CMC wall structure with integral cooling channels

[0001] The invention relates generally to ceramic matrix composites (CMC), and more particularly to a cooled CMC wall structure suitable for fabrication with oxide-oxide CMC materials.

[0002] Engine components exposed to the hot combustion gas flow of combustion turbine engines may be formed of a ceramic refractory material. A ceramic matrix composite (CMC) lamellate wall structure with a high temperature ceramic insulation coating, commonly referred to as friable grade insulation (FGI), is described in commonly assigned U.S. Pat. No. 6,197,424. Current materials of this type provide strength and temperature stability to temperatures approaching 1700° C. Cooling of such structures is generally limited to back side air impingement cooling.

[0003] Future combustion turbine designs are expected to require ever increasing firing temperatures that may exceed the operating limits of such designs. An actively cooled CMC wall structure is described in commonly assigned U.S. Pat. No. 6,746,755 where cooling tubes are disposed between the layers of CMC material. Further improvements to permit operation at even higher temperatures are desired.

[0013] The present inventors have found that existing 2D laminate CMC structures are sometimes limited by their relatively low interlaminar strength. An increase in the thickness of the CMC structure will often compensate for relatively low interlaminar strength, however, an increased thickness increases cost, size and weight and reduces the effectiveness of backside cooling. Three dimensional CMC architectures may be used; however, the present inventors have also found that 3D architecture preforms that are significantly greater in thickness than a single fabric ply cannot be infiltrated readily with current matrix infiltration methods. The CMC wall structure geometry of the present invention provides improved performance in interlaminar strength while also providing a means for effective matrix infiltration.

[0014] FIG. 1 is a sectional view of a first of three embodiments of the present invention that are described herein. Reference numerals used to describe features illustrated in the drawings may include the suffix “A” for features unique to the first described embodiment, or they may include the suffix “B” for features unique to the second described embodiment. The third described embodiment includes features selected from the first (A) and the second (B) embodiments.

[0015] CMC wall 20A of FIG. 1 is assembled from first and second CMC sheets 22A, 24A formed of thin 3D weaves with integral cylindrical tubes 26A, 30A providing fluid cooling channels 28A, 32A. In each sheet, the tubes 26A or 30A are connected in a parallel sequence by spans 29A that are generally aligned between the centerlines of each pair of adjacent tubes 26A or 30A. This forms a corrugated first and second surface 36A, 38A on each sheet 22A, 24A. The sheets 22A, 24A are stacked in a nested configuration as in FIG. 1 to construct an interlocking CMC sandwich with a corrugated front surface 36A that provides an improved bonding surface (when compared to prior art non-corrugated planar or curved surfaces) for an insulating layer 40A. The nested CMC corrugations 36A, 38A also provide improved bonding between the CMC sheets 22A, 22B. The resulting insulated CMC structure 20A has a front surface 42A exposed to hot combustion gasses 41, and a corrugated back surface 44A, and it exhibits improved interlaminar shear and tensile strength when compared to prior art designs. The front row of cooling tubes 26A (i.e. closest to the heated surface 42A) protrudes into the insulating layer 40A and provides improved cooling effectiveness for the entire volume of CMC material throughout the wall structure.

[0016] FIG. 2 illustrates two CMC sheets 22A, 24A before stacking. The tubes 26A, 30A may be woven around circular rods 34A and connected by spans 29A aligned with the rod centerlines. The rods 34A may be of a fugitive material. This forms a substantially symmetric sheet structure 22A that can be nested and interlocked with one or more other sheets 24A as shown in FIG. 1, providing increased bond surfaces and tortuous interlaminar stress paths in the wall 20A. The walls of the tubes 26A, 30A and the spans 29A between them are fully accessible prior to stacking of the sheets 22A, 24A, so they can be infiltrated using conventional matrix transfer methods. While prior art full 3D weave options have been proven for non-oxide CMCs and polymer composites, they have not been feasible for processing oxide-matrix CMCs. The present invention may advantageously be applied to oxide-matrix CMCs. In one embodiment the thickness of the spans 29A is between 1 and 2 times the thickness of the walls of the tubes 26A, 30A. The CMC layers may be bonded with an adhesive (not shown) or an integral sinter bond formed by co-processing of the layers. The insulating layer 40A may be cast directly onto the corrugated surface 36A and may be co-processed with the CMC material in one embodiment.

[0017] FIG. 3 illustrates a CMC wall structure as in FIG. 1 with coolant fluid inlets 46, 47, transfer channels 48, and fluid outlets 50, 52, 54. These fluid paths 46, 47 48, 50, 52, 54 are shown schematically in the same plane for clarity only. For example, the fluid inlets 46 may be offset from the transfer channels 48 along an axial length of each back row tube 30A, and the transfer channels 48 may be offset from the fluid outlets 50, 52, 54, along an axial length of each front row tube 26A, so that a cooling fluid 56 flows within a cooling channel 28A, 32A for given distance before exiting it. The fluid inlets 46, 47 conduct a cooling fluid 56 such as air from the back side 44A of the wall structure 20A into the cooling channels 32A, 28A. The fluid 56 may flow along a cooling channel then transfer to another channel via a transfer channel 48. The heated cooling fluid may then exit the front surface 42A of the insulating layer 40A. Alternate fluid outlet configurations 50, 52, and 54 are shown as examples. A plurality of fluid outlets such as 52 along each front row cooling channel 28A may be angled relative to normal to the surface 42A and/or may be fan shaped at the exit for maximum film cooling effectiveness. Cooling fluid may first enter a front row channel 28A through inlet 47 so that the coolest cooling fluid is applied to the highest temperature location of the wall. After passing along a distance of channel 28A, the somewhat heated fluid may then pass through a transfer channel 48 to a back row channel 32A where the cooling demand is somewhat reduced due to the increased distance from the heated surface 42A. After being further heated in channel 32A, the now-spent cooling fluid may pass into the hot combustion fluid gas path 41 through outlet 54. The various inlets, outlets and transfer channels may be formed by processes well known in the art, such as by using fugitive materials during lay-up of the wall fibers, or by mechanical removal of material from the wall such as by drilling.

[0018] FIGS. 4 and 5 illustrate an embodiment B in which first and second CMC sheets 22B, 24B each have semi-cylindrical tubes 26B, 30B providing fluid cooling channels 28B, 32B. In each sheet, these tubes 26B, 30B are connected in a parallel sequence by spans 29B that are generally aligned along a common side of the tubes 26B, 30B. This forms a smooth first surface 36B and a corrugated second surface 38B on each sheet 22B, 24B. The sheets 22B, 24B are stacked in a nested configuration with meshing corrugated surfaces as shown in FIG. 5 to construct an interlocking CMC sandwich with non-corrugated surfaces. An insulating layer 40B may be applied to a front surface 36B of this sandwich, resulting in a CMC wall 20B with smooth, non-corrugated (either planar or smoothly curved) front and back surfaces 42B, 44B. Embodiment B provides improved 3D weave CMC matrix infiltration and interlaminar bonding when compared to prior art designs. As in embodiment A, each of the sheets 22B, 24B can be impregnated individually with a ceramic matrix more effectively than if the complete CMC sandwich structure were made from an integrally woven preform. The interlocking corrugations 38B provide superior shear strength and interlaminar tensile strength. The resulting assembly forms an interlocked truss-core wall structure. FIG. 6 illustrates that the spans 29B of each sheet 22B, 24B may be formed integrally with the respective tubes 26B, 30B, including continuous ceramic fibers or tows 58 crossing the spans. FIG. 7 illustrates a geometry in which the spans 29B have generally the same thickness as the walls of the tubes 26B.

[0019] FIG. 8 shows an embodiment C that combines a front sheet 22A of embodiment A with a back sheet 24B of embodiment B to form a hybrid wall structure 20C. This embodiment provides improved interlaminar strength, improved surface layer bonding strength, and a smooth back surface 44B, which can allow a thinner wall structure 20C than wall 20A of FIG. 1.

[0020] While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. For example, the fluid inlet 46, transfer 48, and outlet channels 50, 52, 54 shown in FIG. 3 may optionally be used with any of the embodiments A, B, C. Further, while only two sheets of CMC material are illustrated, additional layers may be used. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.