U.S. patent application number 12/847449 was filed with the patent office on 2011-10-20 for ni-based single crystal superalloy with good creep property.
This patent application is currently assigned to KOREA INSTITUTE OF MACHINERY & MATERIALS. Invention is credited to Young Keun Ahn, Baig Gyu Choi, Hyun Uk Hong, Hi Won Jeong, Chang Yong Jo, In Soo Kim, Seong Moon Seo, Young Soo Yoo.
Application Number | 20110256018 12/847449 |
Document ID | / |
Family ID | 44788326 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110256018 |
Kind Code |
A1 |
Choi; Baig Gyu ; et
al. |
October 20, 2011 |
Ni-Based Single Crystal Superalloy with Good Creep Property
Abstract
A Ni-based single crystal superalloy with good resistance to
creep deformation and creep life at a high temperature is formed by
adjusting the quantity of relatively inexpensive alloy elements
while minimizing the quantity of expensive alloy elements. The
Ni-based single crystal superalloy with good creep properties
comprises Co: 11.5.about.13.5%, Cr: 3.0.about.5.0%, Mo:
0.7.about.2.0%, W: 8.5.about.10.5%, Al: 4.5.about.6.5%, Ti:
0.5.about.2.0%, Ta: 6.0.about.8.0%, Re: 2.0.about.4.0%, Ru:
0.1.about.2.0% in Weight %, with the rest of the superalloy
comprising Ni and other inevitable impurities. In addition, the
superalloy has a mixed structure of the .gamma. matrix and .gamma.'
particles.
Inventors: |
Choi; Baig Gyu;
(Changwon-si, KR) ; Jo; Chang Yong; (Changwon-si,
KR) ; Kim; In Soo; (Changwon-si, KR) ; Ahn;
Young Keun; (Changwon-si, KR) ; Yoo; Young Soo;
(Changwon-si, KR) ; Jeong; Hi Won; (Gimhae-si,
KR) ; Seo; Seong Moon; (Gimhae-si, KR) ; Hong;
Hyun Uk; (Changwon-si, KR) |
Assignee: |
KOREA INSTITUTE OF MACHINERY &
MATERIALS
Changwon-city
KR
|
Family ID: |
44788326 |
Appl. No.: |
12/847449 |
Filed: |
July 30, 2010 |
Current U.S.
Class: |
420/444 ;
420/588 |
Current CPC
Class: |
C22C 19/03 20130101;
C30B 29/52 20130101; C22C 19/057 20130101; C30B 11/00 20130101;
C22C 19/05 20130101 |
Class at
Publication: |
420/444 ;
420/588 |
International
Class: |
C22C 19/05 20060101
C22C019/05; C22C 30/00 20060101 C22C030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2010 |
KR |
10-2010-0034314 |
Claims
1. A Ni-based single crystal superalloy comprising: Co:
11.5.about.13.5%, Cr: 3.0.about.5.0%, Mo: 0.7.about.2.0%, W:
8.5.about.10.5%, Al: 4.56.5%, Ti: 1.02.about.2.0%, Ta:
6.0.about.8.0%, Re: 2.0.about.4.0%, Ru: 0.1.about.2.0% in weight %,
and Ni.
2. The Ni-based single crystal superalloy of claim 1, wherein the
superalloy has a mixed structure of .gamma. matrix and .gamma.'
particles.
3-11. (canceled)
12. A Ni-based single crystal superalloy consisting essentially of:
Co: 11.5.about.13.5%, Cr: 3.0.about.5.0%, Mo: 0.7.about.2.0%, W:
8.5.about.10.5%, Al: 4.5.about.6.5%, Ti: 1.02.about.2.0%, Ta:
6.0.about.8.0%, Re: 2.0.about.4.0%, Ru: 0.1.about.2.0% in weight %,
and Ni.
13. A Ni-based single crystal superalloy consisting of: Co:
11.5.about.13.5%, Cr: 3.0.about.5.0%, Mo: 0.72.0%, W:
8.5.about.10.5%, Al: 4.5.about.6.5%, Ti: 1.02.about.2.0%, Ta:
6.0.about.8.0%, Re: 2.0.about.4.0%, Ru: 0.1.about.2.0% in weight %,
and Ni.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims foreign priority under 35 U.S.C.
.sctn.119(a)-(d) to Application No. KR 10-2010-0034314 filed on
Apr. 14, 2010, entitled "Ni-Based Single Crystal Superalloy with
Good Creep Property," the entire contents of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to Ni-based single crystal
superalloy with improved creep resistance at high temperature.
BACKGROUND
[0003] Ni-based 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
superalloys has increased because of their excellent
high-temperature mechanical properties compared with conventionally
cast polycrystalline superalloys and directionally solidified
superalloys.
[0004] A single crystal superalloy is strengthened by the
precipitates of intermetallic .gamma.' (L1.sub.2 structure), a
hardening phase having ordered structure within a matrix, and its
matrix being reinforced by adding alloying elements like W, Mo, Re,
etc. The generation of a single crystal superalloy is classified by
Re content, an alloying element; that is, the 1.sup.st generation
contains no Re content, the 2.sup.nd generation contains 3% of Re,
the 3.sup.rd generation contains 6% of Re, etc. Also, the 4.sup.th
generation with Ru addition has recently been developed.
[0005] Although creep resistance, one of the most important
properties in using a superalloy at high temperature, has improved
as technology has developed, the price of superalloys has also
increased due to an increase in the addition of expensive elements.
For this reason, CMSX-4 (U.S. Pat. No. 4,643,782), the 2.sup.nd
generation single crystal alloy containing 3% of Re developed by
Cannon Muskegon, U.S., is most commonly used at the present
time.
[0006] However, as environmental issues like global warming have
acquired greater importance, the necessity of enhancing the
efficiency of gas turbines by increasing the operating temperature
has become a major concern. Therefore, the temperature capability
and the creep life of blades and vanes used in the most extreme
environments among gas turbine parts are becoming more important.
Accordingly, development of a single crystal superalloy with better
creep properties at high temperature than known superalloys is
becoming more important.
[0007] Additionally, while creep rupture time of the parts used in
high temperature applications is crucial as explained above,
resistance to creep deformation is also a very significant factor,
because deformed parts cannot be used for their original purpose or
their efficiency becomes worse. Thus, production of a single
crystal superalloy with good high-temperature property, long creep
life, and excellent resistance to creep deformation is required by
adjusting the amount of relatively inexpensive alloying elements
while minimizing the amount of expensive alloying elements.
SUMMARY
[0008] Accordingly, the present invention aims to provide a
Ni-based single crystal superalloy with good high-temperature
properties, long creep life, and excellent resistance to creep
deformation that is made by adjusting the amount of relatively
cheap alloy elements while minimizing the amount of expensive alloy
elements.
[0009] A Ni-based single crystal superalloy with good creep
properties according to the present invention includes Co:
11.5.about.13.5%, Cr: 3.0.about.5.0%, Mo: 0.7.about.2.0%, W:
8.5.about.10.5%, Al: 4.5.about.6.5%, Ti: 0.5.about.2.0%, Ta:
6.0.about.8.0%, Re: 2.0.about.4.0%, Ru: 0.1.about.2.0% in Weight %,
and the rest is Ni and other unavoidable impurities. The above
superalloy may have a mixed structure of the .gamma. matrix and
.gamma.' particles.
[0010] According to the Ni-based single crystal superalloy with
good creep properties of the present invention, it is possible to
obtain an alloy with prolonged creep rupture life and significantly
improved the time to 1% Creep Strain representing resistance to
creep deformation by producing single crystal superalloy includes
Co: 11.5.about.13.5%, Cr: 3.0.about.5.0%, Mo: 0.7.about.2.0%, W:
8.5.about.10.5%, Al: 4.5.about.6.5%, Ti: 0.5.about.2.0%, Ta:
6.0.about.8.0%, Re: 2.0.about.4.0%, Ru: 0.1.about.2.0% in Weight %,
and the rest containing Ni and other unavoidable impurities.
[0011] 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,
BRIEF DESCRIPTION OF THE DRAWING
[0012] FIG. 1 is a graph that shows creep life and variation of
creep strain with time when creep tests are performed with Ni-based
superalloy according to the present invention at the condition of
950.degree. C./355 MPa.
DETAILED DESCRIPTION
[0013] A Ni-based single crystal superalloy with good creep
properties 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 of a superalloy at high
temperature. The Ni-based superalloy has the following major
features.
[0014] A Ni-based 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, .gamma.' (L1.sub.2 structure) having an ordered
structure forms by adding Al and Ti in the .gamma.-phase matrix,
and the matrix is reinforced by adding solid solution hardening
elements like W, Mo, Re, Ru, etc. Like this, the Ni-based single
crystal superalloy is characterized by more improved creep
properties than commonly used alloy by adjusting the amount of
alloying elements.
[0015] In order to get the Ni-based single crystal superalloy with
good creep property in the present invention, master ingots are
cast using a vacuum induction melting process. Then, single crystal
specimens are produced from each master ingot respectively by the
Bridgman method. Next, microstructure consisting of two phases of
.gamma. and .gamma.' can be obtained by applying heat treatment to
the specimens.
Composition of the Alloy
[0016] The Ni-based superalloy of 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-based alloy as 100. For simplicity, explanation of Ni
and other inevitable impurities will be omitted.
(1) Cobalt (Co): 11.5.about.43.5%
[0017] Cobalt influences solution treatment temperatures by
changing a .gamma.' solidus, a major hardening phase of Ni-base
superalloy, and .gamma. solidus, a matrix, in addition to solid
solution hardening. It also improves high temperature corrosion
resistance. Creep property becomes worse if the 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 the Co content is more than 13.5%.
(2) Chrome (Cr): 3.5.about.5.0%
[0018] Chrome improves corrosion resistance of the 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 poor if
Cr content is less than 3.5%, while more than 5.0% Cr content may
lower the creep property and create TCP phases that negatively
influence mechanical properties in the event of long exposure at
high temperature.
(3) Molybdenum (Mo): 0.7.about.2.0%
[0019] Molybdenum improves properties of the 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 a solid solution hardening effect under 0.7%, while more
than 2.0% increases the density.
(4) Tungsten (W): 8.5.about.10.5%
[0020] 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.
(5) Aluminum (Al): 4.5.about.6.5%
[0021] Aluminum is an essential element to improve high temperature
creep property because it is a constitutive element of .gamma.', a
major hardening phase of the Ni-based superalloy. In addition, it
improves oxidation resistance. However, creep strength lowers under
4.5%, while mechanical properties worsen due to precipitate of
excessive .gamma.' phases in case of adding more than 6.5%.
(6) Titanium (Ti): 0.5.about.2.0%
[0022] Titanium, like Aluminum, improves creep strength as a
constitutive element of .gamma.' phase and enhances corrosion
resistance. Therefore, more than 0.5% should be added. However, the
amount should be limited to 2.0% because excessive addition may
reduce oxidation resistance.
(7) Tantalum (Ta): 6.0.about.8.0%
[0023] Tantalum improves creep strength by hardening .gamma.'
phases. 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. However, if more than 8.0% is added,
harmful .delta. phases can be precipitated.
(8) Rhenium (Re): 2.0.about.4.0%
[0024] 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
the superalloy. Yet, a large quantity lowers phase stability,
increases density and raises the price; therefore, the present
invention limits the amount of Rhenium to 2.0.about.4.0%.
(9) Ruthenium (Ru): 0.1.about.2.0%
[0025] Ruthenium improves high temperature properties by inhibiting
creation of TCP phases through broadening the solid solution range
of .gamma.' phase and contributing to homogenization of
segregation. Accordingly, in the present invention Ruthenium is
added to enhance resistance to creep deformation as well as creep
life of the superalloy. However, the amount is limited to
0.1.about.2.0% because the cost of the superalloy becomes expensive
and the density increases if a large quantity of Ruthenium is
contained.
[0026] The present inventions will be explained in more detail
through the following embodiments.
[0027] Table 1 shows the chemical composition of a single crystal
superalloy according to the present invention and an alloy compared
with the superalloy.
[0028] According to Table 1, Test Material 1 presents the
composition of a Ni-based alloy with 1.0 weight % of Ru added,
while Test Material 2 shows a case with 0.5 weight % of Ru. In
contrast, all the Comparative Test Materials do not contain Ru,
while Comparative Test Material 1 does not contain Re as well. In
addition, although Comparative Test Material 2 contains Re, more Cr
content is contained, while Comparative Test Material 3 has less Co
content contained. Comparative Test Material 4 is CMSX-4 that is
being most commonly used at the present time.
[0029] The above Test Materials and Comparative Test Materials were
produced as follows. First, master ingots were cast using a vacuum
induction melting process. Then, single crystal specimens of 15 mm
diameter and 180 mm length were produced by the Bridgman method
with drawal rate of 4.0 mm/min. Next, a microstructure consisting
of two phases of .gamma. and .gamma.' was obtained by applying heat
to the specimens.
TABLE-US-00001 TABLE 1 Alloy Co Cr Mo W Al Ti Ta Re Ru Hf Test 1
11.44 4.07 1.03 8.48 5.47 1.02 6.95 3.02 1.02 0 Materials 2 11.51
4.11 1.02 8.51 5.46 1.03 7.01 2.97 0.51 0 Comparative 1 11.02 4.03
0.48 8.07 5.51 1.01 6.81 0 0 0 Test 2 10.99 8.02 0.52 8.12 5.50
1.02 7.02 2.99 0 0 Materials 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
[0030] Table 2 shows creep life and time to 1% creep strain when
creep tests are conducted by applying stress of 355 MPa at
950.degree. 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.degree. C./355 MPa.
TABLE-US-00002 TABLE 2 Test Test Comparative Comparative
Comparative Comparative Material Material Test Test Test Test
Classification 1 2 Material 1 Material 2 Material 3 Material 4
Creep Rupture 211.7 192.3 10.1 71.0 142.3 123.1 Time (Hour) Time to
1% 112.0 87.0 0.8 29.0 40.0 57.0 Creep Strain (Hour)
[0031] As is seen from Table 2 and FIG. 1, the creep properties of
a Ni-based alloy is greatly dependent on Re content. That is, it is
found that Comparative Test Material 1 with no Re shows
significantly shorter Creep Rupture Time and Time to 1% Creep
Strain than other Test Materials or Comparative Test Materials. In
addition, comparing Test Materials 1.about.2 containing Re and Ru
with Comparative Test Materials 2.about.4 with Re without Ru, it is
found that Ru plays a principal role in improving creep property of
the Ni-based alloy. Of course, selecting contents of other alloying
elements is necessary in order to improve the creep properties by
Ru stated above.
[0032] In the concrete, Creep Rupture Time of Test Materials
1.about.2 containing Ru was 192.3.about.211.7 hours, while Time to
1% Creep Strain was 87.0.about.112.0 hours. On the other hand,
Comparative Test Materials 2.about.4 without Ru presented was
71.0.about.123.1 hours of Creep Rupture Time and 29.0.about.57.0
hours of Time to 1% Creep Strain. In comparison between Comparative
Test Material 4 with relatively good creep properties and Test
Material 1 of the present invention, it was found that Test
Material 1 of the present invention showed almost double the Creep
Rupture Time and Time to 1% Creep Strain compared with Comparative
Test Material 4.
[0033] 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.
* * * * *