US20120237391A1 - Ni-Base Single Crystal Superalloy with Enhanced Creep Property - Google Patents
Ni-Base Single Crystal Superalloy with Enhanced Creep Property Download PDFInfo
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- US20120237391A1 US20120237391A1 US13/419,487 US201213419487A US2012237391A1 US 20120237391 A1 US20120237391 A1 US 20120237391A1 US 201213419487 A US201213419487 A US 201213419487A US 2012237391 A1 US2012237391 A1 US 2012237391A1
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- 229910000601 superalloy Inorganic materials 0.000 title claims abstract description 44
- 239000013078 crystal Substances 0.000 title claims abstract description 28
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 12
- 229910052702 rhenium Inorganic materials 0.000 claims abstract description 12
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 11
- 229910052721 tungsten Inorganic materials 0.000 claims abstract description 11
- 229910052707 ruthenium Inorganic materials 0.000 claims abstract description 10
- 239000011159 matrix material Substances 0.000 claims abstract description 9
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 9
- 239000000203 mixture Substances 0.000 claims abstract description 7
- 229910052715 tantalum Inorganic materials 0.000 claims abstract description 7
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 5
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 239000002245 particle Substances 0.000 claims abstract description 4
- 238000012360 testing method Methods 0.000 description 28
- 239000000463 material Substances 0.000 description 26
- 239000010936 titanium Substances 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 12
- 229910045601 alloy Inorganic materials 0.000 description 11
- 239000000956 alloy Substances 0.000 description 11
- 239000006104 solid solution Substances 0.000 description 10
- 238000005275 alloying Methods 0.000 description 7
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 238000005260 corrosion Methods 0.000 description 4
- WUAPFZMCVAUBPE-UHFFFAOYSA-N rhenium atom Chemical compound [Re] WUAPFZMCVAUBPE-UHFFFAOYSA-N 0.000 description 4
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 4
- 239000010937 tungsten Substances 0.000 description 4
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 3
- 229910001011 CMSX-4 Inorganic materials 0.000 description 2
- 206010014970 Ephelides Diseases 0.000 description 2
- 208000003351 Melanosis Diseases 0.000 description 2
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- 229910017052 cobalt Inorganic materials 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000011733 molybdenum Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000010308 vacuum induction melting process Methods 0.000 description 2
- -1 Aluminum Chemical compound 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
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- 238000011161 development Methods 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
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- 239000007788 liquid Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
- C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
- C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
- C22C19/057—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being less 10%
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
Definitions
- the present invention relates to Ni-base single crystal superalloy, particularly, Ni-base single crystal superalloy with enhanced creep resistance and creep rupture time at high temperature by adjusting content of elements that form gamma prime ( ⁇ ′), a hardening phase.
- ⁇ ′ gamma prime
- Ni-base superalloys are widely used as materials for major parts like blades and vanes of gas turbines for aircraft engines and for power generation.
- the application of single crystal superalloy increased because of its excellent high temperature mechanical properties compared with conventionally cast polycrystalline superalloy and directionally solidified superalloy.
- Single crystal superalloy is strengthened by the precipitates of intermetallic ⁇ ′(L1 2 structure), a hardening phase having ordered structure within a matrix, and its matrix reinforced by adding alloying elements like W, Mo, Re, etc.
- the generation of single crystal superalloy is classified by Re content, an alloying element; that is, the 1 st generation contains no Re content, the 2 nd generation contains 3% of Re, the 3 rd generation contains 6% of Re, etc. Also, the 4 th generation with Ru addition was recently developed. Although temperature capability and creep resistance at high temperature have been improved as the generation is updated, the price of superalloy also went up because of an increase in addition of expensive elements such as Re, Ru, etc. For this reason, CMSX-4 (U.S. Pat. No. 4,643,782), the 2 nd generation single crystal alloy containing 3% of Re developed by Cannon Muskegon, U.S., is being most commonly used at the present time.
- solid solution hardening elements such as W, Mo, Re, etc.
- creep property can be also enhanced by adjusting Al or Ti content that forms ⁇ ′, a hardening phase having ordered structure (L1 2 structure). It is necessary to study the latter because it can suppress price raise compared with the former that enhances creep property through solid solution hardening by adding expensive elements such as Re, etc.
- the present invention aims to provide Ni-base single crystal superalloy with good high-temperature property, particularly long creep life and excellent resistance to creep deformation, by adjusting content of Al and Ti that form a gamma prime ( ⁇ ′), a major hardening phase of the Ni-base single crystal superalloy.
- ⁇ ′ gamma prime
- Ni-base single crystal superalloy with good creep property in the present invention consists of Co: 11.5 ⁇ 13.5%, Cr: 3.0 ⁇ 5.0%, Mo: 0.7 ⁇ 2.0%, W: 8.5 ⁇ 10.5%, Al: 3.5 ⁇ 5.5%, Ti: 2.5 ⁇ 4.5%, Ta: 6.0 ⁇ 8.0%, Re: 2.0 ⁇ 4.0%, Ru: 0.1 ⁇ 2.0% in Weight %, and the rest is Ni and other unavoidable impurities.
- composition ratio of Al/Ti is 0.7 ⁇ 2.2.
- the above superalloy may have a mixed structure of the ⁇ matrix and ⁇ ′ particles.
- Ni-base single crystal superalloy with good creep property of the present invention it is possible to obtain alloy with prolonged creep rupture life and significantly improved Time to 1% Creep Strain representing resistance to creep deformation through increasing misfit, a difference of lattice constant between the ⁇ matrix and ⁇ ′ particles, and reducing stacking fault energy, by producing single crystal superalloy consisting of Co: 11.5 ⁇ 13.5%, Cr: 3.0 ⁇ 5.0%, Mo: 0.7 ⁇ 2.0%, W: 8.5 ⁇ 10.5%, Al: 3.5 ⁇ 5.5%, Ti: 2.5 ⁇ 3.5%, Ta: 6.0 ⁇ 8.0%, Re: 2.0 ⁇ 4.0%, Ru: 0.1 ⁇ 2.0% in Weight %, and the rest containing Ni and other unavoidable impurities.
- FIG. 1 is a graph that shows creep life and variation of creep strain with time when creep tests are performed with Ni-base superalloy according to the present invention at the condition of 950° C./355 MPa.
- FIG. 2 is a photo of microstructure observed with a TEM(Transmission Electron Microscope) after a creep experiment for Test Material 1, Comparative Test Materials 1 and 2 of the present invention.
- Ni-base single crystal superalloy with good creep property will be explained in the following embodiment.
- the creep property here means resistance to creep deformation as well as creep rupture life that is essential to use superalloy at high temperature.
- the said Ni-base superalloy has the following major features.
- Ni-base single crystal superalloy with good creep property in the present invention obtains high temperature strength by both precipitation hardening and solid solution hardening.
- a hardening phase, ⁇ ′ having ordered structure(L1 2 structure) forms by adding Al and Ti in the ⁇ -phase matrix, and the matrix is reinforced by adding solid solution hardening elements like W, Mo, Re, Ru, etc.
- the Ni-base single crystal superalloy in the present invention is characterized by maximizing creep property by changing stacking fault energy through increasing Ti content and decreasing Al content, and also characterized by more enhanced creep properties than commonly used alloy.
- the Ni-base superalloy in the present invention has the following composition for each element.
- the reason for limiting amounts of each element will be explained here.
- the below weight % is gained by converting the amount added to weigh while defining the entire Ni-base alloy as 100. In order to make it easy, explanation of Ni and other inevitable impurities will be omitted.
- Cobalt influences solution treatment temperatures by changing a ⁇ ′ solidus, a major hardening phase of Ni-base superalloy, and ⁇ solidus, a matrix, in addition to solid solution hardening. It also improves high temperature corrosion resistance. Creep property becomes worse if Co content is less than 11.5%, while it is difficult to decide heat treatment conditions because the temperature range of solution treatment becomes narrow if Co content is more than 13.5%.
- Chrome improves corrosion resistance of superalloy, however, the amount of Chrome is limited because it may produce carbides or TCP (Topologically Close Packed) phases which are detrimental to creep behavior. Corrosion resistance becomes bad if Cr content is less than 3.5%, while more than 5.0% Cr content may lower creep property and create TCP phases that negatively influence mechanical properties in case of long exposure at high temperature.
- Molybdenum improves property of superalloy at high temperature as a solid solution hardening element. However, a large amount may increase density and create TCP phases. It is hard to expect solid solution hardening effect under 0.7%, while more than 2.0% increase the density.
- Tungsten is an element that enhances creep strength by solid solution hardening. However, a large amount may increase density, and lower toughness, corrosion resistance and phase stability. In addition, a possibility of casting defects like freckles increases at a time of single crystal and directional solidification. Accordingly, more than 8.5% Tungsten is added for improving high temperature strength while Tungsten content is limited to 10.5% in order to inhibit undesirable effects.
- Aluminum is an essential element to improve high temperature creep property because it is a constitutive element of ⁇ ′, a major hardening phase of Ni-base superalloy. In addition, it improves oxidation resistance. However, creep strength lowers under 3.5% while mechanical property may become worse due to precipitate of excessive ⁇ ′ phases in case of adding more than 5.5%. Although absolute quantity of Al is important, an association with Ti content, another ⁇ ′ phase forming element, is also important.
- Titanium (Ti) 2.5 ⁇ 4.5%
- Titanium like Aluminum, improves creep strength as a constitutive element of a ⁇ ′ phase. Particularly, more than 2.5% should be added in order to enhance creep property because addition of Ti increases misfit and decreases stacking fault energy. However, the amount should be limited to 4.5% because excessive addition may reduce oxidation resistance and lower phase stability.
- Tantalum (Ta) 6.0 ⁇ 8.0%
- Tantalum improves creep strength by hardening ion resis.
- partitioning of tantalum to interdendritic region increases the density of interdendritic liquid, resulting in inhibition of freckles, one of casting defects. Therefore, more than 6.0% content is required. But if more than 8.0% are added, harmful ⁇ phases can be precipitated.
- Rhenium (Re) 2.0 ⁇ 4.0%
- Rhenium a solid solution hardening element, greatly contributes to improvement of creep property because its diffusivity is very low. In other words, Rhenium considerably improves resistance to creep deformation as well as creep life of superalloy. Yet, a large quantity lowers phase stability, increases density and raises the price, therefore, the present invention limited the amount of Rhenium to 2.0 ⁇ 4.0%.
- Ruthenium improves high temperature property by inhibiting creation of TCP phases through broadening the solid solution range of ⁇ ′ phase and contributing to homogenization of segregation. Accordingly, in the present study Ruthenium is added to enhance resistance to creep deformation as well as creep life of superalloy. However, the amount is limited to 0.1 ⁇ 2.0% because the price of superalloy becomes expensive and the density increases if a large quantity of Ruthenium is contained.
- Table 1 shows the chemical composition of single crystal superalloy according to the present invention and alloy compared with the said superalloy.
- Test Material 1 presents the composition of Ni-base alloy with 4.5 weight % of Al and 3.0 weight % of Ti added, while Test Material 2 shows a case with 5.0 weight % of Al and 2.5 weight % of Ti added.
- Comparative Test Material 1 is alloy with 5.5 weight % of Al and 1.0 weight % of Ti added, and Comparative Test Material 2 is CMSX-4 that is being most commonly used at the present time.
- Test Materials and Comparative Test Materials were produced as follows. First of all, master ingots were cast using vacuum induction melting process. Then, single crystal specimens of 15 mm diameter and 180 mm length were produced by the Bridgman method with withdrawal rate of 4.0 mm/min. And then, microstructure consisting of two phases of ⁇ and ⁇ ′ can be obtained by applying heat to the specimens.
- FIG. 1 is a graph that shows variation of creep strain with time when creep tests are performed at the condition of 950° C./355 MPa.
- creep property of Ni-base alloy is greatly dependent on content of Al and Ti, gamma prime ( ⁇ ′) forming elements. That is, it is found that Test Material 1 with relatively higher Ti content and lower Al content shows significantly longer Creep Rupture Time and Time to 1% Creep Strain than other Test Materials or Comparative Test Materials. Of course, optimizing contents of other alloying elements is necessary in order to improve creep property by adjusting the gamma prime phase forming elements.
- Creep Rupture Time of Test Materials 1 ⁇ 2 with relatively higher Ti content and lower Al content was 270.2 ⁇ 301.8 hours while Time to 1% Creep Strain was 151.9 ⁇ 197.0 hours.
- Comparative Test Materials 1 ⁇ 2 presented 123.1 ⁇ 211.7 hours of Creep Rupture Time and 57.0 ⁇ 112.0 hours of Time to 1% Creep Strain. Therefore, it was found that Test Material 1 ⁇ 2 of the present invention showed longer Creep Rupture Time and Time to 1% Creep Strain compared with Comparative Test Material 1 ⁇ 2.
- FIG. 2 is a photo of microstructure observed with TEM(Transmission Electron Microscope) after a creep experiments for Test Material 1, Comparative Test Materials 1 and 2 of the present invention.
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Abstract
The present invention provides Ni-base single crystal superalloy with good high-temperature property, particularly long creep life and excellent resistance to creep deformation, by adjusting content of Al and Ti that form a gamma prime (γ′), a major hardening phase of the Ni-base single crystal superalloy. The Ni-base single crystal superalloy comprise Co: 11.5˜13.5%, Cr: 3.0˜5.0%, Mo: 0.7˜2.0%, W: 8.5˜10.5%, Al: 3.5˜5.5%, Ti: 2.5˜4.5%, Ta: 6.0˜8.0%, Re: 2.0˜4.0%, Ru: 0.1˜2.0% in Weight %, and the rest is Ni and other inevitable impurities. And composition ratio of Al/Ti is 0.7˜2.2. In addition, the superalloy has a mixed structure of the γ matrix and γ′ particles.
Description
- This application claims foreign priority under 35 U.S.C. §119(a)-(d) to Application No. KR 10-2011-0023290 filed on Mar. 16, 2011, entitled “Ni-Base Single Crystal Superalloy with Enhanced Creep Property,” the entire contents of which are hereby incorporated by reference.
- The present invention relates to Ni-base single crystal superalloy, particularly, Ni-base single crystal superalloy with enhanced creep resistance and creep rupture time at high temperature by adjusting content of elements that form gamma prime (γ′), a hardening phase.
- Ni-base superalloys are widely used as materials for major parts like blades and vanes of gas turbines for aircraft engines and for power generation. The application of single crystal superalloy increased because of its excellent high temperature mechanical properties compared with conventionally cast polycrystalline superalloy and directionally solidified superalloy.
- Single crystal superalloy is strengthened by the precipitates of intermetallic γ′(L12 structure), a hardening phase having ordered structure within a matrix, and its matrix reinforced by adding alloying elements like W, Mo, Re, etc.
- However, as environmental issues like global warming are on the rise, the necessity to enhance efficiency of the gas turbines by increasing the operation temperature becomes a matter of big concern. Therefore, temperature capability and creep life of blades and vanes used in the most extreme environment among gas turbine parts are getting important. Accordingly, development of single crystal superalloy with better creep property at high temperature than prior art is becoming more important.
- The generation of single crystal superalloy is classified by Re content, an alloying element; that is, the 1st generation contains no Re content, the 2nd generation contains 3% of Re, the 3rd generation contains 6% of Re, etc. Also, the 4th generation with Ru addition was recently developed. Although temperature capability and creep resistance at high temperature have been improved as the generation is updated, the price of superalloy also went up because of an increase in addition of expensive elements such as Re, Ru, etc. For this reason, CMSX-4 (U.S. Pat. No. 4,643,782), the 2nd generation single crystal alloy containing 3% of Re developed by Cannon Muskegon, U.S., is being most commonly used at the present time.
- In order to satisfy the need of developing single crystal superalloy with excellent temperature capability and creep resistance, adjusting content of other alloying elements while minimizing expensive alloying elements is regarded as an effective alloying design method. In case of parts that are used at high temperature, creep resistance is also a very important factor to be considered for alloying design because deformed parts cannot be used properly as per their original purposes or lower efficiency although creep lifetime is important.
- As mentioned above, solid solution hardening elements such as W, Mo, Re, etc. can be adjusted in order to improve creep property of superalloy. In addition to this, creep property can be also enhanced by adjusting Al or Ti content that forms γ′, a hardening phase having ordered structure (L12 structure). It is necessary to study the latter because it can suppress price raise compared with the former that enhances creep property through solid solution hardening by adding expensive elements such as Re, etc.
- Accordingly, the present invention aims to provide Ni-base single crystal superalloy with good high-temperature property, particularly long creep life and excellent resistance to creep deformation, by adjusting content of Al and Ti that form a gamma prime (γ′), a major hardening phase of the Ni-base single crystal superalloy.
- Ni-base single crystal superalloy with good creep property in the present invention consists of Co: 11.5˜13.5%, Cr: 3.0˜5.0%, Mo: 0.7˜2.0%, W: 8.5˜10.5%, Al: 3.5˜5.5%, Ti: 2.5˜4.5%, Ta: 6.0˜8.0%, Re: 2.0˜4.0%, Ru: 0.1˜2.0% in Weight %, and the rest is Ni and other unavoidable impurities. At this time, composition ratio of Al/Ti is 0.7˜2.2. The above superalloy may have a mixed structure of the γ matrix and γ′ particles.
- According to the Ni-base single crystal superalloy with good creep property of the present invention, it is possible to obtain alloy with prolonged creep rupture life and significantly improved Time to 1% Creep Strain representing resistance to creep deformation through increasing misfit, a difference of lattice constant between the γ matrix and γ′ particles, and reducing stacking fault energy, by producing single crystal superalloy consisting of Co: 11.5˜13.5%, Cr: 3.0˜5.0%, Mo: 0.7˜2.0%, W: 8.5˜10.5%, Al: 3.5˜5.5%, Ti: 2.5˜3.5%, Ta: 6.0˜8.0%, Re: 2.0˜4.0%, Ru: 0.1˜2.0% in Weight %, and the rest containing Ni and other unavoidable impurities.
- The foregoing and other objects, features, aspects and advantages of the present invention will be more clearly understood from the following detailed description with the accompanying drawing.
-
FIG. 1 is a graph that shows creep life and variation of creep strain with time when creep tests are performed with Ni-base superalloy according to the present invention at the condition of 950° C./355 MPa. -
FIG. 2 is a photo of microstructure observed with a TEM(Transmission Electron Microscope) after a creep experiment forTest Material 1, Comparative TestMaterials - Ni-base single crystal superalloy with good creep property will be explained in the following embodiment. The creep property here means resistance to creep deformation as well as creep rupture life that is essential to use superalloy at high temperature. The said Ni-base superalloy has the following major features.
- Ni-base single crystal superalloy with good creep property in the present invention obtains high temperature strength by both precipitation hardening and solid solution hardening.
- A hardening phase, γ′ having ordered structure(L12 structure) forms by adding Al and Ti in the γ-phase matrix, and the matrix is reinforced by adding solid solution hardening elements like W, Mo, Re, Ru, etc. Particularly, the Ni-base single crystal superalloy in the present invention is characterized by maximizing creep property by changing stacking fault energy through increasing Ti content and decreasing Al content, and also characterized by more enhanced creep properties than commonly used alloy.
- In order to get the Ni-base single crystal superalloy with good creep property in the present invention, master ingots are cast using vacuum induction melting process. Then, single crystal specimens are produced from each master ingot respectively by the Bridgman method. And then, microstructure consisting of two phases of γ and γ′ can be obtained by applying heat treatment to the specimens.
- The Ni-base superalloy in the present invention has the following composition for each element. The reason for limiting amounts of each element will be explained here. The below weight % is gained by converting the amount added to weigh while defining the entire Ni-base alloy as 100. In order to make it easy, explanation of Ni and other inevitable impurities will be omitted.
- Cobalt influences solution treatment temperatures by changing a γ′ solidus, a major hardening phase of Ni-base superalloy, and γ solidus, a matrix, in addition to solid solution hardening. It also improves high temperature corrosion resistance. Creep property becomes worse if Co content is less than 11.5%, while it is difficult to decide heat treatment conditions because the temperature range of solution treatment becomes narrow if Co content is more than 13.5%.
- Chrome improves corrosion resistance of superalloy, however, the amount of Chrome is limited because it may produce carbides or TCP (Topologically Close Packed) phases which are detrimental to creep behavior. Corrosion resistance becomes bad if Cr content is less than 3.5%, while more than 5.0% Cr content may lower creep property and create TCP phases that negatively influence mechanical properties in case of long exposure at high temperature.
- Molybdenum improves property of superalloy at high temperature as a solid solution hardening element. However, a large amount may increase density and create TCP phases. It is hard to expect solid solution hardening effect under 0.7%, while more than 2.0% increase the density.
- Tungsten is an element that enhances creep strength by solid solution hardening. However, a large amount may increase density, and lower toughness, corrosion resistance and phase stability. In addition, a possibility of casting defects like freckles increases at a time of single crystal and directional solidification. Accordingly, more than 8.5% Tungsten is added for improving high temperature strength while Tungsten content is limited to 10.5% in order to inhibit undesirable effects.
- Aluminum is an essential element to improve high temperature creep property because it is a constitutive element of γ′, a major hardening phase of Ni-base superalloy. In addition, it improves oxidation resistance. However, creep strength lowers under 3.5% while mechanical property may become worse due to precipitate of excessive γ′ phases in case of adding more than 5.5%. Although absolute quantity of Al is important, an association with Ti content, another γ′ phase forming element, is also important.
- Titanium, like Aluminum, improves creep strength as a constitutive element of a γ′ phase. Particularly, more than 2.5% should be added in order to enhance creep property because addition of Ti increases misfit and decreases stacking fault energy. However, the amount should be limited to 4.5% because excessive addition may reduce oxidation resistance and lower phase stability.
- Tantalum improves creep strength by hardening ion resis. In addition, partitioning of tantalum to interdendritic region increases the density of interdendritic liquid, resulting in inhibition of freckles, one of casting defects. Therefore, more than 6.0% content is required. But if more than 8.0% are added, harmful δ phases can be precipitated.
- Rhenium, a solid solution hardening element, greatly contributes to improvement of creep property because its diffusivity is very low. In other words, Rhenium considerably improves resistance to creep deformation as well as creep life of superalloy. Yet, a large quantity lowers phase stability, increases density and raises the price, therefore, the present invention limited the amount of Rhenium to 2.0˜4.0%.
- Ruthenium improves high temperature property by inhibiting creation of TCP phases through broadening the solid solution range of γ′ phase and contributing to homogenization of segregation. Accordingly, in the present study Ruthenium is added to enhance resistance to creep deformation as well as creep life of superalloy. However, the amount is limited to 0.1˜2.0% because the price of superalloy becomes expensive and the density increases if a large quantity of Ruthenium is contained.
- The present inventions will be explained in more detail through the following embodiments.
- [Table 1] shows the chemical composition of single crystal superalloy according to the present invention and alloy compared with the said superalloy.
- According to [Table 1],
Test Material 1 presents the composition of Ni-base alloy with 4.5 weight % of Al and 3.0 weight % of Ti added, whileTest Material 2 shows a case with 5.0 weight % of Al and 2.5 weight % of Ti added. On the contrary,Comparative Test Material 1 is alloy with 5.5 weight % of Al and 1.0 weight % of Ti added, andComparative Test Material 2 is CMSX-4 that is being most commonly used at the present time. -
TABLE 1 Alloy Co Cr Mo W Al Ti Ta Re Ru Hf Al/ Ti Test 1 11.59 3.99 0.98 8.54 4.45 3.00 6.92 2.98 0.98 0 1.48 Materials 2 11.57 4.07 1.02 8.59 5.02 2.51 7.01 2.97 0.97 0 2.00 Comparative 1 11.66 4.07 1.03 8.68 5.47 1.02 6.95 3.02 1.02 0 5.36 Test Materials 2 9.60 6.40 0.61 6.40 5.65 1.01 6.50 2.90 0 0.10 5.45 - The above Test Materials and Comparative Test Materials were produced as follows. First of all, master ingots were cast using vacuum induction melting process. Then, single crystal specimens of 15 mm diameter and 180 mm length were produced by the Bridgman method with withdrawal rate of 4.0 mm/min. And then, microstructure consisting of two phases of γ and γ′ can be obtained by applying heat to the specimens.
- [Table 2] shows creep life and time to 1% creep strain when creep tests are conducted by applying stress of 355 MPa at 950° C. with the above alloys. [
FIG. 1 ] is a graph that shows variation of creep strain with time when creep tests are performed at the condition of 950° C./355 MPa. -
TABLE 2 Comparative Comparative Test Test Test Test Classification Material 1 Material 2Material 1Material 2Creep Rupture 301.8 270.2 211.7 123.1 Time (Hour) Time to 1% Creep 197.0 151.9 112.0 57.0 Strain (Hour) - As we know from [Table 2] and [
FIG. 1 ], creep property of Ni-base alloy is greatly dependent on content of Al and Ti, gamma prime (γ′) forming elements. That is, it is found thatTest Material 1 with relatively higher Ti content and lower Al content shows significantly longer Creep Rupture Time and Time to 1% Creep Strain than other Test Materials or Comparative Test Materials. Of course, optimizing contents of other alloying elements is necessary in order to improve creep property by adjusting the gamma prime phase forming elements. - In the concrete, Creep Rupture Time of
Test Materials 1˜2 with relatively higher Ti content and lower Al content was 270.2˜301.8 hours while Time to 1% Creep Strain was 151.9˜197.0 hours. On the other hand,Comparative Test Materials 1˜2 presented 123.1˜211.7 hours of Creep Rupture Time and 57.0˜112.0 hours of Time to 1% Creep Strain. Therefore, it was found thatTest Material 1˜2 of the present invention showed longer Creep Rupture Time and Time to 1% Creep Strain compared withComparative Test Material 1˜2. -
FIG. 2 is a photo of microstructure observed with TEM(Transmission Electron Microscope) after a creep experiments forTest Material 1,Comparative Test Materials - According to
FIG. 2 , although superdislocation is observed mainly inside of γ′, a hardening phase, after the experiment in case ofComparative Test Materials Test Material 1. This is because formation of stacking fault becomes easier since sacking fault energy is lowered due to increase of Ti content. Dislocation mobility would be reduced by the dissociation of perfect dislocation into partial dislocations and stacking fault surrounded by them. Low dislocation mobility in γ′ enhances the resistance to creep deformation. Therefore, it is found that creep property is improved by an increase of Ti content. - As the present invention may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, therefore, various variations are possible by a person of ordinary skill in the pertinent art within the range of technical features of the present invention.
Claims (2)
1. Ni-base single crystal superalloy with good creep property consisting of Co: 11.5˜13.5%, Cr: 3.0˜5.0%, Mo: 0.7˜2.0%, W: 8.5˜10.5%, Al: 3.5˜5.5%, Ti: 2.5˜4.5%, Ta: 6.0˜8.0%, Re: 2.0˜4.0%, Ru: 0.1˜2.0% in Weight %, and the rest containing Ni and other inevitable impurities, and composition ratio of Al/Ti is 0.7˜2.2.
2. The Ni-base single crystal superalloy with good creep property according to claim 1 , wherein the superalloy has a mixed structure of the γ matrix and γ′ particles.
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CN111027198A (en) * | 2019-12-03 | 2020-04-17 | 西北工业大学 | Nickel-based single crystal alloy creep life prediction method considering topological close-packed phase evolution |
CN112630044A (en) * | 2020-11-19 | 2021-04-09 | 西北工业大学 | Creep life prediction method of nickel-based single crystal alloy based on crystal orientation |
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JPWO2015020007A1 (en) * | 2013-08-05 | 2017-03-02 | 国立研究開発法人物質・材料研究機構 | Oxide particle dispersion strengthened Ni-base superalloy |
KR102114253B1 (en) * | 2018-02-26 | 2020-05-22 | 한국기계연구원 | Ni based superalloy with high creep strength and manufacturing method thereof |
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US7169241B2 (en) * | 2003-05-09 | 2007-01-30 | Hitachi, Ltd. | Ni-based superalloy having high oxidation resistance and gas turbine part |
US7473326B2 (en) * | 2002-03-27 | 2009-01-06 | National Institute For Materials Science | Ni-base directionally solidified superalloy and Ni-base single crystal superalloy |
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WO1997038144A1 (en) * | 1996-04-10 | 1997-10-16 | The Penn State Research Foundation | Improved superalloys with improved oxidation resistance and weldability |
US6007645A (en) * | 1996-12-11 | 1999-12-28 | United Technologies Corporation | Advanced high strength, highly oxidation resistant single crystal superalloy compositions having low chromium content |
JPH11310839A (en) * | 1998-04-28 | 1999-11-09 | Hitachi Ltd | Grain-oriented solidification casting of high strength nickel-base superalloy |
JP5073905B2 (en) * | 2000-02-29 | 2012-11-14 | ゼネラル・エレクトリック・カンパニイ | Nickel-base superalloy and turbine parts manufactured from the superalloy |
US20030041930A1 (en) * | 2001-08-30 | 2003-03-06 | Deluca Daniel P. | Modified advanced high strength single crystal superalloy composition |
JP3944582B2 (en) * | 2003-09-22 | 2007-07-11 | 独立行政法人物質・材料研究機構 | Ni-base superalloy |
JP4230970B2 (en) * | 2004-08-09 | 2009-02-25 | 株式会社日立製作所 | Ni-base superalloys for unidirectional solidification with excellent solidification direction strength and grain boundary strength, castings and high-temperature parts for gas turbines |
SE528807C2 (en) * | 2004-12-23 | 2007-02-20 | Siemens Ag | Component of a superalloy containing palladium for use in a high temperature environment and use of palladium for resistance to hydrogen embrittlement |
JP5344453B2 (en) * | 2005-09-27 | 2013-11-20 | 独立行政法人物質・材料研究機構 | Ni-base superalloy with excellent oxidation resistance |
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US7473326B2 (en) * | 2002-03-27 | 2009-01-06 | National Institute For Materials Science | Ni-base directionally solidified superalloy and Ni-base single crystal superalloy |
US7169241B2 (en) * | 2003-05-09 | 2007-01-30 | Hitachi, Ltd. | Ni-based superalloy having high oxidation resistance and gas turbine part |
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CN111027198A (en) * | 2019-12-03 | 2020-04-17 | 西北工业大学 | Nickel-based single crystal alloy creep life prediction method considering topological close-packed phase evolution |
CN112630044A (en) * | 2020-11-19 | 2021-04-09 | 西北工业大学 | Creep life prediction method of nickel-based single crystal alloy based on crystal orientation |
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