Coherent light generators – Particular resonant cavity – Specified cavity component
Reexamination Certificate
1999-04-19
2001-01-30
Bueker, Richard (Department: 1763)
Coherent light generators
Particular resonant cavity
Specified cavity component
C359S585000, C359S584000, C359S586000
Reexamination Certificate
active
06181727
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to coatings for components exposed to high temperatures, such as coating chamber components of coating apparatuses. More particularly, this invention is directed to a reflective coating for a coating chamber component of a coating apparatus, by which the maximum temperature sustained by the component during the coating process is reduced.
BACKGROUND OF THE INVENTION
Physical vapor deposition (PVD) is a known film deposition technique that entails heating a material in a vacuum to a temperature at which the material vaporizes and then condenses on a relatively cooler substrate. For various reasons, metallic and ceramic coatings for gas turbine engine components are often deposited by PVD. For example, electron beam physical vapor deposition (EBPVD) is used to produce a desirable columnar grain structure for ceramic topcoat layers of thermal barrier coating (TBC) systems. The ceramic material often preferred is yttria-stabilized zirconia (YSZ), which must be heated to about 4000 K to about 4300 K to produce a YSZ vapor that subsequently condenses on the component.
Gas turbine engine components typically sustain temperatures in excess of 1700° F. (about 927° C.) during coating by PVD. As a result of stringent requirements to control temperature uniformity during the coating cycle, a “working zone” is typically established in the PVD coating chamber within which sufficient temperature and coating vapor uniformity can be maintained to meet processing requirements. Components to be coated must be held and manipulated in the working zone of the coating chamber using complex tooling and fixturing. As a result, this tooling and fixturing is exposed to the same elevated temperatures seen by the components receiving the PVD coating, necessitating that the tooling and fixturing be fabricated from materials that can survive the high-temperature coating environment of a PVD coating chamber. Notable examples are the gears required to rotate components in order to deposit by EBPVD a ceramic layer with a columnar grain structure.
Though high-temperature materials are used to form the tooling and fixturing, repetitive high-temperature exposures and associated thermal cycling results in physical degradation of these components, which necessitates their replacement on a routine basis. Because of the costs associated with their complexity and high temperature capability, it would be desirable if the frequency of replacing PVD components, tooling and fixturing could be reduced.
BRIEF SUMMARY OF THE INVENTION
The present invention generally provides a component for use in a high-temperature coating chamber such as that of a PVD apparatus. The invention is particularly directed to a thermally-reflective coating for those coating chamber components that must repeatedly survive the high temperatures within the working zone of a PVD apparatus. The reflective coating serves as a barrier to radiant heat transfer to the component by reflecting thermal radiation within the coating chamber, and particularly thermal radiation at wavelengths at which radiant heat transfer to the component is greatest from the surrounding chamber environment.
In accordance with this invention, the thermally-reflective coating comprises at least one pair of reflective layers, each layer being formed of a material that is essentially transparent to electromagnetic wavelengths of between 500 and 3000 nanometers (nm). In addition, the material of the outermost layer of the pair has a higher index of refraction than the material of the second layer of the pair. Coatings of this invention have been shown to increase the average reflectivity of a PVD coating chamber component formed of steel from about 70% to more than 90% over an electromagnetic wavelength range of about 380 to about 1500 nm, which is within the spectrum for thermal radiation (near-infrared) emitted by molten ceramic materials, and therefore the cause of considerable heating during the deposition of ceramic materials. Accordingly, the operating temperature of a coating chamber component can be significantly reduced by the thermally-reflective coating of this invention. Also reduced are thermal gradients within the component, which particularly occur if only a portion of the component is within the working zone of the coating chamber.
From the above, it can be seen that the advantages of this invention include the ability to improve the life of critical components, tooling and fixturing used in the coating chamber of a PVD coating apparatus. As a result, the cost of operating the coating apparatus is reduced. The reflective coating of this invention is able to achieve these advantages while present in thicknesses of less than 5000 nm, which allows the coating to be applied to standard tooling and fixturing without resulting in any significant dimensional or tolerance issues. The reflective coating of this invention has also been found to be very hard and durable, reducing the concern for damage due to handling. Finally, PVD metallic and ceramic coatings do not adhere well to the reflective coating, so that removal of any PVD coating that is inadvertently deposited on the component can be easily removed.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
REFERENCES:
patent: 5576885 (1996-11-01), Lowe et al.
patent: 5972114 (1999-10-01), Yonenaga et al.
patent: 6021152 (2000-02-01), Olsen et al.
patent: 6025575 (2000-02-01), Park et al.
U.S. Patent application Ser. No. 09/224,891, filed Dec. 31, 1998, “Heating Apparatus for a Welding Operation and Method Therefor” by Jeffrey A. Conner, et al.
Ackerman John F.
Conner Jeffrey A.
Evans, Sr. John D.
Maricocchi Antonio F.
Stowell William R.
Bueker Richard
General Electric Company
Gressel Gerry S.
Hassanzadeh P.
Hess Andrew C.
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