Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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NICKEL BASE SUPERALLOY COMPOSITIONS
BEING SUBSTANTIALLY FREE OF RHENIUM AND
SUPERALLOY ARTICLES
CROSS-REFERENCE TO RELATED APPLCIATIONS
[0001] This Application claims priority to U.S. Provisional Application Serial
Number 60/969,360, filed August 31, 2007, which is herein incorporated by
reference in
its entirety.
FIELD OF THE INVENTION
[0002] Embodiments disclosed herein pertain generally to nickel base
superalloys and articles of manufacture comprising nickel base superalloys.
Disclosed
embodiments may be utilized for components disposed in hot sections of a gas
turbine
engine, and more particularly for use in non-creep limited applications, such
as turbine
nozzles and shrouds.
BACKGROUND OF THE INVENTION
[0003] The efficiency of gas turbine engines depends significantly on the
operating temperature of the various engine components with increased
operating
temperatures resulting in increased efficiencies. The search for increased
efficiencies has
led to the development of superalloys capable of withstanding increasingly
higher
temperatures while maintaining their structural integrity.
[0004] Nickel-base superalloys are used extensively throughout the aeroengine
in turbine blade, nozzle, and shroud applications. Aeroengine designs for
improved
engine performance require alloys with increasingly higher temperature
capability.
Although shroud and nozzle applications do not require the same level of high
temperature creep resistance as blade applications, they do require similar
resistance to
thermal mechanical failure and environmental degradation. Superalloys are used
for
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these demanding applications because they maintain their strength at up to 90%
of their
melting temperature and have excellent environmental resistance.
[0005] Single crystal (SC) superalloys may be divided into "four generations"
based on similarities in alloy composition and performance. A defining
characteristic of
so-called "first generation" SC superalloys is the absence of the alloying
element rhenium
(Re). For example, US Patents 5,154,884; 5,399,313; 4,582,548; and 4,209,348
each
discloses superalloy compositions substantially free of Re.
[0006] A representative SC nickel-base superalloy is known in the art as Rene
N4 having a nominal composition of: 6.0-7.0% Co, 9.5-10.0% Cr, 1.5% Mo, 6.0%
W,
4.8% Ta, 4.2% Al, 3.5% Ti, 0.5% Nb, 0.01 maximum % B, 0.2 maximum % Hf, and
balance essentially Ni and C wherein C is specified as 0.01% (100 ppm)
maximum.
Mach 1 velocity cyclic oxidation Test at 2150 F data for a Rene N4 superalloy
and an
AMl superalloy are provided for comparative purposes in the accompanying
Figures.
[0007] It was discovered that the addition of about 3 wt% Re to superalloy
compositions provides about a 50 F (28 C) improvement in rupture creep
capability and
the accompanying fatigue benefits. Production alloys such as CMSX-4, PWA-1484
and
Rene N5 all contain about 3 wt% Re. These "second-generation" alloys are
disclosed, for
example, in US Patents 4,719,080; 4,643,782; 6,074,602 and 6,444,057.
[0008] U.S. Patent 4,719,080 provides a relationship between compositional
elements called a "P-value" defined as P = - 200 Cr + 80 Mo - 20 Mo2 - 250 Ti2
- 50 (Ti
x Ta) + 15 Cb + 200 W - 14 W2 +30Ta-1.5Ta2 +2.5Co+1200A1-100A12 +100
Re + 1000 Hf - 2000 W + 700 Hf3 - 2000 V - 500 C - 15000 B - 500 Zr. The
patent
stresses that a higher "P-value" correlates with high strength in combination
with
stability, heat treatability, and resistance to oxidation and corrosion. In
particular, the
superalloy compositions disclosed in the patent are constrained by "P-values"
greater
than 3360.
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[0009] U.S. Patent 6,074,602 is directed to nickel-base superalloys suitable
for
making single-crystal castings. The superalloys disclosed therein include, in
weight
percentages: 5-10 Cr, 5-10 Co, 0-2 Mo, 3-8 W, 3-8 Ta, 0-2 Ti, 5-7 Al, up to 6
Re, 0.08-
0.2 Hf, 0.03-0.07 C, 0.003-0.006 B, 0.0-0.04 Y, the balance being nickel and
incidental
impurities. These superalloys exhibit increased temperature capability, based
on stress
rupture strength and low and high cycle fatigue properties, as compared to the
first-
generation nickel-base superalloys. Further, the superalloys exhibit better
resistance to
cyclic oxidation degradation and hot corrosion than first-generation
superalloys.
[0010] US Patents 5,151,249; 5,366,695; 6,007,645 and 6,966,956 are directed
to third- and fourth-generation superalloys. Generally, third-generation
superalloys are
characterized by inclusion of about 6 wt % Re; fourth generation superalloys
include
about 6 wt% Re, as well as the alloying element Ru. These superalloy
compositions
illustrate the value of increased Re additions in terms of mechanical
performance.
[0011] First generation SC superalloys do not offer the thermal mechanical
failure (TMF) resistance or the environmental resistance required in many hot
section
components such as turbine nozzles and shrouds. Also, first-generation SC
superalloys
do not offer acceptable high temperature oxidation resistance for these
components.
[0012] Currently, aeroengines predominantly use second-generation type
superalloys in an increasing number of hot section applications. The alloying
element Re
is the most potent solid solution strengthener known for this class of
superalloys and
therefore it has been used extensively as an alloying addition in SC and
columnar-grained
directionally solidified (DS) superalloys. The second-generation superalloys
exhibit
exceptional high temperature oxidation capability balanced with satisfactory
mechanical
properties.
[0013] Known superalloy compositions having lower Re content have not been
able to provide the properties obtainable from second-generation superalloys.
In
particular, in U.S. Patent 4,719,080, the data for one alloy (namely, Bl)
having less than
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2.9% Re show properties comparable to first-generation, i.e., no Re,
superalloys. Thus,
in the development of superalloy compositions, the trend has been to use at
least 3 wt%
Re to obtain a satisfactory balance of oxidation resistance and high
temperature strength.
[0014] However, the cost of the raw materials, and the global shortage of Re
in
particular, provides a challenge to develop superalloy compositions able to
provide the
demonstrated improved mechanical properties and oxidation resistance of second
generation superalloys, but at low, and preferably 0% Re levels.
[0015] Accordingly, it would be desirable to provide nickel-base superalloy
compositions being substantially free of rhenium that are able to provide
desired high
temperature mechanical properties and oxidation resistance.
BRIEF DESCRIPTION OF THE INVENTION
[0016] The above-mentioned need or needs may be met by exemplary
embodiments which provide nickel-base superalloy compositions able to provide
the
desired thermal mechanical properties, creep strength, and oxidation
resistance with
substantially no Re content.
[0017] An exemplary embodiment provides a nickel base superalloy
composition including, in percentages by weight: about 5-8 Cr; about 7-8 Co;
about 1.3-
2.2 Mo; about 4.75-6.75 W; about 6.0-7.0 Ta; if present, up to about 0.5 Ti;
about 6.0-6.4
Al; if present, up to about 1.3 Re; about 0.15-0.6 Hf; if present, from about
0.03-0.06 C;
if present, up to about 0.004 B; if present, one or more rare earths selected
from Y, La,
and Ce up to about 0.03 total, the balance being nickel and incidental
impurities.
[0018] An exemplary embodiment provides a nickel base single-crystal article
comprising a superalloy including, in percentages by weight: about 5-8 Cr;
about 7-8 Co;
about 1.3-2.2 Mo; about 4.75-6.75 W; about 6.0-7.0 Ta; if present, up to about
0.5 Ti;
about 6.0-6.4 Al; if present, up to about 1.3 Re; about 0.15-0.6 Hf, if
present, from about
0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare
earths selected
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from Y, La, and Ce up to about 0.03 total, the balance being nickel and
incidental
impurities.
[0019] An exemplary embodiment provides a gas turbine engine component
cast from a nickel base superalloy composition comprising: about 5-8 Cr; about
7-8 Co;
about 1.3-2.2 Mo; about 4.75-6.75 W; about 6.0-7.0 Ta; if present, up to about
0.5 Ti;
about 6.0-6.4 Al; if present, up to about 1.3 Re; about 0.15-0.6 Hf, if
present, from about
0.03-0.06 C; if present, up to about 0.004 B; if present, one or more rare
earths selected
from Y, La, and Ce up to about 0.03 total, the balance being nickel and
incidental
impurities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The subject matter which is regarded as the invention is particularly
pointed out and distinctly claimed in the concluding part of the
specification. The
invention, however, may be best understood by reference to the following
description
taken in conjunction with the accompanying drawing figures in which:
[0021] FIG. 1 is a graphical representation of comparative sustained-peak low
cycle fatigue (SPLCF) properties.
[0022] FIG. 2 is a graphical representation of comparative Mach 1 Velocity
Cyclic Oxidation Test data at 2150 F.
[0023] FIG. 3 is a graphical representation of comparative Mach 1 Velocity
Cyclic Oxidation Test data at 2000 F.
[0024] FIG. 4 is a graphical representation of comparative Mach 1 Velocity
Cyclic Oxidation Test data at 2150 F.
[0025] FIG. 5 is a graphical representation of creep rupture data at 2100
F/10
ksi, normalized to a second-generation nickel base superalloy having about 3
wt% Re
content.
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[0026] FIG. 6 is a graphical representation of creep rupture data at 1600 F,
1800 F, 2000 F, and 2100 F, normalized to a second-generation nickel base
superalloy
having about 3 wt% Re.
[0027] FIG. 7 is a graphical representation of SPLCF data at 2000 F and 1600
F, normalized to a second-generation nickel base superalloy having about 3 wt%
Re.
[0028] FIG. 8 is a graphical representation of SPLCF data at 2000 F,
normalized to a second-generation nickel base superalloy having about 3 wt%
Re.
[0029] FIG. 9 is a schematic representation of an exemplary gas turbine engine
turbine blade.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Referring to the drawings wherein identical reference numerals denote
the same elements throughout the various views, FIG. 9 depicts a component
article 20 of
the gas turbine engine, illustrated as a gas turbine blade 22. The gas turbine
blade 22
includes an airfoil 24, and attachment 26 in the form of the dovetail to
attach the gas
turbine blade 22 to the turbine disc (not shown), and a laterally extending
platform 28
intermediate the airfoil 24 and the attachment 26. In one exemplary
embodiment, a
component article 20 is substantially a single crystal. That is, the component
article 20 is
at least about 80% by volume, and more preferably at least about 95% by
volume, a
single grain with a single crystallographic orientation. There may be minor
volume
fractions of other crystallographic orientations and also regions separated by
low-angle
boundaries. The single-crystal structure is prepared by the directional
solidification of an
alloy composition by methods known to those with skill in the art. In another
exemplary
embodiment, the component article 20 is a directionally oriented poly-crystal,
in which
there are at least several grains all with a commonly oriented preferred
growth direction.
[0031 ] The alloy composition discussed herein may be employed in other gas
turbine engine components such as nozzles, shrouds, and splash plates.
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[0032] Embodiments disclosed herein balance the contributions of various
alloying elements to the thermal mechanical properties, creep strength, and
oxidation
resistance of the compositions while minimizing detrimental effects. All
values are
expressed as a percentage by weight unless otherwise noted.
[0033] For example, certain embodiments disclosed herein include at least
about 5% chromium (Cr). Amounts less than about 5% may reduce the hot
corrosion
resistance. Amounts greater than about 8% may lead to topologically close-
packed
(TCP) phase instability and poor cyclic oxidation resistance.
[0034] Certain embodiments disclosed herein include at least about 7% to about
8% Co. Lower amounts of cobalt may reduce alloy stability. Greater amounts may
reduce the gamma prime solvus temperature, thus impacting high temperature
strength
and oxidation resistance.
[0035] Certain embodiments disclosed herein include molybdenum (Mo) in
amounts from about 1.3% to 2.2%. The minimum value is sufficient to impart
solid
solution strengthening. Amounts exceeding the maximum may lead to surface
instability.
Greater amounts of Mo may also negatively impact both hot corrosion and
oxidation
resistance.
[0036] Certain embodiments disclosed herein include tungsten (W) in amounts
from about 4.75% to about 6.75%. Lower amounts of W may decrease strength.
Higher
amounts may produce instability with respect to TCP phase formation. Higher
amounts
may also reduce oxidation capability.
[0037] Certain embodiments disclosed herein may include tantalum (Ta) in
amounts from about 6.0% to about 7.0%. Other embodiments may include Ta in
amounts from about 6.25% to about 6.5%.
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[0038] Certain embodiments disclosed herein may include aluminum (Al) in
amounts from about 6.0% to about 6.5%. Other embodiments may include from
about
6.2% to about 6.5% Al.
[0039] Certain embodiments disclosed herein may optionally include up to
about 0.5% titanium (Ti). Titanium is a potent gamma prime hardener. The
optional Ti
addition can strengthen the gamma prime phase, thus improving creep
capability.
However, oxidation resistance can be adversely affected by the addition of Ti,
especially
at levels greater than about 0.5%.
[0040] In an exemplary embodiment, a superalloy composition includes
substantially no Re content. By "substantially no Re content" it is meant that
Re
additions are not nominally called for in an exemplary composition. However,
it is
envisioned that compatible revert alloy (i.e., used, scrap, or otherwise
reclaimed, alloy)
may be utilized to provide exemplary superalloy compositions. In such
embodiments, Re
may be present in amounts up to about 1.3%.
[0041] Certain embodiments disclosed herein include hafnium (Hf) in amounts
of from about 0.15% to about 0.6%. Hafnium is utilized to improve the
oxidation and hot
corrosion resistance of coated alloys and can improve the life of an applied
thermal
barrier coating. Hafnium additions of about 0.7% can be satisfactory, but
additions of
greater than about 1% adversely impact stress rupture properties and the
incipient melting
temperature.
[0042] Certain embodiments disclosed herein may include up to about 0.004%
boron (B). B provides strains for low angle boundaries and enhanced
acceptability limits
for components having low angle grain boundaries.
[0043] Carbon (C), if present, may be included in amounts of from about 0.03%
to about 0.06%. The lower limit provides sufficient C to allow for a cleaner
melting
alloy and to aid in promoting corrosion resistance.
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[0044] Rare earth additions, i.e., yttrium (Y), lanthanum (La), and cerium
(Ce),
may be optionally provided in certain embodiments in amounts up to about
0.03%.
These additions may improve oxidation resistance by enhancing the retention of
the
protective alumina scale. Greater amounts may promote mold/metal reaction at
the
casting surface, increasing the component inclusion content.
[0045] An exemplary embodiment includes a nickel base superalloy
comprising, in weight percent, a nominal composition comprising: 6.0 Cr, 7.5
Co, 1.5-2.0
Mo, 6.0-6.5 W, 6.5 Ta, 0 Ti, 6.2 Al, 0 Re, 0.15 to 0.6 Hf, 0.03-0.06 C, 0.004
B, the
balance being nickel and incidental impurities. Certain exemplary embodiments
are
further characterized by P-values of less than 3360, wherein the P-values are
determined
in accordance with the relationship provided above. In exemplary embodiments,
the P-
values are less than 3250.
[0046] Table 1 below provides an exemplary composition series and associated
Re ratios and P-values. The "Re Ratio" is defined herein as the ratio of wt%
Re to the
total of wt% W plus wt% Mo. For exemplary embodiments comprising substantially
no
Re, the Re ratio is essentially zero (e.g., alloys 1-4, 15 and 16). The values
for each
composition are given in weight %, the balance being nickel and incidental
impurities.
For comparative purposes, a nominal composition, Re ratio, and P value is
provided for
Rene N5.
[0047] Table 2 below provides another exemplary composition series,
associated Re ratios, and Creep Rupture (CR) data, normalized to a second-
generation
(i.e. 3% Re) nickel base superalloy. The exemplary compositions in Table 2
provide
compositions having about 1 wt% Re which are able to provide desired creep
rupture
strength. Data from Table 2 as compared to a second-generation alloy (3 wt%
Re) and a
first generation alloy (0 wt% Re) is presented in FIG. 8.
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TABLE 1
Alloy Al Ta Cr W Mo Re Co C B Hf Re P-
Ratio Value
R N5 6.2 6.5 7 5 15 3 75 005 0004 015 046 3069
1 6.2 65 6 6 15 0 75 003 0004 015 000 3025
2 6.2 65 6 6 2 0 75 003 0004 015 000 3030
3 6.2 65 6 65 15 0 75 003 0004 015 000 3037
4 6.2 65 6 65 2 0 75 003 0004 015 000 3042
6.2 65 6 6 15 15 75 003 0004 015 020 3175
6 6.2 65 6 6 15 2 75 003 0004 015 027 3225
7 6.2 65 6 6 2 2 75 003 0004 015 025 3230
8 6.2 65 6 6 2 15 75 003 0004 015 019 3180
9 6.2 65 6 65 15 15 75 003 0004 015 019 3187
6.2 65 6 65 15 2 75 003 0004 015 025 3237
11 6.2 65 6 65 2 2 75 003 0004 015 024 3242
12 6.2 65 6 65 2 15 75 003 0004 0.15 018 3192
13 6.2 65 6 6 15 15 75 003 0004 06 020 3099
14 6.2 65 6 65 2 15 75 003 0004 06 018 3116
6.2 65 6 65 15 0 75 003 0004 0.6 000 2961
16 6.2 6.5 6 6 2 0 7.5 0.03 0.004 0.6 0.00 2954
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TABLE 2
Alloy Al Ta Cr W Mo Re Co C B Ti Re N. CR
Ratio (hrs)
1 A 6.2 7 6 6.5 175 1 73 004 0004 03 014 103
2A 6.2 6.5 6 65 225 1 73 004 0004 0 018 105
3A 6.2 7 6 6 225 1 73 004 0004 0 019 106
4A 6.2 6 6 6.5 225 1 73 004 0004 03 018 106
5A 6.2 65 6 6 225 1 73 004 0004 03 019 110
6A 6.2 7 6 5.5 225 1 73 004 0004 03 020 110
7A 6.2 65 6 6.5 2 1 73 004 0004 03 016 111
8A 6.2 7 6 6 2 1 73 004 0004 03 017 112
9A 6.2 7 6 6.5 225 1 73 004 0004 0 018 121
10A 6.2 625 6.4 6.5 225 1 75 004 0004 03 017 125
11 A 6.2 65 6 6.5 225 1 73 004 0004 03 018 127
12A 6.2 7 6 6.5 2 1 73 004 0004 03 016 130
13A 6.2 7 6 6 225 1 73 004 0004 03 019 135
14A 6.2 7 6.4 6.5 225 1 7.5 004 0004 03 017 1.38
15A 6.2 7 6.4 6 225 1 75 004 0004 0 018 140
16A 6.2 6.5 6.4 6.5 2.25 1 7.5 0.04 0.004 0.3 0.17 1.46
17A 6.2 7 6 6.5 2.25 1 7.3 0.04 0.004 0.3 0.18 1.62
[0048] FIG. 1 illustrates the improved sustained-peak low cycle fatigue
(SPLCF) properties of certain embodiments disclosed herein that are beyond
that of first-
generation superalloys, and more comparable to second-generation superalloys.
First
generation SC superalloys do not offer thermal mechanical failure (TMF)
resistance
required in many hot section components. SPLCF is driven by a unique
combination of
properties, one of which is oxidation resistance. SPLCF or TMF capability is
important
for cooled hardware because of the temperature gradient within the part.
[0049] FIG. 2 provides a comparative graphical representation of data showing
weight loss over time during a Mach 1 Velocity Cyclic Oxidation Test at 2150
F,
illustrating improved oxidation resistance for certain embodiments disclosed
herein.
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[0050] FIG. 3 provides a comparative graphical representation of data showing
weight loss over time during a Mach 1 Velocity Cyclic Oxidation Test at 2000
F,
illustrating improved oxidation resistance for certain embodiments disclosed
herein.
[0051] FIG. 4 provides a comparative graphical representation of data showing
weight loss over time during a Mach 1 Velocity Cyclic Oxidation Test at 2000
F,
illustrating improved oxidation resistance for certain embodiments disclosed
herein.
[0052] FIG. 5 is a graphical representation of creep rupture data at 2100
F/10
ksi, normalized to a second-generation nickel base superalloy having about 3
wt% Re
content. Certain embodiments disclosed herein compare favorably with the
second-
generation superalloys, and exhibit marked improvement over first-generation
superalloys. It is believed that stability of the gamma prime phase,
especially at
temperatures in excess of 2100 F, contributes to the improved properties. In
certain of
the compositions disclosed herein, the volume fraction of the gamma prime
phase at 2150
F is about 46%, comparable to second-generation superalloys, and generally
greater than
first-generation superalloys. The relative stability of the gamma prime phase
benefits the
SPLCF resistance and positively affects the creep rupture properties at 2100
F.
[0053] Creep rupture data, normalized to a second-generation nickel base
superalloy illustrate that embodiments disclosed herein having low Re content
are more
comparable to second-generation superalloys than first-generation superalloys.
Normalized creep rupture data at 1600 F, 1800 F, 2000 F, and 2100 F for
alloy 5-
alloy 14 (Table 1) is provided in FIG. 6.
[0054] FIG. 7 is a graphical representation of SPLCF data at 2000 F and 1600
F, normalized to a second-generation nickel base superalloy having about 3 wt%
Re.
[0055] FIG. 8 is a graphical representation of SPLCF data at 2000 F,
normalized to a second-generation nickel base superalloy having about 3 wt%
Re.
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[0056] Superalloy compositions disclosed herein may be utilized to produce
single crystal articles having temperature capability on par with articles
made from
second-generation superalloys. An article so produced may be a component for a
gas
turbine engine. Such an article may be an airfoil member for a gas turbine
engine blade
or vane. The article so produced may be a nozzle, shroud, splash plate, or
other high
temperature component.
[0057] Certain exemplary embodiments disclosed herein may be especially
useful when directionally solidified as hot-section components of aircraft gas
turbine
engines, particularly rotating blades.
[0058] A method for producing any of the articles of manufacture disclosed
herein includes preparing a nickel base single crystal superalloy element
material having
a chemical composition as set forth in the disclosed embodiments, from raw
materials
containing nickel, cobalt, chromium, molybdenum, tungsten, aluminum, tantalum,
optionally titanium, substantially 0 wt% rhenium, hafinium, optionally carbon,
optionally
one or more of yttrium, cesium, and lanthanum. The superalloy element material
is
subjected to suitable heat treatment and suitable subsequent casting
processes. Alternate
embodiments include substituting revert superalloy material for at least a
portion of the
raw materials. Thus, embodiments nominally reciting no Re content may include
up to
about 1.3 wt% Re upon use of revert material.
[0059] Thus, superalloy compositions disclosed herein provide the desired
thermal mechanical properties, creep strength, and oxidation resistance with
reduced Re
content by balancing the contributions of compositional elements.
[0060] This written description uses examples to disclose the invention,
including the best mode, and also to enable any person skilled in the art to
make and use
the invention. The patentable scope of the invention is defined by the claims,
and may
include other examples that occur to those skilled in the art. Such other
examples are
intended to be within the scope of the claims if they have structural elements
that do not
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differ from the literal language of the claims, or if they include equivalent
structural
elements with insubstantial differences from the literal languages of the
claims.
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