A boron microalloyed fourth generation nickel-based single crystal superalloy and a preparation method and application thereof

Abstract

The application discloses a boron micro-alloyed fourth-generation nickel-based single crystal high-temperature alloy and a preparation method and application thereof, and the composition is as follows in percentage by mass: 5.5%-6.5% of Al, 12%-14% of Co, 5.5%-6.5% of W, 3.5%-4.5% of Cr, 7.5%-8.5% of Ta, 5-6% of Re, 2.5-3.5% of Ru, 0.1-0.2% of Hf, 0.006% or less of C, 0.003-0.007% of B, the balance of Ni and inevitable impurities. The boron micro-alloyed fourth-generation nickel-based single crystal high-temperature alloy accurately controls the carbon and boron content in the alloy composition to be below 70ppm, has no eutectic structure and no boride, boron elements are segregated at the gamma / gamma' interface, effectively improves the two-phase interface bonding force, and has excellent high-temperature creep performance.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy casting, and particularly relates to a boron microalloyed fourth-generation nickel-based single-crystal high-temperature alloy, its preparation method and application. Background Technology

[0002] Guide vanes and working blades, as two of the most critical components of modern advanced aero-engines, are primarily made of nickel-based single-crystal superalloys. With the continuous improvement of aero-engine thermal efficiency, the service environment of blades is becoming increasingly harsh, necessitating the addition of more and more refractory elements to single-crystal superalloys and increasingly complex geometries. However, both of these methods significantly increase the tendency for defects such as small-angle grain boundaries and orientation deviations to occur in the blade body and plateau region of single-crystal blades.

[0003] Adding trace elements is an effective way to improve dendrite orientation deviation defects in single-crystal superalloys and optimize their casting performance. The mechanism mainly involves the formation of second phases such as carbides and borides at small-angle grain boundary defects by trace elements like carbon, boron, and hafnium, thereby achieving grain boundary strengthening. However, excessive addition of carbon and boron leads to a sharp increase in the size and content of carbides and low-melting-point eutectics, becoming a major source of microcrack initiation and propagation during the service of single-crystal blades, thus seriously impairing the long-term service reliability of aero-engines.

[0004] In the literature “YS Zhao, J. Zhang, FY Song, CG Liu, YY Guo, YF Liu, YS Luo, DZ Tang, Prog. Nat. Sci. Mater. 30 (2020) 371-381.” and “YS Zhao, CG Liu, YY Guo, YF Liu, J. Zhang, YS Luo, DZ Tang, Prog. Nat. Sci. Mater. 28 (2018) 483-488.”, second-generation single-crystal superalloys DD11 with boron contents of 100 ppm and 200 ppm were prepared using high-speed solidification, respectively. The study found that after standard heat treatment, the presence of residual eutectic and M3B2 borides became the main sources of crack initiation and propagation, leading to a significant decrease in the high-temperature creep performance of the alloy. Therefore, it is essential to precisely control the carbon and boron elements in nickel-based single-crystal superalloys. In addition, the strengthening effect of carbon and boron elements in the grain boundaries of equiaxed superalloys has been proven to be very effective. Therefore, introducing this grain boundary engineering into single-crystal superalloys to achieve phase boundary strengthening has become a new future idea for the composition design of advanced single-crystal superalloys.

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a boron-microalloyed fourth-generation nickel-based single-crystal superalloy. The boron-microalloyed fourth-generation nickel-based single-crystal superalloy provided by the present invention precisely controls the carbon and boron content in the alloy composition to below 70 ppm, has no eutectic structure and no borides, and the boron element segregates at the γ / γ′ interface, effectively improving the interfacial bonding force between the two phases, thus giving it excellent high-temperature creep performance.

[0006] The second objective of this invention is to provide a method for preparing boron microalloyed fourth-generation nickel-based single-crystal superalloys.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention discloses a boron-microalloyed fourth-generation nickel-based single-crystal superalloy, with the following composition by mass percentage: Al 5.5%-6.5%, Co 12%-14%, W 5.5%-6.5%, Cr 3.5%-4.5%, Ta 7.5%-8.5%, Re 5-6%, Ru 2.5-3.5%, Hf 0.1-0.2%, C≤0.006%, B 0.003-0.007%, and Ni as the balance and unavoidable impurities.

[0009] The boron-microalloyed fourth-generation nickel-based single-crystal superalloy provided by this invention, on the one hand, precisely controls the amount of boron incorporated, and on the other hand, the alloy composition does not contain molybdenum and has a low wylene content, which suppresses the precipitation tendency of M3B2 type borides. In addition, the interaction of other alloy components results in the formation of a eutectic structure without borides after complete heat treatment. Boron elements are segregated at the γ / γ′ interface, which effectively improves the interfacial bonding force between the two phases and gives it excellent high-temperature creep performance.

[0010] Preferably, the boron microalloyed fourth-generation nickel-based single-crystal superalloy has the following composition by mass percentage: Al 5.5%-6.5%, Co 12%-14%, W 5.5%-6.5%, Cr 3.5%-4.5%, Ta 7.5%-8.5%, Re 5-6%, Ru 2.5-3.5%, Hf 0.1-0.2%, C≤0.006%, B 0.0035-0.0065%, and Ni as the balance and unavoidable impurities.

[0011] Preferably, the microstructure of the boron-microalloyed fourth-generation nickel-based single-crystal superalloy comprises a γ matrix and a γ′ reinforcing phase, wherein the volume fraction of the γ′ reinforcing phase in the fourth-generation nickel-based single-crystal superalloy is 60-65%, the average size of the γ′ reinforcing phase is 320-340 nm, the channel width of the γ matrix is ​​54-56 nm, the fourth-generation nickel-based single-crystal superalloy does not contain borides, and boron elements are segregated at the γ / γ′ interface.

[0012] The boron microalloyed fourth-generation nickel-based single-crystal superalloy provided in this invention has a high volume fraction and optimally sized γ′ strengthening phase that can hinder the intrusion of matrix dislocations at high temperatures. The narrower γ matrix channels greatly limit the slip and climb space of dislocations in the matrix, thereby significantly improving the creep fracture life of the alloy at high temperatures.

[0013] The boron microalloyed fourth-generation nickel-based single-crystal superalloy provided by this invention can achieve a high-temperature creep life of 241h under 1100℃ / 150 MPa conditions, which is much higher than that of the single-crystal alloy before boron microalloying.

[0014] This invention also provides a method for preparing a boron-microalloyed fourth-generation nickel-based single-crystal high-temperature alloy. The method involves first melting a non-boron-microalloyed fourth-generation nickel-based single-crystal high-temperature alloy master alloy ingot according to a designed composition ratio, then melting it again to obtain a master alloy melt. A Ni-20%B intermediate alloy is added to the master alloy melt, and the mixture is melted a second time to obtain a boron-microalloyed master alloy ingot. The boron-microalloyed master alloy ingot is then directionally solidified to obtain a boron-microalloyed fourth-generation nickel-based single-crystal high-temperature alloy billet. The billet is then subjected to solution treatment, a first aging treatment, and a second aging treatment to obtain the fourth-generation nickel-based single-crystal high-temperature alloy.

[0015] In this invention, metal raw materials other than boron are first prepared according to the designed composition ratio and smelted to obtain a boron-free microalloyed fourth-generation nickel-based single-crystal superalloy master alloy ingot. This ingot is then remelted, heated above the alloy liquidus line, and a Ni-20%B master alloy is added. After remelting, a boron-microalloyed master alloy ingot is obtained. Experiments have shown that by using this smelting sequence and the Ni-20%B master alloy as the boron source, the preparation method of this invention can ultimately obtain a fourth-generation nickel-based single-crystal superalloy without eutectic structure and borides after complete heat treatment, with boron segregating at the γ / γ′ interface. Simultaneously, the boron content in the alloy composition can be precisely controlled.

[0016] In this invention, Ni-20%B master alloy refers to Ni-20%B master alloy with a mass fraction of 20%.

[0017] In actual operation, the boron-free microalloyed fourth-generation nickel-based single-crystal high-temperature alloy master alloy ingot is precisely analyzed using glow discharge mass spectrometry to determine the alloy composition, confirming that the content of the measured element is within the alloy composition range. Then, the master alloy ingot is remelted in a vacuum induction melting furnace, reheated above the alloy liquidus line, and Ni-20%B master alloy is added. After remelting, a boron microalloyed master alloy ingot is obtained. The boron microalloyed fourth-generation nickel-based single-crystal high-temperature alloy master alloy ingot is then again precisely analyzed using glow discharge mass spectrometry to confirm that the content of the measured element is within the alloy composition range.

[0018] In this invention, the carbon content is controlled through a strict refining process.

[0019] Preferably, the first melting is vacuum melting, the temperature of the first melting is 1550-1600ºC, the melting time is 10-30 min, and the vacuum pressure is ≤6×10⁻⁶. -3 MPa.

[0020] Preferably, the second melting is vacuum melting, the temperature of the second melting is 1550-1600ºC, the time of the second melting is 10-30 min, and the vacuum pressure is ≤6×10. -3 MPa.

[0021] In actual operation, the boron microalloyed master alloy ingot is ground, polished and cleaned with alcohol, and then the master alloy is directionally solidified to obtain a boron microalloyed fourth-generation nickel-based single crystal high-temperature alloy test rod.

[0022] Preferably, the directional solidification process is as follows: first, the boron microalloyed master alloy ingot is melted at 1540-1550℃. After the boron microalloyed master alloy ingot melts, the temperature is raised to 1575-1585℃ and held for 3-5 minutes for refining. Then, the temperature is lowered to 1545-1555℃ and poured into a mold shell. After standing for 4-6 minutes, the mold shell is solidified downwards at a pulling speed of 2-4 mm / min.

[0023] In a further preferred embodiment, the shell is first preheated in a directional solidification furnace, with the upper zone temperature controlled at 1515-1525℃ and the lower zone temperature controlled at 1545-1555℃, and the vacuum degree ≤1×10⁻⁶. -2 MPa, preheating and holding time is 30-35 min.

[0024] In this invention, during directional solidification, since the water-cooled copper plate connecting the mold shell is placed in the lower zone of the directional solidification furnace, the temperature in the lower zone is selected to be 30°C higher than that in the upper zone to ensure the uniformity of the furnace temperature field during directional solidification. During the directional solidification process, after the ingot is completely melted, the temperature is rapidly increased for refining to make the alloy composition uniform and remove inclusions and gases. After refining, the melt is cooled and poured into the mold shell, and then left to stand for 4-6 minutes to ensure that the composition of the melt is uniform throughout, avoiding local enrichment of B and W elements in the alloy structure, thereby avoiding the formation of borides and the loss of boron elements during the melting of the master alloy. Finally, a relatively low pulling speed is used to solidify the mold shell downwards.

[0025] Experiments have shown that during directional solidification, excessively high refining temperatures lead to excessive volatilization of the original small amount of boron (B) and the normal amount of chromium (Cr) in the alloy; excessively low refining temperatures prevent the complete removal of impurities and residual gases from the alloy, resulting in a higher impurity content. Both of these conditions cause deviations in the alloy composition, leading to the formation of borides. After the molten metal is poured into the mold, it needs to be allowed to stand. If the standing time is too short, the alloy composition becomes uneven, causing local enrichment of boron and chromium (W) in the alloy, resulting in the formation of borides. If the standing time is too long, excessive volatilization of the original small amount of boron (B) and the normal amount of chromium (Cr) in the alloy also causes deviations in the alloy composition.

[0026] Furthermore, compared to lower-generation single-crystal superalloys, fourth-generation nickel-based single-crystal superalloys have a higher content of refractory elements, which increases the tendency for defect formation during directional solidification. The present invention uses a lower pulling rate to achieve more sufficient feeding and solute diffusion, reducing micro-shrinkage and segregation between dendrites; it also helps the solidification interface to advance more smoothly, avoiding impurities and freckle defects caused by localized overcooling.

[0027] Preferably, the mold shell is preheated inside the furnace for 30-35 minutes. This process completely removes volatile substances such as water vapor introduced by the mold shell, ensuring the vacuum level inside the furnace and the purity of the alloy melt.

[0028] Preferably, the solution heat treatment is carried out under a protective atmosphere. The solution heat treatment process is as follows: first, the temperature is raised to 1320-1325℃ and held for 15-17 hours, then the temperature is raised to 1330-1335℃ and held for 15-17 hours. After the solution heat treatment is completed, air cooling is performed.

[0029] In this invention, by employing the aforementioned two-stage solution heat treatment and holding at high temperature for an extended period, atomic diffusion is utilized to dissolve the eutectic structure between dendrites, reducing dendrite segregation. During experimental exploration, the inventors also attempted single-stage heat treatment and multi-stage solution heat treatment (more than two stages), but the results were far inferior to this invention. Experiments revealed that, due to the severe elemental segregation in the dendrite trunk and between dendrites of high-generation single-crystal superalloys, the dissolution temperature of the γ′ phase between dendrites is much lower than that of the dendrite trunk, resulting in an average solution heat treatment temperature range of only 10-15°C. If a single solution heat treatment is used, a higher solution temperature is required to eliminate the eutectic structure and reduce segregation, which easily leads to the formation of initial melting voids at the interdendritic eutectic sites, severely impairing the alloy's creep properties. If a multi-stage solution heat treatment is used, although the initial melting of the alloy can be avoided, a longer solution time is required to dissolve the coarse γ′ strengthening phase between dendrites at high temperatures, greatly reducing the production efficiency of the alloy. At the same time, experiments show that when the two-stage and multi-stage solution heat treatment times are the same, the multi-stage solution heat treatment cannot completely eliminate the eutectic structure. This invention employs a two-step solution heat treatment. Using a lower first-stage solution temperature can reduce the degree of elemental segregation between dendrite trunks and dendrites, increasing the initial melting temperature of the alloy. Since the alloy's solution heat treatment range is relatively small, a second-stage solution heat treatment is performed by slightly increasing the solution temperature on the basis of the first-stage solution heat treatment, achieving the goal of completely dissolving the interdendritic eutectic structure and further reducing dendrite segregation.

[0030] In a further preferred embodiment, during the solution treatment process, the heating rate from 1000°C to 1200°C is controlled at 5-6°C / min, and the heating rate above 1200°C is ≤5°C / min.

[0031] Preferably, the first aging heat treatment is carried out under a protective atmosphere, the temperature of the first aging heat treatment is 1145-1155℃, the holding time is 4-5 h, and after the first aging heat treatment is completed, air cooling is performed.

[0032] During an aging heat treatment process, the alloy is heated to a high temperature to dissolve the γ′ phase and form a supersaturated solid solution. During the cooling process, a large amount of γ′ phase is re-precipitated to increase the volume fraction of the γ′ phase.

[0033] In a further preferred embodiment, during the single aging heat treatment, the heating rate above 1000℃ is 5-6℃ / min. This heating rate is chosen to avoid localized overheating of the alloy specimen during rapid heating, ensuring temperature uniformity of the alloy specimen as a whole during the heating process, ultimately resulting in an alloy specimen with a uniform microstructure.

[0034] In actual operation, before the solution heat treatment and the first aging heat treatment, the air in the furnace tube needs to be purged with argon gas, and argon gas protection is provided during the heat preservation process to avoid oxidation of the alloy test bar during the heat treatment process.

[0035] Preferably, the secondary aging heat treatment temperature is 865-875℃, the holding time is 23-25 ​​h, the heating rate is 8-10℃ / min, and the cooling method is air cooling.

[0036] Secondary aging heat treatment adjusts the cubicity and size of the large amount of γ′ phase precipitated during the primary aging heat treatment, thereby improving the precipitation strengthening effect of the alloy.

[0037] This invention also provides an application of boron microalloyed fourth-generation nickel-based single-crystal superalloy, which is used to prepare guide vanes and working blades in advanced aero-engines.

[0038] Beneficial effects

[0039] (1) This invention utilizes the advantage of boron in grain boundary engineering to enhance grain boundary bonding by segregating at the grain boundaries of equiaxed superalloys. By adding trace amounts of boron to the fourth-generation nickel-based single-crystal superalloy, it causes boron to segregate to the γ / γ′ interface, thereby enhancing the weakest two-phase interface structure of the single-crystal superalloy during high-temperature deformation and improving the strength of the alloy at high temperatures.

[0040] (2) The trace amount of boron added in this invention is insufficient to form borides in the fourth-generation nickel-based single crystal high-temperature alloy, thus avoiding the disadvantage of local stress concentration during high-temperature deformation, which leads to premature fracture of the alloy.

[0041] (3) The addition of trace amounts of boron in this invention changes the distribution of refractory elements in the γ-γ′ phases and increases the mismatch between the two phases, thereby accelerating the formation and densification of the dislocation network during the high-temperature creep process of the alloy, hindering the cutting of the γ′ strengthening phase by the matrix dislocations, and greatly improving the high-temperature creep performance of the alloy.

[0042] (4) Compared with the current advanced nickel-based single crystal high-temperature alloys, which add a large number of refractory elements such as Re, Ru and Ir to improve the high-temperature performance of the alloy, the addition of trace B elements in this invention is less costly and the addition method is simpler and more convenient. Attached Figure Description

[0043] Figure 1 This invention compares the high-temperature creep life of un-microalloyed, boron-microalloyed, carbon-microalloyed, and carbon-hafnium-microalloyed fourth-generation nickel-based single-crystal superalloys under 1100℃ / 150 MPa conditions.

[0044] Figure 2 The images show SEM images of the fourth-generation nickel-based single-crystal superalloys of the present invention after complete heat treatment, including boron-free microalloying, boron microalloying, carbon microalloying, and carbon hafnium microalloying.

[0045] Figure 3 This is a one-dimensional elemental distribution diagram showing the segregation of boron at the γ / γ′ interface in the boron microalloyed fourth-generation nickel-based single-crystal superalloy after complete heat treatment.

[0046] Figure 4 This is a comparison diagram of the two-phase mismatch degree after complete heat treatment of the fourth-generation nickel-based single-crystal superalloys of boron-free microalloying and boron microalloying versus carbon microalloying and carbon hafnium microalloying. Detailed Implementation

[0047] This invention provides a boron microalloyed fourth-generation nickel-based single-crystal high-temperature alloy with the following composition: Al 5.5%-6.5%, Co 12%-14%, W 5.5%-6.5%, Cr 3.5%-4.5%, Ta 7.5%-8.5%, Re 5-6%, Ru 2.5-3.5%, Hf 0.1-0.2%, C≤0.006%, B 0.003-0.007%, impurities ≤0.01%, and Ni as the balance. The percentages of each component are by mass.

[0048] It should be noted that in recent years, boron microalloying to induce segregation at grain boundaries in equiaxed superalloys has been an important method for improving material properties. Boron segregation along grain boundaries or altering the morphology of grain boundary compounds reduces interfacial energy, thereby strengthening grain boundary bonding and improving the high-temperature mechanical properties of the alloy. However, research on the strengthening of phase boundaries by trace elements in nickel-based single-crystal superalloys is rarely reported, as excessive boron leading to the formation of low-melting-point eutectics and brittle phases such as borides is generally considered a detrimental factor. In this study, by reasonably reducing the boron content in nickel-based single-crystal superalloys, boron segregation to the γ / γ′ interface was achieved while avoiding the formation of borides in the microstructure. This improved the interfacial strength and phase mismatch between the two phases, significantly enhancing the high-temperature creep performance of the fourth-generation nickel-based single-crystal superalloy.

[0049] In addition, the carbon content is strictly controlled to below 0.006% in this invention to avoid the consumption of refractory elements in single-crystal superalloys by the formation of carbides, and to reduce the damage to the solid solution strengthening effect of the alloy matrix caused by the formation of such brittle phases.

[0050] In addition, the boron content in this invention is strictly controlled below 70 ppm, which does not significantly affect the microstructure of the boron microalloyed alloy matrix, including the width of the γ matrix channel, the volume fraction and size of the γ′ strengthening phase, thus ensuring the solid solution strengthening and precipitation strengthening effects of the boron microalloyed fourth-generation single-crystal high-temperature alloy.

[0051] In some specific embodiments, the aforementioned boron microalloyed fourth-generation nickel-based single-crystal superalloy has the following composition by mass percentage: Al 5.5%-6.5%, Co 12%-14%, W 5.5%-6.5%, Cr 3.5%-4.5%, Ta 7.5%-8.5%, Re 5-6%, Ru 2.5-3.5%, Hf 0.1-0.2%, C≤0.006%, B 0.003-0.007%, with Ni as the balance and unavoidable impurities. For example, it could be Al 5.91%, Co 13.05%, W 5.91%, Cr 3.93%, Ta 8.06%, Re 5.52%, Ru 2.91%, Hf 0.11%, C 0.005%, B 0.0037%, impurities ≤0.01%, with Ni as the balance, where the percentages of each component are mass percentages.

[0052] In some specific embodiments, the above-mentioned boron microalloyed fourth-generation nickel-based single-crystal superalloy has a high-temperature creep life of 241 h under the conditions of 1100℃ / 150MPa, which is higher than that of the single-crystal alloy before boron microalloying.

[0053] This invention also provides a method for preparing the boron microalloyed nickel-based single-crystal superalloy described in the above technical solution, comprising the following steps:

[0054] The chemical composition of the boron-free microalloyed fourth-generation nickel-based single-crystal superalloy, by mass percentage, is: Al 5.5%-6.5%, Co 12%-14%, W 5.5%-6.5%, Cr 3.5%-4.5%, Ta 7.5%-8.5%, Re 5-6%, Ru 2.5-3.5%, Hf 0.1-0.2%, C≤0.006%, Ni as balance and unavoidable impurities. This is then added to a vacuum induction melting furnace for smelting to obtain the master alloy ingot of the boron-free microalloyed single-crystal superalloy.

[0055] The alloy composition of the boron-free microalloyed fourth-generation nickel-based single-crystal superalloy was precisely determined using glow discharge mass spectrometry to ensure that the content of the measured element was within the specified alloy composition range. Subsequently, the boron-free microalloyed ingot was remelted in a vacuum induction melting furnace, reheated above the alloy liquidus line, and then Ni-20%B master alloy was added. After remelting, the boron-free microalloyed ingot was obtained.

[0056] The boron microalloyed fourth-generation nickel-based single-crystal high-temperature alloy master alloy ingot was again precisely analyzed using glow discharge mass spectrometry to determine the content of the measured element within the range of the alloy composition.

[0057] In some specific embodiments, the amount of Ni-20%B master alloy used relative to 10,000 g of boron-free microalloyed fourth-generation nickel-based single-crystal superalloy includes 3-5 g; wherein, the amount of Ni-20%B master alloy used can be selected as 4 g.

[0058] In some specific embodiments, the vacuum pressure for vacuum melting is: 6 × 10⁻⁶ -3 MPa; vacuum melting temperature is 1550-1600ºC; vacuum melting time is 10-30min.

[0059] In some specific embodiments, the above-mentioned boron microalloyed master alloy ingot is surface-ground, polished, and cleaned with alcohol, and then the master alloy is directionally solidified to obtain a boron microalloyed fourth-generation nickel-based single crystal high-temperature alloy test bar.

[0060] In some specific embodiments, the parameters of the directional solidification process are: vacuum pressure of 1×10⁻⁶. -2 MPa; The directional solidification process uses an upper zone temperature of 1515-1525℃, a lower zone temperature of 1545-1555℃, and a melting temperature of 1540-1550℃. After the boron microalloyed master alloy ingot melts, the temperature is raised to 1575-1585℃ and held for 3-5 minutes for refining. Then, the temperature is lowered to 1545-1555℃ and poured into a mold. After standing for 4-6 minutes, the mold is pulled downwards at a speed of 2-4 mm / min to solidify. This invention, using this casting process, helps to remove inclusions in the alloy composition and avoids the loss of trace element boron during the master alloy melting process.

[0061] In some specific embodiments, during the directional solidification process, the mold shell needs to be preheated and held at that temperature for 30-35 minutes after entering the directional furnace to ensure the complete removal of volatile substances such as water vapor brought in by the mold shell, thus ensuring the vacuum level inside the furnace and the purity of the alloy melt.

[0062] After obtaining boron microalloyed fourth-generation nickel-based single-crystal high-temperature alloy test rods, solution heat treatment, first aging heat treatment and second aging heat treatment were carried out on them.

[0063] In some specific embodiments, the first-step solution heat treatment temperature is 1320-1325℃, and the holding time is 15-17 hours. The second-step solution heat treatment temperature is raised again to 1330-1335℃ based on the first step, and held for 15-17 hours. During the heating process, the heating rate from 1000℃ to 1200℃ is 5-6℃ / min, and the heating rate above 1200℃ is ≤5℃ / min. In this invention, the solution heat treatment is a process of holding at high temperature for a long time, utilizing atomic diffusion to dissolve the eutectic structure between dendrites and reduce dendrite segregation.

[0064] In some specific embodiments, before performing an aging heat treatment, the single crystal specimen after solution heat treatment is cooled to room temperature in air.

[0065] In some specific embodiments, the initial aging heat treatment temperature is 1145-1155℃, held for 4-5 h, and the heating rate above 1000℃ is 5-6℃ / min. At this temperature, the alloy is heated to a high temperature to dissolve the γ′ phase and form a supersaturated solid solution. During the cooling process, a large amount of γ′ phase is re-precipitated to increase the volume fraction of the γ′ phase.

[0066] In some specific embodiments, before performing the secondary aging heat treatment, the single crystal test rod after the primary aging heat treatment is cooled to room temperature in air.

[0067] In some specific embodiments, the secondary aging heat treatment temperature is 865-875℃, the holding time is 23-25 ​​h, and the heating rate is 10℃ / min. In this invention, the secondary aging heat treatment adjusts the cubicity and size of the large amount of γ′ phase precipitated during the primary aging heat treatment, thereby improving the precipitation strengthening effect of the alloy.

[0068] In some specific embodiments, the air in the furnace tube needs to be purged with argon before solution heat treatment and primary aging heat treatment, and argon protection is maintained throughout the heat preservation process to avoid oxidation of the single crystal test rod during heat treatment.

[0069] Finally, the boron microalloyed fourth-generation nickel-based single crystal high-temperature alloy test bars after the above heat treatment were processed into standard creep test bars according to national standards, and high-temperature creep tests at 1100℃ / 150 MPa were conducted using a CTM105-A1 creep tester to obtain the high-temperature creep life of the boron microalloyed fourth-generation nickel-based single crystal high-temperature alloy.

[0070] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0071] Example 1

[0072] The composition of the boron microalloyed fourth-generation nickel-based single-crystal superalloy in Example 1, by mass percentage, is as follows: Al 5.91%, Co 13.05%, W 5.91%, Cr 3.93%, Ta 8.06%, Re 5.52%, Ru 2.91%, Hf 0.11%, C 0.005%, B 0.0037%, impurities ≤0.01%, and Ni as the balance. The specific steps are as follows:

[0073] First, according to the above-mentioned mass composition, the components of the boron-free microalloyed fourth-generation nickel-based single-crystal superalloy were weighed and melted to form a master alloy ingot, thus obtaining a boron-free microalloyed alloy ingot; vacuum pressure 6×10 -3 The melting pressure was set at 1550℃, and the vacuum melting time was 10 min. After the master alloy ingot was completely melted, 4 g of Ni-20%B master alloy was added to the crucible through the charging bin of a vacuum induction melting furnace, after being wrapped in nickel foil. The melting process was repeated 5 times, with electromagnetic stirring used to reduce macroscopic segregation and ensure uniform distribution of the added boron components, thus obtaining a boron microalloyed alloy ingot.

[0074] After surface grinding and polishing, and cleaning with alcohol, the two types of master alloy ingots were placed under a vacuum pressure of 1×10⁻⁶. -2 In a high-speed solidification furnace at MPa, the temperature is raised from room temperature to 1550°C within 30 minutes. After the ingot is completely melted, the temperature is rapidly raised to 1580°C and held for 4 minutes for refining to homogenize the alloy composition and remove inclusions. Then, the melt is rapidly cooled to 1550°C and poured at a rate of 1 kg / s into a single-crystal test specimen shell, which has already been held in the furnace for 30 minutes. During directional solidification, the upper zone temperature is 1520°C and the lower zone temperature is 1550°C. After the melt is poured into the shell, it is allowed to stand for 5 minutes to ensure uniform composition throughout. Then, the shell is pulled downwards at a rate of 3 mm / min for solidification. After the single-crystal test specimen shell cools naturally to room temperature, it is broken open, and the cooled single-crystal alloy is removed.

[0075] After separating the single-crystal test bar from the riser, the test bar was placed in a tube furnace for solution heat treatment, primary aging heat treatment, and secondary aging heat treatment. Solution heat treatment: The temperature was increased from room temperature to 1000℃ at 10℃ / min, then to 1200℃ at 5℃ / min, and then to 1325℃ at 2℃ / min, held for 16 h, followed by increasing the temperature to 1333℃ at 2℃ / min and holding for 16 h, under argon protection, and then cooled to room temperature in air. Primary aging heat treatment: The temperature was increased from room temperature to 1000℃ at 10℃ / min, then to 1150℃ at 5℃ / min, held for 4 h, under argon protection, and then cooled to room temperature in air. Secondary aging heat treatment: The temperature was increased from room temperature to 870℃ at 10℃ / min, held for 24 h, and then cooled to room temperature in air, yielding a boron microalloyed fourth-generation nickel-based single-crystal superalloy.

[0076] Example 2

[0077] The difference from Example 1 is that the boron mass percentage in the boron microalloyed fourth-generation nickel-based single crystal superalloy is 0.0045%.

[0078] Example 3

[0079] The difference from Example 1 is that the boron mass percentage in the boron microalloyed fourth-generation nickel-based single-crystal superalloy is 0.0063%.

[0080] Comparative Example 1

[0081] The difference from Example 1 is that no Ni-B master alloy was added in the vacuum melting preparation of the master alloy. Other directional solidification processes and complete heat treatment processes are consistent with the boron microalloyed single crystal test rod preparation method in Example 1, ensuring that the difference in microstructure and high-temperature creep properties of the two alloys is due to the influence of boron, and obtaining boron-free microalloyed nickel-based single crystal high-temperature alloy test rods.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that a carbon microalloying method is used, and 4 g of elemental graphite is added during the vacuum melting process to prepare the master alloy. The remaining alloy composition is the same as that of Example 1 and Comparative Example 1. The remaining vacuum melting process, directional solidification process and complete heat treatment process are the same as those used in Example 1 for preparing boron microalloyed single crystal test rods, and carbon microalloyed nickel-based single crystal high-temperature alloy test rods are obtained.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that a carbon hafnium microalloying method was used. During the vacuum melting process to prepare the master alloy, 4 g of elemental graphite and 250 g of Ni-20%Hf master alloy were added. The remaining alloy composition was the same as that of Example 1, Comparative Example 2, and Comparative Example 3. The remaining vacuum melting process, directional solidification process, and complete heat treatment process were the same as those used in Example 1 for preparing boron element microalloyed single crystal test rods, resulting in carbon hafnium microalloyed nickel-based single crystal high-temperature alloy test rods.

[0086] Performance testing

[0087] Wherein 0.0037B, 0.0045B, and 0.0063B represent the boron-microalloyed fourth-generation nickel-based single-crystal superalloys prepared in Examples 1-3, respectively; 0B represents the boron-free microalloyed fourth-generation nickel-based single-crystal superalloy prepared in Comparative Example 1; 0.03C represents the carbon microalloyed fourth-generation nickel-based single-crystal superalloy prepared in Comparative Example 2; and 0.03C+0.4Hf represents the carbon-hafnium microalloyed fourth-generation nickel-based single-crystal superalloy prepared in Comparative Example 3. The high-temperature creep life and microstructure of the 0.0037B alloy are compared with those of Comparative Examples 1-3.

[0088] Figure 1 These are SEM images of the fourth-generation nickel-based single-crystal superalloys (non-boron microalloyed, boron microalloyed, carbon microalloyed, and carbon hafnium microalloyed) after complete heat treatment. Statistical analysis using Image Pro Plus software shows that the γ′ phase volume fractions of the four alloys are 65.2%, 62.5%, 65.6%, and 64.7%, respectively; the average γ′ phase sizes are 323 nm, 332 nm, 352 nm, and 351 nm, respectively; and the average widths of the γ matrix channels are 54 nm, 56 nm, 51 nm, and 53 nm, respectively. It can be seen that after microalloying, the γ′ phase volume fraction of all four alloys is above 60%, and the average γ′ phase size is between 300-400 nm, which represents the optimal microstructure for high-temperature service performance of single-crystal alloys. However, a large number of Chinese character-shaped and blocky MC-type carbides appear in the carbon microalloyed and carbon hafnium microalloyed alloys, which become the source of crack initiation and propagation during high-temperature creep, severely impairing the high-temperature creep performance of the alloys. In addition, the γ / γ′ interface in the boron microalloyed single-crystal alloy was observed using APT, revealing a boron segregation phenomenon at the interface. This successfully strengthened the weak points in the single-crystal superalloy during high-temperature creep using interface engineering methods. Figure 2 As shown.

[0089] The γ-γ′ phase mismatch of the four alloys mentioned above was tested using Bruker D8 Discover high-resolution XRD, such as... Figure 3 As shown, it can be seen that the smaller atomic radius of boron enables the boron microalloyed fourth-generation nickel-based single-crystal superalloy to have a larger two-phase mismatch, which can provide a greater driving force for the formation of a dense dislocation network during high-temperature creep, thereby hindering the matrix dislocation from cutting the γ′ phase, and greatly improving the high-temperature creep performance of the boron microalloyed fourth-generation nickel-based single-crystal superalloy.

[0090] The fourth-generation nickel-based single-crystal superalloys prepared in Examples 1-3 and Comparative Examples 1-3 were processed into circular rod-shaped specimens with a gauge length of 25 mm and a gauge diameter of 5 mm. High-temperature creep tests were conducted at 1100℃ / 150 MPa on a CTM105-A1 creep tester. Figure 4 It can be seen that the boron microalloyed fourth-generation nickel-based single-crystal superalloys prepared in Examples 1-3 have high-temperature creep lives of 241.3 h, 225.5 h, and 235.2 h at 1100 °C / 150 MPa, respectively. In contrast, the boron-free, carbon-microalloyed, and hafnium-carbon microalloyed fourth-generation nickel-based single-crystal superalloys prepared in Comparative Examples 1-3 have high-temperature creep lives of 181.2 h, 130.2 h, and 65.4 h, respectively. This demonstrates that trace amounts of boron can significantly improve the high-temperature creep life of fourth-generation nickel-based single-crystal superalloys.

[0091] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A boron-microalloyed fourth-generation nickel-based single-crystal superalloy, characterized in that: The composition by mass percentage is as follows: Al 5.5%-6.5%, Co 12%-14%, W 5.5%-6.5%, Cr 3.5%-4.5%, Ta 7.5%-8.5%, Re 5-6%, Ru 2.5-3.5%, Hf 0.1-0.2%, C≤0.006%, B 0.003-0.007%, Ni balance and unavoidable impurities.

2. The boron microalloyed fourth-generation nickel-based single-crystal superalloy according to claim 1, characterized in that: The boron microalloyed fourth-generation nickel-based single-crystal superalloy has the following composition by mass percentage: Al 5.5%-6.5%, Co 12%-14%, W 5.5%-6.5%, Cr 3.5%-4.5%, Ta 7.5%-8.5%, Re 5-6%, Ru 2.5-3.5%, Hf 0.1-0.2%, C≤0.006%, B 0.0035-0.0065%, and Ni as balance and unavoidable impurities.

3. A boron-microalloyed fourth-generation nickel-based single-crystal superalloy according to claim 1 or 2, characterized in that: The microstructure of the boron-microalloyed fourth-generation nickel-based single-crystal superalloy comprises a γ matrix and a γ′ reinforcing phase, wherein the volume fraction of the γ′ reinforcing phase in the fourth-generation nickel-based single-crystal superalloy is 60-65%, the average size of the γ′ reinforcing phase is 320-340 nm, the channel width of the γ matrix is ​​54-56 nm, the fourth-generation nickel-based single-crystal superalloy does not contain borides, and boron elements are segregated at the γ / γ′ interface.

4. A method for preparing a boron-microalloyed fourth-generation nickel-based single-crystal superalloy according to any one of claims 1-3, characterized in that: According to the designed composition ratio, metal raw materials other than boron are smelted for the first time to obtain a boron-free microalloyed fourth-generation nickel-based single-crystal high-temperature alloy master alloy ingot. It is then melted again to obtain a master alloy melt. Ni-20%B master alloy is added to the master alloy melt and smelted for the second time to obtain a boron microalloyed master alloy ingot. The boron microalloyed master alloy ingot is then directionally solidified to obtain a boron microalloyed fourth-generation nickel-based single-crystal high-temperature alloy billet. The billet is then subjected to solution treatment, one aging treatment, and two aging treatments to obtain the fourth-generation nickel-based single-crystal high-temperature alloy.

5. The method for preparing a boron microalloyed fourth-generation nickel-based single-crystal superalloy according to claim 4, characterized in that: The first melting process is vacuum melting, with a temperature of 1550-1600ºC and a melting time of 10-30 minutes. The vacuum pressure is ≤6×10⁻⁶. -3 MPa; The second melting process is vacuum melting, with a temperature of 1550-1600ºC and a melting time of 10-30 minutes. The vacuum pressure is ≤6×10⁻⁶. -3 MPa.

6. The method for preparing a boron microalloyed fourth-generation nickel-based single-crystal superalloy according to claim 4, characterized in that: The directional solidification process is as follows: First, the boron microalloyed master alloy ingot is melted at 1540-1550℃. After the boron microalloyed master alloy ingot melts, the temperature is raised to 1575-1585℃ and held for 3-5 minutes for refining. Then, the temperature is lowered to 1545-1555℃ and poured into a mold shell. After standing for 4-6 minutes, the mold shell is solidified downwards at a pulling speed of 2-4 mm / min. The shell is first preheated in a directional solidification furnace, with the upper zone temperature controlled at 1515-1525℃ and the lower zone temperature controlled at 1545-1555℃, and the vacuum degree ≤1×10⁻⁶. -2 MPa, preheating and holding time is 30-35 min.

7. The method for preparing a boron microalloyed fourth-generation nickel-based single-crystal superalloy according to claim 4, characterized in that: The shell is preheated and kept warm for 30-35 minutes.

8. The method for preparing a boron microalloyed fourth-generation nickel-based single-crystal superalloy according to claim 4, characterized in that: The solution heat treatment is carried out under a protective atmosphere. The solution heat treatment process is as follows: first, the temperature is raised to 1320-1325℃ and held for 15-17 hours, then the temperature is raised to 1330-1335℃ and held for 15-17 hours. After the solution heat treatment is completed, air cooling is performed. During the solution treatment, the heating rate from 1000℃ to 1200℃ is controlled at 5-6℃ / min, and the heating rate above 1200℃ is ≤5℃ / min.

9. The method for preparing a boron-microalloyed fourth-generation nickel-based single-crystal superalloy according to claim 4, characterized in that: The first aging heat treatment is carried out under a protective atmosphere. The temperature of the first aging heat treatment is 1145-1155℃, and the holding time is 4-5 h. After the first aging heat treatment is completed, air cooling is performed. During the aforementioned aging heat treatment, the heating rate above 1000℃ is 5-6℃ / min; The secondary aging heat treatment is performed at a temperature of 865-875℃, with a holding time of 23-25 ​​h, a heating rate of 8-10℃ / min, and air cooling.

10. The application of the boron microalloyed fourth-generation nickel-based single-crystal superalloy according to any one of claims 1-3, characterized in that: The boron-microalloyed fourth-generation nickel-based single-crystal superalloy was used to prepare guide vanes and working blades for advanced aero engines.

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