Patent Publication Number: US-2021172328-A1

Title: Environmental barrier coating with oxygen-scavenging particles having barrier shell

Description:
BACKGROUND 
     Components in a gas turbine engine often include barrier coatings to protect the underlying component from the effects of the severe operating environment. Barrier coatings are available in numerous varieties, which can include thermal barrier coatings and environmental barrier coatings. Thermal barrier coatings are typically designed for maximizing thermal insulation of a component from the surrounding high-temperature environment. Environmental barrier coatings are typically designed for maximizing resistance of infiltration or attack by the environment. 
     SUMMARY 
     A gas turbine engine article according to an example of the present disclosure includes a substrate and an environmental barrier coating disposed on the substrate. The environmental barrier coating has oxygen-scavenging particles. Each oxygen-scavenging particle has a silicon-containing core particle encased in an oxygen barrier shell. 
     In a further embodiment of any of the foregoing embodiments, the silicon-containing core particle is a silicide of a metal selected from the group consisting of Mo, Nb, Zr, Hf, Ti, W, Y, Yb, Cr, V, Ta, Zn, Al—Si alloys and combinations thereof, and the oxygen barrier shell is a compound of the metal with an element selected from the group consisting of Si, B, C, O, Al, and combinations thereof. 
     In a further embodiment of any of the foregoing embodiments, the silicide is selected from the group consisting of MoSi 2 , Mo 5 Si 3 , NbSi 2 , ZrSi 2 , HfSi 2 , TiSi 2 . WSi 2 , YSi 2 , YbSi 2 , CrSi 2 , VSi 2 , TaSi 2 , SiC, SiOC, SiCNO, SiAlON, and combinations thereof. 
     In a further embodiment of any of the foregoing embodiments, the oxygen barrier shell is a compound of a metal and an element. The metal is selected from the group consisting of Mo, Nb, Zr, Hf, Ti, W, Y, Yb, Cr, V, Ta, Zn, Al—Si alloys and combinations thereof, and the element is selected from the group consisting of Si, B, C, O, Al, and combinations thereof. 
     In a further embodiment of any of the foregoing embodiments, the oxygen barrier shell is Mo—Si—B. 
     In a further embodiment of any of the foregoing embodiments, the oxygen barrier shell is Mo—Si—B—Al—O. 
     In a further embodiment of any of the foregoing embodiments, the oxygen barrier shell is multi-layered. 
     In a further embodiment of any of the foregoing embodiments, the oxygen barrier shell includes layers selected from the group consisting of Mo 5 Si 3 , Mo 5 SiB 2 , MoB 2 , MoSi 2 , and combinations thereof. 
     In a further embodiment of any of the foregoing embodiments, the silicon-containing core particle defines a maximum particle dimension, and the oxygen barrier shell has a shell thickness that is from 0.2% to 40% of the maximum particle dimension. 
     In a further embodiment of any of the foregoing embodiments, the environmental barrier coating has a matrix. The matrix includes silica, and the oxygen-scavenging particles are dispersed through the matrix. 
     In a further embodiment of any of the foregoing embodiments, the silicon-containing core particle is a silicide of a metal selected from the group consisting of Mo, Nb, Zr, Hf, Ti, W, Y, Yb, Cr, V, Ta, Zn, Al—Si alloys and combinations thereof, and the oxygen barrier shell is a compound of the metal with an element selected from the group consisting of Si, B, C, O, Al, and combinations thereof. 
     In a further embodiment of any of the foregoing embodiments, the silicon-containing core particle is selected from the group consisting of silicon carbide, silicon oxycarbide, silicon oxycarbonitride, silicon aluminum oxynitride, and combinations thereof. 
     A method of fabricating a gas turbine engine article according to an example of the present disclosure includes providing a substrate and oxygen-scavenging particles. Each oxygen-scavenging particle includes a silicon-containing core particle encased in an oxygen barrier shell, and depositing the oxygen-scavenging particles on the substrate to form an environmental barrier coating. 
     In a further embodiment of any of the foregoing embodiments, the providing of the oxygen-scavenging particles includes forming the oxygen barrier shell on the silicon-containing core particle. 
     In a further embodiment of any of the foregoing embodiments, the depositing involves at least one of thermal spraying or slurry processing. 
     In a further embodiment of any of the foregoing embodiments, the depositing includes depositing a matrix that comprises silica, and the oxygen-scavenging particles are dispersed through the matrix. 
     In a further embodiment of any of the foregoing embodiments, the silicon-containing core particle is a silicide of a metal selected from the group consisting of Mo, Nb, Zr, Hf, Ti, W, Y, Yb, Cr, V, Ta, Zn, Al—Si alloys and combinations thereof, and the oxygen barrier shell is a compound of the metal with an element selected from the group consisting of Si, B, C, O, Al, and combinations thereof. 
     In a further embodiment of any of the foregoing embodiments, the oxygen barrier shell is multi-layered. 
     In a further embodiment of any of the foregoing embodiments, the silicon-containing core particle is selected from the group consisting of silicon carbide, silicon oxycarbide, silicon oxycarbonitride, silicon aluminum oxynitride, and combinations thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  illustrates a gas turbine engine. 
         FIG. 2  illustrates an example article of the gas turbine engine. 
         FIG. 3  illustrates an isolated view of an oxygen-scavenging particle. 
         FIG. 4  illustrates another example of an oxygen-scavenging particle with a multi-layered shell. 
         FIG. 5  illustrates a method of fabricating the article. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . The fan section  22  drives air along a bypass flow path B in a bypass duct defined within a nacelle  15 , and also drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects, a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated as a geared architecture  48  to drive a fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  may be arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of the low pressure compressor, or aft of the combustor section  26  or even aft of turbine section  28 , and fan  42  may be positioned forward or aft of the location of gear system  48 . 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1 and less than about 5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]{circumflex over ( )}0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 meters/second). 
       FIG. 2  illustrates an example article  60  of the gas turbine engine  20 . For example, although shown schematically, the article  60  may be a turbine blade, a turbine vane, a blade outer air seal, a combustor component, or other component that is subjected to high temperature gases in the engine  20 . 
     The article  60  includes a substrate  62 . For example, the substrate  62  is a high temperature metallic alloy or a ceramic material, such as a monolithic ceramic or a ceramic matrix composite (“CMC”). Example ceramic materials may include, but are not limited to, silicon-containing ceramics. The silicon-containing ceramic may be, but is not limited to, silicon carbide (SiC) or silicon nitride (Si 3 N 4 ). An example CMC may be a SiC/SiC CMC in which SiC fibers are disposed within a SiC matrix. Example metallic alloys may include, but are not limited to, Ni based super alloys, Mo based alloys, Ta—W based alloys, alloys containing Mo, Ta, W, Ni, Ti, Al Hf, Zr, Nb, Si elements. 
     The material of the substrate  62  may be subject to degradation, such as oxidation and steam recession, in the high temperature combustion gases in the core flow path C. In this regard, the article  60  includes an environmental barrier coating  64  (“EBC  64 ”) that is disposed on the substrate  62 . Most typically, the EBC  64  is located on the exposed, gas path side of the substrate  62  in the core flow path C of the engine  20 . 
     The EBC  64  may include multiple layers and materials that are designed, for example, to provide structural integrity and resistance to infiltration and/or attack by environmental substances. In the illustrated example, the EBC  64  includes, but is not limited to, an oxygen barrier layer  66  and a topcoat  68 . In modified examples, the topcoat  68  may be a steam barrier or may be excluded and/or additional layers may be used. The topcoat  68  is not particularly limited and may include a composition that is selected from HfO 2 , rare earth monosilicate (RESiO 5 ), HfSiO 4 , Y 2 Si 2 O 7 , Yb 2 Si 2 O 7 , alkaline earth alumino-silicates (AEAl 2 Si 2 O 8 ) and combinations thereof. Rare earth elements include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y). Alkaline earth elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). 
     The oxygen barrier layer  66  includes oxygen-scavenging particles  70  (“particles  70 ”). The term “oxygen-scavenging” refers to material in which one or more compounds are reactive with oxygen under typical conditions in the engine  20  to limit oxygen from reaching the underlying substrate  62 . In the illustrated example, the particles  70  are dispersed though a matrix  72  but may alternatively be used alone. For instance, the matrix  72  is composed of at least a predominant amount by volume percent of silica but may also include additional additives for further functionality of the oxygen barrier layer  66 . 
       FIG. 3  illustrates an isolated, sectioned view of a representative one of the particles  70 . The particle  70  includes a silicon-containing core particle  74  that is encased in an oxygen barrier shell  76 . The core particle  74  is composed of a silicon-containing material that serves as an oxygen scavenger in the oxygen barrier layer  66 . For example, the silicon-containing material is a silicide, such as a rare earth silicide or a transition metal silicide. In examples, the silicide is a silicide of a metal selected from Mo, Nb, Zr, Hf, Ti, W, Al, Y, Yb, Cr, W, V, Ta, or Zn, or combinations thereof. For example, the silicides are selected from MoSi 2 , Mo 5 Si 3 , NbSi 2 , ZrSi 2 , HfSi 2 , TiSi 2 . WSi 2 , YSi 2 , YbSi 2 , CrSi 2 , VSi 2 , TaSi 2 , alloys of Si with Al or other metals and combination thereof. Other examples of silicon-containing material includes silicon carbide (SiC), silicon oxycarbide (SiOC), silicon oxycarbonitride (SiCNO) and silicon aluminum oxynitride (SiAlON). 
     The silicon-containing material of the core particle  74  functions to capture oxygen that diffuses into the EBC  64 , thereby limiting oxygen from reaching the underlying substrate  62 . The silicon-containing material is functional for this purpose in the engine  20  at high continuous use temperatures of more than 1400° C. At such high temperatures the silicon-containing materials form an oxide scale. The scale slows oxidation and permits the silicon-containing material to provide a stable scavenging function in oxidative environments without undue oxidation. While many EBCs are designed to withstand high or maximum use temperatures, intermediate temperatures may ultimately be more detrimental to the silicon-containing materials. For instance, at temperatures in the vicinity of 500° C. to 1000° C., pesting occurs in which insufficient stable oxide scale is generated. The lack of stable oxide scale results in rapid oxidation of the oxygen scavenging materials, thereby reducing the scavenging functionality over time. The temperature range that pesting occurs varies with materials. Pesting occurs at 500° C.-700° C. for metal containing silicides or silicon-metal alloys, and 700° C.-1000° C. for silicon-containing material without metals. Boron can be mixed into an EBC and then diffused to the silicon-containing particles, however, this requires excessive amounts of boron that can debit other properties. As the engine  20  may spend considerable time at those intermediate temperatures at which pesting occurs, the oxygen barrier shell  76  serves to control oxygen diffusion into the core particle  74  over the intermediate temperatures. The particles  70  are thus engineered for enhanced durability over the full range of operational temperatures. 
     The oxygen barrier shell  76  is a material that includes the metal or combination of metals as in the core particle  74 , in a compound with an element selected from Si, B, C, O, Al, or combinations thereof. Examples include, but are not limited to, Nb—Si—B, Nb—Si—B—O, Zr—Si—B, Zr—Si—B—O, Hf—Si—B, Hf—Si—B—O, Ti—Si—B, Ti—Si—B—O, Y—Si—B, Y—Si—B—O, Ta—Si—B, Ta—Si—B—O, Al 2 O 3 , and combinations thereof. In one example, the oxygen barrier shell  76  is selected from Mo—Si—B, Mo—Si—B—O, Mo—Si—B—Al—O, or combinations thereof for core particles containing Mo. For example, the oxygen barrier shell  76 , such as the Mo—Si—B, may be in the form of layers or mixed phases. For Mo—Si—B, the phases are one or more of Mo 5 Si 3 , Mo 3 Si Mo 5 SiB 2 , MoB, MoSi 2 , and/or Mo—Si—B alloy and the Mo—Si—B—O may be in the form of a Mo-containing borosilicate glass. Additionally, the oxygen barrier shell  76 , such as the Mo—Si—B, Mo—Si—B—O, Mo—Si—B—Al—O, are self-healing. In the event that the oxygen barrier shell  76  is damaged, such as due to thermal stress, the oxygen barrier shell  76  can regenerate. For instance, for Mo—Si—B—Al—O, a Mo and Al containing borosilicate layer may develop below the shell  76  and provide barrier protection and healing capability. Core particles  74  containing other metals can also form metal-Si—B, metal-Si—B—O, or metal-Si—B—Al—O shell materials accordingly. The phases can include metal silicides, metal borides, metal containing borosilicate or alumino-borosilicate glasses. 
     The oxygen barrier shell  76  serves to limit oxygen diffusion over the intermediate temperatures of interest, yet also permit oxygen diffusion to the core particle  74  at higher or maximum use temperatures. In these regards, the oxygen barrier shell  76  should be thick enough to substantially limit oxygen diffusion at the intermediate temperatures but not so thick as to substantially prevent oxygen diffusion at higher temperatures. In general, useful thicknesses can be expressed in terms of the size of the core particle  74 . For example, the core particle  74  defines a maximum particle dimension D 1 , and the oxygen barrier shell  76  has a shell thickness D 2  that is from 0.2% to 40% of the maximum particle dimension D 1 , and in a further example from 0.2% to 10%. Most typically, the core particle  74  is substantially spherical and D 1  is therefore the particle diameter. If the core particle  74  is oblong, D 1  is the size in the long axis direction. In examples, within the percentages above, the dimension D 1  is about 50 micrometers or less, and D 2  is about 0.1 to 15 micrometers. 
       FIG. 4  illustrates another example oxygen-scavenging particle  170 . In this example, the particle  170  includes an oxygen barrier shell  176  that is multi-layered. In the illustrated example, the oxygen barrier shell  176  includes two layers  176   a/   176   b.  It is to be understood, however, that additional layers may be used. The layers  176   a/   176   b  (or additional layers, if used) are selected from Mo 5 Si 3 , Mo 5 SiB 2 , MoB, MoSi 2 , SiB 4  and/or Mo—Si—B alloy, with at least one of the layers being a boron-containing layer. For example, each of these compounds has different ability with respect to self-healing, oxygen diffusion, and silicon diffusion. Therefore, the layers  176   a/   176   b  may be selected from among the noted compounds or other compounds in order to achieve a desired performance for self-healing and oxidation protection of the underlying core particle  74 . 
       FIG. 5  illustrates a method  80  of fabricating the article  60 . In general, as shown at  82 , the method  80  includes providing the substrate  62  and the oxygen-scavenging particles  70  (or  170 ), and depositing the oxygen-scavenging particles  70  on the substrate to form the environmental barrier coating  64 . As examples, the depositing of the oxygen-scavenging particles  70 , and any matrix  72  material and additives, involves at least one of thermal spraying or slurry processing (e.g., via spraying, dipping, etc.). 
     The oxygen-scavenging particles  70  may be provided as pre-fabricated particles. Alternatively, the method  80  may also include fabricating the oxygen-scavenging particles  70 . For instance, as shown at  84 , starting core particles  74  (one shown) and one or more shell materials  76  are provided. For instance, the core particles  74  and shell materials  76  are provided as starting powders. The shell material  76  may be one or more precursors for the final oxygen barrier shell  76 . As shown at  86 , the shell material  76  is attached onto the exterior surface of the core particle  74 . For example, the shell material  76  can be attached on the core particle  74  by mechanical mixing, acoustic mixing, spray drying, vapor deposition methods, or wet chemical techniques. As shown at  88 , the shell material  76  is then consolidated around the core particle  74 . For example, the consolidating includes thermal processing. In one example, the core particle is MoSi 2 . A boron precursor shell material is then deposited by vapor deposition onto the core particle. The thermal processing is conducted in a non-oxidizing environment to cause a reaction between the MoSi 2  and the B to form Mo 5 Si 3 , Mo 5 SiB 2 , MoB, MoSi 2 , SiB 4  and/or Mo—Si—B alloy. The amount and/or thickness of the boron precursor may be controlled in order to control formation of Mo 5 Si 3 , Mo 5 SiB 2 , MoB, MoSi 2 , SiB 4  and/or Mo—Si—B alloy. The formation of various phases are also dependent on temperature and duration of heat treatment. Heat treatment at 1400° C.-1600° C. for 2-24 hours are required to form boron containing phases. For an oxygen barrier shell  76  formed of Al 2 O 3 , the Al 2 O 3  may be fabricated by sol-gel processing. 
     In one example, particles of boron carbide (B 4 C) or mixed particles of boron carbide (B 4 C) and aluminum oxide (Al 2 O 3 ) were attached onto core particles of MoSi 2  by acoustic mixing. The resulting core particles with attached boron carbide were then thermally processed in an oxidizing environment at a temperature of 700° C. to 1200° C. for 1 hour to 50 hours, for example 1000° C. for 10 hours. The thermal treatment converted the boron carbide and aluminum oxide into a relatively uniform shell layer of glassy Mo—Si—B—O or Mo—Si—B—Al—O around the core particle. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.