U.S. patent application number 12/603152 was filed with the patent office on 2010-06-03 for nickel-containing alloys, method of manufacture thereof and articles derived therefrom.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Ganjiang Feng, Liang Jiang, Ji-Cheng Zhao.
Application Number | 20100135847 12/603152 |
Document ID | / |
Family ID | 43558150 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100135847 |
Kind Code |
A1 |
Jiang; Liang ; et
al. |
June 3, 2010 |
NICKEL-CONTAINING ALLOYS, METHOD OF MANUFACTURE THEREOF AND
ARTICLES DERIVED THEREFROM
Abstract
A nickel-containing alloy is disclosed. The alloy contains about
1.5 to about 4.5 weight percent aluminum; about 1.5 to about 4.5
weight percent titanium; about 0.8 to about 3 weight percent
niobium; about 14 to about 28 weight percent chromium; up to about
0.2 weight percent zirconium; about 10 to about 23 weight percent
cobalt; about 1 to about 3 weight percent tungsten; about 0.05 to
about 0.2 weight percent carbon, about 0.002 to about 0.012 weight
percent boron; and about 40 to about 70 weight percent nickel. The
atomic ratio of aluminum to titanium is at least about 0.5. The
alloy is also substantially free of tantalum. Related processes and
articles are also disclosed.
Inventors: |
Jiang; Liang; (Schenectady,
NY) ; Zhao; Ji-Cheng; (Dublin, OH) ; Feng;
Ganjiang; (Greenville, SC) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
ONE RESEARCH CIRCLE, PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
43558150 |
Appl. No.: |
12/603152 |
Filed: |
October 21, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10675367 |
Sep 30, 2003 |
|
|
|
12603152 |
|
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|
Current U.S.
Class: |
420/448 ;
148/555; 164/47; 420/450 |
Current CPC
Class: |
C22F 1/10 20130101; C22C
19/056 20130101; C22C 19/055 20130101 |
Class at
Publication: |
420/448 ; 164/47;
148/555; 420/450 |
International
Class: |
C22C 19/05 20060101
C22C019/05; B22D 23/00 20060101 B22D023/00; C22F 1/10 20060101
C22F001/10 |
Claims
1. A nickel-containing alloy comprising: about 1.5 to about 4.5
weight percent aluminum; about 1.5 to about 4.5 weight percent
titanium; about 0.8 to about 3 weight percent niobium; about 14 to
about 28 weight percent chromium; about 10 to about 23 weight
percent cobalt; about 1 to about 3 weight percent tungsten; about
0.05 to about 0.2 weight percent carbon; about 0.002 to about 0.012
weight percent boron; and about 40 to about 70 weight percent
nickel, wherein the atomic ratio of aluminum to titanium is greater
than about 1.0; and wherein the alloy is substantially free of
tantalum.
2. The nickel-containing alloy of claim 1, wherein a sum of the
amount of aluminum and titanium is about 2 to about 9 weight
percent of the nickel-containing alloy.
3. The nickel-containing alloy of claim 1, wherein the total amount
of the aluminum, titanium, and niobium is about 2 to about 13
weight percent, based on the weight of the alloy.
4. The nickel-containing alloy of claim 1, further comprising at
least one element selected from the group consisting of zirconium,
hafnium, rhenium, and ruthenium.
5. The nickel-containing alloy of claim 1, containing an eta phase
at a level of less than about 5 volume percent.
6. A nickel-containing alloy comprising: about 1.6 to about 1.8
weight percent aluminum; about 2.2 to about 2.4 weight percent
titanium; about 1.25 to 1.45 weight percent niobium; about 22 to
about 23 weight percent chromium; about 18.5 to about 19.5 weight
percent cobalt; about 0.08 to about 0.12 weight percent carbon;
about 1.9 to about 2.1 weight percent tungsten; about 0.002 to
about 0.006 weight percent boron; up to 0.01 weight percent
zirconium; with the remainder being nickel.
7. A method for manufacturing an article, comprising: (a) casting
an alloy into a mold, wherein the alloy comprises about 1.5 to
about 4.5 weight percent aluminum; about 2.1 to about 4.5 weight
percent titanium; about 0.8 to about 3 weight percent niobium;
about 14 to about 24 weight percent chromium; about 10 to about 23
weight percent cobalt; about 1 to about 3 weight percent of an
element selected from tungsten, rhenium, ruthenium, molybdenum, or
a combination thereof; about 0.05 to about 0.2 weight percent of
carbon; about 0.002 to about 0.012 weight percent of boron; and
about 40 to about 70 weight percent nickel; and (b) solidifying the
casting.
8. The method of claim 7, further comprising directionally
solidifying the casting.
9. The method of claim 8, wherein the casting is an equiaxed
casting.
10. The method of claim 7, further comprising heat-treating the
casting at a temperature of about 1095 to about 1200.degree. C.
11. The method of claim 10, wherein the heat-treatment is conducted
for a period of about 1 to about 4 hours.
12. The method of claim 7, further comprising solution
heat-treating the casting at a temperature of about 750 to about
850.degree. C.
13. A turbine component formed of a material comprising the alloy
of claim 1.
Description
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 10/675,367 (Liang Jiang et al), filed
Sep. 30, 2003. Ser. No. 10/675,367 is hereby incorporated herein by
reference, to the extent it is consistent with the content set
forth herein.
BACKGROUND
[0002] This disclosure is related to nickel-containing alloys,
methods of manufacture thereof and the articles derived therefrom.
High temperature alloys suitable for use in turbine nozzle and
airfoil applications generally display high temperature strength,
corrosion resistance, and properties such as castability and
weldability. Unfortunately, the process of optimizing one property
generally results in the reduction of another. The process of alloy
design generally results in compromises to achieve the best overall
mix of properties to satisfy the various requirements of component
design. In such a design process, rarely is any one property
maximized. Rather, through development of a balanced chemistry and
proper heat treatment, the best compromise among the desired
properties is achieved.
[0003] Cobalt containing alloys are found to be used for first
stage turbine nozzle applications despite their susceptibility to
thermal fatigue cracking. The reason for the acceptance of these
alloys is the ease with which they can be repair welded. However,
in latter stage nozzles, cobalt-based alloys have been found to be
creep limited to the point where downstream creep of the nozzles
can result in unacceptable reductions of turbine diaphragm
clearances. Although cobalt-based alloys with adequate creep
strength for these latter stage nozzle applications are available,
they do not possess the desired weldability characteristics. It is
therefore desirable to find other alloys that display creep
resistance, hot corrosion resistance, castability and weldability,
and that can be used in first stage and later stage turbine nozzle
applications.
BRIEF DESCRIPTION OF THE INVENTION
[0004] Disclosed herein is a nickel-containing alloy, comprising:
[0005] about 1.5 to about 4.5 weight percent aluminum; [0006] about
1.5 to about 4.5 weight percent titanium; [0007] about 0.8 to about
3 weight percent niobium; [0008] about 14 to about 28 weight
percent chromium; [0009] about 10 to about 23 weight percent
cobalt; [0010] about 1 to about 3 weight percent tungsten; [0011]
about 0.05 to about 0.2 weight percent carbon; [0012] about 0.002
to about 0.012 weight percent boron; and [0013] about 40 to about
70 weight percent nickel,
[0014] wherein the atomic ratio of aluminum to titanium is greater
than about 1.0; and
[0015] wherein the alloy is substantially free of tantalum.
[0016] Other embodiments of this invention are directed to methods
for manufacturing an article, comprising the casting of an alloy
with a composition such as that described herein; as well as
articles derived from these alloy compositions.
BRIEF DESCRIPTION OF THE DRAWING
[0017] FIG. 1 is graphical representation of the strain versus time
for two samples subjected to a constant stress of 15 ksi at a
temperature of 871.degree. C.
[0018] FIG. 2 is a graph depicting time-to-creep strain
relationships, for various alloy compositions.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0019] Disclosed herein is a nickel-containing alloy for use in
turbine applications. The nickel-containing alloy can
advantageously be used for both first stage and later stage turbine
nozzle applications as well as for use in large buckets for
turbines. The nickel-containing alloy comprises nickel, chromium,
cobalt, tungsten, aluminum, titanium, niobium, and other necessary
elements. In particular, the nickel-containing alloy has a unique
combination of concentrations of aluminum and titanium when
compared with other similar alloys. This results in a decrease or
elimination of the presence of undesirable phases such as the eta
(.eta.) phase, with an hexagonal crystal structure and a formula of
M.sub.3Ti, where M is nickel or an alloy of nickel, such as
nickel-cobalt, and the like. This decrease in the .eta. phase,
promotes an increase in the creep resistance, as well as renders
the alloy metallurgically stable at high temperatures, e.g., above
600.degree. C. In general, the eta phase is present at a level of
less than about 5 volume percent, and often, less than about 2
volume percent. In some preferred embodiments, the eta phase is
present at a level less than about 0.5 volume percent, e.g., the
alloy is substantially free of the eta phase.
[0020] The nickel-containing alloys for embodiments of this
invention also contain chromium, usually at a level of about 14 to
about 28 weight percent, and in preferred embodiments, about 14 to
about 24 weight percent. (More specific ranges are described
below).
[0021] Moreover, in preferred embodiments, the nickel alloys must
contain a core sub-group of elements--aluminum, titanium, and
niobium. As further described below, these elements, at the levels
described herein, provide some of the key strengthening mechanisms
for the composition, via the presence of the gamma-prime (.gamma.')
phase.
[0022] Optional metals that may be added to the nickel-containing
alloy are cobalt, carbon, zirconium, tungsten, boron, hafnium,
rhenium, ruthenium, molybdenum, or a combination comprising at
least one of the foregoing metals. In some preferred embodiments,
the alloys must contain at least zirconium, cobalt, and tungsten as
additional constituents, at the levels described herein. In other
preferred embodiments, the alloy compositions must contain boron
and carbon.
[0023] In one embodiment, the nickel-containing alloy comprises
aluminum and titanium in an amount of about 2 to about 9 weight
percent (wt. %), of the nickel-containing alloy. Within this range,
an amount of aluminum combined with titanium of greater than or
equal to about 2.5 wt. %, preferably greater than or equal to about
3.0 wt. %, and more preferably greater than or equal to about 4 wt.
% of the nickel-containing alloy may be used. Also desirable within
this range, are amounts of less than or equal to about 8.8,
preferably less than or equal to about 8.6, and more preferably
less than or equal to about 8.0 wt. % of the nickel-containing
alloy.
[0024] The aluminum content in the nickel-containing alloy is about
1.5 to about 4.5 wt. % of the nickel-containing alloy. Preferred
values of aluminum are greater than or equal to about 1.6, with
greater than or equal to about 1.7 more preferred. Preferred values
of aluminum are less than or equal to about 4.00, with less than or
equal to about 3 more preferred, and less than or equal to about
2.5 wt. % even more preferred. The titanium content in the
nickel-containing alloy is about 1.5 to about 4.5 wt. %, of the
nickel-containing alloy. Preferred values of titanium are greater
than or equal to about 1.65, with greater than or equal to about 2
more preferred, and greater than or equal to about 2.25 wt. % even
more preferred. Preferred values of titanium are less than or equal
to about 4, with less than or equal to about 3.5 more preferred,
and less than or equal to about 3 wt. % even more preferred. (The
relative amounts of aluminum and titanium are subject to the
proportions for these two elements, noted below).
[0025] In embodiments of this invention, the atomic ratio of
aluminum to titanium in the nickel-containing alloy must be at
least about 0.5. In some highly preferred embodiments, the atomic
ratio of aluminum to titanium is greater than about 1.0. An
aluminum to titanium atomic ratio within this range generally
permits the improvement of hot corrosion resistance, weldability,
and castability.
[0026] In another embodiment, it is desirable to control the sum of
aluminum, titanium, and niobium present in the nickel-containing
alloy to an amount of about 2 to about 13 weight percent, which is
effective to maintain the gamma-prime (.gamma.') phase. A preferred
value for the .gamma.' phase is 15 to 45 volume percent. Strength
in high temperature nickel-containing alloys generally derives from
several different mechanisms such as the precipitation
strengthening of a .gamma.' phase, solid solution strengthening and
carbide strengthening at grain boundaries. The (.gamma.') phase
consists of [Ni.sub.3(Al, Ti)]. Of these, precipitation
strengthening of the .gamma.' phase is the primary strengthening
mechanism for the nickel-containing alloys.
[0027] In order to attain the best compromise among alloy
properties for gas turbine nozzle and airfoil applications, the
content of the primary precipitation-strengthening elements, i.e.,
titanium, aluminum, and niobium is maintained in an amount of about
2 to about 13 wt. %, of the nickel-containing alloy. Within this
range, it is generally desirable to have an amount of titanium,
aluminum and niobium greater than or equal to about 4.35,
preferably greater than or equal to about 4.5, and more preferably
greater than or equal to about 4.75 wt. %, of the nickel-containing
alloy. Also desirable within this range, are amounts of less than
or equal to about 11.5, preferably less than or equal to about 11,
and more preferably less than or equal to about 10 wt. %, of the
nickel-containing alloy. By maintaining the amount of aluminum,
titanium and niobium within the aforementioned limits, a good
balance between creep resistance and weldability properties is
achieved. In addition, the levels of carbon and zirconium (when
present) have been carefully balanced and controlled to increase
the castability of the nickel-containing alloy.
[0028] In another embodiment, the nickel-containing alloy is devoid
of tantalum. While tantalum can be an important constituent in a
variety of nickel-based alloys, its presence in most embodiments of
the present invention is undesirable. The absence of tantalum can
result in very considerable improvements in creep strength, as
described in the examples of this disclosure. Moreover, in many
instances, the presence of tantalum, a relatively dense element,
can unnecessarily add to the weight of components made from the
alloy, and any excess weight in parts such as aircraft turbine
components can be problematic. Furthermore, tantalum, a relatively
expensive element, can also unnecessarily add to the cost of the
alloy composition.
[0029] For most embodiments of this invention, it is generally
desirable to have the niobium present in an amount of up to about 3
wt. %, of the nickel-containing alloy. Within this range, amounts
of less than or equal to about 2.5, preferably less than or equal
to about 2.0, and more preferably less than or equal to about 1.75
wt. % may be used. An exemplary value of niobium is about 1.35 wt.
% of the nickel-containing alloy.
[0030] Chromium is generally present in an amount of about 14 to
about 28 wt. %, of the nickel-containing alloy. Within this range,
it is sometimes (but not always) desirable to use the chromium in
amounts of greater than or equal to about 16, preferably greater
than or equal to about 17, and more preferably greater than or
equal to about 20 wt. %, of the nickel-containing alloy. Also
desirable within this range, is an amount of less than or equal to
about 27, preferably less than or equal to about 26, and more
preferably less than or equal to about 25 wt. %, of the
nickel-containing alloy. An exemplary amount of chromium is about
22 to about 23 wt. % of the total nickel-containing alloy.
[0031] In the described alloys, nickel is present in an amount of
about 40 to about 70 wt. % of the alloy. Within this range, it is
generally desirable to use the nickel in amounts of greater than or
equal to about 43, preferably greater than or equal to about 44,
and more preferably greater than or equal to about 46 wt. %, of the
nickel-containing alloy. Also desirable within this range, is an
amount of less than or equal to about 65, preferably less than or
equal to about 60, and more preferably less than or equal to about
55 wt. %, of the nickel-containing alloy. An exemplary amount of
nickel is about 45 to about 55 wt. % of the nickel-containing
alloy.
[0032] Cobalt is generally added in amounts of about 10 to about 24
wt. %, of the total nickel-containing alloy. Within this range,
amounts of greater than or equal to about 14, preferably greater
than or equal to about 15, and more preferably greater than or
equal to about 17 wt. %, of the nickel-containing alloy may be
used. Also desirable for use within this range are amounts of less
than or equal to about 23.5, preferably less than or equal to about
22.5, and more preferably less than or equal to about 21 wt. %, of
the total nickel-containing alloy. An exemplary amount of cobalt is
about 18.5 to about 19.5 wt. % of the total nickel-containing
alloy.
[0033] Carbon is generally added in amounts of less than 0.15 wt.
%. A preferred amount of carbon is 0.05 to about 0.2 wt %. The
carbon generally alloys with metals like titanium, tungsten and the
like to form monocarbides. Carbide formation in many instances is
important for improving grain boundary strength for embodiments of
this invention. Generally the titanium and/or the tungsten in the
monocarbide constitutes an amount of less than or equal to about 80
wt. % of the carbide phase. An exemplary amount of carbon is about
0.02 to about 0.15 wt. %, of the nickel-containing alloy.
[0034] Tungsten may be present in at levels of less than or equal
to about 3 wt. %, of the nickel-containing alloy. In some
instances, tungsten may be substituted by molybdenum, rhenium,
ruthenium, and the like. However, preferred embodiments often call
for the presence of tungsten itself. An exemplary amount of
tungsten is about 1.9 to about 2.1 wt. %, of the nickel-containing
alloy.
[0035] Boron may also be present in amounts of less than or equal
to about 0.025 wt. %, of the nickel-containing alloy. A preferred
amount of boron is about 0.002 to about 0.012 wt % of the
nickel-containing alloy. The boron generally reacts with the metals
in the nickel-containing alloy to form metal borides, which are
also important in some embodiments, for improving creep strength
and grain boundary strength. An exemplary amount of boron in the
nickel-containing alloy is about 0.002 to about 0.006 wt. %, of the
nickel-containing alloy.
[0036] Zirconium may also added in amounts of less than or equal to
about 0.2 wt. %, of the nickel-containing alloy. In some
embodiments, zirconium may be substituted with hafnium, if desired.
An exemplary amount of zirconium is about 0.01 wt. % to about 0.2
wt. % of the nickel-containing alloy.
[0037] The nickel-containing alloy may be processed in one of
several existing methods to form components for a gas turbine.
Examples of such components include rotating buckets (or blades),
non-rotating nozzles (or vanes), shrouds, combustors, and the like.
Preferred components for utilizing the nickel-containing alloy are
nozzles and buckets in gas turbines. The turbine components may be
formed by a variety of different processes such as, but not limited
to, powder metallurgy processes (e.g., sintering, hot pressing, hot
isostatic processing, hot vacuum compaction, and the like), ingot
casting followed by directional solidification, investment casting,
ingot casting followed by thermo-mechanical treatment,
near-net-shape casting, chemical vapor deposition, physical vapor
deposition, and the like. Preferred processes are ingot casting
followed by directional solidification and investment casting.
[0038] In one embodiment, in one manner of manufacturing a gas
turbine airfoil from the nickel-containing alloy, the components of
the nickel-containing alloy in the form of a powder, particulates,
or the like, are heated to a temperature of about 1350 to about
1750.degree. C., to melt the metal components.
[0039] The molten metal may then be poured into a mold in a casting
process to produce the desired shape. The casting process may
involve investment casting, ingot casting, or the like. Investment
casting is generally used to make parts that cannot be produced by
normal manufacturing techniques, such as turbine buckets that have
complex shapes, or turbine components that have to withstand high
temperatures. The mold is made by making a pattern using wax or
another material that can be melted away. This wax pattern is
dipped in refractory slurry, which coats the wax pattern and forms
a skin. This is dried and the process of dipping in the slurry and
drying is repeated until a robust thickness is achieved. After
this, the entire pattern is placed in an oven and the wax is melted
away. This leads to a mold that can be filled with the molten
nickel-containing alloy. Because the mold is formed around a
one-piece pattern, (which does not have to be pulled out from the
mold as in a traditional sand casting process), very intricate
parts and undercuts can be made. The wax pattern itself is made by
duplication, e.g., using a stereolithography or similar model which
has been fabricated using a computer solid model master.
[0040] Just before the pour, the mold is pre-heated to about
1000.degree. C. to remove any residues of wax, as well as to harden
the binder. The pour in the pre-heated mold also ensures that the
mold will fill completely. Pouring can be done using gravity,
pressure, inert gas, or vacuum conditions. The preferred embodiment
is to cast in vacuum. In another embodiment, ingot casting may be
used to form the turbine components. After the casting, the melt in
the mold is directionally solidified. Directional solidification
generally results in elongated grains in the direction of growth.
This can in turn result in higher creep strength for the airfoil,
as compared to an equiaxed cast. The cost of directional
solidification is sometimes higher than that of the equiaxed
casting. Depending on the specified requirements of the airfoil, it
can be either equiaxed or directional solidified. Following
directional and/or equiaxed solidification, the castings are air
cooled.
[0041] The castings comprising the nickel-containing alloy may then
optionally be subjected to different heat treatments in order to
optimize the strength, as well as to increase creep resistance. In
one embodiment, the casting is heat-treated at temperatures of
about 1095.degree. C. to about 1200.degree. C., to optimize the
yield strength and to reduce creep resistance. This heat treatment
is generally conducted for a time period of about 1 to about 6
hours. The preferred time period for the heat treatment is 4 hours.
In another embodiment, a heat-treatment cycle may be used to reduce
the creep resistance. As an example, the cycle may comprise heating
the casting to a temperature of about 1150.degree. C. for 4 hours,
followed by 1000.degree. C. for 6 hours, followed by 900.degree. C.
for 24 hours, and concluding with 700.degree. C. for 16 hours. This
heat treatment yields significantly improved values of tensile
strength and yield strength.
[0042] In yet another embodiment, the material is solution
heat-treated at a temperature of 750.degree. C. to about
850.degree. C. The solution treatment is generally carried out for
a time period of about 8 to about 36 hours. An exemplary time
period is about 24 hours. In general, the heat treatment and the
solution heat treatment is used to reduce the presence of any
undesirable phases such as the .eta. phase.
[0043] The casting may optionally be subjected to hot isostatic
pressing (HIP). The hot iso static pressing is generally preferred
for its ability to facilitate substantially reduced porosity and
reduced shrinkage in the production of such components. Generally,
process conditions for hot iso static pressing are chosen so as to
achieve consolidation, wherein the final composite has a porosity
less than or equal to about 10 volume percent, and more preferably,
less than or equal to about 2 volume percent, based on the total
volume of the composite article. This process generally involves
the application of high pressure and temperatures through the
medium of a pressurizing gas to remove internal porosity and voids,
thus increasing density and improving the properties of the
resultant composite. Hot isostatic pressing is generally conducted
at temperatures of greater than or equal to about 1000.degree. C.,
and in some instances, greater than or equal to about 1050.degree.
C. In some preferred embodiments, hot isostatic pressing is carried
out at a temperature greater than or equal to about 1150.degree. C.
The gas pressures utilized during hot iso static pressing are
generally greater than or equal to about 100 mega Pascals (MPa),
preferably greater than or equal to about 150 MPa, and more
preferably greater than or equal to about 200 MPa. Preferred gases
used for the process include, but are not limited to, argon,
nitrogen, helium, xenon and combinations comprising one of the
foregoing.
[0044] As stated above, the nickel-containing alloys may be
advantageously used for large airfoils in large turbines. The
reduction in the undesirable phases such as the .eta. phase and an
increase in the volume fraction of the .gamma.' phase to about 15
to 45 volume percent of the nickel-containing alloy, permit the
nickel-containing alloy to show improved creep resistance, high
temperature corrosion resistance and improved castability and
weldability.
[0045] The following examples, which are meant to be exemplary, not
limiting, illustrate compositions and methods of manufacturing some
of the various embodiments of the nickel-containing alloy using
various materials and apparatus.
EXAMPLES
Example 1
[0046] This example was undertaken to demonstrate the improvement
in properties of a nickel-containing alloy that does not contain
any tantalum versus a comparative nickel-containing alloy sample
containing tantalum. The samples having the comparative composition
as well as those embodying the present modification are shown in
Table 1. From the table, it may be seen that the comparative sample
(sample #1) has tantalum, whereas the other samples (samples #2-6)
do not possess tantalum.
[0047] The samples were prepared by taking the various components
of the samples shown in the Table 1 and heating them to a
temperature of 1550.degree. C., to create a melt which was then
cast. The samples were air cooled. The samples were annealed at
1150.degree. C. for 4 hours, and aged at 780.degree. C. for 24
hours. The samples were subjected to creep testing in a tensile
testing machine at a temperature of 1600.degree. F. (871.degree.
C.), under a stress of 15 kilograms per square inch (Ksi). The time
taken to reach a strain of 1% was measured and recorded as a
function of the sample's ability to display creep resistance. The
sample is a cylindrical dog-bone type standard creep sample with a
total length of 4 inches and the gauge diameter of about 0.25
inch.
TABLE-US-00001 TABLE 1 Carbon Chromium Cobalt Tungsten Niobium
Tantalum Titanium Aluminum Zirconium Boron Nickel Sample # (wt %)
(wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt
%) Comparative 0.1 22.5 19 2 0.8 1 2.3 1.2 0.01 0.004 51.05 sample
#1 #2 0.1 22.5 19 2 1.35 0 2.3 1.7 0.01 0.004 51.03 #3 0.1 22.5 19
2 1.35 0 1.6 1.6 0.01 0.004 51.83 #4 0.1 22.5 19 2 1.35 0 1.95 1.4
0.01 0.004 51.68 #5 0.1 22.5 19 2 1.64 0 1.77 1.51 0.01 0.004
51.46
[0048] The results of the creep tests are shown in FIG. 1, where
the time taken to reach a strain of about 0.5% and 1% is compared
for both samples. From the figure, it may be seen that there is a
200% improvement in creep displayed by the samples that are devoid
of tantalum over the comparative sample, which as noted above, has
tantalum. Similarly at a 1% strain, the sample that is devoid of
tantalum shows a 220% improvement in creep over the comparative
composition.
[0049] A metallographic and image analysis performed on Samples
#2-6 shows that each of them had about the same amount of the
.gamma.' phase, with very little of the undesirable .eta.
phase.
[0050] From the above example, it may be seen that the
nickel-containing alloy that does not contain tantalum displays
superior creep resistance properties over those that do, and hence
may be advantageously used in high temperature applications such as
in gas turbines and the like. The turbines comprising the
nickel-containing alloys may be used in aircraft and spacecraft,
land based power generation systems and craft that travel on and in
water such as ships, submarines, barges, and the like.
Example 2
[0051] This example demonstrates advantages of several embodiments
of the present invention. Three samples were prepared by combining
the listed components (Table 2) in the melt, at temperatures in the
range of about 2700.degree. F. (1482.degree. C.) to 2800.degree. F.
(1538.degree. C.). The molten alloys were then cast in a suitable
ceramic mold, by a conventional investment casting technique.
[0052] With reference to Table 2, below, compositions for Samples
A, B, and C are provided, in weight percentages (and the
aluminum/titanium ratio is listed, in atomic percent). (Sample A
was a commercial alloy)
TABLE-US-00002 TABLE 2 Al/Ti Sample Atomic (wt %) Ni Co Cr Mo.sup.a
W Al Ti Nb Ta Hf C Fe TOTAL Ratio A Balance* 20 20 5.8 0 0.5 2.2 0
0 0 0.1 0.7 99.30** 0.40 B Balance* 19 22.5 <0.2 2 1.2 2.3 1.35
0 0 0.1 0 99.60** 0.93 C Balance* 19 22.5 <0.2 2 1.7 2.3 1.35 0
0 0.1 0 100.20** 1.30 .sup.aIn Samples B and C, molybdenum is at
impurity levels. *Nickel level approximately 50-52 wt %
**Approximate total
[0053] Sample A is outside the scope of the present invention,
based on several factors. For example, Sample A did not contain any
tungsten or niobium. Moreover, sample A contained an
aluminum/titanium ratio (atomic) of less than 1. As described
herein, the Al/Ti ratio is a key parameter, generally independent
of the other differences in constituents, shown in Table 2, e.g.,
the differences in molybdenum and tungsten levels. Sample B is
within the scope of some of the embodiments of the invention, e.g.,
where the Al/Ti ratio must be at least about 0.5. However, it is
outside the scope of some of the preferred embodiments of the
invention, where the Al/Ti ratio must be greater than about 1.0.
Sample C was within the scope of embodiments of this invention.
[0054] Sample A had substantial amounts of the "eta" phase after
thermal exposure at elevated temperatures, which is undesirable for
our invention. Sample C was substantially free of the eta phase, in
the as-cast condition, and after thermal exposure at elevated
temperatures. (Sample A also had an insufficient level of gamma
prime (.gamma.')-forming elements, based on requirements for our
alloy compositions).
[0055] Test coupons were machined from cast and heat-treated alloys
via wire EDM (Electrical Discharge Machining), and
grinding-machining. The coupons had dimensions of approximately 5
inches (12.7 cm) in length, and 0.75 inch (1.9 cm) in diameter. The
coupons were tested for creep resistance properties, according to
the ASTM creep-testing standard, E139.
[0056] FIG. 2, attached, is a graph depicting time-to-1% creep
strain, at 1600.degree. F. (871.degree. C.) temperature, and at the
same stress level. As shown in the figure, Sample C exhibited a
large increase in creep resistance, as compared to Sample B, and a
very large increase, as compared to Sample A. The estimated
time-to-1% creep strain level for Sample A was 110 hours, and for
Sample B, 1450 hours. The estimated time-to-1% creep strain level
for Sample C was 3050 hours. (Sample C was also found to be
superior in creep resistance to other nickel-based commercial
alloys, e.g., those containing insufficient levels of
aluminum).
[0057] These results were also surprising for other reasons. For
example, a review of the respective compositions for samples A and
C shows that the level (total) of the precipitation-strengthening
elements, aluminum, titanium, and niobium, increased by 89%, for
Sample C, as compared to Sample A, yet the increase in creep
resistance was about 2800%.
[0058] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *