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NANOSTRUCTURED METALLIC COMPOSITE COATING FOR CLEARANCE CONTROL

IP.com Disclosure Number: IPCOM000191501D
Publication Date: 2010-Jan-06
Document File: 6 page(s) / 236K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method for effective clearance control is disclosed. The method provides a nanostructured metallic composite coating consisting of a high temperature oxidation and corrosion resistant metallic matrix reinforced by inert hard nano oxide particulates.

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RP13206

NANOSTRUCTURED METALLIC COMPOSITE COATING FOR CLEARANCE CONTROL

BRIEF ABSTRACT

    A method for effective clearance control is disclosed. The method provides a nanostructured metallic composite coating consisting of a high temperature oxidation and corrosion resistant metallic matrix reinforced by inert hard nano oxide particulates.

KEYWORDS

Turbine airfoils, rotating parts, materials & coatings, repair technology, MCrAlY, hard particulates, metallic matrix, CoNiCrAlY

DETAILED DESCRIPTION

    A tight clearance between rotating structures and stationary structures (or stator) of a machine are essential to maintain high operating efficiency and power. The rotating structures include airfoils in aircraft engines and buckets in power generation turbines among others. During operations, there are instances when the power or thrust output of an engine is rapidly increased, such as during takeoff in an aircraft engine, or a surge in power output to meet peak grid demand. During such instances, the rotating structures sometimes interfere with the stationary structures resulting in a high speed rub.

    The high speed rub causes excessive wear and tear of the rotating structures. Further, a rotating blade tip may undergo local melting and scab over

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RP13206

stationary shrouds resulting in formation of a hard oxidized scab on the stationary shrouds. Such a scab continues to rub against the blade tip constantly and also makes contacts at shorter incursions, thereby increasing the wear of the airfoil or the bucket tip. Such wear and tear of the stationary and rotating structures leads to a progressive reduction in operating efficiency, and increased specific fuel consumption (SFC) for same power or thrust generation.

    Conventionally, interference or rub between the rotating structures and the stationary structures is mitigated by a process called active clearance control. In active clearance control, cooling airflow through the stator and the rotating structures is controlled. However, the active clearance control process reduces the extent of rub, but does not eliminate the rub completely.

    Alternately, hard abrasive coatings are deposited on the blade, airfoil or bucket tips. These coatings include plasma sprayed aluminum oxide, entrapment plated cubic boron nitride, entrapment plated alumina and MCrAlY- Alumina particulate composites among others. Another technique used to mitigate interference or rub between the rotating structures and the stationary structures is porous abradable coatings on the stationary structures. These porous coatings are of nickel aluminum, nickel graphite in high pressure compressors, CoNiCrAlY coatings or porous yttria stabilized zirconia among others. Coatings are used so that the rub events can be accommodated by preferential cutting and wear of the coating.

    However, all such conventio...