KR20110114928A - Ni base single crystal superalloy with good creep property - Google Patents

Abstract

By controlling the amount of other relatively inexpensive alloying elements while minimizing the addition of expensive alloying elements, a single crystal nickel base superalloy with excellent high temperature characteristics, especially creep life as well as resistance to creep deformation is provided. The nickel-based super heat-resistant alloy has a weight percentage of Co: 11.5-13.5%, Cr: 3.0-5.0%, Mo: 0.7-2.0%, W: 8.5-10.5%, Al: 4.5-6.5%, Ti: 0.5-2.0 %, Ta: 6.0-8.0%, Re: 2.0-4.0%, Ru: 0.1-2.0%, and the rest is made up of Ni and other unavoidable impurities. It also has a mixed structure of the γ matrix and γ 'precipitate.

Description

Ni base single crystal superalloy with good creep property

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal nickel base alloy, and more particularly, to a single crystal nickel base super heat resistant alloy having improved resistance to deformation by creep at high temperatures and a break life due to creep.

Nickel-based superalloys are widely used in blades and vanes, which are the main components of industrial gas turbines used for aircraft engines and power generation. The super-alloy in the single crystal state of the super-alloy alloy has excellent creep characteristics and superior heat resistance compared to polycrystalline and unidirectional solidified super-alloy alloys, and is used as a material for blades and vanes in the most extreme environments of gas turbines.

For this purpose, the single crystal super heat-resistant alloy is obtained by adding Al and Ti to form γ '(L1 ₂ structure), which is a regular lattice strengthening phase, in the matrix to obtain high temperature strength, and adding alloy elements such as W, Mo, and Re to obtain Use to strengthen. On the other hand, single crystal super heat-resistant alloys are classified according to the Re content, which is an alloying element, and are classified into 1st generation, 3% generation, 3% generation, etc. Fourth generation single crystal alloys are also being developed.

As the technology advances, the creep property, which is the most important property for the use of super heat-resistant alloy at high temperature, has been improved, but the price of the alloy has also increased due to the addition of expensive elements. For this reason, CMSX-4 (US Patent No. 4,643,782) developed by Canon Muskegon, USA, the second-generation single crystal alloy having a Re content of 3%, is the most widely used commercial alloy.

However, as environmental problems such as global warming emerge, the necessity for increasing the efficiency of existing power generation methods is increasing along with the study of new power generation methods to reduce or eliminate CO ₂ emissions. In response to this, the operating temperature of gas turbines is continuously increasing. For this reason, the temperature acceptance and creep life at high temperatures of blades and vanes used in the most extreme environments of gas turbine components are becoming important. Therefore, there is an increasing need for the development of a single crystal super heat resistant alloy having high temperature creep characteristics superior to the prior art.

In addition, in the case of parts used at high temperatures, the creep life reaching the creep rupture described above is also important, but if the shape of the part is changed, it cannot be continuously used for its original purpose or the efficiency is low, so the resistance to creep deformation is very high. It is an important factor. In other words, by controlling the amount of other relatively inexpensive alloy elements while minimizing the addition of expensive alloy elements, a single crystal super heat resistant alloy having excellent high temperature characteristics, particularly creep life and resistance to creep deformation is required. .

Therefore, the technical problem to be achieved by the present invention is to control the amount of other relatively inexpensive alloy elements in a state in which the addition of expensive alloy elements is minimized, and thus the single crystal has excellent resistance to creep deformation as well as high temperature characteristics. It is to provide a nickel-based super heat-resistant alloy.

Single crystal nickel-based super heat-resistant alloy excellent in creep properties of the present invention for achieving the above object, by weight% Co: 11.5-13.5%, Cr: 3.0-5.0%, Mo: 0.7-2.0%, W: 8.5-10.5 %, Al: 4.5-6.5%, Ti: 0.5-2.0%, Ta: 6.0-8.0%, Re: 2.0-4.0%, Ru: 0.1-2.0%, and the rest consists of Ni and other unavoidable impurities. Here, the super heat-resistant alloy may have a mixed structure of γ matrix and γ 'precipitate.

According to the single crystal nickel-based super heat-resistant alloy excellent in creep properties of the present invention, Co: 11.5-13.5%, Cr: 3.0-5.0%, Mo: 0.7-2.0%, W: 8.5-10.5%, Al: 4.5 ~ 6.5%, Ti: 0.5 ~ 2.0%, Ta: 6.0 ~ 8.0%, Re: 2.0 ~ 4.0%, Ru: 0.1 ~ 2.0%, and the rest is made of a super-crystalline alloy made of Ni and other unavoidable impurities as a single crystal In addition, it is possible to obtain an alloy which not only increases the creep rupture life but also significantly increases the 1% creep reach life, which is resistant to creep deformation.

1 is a graph showing a change in creep deformation amount and creep life time according to the time when creep experiment is performed under the conditions of 950 ° C./355 MPa of a nickel-based superheat-resistant alloy according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

In the following examples, single crystal nickel-based superheat-resistant alloys having excellent creep characteristics will be described. Here, the creep property refers to the creep life as well as resistance to creep deformation, which is necessary for the use of the superheat resistant alloy at high temperatures. The nickel-based superalloy has the following main features.

In the single crystal nickel-based super heat-resistant alloy having excellent creep characteristics according to the present invention, Al and Ti are added to form γ '(L1 ₂ structure), which is a regular lattice strengthening phase, in a matrix of γ-phase to obtain high-temperature strength, W, Mo Obtained by strengthening the matrix by adding alloying elements such as Re, Ru, etc. By controlling the amount of alloying elements as described above, it is characterized by maximizing creep characteristics and having improved creep characteristics compared to commercial alloys.

The nickel-based superheat-resistant alloy according to the present invention first prepares a mother alloy by a conventional vacuum induction melting method. After that, single crystal specimens are produced by the Bridgeman method for each of the prepared master alloys using a one-way solidification furnace. The specimen is subjected to a heat treatment to obtain a microstructure consisting of two phases, γ and γ '.

[The furtherance of alloy]

The nickel-based superheat-resistant alloy of the present invention has the following composition by weight%, and the reason for numerical limitation according to each composition will be described together. The weight% below shows the amount added when the entire nickel-based alloy is 100. For convenience of description, descriptions of nickel groups and other unavoidable impurities will be omitted.

(1) Cobalt (Co): 11.5-13.5%

In addition to the role of strengthening the solid solution, Co changes the solidus line of γ 'which is the main reinforcement phase of nickel-based super heat-resistant alloy and the solidarity of γ which is known to affect the temperature at which solution can be treated. It also improves high temperature corrosion resistance. If the Co content is lower than 11.5%, the creep property is lowered. If the Co content is too high, the temperature range that can be subjected to the solution treatment becomes small, so that it is difficult to determine the heat treatment condition.

(2) Chromium (Cr): 3.5 ~ 5.0%

While chromium plays a role in improving corrosion resistance in super alloys, it can generate carbides or topologically close packed (TCP) phases and is limited in quantity because it does not contribute to heat resistance. If less than 3.5% is added, corrosion resistance may be caused. If it is added more than 5.0%, creep property may be degraded, and a TCP phase may be generated, which may adversely affect the mechanical properties at prolonged exposure at high temperatures.

(3) Molybdenum (Mo): 0.7 ~ 2.0%

Molybdenum is a solid solution strengthening element to improve the high temperature characteristics of super heat resistant alloys. However, if a large amount is added, the density may be high and a TCP phase may be generated. It is difficult to expect a solid employment effect below 0.7%, and the density increases when added above 2.0%.

(4) Tungsten (W): 8.5 ~ 10.5%

Tungsten is an element that increases creep strength by solid solution strengthening. However, when a large amount is added, density increases, toughness and corrosion resistance fall, and phase stability falls. In addition, when single crystal and unidirectional solidification occur, the possibility of casting defects such as freckles increases. Therefore, more than 8.5% of tungsten is added for high temperature strength, and the content is limited to 10.5% in order to suppress undesirable effects that may occur when a large amount is added.

(5) Aluminum (Al): 4.5 ~ 6.5%

Since aluminum is a constituent element of γ 'which is the main reinforcing phase of nickel-based superheat-resistant alloys, aluminum is absolutely necessary for improving high temperature creep characteristics. It also contributes to the improvement of oxidation resistance. However, at 4.5% or less, the creep strength is lowered, and when added at 6.5% or more, the mechanical properties are lowered due to excessive precipitation of the γ 'phase.

(6) Titanium (Ti): 0.5-2.0%

Titanium, like aluminum, is a member of the γ 'phase, which helps increase creep strength and contributes to corrosion resistance. However, when excessively added, oxidation resistance is reduced, so it is limited to 2.0%.

(7) Tantalum (Ta): 6.0 ~ 8.0%

Tantalum is dissolved in the γ 'phase, which is the main strengthening phase, and serves to strengthen the γ' phase, thereby contributing to the improvement of creep strength. In addition, segregation in the interdendritic region increases the density of the region, thereby suppressing the formation of cast defects, which are casting defects. Therefore, a content of 6.0% or more is required. However, when 8.0% or more is added, the δ phase may precipitate, leading to deterioration of properties.

(8) Rhenium (Re): 2.0 ~ 4.0%

Rhenium is a solid solution strengthening element, and the diffusion rate is very slow, which greatly contributes to the improvement of creep characteristics. In other words, by adding rhenium, the superalloy is greatly improved in creep life as well as resistance to creep deformation, which is essential for use at high temperatures. However, when a large amount is contained, the phase stability is lowered, the density is higher, and the price is expensive. Therefore, the present invention is limited to have a range of 2.0 to 4.0%.

(9) Rudenium (Ru): 0.1-2.0%

Rudenium acts as a solid solution element to strengthen the matrix. It improves high temperature properties such as broadening the area where the γ 'phase can be dissolved and contributing to homogenization of segregation, inhibiting the generation of TCP phase. Accordingly, in the present invention, it is added to increase the resistance to creep deformation as well as the creep life, which is necessary for the use of the super heat-resistant alloy at a high temperature. However, when a large amount of rudenium is added, the alloy price is high and the density increases, so it is added in the range of 0.1 to 2.0%.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Table 1 shows the chemical composition of the single crystal super heat resistant alloy to which the embodiment of the present invention is applied and the alloy compared with the super heat resistant alloy.

According to Table 1, Test Material 1 shows the composition of a nickel-based alloy to which 1.0% by weight of Ru is added, and Test Material 2 shows a case where 0.5% by weight of Ru. On the contrary, the comparative specimens were all free of Ru, and Comparative Experiment 1 was an alloy without Re added thereto. In addition, Comparative Test Material 2 is an alloy containing Re but increasing Cr content, and Comparative Test Material 3 is an alloy having reduced Co content. Comparative Sample 4 is CMSX-4, which is the most widely used commercial single crystal alloy.

The test materials and the comparative test materials are first manufactured by the conventional vacuum induction melting method, then using a one-way solidification furnace for each of the produced master alloys by a bridgeman method 15mm in diameter, Single crystal specimens were prepared by withdrawing at a speed of 4.0 mm / min using a single crystal mold having six rod-shaped specimens of 180 mm in length. The specimen was subjected to heat treatment to obtain a microstructure consisting of two phases, γ and γ '.

alloy Co Cr Mo W Al Ti Ta Re Ru Hf Experiment
One 11.44 4.07 1.03 8.48 5.47 1.02 6.95 3.02 1.02 0 2 11.51 4.11 1.02 8.51 5.46 1.03 7.01 2.97 0.51 0 compare
Experiment

One 11.02 4.03 0.48 8.07 5.51 1.01 6.81 0 0 0 2 10.99 8.02 0.52 8.12 5.50 1.02 7.02 2.99 0 0 3 5.02 4.10 0.52 7.99 5.48 0.98 7.02 3.01 0 0 4 9.60 6.40 0.61 6.40 5.65 1.01 6.50 2.90 0 0.10

Table 2 shows creep life and creep life when creep experiments were performed at 950 ° C. under 355 MPa stress and reached 1% creep elongation. 1 is a graph showing the change in creep deformation amount and creep life with time when the creep experiment is performed under the conditions shown in Table 2. FIG.

division Experiment 1 Experiment 2 compare
Experiment 1 compare
Experiment 2 compare
Experiment 3 compare
Experiment 4 Creep Break Time
(time) 211.7 192.3 10.1 71.0 142.3 123.1 1% creep strain
Reach time (hours) 112.0 87.0 0.8 29.0 40.0 57.0

As can be seen from Table 2 and FIG. 1, the creep properties of the nickel-based alloy are highly dependent on Re. That is, the comparative test material 1 without adding Re showed that the creep rupture time and the 1% creep strain arrival time were significantly smaller than those of the other test materials or the comparative test materials. In addition, when comparing Test Materials 1 and 2 with Re and Ru, and Comparative Test Materials 2-4 with Re but without Ru, Ru plays a major role in improving creep characteristics in nickel-based alloys. It can be seen that there is. Of course, in order to improve the creep properties due to such Ru, it is necessary to optimize the content of other alloying elements.

Specifically, the creep rupture time of Test Material 1 and Test Material 2 to which Ru was added was 192.3 to 211.7 hours, and the 1% creep deformation arrival time was 87.0 to 112.0 hours. On the contrary, Comparative Test Materials 2 to 4 without adding Ru had a creep rupture time of 71.0 to 121.3 hours, and a 1% creep strain arrival time of 29.0 to 57.0 hours. Even if the comparative test material 4 having excellent creep properties is compared with the test material 1 of the present invention, the test material 1 of the present invention showed that the creep rupture time and the creep deformation arrival time were increased by almost twice that of the comparative test material 4. Could.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but many variations and modifications may be made without departing from the scope of the present invention. It is possible.

Claims (2)

By weight% Co: 11.5-13.5%, Cr: 3.0-5.0%, Mo: 0.7-2.0%, W: 8.5-10.5%, Al: 4.5-6.5%, Ti: 0.5-2.0%, Ta: 6.0-8.0 %, Re: 2.0 ~ 4.0%, Ru: 0.1 ~ 2.0%, the remainder is a single crystal nickel-based super heat-resistant alloy with excellent creep properties consisting of Ni and other unavoidable impurities. 2. The single crystal nickel-based super heat resistant alloy having excellent creep characteristics according to claim 1, wherein the super heat resistant alloy has a mixed structure of a? Matrix and a? 'Precipitate.

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