U.S. patent application number 12/173983 was filed with the patent office on 2009-02-12 for corrosion resistant alloy compositions with enhanced castability and mechanical properties.
This patent application is currently assigned to SIEMENS POWER GENERATION, INC.. Invention is credited to Douglas J. Arrell, Gerhard E. Fuchs, Allister W. James.
Application Number | 20090041615 12/173983 |
Document ID | / |
Family ID | 40346733 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090041615 |
Kind Code |
A1 |
James; Allister W. ; et
al. |
February 12, 2009 |
Corrosion Resistant Alloy Compositions with Enhanced Castability
and Mechanical Properties
Abstract
Disclosed are novel nickel-base alloy compositions that may be
cast as a single crystal or directionally solidified alloy
consisting essentially of, by weight: 8-12% Cr, 10-14% Co, 0.3-0.9%
Mo, 3-7% W, 2-8% Ta, 2.0-5.5% Al, 1.5-5.0% Ti, up to 2% Nb, less
than 0.1% B, less than 0.1% Zr, 0.05-0.15% C, less than 0.5% Hf,
2-4% Re, 0.05-0.2% Si, up to 0.015% S, up to 0.1% La, up to 0.1% Y,
up to 0.1% Ce, up to 0.1% Nd, up to 0.1% Dy, up to 0.1% Pr, up to
0.1% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
0.001-0.1%. The compositions for the nickel-base superalloy have a
balance between oxidation resistance, corrosion resistance,
castability, and mechanical properties, such as creep resistance
and thermo-mechanical fatigue resistance.
Inventors: |
James; Allister W.;
(Orlando, FL) ; Fuchs; Gerhard E.; (Gainesville,
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.
Orlando
FL
|
Family ID: |
40346733 |
Appl. No.: |
12/173983 |
Filed: |
July 16, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60955092 |
Aug 10, 2007 |
|
|
|
Current U.S.
Class: |
420/443 |
Current CPC
Class: |
C22C 19/057 20130101;
C22C 30/00 20130101; C22C 19/056 20130101 |
Class at
Publication: |
420/443 |
International
Class: |
C22C 19/05 20060101
C22C019/05 |
Claims
1. A nickel base alloy composition consisting essentially of, by
weight percent, 8-12% Cr, 10-14% Co, 0.3-0.9% Mo, 3-7% W, 2-8% Ta,
2.0-5.5% Al, 1.5-5.0% Ti, up to 2% Nb, less than 0.1% B, less than
0.1% Zr, 0.05-0.15% C, less than 0.5% Hf, 2-4% Re, 0.05-0.2% Si, up
to 0.015% S, up to 0.1% La, up to 0.1% Y, up to 0.1% Ce, up to 0.1%
Nd, up to 0.1% Dy, up to 0.1% Pr, up to 0.1% Gd, balance is Ni, and
wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is 0.001-0.1%.
2. The composition of claim 1 selected for its thermo-mechanical
fatigue resistance and comprising 2-6% Ta, 2-5% Al, and 3-5%
Ti.
3. The composition of claim 1 selected for its creep resistance and
comprising 4-8% Ta, 3.5-5.5% Al, and 1.5-4.0 Ti.
4. The composition of claim 1 selected for its thermo-mechanical
fatigue resistance, ability to be cast as a single crystal alloy
and comprising 9.5-10.5% Cr, 11.5-12.5% Co, 0.45-0.75% Mo, 4.4-5.4%
W, 3.4-4.4% Ta, 3.1-4.0% Al, 3.9-4.25% Ti, up to 0.5% Nb, less than
0.02% B, less than 0.02% Zr, 0.05-0.11% C, less than 0.25% Hf,
2.5-3.5% Re, 0.1-0.15% Si, up to 0.015% S, up to 0.05% La, up to
0.05% Y, up to 0.05% Ce, up to 0.05% Nd, up to 0.05% Dy, up to
0.05% Pr, up to 0.05% Gd, balance is Ni, and wherein
(La+Y+Ce+Nd+Dy+Pr+Gd) is 0.01-0.05%.
5. The composition of claim 1 selected for its thermo-mechanical
fatigue resistance, ability to be cast as a directionally
solidified alloy and comprising 9.5-10.5% Cr, 11.5-12.5% Co,
0.45-0.75% Mo, 4.4-5.4% W, 3.4-4.4% Ta, 3.1-4.0% Al, 3.9-4.25% Ti,
up to 0.5% Nb, 0.005-0.015% B, up to 0.02% Zr, 0.05-0.11% C, less
than 0.25% Hf, 2.5-3.5% Re, 0.1-0.15% Si, up to 0.015% S, up to
0.05% La, up to 0.05% Y, up to 0.05% Ce, up to 0.05% Nd, up to
0.05% Dy, up to 0.05% Pr, up to 0.05% Gd, balance is Ni, and
wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is 0.01-0.05%.
6. The composition of claim 1 selected for its creep resistance,
ability to be cast as a single crystal alloy and comprising
9.5-10.5% Cr, 11.5-12.5% Co, 0.45-0.75% Mo, 4.4-5.4% W, 5.5-6.5%
Ta, 4.2-4.8% Al, 2.0-2.8% Ti, up to 0.5% Nb, less than 0.02% B,
less than 0.02% Zr, 0.05-0.11% C, less than 0.25% Hf, 2.5-3.5% Re,
0.1-0.15% Si, up to 0.015% S, up to 0.05% La, up to 0.05% Y, up to
0.05% Ce, up to 0.05% Nd, up to 0.05% Dy, up to 0.05% Pr, up to
0.05% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
0.01-0.05%.
7. The composition of claim 1 selected for its creep resistance,
ability to be cast as a directionally solidified alloy and
comprising 9.5-10.5% Cr, 11.5-12.5% Co, 0.45-0.75% Mo, 4.4-5.4% W,
5.5-6.5% Ta, 4.2-4.8% Al, 2.0-2.8% Ti, up to 0.5% Nb, 0.005-0.015%
B, less than 0.02% Zr, 0.05-0.11% C, less than 0.25% Hf, 2.5-3.5%
Re, 0.1-0.15% Si, up to 0.015% S, up to 0.05% La, up to 0.05% Y, up
to 0.05% Ce, up to 0.05% Nd, up to 0.05% Dy, up to 0.05% Pr, up to
0.05% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
0.01-0.05%.
8. The composition of claim 1 selected for its thermo-mechanical
fatigue resistance, ability to be cast as a single crystal alloy
and comprising 10.0% Cr, 12.0% Co, 0.6% Mo, 4.9% W, 3.9% Ta, 3.5%
Al, 3.9% Ti, less than 0.01% B, less than 0.01% Zr, 0.07% C, less
than 0.1% Hf, 3.0% Re, less than 0.12% Si, up to 0.015% S, up to
0.02% La, up to 0.02% Y, up to 0.02% Ce, up to 0.02% Nd, up to
0.02% Dy, up to 0.02% Pr, up to 0.02% Gd, balance is Ni, and
wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is 0.03%.
9. The composition of claim 1 selected for its thermo-mechanical
fatigue resistance, ability to be cast as a directionally
solidified alloy and comprising 10.0% Cr, 12.0% Co, 0.6% Mo, 4.9%
W, 3.9% Ta, 3.5% Al, 3.9% Ti, 0.01% B, 0.0075% Zr, 0.09% C, 0.1%
Hf, 3.0% Re, less than 0.12% Si, up to 0.015% S, up to 0.02% La, up
to 0.02% Y, up to 0.02% Ce, up to 0.02% Nd, up to 0.02% Dy, up to
0.02% Pr, up to 0.02% Gd, balance is Ni, and wherein
(La+Y+Ce+Nd+Dy+Pr+Gd) is 0.03%.
10. The composition of claim 1 selected for its creep resistance,
ability to be cast as a single crystal alloy and comprising 10.0%
Cr, 12.0% Co, 0.6% Mo, 4.9% W, 6.0% Ta, 4.5% Al, 2.4% Ti, less than
0.01% B, less than 0.01% Zr, 0.07% C, less than 0.1% Hf, 3.0% Re,
less than 0.12% Si, up to 0.015% S, up to 0.02% La, up to 0.02% Y,
up to 0.02% Ce, up to 0.02% Nd, up to 0.02% Dy, up to 0.02% Pr, up
to 0.02% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
0.03%.
11. The composition of claim 1 selected for its creep resistance,
ability to be cast as a directionally solidified alloy and
comprising 10.0% Cr, 12.0% Co, 0.6% Mo, 4.9% W, 6.0% Ta, 4.5% Al,
2.4% Ti, 0.01% B, 0.0075% Zr, 0.09% C, 0.1% Hf, 3.0% Re, less than
0.12% Si, up to 0.015% S, up to 0.02% La, up to 0.02% Y, up to
0.02% Ce, up to 0.02% Nd, up to 0.02% Dy, up to 0.02% Pr, up to
0.02% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
0.03%.
Description
[0001] This application claims benefit of the 10 Aug. 2007 filing
date of U.S. Provisional Patent Application No. 60/955,092.
FIELD OF THE INVENTION
[0002] This invention relates in general to the field of nickel
base superalloys possessing improved oxidation resistance,
corrosion resistance, castability, and mechanical properties such
as creep resistance and thermo-mechanical fatigue resistance. The
present invention relates to alloys that may be cast as a single
crystal or directionally solidified.
BACKGROUND OF THE INVENTION
[0003] Nickel base superalloys are alloys composed primarily of
nickel with the addition of several other elements selected for
their ability to survive an overall high temperature, high stress,
and highly oxidative environment. Typically, this environment is
that of a gas turbine engine.
[0004] The greatest difficulty encountered with the gas turbine
environment is that the goals of creep resistance,
thermo-mechanical fatigue resistance, and corrosion resistance are
at odds with each other. Alloys with greater creep resistance
typically sacrifice hot corrosion resistance and thermo-mechanical
fatigue resistance. Alloys with greater hot corrosion resistance
come at the expense of poor creep resistance and thermo-mechanical
fatigue resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] This invention is explained in the following description in
view of the drawings that show:
[0006] FIG. 1 illustrates comparative creep testing of embodiments
of the present invention (called Alloys A and B) and a prior art
alloy PWA 1483.
[0007] FIG. 2 is a micrograph of Alloy A, after elevated
temperature exposure to a thermally oxidized coal derived syngas
test environment.
[0008] FIG. 3 is a micrograph of Alloy B, after elevated
temperature exposure to a thermally oxidized coal derived syngas
test environment.
[0009] FIG. 4 is a micrograph of the prior art alloy SieMet DS (PWA
1483 modified with grain boundary strengthening elements) after
elevated temperature exposure to a thermally oxidized coal derived
syngas test environment.
[0010] FIG. 5 is a micrograph of another prior art alloy CM247LC
after elevated temperature exposure to a thermally oxidized coal
derived syngas test environment.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The present invention provides an alloy composition that may
be cast as a single crystal alloy or may be directionally
solidified, and that has better castability than the prior art
alloy available from Cannon-Muskegon Corporation under the
registered trademark CMSX-4, has better corrosion resistance than
alloy CM247LC available from that same source, and has better
mechanical properties than the prior art alloy available through
United Technologies Corporation under the trademark PWA 1483.
Typical weight percent compositions of these prior art alloys are
shown in Table 1.
TABLE-US-00001 TABLE 1 CMSX-4 PWA 1483 CM247LC Min Max Min Max Min
Max Co 9.3 10.0 8.5 9.5 9.0 9.5 Cr 6.4 6.6 11.6 12.7 8.0 8.5 Ti 0.9
1.1 3.9 4.25 0.6 0.9 Al 5.4 5.75 3.4 3.8 5.4 5.7 Ta 6.3 6.75 4.8
5.2 3.1 3.3 Mo 0.5 0.7 1.65 2.15 0.4 0.6 W 6.2 6.6 3.5 4.1 9.3 9.7
Hf 0.07 0.12 0 75 ppm 1.0 1.6 Re 2.8 3.1 -- -- -- -- C 0 60 ppm
0.05 0.09 0.07 0.08 B 0 25 ppm 0 30 ppm .01 .02 Zr 0 75 ppm 0 75
ppm .005 0.02
[0012] The novel alloy compositions disclosed herein offer an
improved set of properties that are particularly useful for
application in Integrated Gasification Combined Cycle (IGCC) syngas
fired gas turbines where relatively low quality fuels and high
operating temperatures result in a highly corrosive
environment.
[0013] Alloys of the present invention include Chromium (Cr) from
8-12 weight percent or about 10 weight percent to provide the
compositions with a desired level of high temperature corrosion
resistance.
[0014] Alloys of the present invention may include Aluminum (Al) at
a concentration that is lower than is generally observed in highly
oxidation resistant alloys, for example as low as 2 weight percent
or in the range of 2.0-5.5 weight percent. Rare earth elements,
Yftrium (Y), Silicon (Si), and Hafnium (Hf) are included to
compensate for the reduction in Aluminum (Al) and to provide
increased oxidation resistance.
[0015] The alloy compositions disclosed herein have intentional
additions of rare earth elements Lanthanum (La), Yttrium (Y),
Gadolinium (Gd), Praseodymium (Pr), Dysprosium (Dy), Neodymium
(Nd), and Erbium (Er) in combined amounts of up to 0.1 weight
percent. These rare earth additions provide improved oxidation
resistance of the inventive alloys and enhance the compatibility of
the alloy compositions with various coatings. The rare earth
additions also aid in increasing the life of any overlying
protective ceramic coating. The increase in coating life through
the addition of rare earth elements is attributed to their ability
to form sulfides and oxi-sulfides that reduce the residual Sulfur
(S) content and prevent the diffusion of sulfur atoms to the
alumina scale that is formed at the boundary between the coating
and the substrate alloy.
[0016] Silicon (Si) is intentionally added to the present alloys to
support the formation of a protective silicon dioxide surface oxide
layer. The silicon dioxide provides enhanced oxidation resistance
as the film is less susceptible to cracking compared with other
protective oxide films. Excessive additions of silicon are
detrimental to the performance of the alloy; consequently, an
addition of less than 0.15 weight percent or in the range of
0.05-0.2 weight percent is preferred.
[0017] The intentional addition of Hafnium (Hf) at levels similar
to those of Silicon or less than 0.5 weight percent serves to
further enhance the oxidation resistance.
[0018] An alloy composition consisting essentially of, by weight
percent, 8-12% Cr, 10-14% Co, 0.3-0.9% Mo, 3-7% W, 2-8% Ta,
2.0-5.5% Al, 1.5-5.0% Ti, up to 2% Nb, less than 0.1% B, less than
0.1% Zr, 0.05-0.15% C, less than 0.5% Hf, 2-4% Re, 0.05-0.2% Si, up
to 0.015% S (without intentional sulfur addition), up to 0.1% La,
up to 0.1% Y, up to 0.1% Ce, up to 0.1% Nd, up to 0.1% Dy, up to
0.1% Pr, up to 0.1% Gd, balance is Ni, and wherein
(La+Y+Ce+Nd+Dy+Pr+Gd) is 0.001-0.1%, provides for an overall range
of alloys that exhibit creep resistance, thermo-mechanical fatigue
resistance, corrosion resistance, and the ability to be cast as a
single crystal or directionally solidified alloy. All compositions
herein are specified in weight percent values unless specified
otherwise.
[0019] The alloy composition from the above, but with the following
ranges: 2-6% Ta, 2-5% Al, and 3-5% Ti, is selected to optimize its
thermo-mechanical fatigue resistance.
[0020] The alloy composition from the above, but with the following
ranges: 4-8% Ta, 3.5-5.5% Al, and 1.5-4.0% Ti, is selected to
optimize its creep resistance.
[0021] The alloy composition from the above, but with the following
ranges: 9.5-10.5% Cr, 11.5-12.5% Co, 0.45-0.75% Mo, 4.4-5.4% W,
3.4-4.4% Ta, 3.1-4.0% Al, 3.9-4.25% Ti, up to 0.5% Nb, less than
0.02% B, less than 0.02% Zr, 0.05-0.11% C, less than 0.25% Hf,
2.5-3.5% Re, 0.1-0.15% Si, up to 0.015% S (again with no
intentional sulfur addition), up to 0.05% La, up to 0.05% Y, up to
0.05% Ce, up to 0.05% Nd, up to 0.05% Dy, up to 0.05% Pr, up to
0.05% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
0.01-0.05%, is selected for its thermo-mechanical fatigue
resistance, ability to be cast as a single crystal alloy.
[0022] The alloy composition from the above, but with the following
ranges: 9.5-10.5% Cr, 11.5-12.5% Co, 0.45-0.75% Mo, 4.4-5.4% W,
3.4-4.4% Ta, 3.1-4.0% Al, 3.9-4.25% Ti, up to 0.5% Nb, 0.005-0.015%
B, up to 0.02% Zr, 0.05-0.11% C, less than 0.25% Hf, 2.5-3.5% Re,
0.1-0.15% Si, up to 0.015% S (again with no intentional sulfur
addition), up to 0.05% La, up to 0.05% Y, up to 0.05% Ce, up to
0.05% Nd, up to 0.05% Dy, up to 0.05% Pr, up to 0.05% Gd, balance
is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is 0.01-0.05%, is selected
for its thermo-mechanical fatigue resistance, ability to be cast as
a directionally solidified alloy.
[0023] The alloy composition from the above, but with the following
ranges: 9.5-10.5% Cr, 11.5-12.5% Co, 0.45-0.75% Mo, 4.4-5.4% W,
5.5-6.5% Ta, 4.2-4.8% Al, 2.0-2.8% Ti, up to 0.5% Nb, less than
0.02% B, less than 0.02% Zr, 0.05-0.11% C, less than 0.25% Hf,
2.5-3.5% Re, 0.1-0.15% Si, up to 0.015% S (again with no
intentional sulfur addition), up to 0.05% La, up to 0.05% Y, up to
0.05% Ce, up to 0.05% Nd, up to 0.05% Dy, up to 0.05% Pr, up to
0.05% Gd, balance is Ni, and wherein (La+Y+Ce+Nd +Dy+Pr+Gd) is
0.01-0.05%, is selected for its creep resistance, ability to be
cast as a single crystal alloy.
[0024] The alloy composition from the above, but with the following
ranges: 9.5-10.5% Cr, 11.5-12.5% Co, 0.45-0.75% Mo, 4.4-5.4% W,
5.5-6.5% Ta, 4.2-4.8% Al, 2.0-2.8% Ti, up to 0.5% Nb, 0.005-0.015%
B, less than 0.02% Zr, 0.05-0.11% C, less than 0.25% Hf, 2.5-3.5%
Re, 0.1-0.15% Si, up to 0.015% S (again with no intentional sulfur
addition), up to 0.05% La, up to 0.05% Y, up to 0.05% Ce, up to
0.05% Nd, up to 0.05% Dy, up to 0.05% Pr, up to 0.05% Gd, balance
is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is 0.01-0.05%, is selected
for its creep resistance, ability to be cast as a directionally
solidified alloy.
[0025] The alloy composition from the above, but with the following
ranges: 10.0% Cr, 12.0% Co, 0.6% Mo, 4.9% W, 3.9% Ta, 3.5% Al, 3.9%
Ti, less than 0.01% B, less than 0.01% Zr, 0.07% C, less than 0.1%
Hf, 3.0% Re, less than 0.12% Si, up to 0.015% S (again with no
intentional sulfur addition), up to 0.02% La, up to 0.02% Y, up to
0.02% Ce, up to 0.02% Nd, up to 0.02% Dy, up to 0.02% Pr, up to
0.02% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
between 150 and 400 ppm, is selected for its thermo-mechanical
fatigue resistance, ability to be cast as a single crystal
alloy.
[0026] The alloy composition from the above, but with the following
ranges: 10.0% Cr, 12.0% Co, 0.6% Mo, 4.9% W, 3.9% Ta, 3.5% Al, 3.9%
Ti, 0.01% B, 0.0075% Zr, 0.09% C, 0.1% Hf, 3.0% Re, less than 0.12%
Si, up to 0.015% S (again with no intentional sulfur addition), up
to 0.02% La, up to 0.02% Y, up to 0.02% Ce, up to 0.02% Nd, up to
0.02% Dy, up to 0.02% Pr, up to 0.02% Gd, balance is Ni, and
wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is between 150 and 400 ppm, is
selected for its thermo-mechanical fatigue resistance, ability to
be cast as a directionally solidified alloy.
[0027] The alloy composition from the above, but with the following
ranges: 10.0% Cr, 12.0% Co, 0.6% Mo, 4.9% W, 6.0% Ta, 4.5% Al, 2.4%
Ti, less than 0.01% B, less than 0.01% Zr, 0.07% C, less than 0.1%
Hf, 3.0% Re, less than 0.12% Si, up to 0.015% S (again with no
intentional sulfur addition), up to 0.02% La, up to 0.02% Y, up to
0.02% Ce, up to 0.02% Nd, up to 0.02% Dy, up to 0.02% Pr, up to
0.02% Gd, balance is Ni, and wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is
between 150 and 400 ppm (0.015%-0.04%), is selected for its creep
resistance, ability to be cast as a single crystal alloy.
[0028] The alloy composition from the above, but with the following
ranges: 10.0% Cr, 12.0% Co, 0.6% Mo, 4.9% W, 6.0% Ta, 4.5% Al, 2.4%
Ti, 0.01% B, 0.0075% Zr, 0.09% C, 0.1% Hf, 3.0% Re, less than 0.12%
Si, up to 0.015% S (again with no intentional sulfur addition), up
to 0.02% La, up to 0.02% Y, up to 0.02% Ce, up to 0.02% Nd, up to
0.02% Dy, up to 0.02% Pr, up to 0.02% Gd, balance is Ni, and
wherein (La+Y+Ce+Nd+Dy+Pr+Gd) is between 150 and 400 ppm
(0.015%-0.04%), is selected for its creep resistance, ability to be
cast as a directionally solidified alloy.
[0029] The compositions of this invention may be cast with
processes known in the art.
[0030] FIG. 1 is a comparison of the creep properties of two
embodiments of the present invention with those of prior art PWA
1483. The test was conducted at a temperature of 850.degree. C.
Alloy A has increased refractory metal content and the addition of
3 weight percent Rhenium (Re), as shown in Table 2. Alloy A is an
example of an embodiment of the alloy composition that is designed
to be cast as a single crystal and have improved thermo-mechanical
fatigue resistance at the expense of some creep resistance. Alloy B
is an example of an embodiment of the alloy composition that is
designed to be cast as a single crystal and have improved creep
resistance at the expense of some thermo-mechanical fatigue
resistance.
TABLE-US-00002 TABLE 2 Exemplary Compositions (Weight percent).
Alloy ID Ni Cr Co Mo W Re Ta Al Ti C Rare Earth Alloy A Bal. 10 12
0.6 4.9 3 3.9 3.5 3.9 0.07 0.03 Alloy B Bal. 10 12 0.6 4.9 3 6 4.5
2.4 0.07 0.03 PWA 1483 Bal. 12.2 9 1.9 3.8 -- 5 3.6 4.2 0.07 --
CMSX-4 Bal. 6.5 9.6 0.6 6.4 3 6.5 5.6 1 <0.006 --
[0031] FIGS. 2-5 are Scanning Electron Microscope (SEM) slides that
show various alloys after exposure to the same thermally oxidized
coal derived syngas environment at about 1,000.degree. C. Both of
the novel alloys (FIGS. 2-3) have survived the environment and
Alloy B (FIG. 3) shows particularly good condition with little
evidence of corrosive attack. The Siemet DS (PWA 1483 modified with
grain boundary strengthening elements) shows sub-surface
penetration as seen in FIG. 4 and the protective oxide has spalled
on the CM247LC as seen in FIG. 5.
[0032] While various embodiments of the present invention have been
shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous
variations, changes and substitutions may be made without departing
from the invention herein. Accordingly, it is intended that the
invention be limited only by the spirit and scope of the appended
claims.
* * * * *