Patent Application
20120276355
The invention relates to particle impact resistant thermal barrier coatings, particularly on internal turbine components.
Some components of gas turbine engines, such as vanes and blades, operate at temperatures up to about 1500° C. Ceramic thermal barrier coatings (TBCs) are used to insulate such components from heat, reduce surface oxidation, and reduce wear and damage caused by ingestion of foreign objects from the external air intake or from debris within the engine. Impacts from foreign objects and debris can spall the TBC, reducing its life. Hard particles commonly ranging from about 5 to 100 microns in diameter erode surfaces bounding the working gas flow path. The present coating and method reduces and controls such damage.
The invention is explained in the following description in view of the drawings that show:
The TBC 26 may comprise yttria-stabilized zirconia (YSZ) or a gadolinium zirconate (GZO) such as Gd2 Zr2O7 and/or other TBC materials known in the art. The TBC layer 26 may cover the exterior surface 23 of a turbine component in the working gas flow. Two additional protective layers 27 and 30 may cover some or all of the TBC 26 for particle impact protection.
Impact-absorbing layer 27 is a relatively soft anisotropic layer that absorbs the energy of particle impacts and stops vertical crack propagation. Layer 27 may be applied by a thermal spray process, such as plasma spray, that produces overlapping pancake-like lamellae 28 called “splats” with respective diameters oriented parallel to the substrate surface 23, forming a porous, compliant, planar-grained layer. The overlapping splats 28 block vertical crack propagation. “Vertical” means normal to the substrate surface 23. Layer 27 may have less than 75% of theoretical density, due to voids 29. A desired density can be achieved by setting thermal spray parameters such as feedstock, plasma gas composition and flow rate, energy input, torch offset distance, and substrate cooling, as known in the art.
Armor layer 30 is a relatively hard layer designed to crack along vertical fractures 32 into a geometry of fracture plates 34 (
Each protective layer 27, 30 has a specialized role. These two layers work synergistically to limit damage both horizontally and vertically, and to absorb impact energy, thus protecting the TBC 26. To reduce cost and weight, the protective layers 27, 30 may be limited to areas where damaging particle impacts occur, such as the leading edges of blades, vanes, and other parts.
All layers 24, 26, 27, and 30 may be applied by a thermal spray process such as plasma spray or high velocity oxygen fuel spray. The protective layers 27 and 30 may use the same materials as layer 26, but with different spray parameters. Alternately, different materials may be used for different layers. The thickness of layer 30 may be engineered in conjunction with its hardness such that process shrinkage of layer 30 produces fracture plates 34 of the desired sizes.
The impact-absorbing layer 27 may have 10-35% greater porosity than the armor layer 30, and especially 15-35% more porosity. For example, the TBC 26 may be formed of 7-9 mol % YSZ with 9-15% porosity, the impact-absorbing layer 27 may be formed of 7-9 mol % YSZ with 25-35% porosity, and the armor layer 30 may be formed of 7-9 mol % YSZ with 2-10% porosity.
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.
