JPS63118059A - Adiabatic coating method and gas turbine combustor - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to plasma sprayed ceramic thermal barrier coating inks used to protect substrates from high temperatures.

Background of the Technology Gas turbine engines derive their thrust and other power output from the combustion of fuel. Since both engine power and economy improve at higher temperatures, there has been a constant trend in gas turbine engine technology to increase engine operating temperatures. Over the years, this trend has led to research and development efforts to improve materials. While early gas turbine engines were based primarily on alloys derived from ordinary steel, modern gas turbine engines rely on superalloys, often based on nickel and cobalt, used in critical conditions. For some time now it appears that the properties of metallic materials are approaching, or perhaps already reaching, their limits. Demand for high temperature resistance continues.

Although research is being conducted to develop ceramic turbine materials, it is still at a very preliminary stage and many difficult issues must be overcome before ceramics can serve as a structural material in gas turbine engines.

Naturally, attempts have been made to insulate metal substrates by using ceramics as coatings, thereby increasing engine operating temperatures without damaging the substrate. Although such attempts have been reported to have had some success, the durability of ceramic thermal barrier coatings nevertheless remains a critical issue because such coatings are used in conjunction with humans and safety considerations are of paramount importance. This is because it requires extreme durability. The basic approach that has been commonly followed is to apply an oxidation-resistant metal bond coat to the substrate and then apply a ceramic coating or optionally a metal-mixed ceramic coating over the bond coat. In some patents, this bond coat includes M Cr A
It has been proposed to use IY-based materials. MCr
AIY-based materials were developed as protective coatings to protect metal parts from oxidation and corrosion under high temperature conditions. Examples of such MCrAIY-based coatings are disclosed in U.S. Pat. No. 3,676.085;
No. 6 and No. 4,585,481.

- The currently preferred ceramic component is zirconia,
Since zirconia undergoes a phase transformation at about 9820C (1800@F), it is necessary to add additives to the zirconia to obtain a stable or at least controlled microstructure at high temperatures.

Patents that may be of particular relevance to this field include U.S. Patent No. 4,055. ．． No. 705, which includes N1CrA
A thermal barrier coating method has been proposed using an IY bonding coat and a ceramic coating based on zirconia and containing, for example, 12% ittria for stabilization. A similar thermal barrier coating is described in U.S. Pat. Special mention is made of types of thermal barrier coatings that are graded to 100% ceramic. In the patent, M Cr A I Y bonding coat,
In particular, N1CoCrAIY is described and the use of yttria stabilized zirconia is mentioned.

The ceramic thermal barrier coating described in US Pat. No. 4,328,285 includes a coating of cerium oxide stabilized zirconia over a Co Cr, AIY or N1CrAIY bond coat. Thermal barrier coatings described in U.S. Pat. No. 4,335°190 include N1CrAIY or CoCrAIY
The Y bond coat has a speckled coating of ittria-stabilized zirconia on top of which is plasma sprayed a coating of ittria-stabilized zirconia. U.S. Patent No. 4.402
, 992 describes a method of applying a ceramic thermal barrier coating to hollow turbine metal parts having cooling holes without blocking the cooling holes. The coating features N1CrAIY or CoCrA with a coating of ittria-stabilized zirconia.
It's in the IY bonding coat. U.S. Patent No. 4,457
．． No. 948 describes a method for creating a favorable crack pattern in ceramic thermal barrier coatings to increase their durability. The coating is N1CrAIY
Consists of a bond coat and a zirconia coating fully stabilized by ittria. Another ceramic thermal barrier coating is described in US Pat. No. 4,481.151, in which the bond coat is composed of N1CrAIY or CoCrAIY, but the yttrium component can be replaced with ytterbium. The ceramic component is zirconia partially stabilized with yttria or ytterbium.

U.S. Patent No. 4.535°033 is the aforementioned U.S. Patent No. 4.
．． No. 481,151, a continuation-in-part application, describes ceramic thermal barrier coatings 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 N1CoAIY bonding coat is produced by plasma spraying in the atmosphere on the surface of a substrate that 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, containing approximately 7% intria to provide adequate stability, and is coated with atmospheric plasma on the NiCoCrAlY bond coat described above. thermal sprayed.

Such synthetic coatings may include other types of M Cr A I
Surprisingly durable compared to similar thermal barrier coatings using Y-based bond coats and ceramic top coats. By using zirconia stabilized with 796 yttria, such coatings can withstand use at higher temperatures compared to other zirconia stabilizers or other thermal barrier coatings that use different amounts of yttria. obtain. By using atmospheric pressure plasma spraying versus plasma spraying in a low pressure chamber, preheating of the substrate and post-spray heat treatment are eliminated. The present invention particularly relates to coating parts of thin metal sheets that are susceptible to distortion during heat treatment.

The above and other objects, features and advantages of the present invention will become more apparent from the following preferred embodiments and accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION The benefits of the present invention are clearly illustrated in FIG.

FIG. 1 is a graph comparing the life of several different ceramic thermal barrier coatings when subjected to very vigorous testing at temperatures of 1107'C (2025'F). The test consists of a 6 minute thermal cycle, during which the coated substrate (sheet metal substrate)
from about 93°C (200°F) to about 1107°C (20
The temperature was raised to 25°F (25°F) in 2 minutes, held at 11076C (2025°F) for 2 minutes, and then forced to cool down to about 93°C ('200°F) in 2 minutes. This is an intense test, using conditions that are more severe than those encountered by typical gas turbine engines. The figure shows the time until failure, and the number of cycles is obtained by multiplying the number of hours by ten.

The leftmost bar (A) in the table in the figure represents a coating used commercially in gas turbine engines, approximately 9826C (1
800°F). The coating consists of CoCrAIY (23
%Cr, 13%A1.0.65%Y5 balance Co) applied on top of the bond coat. The leftmost coating is a graded coating in which the CoCrAIY composition decreases through the thickness of the coating from 10006 on the bond coat to 0% on the outer coating at the surface. The other coatings in the table are two-layer coatings that are not graded coatings. Such a graded coating (A) showed the shortest life and failure occurred in the graded part of the coating because oxidation of the finely divided metal components caused the coating to swell. This is because spalling occurs as a result.

Although this coating fails in an unusually short amount of time due to the failure nature of the coating and the harsh test conditions, the typical maximum operating temperature for this coating is approximately 982°C (1982°C).
800°F).

The remaining coatings in the table fail due to spalling and cracking within the ceramic component. Spalling at the interface between the ceramic and bond coat is not a problem. Analysis of the failure mode in the case of this type of ceramic coating leads to the following conclusion: the bond coat material does not play a significant role in the behavior of the coating; rather, the behavior of the coating is essentially One might conclude that it is determined by the properties of the ceramic material. As will be shown later, this inference is surprisingly untrue.

The next bar (B) in the same table has the same ceramic component21
% magnesium oxide stabilized zirconia, but is a two-layer coating with a 100% ceramic layer on top of the bond coat. In this example, the bond coat is a simple aluminum alloy with 22 wt% nickel.

The third bar (C) in the same table shows the same 21% magnesium oxide stabilized zirconia with a NiCoCrAlY bond coat (nominal composition 23% Co, 17% Cr, 12%
．． 5% Al, 0.45% Y1, balance Ni). Both the bond coat and the ceramic layer of this coating were deposited by plasma spraying in the atmosphere. Interestingly, the third coating in the same table improved the lifetime by about twice as much as the 21% magnesium oxide stabilized zirconia coating applied to the Ni-22% A1 alloy bond coat. The results show that the bond coat does not affect the behavior of the coating. All of the 21% magnesium oxide stabilized zirconia-based coatings were tested as a result of the magnesium oxide material, which is more unstable than the ceramic, volatilizing due to high temperatures and beyond which time the ceramic becomes unstable. Or zirconia at 1038°C (1900°
At temperatures above F), it appears that eventually a monoclinic crystalline phase forms and failure occurs as an effect of producing more microscopic thermodynamic stress/ratcheting. Athermally periodic zirconia, which is unstable when used in gas turbines, is a monoclinic crystalline phase. The two coatings shown above use zirconia partially stabilized with about 7% ittria; however, this type of stabilized zirconia can be It does not deteriorate due to heat unless the temperature rises.

The fourth bar (D) in the same table shows that N1CoCrAIY (23%
Co, 17% Cr, 12.5% Al, 0.45% Y1 balance Ni) was applied on the bonding coat,
Unlike other coatings, in this method the metal components were applied by low-pressure plasma spraying, ie, in a low-pressure chamber where the pressure was reduced to approximately 5 mm/g prior to spraying. This type of low-pressure plasma spraying has been shown in the past to be able to provide significantly higher thermal barrier coatings because there are fewer oxides and porosity in the metal bond coat and better integration and adhesion. . The characteristic of low-pressure chamber thermal spraying is that the substrate is heated to 871'C (1600°F) - 9820C before thermal spraying.
(1800°F).

Such a coating is 7.62-15.24cmC5-
6 inch) turbine blades, but impractical for composite sheet metal combustors. This is because the size of such a combustor is 30.48-91°44
cm (1-3 ft) and a thin sheet metal piece of 0.508-1.016 mm (0.02-0°04
This is because it is a composite assembly that is easily bent due to in). FIG. 2 is a schematic diagram of a gas turbine combustor.

Even in plasma sprayed metal bond coats such as N1CoCrAIY, a weak metal substrate-metal bond coat interface is formed below atmospheric pressure. Requires high temperature heat treatment. This heat treatment means that sheet metal elements, which tend to curve, cannot undergo this type of coating. Thus, when this type of coating is used on larger sheet metal parts such as combustors, there is less need to apply the coating in a vacuum chamber. This is because the combustor is too large and inconvenient for such readily available low pressure plasma spray methods. This type of coating by low pressure plasma spraying with subsequent secondary heat treatment has been used commercially with some success. However, its application is limited to use in small turbine blades and vanes with considerable structural strength. In contrast, atmospheric pressure plasma spraying maintains the substrate below 2609C (500°F) and requires no post-spray heat treatment. Previous experience with atmospheric pressure spraying would have predicted that the results of atmospheric spraying would be significantly inferior to areas sprayed in a low pressure chamber. The bond coat produced by thermal spraying in a low pressure chamber has an oxide content of 0.5% or less and a porosity of 1-2%. Atmospheric spray coatings are 3-5% oxide and 5-15%
It has a porosity of

The last bar (E) in the figure shows the behavior of the coating according to the invention. The behavior of the inventive coating is exactly the same as that of the best coating described above, despite the fact that the inventive coating was applied in air and was not subjected to any subsequent heat treatment. I understand.

The present invention derives some of its beneficial features from the use of a NiCoCrAlY bond coat. It appears to be the case that the above benefits are obtained despite the fact that failure occurs within the ceramic coating rather than at the interface between the bond coat and the ceramic coating. Although the exact mechanism by which the use of a NiCoCrAlY bond coat benefits coating behavior is not well understood, NiC.

The enhanced ductility of N1CoCrAIY coatings compared to CrAIY and CoCrAIY bond coats (as described in U.S. Pat. No. 3,928,026) is undoubtedly related and has not been generally supported in the art to date. There is.

The ceramic component of the present invention, zirconia stabilized with 6% to 8% ittria, is superior to zirconia coatings stabilized to different degrees with different additives that have been used in the prior art. It is also true that some materials are more durable than others. This is illustrated by comparing zirconia stabilized with magnesium oxide and zirconia stabilized with ittria on the graph above. Both coatings are NiCoCrAlY
Applied on the bonding coat. Test temperature 10930
In other tests conducted at 2000°F, zirconia stabilized with 7% yttria was approximately twice as durable as one piece of zirconia stabilized with 12% yttria; It shows about five times the durability compared to zirconia stabilized (entirely) with Ittria.

The present invention can be applied to superalloy bodies as shown below.

In general, there are no restrictions on the composition of the substrate as long as it has the necessary mechanical properties at the operating temperature. Although the substrate surface must be clean and properly treated, grid blasting increases the surface area and strengthens the bond between the metal bond coat and the substrate due to the slightly roughened surface. The bond coat is applied to the substrate by plasma spraying. The conditions for this plasma spraying are the same as those for the ceramic component spraying described below. The bonding coat material is N1CoCrAIY and has the following range, namely 15
-40%Co, 10-40%Cr, 6-15%A1.0
．． 7%Si, 0-2゜0%Hf, 0.01-1゜0%Y
The remainder has a composition that is substantially Ni1, and the particle size is preferably within the range of US standard sieve 170+325 mesh. The thickness of the bonding coat is preferably 0.0762-0.381ml (
0,003-0,015in). There is no benefit to increasing the thickness of the bond coat. The thickness of the bonding coat is approximately 0.0762ma+(0,00
3 In) or less is dangerous. That is about 0.076
Plasma spray coatings much thinner than 2 mm (0,003 inches) tend to leave exposed areas on the substrate, and ceramic coatings do not bond well to exposed substrates.

In such a case, catastrophic damage due to spalling will quickly occur. Plasma spraying of the bond coat onto the pretreated substrate should preferably be done within an optimum time period, preferably approximately 2 to Should be done within time.

The bond coated substrate is then coated with a 6-8% yttria stabilized zirconia coating. The diameter of the sprayed particles is preferably 60 μm (
average), the output flow rate is 50 glll/win, and the plasma spray conditions are 35 volt and 800 gll/win.
In aIIlp, an argon-helium mixture is used as a carrier gas in a plasma-powered gun. The gun is held approximately 7.62 cm (31n) away from the substrate surface and approximately 22.56 m/11in (74 f't/in) relative to the substrate surface.
ll1in). Application of the ceramic coating to the bond coated substrate should again preferably occur within approximately two hours to minimize contamination and other problems.

Although preferred embodiments of the present invention have been shown and explained,
It will be appreciated by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

Figure 1 shows the time to fracture in a cyclic test conducted at a temperature of 1107°C (2025” F) for various combinations of metal bond coat and ceramic outer coating on sheet metal specimens. 2 is a bar graph. FIG. 2 is a schematic diagram of a gas turbine combustion chamber.

Claims (2)

[Claims] (1) A durable heat insulating coating is applied to the metal base, (a) a clean base surface is prepared, and (b) the thickness is 0.127-0.381mm (0.005mm).
15-40% Co, 10-40% Cr,
6-15% Al, 0-2% Hf, 0-7% Si, 0.0
(c) Welding a metal bonding coat having a composition consisting of 1-1.0% Y and the remainder substantially Ni; (c) a thickness of 0.254-0.381 mm (0.01-
depositing a ceramic coating of zirconia stabilized with 6-8 wt% yttria by plasma spraying in air to a thickness of 0.015 in. (2) a sheet metal gas turbine combustor having a thermal barrier coating on at least a portion thereof; (b) a NiCoCrAlY bond coat applied to at least a portion of the sheet metal assembly by plasma spraying; (c) a zirconia coating containing 6% to 8% yttria and fixed by plasma spraying; a gas turbine combustor, wherein the composite sheet metal assembly is substantially free from distortion as a result of being plasma sprayed in the atmosphere without undergoing associated heat treatment before or after plasma spraying. .