A high-strength equiaxed crystal cast superalloy

Abstract

The present invention relates to a high-strength equiaxed crystal cast superalloy, belonging to the technical field of cast superalloys. The chemical composition of the alloy is by mass percentage: C 0.15% - 0.19%, Cr 8.4% - 9.2%, Co 9.5% - 10.3%, Mo 1.4% - 2.0%, W 9.8% - 10.5%, Al 5.2% - 5.7%, Ti 2.3% - 2.8%, Nb 0.8% - 1.2%, B 0.015% - 0.034%, Zr 0.02% - 0.039%, Y 0.0001% - 0.005%, Ce 0.0005% - 0.01%, and the balance is Ni. The present invention has high high-temperature strength and good oxidation and corrosion resistance, with superior comprehensive performance and low cost. It is suitable for use as turbine guide vanes, turbine working blades, and integral turbine guides of aviation and aerospace engines, etc., and can also be used as high-temperature molds.

Description

Technical Field

[0001] The present invention belongs to the technical field of casting high-temperature alloys and provides a high-strength equiaxed crystal casting high-temperature alloy, which is mainly suitable for preparing gas turbine guide blades working below 1050°C, gas turbine working blades working below 1000°C and integral turbine guide vanes, and can also be used as a high-temperature mold. Background Art

[0002] In modern advanced aircraft engines, the amount of high-temperature alloy materials accounts for 40% to 60% of the total engine volume. Every increase in the thrust-to-weight ratio of the engine is strongly dependent on the progress of high-temperature alloys. As the thrust-to-weight ratio of the engine continues to increase, the turbine inlet temperature increases significantly, and the turbine blade material gradually develops from equiaxed crystal alloys to oriented and single crystal alloys, and its temperature bearing capacity continues to improve. At present, oriented and single crystal alloys have become the dominant materials for aircraft engine turbine blades, but equiaxed crystal high-temperature alloys are still widely used in turbine blades, integral blade disks, integral guides of casings, and other high-temperature structural parts with slightly lower temperature bearing, such as K403, K417G, MAR-M200, IN100, ЖС6K, etc., which can significantly reduce the difficulty and cost of blade manufacturing. For example, the low-pressure turbine blades of the CFM56-5 / 7 engine use IN100 and Rene77 alloys; the low-pressure turbine blades of the V2500 engine use ordinary casting alloys IN100 and IN713 alloys. The low-pressure turbine blades and low-pressure guide blades of a domestic engine are both made of K417G alloy. In addition, equiaxed alloys are also widely used in high-temperature components of gas turbines (working blades, guide blades, turbine nozzles, etc.), such as Rene80, X-40, In738, In792, In939, GTD 111, GTD 222, ЧС88y-ВИ, ЧС91, etc.

[0003] As the thrust-to-weight ratio of engines continues to increase, the requirements for the temperature bearing capacity of equiaxed crystal casting high-temperature alloys are also getting higher and higher. In order to meet the needs of advanced aircraft engines and gas turbines, it is necessary to develop equiaxed crystal casting high-temperature alloys with high temperature bearing capacity. Some high-strength equiaxed crystal casting high-temperature alloys developed in China have been used as turbine working blades, turbine guide blades, turbine outer rings, etc. on various types of domestic aircraft engines. During their use, they have exposed problems such as unstable alloy performance and poor high-temperature microstructure stability. For example, the high-temperature endurance life does not meet the technical index requirements, and TCP is easily precipitated. This is related to the wide range of alloy composition and large fluctuations in alloy composition. For example, there are only upper limit requirements for micro-alloying elements, but no lower limit requirements. As a result, the alloy performance varies greatly. Even for the same brand of alloy, the actual alloy composition varies greatly between different manufacturers and different production batches, which is not conducive to the performance of aircraft engines. Summary of the invention

[0004] The object of the present invention is:

[0005] To meet the requirements of advanced aero-engines, the present invention provides a high-strength equiaxed crystal cast superalloy, which contains a relatively high content of W, appropriate amounts of Cr, Co, Mo, Nb, Ti, Al, and is microalloyed with Y, Ce, Zr, B, C. Through the synergistic effect of second-phase strengthening, solid-solution strengthening, and grain-boundary strengthening, the alloy has excellent high-temperature strength, good oxidation and corrosion resistance, and does not contain rare and precious elements, with low cost.

[0006] To solve this technical problem, the technical solution of the present invention is:

[0007] A high-strength equiaxed crystal cast superalloy, by mass percentage, its chemical composition is: C 0.15% - 0.19%, Cr 8.4% - 9.0%, Co 9.5% - 10.3%, Mo 1.4% - 2.0%, W 9.8% - 10.5%, Al 5.2% - 5.7%, Ti 2.3% - 2.8%, Nb 0.8% - 1.2%, B 0.015% - 0.034%, Zr 0.02% - 0.039%, Y 0.0001% - 0.005%, Ce 0.0005% - 0.01%, and the balance is Ni and inevitable trace impurity elements.

[0008] The requirements for the element content in the superalloy are that 7.7% ≤ Al + Ti ≤ 8.3%, and the mass ratio of Al to Ti is 1.95 - 2.35.

[0009] For equiaxed crystal cast superalloys, their phase composition mainly includes γ phase (Ni solid solution), γ' phase (Ni3(Al,Ti)), and carbide phase. Among them, the γ phase is the matrix, and the γ' phase and carbide phase are both strengthening phases. The alloy strengthening methods include second-phase strengthening, solid-solution strengthening, and grain-boundary strengthening. The reasonable ratio of alloying elements is the guarantee of the good comprehensive performance of the alloy. The Ni3(Al,Ti) phase is the main strengthening phase of nickel-based superalloys. Generally, the high-temperature strength of the alloy increases with the increase in the content of the Ni3(Al,Ti) phase. When its content exceeds 50%, the alloy has good high-temperature strength. However, if the content of the Ni3(Al,Ti) phase exceeds 55%, it means that the content of the γ phase is relatively low. Alloying elements such as W and Mo are mainly dissolved in the γ phase. The decrease in the content of the γ phase will lead to the precipitation of harmful TCP phases such as the μ phase, resulting in a decrease in the high-temperature strength and tissue stability of the alloy. Both Al and Ti are elements for forming Ni3(Al,Ti), and their contents strongly affect the alloy performance. Therefore, the present invention not only needs to control the contents of Al and Ti separately, but also needs to control the total amount of Al + Ti to be 7.7% - 8.3% to make the content of the Ni3(Al,Ti) phase reach 50% - 55%.

[0010] In this application, the mass ratio of Al to Ti is 1.95 to 2.35. The mass ratio of Al and Ti affects the strength and corrosion resistance of the alloy. Among them, Al contributes relatively more to the strength, and Ti contributes relatively better to the corrosion resistance. If the mass ratio of Al and Ti is relatively high, the strength is good but the corrosion resistance is poor. The gas in the aeroengine has a corrosive atmosphere, which is likely to damage the turbine working blades, turbine guide vanes, turbine outer rings, etc. If the mass ratio of Al and Ti is relatively low, although the corrosion resistance is relatively excellent, it may be difficult to meet the strength index requirements mentioned in the background art.

[0011] Furthermore, the element content in the superalloy is required to satisfy 12.3% ≤ W + Mo + Nb ≤ 13.3%.

[0012] The solution strengthening of the cast alloy is usually achieved by refractory elements such as W, Mo, Nb, Ta, Re, Ru, etc. dissolving into the matrix and Ni3(Al,Ti) to cause lattice distortion. Among them, W is dissolved in the γ and γ' phases in equal amounts, and has a good solution strengthening effect on both; most of Mo is dissolved in the γ matrix, and only about 1 / 4 is dissolved in the γ' phase. Mo mainly strengthens the γ matrix, but when the Mo content is too high, TCP phase is likely to precipitate; while Nb mainly has a solution strengthening effect on the γ' phase. In the present invention, W is used as the main solution strengthening element, and at the same time, Mo and Nb are used for complex alloying to balance the strengthening effects of W and Mo on the γ matrix, and also balance the strengthening effects on the γ matrix and γ' phase. At the same time, the total amount of W + Mo + Nb in the present invention is controlled to be 12.3% - 13.3% to achieve sufficient strengthening of the alloy, avoiding insufficient solution strengthening caused by too low total amount of refractory elements, and at the same time avoiding the precipitation of TCP phase due to too high content of refractory elements.

[0013] In a preferred embodiment, C is 0.16% - 0.18%, Cr is 8.4% - 8.9%, Co is 9.8% - 10.3%, Mo is 1.4% - 1.9%, W is 9.8% - 10.3%, Al is 5.2% - 5.6%, and Ti is 2.3% - 2.6%.

[0014] The Y content in the alloy is 0.0005% to 0.003%, and the Ce content is 0.001% to 0.006%. The B content in the alloy is 0.015% to 0.025%, and the Zr content is 0.025% to 0.039%. The rare earth element Y and Ce microalloying technology has a significant effect on improving the high-temperature oxidation resistance of the alloy, and has desulfurization and deoxidation effects, purifies the grain boundaries, and reduces the harmful effects of oxygen and sulfur on the grain boundaries. In addition, the rare earth element Y improves the morphology and distribution of carbides and improves the thermal stability of carbides; Ce improves the stability of the γ' phase. However, excessive Y and Ce contents will cause the precipitation of Y-rich and Ce-rich phases, resulting in a significant decrease in alloy performance. Therefore, the Y and Ce contents need to be appropriate, which are 0.0001% to 0.005% Y and 0.0005% to 0.01% Ce in the present invention.

[0015] The high-strength equiaxed crystal casting high-temperature alloy adopts a vacuum induction furnace to prepare alloy test bars, the alloy pouring temperature is 1440°C to 1500°C, and the mold shell temperature is 850°C to 950°C.

[0016] The heat treatment process of the high-strength equiaxed crystal casting high-temperature alloy is 1200° C. to 1220° C., heat preservation for 3 to 5 hours, and air cooling to room temperature.

[0017] The high-strength equiaxed crystal casting high-temperature alloy has excellent high-temperature strength, and the creep strength σ 0.2 The high temperature alloy is used to prepare gas turbine blades, integral turbine guide vanes and gas turbine guide vanes working at temperatures below 1000°C and below 1050°C.

[0018] For equiaxed crystal casting high-temperature alloys, carbides are also important strengthening phases. C preferentially combines with elements such as Ti and Nb to form MC phases. When the W / Mo and Cr contents are very high, M6C and M6C may also precipitate. 23 C6, the number, size, shape and distribution of carbides all significantly affect their strengthening effect. The C content directly affects the number of carbides. At the same time, C is also an important grain boundary strengthening element. Therefore, C is a very important microalloying element for equiaxed crystal casting high-temperature alloys. If the C content is too low, the number of carbides is insufficient and the strengthening effect is insufficient; if the C content is too high, the number of carbides is too large, resulting in a decrease in alloy plasticity and a large amount of solid solution strengthening elements is consumed, which is not conducive to the strength of the alloy. Therefore, the present invention controls the C content to 0.15% to 0.19%.

[0019] There are many grain boundaries in equiaxed crystal casting high-temperature alloys, and the grain boundary strength has a significant effect on the medium and high temperature strength of the alloy. B and Zr are important grain boundary strengthening elements. B atoms are enriched at the grain boundaries, increasing the grain boundary bonding force, reducing the content of harmful elements at the grain boundaries, and inhibiting the precipitation of harmful phases at the grain boundaries, which have a significant effect on the durability and creep properties of the alloy; Zr atoms are also concentrated at the grain boundaries, reducing grain boundary defects, improving grain boundary strength, while reducing the grain boundary interface energy, changing the morphology and size of the grain boundary phase, and effectively preventing grains from sliding along the crystal. In addition, Zr can also combine with S to form sulfides or sulfur carbides, reducing the S content of the alloy. If the B and Zr content is too low, the grain boundaries cannot be sufficiently strengthened, and the insufficient grain boundary strength leads to a decrease in the performance of the alloy; if the B and Zr content is too high, it will lead to the formation of second phases such as borides and Ni5Zr, which is also unfavorable to the performance of the alloy. Therefore, for the alloy composition of the present invention, the content of trace elements such as B and Zr needs to be controlled within an appropriate range.

[0020] Co has an inhibitory effect on the precipitation of TCP phase, but too high a Co content will reduce the solid solution temperature, resulting in a reduction in the high temperature performance of the alloy. To ensure the high temperature performance of the alloy, the Co content in the present invention is controlled at 9.5% to 10.3%.

[0021] Cr is a key element to improve the hot corrosion performance of alloys. An appropriate amount of Cr must be added to the alloy to ensure hot corrosion resistance. However, since the content of refractory elements such as W, Mo, and Nb in the alloy of the present invention is relatively high, adding a large amount of Cr will increase the tendency of alloy σ phase precipitation, which is unfavorable to the performance of the alloy. Therefore, the present invention controls the Cr content to 8.4% to 9.2%.

[0022] Compared with the prior art, the solution provided by this application includes at least the following beneficial technical effects:

[0023] (1) A high-strength equiaxed crystal casting high-temperature alloy provided by the present invention is compositely alloyed by adding W, Mo, Nb, Cr, Co, Ti, Al and other elements, and the composition range of the main alloying elements such as W, Cr, Co, Mo, Nb, Ti, Al is reasonably adjusted, and the total amount of Al+Ti is controlled to be 7.7% to 8.3%, so that the Ni3(Al, Ti) phase content reaches 50%-55%; at the same time, the total amount of W+Mo+Nb is controlled to be 12.3% to 13.3%, so as to fully strengthen the alloy and avoid the precipitation of TCP phase due to excessive content of refractory elements; through the synergistic effect of Ni3(Al, Ti) second phase strengthening and solid solution strengthening, the alloy of the present invention has excellent high-temperature strength, especially the creep performance is significantly better than that of K403, K417G and other alloys, as shown in Table 1 below.

[0024] Table 1 Comparison of the rupture and creep strength of the alloy of the present invention and domestic equiaxed alloys (MPa)

[0025]

[0026] a The creep life is 61 h; b The creep life is 105 h

[0027] (2) A kind of high-strength equiaxed crystal cast superalloy provided by the present invention, by reasonably adjusting the contents of antioxidant elements Al and Cr, controlling the mass ratio of Al to Ti to be 1.95 - 2.35, and adding appropriate amounts of rare earth elements Y and Ce, enables the alloy to have excellent oxidation and corrosion resistance. The static oxidation resistance at 1000 °C can reach the complete oxidation resistance level, and the gas hot corrosion resistance at 900 °C is excellent. See Examples 1 - 3 for details.

[0028] (3) Compared with the existing equiaxed crystal cast superalloys, a kind of high-strength equiaxed crystal cast superalloy provided by the present invention controls the contents of microalloying elements such as Y, Ce, B, Zr, and C within an appropriate range. Through grain boundary strengthening and carbide strengthening, the high-temperature strength of the alloy of the present invention is further improved, and at the same time, it has excellent high-temperature oxidation resistance. Y, Ce, B, Zr, and C are the key microalloying elements for the alloy of the present invention to have excellent comprehensive properties. See Examples 7 and 8 for details.

[0029] (4) A kind of high-strength equiaxed crystal cast superalloy provided by the present invention does not contain precious elements such as Ta, Re, and Ru, and has low cost. Brief Description of the Drawings

[0030] Figure 1 is the morphology of acicular TCP phase in the alloy of the present invention with the total amount of W + Mo + Nb reaching 14%;

[0031] Figure 2 is the morphology of carbide in the alloy of the present invention with a Y content of 0.001%;

[0032] Figure 3 is the morphology of carbide in the alloy of the present invention with a Y content of 0.01%;

[0033] Figure 4 is the morphology of Y-rich phase in the alloy of the present invention with a Y content of 0.04%;

[0034] Figure 5 is the morphology of carbide in the alloy of the present invention without Y and Ce. Detailed Description of the Embodiments

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in combination with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0036] The preparation processes used in all the examples and comparative examples are the same. That is, a vacuum induction melting process is used to prepare the base composition alloy, and a common casting process is used to prepare test bars in a vacuum melting and casting furnace. When preparing the test bars, appropriate amounts of elements such as Al, Ti, W, Mo, Y, Ce, B, and Zr are added to adjust the alloy composition. All test bars are cast with a pouring temperature of 1440 °C to 1500 °C and a mold shell temperature of 850 °C - 950 °C. Subsequently, all test bars are heat-treated at 1210 °C for 4 h with air cooling, and then processed into mechanical property specimens to test their creep rupture life at 975 °C / 225 MPa.

[0037] Examples 1 - 3:

[0038] To illustrate the influence of the total amount of Al + Ti on the properties of this alloy, Examples 1 - 3 and Comparative Examples 1 - 2 were conducted. Their alloy compositions and creep rupture lives at 975 °C / 225 MPa are shown in Tables 2 and 3 respectively. It can be seen that in the current alloy system, when the total amount of Al + Ti is 7.7% - 8.3% and the mass ratio of Al to Ti is 1.95 - 2.35, the alloy of the present invention has good high-temperature creep rupture properties and good oxidation and corrosion resistance. The oxidation resistance at 1000 °C is a complete oxidation resistance level according to HB5258 - 2000, and the average corrosion rate of gas hot corrosion at 900 °C is 1.04 g / (m 2 ·h), which is far better than DZ4 and DZ22 alloys. However, when the total amount of Al + Ti is too high or too low, the high-temperature creep rupture properties of the alloy will significantly decrease.

[0039] Examples 4 - 6:

[0040] Regarding the influence of the total amount control of W + Mo + Nb on the properties of this alloy, Examples 4 - 6 and Comparative Examples 3 - 4 were conducted. Their alloy compositions and creep rupture lives at 975 °C / 225 MPa are shown in Tables 2 and 3 respectively. It can be seen that the total amount of W + Mo + Nb has a significant influence on the high-temperature creep rupture properties of the alloy. When the total amount of W + Mo + Nb is too high or too low, the high-temperature creep rupture properties of the alloy will significantly decrease. The reason is that when the total amount of W + Mo + Nb is too high, acicular TCP phases will precipitate (as Figure 1 shown), and when the total amount of W + Mo + Nb is too low, the alloy is not sufficiently strengthened.

[0041] Examples 7 - 8:

[0042] In view of the influence of rare earth elements on the performance of the alloy, Examples 7-8 and Comparative Examples 5-7 were prepared, and their alloy compositions and 975°C / 225MPa rupture life are shown in Table 2 and Table 3, respectively. It can be seen that the content of rare earth elements such as Y and Ce should be controlled within an appropriate range. When the Y content is 0.01% or the Ce content is 0.015%, the 975°C / 225MPa rupture life of the alloy decreases from more than 60h to less than 20h. This is mainly because the excessive Y and Ce content changes the carbide from a loose skeleton to a block (such as attached Figure 2 , Figure 3 As shown), there are even Y-rich and Ce-rich phases ( Figure 4 ), which leads to a significant decrease in the high temperature durability of the alloy; when the alloy does not contain Y and Ce, the carbides in the alloy present a tight skeleton ( Figure 5 ), the 975℃ / 225MPa endurance life of the alloy is less than 40h, which is also significantly lower than the endurance life of the alloy containing appropriate amount of Y and Ce (more than 60h).

[0043] Embodiment 9-10:

[0044] In view of the influence of grain boundary strengthening elements such as B and Zr on the performance of the present alloy, Examples 9-10 and Comparative Examples 8-10 were prepared, and their alloy compositions and 975℃ / 225MPa endurance life are shown in Table 2 and Table 3, respectively. It can be seen that the 975℃ / 225MPa endurance life of Examples 9-10 is 65-67h, while the 975℃ / 225MPa endurance life of Comparative Examples 8 and 9 is 35h and 32h, respectively. It can be seen that too low content of B and Zr leads to a significant decrease in the high temperature endurance performance of the alloy of the present invention. When B and Zr are not contained in the alloy, the alloy performance will be further reduced. This is because the present alloy is an equiaxed crystal alloy with many grain boundaries in the alloy, and the lack of sufficient grain boundary strengthening elements weakens its grain boundaries. Therefore, the content of B and Zr in the alloy should be controlled within an appropriate range.

[0045] Table 2 Composition (wt.%) of high-strength equiaxed crystal casting high-temperature alloy and its 975℃ / 225MPa rupture life

[0046]

[0047] Table 3 Comparative alloy composition (wt.%) and 975℃ / 225MPa rupture life

[0048]

Claims

1. A high-strength equiaxed crystal cast superalloy, characterized in that, By mass percentage, its chemical composition is: C 0.15% - 0.19%, Cr 8.4% - 9.0%, Co 9.5% - 10.3%, Mo 1.4% - 2.0%, W 9.8% - 10.5%, Al 5.2% - 5.7%, Ti 2.3% - 2.8%, Nb 0.8% - 1.2%, B 0.015% - 0.034%, Zr 0.02% - 0.039%, Y 0.001% - 0.005%, Ce 0.002% - 0.01%, and the balance is Ni and inevitable trace impurity elements; In the alloy, 7.7% ≤ Al + Ti ≤ 8.3%, and the mass ratio of Al to Ti is 1.95 - 2.35; In the alloy, 12.3% ≤ W + Mo + Nb ≤ 13.3%; The heat treatment process of the alloy is 1200°C - 1220°C, holding for 3 - 5 h, and air cooling to room temperature.

2. The high-strength equiaxed crystal cast superalloy according to claim 1, characterized in that, C 0.16% - 0.18%, Cr 8.4% - 8.9%, Co 9.8% - 10.3%, Mo 1.4% - 1.9%, W 9.8% - 10.3%, Al 5.2% - 5.6%, Ti 2.3% - 2.6%.

3. The high-strength equiaxed crystal cast superalloy according to claim 1, characterized in that, The Y content in the alloy is 0.001% - 0.003%, and the Ce content is 0.002% - 0.006%.

4. The high-strength equiaxed crystal cast superalloy according to claim 1, wherein The B content in the alloy is 0.015% - 0.025%, and the Zr content is 0.025% - 0.039%.

5. The high-strength equiaxed crystal cast superalloy according to claim 1, wherein, The alloy test bars are prepared by a vacuum induction furnace. The pouring temperature of the alloy is 1440°C - 1500°C, and the mold shell temperature is 850°C - 950°C.

6. The high-strength equiaxed crystal cast superalloy according to claim 1, wherein, The high-strength equiaxed crystal cast superalloy has a creep strength σ 0.2 of 118 MPa at 1000°C for 100 h, and a rupture strength of 166.9 MPa at 1000°C / 100 h.

7. The high-strength equiaxed crystal cast superalloy according to claim 1, characterized in that, The said superalloy is used to prepare gas turbine working blades operating below 1000°C, integral turbine guides, and gas turbine guide vanes operating below 1050°C.

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