CA1339403C - Thermal barrier coating for superalloy components - Google Patents

Abstract

An improvement in a thermal barrier coating for superalloy turbine engine components subjected to high operating temperatures, such as turbine airfoils, e.g., vanes and blades, is disclosed which eliminates the expensive MCrAlY oxidation resistant bond coating underlayer for a columnar grained ceramic thermal barrier coating. In accordance with my present invention, a relatively low cost thermal barrier coating system for superalloy turbine components is provided which utilizes a diffusion aluminide coating layer as the oxidation resistant bonding surface for the columnar grained ceramic insulating coating.

Description

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 ~ 73101-2 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 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 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 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-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, ~, 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 ~., 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.

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 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 ~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 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.

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-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 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.

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 .

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.

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.

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%) 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.

Claims (37)

1. A superalloy article of manufacture of the type having a ceramic thermal barrier coating on at least a portion of its surface, comprising:
(a) a superalloy substrate;
(b) an adherent diffusion aluminide coating applied to said portion of the substrate and adapted to be a reservoir of aluminum for the subsequent in situ formation of an alumina protective scale on said aluminide coated substrate; and (c) a columnar grained ceramic coating bonded directly to said aluminide coating and adapted to allow in situ oxidation of said aluminide to alumina.

2. The article of Claim 1 wherein said diffusion aluminide coating is from 0.5 to 5 mils thick.

3. The article of Claim 1 wherein the ceramic coating is from 0.5 to 50 mils thick.

4. The article of Claim 1 wherein said diffusion aluminide coating is modified by at least one of the elements selected from the group consisting of Pt, Rh, Si, Hf, Cr, Mn, Ta, and Cb.

5. The article of Claim 1 wherein said diffusion aluminide coating is modified by dispersed particles selected from the group consisting of alumina, yttria or hafnia.

6. The article of Claim 1 having an MCrAlY overlay coating applied to the superalloy substrate under the diffusion aluminide coating, wherein M = Ni, Co or Fe.

7. The article of Claim 1 wherein an adherent alumina layer is formed between said aluminide coating and said ceramic coating.

8. The article of Claim 1 wherein said ceramic coating is yttria-stabilized zirconia.

9. The article of Claim 1 wherein said ceramic coating is zirconia stabilized with at least one oxide selected from the group consisting of CaO, MgO, and CeO2.

10. The article of Claim 1 wherein said ceramic coating is selected from the group consisting of alumina, ceria, yttria-stabilized hafnia, zirconium silicate and mullite.

11. The article of Claim 1 wherein said ceramic coating is selected from the group consisting of borides and nitrides.

12. The article of Claim 1 wherein up to 0.1 mil of the ceramic adjacent to the alumina scale has a denser microstructure, which may vary from equiaxed grains to columnar grains with the balance of the ceramic coating having a fully columnar grained microstructure.

13. The article of Claim 1 wherein the exterior of the ceramic coating is densified by glazing.

14. The method for producing a superalloy article having an adherent ceramic thermal barrier coating thereon, comprising the steps:
(a) providing a superalloy substrate with a clean surface;
(b) applying a diffusion aluminide layer to the clean superalloy substrate surface, and (c) applying a columnar grained ceramic coating to the diffusion aluminide layer on said superalloy substrate.

15. The method of Claim 14 including a step of forming an adherent alumina layer on said diffusion aluminide coating.

16. The method of Claim 15 wherein said alumina layer is formed on said aluminide coating by heat treating the ceramic coated article in an oxygen containing atmosphere at a temperature of between 1600 and 2100°F.

17. The method of Claim 14 including a step of modifying the substrate surface by applying a material selected from the group consisting of Pt, Rh, Si, Hf, Cr, Ta, Cb, alumina, yttria, hafnia, and a MCrAlY surface layer, prior to aluminiding.

18. The method of Claim 14 including the step of densifying the exterior of the ceramic coating by electron beam glazing.

19. The method of Claim 14 including the step of densifying the exterior of the ceramic coating by laser glazing.

20. The method of Claim 14 wherein said columnar grained ceramic coating is applied by vapor deposition.

21. A superalloy article having a thermal barrier coating system thereon, comprising:
a substrate made of a material selected from the group consisting of a nickel-based superalloy and a cobalt-based superalloy; and a thermal barrier coating system on the substrate, the thermal barrier coating system including an intermetallic bond coat overlying the substrate, the bond coat being selected from the group consisting of a nickel aluminide and a platinum aluminide intermetallic compound, a thermally grown aluminum oxide layer overlying the intermetallic bond coat, and a columnar grained ceramic topcoat overlying the aluminum oxide layer.

22. The article of claim 21, wherein the intermetallic bond coat is from about 0.001 to about 0.005 inches thick.

23. The article of claim 21, wherein the ceramic topcoat is from about 1 to 1000 microns thick.

24. The article of claim 21, wherein the ceramic topcoat includes zirconium oxide and yttrium oxide.

25. The article of claim 21, wherein the ceramic topcoat is zirconium oxide plus from 0 to about 20 percent by weight yttrium oxide.

26. The article of claim 21, wherein the article is a gas turbine blade.

27. The article of claim 21, wherein the intermetallic bond coat includes at least one alloying element that does not alter the intermetallic character of the coating.

28. The article of claim 22, wherein the layer of aluminum oxide is less that about 1 micron thick.

29. A superalloy article having a thermal barrier coating system thereon, comprising:
a substrate made of superalloy selected from the group consisting of a nickel-based superalloy and a cobalt-based superalloy; and a thermal barrier coating system on the substrate, the thermal barrier coating system including an aluminide intermetallic bond coat upon the substrate, the bond coat being selected from the group consisting of a nickel aluminide and a platinum aluminide, the bond coat having a thickness of from about 0.001 to about 0.005 inches thick, a layer of thermally grown aluminum oxide upon the intermetallic bond coat, the layer of aluminum oxide being less than about 1 micron thick, and a ceramic topcoat upon the layer of aluminum oxide, the ceramic topcoat having a composition of zirconium oxide plus from about 0 to about 20 weight percent yttrium oxide and a columnar grain structure wherein the columnar axis is substantially perpendicular to the surface of the intermetallic bond coat.

30. The article of claim 29, wherein the nickel aluminide is NiAl.

31. A process for preparing a superalloy article having a thermal barrier coating system thereon, comprising:

furnishing a substrate made of a nickel-based superalloy;
depositing upon the surface of the substrate an aluminide intermetallic bond coating that has a substantially smooth upper surface, said bond coating being selected from the group consisting of a nickel aluminide and a platinum aluminide intermetallic compound;
thermally oxidizing the upper surface of the intermetallic bond coat to form an aluminum oxide layer; and depositing upon the surface of the aluminum oxide layer a columnar grained ceramic topcoat by physical vapour deposition.

32. The process of claim 31, wherein the temperature of the substrate during the step of depositing the intermetallic bond coat is less than about 2100°F.

33. The process of claim 31, wherein the temperate of the substrate during the step of depositing the ceramic topcoat is from about 1500°F to about 2100°F.

34. The process of claim 31, wherein the aluminide is platinum rhodium aluminide.

35. A thermal barrier coating system for metallic substrates, comprising:
an intermetallic bond coat overlying a substrate selected from the group consisting of nickel-based, cobalt-based and iron based superalloys, the bond coat being selected from the group consisting of a nickel aluminide and a platinum aluminide intermetallic compound, and a columnar grained ceramic topcoat overlying the intermetallic bond coat.

36. The coating system of claim 35, wherein the bond coat is oxidized to form an aluminum oxide layer between the bond coat and the topcoat.

37. A superalloy article having a thermal barrier coating system thereon, comprising:
a substrate made of a material selected from the group consisting of a nickel-based superalloy and cobalt-based superalloy, and a thermal barrier coating system on the substrate, the thermal barrier coating system including an intermetallic bond coat overlying the substrate, the bond coat being selected from the group consisting of a nickel aluminide and a platinum aluminide intermetallic compound, a thermally grown aluminum oxide layer overlying the intermetallic bond coat, and a columnar grained ceramic topcoat overlying the aluminum oxide layer.