Note: Descriptions are shown in the official language in which they were submitted.
1339 1~3
BACKGROUND OF THE INVENTION
Gas turblne engine fuel efficiency typically
improves as turbine gas temperatures lncrease. Consequently,
air-cooled superalloy alrfolls have been developed to enhance
engine performance. Further improvements in turbine
performance and component durability can be obtained by the
use of protective thermal barrier coatings which lnsulate the
component and lnhibit oxidation and hot corrosion
~accelerated oxidation by fuel and air lmpurities such as
sulfur and salt) of the superalloy.
A partlcular type of ceramlc coatlng whlch ls
adherent to the metalllc component but yet resistant to
spalling during thermal cycling, is known as a columnar
gralned ceramlc thermal barrler coatlng. The ceramlc coating
layer has a columnar gralned mlcrostructure and is bonded to
the metal structure. Porosity between the individual columns
permits the columnar grained coating to expand and contract
without developing stresses sufficient to induce spalling.
In accordance with present practice, the metallic article to
be protected with the thermal barrier ceramic coating must
first be coated with an adherent MCrAlY (M = Ni, Co, Fe) bond
coating under layer which ls composltlonally tallored to grow
an adherent, predomlnately aluminum oxide scale, which
lnhlblts oxldation of the superalloy and provldes a
satlsfactory bonding surface for the ceramlc coating layer.
The cost of the MCrAlY underlayer, which is
normally applied by vapor deposition or other conventional
coatlng techniques, adds substantlally to the total cost of
-1- T
~ 73101-2
1339403
the thermal barrler coatlng system.
DISCUSSION OF THE PRIOR ART
My patents No. 4,321,311; 4,401,697 and 4,405,659
and those of Ullon and Ruckle, 4,321,310 and 4,405,660
dlsclose a thermal barrier coating system for a superalloy,
formed by first applying a 1 to 10 mll thlck MCrAlY vapor
deposltlon coating on the superalloy substrate followed by
the formatlon of a thln, thermally grown alumlnum oxlde
(alumina) layer to which the columnar graln ceramic thermal
barrier coatlng, e.g. zlrconla stablllzed wlth yttrla oxlde,
ls applied.
When uslng thermal barrler coatlngs of the type
descrlbed ln my patent No. 4,321,311, lt ls common practlce
to also coat lnternal alr-coollng passages with a dlffusion
aluminide coating to inhiblt oxldatlon at those locatlons.
Durlng appllcation of the aluminide coating to internal
surfaces, external component surfaces will also be coated
with a diffusion aluminide unless they are masked. Patent
No. 4,005,989 teaches that an aluminide coating layer under
an MCrAlY coating wlll lncrease coatlng durability.
Consequently, my patent No. 4,321,311 also teaches that an
MCrAlY coatlng over a diffusion aluminide coating will
provide an acceptable surface for subsequent application of a
columnar grained ceramlc thermal barrler coatlng layer.
Reissue Patent No. 31,339 discloses the application
of a MCrAlY bond coat to the superalloy substrate, by plasma
spraying, followed by application of an alumlnide coatlng on
the MCrAlY bond coating, followed by hot lsostatlc pressure
-- 2
73101-2
treatment of the assemblage. 13 3 9 4 ~ 3
None of the above references, however, suggest that
a columnar gralned ceramlc thermal barrler coatlng wlll
perform satlsfactorlly lf applled dlrectly to a dlffuslon
alumlnlde coatlng formed on the superalloy substrate.
DISCLOSURE OF THE INVENTION
In many lnstances, lower cost dlffuslon alumlnlde
coatlng6 are sufflclent to provlde requlred oxldlzatlon
reslstance to both lnternal and external surfaces of turblne
alrfolls. However, an lnsulative ceramlc layer on the
external alrfoll surfaces wlll further lmprove component
durablllty by reduclng both metal temperatures and the
magnltude of thermal stralns ln the metal. Alternatlvely,
the beneflt of a ceramlc layer can be utlllzed to lncrease
turblne performance by permlttlng coollng alr requlrements to
be reduced or by allowlng turblne lnlet temperatures to be
lncreased.
In my prlor patent No. 4,321,311, I utlllzed an
MCrAlY bond coatlng to both lnhlblt oxldlzatlon and provlde a
bondlng surface for the ceramlc layer. In most gas turblne
appllcatlons, however, lt ls not necessary to use an
expenslve MCrAlY coatlng to lnhlblt oxldlzatlon. It was
subsequently discovered that for superalloys it is
not necessary to utlllze an MCrAlY coatlng layer to develop
an adherent alumlna scale, whlch ls necessary for ceramlc
layer adheslon. In several lnstances, lt was dlscovered that
a lower cost dlffuslon aluminlde coatlng could thermally grow
an alumlna scale wlth sufflclent adheslon for a vlable
-- 3
73101-2
1339~3
bonding surface. Consequently, the cost of a thermal barrler
coatlng can be slgnlflcantly reduced ln those lnstances where
the diffuslon alumlnlde coatlng provldes an adequate bondlng
surface.
Alr-cooled turblne blades are typlcally alumlnlzed
on lnternal surfaces to lnhlblt oxldlzatlon. However, slnce
the dlffuslon alumlnlzing process ls multl-dlrectlonal, it
can provlde an alumlnlde layer on the entlre blade, l.e. both
lnterlor and exterlor, and ln many lnstances thls diffuslon
alumlnide coatlng provldes adequate oxldlzatlon reslstance.
In accordance wlth my present lnventlon, lt has been found
that the ceramlc thermal barrler coatlng may be applled
dlrectly to the dlffuslon alumlnlde coatlng, thus ellmlnatlng
the expenslve MCrAlY coatlng layer. The ceramlc thermal
barrler coatlng, ln contrast to the alumlnlde appllcatlon
process, ls applled by a llne-of-slght process whlch coats
only the deslred portlon of the component, l.e. the exterlor
portlon of the alrfoll.
Accordlngly, the present lnventlon provldes a
superalloy artlcle of manufacture of the type havlng a
ceramlc thermal barrler coatlng on at least a portlon of lts
surface, comprlslng:
(a) a superalloy substrate,
(b) an adherent, dlffuslon-alumlnlde coatlng
applled to sald portlon of the substrate and adapted to be a
reservolr of alumlnum for the subsequent ln sltu formatlon of
an alumlna protectlve scale on sald alumlnlde coated
substrate, and
-- 4
73101-2
133~3
(c) a columnar grained ceramlc coating bonded
dlrectly to sald alumlnide coatlng and adapted to allow ln
sltu oxldatlon of said alumlnide to alumlna.
The present lnventlon also provldes the method for
produclng a superalloy artlcle havlng an adherent ceramlc
thermal barrler coatlng thereon, comprlslng the steps:
(a) provldlng a superalloy substrate wlth a clean
surface;
(b) applylng a dlffuslon alumlnlde layer to the
clean superalloy substrate surface, and
(c) applylng a columnar gralned ceramlc coating to
the dlffuslon alumlnlde layer on sald superalloy substrate.
The present lnventlon also provides a superalloy
article having a thermal barrier coating system thereon,
comprlsing: a substrate made of a material selected from the
group conslstlng of a nlckel-based superalloy and a cobalt-
based superalloy; and a thermal barrler coatlng system on the
substrate, the thermal barrler coatlng system lncludlng an
lntermetalllc bond coat overlylng the substrate, the bond
coat belng selected from the group conslstlng of a nlckel
alumlnlde and a platlnum alumlnlde lntermetalllc compound, a
thermally grown alumlnum oxlde layer overlylng the
lntermetalllc bond coat, and a columnar grained ceramlc
topcoat overlylng the alumlnum oxlde layer.
The present invention also provides a superalloy
article havlng a thermal barrler coatlng system thereon,
comprlslng: a substrate made of superalloy selected from the
group conslstlng of a nickel-based superalloy and a cobalt-
-- 5
73101-2
1339~3
based superalloy; and a thermal barrier coating system on the
substrate, the thermal barrier coatlng system includlng an
alumlnide lntermetalllc bond coat upon the substrate, the
bond coat belng selected from the group conslstlng of a
nlckel alumlnlde and a platlnum alumlnlde, the bond coat
havlng a thlckness of from about 0.001 to about 0.005 lnches
thlck, a layer of thermally grown alumlnum oxlde upon the
intermetallic bond coat, the layer of alumlnum oxlde belng
less than about l micron thick, and a ceramic topcoat upon
the layer of alumlnum oxlde, the ceramlc topcoat havlng a
composltlon of zlrconlum oxlde plus from about 0 to about 20
welght percent yttrlum oxlde and a columnar graln structure
whereln the columnar axls ls substantlally perpendlcular to
the surface of the lntermetalllc bond coat.
The present lnventlon also provldes a process for
preparing a superalloy article havlng a thermal barrier
coatlng system thereon, comprlslng: furnlshlng a substrate
made of a nlckel-based superalloy; depositlng upon the
surface of the substrate an alumlnum lntermetallic coating
that has a substantlally smooth upper surface, sald bond
coating being selected from the group conslsting of a nickel
alumlnlde and a platlnum alumlnlde lntermetalllc compound;
thermally oxldlzlng the upper surface of the lntermetalllc
coatlng to form an alumlnum oxlde layer; and deposltlng upon
the surface of the alumlnum oxide layer a columnar grained
ceramlc topcoat by physlcal vapour deposltion.
The present invention also provldes a superalloy
artlcle havlng a thermal barrler coatlng system thereon,
-- 6
73101-2
~,
1339~3
comprlsing: a substrate made of a material selected from the
group consistlng of a nickel-based superalloy and cobalt-
based superalloy, and a thermal barrler coatlng system on the
substrate, the thermal barrler coatlng system lncludlng an
intermetalllc bond coat overlylng the substrate, the bond
coat being selected from the group conslstlng of a nlckel
aluminlde and a platinum aluminide intermetallic compound, a
thermally grown aluminum oxlde layer overlylng the
intermetalllc bond coat, and a ceramlc topcoat overlylng the
alumlnum oxide layer.
The present lnventlon also provides a thermal
barrler coatlng system for metalllc substrates, comprlslng:
an lntermetalllc bond coat overlylng a substrate selected
from the group conslsting of a nickel-based, cobalt-based and
iron-base superalloys, the bond coat being selected from the
group consisting of a nickel alumlnlde and a platlnum
alumlnide intermetallic compound, and a ceramic topcoat
overlying the intermetallic coating.
Although coatlngs of thls invention have been
thusfar developed for their thermal barrier benefits, other
uses can also be anticipated. In partlcular, thln ceramic
coatings (e.g. stabllized zirconla, zlrcon) applled on top of
dlffuslon alumlnldes have potential value ln lnhlbltlng hot
corroslon attack of the component by fuel and alr impuritles
(e.g., sulfur and salt). Subsequent densiflcatlon of the
outer surface of the columnar ceramlc layer (e.g. by laser
glazing) would increase the surface density and hardness and
thus provide a barrier to lnhlblt both hot corroslon and
-- 7
73101-2
~.,
133~403
erosion from lngested sand or combustor produced carbon
partlcles.
BRIEF DESCRIPTION OF THE DRAWINGS
My lnventlon wlll be descrlbed herelnafter wlth
reference to the accompanylng drawlngs, whereln
Flgure 1 ls a cross sectlonal vlew of a magnlfled
schematlc drawlng of the coatlng of the lnventlon;
Figure 2 is a photomlcrograph of a superalloy
substrate coated ln accordance with my inventlon; and
Figure 3 ls a photograph showing turblne blades
coated ln accordance wlth thls lnventlon.
DESCRIPTION OF THE PREFERRED EMBODIMENT
My present lnventlon lnvolves a thermal barrler
coated turbine component which lnclude two inter-related
layers on the superalloy substrate. The base metal or
substrate of my present inventlon may be nickel, cobalt or
lron base high temperature alloys used for turblne alrfoll
appllcatlons, l.e. blades or vanes. My present lnventlon ls
partlcularly applicable to hafnium and/or zirconium
containing superalloys such as MAR-M247, IN-100 and MAR-M
509, the composltlons of whlch are shown ln Table 1.
TABLE 1
ALLOY Mo W Ta Al Ti Cr Co Hf V Zr C B Ni
MAR-M247 .65 10 3.3 5.5 1.05 8.4 10 1.4 - .055 .15 .15 bal.
IN-100 3.0 - - 5.5 4.7 9.5 15.0 1.0 .06 .17 .015 bal.
MAR-M509 - 7.0 5.5 - O.25 23.4 Bal. - - .5 .6 - 10.0
73101-2
C
1:~39~3
Diffusion aluminide coatings have adequate oxide
scale adheslon on hafnlum and/or zlrconlum contalnlng
superalloys. Oxlde scale adhesion may be promoted for
coatings of my present lnvention on superalloys whlch do not
contaln hafnlum, or a slmllar element, such as La, by the use
of complex dlffuslon alumlnldes; i.e. alumlnide coatings
containing additions of elements which promote oxide scale
adhesion, such as Pt, Rh, Si, and Hf.
The diffusion aluminide coating used in connection
wlth my present lnvention can be applled by standard
commerclally avallable alumlnlde processes whereby alumlnum
ls reacted at the substrate surface to form an alumlnum
intermetalllc compound whlch provldes a reservolr for the
alumina scale oxidation reslstant layer. Thus the aluminide
coating is predominately composed of aluminum intermetallic
[e.g. NiAl, CoAl, FeAl and (Nl, Co, Fe) Al phases] formed by
reacting aluminum vapor species, alumlnum rlch alloy powder
or surface layer with the substrate elements in the outer
layer of the superalloy component. This layer is typically
well bonded to the substrate. Aluminiding may be
accomplished by one of several conventional prior art
technlques, such as, the pack cementatlon process, spraylng,
chemical vapor deposition, electrophoresis, sputtering, and
slurry slnterlng wlth an alumlnum rlch vapor and approprlate
dlffuslon heat treatments. The alumlnldlng layer may be
applled at a temperature from room temperature to 2100~F
depending upon the particular aluminiding process employed.
The aluminldlng layer for my present invention, should be
g
~ 73101-2
133~0~
applied to a thickness of about 1 to 5 mils.
Other beneficial elements can also be lncorporated
into diffusion aluminlde coatings by a variety of processes.
Beneflcial elements lnclude Pt, Sl, Hf and oxlde partlcles,
such as alumlna, yttria, hafnia, for enhancement of alumina
scale adhesion, Cr and Mn for hot corroslon reslstance, Rh,
Ta and Cb for diffusional stability and/or oxidation
reslstance and Nl, Co for lncreaslng ductlllty or lnclplent
meltlng llmlts. These elements can be added to the surface
of the component prlor to alumlnlzlng by a wide range of
processes including electroplating, pack cementation,
chemical vapor depositlon, powder metal layer deposltlon,
thermal spray or physlcal vapor deposition processes. Some
methods of coating, such as slurry fusion, permlt some or all
of the beneflclal coatlng elements, lncludlng the alumlnum,
to be added concurrently. Other processes, such as chemlcal
vapor deposltlon and pack cementatlon, can be modlfled to
concurrently apply elements such as Sl and Cr wlth the
alumlnum. In addltlon, lt ls obvlous to those skllled ln the
art that dlffuslon alumlnlde coatlngs wlll contaln all
elements present wlthln the surface layer of the substrate.
In the speclfic case of platlnum modlfled dlffuslon
aluminide coatlng layers, the coating phases ad~acent to the
alum~na scale wlll be platlnum aluminlde and/or nlckel-
platinum alumlnlde phases (on a Nl-base superalloy).
The diffusion alumlnlde coating in accordance with
my present invention provldes aluminum rich intermetalllc
phase(s) at the surface of the substrate which serve as an
-- 10 --
73101-2
~1',
13~9403
aluminum reservolr for subsequent alumina scale growth. An
alumlna scale or layer ls utllized ln my present lnventlon
between the dlffusion alumlnide coatlng and the ceramic layer
to provlde both oxldatlon reslstance and a bondlng surface
for the ceramlc layer. The alumlna layer may be formed
before the ceramlc thermal barrler coatlng ls applled or
formed durlng appllcatlon of the thermal barrler columnar
gralned coatlng. The alumlna scale can also be grown
subsequent to the applicatlon of the ceramic coating by
heatlng the coated artlcle ln an oxygen contalnlng atmosphere
at a temperature consistent with the temperature capablllty
of the superalloy, or by exposure to the turblne envlronment.
The sub-mlcron thlck alumlna scale wlll thlcken on the
alumlnlde surface by heatlng the materlal to normal turblne
exposure condltlons. The thickness of the alumlna scale ls
preferably sub-mlcron (up to about one mlcron).
The thermal barrler coatlng whlch ls applled as the
flnal coatlng layer ln my present lnventlon, ls a columnar
gralned ceramlc coatlng whlch ls tlghtly bonded to the
underlylng alumlna fllm on the alumlnlde coatlng, whlch ls
applled to the substrate. The columnar gralns are oriented
substantlally perpendlcular to the surface of the substrate
wlth lnterstlces between the lndlvldual columns extendlng
from the surface of the thermal barrler coatlng down to or
near (wlthln a few mlcrons) the alumlna fllm on the alumlnide
coating. The columnar gralned structure of thls type of
thermal barrler coating mlnlmlzes any stresses assoclated
wlth the dlfference ln the co-efflcients of thermal expanslon
- 11 --
73101-2
13~9~L0~
between the substrate and the thermal barrler coating, which
would otherwlse cause a failure ln a dense or contlnuous
ceramlc thermal barrler coatlng. When heated or cooled, the
substrate expands (or contracts) at a greater rate than the
ceramic thermal barrler coatlng. Gaps between the ceramlc
columnar gralns permlt the gralns to expand and contract
without produclng sufflclent stress to lnduce spalling or
cracking of the thermal barrler coatlng. This llmlts the
stress at the lnterface between the substrate and the thermal
barrler coatlng, thus preventlng fractures ln the ceramlc
coatlng.
The columnar graln thermal barrler coatlng used in
my present lnventlon may be any of the conventlonal ceramlc
composltions used for this purpose. Currently the straln-
tolerant zlrconla coatlngs are belleved to be particularly
effectlve as thermal barrier coatlngs; however, my present
lnventlon ls equally applicable to other ceramlc thermal
barrler coatlngs. A preferred ceramic coating ls the yttria
stablllzed zirconla coating. These zlrconla ceramlc layers
have a thermal conductlvlty that ls about 1 and one-half
orders of magnltude lower than that of the typlcal superalloy
substrate such as MAR-M247. The zlrconla may be stabllized
wlth CaO, MgO, CeO2 as well as Y2O3. Other ceramlcs which
are belleved to be useful as the columnar type coatlng
materlals wlthln the scope of my present lnventlon are
alumlna, cerla, hafnla (yttrla-stablllzed), mulllte,
zirconium slllcate and certaln borldes and nltrldes, e.g.
tltanium diborlde, and slllcon nltrlde.
- 12 -
73101-2
1339~03
The columnar ceramic materlal may have some degree
of solld solublllty wlth the alumlna scale. Also the
partlcular ceramic materlal selected for use as the columnar
graln thermal barrler coating should be stable ln the hlgh
temperature envlronment of a gas turbine.
The ceramlc layer may be applled by a prlor art
technique whlch provldes an open columnar mlcrostructure,
preferably the electron beam evaporatlon-physlcal vapor
deposltlon process. The thlckness of the ceramic layer may
vary from 1 to lOOO~m but ls typlcally ln the 50 to 300~m
range for typlcal thermal barrler appllcatlons.
The electron beam evaporation-physlcal vapor
deposltlon process for applylng the thermal barrler coatlng
ls a modlflcatlon of the standard hlgh-rate vapor deposltlon
process for metalllc coatlngs. Power to evaporate the
ceramlc coatlng materlal ls provided by a hlgh-energy
electron beam gun. The zlrconla vapor produced by
evaporatlon of the zlrconla target materlal, condenses onto
the turblne alrfoll component to form the thermal barrler
coatlng. Zlrconla coatlng deposltlon rates are typlcally ln
the range of about 0.01 to 1.0 mlls per mlnute. The parts to
be coated are preheated ln a load lock by elther radlant or
electron beam heat sources and/or heated ln the coatlng
chamber prlor to exposure to the ceramlc vapor. Durlng
coatlng, the component temperature ls typlcally malntalned ln
the 1500 to 2100~F range. Slnce zirconla becomes somewhat
oxygen deflclent due to partlal dlssoclatlon durlng
evaporatlon ln a vacuum, oxygen ls also bled lnto the yttrla-
- 13 -
C 73101-2
l33s~a3
stabillzed zlrconia vapor cloud to mlnimize any deviation
from stolchiometry during coating.
By my present inventlon the ceramlc thermal barrler
coating ls applled dlrectly to the diffuslon alumlnide
metallic coating.
In accordance wlth my present lnventlon, ceramic
coatlngs on turblne alrfolls accommodate large strains
wlthout developlng stresses of a sufflclent magnltude to
cause spalllng. Thls strain tolerance ls achleved by the
above-mentloned mlcrostructural dlscontlnultles wlthin the
columnar grained ceramlc lnsulatlve layer, whlch permlts the
ceramlc-layer straln to be accommodated wlth mlnlmal stress
on the ceramlc to metal lnterface reglon.
Flgure 1 ls a schematlc cross-sectlonal llne
drawlng showlng a coatlng ln accordance with my present
lnventlon, whereln the alumlnlde coating 5 ls applled to the
superalloy substrate 6 and an adherent alumina scale layer 7
is formed on the aluminide coating 5. The columnar grain
ceramic layer 8 overlays the alumlna layer 7.
Flgure 2 ls a photomlcrograph of a zirconia
insulative layer deposited on superalloy substrate ln
accordance wlth my present lnvention. In thls thermal
barrler coatlng system, a dlffuslon alumlnlde oxldatlon
reslstant layer 10 was deposlted directly on the MAR-M247
superalloy substrate 12 and a yttrla-stabillzed zlrconla
thermal barrler coatlng 14 was applled to the substrate. As
may be seen from Flgure 2, a thln alumlna fllm 16 ls formed
between the dlffuslon alumlnlde coatlng and the zlrconla
- 14 -
C 73101-2
133~
coatlng. The Hf content of the superalloy substrate enhances
the adheslon of the alumlna layer formed on the alumlnlde and
to whlch the zirconla layer ls adherred.
Flgure 3 ls a photograph of a turbo-prop englne
turblne showlng hlgh pressure turblne blades mounted ln dlsc
20. Blades 22 and 24 shown as whltlsh, have been coated ln
accordance wlth my present lnventlon wlth yttrla-stablllzed
zlrconla. The blades are shown subsequent to 240 hours
servlce ln a TPE 331-10 Turbo-prop Englne.
EXAMPLE 1
TPE 331-10 turboprop englne hlgh pressure turblne
blades of IN-100 alloy were coated wlth a dlffuslon alumlnlde
plus EB-PVD yttrla-stablllzed zlrconla system. The
commerclally avallable Chromalloy RT-21 pack cementatlon
dlffuslon nlckel alumlnide coatlng was applled to a nomlnal
thlckness of 2 mils. Followlng appllcatlon of the dlffuslon
alumlnlde coatlng layer, the yttrla ~approxlmately 20%)
stablllzed zlrconla coatlng layer was applled to the surface
of the alumlnlde coated blades, by the commerclal Alrco
Temescal EB-PVD process. The thlckness of the zlrconla
coatlng was also 2 mlls. The ceramlc coatlng was applled by
evaporatlng a yttrla-stablllzed zlrconla lngot wlth power
provlded by a hlgh-energy electron beam gun focused
magnetlcally onto the zlrconla target, whlch was the vapor
source. The cloud of zlrconla vapor ls produced by the
evaporatlon of the zlrconla target materlal and vapor from
thls cloud condensed onto the blades at a rate of about 0.2
mll/mln. to form the ceramlc coatlng layer. Substrate
- 15 -
C 73101-2
.
1~394~3
temperature durlng coating was about 1800~F.
The coated blades were then lnstalled ln the TPE
331-10 engine and successfully tested for 240 hours of engine
operatlng tlme. Flgure 3 shows the blades after the test,
confirmlng that the blades were in good condition after the
240 hour englne test.
EXAMPLE 2
A burner rlg specimen MAR-M247 was dlffusion
aluminlde coated wlth the Chromalloy RT-21* pack cementation
process to a nomlnal thlckness of 2 mlls and then a 5 mll
thlck Y2O3 stablllzed zlrconla coatlng applled by a
commerclal Alrco Temescal EB-PVD* process. A second burner
rlg speclmen was dlffuslon alumlnlde coated wlth Chromalloy's
RT 22 process whlch provldes a Pt-modlfled alumlnlde coatlng,
and the same columnar gralned ceramlc coating applled. The
burner rlg speclmens were sub~ected to a test cycle
comprlslng 4 mlnutes at 2100~F followed by 2 mlnutes of
forced alr coollng. The speclmens wlthstood 400 cycles over
a 40 hour perlod.
EXAMPLE 3
ATF3-6 turbofan englne hlgh pressure turblne
palred-vanes of the MAR-M 509 alloy were coated wlth a
dlffuslon alumlnlde plus EB-PVD yttrla-stablllzed zlrconla
system ln accordance wlth thls lnventlon. The commerclally
avallable chromalloy RT-19 pack cementatlon dlffuslon cobalt
alumlnlde coatlng was applled to a nomlnal thickness of 2
mlls. Followlng appllcatlon of the dlffuslon alumlnlde
coatlng layer, the yttria-stabilized (approximately 20%)
- 16 -
C 73101-2
1339~3
zlrconla coatlng layer was applled to the surface of the
alumlnlde coated vanes by a commerclally avallable Alrco
Temescal EB-PVD process. The nominal thlckness of the
zlrconla coatlng was 3 to 8 mlls.
These thermal barrler coated palred vanes were
concurrently evaluated wlth palred vanes coated wlth only the
dlffuslon alumlnlde for 217 hours in an ATF 3-6 test englne.
Post-test examination lndlcated that the durablllty of the
thermal barrler coated vanes was lncreased relatlve to the
vanes wlthout the lnsulatlve zlrconla coatlng layer.
Whlle my present lnventlon has been descrlbed
hereln wlth a certaln degree of partlcularlty ln reference to
certaln speclflc coatlng and alloy composltlons whlch were
formulated and tested, lt ls to be understood that the scope
of my lnventlon ls not llmlted thereto, but should be
afforded the full scope of the appended clalms.
- 17 -
C 73101-2
