Medium temperature high strength cast nickel-based superalloy, method of making and structural component

Abstract

The application relates to the technical field of cast nickel-based high-temperature alloys, in particular to a medium-temperature high-strength cast nickel-based high-temperature alloy, a preparation method thereof and a structural member. The medium-temperature high-strength cast nickel-based high-temperature alloy comprises, in percentage by mass, Al 1-5%, Ti 5-10%, Co 18-25%, Cr 7-13%, W+Mo 2-6%, B 0.07-0.2%, Zr <0.05%, and the balance of Ni; the sum of the mass percentage of Al and the mass percentage of Ti satisfies Al+Ti >=9%; and the ratio of the mass percentage of Ti to the mass percentage of Al satisfies 1.5 <= Ti / Al <=4. The types and contents of alloy elements are controlled, so that the nickel-based high-temperature alloy has excellent medium-low-temperature mechanical properties and casting processability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cast nickel-based superalloys, in particular to a medium-temperature high-strength cast nickel-based superalloy, a preparation method thereof and a structural part. BACKGROUND

[0002] Nickel-based superalloys are widely used in hot-end components such as blisks, turbine working blades and load-bearing casings of aero-engines and gas turbines due to their excellent properties. The main strengthening phase γ' phase in the nickel-based superalloy is coherently precipitated from the γ matrix in the form of Ni3(Al, Ti), and Al and Ti elements are the main γ' phase forming elements. The contents of these two elements determine the size, morphology, distribution and lattice mismatch degree of the γ' phase with the γ phase, thereby having an important influence on the performance of the alloy. Generally, the deformed nickel-based superalloy has relatively low Al and Ti contents and excellent mechanical properties at medium and low temperatures; the nickel-based alloy with high Al and Ti contents has more advantages in high-temperature mechanical properties, but is mainly used in casting process due to its difficulty in deformation. Therefore, the traditional deformed and cast nickel-based superalloys are suitable for different service temperatures and environments, respectively.

[0003] Generally, the cast nickel-based superalloy with high Al and Ti contents has excellent mechanical properties at high temperatures, and the service temperature can be as high as 1000℃ or above, but the mechanical properties of this kind of cast nickel-based superalloy at medium and low temperatures are not obvious. In recent years, in order to meet the weight reduction demand of future installation, improve the reliability of products and reduce the failure rate during service, new aero-engines adopt high-structural-efficiency integration and lightweight design, and high-temperature alloy integral casting is more and more widely used in the aerospace industry. Some blisk and load-bearing casing components require materials to have good casting processability, and since their service temperature is between 600-900℃, the materials are also required to have excellent mechanical properties at medium and low temperatures.

[0004] At present, the materials widely used in blisks and turbine working blades mainly include K403, K417, K418 and K424, which have good high-temperature mechanical properties. With the development of new-generation aero-engines, the requirements for the casting processability and mechanical properties at medium and low temperatures of materials for various complex-structure integral castings such as blisks, turbine working blades and load-bearing casings are higher. Therefore, it is urgent to develop a high-temperature alloy with excellent casting processability and mechanical properties at medium and low temperatures.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The application aims to provide a medium-temperature high-strength cast nickel-based superalloy, a preparation method thereof and a structural member.

[0007] To achieve the above-mentioned purpose of the application, the first aspect of the application provides a medium-temperature high-strength cast nickel-based superalloy, which comprises, in percentage by mass: Al 1% to 5%, Ti 5% to 10%, Co 18% to 25%, Cr 7% to 13%, W+Mo 2% to 6%, B 0.07% to 0.2%, Zr <0.05%, and the balance of Ni.

[0008] The sum of the mass percentage of Al and the mass percentage of Ti satisfies: Al+Ti≥9%.

[0009] The ratio of the mass percentage of Ti to the mass percentage of Al satisfies: 1.5≤Ti / Al≤4.

[0010] In the specific embodiment of the application, the mass percentage of C in the alloy is <0.06%. Further, the alloy does not contain C element.

[0011] In the specific embodiment of the application, the phase composition of the alloy comprises: matrix γ phase, dendritic trunk γ' phase, γ / γ' eutectic phase and boride.

[0012] In the specific embodiment of the application, the volume fraction of the γ / γ' eutectic phase in the alloy is 15% to 55%.

[0013] In the specific embodiment of the application, the volume fraction of the boride in the alloy is 1% to 3%.

[0014] In the specific embodiment of the application, the phase composition of the alloy does not contain carbide.

[0015] The second aspect of the application provides a preparation method of the medium-temperature high-strength nickel-based superalloy according to the first aspect of the application, which comprises the following steps: according to the component of the medium-temperature high-strength nickel-based superalloy according to the first aspect, material is allocated, vacuum induction melting is performed, and then pouring is performed.

[0016] The third aspect of the application provides a structural member, which is prepared by using the medium-temperature high-strength nickel-based superalloy according to the first aspect of the application.

[0017] In the specific embodiment of the application, the room-temperature tensile property of the structural member satisfies: tensile strength ≥1150MPa.

[0018] In the specific embodiment of the present application, the 700 DEG C tensile property of the structural part satisfies: tensile strength >= 1000 MPa.

[0019] In the specific embodiment of the present application, the structural part has a stress-rupture life >= 120 h under the condition of 760 DEG C / 662 MPa; and the structural part has a stress-rupture life >= 100 h under the condition of 800 DEG C / 540 MPa.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The present application controls the types and contents of alloying elements, and under the premise of ensuring excellent mechanical properties of the alloy at low and medium temperatures, fully improves the casting process and microstructure stability of the alloy to meet the use requirements of the overall casting complex structural part. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art of the present application, the drawings needed in the specific embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0023] Figure 1 The as-cast optical microscope microstructure of the nickel-based superalloy provided for the embodiment 2 of the present application;

[0024] Figure 2 The as-cast SEM microstructure of the nickel-based superalloy provided for the embodiment 2 of the present application;

[0025] Figure 3 The comparison chart of the micro-porosity tendency of different alloys of the present application;

[0026] Figure 4 The comparison chart of the hot cracking tendency of different alloys of the present application. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be described clearly and completely in the following with reference to the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The specific conditions are not indicated in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not indicated by the manufacturer, and are conventional products that can be purchased in the market.

[0028] With the development of new generation of aero-engine, the casting process and the mechanical properties at medium and low temperature of the materials for the complex structure castings such as blisk, turbine working blade and load-bearing casing are required more highly. In the traditional K403, K417, K418 and K424 alloys, the content of Al and Ti is high, which ensures the high temperature mechanical properties of the alloy to some extent, but the casting process and the mechanical properties at medium and low temperature are poor.

[0029] Therefore, the first aspect of the present application provides a medium temperature high strength cast nickel-based superalloy, which comprises, by mass percentage: Al 1% to 5%, Ti 5% to 10%, Co 18% to 25%, Cr 7% to 13%, W+Mo 2% to 6%, B 0.07% to 0.2%, Zr <0.05%, and the balance of Ni.

[0030] The sum of the mass percentage of Al and the mass percentage of Ti satisfies: Al+Ti≥9%;

[0031] The ratio of the mass percentage of Ti and the mass percentage of Al satisfies: 1.5≤Ti / Al≤4.

[0032] Based on the effects of the elements in the alloy, the present application designs the types of the elements in the alloy and controls the content of Al, Ti, B, Co, Cr and Mo, so that the casting process and the microstructure stability of the alloy are improved sufficiently under the premise of ensuring the excellent mechanical properties at medium and low temperature, and a nickel-based superalloy meeting the use requirements of the complex structure castings is obtained.

[0033] The γ / γ' eutectic phase is crucial to the mechanical properties at medium and low temperature of the cast nickel-based superalloy, and the present application controls the types and content of the alloying elements, so that the morphology and volume fraction of the eutectic phase are controlled reasonably, and the strength of the alloy at medium and low temperature is improved. Specifically, the present application adopts high Al and Ti content and high Ti / Al ratio, so that the precipitation of the γ / γ' eutectic phase is promoted, and the mechanical properties of the alloy are improved greatly. Meanwhile, high B content is adopted in the present application, which can promote the formation of the γ / γ' eutectic phase and the formation of borides, and the borides with excellent microstructure stability at high temperature can effectively prevent the migration of the grain boundary; on the other hand, the flowability of the B-rich melt is better, and the connectivity of the interdendritic region in the late solidification stage can be ensured by increasing the content of B, so that the casting process of the alloy is improved significantly. The present application adopts high Al and Ti content, high Ti / Al ratio and high B content, so that the casting process and the mechanical properties at medium and low temperature of the nickel-based superalloy are improved.

[0034] In addition, the alloy of the present application cooperatively uses a certain Co element to reduce the stacking fault energy of the matrix and promote the nanotwinning strengthening mechanism; cooperatively uses a certain Cr element to improve the oxidation resistance and corrosion resistance of the alloy; and cooperatively uses a certain amount of Mo and W elements to have a solid solution strengthening effect on the matrix. Through the synergistic effect of the above elements, the cast nickel-based superalloy with excellent mechanical properties at medium and low temperatures, casting process and microstructure stability is obtained.

[0035] The Al element is a γ'-Ni3Al forming element, and the increase of the Al content increases the content of the γ' phase, improves the high temperature strength of the alloy, and also reduces the specific gravity of the alloy; in addition, a dense and stable Al2O3 film can be formed on the surface of the alloy during high temperature oxidation, which is beneficial to improve the high temperature oxidation resistance of the alloy. However, the present application found that in the alloy system of the present application, too high Al content will cause the precipitation temperature of the γ / γ' eutectic phase to increase during solidification, resulting in poor casting process of the alloy. The Al element content in the alloy of the present application is 1wt%-5wt%, for example, it can be 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt% or a range consisting of any two of them, in order to ensure the mechanical properties, oxidation and corrosion resistance and casting process of the alloy.

[0036] The Ti element is also a γ' phase forming element, and Ti atoms can replace Al atoms in Ni3Al to form Ni3(Al, Ti), and the increase of Ti content is beneficial to reduce the specific gravity of Ni3Al-based alloy. Under the condition of a certain Al content, the amount of γ' phase increases with the increase of Ti content, and Ti atoms can also increase the antiphase domain boundary energy of γ' phase, thereby improving the room temperature and high temperature strength of the alloy. The formation of γ / γ' eutectic phase is mainly related to the Ti content, and the increase of Ti content and Ti / Al ratio can appropriately promote the formation of γ / γ' eutectic phase. However, in the alloy system of the present application, too high Ti content will cause the deterioration of the eutectic morphology, which will adversely affect the mechanical properties of the alloy. The Ti element content in the alloy of the present application is 5wt%-10wt%, for example, it can be 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt% or a range consisting of any two of them, in order to comprehensively improve the effect of Ti element on the microstructure and properties of the alloy.

[0037] B element is a micro-alloying element. The enrichment of B atoms at grain boundaries can increase the grain boundary binding force and improve the grain boundary strength. The addition of B element can significantly reduce the precipitation temperature of γ / γ' eutectic phase and boride, so that the eutectic reaction occurs at a greater undercooling, thereby increasing the content of γ / γ' eutectic phase and promoting the formation of boride at the grain boundary, so as to improve the strength and endurance life of the alloy to some extent. At the same time, the addition of B element can promote the formation of boride at the grain boundary. The boride has very good organizational stability at medium and low temperatures, so increasing the content of B element can improve the strength and endurance life of the alloy to some extent. In addition, the addition of B element can significantly reduce the porosity tendency and hot cracking sensitivity during casting, and improve the casting process of the alloy. B element can significantly slow down the segregation of elements around the γ / γ' eutectic and liquid phase, reduce the content of harmful elements at the grain boundary, and inhibit the formation of η-Ni3(Al, Ti) phase at the end of eutectic reaction. However, too high B content will reduce the incipient melting temperature of the alloy, and also cause too much γ / γ' eutectic content, resulting in weakened dendrite lapping and insufficient strength in the later solidification stage. The B element content in the alloy of the present application is 0.07wt% to 0.2wt%, for example, it can be 0.07wt%, 0.1wt%, 0.12wt%, 0.15wt%, 0.18wt%, 0.2wt% or a range consisting of any two of them, in order to ensure the incipient melting temperature, mechanical properties and casting process of the alloy.

[0038] The addition of Co element in Ni-based alloy can significantly reduce the stacking fault energy of γ matrix, thereby facilitating the formation of stacking faults and nanotwins. Nanotwins have a special low-energy structure, good thermal stability at high temperatures, can interact with γ' phase, and can hinder the movement of dislocations through the twin lamella, effectively avoiding stress concentration, which can improve the strength while improving the plasticity. In addition, the specific gravity of Co element is similar to that of Ni element, and the increase of Co element content in Ni-based alloy will not increase the specific gravity of the alloy. Compared with the addition of refractory metal elements such as Ta, the nanotwin strengthening mechanism produced by Co element has more advantages in improving the mechanical properties of nickel-based superalloys. The Co element content in the alloy of the present application is 18wt% to 25wt%, for example, it can be 18wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt% or a range consisting of any two of them, preferably 20wt% to 25wt%, by appropriately increasing the Co element content to promote nanotwin strengthening, so as to improve the mechanical properties of nickel-based superalloys and avoid the increase of alloy specific gravity.

[0039] The Cr element in the nickel-based high-temperature alloy mainly plays a role in improving the oxidation resistance and corrosion resistance. As a gamma phase forming element, the Cr element is mainly solid-solved in the gamma phase, which can reduce the size of the gamma' phase, increase the cubic degree of the gamma' phase, and increase the mismatch degree of the gamma / gamma' two phases. However, the solid solubility of the Cr element in the gamma phase is limited, and the solid solution strengthening effect is also weak. A large amount of Cr element is easy to cause the alloy to precipitate a Cr-rich phase at high temperature, which reduces the microstructure stability of the alloy at high temperature, thereby deteriorating the high-temperature mechanical properties. The content of the Cr element in the alloy of the present application is 7wt%-13wt%, for example, it can be 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt% or a range composed of any two of them, so as to comprehensively improve the influence of the Cr element on the microstructure and properties of the alloy of the present application.

[0040] The W+Mo of the present application refers to the sum of the mass percentages of W element and Mo element. The alloy of the present application can only contain W element, only contain Mo element, or contain both W element and Mo element, as long as the sum of the mass percentages of the two is within the limited range. Both W element and Mo element can effectively solid-solution strengthen the gamma matrix. Moreover, W and Mo atoms can replace Al atoms in Ni3Al, increase the mismatch degree of the gamma / gamma' two phases, and promote the strengthening effect of the gamma' phase. In addition, Mo element is a forming element of M3B2 type boride, and M3B2 boride has low melting point characteristics. The total content of W element and Mo element in the alloy of the present application is controlled at 2wt%-6wt%, for example, it can be 2wt%, 3wt%, 4wt%, 5wt%, 6wt% or a range composed of any two of them. On the one hand, it ensures the strengthening effect of W and Mo elements and the formation of an appropriate amount of boride. On the other hand, due to the high content of B element in the alloy of the present application, the addition of excessive Mo element is avoided to cause the formation of excessive low melting point phase, while the low specific gravity characteristics of the alloy are ensured.

[0041] In the present application, the sum of the mass percentages of Al and Ti satisfies: Al+Ti≥9%, for example, the sum of the mass percentages of Al and Ti can be 9%, 9.5%, 9.8%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13% or a range composed of any two of them, so as to ensure sufficient gamma' content and gamma / gamma' eutectic phase content, improve the strength of the alloy, and reduce the specific gravity of the alloy.

[0042] The ratio of the mass percentage of Ti to the mass percentage of Al in the present application satisfies: 1.5≤Ti / Al≤4, and the increase of the content of Ti element and the increase of the Ti / Al ratio help to promote the formation of γ / γ' eutectic phase. Ti element is a strong positive segregation element, and the content of Ti element in the later solidified liquid phase is higher, therefore, the γ / γ' eutectic phase in the alloy exists in multiple different forms at the same time, forming eutectic clusters containing filamentous, fan-shaped and light plate-shaped eutectic. The inventors of the present application found that with the increase of the content of Ti element and the increase of the Ti / Al ratio, the morphology of the γ / γ' eutectic phase changes from “filamentous→fan-shaped→light plate-shaped”, when the Ti / Al ratio is too high, it will cause the deterioration of the eutectic morphology, the size of the eutectic cluster is too large, and the number of light plate-shaped eutectic γ' phase is too much, it will also cause a large number of needle-shaped or flaky η-Ni3(Ti, Al) phase to precipitate, and have an adverse effect on the mechanical properties of the alloy. The present application further regulates the Ti / Al ratio in the above range, for example, the Ti / Al ratio can be 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4 or a range formed by any two of them, so as to obtain a suitable size and morphology of the γ / γ' eutectic phase, and improve the medium and low temperature strength of the alloy.

[0043] In the specific embodiments of the present application, the mass percentage of C in the alloy is <0.06%, for example, it can be <0.05%, <0.04%, <0.03%, <0.02%, <0.01%, <0.005% and the like. Further, the alloy does not contain C element. Traditional cast nickel-based superalloy usually contains a certain amount of C element, and C element is usually used as an alloying element to form carbide for precipitation strengthening. Influenced by the variety of alloying elements, there are many types of carbides in the superalloy. The cast superalloy is in a thermodynamically unstable state, and with the increase of temperature during heat treatment or service, the carbide will decompose and decompose, and the transformation between different types of carbides will also occur, and a large amount of secondary carbide will be precipitated. The change of the type, number, morphology, size and distribution of carbide will greatly affect the plasticity and sensitivity to stress concentration of the alloy, and finally affect the mechanical properties of the alloy. In the alloy of the present application, C element is not added as an alloying element, and there is no carbide; but the boride precipitate phase formed by B element at the grain boundary is used to prevent the migration of the grain boundary. The microstructure stability of boride at high temperature is better than that of carbide, and there is no decomposition and transformation in a higher temperature range, so that the alloy has more stable microstructure stability and mechanical properties.

[0044] In actual operation, the element C in the alloy of the present application is not added as an alloying element, and can be added in the form of graphite during the smelting process of the alloy, and chemically reacts with oxygen in the alloy melt to form CO gas, thereby removing the harmful gas oxygen. However, the alloy of the present application does not contain carbide phase in the phase composition.

[0045] In the detailed embodiment of the present application, the phase composition of the alloy includes: matrix γ phase, dendrite trunk γ' phase, γ / γ' eutectic phase and boride.

[0046] In the detailed embodiment of the present application, the volume fraction of the γ / γ' eutectic phase in the alloy is 15% to 55%, for example, can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or a range consisting of any two of them.

[0047] In the detailed embodiment of the present application, the volume fraction of the boride in the alloy is 1% to 3%, for example, can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3% or a range consisting of any two of them.

[0048] In the detailed embodiment of the present application, the alloy does not contain carbide in the phase composition.

[0049] The present application adopts high Al and Ti content, cooperates with high Ti / Al ratio and high B content, promotes the formation of γ / γ' eutectic phase, and ensures a certain amount of boride precipitated phase, and takes into account the improvement of the mechanical properties and casting process of the alloy, etc.

[0050] The second aspect of the present application provides a preparation method of the medium-temperature high-strength cast nickel-based superalloy of the first aspect of the present application, which comprises the following steps: according to the component of the medium-temperature high-strength cast nickel-based superalloy of the first aspect, vacuum induction melting is carried out, and then pouring is carried out.

[0051] The raw materials of the elements in the alloy can be used as follows, but are not limited to this, for example, electrolytic nickel, metal aluminum, titanium sponge, metal cobalt, metal chromium, metal molybdenum, nickel boron, etc. can be used as raw materials.

[0052] The present application provides a specific preparation method, but not limited to, the vacuum induction melting can include: according to the alloy component batching, placing electrolytic nickel, metal chromium at the bottom of the crucible, metal molybdenum at the top of the crucible, and other elements from the hopper; heating electrolytic nickel, metal chromium, metal cobalt, and metal molybdenum, after the electrolytic nickel is red-hot, first small power power supply to remove hydrogen, and then large power power supply to full melting, starting refining, the refining temperature is 1500-1550℃, the refining time is 10-45min, and the vacuum degree during refining is <10Pa; cooling to near the condensate shell, adding argon, adding metal aluminum after dissolving, adding sponge titanium and nickel boron after cleaning, when the liquid surface is clean, large power stirring is uniform, and the steel liquid temperature is controlled at 1400-1480℃ for pouring. Among them, the specific refining time is adjusted regularly according to the amount of steel liquid.

[0053] In the specific embodiment of the present application, the melt of the nickel-based superalloy of the present application has a melt viscosity of ≤6.31 mpa·s at 1380-1500℃, for example 4.97-6.31 mpa·s.

[0054] The third aspect of the present application provides a structural member made of the medium-temperature high-strength cast nickel-based superalloy of the first aspect of the present application.

[0055] Among them, the structural member can include a whole cast complex structural member, for example, but not limited to, a whole blade disk, a turbine working blade, a force-bearing case, etc.

[0056] In the specific embodiment of the present application, the room temperature tensile property of the structural member meets: tensile strength ≥1150MPa, for example, it can be 1150MPa, 1170MPa, 1190MPa, 1200MPa, 1210MPa, 1230MPa, 1250MPa or a range consisting of any two of them.

[0057] In the specific embodiment of the present application, the 700℃ tensile property of the structural member meets: tensile strength ≥1000MPa, for example, it can be 1000MPa, 1020MPa, 1040MPa, 1060MPa, 1080MPa, 1100MPa or a range consisting of any two of them.

[0058] In the specific embodiment of the present application, the structural member has a creep life ≥120h under the condition of 760℃ / 662MPa, for example, it can be 120h, 130h, 140h, 150h, 160h, 170h, 180h, 190h, 200h or a range consisting of any two of them; the structural member has a creep life ≥100h under the condition of 800℃ / 540MPa, for example, it can be 100h, 120h, 140h, 160h, 180h or a range consisting of any two of them.

[0059] Examples 1-6

[0060] Embodiments 1-6 respectively provide a medium-temperature high-strength cast nickel-based superalloy and a preparation method thereof. The composition of the medium-temperature high-strength cast nickel-based superalloy is shown in Table 1.

[0061] The preparation method of the medium-temperature high-strength cast nickel-based superalloy comprises the following steps:

[0062] (1) Electrolytic nickel, metallic aluminum, sponge titanium, metallic cobalt, metallic chromium, metallic molybdenum, and nickel boron are selected as raw materials, and the raw materials are weighed according to the actual alloy composition for standby.

[0063] (2) The electrolytic nickel and the metallic chromium are placed at the bottom of the crucible, the metallic molybdenum is placed at the top of the crucible, and the other elements are added from the hopper; the melting is performed in a vacuum induction furnace, the electrolytic nickel, the metallic chromium, the metallic cobalt, and the metallic molybdenum are heated, after the electrolytic nickel is red-hot, a small power is supplied for 10 minutes to remove hydrogen, then a large power is supplied until full melting, the refining is started, the refining temperature is 1530-1540℃, the refining is performed for 30 minutes, and the vacuum degree is less than 10 Pa during the refining; argon is added after the temperature is lowered to be close to the condensate shell, the metallic aluminum is added after the solution is clear, the sponge titanium and the nickel boron are added, after the liquid surface is clean, a large power is stirred for about 1-2 minutes, and the steel liquid is poured when the temperature is controlled to be 1440±10℃.

[0064] Table 1 Composition of different medium-temperature high-strength cast nickel-based superalloys (wt%)

[0065] Number Al Ti Co Cr Mo W B Ni Example 1 2.0 7.0 18.0 7.0 2.0 0 0.20 Remainder Example 2 2.5 9.0 21.0 8.0 3.0 0.5 0.16 Remainder Example 3 3.0 10.0 22.0 9.0 4.0 0.5 0.13 Remainder Example 4 3.5 8.5 23.0 10.0 4.5 0 0.12 Remainder Example 5 4.0 8.0 24.0 11.5 5.0 0 0.10 Remainder Example 6 4.5 7.5 25.0 13.0 6.0 0 0.07 Remainder

[0066] Comparative Examples 1-11

[0067] Comparative Examples 1-11 respectively provide a nickel-based superalloy and a preparation method thereof. The preparation method refers to Embodiment 1, and the difference lies in that the composition of the nickel-based superalloy is different. The composition of the nickel-based superalloy of Comparative Examples 1-11 is shown in Table 2.

[0068] Table 2 Composition of different nickel-based superalloys (wt%)

[0069]

[0070]

[0071] Comparative Example 12

[0072] Comparative Example 12 provides a high-temperature alloy K403 alloy, which comprises the following components in percentage by mass: Al 5.5%, Ti 2.5%, Co 5.0%, Cr 12.0%, Mo 4.0%, B 0.015%, W 5.0%, Fe 1.0%, Zr 0.05%, Ce 0.01%, C 0.15%, and the balance is Ni.

[0073] Comparative Example 13

[0074] Comparative Example 13 provides a high-temperature alloy K418, comprising the following components by mass percentage: Al 6.0%, Ti 1.0%, Cr 12.0%, Mo 4.0%, B 0.015%, Nb 2.0%, Fe 0.5%, Zr 0.10%, C 0.10%, with the balance being Ni.

[0075] Experimental Example 1

[0076] Figure 1 and Figure 2 The images show the as-cast optical microscopy (OIM) and SEM (Sequencing Microscopy) microstructures of the nickel-based superalloy provided in Example 2 of this invention. As can be seen from the images, the as-cast precipitates of the alloy of this invention mainly include γ / γ' eutectic phase, borides, and dendritic γ'. The volume fraction and size of the γ / γ' eutectic phase and borides in the alloys of different embodiments and comparative examples of this invention were statistically analyzed, and the results are shown in Table 3.

[0077] Table 3. Volume fraction and average size of precipitated phases in different alloys

[0078]

[0079]

[0080] The room temperature tensile properties, 700°C tensile properties, and high temperature creep properties of the alloys of different embodiments and comparative examples of the present invention were further tested. The test results are shown in Tables 4 and 5.

[0081] Table 4 Tensile property test results of different alloys

[0082]

[0083]

[0084] Table 5. Test results of high-temperature creep resistance of different alloys

[0085]

[0086]

[0087] The test results above show that the alloy of the present invention exhibits tensile strengths of over 1150 MPa at room temperature and over 1000 MPa at 700℃, and creep rupture lifespans of over 120 hours at 760℃ / 662 MPa and over 100 hours at 800℃ / 540 MPa, all significantly improved compared to K403 and K418 alloys. This demonstrates that the alloy of the present invention possesses superior mechanical properties at medium and low temperatures.

[0088] Experiment Example 2

[0089] The melt viscosity of the alloys of different embodiments and comparative examples of the present application in the range of 1400-1500℃ was calculated, and the calculation results are shown in Table 6.

[0090] Table 6 Melt viscosity (mpa·s) of different alloys

[0091]

[0092]

[0093] As can be seen from the above table, the melt viscosity of the alloy of the present application in the range of 1400-1500℃ is significantly lower than that of K403 alloy and K418 alloy. High viscosity of the alloy melt represents poor flowability of the melt and poor casting filling capacity of the alloy. As can be seen from the viscosity data, the flowability of the melt of the alloy of the present application is better, and the casting processability of the alloy is also better.

[0094] Carldon K et al. proposed a dimensionless micro-porosity criterion model based on the classic Niyama criterion, and the micro-porosity tendency of the alloys of Example 4 and Comparative Examples 12-13 of the present application was evaluated by the model, and the relationship between the dimensionless Niyama value and the micro-porosity index is shown in Figure 3 . The greater the micro-porosity criterion value N y * , the smaller the micro-porosity tendency. Under the same micro-porosity index f p , the micro-porosity criterion value N y * of the alloy is the smallest. In order from large to small, it is: Comparative Example 13 alloy > Example 4 alloy > Comparative Example 12 alloy, i.e. the micro-porosity tendency of K418 alloy is the smallest, the alloy of Example 4 of the present application is the second, and the micro-porosity tendency of K403 alloy is the largest.

[0095] Hot cracking tendency is another standard that can reflect the casting processability of the alloy. When the volume increase amount of the un-solidified area between two adjacent dendritic crystals caused by strain cannot be balanced by the flow of the liquid alloy and the transverse growth amount of the two dendritic crystals, a hot crack will be formed at the place. Kou et al. proposed a hot cracking tendency criterion model, and the greater the Kou value, the greater the hot cracking tendency. The hot cracking tendency of the alloys of Example 4 and Comparative Examples 12-13 of the present application was evaluated by the model, and the results are shown in Figure 4 . As can be seen from the figure, the hot cracking tendency of K418 alloy is the largest, that of K403 alloy is the second, and the hot cracking tendency of the alloy of Example 4 of the present application is the smallest.

[0096] In summary, the nickel-based high-temperature alloy of the present application has excellent mechanical properties at medium and low temperatures and casting processability, and can meet the use requirements of integral casting of complex structural parts.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A medium temperature, high strength cast nickel-base superalloy characterized by, comprising, by mass percent: Al 1% to 5%, Ti 5% to 10%, Co 18% to 25%, Cr 7% to 13%, W+Mo 2% to 6%, B 0.07% to 0.2%, Zr <0.05%, and the balance Ni; the sum of the mass percent of Al and the mass percent of Ti satisfies: Al+Ti≥9%; the ratio of the mass percent of Ti and the mass percent of Al satisfies: 1.5≤Ti / Al≤4; the phase composition of the alloy comprises: a matrix γ phase, a dendrite stem γ' phase, a γ / γ' eutectic phase, and a boride; the volume fraction of the γ / γ' eutectic phase is 15% to 55%; the volume fraction of the boride is 1% to 3%; and the phase composition of the alloy does not contain carbide.

2. The intermediate temperature high-strength cast nickel-base superalloy of claim 1, wherein, in the alloy, the mass percent of C is <0.06%.

3. The intermediate temperature high-strength cast nickel-base superalloy of claim 1, wherein, the alloy does not contain C element.

4. A method of producing a medium temperature high strength cast nickel-based superalloy, characterised in that, comprising the following steps: ingredient dispensing of the medium-temperature high-strength cast nickel-based superalloy according to any one of claims 1 to 3, vacuum induction melting, and then pouring.

5. A structural member, characterized by prepared by using the medium-temperature high-strength cast nickel-based superalloy according to any one of claims 1 to 3.

6. The structural member of claim 5, wherein has at least one of the following characteristics: (1) the room temperature tensile property of the structural part satisfies: tensile strength≥1150MPa; (2) the 700℃ tensile property of the structural part satisfies: tensile strength≥1000MPa; (3) the structural part has a stress-rupture life≥120h under the condition of 760℃ / 662MPa; and the structural part has a stress-rupture life≥100h under the condition of 800℃ / 540MPa.

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