Abradable strain-tolerant ceramic coated turbine shroud
AssigneeAllied-Signal Inc.
InventorThomas E. Strangman
Life of this patent
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Abstract
An abradable ceramic coated turbine shroud structure includes a grid of slant-steps isolated by grooves in a superalloy metal shroud substrate. A thin NiCrAlY bonding layer is formed on the machined slant-steps. A stabilized zirconia layer is plasma sprayed on the bonding layer at a sufficiently large spray angle to cause formation of deep shadow gaps in the zirconia layer. The shadow gaps provide a high degree of thermal strain tolerance, avoiding spalling. The exposed surface of the zirconia layer is machined nearly to the shadow gap ends. The turbine blade tips are treated to minimize blade tip wear during initial abrading of the zirconia layer. The procedure results in very close blade tip-to-shroud tolerances after the initial abrading.
Claims25
An abradable turbine shroud comprising in combination:
- (a) a shroud substrate having an inner surface;
- (b) an array of steps on the inner surface, each step including a first face having a relatively small slope and a second face adjoining the first face at a corner and having an approximately vertical slope;
- (c) an array of grooves in the inner surface, which separate the respective steps into rows;
- (d) a layer of ceramic attached to the first faces of the steps;
- and
- (e) a plurality of shadow gaps in the ceramic layer, each shadow gap extending a substantial portion of the way through the ceramic layer from an edge of a step.
In a gas turbine, the improvement comprising:
- (a) a shroud substrate having an inner surface;
- (b) an array of raised areas on the inner surface, each raised area having a steep edge;
- (c) an array of grooves betwen the respective raised areas and further segmenting the respective raised areas;
- (d) a layer of ceramic attached to the inner surface, the array of grooves effectively segmenting the inner surface;
- (e) a plurality of shadow gaps in the ceramic layer, each shadow gap extending from a steep edge a substantial portion of the way through the ceramic layer, the layer of ceramic and the shadow gaps therein forming a segmented abradable ceramic turbine shroud liner;
- (f) a plurality of turbine blades surrounded by the segmented abradable ceramic turbine shroud liner;
- and
- (g) hardened means disposed on an outer tip of each of the turbine blades for abrading the major surface of the ceramic layer.
A lined shroud comprising in combination:
- (a) a shroud substrate having an inner surface;
- (b) an array of steps on the inner surface, each step including a steep edge;
- (c) a layer of ceramic attached to the inner surface;
- and
- (d) a plurality of shadow gaps in the ceramic layer, each shadow gap extending from a respective steep edge a substantial portion of the way through the ceramic layer, the shadow gaps segmenting the ceramic layer to minimize spalling thereof by accommodating strains therein.
A lined shroud comprising in combination:
- (a) a shroud substrate having an inner surface;
- (b) an array of surface discontinuities on the inner surface, each surface discontinuity including a plurality of grooves separating an array of raised areas, each discontinuity having a steep edge;
- (c) a ceramic layer attached to the raised areas;
- and
- (d) a plurality of shadow gaps in the ceramic layer, each shadow gap extending from a steep edge a substantial portion of the way through the ceramic layer and effectively segmenting the ceramic layer.
Dependencies are inferred from the claim text.