DE10238551A1 - Production of a composite component used as a sealing element in gas turbines comprises joining a structure to a support by soldering using aluminum as the solder material - Google Patents

Abstract

Production of a composite component comprises joining a structure (2) to a support (1) by soldering using aluminum as the solder material. The structure and the support are made from high melting alloys made from iron, nickel, cobalt, chromium, titanium or other combination.

Description

The invention relates to a Method for producing a composite component with a carrier and a structure attached to this according to the preamble of the main claim.

The invention relates in detail on a process for the production of components that form a composite made of a solid, fully dense metallic material and one less dense, porous metallic Form structure, or the connection of several fully dense or porous structures.

Frequently there is the task in manufacturing technology, less dense, porous structures, which have a non-load-bearing function and are therefore referred to as functional surfaces be connected to a component that consists of a fully sealed and therefore structurally rigid and load-bearing material is manufactured. This is the case, for example, when producing segments or rings for brushable gas path seals, like you often in the construction of thermal turbomachinery, for example in gas turbine construction, be used. There is a made of thin metal foils, less dense, honeycomb-like cell structure with a supporting structure connected, which are made of solid sheet metal structures or cast components is.

In other cases, highly porous fiber components, such as fiber mats made of thin, metallic wires or short metal fibers are made with supporting structures made of fully sealed castings or sheet metal components connected.

The functional task is there the porous Working surface frequently therein, as an expansion isolator and / or thermal isolator between the full metal structure and one for example by thermal Syringes, such as plasma syringes, on the ceramic layer produced on the porous structure to serve. The porous Structure resembles the differences through elastic deformations in the thermal expansion between metal structure and ceramic off, so that with rapid temperature changes, cracking and chipping of the ceramic layer is avoided.

In addition, such an insulation layer through their porous Character the property, the ceramic layer relatively well anchor as the porous Layer partially infiltrated by the ceramic layer applied to it can be. Such a structure (full metal - porous strain insulator - ceramic Surface) fulfilled thereby frequently the task of a thermal insulator, especially if as a ceramic layer, a poorly heat-conducting ceramic, such as Aluminum oxide or zirconium oxide, which is used in addition also a certain amount of inner porosity can have.

Here come as porous structures in particular honeycomb components made of thin Metal foils, metallic foams, metallic hollow sphere structures or metallic fiber components, which are made of thin wires or short metal fibers are used.

Composite components of the described Art are from the prior art, for example, as mentioned, as Sealing elements known, for example for gas turbines or thermal Turbomachinery. The sealing elements are so-called brushable sealing segments used. The honeycomb structure is common using a special solder and / or diffusion process applied to the carrier. The carrier itself is designed, for example, in the form of a cast part or a sheet metal part, approximately in the form of a ring or a ring segment.

Around a column between a fixed one and to seal a rotating component, such as with blades or waves, or to keep such a gap as small as possible and thus the performance and / or the efficiency of the thermal turbomachine or to improve the gas turbine, the aforementioned touchable Abradable seals are used. Especially in the hot turbine part such honeycomb-like sealing structures are used. This consist of thin Strips of metal foils, which are assembled into honeycomb structures are. The metal foils are cut to a specified width cut and reshaped to be flattened and in different Film strips protruding parallel to each other downwards or upwards Plateaus arise. By lining up or stacking a variety of such shaped metal foil strips is created the well-known honeycomb structure.

The honeycomb structure or produced in this way Cell structure serves as a seal that can be touched. It is built that they rotate quickly against rotating components with little resistance opposed and thus the rotating components, such as blades, from injury preserved.

As a method of connecting a porous structure essentially come to a load-bearing full metal structure two methods of application, namely high temperature sintering or brazing.

While high-temperature sintering is a variant for connecting the components of the porous functional layer, such as metal fibers, to themselves and thus giving the porous structure a minimum degree of internal structural rigidity, the properties of sintered compounds of the porous functional structure with the solid metal are often sufficient not sufficient to remove the mechanical loads and stresses occurring at the connection point. A composite produced by high-temperature soldering usually has higher mechanical strengths and is therefore preferred.

Since the composite components in question are usually exposed to high temperatures, both the all-metal support structure and the less dense, porous metal structure are mostly made of metals suitable for high temperatures, such as heat-resistant steel made of nickel-based or cobalt-based alloys. According to the state of the art, these are connected to one another using common hard solders. Such common hard solders are alloys with a usually high content of nickel, cobalt or also precious metals, such as palladium. Since these alloys have a high melting point, alloy elements, such as boron, which lower the melting point, are added to lower it and thus to produce a usable hard solder. Another variant, which is known from the prior art, consists in forming the brazing alloys in the form of eutectic alloys with an intrinsically low melting point. For example, eutectic or near-eutectic compositions in the nickel-silicon or nickel-palladium system are known. The brazing alloys known from the prior art thus have a solidus temperature in the range from approximately 800 to 1300 ° C. A disadvantage of the solutions known from the prior art is that low-melting brazing alloys containing precious metals are very expensive. The addition of the melting point-lowering elements boron and silicon in the considerably cheaper, noble metal-free hard solders based on nickel or cobalt has the disadvantage that, while the solder is in the molten state, it diffuses into the base materials of the components to be connected and there with the alloying elements of the base materials form brittle and mostly little oxidation-resistant intermetallic compounds. Chromium borides of the general type Cr _x B _y are known, for example, which are known to embrittle the base materials and are susceptible to oxidation attack. In addition, the disadvantageous borides and silicides are also found in the re-solidified solder and there in particular at the grain boundaries. Overall, when using common nickel and cobalt base solders, non-optimal bonds between the supporting structure and the porous functional structure arise in terms of ductility and corrosion resistance.

In the state of the art known sealing elements, the individual is connected Layers of the honeycomb structure with one another and the fastening of the honeycomb structure on the carrier by means of a soldering process. As explained above, common hard solders are also used here, such as alloys with a high nickel or cobalt content. This one Nickel or cobalt alloys have high melting points to lower the melting temperature and thus to generate a usable hard solder material melting point lowering alloy elements, such as boron. Another variant is, as explained, the Brazing alloys in the form of eutectic alloys with an intrinsically low Form melting point. Such are eutectic or near-eutectic compositions known in the nickel-silicon system. The state of the art Known brazing alloys have a solidus temperature in the range of 800 to 1300 ° C.

The melting point-lowering elements, such as boron or silicon, also have the disadvantages mentioned here. While the brazing alloy is in the molten state, these elements diffuse into the material of the honeycomb structure and into the material of the carrier and, for example, form intermetallic compounds, such as borides or silicides, of the Cr _x B _y type, with the alloying elements of these materials. These intermetallic compounds are usually found at the grain boundaries of the base materials or at the grain boundaries of the re-solidified solder. They lead to embrittlement of the base materials and the solder and thus the entire composite of the sealing element.

Another disadvantage is that some of the resulting intermetallic compounds, such as chromium borides (Cr _x B _y ), are susceptible to corrosion.

Since the sealing elements according to the invention through hot Process media are exposed to high operating temperatures, they must against hot gas attack and thus against high temperature oxidation, high temperature sulfidation andl or be resistant to high temperature carburization. This will be the case with the Achieved sealing elements known from the prior art that you can use highly chromium-alloyed nickel-based alloys as a material for the Honeycomb structure used.

The invention is based on the object Method for producing a composite component of the aforementioned Type to create, which with a simple structure and simple design economical and is safe to use and the disadvantages of the state of the Technology avoids.

According to the invention, the object is achieved by Combination of features of the subordinate claims solved, which show subclaims further advantageous embodiments of the invention.

According to the invention it is therefore provided that connecting the structure to the carrier by means of a soldering process takes place, in which as a soldering material either pure aluminum or an aluminum alloy is used becomes.

According to the invention, it is provided that neither the carrier nor the structure are made from aluminum materials or aluminum base materials. Rather, both the support and the structure are made of high-melting alloys which are based on iron, nickel, cobalt, chromium, titanium or their combinations.

According to the invention is therefore with regard to Sealing structure provided that the connection of the individual layers the honeycomb structure and connecting the honeycomb structure to the carrier by means of a soldering takes place, in which as a soldering material either pure aluminum or an aluminum alloy is used becomes.

The method according to the invention stands out through a number of significant advantages.

According to the invention, a method for Production of a composite component, which consists of a fully metallic and 100% dense support structure and one attached to it porous up highly porous metallic functional structure, which is simple and inexpensive is designed and, as explained below, the disadvantages of the prior art who avoids technology.

By using pure aluminum or individual aluminum alloys is avoided that brittle and corrosion-prone borides or form silicides.

Furthermore, the method according to the invention results the advantage that the very thin elements that make up the porous Functional structure is built up, for example thin metal fibers, hollow spherical structures, Honeycomb components made of thin metal foils etc. or the full-density support structure, not through diffusion of nickel or cobalt adversely change in their metallic composition. A unfavorable change by the diffusion of nickel or cobalt e.g. at the state of the Technology given that the alloy content of aluminum, the in common High temperature materials carrier resistance to hot gas corrosion is locally reduced or diluted becomes. When using the invention aluminum-based solders, on the other hand, even do the opposite, namely one local enrichment with aluminum in the zones influenced by the solder in the base materials, i.e. in the fully sealed support structure and achieved in the elements of the sparse, porous structure.

Furthermore, according to the invention the diffusion of aluminum can also be achieved in Connection with the use of a nickel-containing base material a high-melting and very good oxidation-resistant nickel-aluminum compound, such as NiAlide nickel aluminide, during the soldering process. Mostly can be achieved that moderately oxidation-resistant base materials through the soldering process at least locally, namely in the area of the zone influenced by the solder, by aluminum enrichment improved resistance to oxidation and hot gas corrosion receive.

Due to the special method according to the invention, in which essentially with aluminum or an aluminum alloy If the solder is used, the material of the honeycomb structure is also used reinforced in itself, whereby both the material of the carrier and the material the honeycomb structure is enriched with aluminum. So it turns out the sealing element according to the invention in particular in terms of its thermal resistance and durability against hot gas attacks as particularly advantageous.

According to the invention from the state the disadvantages known in the art are overcome in that the soldering material pure aluminum or aluminum alloys can be used. By the soldering process at a comparatively low temperature, the aluminum or the aluminum alloy completely converted into melt. The soldering process is above the melting temperature of the aluminum or above the liquidus temperature the aluminum alloy. The molten Aluminum loosens the material of the honeycomb structure and the base material of the carrier partially, which increases the melting point of the resulting Aluminum alloy increased and the aluminum solidifies isothermally and thus a composite of Cell structure generated with the support structure. In addition, the Walls of the Honeycomb structure.

In another cheap An embodiment of the invention provides that heat treatment follows he follows. You can at soldering temperature (constant temperature) or at a temperature higher than the soldering temperature is to be carried out. This results in a concentration compensation by diffusion, whereby especially the interior of the film-like material of the honeycomb structure over the Surface layer of the carrier material enriched with aluminum becomes. As a result, the oxidation and hot gas corrosion resistance is significantly improved.

The aluminum according to the invention or the aluminum alloy, which are used as brazing alloys can be used in many different ways Way to be applied.

For example, it is possible that Honeycomb structure initially like this to generate the individual folded or reshaped layers by resistance spot welding fixed to each other. This is done so that the layers or folded film strips stand upright to the surface of the carrier. In the resulting cells closed on one side at the bottom can be aluminum or aluminum alloy powder filled become. This structure is, for example, in a vacuum soldering furnace heated to a temperature of about 660 to 1100 ° C. This causes the aluminum to melt or the aluminum alloy, then solidifies and leads to the described diffusion processes.

However, the pure aluminum powder or the aluminum alloy powder can also be introduced into the cellular honeycomb structure, for example by thermal spraying. Likewise, the honeycomb bodies applied to the supporting structure by resistance welding can be surface-enriched with aluminum by bath aluminizing or pack aluminizing. It is also possible to use a PVD or a CVD process.

In a particularly cheap An embodiment of the invention provides that the aluminum solder or the as a soldering material serving aluminum alloy in advance on the surface of the Layers of the honeycomb structure is applied. This variant offers the advantage that not only the double-layer walls of the honeycomb structure, but also the other cell walls, which are formed only in one layer, wetted with aluminum or an aluminum alloy and during of the processing process can be enriched with aluminum. The The aluminum solder can be applied, for example, by dip aluminizing or a bath aluminization. It is also possible to use PVD or CVD process on the finished film. It is also possible, the film before finish rolling with aluminum or a suitable one Rolling aluminum alloy.

In an advantageous further development it also possible to use an aluminum foil. This is used in manufacturing the honeycomb structure is deformed in the same way as the layers of the base material and incorporated directly into the structure of the honeycomb structure, so that the aluminum is optimally pre-placed in the cell structure.

Regarding the temperatures required a vote according to the invention to the alloys and to the respective structural measures possible. It is possible, too, choose the temperature range between 550 and 1150 ° C.

Comparing the prior art with the present invention reveals that the addition of aluminum has a particularly favorable effect on the resistance to hot gas corrosion. The reason for this is that the aluminum content under oxidizing hot gas conditions results in the formation of dense and firmly adhering aluminum oxide layers (Al ₂ O ₃ ). This superficial aluminum oxide layer protects the material very effectively against further attack by hot gas at high application temperatures.

In the absence of aluminum in The alloying element chromium can also function as the matrix Aluminum, however with a significantly lower protective effect at high temperatures. This results in the disadvantages known from the prior art. With the usual Foil materials used to manufacture the honeycomb structure are for reasons the processability in the state of the art only uses materials, the, if any, only marginally are alloyed with aluminum. Even those known from the prior art Hard solders are usually not at all alloyed with aluminum. This and the presence of intermetallic Maintain connections in a plumb line to a usually low resistance to hot gas corrosion the braze solder. Overall, the one known from the prior art The structure is therefore not resistant to oxidation and hot gas corrosion. In particular represent the free and solder wetted surfaces of the sealing element weak points in the prior art with regard to hot gas resistance in gas turbine use.

The invention relates, as already indicated above, on a honeycomb structure, which is the base material does not include aluminum. Base materials or base alloys are in particular iron-based alloys, nickel-based alloys, cobalt-based alloys or titanium-based alloys or their combinations.

The same applies to the choice of material for the carrier.

According to the invention, it is particularly advantageous if both the aluminum content of the soldering material and the temperature control the soldering process be designed so that the intermetallic phase produces NiAl becomes.

According to the invention, the structure can be more preferred Way also in the form of a metallic fiber structure or a hollow sphere structure or be in the form of a metallic sponge.

The invention further relates both on soldering processes, where you work without flux, as well as soldering with flux. Suitable fluxes can include fluorides, in particular potassium aluminum fluoride.

The invention is described below of embodiments described in connection with the drawing. It shows:

1 2 shows a schematic side sectional view of a composite component according to the invention,

2 an enlarged view of the area "A" of 1 .

3 a view of another embodiment, analogous to the representation of the 2 .

4 is a schematic representation of the structure of the honeycomb structure according to the invention, and

5 a perspective, greatly simplified representation of the structure of a sealing element according to the invention.

The 1 shows a schematic side sectional view of an example of a composite component according to the invention with a carrier 1 , which can be a sheet metal or a cast metal body. On this is a structure 2 applied, which can be made in the form of a porous metal structure, such as a fiber structure or a metallic hollow sphere structure, and forms a functional structure or a functional body.

On the structure 2 can also have a ceramic layer 14 be upset. With the reference symbol 15 is an interface between the carrier 1 and the structure 2 referred to, which is designed according to the invention as a solder joint.

The 2 shows an enlarged view of the detail "A" of 1 , The curly bracket shows the thickness of the structure 2 , At the in 2 The embodiment shown is the porous structure 2 from metallic fibers or wires 16 constructed, which have a circular cross section d.

The individual elements of the porous structure 2 are about sintered contact points 17 more or less firmly connected and give the porous structure 2 sufficient structural strength.

The connection of the porous structure 2 (Structural body) on the fully dense metallic support 1 (Supporting structure) is carried out by means of a solder 18 that both the porous structure 2 as well as the carrier 1 wetted. Due to the molten state of the solder 18 Alloy components of the metallic solder diffuse during the soldering process 18 in the carrier 1 and into the elements 16 (Fibers, wires) that make up the porous structure 2 is built up and define the solder material (solder 18 ) affected zones 19 in the porous structure 2 and zones 20 in the fully dense basic structure (carrier 1 ). In the case of the use of nickel or cobalt base solders according to the prior art, these zones are those in which the unfavorable intermetallic precipitates such as borides or silicides are found. In the case of the use of solders according to the prior art, these zones are also those in which the aluminum content of the base materials is reduced due to the diffusion of nickel or cobalt from the solder, because it is diluted.

In contrast, the zones 19 and 20 enriched with aluminum in the process according to the invention.

Through a heat treatment at temperatures that are equal to or higher than the melting temperature of the aluminum-solder alloy used, a further concentration compensation takes place, in which further areas of the elements of the porous structure 2 or the carrier 1 be enriched with aluminum.

At the same time, components of the base materials also diffuse into the solder 18 , which in the best case leads to an increase in the melting point of the solder. With complete diffusion compensation, a connection zone is created which has a solidus temperature similar to that of the base materials used and is therefore suitable for high-temperature use. In addition, the connection zone is essentially free of interfering connections. It also shows through the high content of aluminum in the original solder 18 and good high-temperature oxidation resistance in the base materials to be joined.

The 3 shows similar structural elements as the 2 , In contrast to this, however, is the dense or porous structure 2 made up of hollow metal spheres. These are in turn, for example via a sintering process, at the contact points 17 interconnected to within the porous structure 2 to generate at least a minimum level of structural strength. The entire porous structure 2 is, as described, by means of the solder 18 with the all-metal support structure (support 1 ) connected.

The aluminum solder can be used as a metallic foil between the carrier 1 and the functional body (structure 2 ) is inserted, or as a coating on the carrier 1 or the structure 2 be introduced into the method according to the invention or the soldering process.

The 4 shows the structure of a honeycomb structure according to the invention in a schematic manner 2 , This is made up of individual layers 3 . 4 . 5 . 6 . 7 composed of profiled, thin, foil-like, metallic sheets. The individual sheets are folded and are designed so that individual plateaus 8th . 9 form, which point upwards or downwards and are parallel to each other. The individual plateaus are marked by slopes 11 . 12 connected with each other. The stacking of the individual layers thus results in a honeycomb-like structure, which areas with a single-layer wall thickness, caused by the bevels 11 . 12 are formed, as well as areas with a double wall thickness through the plateaus 8th . 9 are formed. The plateau areas 8th . 9 are by spot welds 13 fixed together. The result is a honeycomb structure with a honeycomb height w, a honeycomb width b, a layer thickness in the single-layer areas of s, and a layer thickness in the double-layer areas of g. In 4 the base area of the plateaus is designated m, while the slopes have a length of k. The diagonal length of the respective honeycomb is designated with y. The 5 shows a simplified perspective view of a carrier 1 , which can be configured as a cast part or sheet metal stamping part. It can be flat or ring-shaped or in the form of ring segments. The cell structure formed by the honeycomb structure is applied to the surface of the support structure or the carrier in such a way that the original film strips (layers) of the honeycomb structure 2 stand upright, i.e. at an angle of 90 ° to the surface of the carrier, as shown in 5 is shown. With H there is the width of the film strips and thus the thickness of the honeycomb structure formed from the cells 2 shown. The reference symbol L represents the direction parallel to the double walls and at the same time the direction of the relative movement of rotating components which graze. The reference symbol B shows the width of the brushable area of the sealing element according to the invention.

For example, a film made of a high-temperature material, such as Hayes 214, can be used as material for the honeycomb structure or PM 2000. The carrier can be made of a nickel-based investment casting alloy such as C1023.

The invention is not shown on the embodiments limited, rather, there are various modifications and Modification options also outside the field of application of thermal turbomachinery.

1

carrier

2

structure

3-7

documents the honeycomb structure

8th, 9

plateau

11 12

slope

13

spot welding

14

ceramic layer

15

interface

16

Fiber, wire

17

contact point

18

solder

19

Zone

20

Zone

d

cross-section from 16

Claims (20)

Method for producing a composite component with a carrier ( 1 ) and a structure attached to it ( 2 ), characterized in that the connection of the structure ( 2 ) with the carrier ( 1 ) by means of a soldering process in which aluminum is used as the soldering material, neither the carrier ( 1 ) still the structure ( 2 ) are made of aluminum or aluminum-based materials, the carrier ( 1 ) and the structure ( 2 ) are made on high-melting alloys based on iron, nickel, cobalt, chromium, titanium or their combinations. A method according to claim 1, characterized in that the Solder with a soldering temperature above the melting temperature of the aluminum. Method for producing a sealing element with a carrier ( 1 ) and a honeycomb structure attached to it ( 2 ), characterized in that the connection of the structure ( 2 ) with the carrier ( 1 ) by means of a soldering process in which an aluminum alloy is used as the soldering material. A method according to claim 3, characterized in that the Solder with a soldering temperature above the liquidus temperature of the aluminum alloy. Method according to one of claims 1 to 4, characterized in that that subsequent heat treatment at soldering temperature he follows. Method according to one of claims 1 to 4, characterized in that that subsequent heat treatment at a temperature higher than the soldering temperature he follows. Method according to one of claims 1 to 6, characterized in that that the solder material is applied in powder form. Method according to one of claims 1 to 6, characterized in that that is the soldering material is applied by thermal spraying. Method according to one of claims 1 to 6, characterized in that that the solder material through Bath aluminization is applied. Method according to one of claims 1 to 6, characterized in that that the solder material through Pack aluminization is applied. Method according to one of claims 1 to 6, characterized in that that the solder material through a PVD coating is applied. Method according to one of claims 1 to 6, characterized in that that the solder material through a CVD coating is applied. Method according to one of claims 1 to 12, characterized in that the soldering material before processing on at least one surface of the material for the structure ( 2 ) is applied. Method according to one of claims 1 to 13, characterized in that the soldering material in the form of an additional film on at least one surface of the material for the structure ( 2 ) is applied. Method according to one of claims 1 to 6 and 13 to 14, characterized in that the surface of the elements to be connected before the soldering process with the surface cleaning, low-melting flux is coated. A method according to claim 15, characterized in that as Flux fluoride can be used. A method according to claim 15 and 16, characterized in that Potassium aluminum fluorides in particular can be used as fluxes. Method according to one of claims 1 to 17, characterized in that the aluminum content and the temperature control are designed so that the intermetallic base NiAl is produced. Method according to one of claims 1 to 18, characterized in that the structure ( 2 ) is designed in the form of a metallic fiber structure. Method according to one of claims 1 to 18, characterized in that the structure ( 2 ) is designed in the form of a hollow spherical structure or a metallic sponge.