EP2316988B1 - Wear-resistant and oxidation-resistant turbine blade - Google Patents

Description

Technical area

The invention relates to the field of power plant and materials technology. It relates to a wear and oxidation resistant turbine blade and a manufacturing method for such a wear and oxidation resistant turbine blade.

State of the art

The reduction of leakage losses in turbines has been the subject of intensive development work for several decades. During operation of a gas turbine, a relative movement between the rotor and the housing is unavoidable. The resulting wear of the housing or the blades causes the sealing effect is no longer given. The solution to this problem is a combination of thick Abradable coatings on the heat shield provided with abrasive protective layers on the blade tips.

Already since the 70s of the last century methods are known to apply additional coatings on blade tips or to increase the wear resistance by a suitable modification of the blade tip. Various methods have also been proposed for simultaneously rendering such protective layers resistant to frictional contacts and oxidation caused by the hot gas by a combination of abrasive particles (carbides, nitrides, etc.) with oxidation-resistant materials. However, many of the proposed methods are costly to manufacture and complex, making commercial use difficult.

One of the popular strategies is therefore to dispense with the wear protection of the blade tip completely and to provide the heat shield with special, porous ceramic Einreibschichten. Due to their high porosity, they can also be rubbed to a certain extent by unprotected blade tips. However, this method involves considerable technical risks because the porous ceramic rubbing layers do not ensure the same erosion resistance as dense layers. There is also a risk of operational changes in the porous ceramic rubbing layers (compaction by sintering), which can have a negative effect on the tribological properties. For this reason, when using ceramic protective layers on heat shields, a combination with wear-resistant (abrasive) blade tips is advisable.

In recent decades, several methods for producing abrasive blade tips have been developed and protected by numerous patents, see eg US 6194086 B1 , The use of laser deposition welding (English: Laser Metal Forming, abbreviated to LMF) for the construction of abrasive blade tips has been known since the beginning of the 90s (see for example DE 10 2004 059 904 A1 ), but this method is still rarely used on an industrial scale.

Further relevant procedures are from the applications GB 2075 129 A and WO 2009/083000 A1 known.

Presentation of the invention

The aim of the invention is to avoid the disadvantages of the known prior art. The invention has for its object to develop a wear and oxidation resistant turbine blade, which is applicable both for the manufacture of new parts, as well as for reconditioning (retrofit) and for their production of the existing manufacturing process must be minimally adjusted.

The peculiarity of the design of such a component described here consists in the best possible compatibility with conventional turbine blades and their manufacturing processes. This requires only little effort for the conversion of current production processes and opens up very interesting prospects for reconditioning and retrofitting.

• die mindestens eine erste oxidationsbeständige Schutzschicht ist eine metallische Schicht, insbesondere eine MCrAlY-Schicht (M = Ni, Co oder Kombination beider Elemente)
• diese erste Schutzschicht ist zumindest an der inneren und äusseren Kronenkante bzw. Steg kante angeordnet,
• diese erste Schutzschicht ist an der radial aussen gelegenen Schaufelspitze der Turbinenschaufel nicht vorhanden und
• die radial aussen gelegene Schaufelspitze besteht aus einer mittels bekanntem Laserauftragsschweissen aufgebauten zweiten mindestens einlagigen verschleiss- und oxidationsbeständigen Schutzschicht, wobei diese zweite Schutzschicht auf der Schaufelspitze entlang der äusseren und/oder inneren Kronenkante bzw. Stegkante zumindest teilweise mit der dort angeordneten ersten metallischen Schutzschicht überlappt.

According to the invention this object is achieved in that the wear and oxidation resistant turbine blade according to the preamble of claim 1 is characterized by the following features:

• the at least one first oxidation-resistant protective layer is a metallic layer, in particular an MCrAlY layer (M = Ni, Co or combination of both elements)
• this first protective layer is arranged at least on the inner and outer crown edge or web edge,
• this first protective layer is not present at the radially outer blade tip of the turbine blade and
• the blade tip located radially outward consists of a second at least single-layer wear and oxidation-resistant protective layer constructed by means of known laser deposition welding, this second protective layer resting on the blade tip along the blade tip outer and / or inner crown edge or web edge overlaps at least partially with the first metallic protective layer arranged there.

• die mindestens eine oxidationsbeständige Schutzschicht an der radial aussen gelegenen Schaufelspitze wird durch kontrollierte mechanische Bearbeitung, insbesondere Abschleifen, CNC Fräsen, und/oder chemisches Entschichten, entfernt und
• die verschleiss- und oxidationsbeständige Schutzschicht wird anschliessend mittels bekanntem Laserauftragsschweissen in einer Lage oder in mehreren Lagen auf die Schaufelspitze derart aufgebracht, dass sie entlang der äusseren und/oder inneren Kronenkante bzw. Stegkante zumindest teilweise mit der vorher aufgebrachten ersten metallischen Schutzschicht, aber nicht mit der wahlweise vorher aufgebrachten keramischen Wärmedämmschicht (TBC = Thermal Barrier Coating) überlappt.

The inventive method for producing a turbine blade according to the preamble of claim 12 is characterized by the following features:

• the at least one oxidation-resistant protective layer on the radially outer blade tip is removed by controlled mechanical processing, in particular grinding, CNC milling, and / or chemical stripping, and
• the wear-resistant and oxidation-resistant protective layer is subsequently applied to the blade tip by means of known laser deposition welding in one layer or in several layers such that it at least partially coincides with the previously applied first metallic protective layer along the outer and / or inner crown edge or web edge overlaps the optionally previously applied ceramic thermal barrier coating (TBC = Thermal Barrier Coating).

The advantages of the invention are that the main body of the turbine blade is protected against oxidation on all critical surfaces that are exposed to the hot gas and at the same time the blade tip is tolerant to frictional contacts with the heat shield, which is a reduction of the hot gas gap and thus a reduction of leakage losses allowed. In this way, the efficiency of the turbine can be significantly increased.

The blade according to the invention can be produced by a cost-effective and easily implementable method.

Due to the increased wear resistance of the turbine blade against friction contacts relatively dense ceramic coatings on the Heat shields are applied. Thus, a good rub-in behavior can be combined with the required long-term erosion resistance of the ceramic coatings on the heat shields.

It is particularly advantageous that the turbine blade can be scooped into the rotor of the turbine directly after laser deposition welding (LMF step) without further heat treatment and thus used for turbine operation.

Further advantageous embodiments are described in the subclaims.

Thus, for example, the metallic protective layer may be covered by a ceramic thermal barrier coating and the second oxidation and wear resistant protective layer applied by laser deposition welding at least partially overlaps only with the metallic protective layer, but not with the ceramic thermal barrier coating. This achieves optimal oxidation protection and does not adversely affect the integrity of the TBC, i. a spalling of the TBC is prevented.

Furthermore, it is advantageous if the wear-resistant and oxidation-resistant protective layer consists of an abrasive material, which is preferably cubic boron nitride (cBN), and of an oxidation-resistant metallic binder material, in particular having the following chemical composition (in% by weight): 30 Cr, 5-10 Al, 0.3-1.2 Y, 0.1-1.2 Si, 0-2 others, balance Ni, Co.

It is also advantageous if the proportion of abrasive material in the wear-resistant and oxidation-resistant multilayer protective layer increases in the radial direction to the outside, because this ensures optimum adaptation to the stress conditions.

The invention can be used for all blade types of a turbine. For blades without shroud, the abrasive layer is applied to the crown (or part of the crown). For shovels with shroud, the method for better wear protection of the shroud web can be used.

The described realization of the turbine blade is applicable both for the manufacture of new parts, as well as for the reconditioning (retrofit). In doing so, the existing production process has to be adapted only minimally.

A particularly interesting commercial potential exists in the retrofitting or reconditioning of existing blades. Such blades can be modified with the inventive method to achieve lower leakage losses and thus improved efficiency of the turbine when installing new. For this option, it is not necessary to remove any existing protective layer on the blade, which allows a simplified manufacturing process.

Brief description of the drawings

Fig. 1

eine Turbinenschaufel für den Rotor einer Gasturbine mit einer als Krone ausgebildeten Schaufelspitze gemäss einem ersten Ausführungsbeispiel der Erfindung;

Fig. 2

einen schematischen Schnitt entlang der Linie II-II in Fig. 1;

Fig. 3

fotographische Aufnahmen von mit dem LMF-Verfahren erzeugten verschleiss- und oxidationsbeständigen Panzerungen von Turbinenschaufelspitzen in zwei erfindungsgemässen Varianten;

Fig. 4

eine schematische Darstellung eines weiteren Ausführungsbeispieles der Erfindung anhand einer Turbinenschaufel mit Deckband;

Fig. 5

die Fertigungsabfolge bei der Herstellung einer Turbinenschaufel gemäss der Erfindung in zwei Varianten;

Fig. 6

die Fertigungsabfolge bei der Herstellung einer Turbinenschaufel gemäss der Erfindung in einer weiteren Variante und

Fig. 7

eine beispielhafte Beschichtungsvorrichtung für das LMF Verfahren.

In the drawings, embodiments of the invention are shown. Show it:

Fig. 1

a turbine blade for the rotor of a gas turbine with a trained as a crown blade tip according to a first embodiment of the invention;

Fig. 2

a schematic section along the line II-II in Fig. 1 ;

Fig. 3

Photographs of LMF-produced wear and oxidation-resistant armor plating of turbine blade tips in two variants according to the invention;

Fig. 4

a schematic representation of another embodiment of the invention with reference to a turbine blade with shroud;

Fig. 5

the manufacturing sequence in the manufacture of a turbine blade according to the invention in two variants;

Fig. 6

the production sequence in the manufacture of a turbine blade according to the invention in a further variant and

Fig. 7

an exemplary coating device for the LMF process.

Ways to carry out the invention

Hereinafter, the invention with reference to embodiments and the Fig. 1 to 6 explained in more detail.

Fig. 1 shows a perspective view of a turbine blade 1 for a (here only schematically indicated) rotor 13 of a gas turbine, while in Fig. 2 a section along the line II-II in Fig. 1 is shown enlarged. The turbine blade 1 has an airfoil 2 which extends in the radial direction r (relative to the rotor) and which is formed on the blade tip 9 as a crown 3 with inner and outer crown edges extending in the radial direction. The base material of the airfoil is, for example, a nickel-base superalloy. The surface of the airfoil is at least on the crown edges (s. Fig. 2 ) coated with an oxidation-resistant protective layer 4, here a metallic MCrAIY layer, which was preferably applied by known per se plasma spraying. At the radially outermost blade tip 9 of the turbine blade 1, this metallic protective layer 4 does not exist, either because no such protective layer has been applied in the preceding process steps for the production of the turbine blade, or because this with the aid mechanical and / or chemical methods has been removed. In a last method step for the production of the finished turbine blade, according to the invention, the radially outer blade tip is constructed from a second wear and oxidation resistant protective layer 5 constructed by known laser deposition welding, this second protective layer 5 at least partially on the blade tip 9 along the outer and / or inner crown edge overlaps with the first metallic protective layer 4 arranged there. The protective layer 5 can be single-layer or multi-layered. In particular, with multilayer overlapping protective layers 5, which are applied by means of LMF, a variation of the length L of the turbine blade 1 can be realized well.

The protective layer 5 consists of an abrasive material 6, which is preferably cubic boron nitride (cBN), and an oxidation-resistant binder material which preferably has the following chemical composition (in% by weight): 15-30 Cr, 5-10 Al, 0.3- 1.2 Y, 0.1-1.2 Si, 0-2 others, balance Ni, Co. A concretely used suitable binder material is z. For example, the commercial alloy Amdry995.

This is especially good on the Fig. 3a and 3b to see the photos of coated according to the invention blade tips. In the wear-resistant and oxidation-resistant protective layer 5, one can very well recognize the pointed cBN particles as abrasive material 6, which are embedded in the binder material 7. This protective layer 5 was by LMF using a fiber-coupled high-power diode laser with max. 1000W output power realized. In Fig. 3a (left) partially overlaps the new coating with an MCrAIY protective layer 4 previously applied by plasma spraying Fig. 3b the turbine blade 1 on the MCrAIY layer 4 has an additional ceramic thermal barrier coating (TBC) 4a.

Fig. 4 schematically shows a further embodiment of a turbine blade 1 according to the invention with a shroud 11, which is arranged radially outward on the blade tip and a web 12 has. Again, by the applied by LMF wear and oxidation resistant protective layer 5, which at least partially overlaps the metallic protective layer 4, a very good quality blade can be achieved.

The special feature of the approach described here is the special design of such a wear-resistant protective layer 5. The single-layer or multi-layer 5 is applied so that it at least partially overlaps with other existing protective layers 4. The already existing protective layers 4 are e.g. MCrAlY layers known in the art (M = Ni, Co, or a combination of both) which protect the surfaces of the airfoil against oxidation and corrosion in most highly loaded turbine blades. Furthermore, a ceramic insulating layer (TBC, Thermal Barrier Coating) may additionally be applied to this MCrAlY layer on the blade, the integrity of which is not impaired by the proposed method.

• Bei der MCrAlY-Beschichtung muss die Oberfläche durch Sandstrahlen und/oder Reinigung mit übertragenem Lichtbogen vorgängig von Oxiden befreit werden, um eine optimale Anbindung zu gewährleisten. Eine mit herkömmlichen (z.B galvanischen) Verfahren aufgebrachte Abrasivschicht, müsste während der Vorbereitung zur MCrAIY-Beschichtung durch eine entsprechende Maskierung gegen Schädigung geschützt werden, was Zusatzaufwand und Zusatzkosten verursachen würde.
• MCrAlY-Beschichtungen werden meist durch Plasmaspritzen hergestellt. Im Anschluss an das Aufbringen der Beschichtung ist ein Diffusions-Wärmebehandlungsschritt bei Temperaturen im Bereich >1050°C erforderlich. Bei diesem Prozessschritt können durch die hohen Temperaturen die Eigenschaften von vorher aufgebrachten Abrasivbeschichtungen negativ beeinflusst werden.

The proposed embodiment of an oxidation-resistant abrasive layer on the blade tip ensured by the overlap with the existing protective layers efficient protection of exposed to the hot gas surfaces of the blade tip. An application of this wear protection layer by the LMF method also makes it possible to use this coating operation as the last manufacturing step in the manufacturing process. This bypasses the following technical issues:

• For the MCrAlY coating, sandblasting and / or transferred-arc cleaning must be used to remove oxides from the surface to ensure optimum bonding. An applied with conventional (eg galvanic) abrasive layer, would have during preparation for MCrAIY coating by an appropriate masking against Be protected damage, which would cause additional expense and additional costs.
• MCrAlY coatings are mostly produced by plasma spraying. Subsequent to application of the coating, a diffusion annealing step at temperatures in the range> 1050 ° C is required. In this process step, the high temperatures can adversely affect the properties of previously applied abrasive coatings.

Og problems are avoided if, as described here, the abrasive layer is applied as the last step in the process chain by laser deposition welding. A simple and cost-effective implementation is to remove the radially outwardly located MCrAlY (possibly also TBC) layer (s) by milling or grinding or by chemical process by a defined amount completely. Subsequently, the wear-resistant layer is applied by LMF to the now exposed base material. The decisive factor here is the locally very limited action of the laser beam, which keeps the effects on the adjacent areas of the blade very low in the case of controlled process control. It is thus possible to apply such a wear-resistant layer in the immediate vicinity of a TBC protective layer without damaging it (see, for example, US Pat Fig. 4b ).

In contrast to conventional (eg galvanic) coating methods, the surfaces of the turbine blade 1 (eg the blade root) which are not to be coated need not be protected by a masking method. The LMF process is a welding process and produces a stable metallurgical bond with the main body of the blade without additional diffusion heat treatment. Due to the low local heat input, the local hardening is kept small despite the rapid solidification process. Thus, the component immediately after the application of the Wear-resistant protective layer can be installed without further subsequent steps.

Fig. 5 shows various implementation options. In the first design variant ( Fig. 5a to 5c ), the wear-resistant MCrAlY protective layer 4 is first applied to the blade 1, for example by plasma spraying. Subsequently, this protective layer 4 is locally removed at the blade tip, for example by milling or grinding ( Fig. 5b ). As a last operation, the wear and oxidation resistant protective layer 5 is applied by the LMF method. The last applied protective layer 5 overlaps at least partially with the previously applied oxidation-resistant MCrAlY protective layer 4 (FIG. Fig. 5c ). As a result, the entire blade body is protected against oxidation at high operating temperatures.

As already described above, it is possible to provide the blade tip with an additional heat-insulating layer 4a in a further preceding production step. In the in Fig. 5f shown design variant is the wear-resistant protective layer 5 only after the TBC coating 4a (FIG. Fig. 5d ) and the grinding of MCrAlY layer 4 and TBC layer 4a (FIG. Fig. 5e ) is applied to the blade tip by laser metal forming. In this case, it is ensured by suitable guidance of the coating head (for example by a robot or a CNC) that no interaction of the laser beam with the ceramic coating takes place during the LMF process. However, as in the first variant, the wear-resistant and oxidation-resistant protective layer 5 overlaps with the previously applied MCrAlY protective layer 4 in order to ensure optimum protection of the airfoil 1 against oxidation. Due to the localized and minimized heat input, the LMF method can be performed in close proximity to the ceramic thermal barrier coating 4a, without the TBC flaking off.

Another embodiment is in Fig. 6 This variant can be used, for example, when the crown 3 of the turbine blade 1 is so wide that the wear-resistant and oxidation-resistant protective layer 5 can not be applied with a single welding track. In such cases, initially at least one multilane, overlapping intermediate layer 8 of oxidation-resistant binder material 7 can be applied. Subsequently, at least one further track is applied with combined supply of binder material 7 and abrasive material 6 to the first deposited layer (s). It is not necessary that the abrasive particles 6 are distributed over the entire width of the blade tip 9. Thus, the in Fig. 6 shown variant cost-optimized production of oxidation and wear resistant blade tip.

Fig. 7 shows by way of example a coating device 14 for carrying out the last step of the inventive method. The device 14 is in EP 1 476 272 B1 described in detail, the content of this document is part of the present application. In the case of laser deposition welding of the blade tip 9, abrasive material 6 and oxidation-resistant binder material 7 are mixed in a powder nozzle, transported by means of a carrier gas 15 and then injected concentrically around the laser beam 10 as a focused powder jet into the melt pool 16 produced by the laser beam 10 at the blade tip 9. In addition, during laser deposition welding, the temperature or temperature distribution in the molten bath is recorded online (optical temperature signal 17) and this information is not recorded with the help of a Fig. 7 used to control the laser power during laser deposition welding and / or to control the relative movement between the laser beam 10 and the turbine blade 1 controlled.

The invention can be used in many ways for deckless turbine blades, but also for components with shroud. Attention must be paid to the service life of the abrasive coating, which depends on the respective operating conditions (temperature, fuel). By a good distribution and complete embedding of Abrasivteilchen in the oxidation-resistant binder matrix lifetime optimization is achieved. Nevertheless, the main object of the invention is to protect the turbine blade tip, especially during the break-in period. This corresponds to a duration of several tens to several hundred operating hours.

Of course, the invention is not limited to the described embodiments.

LIST OF REFERENCE NUMBERS

1

turbine blade

2

airfoil

3

Crown

4, 4a

first oxidation-resistant protective layer (4 metallic layer, 4a ceramic thermal barrier layer)

5

second wear and oxidation resistant protective layer

6

abrasive

7

binder material

8th

Intermediate layer of oxidation-resistant binder material

9

blade tip

10

laser beam

11

shroud

12

web

13

rotor

14

coater

15

carrier gas

16

melting bath

17

optical temperature signal

r

radial direction

L

Length of the turbine blade

Claims (15)

1. Turbine blade (1) for the rotor (13) of a turbine, having a main blade section (2), which has a blade tip (9), extends in the radial direction (r) and is formed at the blade tip (9) either as a crown (3) with an inner and outer crown edge extending in the radial direction (r) or as a shroud (11) with a web (12), which extends in the radial direction and has lateral edges, wherein at least certain zones on the surface of the main blade section (2) are provided with at least one first protective coating (4, 4a) consisting of oxidation-resistant material, characterized in that

   - the at least one first, oxidation-resistant protective coating (4) is a metallic coating, namely an MCrAlY coating,

   - said first protective coating (4) is arranged at least at the inner and/or outer crown edge or at the web edges,

   - said first protective coating (4) is not present at the radially outer blade tip (9) of the turbine blade (1), and

   - the radially outer blade tip (9) consists of a second, at least single-layer wear-resistant and oxidation-resistant protective coating (5) which is built up by known laser metal forming, wherein said second protective coating (5) on the blade tip (9) overlaps along the outer and/or inner crown edge or the web edges at least partially with the first, metallic protective coating (4) arranged there.
2. Turbine blade (1) according to Claim 1, characterized in that the at least one metallic protective coating (4) is covered by a ceramic thermal barrier coating (4a), and wherein the second, oxidation-resistant and wear-resistant protective coating (5) which is applied by laser metal forming overlaps at least partially only with the metallic protective coating (4), but not with the ceramic thermal barrier coating (4a).
3. Turbine blade (1) according to Claim 1 or 2, characterized in that the wear-resistant and oxidation-resistant protective coating (5) consists of an abrasive material (6) and an oxidation-resistant metallic binder material (7).
4. Turbine blade (1) according to Claim 3, characterized in that the abrasive material (6) is cubic boron nitride (cBN).
5. Turbine blade (1) according to Claim 3, characterized in that the oxidation-resistant binder material (7) has the following chemical composition (amounts in % by weight): 15-30 Cr, 5-10 Al, 0.3-1.2 Y, 0.1-1.2 Si, 0-2 others, remainder Ni, Co.
6. Turbine blade (1) according to Claim 3, characterized in that the proportion of abrasive material (6) in the protective coating (5), if said coating has a multi-layer form, increases outward in the radial direction (r).
7. Turbine blade (1) according to Claim 1 or 2, characterized in that an intermediate coating (8), which consists exclusively of oxidation-resistant binder material (7), is additionally arranged between the first, metallic protective coating (4) and the second, wear-resistant and oxidation-resistant protective coating (5), wherein the intermediate coating (8) at least partially overlaps the first protective coating (4) and wherein the second protective coating (5) in turn at least partially overlaps the intermediate coating (8).
8. Turbine blade (1) according to one of Claims 1 to 7, characterized in that the turbine blade (1) is a reconditioned turbine blade.
9. Turbine blade (1) according to Claim 8, characterized in that the turbine blade was used in a preceding service interval of the turbine without an abrasive blade tip (9).
10. Turbine blade (1) according to one of Claims 1 to 9, characterized in that the turbine blade (1) is a new component.
11. Turbine blade (1) according to one of Claims 1 to 10 having a length (L), characterized in that the length (L) can be varied by the coatings (5) built up by laser metal forming.
12. Method for producing a turbine blade (1) according to one of Claims 1 to 11, wherein, in a preceding production step, at least certain zones on the surface of the main blade section (2) of the turbine blade (1) are coated with the oxidation-resistant, metallic protective coating (4), namely the MCrAlY coating, and an oxidation-resistant, ceramic thermal barrier coating (4a) is optionally applied to said protective coating (4), characterized in that

    - the at least one oxidation-resistant protective coating (4, 4a) on the radially outer blade tip (9) is removed by controlled machining and/or chemical coating removal, and then

    - the wear-resistant and oxidation-resistant protective coating (5) is applied to the blade tip (9) in one layer or in a plurality of layers by known laser metal forming, such that said coating overlaps along the outer and/or inner crown edge or the web edges at least partially with the first, metallic protective coating (4) applied beforehand, but not with the ceramic thermal barrier coating (4a) optionally applied beforehand.
13. Method according to Claim 12, characterized in that the controlled machining is carried out by grinding away or CNC milling.
14. Method according to Claim 12, characterized in that, during the laser metal forming step of the blade tip (9), abrasive material (6) and oxidation-resistant binder material (7) are mixed in a powder nozzle and then injected concentrically about the laser beam (10) as a focused jet of powder into the melt pool produced by the laser beam (10) on the blade tip (9).
15. Method according to Claim 12 or 14, characterized in that the temperature or temperature distribution in the melt pool is additionally recorded online during the laser metal forming, and in that this information is used, with the aid of a control system, to control the laser power during the laser metal forming and/or to change the relative movement between the laser beam (10) and the turbine blade (1) in a controlled manner.

Images