Fabrication of an article having a protective coating with a...

Stock material or miscellaneous articles – Composite – Of metal

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C148S276000, C148S277000, C148S285000, C427S248100, C427S250000, C427S255320, C428S623000, C428S469000

Reexamination Certificate

active

06652982

ABSTRACT:

This invention relates to protective systems such as used to protect some components of gas turbine engines and, more particularly, to the protective-coating surface and the protective coating composition.
BACKGROUND OF THE INVENTION
Higher operating temperatures for gas turbine engines are continuously sought in order to increase their efficiency. However, as operating temperatures increase, the high-temperature durability of the components of the engine must correspondingly increase. Significant advances in high-temperature capabilities have been achieved through the formulation of nickel- and cobalt-base superalloys. Nonetheless, when used to form components of the turbine, combustor and augmentor sections of a gas turbine engine, such alloys alone are often susceptible to damage by oxidation and hot corrosion attack and may not retain adequate mechanical properties. For this reason, these components are often protected by an environmental and/or thermal-insulating coating, the latter of which is termed a thermal barrier coating (TBC) system. Ceramic materials and particularly yttria-stabilized zirconia (YSZ) are widely used as a thermal barrier coating (TBC), or topcoat, of TBC systems used on gas turbine engine components. The TBC employed in the highest-temperature regions of gas turbine engines is typically deposited by electron beam physical vapor deposition (EBPVD) techniques that yield a columnar grain structure which is able to expand and contract without causing damaging stresses that lead to spallation.
To be effective, TBC systems must have low thermal conductivity, strongly adhere to the article, and remain adherent throughout many heating and cooling cycles. The latter requirement is particularly demanding due to the different coefficients of thermal expansion between ceramic topcoat materials and the superalloy substrates they protect. To promote adhesion and extend the service life of a TBC system, an oxidation-resistant bond coat is usually employed. Bond coats are typically in the form of overlay coatings such as MCrAlX (where M is iron, cobalt, and/or nickel, and X is yttrium or another rare earth element), or diffusion aluminide coatings. A notable example of a diffusion aluminide bond coat contains platinum aluminide (NiPtAl) intermetallic. When a bond coat is applied, a zone of interdiffusion forms between the substrate and the bond coat. This zone is typically referred to as a diffusion zone.
During the deposition of the ceramic TBC and subsequent exposures to high temperatures, such as during engine service, bond coats of the type described above oxidize to form a tightly adherent alumina (aluminum oxide or Al
2
O
3
) layer or scale that protects the underlying structure from catastrophic oxidation and also adheres the TBC to the bond coat. The service life of a TBC system is typically limited by spallation at or near the interfaces of the alumina scale with the bond coat or with the TBC. The spallation is induced by thermal fatigue as the article substrate and the thermal barrier coating system are repeatedly heated and cooled during engine service.
There is a need for an understanding of the specific mechanisms that lead to the thermal fatigue failure of the protective system, and for structures that extend the life of the coating before the incidence of such failure. The present invention fulfills this need, and further provides related advantages.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an approach for fabricating an article protected by a protective system, and articles protected by the protective system. The life of the protective system is extended under conditions of thermal fatigue by delaying the onset of the alumina scale interface failure mode. The present approach is applicable to environmental-coating protective systems where there is no thermal barrier coating present. However, it realizes its greatest advantages when used in thermal barrier coating systems where the protective coating is a bond coat and a ceramic thermal barrier coating overlies the bond coat.
A method of fabricating an article having a protective coating thereon comprises the steps of providing an article substrate having a substrate surface, thereafter producing a flattened protective coating on the substrate surface by depositing a protective coating on the substrate surface, the protective coating having a protective-coating surface, and processing the protective coating to achieve the flattened protective-coating surface. The protective coating is thereafter optionally exposed to an environment wherein the protective-coating surface is controllably oxidized. The article substrate and protective coating have an average sulfur content of less than about 10 (more preferably less than 5, and most preferably less than 1) parts per million by weight at depths measured from the protective-coating surface to a depth of about 50 micrometers below the protective-coating surface. Optionally but preferably, a ceramic thermal barrier coating is deposited overlying the pre-oxidized protective-coating, so that the protective coating constitutes a bond coat for the thermal barrier coating.
The article substrate preferably is a nickel-base superalloy, and most preferably is a component of a gas turbine engine. The protective coating may be a diffusion aluminide protective coating such as a platinum aluminide protective coating, or it may be an overlay protective coating.
The protective coating may be flattened without removing material from the protective-coating surface, as by peening the protective coating. Alternatively, the protective coating may be flattened by removing material from the protective-coating surface, as by polishing the protective coating. Desirably, the step of processing the protective coating produces a protective-coating surface wherein an average grain boundary displacement height of the protective coating is less than about 3 micrometers, more preferably less than about 1 micrometer, even more preferably less than about 0.5 micrometer, and most preferably substantially zero, over at least about 40 percent of the surface area of the protective coating but more preferably over the entire surface area of the protective coating. Where the processing is accomplished by polishing, the average grain boundary displacement height may be substantially zero in the polished areas, where the polishing is to a mirror finish. In most cases, the step of processing the protective coating is performed after the step of depositing the protective coating is complete. In some cases, however, the steps of depositing the protective coating and processing the protective coating are performed concurrently. Additionally, it is preferred that at least about 40 percent, and more preferably all, of the surface of the protective coating is flattened to have a grain displacement height of less than about 3 micrometers, more preferably less than about 1 micrometer, even more preferably less than about 0.5 micrometer, and most preferably substantially zero.
The optional step of controllable oxidation preferably includes the step of heating the protective coating in an atmosphere having a partial pressure of oxygen of from about 10
−5
mbar to about 10
3
mbar, more preferably from about 10
−5
mbar to about 10
−2
mbar, at an oxidizing temperature of from about 1800° F. to about 2100° F., and for a time of from about ½ hour to about 3 hours. Most preferably, the controllable oxidation is performed by heating the protective coating to a pre-oxidation temperature of from about 2000° F. to about 2100° F. in a heating time of no more than about 45 minutes, preferably from about 1 to about 45 minutes, and more preferably from about 15 to about 35 minutes, and thereafter holding at the pre-oxidation temperature for a time of from about ½ hour to about 3 hours, in an atmosphere having a partial pressure of oxygen of about 10
−4
mbar.
An article having a protective coating thereon comprises an article substrate having a substrate surf

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Fabrication of an article having a protective coating with a... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Fabrication of an article having a protective coating with a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fabrication of an article having a protective coating with a... will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3150175

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.