Method of producing a hot gas component of a turbomachine including an embedded channel

A component, especially a hot gas component of a turbomachine, has at least one passage (7, 7′), especially a cooling passage, which is embedded in an outer wall (5) of the component (1) of the turbomachine and basically extends parallel to the surface (6) of the component (1). The component (1) has a basic body (8) and at least one coating (9) which is applied to the basic body on the outside, and the passage (7, 7′) on one hand is formed by a cavity which is formed in the basic body (8), and on the other hand is closed off towards the surface (6) of the component (1) by the coating (9).

BACKGROUND

1. Field of Endeavor

The present invention relates to a component, especially a hot gas component of a turbomachine, with at least one passage which is embedded in an outer wall of the component and basically extends parallel to and close to the surface of the component, which passage is especially to serve for intake of a cooling medium.

Furthermore, the invention relates to a method for producing at least one such passage in a component.

2. Brief Description of the Related Art

Modern turbomachines, like, for example, gas turbines, are exposed to high loads during operation. They are often operated with hot gases at more than 800° C., and at the same time are subjected to high mechanical loads. The increase of turbine output capacity during the last decades is fundamentally based on two improvements. On one hand, continuously new efficient materials were developed, like, for example, monocrystal alloys, as a result of which the load capacity of the components which lie in the flow cross section of the hot gases could be increased, and on the other hand, cooling systems and temperature protective coatings, which were improved time and again, were developed, which resulted in an increase of the turbine inlet temperatures, and, as a result, an increase of the turbine output. Monocrystal alloys, like, for example, CMSX2, CMSX4, or MK4, have especially led to an appreciable reduction of the temperature sensitivity, and, as a result, to appreciably improved mechanical properties at high temperatures. Since the output capacity of gas turbines is directly coupled with the inlet temperature of the hot gases, for years a continuous increase of the hot gas temperature has been noted, so that especially in the first turbine stages gas temperatures are already achieved which exceed the melting temperatures of the alloys which are used there. In order to prevent damage of the hot gas components or the alloys which are used, as the case may be, complex internal cooling systems were developed, which cool the components which lie in the flow cross section in such a way that these lie below a critical temperature limit at which the components would be damaged. In this case, it is common to all cooling systems that a compromise has to be made between the desired cooling effect, the amount of cooling air which is available, and the costs.

The cooling air which is required for cooling is generally delivered from a compressor and, by means of an internal cooling system, is distributed to the components which are to be cooled.

As a rule, different cooling methods, like, for example, such methods which are based on a convective heat transfer, are combined with a film cooling or transpiration cooling. In this case, the components have internal cooling passages, for example, which extend in serpentine-like fashion and which interact in a communicating manner with a multiplicity of discharge openings on a surface of the component, as a result of which a film cooling or transpiration cooling is created. An especially effective cooling is achieved in this case, if the wall which is to be cooled has a wall thickness which is as small as possible (EP 0 964 981).

Calculations have proved that in a development of a cooling method of a hot gas component to the effect that a system of cooling passages which is close to the surface is created, which cooling passages communicate at least by their one end with the internal cooling medium passages which pass through the inside of the blade mostly in serpentine form, while at least one other end is connected to cooling paths which lead to the surface and effect a film cooling or transpiration cooling there, lead to an increase of the turbine inlet temperature by 50K to 125K, and lead to a significant enhancement of the machine output as a result of it, without additional consumption of cooling air.

Since, however, as a result of the cooling of the components, especially of the turbine blades, the overall efficiency of the power plant decreases, a compromise also has to be found here between turbine output and turbine cooling.

Another efficient, convective cooling system is effected by means of coolable wall structures, as it is proposed, for example, in EP 1 462 611, EP 1 462 612, and EP 1 462 613. In this case, the walls of the hot gas components are equipped with a network of cooling passages. In the interests of effective cooling, it is advantageous to construct these walls very thinly and to lay out the cooling passages close to the thermally stressed surface. In this way, an efficient cooling can be provided. However, such internal cooling passages are exceptionally complicated to produce in the manufacturing process and, therefore, are disproportionately expensive.

To alleviate this disadvantage, a method for producing or repairing cooling passages, which are close to the surface, in a hot gas component of the gas turbine has become known, which is basically based on a profile being applied to a basic body of this component, which profile corresponds to the later structure of the cooling passages. This can be carried out either in the way by a thermally stable filling material in a corresponding structure being applied to the surface of the basic body, or by this structure first being mechanically machined from out of the surface of the basic body and the cavities which result from it then being filled with the thermally stable filling material. In a subsequent step, a coating material is applied by means of a coating method, at least in the region of the cooling structure. The cooling passages are opened by means of subsequent removal of the filling material.

This proposal which forms a generic type is disclosed in EP 1 065 026 and also in later publications, like EP 1 462 611 and EP 1 462 612.

By means of these solutions, it will be possible on one hand to create a cooling passage network in a component of a turbomachine, which on one hand brings about an efficient cooling of the component on account of its position which is arranged just beneath the surface of the outer wall, and which on the other hand can dispense with costly casting molds and results in lower scrap rates. The cooling passages, which are embedded in the outer wall of the component, can generally also be combined with other cooling strategies, like, for example, the transpiration cooling which is described above, as a result of which a high flexibility and a broadened application spectrum can be achieved.

In this method, however, the relatively high manufacturing cost is still disadvantageous, especially the regular requirement of an aftertreatment for the subsequent removal of the filling material.

SUMMARY

One of numerous aspect of the present invention is based on making available a component of a turbomachine of the aforementioned type, which especially has an enhanced cooling system with greatly reduced manufacturing cost. Furthermore, another aspect of the present invention is based on making available a method for producing at least one passage which is embedded in an outer wall of such a component.

Another aspect of the present invention is based first producing in a first step the structure of the cooling medium passages on the surface of the basic body in a component of a turbomachine of the aforementioned type, and, in a further step, applying a coating material while directly bridging the cooling medium passages which are produced, without these being masked with a filling material.

According to principles of the present invention, it is possible, therefore, to create a number of cooling passages in a component of a turbomachine which on one hand are simple to produce, and on the other hand bring about efficient cooling of the component on account of their position which is arranged just below the surface of the outer wall, wherein a costly aftertreatment of the component for the purpose of removing filling material and for opening the cooling medium passages which are produced, can be omitted. Production effort, and, as a result, production costs, can also be appreciably reduced. The cavities which are introduced in the basic body can be fully automatically produced or applied, as the case may be, just as the coating, as a result of which an especially high quality, and, as a result, a high service life, ensue.

The cooling passages, which are embedded in the outer wall of the component, can generally also be combined with other cooling strategies, like, for example, transpiration cooling which is described above, as result of which an especially high flexibility and a broadened application spectrum can be achieved.

The basic body expediently has an equidirectional grain structure and/or monocrystal structure. Monocrystal structures are spoken of when the building blocks of the crystal, consequently the ions, atoms, or molecules, form a unitary, homogenous crystal lattice. By means of such a monocrystal, a slipping of the grains along the grain boundaries, for example as a result of the centrifugal forces which prevail in the turbine, is avoided, since in monocrystals there is only just one single grain which at the same time is the crystal.

In a further advantageous embodiment of the invention, at least one passage communicates with at least one discharge opening which leads to the surface of the component. As a result of this, the especially effective cooling system which extends closely beneath the surface is combined with a known film cooling, which by permanent discharge of cooling air through the discharge openings creates a cooling medium film which is distributed over the surface of the component. In this case, it concerns a so-called open cooling system, in which permanent cooling medium, as a rule air, from a cooling medium source of relatively high pressure, for example which is branched from the compressor of a gas turbine plant, is directed into the component which is to be cooled through its internal cooling passages up to the discharge openings in the outer wall.

In a further advantageous embodiment, a passage longitudinal axis is at a distance of less than 3 mm from the surface of the component. As a result of this, a direct and quick transfer of the cooling action onto the surface is possible, as a result of which an especially high cooling effect can be achieved. Furthermore, it is conceivable in this case that a plurality of passages forms a communicating passage network and so bring about a uniform, areal cooling of the surface of the component. By means of different cross sections inside the cooling passage network, furthermore, the accurate distribution of the cooling air in the component can be influenced, so that, for example, regions which are to be cooled more intensely are equipped with cooling passages of larger cross section, whereas regions which are to be cooled less intensely have cooling passages with smaller cross section.

A width of the cavity, at least in the region of a surface, is expediently less than 1 mm. The width is preferably even only 0.2 mm, as a result of which bridging of the cavity width by the applied coating is simplified. In the case of a small cavity width, too great a penetration of the applied coating into the cavity is also avoided, since the two edges or the two cavity walls, as the case may be, have a large surface in comparison to the amount of coating which has penetrated, and, as a result, bring about a quick hardening of the coating. The small width of the cavity, furthermore, has the advantage that in comparison to cavities with larger width, a close-meshed network of cooling passages can be extended on the surface of the component or of a turbine blade respectively, and, as a result, a more uniform cooling performance or individually better adaptable cooling performance, as the case may be, can be achieved.

Further important features and advantages of the turbomachine according to the invention result from the drawings, and from the associated description of the figures, with reference to the drawings.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

According toFIG. 1, a component1of a turbomachine, which apart from that is not shown, has a region2which during operation of the turbomachine is flow-washed by hot gases. In the case of the component1, as exemplarily shown inFIG. 1, it can be a blade3, stator blade or rotor blade of a gas turbine. At its seated end, the blade3leads into a blade root4, by which the blade is fastened, for example, to a stator or a rotor. In order to increase the output capacity of the turbine, turbine inlet temperatures which are as high as possible are desired. High turbine inlet temperatures, however, disadvantageously affect the service life of the components1which are exposed to hot gas as long as these are not adequately protected. For protection of the components1against the high temperatures of the hot gases, two different methods are principally adopted. On one hand, it is attempted to positively influence the temperature resistance of the components1which are in direct contact with the hot gases, by a corresponding material selection, like, for example, by the use of nickel-based alloys and/or thermal protection layers, and on the other hand, the components1are actively cooled.

A good example, for the progress in material science, is so-called monocrystal alloys, like, for example, CMSX2, CMSX4, or MK4, which are frequently used in modern machine construction. Crystals, the building blocks of which form a unitary, homogenous crystal lattice, are referred to as monocrystals.

In addition to the material selection which was mentioned, the blade3, furthermore, can be protected against damage by the hot gases by cooling.

According toFIG. 2, for this purpose the blade3has passages7,7′, especially cooling passages, which are embedded at least in one region of an outer wall5and which basically extend parallel to the surface6of the component1or the blade3, as the case may be. The component1has a basic body8, which, for example, has a equidirectional graining and at least one coating9, for example a connecting layer, which is applied to the basic body8on the outer side. The passage7,7′ in this case is formed on one hand by a cavity which is introduced in the basic body8, and on the other hand is closed off towards the surface6of the component1by the coating9. Furthermore, it can be provided that the coating9on the outside supports a thermal protection layer10. The coating9in this case, for example, can be a metal coating which protects the basic body8against hot temperature oxidation and temperature corrosion. In this case, the coating9can include the same material as the basic body8and/or, for example, can be a MCRALY alloy, wherein M stands for nickel, cobalt, iron, or a combination of these elements. The preferably metal coating9in this case can have a layer thickness of 100 μm to 600 μm. In addition to the protection function, the coating9fulfills a further function, specifically the provision of an adhesion layer for the temperature/thermal protection layer10which is arranged on the coating9on the outside. The thermal protection layer10in this case can be formed from a ceramic material, like, for example, ZrO2, and on account of its insulating action reduces the thermal stress for the components which lie beneath it. The thermal protection layer10can be applied, for example, by a plasma spray process or an electron beam evaporation process.

FIG. 3shows a detailed cross section in the region of the surface6of the component1or surface of the blade3, as the case may be, wherein two passages7and7′ are exemplarily shown, which differ in their cross section. The cooling passages7,7′ in this case are embedded in the basic body8and have an opening towards the initially uncoated surface of the basic body8. As shown inFIG. 3, the openings of the passages7and7′ are bridged and closed off by the coating9which is arranged in the opening region in each case. In this case, the coating9, as shown inFIG. 3, can only be arranged in the region of the openings of the passages7,7′, or they can cover the basic body8along its entire surface, as shown inFIG. 6. It is also conceivable that at least one passage7,7′ communicates with at least one discharge opening, which is not shown, which leads to the surface of the component1and as a result creates a film cooling along the surface6.

In order to fully develop the cooling action of the passages7,7′, these have to be integrated into a cooling circuit of the turbomachine, so that a through-flow of cooling medium through the passages7,7′ can be achieved. It is also conceivable that a plurality of passages7,7′ form a communicating passage network, which is shown according toFIG. 3by a connecting passage11which is shown by discontinuous lines. Furthermore, it is necessary for an effective cooling of the blade3or the component1, as the case may be, that the passages7,7′ lie as close as possible to the surface6of the component1. Therefore, a passage longitudinal axis12, which according toFIG. 3basically extends orthogonally to the illustration plane, is preferably at a distance of less than 3 mm from the surface6of the component1or the blade3, as the case may be.

Furthermore, it is advantageous if a length/diameter ratio of at least one passage7,7′ is greater than five. Furthermore, in order to ensure a reliable closing off of the passage7,7′ towards the surface6of the component1, a width of the cavity or the passage7,7′, as the case may be, is less than 1 mm, preferably in the region of about 0.2 mm. In this case, different cross sectional shapes of the passages7and7′ are shown according toFIG. 3, wherein the passage7tapers in its width towards the surface6of the component, while the passage7′ has a constant width.

A directly bridged passage7is shown inFIG. 4, wherein the coating9in the region of the passage7has a pillar-like construction of fine dendrites. The orientation of the dendrites in this case is parallel to the orientation of the substrate of the basic body8and at the same time epitaxially hardens with the substrate. This is especially advantageous when the component1or the blade3, as the case may be, is subjected to a cyclic thermal and mechanical stress, as this is the case, for example, in gas turbines. InFIG. 4it is exemplarily indicated that the side edges of the passage7which are oriented towards the coating9can melt off or melt down, as the case may be, when applying the coating9and can then deviate considerably from the original shape, which is shown by a discontinuously drawn line.

According toFIG. 5, a passage7which is produced according to the same method is shown, wherein in this case the structure was modified in an advantageous way, for example by laser melting, after applying the coating9. Furthermore, the basic body8is able to have been preheated, especially by a laser, before the metal forming. As a preheating temperature, for example 1100° C. comes into consideration, as a result of which high temperature gradients inside the interaction zone, and therefore inside a connecting zone between coating9and basic body8, can be reduced. At the same time, the higher ductility of the base material, as result of heating it, and also the lower temperature gradients, contribute to a reduction of a risk of cracks during hardening of the coating9.

A method for producing at least one passage7, which is embedded in an outer wall5of a component1of a turbomachine by coating the outer surface6, is to be briefly described in the following.

In a first method step, a passage-like cavity, called a passage7,7′, is first introduced in the basic body8of the component1. This can be carried out, for example, mechanically and/or electrochemically and/or photochemically and/or by a laser, especially by a short pulse laser.

After that, a local surface melting of the basic body8, at least on the two sides of the passage7,7′, is carried out, wherein again a laser is also used in this case for melting the basic body8.

The application and melting of a coating9, at least in the region of the passage7,7′, is carried out in one working cycle with the melting of the basic body8, wherein the coating9, the process temperature, and the width of the passage7,7′ are matched to each other so that the molten coating material, owing to its surface tension, does not penetrate into the passage7,7′. Therefore, no filling material is required for closing off the passage7,7′, as this is the case in the production processes according to the prior art. Rather, for example, a metal powder is used, which in the molten state forms a bridge across the passage7,7′ on account of its surface tension and, as a result, closes this off towards the surface6of the component1. It is important for a preferred embodiment that the material properties of the coating powder are tailored to the respective coating process, so that the creation of a monocrystal structure is benefited. The application of the coating9to the basic body8can be carried out, for example, by plasma spraying and/or by an electron beam evaporation process and/or by a laser. A LMF method (laser metal forming), especially an E-LMF method (epitaxial LMF), will be preferable for producing an epitaxial coating, and therefore a monocrystalline coating9, on the basic body8which is preferably also monocrystalline.

Finally, a controlled cooling and hardening of the molten coating material can be carried out in such a way that a metallurgical connection to the basic body8on the two sides of the passage7,7′ is achieved, and the passage7,7′ is bridged towards the surface6by the hardening coating material. After that, the surface6can subsequently be processed and/or smoothed by a laser, as a result of which a modified surface6can be achieved. This “modification” is preferably the creation of a monocrystalline structure inside the coating9.

The cross sectional shape and the dimensioning of the passage7,7′ in this case can be accurately controlled, as a result of which the desired cross sectional shape of the passages7,7′ can be relatively accurately formed and the course of the passage7,7′ can also be largely accurately defined.

With an LMF method, the melting of the basic body8and the application and also the melting of the coating material can be carried out simultaneously, which simplifies the application of the coating9. The use of an E-LMF method, by suitable selection of the method parameters, creates the possibility of allowing the coating9to harden in a monocrystalline manner, wherein at the same time the possibility is presented to basically produce the same crystallographic orientation for the coating9and for the basic body8. By this crystallographic orientation of the coating9and the basic body8, which is the same after cooling, the thermophysical properties of the coating material can be the same as those of the basic body8, on account of the propagating dendrite arms and the pillar-like growth, as a result of which the service life can be increased.

As already indicated further above, the application of the coating9and the surface modification can be designed as a two-step process, in which, in a first step, the coating9can be applied to the basic body8by a suitable method (see above), and in which, in a second step, the monocrystalline structure can be realized inside the coating9by a suitable remelting method, for example by a suitable laser.

By the arrangement or production of the cooling passages7,7′ according to principles of the present invention, as the case may be, an effective cooling of the component1can be achieved, and, therefore, the tolerable turbine inlet temperature can be increased by 50K to 125K. Naturally, the passages7,7′ which are produced according to the invention can also be combined with other cooling methods, like, for example, a transpiration cooling method.

According toFIG. 6, the coating9in another embodiment can also be applied to the basic body8so that it extends across a plurality of passages7or covers a section of the basic body8which includes a plurality of passages7, as the case may be. It is especially possible to provide the entire surface6of the respective component1, which is exposed to thermal stress, first with the coating9and then with the thermal protection layer10.

Furthermore, when applying the coating9, attention can be paid to a first phase of hardening of the coating material being of the γ type. By adjusting the method parameters, attention can be additionally or alternatively paid to a so-called CET (columnar-to-equiaxed-transition), therefore a transition from a directed to a globulitic crystal structure, being avoided. For this purpose, it is additionally or alternatively expedient to select the method parameters and the coating material so that, as far as possible, the formation of new crystallization germs when applying the coating9is avoided. In this way, an epitaxial construction of the coating9on the basic body8can especially be achieved.

It is basically possible that the monocrystal structure which is preferred for the basic body8is altered as a result of applying the coating9. By an additional melting process, a reconstruction of the monocrystal structure of the basic body8can be expediently achieved. This additional melting process can be carried out, for example, at the same time with the melting of the coating9, in order to transform in this a polycrystalline structure into a monocrystal structure.