Coating processes – Coating by vapor – gas – or smoke – Carbon or carbide coating
Reexamination Certificate
2001-11-07
2003-12-30
Pianalto, Bernard (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Carbon or carbide coating
C427S249100, C427S249190, C427S255150, C427S255190, C427S255260, C427S255280, C427S255290, C427S255310, C427S255320, C427S255360, C427S255380, C427S255391, C427S255700, C427S294000
Reexamination Certificate
active
06669989
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the production of coatings on a substrate.
More particularly, the invention relates to production of coatings having an outermost ceramic layer and functional and compositional gradients between the outermost ceramic layer and the substrate. The inventive functionally graded coatings provide protection from heat, oxidation, corrosion, erosion and wear of parts such as, for example, gas turbines or internal combustion engines.
Over the last 10 to 15 years improvement of protective coatings has been aimed at creation of coatings having specific discrete gradients or layers of coating composition and coating structure from the substrate to the coating upper layer. Characteristic examples of these coatings can be the thermalbarrier coatings deposited on metal substrates wherein the coating has a discrete, layered variation in composition across the thickness of the coating from the substrate to an outer ceramic layer. Such layered graded coatings are produced in several stages, using various materials (metals, alloys, ceramics) and technological processes for each layer.
U.S. Pat. No. 4,401,697 of Aug. 30, 1983 (T. E. Strangman) describes a three-layered thermal-barrier coating which consists of a bond coat of a oxidation resistant and corrosion resistant alloy of MCrAlY type material of 25-250 &mgr;m thickness, an outer ceramic layer consisting of stabilized ZrO
2
with a columnar structure and an interlayer of Al
2
O
3
of 0.25-2.5 &mgr;m thickness. The MCrAlY alloy comprises, for instance, 18 wt. % Cr, 23 wt. % Co, 12.5 wt. % Al, 0.3 wt. % Y, the remainder being Ni. The MCrAlY alloy bond coat is deposited onto the metal substrate surface by electron beam evaporation of an ingot of MCrAlY alloy. Then the coated surface is subjected to mechanical treatment (for instance, shot peening); the part is annealed and again placed into the vacuum chamber. The outer ceramic coating is produced by electron beam evaporation of a ceramic ingot of stabilized ZrO
2
oxide and deposition of the vapor onto the bond coat. A thin interlayer of Al
2
O
3
is subsequently produced during annealing of the coated substrate in an oxygen-containing atmosphere. This interlayer provides good adhesion on Al
2
O
3
/ZrO
2
interface and slows down the oxidation of MCrAlY surface under high temperature service of the coating.
U.S. Pat. No. 4,676,994 of Jun. 30, 1987 (R. E. Demaray) recommends a four-layer coating which consists of a MCrAlY type alloy bond coat, a thin intermediate layer of Al
2
O
3
and an outer two-layer coating of stabilized ZrO
2
. The MCrAlY bond coat of approximately 120 &mgr;m thickness may be produced by electron beam evaporation of a MCrAlY ingot. After appropriate mechanical treatment of the surface (grit blasting), the part is placed into a vacuum furnace at a pressure of approximately 2×10
−4
mm Hg, heated to 980° C. and soaked for about 10 minutes. This results in formation on the MCrAlY surface of an Al
2
O
3
containing layer 1.0-2.0 &mgr;m thick. Then a ceramic ingot of ZrO
2
is evaporated by the electron beam under a vacuum of 10
−4
mm Hg and a dense (≈94% ) layer of ZrO
2
approximately 50 &mgr;m thick, is deposited. Subsequently, oxygen is bled into the chamber, and at the pressure of 5×10
−1
to 1×10
−3
mm Hg deposition of a less dense upper layer of ZrO
2
with a columnar structure approximately 100 &mgr;m thick, is completed. This layer has a lower heat conductivity and satisfactory mechanical relaxation ability.
U.S. Pat. No. 4,880,614 of Nov. 14, 1989 (T. E. Strangman et al) describes a thermal-barrier coating that consists of five layers. The first layer deposited on the substrate comprises diffusion aluminides produced by known processes. The second layer is of an alloy of the MCrAlY type deposited by electron beam evaporation or other methods. The third layer is a thin layer of super pure alpha Al
2
O
3
produced by chemical vapor deposition (CVD). The fourth layer is a stabilized ZrO
2
ceramic layer with a columnar structure, or other ceramics, deposited by electron beam evaporation. The fifth layer, a hard, dense, glazed outer ceramic layer, is produced by laser melting of the edges of the columnar crystallites. The fifth layer is intended to increase erosion resistance. The layer of diffusion aluminides and MCrAlY layer are intended to increase the oxidation and corrosion resistance of thermal-barrier coatings and thus to extend the service life of the coated part.
In European Patent EP 0814178 (D. S. Rickerby) a thermal-barrier coating consisting of seven layers is described. The first layer is a surface of nickel or cobalt base superalloy enriched in a metal of the platinum group, predominantly platinum. It is produced by deposition of a platinum layer 5-8 &mgr;m thick by electroplating and subsequent diffusion annealing in the temperature range of 800 to 1200° C. The second layer, a bond coat is made of an alloy that contains aluminum in the amount of 5-40 wt. %, for instance, MCrAlY type alloys or nickel aluminides or cobalt aluminides. The bond coat is deposited by a vacuum plasma process. The third and fourth layers are an enriched with platinum (or another metal of the platinum group) bond coat and a layer of platinum aluminide (or another aluminide), respectively. These layers are produced by electroplating of platinum or another metal of the platinum group on the bond coat surface and subsequent annealing of the plated substrate in the temperature range of 1000-1200° C. The fifth, sixth and seventh layers are thin layers of gamma phase alumina which is enriched in platinum, a thin layer of pure alumina and an upper ceramic layer of yttrium-stabilized zirconia with a columnar structure, respectively. They are produced using repeated thermal cycles of electron beam evaporation and deposition of ceramic material followed by oxygen bleeding into the vacuum chamber.
U.S. Pat. No. 5,891,267 of Apr. 6, 1999 (J. C. Schaeffer et al) proposes a four-layer coating. The first layer is produced by carbidization of the substrate surface using superalloys which contain carbide forming elements, namely Mo, W, Re, Ta, Ti, Cr, Hf, Zr. Carbidization is performed using conventional furnaces in a mixed atmosphere of hydrogen and methane at lowered pressure and temperature of 900-1200° C. for one to four hours. The first layer, saturated with carbon, has a thickness of up to 100 &mgr;m and contains 25-75 vol. percent carbides. It is followed by a second layer, namely an aluminum-rich bond coat of diffusion aluminum or MCrAlY type alloy produced by known methods. The third, thin layer of Al
2
O
3
and the fourth ceramic layer of ZrO
2
-(6-8) wt. % Y
2
O
3
with a columnar structure are also produced by known methods, typically physical vapor deposition.
A characteristic feature of the above examples, as well as many other patents that have not been cited, is the multi-stage processing required for production of the layered gradient protective coatings. Typically there is a need to use 2, 3 or more technologically different processes involving different equipment and handling therebetween. Additionally, intermediate treatments of the layer surfaces between stages are required. As a result, known processes for forming layered functionally graded coatings require considerable power consumption, time and expense. Additionally, it is difficult to precisely repeat all of the process parameters for each of the required complex steps in known processes for forming layered functionally graded coatings. Variation of process parameters in any of the stages during the involved multi-step processing results in a low probability of complete repeatability of coating composition and structure; i.e., of coating quality, from part to part. Further, the known coating technologies between the metal and ceramic layers cannot be regarded as optimal in terms of producing flat interfaces. In terms of performance of the ceramic layers, smoothly varying transitions from metal to ceramics are preferable
Movchan Boris A.
Nerodenko Leonila M.
Rudoy Jury E.
Alix Yale & Ristas, LLP
International Center for Electron Beam Technologies of E. O. Pat
Pianalto Bernard
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