Patent ID: 12227463

DETAILED DESCRIPTION

FIG.1schematically illustrates a gas turbine engine20. The gas turbine engine20is disclosed herein as a two-spool turbofan that generally incorporates a fan section22, a compressor section24, a combustor section26and a turbine section28. The fan section22drives air along a bypass flow path B in a bypass duct defined within a housing15such as a fan case or nacelle, and also drives air along a core flow path C for compression and communication into the combustor section26then expansion through the turbine section28. 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 engine20generally includes a low speed spool30and a high speed spool32mounted for rotation about an engine central longitudinal axis A relative to an engine static structure36via several bearing systems38. It should be understood that various bearing systems38at various locations may alternatively or additionally be provided, and the location of bearing systems38may be varied as appropriate to the application.

The low speed spool30generally includes an inner shaft40that interconnects, a first (or low) pressure compressor44and a first (or low) pressure turbine46. The inner shaft40is connected to the fan42through a speed change mechanism, which in exemplary gas turbine engine20is illustrated as a geared architecture48to drive a fan42at a lower speed than the low speed spool30. The high speed spool32includes an outer shaft50that interconnects a second (or high) pressure compressor52and a second (or high) pressure turbine54. A combustor56is arranged in the exemplary gas turbine20between the high pressure compressor52and the high pressure turbine54. A mid-turbine frame57of the engine static structure36may be arranged generally between the high pressure turbine54and the low pressure turbine46. The mid-turbine frame57further supports bearing systems38in the turbine section28. The inner shaft40and the outer shaft50are concentric and rotate via bearing systems38about the engine central longitudinal axis A which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor44then the high pressure compressor52, mixed and burned with fuel in the combustor56, then expanded through the high pressure turbine54and low pressure turbine46. The mid-turbine frame57includes airfoils59which are in the core airflow path C. The turbines46,54rotationally drive the respective low speed spool30and high speed spool32in response to the expansion. It will be appreciated that each of the positions of the fan section22, compressor section24, combustor section26, turbine section28, and fan drive gear system48may be varied. For example, gear system48may be located aft of the low pressure compressor, or aft of the combustor section26or even aft of turbine section28, and fan42may be positioned forward or aft of the location of gear system48.

The engine20in one example is a high-bypass geared aircraft engine. In a further example, the engine20bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), and can be less than or equal to about 18.0, or more narrowly can be less than or equal to 16.0. The geared architecture48is 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. The gear reduction ratio may be less than or equal to 4.0. The low pressure turbine46has a pressure ratio that is greater than about five. The low pressure turbine pressure ratio can be less than or equal to 13.0, or more narrowly less than or equal to 12.0. In one disclosed embodiment, the engine20bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor44, and the low pressure turbine46has a pressure ratio that is greater than about five 5:1. Low pressure turbine46pressure ratio is pressure measured prior to an inlet of low pressure turbine46as related to the pressure at the outlet of the low pressure turbine46prior to an exhaust nozzle. The geared architecture48may 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 section22of the engine20is 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 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. The engine parameters described above and those in this paragraph are measured at this condition unless otherwise specified. “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, or more narrowly greater than or equal to 1.25. “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)]0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150.0 ft/second (350.5 meters/second), and can be greater than or equal to 1000.0 ft/second (304.8 meters/second).

FIG.2schematically illustrates a representative portion of an example article100for the gas turbine engine20that includes a composite material102that is used as a barrier layer. The article100can be, for example, an airfoil in the compressor section24or turbine section28, a combustor liner panel in the combustor section26, a blade outer air seal, or another component that would benefit from the examples herein. In this example, the composite material102is used as an environmental barrier layer to protect an underlying substrate104from environmental conditions, as well as thermal conditions in some cases. The article100can be made from a ceramic-based material, such as a ceramic matrix composite (CMC) material, or a metallic material, such as a refractory metal or refractory metal alloy. As will be appreciated, the composite material102can be used as a stand-alone barrier layer, as an outermost/top coat with additional underlying layers, or in combination with other coating under- or over-layers, such as, but not limited to, ceramic-based topcoats.

The composite material102includes a matrix106, a dispersion of “gettering” particles108, and a dispersion of “diffusive” particles110. The matrix106can be, in one example, silicon dioxide (SiO2). Other possible matrices106include other silicates such as silicate glasses, partially crystalline glasses or crystalline silicates such as hafnium silicate or rare earth silicates. The barrier layer formed of the composite material102protects the underlying substrate104from oxygen and water, primarily in the form of steam. For example, the substrate104can be a ceramic-based substrate, such as a CMC material. The gettering particles108and the diffusive particles110of the barrier layer function as an oxygen and steam diffusion barrier to limit the exposure of the underlying substrate104to oxygen and/or steam from the surrounding environment. The gettering particles108are reactive with respect to oxidants and/or water and mitigate oxidants and/or water from diffusing through the barrier layer. Without being bound by any particular theory, the diffusive particles110enhance oxidation and steam protection by diffusing to the outer surface of the barrier layer opposite of the substrate104and forming a sealing layer that seals the underlying substrate104from oxygen/steam exposure. Further, the diffusion behavior of the diffusive particles110may operate to seal any microcracks that could form in the barrier layer. Sealing the micro-cracks could prevent oxygen from infiltrating the barrier layer, which further enhances the oxidation resistance of the barrier layer. One example diffusive particle110is barium-magnesium alumino-silicate particles (“BMAS particles110”), though other examples are contemplated.

FIG.3shows another example article200that includes the composite material102as a barrier layer arranged on the substrate104. In this example, the article200additionally includes a ceramic-based top coat114interfaced with the barrier layer. As an example, the ceramic-based top coat114can include one or more layers of an oxide-based material. The oxide-based material can be, for instance, hafnium-based oxides, yttrium-based oxides (such as hafnia, hafnium silicate, yttrium silicate, yttria stabilized zirconia or gadolinia stabilized zirconia), or combinations thereof, but is not limited to such oxides.

The gettering particles108are reactive with respect to oxidant particles and/or water, which could diffuse into the barrier layer102. In this way, the gettering particles108could reduce the likelihood of those oxidant molecules from reaching and oxidizing the substrate104. The gettering particles108generally include silicon, and in some particular examples are intermetallic silicides. The metal components can be refractory metals, in some examples. Refractory metals include Mo, W, Nb, Ta, Cr, Ti, Zr, Hf, V, and Y. Example intermetallic silicides are MoSi2and WSi2. Complex or alloyed silicides are also contemplated, such as Mo—Ta—Si, Mo—W—Si, Mo—Si—C, or Mo—Si—B alloys. Some particular example complex alloyed silicides are W0.4Mo0.4Cr0.2Si2and W0.2Ta0.2Mo0.2Nb0.4-xδxSi2; where δ is Ti, Hf, or Zr, and x is less than 0.1. Other complex alloyed silicides are also contemplated. The gettering particles108can include mixtures of silicides.

The composite material102can be fabricated by a slurry coating method400, which is schematically shown inFIG.4. In step402, a slurry is prepared by mixing components for the gettering particles108, diffusive particles110, and matrix material106in a carrier fluid. The slurry can be aqueous, e.g., the carrier fluid is water or water-based. The components for the gettering particles108include elemental precursors for the desired silicide. For example, if the desired silicide is MoSi2, the slurry includes elemental precursors Mo and Si. Some of the elemental precursors can be drawn from components of the diffusive particles110/matrix106. For instance, if the matrix106is or includes silica, elemental silicon can be silicon in the silica, though in other examples elemental silicon could also be added. Metallic elemental precursors can be in powder form. The slurry can be mixed by agitation or ball milling, or any other known method. The mixing encourages the elemental precursor materials to be near one another, touch, or become embedded in one another. For example, silicon can become embedded in Mo particles. This is known as “mechanical alloying.”

In step404, the slurry is applied to the underlying substrate104by painting, dipping, spraying, or any other known method.

In step406, the slurry is subjected to a low-heat treatment at room temperature or at a slightly elevated temperature. This removes all or most of the carrier fluid and situates the other slurry components on the substrate104without sintering the slurry. The low-heat treatment is performed at temperatures substantially lower than the sintering temperatures in step410, discussed below. In one example, the low-heat treatment is performed at temperatures of less than about 500° C. In one example, the slurry is dried and cured at about 200° C. for at least 15 minutes to ensure proper cross-linking of the coating. The low-heat treatment step can occur in an air environment.

In step408, the topcoat114is applied over the coating after step406. The topcoat can be applied by any known method. One particular example is plasma spraying. In other examples, the topcoat114can be applied after the sintering step410(discussed below).

In step410, the coating from step406(with or without the topcoat114) is sintered to form composite material102. Sintering includes heating the coating to temperatures that exceed about 1000° C. in an inert atmosphere. The heating encourages reactions between the elemental precursors of the gettering particles108to react with one another and form the silicide gettering particles108, which are already near one another, touching, or embedded in one another as a result of the mixing in step402. As noted above, the elemental precursors could be separately added to the slurry or could be in other components such as the diffusive particles110and/or matrix106. For instance, for MoSi2, elemental Mo in the form of Mo powder could react with elemental silicon in the form of Si powder. In this way, the gettering particles108are formed in situ. These silicide-forming reactions are exothermic reactions, meaning as the reactions proceed they give off heat. Therefore, the sintering step410can occur at temperatures lower than traditional methods of forming composite material102, where the gettering particles108are pre-fabricated and added to the slurry in step402, by taking advantage of the exothermic silicide-forming reactions. For example, in the traditional method, the composite material102is sintered at temperatures of about 1500° C. or greater. In the instant method400, the sintering step410can be performed at temperatures of about 100° C. to about 500° C. lower, e.g., at temperatures between about 1000° C. and about 1400° C., by taking advantage of the exothermic in situ formation of the silicide gettering particles108. The lower curing temperature can improve the longevity of the underlying substrate104, especially if the underlying substrate104is or includes a material that is sensitive to long-term exposure to very high curing temperatures.

Additionally, the in situ formation of silicide gettering particles108via the method400allows for the use of complex alloyed silicides, or combinations of silicides, by simply including the elemental precursor materials in the slurry. For instance, MoSi2and Mo5Si3C gettering particles108can be formed by including carbon (or a carbon-containing component), silicon (or a silicon-containing component) and elemental Mo powder. A mixture of elemental Mo, Si, and C powders could be added to the slurry. Alternatively, Mo2C, Mo, and Si powders could be added to the slurry. Mo—Ta-silicides can also easily be included just by adding elemental Ta powder to the slurry that contains elemental Mo and elemental Si powders. Other silicides, such as Ti-containing silicides, can be formed in a similar manner. Thus, a wider range of silicides and resulting properties (including gettering properties or other desirable properties such as thermal protection, mechanical strength, etc.) can be achieved, depending on the desired application for the composite material102.

In some examples, energy other than heat energy can be applied to the coating in step410to assist in inducing the silicide-forming reactions discussed above. The energy can be in the form of sound energy or electrical energy, for instance.

In examples where the topcoat114is applied prior to the curing step410, the topcoat114can have a thermal insulating effect during the curing step410. In other words, the topcoat114can capture heat from the exothermic silicide-forming reactions in the coating. Elevated temperatures can in some examples reduce the time required for the curing step410.

The maximum temperature the slurry can reach due to the heat released by the exothermic silicide-forming reactions in step410discussed above depends upon the follow factors: (1) the temperature at which that reaction is initiated in the slurry (e.g., approximately the temperature at which the sintering step410takes place); (2) the volume fraction of the silicide-forming materials within the slurry (e.g., the volume fraction of the elemental precursors of the gettering particles108); (3) the heat capacity of the constituents of the slurry; and (4) the thermal diffusivity of the adjacent layers to the slurry, e.g., the substrate104and/or topcoat114. With these considerations, the temperature increase associated with the exothermic reaction can be controlled. An example of the limit case in which the adjacent layers are perfect insulators (adiabatic heating) assuming a sintering temperature of 1000° C. is presented inFIG.6, along with examples where adjacent layers have 90%, 75%, and 50% heat retention. In this example, MoSi2is an elemental precursor of the gettering particles108. As shown inFIG.6, depending on the volume fraction of MoSi2in the slurry, the exothermic reactions can raise the temperature of the slurry significantly, up to about 2000° C. in some cases.

In one example shown inFIG.5, another example component300has composite material202with silicide gettering particles208resulting from the method400with platelet-like shapes, e.g., the gettering particles208have an aspect ratio that is not equal to 1. The composite material202is disposed on a substrate204. In some examples, the aspect ratio of the gettering particles208is less than about 5:1, and the gettering particles208comprise at least about vol. % of the composite material202. In a particular example, a major axis of the platelet gettering particles208is substantially parallel to a surface of the substrate104. Thus the platelet gettering particles208are substantially aligned with one another and with respect to the surface of the substrate104. The common alignment of the platelet gettering particles208encourages the formation of an interconnected matrix of platelet gettering particles208. The interconnected matrix can impart mechanical strength to the composite material202. Additionally, the interconnected matrix of platelet gettering particles208has lower surface-area-to-volume ratio as compared to a dispersion of non-interconnected particles which provides less surface area that is available for reaction with oxidants as discussed above, and can therefore extend the duration through which the barrier layer102imparts oxidation resistance of the composite material202. In some examples, the interconnected matrix of platelet gettering particles208can have a surface area to volume ratio of less 200,000:1 meters−1.

In general, the silicide gettering particles208have a shape that tracks the shape of the elemental precursor components after the mixing in step402discussed above. Some mixing processes, such as ball milling, can encourage the formation of the platelet-like shapes. Moreover, the gettering particles208form in a location within the composite material202that is generally the same location as the location of the elemental precursors after the applying step202discussed above.

The example component300can optionally include the topcoat114as discussed above.

Although the different examples are illustrated as having specific components, the examples of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the embodiments in combination with features or components from any of the other embodiments.

The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.