Method of making an 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.
Claims11
A method of making a gas turbine comprising the steps of:
- (a) providing a shroud substrate having a smooth inner surface;
- (b) forming an array of steps on the inner surface so that each step includes a first face having a small slope and a second face adjoining the first face at a corner and having an approximately vertical slope, and also forming an array of intersecting grooves which separate the steps;
- (c) performing a line of sight deposition of ceramic material uniformly over the steps at a spray angle that prevents ceramic from being directly deposited on the second faces so that a plurality of shadow gaps are formed in the ceramic layer as it is deposited, each shadow gap extending above an edge of a step through a substantial portion of the ceramic layer;
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- (d) machining a major exposed surface of the ceramic layer to provide an abradable ceramic liner on the inner surface of the shroud substrate.
A method of making a lined shroud comprising the steps of:
- (a) providing a shroud substrate of material having a smooth inner surface;
- (b) forming an array of discontinuities on the inner surface including an array of intersecting grooves separating an array of raised areas, each discontinuity including a steep edge;
- and
- (c) performing a line of sight deposition of ceramic material uniformly on the inner surface at a spray angle that prevents ceramic from being directly deposited on the steep edges so that a plurality of shadow gaps are formed in the ceramic layer as it is deposited, each shadow gap extending from a steep edge through a substantial portion of the ceramic layer and segmenting the ceramic layer.
Dependencies are inferred from the claim text.