Patent Application
20100266391
This invention relates to thermal barriers and, more particularly, to a ceramic or metal foam thermal barrier that may be mechanically attached to a support.
Components that are exposed to high temperatures, such as gas turbine engine components, typically include a protective coating system having one or more coating layers. For example, turbine blades, turbine vanes, combustor linings, and blade outer air seals may include a coating system or liner to protect from erosion, oxidation, corrosion or the like to thereby enhance durability or maintain efficient operation of the engine.
Typical coating systems include a ceramic coating that is applied onto a substrate. Additional intermediate layers, such as bond coats, may be used between the ceramic coating and the substrate. Although effective, under certain thermal conditions, ceramic coatings may crack, erode, oxidize, or otherwise corrode to cause spalling.
Accordingly, there is a need for other types of structures that have enhanced thermal resistance and a method for securing the structures to a component or support.
An example thermal barrier includes a thermal barrier member having at least one material selected from a metal foam or a ceramic foam. The thermal barrier member includes an attachment section for securing the thermal barrier member with a corresponding attachment section of a support.
In one example, the attachment section of the thermal barrier member is a slot for removably securing the thermal barrier member with the corresponding attachment section of the support. In some examples, the thermal barrier member includes a porosity gradient between sides of the thermal barrier member.
In a disclosed example, the thermal barrier member is part of a blade outer air seal within a turbine engine, where the turbine engine includes a combustion section and a turbine section downstream of the combustion section. The blade outer air seal is located radially outwards of a turbine blade of the turbine section.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.
As is known, air compressed in the compressor section 16 is mixed with fuel and burned in the combustion section 18 to produce combustion gases that are expanded in the turbine section 20.
In the disclosed example, the thermal barrier member 46 includes attachment sections 48 for mechanically interlocking with the supports 32a. The attachment sections 48 each include a slot 50 that receives corresponding tabs 52 of the supports 32a.
The thermal barrier member 46 includes a leading edge 54, a trailing edge 56, circumferential sides 58, a radially inner side 60, and a radially outer side 62 relative to the engine centerline 12. In the disclosed example, the slots 50 extend through the respective leading edge 54 and trailing edge 56. The location of the slots 50 at the leading edge 54 and trailing edge 56 provides the benefit of permitting the thermal barrier member 46 to directly seal against a circumferentially neighboring seal member 30 in the ring assembly. The location also leaves the radially outer side 62 unobstructed to provide an open area for cooling fluid flow, if cooling is used.
In one example, a plurality of the thermal barrier members 46 are assembled circumferentially side by side around a circumference of the engine 10 into the ring assembly. For example, each of the thermal barrier members 46 may be removably slid onto the supports 32a, as indicated by arrow 63. Alternatively, the slots 50 may extend through the circumferential sides 58 such that the thermal barrier member 46 axially slides onto the supports 32a.
In the disclosed example, the thermal barrier member 46 includes a foam structure. For example, the foam structure may include a ceramic foam or a metal foam that is formed into a tile. In one example, the ceramic foam includes a ceramic material selected from at least one of zirconia, yttria-stabilized zirconia, silicon carbide, alumina, titania, or mullite. In a further example, the yttria-stabilized zirconia includes about 7 wt % of the yttria and a balance of zirconia or about 20 wt % of the yttria and a balance of the zirconia.
If the foam structure is metal foam, the metal foam may include at least one metal selected from a nickel-based alloy, a cobalt-based alloy, a molybdenum-based alloy, or a niobium-based alloy. Given this description, one of ordinary skill in the art will be able to recognize other foam structures that are suitable to fit their particular needs.
The foam structure of the thermal barrier member 46 may be fabricated using any suitable method. For example, a slurry of metal or ceramic particles may be infiltrated into a porous polymer foam and heated to remove the polymer and sinter the metal or ceramic particles together to form a foam structure. Alternatively, a foaming agent may be used in combination with a metal or ceramic slurry to form pores upon heating the slurry to sinter the metal or ceramic particles together.
In another example, polymer particles may be mixed with a slurry having metal or ceramic particles and formed into a green body. The green body may then be heated to thermally remove the polymer particles and form pores in the green body. The green body is then heated to sinter the metal or ceramic particles together. Given this description, one of ordinary skill in the art will recognize other suitable foam structure fabrication methods to meet their particular needs.
Optionally, the thermal barrier member 46 may include a porosity gradient 64 that extends between the radially outer side 62 and the radially inner side 60. For example, the porosity gradient 64 may include a larger average pore size near the radially inner side 60 and a relatively smaller average pore size near the radially outer side 62. The pore gradient 64 may provide the benefit of enhanced abradability at the radially inner side 60 for contact with tips of the turbine blades 22 and enhanced structural strength through the body of the thermal barrier member 46 for resisting stresses between the support 32a and the thermal barrier member 46.
Optionally, a cooling source 66 may be used to provide cooling air to the thermal barrier member 46. For example, the cooling source 66 is an impingement cooling arrangement provided by a bleed flow from a relatively cool air stream through the gas turbine engine 10. The cooling source 66 provides cooling air on the radially outer side 62. The cooling air infiltrates the pores of the foam structure of the thermal barrier member 46. The open cell pores relatively uniformly distribute the cooling air through the thermal barrier member 46 to provide uniform cooling. Using the pores to evenly distribute the cooling air may permit machined or formed cooling passages to be eliminated in at least some examples.
The thermal barrier member 76 is similar to the thermal barrier member 46 of the previous example, except that the attachment section 78 opens to the radially outer side 62 and has a different shape. The attachment section 78 includes a T-shaped slot 80 formed in the thermal barrier member 76. The T-shaped slot 80 corresponds to a T-shape of the support 32b such that the slot 80 and the support 32b mechanically interlock to secure the thermal barrier member 76 to the support 32b. In one example, the thermal barrier member 76 can be removably assembly with the support 32b.
The slot 80 of the thermal barrier member 76 may be formed in any suitable manner as discussed above and with any desired orientation relative to the circumferential sides 58, leading edge 54, and trailing edge 56. For example, the slot 80 can be machined into the thermal barrier member 76, such as by using a cutting tool or electro-discharge machining. Alternatively, the slot 80 can be formed in the thermal barrier member 76 during fabrication of the thermal barrier member 76, such as by forming the slurries described above into a green body having a desired shape.
In this example, the curved walls 92 of the slot 90 provide the benefit of providing relatively low stress interfaces between the thermal barrier member 86 and the support 32c that avoids stress concentrators that may be associated with relatively sharp angle interfaces.
In this example, the thermal barrier member 96 is similar to the thermal barrier members 86, 76, and 48 of the previous examples except that the attachment section 98 and support 32d have different shapes. In the disclosed example, the attachment section 98 includes a slot 100 that extends between the radially outer side 62 and the radially inner side 60. The slot 100 may be formed in any suitable manner as discussed above and with any desired orientation relative to the circumferential sides 58, leading edge 54, and trailing edge 56. In this example, the slot 100 tapers, or narrows, from the radially inner side 60 to the radially outer side 62 to form a frustoconical cavity.
The support 32d in this example is a bolt 102 having a head 104 connected with a threaded shank 106. The bolt extends through the slot 100 such that the head 104 is received within the frustoconical cavity and is flush with or recessed below the radially inner side 60. The bolt 102 may be secured to the outer case 32 to secure the thermal barrier member 96 within the gas turbine engine 10.
A cooling passage 108 extends through the threaded shank 106 into the head 104. The cooling passage 108 divides into a plurality of second cooling passages 110 that open out to the radially inner side 60. The cooling passages 108 and 110 receive cooling air from the cooling source 66 to maintain the radially inner side 60 at a desired temperature.
The supports 32a, 32b, 32c, and 32d in any of the above examples may be formed from any suitable material. For example, the supports 32a, 32b, 32c, and 32d comprise a metal or metal alloy, such as a nickel-based alloy, a cobalt-based alloy, a molybdenum-based alloy, or a niobium-based alloy. In some examples, the supports 32a, 32b, 32c, and 32d are solid. However, in other examples, the supports 32a, 32b, 32c, and 32d include an open cell foam structure as discussed above, which permits cooling air from the cooling sources 66 to flow there through to cool the supports 32a, 32b, 32c, and 32d and respective thermal barrier members 46, 76, 86, and 96.
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 the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.
