A high-strength, low-crack-sensitive nickel-based cast equiaxed superalloy

Abstract

The application discloses a high-strength low-crack-sensitive nickel-based cast isometric high-temperature alloy, and the alloy chemical composition comprises, in percentage by mass, the balance being Ni; the mass fraction ratio of Ti and Al elements is 0.5-1.5; the sum of the mass fractions of Ti and Al elements is 0.5-1.5; the sum of the mass fractions of Ta, Mo and W elements is 0.5-1.5; and the sum of the mass fractions of C, B and Zr elements is 0.01-0.05. The application controls the total amount of Al and Ti elements to reduce the crack tendency in the alloy, controls the ratio to form a proper volume fraction of precipitated phase, forms solid solution strengthening to enhance the intracrystalline strength, contains only trace discontinuous carbide at the grain boundary, improves the balance of the intracrystalline strength and the grain boundary strength, and improves the room-temperature tensile property and the endurance life of the alloy.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy technology, specifically relating to a high-strength, low-crack-sensitivity nickel-based cast equiaxed high-temperature alloy. Background Technology

[0002] Nickel-based superalloys are widely used in the hot-end core components of equipment such as aerospace engines and industrial gas turbines due to their excellent comprehensive mechanical properties, good oxidation resistance, and hot corrosion resistance at high temperatures. Among them, nickel-based cast equiaxed superalloys occupy a mainstream position in the manufacture of large and complex structural parts (such as turbine disks and turbine blades) due to their relatively low manufacturing cost and good microstructure and properties. Traditional high-performance nickel-based cast superalloys mainly rely on three methods to improve mechanical properties: first, solid solution strengthening by adding refractory elements such as Mo, W, and Ta; second, forming a high content of elements such as Al and Ti to form a high-performance alloy. The main method is to improve the intracrystalline strength by using coherent precipitate strengthening phases; the third method is to add grain boundary strengthening elements such as C, B, and Zr to precipitate carbides or borides at the grain boundaries to pin the grain boundaries and prevent grain boundary slippage.

[0003] However, with the continuous improvement of the performance of aerospace engines and industrial gas turbines, the performance requirements for high-temperature alloys used in turbine blade structures are also becoming increasingly stringent. In pursuit of higher strength, existing alloy designs often tend to incorporate large amounts of Al and Ti elements, resulting in intragranular... The volume fraction of the strengthening phase is significantly increased. While this design approach significantly improves the macroscopic strength of the alloy, it introduces serious technical drawbacks. The excessively high volume fraction... The presence of these phases results in extremely high intragranular strength and deformation resistance. During the cooling and solidification process of castings or subsequent welding and heat treatment, the difficulty in achieving plastic coordination deformation within the grains leads to a high concentration of thermal or shrinkage stresses at relatively weak grain boundaries, resulting in the initiation and propagation of hot cracks or strain-aging cracks. Furthermore, for components such as turbine stator blades, subsequent welding repairs are often required, and high Al and Ti content significantly promotes weld crack formation, making welding difficult. In addition, existing high-strength alloys typically increase the content of grain boundary strengthening elements such as C, B, and Zr to match the extremely high intragranular strength. This easily leads to the precipitation of continuously distributed, coarse-sized primary carbides and eutectic structures at grain boundaries. These continuously distributed hard and brittle phases often become crack initiation sites under stress, significantly increasing the alloy's crack susceptibility and causing a substantial decrease in plasticity.

[0004] Therefore, how to effectively reduce the crack susceptibility during solidification and welding while maintaining the high strength of the alloy, and improve its plasticity and processing properties, has become a key technical challenge that urgently needs to be solved in the field of nickel-based superalloys for gas turbine blades. Developing a novel high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy with a good match between intragranular and grain boundary strength and a more rational microstructure has significant engineering application value for improving the reliability and service life of gas turbine blades. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength, low-crack-susceptibility nickel-based cast equiaxed high-temperature alloy.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy, with the following chemical composition by mass percentage: , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

[0008] A further improvement of this invention is that, by mass percentage, the alloy chemical composition... , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

[0009] A further improvement of this invention is that, after heat treatment, the alloy exhibits [certain improvements] within the grains. The volume fraction of the strengthening phase shall not exceed .

[0010] A further improvement of the present invention is that, after heat treatment, only trace amounts of discontinuous carbides exist at the grain boundaries of the alloy.

[0011] A further improvement of this invention is that, after heat treatment, the tensile yield strength of the alloy at room temperature is not less than [a certain value]. Tensile strength not less than The elongation rate is not less than ; and Under certain conditions, the service life is not less than ; and Under certain conditions, the service life is not less than .

[0012] Addressing the challenge of rapidly increasing crack susceptibility alongside high strength in current nickel-based cast equiaxed superalloys, the alloy design concept and innovation of this invention lies in improving casting / welding crack susceptibility while maintaining high-temperature strength. Traditional approaches often compromise one aspect for another, while this solution reduces the low melting point that induces cracks by regulating the strengthening mechanism and decreasing precipitation strengthening (Ti, Al) and grain boundary elements (C, B, Zr). Eutectic structure and carboroides reduce crack susceptibility; solid solution strengthening (Ta, Mo, W) compensates for the strength loss caused by reduced precipitation strengthening (Ti, Al) and grain boundary elements (C, B, Zr). By controlling the total mass fraction of Ti and Al and their ratio, the intragranular structure after heat treatment was successfully improved. The volume fraction of the strengthening phase is limited to below 45%, overcoming the limitations of traditional high-strength alloys. The high concentration of certain phases leads to a significant technical defect in intragranular deformation resistance. Simultaneously, the alloy strictly limits the total content of grain boundary strengthening trace elements such as C, B, and Zr, effectively preventing the precipitation of continuous, coarse primary carbides and hard, brittle eutectic structures at grain boundaries, resulting in only trace amounts of discontinuous carbides at the grain boundaries after heat treatment. Furthermore, the appropriate addition of refractory elements such as Mo, W, and Ta enables effective solid solution strengthening. This invention, through innovative synergistic control of alloy composition and microstructure, optimizes and improves the balance between intragranular strength and grain boundary strength at the microscopic level.

[0013] The specific basis for the selection of alloying elements and their composition range in this invention is as follows:

[0014] Ti and Al are The main forming elements of the strengthening phase, their total amount and proportion directly determine the... The volume fraction and stability of the phase. This invention will... Total content strictly controlled at and will The ratio is limited to To ensure the intracrystalline structure after heat treatment Phase volume fraction not exceeding This approach provides sufficient precipitation strengthening for the alloy while avoiding the negative effects of precipitation. Excessive eutectic phase leads to excessive resistance to deformation within the grains, thereby effectively improving the plastic coordination deformation capacity within the grains, while reducing the formation of eutectic phases and reducing crack formation during solidification, welding and other processes.

[0015] Grain boundary strengthening elements C, B, and Zr readily form continuous, coarse primary carbides, borides, and low-melting-point eutectic structures at grain boundaries in conventional alloys, which are the main causes of hot cracking and strain-aging cracking. This invention addresses these issues by strictly limiting… , , And control the total amount of the three This results in the alloy exhibiting only a small amount of discontinuous carbide morphology at the grain boundaries after heat treatment, significantly reducing the crack sensitivity of the grain boundaries and improving the welding and casting process performance of the alloy.

[0016] Refractory elements Mo, W, and Ta, due to their large atomic radii, can effectively expand [the range of refractory elements]. phase and The lattice mismatch between phases promotes the formation of a high-density dislocation network at the phase interface, comprehensively improving the alloy's resistance to high-temperature creep. However, if the addition amount is too high, it will not only promote the precipitation of harmful topologically close-packed phases, but also cause severe compositional segregation during the melting and solidification process. By controlling... Total amount in Within a certain range, it can exert a strong solid solution strengthening effect while avoiding the precipitation of harmful phases and severe component segregation due to excessive addition, thus maintaining the high-temperature stability of the tissue.

[0017] Co is mainly dissolved in the matrix, playing a role in solid solution strengthening and reducing... The dissolution temperature of the phase is controlled, thus broadening the heat treatment process window. Its limitation is that excessively high Co content promotes the precipitation of harmful topologically close-packed phases, reducing long-term microstructure stability and increasing alloy costs. This invention controls it within... While ensuring sufficient enhancement effect, it effectively suppresses the risk of formation of harmful topologically dense phases.

[0018] Cr is an indispensable element for ensuring the alloy's resistance to oxidation and hot corrosion. At high temperatures, it can form a dense matrix on the surface. An oxide film is formed, which also has a certain solid solution strengthening effect. Its limitation is that excessive Cr strongly promotes the precipitation of brittle and harmful phases such as the σ phase, severely deteriorating the alloy's plasticity and creep rupture life. This invention defines it as... While meeting the requirements for corrosion resistance, it avoids the high precipitation tendency range of harmful phases.

[0019] In addition, Nb is an effective enhancing element that can improve... The volume fraction and thermal stability of the phases enhance the precipitation effect and help improve the alloy's resistance to grain boundary corrosion. Hf can improve melt fluidity and inhibit the formation of casting defects, thus improving the casting performance of nickel-based superalloys. Adding trace amounts of Nb and Hf can further optimize the grain boundary structure and... Phase stability and improved casting properties, the range of which is , .

[0020] The beneficial effect of this invention is that by simultaneously confining precipitation strengthening elements (Ti, Al) and grain boundary elements (C, B, Zr) within a specific narrow window, a dual synergistic crack-resistant mechanism is achieved, which delays stress generation within the matrix and suppresses low-melting-point liquid films at grain boundaries. While existing technologies mention that reducing certain elements can improve cracking, they fail to recognize the multi-stage complexity of high-temperature alloy cracking. Ti and Al control strain-aging cracking: Ti and Al determine... The precipitation kinetics of the phase. If precipitation is too rapid or the volume fraction is too large, it can generate enormous internal stresses during heat treatment or weld cooling. Controlled It is to delay The precipitation kinetics window of the phase increases the ductility of the material. C, B, and Zr control the grain boundary liquid phase cracking: these elements are very prone to segregation at grain boundaries, forming low-melting-point eutectic phases (such as borides and carbides). Reducing C, B, and Zr can reduce the formation of grain boundary liquid films.

[0021] The beneficial effect of this invention is that it reduces... In the technical context of total loss intensity, by Compared to locking in This achieves strength-oriented compensation under low total quantity constraints. The total amount controls the hard boundary of crack sensitivity: existing technology believes that to achieve low cracking, the total amount of strengthening elements must be reduced overall. This invention will... The sum of the mass fractions is strictly limited to The purpose of this interval is to lock in a macroscopic safety window that can effectively prevent cracking. The quality ratio control is under low total quantity constraints Phase enhancement potential and macro-intensity compensation: Existing technologies generally ignore the role of relative ratios under low total quantity constraints. At that time: Although the Ti content was relatively higher, The stability of the phase decreases, or large-sized primary phases are formed during solidification. This phase leads to poor strengthening effect and may even be detrimental to crack sensitivity. Compare At that time: the Al content was relatively higher, resulting in... Coherent strains are weak, with insufficient strengthening potential, and cannot effectively compensate for the loss of strength. Inside this narrow window, The amount and morphology of the phase precipitation are coherent with the matrix strain and stability, which can maximize the precipitation strengthening potential of limited strengthening elements and achieve strength maintenance at low total amounts.

[0022] The beneficial effects of this invention are that it alleviates the situation of high strength and high crack susceptibility occurring simultaneously in the field of nickel-based cast superalloys. Thanks to the aforementioned rational strength-toughness matching design, this alloy significantly improves the intragranular plasticity and deformation coordination capabilities, effectively preventing the high concentration of thermal or shrinkage stress at weak grain boundaries. This greatly reduces the crack susceptibility (including hot cracking and strain-aging cracking) of large and complex castings during cooling solidification, subsequent welding, and heat treatment. In terms of macroscopic mechanical properties, this alloy achieves an excellent combination of strength and plasticity, with a room temperature tensile yield strength not lower than […]. Tensile strength not less than And the elongation rate remains above; and Under certain conditions, the service life is not less than ; and Under certain conditions, the service life is not less than This combination of high strength, high plasticity, and excellent machinability meets the stringent service requirements of hot-end core components such as turbine stator blades in industrial gas turbines, and can effectively improve the manufacturing qualification rate and long-term operational reliability of equipment. Attached Figure Description

[0023] Figure 1 This is a backscattered electron image of the alloy grains after heat treatment in Example 1 of this invention.

[0024] Figure 2 This is a secondary electron image of the intracrystalline microstructure of the alloy after heat treatment in Example 1 of this invention.

[0025] Figure 3 This is a secondary electron image of the grain boundary microstructure of the alloy after heat treatment in Example 1 of this invention. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0027] A high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy, with the following chemical composition by mass percentage: , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

[0028] Preferably, a high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy, with the following chemical composition by mass percentage: , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

[0029] After the alloy meeting the above conditions is smelted into a master alloy, it is remelted and solidified to prepare an equiaxed alloy. For the cast alloy, a solution treatment and aging process can be used. To obtain high-strength, low-crack-susceptibility nickel-based cast equiaxed high-temperature alloys.

[0030] The following are specific embodiments and comparative examples:

[0031] Example 1

[0032] A high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy, comprising, by mass percentage, , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is 1.13, and the sum of the mass fractions of Ti and Al is... The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B, and Zr is .

[0033] Example 2

[0034] A high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy, comprising, by mass percentage, , , The balance is Ni; the mass fraction ratio of Ti to Al is 1.11, and the sum of the mass fractions of Ti and Al is... The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B, and Zr is .

[0035] Example 3

[0036] A high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy, comprising, by mass percentage, , , The balance is Ni; the mass fraction ratio of Ti to Al is 1.18, and the sum of the mass fractions of Ti and Al is... The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B, and Zr is .

[0037] Comparative Example 1

[0038] A nickel-based cast equiaxed superalloy, comprising, by mass percentage, , , The balance is Ni; the mass fraction ratio of Ti to Al is 0.82, and the sum of the mass fractions of Ti and Al is... The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B, and Zr is .

[0039] Comparative Example 2

[0040] A nickel-based cast equiaxed superalloy, alloy designation IN738LC, comprising, by mass percentage, , , The balance is Ni; the mass fraction ratio of Ti to Al is 1.01, and the sum of the mass fractions of Ti and Al is... The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B, and Zr is .

[0041] Comparative Example 3

[0042] A nickel-based cast equiaxed superalloy, alloy grade: By mass percentage, including , The balance is Ni; the mass fraction ratio of Ti to Al is 1.68, and the sum of the mass fractions of Ti and Al is... The sum of the mass fractions of Mo and W is The sum of the mass fractions of C, B, and Zr is .

[0043] Table 1 shows the results of heat treatment for Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3. Phase volume fraction, room temperature tensile properties, and creep life. Examples 1, 2, and 3 of this invention... The volume fractions of the strengthening phases are respectively In contrast, Comparative Example 1 Phase volume fraction is Comparative Examples 2 and 3, representing traditional high-strength alloys, Phase volume fractions were as high as Regarding room temperature tensile properties, the yield strength of the embodiments of the present invention is slightly lower than that of the comparative example, while the tensile strength and elongation are significantly higher. Regarding creep rupture life, the creep rupture life of the embodiments of the present invention is higher than that of comparative examples 1 and 2, but lower than that of comparative example 3.

[0044] Table 1. Microstructure characteristics, tensile properties, and durability of the Examples and Comparative Examples

[0045]

[0046] Comprehensive comparative data shows that, through the control of the total amount and ratio of Ti and Al, and the strict restriction of grain boundary strengthening elements such as C, B, and Zr, this invention enables the alloy to obtain a more reasonable microstructure after heat treatment, thereby reducing... By optimizing the phase volume fraction and grain boundary structure, an excellent balance between strength and ductility is achieved, significantly reducing the alloy's brittle fracture tendency. Compared to traditional grades, the alloy of this invention significantly improves the material's ductility and deformation coordination while maintaining comparable or higher strength levels. This high strength and toughness, along with low crack sensitivity, is of crucial technical significance for solving the cracking problem of large and complex castings during solidification and subsequent hot working, and can significantly improve the service life and reliability of hot-end components in aerospace engines and industrial gas turbines.

[0047] Figure 1 The image shows a backscattered electron image of the alloy grains after heat treatment in Example 1, revealing trace amounts of carbide precipitation at the grain boundaries. Figure 2 These are secondary electron images of the intragranular alloy microstructure after heat treatment in Example 1. The phase morphology is flower-like, and the volume fraction is close to . Figure 3 These are secondary electron images of the microstructure of the grain boundary alloy after heat treatment in Example 1, showing the grain boundaries. The phase morphology is irregular blocky, which acts as a pinning agent at grain boundaries.

[0048] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy, characterized in that: Chemical composition of alloy by mass percentage , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

2. The high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy according to claim 1, characterized in that: Chemical composition of alloy by mass percentage , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

3. The high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy according to claim 1, characterized in that: After heat treatment, the alloy's intragranular structure... The volume fraction of the strengthening phase shall not exceed .

4. The high-strength, low-crack-susceptibility nickel-based cast equiaxed superalloy according to claim 1, characterized in that: After heat treatment, the yield strength of the alloy at room temperature is not less than Tensile strength not less than The elongation rate is not less than ; and Under certain conditions, the service life is not less than ; Under 150MPa conditions, the service life is not less than 40 hours.

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