EP2498947A1

EP2498947A1 - Method for welding workpieces made of highly heat-resistant superalloys, including a particular mass feed rate of the welding filler material

Info

Publication number: EP2498947A1
Application number: EP10776679A
Authority: EP
Inventors: Bernd Burbaum; Andres Gasser; Torsten Jambor; Stefanie Linnenbrink; Norbert Pirch; Nikolai Arjakine; Georg Bostanjoglo; Torsten Melzer-Jokisch; Selim Mokadem; Michael Ott; Rolf WILKENHÖNER
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Siemens AG
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Siemens AG
Priority date: 2009-11-13
Filing date: 2010-11-10
Publication date: 2012-09-19
Also published as: CN102639283B; CN102639283A; EP2322313A1; RU2012124077A; RU2510994C2; WO2011058045A1; US20120267347A1; US9035213B2

Abstract

The invention relates to a welding method for welding workpieces (9) made of highly heat-resistant superalloys. Said method includes: generating a heat input zone (11) on the workpiece surface (10) by means of a heat source (3); feeding welding filler material (13) into the heat input zone by means of a feeding device (5); and generating a relative motion between the heat source (3) and the feeding device (5) on one hand and the workpiece surface (10) on the other hand by means of a conveying device (15). Furthermore, according to the welding method, the mass feed rate is ≤ 350 mg/min.

Description

PROCESS FOR WELDING WORKPIECES FROM HIGH-WALL-RESISTANT SUPER ALLOYS WITH A SPECIAL MASS FEEDING RATE OF THE WELDING ADDITIVE MATERIAL

The present invention relates to a method for

Welding of workpieces, in particular of

Gas turbine workpieces, for example of gas turbine show ^¬ feln.

Blades of gas turbines are exposed to high temperatures and heavy mechanical loads during operation. For such components, nickel-based superalloys are therefore preferably used, which can be strengthened by precipitation of a γ 'phase. However, over time, cracks can occur in the blades that continue to expand over time. Such cracks eg due to the extreme mechanical stress during operation of a gas turbine, but they can also already occur during the manufacturing process ^¬. Since the production of turbine blades and other workpieces from such superalloys is complex and costly, it is endeavored to produce as little waste as possible in the production and to ensure a long life of the products produced.

In operation, gas turbine blades are regularly maintained and replaced if necessary, due to be ^¬ drive-related stress proper functioning can not be readily ensured. In order to enable a further use of exchanged turbine blades, they are worked up again as far as possible. They can then be used again in a gas turbine. As part of such reprocessing, for example, a build-up welding in damaged areas may be necessary to restore the original wall thickness.

Turbine blades that have already cracked during the manufacturing process can, for example, with build-up welding be made ready for use, so that the committee can be reduced in the production.

However, the γ '-reinforced nickel-base superalloys are currently difficult to weld by means of conventional welding processes with similar additives. The reason for this is that microsegregations so microscopic Entmi ^¬ mixtures of the melt must be avoided. In addition, the welding process itself can lead to the generation of cracks in the welded area during subsequent heat treatments. This is due to residual welding stresses caused by plastic deformation during heat input during

Welding. The difficult weldability of the γ 'to bypass -gehärteten nickel ^¬ base superalloys, is often associated with ductile welding consumables, such as with nickel-based alloys without γ' welded -Härtung. A typical representative of such a nickel-base alloy without γ 'hardening is, for example

IN625. The ductility of the non-γ '-gehärteten Zusatzwerkstof ^¬ fes allows the reduction of welding stresses by plastic deformation during the first heat treatment after welding. However, the uncured alloys possess in comparison to γ '-gehärteten nickel base superalloys lower high-temperature strength (both low tensile ^¬ ness and low creep rupture strength). It is therefore preferable to apply ver ^¬ without ductile filler metal welding process. These methods can be divided into two classes, namely methods in which an overaging of the base material to increase the ductility by means Vergröbe ^¬ tion of the γ 'phase takes place, and methods in which the welding process is carried out at a preheated substrate. Performing the welding process in a pre-heated substrate ^¬ reduces welding stresses by recovery during the welding process.

A welding process with preceding overaging is described for example in US 6,120,624, a welding process, which is performed on a preheated workpiece, for example in US 5,319,179.

However, the two aforementioned welding methods without ductile welding consumables are also associated with disadvantages. For example, in a study conducted prior to the welding process aging a corresponding Heat Treatment ^¬ development of γ 'is -härtbaren nickel-base superalloy, carried out prior to welding to the aging of the γ' to cause phase. The ductility of the base material is significantly increased. This increase in ductility makes it possible to weld the material at room temperature. In addition, it can be cold-directed. Furthermore, such a heat treatment allows the use of nickel-base superalloys such as Rene41 or Haynes282 as welding additive. Although these form γ 'phases in the microstructure, but only with a significantly lower volume fraction than the typical γ' -containing nickel-base superalloys which are nowadays used for gas turbine hot gas components such as gas turbine blades (for example IN738LC, IN939, Rene80,

IN6203DS, PWA1483SX, Alloy 247, etc.). Therefore, even when over-aging occurs before the welding process, no fully-structural welds can be made. When a preheating of the turbine blade takes place, the temperature difference and the resulting Spannungsgra ^¬ is reduced between the weld and the rest of the turbine blade, whereby the formation of weld cracks in components made of nickel-based superalloys can be avoided. Such methods, in which a preheating of the turbine blade to temperatures between 900 ° C and 1000 ° C with ^{¬ means} induction coils, but must be carried out under protective gas, which complicates the welding process and expensive. In addition, this method can not be performed on all areas of the workpiece due to lack of accessibility of befindli ^¬ in a protective gas container workpiece. There is therefore a need for an alternative welding method for build-up welding, which is suitable in particular for γ'-hardened nickel-based superalloys and does not have the abovementioned disadvantages or only to a reduced extent.

The object is achieved by a method for build-up welding according to claim 1.

The dependent claims contain advantageous

Embodiments of the invention and can be advantageously combined with each other as desired.

In the inventive method for welding workpieces made of high temperature superalloys a Aufbrin- occurs gene of welding material on the workpiece surface by means of a heat transfer zone and a feed zone to ^¬ drove the welding filler material in the heat transfer zone. The heat input zone and the feed zone are moved over the workpiece surface during welding. The movement can take place along a welding direction, for example on a linear path or in a path oscillating around the welding direction.

The mass feed rate according to the invention is -S 350 mg / min. In a further development of the method, the welding ^¬ parameters are selected so that the cooling rate is at least 8000 K / s during the solidification of the material.

The main parameters available for setting the cooling rate of at least 8000 K / s during the solidification of the material are the process parameters with respect to the welding power and the diameter of the heat input zone, for example in the form of a laser power and a diameter of the laser beam, the feed (the process speed ) and, if necessary, the flow of supplied filler metal. Depending on the type of laser source used, the required cooling rate for the material to be welded can be adjusted by suitable adaptation of these parameters. The process speed in this case may be at least 250 mm / min, in particular more than 500 mm / min. For example, the welding power and the diameter of the heat input zone can at a process speed of more than 500 mm / min, the procedural ^¬ rensparameter respect. Be set so that the cool down ^¬ rate during the solidification of the material is at least 8000 K / s be ^¬ carries.

Due to the high cooling rate and high solidification rate, the distribution coefficient is increased to such an extent that micro-segregation, ie microscopic separation of the melt, is largely avoided. The melt in the weld he ^¬ stares dendritic, that is, in a tree-like structure, wherein the growth directions of the dendrites along the welding track vary as the orientation of the possible directions of growth of the dendrites varied to the temperature gradient in the solidification front. That the direction of growth with the ge ^¬ slightest tendency to temperature gradients or with the lowest growth rate prevails. In addition, bacteria form in front of the solidification front, the currency ^¬ rend caught the solidification of the solidification front ^¬ to. These germs initiate dendrite growth directions that are statistically distributed. . The novel process is suitable for example for welding ^¬ SEN of workpieces from a γ '-containing nickel-base super alloy by means of a welding material having a γ' - is forming nickel-based superalloy material. It can then be a high strength in the weld metal due to the use of similar filler material and an acceptable

Welding quality, ie a very low number of cracks and a very low average crack length can be achieved. ^¬ on the basis of the possibility to carry out the welding process at room temperature with a locally on the molten bath that are available protective gas atmosphere, achieved according to the invention ^¬ welding method has a high efficiency. The method can be designed, in particular, as a build-up welding method in which the deposition of welding filler metal takes place in layers. In this case, the welding ^directions of successive layers can be rotated ^relative to one another, in particular by 90 °. By the rotation of the welding direction of different layers connection errors between the layers can be avoided, especially when the heat input zone and the feed zone also along the

Welding direction are moved in a direction about the welding direction oscillating path over the workpiece surface.

The irregularly distributed dendrite orientation is found mainly in the upper half of the welding track. Advantageously, therefore, in the method according to the invention a previously applied layer in less than half of their

Layer thickness melted again. The crystal structure of ^¬ remelted regions is taken during solidification. Due to the low remelting depth is ensured ge ^¬ that the solidification front seated on an area of irregularly distributed dendrite. This results in the result of a multi-layer welding that a polycrystal is generated with grains whose

Diameters are very small on average. Grain boundaries generally provide a weak point with respect to the cracking of transient voltages during the welding process or a subsequent heat treatment. Due to the small extension of a grain boundary in the plane and the irregular ^¬ uniform orientation in the welded with the inventive method, the weld, the weld with respect to the cracking insensitive so that the welding process can be performed at room temperature.

The inventive method can be applied to both polykristalli ^¬ nen as well as directionally solidified or single-crystal substrates. In all these cases, a γ '-containing nickel-based superalloy can be used as a welding additive. In the context of the welding ^{method according to} the invention, a heat treatment can be carried out on the application of the filler ^metal . With a matched to the weld heat treatment so the desired γ 'morphology can be adjusted. This serves to further improve the strength of the weld metal.

A welding device according to the invention to welding of high temperature superalloys, which is suitable for performing the ER inventive method, comprises a heat ^¬ source for generating a heat input zone on the work ^¬ piece surface, a supply means for supplying welding filler material comprising a heat source and a transmembrane ^¬ port device for Generating a relative movement between the heat input zone and the supply device on the one hand and the workpiece surface on the other. The transport ^device is advantageously connected to the heat source and the feed direction for the filler metal in order to move the heat source and the supply device in order to bring about the relative movement. This is usually less expensive than moving the workpiece. In particular, a laser can be used as the heat source in the welding device according to the invention. The welding device according to the invention further comprises ^¬ erprogramm a control unit with a tax, which adjusts the welding parameters, that the cooling rate is at least 8000 Kelvin per second during the solidification of the material. In particular, the Steuerein ^¬ standardize the welding parameters related to. The welding performance as well as the diameter of the heat introduction zone set so that the cooling rate is at least 8000 Kelvin per second during the solidification of the material. The welding can be carried out here with a process speed of at least 250 mm per minute, in particular with a process speed of more than 500 mm per minute.

The relative movement can in particular be controlled so that the heat input zone and the feed zone along a

Welding direction on a oscillating around the welding direction- to move the path over the workpiece surface. In addition, the control unit can perform the relative movement with or without oscillation so that the welding directions are rotated in successive layers against each other, for example. around 90 °.

Further features, properties and advantages of the present invention will become apparent from the following description of embodiments with reference to the accompanying figures.

Figure 1 shows an example of a gas turbine in a longitudinal ^¬ partial section.

FIG. 2 shows a turbine blade in a perspective view.

Figure 3 shows a gas turbine combustor in a partially sectioned perspective view.

FIG. 4 shows a schematic representation of the welding device according to the invention.

FIG. 5 shows the welding path for a first layer of welding filler material.

FIG. 6 shows the welding path for a second layer

Welding filler.

FIG. 1 shows by way of example a gas turbine 100 in a longitudinal partial section.

The gas turbine 100 has inside a rotatably mounted about a rotation axis 102 rotor 103 with a shaft 101, which is also referred to as a turbine runner.

Along the rotor 103 follow one another an intake housing 104, a compressor 105, for example, a toroidal combustion chamber 110, in particular annular combustion chamber, with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust housing 109th The annular combustion chamber 110 communicates with an annular annular hot gas channel 111, for example. There, for example, four turbine stages 112 connected in series form the turbine 108.

Each turbine stage 112 is formed, for example, from two blade ^rings . As seen in the direction of flow of a working medium 113, in the hot gas channel 111 of a row of guide vanes 115, a series 125 formed of rotor blades 120 follows.

The guide vanes 130 are fastened to an inner housing 138 of a stator 143, whereas the moving blades 120 of a row 125 are attached to the rotor 103 by means of a turbine disk 133, for example.

Coupled to the rotor 103 is a generator or work machine (not shown).

During operation of the gas turbine 100 104 air 135 is sucked by the compressor 105 through the intake housing and ver ^¬ seals. The 105 ^¬ be compressed air provided at the turbine end of the compressor is ge ^¬ leads to the burners 107, where it is mixed with a fuel. The mixture is then burned to form the working medium 113 in the combustion chamber 110. From there, the working medium flows

113 along the hot gas channel 111 past the guide vanes 130 and the blades 120. On the blades 120, the working medium 113 expands in a pulse-transmitting manner, so that the blades 120 drive the rotor 103 and this drives the machine coupled to it.

The components exposed to the hot working medium 113 are subject to thermal loads during operation of the gas turbine 100. The guide vanes 130 and rotor blades 120 of the first turbine stage 112, viewed in the flow direction of the working medium 113, are subjected to the greatest thermal stress in addition to the heat shield elements lining the annular combustion chamber 110. To withstand the prevailing temperatures, they can be cooled by means of a coolant. Likewise, substrates of the components can have a directional structure, ie they are monocrystalline (SX structure) or have only longitudinal grains (DS structure).

Iron, nickel or cobalt-based superalloys are used as material for the components, in particular for the turbine blades 120, 130 and components of the combustion chamber 110.

Such superalloys are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949.

Also, the blades 120, 130 may be anti-corrosion coatings (MCrAlX; M is at least one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and is yttrium (Y) and / or silicon , Scandium (Sc) and / or at least one element of the rare earth or hafnium). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. On the MCrAlX may still be present a thermal barrier coating, and consists for example of Zr02, Y203-Zr02, ie it is not, partially or completely stabilized by Ytt ^¬ riumoxid and / or calcium oxide and / or magnesium oxide. Suitable coating processes, such as electron beam evaporation (EB-PVD), produce stalk-shaped grains in the thermal barrier coating.

The guide vane 130 has an inner housing 138 of the turbine 108 facing guide vane root (not Darge here provides ^¬) and a side opposite the guide-blade root vane root. The vane head is the rotor 103 facing and fixed to a mounting ring 140 of the stator 143.

2 shows a perspective view of a rotor blade 120 or guide vane show ^¬ 130 of a turbomachine, which extends along a longitudinal axis of the 121st

The turbomachine may be a gas turbine of an aircraft or a power plant for power generation, a steam turbine or a compressor.

The blade 120, 130 has along the ^longitudinal axis 121 to each other, a securing region 400, an adjoining blade or vane platform 403 and a blade 406 and a blade tip 415.

As a guide blade 130, the blade 130 may have at its blade tip ^¬ 415 another platform (not shown).

In the mounting region 400, a blade root 183 is formed, which serves for attachment of the blades 120, 130 to a shaft or a disc (not shown).

The blade root 183 is, for example, as a hammerhead out staltet ^¬. Other designs as Christmas tree or Schwalbenschwanzfuß are possible. The blade 120, 130 has for a medium which flows past the scene ^¬ felblatt 406 on a leading edge 409 and a ^trailing edge 412th

In conventional blades 120, 130, in all areas 400, 403, 406 of the blade 120, 130, for example, ^massive metallic materials, in particular superalloys, are used. Such superalloys are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. The blade 120, 130 can be made by a casting process, also by directional solidification, by a forging process, by a milling process or combinations thereof. Workpieces with a monocrystalline structure or structures are used as components for machines which are exposed to high mechanical, thermal and / or chemical stresses during operation.

The production of such monocrystalline workpieces takes place e.g. by directed solidification from the melt. These are casting processes in which the liquid metallic alloy is transformed into a monocrystalline structure, i. to the single-crystal workpiece, or directionally solidified.

Here, dendritic crystals are aligned along the heat flow and form either a columnar grain structure (columnar, ie grains that run the entire length of the workpiece and here, in common parlance, referred to as directionally solidified) or a monocrystalline structure, ie the whole workpiece be ^¬ is made of a single crystal. In these methods, you have to avoid solidification transition to globular (polycrystalline), since non-directional growth inevitably forms transverse and longitudinal grain boundaries ^¬ which make the good properties of the directionally solidified or single-crystal component naught.

If the term generally refers to directionally solidified structures, it means both single crystals which have no grain boundaries or at most small-angle grain boundaries, as well as columnar crystal structures which are probably grain boundaries running in the longitudinal direction but no transverse grain boundaries. have boundaries. These second-mentioned crystalline structures are also known as directionally solidified structures.

Such methods are known from US Pat. No. 6,024,792 and EP 0 892 090 A1.

Likewise, the blades 120, 130 may have coatings against corrosion or oxidation, e.g. B. (MCrAlX, M is at least one element of the group iron (Fe), cobalt (Co),

Nickel (Ni), X is an active element and stands for yttrium (Y) and / or silicon and / or at least one element of the rare earths, or hafnium (Hf)). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1.

The density is preferably 95% of the theoretical

Density.

A protective aluminum oxide layer (TGO = thermal grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer).

Preferably, the layer composition comprises Co-30Ni-28Cr-8A1-0, 6Y-0, 7Si or Co-28Ni-24Cr-10Al-0, 6Y. Besides these cobalt-based protective coatings, nickel-based protective layers such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-IIAl-O, 4Y-2Re or Ni-25Co-17Cr-10A1-0, 4Y-1 are also preferably used , 5Re. On the MCrAlX may still be present a thermal barrier coating, which is preferably the outermost layer, and consists for example of Zr0 ₂ , Y2Ü3-Zr02, ie it is not, partially ^¬ or fully stabilized by yttria

and / or calcium oxide and / or magnesium oxide.

The thermal barrier coating covers the entire MCrAlX layer. Suitable coating processes, such as electron beam evaporation (EB-PVD), produce stalk-shaped grains in the thermal barrier coating. Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat insulation layer may have ^¬ porous, micro- or macro-cracked ^compatible grains for better thermal shock resistance. The thermal barrier coating is therefore preferably more porous than the

MCrAlX layer.

Refurbishment means that components 120, 130 may have to be freed of protective layers after use (eg by sandblasting). This is followed by removal of the corrosion and / or oxidation layers or products. Optionally, even cracks in the component 120, 130 are repaired. Thereafter, a ^¬ As the coating of the component 120, 130, after which the component 120, the 130th

The blade 120, 130 may be hollow or solid. If the blade 120, 130 is to be cooled, it is hollow and also has, if necessary, film cooling holes 418 ^(indicated by dashed lines) on.

FIG. 3 shows a combustion chamber 110 of a gas turbine.

The combustion chamber 110 is configured, for example, as so-called ^an annular ^combustion chamber, in which are arranged a plurality of in the circumferential direction about an axis of rotation 102

Burners 107 open into a common combustion chamber space 154, the flames 156 produce. For this purpose, the combustion chamber 110 is configured in its entirety as an annular structure, which is positioned around the axis of rotation 102 around.

To achieve a comparatively high efficiency, the combustion chamber 110 is designed for a comparatively high temperature of the working medium M of about 1000 ° C to 1600 ° C. Around Even with these, for the materials unfavorable operating parameters a comparatively long service life ermög ^¬ union, the combustion chamber wall 153 is provided on its the Arbeitsme ^¬ medium M side facing with an inner lining formed of heat shield elements 155.

Each heat shield element 155 made of an alloy is equipped on the working fluid side with a particularly heat-resistant protective layer (MCrAlX layer and / or ceramic coating) or is made of high-temperature-resistant material (solid ceramic blocks).

These protective layers may be similar to the turbine blades, so for example MCrAlX means: M is at least one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and / or silicon and / or at least one element of the rare earths, or hafnium (Hf). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1.

On the MCrAlX, for example, a ceramic Wär ^¬ medämmschicht be present and consists for example of ZrÜ2, Y203 ^~ Zr02, ie it is not, partially or completely stabilized by yttrium and / or calcium oxide and / or magnesium oxide.

By suitable coating methods, e.g. Electron beam evaporation (EB-PVD) produces stalk-shaped grains in the thermal barrier coating.

Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat insulating layer can ^¬ ner to have better thermal shock resistance porous, micro- or macro-cracked pERSonal.

Reprocessing (Refurbishment) means that ^heat shield elements 155, after being used, where appropriate, Protective layers must be freed (eg by sandblasting). This is followed by removal of the corrosion and / or oxidation layers or products. If necessary, cracks in the heat shield element 155 are also repaired.

Then recoated and the Hitzeschildele ^¬ elements 155, after use of the heat shield elements 155 is performed.

Due to the high temperatures inside the combustion chamber 110 may also be provided for the heat shield elements 155 and for their holding elements, a cooling system. The heat shield elements 155 are then, for example, hollow and possibly still have cooling holes (not shown) which open into the combustion chamber space 154.

FIG. 4 shows a highly schematic representation of a welding device 1. This comprises a laser 3 and a powder feed device 5 with which a powdered welding filler can be applied to the region of a workpiece 9 to be welded. By means of the laser radiation, a heat input zone 11 is formed on the workpiece surface, in which also the powder 13 is introduced from the powder feed device 5. The laser is preferably a 300W laser, in particular a Nd-YAG laser, very particularly with λ = l, 06ym. The laser power is between 100W and 300W, and preferably between 100W and 200W, more particularly between 100W and 150W. Thus, advantageously, the welding material is melted well and also melted the ground, thus resulting in a tight weld.

The laser 3 and the powder feeder 5 are arranged on a scanning device 15, which is a displacement of the

Laser 3 and the powder feeder 5 in two dimensions along the component surface (x and y directions in Figure 4) with the area to be welded 7 allows. The Process speed is at least 250mm / min,

especially 400mm / min - 600mm / min, very particular

500mm / min. So is an advantageous heat input in the

Welding material and the substrate possible.

Furthermore, the scanning device 15 of the present embodiment allows a displacement of the laser 3 and the powder feeder 5 perpendicular to the component surface (z direction in Figure 4). With the aid of the scanning device 15, the heat input zone and the impact zone of the powder can thus be displaced along a predetermined path. When

Scanning device can, for example, find a robotic arm use. The diameter of the laser beam is in particular 500μη to 700μιη, especially 600μη. Thus, the supplied welding material can be heated advantageously.

The control of the movement mediated by the scanning device 15 is effected by a control unit 17, which also controls the other parameters of the welding process. In the ^¬ difference to the present embodiment, the control of other parameters of the welding process but also by an additional control, that is separated from the STEU ^¬ augmentation of the movement sequence, take place. Furthermore, in contrast to the illustrated embodiment, instead of the scanning device 15 for moving the laser 3 and the powder feed device 5, a movable component holder can also be used. In the context of the invention, only the relative movement between the laser 3 and the powder feeder 5 on the one hand and the workpiece 9 is important. The method according to the invention for build-up welding of a workpiece surface can be used for material application, in particular for multilayer material application, on the region 7 of a component 9 to be welded. The component 9 does not need to be preheated or over-aged by means of a heat treatment.

Subsequently, the method will be described on the surface 10 of a turbine blade 9 as a workpiece by means of build-up welding described. The turbine blade of the present embodiment is made of a γ '-reinforced nickel base superalloy, for example, IN738LC, IN939, Rene80, IN6203DS, PWA1483SX, Alloy 247, etc. The area to be welded 7 in the surface 10 of the turbine blade 9 is electrodeposited in layers , wherein the heat input zone to ^{¬ together} with the impact area for the powder 13 along a welding direction over the area to be welded 7 of the turbine blade 9 are moved. The powder 13 in the present case is a powder of a γ '-containing nickel-base superalloy, for example from IN 738LC, IN 939, Rene 80, IN

6203DS, PWA 1483, Alloy 247. etc.

The path PI traveled by the heat input zone 11 and the impact area of the powder 13 during buildup welding of the first layer on the region 7 to be welded is shown schematically in FIG. The figure shows the turbine blade 9 with the region to be welded 7 and the welding direction Sl during deposition welding of the first layer 19. The heat input zone 11, which simultaneously represents the impact area for the powder 13, but is not linearly displaced along the welding direction Sl, but it oscillates during the displacement along the welding direction simultaneously in a direction perpendicular to the welding direction. This is followed by the heat input zone 11 and the impact area of the powder

13 a meandering path PI over the area to be welded. 7

For the build-up welding of the second layer 21 (FIG. 4), the laser 3 and the powder feed device 5 are displaced slightly along the z-direction of the scanning device 15. In addition, in the present embodiment, the welding direction S2 is rotated by 90 ° with respect to the welding direction S1 for the first layer. The path P2 of the heat input zone 11 and the impingement area for the powder 13 during buildup welding of the second layer 21 is shown in FIG. Even when on ^¬ up welding of the second layer 21 11 oscillates the heat input zone together with the impingement of the powder 13 in a direction perpendicular to the welding direction S2. Overall, therefore, a meander-shaped path P2 of the heat input zone 11 and the impact area for the powder 13 results over the region 7 to be welded.

The paths described in the context of the exemplary embodiment represent only one of various possible variants. In principle, there are several possibilities for performing the welding: 1. unidirectional or 2. bidirectional (for example, meandering) build-up welding. At each of these

Variants, the tracks (paths) of the 2nd layer can be parallel offset or welded perpendicular to the tracks (paths) of the first layer. All of these variants can be used in the context of the method according to the invention.

In the process of the laser and the powder supply unit, the oscillation can be selected such that the entire area to be welded 7 is swept with a single path along the welding direction, as shown in FIG. 5, or so that only a part of the area to be welded 7 is swept over and for cladding the entire area several adjacent paths P2 in

Welding direction S2 are traversed, as shown in Figure 6.

The method of the heat input zone 11 and the Auftreffbe ^¬ realm of the powder 13 along the path PI or P2 is performed in the present embodiment with a process con ^¬ speed of at least 500 mm / min.

The mass feed rate is -S 350 mg / min, preferably

-S 330mg / min (Since it is a build-up welding, the value zero is excluded, so at least 50 mg / min, in particular at least 100mg / min). This has the advantage that the supplied welding material melts very well, receives a high temperature and thus cools down more during cooling. The laser power, the beam diameter and the powder flow are chosen so that the cooling rate of the swept area during solidification is greater than 8000K / s. When applying the second layer 21, the process parameters in terms of laser power and beam diameter are also chosen so that the remelting depth, to which the first layer 19 is reflowed, less than 50% of the track height of the first layer 19, is. The

Remelting depth is indicated by dashed lines in FIG. Basically, other than those in the present

Example given process speed possible, in which case the other parameters laser power, beam diameter and powder flow must be adjusted accordingly. The high cooling rate and high speed Erstarrungsgeschwin ^¬ the partition coefficient is increased so that microsegregations be largely avoided. The induced by the heat input zone 11 melt solidifies dendri ^¬ table, wherein the crystal structure of the present again in the range up molten crystal structure is adopted. The growth directions of the dendrites vary along a path PI, P2. The reason for this is that the orientation of the possible growth directions of the dendrites to the temperature gradient varies, with the

Growth direction interspersed with the lowest tendency to the temperature gradient or with the lowest growth rate. In addition, germs that form before the solidification front, and which are caught up by the solidification front during solidification, initiate dendrite growth directions that are statistically distributed. This irregular ver ^¬ shared dendrite are predominantly found in the upper half of a layer 19. The low melting reconstruction depth is therefore ensured that the solidification front ^¬ builds on an area with irregularly distributed dendrite what welding at a Mehrlagenauftrag- to results in that a polycrystal is generated with grains whose average diameter is very small. As a result, the welded area of the turbine blade 9 is insensitive to cracking.

After the application of the required number of layers 19, 21 is carried out, the turbine blade 9 may be a Wärmebe ^¬ act are subjected to the leads to the desired γ 'morphology is established. This serves to further improve the strength of the welded portion of the turbine blade 9.

With the method according to the invention, a build-up welding can take place at room temperature and without prior aging of the component to be welded, the formation of solidification cracks and re-melting cracks being suppressed. This leads to the result to a quality of the weld, the weld of a structural particular hochbe ^¬ congested areas of gas turbine blades, but also other components, is acceptable. At the same time there is only a very slight influence of the base material, since Because of the small heat-affected zone (there is no Vorhei ^¬ zen) and the suppression of reflow cracks in the heat affected zone, only a very low heat input into the substrate occurs.

Claims

claims

1. A method for welding workpieces (9) made of highly heat-resistant superalloys,

in which an application of welding filler material (13) on the workpiece surface (10) by means of a heat input ^¬ zone (11) and

a feed zone for feeding the filler metal into the heat input zone (11),

wherein the heat transfer zone (11) and the feed zone of a ^¬ hand and the workpiece surface (10) on the other hand are moved relative to each other,

wherein the mass feed rate of the filler metal is <350 mg / min.

2. The method according to claim 1,

characterized in that

the mass feed rate is ^ 330mg / min,

especially ^ 300mg / min.

3. The method according to claim 1 or 2,

that at least the welding parameters welding power,

Process speed, diameter of a welding beam are chosen so

that the cooling rate during the solidification of the material min ^¬ is least 8000 Kelvin per second (K / s)

4. The method according to claim 1, 2 or 3,

characterized in that the welding parameters with respect to the welding power and the diameter of the heat input zone are set so that the cooling rate during the solidification of the material is at least 8000 Kelvin per second (K / s).

5. The method according to claim 1 or claim 3,

characterized in that the process speed is at least 250mm / min, in particular 400mm / min - 600mm / min,

especially 500mm / min.

6. The method according to claim 1, 2, 3, 4 or 5,

in which the weld is produced by layer-wise application of welding filler material (13).

7. The method according to claim 6,

in which the previous layer (19) is melted.

8. The method according to claim 7,

characterized in that a previously applied layer (19) is melted again in less than half its layer thickness.

9. The method according to claim 5, 6, 7 or claim 8,

characterized in that for each layer (19, 21) the heat input zone (11) and the

Supply zone along a welding direction (Sl, S2) are moved relative to the workpiece surface (10) and

the welding directions (Sl, S2) of successive layers (19, 21) are turned against each other.

10. The method according to one or more of claims 1 to 9,

characterized in that the heat input zone (11) and

the feed zone

along a welding direction (Sl, S2) on a path (PI, P2) oscillating around the welding direction relative to

Workpiece surface (10) are moved.

11. The method according to one or more of claims 1 to 10,

characterized in that the workpiece (9) comprises a γ '-containing nickel-base superalloy,

in particular, consists of and

the welding filler material (13) is a γ '-forming

Nickel base superalloy material.

12. The method according to one or more of claims 1 to 11,

characterized in that the application of the welding filler material (13) is followed by a heat treatment.

13. The method according to one or more of claims 1 to 11,

where a 300W laser is used.

14. The method according to claim 12,

where an Nd-YAG laser is used,

in particular with λ = 1.06ym.

15. The method according to claim 13 or 14,

where the laser power is 100W to 300W,

especially 100W to 200W,

especially 100W to 150W.

16. Method according to one or more of the preceding

Claims,

in which the diameter of a laser beam is 500μη to δθθμιη, in particular 600μη.

17. Method according to one or more of the preceding

Claims,

in which a polycrystalline weld (19, 21) is achieved.

18. Method according to one or more of the preceding

Claims,

where the mass feed rate is at least 50mg / min,

in particular at least 100 min / min.