U.S. patent application number 11/788301 was filed with the patent office on 2008-10-23 for oxidation resistant superalloy.
This patent application is currently assigned to Siemens Power Generation, Inc.. Invention is credited to Douglas J. Arrell, Allister W. James.
Application Number | 20080260571 11/788301 |
Document ID | / |
Family ID | 39872375 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080260571 |
Kind Code |
A1 |
Arrell; Douglas J. ; et
al. |
October 23, 2008 |
Oxidation resistant superalloy
Abstract
A nickel-based superalloy that forms a chromia scale in an
oxidizing environment is disclosed. The alloy provides good
oxidation resistance at temperatures below 900.degree. C. in a dry
or moist atmosphere. The superalloy is well-suited for components
of gas or steam turbine engines including blades and vanes.
Inventors: |
Arrell; Douglas J.; (Oviedo,
FL) ; James; Allister W.; (Orlando, FL) |
Correspondence
Address: |
Siemens Corporation;Intellectual Property Department
170 Wood Avenue South
Iselin
NJ
08830
US
|
Assignee: |
Siemens Power Generation,
Inc.
|
Family ID: |
39872375 |
Appl. No.: |
11/788301 |
Filed: |
April 19, 2007 |
Current U.S.
Class: |
420/443 ;
420/448 |
Current CPC
Class: |
C22C 19/05 20130101 |
Class at
Publication: |
420/443 ;
420/448 |
International
Class: |
C22C 19/05 20060101
C22C019/05 |
Claims
1. A nickel-based superalloy expressed in weight percentages
consisting essentially of: 15.5 to 18.5 Cr; 14.0 to 15.5 Co; 2.5 to
3.5 Mo; 2.0 to 3.5 Al; 4.0 to 5.5 Ti; 0.5 to 2.0 W; 0 to 1.5 Hf; 0
to 2.0 Fe; 0 to 1.0 Si; 0.01 to 0.1 B; 0 to 0.1 Zr; 0.03 to 0.20 C;
0 to 0.5 at least one rare earth elements selected from the group
of Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; less than 0.1 S; and balance
formed from Ni.
2. The superalloy of claim 1, wherein the superalloy expressed in
weight percentages consisting essentially of: 15.5 to 16.5 Cr; 14.0
to 15.5 Co; 2.75 to 3.25 Mo; 2.25 to 2.75 Al; 4.75 to 5.25 Ti; 1.0
to 1.5 W; 0 to 1.0 Hf; 0 to 0.5 Fe; 0 to 0.5 Si; 0.01 to 0.02 B;
0.025 to 0.08 Zr; 0.03 to 0.10 C; 0 to 0.2 at least one rare earth
elements selected from the group of Y, La, Ce, Nb, Dy, Pr, Sm, and
Gd; less than 10 ppm S; and the balance formed from Ni.
3. The superalloy of claim 1, wherein the superalloy expressed in
weight percentages consisting essentially of: 15.5 to 16.5 Cr;
14.25 to 14.75 Co; 2.80 to 3.20 Mo; 2.30 to 2.60 Al; 4.80 to 5.20
Ti; 1.2 to 1.5 W; 0.10 to 0.15 Hf; O to 0.2 Fe; 0.10 to 0.15 Si;
0.01 to 0.02 B; 0.025 to 0.050 Zr; 0.03 to 0.04 C; 250 to 750 ppm
at least one rare earth elements selected from the group of Y, La,
Ce, Nb, Dy, Pr, Sm, and Gd; less than 2 ppm S; and the balance
formed from Ni.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a nickel-based superalloy that
forms a protective chromia layer in an oxidizing atmosphere.
BACKGROUND OF THE INVENTION
[0002] Nickel-based superalloys have a very good material strength
at elevated temperatures. These properties permit their use in
components for gas turbine engines where the retention of excellent
mechanical properties at high temperatures is required for typical
lifetimes in excess of 100,000 hours. Components within an
industrial gas turbine are exposed to a range of temperatures
depending upon where the component is located in the turbine. For
example, last stage turbine blades see intermediate temperatures
and do not require and are not covered by a thermal barrier
coating. The last stage turbine blades are protected by the surface
oxide layer that forms upon exposure to the oxidizing
environment.
[0003] The metallurgy of superalloys is a sophisticated and well
developed field. Optimization of the composition of superalloys
consists of defining the amounts of elements which are desirably
present, and the amounts of elements which are desirably absent.
These impurities can in some cases be completely eliminated from
the composition through the judicious selection of melt stock
material; however, some elements cannot be readily eliminated. One
impurity which has long been recognized as being detrimental is
sulfur. Sulfur was initially identified as being detrimental to
mechanical properties, and its presence in alloy compositions was
limited for that reason. However, the sulfur levels which do not
present significant loss of mechanical properties, a bulk property,
can in some cases still be highly detrimental to oxidation
resistance, a surface property.
[0004] Oxidation resistance of superalloys is primarily due to the
presence of an adherent surface oxide scale. The composition and
nature of oxide scales depends on the composition of the alloy and
the environment in which the superalloy component operates.
Typically, the oxide is either alumina or chromia. These oxides are
formed by a selective oxidation of the component in the alloy. A
continuous oxide scale of predominately or exclusively one metal
occurs where a metal at or above a critical concentration in the
alloy oxidizes preferentially over more noble metals, such that the
sufficiently high concentration less noble element diffuses to and
into the scale, forming more of the selective oxide while the more
noble metal diffuses from the scale into the alloy. The composition
and thickness of the protective oxide scale formed depends on a
number of factors including the relative concentration of the
metals in the alloy, the relative nobilities of the metals in the
substrate, and oxygen solubility and diffusivity in the alloy. As
the temperature changes, the diffusion rates and solubilities of
the metals and oxygen will change. Typically, the formation of an
alumina scale is favored by higher temperatures. Some alloys form
chromia scales at lower temperatures and alumina scales at higher
temperatures where aluminum no longer precipitates internally.
Generally maximum protection via alumina occurs by formation at a
temperature range, in excess of 1,000.degree. C. The selective
oxidation can also be enhanced by the incorporation of reactive
metals such as rare earth elements.
[0005] Moisture affects the degradation and debonding of the
protective oxide. This is particularly critical for steam turbines,
where superalloys are replacing steel as the temperature at which
the turbine operates increases. The temperatures at which a steam
turbine operates are typically lower than the temperatures where
gas turbine operates. The presence of water vapor generally lowers
the oxidation stability of the superalloy, as the oxide scale is
either poorly formed, or is not stable to the water vapor
containing oxidizing environment. Selective oxidation to alumina is
not favored in a water containing atmosphere, particularly at lower
temperatures. At higher temperatures, in excess of 900.degree. C.,
water vapor can promote the formation of volatile species that
remove chromia scale and can ultimately result in the loss of
oxidation protection by a chromia scale.
[0006] Hence the identification of superalloys that provides good
oxidation resistance to components, particularly for components
that must operate in the presence of water vapor.
SUMMARY OF THE INVENTION
[0007] This invention is directed to a nickel-based superalloy that
forms a highly adherent chromia surface layer when exposed to an
oxidizing environment at intermediate elevated temperatures. The
nickel-based super alloy may be used together with industrial gas
turbine components operating at intermediate temperatures, such as
last stage turbine blades, which are not protected by a coating.
The life of such components may be greatly extended by forming an
outer layer of alumina or chromia.
[0008] In one embodiment, the nickel-based superalloy may be formed
from materials in the following weight percentages: 15.5 to 18.5
Cr; 14.0 to 15.5 Co; 2.5 to 3.5 Mo; 2.0 to 3.5 Al; 4.0 to 5.5 Ti;
0.5 to 2.0 W; 0 to 1.5 Hf; 0 to 2.0 Fe; 0 to 1.0 Si; 0.01 to 0.1 B;
0 to 0.1 Zr; 0.03 to 0.20 C; 0 to 0.5 at least one rare earth
elements selected from the group of Y, La, Ce, Nb, Dy, Pr, Sm, and
Gd; less than 0.1 S; and the balance formed from Ni. A preferred
superalloy may be formed from materials in the following weight
percentages: 15.5 to 16.5 Cr; 14.0 to 15.5 Co; 2.75 to 3.25 Mo;
2.25 to 2.75 Al; 4.75 to 5.25 Ti; 1.0 to 1.5 W; 0 to 1.0 Hf; 0 to
0.5 Fe; 0 to 0.5 Si; 0.01 to 0.02 B; 0.025 to 0.08 Zr; 0.03 to 0.10
C; 0 to 0.2 at least one rare earth elements selected from the
group of Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; less than 10 ppm S; and
the balance formed from Ni. A more preferred superalloy may be
formed from materials in the following weight percentages: 15.5 to
16.5 Cr; 14.25 to 14.75 Co; 2.80 to 3.20 Mo; 2.30 to 2.60 Al; 4.80
to 5.20 Ti; 1.2 to 1.5 W; 0.10 to 0.15 Hf; 0 to 0.2 Fe; 0.10 to
0.15 Si; 0.01 to 0.02 B; 0.025 to 0.050 Zr; 0.03 to 0.04 C; 250 to
750 ppm at least one rare earth elements selected from the group of
Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; less than 2 ppm S; and the
balance formed from Ni.
DETAILED DESCRIPTION OF THE INVENTION
[0009] This invention is directed to a nickel-based superalloy that
forms a highly adherent chromia surface layer when exposed to an
oxidizing environment at intermediate elevated temperatures. The
nickel-based super alloy may be used together with industrial gas
turbine components operating at intermediate temperatures, such as
last stage turbine blades, which are not protected by a coating.
The life of such components may be greatly extended by forming an
outer layer of alumina or chromia.
[0010] In one embodiment, the superalloy can form and maintain a
well adhered protective chromia scale for use at intermediate
temperatures, which provides oxidation resistance when exposed to a
dry or moist gas and is suitable for components used in a gas or
steam turbine engine. The superalloy may be formed from materials
in the following weight percentages: 15.5 to 18.5 Cr; 14.0 to 15.5
Co; 2.5 to 3.5 Mo; 2.0 to 3.5 Al; 4.0 to 5.5 Ti; 0.5 to 2.0 W; 0 to
1.5 Hf; 0 to 2.0 Fe; 0 to 1.0 Si; 0.01 to 0.1 B; 0 to 0.1 Zr; 0.03
to 0.20 C; 0 to 0.5 at least one rare earth elements selected from
the group of Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; less than 0.1 S;
and the balance formed from Ni.
[0011] A preferred superalloy may be formed from materials in the
following weight percentages: 15.5 to 16.5 Cr; 14.0 to 15.5 Co;
2.75 to 3.25 Mo; 2.25 to 2.75 Al; 4.75 to 5.25 Ti; 1.0 to 1.5 W; 0
to 1.0 Hf; 0 to 0.5 Fe; 0 to 0.5 Si; 0.01 to 0.02 B; 0.025 to 0.08
Zr; 0.03 to 0.10 C; 0 to 0.2 at least one rare earth elements
selected from the group of Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; less
than 10 ppm S; and the balance formed from Ni. A more preferred
superalloy composition may be formed from materials in the
following weight percentages: 15.5 to 16.5 Cr; 14.25 to 14.75 Co;
2.80 to 3.20 Mo; 2.30 to 2.60 Al; 4.80 to 5.20 Ti; 1.2 to 1.5 W;
0.10 to 0.15 Hf; 0 to 0.2 Fe; 0.10 to 0.15 Si; 0.01 to 0.02 B;
0.025 to 0.050 Zr; 0.03 to 0.04 C; 250 to 750 ppm at least one rare
earth elements selected from the group of Y, La, Ce, Nb, Dy, Pr,
Sm, and Gd; less than 2 ppm S; and the balance formed from Ni.
[0012] The superalloy of the present invention is intended to be
used for components where a chromia scale provides oxidation
resistance. It is also intended that components produced from this
superalloy be used at intermediate temperatures generally in the
range of between 450.degree. C. to 750.degree. C. and are not
intended for service at temperatures of above 900.degree. C. The
turbine components prepared from the inventive superalloy can be
used in the presence of a dry gas or with a gas that includes water
vapor. Therefore, the components from the inventive superalloy can
be used in either a gas or steam turbine engine.
[0013] The inventive superalloy may have a chromium (Cr) content
between 15.5 and 18.5 weight percent. This level of Cr supports the
formation of a chromia scale with little or no other metal oxides
included in the scale. To assure an excellent well adhered chromia
scale, the scale should be almost exclusively chromia with little
content of other metals. The preferred level is 15.5 to 16.5 weight
percent Cr, which assures that a well adhered chromia scale
forms.
[0014] Aluminum (Al) is included in the superalloy at levels of 2.0
to 3.5 weight percent. At the intermediate temperatures for use of
the inventive superalloy, the level of Al is insufficient to form
an alumina scale rather than remain primarily as an alloy element
in the gamma prime phase.
[0015] Titanium (Ti) is included at 4.0 to 5.5 weight percent in
the inventive alloy and, in general, will reside in the gamma prime
phase of the superalloy where it acts as a solid-solute
strengthener. In most cases, titania will not be present in the
chromia scale. However, some titania can be included in the chromia
scale when the scale is formed near the upper temperature limits
for use of the inventive superalloy. The titania can reside at the
gas/chromia interface and act as a physical barrier to the loss of
volatile chromium oxide species.
[0016] Sulfur (S) is preferably absent from the superalloy, but is
generally present as an impurity in the superalloy. Spalling of the
oxide scale is promoted by S and for this reason S must be bound
into the superalloy or be present at a very low level, and is
preferably below 10 ppm.
[0017] One or more rare earth elements selected from the group of
Y, La, Ce, Nb, Dy, Pr, Sm, and Gd can be included in the inventive
superalloy. The inclusion of the rare earths aids in the formation,
adherence, and maintenance of the chromia scale. The rare earth
elements also selectively combine with sulfur to form refractory
sulfides in the superalloy, preventing sulfur migration to the
scale where it is detrimental to chromia adhesion to the
superalloy.
[0018] Cobalt (Co) replaces nickel (Ni) in the gamma-phase to
strengthen the matrix in solid solution. Co is included in the
range of 14.0 to 15.5 percent by weight in the present invention to
strengthen the matrix in solid solution. A preferred range for Co
is from 8.5 to 9.5 percent by weight.
[0019] Tungsten (W) is a solid-solute strengthener of the
gamma-phase. In the present invention, a W content is included at
0.5 to 2.0 weight percent and is preferably 1.0 to 1.5 weight
percent.
[0020] Alternatives for the alloy composition and other variations
within the range provided will be apparent to those skilled in the
art. Variations and modifications can be made without departing
from the scope and spirit of the invention as defined by the
following claims.
* * * * *