U.S. patent number RE29,920 [Application Number 05/767,956] was granted by the patent office on 1979-02-27 for high temperature alloys.
Invention is credited to James F. Baldwin.
United States Patent |
RE29,920 |
Baldwin |
February 27, 1979 |
**Please see images for:
( Certificate of Correction ) ** |
High temperature alloys
Abstract
Nickel base superalloys in which critical amounts of boron are
employed to enhance creep-rupture strength and ductility in the
1,300.degree. F.-1,800.degree. F. temperature range. Creep-rupture
strength and ductility at temperatures around 1,800.degree. F. also
is enhanced by employing amounts of carbon below a critical upper
limit. These alloys are particularly useful in the form of castings
as gas turbine engine components.
Inventors: |
Baldwin; James F. (Delray
Beach, FL) |
Family
ID: |
24394281 |
Appl.
No.: |
05/767,956 |
Filed: |
February 11, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
598111 |
Jul 29, 1975 |
RE.28681 |
Jan 13, 1976 |
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Reissue of: |
346815 |
Apr 2, 1973 |
03869284 |
Mar 4, 1975 |
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Current U.S.
Class: |
420/445; 420/447;
420/448; 420/449; 420/588 |
Current CPC
Class: |
C22C
19/055 (20130101) |
Current International
Class: |
C22C
19/05 (20060101); C22C 019/05 () |
Field of
Search: |
;75/171,170,134F
;148/32,32.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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667661 |
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Jul 1963 |
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CA |
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863912 |
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Mar 1961 |
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GB |
|
1013347 |
|
Dec 1965 |
|
GB |
|
1034603 |
|
Jun 1966 |
|
GB |
|
1268844 |
|
Mar 1972 |
|
GB |
|
1302160 |
|
Jan 1973 |
|
GB |
|
Other References
F F. Khimiushin, High Temperature Steels and Alloys, Metallurgiya,
Pub. House, Moscow, (1969), FTD-HC-23-391, Parts I and II,
(1971)..
|
Primary Examiner: Dean; R.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow &
Garrett
Claims
What is claimed is: .Badd..[.
1. A nickel base alloy for use at relatively high temperatures
consisting essentially of the following elements in the weight
percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount of from about 35% to 85% by
weight..]..Baddend. .[.2. The nickel base alloy of claim 1 wherein
the carbon content is no more than 0.025% by weight..]. .Badd..[.3.
The nickel base alloy of claim 1 wherein the boron content is about
0.075% to 0.2% by weight..]..Baddend. .Badd..[.4. A cast component
for use in a gas turbine engine formed of the alloy of claim
1..]..Baddend. .Badd..[.5. The component of claim 4 in which said
component is a turbine blade..]..Baddend. .Badd..[.6. The component
of claim 4 in which said component is a disk..]..Baddend.
.Badd..[.7. The component of claim 4 in which said component is an
integral wheel comprising a disk and turbine blade..]..Baddend.
.Badd..[.8. A cast component for use in a gas turbine engine formed
of the alloy of claim 3..]..Baddend. .Badd..[.9. The component of
claim 8 wherein said component is a turbine blade..]..Baddend.
.Badd..[.10. The component of claim 8 wherein said component is a
disk..]..Baddend. .Badd..[.11. The component of claim 8 wherein
said component is an integral wheel comprising a disk and turbine
blade..]..Baddend. .Badd..[..[.12. A shaped object of the alloy of
claim .Badd..[.1.]. .Baddend..Iadd.50 .Iaddend.capable of
withstanding an applied stress of 94,000 psi at 1,400.degree. F.
without rupture for a time in excess of 120 hours..]..].
.Badd..[..[.13. A shaped object of the alloy of claim
.Badd..[.1.]..Baddend. .Iadd.12 .Iaddend.capable of withstanding an
applied stress of 29,000 psi at 1,800.degree. F. without rupture
for a time in excess of 40 hours..]..]. .Badd..[..[.14. The alloy
of claim .Badd..[.1.]..Baddend. .Iadd.50 .Iaddend. which contains,
on a weight basis, about 6.0% to about 17% chromium, about 2% to
about 8% aluminum, .[.about 0.75% to about 3% titanium, about 2% to
about 17% cobalt,.]. and about 40% to 80% by weight
nickel..]..]. .Badd..[..[.15. The nickel base alloy of claim 14
wherein the carbon content is no more than 0.025% by
weight..]..]..Baddend. .Badd..[..[.16. A cast component for use in
a gas turbine engine formed of the alloy of claim
14..]..]..Baddend. .Badd..[..[.17. A cast component for use in a
gas turbine engine formed of the alloy of claim 15..]..]..Baddend.
.Badd..[..[.18. The alloy of claim .Badd.1.]..Baddend. .Iadd.50
.Iaddend.which contains, on a weight basis, about 5% to 12%
chromium, about 4% to about 8% aluminum, .[.about 0.75% to about
2.5% titanium,.]. about 5% to about 15.5% cobalt, and about 40% to
80% by weight nickel..]..]. .Badd..[..[.19. The nickel base alloy
of claim 18 wherein the carbon content is no more than 0.025 by
weight..]..]..Baddend. .Badd..[..[.20. A cast component for use in
a gas turbine engine formed of the alloy of claim
18..]..]..Baddend. .Badd..[..[.21. A cast component for use in a
gas turbine engine formed of the alloy of claim 19..]..]..Baddend.
.Badd..[..[.22. A nickel base alloy for use at relatively high
temperatures consisting essentially of the following elements in
the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount of from about 40% to 80% by
weight..]..]..Baddend. .Badd..[..[.23. The nickel base alloy of
claim 22 wherein the boron content is about 0.07% to about 0.25% by
weight..]..]..Baddend. .Badd..[..[.24. The nickel base alloy of
claim 22 wherein the carbon content is no more than 0.025 by
weight..]..]..Baddend. .Badd..[..[.25. A cast component for use in
a gas turbine engine formed of the alloy of claim
22..]..]..Baddend. .Badd..[..[.26. A cast component for use in gas
turbine engine formed of the alloy of claim 24..]..]..Baddend.
.Badd..[..[.27. A nickel base alloy for use at relatively high
temperatures consisting essentially of the following elements in
the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy..]..]..Baddend.
.Badd..[..[.28. The nickel base alloy of claim 27 wherein the boron
content is about 0.07% to
about 0.25% by weight..]..]..Baddend. .Badd..[..[.29. The nickel
base alloy of claim 27 wherein the carbon content is no more than
0.025% by weight..]..]..Baddend. .Badd..[..[.30. A cast component
for use in a gas turbine engine formed of the alloy of claim
27..]..]..Baddend. .Badd..[..[.31. The component of claim 30 in
which said component is a turbine blade..]..]..Baddend.
.Badd..[..[.32. A cast component for use in a gas turbine engine
formed of the alloy of claim 29..]..]..Baddend. .Badd..[..[.33. The
component of claim 32 wherein said component is a turbine
blade..]..]..Baddend. .Badd..[..[.34. A shaped object of the alloy
of claim 27 capable of withstanding an applied stress of 94,000 psi
at 1,400.degree. F. without rupture for a time in excess of 120
hours..]..]..Baddend. .Badd..[..[.35. A shaped object of the alloy
of claim 29 capable of withstanding an applied stress of 29,000 psi
at 1,800.degree. F. without rupture for a time in excess of 40
hours..]..]..Baddend. .Badd..[..[.36. A nickel base alloy for use
at relatively high temperatures consisting essentially of the
following elements in the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount of from about 40% to 80% by
weight..]..]..Baddend. .Badd..[..[.37. The nickel base alloy of
claim 36 wherein the boron content is about 0.07% to about 0.25% by
weight..]..]..Baddend. .Badd..[..[.38. The nickel base alloy of
claim 36 wherein the carbon content is no more than 0.025% by
weight..]..]..Baddend. .Badd..[..[.39. A cast component for use in
a gas turbine engine formed of the alloy of claim
36..]..]..Baddend. .Badd..[..[.40. A cast component for use in a
gas turbine engine formed of the alloy of claim 38..]..]..Baddend.
.Badd..[..[.41. A nickel base alloy for use at relatively high
temperatures consisting essentially of the following elements in
the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy..]..]..Baddend.
.Badd..[..[.42. The nickel base alloy of claim 41 wherein the boron
content is about 0.07% to about 0.25% by weight..]..]..Baddend.
.Badd..[..[.43. The nickel base alloy of claim 41 wherein the
carbon content is no more than 0.025% by
weight..]..]..Baddend. .Badd..[..[.44. A cast component for use in
a gas turbine engine formed of the alloy of claim
41..]..]..Baddend. .Badd..[..[.45. The component of claim 44 in
which said component is a turbine blade..]..]..Baddend.
.Badd..[..[.46. A cast component for use in a gas turbine engine
formed of the alloy of claim 43..]..]..Baddend. .Badd..[..[.47. The
component of claim 46 wherein said component is a turbine
blade..]..]..Baddend. .Badd..[..[.48. A shaped object of the alloy
of claim 41 capable of withstanding an applied stress of 94,000 psi
at 1,400.degree. F. without rupture for a time in excess of 120
hours..]..]..Baddend. .Badd..[..[.49. A shaped object of the alloy
of claim 43 capable of withstanding an applied stress of 29,000 psi
at 1,800.degree. F. without rupture for a time in excess of 40
hours..]..]..Baddend. .Badd..[..[.50. A nickel base alloy for use
at relatively high temperatures consisting essentially of the
following elements in the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount of from about 35% to 85% by
weight..]..]..Baddend. .Badd..[..[.51. The nickel base alloy of
claim 50 wherein the boron content is about 0.07% to about 0.25% by
weight..]..]..Baddend. .Badd..[..[.52. The nickel base alloy of
claim 51 wherein the carbon content is no more than 0.025% by
weight..]..]..Baddend. .Badd..[..[.53. A cast component for use in
a gas turbine engine formed of the alloy of claim
50..]..]..Baddend. .Iadd..[..[.54. The nickel base alloy of claim
50 wherein the molybdenum content is 0.00 - 3% and the tungsten
content is 5 - 20%..]..]..Iaddend. .Iadd..[..[.55. The nickel base
alloy of claim 50 wherein the molybdenum content is 3 - 8%, the
tungsten content is < 2.5%, and the tantalum content is 2.3 -
10%..]..]..Iaddend. .Iadd..[..[.56. The nickel base alloy of claim
50 wherein the cobalt content is 5 to 15.5%
cobalt..]..]..Iaddend. .Iadd.57. A nickel base alloy for use at
relatively high temperatures consisting essentially of the
following elements in the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight..Iaddend. .Iadd.58. The nickel
base alloy of claim 57 wherein the tungsten and vanadium contents
are
essentially 0..Iaddend. .Iadd.59. A cast component for use in a
gas
turbine engine formed of the alloy of claim 57..Iaddend. .Iadd.60.
The nickel base alloy of claim 57 wherein the carbon content is no
more than 0.025% by weight..Iaddend. .Iadd..[..[.61. A nickel base
alloy for use at relatively high temperatures consisting
essentially of the following elements in the weight percent ranges
set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount of from about 35% to 85% by
weight..]..]..Iaddend. .Iadd..[..[.62. The nickel base alloy of
claim 61 wherein the carbon content is no more than 0.025% by
weight..]..]..Iaddend. .Iadd..[..[.63. The nickel base alloy of
claim 61 wherein the chromium content is 5 - 12% and the tungsten
content is 5 - 20%..]..]..Iaddend. .Iadd..[..[.64. The alloy of
claim 61, which contains, on a weight basis, about 2.3% to about
10% tantalum..]..]..Iaddend. .Iadd..[..[.65. The alloy of claim 64
which contains, on a weight basis, 5 - 20% tungsten..]..]..Iaddend.
.Iadd..[..[.66. The alloy of claim 61, which contains, on a weight
basis, less than 3% tantalum..]..]..Iaddend. .Iadd..[..[.67. The
alloy of claim 14 which contains, on a weight basis, 0 to about 3%
molybdenum, 0 to about 3% tantalum, about 5% to about 20% tungsten,
and about 0.001 to about 0.5% zirconium..]..]..Iaddend.
.Iadd..[..[.68. The alloy of claim 18, which contains, on a weight
basis, about 3% to about 8% molybdenum, about 2.3%
to about 10% tantalum, and 0 to about 2.5% tungsten..]..]..Iaddend.
69. .Badd.A nickel base alloy for use at relatively high
temperatures consisting essentially of the following elements in
the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight. .Baddend. 70. .Badd.The nickel
base alloy of claim 69 wherein the carbon content is less than
0.02% by weight.
.Baddend. 71. .Badd.The nickel base alloy of claim 69 wherein the
molybdenum content is 0.00-3% and the tungsten content is 5-20%.
.Baddend.
2. .Badd.The nickel base alloy of claim 69 wherein the molybdenum
content is 3-8%, the tungsten content is < 2.5%, and the
tantalum content is
2.3-10%. .Baddend. 73. .Badd.The nickel base alloy of claim 69
wherein the
cobalt content is 5 to 15.5% cobalt. .Baddend. 74. .Badd.The nickel
base
alloy of claim 73 wherein the molybdenum content is < 3.
.Baddend. 75. .Badd.The nickel base alloy of claim 74 wherein the
chromium content
is 5-12% and the tungsten content is 5-20%. .Baddend. 76. .Badd.The
alloy of claim 74, which contains, on a weight basis, about 2.3% to
about 10%
tantalum. .Baddend. 77. .Badd.The alloy of claim 76 which contains,
on a
weight basis, 5-20% tungsten. .Baddend. 78. .Badd.The alloy of
claim 74,
which contains, on a weight basis, less than 3% tantalum. .Baddend.
79. .Badd.The alloy of claim 69 which contains, on a weight basis,
about 6.0% to about 17% chromium, about 2% to about 8% aluminum,
and about 40%
to 80% by weight nickel. .Baddend. 80. .Badd.The nickel base alloy
of claim 79 wherein the carbon content is no more than 0.025% by
weight.
.Baddend. 81. .Badd.The alloy of claim 79 which contains, on a
weight basis, 0 to about 3% molybdenum, 0 to about 3% tantalum,
about 11% to about 16% tungsten, and about 0.001 to about 0.5%
zirconium. .Baddend.
.Badd.The alloy of claim 69 which contains, on a weight basis,
about 5% to 12% chromium, about 4% to about 8% aluminum, about 5%
to about 15.5%
cobalt, and about 40% to 80% by weight nickel. .Baddend. 83.
.Badd.The nickel base alloy of claim 82 wherein the carbon content
is no more than
0.025% by weight. .Baddend. 84. .Badd.The alloy of claim 82 which
contains, on a weight basis, about 3% to about 8% molybdenum, about
2.3%
to about 10% tantalum, and 0 to about 2.5% tungsten. .Baddend. 85.
.Badd.A cast component for use in a gas turbine engine formed of
the alloy of
claim 69. .Baddend. 86. .Badd.A shaped object of the alloy of claim
69 capable of withstanding an applied stress of 94,000 psi at
1,400.degree.
F. without rupture for a time in excess of 120 hours. .Baddend. 87.
.Badd.The nickel base alloy of claim 69 wherein the following
elements are in the weight percent ranges set forth:
88. .Badd.The nickel base alloy of claim 69 wherein the following
elements are in the weight percent ranges set forth:
89. .Badd.A nickel base alloy for use at relatively high
temperatures consisting essentially of the following elements in
the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount of from about 35% to 85% by weight, said boron
and carbon contents being effective to enhance creep-rupture
strength and ductility of said alloy in the 1300.degree. F to
1500.degree. F temperature range without substantially
deleteriously affecting creep-rupture strength and ductility of
said alloy at temperatures in the 1700.degree. F to 1900.degree.
F
range. .Baddend. 90. .Badd.A nickel base alloy for use at
relatively high temperatures consisting essentially of the
following elements in the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight. .Baddend. 91. .Badd.The nickel
base alloy of claim 90 wherein the boron content is about 0.07% to
about 0.25%
by weight. .Baddend. 92. .Badd.The nickel base alloy of claim 90
wherein
the carbon content is less than 0.02% by weight. .Baddend. 93.
.Badd.A nickel base alloy for use at relatively high temperatures
consisting essentially of the following elements in the weight
percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight. .Baddend. 94. .Badd.The nickel
base alloy of claim 93, which contains, on a weight basis, about 5
to about
15.5 cobalt and < 3 molybdenum. .Baddend. 95. .Badd.The alloy of
claim
94, which contains, on a weight basis, 5-20% tungsten. .Baddend.
96. .Badd.The nickel base alloy of claim 93 wherein the molybdenum
content
is 3-8% and the tungsten content is 0 to 2.5%. .Baddend. 97.
.Badd.The alloy of claim 96 which contains, on a weight basis,
about 5% to 12% chromium, about 4% to about 8% aluminum, about 5%
to about 15.5% cobalt,
and about 40% to 80% by weight nickel. .Baddend. 98. .Badd.The
nickel base alloy of claim 97 which contains, on a weight basis, 0
to 0.2 columbium.
.Baddend. 99. .Badd.The nickel base alloy of claim 97 wherein the
following elements are in the weight percent ranges set forth:
100. .Badd.A nickel base alloy for use at relatively high
temperatures consisting essentially of the following elements in
the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight. .Baddend. 101. .Badd.The nickel
base alloy of claim 100 wherein said boron and carbon contents are
effective to enhance creep-rupture strength and ductility of said
alloy in the 1300.degree. F. to 1500.degree. F. temperature range
without substantially deleteriously affecting creep-rupture
strength and ductility of said alloy at temperatures in the
1700.degree. F. to 1900.degree. F. range. .Baddend.
02. .Badd.The nickel base alloy of claim 100 wherein the carbon
content is
less than 0.02% by weight. .Baddend. 103. .Badd.A nickel base alloy
for use at relatively high temperatures consisting essentially of
the following elements in the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight. .Baddend. 104. .Badd.The nickel
base alloy of claim 103 wherein the boron content is about 0.07% to
about 0.25%
by weight. .Baddend. 105. .Badd.The nickel base alloy of claim 103
wherein
the carbon content is less than 0.02% by weight. .Baddend. 106.
.Badd.A nickel base alloy for use at relatively high temperatures
consisting essentially of the following elements in the weight
percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight. .Baddend. 107. .Badd.The nickel
base alloy of claim 106 wherein the boron content is about 0.07% to
about 0.25%
by weight. .Baddend. 108. .Badd.The nickel base alloy of claim
106
wherein the carbon content is less than 0.02% by weight. .Baddend.
109. .Badd.A nickel base alloy for use at relatively high
temperatures consisting essentially of the following elements in
the weight percent ranges set forth:
the balance of the alloy being essentially nickel and minor amounts
of impurities and incidental elements which do not detrimentally
affect the basic characteristics of the alloy, said nickel being
present in an amount
of from about 35% to 85% by weight. .Baddend. 110. .Badd.The nickel
base alloy of claim 109 wherein the boron content is about 0.07% to
about 0.25%
by weight. .Baddend. 111. .Badd.The nickel base alloy of claim 109
wherein the carbon content is less than 0.02% by weight.
Description
FIELD OF THE INVENTION
This invention relates to nickel-base alloys having relatively
great tensile strength at high temperatures and to castings made
from such alloys. The nickel-base superalloys of the present
invention are particularly useful for fabricating components of gas
turbine engines, such as turbine blades, turbine vanes, integral
wheels, and the like.
BACKGROUND OF THE INVENTION
There are a number of precipitation strengthened nickel-base
superalloys which, because of their strength at high temperatures,
are used as materials in fabricating components for use in high
temperature sections of gas turbines. The precipitate involved is
an intermetallic compound, generally referred to as gamma prime,
having the generic formula (Ni.sub.3 (Al, Ti). Alloys hardened by
such precipitates are referred to as gamma prime strengthened
superalloys. In recent years, while characteristics of such alloys
at lower temperatures have not altogether been ignored, the greater
emphasis in the development of improved alloys has been centered
around performance at high temperatures. High temperature
performance has been of concern because of the fact that in new
engine designs, as .[..[.gar.]..]. .Badd.gas .Baddend.turbine
operating temperatures are increasing to meet the demands for
higher efficiency and power output. High temperature performance
properties of particular concern include stress-rupture and creep
strength, resistance to thermal fatigue, and corrosion
resistance.
It is known that thermal fatigue properties are associated with
intermediate temperature (1,300.degree. F. - 1,500.degree. F.)
ductility. The greater the ductility in this range, the more
resistant the alloy is to thermal fatigue. As a general rule,
alloys with high temperature rupture and creep strength have
inadequate thermal fatigue and hot corrosion resistance.
Conversely, alloys with good hot corrosion resistance show poor
high temperature rupture, creep and thermal fatigue properties.
While much work has been done in the development of precipitation
strengthened high temperature superalloys, no alloy has been found
to be entirely satisfactory with respect to fulfilling the
strength, ductility and thermal fatigue requirements needed in gas
turbine components. Indeed, in recent superalloy developments,
strength improvements obtained through composition modification
generally have resulted in reduced ductility. In the same manner,
alloys designed for improved ductility or toughness or hot
corrosion resistance generally possess inadequate strength.
Superalloys suitable for fabricating gas turbine components
desirably possess good creep-rupture strength, i.e., resist
excessive creep or rupture for long periods of time while under
stress at high temperatures. Such alloys also desirably possess
good creep-rupture ductility, i.e., deform uniformly and
predictably while under stress at high temperature, rather than
crack and fracture. Alloys that lack ductility will tolerate little
deformation before the onset of crack nucleation, rapid crack
propagation, and failure. Use of a material lacking adequate
ductility can result in unpredictable and catastrophic engine
component failure. A characteristic peculiar to the gamma prime
strengthened superalloys is that they are subject to a sharp
decrease in creep-rupture ductility and tensile strength at
temperatures between about 1,300.degree. F. and 1,500.degree. F.
The decrease in ductility is commonly referred to as the "ductility
trough," as ductility is higher at temperatures below 1,300.degree.
F. and above 1,500.degree. F. It generally has been observed that
the higher the strength of an alloy, the more pronounced will be
the ductility decrease within the "ductility trough" temperature
range. An example would be MAR-M200 (U.S. Pat. No. 3,164,465). This
alloy possesses adequate strength for most advanced gas turbine
engine requirements, but lack of 1,400.degree. F. ductility in the
conventionally cast material precludes its usefulness for turbine
components.
To circumvent the low ductility problem while retaining usable high
temperature strength, the art, in recent years, has turned to a
casting process known as directional solidification. This
technique, disclosed in U.S. Pat. No. 3,260,505, eliminates grain
boundaries that lay in a direction transverse to the direction of
applied stress in the component. While directional solidification
eliminates a major cause of low longitudinal creep-rupture
ductility, it is an expensive procedure and is therefore used only
in specialized cases where cost is not a major concern.
It has also been attempted to circumvent ductility trough problems
by introducing hafnium to nickel-base superalloys (see, e.g., U.S.
Pat. Nos. 3,005,705; 3,677,746; 3,677,746; 3,677,747; and
3,677,748). The addition of very dense and expensive hafnium
imposes higher raw material costs and increases the unit weight of
the alloys. Increased weight, of course, is a serious disadvantage
in alloys intended for aircraft engine components. As is apparent,
the lack of the combination of high temperature creep-rupture
strength and ductility remains a major inadequacy in existing
superalloy compositions. These inadequacies are particularly acute
since they impair the usefulness of superalloys for many of their
intended applications, i.e., formation of gas turbine
components.
The alloys of the present invention have improved high temperature
strength and corrosion resistance. These alloys are capable of
withstanding prolonged operation at temperatures up to about
2,000.degree. F. or higher, and may be formed into highly
advantageous castings.
In accordance with the present invention, alloy compositions have
been discovered which possess unique and unusually high
creep-rupture strength and ductility in the polycrystalline
(non-directionally solidified) form. Specifically, a previously
unrecognized criticality has been discovered in the amounts of two
alloying elements (boron and carbon) included in chromium,
aluminum, and titanium containing nickel base superalloy
compositions.
The desirability of adding boron and carbon to high temperature
alloys is well documented in the prior art technical and patent
literature. The alloy characteristics generally enhanced by the
addition of some boron and carbon include ductility, strength,
forgeability and in some cases, castability. The present level of
technology in the field of superalloy physical metallurgy does not
enable precise definition or explanation of the exact mechanism
responsible for this property enhancement. Yet one versed in the
art of superalloy development recognizes the necessity for the
presence of both elements.
While it is known that the role of both carbon and boron in nickel
superalloys is complex and dynamic, some generalizations can be
drawn. Carbon appears in the form of complex carbides which prefer
grain boundaries as location sites. Detrimental effects on
ductility have been noted with certain grain boundary carbide
morphologies. This indicates that carbon should be maintained at
low levels. On the other hand, it also has been observed that low
carbon content results in sharply reduced high temperature creep
life. It is generally believed, since carbides exert a significant
and beneficial effect on rupture strength at high temperature, that
carbon should be part of superalloy composition.
Boron is considered an essential ingredient in superalloys. In
superalloys, boron in the form of complex borides, is also located
at grain boundaries. Grain boundary morphology of superalloys is
significant because high temperature creep and rupture failures
initiate at and propogate along grain boundaries. Complex borides
at grain boundaries reduce the onset of grain boundary tearing
under rupture loading.
Typical cast superalloys of the prior art preferably contain carbon
in an amount of about 0.10% to about 0.25% by weight. In typical
prior art wrought alloys, the carbon content range is between about
0.03% and about 0.15% by weight. For example, in a commercial alloy
known as INCO 713, the carbon content is kept as low as 0.05% by
weight. Boron content in over fifty prior art alloys studies,
preferably is held between 0.007% and 0.03% by weight of the
composition. The very small amount of boron used in these
commercial alloys demonstrates the potency of the element in
affecting properties.
The present invention is based, in part, on the discovery of an
unusual and unexpected improvement, in both 1,400.degree. F.
creep-rupture strength and ductility of gamma prime strengthened
nickel-base superalloys, obtained by increasing boron content up to
about twenty times the accepted optimum level. Maintenance of the
boron content within this critical range of the present invention
not only eliminates the problem discussed earlier, relating to the
ductility trough present at temperatures between about
1,300.degree. F. and 1,500.degree. F., but results in a marked
increase in creep-rupture strength at those temperatures.
It has also been discovered, in accordance with the present
invention, that by reducing the carbon content to a critical upper
limit below the amount generally employed in superalloys, it is
possible to both effect the improvement in 1,400.degree. F.
properties and maintain or improve creep-rupture strength and
ductility at temperatures around 1,800.degree. F. This aspect of
the present invention is important with respect to items such as
gas turbine components requiring enhanced properties at both
1,400.degree. F. and 1,800.degree. F.
Among the alloys of the prior art which will exhibit enhanced
properties by following the teachings of the present invention are
those disclosed in U.S. Pat. Nos. 3,310,399; 3,164,465; 3,061,426;
and 3,619,182. While many of the alloy compositions disclosed in
these patents are similar to, and generically overlap with, the
alloys of the present invention, none of these patents disclosed,
nor do corresponding commercial alloy have, the unusual and
surprisingly advantageous properties and characteristics of the
alloys of the present invention. This is because of the prior art
fails to recognize the critical carbon and boron content ranges of
the alloys of the present invention. All of the commercial alloys
derived from the patents referred to above contain substantially
less than the minimum boron content used in the alloys of the
present invention. Additionally, while at least some of these
patents suggest broad boron content ranges which overlap the boron
content range of the present invention, there is no recognition
that high temperature properties will maximize in a narrow range
within these broadly disclosed ranges.
The alloys of the present invention, which have very good stress
rupture life at elevated temperatures, contain required minimum
amounts of nickel, chromium, aluminum and titanium. The chromium
affords primary corrosion resistance while the remaining components
are essential to the formation of the gamma prime intermetallic
compound. Ni.sub.3 (Al, Ti), which forms the basic superalloy
structure of this invention. The Ni.sub.3 (Al, Ti) precipitate
lends to these alloys their required high temperature strength, and
titanium is an important element in providing the strength
properties of the present alloys at both room temperature and at
elevated temperatures. The presence of significant amounts of Ti
strengthener in the present alloys renders them significantly
different in character from lower temperature alloys such as those
of U.S. Pat. No. 3,005,704, which excludes Ti from its alloys.
SUMMARY OF THE INVENTION
In general terms, the present invention pertains to gamma prime
phase strengthened superalloys. These alloys are specifically
adapted to be employed in cast shapes under conditions of high
stress at high temperature. The invention also concerns cast
components for use in gas turbine engines made from such
alloys.
The alloys of the present invention are predominantly nickel, i.e.,
at least 35% nickel, and contain in varying amounts, chromium,
aluminum, titanium, and boron. One or more of the elements carbon,
cobalt, zirconium, molybdenum, tantalum, rhenium, columbium,
vanadium, and tungsten may also be included in these alloys. In
addition, the alloys of the present invention may contain minor
amounts of other elements ordinarily included in superalloys by
those skilled in the art which will not substantially deleteriously
effect the important characteristics of the alloy or which are
inadvertently included in such alloys by virtue of impurity levels
in commercial grades of alloying ingredients.
It is a principal object of the present invention to include in the
aforedescribed alloys amounts of boron within the range of 0.05% to
0.3% by weight of enhance creep-rupture strength and ductility at
temperatures around 1,400.degree. F. In accordance with preferred
embodiments of the present invention, in addition to maintaining
the boron content within the range specified, the carbon content of
the alloys is maintained below about 0.05% by weight. By
additionally maintaining the carbon content below this critical
upper limit, it is possible to effect creep-rupture strength and
ductility improvement at temperatures around 1,400.degree. F.
while, at the same time, maintaining or improving creep-rupture
strength and ductility at temperatures around 1,800.degree. F.
Table I sets forth a broad range and two different narrower ranges,
in terms of percent by weight, of elements employed in the alloys
of the present invention. It should be understood that the
tabulation in Table I relates to each element individually and is
not intended to solely define composite of broad and narrow ranges.
Nevertheless, composites of the narrower ranges specified in Table
I represent preferred embodiments.
A particularly preferred alloy composition, in percentages by
weight, consists essentially of about 8.0% to about 10.25%
chromium, about 4.75 to about 5.5% aluminum, about 1.0% to about
2.5% titanium, about 0.05 to about 0.30% (and more preferably about
0.075% to about 0.2%) boron, up to about 0.17% (and more preferably
less than 0.05%) carbon, about 8% to about 12% cobalt, about 0.75%
to about 1.8% columbium, about 11% to about 16% tungsten, up to
0.20% zirconium, and the balance essentially nickel and minor
amounts of impurities and incidental elements which do not
detrimentally affect the basic characteristics of the alloy.
TABLE I ______________________________________ ELE- BROAD MENT
RANGE NARROWER RANGES ______________________________________ Cr 5.0
- 22 6.0 -17 5 -12 Al 0.2 - 8 2 -8 4 -8 Ti 0.5 - 7 0.75 -3 0.75
-2.5 B 0.05 - 0.30 0.07 -0.25 0.075 -0.20 C 0.00 - 0.35 <0.05
<0.05 Co 0.00 - 20 2 -17 5 -15.5 Cb 0.00 - 3 0.25 -3 <0.20 Mo
0.00 - 8 <3 3 -8 Ta 0.00 - 10 <3 2.3 -10 V 0.00 - 2 -- -- W
0.00 - 20 5 -20 <2.5 Zr 0.00 - 1.00 0.001 -0.5 <1 Re 0.00 - 2
-- -- Ni 35 - 85 40 -80 40 -80
______________________________________
Another particularly preferred alloy composition, in percentages by
weight, consists essentially of about 7.5% to about 8.5% chromium,
about 5.75% to 6.25% aluminum, about 0.8% to about 1.2% titanium,
about 0.05% to about 0.30% (and more preferably about 0.075% to
about 0.2%) boron, up to about 0.13% (and more preferably less than
0.05%) carbon, about 9.5% to about 10.5% cobalt, about 5.75% to
about 6.25% molbdenum, about 4.0% to about 4.5% tantalum, 0.05% to
0.10% zirconium, and the balance essentially nickel and minor
amounts of impurities and incidental elements which do not
detrimentally affect the basic characteristics of the alloy.
Impurities and incidental elements which may be present in the
alloys of the present invention include manganese, copper, and
silicon in amounts of not more than 0.50%, sulfur and phosphorus in
amounts of not more than 0.20%, and iron in amounts of not more
than 2.0%. Impurities such as nitrogen, hydrogen, tin, lead,
bismuth, calcium, and magnesium should be held to as low a
concentration as practical.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graphical plot of percent creep elongation against time
for two alloys, one within the ambit of the present invention, and
the other outside the ambit of the present invention.
FIG. 2 is a plot of creep-rupture life in hours against the boron
content in weight percent of certain nickel base alloys at both
1,400.degree. F. - 94,000 psi and 1,800.degree. F. - 29,000 psi.
The creep-rupture life at 1,400.degree. F. - 94,000 psi and
1,800.degree. F. - 29,000 psi for commercial alloys similar to the
alloy of the plot, but outside the ambit of the present invention,
is also noted on the plot.
FIG. 3 is similar to FIG. 2 but plots percent creep elongation
against boron content, rather than creep rupture life against boron
content.
FIG. 4 is a reproduction of a photomicrograph at a magnification of
300, of a commercial alloy outside the ambit of the present
invention.
FIG. 5 is a reproduction of a photomicrograph, at a magnification
of 300, of an alloy (comparable to the alloy of FIG. 4) within the
ambit of the present invention.
FIG. 6 is a reproduction of a photomicrograph, at a magnification
of 7,000, of the same alloy shown in the photomicrograph of FIG.
4.
FIG. 7 is a reproduction of a photomicrograph, at a magnification
of 7,000, of the same alloy shown in the photomicrograph of FIG.
5.
DESCRIPTION OF THE EXAMPLES AND PREFERRED EMBODIMENTS
The alloys of the present invention, containing boron within the
critical range of 0.05% to 0.3% by weight, exhibit enhanced creep
rupture strength and ductility in the 1,300.degree. F. to
1,500.degree. F. temperature range over prior art gamma prime
strengthened nickel base superalloys. Thus the alloys of the
present invention are capable of withstanding an applied stress of
94,000 psi at 1,400.degree. F. without rupture for a time in excess
of 120 hours. Further, this improvement in strength and ductility
properties in the intermediate temperature range (1,300.degree. F.
- 1,500.degree. F.) is accompanied by a pronounced beneficial
effect on high temperature (above 1,700.degree. F.) thermal fatigue
properties. Alloys of the present invention, having improved
intermediate temperature strength and ductility, demonstrate great
advantage in resistance to high temperature thermal fatigue
cracking over alloys containing boron in amounts outside the
critical range of the present invention.
Designers of gas turbine engines place great importance upon the
selection of capable and reliable material. This is particularly
true for rotating components in large aircraft engines where
unpredictable engine component failure could endanger the aircraft
and its occupants. One of the more critical components in this
.[..[.calss.]..]. .Badd.class .Baddend.of engines is the hot
section or turbine blade. Because of the severe conditions of
temperature and stress to which these components are subjected,
they must be formed of high strength superalloys.
Usual designs involve the mechanical attachment of turbine blades
around the periphery of a wheel or disk which rotates at high
speed. In operation, hot gases pass over the airfoil portion of the
blades, causing the blades and disk to rotate at high speed. The
hot gases raise the metal temperatures and the high rotational
speed of the disk imposes stress due to centrifugal loading. The
attachment, or root portion of the blade is heated only to moderate
temperatures due to the cooling effect of the massive disk. The
temperature to which the root section of the blade is heated is
frequently in the ductility trough temperature range (1,300.degree.
F. to 1,500.degree. F.). It is an essential mechanical property of
an alloy being used for such blades that it be capable of deforming
predictably in the root section at temperatures around
1,400.degree. F. while withstanding mechanically imposed strain
without cracking, i.e., the alloy must possess reasonable
ductility. The alloys of the present invention, containing boron
within the critical range of 0.05% to 0.30% by weight, demonstrate
great advantage in strength and ductility in the 1,400.degree. F.
temperature range over prior art alloys intended for use in turbine
blades.
The rotating turbine disk, to which the blade root is attached,
also requires high resistance to creep and rupture along with
ductility and strength to resist fatigue and crack propagation.
Accordingly, the alloys described herein provide enhanced
properties desirable in disk alloys.
Manufacturers of small gas turbine engines generally employ an
integral wheel rather than an assembly of individual disks and
blades. These integral wheels, consisting of a single component
comprising a disk having radially extending blade airfoils at the
disk periphery, is usually manufactured by investment casting.
Normal modes of operation for small engines subject such components
to rapid heating and cooling. This normal mode of operation results
in premature cracking at the disk rim between the blade airfoils,
because of low cycle thermal and mechanical fatigue. Since the disk
rin in many engine designs operates up to about 1,400.degree. F.,
the alloys of the present invention enhance the overall performance
of integral wheels.
The formulations of several of the more important prior art alloys
which are currently commercially used in turbine engines are
tabulated in Table II. The values tabulated represent the amount of
each ingredient present in terms of weight percent. The amount of
boron and carbon present in each formulation is considered by the
prior art to be approximately optimum. With respect to each of the
alloys, designated A, B, C, D, E, and F, the U.S. Patent and
commercial designation is indicated in the table.
For purposes of comparison, example alloys, compositionally similar
to the commercial alloys of Table II, but containing boron within
the critical range of the present invention, were prepared.
Analyses of these example alloys (designated A-1, B-1, etc.) are
presented in Table III. Standard cast-to-size test bars (0.25 inch
in diameter) of the alloys of Table II and the example alloys of
Table III were prepared by melting and casting under vacuum into
shell molds. All example alloy specimens were heat treated under a
protective atmosphere at 1,975.degree. F. for four hours and then
air cooled. The example alloys were also subjected to an aging heat
treatment at 1,650.degree. F. for ten hours. Each of the commercial
alloys of Table II was heat treated in accordance with the practice
recommended by the alloy developer.
Table IV shows the comparative creep-rupture strength (as measured
by time to rupture) and ductility, (as measured by prior creep) of
both commercial alloys A, B, C, and E, and example alloys A-1, B-1,
C-1, C-2, C-3 and E-1. All alloys were tested at 1,400.degree. F.
under a stress of 94,000 psi.
The data in Table IV shows a very significant improvement in both
1,400.degree. F. creep-rupture strength and ductility for alloys
having a boron content within the critical range of the present
invention. At 0.20 weight percent boron, the properties of Example
C-3, although decreasing from Example C-2, still show a marked
improvement over Alloy C.
The data set forth in Tables II-IV demonstrates that the utility of
nickel-base superalloys for use in gas turbine engine components in
which maximum service temperature does not exceed about
1,400.degree. F. is greatly enhanced by increasing boron content to
an effective level previously considered excessive.
TABLE II ______________________________________ A* B* C* D* E* F*
______________________________________ C 0.10 0.10 0.15 0.15 0.18
0.21 Cr 8.0 10.0 9.0 9.0 10.0 12.5 Co 10.0 10.0 10.0 10.0 15.0 9.0
W -- -- 12.5 10.0 -- 3.9 .Badd. Mo.Baddend. 6.0 3.0 -- 2.5 3.0 2.0
.[..[.o.]..]. Ta 4.25 7.0 -- 1.5 -- 3.9 Ti 1.0 1.0 2.0 1.5 4.7 4.2
Al 6.0 6.0 5.0 5.5 5.5 3.2 B 0.015 0.015 0.015 0.015 0.015 0.02 Zr
0.10 0.10 0.05 0.05 0.06 0.10 Cb -- -- 1.0 -- -- -- V -- -- -- --
1.0 -- Ni (1) (1) (1) (1) (1) (1)
______________________________________ A* 3,310,399 B-1900 B*
3,310,399 B-1910 C* 3,164,465 MAR-M200 D* 3,164,465 MAR-M246 E*
3,061,426 IN-100 F* 3,619,182 IN-792 (1) Balance
TABLE III ______________________________________ EXAMPLE NO. A-1
B-1 C-1 C-2 C-3 E-1 ______________________________________ C 0.12
0.11 0.15 0.09 0.15 0.18 Cr 7.87 10.2 8.75 9.30 8.75 10.1 Co 10.15
10.0 10.1 10.3 10.1 15.1 W -- -- 12.0 12.81 12.0 -- Mo 6.06 3.05 --
-- -- 3.01 Ta 4.40 6.75 -- -- -- -- Ti 1.08 1.12 1.98 2.08 1.98
4.80 Al 5.95 6.30 4.99 4.80 4.99 5.33 B 0.10 0.10 0.10 0.13 0.20
0.10 Zr 0.05 0.14 0.06 0.03 0.06 0.06 Cb -- -- 1.23 1.20 1.23 -- V
-- -- -- -- -- 0.86 Ni (1) (1) (1) (1) (1) (1)
______________________________________ (1) Balance
TABLE IV ______________________________________ Creep-Rupture
Properties 1400F./94,000 psi Boron Content Rupture Life Prior Creep
wt. %) (hr.) (%) ______________________________________ Alloy A
0.016 31.0 1.98 Example No.: A-1 0.10 229.6 6.80 Alloy B 0.015
102.1 3.68 Example No.: B-1 0.10 297.2 8.95 Alloy C 0.015 46.7 0.51
Example No.: C-1 0.10 400.6 3.60 C-2 0.13 442.6 6.45 C-3 0.20 245.5
2.35 Alloy E 0.012 26.6 0.96 Example No.: F-1 0.10 345.0 5.25
______________________________________ Prior creep indicates the
last creep reading prior to specimen failure
The need for improved higher temperature (greater than
1,700.degree. F.) creep capability in gas turbine alloys is of
comparable importance to effecting an improvement in 1,400.degree.
F. creep-rupture strength and ductility. Therefore, the effect of
the high boron range upon the creep-rupture properties in the
1,700.degree. F. to 1,900.degree. F. temperature range was studied
by conducting creep-rupture tests on heat treated standard
cast-to-size test bars at 1,800.degree. F. under a stress of 29,000
psi.
Results of that testing show that the high boron levels,
demonstrated as being unusually effective for 1,400.degree. F.
properties, were deleterious to 1,800.degree. F. rupture strength.
The effect was a weakening of the resistance of all alloys in Table
II to creep deformation and a noticeable increase in ductility,
i.e., a weaker but more ductile material. For gas turbine
components requiring both 1,400.degree. F. and 1,800.degree. F.
creep-rupture strength and ductility, use of the alloys shown in
Table II would involve the unacceptable tradeoff of improved
1,400.degree. F. ductility at the expense of decreased
1,800.degree. F. strength.
It has been discovered, in further accord with the present
invention, that by reducing the carbon content to a critical upper
limit of no more than about 0.05 weight percent, it is possible to
both effect the improvement in 1,400.degree. F. properties and
approximately maintain, and in some cases improve, creep-rupture
strength and ductility at 1,800.degree. F. Alloys of the present
invention, containing less than 0.05 weight percent carbon are
capable of withstanding an applied stress of 29,000 psi at
1,800.degree. F. without rupture for a time in excess of 40
hours.
The low carbon aspect of the present invention is particularly
important with respect to turbine components requiring enhanced
properties at both 1,400.degree. F. and 1,800.degree. F. As
previously noted, properties at around 1,400.degree. F. are
particularly important with respect to the root sections of turbine
blades. However, the hot gases passing across the airfoil portion
of the blade raise metal temperatures into the 1,700.degree. F. to
1,900.degree. F. temperature range. Accordingly, turbine blades
desirably require an alloy having good high temperature properties
throughout the temperature range of from about 1,300.degree. F. to
about 1,900.degree. F. or higher.
To demonstrate the utility and advantages of the low carbon feature
of the present invention, thirty pound heats of example alloys A-2,
B-2, C-4 through D-1, E-2 through 9, and F-1 were prepared by
melting under vacuum. Standard test bars (0.25 inch diameter) were
cast under vacuum into shell molds and all specimens were heat
treated under a protective atmosphere at 1,975.degree. F. for four
hours. After air cooling, all specimens were subjected to an aging
heat treatment of 1,650.degree. F. for ten hours. Analyses for
series A,B,D, and F example alloys are shown in Table V. Analyses
for series C and E example alloys are shown, respectively, in
Tables IV and VII. In all six series compositions, carbon has been
reduced to as low a level as possible using normal master alloys
and metals in the preparation of each heat. Such a technique is
representative of typical commercial practice. Intentional carbon
was added however, where appropriate, to determinate the critical
upper limit.
Creep-rupture tests were conducted at 1,800.degree. F. under a
stress of 29,000 psi and at 1,400.degree. F. under a stress of
94,000 psi on all low carbon example alloys. For comparative
purposes, the same tests were conducted on the commercial alloys of
A,B,C,D,E, and F of Table II. The commercial alloy test bars were
heat treated in accordance with the procedures recommended by the
producers to achieve maximum mechanical properties. Creep-rupture
data for commercial alloys D and F under these conditions were
obtained from technical literature provided by the respective alloy
producers.
The data of Table VII demonstrates the applicability of the present
invention to a wide range of superalloys. The four example alloys
corresponding to the four commercial alloys designated A,B,D, and F
had boron and carbon levels approaching the target compositions,
i.e., 0.01 weight percent carbon and 0.10 and 0.12 weight percent
boron. The comparative test results between the commercial alloys
A, B, D, and F and corresponding series A, B, D and F example
alloys set forth in Table VIII shows in all cases that very
significant improvements are effected at both 1,400.degree. F. and
1,800.degree. F. in rupture life and ductility.
TABLE V ______________________________________ EXAMPLE NO. A-2 B-2
D-1 F-1 ______________________________________ C 0.014 0.040 0.009
0.009 Cr 9.75 10.56 9.66 11.35 Co 12.15 11.76 10.91 9.43 W -- --
9.66 4.18 Mo 5.89 3.10 2.43 2.04 Ta 3.71 5.70 1.50 4.23 Ti 0.96
0.99 1.38 3.69 Al 5.95 6.03 5.19 3.92 B 0.081 0.109 0.084 0.096 Zr
0.073 0.084 0.062 0.083 Ni (1) (1) (1) (1)
______________________________________ (1) Balance
TABLE VI
__________________________________________________________________________
EXAMPLE NO. C-4 C-5 C-6 C-7 C-8 C-9 C-10 C-11 C-12 C-13
__________________________________________________________________________
C 0.011 0.010 0.014 0.012 0.011 0.018 0.018 0.045 0.023 0.033 Cr
9.33 8.33 8.89 8.61 8.64 8.97 8.96 9.50 9.54 10.00 Co 10.66 10.70
10.64 10.66 10.71 10.78 10.60 10.50 10.69 10.54 W 12.41 12.40 12.74
12.84 12.48 12.55 12.41 12.5 11.84 13.15 Ti 1.76 1.78 1.77 1.78
1.75 1.77 1.76 2.0 1.75 1.75 Al 5.65 5.53 5.63 5.80 5.41 5.13 5.15
4.98 4.76 4.76 B 0.02 0.03 0.08 0.14 0.15 0.20 0.235 0.10 0.28 0.39
Zr 0.077 0.075 0.079 0.068 0.074 0.065 0.054 0.060 0.053 0.038 Cb
0.95 0.95 0.92 0.92 0.92 0.91 0.85 1.09 0.88 0.79 Ni (1) (1) (1)
(1) (1) (1) (1) (1) (1) (1)
__________________________________________________________________________
(1) Balance
TABLE VII
__________________________________________________________________________
EXAMPLE NO. E-2 E-3 E-4 E-5 E-6 E-7 E-8 E-9
__________________________________________________________________________
C 0.010 0.008 0.008 0.008 0.010 0.011 0.012 0.012 Cr 8.56 9.10 8.95
9.67 9.87 9.87 10.22 10.05 Co 16.60 16.67 16.62 16.62 16.62 16.86
16.80 16.69 Mo 3.01 2.94 3.17 3.06 3.03 3.25 3.33 3.32 Ti 4.89 4.90
4.88 4.74 4.91 4.64 4.64 4.56 Al 5.58 5.71 5.60 5.61 5.63 5.22 5.23
5.23 B 0.018 0.044 0.088 0.090 0.125 0.170 0.180 0.220 Zr 0.079
0.067 0.074 0.071 0.060 0.067 0.069 0.064 V 1.06 1.07 1.07 1.08
1.06 0.996 1.01 1.01 Ni (1) (1) (1) (1) (1) (1) (1) (1)
__________________________________________________________________________
(1) Balance
TABLE VIII ______________________________________ Creep-Rupture
Properties 1400F./94,000psi 1800F./29,000psi Prior Final Boron
Carbon Life Creep Life Elong. (wt. %) (wt. %) (hr.) (%) (hr.) (%)
______________________________________ Alloy A 0.016 0.12 31.0 1.98
53.2 6.0 Example No.: A-2 0.081 0.014 146.5 7.3 44.8 9.9 Alloy B
0.010 0.11 102.1 3.68 50.3 9.3 Example No.: B-2 0.109 0.040 206.0
5.1 52.4 13.0 Alloy D 0.015 0.15 120.0 2.2 50.0 5.0 Example No.:
D-1 0.084 0.009 432.8 4.3 58.1 4.8 Alloy F 0.02 0.21 62.0 3.5 30.0
11.0 Example No.: l-F-1 0.096 0.009 254.4 8.1 79.2 11.7
______________________________________
The most pronounced effect noted is with alloy F in which
1,400.degree. F. rupture life is increased by more than a factor of
four, while ductility is doubled. At 1,800.degree. F. the time to
rupture is more than doubled, an unusually large increase.
Comparative results of the testing between alloy C and the
respective Series C example alloys is shown in Table IX. The
1,400.degree. F. results show strength comparable to the previous
high carbon alloy results set forth in Table IV. This demonstrates
that the boron is effective in improving 1,400.degree. F.
properties regardless of carbon level. The 1,800.degree. F. results
show creep-rupture life increasing with increasing boron to about
0.15 weight percent. Above 0.15 weight percent boron, strength
falls off slightly. Example alloy C-4 shows very good rupture life
at 1,400.degree. F., but the low level of both boron and carbon
causes low ductility in the 1,800.degree. F. test. In addition, the
combination of low boron and low carbon contents causes poor
castability and a tendency for castings to crack on cooldown during
solidification. The minimum boron required to circumvent these
problems in the low carbon alloys is about 0.05 weight percent.
Comparative results of testing between alloy E and the respective
Series E example alloys is shown in Table X. In these data it is
seen that although the 1,400.degree. F. strength is below the high
carbon counterparts reported in Table IV, the improvement over
commercial alloy E is significant.
TABLE IX ______________________________________ Creep-Rupture
Properties 1400F./94,000psi 1800F./29,000psi Prior Final Boron
Carbon Life Creep Life Elong. (wt. %) (wt. %) (hr.) (%) (hr.) (%)
______________________________________ Alloy C 0.015 0.15 46.7 0.51
96.8 7.5 Example No.: C-4 0.02 0.011 314.8 3.50 73.6 2.2 C-5 0.03
0.010 392.2 2.57 85.2 2.4 C-6 0.08 0.014 448.0 2.36 113.9 4.2 C-7
0.14 0.012 452.9 3.53 122.4 6.0 C-8 0.15 0.011 468.6 2.21 128.3 5.8
C-9 0.20 0.018 459.8 2.03 117.1 4.5 C-10 0.235 0.018 458.6 1.57
64.8 4.2 C-11 0.10 0.045 397.2 2.59 92.3 7.0 C-12 0.28 0.023 347.4
2.11 43.0 4.6 C-13 0.39 0.033 80.7 1.56 14.7 11.1
______________________________________
TABLE X ______________________________________ Creep-Rupture
Properties 1400F./94,000psi 1800F./29,000psi Prior Final Boron
Carbon Life Creep Life Elong. (wt. %) (wt. %) (hr.) (%) (hr.) (%)
______________________________________ Alloy E 0.015 0.18 26.6 0.95
41.9 8.5 Example No.: E-2 0.018 0.010 38.6 2.32 27.0 5.2 E-3 0.044
0.008 68.1 5.44 48.6 11.4 E-4 0.088 0.008 104.2 5.92 41.3 12.3 E-5
0.090 0.008 117.2 5.91 38.1 11.7 E-6 0.125 0.010 174.1 4.86 41.2
13.8 E-7 0.170 0.011 266.3 5.03 36.5 11.9 E-8 0.180 0.012 302.2
4.90 31.9 10.1 E-9 0.220 0.012 357.6 5.50 27.6 11.8
______________________________________
In addition, the 1,800.degree. F. properties are maintained within
a boron range of about 0.05 to 0.15 weight percent. At 0.22 weight
percent boron in Example alloy E-9, the 1,800.degree. F. strength
is about sixty percent that of commercial alloy E.
The creep-rupture data discussed previously and presented in Tables
IV, V, VIII, IX and X were developed using standard cast-to-size
test bars with a 0.250 inch diameter gage section. To demonstrate
that the property enhancement is applicable to turbine components,
several turbine blade castings were produced from alloy C-7 and
specimens cut from those castings. Testing was conducted under the
same temperature and stress conditions previously employed and
results are present in Table XI. The data show the expected
reduction in capability compared to test bar properties, but the
level of strength and ductility are exceptionally attractive for
specimens machined from turbine component castings.
Another major concern of gas turbine engine builders in the
selection of high temperature materials is the ability of the
selected alloy to retain initial or starting properties after long
time, high temperature exposure. Example Alloy C-7 cast-to-size
test bars were subjected to creep testing at 1,500.degree. F. under
a stress of 40,000 psi for 1,000 hours and examined
microstructurally. No deleterious phase formation was observed and
subsequent creep-rupture testing was conducted at 1,400.degree. F.
and 94,000 psi for comparison with the same alloy in the as-heat
treated condition.
TABLE XI ______________________________________ Creep-Rupture
Properties 1400F./94,000psi 1800F./29,000psi Life Prior Life Final
Specimen No. (hr.) Creep (%) (hr.) Elong. (%)
______________________________________ 1 371.9 4.36 42.5 4.5 2
264.4 3.38 63.3 7.1 3 172.4 2.00 54.4 5.1 4 281.5 3.50 39.6 11.4 5
49.4 7.2 b 46.1 11.5 ______________________________________
TABLE XII ______________________________________ Creep-Rupture
Properties 1400F./94,000psi Life Prior Example No. Specimen
Condition (hr.) Creep (%) ______________________________________
C-7 As-heat treated 452.9 3.53 C-7 Heat treated plus 463.3 4.03
1500F exposure for 1000 hours under stress of 40,000psi
______________________________________
Results shown in Table XII reveal essentially no change in rupture
life and an improvement in 1,400.degree. F. ductility.
FIG. 1 shows the creep characteristics of typical Alloy C and one
of the example alloy C-7 test bars in the 1,400.degree. F. test. In
FIG. 1, percent creep elongation is plotted against time. The
improved results obtained with the alloys of the present invention
are dramatically demonstrated.
FIGS. 2 and 3 further demonstrate the critical relationship between
boron content and strength and ductility. FIG. 2 is a plot of creep
rupture life in hours against the boron content in weight percent
of C series, low carbon (less than 0.05% by weight), alloys at both
1,400.degree. F. -94,000 psi and 1,800.degree. F. - 29,000 psi. The
creep rupture life for commercial alloy C at 1,400.degree. F. -
94,000 psi and 1,800.degree. F. - 29,000 psi for commercial alloy C
is noted on the plot at, respectively, points A and B. As is
apparent, substantial improvements in creep rupture life are
obtained at 1,400.degree. F. by maintaining the boron content
within the critical range of the present invention.
FIG. 3 is a plot of percent creep elongation against boron content
for C series, low carbon alloys at both 1,400.degree. F. - 94,000
psi and 1,800.degree. F. - 29,000 psi. The percent creep elongation
for commercial alloy C at both 1,400.degree. F. - 94,000 psi and
1,800.degree. F. - 29,000 psi is also noted on this plot,
respectively, at points A and B. Again substantial improvements are
apparent at 1,400.degree. F. with respect to alloys containing
boron within the critical range of the present invention. While the
percent creep elongation obtained at 1,800.degree. F. with alloys
within the ambit of the present invention is not as high as that of
the commercial alloy, highly acceptable levels are achieved.
Metallographic examination was conducted in an attempt to explain
the mechanism responsible for the observed property enhancement.
FIG. 4 shows the normal microstructure of commercial Alloy C in the
as-cast condition at 300 magnifications. The light etching dendrite
arms or branch-like areas indicate tungsten segregation. A few
titanium rich carbides are visible in the lower center portion of
the photomicrograph.
The photomicrograph of FIG. 5 also at 300 magnifications, shows the
profound microstructural change resulting from the added boron and
reduced carbon of example alloy C-7. Reducing carbon to less than
0.02 weight percent frees titanium previously tied up as a stable
carbide. The increased available titanium in the alloy results in
the formation of gamma-gamma prime eutectic in the grain
boundaries, a microstructural effect known to enhance 1,400.degree.
F. ductility. The boron addition results in the formation of
discrete grain bondary particles, identified by electron-beam
micro-probe analysis as an M.sub.3 B.sub.2 type boride where M (in
the C alloy series) is chromium and tungsten. These grain boundary
particles are responsible for restoring 1,800.degree. F.
creep-rupture ductility to low carbon alloys.
Electron photomicrographs of commercial alloy C and example alloy
C-7, at 7,000 magnifications, are shown, respectively, in FIGS. 6
and 7. FIG. 6 shows, as previously stated to be the general case,
borides located at the grain boundaries. In FIG. 7, a boride
precipitate within each gamma prime particle may be observed, a
phenomenon absent in superalloys of the more conventional
compositions. The presence of the very fine boride particles
appears to retard dislocation movement through the gamma-prime
particles and, in essence, provides dispersion strengthening for
improved resistance to creep deformation at 1,800.degree. F. This
microstructural effect has not been observed in commercial
alloys.
Many of the alloys of the present invention may be extruded and hot
forged. Wrought, high strength nickel-base superalloys are
generally employed in applications where ductility and fracture
roughness in the 1,000.degree. F. to 1,500.degree. F. temperature
range are of prime concern. Such applications include gas turbine
engine turbine and compressor disks. The series E alloys of the
present invention may be hot forged, using conventional techniques,
into shaped articles having the characteristics considered to be
essential in advanced wrought alloys. For example, alloys E-1 and
E-5 have responded very satisfactorily to extrusion and forging in
the 2,000.degree. F. to 2,200.degree. F. temperature range in
anticipation of the requirements for advanced wrought disk and
blade materials.
The present invention also anticipates the use of powder metallurgy
for controlling the size, morphology and distribution of the boride
microconstituents previously described.
The invention in its broader aspects is not limited to the specific
embodiments shown and described. Departures may be made therefrom
within the scope of the accompanying claims without departing from
the principles of the invention and without sacrificing its chief
advantages.
* * * * *