U.S. patent number 3,928,026 [Application Number 05/469,186] was granted by the patent office on 1975-12-23 for high temperature nicocraly coatings.
This patent grant is currently assigned to United Technologies Corporation. Invention is credited to Richard C. Elam, George W. Goward, Ralph J. Hecht.
United States Patent |
3,928,026 |
Hecht , et al. |
December 23, 1975 |
High temperature nicocraly coatings
Abstract
A highly ductile coating for the nickel- and cobalt-base
superalloys having long term elevated temperature oxidation-erosion
and sulfidation resistance and diffusional stability consists
essentially of, by weight, 11-48% Co, 10-40% Cr, 9-15% Al, 0.1-1.0%
reactive metal selected from the group consisting of yttrium,
scandium, thorium, lanthanum and the other rare earth elements,
balance essentially Ni, the nickel content being at least about
15%.
Inventors: |
Hecht; Ralph J. (West Palm
Beach, FL), Goward; George W. (North Haven, CT), Elam;
Richard C. (Manchester, CT) |
Assignee: |
United Technologies Corporation
(Hartford, CT)
|
Family
ID: |
23862796 |
Appl.
No.: |
05/469,186 |
Filed: |
May 13, 1974 |
Current U.S.
Class: |
428/615; 420/486;
428/668; 428/686; 416/241R; 420/588; 428/678; 428/926 |
Current CPC
Class: |
C22C
19/052 (20130101); C23C 30/00 (20130101); C23C
14/16 (20130101); C22C 19/07 (20130101); Y10S
428/926 (20130101); Y10T 428/12861 (20150115); Y10T
428/12931 (20150115); Y10T 428/12986 (20150115); Y10T
428/12493 (20150115) |
Current International
Class: |
C23C
30/00 (20060101); C22C 19/07 (20060101); C22C
19/05 (20060101); C23C 14/16 (20060101); C22C
030/00 () |
Field of
Search: |
;29/194
;75/134F,171 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Weise; E. L.
Attorney, Agent or Firm: Del Ponti; John D.
Government Interests
BACKGROUND OF THE INVENTION
The invention described in claims 5 and 6 was made in the course of
or under a contract or subcontract thereunder with the Department
of the Air Force.
Claims
What is claimed is:
1. A coating composition for the nickel-base and cobalt-base alloys
which consists essentially of, by weight, 11-48% cobalt, 10-40%
chromium, 9-15% aluminum, 0.01-1.0% of a reactive metal selected
from the group consisting of yttrium, scandium, thorium, lanthanum
and other rare earth elements balance essentially nickel, the
nickel content being at least about 15%.
2. A coating composition for the nickel-base and cobalt-base alloys
which consist essentially of, by weight, 15-40% cobalt, 12-30%
chromium, 10-15% aluminum, 0.01-1.0% yttrium, balance essentially
nickel, the nickel content being at least about 15%.
3. A coating composition for the nickel-base and cobalt-base alloys
which consists essentially of, by weight, 25-40% cobalt, 14-22%
chromium, 13-15% aluminum, 0.01-1.0% yttrium, balance essentially
nickel.
4. A coating composition for the nickel-base and cobalt-base alloys
which consists essentially of, by weight, 15-35% cobalt, 14-22%
chromium, 10-13% aluminum, 0.01-1.0% yttrium, balance essentially
nickel.
5. A coating composition for the nickel-base and cobalt-base alloys
which consists essentially of, by weight, 32.5% cobalt, 20%
chromium, 12% aluminum, 0.5% yttrium, balance essentially
nickel.
6. A coating composition for the nickel-base and cobalt-base alloys
which consists essentially of, by weight, 20% nickel, 20% chromium,
12% aluminum, 0.5% yttrium, balance essentially cobalt.
7. A gas turbine engine component comprising a nickel-base or
cobalt-base superalloy coated to a thickness of at least about
0.003 inch with a coating consisting essentially of, by weight,
11-48% cobalt, 10-40% chromium, 9-15% aluminum, 0.01-1.0% of a
reactive metal selected from the group consisting of yttrium,
scandium, thorium and other rare earth elements, balance
essentially nickel, the nickel content being at least about
15%.
8. A gas turbine engine component comprising a nickel-base or
cobalt-base superalloy coated to a thickness of at least about
0.003 inch with a coating consisting essentially of, by weight,
15-40% cobalt, 12-30% chromium, 10-15% aluminum, 0.01-1.0% yttrium,
balance essentially nickel, the nickel content being at least about
15%.
9. A gas turbine engine component comprising a nickel-base or
cobalt-base superalloy coated to a thickness of at least about
0.003 inch with a coating consisting essentially of, by weight
25-40% cobalt, 14-22% chromium, 13-15% aluminum, 0.01-1.0% yttrium,
balance essentially nickel.
10. A gas turbine engine component comprising a nickel-base or
cobalt-base superalloy coated to a thickness of at least about
0.003 inch with a coating consisting essentially of, by weight,
15-35% cobalt, 14-22% chromium, 10-13% aluminum, 0.01-1.0 yttrium,
balance essentially nickel.
Description
The present invention relates to coatings and coated articles and
more particularly to coatings for the nickel- and cobalt-base
superalloys having high ductility while retaining desirable
stability and elevated temperature oxidation and hot corrosion
resistance.
Design trends for advanced gas turbine engines are toward ever
increasing turbine inlet temperatures, and the demands on turbine
materials have increased to the extent where contemporary aluminide
coating systems can be the life limiting component of alloy-coating
composites. Coatings are prone to failure by a variety of
mechanisms. Aluminide coatings can be, for example, a source of
fracture initiation in fatigue. Coating ductility has been found to
be an important determinant in fatigue life since at relatively low
temperatures aluminide coatings tend to crack in a brittle manner
at low strains in the tensile portions of the fatigue cycle.
Although various coatings, such as the CoCrAlY type coatings
described in the patent to Evans and Elam U.S. Pat. No. 3,676,085,
the NiCrAlY type coatings described in the patent to Goward, Boone
and Pettit U.S. Pat. No. 3,754,903 and the FeCrAlY type coatings
described in the patent to Talboom and Grafwallner U.S. Pat. No.
3,542,530 have in the past provided significant improvements in the
lifetimes of the superalloys, further improvements are, of course,
desirable. In particular, an improved coating having properties
comparable to the conventional coating alloys together with
significantly improved ductility would be desirable and useful.
Such an improved coating is found in the
nickel-cobalt-chromium-aluminum-yttrium system as described
herein.
SUMMARY OF THE INVENTION
In brief, the present invention relates to a
nickel-cobalt-chromium-aluminum-yttrium coating alloy having
greatly improved ductility as well as other properties which
together render it eminently suitable for use in gas turbine engine
hardware and other rigorous environments. The invention more
particularly relates to a high ductility coating alloy which
possesses both oxidation-erosion and sulfidation resistance and
which consists of a particular combination of nickel, cobalt,
chromium, aluminum and a reactive metal selected from the group
consisting of yttrium, scandium, thorium, lanthanum and the other
rare earth elements. The invention contemplates a coating
composition consisting essentially of, by weight, 11-48% cobalt,
10-40% chromium, 9-15% aluminum, 0.01-1.0% of a reactive metal
selected from the group consisting of yttrium, scandium, thorium,
lanthanum and other rare earth elements, balance essentially
nickel, the nickel content being at least about 15%.
Advantageously, the coating composition consists essentially of, by
weight, about 15-40% cobalt, 12-30% chromium, 10-15% aluminum,
0.01-1.0% yttrium, balance essentially nickel, the nickel content
being at least about 15%.
In one preferred embodiment, the coating composition consists
essentially of, by weight, about 25-40% cobalt, 14-22% chromium,
13-15% aluminum, 0.01-1.0% yttrium, balance essentially nickel.
In another preferred embodiment, the coating composition consists
essentially of, by weight, about 15-35% cobalt, 14-22% chromium,
10-13% aluminum, 0.01-1.0% yttrium, balance essentially nickel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph which dramatically illustrates the ductility
behavior of various nickel-cobalt-chromium-aluminum-yttrium coating
alloys as compared to representative CoCrAlY and NiCrAlY coating
alloys.
FIG. 2 is a graph showing ductility as a function of temperature of
some NiCoCrAlY coating alloys as compared to representative CoCrAlY
and NiCrAlY coating alloys.
FIG. 3 is a graph illustrating the diffusional stability of various
nickel-cobalt-chromium-aluminum-yttrium coating alloys as compared
to representative CoCrAlY and NiCrAlY coating alloys.
FIG. 4 is a graph illustrating the oxidation characteristics of
various nickel-cobalt-chromium-aluminum-yttrium coating alloys as
compared to representative CoCrAlY and NiCrAlY coating alloys.
FIG. 5 is a graph illustrating the sulfidation characteristics of
various nickel-cobalt-chromium-aluminum-yttrium coating alloys as
compared to representative CoCrAlY and NiCrAlY coating alloys.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the description which follows, reference will be made to various
of the conventional or contemporary nickel-base and cobalt-base
superalloys. Representative of alloys of this nature are those
identified in the industry as follows:
NOMINAL COMPOSITION ALLOY DESIGNATION (Percent by weight)
______________________________________ B-1900 8 Cr, 10 Co, 1 Ti, 6
Al, 6 Mo, .11 C, 4.3 Ta, .15 B, .07 Zr, balance Ni MAR-M302 21.5
Cr, 10 W, 9 Ta, .85 C, .25 Zr, 1 Fe, balance Co TD Cobalt Alloy 20
Ni, 18 Cr, 2 ThO.sub.2, balance Co TD Cobalt Alloy 20 Ni, 30 Cr, 3
ThO.sub.2, balance Co IN 100 10 Cr, 15 Co, 4.5 Ti, 5.5 Al, 3 Mo,
.17 C, .75 V, .075 Zr, .015 B, balance Ni MAR-M200 9 Cr, 10 Co, 2
Ti, 5 Al, 12.5 W, .15 C, 1 Nb, .05 Zr, .015 B, balance Ni WI 52 21
Cr, 1.75 Fe, 11 W, 2(Nb + Ta), .45 C, balance Co Udimet 700 15 Cr,
18.5 Co, 3.3 Ti, 4.3 Al, 5 Mo, .07 C, .03 B, balance Ni
______________________________________
It will be appreciated that while the superalloys including those
which are directionally solidified, taken as a class, are generally
oxidation resistant, it is a necessary and usual practice to coat
certain of the components formed therefrom in order to improve
their oxidation, sulfidation, erosion and thermal shock resistance
and thus extend their operating lives in advanced gas turbine
engines.
As noted hereinbefore, the CoCrAlY and NiCrAlY coatings have
provided significant improvements in the lifetimes of the
superalloys. However, it was found that NiCrAlY coatings, while
providing extremely high oxidation resistance and diffusional
stability required improvement in sulfidation resistance and that
CoCrAlY coatings, while providing extremely high sulfidation
resistance required improvement in oxidation resistance and
diffusional stability. In an effort to develop a better combination
of properties, a variety of overlay coatings was evaluated. It was
found that coating alloys of a composition, by weight, of 11-48%
cobalt, 10-40% chromium, 9-15% aluminum, 0.01-1.0% reactive metal
selected from the group consisting of yttrium, scandium, thorium,
lanthanum and the other rare earth elements, balance essentially
nickel, the nickel content being at least about 15%, preferably
15-40% cobalt, 12-30% chromium, 10-15% aluminum, 0.01-1.0% yttrium,
balance essentially nickel, the nickel content being at least about
15%, and most preferably (1) 25-40% Co, 14-22% Cr, 13-15% Al,
0.01-1.0% Y, balance essentially Ni and (2) 15-35% Co, 14-22% Cr,
10-13% Al, 0.01-1.0% Y, balance essentially Ni dramatically and
unexpectedly gave an increase in ductility while providing a
satisfactory and adjustable balance of oxidation and hot corrosion
resistance as well as acceptably low interdiffusional
characteristics. While it had been known that certain of the useful
NiCrAlY coatings exhibited a ductility higher than certain of the
useful CoCrAlY coatings and it had been surmised therefore that a
substitution of some nickel for the cobalt in the CoCrAlY
composition might improve ductility, it was surprising and
unexpected that the nickel-cobalt-chromium-aluminum-yttrium system
as defined above would provide a ductility improvement which was
markedly superior to either the NiCrAlY or CoCrAlY.
While not completely understood at the present time, it appears
that there is a correlation between coating ductility and the
phases present. More specifically, chemistry changes which increase
the amount and continuity of the (Ni, Co) solid solution phase,
.gamma., tend to increase coating ductility while chemistry changes
which increase the amount and continuity of the (Ni, Co) Al,
.beta., Ni.sub.3 Al, .gamma.', and Cr, .alpha., tend to decrease
ductility. Correlation of coating microstructure with coating
chemistry indicates that, in the
nickel-cobalt-chromium-aluminum-yttrium system herein described,
desirable .gamma. - .beta. microstructures are obtained at a higher
aluminum content, the increased stability of the .gamma. - .beta.
microstructure caused by cobalt additions to NiCrAlY being the
result of a significant reduction of the amount of .gamma.'
(Ni.sub.3 Al) and .alpha.(chromium) phases which are precipitated
at lower temperatures.
Those skilled in the art will recognize that certain other elements
are known to be compatible with the basic chemistry of the present
alloys. Accordingly, other elements such as tantalum or hafnium may
be advantageously added to the alloy as required in certain
applications for modification of the mechanical, diffusional or hot
corrosion characteristics of the coating.
In coating the nickel-base and cobalt-base turbine blades and vanes
the surfaces to be coated are first thoroughly cleaned free of all
dirt, grease and other objectional foreign matter followed by
conditioning by abrasive blasting. The coating is achieved by vapor
deposition from a suitably heated molten pool of the coating
material held in a vacuum chamber at 10.sup.-.sup.4 torr or better.
The ingot melted and evaporated by electron beam heating has
essentially the same chemistry as that of the desired finished
coating.
Parts are preferably preheated to 1750.degree.F .+-. 50.degree. for
5 to 6 minutes before deposition is initiated and this temperature
is maintained throughout the coating operation. Deposition time
varies somewhat but is controlled to obtain the preferred coating
thickness of 0.003-0.005 inch. Subsequent cooling to below
1000.degree.F is accomplished in a nonoxidizing atmosphere.
Following the coating step, the parts may be heat treated for 1
hour at 1900.degree.F .+-. 25.degree. in vacuum to more fully bond
the coating to the substrate and provide for easier peening.
The coated articles may be dry glass bead peened using 0.007-0.011
inch diameter beads with an intensity equivalent to 19 N. In
general, the peening is conducted in accordance with the provisions
of the processing specification AMS 2430. The parts may then be
heated to 1975.degree.F .+-. 25.degree. in dry argon, dry hydrogen
or vacuum; held at heat for 4 hours; and cooled in the protective
atmosphere at a rate equivalent to air cooling. Blades and vanes so
processed exhibit a coating thickness, excluding the diffused zone
of 0.003-0.005 inch.
Of course, it will be recognized that other methods for applying
the coatings may be practiced, such as sputtering, ion plating or
plasma spraying, without departing from the intent of the present
invention.
Referring to FIG. 1, a graph is shown of the unexpected ductility
behavior of various nickel-cobalt-chromium-aluminum-yttrium coating
alloys as compared to representative CoCrAlY and NiCrAlY coating
alloys. The results shown therein were obtained by measuring strain
to fracture of coatings deposited on tensile specimens of
appropriate superalloys. In particular, Curve A is a plot showing
the effects of substituting various amounts of cobalt for nickel in
a NiCrAlY alloy having a nominal composition of, by weight,
Ni-19Cr-14Al-0.5Y while Curve B is a plot showing the effects of
substituting various amounts of cobalt for nickel in a NiCrAlY
alloy having a nominal composition of, by weight,
Ni-19Cr-12.5Al-0.5Y. As is evident from the drawing, dramatic
increases in ductility are obtained and it has been found, in
general, that NiCoCrAlY, or CoNiCrAlY as the case may be, coating
alloys have compositional ranges consisting essentially of, by
weight, 11-48% Co, 10-40% Cr, 9-15% Al, 0.1-1.0% reactive metal
selected from the group consisting of yttrium, scandium, thorium,
lanthanum and the other rare earth elements, balance essentially
nickel (at least about 15%), preferably 15-40% Co, 12-30% Cr,
10-15% Al, 0.1-1.0% Y, balance essentially Ni, the nickel content
being at least about 15%, will be effective in this regard. As will
be appreciated, with the higher Al content, as shown by Curve A, a
generally higher range of cobalt is preferred, a preferred coating
consisting essentially of 25-40% Co, 14-22% Cr, 13-15% Al,
0.01-1.0% Y, balance essentially Ni. With lower Al content, as
shown by Curve B, a generally lower range of cobalt is preferred, a
preferred coating consisting essentially of 15-35% Co, 14-22% Cr,
10-13% Al, 0.01-0.1% Y. In FIG. 2, ductility curves for selected
coatings show ductility as a function of temperature and indicate
the markedly superior tensile cracking resistance of the NiCoCrAlY
coatings.
In one series of thermomechanical fatigue tests, a directionally
solidified specimen substrate of MAR-M200 (with hafnium) was coated
with Ni-24Co-16Cr-12.5Al-40.3Y and run on a thermomechanical
fatigue machine which pushes and pulls the specimen in severe
fatigue and temperature cycles which simulate the
strain-temperature cycle of a cooled turbine blade. A number of
identical substrates were coated with Co-20Cr-12Al-0.5Y and another
number with a diffusion aluminide coating. Both the CoCrAlY and the
diffusion aluminide coated specimens failed after approximately
1,000 cycles or less on the thermomechanical fatigue machine
whereas the NiCoCrAlY coated specimen did not fail until after
1,925 cycles.
Referring to FIGS. 3-5, a comparison of the interdiffusional,
oxidation resistance and corrosion resistance properties of various
NiCoCrAlY alloy coatings is shown. In the drawings, 3-5 mil
coatings of NiCoCrAlY alloy consisting essentially of the indicated
amounts of cobalt, 18-21% Cr, 13-14% Al and 0.05-0.8% Y were vapor
deposited onto B-1900 substrates as well as onto directionally
solidified MAR-M200 (plus Hf) substrates (erosion bars). In FIG. 3,
the coated samples were aged 100 hours in air at the indicated
temperature. In FIG. 4, coated components were subjected to
2000.degree.F cyclic burner-rig oxidation tests (2000.degree.F, 29
minutes -- forced air cool, 1 minute, JP 5 fuel used) for up to
2,100 hours (2,030 hours hot time). In FIG. 5, coated components
were treated under cyclic conditions (1,750.degree.F, 3 minutes --
2000.degree.F, 2 minutes -- cool, 2 minutes) in a high velocity hot
gas stream derived from the combustion of JP 5 jet fuel, with 35
ppm salt/air added. As will be appreciated, the claimed NiCoCrAlY
coatings, while giving unexpectedly increased ductility also
simultaneously give adjustable and satisfactory degrees of
interdiffusion and oxidation and hot corrosion resistance.
For a clearer understanding of the invention and, in addition to
the data given in the drawings, other specific examples are set
forth below.
EXAMPLES 1-5
Five B-1900 Ni-base alloy erosion bars were coated with a 3-5 mil
thick alloy having a composition, consisting essentially of, by
weight, Co-20Ni-24Cr-15Al-0.75Y generally in accordance with the
procedures outlined above. The coated erosion bars were subjected
to 62.5 hours of vane cyclic sulfidation testing (1750.degree.F, 3
minutes -- 2050.degree.F, 2 minutes -- cool, 2 minutes with 35 ppm
artificial sea salt: air ingested after combustion and using JP 5
fuel). The coatings exhibited a specific life of from 21.1-24.4
hours/mil and were comparable to Fe-27Cr-13Al-.75Y coatings which
exhibited specific lifetimes of 22.2-27.9 hours/mil.
EXAMPLE 6
A 3.6 mil coating of Co-20Ni-24Cr-15Al-0.75Y was vapor deposited
onto a MAR-M302 Co-base alloy erosion bar and subjected to a
modified vane cyclic sulfidation test (1750.degree.F, 3 minutes --
2150.degree.F, 2 minutes -- cool, 2 minutes with 35 ppm artificial
sea salt: air ingested after combustion using JP 5 fuel) in order
to evaluate diffusional stability combined with the very high
temperature sulfidation. The coating had a failure time of 162
hours and a specific life of 45 hours/mil.
EXAMPLES 7-10
Two B-1900 Ni-base alloy erosion bars and two MAR-M302 Co-base
alloy erosion bars were coated with nominally three mil thick
coatings of Co-20Ni-24Cr-15Al-0.75Y as above and were subjected to
oxidation-erosion testing at 2000.degree.F until failure. The
B-1900 coatings failed at 263.2 and 153.7 hours while the MAR-M302
coatings both failed at 309.2 hours.
EXAMPLES 11-14
Coatings consisting essentially of Co-20Ni-20Cr-12Al-0.5Y,
Co-20Ni-16Cr-16Al-0.5Y, Ni-32.5Co-20Cr-12Al-0.5Y and
Co-20Cr-12Al-0.5Y were vapor deposited to thicknesses of 4.5-5.5
mil on Co-20Ni-18Cr-2ThO.sub.2 alloy airfoil specimens. All
coatings were essentially a two phase mixture of beta CoAl or
(CoNi)Al and gamma solid solution. The Co-20Ni-16Cr-16Al-0.5Y
coatings were predominantly beta with a small volume percent solid
solution gamma phase. The beta phase was continuous and represented
an undesirable structure because of its potential low
strain-to-crack characteristics. The Co-20Ni-20Cr-12Al-0.5Y and the
Co-20Cr-12Al-0.5Y coatings also exhibited a continuous beta type
structure but contained substantially more gamma. The
Ni-32.5Co-20Cr-12Al-0.5Y had a desired two phase plus gamma
structure with the gamma phase being the continuous matrix
phase.
These systems were exposed in a static air environment for 100
hours at 2000.degree.F, 2100.degree.F, 2200.degree.F and
2400.degree.F to evaluate stability and elemental interactions. The
resultant coating hardness after exposure, showed no detrimental
change in hardness or brittle layer formation. The
Co-20Ni-16Cr-16Al-0.5Y composition retained its continuous beta
structure during exposure and, due to its high crack susceptibility
was not tested further. The other coating systems retained or
transformed to a two phase mixture of beta in a continuous gamma
matrix. The best stability was obtained with the
Ni-32.5Co-20Cr-12Al-0.5Y coating.
Additional airfoil shaped specimens of Co-20Ni-18Cr-2ThO.sub.2 were
vapor deposition coated with Co-20Cr-12Al-0.5Y,
Co-20Ni-20Cr-12Al-0.5Y and Ni-32.5Co-20Cr-12Al-0.5Y to a thickness
of 4.5-5.5 mil using the same techniques and subjected to
1800.degree.F, 2000.degree.F, 2200.degree.F and 2400.degree.F
isothermal oxidation testing, to 2200.degree.F cyclic oxidation
testing (1750.degree.F, 3 minutes -- 2200.degree.F, 2 minutes --
cool, 2 minutes) and to 2200.degree.F cyclic hot corrosion testing
(1750.degree.F, 3 minutes - 2200.degree.F, 2 minutes - cool, 2
minutes). In all testing the airfoil samples were rotated at 1,750
rpm in a 400-500 feet/second gas stream of combusted JP 5 fuel. For
cyclic hot corrosion testing, the fuel was doped with 0.3% butyl
disulfide and synthetic sea salt solution was injected into the
combusted flame to yield a 3.5 ppm salt concentration in the burner
flame.
The 1800.degree.F and 2000.degree.F isothermal oxidation tests were
discontinued at 214 and 222 hours, respectively. All specimens
shows no visual signs of degradation. Based on metallographic
examination of specimens from the 1800.degree.F tests, coating
degradation was least for the Ni-32.5Co-20Cr-12Al-0.5Y. Also in the
2000.degree.F test, the NiCoCrAlY coating exhibited the least
degradation. The extent of degradation of the CoNiCrAlY and CoCrAlY
coatings was approximately equal.
The 2200.degree.F isothermal oxidation test was discontinued at 305
hours. Again the NiCoCrAlY coating showed the least degradation
while the CoCrAlY coating showed the most.
The 2400.degree.F isothermal oxidation test was run to coating
failure. Of the three coatings systems evaluated, the NiCoCrAlY
composition exhibited the longest life, 226 hours.
The cyclic oxidation and cyclic hot corrosion tests were
discontinued at 207 (59 hours hot time) and 204 (58 hours hot time)
hours, respectively. Coating failure had not occurred. Essentially
no difference was observed in the structure between the three
samples in the hot corrosion test. However, in the cyclic oxidation
test, the Ni-32.5Co-20Cr-12Al-0.5Y coating exhibited a far greater
amount of retained beta than either of the other two.
EXAMPLES 15-16
In a series of especially severe engine tests, first stage turbine
blades of the alloys indicated were coated as indicated in Table I
and run for 297 hours including 2,000 cycles (acceleration to full
takeoff power followed by holding for a period of time, rapid
deceleration to idle power and holding for a period of time). Over
100 cycles were with water injection (for thrust augmentation)
which imposed the severest possible thermal shock to the
coatings.
Table I
__________________________________________________________________________
Number Number with Percent with Alloy Coating Tested Cracked
Coatings Cracked Coatings
__________________________________________________________________________
B-1900 & Hf platinum aluminide 8 8 100 " rhodium aluminide 7 7
100 " high temperature pack aluminide 14 13 93 " low temperature
pack aluminide 56 56 100 "Ni-18Cr-14Al-0.5Y 4 4 100 "
Ni-12Cr-14Al-0.5Y 2 2 100 " Ni-18Cr-10Al-0.5Y 2 2 100
"Ni-12Cr-12Al-0.5Y 3 3 100 " Ni-18Cr-12Al-0.5Y 3 3 100
Directionally solidified MAR-M200 & Hf Ni-18Cr-12Al-0.5Y 7 5 71
B-1900 & Hf Ni-11Co-22Cr-11Al-0.06Y 5 0 0 "
Ni-20Co-16Cr-11.5Al-0.05Y 5 0 0
__________________________________________________________________________
While NiCrAlY had not previously cracked in other engine tests and
is therefore considered acceptable for most engine conditions, this
test was particularly severe and, as shown, only the NiCoCrAlY
coated blades were completely free of coating cracks. In similar
tests, CoCrAlY coatings consistently cracked.
It has been clearly established that the inventive alloy coatings
are effective not only in providing long term oxidation resistance,
corrosion resistance and stability but dramatically improved
ductility.
What has been set forth above is intended primarily as exemplary to
enable those skilled in the art to practice the invention and it
should therefore be understood that, within the scope of the
appended claims, the invention may be practiced in other ways than
as specifically described.
* * * * *