1. Technical Field
This disclosure relates to Electron Beam Physical Vapor Deposited Thermal Barrier Coatings (EB-PVD TBC) and methods for applying the same to a substrate in general, and to such coatings and methods that utilize a thermally grown oxide for ceramic to metallic adhesion in particular.
2. Background Information
Thermal barrier coating (TBC) systems have been developed to fulfill the demands placed on current high-temperature Ni-base superalloys for gas turbine applications in both aero engine and land based gas turbines. TBC systems typically consist of a ceramic (e.g., yttria-stabilized zirconia) top layer that has low thermal conductivity, is chemically inert in combustion atmospheres, and that is reasonably compatible with Ni-base superalloys. The ceramic top layer is often applied by a deposition process such as Electron Beam Physical Vapor Deposition (EB-PVD). To ensure adequate bonding between the ceramic topcoat and the metallic substrate, it is common (but not required) to use a bond coat (e.g., NiCoCrAlY) disposed between the ceramic top coat and the metallic substrate. Ceramic adhesion to the bond coat depends on the formation of a thin, slow-growing oxide layer (also designated as TGO: thermally grown oxide) developing on the bond coat.
TGOs grown from a NiCoCrAlY or similar bond coat in a vacuum (at about 100 to 10−6 Torr) at temperatures less than 1800° F. will include certain oxides (e.g., eta phase alumina, and transition oxides, also referred to herein as “low temperature oxides”) that assume a voluminous, low integrity form that tend to have lower adhesion to the bond coat than other oxides. TBCs attached to these oxides will, therefore, be subject to these weaker bonds, and may be the basis for spallation.
According to one aspect of the invention, a method for forming thermally grown alpha alumina oxide scale on a substrate is provided. The method includes the steps of: a) providing a heating chamber having a heat source and an oxidizing gas source selectively operable to provide a stream of oxidizing gas; b) providing at least one substrate (e.g., airfoil, turbine blade, stator vane, etc.) disposed in the heating chamber, which substrate has a composition sufficient to permit formation of an alpha alumina scale on one or more surfaces; c) maintaining a vacuum in the heating chamber at a level that inhibits formation of one or more low temperature oxides on the one or more surfaces of the substrate; d) heating at least one of the one or more surfaces of the substrate to a predetermined temperature at or above 1800 degrees Fahrenheit; and e) directing the stream of oxidizing gas at a controlled rate to the one or more heated surfaces of the substrate.
According to another aspect of the invention, a method for conditioning a surface of a substrate prior to coating the surface is provided. The method includes the steps of: a) providing a coating chamber and a heating chamber, which heating chamber has a heat source; b) treating one or more surfaces of a substrate within the heating chamber by establishing a vacuum in the heating chamber, heating a surface of the substrate to a predetermined temperature, and directing a stream of oxidizing gas to the heated one or more surfaces of the substrate to form an oxide layer thereon; and c) coating the treated surface of the substrate in the coating chamber.
According to still another aspect of the invention, a system for forming a thermally grown oxide on a surface of at least one substrate is provided. The system includes a heating chamber, a vacuum pump, a heat source, and an oxidizing gas inlet. The heating chamber has a target location for locating the substrate. The vacuum pump is connected to the heating chamber and is selectively operable to establish a vacuum within the heating chamber. The heat source is disposed within the heating chamber, and is operable to radiate heat energy to the target location. The oxidizing gas inlet is disposed within the heating chamber, and is positioned to direct oxidizing gas to the target location for forming an oxide layer on the surface of the substrate.
The foregoing features of the invention will become more apparent in light of the following description and the accompanying drawings.
Now referring to
The preheating chamber 16 is adapted to maintain a vacuum at or below approximately 10−3 Torr (e.g., between approximately 10−3 to 10−8 Torr). Alternatively, the preheating chamber 16 can be adapted to maintain the vacuum at or below approximately 10−4 Torr (e.g., between approximately 10−4 to 10−6 Torr). The requisite vacuum may vary slightly depending upon the application at hand, thereby necessitating a preheating chamber adapted accordingly. The preheating chamber 16 has a target location 28 for locating the substrate 14 during a treatment/pre-treatment process, and houses a vacuum pump inlet 30 (hereinafter “vacuum inlet”), a radiant heat source 32 (hereinafter “heat source”), and at least one oxidizing gas inlet 34 (hereinafter “gas inlet”). The vacuum inlet 30 connects the diffusion pump to the preheating chamber 16. The heat source 32 is adapted to heat the surface 12 of the substrate 14. Surface 12 of the substrate 14 is aligned to receive the radiant heating from the heating source. The gas inlet 34 connects an oxidizing gas source 36 (hereinafter “gas source”) to the preheating chamber 16.
In the specific embodiment illustrated in
The coating chamber 18 is configured to deposit, for example, a ceramic (e.g., a TBC) coating on the surface of the substrate 14 by an EB-PVD process. EB-PVD coating chambers are well known in the art, and the present invention is not limited to any particular configuration thereof. Some examples of suitable EB-PVD coating chambers and processes are disclosed in U.S. Pat. No. 5,087,477 to Giggins, Jr. et al., and U.S. Publication No. 2008/0160171 (application Ser. No. 11/647,960) to Barabash et al., which are hereby incorporated by reference in their entirety.
In the embodiment in
Referring to
The heat source 32 heats the surface 12 of the substrate 14 via thermal radiation to a temperature above approximately 1800° F. For most applications, an acceptable substrate surface temperature range is about 1800° F. to about 1950° F., and substrate surface temperatures above 1830° F. work particularly well. For example, in the embodiment in
Thus, for favorable adhesion of TBC ceramic on a bond coat (or on a substrate or other coating), a cohesive alpha alumina scale or layer (i.e., serves as a “metallic-ceramic bond”) is desirable. Other thermally grown oxides can adversely affect TBC ceramic adhesion. The surface temperature of the substrate 14 should be rapidly heated above 1800° F. (e.g., to or above approximately 1830° F.) to reduce the quantity of the undesirable theta phase alumina, and other undesirable metallic oxides, that may form on the surface 12 of the bond coated substrate 14 at temperatures below 1800° F.
Referring again to
To form the alpha alumina layer on a large, compound, and/or irregular surface, the substrate 14 can be re-orientated (e.g., rotated, shifted, etc.) such that each portion of the surface is successively aligned with (e.g., directly below) the heat source 32 For example, referring to
After the TGO is developed on the coating required surface of substrate 14 treated in the preheating chamber 16, the substrate 14 is directed, via the sting 50, from the preheating chamber 16 to the coating chamber 18 through a respective second gate valve 22. In the coating chamber 18, the surface 12 of the substrate 14 is coated with, for example, a ceramic (e.g., TBC, etc.). The coating can be applied using any suitable deposition process such as, but not limited to, electron beam physical vapor deposition. When the surface of the substrate 14 has been coated, the substrate 14 is directed, through a respective third gate valve 24, out of the coating chamber 18 and the coating system 10. The flow chart shown in
While various embodiments of the present invention have been disclosed, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the present invention is not to be restricted except in light of the attached claims and their equivalents.
Number | Name | Date | Kind |
---|---|---|---|
4676994 | Demaray | Jun 1987 | A |
4880614 | Strangman et al. | Nov 1989 | A |
4952556 | Mantese et al. | Aug 1990 | A |
5087477 | Giggins, Jr. et al. | Feb 1992 | A |
5243169 | Tateno et al. | Sep 1993 | A |
5716720 | Murphy | Feb 1998 | A |
5856027 | Murphy | Jan 1999 | A |
6301434 | McDiarmid et al. | Oct 2001 | B1 |
6478888 | Burns | Nov 2002 | B1 |
6730422 | Litton et al. | May 2004 | B2 |
7037560 | Shinriki et al. | May 2006 | B1 |
7226672 | Litton et al. | Jun 2007 | B2 |
7291408 | Litton et al. | Nov 2007 | B2 |
7326470 | Ulion et al. | Feb 2008 | B2 |
7422771 | Pietraszkiewicz et al. | Sep 2008 | B2 |
7455913 | Freling et al. | Nov 2008 | B2 |
7476450 | Maloney et al. | Jan 2009 | B2 |
7579087 | Maloney et al. | Aug 2009 | B2 |
7622195 | Schlichting et al. | Nov 2009 | B2 |
7662489 | Litton et al. | Feb 2010 | B2 |
20020152961 | Burns | Oct 2002 | A1 |
20020185062 | Halpin | Dec 2002 | A1 |
20030041928 | Spitsberg et al. | Mar 2003 | A1 |
20030157363 | Rigney et al. | Aug 2003 | A1 |
20030219605 | Molian et al. | Nov 2003 | A1 |
20070125770 | Hamaguchi | Jun 2007 | A1 |
20080292873 | Nijdam et al. | Nov 2008 | A1 |
20100104766 | Neal et al. | Apr 2010 | A1 |
Number | Date | Country |
---|---|---|
1908857 | Apr 2008 | EP |
2048404 | Feb 1990 | JP |
Entry |
---|
Awaji, JP2048404, Feb. 1990, English abstract of document from applicants IDS Jan. 21, 2013. |
Extended EP Search Report, Apr. 26, 2011. |
Number | Date | Country | |
---|---|---|---|
20110217464 A1 | Sep 2011 | US |