JP2826824B2 - Thermal insulation coating method and gas turbine combustor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a plasma-sprayed ceramic thermal barrier coating used to protect substrates from high temperatures. BACKGROUND OF THE INVENTION Gas turbine engines obtain their thrust and other power by burning fuel. As engine power and economy both improve at higher temperatures, the technical field of gas turbine engines has tended to constantly increase engine operating temperatures. Research and development has been conducted over the years to improve the material to this trend. Early gas turbine engines were primarily based on alloys derived from ordinary steel,
Modern gas turbine engines rely on nickel and cobalt based superalloys often used in critical conditions. For some time now, the properties of metallic materials appear to be approaching their limits, or have probably already been reached. However, the demand for high temperature resistance continues. Although research is underway to develop ceramic turbine materials, it is still a very preliminary stage and many difficult problems must be overcome before ceramics can serve as structural materials for gas turbine engines. Naturally, attempts have been made to use ceramics as a coating to insulate the metal substrate and thereby increase the operating temperature of the engine without damaging the substrate. Although such attempts have been reported to have been somewhat successful, the durability of ceramic thermal barrier coatings remains an important issue, despite the fact that such coatings are used in connection with humans and safety considerations. This is because a minimum durability is required. The basic approach that has been generally taken is to apply an oxidation resistant metal bond coat to the substrate and then to apply a ceramic coating or optionally a mixed metal ceramic coating on this bond coat. Several patents have proposed using MCrAlY-based materials for this bond coat. MCrAlY-based materials were developed for protective coatings to protect metal parts from oxidation and corrosion under high temperature conditions. Examples of such MCrAlY-based coatings are described in U.S. Pat.
Nos. 3,928,026 and 4,585,481. The presently preferred ceramic component is zirconia, but zirconia undergoes a phase transformation at about 982 ° C. (1800 ° F.), so an additive to zirconia to obtain a stable or at least controlled microstructure at elevated temperatures. Need to be added. Patents which may be of particular relevance in this field include U.S. Pat.No. 4,055,705, which includes a NiCrAlY bond coat and zirconia based for stabilization, for example.
Thermal barrier coating methods using a ceramic coating containing 12% yttria have been proposed. A similar thermal barrier coating is described in U.S. Pat.No. 4,248,940, which has a common applicant with the present application, but the composition of the coating is 10
It is noted that this type of thermal barrier coating is graded from 0% metal to 100% ceramic on the outer surface. The patent describes an MCrAlY based bond coat, especially NiCoCrAlY, and mentions the use of zirconia stabilized by yttria. In the ceramic thermal barrier coating described in U.S. Pat. No. 4,328,285, a cerium oxide stabilized zirconia coating is applied over a CoCrAlY or NiCrAlY bond coat. US Patent 4,33
In the thermal barrier coating described in 5,190, NiCrA
The lY or CoCrAlY bond coat is provided with a spot-like coating of yttria-stabilized zirconia, which is further plasma sprayed with a coating of yttria-stabilized zirconia. U.S. Pat. No. 4,402,992 describes a method for ceramic thermal barrier coating of a hollow turbine metal component having cooling holes without blocking the cooling holes. The coating is characterized by a NiCrAlY or CoCrAlY bond coat with a coating of zirconia stabilized with yttria. U.S. Pat. No. 4,457,948 describes a method of creating a desirable crack pattern in a ceramic thermal barrier coating to increase its durability.
The coating comprises a NiCrAlY bond coat and a zirconia coating sufficiently stabilized by yttria. U.S. Pat. No. 4,481,151 describes another ceramic thermal barrier coating in which the bond coat is composed of NiCrAlY or CoCrAlY, but the yttrium component can be replaced by ytterbium. The ceramic component is zirconia partially stabilized by yttria or ytterbium. U.S. Pat.No. 4,535,033 is a U.S. Pat.
No. 51 is a continuation-in-part application that describes a ceramic thermal barrier coating with zirconia stabilized by ytterbia. DISCLOSURE OF THE INVENTION One of the objects of the present invention is to disclose a ceramic thermal barrier coating that has surprisingly high durability compared to similar ceramic thermal barrier coatings known in the art. According to the invention, the NiCoAlY bond coat is produced by plasma spraying in air on the surface of the substrate which has been previously treated in a suitable manner to protect the substrate. The ceramic of the present invention is composed of zirconia partially stabilized with yttria and contains about 7% yttria for proper stability,
Plasma spraying is performed on the NiCoCrAlY bond coat in the air. Such synthetic coatings are available in other types of
Surprisingly high durability compared to similar thermal barrier coatings using MCrAlY based bond coats and ceramic top coats. By using zirconia stabilized with 7% yttria, such coatings can be used at higher temperatures compared to other zirconia stabilizing materials or other thermal barrier coatings using a different amount of yttria. I can stand it. By using atmospheric pressure plasma spraying for plasma spraying in a low pressure chamber, preheating of the substrate and heat treatment after spraying can be omitted. The present invention particularly relates to the case of coating a thin metal sheet portion that is likely to be distorted during heat treatment. The above and other objects, features and advantages of the present invention will become more apparent from the preferred embodiments described below and the accompanying drawings. BEST MODE FOR CARRYING OUT THE INVENTION The benefits of the present invention are clearly illustrated in FIG. First
The figure is a graph comparing the life of several different ceramic thermal barrier coatings when performing very aggressive testing at a temperature of 1107 ° C (2025 ° F). This test consisted of a 6-minute thermal cycle, in which the coated substrate (metal sheet) during one cycle was approximately 93 ° C (200 ° C).
F) to about 1107 ° C. (2025 ° F.) in 2 minutes, maintain the temperature at 1107 ° C. (2025 ° F.) for 2 minutes, and then forcibly cool it to about 93 ° C. (200 ° C.) in 2 minutes The temperature was lowered to F). This is an intense test, using conditions that are more severe than those encountered with a typical gas turbine engine. The figure shows the time until breakage, and the number of cycles is obtained by multiplying the number of hours by ten. The bar (A) at the left end of the table in the figure shows the coating used at about 982 ° C. (180
0 ° F). The coating is made of CoCrAlY (23% Cr, 13% Al, 0.65% Y,
The remainder Co) is composed of those applied on the bonding coat. The composition at the left end has a composition of CoCrAlY of 100 on the bonding coat in the thickness direction of the coating.
% Of the outer coating on the surface. Other coatings in the table are non-gradient coatings, two-layer coatings. Such a graded coating (A) exhibited the shortest life, with failure occurring in the graded portion of the coating, where oxidation of the finely divided metal components caused the coating to bulge. As a result, spalling occurs. Although this coating breaks abnormally short due to the nature of the coating failure and the harsh test conditions, the typical maximum operating temperature of this coating is about 982 °
C (1800 ° F). The remaining coatings in the table break due to spalling and cracking in the ceramic component. Spalling at the interface between the ceramic and the bonding coat is not a problem. By analyzing the mode of failure for this type of ceramic coating, the following inferences were made:
That is, it may be inferred that the bond coat material does not play an important role in the behavior of the coating, but rather that the behavior of the coating is basically determined by the properties of the ceramic material. As will be shown later, this inference is surprisingly not true. The next bar (B) in the table is the same ceramic component 21
% Zirconia stabilized with magnesium oxide, but a two-layer coating with a 100% ceramic layer on the bond coat. In this embodiment, the bond coat is a simple aluminum alloy with 22% nickel. The third bar (C) in the table shows the same zirconia stabilized with 21% magnesium oxide as NiCoCrAlY bond coat (nominal composition 23% Co, 17% Cr, 12.5% Al, 0.45% Y,
This is applied on the remaining Ni). Both the bond coat of this coating and the ceramic layer were deposited by plasma spraying in air. Interestingly, the third coating in the table is the 21% magnesium oxide stabilized zirconia coating described above.
It shows about a two-fold improvement in service life when applied to a Ni-22% Al alloy bond coat, demonstrating that the bond coat does not affect the behavior of the coating. All of the zirconia-based coatings stabilized by 21% magnesium oxide have been found to result in the instability of the magnesium oxide material, which is less stable than the ceramic, due to the high temperature and volatilization beyond that time, and / or as a result of the ceramic becoming unstable. Or zirconia is 1038 ° C (19
At temperatures above 00 ° F), it appears that a monoclinic crystal phase is ultimately formed and breaks as an effect of causing microscopic thermodynamic stress / ratcheting. Non-thermally periodic zirconia, which is unstable when used in gas turbines, is a monoclinic crystalline phase. The two coatings shown in the figure use zirconia partially stabilized with about 7% yttria, but stabilized zirconia of this type is used at temperatures above about 1204 ° C (2200 ° F). If it does not reach the temperature, it does not deteriorate. The fourth bar (D) in the table shows zirconia partially stabilized with 7% yttria with NiCoCrAlY (23% Co, 17% C
r, 12.5% Al, 0.45% Y, balance Ni) It is applied on the bonding coat, but unlike other coatings,
In this method, the metal component was applied by low pressure plasma spraying, that is, spraying in a low pressure chamber in which the pressure was reduced to about 5 mmHg before spraying. It has been shown in the past that this type of low pressure plasma spraying can provide a much higher degree of thermal barrier coating because of the lower oxides and porosity in the metal bond coat and better integration and adhesion. . The feature of low pressure chamber spraying is that the base material is 871 ° C (1600 ° F)-982 before spraying.
° C (1800 ° F). Such coatings are practical for 3-6 in. Turbine blades, but impractical for composite sheet metal combustors. This is because such a combustor is of the order of 30.48-91.44 cm (1-3 ft), and is a composite assembly that is easily bent by a thin sheet-like piece of metal 0.508-1.016 mm (0.02-0.04 in). FIG. 2 is a schematic diagram of a gas turbine combustor. Even in a plasma sprayed metal bond coat such as NiCoCrAlY, a weak metal base-metal bond coat interface is formed below atmospheric pressure. Requires high temperature heat treatment. This heat treatment means that sheet metal elements that tend to be curved cannot receive this type of coating. Thus, when using this type of coating on larger sheet metal parts such as combustors, there is less need to apply the coating in a vacuum chamber. Because the combustor is too large and inconvenient for such a readily available low pressure plasma spray process. This type of coating by low pressure plasma spraying followed by a secondary heat treatment has been used commercially with some success.
However, its application is limited to use on small turbine blades and vanes having considerable structural strength. In contrast, the substrate is 260 ° in atmospheric pressure plasma spraying.
C (500 ° F) or less, no heat treatment after thermal spraying is required. Experience with atmospheric pressure spraying has predicted that the results of atmospheric pressure spraying will be clearly inferior to those sprayed in low pressure chambers. The bond coat by low pressure chamber spraying has an oxide content of 0.5% or less and a porosity of about 1-
2%. 3-5% coating by atmospheric pressure spraying
And a porosity of 5-15%. The last bar (E) in the figure shows the behavior of the coating according to the invention. The behavior of the coating of the invention is exactly the same as that of the best coating described above, despite the fact that the coating of the invention has been applied in air and has not been subjected to a subsequent heat treatment. I understand. The present invention derives some of its beneficial features therefrom by using a NiCoCrAlY bond coat.
It is true that the above benefits are obtained despite the fact that the failure occurs in the ceramic coating and not at the interface between the bond coat and the ceramic coating. The exact mechanism by which the use of a NiCoCrAlY bond coat benefits the behavior of the coating is not well understood, but the enhanced ductility of the NiCoCrAlY coating compared to NiCoCrAlY and CoCrAlY bond coats (as described in US Pat. No. 3,928,026) ) Is undoubtedly and generally supported technically to date. The ceramic component of the present invention, namely 6
% To 8% zirconia stabilized with yttria
It is also true that some of the zirconia coatings, which have been stabilized to a different extent by different additives used in the prior art, are more durable. This is shown by comparing the zirconia stabilized with magnesium oxide with the zirconia stabilized with yttria on the graph. Both coatings were applied over a NiCoCrAlY bond coat. In another test performed at a test temperature of 1093 ° C (2000 ° F), 7
% Zirconia stabilized with yttria is about twice as durable as zirconia stabilized with 12% yttria, and about twice as durable as zirconia stabilized (overall) with 20% yttria It shows five times the durability. The present invention can be applied to a superalloy substrate as described below. In general, the composition of the substrate is, of course, not limited as long as it has the necessary mechanical properties at the operating temperature.
The ground surface must be clean and properly treated, but the slightly roughened surface increases the surface area and increases the bond between the metal bond coat and the substrate according to the grit blast method. The bond coat is applied to the substrate by plasma spraying. The conditions for the plasma spraying are the same as those for the following ceramic component spraying. The bond coat material is NiCoCrAlY and has the following range: 15-40
% Co, 10-40% Cr, 6-15% Al, 0.7% Si, 0-2.0% H
f, 0.01-1.0% Y, the balance being substantially Ni, and the particle size is preferably US standard sieve -170 + 3.
The size is within the range of 25 mesh. In this case, cobalt imparts flexible elongation to the bond coat, but its effect is insufficient at 15% or less.
%, The bond coat becomes too soft. Chromium imparts corrosion resistance and oxidation resistance to the bond coat, but if its content is less than 10%, its action is insufficient, and if it exceeds 40%, the ductility of the bond coat is impaired. Aluminum imparts oxidation resistance to the bond coat, but its effect is insufficient if it is less than 6%, and if it is 15% or more, it has the disadvantage of lowering the melting point of the bond coat. Yttrium gives long-term oxidation resistance to the bond coat, but 0.01%
%, The effect is insufficient, and if it exceeds 0.1%, a low melting point phase may be formed in the bond coat. Although hafnium and silicon are not essential components for the present invention, they provide the long-term oxidation resistance to the bond coat similarly to yttrium, and thus may be contained in the above-described amounts. The thickness of the bond coat is preferably 0.0762-0.381 mm (0.003-0.015 inch). There is no benefit to increasing the thickness of the bond coat. Bonding coat thickness is about 0.0762mm
(0.003in) or less is dangerous. That is about 0.0762m
Plasma sprayed coatings much thinner than 0.003 in (m) tend to produce exposed areas on the substrate and ceramic coatings do not bond well to the exposed substrate. In such a case, catastrophic damage due to spalling is immediately caused. The plasma spraying of the bond coat on the pretreated substrate should preferably occur within an optimal time, and is preferably about 2 to minimize the potential for contamination of the substrate, for example, oxidation. Should be within hours. The base material coated with the bond coat is next 6-8%
A coating of zirconia stabilized with yttria is applied to a thickness of 0.254-0.381 mm (0.01-0.015 in). The diameter of the particles to be sprayed is preferably 60 μm (average), the output flow rate is 50 gm / min, the conditions for plasma spraying are 35 volts and 800 amps, using an argon helium mixture as carrier gas in the plasma power gun. The gun is held approximately 7.62 cm (3 in) from the ground and translates at a rate of approximately 22.56 m / min (74 ft / min) relative to the ground. Applying the ceramic coating to the bond-coated substrate, again, should preferably be within about 2 hours to minimize contamination and other problems. While the preferred embodiment of the invention has been illustrated and described, it will be appreciated by those skilled in the art that various changes in form and detail can be made without departing from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the results of a repeated test conducted at a temperature of 1107 ° C. (2025 ° F.) on various combinations of metal bond coats and ceramic outer coatings on sheet metal samples. It is a bar graph which shows the time which led to crushing. FIG. 2 is a schematic diagram of a gas turbine combustion chamber.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Keith Douglas Schaeffler               Weather, Connecticut, United States               Worthfield, Old Common               143 (72) Inventor Charles Edward Bevan               Corch, Connecticut, United States               Esther, P.O.Box 403                (56) References JP-A-52-33842 (JP, A)                 JP-A-56-102580 (JP, A)                 JP-A-53-33931 (JP, A)                 Special table 57-500291 (JP, A)

Claims (1)

(57) [Claims] The method of applying a durable thermal insulation coat to the metal substrate, (a) preparing a clean substrate, and (b) in air until the thickness becomes 0.0762-0.381mm (0.003-0.015in) 15-40% Co, 10%
-40% Cr, 6-15% Al, 0.01-1.0% Y, the balance being welded with a metal bond coat having a composition substantially composed of Ni. (C) Thickness of 0.254-0.381mm (0.01- A method of welding a ceramic coat of zirconia stabilized with 6-8 wt% yttria to 0.015 in) by plasma spraying in air, wherein no heat treatment is performed before and after said plasma spraying. 2. (A) 15-40% Co, 10-40% Cr, 6-15 applied to at least a part of the metal sheet by plasma spraying in air.
(B) a zirconia coat containing 6% -8% yttria and fixed by plasma spraying in the air containing (b) 6% -8% yttria. And a metal sheet in a state where substantially no distortion is caused by not being subjected to heat treatment before and after the plasma spraying.