Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-03-14
2001-11-13
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S161000, C428S163000, C428S164000, C428S172000, C427S248100, C427S271000, C427S299000
Reexamination Certificate
active
06316078
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention pertains to the art of thermal barrier coating systems having enhanced resistance to spallation in components exposed to high temperatures, and more specifically to a segmented thermal barrier coating system resulting from modification of the substrate surface and/or modification of one or more layers of a thermal barrier coating.
2. Description of the Related Art
Thermal barrier coatings (TBC) are known in the art in order to protect components which are subjected to high temperature operations. Generally, the thermal barrier coating system includes a ceramic layer for thermal insulation of the component in combination with an additional layer called a bond coat located between the substrate and the ceramic layer. The bond coat typically serves to increase adherence of the ceramic layer on the metallic substrate and protect the underlying substrate from oxidation.
When the substrate is subjected to repeated heating/cooling cycles, thermally induced stresses and strains are produced and accumulate within the thermal barrier coating system. The most common mechanism of failure of the thermal barrier coating system is the spallation of the coating in local regions of the protected component. A crack is produced in the thermal barrier coating where it propagates until a portion of the coating system flakes or chips away. Such spallation failure may occur in patches or over an entire surface.
A number of techniques have been developed to reduce the tendency toward spallation failure of the thermal barrier coating. For example, U.S. Pat. No. 5,558,922 to Gupta discloses a thermal barrier coating for reducing long range stresses. Grooves are formed in the thermal barrier coating in a grid-like pattern, with a groove width of 0.1-0.5 mm (0.004-0.02 inches) and widely spaced from 10-250 mm (0.4-10 inches). This technique is usually directed for use with thick (750 micron, 0.03 inch) TBCs.
As disclosed in U.S. Pat. No. 5,840,434 to Kojima, a segmented thermal barrier coating is produced by separation between columns of the thermal barrier coating grains. This microstructure is produced by control of a physical vapor deposition (PVD) process. The induced cracks are very fine, from 5-10 microns, and closely spaced, about 100-200 microns.
U.S. Pat. No. 5,652,044 to Rickerby discloses a thermal barrier coating comprising a plurality of alternating layers to produce a plurality of interfaces substantially parallel to the metallic substrate/bond coating interface. The structure in the alternating layers is columnar, similar to the microstructure taught in the Kojima reference.
U.S. Pat. No. 5,419,971 to Skelly discloses a very fine surface texturing by means of a grid pattern of v-shaped grooves produced by laser grooving for the purpose of impeding crack growth at the interface of the thermal bond coat and the substrate. The surface features are only about 0.0005 inches deep by 0.0005 inches wide and spaced about 0.005 inches apart.
Other art relevant to the present invention includes U.S. Pat. No. 5,538,796 to Schaeffer et al. wherein an electron beam physical vapor deposition (EB-PVD) thermal barrier coating deposited on a low sulfur or hydrogen annealed single crystal superalloy is disclosed.
Additionally, U.S. Pat. No. 5,302,465 to Miller et al. describes a technique for depositing a yttria stabilized zirconia thermal barrier coating directly onto an oxidation resistant metal without a bond coat.
Although progress has been made, there still exists a need in the art to reduce spallation failure for components subjected to hostile environments.
SUMMARY OF THE INVENTION
The present invention is directed to a macro-segmented thermal barrier coating system wherein each local segment provides increased resistance to spallation. In addition, the macro-segmentation of the thermal barrier retards crack propagation between segments so that the life of the coated component is increased even after local spallation occurs.
In accordance with the present invention, an article protected by a thermal barrier coating system is provided. The article includes a substrate having a first surface for supporting a thermal barrier coating, a thermal barrier coating including a thermal barrier layer being associated with a thickness T, and means for segmenting the thermal barrier coating. The segmenting means includes a plurality of three dimensional features positioned along an imaginary grid defined in a predetermined relationship to the first surface of the substrate. The imaginary grid defines cells of dimension D
1
×D
2
wherein D
1
has a value in the range of 0.05 inches to 0.30 inches, inclusive and D
2
has a value in the range of 0.05 inches to 0.30 inches, inclusive.
According to one aspect of the invention, the imaginary grid may be coincident with the first surface of the substrate and the features are raised ribs formed on the first surface. The ribs have an associated rib height, R.
According to another aspect of the invention, the ribs may be continuous.
According to another aspect of the invention, the ribs may be discontinuous.
According to another aspect of the invention, R has a value approximately 25% to 100% of T.
According to another aspect of the invention, the imaginary grid is coincident with the first surface of the substrate and the features are grooves formed in the first surface. The grooves have an associated groove depth, G.
According to another aspect of the invention, G has a value approximately 25% to 100% of T.
According to another aspect of the invention, the thermal barrier coating further includes a bond coat layer intermediate the substrate and the thermal barrier layer and the imaginary grid is coincident with a first surface of the bond coat layer. The features may be raised ribs formed on the first surface of the bond coat layer.
According to another aspect of the invention, the thermal barrier coating further includes a bond coat layer intermediate the substrate and the thermal barrier layer and the imaginary grid is coincident with a first surface of the bond coat layer. The features may be grooves formed in the first surface of the bond coat layer.
According to another aspect of the invention, T has a value from approximately 0.002 inches (0.005 cm) to 0.03 inches (0.075 cm), inclusive.
According to another aspect of the invention, the features are associated with a width W, and D
1
has a value at least 10W.
According to another aspect of the invention, a method for preparing a coated article having a segmented thermal barrier coating is provided. The method comprises the steps of furnishing a substrate having a first surface; imposing an imaginary grid defining cells of dimension D
1
×D
2
in a predetermined relationship to the first surface, wherein D
1
has a value in the range of 0.05 inches to 0.30 inches, inclusive, and D
2
has a value in the range of 0.05 inches to 0.30 inches, inclusive; providing a plurality of three-dimensional features positioned along the imaginary grid; and, applying the thermal barrier coating including a thermal barrier layer to the substrate.
According to another aspect of the invention, the step of providing a plurality of three-dimensional features includes providing raised ribs on the first surface of the substrate, wherein said ribs have a associated rib height R.
According to another aspect of the invention, the step of providing a plurality of three-dimensional features includes providing grooves in the first surface of the substrate, wherein the grooves have a associated groove depth G.
According to another aspect of the invention, the step of applying the thermal barrier coating includes applying a bond coat layer intermediate the substrate and the thermal barrier layer.
According to another aspect of the invention, the step of providing a plurality of three-dimensional features includes providing raised ribs on a first surface of the bond coat layer, wherein the ribs have an associated rib height R.
According to another aspect of the invention, t
Loney Donald J.
Stone Kent N.
The United States of America as represented by the Administrator
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