C-M
Erickson Single crystal nickel-based superalloy (CMSX-10) 1994 US5366695A
Publication
Number: US5366695A
Publication
Date: 1994-11-22
Priority
Number: US1992905462A
Application
Date: 1992-06-29
Title:
Single crystal nickel-based superalloy
Inventor
- w/address: Erickson Gary
L.,Muskegon,MI,US
Assignee/Applicant:
Cannon Muskegon Corporation,Muskegon,MI,US
Front Page Drawing:
Abstract:
This invention relates to a nickel-based superalloy
comprising the following elements in percent by weight: from about 5.0 to about
7.0 percent rhenium, from about 1.8 to about 4.0 percent chromium, from about
1.5 to about 9.0 percent cobalt, from about 7.0 to about 10.0 percent tantalum,
from about 3.5 to about 7.5 percent tungsten, from about 5.0 to about 7.0
percent aluminum, from about 0.1 to about 1.2 percent titanium, from about 0 to
about 0.5 percent columbium, from about 0.25 to about 2.0 percent molybdenum,
from about 0 to about 0.15 percent hafnium, and the balance nickel+incidental
impurities, the superalloy having a phasial stability number N.sub.v3B less
than about 2.10.
First Claim:
1. A nickel-based
superalloy comprising the following elements in percent by weight:
______________________________________
Rhenium about 5.0-7.0
Chromium about 1.8-4.0
Cobalt about 1.5-9.0
Tantalum about
7.0-10.0
Tungsten about 3.5-7.5
Aluminum about 5.0-7.0
Titanium about 0.1-1.2
Columbium about 0-0.5
Molybdenum about
0.25-2.0
Hafnium about 0-0.15
Carbon (Incidental
Impurity)
about 0-0.04
Nickel + Other
Incidental
balance
Impurities
______________________________________
said superalloy having
a phasial stability number N v3B less than about 2.10.
Description w/Pub Language: BACKGROUND OF THE INVENTION
1. Field of the
Invention
This invention relates
to single crystal nickel-based superalloys and, more particularly, single
crystal nickel-based superalloys and articles made therefrom for use in
advanced gas turbine engines under high stress, high temperature conditions.
2. Description of the
Prior Art
Advances over recent
years in the metal temperature and stress capability of single crystal articles
have been the result of the continuing development of single crystal
superalloys, as well as improvements in casting processes and engine
application technology. These single crystal superalloy articles include
rotating and stationary turbine blades and vanes found in the hot sections of
gas turbine engines. However, gas turbine engine design goals have remained the
same during the past decades. These goals include the desire to increase engine
operating temperature, rotational speed, thrust-to-weight ratio, fuel
efficiency, and engine component durability and reliability.
The basic technology
of alloys for the casting of single crystal components is described in U.S.
Pat. Nos. 3,494,709; 4,116,723 and 4,209, 348. Development work resulted in
first generation nickel-based superalloys, which were materially improved over
those described in the aforementioned patents. However, these first generation
nickel-based superalloys contained no rhenium. Examples of such first
generation nickel-based superalloys, commercially known as CMSX-2 alloy and
CMSX-3 alloy produced by Cannon-Muskegon Corporation, assignee of the present
application, are described in U.S. Pat. No. 4,582, 548. Further development
work resulted in second generation nickel-based superalloys having improved
creep strength/creep rate. These second generation nickel-based superalloys
have a moderate rhenium content of about 3 weight percent. An example of such a
second generation nickel-based superalloy is described in U.S. Pat. No.
4,643,782. This patent discloses a superalloy, commercially known as CMSX-4
alloy, having a specific nickel-based composition including a rhenium content
in the range of 2.8-3.2 weight percent. The present invention provides the next
generation of nickel-based superalloys having higher total refractory element
(W+Re+Mo+ Ta) content and improved mechanical properties.
Single crystal
articles are generally produced having the low-modulus (001) crystallographic
orientation parallel to the component dendritic growth pattern or blade
stacking fault axis. Face-centered cubic (FCC) superalloy single crystals grown
in the (001) direction provide extremely good thermal fatigue resistance
relative to conventionally cast articles. Since these single crystal articles
have no grain boundaries, alloy design without grain boundary strengtheners,
such as carbon, boron and zirconium, is possible. As these elements are alloy
melting point depressants, their reduction from an alloy design provides a
greater potential for high temperature mechanical strength achievement since
more complete gamma prime solution and microstructural homogenization can be
achieved relative to directionally solidified (DS) columnar grain and conventionally
cast materials. Their reduction also makes possible a higher incipient melting
temperature.
These process benefits
are not necessarily realized unless a multi-faceted alloy design approach is
undertaken. Alloys must be designed to avoid tendency for casting defect
formation such as freckles, slivers, spurious grains and recrystallization.
Additionally, the alloys must provide an adequate heat treatment window
(numeric difference between an alloy's gamma prime solvus and incipient melting
point) to allow for nearly complete gamma prime solutioning. At the same time,
the alloy compositional balance should be designed to provide an adequate blend
of engineering properties necessary for operation in gas turbine engines.
Selected properties generally considered important by gas turbine engine
designers include: elevated temperature creep-rupture strength,
thermo-mechanical fatigue resistance, impact resistance plus hot corrosion and
oxidation resistance.
An alloy designer can
attempt to improve one or two of these design properties by adjusting the
compositional balance of known superalloys. However, it is extremely difficult
to improve more than one or two of the design properties without significantly
or even severely compromising the remaining properties. The unique superalloy
of the present invention provides an excellent blend of the properties
necessary for use in producing single crystal articles for operation in gas
turbine engine hot sections.
SUMMARY OF THE
INVENTION
This invention relates
to a nickel-based superalloy comprising the following elements in percent by
weight: from about 5.0 to about 7.0 percent rhenium, from about 1.8 to about
4.0 percent chromium, from about 1.5 to about 9.0 percent cobalt, from about
7.0 to about 10.0 percent tantalum, from about 3.5 to about 7.5 percent
tungsten, from about 5.0 to about 7.0 percent aluminum, from about 0.1 to about
1.2 percent titanium, from about 0 to about 0.5 percent columbium, from about
0.25 to about 2.0 percent molybdenum, from about 0 to about 0.15 percent
hafnium, and the balance nickel plus incidental impurities, the superalloy
having a phasial stability number N.sub.v3B less than about 2. 10.
Advantageously, this
superalloy composition may be further comprised of (percentages are in weight
percent) from about 0 to about 0. 04 percent carbon, from about 0 to about 0.01
percent boron, from about 0 to about 0. 01 percent yttrium, from about 0 to
about 0.01 percent cerium and from about 0 to about 0.01 percent lanthanum.
Although incidental impurities should be kept to the least amount possible, the
superalloy can also be comprised of from about 0 to about 0.04 percent
manganese, from about 0 to about 0.05 percent silicon, from about 0 to about
0.01 percent zirconium, from about 0 to about 0.001 percent sulfur, and from
about 0 to about 0.10 percent vanadium. In all cases, the base element is
nickel. Furthermore, this superalloy can advantageously have a phasial
stability number N.sub.v3B less than about 1.85, and a chromium content of from
about 1.8 to about 3.0 percent, a rhenium content of from about 5. 5 to about
6.5 percent, and a cobalt content of from about 2.0 to about 5. 0 percent. This
invention provides a superalloy having an increased resistance to creep under
high stress, high temperature conditions, particularly up to about 1975° F.
Single crystal
articles can be suitably made from the superalloy of this invention. The
article can be a component for a turbine engine and, more particularly, the
component can be a gas turbine blade or gas turbine vane.
The superalloy
compositions of this invention have a critically balanced alloy chemistry which
results in a unique blend of desirable properties. These properties include:
excellent single crystal component castability, particularly for moderately
sized blade and vane components; adequate cast component solutionability;
excellent resistance to single crystal cast component recrystallization;
ultra-high creep-rupture strength to about 1975° F.; extremely good low cycle
fatigue strength; extremely good high cycle fatigue strength; high impact
strength; very good bare hot corrosion resistance; very good bare oxidation
resistance; and adequate microstructural stability, such as resistance to the
undesirable, brittle phases called topologically close-packed (TCP) phases.
Accordingly, it is an
object of the present to provide superalloy compositions and single crystal
articles made therefrom having a unique blend of desirable properties. It is a
further object of the present invention to provide superalloys and single
crystal articles made therefrom for use in advanced gas turbine engines under
high stress, high temperature conditions, such as up to about 1975° F. These
and other objects and advantages of the present invention will be apparent to
those skilled in the art upon reference to the following description of the
preferred embodiments.
BRIEF DESCRIPTION OF
THE DRAWINGS
FIG. 1 is a chart of
hot corrosion test results performed to 117 hours on one embodiment of the
alloy of this invention and on two prior art alloys;
FIG. 2 is a chart of
hot corrosion test results performed to 144 hours on another embodiment of the
alloy of this invention and on a prior art alloy.
DESCRIPTION OF THE
PREFERRED EMBODIMENTS
The nickel-based
superalloy of the present invention comprises the following elements in percent
by weight:
______________________________________
Rhenium about 5.0-7.0
Chromium about 1.8-4.0
Cobalt about 1.5-9.0
Tantalum about
7.0-10.0
Tungsten about 3.5-7.5
Aluminum about 5.0-7.0
Titanium about 0.1-1.2
Columbium about 0-0.5
Molybdenum about
0.25-2.0
Hafnium about 0-0.15
Nickel + Incidental
balance
Impurities
______________________________________
This superalloy
composition also has a phasial stability number N. sub. v3B less than about
2.10. Further, this invention has a critically balanced alloy chemistry which
results in a unique blend of desirable properties. These properties include
increased creep-rupture strength relative to prior art single crystal
superalloys, single crystal component castability, cast component
solutionability, single crystal component resistance to recrystallization,
fatigue strength, impact strength, bare hot corrosion resistance, bare
oxidation resistance, and microstructural stability, including resistance to
TCP phase formation under high stress, high temperature conditions,
Unlike prior
nickel-based superalloys known in the art, the superalloys of the present invention
have a low chromium, low cobalt and high rhenium content. The chromium is about
1.8-4.0% by weight. Advantageously, the chromium content is from 1.8% to 3.0%
by weight. This chromium content is significantly lower than that typically
found in prior art single crystal nickel-based superalloys. In the present
superalloy, chromium provides hot corrosion resistance, although it may also
assist with the alloy's oxidation capability. Tantalum and rhenium also assist
toward hot corrosion property attainment, and aluminum is present at sufficient
levels to provide adequate oxidation resistance, so that relatively low
addition of chromium is tolerable in this alloy. Besides lowering the alloy's
gamma prime solvus, chromium contributes to the formation of Cr, Re, W-rich TCP
phase and must be balanced accordingly in these compositions.
The cobalt content is
about 1.5-9.0% by weight. Advantageously, the cobalt content is from 2.0% to
5.0% by weight. This cobalt content is lower than that typically found in prior
art single crystal nickel-based superalloys. In the present superalloy, cobalt
assists in providing an appropriate heat treatment window since it has the
effect of lowering the alloy's gamma prime solvus while generally not affecting
its incipient melting point. Rhenium-containing alloys are generally designed
with much higher cobalt content than the present invention for the purpose of
imparting increased solid solubility and phasial stability. However, the
superalloys of the present invention unexpectedly show that much lower cobalt
contents are possible and desirable toward providing optimized phasial
stability, including control of TCP phase formation.
The rhenium content is
about 5.0-7.0% by weight and, advantageously, rhenium is present in an amount of
from 5.5% to 6.5% by weight. The amount of rhenium in the superalloy of the
present invention is significantly greater than the rhenium content of prior
art single crystal nickel-based superalloys. Furthermore, the superalloys of
this invention are generally designed with an increased level of refractory
element content, e.g., W+Re+Mo+Ta. The tungsten content is about 3.5-7. 5% by
weight and, advantageously, the amount of tungsten is from 3.5% to 6.5% by
weight. Tungsten is added since it is an effective solid solution strengthener
and it contributes to strengthening the gamma prime. Additionally, tungsten is
effective in raising the alloy's incipient melting temperature. The amount of
tungsten added to these superalloys is balanced with the amount of rhenium
added since they both contribute to, the formation of "freckle"
defects during the single crystal investment casting process. They also both
strongly effect the propensity for TCP phase formation.
Similar to tungsten,
rhenium is effective in raising the alloy's incipient melting point. However,
rhenium is a more effective strengthener than tungsten, molybdenum and tantalum
in terms of elevated temperature creep-rupture and, therefore, rhenium is added
appropriately. Additionally, rhenium has a positive influence on this alloy's
hot corrosion resistance. Moreover, rhenium partitions primarily to the gamma
matrix, and it is effective in slowing gamma prime particle growth during high
temperature, high stress conditions. Besides requiring the balancing of rhenium
with tungsten for castability reasons, W+Re must also be set at a level
consistent with minimizing TCP phase formation. In general, the TCP phases
which occur in such material are rich in chromium, tungsten, and rhenium
content, with rhenium being present in the greatest proportion. Thus, careful
Re/W ratio control is necessary in this alloy to control the propensity for TCP
phase formation.
The molybdenum content
is about 0.25-2.0% by weight. Advantageously, molybdenum is present in an
amount of from 0.25% to 1.5% by weight. Molybdenum is a good solid solution
strengthener, but it is not as effective as tungsten, rhenium and tantalum.
However, since the alloy's density is always a design consideration, and the
molybdenum atom is lighter than the other solid solution strengtheners, the
addition of molybdenum is a means of assisting control of the overall alloy
density in the compositions of this invention.
The tantalum content
is about 7.0-10.0% by weight and, advantageously, the tantalum content is from
8.0% to 10.0% by weight. Tantalum is a significant contributor to this alloy's
strength through means of solid solution strengthening and enhancement of gamma
prime particle strength (tantalum also partitions to the gamma prime phase). In
this alloy, tantalum is able to be utilized at relatively high concentration
since it does not contribute to TCP phase formation. Additionally, tantalum is
an attractive single crystal alloy additive in this composition since it
assists in preventing "freckle" defect formation during the single
crystal casting process. Tantalum is also beneficial in this composition since
it tends to raise this alloy's gamma prime solvus, and it is effective toward
promoting good alloy oxidation and hot corrosion resistance, along with
aluminide coating durability.
The aluminum content
is about 5.0-7.0% by weight. Furthermore, the amount of aluminum present in
this composition is advantageously from 5. 3% to 6.5% by weight. Aluminum and
titanium are the primary elements comprising the gamma prime phase. These
elements are added in this composition in a proportion and ratio consistent
with achieving adequate alloy castability, solution heat treatability, phasial
stability and high mechanical strength. Aluminum is also added to this alloy in
proportions sufficient to provide oxidation resistance.
The titanium content
is about 0.1-1.2% by weight. Advantageously, titanium is present in this
composition in an amount from 0.2% to 0.8% by weight. Titanium is generally
beneficial to the alloy's hot corrosion resistance, but it can have a negative
effect to oxidation resistance, alloy castability and alloy response to
solution heat treatment. Accordingly, the titanium content must be maintained
within the stated range of this composition.
The columbium content
is about 0-0.5% by weight and, advantageously, the columbium content is from 0
to 0.3% by weight. Columbium is a gamma prime forming element and it is an
effective strengthener in the nickel-based superalloys of this invention. Generally,
however, columbium is a detriment to alloy oxidation and hot corrosion
properties, so its addition to the composition of this invention is minimized.
Moreover, columbium is added to this invention's composition for the purpose of
gettering carbon, which can be chemi-sorbed into component surfaces during
non-optimized vacuum solution heat treatment procedures. Any carbon pick-up
will tend to form columbium carbide instead of titanium or tantalum carbide,
thereby preserving the greatest proportion of titanium and/or tantalum for
gamma prime and/or solid solution strengthening in this alloy.
The hafnium content is
about 0-0.15% by weight and, advantageously, hafnium is present in an amount
from 0.02 to 0.05% by weight. Hafnium is added in a small proportion to the
present composition in order to assist with coating adherence. Hafnium
generally partitions to the gamma prime phase.
The balance of this
invention's superalloy composition is comprised of nickel and small amounts of
incidental impurities. Generally, these incidental impurities are entrained
from the industrial process of production, and they should be kept to the least
amount possible in the composition so that they do not affect the advantageous
aspects of the superalloy. For example, these incidental impurities may include
up to about 0.04% by weight manganese, up to about 0.05% by weight silicon, up
to about 0.01% by weight zirconium, up to about 0. 001% by weight sulfur, and
up to about 0.10% by weight vanadium. Amounts of these impurities which exceed
the stated amounts could have an adverse effect upon the resulting alloy's
properties.
Additionally, the
superalloy may optionally contain about 0-0. 04% by weight carbon, about
0-0.01% by weight boron, about 0-0.01% by weight yttrium, about 0-0.01% by
weight cerium and about 0-0.01% by weight lanthanum.
Not only does the
superalloy of this invention have a composition within the above specified
ranges, but it also has a phasial stability number N.sub. v3B less than about
2.10. Advantageously, the phasial stability number N.sub. v3B is less than 1.85
and, preferably, the phasial stability number N.sub.v3B is less than 1.75. As
can be appreciated by those skilled in the art, N.sub.v3B is defined by the PWA
N-35 method of nickel-based alloy electron vacancy TCP phase control factor
calculation. This calculation is as follows:
EQUATION 1
Conversion for weight
percent to atomic percent: ##EQU1## where: Wi=weight percent of element i
Ai=atomic weight of element i
EQUATION 2
Calculation for the
amount of each element present in the continuous matrix phase:
______________________________________
Element Atomic amount
Rii remaining
______________________________________
Cr R.sub.Cr =
0.97P.sub.Cr-0.375P.sub.B-1.75P.sub.C
Ni
##STR1##
Ti, Al, B,
Ri = O
C, Ta, Cb, Hf
V Rv = 0.5P.sub.V
##STR2##
Mo
##STR3##
______________________________________
*Note:
weight percentage Re
is added to weight percentage W for the calculation
above.
EQUATION 3
Calculation of
N.sub.v3B using atomic factors from Equations 1 and 2 above: ##EQU2## where:
i=each individual element in turn. N.sub.i i=the atomic factor of each element
in matrix.
(N.sub.v) i=the
electron vacancy No. of each respective element.
This calculation is
exemplified in detail in a technical paper entitled "PHACOMP
Revisited", by H. J. Murphy, C. T. Sims and A. M. Beltran, published in
Volume 1 of International Symposium on Structural Stability in Superalloys
(1968), the disclosure which is incorporated by reference herein. As can be
appreciated by those skilled in the art, the phasial stability number for the
superalloys of this invention is critical and must be less than the stated
maximum to provide a stable microstructure and capability for the desired
properties under high temperature, high stress conditions. The phasial
stability number can be determined empirically, once the practitioner skilled
in the art is in possession of the present subject matter.
The superalloy of this
invention can be used to suitably make single crystal articles, such as
components for turbine engines. Preferably, this superalloy is utilized to make
a single crystal casting to be used under high stress, high temperature
conditions characterized by an increased resistance to creep under such
conditions, particularly high temperature conditions up to about 1975° F. While
this superalloy can be used for any purpose requiring high strength castings
incorporating a single crystal, its particular use is in the casting of single
crystal blades and vanes for gas turbine engines. This alloy possesses an
unusual resistance to component recrystallization during solution heat
treatment, which is considered an important alloy characteristic that is
necessary when producing advanced technology, multi-piece, cast bonded single
crystal airfoils. Additionally, this superalloy provides the alloy castability
characteristics believed necessary to produce conventional-process-cast,
moderately-sized turbine airfoils with intricate cooling passages.
While this
superalloy's primary use is in aircraft turbine engines, there are stationary
engine applications requiring the specialized high performance characteristics
of this alloy. This is particularly the case in turbine engines which require
performing characteristics with very restricted clearances, thereby materially
limiting the amount of permissible creep. Engines designed to develop high
performance characteristics are normally operated at higher component
temperatures and, therefore, the problem of creep is increased. Generally,
creep in excess of 1% is considered unacceptable in these cases. The creep
characteristics of known state of the art alloys have limited operating
temperatures and, thus, maximum performance capability. The superalloy of this
invention has an increased resistance to creep under high stress, high
temperature conditions, particularly up to 1975. degree. F.
The single crystal
components made from this invention's compositions can be produced by any of
the single crystal casting techniques known in the art. For example, single
crystal directional solidification processes can be utilized, such as the seed
crystal process and the choke process.
The single crystal
castings made from the superalloy of the present invention are advantageously
subjected to a high temperature aging heat treatment in order to optimize the
creep-rupture properties of these alloys. This invention's single crystal castings
can be aged at a temperature of from about 1950° F. to about 2125° F. for about
1 to about 20 hours. However, as can be appreciated by those skilled in the
art, the optimum aging temperature and time for aging depends on the precise
composition of the superalloy.
This invention
provides superalloy compositions having a unique blend of desirable properties.
These properties include: excellent single crystal component castability,
particularly for moderately sized blade and vane components; excellent cast
component solutionability; excellent resistance to single crystal cast
component recrystallization ultra-high creep-rupture strength to about 1975°
F.; extremely good low cycle fatigue strength; extremely good high cycle
fatigue strength; high impact strength; very good bare hot corrosion
resistance; very good bare oxidation resistance; and microstructural stability,
such as resistance to formation of the undesirable TCP phases. As noted above,
this superalloy has a precise composition with only small permissible
variations in any one element if the unique blend of properties is to be
maintained.
In order to more
clearly illustrate this invention and provide a comparison with representative
superalloys outside the claimed scope of the invention, the examples set forth
below are presented. The following examples are included as being illustrations
of the invention and its relation to other superalloys and articles, and should
not be construed as limiting the scope thereof.
EXAMPLES
A large number of
superalloy test materials were prepared to investigate the compositional
variations and ranges for the superalloys of the present invention. Some of the
alloy compositions tested and reported below fall outside the claimed scope of
the present invention, but are included for comparative purposes to assist in
the understanding of the invention. Representative alloy aim chemistries of
those materials tested are reported in Table I below.
TABLE 1 (See PDF)
Third generation
single crystal alloy development to investigate the compositional variations
for the superalloys of the present invention began with the definition and
evaluation of a series of experimental compositions. Increased creep-rupture
strength was the primary objective of the initial development effort, with
elemental balancing to provide a combination of useful engineering
characteristics following the definition of a base concept for increased
strength.
The initial materials
explored the utility of higher levels of refractory element and gamma prime
forming elements than are present in similar prior art compositions. As shown
in Table 1, the alloy chromium content was reduced to improve alloy stability.
Cobalt content, initially thought to be required for increased solid
solubility, could be significantly reduced. Refractory element content
(W+Re+Mo+Ta) was varied, while the summation of the primary gamma prime
partitioning elements (Ai+ Ti+Ta+Cb) was also varied. The alloy's Re content
was initially explored at conventional levels, but it was found that the Re
level had to be increased.
Standard N.sub.v3B
calculations were performed during the initial alloy design stage to assist
respective alloy phasial stability predictions, with that number varying from
one alloy composition to another.
Some of the alloys
were produced using production-type procedures. These alloys were vacuum
induction melted in the Cannon-Muskegon Corporation V-1 furnace, yielding
approximately 200-300 lbs, of bar product per alloy (see Table 2 below).
Quantities of each compositional iteration, as reported in Table 2, were made
into test bars and test blades by vacuum investment casting. Solution heat
treatment procedures were developed in the laboratory in 3" and 6"
diameter tube furnaces. Gamma prime aging treatments were also performed in the
laboratory.
TABLE 2 (See PDF)
All other specimens
reported in Table 1 above were produced by blending base alloy bar stock with
the virgin elemental additions necessary to achieve the desired composition.
The blending was done during test bar and blade manufacture. The base alloy bar
stock plus virgin additions were placed into the casting furnace melt crucible,
melted and the bath homogenized prior to pouring into an appropriate shell
mold. It is believed that good correlation between alloy aim chemistry and test
bar/blade chemistry was routinely achieved (see Table 3 below).
TABLE 3 (See PDF)
For the CMSX-10D
specimen (see Table 1), high quality virgin elemental additions were vacuum
melted and the refined material was poured into 2" diameter bars. In turn,
a quantity of the resulting bar was used to produce single crystal test
bar/blade specimens by investment casting.
It was apparent that
considerable variation in the investment casting process integrity may have
occurred during specimen manufacture since varying levels of test bar freckle
formation, secondary dendrite arm spacing and property attainment were
apparent. Derivative alloy response to solution treatment (reported in Table 4
below) varied, and was a function of both alloy composition and test specimen
quality.
Heat treatments
developed for the alloy iterations are reported in Table 4 below. Full gamma
prime solutioning was desired for each material, however, this objective was
not universally achieved. Primary gamma prime aging was performed to effect a
more desirable gamma prime particle size and distribution. Secondary gamma prime
aging was performed to effect precipitation of conventional matrix gamma prime
precipitates along with ultra-fine gamma prime precipitates located within the
matrix channels between the primary gamma prime particles for these specimens.
TABLE 4 (See PDF)
Fully heat treated
test bars were creep-rupture tested. The specimens were machined and low-stress
ground to ASTM standard proportional specimen dimension. The specimens were
creep-rupture tested at various condition of temperature and stress, according
to standard ASTM procedure.
A significant factor
of the CMSX-10A alloy design was the shift to higher Re content. At the same
time, W, Cr, Ta and other gamma prime strengtheners were balanced to provide
the desired alloy characteristics and properties. The alloys higher Re level
resulted in significantly improved creep-rupture strength throughout the entire
test regime, as indicated by the results reported in Table 5 below for the
CMSX-10A specimens.
TABLE 5 (See PDF)
Microstructural review
of the failed rupture specimens of this alloy revealed that TCP phase
precipitation occurred during the respective creep-rupture tests, particularly
those at 1900° F. and above. It became apparent that the N.sub.v3B phasial
stability number calculation would be an effective tool in predicting alloy
stability and, effectively, high temperature creep strength for the invention.
Wherein the CMSX-10A
specimen's N.sub.v3B number was 2.08, CMSX-10B was designed to the 2.02 level.
This was accomplished by the further reduction of alloy Cr content and similar
reduction to Co and W+Re level. W was reduced more than the Re in this specimen
since Re is more effective in the solid solution. Additionally, wherein some
loss in W contribution to the gamma prime could be anticipated, it was
sufficiently replaced by the modest increase to Ta content in this composition.
These changes resulted in the CMSX-10B alloy specimen exhibiting even more
improved creep strength at 1800° F. Table 6 reported below illustrates that
three specimens achieved an average life of 961 hours, with 1.0% creep
occurring at an average of 724 hours. However, it was observed that TCP phase
was present at higher temperature.
TABLE 6 (See PDF)
Only about 97-98%
gamma prime solutioning was achieved in the CMSX-10A and-10B materials (see
Table 4) which was insufficient for the purpose of optimizing alloy mechanical
properties and microstructural homogeneity. Attainment of a greater level of
gamma prime solutioning, therefore, became an equal priority in tandem with
improving microstructural stability at temperatures above 1900° F.
To confirm the
suspected composition of the TCP phase forming in the alloys, scanning electron
microscope (SEM) wavelength dispersive x-ray (WDX) microchemistry analyses of CMSX-10B
test bar contained needles was undertaken and compared to the alloys gamma and
gamma prime compositions. The results, reported in Table 7 below, confirm that
the needles were enriched in Cr, W and Re.
TABLE 7 (See PDF)
The calculated
N.sub.v3B numbers were 1.90 for CMSX-10C and 1. 95 for CMSX-10D. Re was
maintained at around 5% while W was further reduced to improve stability in
these specimens. Alloy Ta was increased since it did not participate in TCP
formation and the Ta/W ratio was effectively improved, which assisted with
alloy castability. Chromium was reduced in the-10C specimens but increased to
4.0% in the-10D specimens to provide an opportunity to determine the
suitability of the Cr levels from a hot corrosion standpoint. Co was reduced in
both materials, significantly in the-10D specimen, while Ai+ Ti level was also
reduced to assist in achieving more complete gamma prime solutioning.
Creep-rupture results for the two specimens are reported below in Tables 8 and
9, respectively. Even though the-10D alloy specimens were observed to exhibit
full gamma prime solutioning (as opposed to 99.-99.5% for CMSX-10C) the alloys
greater Cr content, which necessitated a lower Ai+ Ti level, effected lower
properties than attained with CMSX-10C. However, both materials exhibited
improved alloy stability and higher temperature properties, so that attempts to
balance the alloys low and high temperature creep response were favorable.
TABLE 8 (See PDF)
TABLE 9 (See PDF)
The acceptability of
the alloys' low Cr content was confirmed through extremely aggressive
short-term burner rig hot corrosion tests performed at 1650° F., 1% sulfur, 10
ppm sea salt condition. FIGS. 1 and 2 illustrate the results for tests
performed to 117 and 144 hours for the CMSX-10C and CMSX-10D specimens,
respectively. In both cases, the materials performed similar to MAR M 247-type
materials, thereby confirming the suitability of the low Cr alloy design
concept.
With the above-noted
results, another series of alloys, CMSX-10E,-10F,-10G,-10H,-10I,and-12A were
designed, produced and evaluated. The alloys explored Re level ranging
4.8-6.3%, 2.2-3.0% Cr level, 4.7-7. 6% Co level and the remainder balanced to
maintain castability, improve solutionability and improve phasial stability.
The N. sub.v3B number ranged between 1.81-1.89.
One of the series,
CMSX-10F, contained 0.02% C and 0.02% B. These additions were observed to
improve casting yield and may have assisted in providing more consistent
control of single crystal cast article orientation. However, the melting point
depressants, C and B, restricted the specimen's response to solution heat
treatment. The CMSX-10F creep-rupture properties are reported in Table 10
below.
TABLE 10 (See PDF)
The CMSX-10E, G, H and
I, plus CMSX-12A creep-rupture specimen results are reported below in Tables
11, 12, 13, 14, and 15, respectively. The results show a general improvement to
alloy creep-rupture strength above 1900° F. while maintaining extremely good
strength at lower temperatures.
TABLE 11 (See PDF)
TABLE 12 (See PDF)
TABLE 13 (See PDF)
TABLE 14 (See PDF)
TABLE 15 (See PDF)
Varying the primary
gamma prime aging treatment was explored with most of the development activity
concentrated on achieving optimized gamma prime size and distribution through
longer soak times at 1975. degree. F. (see Table 4) since higher temperature aging
treatments accelerated TCP phase formation during the aging cycle.
Ten to twenty-one hour
soak times at 1975° F. were successful since they provided average gamma prime
particles of about 0. 5 um dimension. However, it appeared that shorter primary
gamma prime aging time at higher temperature may be more practical, once more
stable microstructures were defined.
Microchemical SEM WDX
needle particle analyses was performed on a failed CMSX-10G creep-rupture
specimen. The specimen, tested at 1976. degree. F. /28.1 ksi condition,
exhibited needles in its microstructure. The results of the analysis are
reported in Table 16 below and indicate, again, that the needles formed in this
class of material are particularly rich in Re, but are also enrichened with Cr
and W.
TABLE 16 (See PDF)
A standardized test
for resistance to recrystallization was performed on a CMSX-10G test bar. The
test method and the results are reported in Table 17 below. The test results
indicate that the CMSX-10G specimen exhibited similar resistance to cast
process/solution treatment/bonding process recrystallization level in
comparison to CMSX-4 alloy.
TABLE 17
______________________________________
•Method:
A controlled level of
compressive stress is imparted on
the entire surface of
an as-cast test bar. The bar is
then solution heat
treated. Following solution treat-
ment, the bar is
sectioned and the transverse section
is observed
metallographically. Depth of recrystal-
lization measurements
are taken.
•Evaluation Standards:
Resistance to RX
Anticipated in Blade
Alloy Depth of RX
Castings
______________________________________
CMSX-4 .004" Very
Good
SX 792 Entire Bar Very
Poor
CMSX-10G .004"
Very Good
______________________________________
The
CMSX-10Ga-10Ia,-12B,-12C,-10J,-10Ri and-12Ri compositions were defined and
evaluated. No creep-rupture properties were generated for the CMSX-10J
specimen, although test bars were produced and a solution heat treatment
developed. Again, the inclusion of C and B in the-10J composition appeared to
have positive effect to single crystal test specimen yield. Additionally, the
lower levels of C and B than evaluated in CMSX-10F specimen, particularly lower
B, made the material more amenable to solution heat treatment. Ninety-eight to
ninety-nine percent gamma prime solutioning was achieved, as opposed to the
approximate 95% level typical of the CMSX-10F composition.
The CMSX-10Ga and-10Ia
alloys were designed with N.sub.v3B numbers of about 1.70. These alloy
specimens contain about 2.5% Cr, 3.3-4.0% Co, 5. 6-6. 0% Re, greater Ta/W
ratio, reduced Cb, and reduced Ai+Ti content. Such reduction to Cb+AI+Ti level
improved the solutioning characteristics of the materials (see Table 4), plus
assisted achievement of increased alloy stability. Both specimens exhibited
nearly full gamma prime solutioning.
The lowered N.sub.v3B
number continued to show effectiveness in providing better creep-rupture
capability at temperature greater than 1900° F., while maintaining extremely
good creep-strength at lower temperature. CMSX-10Ga test results from specimens
produced with improved casting process controls exhibited 700 hours or more
life with about 475 hours required to creep to 1.0% for 1800° F./36.0 ksi
condition. For higher temperature exposure, the specimen provided the improved
average life of about 500 hours at 2050° F./15.0 ksi condition and average 1.
0% creep deformation that occurred at about 250 hours, as indicated by the results
reported in Table 18 below.
TABLE 18 (See PDF)
1% creep strength is a
significant property. Limiting creep strains to 1.0% and 2.0% is extremely
important to gas turbine component design, since a component's usefulness is
generally measured by its resistance to creep to an approximate 1-2% level, not
its ultimate rupture strength. Many prior art alloys may exhibit attractive
rupture strength at the > 1900° F. level, however, they lack the level of
useful strength, i. e., creep strength to 2.0%, that this invention provides in
tandem with its far superior strength in test conditions below 1900° F.
The CMSX-10Ia
specimens also provided significantly increased creep strength at the higher
temperature extremes, but it did not appear to develop strength as good as the
CMSX-10Ga specimens in lower temperature tests, as indicated by the results in
Table 19 below.
TABLE 19 (See PDF)
Similarly, CMSX-12B,
with Nv3B at 1.80 level and additional chemistry balance as presented in Table
1, provided attractive creep strength at test condition greater than 1900° F.,
but did not perform quite as well as CMSX-10Ga in lower temperature tests, as
indicated by the results reported in Table 20 below.
TABLE 20 (See PDF)
Alloy composition has
the greatest effect on ultimate creep strength. However, some of the variation
experienced between alloy derivatives, and particularly for tests exhibiting
inconsistent results for a given alloy, can be caused by variation in casting
process condition. Casting process thermal gradient variation affects the cast
specimen dendrite arm spacing and ultimately, its response to solution heat
treatment and primary gamma prime aging treatment. It must, therefore, be
recognized that much of the creep-rupture results reported herein may have been
generated under non-optimized conditions and may be capable of improvement.
Improved casting process control may provide casting microstructures more
amenable to solution treatment and study to determine the appropriate primary
gamma prime aging treatment to provide the optimum gamma prime particle size,
which may result in further mechanical property enhancement.
The CMSX-12C
composition was designed to provide a calculated N. sub. v3B number of 1.70.
The alloy Cr content was designed at 2.8% and Co set at 3. 5% aim for this
alloy. An attractive Ta/W ratio was maintained while Re content was moderate at
5.8%. The alloy's Ai+Ti content was reduced, in comparison to the CMSX-12A and
CMSX-12B specimens, to provide improved alloy response to solution procedure.
Similar to the
CMSX-10Ga specimen, the CMSX-12C specimen exhibited an improved balance of
creep strength for test condition ranging 1800°-2100° F., as reported in Table
21 below.
TABLE 21 (See PDF)
With improved casting
process controls, this specimen has shown the following 1.0% longitudinal creep
strengths, as reported in Table 22 below.
TABLE 22
______________________________________
Time to 1.0%
Test Condition Strain
Hrs
______________________________________
1800° F./36.0 ksi
455
2100° F./12.0 ksi
309.3
______________________________________
Both alloys provide
similarly greater rupture strength than CMSX-4 alloy at condition to 1976° F.
Respective improvements to metal temperature capability are reported below in
Table 23.
TABLE 23
______________________________________
Approx.
Strength Advantage
Temperature Relative
to CMSX-4
______________________________________
1800° F.
40° F.
1850° F.
45° F.
1976° F.
43° F.
Based on 1.0% creep
strength,
the respective
approximate advantages are:
1800° F.
+46° F.
1850° F.
+60° F.
1976° F.
+55° F.
Note that the
comparison is not density corrected.
______________________________________
For test temperature
above 1976° F., the test results indicate that the CMSX-10Ga and CMSX-12C
specimens provided slightly lower strength than CMSX-4 alloy. The reduction in
strength advantage for these alloys is believed to be the result of TCP phase
formation. To address this issue, the alloys CMSX-10Gb, CMSX-10L, CMSX-12Ca,
and CMSX-12E, are designed with N.sub.v3B number as low as 1.50 (see Table 1)
to provide greater phasial stability, and effect much improved high temperature
creep-strength while maintaining most of the creep advantage demonstrated for
the 1800°-1976° F. test regime.
The CMSX-10Ri and
CMSX-12Ri compositions were designed at the 1. 91 and 1.92 N.sub.v3B levels,
respectively. These specimens were subjected to the most extensive testing of
properties. They were designed with 2. 65% and 3.4% respective Cr levels, with
other features remaining similar to the aforementioned alloy design
considerations. The properties generated for these two materials confirm the
overall invention design concept with the other material iterations able to
provide similar physical properties and relatively better blends of mechanical
properties.
The CMSX-10Ri and
CMSX-12Ri specimens' respective creep-rupture capabilities are reported below
in Tables 24 and 25.
TABLE 24 (See PDF)
TABLE 25(See PDF)
The method and results
of W and Re microstructural segregation investigation undertaken on fully
solutioned and partially solutioned CMSX-12Ri test specimens are reported in
Table 26 below. The investigation indicated that it is desirable to minimize
the amount of microstructure-contained residual eutectic and that for fully
solutioned specimens, the solution treatments developed for the invention are
successful in minimizing elemental segregation, which is important in attaining
optimized mechanical properties and microstructural stability.
TABLE 26
______________________________________
Alloy: CMSX-12 Ri
Test Specimen:
3/8" Diameter Solid Bar
Specimen Condition:
Fully Solutioned
Solutioned with 2.0%
Residual
Eutectic
Analyses Method:
Microprobe Analyses
+Random array of 350
points across a section at right angles
to the growth
direction
+Seven line scans, 51°
apart, 50 point analyses per line
The standard deviation
of the W and Re measurements
are the measure of
homogeneity
Results:
Standard
Deviations
CMSX-12 Ri W Re
______________________________________
Fully Solutioned 0.27
0.50
2% Residual Eutectic
0.36 0.90
Comparison 0.57 0.60
Typical CMSX-4
______________________________________
Table 27 below reports
results of burner rig hot corrosion test undertaken with the CMSX-12Ri
specimen. The measurements were taken at the bar location which experienced the
maximum attack, i.e., 1652° F. location, with the results showing the DS MAR M
002 alloy experienced approximately 20× more metal loss than the CMSX-12Ri
specimen. Visual observation showed a similar result for the CMSX-10Ri alloy.
Both CMSX-10Ri alloy and CMSX-12Ri alloy showed similar resistance to attack as
CMSX-4 alloy based on visual specimen review at 60, 90 and 120 hours.
TABLE 27 (See PDF)
Table 28 below reports
the results of cyclic oxidation tests undertaken at 2012° F. with March 1 gas
velocity. The CMSX-12Ri specimen was similarly resistant to oxidation attack at
2012° F., however, it was not as good as CMSX-4 at approximately 1886° F. exposure.
TABLE 28
______________________________________
Cyclic Oxidation Test
______________________________________
•15 Minute Cycles to
2012° F. (1100° C.),
Cooled to Ambient
Between Cycles
Mach 1 Gas Velocity
•89 Hours Total With
77 Hours at 2012° F.
CMSX-12 Ri
RESULT: at 1100° C.
Approx. 0.1 mm loss
per side
for every 300 cycles
CMSX-4
Approx. 0.1 mm loss
per side
for every 380 cycles
at 1030° C.
CMSX-12 Ri
Approx. .105 mm loss
per side
after 355 cycles
CMSX-4
Approx. .03 mm loss
per side
after 355 cycles
______________________________________
CMSX-12Ri elevated
temperature tensile data is reported in Table 29 below, while the results of
impact tests are reported in Table 30 below. The CMSX-12Ri elevated temperature
impact strength minimum is similar to CMSX-4 and its maximum occurring at 1742°
F., is better.
TABLE 29 (See PDF)
TABLE 30
______________________________________
IMPACT DATA
CMSX-12 Ri
0.35 Inch Diameter
Plain Cylindrical Specimens
Test Temperature, °F.
1382 1562 1742 1922
______________________________________
CMSX-12 Ri (1 only)
26 J 20 J 60 J 32 J
CMSX-4 (Ave. of 4)
26 J 21 J 42 J 45 J
______________________________________
Further Impact
Property Comparison
•CMSX2-Min. Impact
Strength 16.5 Joules
•SRR 99Min. Impact
Strength 20 Joules
The results of
CMSX-12Ri low cycle fatigue tests undertaken at 1382. degree. F. and 1742° F.
test conditions, with R=0, are reported in Table 31 below. The data indicates
that CMSX-12Ri performance is similar to CMSX-4 at 1382° F. condition, while
the alloy exhibits approximately 2.5 times the typical CMSX-4 life at 1742.
degree. F. condition.
TABLE 31 (See PDF)
Notched low cycle
fatigue test results show the CMSX-12Ri is 21/2 times better than CMSX-4 out to
about 3000 cycles, while at 50000 cycles and above, the alloy performance is
similar to CMSX-4. The results of these tests performed at 1382° F., K.sub.t
=2.0 and R=0 test condition, are reported in Table 32 below.
TABLE 32
______________________________________
NOTCHED LOW CYCLE
FATIGUE
CMSX-12Ri Alloy
1382° F. (750° C.),
K.sub.t = 2.0, R = 0
PEAK STRESS
ksi (MPa) CYCLES
______________________________________
113.13 (780) 4879
107.33 (740) 9784
95.72 (660) 28470
84.12 (580) 49810
81.22 (560)
78.32 (540) >
115,000
75.42 (520) >
115,000
______________________________________
•Results are 21/2
times better than CMSX4 out to about 30000 cycles
•Results are similar
to CMSX4 at 50000 cycles, and above.
High cycle fatigue
test results for the CMSX-10Ri alloy are reported in Table 33 below. For 1742°
F., 100 Hz, R=0 test condition, the alloy exhibited about 21/2 times the
typical CMSX-4 lives.
TABLE 33
______________________________________
HIGH CYCLE FATIGUE
CMSX-10Ri Alloy
1742° F. (950° C.),
100 Hz., R = 0
PEAK STRESS CYCLES
ksi (MPa) (N.sub.f)
______________________________________
81.22 (560) 15.2 ×
10.sup.6
92.82 (640) 3.59 ×
10.sup.6
104.43 (720) 0.6 ×
10.sup.6
______________________________________
*Lives are 21/2 times
better than CMSX4
The CMSX-10Ri and
CMSX-12Ri test data indicates that adequate hot corrosion and oxidation
resistance can be achieved with extremely low alloy chromium content.
Additionally, extremely good thermo-mechanical fatigue tensile and impact
strengths are apparent with the superalloys of this invention.
The results of alloy
specimen density measurements are reported in Table 34 below.
TABLE 34
______________________________________
SINGLE CRYSTAL ALLOY
DENSITY DATA
ALLOY DENSITY
Lbs/In.sup.3
______________________________________
CMSX-10A .324
CMSX-10B .324
CMSX-10C .325
CMSX-10D .325
CMSX-10E .325
CMSX-10F .323
CMSX-10G .322
CMSX-10Ga .322
CMSX-10H .324
CMSX-10I .322
CMSX-10Ia .322
CMSX-10J .327
CMSX-10Gb (10K) .329
CMSX-12A .323
CMSX-12B .325
CMSX-12C .326
CMSX-12Ca (12D) .326
CMSX-10Ri .326
CMSX-10 Ri .323
______________________________________
The alloys of this
invention are amenable to HIP processing. Specimens HIP treated as reported in
Table 35 below, showed nearly complete pore closure and absence from incipient
melting.
TABLE 35
______________________________________
HIP condition
______________________________________
1. Heat Specimens in
the HIP vessel to
2455° F. at mininum
Argon pressure
(approximately 1500
psi) and hold
for 4 hours while
maintaining
2455° F./1500 psi
condition.
2. While maintaining
the 2455° F.
operating temperature,
increase the
Argon pressure over 1
hour to 20
ksi. Soak specimens at
2455° F./20
ksi condition fo 4
hours.
______________________________________
While this invention
has been described with respect to particular embodiments thereof, it is
apparent that numerous other forms and modifications of this invention will be
obvious to those skilled in the art. The appended claims and this invention
generally should be construed to cover all such obvious forms and modifications
which are within the true spirit and scope of the present invention.
Claims: What is
claimed is:
1. A nickel-based
superalloy comprising the following elements in percent by weight:
______________________________________
Rhenium about 5.0-7.0
Chromium about 1.8-4.0
Cobalt about 1.5-9.0
Tantalum about
7.0-10.0
Tungsten about 3.5-7.5
Aluminum about 5.0-7.0
Titanium about 0.1-1.2
Columbium about 0-0.5
Molybdenum about
0.25-2.0
Hafnium about 0-0.15
Carbon (Incidental
Impurity)
about 0-0.04
Nickel + Other
Incidental
balance
Impurities
______________________________________
said superalloy having
a phasial stability number N v3B less than about 2.10.
2. The superalloy of
claim 1 further comprising the following elements in percent by weight:
______________________________________
Boron about 0-0.01
Yttrium about 0-0.01
Cerium about 0-0.01
Lanthanum about 0-0.01
______________________________________
3. The superalloy of
claim 1 further comprising the following elements in percent by weight:
______________________________________
Manganese about 0-0.04
Silicon about 0-0.05
Zirconium about 0-0.01
Sulfur about 0-0.001
Vanadium about 0-0.10
______________________________________
4. The superalloy of
claim 1 wherein said superalloy has a phasial stability number N v3B less than
1.85.
5. The superalloy of
claim 1 wherein said superalloy has a chromium content of from about 1.8 to
about 3.0 percent by weight.
6. The superalloy of
claim 1 wherein said superalloy has a rhenium content of from about 5.5 to
about 6.5 percent by weight.
7. The superalloy of
claim 1 wherein said superalloy has a cobalt content of from about 2.0 to about
5.0 percent by weight.
8. The superalloy of
claim 1 wherein said superalloy has an increased resistance to creep under high
stress, high temperature conditions up to about 1975° F.
9. A single crystal
article made from the superalloy of claim 1.
10. The single crystal
article of claim 9 wherein the article is a component for a turbine engine.
11. The article of
claim 10 wherein the component is a gas turbine blade or gas turbine vane.
12. A nickel-based
superalloy comprising the following elements in percent by weight:
______________________________________
Rhenium 5.5-6.5
Chromium 1.8-3.0
Cobalt 2.0-5.0
Tantalum 8.0-10.0
Tungsten 3.5-6.5
Aluminum 5.3-6.5
Titanium 0.2-0.8
Columbium 0-0.3
Molybdenum 0.25-1.5
Hafnium 0.02-0.05
Carbon (Incidental
Impurity)
about 0-0.04
Nickel + other balance
Incidental Impurities
______________________________________
said superalloy having
a phasial stability number N v3B less than about 1.75.
13. The superalloy of
claim 12 further comprising the following elements in percent by weight:
______________________________________
Boron 0-0.01
Yttrium 0-0.01
Cerium 0-0.01
Lanthanum
0-0.01
______________________________________
14. The superalloy of
claim 12 further comprising the following elements in percent by weight:
______________________________________
Manganese 0-0.04
Silicon 0-0.05
Zirconium 0-0.01
Sulfur 0-0.001
Vanadium 0-0.10
______________________________________
15. A single crystal
article made from the superalloy of claim 12.
16. A single crystal casting
to be used under high stress, high temperature conditions characterized by an
increased resistance to creep under such conditions, said casting being made
from a nickel-based superalloy comprising the following elements in percent by
weight:
______________________________________
Rhenium about 5.0-7.0
Chromium about 1.8-4.0
Cobalt about 1.5-9.0
Tantalum about
7.0-10.0
Tungsten about 3.5-7.5
Aluminum about 5.0-7.0
Titanium about 0.1-1.2
Columbium about 0-0.5
Molybdenum about
0.25-2.0
Hafnium about 0-0.15
Carbon (Incidental
Impurity)
about 0-0.04
Nickel + other balance
Incidental Impurities
______________________________________
______________________________________
Rhenium about 5.0-7.0
Chromium about 1.8-4.0
Cobalt about 1.5-9.0
Tantalum about
7.0-10.0
Tungsten about 3.5-7.5
Aluminum about 5.0-7.0
Titanium about 0.1-1.2
Columbium about 0-0.5
Molybdenum about
0.25-2.0
Hafnium about 0-0.15
Carbon (Incidental
Impurity)
about 0-0.04
Nickel + Other
Incidental
balance
Impurities
______________________________________
said superalloy having
a phasial stability number N v3B less than about 2.10.
17. The single crystal
casting of claim 16 wherein said superalloy further comprises the following
elements in percent by weight:
______________________________________
Boron about 0-0.01
Yttrium about 0-0.01
Cerium about 0-0.01
Lanthanum about 0-0.01
______________________________________
18. The single crystal
casting of claim 16 further comprising the following elements in percent by
weight:
______________________________________
Manganese about 0-0.04
Silicon about 0-0.05
Zirconium about 0-0.01
Sulfur about 0-0.001
Vanadium about 0-0.10
______________________________________
19. The single crystal
casting of claim 16 wherein said superalloy has a phasial stability number N
v3B less than 1.85.
20. The single crystal
casting of claim 16 wherein said superalloy has a chromium content of from
about 1.8 to about 3.0 percent by weight.
21. The single crystal
casting of claim 20 wherein said superalloy has a rhenium content of from about
5.5 to about 6.5 percent by weight.
22. The single crystal
casting of claim 21 wherein said superalloy has a cobalt content of from about
2.0 to about 5.0 percent by weight.
23. The single crystal
casting of claim 16 wherein said superalloy has an increased resistance to
creep under high stress, high temperature conditions up to about 1975° F.
24. The single crystal
casting of claim 16 wherein said casting has been aged at a temperature of from
about 1950° F. to about 2125° F. for about 1 to about 20 hours.
25. The single crystal
casting of claim 16 wherein said casting is a component for a turbine engine.
26. The single crystal
casting of claim 16 wherein said casting is a gas turbine blade.
27. The single crystal
casting of claim 16 wherein said casting is a gas turbine vane.
28. A single crystal
casting to be used under high stress, high temperature conditions up to about
1975° F. characterized by an increased resistance to creep under such
conditions, said casting being made from a nickel-based superalloy comprising
the following elements in percent by weight:
______________________________________
Rhenium about 5.5-6.5
Chromium about 1.8-3.0
Cobalt about 2.0-5.0
Tantalum about
8.0-10.0
Tungsten about 3.5-6.5
Aluminum about 5.3-6.5
Titanium about 0.2-0.8
Columbium about 0-0.3
Molybdenum about
0.25-1.5
Hafnium about
0.02-0.05
Carbon about 0-0.04
Boron about 0-0.01
Yttrium about 0-0.01
Cerium about 0-0.01
Lanthanum about 0-0.01
Manganese about 0-0.04
Silicon about 0-0.05
Zirconium about 0-0.01
Sulfur about 0-0.001
Vanadium about 0-0.10
Nickel balance
______________________________________
said superalloy having
a phasial stability number N v3B less than about 1.75.
29. The single crystal
casting of claim 28 wherein said casting has been aged at a temperature of from
1950° F. to 2125° F. for 1 to 20 hours.
30. The single crystal
casting of claim 28 wherein said casting is a component for a turbine engine.
31. The single crystal
casting of claim 28 wherein said casting is a gas turbine blade.
32. The single crystal
casting of claim 28 wherein said casting is a gas turbine vane.