(19) 9)
`
`Europfiisches Patentamt
`
`European Patent Office
`
`Office européen des brevets
`
`(11)
`
`EP1 142 850 A1
`
`(12)
`
`EUROPEAN PATENT APPLICATION
`
`(43) Date of publication:
`10.10.2001 Bulletin 2001/41
`
`(51) lntCl.7: C04B 41/52
`
`(21) Application number: 01303303.0
`
`(22) Date of filing: 06.04.2001
`
`(84) Designated Contracting States:
`AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU
`MC NL PT SE TR
`
`Designated Extension States:
`AL LT LV MK RO SI
`
`- Nagaraj, Bangalore Aswatha
`West Chester, Ohio 45069 (US)
`Spitsberg, Irene Theodor
`Loveland, Ohio 45140 (US)
`
`(30) Priority: 06.04.2000 US 543956
`
`(71) Applicant: GENERAL ELECTRIC COMPANY
`Schenectady, NY 12345 (US)
`
`(72) Inventors:
`0 Wang, Hongyu
`Niskayuna, New York 12309 (US)
`
`Representative: Szary, Anne Catherine, Dr. et al
`London Patent Operation,
`GE International, |nc.,
`Essex House,
`12-13 Essex Street
`
`London WC2R 3AA (GB)
`
`(54)
`
`Thermallenvironmental barrier coating for silicon-containing materials
`
`Acoating system (1 4) for Si-containing material
`(57)
`(12), such as those used to form articles exposed to high
`temperatures, includingthe hostilethermal environment
`of a gas turbine engine. The coating system (14) is a
`compositionally—graded thermal/environmental barrier
`coating (T/EBC) system (14) that exhibits improved me-
`chanical integrity for high application temperatures that
`necessitate thick protective coatings. The T/EBC sys-
`
`tem (14) includes an intermediate layer (24) containing
`YSZ and BSAS, mullite and/or alumina, which is prefer-
`ably used in combination with a mullite—containing layer
`(20) that overlies the surface of the Si-containing mate-
`rial (12), a layer (22) of BSAS between the mullite—con-
`taining layer (20) and the intermediate layer (24), and a
`thermal-insulating top coat (18) of YSZ overlying the in-
`termediate layer (24).
`
`EP1142850A1
`
`Printed by Jouve, 75001 PARlS (FR)
`
`GE-1008.001
`
`GE-1008.001
`
`

`
`EP1 142 850 A1
`
`Description
`
`[0001] This invention relates to coating systems suit-
`able for protecting components exposed to high—tem—
`perature environments, such as the hostile thermal en-
`vironment of a gas turbine engine. More particularly, this
`invention is directed to a graded thermal/environmental
`barrier coating system for a substrate formed of a ma-
`terial containing silicon.
`[0002] Higher operating temperatures for gas turbine
`engines are continuously sought in order to increase
`their efficiency. However, as operating temperatures in-
`crease, the high temperature durability of the compo-
`nents of the engine must correspondingly increase. Sig-
`nificant advances in high temperature capabilities have
`been achieved through formulation of iron, nickel and
`cobalt—base superalloys. While superalloys have found
`wide use for components throughout gas turbine en-
`gines, alternative materials have been proposed. Mate-
`rials containing silicon, particularly those with silicon
`carbide (SiC) as a matrix material and/or as a reinforcing
`material, are currently being considered for high tem-
`perature applications, such as combustor and other hot
`section components of gas turbine engines.
`[0003]
`In many applications, a protective coating is
`beneficial or required forthe Si—containing material. For
`example, protection with a suitable thermal—insulating
`layer reduces the operating temperature and thermal
`gradient through the material. Additionally, such coat-
`ings should provide environmental protection by inhib-
`iting the major mechanism for degradation of Si—contain—
`ing materials in a corrosive water-containing environ-
`ment, namely, the formation of volatile silicon monoxide
`(SiO) and silicon hydroxide (Si(OH)4) products. Conse-
`quently, besides low thermal conductivity, a critical re-
`quirement of a thermal barrier coating system for a Si-
`containing material is stability in high temperature envi-
`ronments containing water vapors. Other important
`properties for the coating material include a coefficient
`of thermal expansion (CTE) compatible with the SiC-
`containing material, low permeability for oxidants, and
`chemical compatibility with the Si—containing material
`and silica scale formed from oxidation. As a result, suit-
`able protective coatings for gas turbine engine compo-
`nents formed of Si—containing materials essentially have
`a dual function, serving as a thermal barrier and simul-
`taneously providing environmental protection. Acoating
`system having this dual function is termed a thermal/
`environmental barrier coating (T/EBC) system.
`[0004] While various single—|ayer and multilayer T/
`EBC systems have been investigated, each has exhib-
`ited shortcomings relating to the above—noted require-
`ments and properties for compatibility with a Si—contain-
`ing material. For example, a coating of zirconia partially
`or fully stabilized with yttria (YSZ) as a thermal barrier
`layer exhibits excellent environmental resistance by it-
`self, since it does not contain silica in its composition.
`However, YSZ does not adhere well to Si—containing
`
`materials (SiC or silicon) because of a CTE mismatch
`(about 10 ppm/°C for YSZ as compared to about 4.9
`ppm/°C
`for
`SiC/SiC
`composites).
`Mullite
`(3A|2O3-2SiO2) has been proposed as a bond coat for
`YSZ on Si—containing substrate materials to compen-
`sate forthis difference in CTE (mullite having a CTE of
`about 5.5 ppm/°C). However, mullite exhibits significant
`silica activity and volatilization at high-temperatures if
`water (water vapor) is present.
`(BSAS)
`[0005] Barium—strontium—aluminosilicate
`coatings suitable for Si—containing materials exposed to
`temperatures of up to 2400°F (about 1315°C) have also
`been proposed. BSAS provides excellent environmen-
`tal protection and exhibits good thermal barrier proper-
`ties due to its low thermal conductivity. However, for ap-
`plication temperatures approaching the melting temper-
`ature of BSAS (about 1700°C), a BSAS protective coat-
`ing would require a thermal—insu|ating top coat. BSAS
`has been proposed as a bond coat for YSZ in U.S. Pat-
`ent No. 5,985,970 to Spitsberg et al., assigned to the
`assignee of the present invention. The inclusion of a
`BSAS bond coatsignificantly increases the overa||thick-
`ness of the T/EBC system. As application temperatures
`increase further beyond the thermal capability of a Si-
`containing material (limited by a melting temperature of
`about 2560°F (about 1404°C) for silicon), still thicker
`coatings capable of withstanding higher thermal gradi-
`ents are required. However, as coating thickness in-
`creases, strain energy due to the CTE mismatch be-
`tween individual coating layers and the substrate in-
`creases as well, which can cause debonding and spa|—
`lation of the coating system.
`[0006] Accordingly, there is a need for a thick T/EBC
`system for Si—containing materials that enables such
`materialsto be used at application temperatures beyond
`the melting temperature of silicon.
`[0007] The present invention generally provides a
`coating system for Si—containing material, particularly
`those for articles exposed to high temperatures, includ-
`ing the hostile thermal environment of a gas turbine en-
`gine. Examples of such materials include those with a
`dispersion of silicon carbide, silicon carbide and/or sili-
`con particles as a reinforcement material in a metallic
`or nonmetallic matrix, as well as those having a silicon
`carbide, silicon nitride and/or silicon—containing matrix,
`and particularly composite materials that employ silicon
`carbide, silicon nitride and/or silicon as both the rein-
`forcement and matrix materials (e.g., SiC/SiC ceramic
`matrix composites (CMC)).
`[0008] The invention is a compositionally—graded
`thermal/environmental barrier coating (T/EBC) system
`that exhibits improved mechanical integrity for high ap-
`plication temperatures that necessitate thick protective
`coatings, generally on the order of 250 um or more. The
`T/EBC system includes an intermediate layercontaining
`YSZ and mullite, alumina and/or an alkaline earth metal
`aluminosilicate (preferably BSAS), which is preferably
`used in combination with a mullite—containing layer that
`
`GE-1008.002
`
`GE-1008.002
`
`

`
`EP1 142 850 A1
`
`overlies the surface ofthe Si-containing material, a layer
`of an alkaline earth metal aluminosilicate (again, prefer-
`ably BSAS) between the mullite—containing layer and
`the intermediate layer, and a thermal—insulatingtop coat
`of YSZ overlying the intermediate layer. Particular em-
`bodiments are for the intermediate layerto have a sub-
`stantially uniform composition of YSZ and either BSAS,
`mullite or alumina, orto contain sublayers within an in-
`nermost sublayer (contacting the BSAS layer) being
`BSAS, mullite or alumina and an outermost sublayer
`(contacting the YSZ top coat) being YSZ, orto be com-
`positionally graded so that the concentrations of YSZ
`and BSAS, mullite or alumina continuously change
`through the thickness of the intermediate layer.
`[0009] The mullite—containing layer has a CTE above
`that of a Si-containing substrate but less than that of the
`YSZ top coat, and therefore compensates for the differ-
`ence in CTE between the Si-containing substrate and
`the other coating layers. In addition, the mullite—contain-
`ing layer serves as a chemical barrier between BSAS
`layer and the Si-containing substrate to prevent interac-
`tion of BSAS with the silicon oxidation product (SiO2) at
`high temperatures. The BSAS layer provides environ-
`mental protection to the silicon—containing substrate.
`The top coat of YSZ offers excellent thermal protection
`to the Si-containing substrate and the other underlying
`layers ofthe coating system. Finally, the YSZ—containing
`intermediate layer serves as a thermal barrier layerthat
`also provides a CTE transition between the BSAS layer
`and the YSZ top coat as a result of its BSAS, mullite
`and/or alumina content, each of which has a CTE be-
`tween that of YSZ and Si-containing materials.
`[0010] According to this invention, a compositionally—
`graded T/EBC as described above is able to reliably pro-
`vide both thermal and environmental protection to a Si-
`containing substrate at temperatures of up to 2000°C,
`particularly when present at total coating thicknesses of
`250 um or more, as a result of exhibiting improved me-
`chanical integrity as compared to prior art coating sys-
`tems for Si-containing materials.
`[0011] Other objects and advantages of this invention
`will be better appreciated from the following detailed de-
`scription, by way of example, with reference to the draw-
`ing, in which:—
`is a cross—sectional view of a gas tur-
`[0012]
`Figure 1
`bine engine component formed of a Si-containing ma-
`terial and having a thermal/environmental barrier coat-
`ing system in accordance with this invention.
`[0013] The present invention is generally applicable
`to components that operate within environments char-
`acterized by relatively high temperatures, and are there-
`fore subjected to severe thermal cycling and stresses,
`oxidation, and corrosion. Notable examples of such
`components include combustorcomponents, high pres-
`sure turbine vanes, and other hot section components
`of gas turbine engines. A surface region 12 of a hot sec-
`tion component 10 is represented in Figure 1 for pur-
`poses of illustrating the invention. The component 10,
`
`10
`
`or at least the surface region 12 of the component 10,
`is formed of a silicon—containing material such as a SiC/
`SiC CMC, though the invention is generally applicable
`to other materials containing silicon in any form.
`[0014] As shown in Figure 1, the surface region 12 of
`the component 10 is protected by a multilayer T/EBC
`system 14that includes athermal-insulatingtop coat 18.
`The coating system 14 provides environmental protec-
`tion to the underlying surface region 12 as well as re-
`duces the operating temperature of the component 10
`and interior layers 20, 22 and 24 of the coating system
`14, thereby enabling the component 10 to survive within
`highertemperature environments than otherwise possi-
`ble. The preferred material for the top coat 18 is YSZ,
`more preferably about 7 weight percent yttria, though it
`is foreseeable that other ceramic materials could be
`
`used. A suitable thickness range for the YSZ top coat
`18 is about 12.5 to about 1250 um (about 0.0005 to
`about 0.050 inch), with a preferred range of about 125
`to about 750 um (about 0.005 to about 0.030 inch), de-
`pending on the particular application.
`[0015] The major mechanism for degradation of sili-
`con carbide (as well as silicon and other silicon com-
`pounds) in a corrosive environment is the formation of
`volatile silicon monoxide (SiO) and silicon hydroxide (Si
`(OH)4) products. The diffusivity of oxidants in the YSZ
`top coat 18 is generally very high. Therefore, in orderto
`protect the Si-containing surface region 12, the coating
`system 14 must include additional layers beneath the
`top coat 18 that, individually or in combination, exhibit
`low diffusivity to oxidants, e.g., oxygen and water vapor,
`to inhibit oxidation of the silicon carbide within the sur-
`
`face region 12, while also being sufficiently chemically
`and physically compatible with the surface region 12 to
`remain adherent to the region 12 under severe thermal
`conditions.
`
`In a preferred embodiment of this invention,
`[0016]
`the combination of interior layers 20, 22 and 24 shown
`in Figure 1 provides a graded composition that fulfills
`the requirements noted above. A preferred inner layer
`20 of the coating system 14 contains mullite, overwhich
`is deposited a layer 22 of an alkaline earth metal alumi-
`nosilicate, preferably BSAS. According to the invention,
`separating the BSAS layer 22 and the top coat 18 is a
`YSZ—containing layer 24 that also contains mullite, alu-
`mina and/or an alkaline earth metal aluminosilicate
`
`(again, preferably BSAS). The YSZ—containing layer 24
`of the invention promotes the ability of the T/EBC sys-
`tem 14 to thermally and environmentally protect the Si-
`containing surface region 12 over numerous thermal cy-
`cles and at elevated temperatures.
`[0017] The mullite—containing layer 20 serves to ad-
`here the BSAS and YSZ—containing layers 22 and 24 to
`the Si-containing surface region 12, while also prevent-
`ing interactions between the BSAS layer 22 and the Si-
`containing surface region 12 at high temperatures. Mul-
`lite is suitable as the material for the innermost layer of
`the coating system 14 because of its chemical stability
`
`GE-1008.003
`
`GE-1008.003
`
`

`
`EP1 142 850 A1
`
`with Si—containing materials at high temperatures. The
`|ayer20 may also contain BSAS (or even entirely BSAS)
`for less demanding applications, e.g., temperatures be-
`low about 1300°C. The addition of BSAS to the layer 20
`is also relatively compatible with the Si—containing sur-
`face region 12 in terms of having a CTE of about 5.27
`ppm/°C, as compared to a CTE of about 4.9 ppm/°C for
`SiC/SiC CMC. Asuitablethickness range forthe mullite-
`containing layer 20 is about 25 to about 250 um (about
`0.001 to about 0.010 inch), depending on the particular
`application.
`[0018] The BSAS layer 22 overlying the mullite—con—
`taining layer 20 provides excellent environmental pro-
`tection and exhibits good thermal barrier properties due
`to its low thermal conductivity. Particularly, BSAS is able
`to serve as an environmental barrier to the underlying
`mullite—containing layer 20, which would exhibit signifi-
`cant silica activity and volatilization if exposed to water
`vapor at high temperatures. As a result, the BSAS layer
`22 is ableto inhibitthe growth ofan interfacial silica layer
`at the surface region 12 when the component 10 is ex-
`posed to the oxidizing environment of a gas turbine en-
`gine.
`In addition, BSAS is physically compliant with a
`SiC-containing substrate, such asthe surface region 12,
`and is relatively compatible with the mullite—containing
`layer20 and the Si—containing surface region 12 in terms
`of CTE. A suitable thickness range for the BSAS layer
`22 is about 125 to about 500 um (about 0.005 to about
`0.020 inch), depending on the particular application.
`[0019] Three embodiments are contemplated for the
`YSZ-containing layer 24 of this invention. In a first em-
`bodiment, the YSZ-containing layer 24 is a substantially
`homogeneous mixture of YSZ and BSAS, mullite and/
`or alumina, with YSZ constituting up to 90 weight per-
`cent of the layer 24.
`[0020] Alternatively, the layer 24 can be made up of
`discrete sublayers, each with a different composition. In
`this embodiment, the composition of the sublayer con-
`tacting the BSAS layer 22 is preferably essentially
`BSAS, mullite and/or alumina, while the outermost sub-
`layer contacting the YSZ top coat 18 is preferably es-
`sentially YSZ. One or more intermediate sublayers are
`preferably present and have compositions that are in-
`termediate those of the inner and outer sublayers.
`[0021] According to the third embodiment, the YSZ-
`containing layer 24 has a continuously changing com-
`position, from essentially all YSZ adjacent the YSZ top
`coat 18 to essentially all BSAS, mullite and/or alumina
`adjacentthe BSAS layer22. In this embodiment, the lay-
`er 24 has a decreasing concentration of BSAS, mullite
`and/or alumina and an increasing concentration of YSZ
`in a direction away from the BSAS layer 22. In combi-
`nation, the higher concentration of BSAS, mullite and/
`or alumina adjacent the BSAS layer 22 and the higher
`concentration of YSZ adjacent the YSZ top coat 18
`serve to provide a gradually increasing CTE, with a min-
`imum CTE adjacent the BSAS layer22 and a maximum
`CTE adjacent the YSZ top coat 18.
`
`[0022] A suitable thickness for the YSZ-containing
`layer 24 is up to about 500 um (up to about 0.020 inch),
`depending on the particular application and the thick-
`ness of the other layers 20, 22 and 24. High application
`temperatures, e.g., up to 2000°C, necessitatethick pro-
`tective coating systems, generally on the order of 250
`um or more. It is with such coating systems thatthe ben-
`efits of the YSZ-containing layer 24 become more nec-
`essaryto improve the mechanical integrity ofthe coating
`system. The YSZ constituent of this layer 24 serves to
`increase its overall CTE to something closerto the YSZ
`top coat 18.
`[0023] Advantages of using mullite, alumina or a mix-
`ture ofthese with YSZ in the layer24 includetheir higher
`temperature capability as compared to BSAS. Because
`BSAS exhibits low silica activity and low diffusivity to ox-
`idants, a YSZ-containing layer 24 that also contains
`BSAS is also able to serve as an environmental barrier
`
`to the underlying surface region 12. Simultaneously, ad-
`ditions of BSAS to the layer 24 renderthis layer24 more
`compatible with the underlying BSAS layer 22 in terms
`of CTE. Advantageously, BSAS exhibits sufficient envi-
`ronmental resistance such that, if the YSZ top coat 18
`were to spall, the underlying BSAS+YSZ-containing lay-
`er 24 could continue to provide a level of environmental
`protection to the mullite layer 20 and Si—containing sur-
`face region 12.
`is an optional silicon layer
`[0024]
`Shown in Figure 1
`16 between the mullite—containing layer20 and the sur-
`face region 12. In accordance with U.S. Patent Applica-
`tion Serial No. 09/299,418, the inclusion of the silicon
`layer 16 is useful to improve oxidation resistance of the
`surface region 12 and enhance bonding between the
`mullite layer 20 and the surface region 12 ifthe surface
`region 12 contains SiC or silicon nitride (Si3N4). A suit-
`able thickness for the silicon layer 16 is about 12.5 to
`about 250 micrometers.
`
`[0025] As with prior art bond coats and environmental
`coatings, the layers 20, 22 and 24 can be individually
`deposited by air and vacuum plasma spraying (APS and
`VPS, respectively), though it is foreseeable that depo-
`sition could be performed by other known techniques,
`such as chemical vapor deposition (CVD) and high ve-
`locity oxy—fuel (HVOF). The top coat 18 can also be de-
`posited by known techniques, including plasma spray-
`ing and physical vapor deposition (PVD) techniques.
`Thereafter, a heat treatment may be performed after
`deposition of the individual layers 1 6, 20, 22 and 24 and/
`ortop coat 18 to relieve residual stresses created during
`cooling from elevated deposition temperatures.
`[0026] While our invention has been described in
`terms of a preferred embodiment, it is apparent that oth-
`er forms could be adopted by one skilled in the art.
`[0027]
`Forthe sake of good order, various features of
`the invention are set out in the following c|auses:-
`
`1. An article comprising:
`
`GE-1008.004
`
`GE-1008.004
`
`

`
`EP1 142 850 A1
`
`a substrate formed of a silicon-containing ma-
`terial;
`an inner layer overlying the substrate;
`an intermediate layer overlying the inner layer,
`the intermediate layer consisting essentially of
`a thermal—insulating material and at least one
`material selected from the group consisting of
`mullite, alumina and alkaline earth metal alumi-
`nosilicates, the intermediate layer having a co-
`efficient of thermal expansion between that of
`the thermal—insulating material and that of the
`inner layer; and
`a top coat formed of the thermal—insulating ma-
`terial and overlying the intermediate layer.
`
`2. An article as recited in clause 1 , wherein the sub-
`strate is formed of a material selected from the
`
`group consisting of metal matrix composites rein-
`forced with silicon carbide, silicon nitride and/or sil-
`icon, composites having a matrix of silicon carbide,
`silicon nitride and/or silicon, and composites with a
`silicon carbide, silicon nitride and/or silicon matrix
`reinforced with silicon carbide, silicon nitride and/or
`silicon.
`
`3. An article as recited in clause 1 , wherein the inner
`layer contains mullite.
`
`4. An article as recited in clause 3, further compris-
`ing a layer of an alkaline earth metal aluminosilicate
`between the inner layer and the intermediate layer.
`
`5. An article as recited in clause 1 , wherein the inner
`layer consists essentially of barium strontium alu-
`minosilicate.
`
`6. An article as recited in clause 1, wherein the top
`coat consists essentially of yttria—stabilized zirconia.
`
`7. An article as recited in clause 6, wherein the in-
`termediate layer has a substantially uniform com-
`position of yttria—stabilized zirconia and the at least
`one material.
`
`8. An article as recited in clause 6, wherein the in-
`termediate layer comprises sublayers, a first sub-
`layer contacting the inner layer and having a sub-
`stantially uniform composition of at least one mate-
`rial selected from the group consisting of barium
`strontium aluminosilicate, mullite and alumina, a
`second sublayer contacting the topcoat and having
`a substantially uniform composition of yttria—stabi-
`lized zirconia.
`
`9. An article as recited in clause 6, wherein the in-
`termediate layer is compositionally graded, the in-
`termediate layer consisting essentially of barium
`strontium aluminosilicate, mullite and/or alumina at
`
`an interface of the intermediate layerwith the inner
`layer, and consisting essentially of yttria—stabilized
`zirconia at an interface ofthe intermediate layerwith
`the topcoat, the intermediate layer having a de-
`creasing concentration of barium strontium alumi-
`nosilicate, mullite and/or alumina and an increasing
`concentration of yttria—stabilized zirconia in a direc-
`tion away from the inner layer.
`
`10. An article comprising:
`
`a substrate formed of a si|icon—containing ma-
`terial;
`a mullite—containing first layer on the substrate;
`a second layer on thefirst layer, the second lay-
`er consisting essentially of barium strontium
`aluminosilicate;
`a third layer on the second layer, the third layer
`consisting essentially of yttria—stabilized zirco-
`nia and at least one material selected from the
`
`group consisting of barium strontium alumino-
`silicate, mullite and alumina; and
`a top coat of yttria—stabilized zirconia on the
`third layer.
`
`11. An article as recited in clause 10, wherein the
`substrate is formed of a material selected from the
`
`group consisting of metal matrix composites rein-
`forced with silicon carbide, silicon nitride and/or sil-
`icon, composites having a matrix of silicon carbide,
`silicon nitride and/or silicon, and composites with a
`silicon carbide, silicon nitride and/or silicon matrix
`reinforced with silicon carbide, silicon nitride and/or
`silicon.
`
`12. An article as recited in clause 10, wherein the
`first layer is mullite or a mixture of mullite and barium
`strontium aluminosilicate.
`
`13. An article as recited in clause 12, wherein the
`first layer has a thickness of about 25 to about 250
`micrometers.
`
`14. An article as recited in clause 10, wherein the
`first layer consists essentially of mullite.
`
`15. An article as recited in clause 10, wherein the
`first layer consists essentially of a mixture of mullite
`and barium strontium aluminosilicate.
`
`16. An article as recited in clause 10, wherein the
`second layer consists of barium strontium alumino-
`silicate.
`
`17. An article as recited in clause 16, wherein the
`second layer has a thickness of about 125 to about
`500 micrometers.
`
`GE-1008.005
`
`GE-1008.005
`
`

`
`EP1 142 850 A1
`
`10
`
`18. An article as recited in clause 10, wherein the
`third layer as a substantially uniform composition of
`yttria—stabilized zirconia and the at least one mate-
`rial.
`
`19. An article as recited in clause 10, wherein the
`third layer comprises sublayers, a first sublayer
`contacting the second layer and having a substan-
`tially uniform composition of at least one material
`selected from the group consisting of barium stron-
`tium aluminosilicate, mullite and alumina, a second
`sublayer contacting the topcoat and having a sub-
`stantially uniform composition of yttria—stabilized
`zirconia.
`
`20. An article as recited in clause 10, wherein the
`third layer is compositionally graded, the third layer
`consisting essentially of barium strontium alumino—
`silicate, mullite and/or alumina at an interface of the
`third layerwith the second layer, and consisting es-
`sentially of yttria—stabilized zirconia at an interface
`ofthe third layerwith thetopcoat, the third layer hav-
`ing a decreasing concentration of barium strontium
`aluminosilicate, mullite and/or alumina and an in-
`creasing concentration of yttria—stabilized zirconia
`in a direction away from the second layer.
`
`21. An article as recited in clause 10, wherein the
`third layer has a thickness of up to about 500 mi-
`crometers.
`
`22. An article as recited in clause 10, wherein the
`top coat has athickness of about 12.5 to about 1250
`micrometers.
`
`23. An article as recited in clause 10, further com-
`prising a layer of silicon between the first layer and
`the substrate.
`
`24. An article as recited in clause 10, wherein the
`article is a component of a gas turbine engine.
`
`25. A gas turbine engine component formed of a
`si|icon—containing material and having a thermal/
`environmental barrier coating system on a surface
`thereof, the thermal/environmental barrier coating
`system comprising:
`
`a first layer on the surface and consisting es-
`sentially of mullite or a mixture of mullite and
`barium strontium aluminosilicate, the first layer
`having athickness of about 75 to about 250 mi-
`crometers;
`asecond layer on thefirst layer, the second lay-
`er consisting essentially of barium strontium
`aluminosilicate,
`the second layer having a
`thickness of about 125 to about 500 microme-
`
`ters;
`
`a third layer on the second layer, the third layer
`consisting essentially of yttria—stabilized zirco-
`nia and one material selected from the group
`consisting of barium strontium aluminosilicate,
`mullite and alumina, the third layer having a
`thickness of up to about 500 micrometers; and
`a top coat of yttria—stabilized zirconia on the
`third layer, the top coat having a thickness of
`about 12.5 to about 1250 micrometers.
`
`26. A gas turbine engine component as recited in
`clause 25, wherein the component is formed of a
`material selected from the group consisting of metal
`matrix composites reinforced with silicon carbide,
`silicon nitride and/or silicon, composites having a
`matrix of silicon carbide, silicon nitride and/or sili-
`con, and composites with a silicon carbide, silicon
`nitride and/or silicon matrix reinforced with silicon
`
`carbide, silicon nitride and/or silicon.
`
`27. A gas turbine engine component as recited in
`clause 25, wherein the first layer consists essential-
`ly of mullite.
`
`28. A gas turbine engine component as recited in
`clause 25, wherein the first layer consists essential-
`ly of a mixture of mullite and barium strontium alu-
`minosilicate.
`
`29. A gas turbine engine component as recited in
`clause 25, wherein the third layer has a substantial-
`ly uniform composition of a mixture of yttria-stabi-
`lized zirconia and the one material.
`
`30. A gas turbine engine component as recited in
`clause 25, wherein the third layer comprises sub-
`layers, a first sublayer contacting the second layer
`and having a substantially uniform composition of
`barium strontium aluminosilicate, mullite or alumi-
`na, a second sublayer contacting the topcoat and
`having a substantially uniform composition of yttria-
`stabilized zirconia, and at least one intermediate
`sublayer between the first and second sublayers,
`the intermediate sublayer having a composition that
`is intermediatethe compositions ofthefirst and sec-
`ond sublayers.
`
`31. A gas turbine engine component as recited in
`clause 25, wherein the third layer is compositionally
`graded, the third layer consisting essentially of bar-
`ium strontium aluminosilicate, mullite and/or alumi-
`na at an interface of the third layer with the second
`layer, and consisting essentially of yttria—stabilized
`zirconia at an interface ofthethird layerwith the top-
`coat, the third layer having a decreasing concentra-
`tion of barium strontium aluminosilicate, mullite
`and/or alumina and an increasing concentration of
`yttria—stabilized zirconia in a direction away from the
`
`GE-1008.006
`
`GE-1008.006
`
`

`
`EP1 142 850 A1
`
`12
`
`secondlayer
`
`32. A gas turbine engine component as recited in
`clause 25, further comprising a layer of silicon be-
`tween the first layer and the substrate.
`
`Claims
`
`An article (10) comprising:
`
`a substrate (12) formed of a silicon—containing
`material;
`an inner layer (20) overlying the substrate (12);
`an intermediate layer (24) overlying the inner
`layer (20), the intermediate layer (24) consist-
`ing essentially of a therma|—insu|ating material
`and at least one material selected from the
`
`group consisting of mullite, alumina and alka-
`line earth metal aluminosilicates, the interme-
`diate layer (24) having a coefficient of thermal
`expansion between that of the thermal-insu|at-
`ing material and that ofthe inner layer (20); and
`atop coat (18) formed ofthe thermal-insulating
`material and overlying the intermediate layer
`(24).
`
`An article (10) as recited in claim 1 , wherein the sub-
`strate (12) is formed of a material selected from the
`group consisting of metal matrix composites rein-
`forced with silicon carbide, silicon nitride and/or sil-
`icon, composites having a matrix of silicon carbide,
`silicon nitride and/or silicon, and composites with a
`silicon carbide, silicon nitride and/or silicon matrix
`reinforced with silicon carbide, silicon nitride and/or
`silicon.
`
`An article (10) as recited in claim 1 or claim 2,
`wherein the inner layer (20) contains mullite.
`
`An article (10) as recited in any preceding claim, fur-
`thercomprising a layer (22) of an alkaline earth met-
`al aluminosilicate between the inner layer (20) and
`the intermediate layer (24).
`
`An article (1 O) as recited in claim 4, wherein the in-
`ner layer (22) consists essentially of barium stron-
`tium aluminosilicate.
`
`An article (10) as recited in any preceding claim,
`wherein the top coat (18) consists essentially of yt-
`tria—stabilized zirconia.
`
`An article (1 O) as recited in claim 6, wherein the in-
`termediate layer (24) has a substantially uniform
`composition of yttria—stabilized zirconia and the at
`least one material.
`
`8. An article (1 O) as recited in claim 6, wherein the in-
`termediate layer (24) comprises sublayers, a first
`sublayer contacting the inner layer (22) and having
`a substantially uniform composition of at least one
`material selected from the group consisting of bar-
`ium strontium aluminosilicate, mullite and alumina,
`a second sublayer contacting the topcoat (18) and
`having a substantially uniform composition of yttria-
`stabilized zirconia.
`
`An article (10)as recited in claim 6, wherein the in-
`termediate layer (24) is compositionally graded, the
`intermediate layer (24) consisting essentially of bar-
`ium strontium aluminosilicate, mullite and/or alumi-
`na at an interface of the intermediate layer (24) with
`the inner layer (22), and consisting essentially of yt-
`tria—stabilized zirconia at an interface of the inter-
`
`mediate layer (24) with the topcoat (18), the inter-
`mediate layer (24) having a decreasing concentra-
`tion of barium strontium aluminosilicate, mullite
`and/or alumin