Segmented abradable coatings and process (ES) for applying the same

Abstract

A segmented abradable ceramic coating comprises a bond coat layer, at least one segmented 7 weight percent yttria-stabilized zirconia layer disposed upon said bond coat layer, and at least one 12 weight percent yttria-stabilized zirconia layer disposed upon said at least one segmented 7 weight percent yttria-stabilized zirconia layer.

Description

FIELD OF THE INVENTION[0001]The invention relates to coatings and, more particularly, relates to segmented abradable coatings and their coated articles.BACKGROUND OF THE INVENTION[0002]Modern gas turbine engines, particularly those used in aircraft, operate at high rotational speeds and high temperatures for increased performance and efficiency. The turbine of a modern gas turbine engine is typically of an axial flow design and includes a plurality of axial flow stages. Each axial flow stage comprises a plurality of blades mounted radially at the periphery of a disk which is secured to a shaft. A plurality of duct segments surround the stages to limit the leakage of gas flow around the tips of the blades. These duct segments are located on the inner surface of a static housing or casing. The incorporation of the duct segments improves thermal efficiency because more work may be extracted from gas flowing through the stages as opposed to leaking around the blade tips.[0003]Although t...

AI Technical Summary

Problems solved by technology

Although the duct segments limit the leakage of gas flow around the blade tips, they do not completely eliminate the leakage.

It has been found that even minor amounts of gas flow around the blade tips detrimentally affect turbine efficiency.

Thus, gas turbine engine designers proceed to great lengths to devise effective sealing structures.

Unfortunately current coatings, which are typically ceramic, suffer from excessive material loss as a result of erosion or spalling.

In general, erosion is the wearing away of coating material due to factors such as abrasion and corrosion.

Erosion often results from particle impingement during engine operation.

Spalling is typically caused by delamination cracking at the ceramic-metal interface resulting from thermal stress and the aggressive thermal environment.

Ceramic coating loss increases blade tip clearance and thus is detrimental to turbine efficiency, as well as detrimental to the blades themselves.

For example, the blades may become damaged due to the increased temperature at which the engine must then operate to make up for lost thrust.

Images