(19) J

(12)

(43) Date of publication: 22.04.1998 Bulletin 1998/17

(21) Application number: 97117266.3

(22) Date of filing: 06.10.1997

Europaisches Patentamt | | | | | 1 1| | | | | | | 1 1| | | | | | | | | | | |

European Patent Office

Office europeen des brevets (1 1 ) E P 0 8 3 7 2 2 2 A 1

EUROPEAN PATENT A P P L I C A T I O N

ation: (51) |nt. CI.6: F01D 5 /20

(84) Designated Contracting States: Frani, Norman E., AT BE CH DE DK ES Fl FR GB GR IE IT LI LU MC c/0 Alliedsignal Inc. NL PT SE Morristown, NJ 07962 (US) Designated Extension States: Joseph, Stephen S., AL LT LV RO SI c/o Alliedsignal Inc.

Morristown, NJ 07962 (US) (30) Priority: 21.10.1996 US 734756 Narasimhan, Dave,

c/o Alliedsignal Inc. (71) Applicant: AlliedSignal Inc. Morristown, NJ 07962 (US)

Morristown, New Jersey 07962-2245 (US) (74) Representative:

(72) Inventors: Freeman, Jacqueline Carol Draskovich, Barry S., W P. THOMPSON & CO.

c/o Alliedsignal Inc. Celcon House Morristown, NJ 07962 (US) 289-293 High Holborn

London WC1V7HU(GB)

(54) Gas turbine compressor clearance control with abrasive blade tip and abradable shroud

sealing and method of manufacturing

(57) For use in a compressor unit of gas turbine engine, a blade (10) having a tip portion (1 1). An abra- / ^ O ' " " ^ ^ ^ ^ sive portion is formed on the tip portion with the abra- \ ^ Y ^ Y ^ ^ Y ^ sive portion comprising a dispersion of discrete Y / / ^ / / ' / ^ / ^ ^ particles (1 1 A) of cubic boron nitride disposed on the tip ^ 4 ^ \ N > X ^ ^ ^ ^ ^

portion. A shroud (12) is coated with a porous ceramic m W ^ ^ ^ ^ y ^ ^ ^ ^ i i abradable material (13) based on preferably 8% yttria- Y / / / ^ / ^ / / / / / / / \ stabilized zirconia. The abrasive portion of the tip por- Y/ / Y Y / ^ / / /Y^/ / / / \ tion (11) contacts the abradable material (13). In the Y / / / ^ / ^ / ^ / ^ / / ^ / / ' ^ / ^ / a preferred embodiment, the abradable material (13) is Y/^/^Y^/^/^/ / ^ / / / A treated with boron nitride composited polyester that is Y/^/^Y^/ / / / / / / / / / A burned out of the material via thermal exposure to f / / / ^ ^ thereby improve porosity within the abradable material. \/ / / / / / / / / / / / / / \

CM CM CM r- c o CO o Q_ LU

Printed by Xerox (UK) Business Services 2.16.1/3.4

1 EP 0 837 222 A1 2

Description

TECHNICAL FIELD

This invention relates generally to a compressor s blade and shroud for use in a turbine engine, and more particularly, to a compressor blade having an abrasive tip and an abradable shroud for controlling clearance within the gas turbine engine compressor.

10 BACKGROUND OF THE INVENTION

Abradable coatings have been successfully adopted as an industry standard for use in compressor blade clearance control applications. The primary func- 15 tion of these coatings is to provide a rub-tolerant shroud surface that minimizes blade damage in the event a compressor blade rubs the shroud surface. The abrada- ble surface permits engine operation at relatively "tight" tip clearances with attendant benefits in compressor 20 efficiency, i.e., maximum air through the compressor blades for better performance and compression.

Low cost abradable coatings enable compressors to operate at minimum clearance by protecting air foils from non-repairable damage (excessive tip wear and 25 bent blades) during rub events. In the absence of abrad- able coatings, tip incursions into a bare metal shroud may result in considerable, nonrepairable damage to the impeller. Increasing the tip clearance to avoid the rubs may also yield unacceptable losses in perform- 30 ance due to lower compressor efficiency and higher tur- bine temperatures. Tip clearances can be set tight by incorporating abradable coatings that allow for slight rubs without the impeller damage associated with the uncoated shroud design. 35

The three most common high pressure compressor (HPC) coatings are SF aluminum, Metco 52C, and nickel-graphite. These abradable systems have dis- played various levels of performance deficiencies related to coating durability, post-rub surface finish, as- 40 machined surface finish, fire risk, erosion, corrosion, and impeller damage. Durability, surface finish, fire issues, and nonrepairable impeller damage are the most common concerns with the aluminum abradables.

One of the challenges associated with the use of 45 abradables is the fact that the coating properties that promote rub-tolerance, such as friability and/or low shear strength, can result in compromises in shroud surface finish, and in some cases, coating durability. Aluminum-based coatings fit the category of being eas- so ily sheared during a rub without necessarily being porous, and for this reason offer an excellent surface fin- ish. This is especially true in the case of the aluminum- based coatings historically used in many HPC impeller shroud applications. They offer excellent surface finish ss but their long-term use in HPC applications is ultimately limited by melting point and lack of thermal durability. More specifically, as the temperature of the aluminum-

based coating increases, it tends to get "gummy" and the blade tip will smear it around the shroud, thereby creating grooves within the coating that allow air to pass past the blade tip as opposed to between the blades, which deteriorates performance of the compressor. The grooves also cause turbulent air flow at the shroud sur- face. Additionally, the aluminum-based coating can cor- rode. Also, under the right combination of operating conditions, rub debris from an aluminum coating can ignite, and the heat of aluminum combustion can in turn ignite a titanium compressor rotor fire.

Accordingly, apparatus and a method are needed that overcome the shortcomings of the prior art by pro- viding an abrasive tip/abradable shroud system and method for gas turbine compressor clearance control.

SUMMARY OF THE INVENTION

A compressor unit of a gas turbine engine accord- ing to the present invention addresses the shortcomings of the prior art.

In accordance with one aspect of the present inven- tion, a compressor unit of a gas turbine engine com- prises a blade body having a tip portion. An abrasive portion is formed on the tip portion with the abrasive portion comprising a dispersion of discrete particles of cubic boron nitride disposed on the tip portion. A shroud is coated with a porous ceramic abradable material based on 7-9% yttria-stabilized zirconia, and preferably 8% yttria-stabilized zirconia. The abrasive portion of the tip portion contacts the abradable material.

In accordance with a further aspect of the invention, the abradable material is treated with hexagonal boron nitride composited polyester that is burned out of the material via thermal exposure to thereby improve poros- ity within the abradable material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like designations denote like elements, and:

Figure 1 is a sectional view of a blade and blade tip of a compressor unit shown in relation to a shroud having a shroud substrate; Figure 2 is a radial view of a CBN-tipped Ti-6-2-4-2 blade showing abrasive distribution over the tip sur- face.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 illustrates a portion of a blade 10 of a com- pressor unit within a gas turbine engine. For purposes of this invention, the compressor can be either an axial compressor (blade type) or a centrifugal compressor (impeller type). Blade 10 is generally made of titanium.

2

3 EP 0 837 222 A1 4

Blade 10 further has an abrasive tip 1 1 , generally a nickel plate, that has abrasive particles 1 1 A embedded therein. These particles are cubic boron nitride. This abrasive tip portion 11 is attached to Blade 10 via an Entrapment Plating process. In this process, cubic boron nitride particles are attached to tip 10 by means of a nickel plate coating. In essence, the particles are "trapped" into the nickel plate during the plating opera- tion. A company that performs this process is Abrasive Technology, Inc. in Columbus, Ohio. Figure 2 illustrates the distribution of abrasive particles 1 1 A within the nickel plate. Other processes can also be utilized to embed the particles including using a laser, a transfer arc or an electron beam.

A shroud substrate 12 envelopes the compressor unit. The shroud substrate has an abradable coating or liner 13 attached thereto. In the preferred embodiment the shroud coating is based on a thermal barrier coat- ing, yttria-stabilized zirconia, in the range of 7-9%, and most preferably, 8% yttria-stabilized zirconia. Addition- ally in the preferred embodiment, the abradable coating has an increased level of porosity that is achieved through the addition of polyester particles, preferably 5wt% boron nitride-composited polyester powder. A manufacturer of the powder is Sulzer Plasma Technik in Troy, Michigan. Subsequent to spraying of the coating onto shroud 12, the polyester is burned out via thermal exposure, resulting in uniformly distributed porosity.

In operation, blade tip 1 1 contacts abradable coat- ing 1 3 to thereby form a seal to prevent air from passing over the blade tip, thereby forcing air to pass between adjacent blades. Also referred to as rub, this contact between the blade tip and the abradable coating seals the rotor, which minimizes clearances thereby improv- ing performance and efficiency of the compressor.

Cubic boron nitride is utilized on tip 1 1 because it is an extremely hard material almost equal to the hard- ness of diamond. Its use in the cutting tips of airfoil blades in a gas turbine engine is well documented. In order to maximize the efficiency of the blade tip, clear- ances are made small to minimize gas leakage and tur- bulence over the blade tips. Abradable coating 13 is sprayed on shroud substrate 12, which encircles all blades of the compressor. Because of its extreme hard- ness, cubic boron nitride improves the efficiency of the blades in cutting a path into the abradable coating. Unfortunately, cubic boron nitride is not temperature tol- erant for long periods of time. In fact, at temperatures of 1 ,200 to 1 ,300 degrees Fahrenheit, cubic boron nitride begins oxidizing. However, because the compressor unit of the gas turbine engine is not subjected to the high temperatures associated with other portions of the gas turbine engine, it is possible to use both the cubic boron nitride on tip 11 and yttria-stabilized zirconia in abradable coating 13 since the temperature within the compressor unit generally does not exceed 1,100 degrees Fahrenheit.

Yttria-stabilized zirconia abradable coating 13 has

increased temperature capabilities over the prior art alu- minum-based coatings, nickel graphite and other com- monly used compressor abradable coatings. These increased capabilities lead to improved abradability

5 results of no coating melting and pull out, no metal transferred to the blade tip and a wear ratio (shroud wear/blade wear) of approximately 1.0. Also, there is lower thermal distortion of the shroud, tighter build and operating clearances and elimination of compressor

10 fires. The latter is due to blade incursion into the abrad- able coating 13 resulting in low frictional heat genera- tion and non-flammable rub debris. Also, use of yttria- stabilized zirconia abradable coating 13 results in elimi- nation of oxidation/corrosion problems.

15 The benefits of cubic boron nitride abrasively-tipped blade 10 include efficient cutting of ceramic shroud coating 13 during a rub event with insignificant damage or wear to the blade tip. Long-term stability of the abra- sive in the tip, leading to tip protection from potential

20 rubs throughout core life and reduced cost of repair sub- sequent to a blade rub due to the need to only replace the shroud coating from time to time. It will be under- stood that the foregoing description is that of a preferred exemplary embodiment of the invention, and that the

25 invention is not limited to the specific form shown and described. Various modifications may be made in the design and arrangement of the elements set forth herein without departing from the scope of the invention as expressed in the appended claims.

30 Claims

1 . A compressor unit of a gas turbine engine compris- ing:

35 a. a blade body having a tip portion; b. an abrasive portion formed on said tip por- tion, said abrasive portion comprising a disper- sion of discrete particles of cubic boron nitride

40 disposed on said tip portion; and, c. a shroud coated with a porous ceramic abradable material based on 7-9% yttria-stabi- lized zirconia, said abrasive portion contacting said abradable material.

45 2. The unit of Claim 1 wherein said abradable material

is treated with Boron Nitride-composited polyester that is burned out via thermal exposure to improve porosity within said abradable material.

50 3. For use in a compressor unit of a gas turbine

engine, a blade and a shroud, said blade compris- ing a blade body having a tip portion with an abra- sive portion formed thereon comprising a

55 dispersion of discrete particles of cubic boron nitride disposed on said tip portion, and, said shroud being coated with a porous ceramic abrada- ble material based on 7-9% yttria-stabilized zirco-

3

5 EP 0 837 222 A1 6

nia.

4. A method of forming an abrasive blade tip/abrada- ble shroud system for gas turbine compressor clearance control, said method comprising: s

a. forming an abrasive tip on a blade body by entrapping cubic boron nitride particles within a blade tip portion; and, b. forming an abradable shroud coating com- w prised of a porous ceramic abradable material based on 7-9% yttria-stabilized zirconia by attaching said coating to a shroud substrate.

5. The method of Claim 4 wherein said cubic boron is nitride particles are entrapped within a nickel plate blade tip portion during nickel plate coating.

6. The method of Claim 5 wherein said abradable shroud is further formed by treating said abradable 20 material with boron nitride-composited polyester that is burned out via thermal exposure to improve porosity within said abradable material.

25

30

35

40

45

50

4

EP 0 837 222 A1

EP 0 837 222 A1

European Patent Office

EUROPEAN SEARCH REPORT Application Number

EP 97 11 7266

DOCUMENTS CONSIDERED TO BE RELEVANT

Category Citation of document with indication, where appropriate. ot relevant passages Heievant to claim

CLASSIFICATION OF THE APPLICATION (lnt.CI.6)

JS 4 936 745 A (VINE RAYMOND W June 1990 * column 1, paragraph 3 * * column 2, line 45 - line 51 > * column 3, line 15 - line 16 :

ET AL) 26

column 1, column 2, column 3, column 3, column 3, column 4,

3 * line 51 line 16

L.3,4

L-6

F01D5/20

line 30 - line 34 1 i ne 49 - col umn line 13 - line 14

column 4, 1 ine 14 *

line 3 *

US 5 530 050 A ( RANGASWAMY SUBRAMANIAM) 25 1-6 June 1996 * column 1, paragraph 3 * * column 2, paragraph 2 * * column 3, paragraph 3 * * column 3, paragraph 7 * * column 3, paragraph 9 * * column 4. paragraph 1 * * column 4, paragraph 3 * * column 4, paragraph 5 * * column 6, paragraph 1 *

TECHNICAL FIELDS SEARCHED (lnt.CI.6)

F01D

The present search report has been drawn up for all claims

Place of search

THE HAGUE

Date of completion ot the search 27 January 1998 Raspo, F

CATEGORY OF CITED DOCUMENTS

X : particularly relevant if taken alone Y : particularly relevant if combined with another

document of the same category A technological background O : non-written disclosure P : intermediate document

T : theory or principle underlying the invention E : earlier patent document, but published on. or

after the filing date D document cited in the application L : document cited for other reasons & : member of the same patent family, corresponding

document

6

bibliographydescriptionclaimsdrawingssearch report