Patent Application
20100047512
The present invention is generally related to ceramic structures for use in a high temperature combustion environment, and, more particularly, to structural arrangements and techniques for strengthening a surface bond between corresponding surfaces of an insulating ceramic coating and ceramic matrix composite (CMC) substrate, which is thermally protected by the ceramic coating.
Engine components in the hot gas flow of modern combustion turbines are required to operate at ever-increasing temperatures as engine efficiency requirements continue to advance. Ceramics typically have higher heat tolerance and lower thermal conductivities than metals, particularly in the case of oxide-based ceramic materials. For this reason, ceramics have been used both as structural materials in place of metallic materials and as coatings for both metal and ceramic structures. Ceramic matrix composite (CMC) wall structures with ceramic insulation outer coatings, such as described in commonly owned U.S. Pat. No. 6,197,424, have been developed to provide components with the high temperature stability of ceramics without the brittleness of monolithic ceramics.
The versatility of an insulated CMC material may be influenced by the strength of the bond between the insulation and the structural CMC material. For example, some environments and/or engine components may require an incremental bonding strength relative to a baseline bond strength Accordingly, further improvements that increment the bonding strength between the insulation and the structural CMC material are desired.
The invention is explained in the following description in view of the drawings that show:
The inventors of the present invention propose structural arrangements and techniques conducive to strengthening a surface bond between corresponding surfaces of insulating ceramic coating 14 and CMC substrate 12. Aspects of the present invention propose tooling arrangements and methodology innovatively adapted to affect the bonding characteristics between such surfaces.
As shown in
As a result of the urging (e.g., pressure force) applied to the opposing surfaces, teeth 26 penetrate through the surface of the substrate to cut at least some of the fibers beneath the surface of the substrate into split fiber segments 26, as conceptually represented in
In another example embodiment shown in
It is contemplated that in one practical embodiment the respective sets of teeth having the first degree of sharpness and the second degree of sharpness will be arranged in a common tool 40 as illustrated in
In a practical embodiment, the urging force may correspond to a laminate consolidation pressure normally applied during a laminate (e.g., inter-layer) consolidation stage—usually a pressure that in one example embodiment may range from approximately 10 psi to approximately 200 psi. Furthermore, such consolidation normally is applied by a standard tooling (e.g., hard plate) on at least one side of the laminate. Thus, it is contemplated that a tooling arrangement embodying aspects of the present invention may be integrated into the standard tooling used for consolidation and thus it is believed that aspects of the present invention do not entail a post-consolidation process step or adding extra manufacturing steps. It will be appreciated that the values of the consolidation pressure may be adjusted based on the needs of a given application, e.g., size and/or pattern of features.
In this example embodiment, the plurality of surface indents 36 constitutes a second bond-enhancing arrangement between the surface 20 of the ceramic substrate and the corresponding boundary of the coating. Indents enhance the bonding strength by increasing whetted surface area, providing a non-planar crack propagation surface, and allowing the coating particles to nest within the surface of the substrate and span the substrate-coating interface. Thus, in an example embodiment that includes both a cutting arrangement and/or a blunting arrangement, the first and second bond-enhancing arrangements provide in combination a mechanical bonding arrangement between the surface of the ceramic substrate and the corresponding boundary of the coating.
It will be appreciated that the depth and inter-spacing of such indents can be adjusted for a given application based, for example, on any given fiber or fabric characteristics of the substrate and/or the expected size of bodies in the coating (e.g., hollow ceramic spheres). In one example embodiment, the inter-spacing and depth of the indents may be configured to partially or completely accept the largest ceramic spheres that may be present in the coating. This may provide a fit to the spheres conducive to further increment the bonding and avoid characteristics of the interface that can promote crack propagation and delamination. In this example embodiment, the spacing between respective centers of the indents may range from about equal to the diameter (D) of the largest sphere to about an order of magnitude greater than the largest sphere's diameter (e.g., from about D to about 10D). Similarly, the depth of the indents may range from about 20% to about 200% of the diameter (D) of the largest sphere (e.g., from about 0.2D to about 2D). For readers desirous of general background information regarding example considerations for choosing the inter-spacing and depth of the surface indents, in connection with achieving a desired fit with the spheres in the thermal coating, reference is made to U.S. patent application Ser. No. 11/600,709, filed on Nov. 16, 2006 titled “Ceramic Matrix Composite Surfaces With Open Features For Improved Bonding To Coatings”, assigned to the same assignee of the present invention and herein incorporated by reference.
The disclosure above describes various example tooling arrangements that may include a first set of teeth having a first degree of sharpness, a second set of teeth having a second degree of sharpness, and a combination of such arrangements. It will be appreciated by those skilled in the art, that such tooling arrangements are not limited to tooling arrangements having teeth-like projections since many other arrangements may equally provide the desired cutting action and/or blunting action. For example, it is contemplated that a suitably configured wire mesh arrangement may be used in the tooling arrangement. It is further contemplated that a prismatic light diffuser, such as may be made from plastic, may be used equally effective in the tooling arrangement. Accordingly, as used in the present disclosure, the term “teeth” should not be construed as being limited to teeth-like projections from the surface of the tool.
Example variations in the tooling arrangement may include the distribution, spacing, pattern, and depth of the indents or tooling features. Although example penetration depths explored so far (e.g., ranging from approximately 1 mm to approximately 3 mm) and spacing (e.g., ranging from approximately 3 mm to approximately 10 mm) have proven effective, it is contemplated that tooling arrangements that may include pattern variations and/or random depth variation may further strengthen the resulting surface bond.
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. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
