Abradable strain-tolerant ceramic coated turbine shroud

DETAILED DESCRIPTION Accordingly, it is an object of the invention to provide an improved high pressure gas turbine capable of operating at substantially higher efficiency over a longer lifetime than prior gas turbines.
It is another object of the invention to provide an abradable turbine shroud coating that allows reduced blade tip-to-shroud clearances and consequently results in substantially higher efficiency.
It is another object of the invention to increase the oxidation resistance of an abradable turbine shroud and to avoid massive spalling of the ceramic layer due to high thermal strain between the ceramic layer and the superalloy turbine shroud substrate.
It is another object of the invention to provide an abradable ceramic turbine shroud liner or coating that results in high density at a metal bonding interface and lower density and higher abradability at the gas path surface.
It is another object of the invention to provide a rub tolerant ceramic turbine shroud coating that reduces the shroud's cooling requirements, decreases shroud and retainer stresses and associated shroud distortion, minimizes leakage, and delays the onset of blade tip wear.
It is another object of the invention to provide an insulative coating which avoids spalling on a substrate that is subjected to severe high temperature cycling.
Briefly described, and in accordance with one embodiment thereof, the invention provides an abradable turbine shroud coating including a shroud substrate, wherein an array of steps is provided on the inner surface of the shroud substrate, and a segmented coating is provided on the steps such that adjacent steps are segmented from each other by shadow gaps or voids that propagate from the steps upward entirely or nearly through the coating.
The shadow gaps are produced by plasma spraying ceramic onto the steps at a plasma spray angle that prevents the coating from being deposited directly on steep faces of the steps, which in the described embodiment are slant-steps.
In the described embodiment of the invention, longitudinal, circular parallel grooves and slant-steps having the same or similar heights or depths are formed (by machining, casting, etc