Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-01-04
2001-07-17
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192160, C205S080000, C427S331000, C427S422000, C427S585000
Reexamination Certificate
active
06261422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the field of coatings for high-temperature structural materials. This invention comprises the technology, where mainly physical vapor deposition, sputtering in a vacuum and thermal spray processes, are used for production of hollow protective thermal-barrier coatings functioning as high-temperature heat-exchangers, which coatings can be used, e.g., for thermal barrier protection of gas turbine engine blades and other components against degradation by high-temperature oxidation and hot corrosion.
2. Background
Generally, the following described process is used to fabricate a surface heat-exchanger on the substrate of a component: open channels for heat-carrier are made on the surface of the component's material (substrate), then these channels are filled by an extractable filler to the surface level, and the whole of the obtained surface is covered by an unbroken/continuous layer of a material, making an outer shell (the cover), covering the channels, after which the filler is extracted from the channels, and a surface heat-exchanger, as described below, is obtained, consisting of an outer shell, covering open channels cut into the substrate body. The shaping of the open channels in the substrate body is produced by various techniques, e.g., during the casting of the component, or formed by mechanical or electromechanical machining. The channels are filled by an extractable filler, usually, in a paste form. The filler prevents the deposited material of the outer shell from getting into the channels. The formation of the outer shell may be accomplished using various techniques of coating application, e.g., thermal spray, or physical vapor deposition. The material, of which the outer shell is formed, is chosen based on the specific functions to be carried out by the protected component, (e.g., UK Patent Application GB 2172060 A, INT CL F01D 5/00, by Rolls Royce Ltd.; Germany, Patent Application DE 37 06 260, INT CL F 01 D 5/18, by Siemens AG; Japan, Patent Application 61-25 881, INT CL F 01 D 5/18).
In the prior art, surface heat-exchangers are used in various fields when a decrease or an increase of surface temperature of a component is required; chiefly of specific components operating in severe temperature and/or mechanical stress conditions. Also known and used is the method of mounting ready-made heat-exchangers onto the surface of a component.
Usually the elements of such heat-exchangers are produced by the stamping technique and are fixed onto a component surface by soldering or welding. But such heat-exchange surfaces are complex to manufacture and unreliable in operation, which is why they are limited for practical use and cannot be used for gas-turbine engine (GTE) blades, and similar components operating in severe temperature and mechanical stress conditions. Development of effective, reliable surface heat-exchangers possessing a range of protective coating properties is a continual challenge in airspace, power-generation, and rocket technologies.
To adequately describe and illustrate the problem being considered, observation of the use of such surface heat-exchangers for protection of GTE blades from overheating will suffice.
In modern GTE and GTU (gas-turbine units), operational temperatures are more than 1000° C. Improving economic operation and efficiency of a gas-turbine requires an increase in operating temperatures, which could be provided either by cooling GT components during operation, or by using materials with higher temperature and stress resistant properties.
PRIOR PROTOTYPE EXAMPLE
One prior prototype of a surface heat-exchanger is described as a shell (sheath) covering open channels, which are cut into the body of the substrate (the body of the protected component). This type of device and the required technology have a number of significant drawbacks, which lower the quality and operational properties of a surface heat-exchange.
Discussion of drawbacks.
1. In this prototype the partitions between the channels, which are, actually, the partitions of a heat-exchanger, must be wide enough to provide efficient cohesion of the shell with the protected component (the area of the partitions' end-face).
If the areas of cohesion are increased to provide better adhesion of the shell, then areas for cooling channels are decreased, leading to the following disadvantageous consequences:
the channel flow area decreases;
severe and debilitating temperature fluctuations occur within the shell at the conjunction points of cooling channels and adhesion surfaces;
a high level of heat transfer from the shell to the substrate via the partitions, which decreases the protective properties of the shell.
2. The presence of channels in the body of the substrate (in the body of the blade itself) probably greatly reduces its mechanical strength, acting as a concentrator of mechanical tensions.
3. The only type of surface heat-exchanger possible to produce by this technology is the one described above as a prototype.
4. A multi-tier heat-exchanger is impossible to produce using such technology.
5. It is extremely difficult to vary width and configuration of the channels and partitions cross-sections.
6. It is impossible to apply a ceramic coating onto the shell, due to the severe temperature fluctuations within the shell.
SUMMARY OF THE INVENTION
This invention deals with basic principles of the production of hollow thermal-barrier coatings functioning as heat-exchangers, which may be applied for various design embodiments. The coatings consist of an outer shell and an inner framework, joining the outer shell with the surface of the substrate and building up a system of hollows and/or channels in the space between the outer shell and the substrate. In other words, the coatings which can act as heat-exchangers are produced by certain methods of the application of materials, as described below:
1) preparation of the surface of the substrate for application of materials;
2) modeling the hollows and/or channels by application of the auxiliary extractable elements onto the surface of the substrate, which auxiliary elements are made of extractable filler(s);
3) application of the layer of the material of the coating, to form the inner framework on the obtained surface (the obtained surface being comprised of open areas of the substrate (and/or bondcoat) and that of auxiliary elements. Said obtained surface achieved as the result of repeated previous cycles (p.1, 2) will consist of the applied material of the coating and auxiliary elements, and/or a combination thereof).
4) repetition of steps 2 and 3 to complete formation of the framework (preceded by appropriate preparation of the obtained surface);
5) application of the layer of the main material of the coating, forming the outer shell, onto the appropriately prepared surface, which surface is a common surface comprised of the surfaces of the open areas of the framework and the surfaces of the auxiliary elements;
6) final extraction of the auxiliary elements from the assembled body/central portion of the coating.
The object of the present invention is to improve the quality and functional properties of surface heat-exchangers with protective outer shells, due to the elimination of the aforementioned drawbacks by means of:
1. Transpositioning the channels/hollows for a heat-carrier directly into the body of the protective coating.
2. Significant decrease of the partition thickness between the channels/hollows, which will allow
a nearly doubled capacity of the flow area of the channels retaining desired height;
equalization of the temperature within the shell and on the surface of the component;
decrease of heat transfer from the shell to the component, and an increase of heat transfer from the shell to the heat-carrier.
3. Increase in area and strength of surface cohesion.
4. The strength of the protected component is improved because the technology of this invention does not require channels being cut into the body of the comp
IONICA, LLC
Nguyen Nam
VerSteeg Steven H.
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