U.S. patent application number 11/788302 was filed with the patent office on 2008-10-23 for corrosion and oxidation resistant directionally solidified superalloy.
This patent application is currently assigned to Siemens Power Generation, Inc.. Invention is credited to Douglas J. Arrell, Allister W. James.
Application Number | 20080260572 11/788302 |
Document ID | / |
Family ID | 39872376 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080260572 |
Kind Code |
A1 |
James; Allister W. ; et
al. |
October 23, 2008 |
Corrosion and oxidation resistant directionally solidified
superalloy
Abstract
A nickel-based superalloy having a good balance between
corrosion and oxidation resistance. The alloy provides good
mechanical properties. The superalloy is suited for directional
solidification casting but can also be used for conventional or
single crystal casting techniques. The superalloy is well suited
for the hot section components such as blades, vanes and ring
segments for gas turbine engines. The superalloys can be used with
various thermal barrier coatings
Inventors: |
James; Allister W.;
(Orlando, FL) ; Arrell; Douglas J.; (Oviedo,
FL) |
Correspondence
Address: |
Siemens Corporation;Intellectual Property Department
170 Wood Avenue South
Iselin
NJ
08830
US
|
Assignee: |
Siemens Power Generation,
Inc.
|
Family ID: |
39872376 |
Appl. No.: |
11/788302 |
Filed: |
April 19, 2007 |
Current U.S.
Class: |
420/443 |
Current CPC
Class: |
C22C 19/05 20130101 |
Class at
Publication: |
420/443 |
International
Class: |
C22C 19/05 20060101
C22C019/05 |
Claims
1. A nickel-based superalloy expressed in weight percentages
consisting essentially of: 9.5 to 14.0 Cr; 7.0 to 11.0 Co; 1.0 to
2.5 Mo; 3.0 to 6.0 W; 1.0 to 6.0 Ta; 3.0 to 4.0 Al; 3.0 to 5.0 Ti;
0 to 1.0 Nb; 0.05 to 0.2 Hf; 0.05 to 0.2 Si; 0.005 to 0.02 B; 0 to
0.1 Zr; 0.05 to 0.15 C; 0.001 to 0.1 of a mixture of two or more
rare earth metals selected from the group of consisting of Y, La,
Ce, Nb, Dy, Pr, Sm, and Gd; and balance formed from Ni.
2. The superalloy of claim 1, wherein the superalloy consisting
essentially of: 11.6 to 12.7 Cr; 8.5 to 9.5 Co; 1.65 to 2.15 Mo;
3.0 to 4.1 W; 4.8 to 5.2 Ta; 3.4 to 3.8 A1; 3.9 to 4.25 Ti; 0 to
0.5 Nb; 0.1 to 0.15 Hf; 0.1 to 0.15 Si; 0.005 to 0.015 B; 0 to 0.02
Zr; 0.05 to 0.11 C; 0.01 to 0.05 of a mixture of two or more rare
earth metals selected from the group of consisting of Y, La, Ce,
Nb, Dy, Pr, Sm, and Gd; and the balance formed from Ni.
3. The superalloy of claim 1, wherein the superalloy consisting
essentially of: 12.2 Cr; 9.0 Co; 1.9 Mo; 3.8 W; 5.0 Ta; 3.6 Al; 4.1
Ti; <0.2 Nb; 0.12 Hf; 0.12 Si; 0.01 B; 0.0075 Zr; 0.09 C; 0.02
of a mixture of two or more rare earth metals selected from the
group consisting of Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; and the
balance formed from Ni.
Description
FIELD OF THE INVENTION
[0001] The invention relates to nickel-based superalloys usable to
form hot section components of gas turbine engines.
BACKGROUND OF THE INVENTION
[0002] Nickel-based superalloys have a very good material strength
at high temperatures. These properties permit their use in
components for gas turbine engines where the retention of excellent
mechanical properties at high temperatures is required. Hot section
components include vanes, rotating blades and ring segments.
[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. Several
major types of oxide scales exist, which include simple as well as
complex oxides/spinels based primarily on aluminum, cobalt, nickel,
and chromium. When certain rare earth elements (i.e., those
elements with consecutive atomic numbers of 57 to 71, inclusive;
also including yttrium, atomic number 39) are intentionally added
to the superalloy in closely controlled amounts, the oxidation
resistance of components made from such compositions is improved.
This improvement is attributed to the ability of a rare earth
element to reduce the residual sulfur content through the formation
of sulfides and oxysulfides which stabilizes the oxide scale formed
on the component surface improving the resistance of the scale and
any coating thereon to spallation during use of the superalloy
component.
[0005] The use of these superalloys at increasingly higher
temperatures requires that a coating be applied to the superalloy
component for thermal protection. The coating typically consists of
applying a bondcoat to the superalloy and then a thermal barrier
coating (TBC) to the bondcoat. Typical bond coats are alloys of the
type MCrAlX where M is Ni, Co, or Fe and X is commonly Y, Zr, or
Hf. The bondcoat tends to degrade during prolonged high temperature
exposure. The degraded bondcoat does not adequately adhere the
thermal barrier coating to the superalloy component and spallation
of the TBC occurs with complete loss of thermal protection to the
component. The rate at which the bondcoat degrades depends upon the
composition of the superalloy to which it is applied. Generally
alumina forming superalloys exhibit longer bondcoat lifetimes than
chromia forming superalloys. However, it is often preferable to use
high chromium containing superalloys for very high corrosion
resistance. The formation of an alumina scale over that of a
chromia scale can be enhanced by the presence of silicon.
[0006] Hence there remains a need for a superalloy with a lower
propensity to promote bondcoat degradation and significantly
enhance the resistance of the TBC to spallation.
SUMMARY OF THE INVENTION
[0007] This invention is directed to a nickel-based superalloy with
a good balance of corrosion and oxidation resistance. The
nickel-based superalloy is ideally suited to directionally
solidified casting, but may also be produced by conventional
casting or single crystal casting techniques. The superalloy is
well suited for applications in the gas turbine engines as hot
section components such as blades, vanes, and ring segments.
[0008] In one embodiment, the superalloy may be formed from
materials in the following percentages: 9.5 to 14.0 Cr; 7.0 to 11.0
Co; 1.0 to 2.5 Mo; 3.0 to 6.0 W; 1.0 to 6.0 Ta; 3.0 to 4.0 Al; 3.0
to 5.0 Ti; 0 to 1.0 Nb; 0.05 to 0.2 Hf; 0.05 to 0.2 Si; 0.005 to
0.02 B; 0 to 0.1 Zr; 0.05 to 0.15 C, 0.001 to 0.1 of a mixture of
two or more rare earth metals selected from the group of Y, La, Ce,
Nb, Dy, Pr, Sm, and Gd; and the balance formed from Ni. A preferred
superalloy may be formed from materials in the following
percentages: 11.6 to 12.7 Cr; 8.5 to 9.5 Co; 1.65 to 2.15 Mo; 3.0
to 4.1 W; 4.8 to 5.2 Ta; 3.4 to 3.8 Al; 3.9 to 4.25 Ti; 0 to 0.5
Nb; 0.1 to 0.15 Hf; 0.1 to 0.15 Si; 0.005 to 0.015 B; 0 to 0.02 Zr;
0.05 to 0.11 C, 0.01 to 0.05 of a mixture of two or more rare earth
metals selected from the group of Y, La, Ce, Nb, Dy, Pr, Sm, and
Gd; and the balance formed from Ni. The most preferred superalloy
may be formed from materials in the following percentages: 12.2 Cr;
9.0 Co; 1.9 Mo; 3.8 W; 5.0 Ta; 3.6 Al; 4.1 Ti; <0.2 Nb; 0.12 Hf;
0.12 Si; 0.01 B; 0.0075 Zr; 0.09 C, 0.02 of a mixture of two or
more rare earth metals selected from the group of Y, La, Ce, Nb,
Dy, Pr, Sm, and Gd; and the balance formed from Ni.
[0009] An advantage of this invention is that the superalloy has
good mechanical properties and provides a unique balance between
good oxidation characteristics and good corrosion resistance.
DETAILED DESCRIPTION OF THE INVENTION
[0010] This invention is directed to a nickel-based superalloy with
a good balance of corrosion and oxidation resistance. The
nickel-based superalloy is ideally suited to directionally
solidified casting, but may also be produced by conventional
casting or single crystal casting techniques. The superalloy is
well suited for applications in the gas turbine engines as hot
section components such as blades, vanes, and ring segments.
[0011] The superalloy may promote a balance of corrosion and
oxidation resistance suited for directionally solidified casting of
hot section gas turbine engine components. In one embodiment, the
superalloy may be formed from materials in the following
percentages: 9.5 to 14.0 Cr; 7.0 to 11.0 Co; 1.0 to 2.5 Mo; 3.0 to
6.0 W; 1.0 to 6.0 Ta; 3.0 to 4.0 Al; 3.0 to 5.0 Ti; 0 to 1.0 Nb;
0.05 to 0.2 Hf; 0.05 to 0.2 Si; 0.005 to 0.02 B; 0 to 0.1 Zr; 0.05
to 0.15 C, 0.001 to 0.1 total of at least one rare earth metals
selected from the group of Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; and
the balance formed from Ni.
[0012] Chromium (Cr) is included to improve the alloy's
high-temperature corrosion resistance. The reason for limiting the
chromium content to 9.5 to 14.0 weight percent in the present
invention is to assure a good level of corrosion resistance and is
preferably from 11.6 to 12.7 weight percent. The desirable
high-temperature corrosion resistance cannot be ensured at lower
levels.
[0013] Cobalt (Co) replaces nickel (Ni) in the gamma-phase to
strengthen the matrix in solid solution. Co is included in the
range of 7.0 to 11.0 percent by weight in the present invention to
strengthen the matrix in solid solution yet have Co below the level
where the proportion of the gamma prime phase is too low to have
good creep strength. A preferred range for Co is from 8.5 to 9.5
percent by weight.
[0014] Molybdenum (Mo) is a solid-solution strengthener of the
gamma-phase, and can also promote the formation of raft structure,
which strengthens the superalloy at high temperatures. In the
present invention, Mo is included at 1.0 to 2.5 weight percent, and
is preferably 1.65 to 2.15 weight percent. Mo at levels above 3.0
weight percent can be detrimental to the creep strength and
low-cycle fatigue properties of the superalloy.
[0015] Tungsten (W) is a solid-solution strengthener of the
gamma-phase. In the present invention, a W content is included at
3.0 to 6.0 weight percent and is preferably 3.0 to 4.1 weight
percent.
[0016] Aluminum (Al) is an element of the gamma prime phase which
also forms an aluminum oxide surface on the alloy to provide
oxidation resistance. In the present invention, the Al content is
3.0 to 4.0 weight percent which is lower than that generally
required to obtain a good oxidation resistance, however, the
addition of rare earth elements, silicon (Si) and Hafnium (Hf)
compensates for the lower amount of Al. The preferred range of Al
is 3.4 to 3.8 weight percent.
[0017] Titanium (Ti) can replace some of the Al in the gamma prime
phase to form Ni.sub.3(Al,Ti), serving as a solid-solute
strengthener of the gamma prime phase. In the present invention a
Ti is included at 3.0 to 5.0 weight percent and is preferably 3.9
to 4.25 weight percent.
[0018] Tantalum (Ta) is primarily in the gamma prime phase in solid
solution to strengthen the gamma prime phase and contributes to
oxidation resistance. In the present invention, Ta is included at
1.0 to 6.0 weight percent and is preferably at 4.8 to 5.2 weight
percent where it contributes positively to the creep strength of
the superalloy.
[0019] Hafnium (Hf) improves the grain boundary strength of the
superalloy. The present invention includes Hf at 0.05 to 0.2 weight
percent where it also promotes the formation of an alumina surface
and improves the oxidation resistance of the superalloy. At higher
levels of Hf the melting point of the superalloy can be diminished.
The preferred range of Hf is 0.1 to 0.15 weight percent.
[0020] Silicon (Si) is an element that forms an oxide, SiO.sub.2 on
the surface of the resultant alloy which improves the oxidation
resistance. Si is added to the superalloy of the present invention
at a level of 0.05 to 0.2 weight percent. Si can inhibit other
elements participating in the solid solution at levels higher than
0.2 weight percent. A preferred range of Si is 0.1 to 0.15 weight
percent. The inclusion of Hf at levels similar to that of the
silicon enhances the oxidation resistance provided by the Si.
[0021] Niobium (Nb) primarily partitions to and strengthens the
gamma prime phase. Nb acts in concert with the Ta to increase the
solution proportion of the gamma prime phase further enhancing the
strength relative to a superalloy using Ta alone. In the present
invention, Nb can be included at a level up to 1.0 weight percent
and is preferably included at a level of less than 0.5 weight
percent.
[0022] Carbon (C) improves the strength of grain boundaries. In the
present invention, C is included at a range of 0.05 to 0.15 weight
percent. Levels of C above this range can negatively affect the
creep strength of the superalloy. The C is preferably included at a
range of 0.05 to 0.11 weight percent.
[0023] Boron (B) is also included to improve the grain boundary
strength. When the boron is added in excess of 0.05% the creep
strength can be diminished. The content of B in the superalloy of
the present invention is limited to 0.005 to 0.02 weight percent
and preferably between 0.005 and 0.015 weight percent.
[0024] Zirconium (Zr) can also be included to improve the grain
boundary strength of the superalloy. In the present invention, Zr
can be included up to 0.1 weight percent and is preferably up to
0.02 weight percent. Higher levels of Zr can negatively affect the
creep characteristics of the superalloy.
[0025] Rare earth elements Yttrium (Y), Lanthanum (La), Cerium
(Ce), Gadolinium (Gd), Praseodymium (Pr), Dysprosium (Dy),
Neodymium (Nd) and Erbium (Er) promote the formation of the
Al.sub.2O.sub.3 and SiO.sub.2 scale on the superalloy and improve
adhesive property of this protective oxide layer. The presence of
rare earth elements is believed to promote the diffusion of
aluminum to the surface hence increasing the proportion of alumina
in the scale. The inclusion of these rare earth elements also
enhances the compatibility of the superalloy with various coatings.
An excessive addition of the rare earths lowers the solubility of
other elements and for this reason the combined rare earth elements
are not included in excess of 0.1 weight percent. In the present
invention one or more of the rare earths are included in a combined
range of 0.001 to 0.1 weight percent. A preferred range for the
combined rare earth elements is 0.01 to 0.05 weight percent.
[0026] The presence of the rare earth elements enhances the coating
life. This enhancement is attributed to the ability of the rare
earth elements to form sulfides and oxysulfides fixing sulfur
impurities which prevents their diffusion to the surface and
degrades the alumina scale on the superalloy.
[0027] As indicated above, a preferred superalloy for high
corrosion resistance and an improved oxidation resistance may be
formed from materials in the following percentages: 11.6 to 12.7
Cr; 8.5 to 9.5 Co; 1.65 to 2.15 Mo; 3.0 to 4.1 W; 4.8 to 5.2 Ta;
3.4 to 3.8 Al; 3.9 to 4.25 Ti; 0 to 0.5 Nb; 0.1 to 0.15 Hf; 0.1 to
0.15 Si; 0.005 to 0.015 B; 0 to 0.02 Zr; 0.05 to 0.11 C, 0.01 to
0.05 of one or more rare earth metals selected from the group of Y,
La, Ce, Nb, Dy, Pr, Sm, and Gd; and the balance formed from Ni. A
most preferred superalloy composition may be formed from materials
in the following percentages: 12.2 Cr; 9.0 Co; 1.9 Mo; 3.8 W; 5.0
Ta; 3.6 Al; 4.1 Ti; <0.2 Nb; 0.12 Hf; 0.12 Si; 0.01 B; 0.0075
Zr; 0.09 C, 0.02 of a mixture of one or more rare earth metals
selected from the group of Y, La, Ce, Nb, Dy, Pr, Sm, and Gd; and
the balance formed from Ni.
[0028] The superalloy of the present invention is ideally suited
for directionally solidification casting. However, it can be
readily produced by conventional casting or single crystal casting
techniques. The superalloy is well suited for the hot section
components such as blades, vanes and ring segments for gas turbine
engines. The superalloys can be used with various thermal barrier
coatings.
[0029] 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.
* * * * *