U.S. patent application number 10/429950 was filed with the patent office on 2004-01-22 for directionally solidified casting with improved transverse stress rupture strength.
This patent application is currently assigned to Howmet Research Corporation. Invention is credited to Bennett, John K., Corrigan, John, Esser, Winfried, Mayr, Christoph, Mihalisin, John R., Paul, Uwe, Vogt, Russell G..
Application Number | 20040011439 10/429950 |
Document ID | / |
Family ID | 22293385 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040011439 |
Kind Code |
A1 |
Corrigan, John ; et
al. |
January 22, 2004 |
Directionally solidified casting with improved transverse stress
rupture strength
Abstract
Directionally solidified columnar grain nickel base alloy
casting consisting essentially of, in weight %, of about 11.6% to
12.70% Cr, about 8.50 to 9.5% Co, about 1.65% to 2.15% Mo, about
3.5% to 4.10% W, about 4.80% to 5.20% Ta, about 3.40 to 3.80% Al,
about 3.9% to 4.25% Ti, about 0.05% to 0.11% C, about 0.003% to
0.015% B, balance essentially Ni and having substantial transverse
stress rupture strength and ductility as compared to a similar
casting without boron present.
Inventors: |
Corrigan, John; (Yorktown,
VA) ; Vogt, Russell G.; (Yorktown, VA) ;
Mihalisin, John R.; (N. Caldwell, NJ) ; Bennett, John
K.; (Exeter, GB) ; Paul, Uwe; (Aachen, DE)
; Mayr, Christoph; (Oberhausen, DE) ; Esser,
Winfried; (Bochum, DE) |
Correspondence
Address: |
Edward J. Timmer
Walnut Woods Centre
5955 W. Main Street
Kalamazoo
MI
49009
US
|
Assignee: |
Howmet Research Corporation
Siemens Aktiengesellschaft
|
Family ID: |
22293385 |
Appl. No.: |
10/429950 |
Filed: |
May 5, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10429950 |
May 5, 2003 |
|
|
|
09103097 |
Jun 23, 1998 |
|
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Current U.S.
Class: |
148/555 ;
148/428 |
Current CPC
Class: |
C22C 19/057 20130101;
C22C 19/056 20130101 |
Class at
Publication: |
148/555 ;
148/428 |
International
Class: |
C22C 019/05 |
Claims
We claim:
1. A directionally solidified columnar grain nickel base alloy
casting, consisting essentially of, in weight %, of about 9.5% to
14% Cr, about 7% to 11% Co, about 1% to 2.5% Mo, about 3% to 6% W,
about 1% to 6% Ta, about 3% to 4% Al, about 3% to 5% Ti, about 0 to
1% Nb, and balance essentially Ni and B present in an amount
effective to substantially improve transverse stress rupture
strength of said casting as compared to a similar casting without
boron present.
2. The casting of claim 1 wherein B is present in the range of
about 0.003% to about 0.015% by weight.
3. The casting of claim 1 that has a stress rupture life of at
least about 150 hours and elongation of at least about 2.5% when
tested at a temperature of 750 degrees C. (1283 degrees F.) and
stress of 660 Mpa (95.7 Ksi) applied in a direction perpendicular
to a <001> crystal axis of said casting.
4. The casting of claim 1 which is gas turbine engine blade having
a length of about 20 centimeters to about 90 centimeters.
5. A directionally solidified columnar grain nickel base alloy
casting consisting essentially of, in weight %, of about 11.6% to
12.70% Cr, about 8.50 to 9.5% Co, about 1.65% to 2.15% Mo, about
3.5% to 4.10% W, about 4.80% to 5.20% Ta, about 3.40 to 3.80% Al,
about 3.9% to 4.25% Ti, about 0.05% to 0.11% C, about 0.003% to
0.015% B, balance essentially Ni and having substantially improved
transverse stress rupture strength as compared to a similar casting
without boron present.
6. The casting of claim 5 that has a stress rupture life of at
least about 150 hours and elongation of at least about 2.5% when
tested at a temperature of 750 degrees C. (1283 degrees F.) and
stress of 660 Mpa (95.7 Ksi) applied perpendicular to a <001>
crystal axis of said casting.
7. A directionally solidified columnar grain nickel base alloy
casting having a nominal composition consisting essentially of, in
weight %, of about 12.00% Cr, about 9.00% Co, about 1.85% Mo, about
3.70% W, about 5.10% Ta, about 3.60% Al, about 4.00% Ti, about
0.0125% B, about 0.09% C, balance essentially Ni and having a
stress rupture life of at least about 150 hours and elongation of
at least about 2.5% when tested at a temperature of 750 degrees C.
(1283 degrees F.) and stress of 660 Mpa (95.7 Ksi) applied
perpendicular to a <001> crystal axis of said casting.
8. A method of making a directionally solidified casting,
comprising casting an alloy consisting essentially of, in weight %,
of about 9.5% to 14% Cr, about 7% to 11% Co, about 1% to 2.5% Mo,
about 3% to 6% W, about 1% to 6% Ta, about 3% to 4% Al, about 3% to
5% Ti, about 0 to 1% Nb and balance essentially Ni and B in an
amount effective to substantially improve transverse stress rupture
strength into a mold, and directionally solidifying the alloy in
the mold to form a columnar grain casting having substantially
improved transverse stress rupture strength by virture of the
inclusion of boron in said alloy as compared to a similar casting
without boron present.
9. The method of claim 8 wherein B is included in an amount of
about 0.003% to about 0.015% by weight.
10. The method of claim 8 wherein the directionally solidified
casting has a stress rupture life of at least about 150 hours and
elongation of at least about 2.5% when tested at a temperature of
750 degrees C. (1283 degrees F.) and stress of 660 Mpa (95.7 Ksi)
applied perpendicular to a <001> crystal axis of said
casting.
11. A method making a directionally solidified casting, comprising
providing a nickel base alloy consisting essentially of, in weight
%, of about 11.6% to 12.70% Cr, about 8.50 to 9.5% Co, about 1.65%
to 2.15% Mo, about 3.5% to 4.10% W, about 4.80% to 5.20% Ta, about
3.40 to 3.80% Al, about 3.9% to 4.25% Ti, about 0.05% to 0.11% C,
about 0.003% to 0.015% B, and balance essentially Ni, casting the
alloy into a mold, and solidifying the alloy in the mold to form a
casting having a directionally solidified columnar grain
mcirostructure having substantially improved transverse stress
rupture strength as compared to a similar casting without boron
present.
12. Nickel base alloy consisting essentially of, in weight %, of
about 11.6% to 12.70% Cr, about 8.50 to 9.5% Co, about 1.65% to
2.15% Mo, about 3.5% to 4.10% W, about 4.80% to 5.20% Ta, about
3.40 to 3.80% Al, about 3.9% to 4.25% Ti, about 0.05% to 0.11% C,
about 0.003% to 0.015% B, balance essentially Ni.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to nickel base superalloy
castings and, more particularly, to directionally solidified (DS)
nickel base superalloy castings having a columnar grain
microstructure and substantially improved transverse stress rupture
strength and ductility.
BACKGROUND OF THE INVENTION
[0002] U.S. Pat. No. 4,597,809 describes single crystal castings
made from a nickel base superalloy having a matrix with a
composition consisting essentially of, in weight %, of 9.5% to 14%
Cr, 7% to 11% Co, 1% to 2.5% Mo, 3% to 6% W, 1% to 4% Ta, 3% to 4%
Al, 3% to 5% Ti, 6.5% to 8% Al+Ti, 0 to 1% Nb, and balance
essentially nickel with the matrix containing about 0.4 to about
1.5 volume % of a phase based on tantalum carbide as a result of
the inclusion in the alloy of about 0.05% to about 0.15% C and
extra Ta in an amount equal to 1 to 17 times the C content.
[0003] Single crystal castings produced from the aforementioned
nickel base superalloy exhibit inadequate transverse grain boundary
strength. The present inventors attempted to produce directionally
solidified (DS) columnar grain castings of the nickel base
superalloy. However, the directionally solidified (DS) columnar
gain castings produced were unacceptable as DS castings as a result
of the castings exhibiting essentially no transverse grain boundary
strength and no ductility when tested at a temperature of 750
degrees C. (1283 degrees F.) and stress of 660 Mpa (95.7 Ksi). The
transverse grain boundary strength and ductility were so deficient
as to render DS columnar grain castings produced from the
aforementioned nickel base superalloy unsuitable for use as turbine
blades of gas turbine engines.
[0004] An object of the present invention is to provide DS columnar
grain castings based on the aforementioned single crystal nickel
base superalloy having substantially improved transverse stress
rupture strength and ductility to an extent that the DS castings
are acceptable for use as turbine blades of a gas turbine
engine.
[0005] Another object of the present invention is to provide such
DS columnar grain castings based on the aforementioned single
crystal nickel base superalloy having substantially improved
transverse stress rupture strength and ductility without adversely
affecting other mechanical properties and corrosion resistance of
the DS castings.
SUMMARY OF THE INVENTION
[0006] The present invention involves including boron in the nickel
base superalloy described hereabove in a manner discovered to
significantly improve transverse stress rupture strength and
ductility of directionally solidified (DS) columnar grain castings
produced from the boron modified superalloy. In accordance with the
present invention, boron is added to the aforementioned superalloy
composition in an effective amount to substantially improve
transverse stress rupture strength and ductility of directionally
solidified columnar grain castings produced from the boron-modified
superalloy. The boron concentration preferably is controlled in the
range of about 0.003% to about 0.015% by weight of the superalloy
composition to this end. In conjunction with addition of boron to
the superalloy composition, the carbon concentration preferably is
controlled in the range of about 0.05% to about 0.11% by weight of
the superalloy composition.
[0007] A preferred nickel base superalloy in accordance with an
embodiment of the present invention consists essentially of, in
weight %, of about 11.6% to 12.70% Cr, about 8.50 to 9.5% Co, about
1.65% to 2.15% Mo, about 3.5% to 4.10% W, about 4.80% to 5.20% Ta,
about 3.40 to 3.80% Al, about 3.9% to 4.25% Ti, about 0.05% to
0.11% C, about 0.003% to 0.015% B, and balance essentially Ni. The
boron modified nickel base superalloy can be cast as DS columnar
grain castings pursuant to conventional DS casting techniques such
as the well known Bridgeman mold withdrawal technique.
[0008] DS castings produced in this manner typically have a
plurality of columnar grains extending in the direction of the
principal stress axis of the casting with the <001> crystal
axis generally parallel to the principal stress axis. DS columnar
grain castings pursuant to the present invention preferably exhibit
a stress rupture life of at least about 150 hours and elongation of
at least about 2.5% when tested at a temperature of 750 degrees C.
(1283 degrees F.) and stress of 660 Mpa (95.7 Ksi) and will find
use as turbine blades, vanes, outer air seals and other components
of a industrial and aero gas turbine engines.
[0009] The above objects and advantages of the present invention
will become more readily apparent form the following detailed
description taken with the following drawings.
DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A is a photomicrograph at 11.25.times. taken
transverse to the longitudinal axis of a DS cast specimen showing
the columnar grain microstructure.
[0011] FIGS. 1B, 1C and 1D are similar photomicrographs at
50.times., 100.times. and 200.times., respectively, of the columnar
grain microstructure of FIG. 1A.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention involves including boron in a
particular nickel base superalloy in a manner discovered to
unexpectedly and surprisingly provide significantly enhanced
transverse stress rupture strength and ductility of DS columnar
grain castings produced from the boron-modified superalloy. The
nickel base superalloy which is modified pursuant to the present
invention is described in U.S. Pat. No. 4,597,809, the teachings of
which are incorporated herein by reference. A nickel base
superalloy in accordance with an embodiment of the invention
consists essentially of, in weight %, of about 9.5% to 14% Cr,
about 7% to 11% Co, about 1% to 2.5% Mo, about 3% to 6% W, about 1%
to 6% Ta, about 3% to 4% Al, about 3% to 5% Ti, about 0 to 1% Nb,
and balance essentially Ni and B present in an amount effective to
substantially improve transverse stress rupture strength of a DS
casting as compared to a similar casting without boron present.
[0013] The present invention modifies the aforementioned nickel
base superalloy to include boron in the alloy in an amount
discovered effective to provide substantial transverse stress
rupture strength and ductility of a DS columnar grain casting
produced from the alloy as compared to a similar casting without
boron present. Preferably, the nickel base superalloy is modified
by the inclusion of boron in the range of about 0.003% to about
0.015%, preferably 0.010% to 0.015%, by weight of the superalloy
composition to this end. In conjunction with addition of boron to
the superalloy composition, the carbon concentration is controlled
in a preferred range of about 0.05% to about 0.11% by weight of the
superalloy composition. The transverse stress rupture strength and
ductility of DS castings produced from the boron modified nickel
base superalloy are provided to an extent that the castings are
rendered acceptable for use as turbine blades and other components
of gas turbine engines.
[0014] A particularly preferred boron-modified nickel base
superalloy casting composition in accordance with the present
invention consists essentially of, in weight %, of about 11.6% to
12.70% Cr, about 8.50 to 9.5% Co, about 1.65% to 2.15% Mo, about
3.5% to 4.10% W, about 4.80% to 5.20% Ta, about 3.40 to 3.80% Al,
about 3.9% to 4.25% Ti, about 0.05% to 0.11% C, about 0.003% to
0.015% B, and balance essentially Ni and castable to provide a DS
columnar grain microstructure. The DS microstructure of the
columnar grain casting, FIG. 1A, typically includes about 0.4 to
about 1.5 volume % of a phase based on tantalum carbide shown as
light gray particles in FIGS. 1B, 1C and 1D. Some of the light gray
particles in the DS microstructure appear to be eutectic gamma
prime phase. The somewhat rounded dark features dispersed
throughout the DS microstructure in FIGS. 1A through 1D comprise
voids present in the particular cast specimens examined. Although
not wishing to be bound by any theory, it is thought that boron and
carbon tend to migrate to the grain boundaries in the DS
microstructure to add strength and ductility to the grain
boundaries at high service temperatures, for example, 816 degrees
C. (1500 degrees F.) typical of gas turbine engine blades.
[0015] DS columnar grain castings produced from the above
boron-modified nickel base superalloy in accordance with the
present invention typically have the <001> crystal axis
parallel to the principal stress axis of the casting and exhibit a
stress rupture life of at least about 150 hours and elongation of
at least about 2.5% when tested at a temperature of 750 degrees C.
(1283 degrees F.) and stress of 660 Mpa (95.7 Ksi) applied
perpendicular to the <001> crystal axis of the casting.
[0016] For example, the following DS casting tests were conducted
and are offered to further illustrate, but not limit, the present
invention. A heat #1 having a nickel base superalloy composition in
accordance with the aforementioned U.S. Pat. No. 4,597,809 and
heats #1A and #2 of boron modified nickel base superalloy in
accordance with the present invention were prepared with the
following compositions, in weight percentages, set forth in Table
I:
1TABLE I Heat Cr Co Mo W Ta Al Ti C B Ni #1 12.1 9.0 1.8 3.7 5.2
3.6 4.0 0.7 0.001 balance #1A 12.1 9.0 1.8 3.7 5.2 3.6 4.0 0.8
0.010 balance #2 12.1 9.0 1.8 3.7 5.2 3.6 4.0 0.9 0.011 balance
[0017] Each heat was cast to form DS columnar grain non-cored
castings having a rectangular shape for transverse stress rupture
testing pursuant to ASTM E-139 testing procedure. The DS castings
were produced using the conventional Bridgeman mold withdrawal
directional solidification technique. For example, each heat was
melted in a crucible of a conventional casting furnace under a
vacuum of 1 micron and superheated to 1427 degrees C. (2600 degrees
F.). The superheated melt was poured into an investment casting
mold having a facecoat comprising zircon backed by additional
slurry/stucco layers comprising zircon/alumina. The mold was
preheated to 1482 degrees C. (2700 degrees F.) and mounted on a
chill plate to effect unidirectional heat removal from the molten
alloy in the mold. The melt-filled mold on the chill plate was
withdrawn from the furnace into a soldification chamber of the
casting furnace at a vacuum of 1 micron at a withdrawal rate of
6-16 inches per hour. The DS columnar grain castings were cooled to
room temperature under vacuum in the chamber, removed from the mold
in conventional manner using a mechanical knock-out procedure, heat
treated at 1250 degrees C. (2282 degrees F.) for 4 hours, analyzed
for chemistry, and machined to specimen configuration. Stress
rupture testing was conducted in air at a temperature of 750
degrees C. (1283 degrees F.) and stress of 660 Mpa (95.7 Ksi)
applied perpendicular to the <001> crystal axis of the
specimens.
[0018] The results of stress rupture testing are set forth in TABLE
II below where LIFE in hours (HRS) indicates the time to fracture
of the specimen, ELONGATION is the specimen elongation to fracture,
and RED OF AREA is the reduction of area of the specimens to
fracture. The BASELINE data corresponds to test data for Heat #1,
and the #1A and #2 data corresponds to test data for Heat #1A and
#2, respectively. The BASELINE data represent an average of two
stress rupture test specimens, while the #1A and #2 data represent
a single stress rupture test specimen.
2TABLE II # OF TEMPERATURE- STRESS- ELONGATION RED OF ALLOY TESTS
C. (F.) Mpa (KSI) LIFE (HRS) (%) AREA (%) BASELINE 2 750 (1382) 660
(95.7) 0 0 0 #2 1 750 (1382) 660 (95.7) 182 2.6 6.3 #1A 1 750
(1382) 660 (95.7) 275 3.1 4.7
[0019] It is apparent from TABLE II that the DS columnar grain
specimens produced from heat #1 exhibited in effect essentially no
(e.g. zero hours stress rupture life) transverse grain boundary
strength when tested at a temperature of 750 degrees C. (1283
degrees F.) and stress of 660 Mpa (95.7 Ksi). That is, the
specimens failed immediately to provide an essentially zero stress
rupture life. Moreover, the elongation and reduction of area data
were essentially zero. These stress rupture properties are so
deficient as to render the DS columnar grain castings produced from
heat #1 unacceptable for use as turbine blades of gas turbine
engines.
[0020] In contrast, TABLE II reveals that DS columnar grain
specimens produced from heat #1A exhibited a stress rupture life of
275 hours, an elongation of 3.1%, and a reduction of area of 4.7%
and specimens from heat #2 exhibited a stress rupture life of 182
hours, an elongation of 2.6%, and a reduction of area of 6.3% when
tested at a temperature of 750 degrees C. (1283 degrees F.) and
stress of 660 Mpa (95.7 Ksi). These stress rupture properties of
the invention represent an unexpected and surprising improvement
over those of specimens produced from heat #1 and render DS
columnar grain castings produced from heats #1A and #2 more
suitable for use as turbine blades and other components of gas
turbine engines.
[0021] The present invention is effective to provide DS columnar
grain castings with substantial transverse stress rupture strength
and ductility. These properties are achieved without adversely
affecting other mechanical properties, such as tensile strength,
creep strength, fatigue strength, and corrosion resistance of the
DS castings. The present invention is especially useful to provide
large DS columnar grain industrial gas turbine (IGT) blade castings
which have the alloy composition described above to impart
substantial transverse stress rupture strength and ductility to the
castings and which have a length of about 20 centimeters to about
60 centimeters and above, such as about 90 centimeters length, used
throughout the stages of the turbine of stationary industrial gas
turbine engines. The above described boron-modified nickel base
superalloy casting composition can be cast as DS columnar grain or
single crystal components.
[0022] While the invention has been described in terms of specific
embodiments thereof, it is not intended to be limited thereto but
rather only to the extent set forth in the following claims.
* * * * *