.8%, Ru 0–2.2%, Mo 5–9%, Al 4–8%, Ta 1–5%, Cr 1–4%, B 0.002–0.005%, with the balance being Ni.

[0036] In this invention, unless otherwise specified, the elemental composition of the Ni3Al-based single crystal alloy refers to the nominal composition.

[0037] The Ni3Al-based single-crystal alloy provided by this invention, by mass percentage, comprises 1.2–2.8% Re, preferably 1.5–2.5%, more preferably 1.7–2.3%, further preferably 1.9–2.1%, and even more preferably 2%. In this invention, Re is mainly a γ-phase forming element, which can significantly improve the initial melting temperature and creep properties of the alloy. However, excessive Re can easily lead to the precipitation of the TCP phase during service. This invention limits the Re element to the above-mentioned range, which is beneficial for balancing the high temperature resistance and microstructure stability of the alloy.

[0038] The Ni3Al-based single-crystal alloy provided by this invention, by mass percentage, comprises Ru 0-2.2%, preferably 1.0-2.1%, more preferably 1.3-2.0%, further preferably 1.5-1.9%, and even more preferably 1.8%. In this invention, Ru is mainly a γ-phase forming element, which can significantly improve the stability of the alloy structure; limiting the Ru element to the above range in this invention is beneficial to balancing the high temperature resistance and structural stability of the alloy.

[0039] The Ni3Al-based single-crystal alloy provided by this invention, by mass percentage, comprises 5-9% Mo, preferably 5.5-8.1%, more preferably 5.8-7.9%, and even more preferably 6-7%. In this invention, Mo enrichment in the matrix phase can expand the negative lattice mismatch of the γ / γ' microstructure and promote the formation of a dense dislocation network during high-temperature creep, thus improving creep performance. Furthermore, the addition of Mo has a positive impact on the distribution behavior of other alloying elements. For example, due to the influence of Mo, the enrichment of Cr and Re elements in the γ matrix will increase the lattice constant of the γ phase, thereby further improving the negative lattice mismatch. Moreover, the coarsening rate of the γ' phase decreases with increasing Mo content; therefore, the addition of Mo can, to some extent, suppress the coarsening of γ' precipitates. Simultaneously, Mo can suppress the formation of secondary reaction zones (SRZs), and the high-Mo strengthened Ni3Al-based single-crystal high-temperature alloy combines the advantages of low density and high temperature resistance.

[0040] The Ni3Al-based single-crystal alloy provided by this invention, by mass percentage, comprises 4-8% Al, preferably 5-7.7%, more preferably 6-7.5%, and even more preferably 6.5-7%. The Ni3Al-based single-crystal alloy of this invention preferably includes the Ni3Al phase; at room temperature, the volume percentage of the Ni3Al phase in the Ni3Al-based single-crystal alloy is preferably ≥75%, more preferably 77-82%; at service temperature, the volume percentage of the Ni3Al phase in the Ni3Al-based single-crystal alloy is preferably ≥65%, more preferably 70-75%. By controlling the Al element within the above range, this invention satisfies the requirement that the volume percentage of the Ni3Al phase is within the above range under both room temperature and service temperature conditions, thereby contributing to the excellent creep resistance of the Ni3Al-based single-crystal alloy.

[0041] The Ni3Al-based single-crystal alloy provided by this invention, by mass percentage, comprises 1-5% Ta, preferably 1.2-4.2%, more preferably 2.5-3.8%, and even more preferably 3.5%. In this invention, Ta strengthens the alloy through solid solution strengthening and increases the strength of γ' particles, and it also suppresses the formation of freckle defects during casting. However, increasing the Ta content increases the supersaturation and distribution ratio of alloying elements such as Re and Mo in the γ matrix, and it also promotes the precipitation of the TCP phase. This invention controls the Ta content within the above-mentioned range, which is beneficial for balancing the strength and microstructure stability of the alloy.

[0042] The Ni3Al-based single-crystal alloy provided by this invention comprises 1-4% Cr, preferably 1.2-3.5%, more preferably 2-3%, further preferably 2.3-2.7%, and even more preferably 2.5% by mass percentage. In this invention, the role of Cr is to enrich it in the γ matrix, thereby improving the alloy's resistance to oxidation and hot corrosion, and also to provide solid solution strengthening.

[0043] The Ni3Al-based single-crystal alloy provided by this invention comprises 0.002–0.005% B by mass, preferably 0.003–0.004%. In this invention, the role of element B is to enrich at grain boundaries, increasing the bonding force of grain boundaries; moreover, element B can form borides with alloying elements, which are distributed in granular or blocky form at grain boundaries, preventing grain boundary slip and inhibiting the connection and expansion of grain boundary voids; at the same time, it can eliminate the precipitation of harmful phases at grain boundaries and reduce the content of harmful elements at grain boundaries.

[0044] The Ni3Al-based single crystal alloy provided by this invention comprises the balance Ni by weight percentage.

[0045] The crystal orientation of the Ni3Al-based single crystal alloy described in this invention is specifically

[001] orientation.

[0046] This invention controls the amounts of Mo, Re, Ru, Al, Ta, Cr, and B within the aforementioned ranges. Through synergistic effects, the density of the Ni3Al-based single-crystal alloy is reduced, resulting in a lightweight Ni3Al-based single-crystal alloy with lower cost, better microstructural stability, and excellent high-temperature performance. This meets the ultra-high temperature requirements of 1200℃ for key hot-end components of future advanced aero-engines (such as high-temperature turbine blades). Typically, elements such as Al, Ti, Ta, and Nb determine the volume fraction of the γ' phase. However, Nb is detrimental to the alloy's oxidation and hot corrosion properties, while Ti negatively impacts the alloy's oxidation resistance, casting performance, and reaction during solution heat treatment. This invention, by not adding Nb and Ti and controlling the amounts of Mo, Re, Ru, Al, Ta, Cr, and B within the aforementioned ranges, yields a Ni3Al-based single-crystal alloy with excellent high-temperature performance.

[0047] This invention provides a method for preparing the Ni3Al-based single-crystal alloy described above, comprising the following steps:

[0048] Single crystal rods were prepared according to the elemental composition of the Ni3Al-based single crystal alloy.

[0049] The single crystal rod was subjected to solution treatment and aging treatment in sequence to obtain the Ni3Al-based single crystal alloy.

[0050] This invention prepares single crystal rods according to the elemental composition of the Ni3Al-based single crystal alloy. Preferably, this invention prepares a master alloy ingot according to the elemental composition of the Ni3Al-based single crystal alloy, and then uses the master alloy ingot to prepare single crystal rods. This invention does not have a specific limitation on the preparation method of the master alloy ingot; any method well-known to those skilled in the art can be used. In an embodiment of this invention, the master alloy ingot is specifically prepared using a vacuum induction melting method. Preferably, this invention uses a seed crystal method to prepare the single crystal rod; the single crystal rod is specifically a

[001] oriented single crystal rod. In an embodiment of this invention, the master alloy ingot is processed into an alloy ingot of the required size for preparing the single crystal rod. A

[001] oriented seed crystal is placed at the bottom of the film shell. The alloy ingot is then subjected to sandblasting and grinding treatments before being remelted in a single crystal furnace. The working (casting) temperature of the single crystal furnace is set to 1550±10℃, and the crystal pulling rate is set to 4±1mm / min. After casting is completed and the casting has completely cooled, the film shell is broken to obtain the single crystal rod.

[0051] After obtaining the single crystal rod, the present invention sequentially performs solution treatment and aging treatment on the single crystal rod to obtain the Ni3Al-based single crystal alloy. The present invention preferably follows... Figure 1 The process shown is a heat treatment (i.e., solution treatment and aging treatment) process. The solution treatment and aging treatment are described in detail below.

[0052] To meet the high-temperature service requirements, existing single-crystal alloys used in key hot-end components of aero-engines typically incorporate a significant amount of refractory elements, which poses a challenge to the solid solution effect and efficiency of single-crystal alloys. For example, the third-generation single-crystal superalloy CMSX-10, in pursuit of microstructure and compositional homogeneity, requires a total solid solution time of 45 hours, resulting in low solid solution efficiency. Even the fourth-generation single-crystal superalloy, represented by DD476, exhibits significant compositional segregation after solid solution treatment. With increasingly higher turbine inlet temperatures in advanced aero-engines and the adoption of complex double-walled turbine blade structures, the casting performance of single-crystal alloys faces considerable challenges. Research indicates that adding appropriate amounts of trace elements C, B, and Hf can effectively improve the casting performance of single-crystal alloys; however, during casting solidification, trace elements often form low-melting-point eutectic phases with other elements, lowering the initial melting temperature of the alloy. This significantly increases the difficulty and efficiency of microstructure control in highly alloyed single-crystal alloys. In the embodiments of this invention, the solidus temperature (T0) of the Ni3Al-based single-crystal alloy is specifically obtained based on DSC test curves. S ), liquidus temperature (T) L ) and the complete resolution temperature of the γ′ phase (T γ′sol The peak temperature of the DSC heating curve (T) 峰The solidification characteristic temperature, combined with metallographic method, water quenching method and exploration law of alloy initial melting temperature, is used to obtain the initial melting temperature of Ni3Al-based single crystal alloy. Then, the solution treatment regime is determined according to the solidification characteristic temperature and the initial melting temperature. In this invention, the solution treatment temperature is preferably 1300-1345℃, and the solution treatment time is preferably 16-30h. The solution treatment regime provided by this invention has high solution efficiency and good solution effect. Further, the solution treatment of this invention is preferably any one of (1) to (3):

[0053] (1) Hold at 1300℃ for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 8 hours, raise the temperature to 1335℃ and hold for 4 to 12 hours (preferably 6 to 10 hours);

[0054] (2) Hold at 1300℃ for 2 hours, raise the temperature to 1305℃ and hold for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 4 hours, raise the temperature to 1335℃ and hold for 2-10 hours, raise the temperature to 1340℃ and hold for 2-4 hours;

[0055] (3) Keep warm at 1305℃ for 2 hours, raise the temperature to 1310℃ and keep warm for 2 hours, raise the temperature to 1315℃ and keep warm for 2 hours, raise the temperature to 1320℃ and keep warm for 2 hours, raise the temperature to 1325℃ and keep warm for 2 hours, raise the temperature to 1330℃ and keep warm for 2 hours, raise the temperature to 1335℃ and keep warm for 4 hours, raise the temperature to 1340℃ and keep warm for 2 to 10 hours, raise the temperature to 1345℃ and keep warm for 2 to 4 hours.

[0056] The present invention preferably employs the above-mentioned stepwise solution treatment process, which effectively dissolves the primary bulk γ' phase, increases the initial melting temperature of the alloy, and is beneficial to improving the morphology and size of the γ' phase, thereby achieving homogenization of elements and structure.

[0057] After the solution treatment, the alloy obtained by the solution treatment is preferably cooled to room temperature before aging treatment; the cooling method is preferably air cooling. Currently, cooling methods with cooling rates from low to high are generally divided into air cooling, wind cooling, oil cooling, and water cooling. Among them, air cooling has a low cooling rate, resulting in a large γ′ phase precipitation size in the alloy, which affects the mechanical properties of the alloy. Oil cooling and water cooling have excessively high cooling rates, which can easily generate residual stress inside the alloy, thereby promoting the precipitation of TCP phase. Therefore, the present invention preferably uses air cooling. In the present invention, the temperature of the aging treatment is preferably 850-1060℃, and the aging treatment time is preferably 32-42 hours. In the present invention, the aging treatment preferably includes sequential high-temperature aging treatment and low-temperature aging treatment. In this invention, the temperature of the high-temperature aging treatment is preferably 1020–1060°C, more preferably 1030–1050°C, and even more preferably 1040°C; the holding time is preferably 1.5–2.5 h, more preferably 2 h; after the high-temperature aging treatment, the alloy obtained after the high-temperature aging treatment is preferably cooled to room temperature, and then subjected to low-temperature aging treatment; the cooling method is preferably air cooling. In this invention, the temperature of the low-temperature aging treatment is preferably 850–890°C, more preferably 860–880°C, and even more preferably 870°C; the holding time is preferably 31–33 h, more preferably 32 h. After the low-temperature aging treatment, the alloy obtained after the low-temperature aging treatment is preferably cooled to room temperature, and the cooling method is preferably air cooling. This invention preferably adopts a step-by-step aging treatment, wherein the holding time of the high-temperature aging treatment is relatively short, the purpose of which is to adjust the size of the precipitated γ′ phase, and the holding time of the low-temperature aging treatment is relatively long, the process of adjusting the cubicity of the precipitated γ′ phase. The present invention preferably performs aging treatment under the above conditions, and the final Ni3Al-based single crystal alloy has a suitable size of strengthening phase γ′ and good cubicity.

[0058] The heat treatment process provided by this invention can dissolve more than 99% of the eutectic and as-cast γ' phases, precipitate fine cubic γ' phases that are uniformly distributed and regularly arranged, and achieve an ideal uniform distribution of alloy composition, which is beneficial to the stability of the alloy structure and the maximization of the strengthening effect of Re.

[0059] This invention provides the application of the Ni3Al-based single-crystal alloy described in the above-described technical solution or the Ni3Al-based single-crystal alloy prepared by the above-described preparation method in aero-engines. Specifically, the Ni3Al-based single-crystal alloy provided by this invention can be used in key hot-end components of aero-engines, such as combustion chambers, turbine disks, or turbine blades.

[0060] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0061] The technical terms and related explanations involved in this invention are as follows:

[0062] Ni3Al-based single crystal alloy: a single crystal alloy with

[001] crystal orientation based on γ′-Ni3Al, whose γ′ phase volume fraction is usually as high as 70-80%.

[0063] Solution treatment: The alloy is heated to above the remelting temperature of the γ′ phase and the as-cast segregated phase, so that the γ′ phase and the as-cast segregated phase can be fully dissolved into the Ni solid solution. The mixture is held at the temperature for a long time to allow diffusion, and then rapidly cooled to eliminate dendritic segregation and achieve element homogenization; it also dissolves the coarse primary γ′ phase, γ / γ′ eutectic phase and segregated phases from the casting process, thereby increasing the initial melting temperature of the alloy.

[0064] γ phase: γ-Ni phase, FCC structure, usually Mo, Re, Ru, Cr, etc. replace some Ni atoms to achieve solid solution strengthening effect, and is the main toughening phase in Ni3Al-based single crystal alloys;

[0065] γ′ phase: γ′-Ni3Al phase, with Al and Ta as its main forming elements, L12 structure, is the main strengthening phase in Ni3Al-based single crystal alloys, which hinders dislocation movement;

[0066] TCP phase: Topologically Close-Packed (TCP) phase, usually a harmful phase in single-crystal alloys. During long-term service at ultra-high temperature, atoms such as Mo, Re, and Cr precipitate in the γ phase in a supersaturated manner, which reduces the solid solution strengthening effect of the alloy. Moreover, the long needle-shaped TCP phase is prone to stress concentration, which accelerates the failure of the alloy.

[0067] The elemental compositions of the Ni3Al-based single crystal alloys in Examples 1-4 and the second-generation nickel-based single crystal high-temperature alloy DD5 in the prior art are shown in Table 1.

[0068] Table 1. Elemental composition (wt%) of Ni3Al-based single crystal alloys and alloy DD5 in Examples 1-4.

[0069] Alloy class Re Ru Mo Al Ta Cr Co W Hf B Ni Examples 1-4 2 1.8 6 7 3.5 2.5 0 0 0 0.004 Bal. Alloy DD5 3 0 1.5 6.2 6.5 7 7.5 5 0.15 0 Bal.

[0070] In the following examples and test cases, the heat treatment and heat exposure tests were all carried out in a tube furnace. The samples after the heat treatment and heat exposure tests were all cooled by air cooling. Before the heat treatment and heat exposure tests, the tube furnace was calibrated with thermocouples and the temperature of the tube furnace was measured to obtain the uniform temperature zone of the tube furnace, so as to ensure that the samples were heated evenly during the heat treatment and heat exposure tests.

[0071] Examples 1-4

[0072] According to the elemental composition in Table 1, a master alloy ingot was prepared by vacuum induction melting. The master alloy ingot was then processed into an alloy ingot of the required size for preparing a single crystal rod. A Ni3Al-based single crystal alloy

[001] oriented single crystal rod was prepared using the seed crystal method. Specifically, the

[001] oriented seed crystal was placed at the bottom of the film shell. The alloy ingot was then subjected to sandblasting and grinding treatments before being remelted in a single crystal furnace. The working (casting) temperature of the single crystal furnace was set to 1550±10℃, and the crystal pulling rate was set to 4±1mm / min. After casting was completed and the casting had completely cooled, the film shell was broken to obtain a single crystal rod with a size of Φ15×160mm (e.g., Figure 2 (as shown);

[0073] The single crystal rod was subjected to solution treatment (specific conditions are shown in Table 2), and then air-cooled to room temperature to obtain a solution-treated alloy; the solution-treated alloy was held at 1040℃ for 2 hours and then air-cooled to room temperature; then held at 870℃ for 32 hours and then air-cooled to room temperature to obtain a Ni3Al-based single crystal alloy.

[0074] Table 2 shows the specific conditions for solution treatment in Examples 1-4.

[0075]

[0076] In Examples 1-4, the single crystal rod was specifically subjected to DSC testing (DSC heating curves are shown in Figure 1-4). Figure 3 (as shown) and initial melting test (as shown) Figure 4 As shown in the figure, the solidification characteristic temperature and initial melting temperature of Ni3Al-based single crystal alloy were obtained, and the specific conditions for solution treatment were determined based on these conditions.

[0077] Figure 5 The images show SEM images of the solution-treated alloys obtained after solution treatment in Examples 1-4. The results show that, compared with those before solution treatment (i.e., Figure 4 In contrast, after solution treatment, the γ′ phase in the alloy microstructure is uniformly distributed in a cubic shape, and there is almost no element segregation in different regions of the alloy.

[0078] Figure 6 The EDS line scan spectra of the solution-treated alloys obtained after solution treatment in Examples 1 to 4 are shown. The results show that the alloy elements are relatively uniformly distributed after solution treatment, and the specific conditions of solution treatment in Example 3 are the best.

[0079] Figure 7 The image shows a SEM image of the Ni3Al-based single crystal alloy prepared in Example 3. The results show that the strengthening phase γ′ of the Ni3Al-based single crystal alloy obtained after aging treatment has a suitable size and good cubicity.

[0080] Figure 8 The images show SEM images of the Ni3Al-based single crystal alloy prepared in Example 3 after being held at 1200℃ for 250h, 500h, 800h, and 1000h, respectively. Figure 9 The image shows a SEM image of the second-generation nickel-based single-crystal superalloy DD5 after being heated at 1100℃ for 500 hours. The results show that the Ni3Al-based single-crystal alloy in this invention maintains a good microstructure after heat exposure at 1200℃ for different durations, with no TCP phase precipitation and no obvious raft structure formed by the γ′ phase, nor any topological inversion structure, demonstrating good microstructural stability. In contrast, the γ′ phase in the existing second-generation nickel-based single-crystal superalloy DD5 shows significant coarsening and rafting after only 500 hours of heat exposure at 1100℃, resulting in poor microstructural stability.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Ni3Al-based single-crystal alloy, specifically comprising, by mass percentage: Re 2%, Ru 1.8%, Mo 6%, Al 7%, Ta 3.5%, Cr 2.5%, B 0.004%, with the balance being Ni; The preparation method of the Ni3Al-based single crystal alloy includes the following steps: Single crystal rods were prepared according to the elemental composition of the Ni3Al-based single crystal alloy. The single crystal rod was subjected to solution treatment and aging treatment in sequence to obtain the Ni3Al-based single crystal alloy. The solution treatment is any one of (1) to (3): (1) Hold at 1300℃ for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 8 hours, raise the temperature to 1335℃ and hold for 4~12 hours; (2) Hold at 1300℃ for 2 hours, raise the temperature to 1305℃ and hold for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 4 hours, raise the temperature to 1335℃ and hold for 2~10 hours, raise the temperature to 1340℃ and hold for 2~4 hours; (3) Hold at 1305℃ for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 2 hours, raise the temperature to 1335℃ and hold for 4 hours, raise the temperature to 1340℃ and hold for 2~10 hours, raise the temperature to 1345℃ and hold for 2~4 hours; The aging process includes sequential high-temperature aging and low-temperature aging; the high-temperature aging process is performed at a temperature of 1020~1060℃ and a holding time of 1.5~2.5h; the low-temperature aging process is performed at a temperature of 850~890℃ and a holding time of 31~33h.

2. The Ni3Al-based single-crystal alloy according to claim 1, characterized in that, The Ni3Al-based single crystal alloy includes a Ni3Al phase; at room temperature, the volume percentage of the Ni3Al phase in the Ni3Al-based single crystal alloy is ≥75%; at service temperature, the volume percentage of the Ni3Al phase in the Ni3Al-based single crystal alloy is ≥65%.

3. The method for preparing the Ni3Al-based single-crystal alloy according to claim 1 or 2, comprising the following steps: Single crystal rods were prepared according to the elemental composition of the Ni3Al-based single crystal alloy. The single crystal rod was subjected to solution treatment and aging treatment in sequence to obtain the Ni3Al-based single crystal alloy. The solution treatment is any one of (1) to (3): (1) Hold at 1300℃ for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 8 hours, raise the temperature to 1335℃ and hold for 4~12 hours; (2) Hold at 1300℃ for 2 hours, raise the temperature to 1305℃ and hold for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 4 hours, raise the temperature to 1335℃ and hold for 2~10 hours, raise the temperature to 1340℃ and hold for 2~4 hours; (3) Hold at 1305℃ for 2 hours, raise the temperature to 1310℃ and hold for 2 hours, raise the temperature to 1315℃ and hold for 2 hours, raise the temperature to 1320℃ and hold for 2 hours, raise the temperature to 1325℃ and hold for 2 hours, raise the temperature to 1330℃ and hold for 2 hours, raise the temperature to 1335℃ and hold for 4 hours, raise the temperature to 1340℃ and hold for 2~10 hours, raise the temperature to 1345℃ and hold for 2~4 hours; The aging process includes sequential high-temperature aging and low-temperature aging; the high-temperature aging process is performed at a temperature of 1020~1060℃ and a holding time of 1.5~2.5h; the low-temperature aging process is performed at a temperature of 850~890℃ and a holding time of 31~33h.

4. The preparation method according to claim 3, characterized in that, The single crystal rod is prepared by the seed crystal method.

5. The application of the Ni3Al-based single crystal alloy according to claim 1 or 2 or the Ni3Al-based single crystal alloy prepared by the preparation method according to claim 3 or 4 in aero-engines or gas turbines.

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