EP2501516A1

EP2501516A1 - Monocrystalline welding of directionally compacted materials

Info

Publication number: EP2501516A1
Application number: EP10779539A
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: 2009-11-16
Filing date: 2010-11-15
Publication date: 2012-09-26
Also published as: US20120285933A1; RU2012125028A; RU2509639C2; EP2322314A8; WO2011058174A1; CN102612421A; EP2322314A1; CN102612421B

Abstract

The invention relates to a method for directionally compacting a weld seam (13) during build-up welding, in particular for the build-up welding of a substrate (4) of a component (1) that is compacted in a directional manner and comprises dendrites (31), which extend in a substrate dendrite direction (32), wherein the method parameters with respect to feed, laser power, weld beam diameter, powder beam focus and/or powder mass flow are designed such that said parameters result in a local orientation of the temperature gradient (28) to the solidification front (19), which is smaller than 45º with respect to the substrate dendrite direction (32) of the dendrites (31) in the substrate (4), wherein the relative speed is between 30 mm/mm and 100 mm/mm, preferably 50 mm/mm, and/or the power is between 200 W and 500 W, preferably 300 W, and/or the diameter of the laser beam on the surface of the substrate is between 3 mm and 6 mm, preferably 4 mm, and/or the mass feed rate is between 300 mg/mm and 600 mg/mm, preferably 400 mg/m..

Description

Single crystal welding of directionally solidified

materials

The invention relates to a welding method of directionally solidified metallic materials. γ '-reinforced SX nickel-base superalloys can not be matched by conventional welding processes or high-energy processes (laser, electron beam)

Additional materials in overlapping welding paths in one or more layers of the order welding. The problem lies in the fact that even in the case of a single welding path in the near-surface edge area, a structure with misorientation is formed. For the subsequent overlap track, this means that the solidification front in this area has no SX seed at its disposal and the area with misorientation (no SX microstructure) continues to expand in the overlap area. Cracking occurs in this area.

The welding methods used so far are not able to build up a weld metal in γ '-reinforced SX nickel-base superalloys in overlap processing in one or more layers of identical SX microstructure. For a single track on an SX substrate, the local solidification conditions vary such that, depending on position, dendritic growth is initiated from the primary or secondary branches. In this case, of the various possible dendritic growth directions prevails those with the most favorable growth conditions, ie the smallest inclination angle to the temperature gradient. The cause for the formation of misorientations in the SX structure during powder build-up welding of γ '-reinforced SX nickel-base superalloys is z. At the moment not fully understood. It is thought that when dendrites from different growth directions meet, secondary arms may break off and serve as germs for the formation of a misoriented microstructure. In addition, in the surface not serve near edge area completely molten powder ^¬ particulate in the melt as nuclei for the formation of a misoriented structure. To solve the problem, therefore, a process guidance for the powder build-up welding of γ '-reinforced SX nickel-base superalloys is proposed, are realized in the growth conditions that favor only one direction of growth for the dendrites. In addition, the process control ensures complete melting of the powder particles in the melt.

It is therefore an object of the invention o. G. Solve a problem. The object is achieved by a method according to claim 1. To solve this technical problem of forming a non-monocrystalline structure in the near-surface edge region of a single track is a litigation for the

Contract welding with laser radiation proposed in which this problem does not occur or in such a small extent that overlapping in one or more layers without cracking at room temperature is possible.

In the dependent claims further advantageous measures are listed, which are combined with each other Kings ^¬ nen to obtain further advantages.

1 shows a schematic sequence of the method,

FIG. 2 shows a gas turbine,

FIG. 3 shows a turbine blade,

Figure 4 is a list of superalloys. The description and the figures represent only embodiments of the invention. 1 shows the sequence of the method is schematically Darge ^¬ provides with a device. 1

The component 120, 130 to be repaired has a substrate 4 of a superalloy, in particular of a nickel-based superalloy according to FIG.

In particular, the substrate 4 consists of a

Nickel-base superalloy.

The substrate 4 is repaired by applying new material 7, in particular by means of powder, to the surface 5 of the substrate 4 by build-up welding.

This is done by the supply of material 7 and a

Welding beam, preferably a laser beam 10 of a

Laser, which melts at least the supplied material 7 and preferably also partially the substrate. 4

In this case, powder is preferably used. Preferably, the diameter of the powder particles 7 is so small that a

Laser beam completely melt and results in a sufficiently high temperature of the particles 7.

In this case, there is a molten region 16 and an adjoining solidification front 19 on the substrate 4 during welding, and an already solidified region 13 in front of it.

The apparatus of the invention preferably comprises a laser (not shown) with a powder supply unit and a movement system (not shown), with which the

Laser beam interaction zone and the impact area for the powder 7 on the substrate surface 5 can be moved. The component (substrate 4) is preferably neither preheated nor by means of a heat treatment

outdated.

The area to be reconstructed on the substrate 4 is preferably job-welded in layers.

The layers are preferably meander-shaped, unidirectionally or bidirectionally applied, the scan vectors of the

Meandering from one location to another preferably 90 ° be rotated to avoid tying errors between the layers.

The dendrites 31 in the substrate 4 and the dendrites 34 in the up ^¬ transmitted region 13 are shown in FIG. 1

A coordinate system 25 is also shown.

The substrate 4 moves relatively in the x-direction 22 at the scanning speed V _v .

On the solidification front 19 there is the z-temperature gradient 28.

ÖZ

The welding process is performed with process parameters regarding feed rate V _r , laser power, beam diameter and

Powder mass flow carried out to a local

Orientation of the temperature gradient on the

Freezing front leads, which is smaller than 45 ° to the direction of the dendrites 31 in the substrate 4. This ensures that only the growth direction for the dendrites 34 is favored, which continues the dendrite direction 32 in the substrate 4. For this purpose, a beam radius is necessary, which ensures that the part of the three-phase lines that bounds the solidification front 19 is completely covered by the laser beam.

The approximate condition for a suitable inclination of the solidification front 19 to the dendrite direction 32 of the dendrites 31 in the substrate 4 is:

A: absorbance from the substrate,

I _L : laser intensity,

V _v : scan speed, λ: thermal conductivity of the substrate,

T: temperature

Depending on the material, a process window results with respect to the intensity of the laser radiation (approximately top hat), the beam radius relative to the powder beam focus, the feed rate V _v and the powder mass flow.

By completely covering the melt with the

Laser radiation is in the coaxial process control a longer interaction time of the powder particles with the

Laser radiation and thus ensures a higher particle temperature when in contact with the melt. The particle diameter and thus the given

Interaction time should cause a sufficiently high temperature level for complete melting. A sufficiently high temperature level of the melt should be given

Particle temperature and residence time in the melt cause the particles to melt completely.

The process parameters and mechanisms described above ensure the prerequisites for epitaxial monocrystalline growth in the weld metal with an identical dendrite orientation in the substrate. Due to the fact that only one direction of dendrite growth normal to the surface is activated in the welding process, solidification of the melt into the interdendritic space is facilitated during solidification and the formation of hot cracks is avoided.

This results in a quality of the weld which are of a structural weld (z. B. for the purpose of Repara ^¬ tur or addition in a highly stressed region of the device) is acceptable. The relative velocity V _v is between 30mm / min to 100mm / min, preferably 50mm / min.

The power is in the range of 200W to 500W,

preferably at 300W, with the laser beam on the Surface has a diameter of 3mm to 6mmm, preferably 4mm.

The mass feed rate is 300mg / min to 600mg / min, preferably 400mg / min.

FIG. 2 shows by way of example a gas turbine 100 in a partial longitudinal 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, air is sucked in by the compressor 105 through the intake housing 104 and compressed. 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 added to the working medium 113 in the combustion Chamber 110 burned. From there, the working medium 113 flows along the hot gas channel 111 past the guide vanes 130 and the rotor blades 120. On the rotor blades 120, the working medium 113 expands in a pulse-transmitting manner so that the rotor blades 120 drive the rotor 103 and drive 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 may have a directional structure, i. they are monocrystalline (SX structure) or have only longitudinal grains (DS structure).

As a material for the components, in particular for the ^turbine blade or vane 120, 130 and components of the combustion chamber 110. For example, iron-, nickel- or cobalt-based 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.

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 a thermal barrier layer, and consists for example of Zr02, Y203-Zr02, ie is not, partially or completely stabilized by ^yttrium oxide and / or calcium and / or magnesium oxide.

By suitable coating methods, e.g. Electron beam evaporation (EB-PVD) produces 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 faces the rotor 103 and fixed to a mounting ring 140 of the stator 143.

3 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 vane 130, the vane 130 having at its blade ^tip 415 have a further platform (not Darge ^¬ asserted).

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 designed, for example, as a hammer head. 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 regions 400, 403, 406 of the blade 120, 130, for example, ^massive metallic materials, in particular superalloys, are used.

The blade 120, 130 can hereby be manufactured 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, for general language use, referred to as directionally solidified) or a monocrystalline structure, ie the entire workpiece ^¬ is of a single crystal. In these methods, you have to transition to globular (polycrystalline) solidification avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries ^¬ which solidified the directionally the good qualities or monocrystalline component nullify. The term "directionally solidified structures" generally refers to single crystals that have no grain boundaries or at most small angle grain boundaries, as well as stem crystal structures that have grain boundaries running in the longitudinal direction but no transverse grain 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 need to be deprotected after use (e.g., by sandblasting). This is followed by removal of the corrosion and / or oxidation layers or products. If necessary, will also

Cracks in component 120, 130 repaired. Thereafter, a ^¬ As the coating of the component 120, 130, after which the component 120, 130. 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.

Claims

claims

1. A method for directionally solidifying a weld seam (13) during build-up welding,

in particular for build-up welding of a substrate (4) of a component (1, 120, 130),

that (4) is directionally solidified

and dendrites (31),

the (31) extend in a substrate dendrite direction (32),

in which the process parameters relating to feed,

Laser power, welding beam diameter, powder jet focus and / or powder mass flow are designed such that they lead to a local orientation of the Temperaturgra ^¬ serve (28) on a solidification front (19), which is less than 45 ° to the Substratdendritenrichtung (32) of the dendrites (31) in Substrate (4) is,

where the relative speed is between 30mm / min and 100mm / min,

preferably 50mm / min

and or

the power between 200W and 500W,

preferably 300W

and or

the diameter of the laser beam on the surface of the substrate is between 3 mm and 6 mm, preferably 4 mm, and / or

the mass feed rate is between 300 mg / min and 600 mg / min, preferably at 400 mg / min.

2. The method according to claim 1,

in which a melt (16) is formed on and in the substrate (4),

which is generated by the supply of powder (7) and / or material of the substrate (4),

and wherein the melt (16) completely from a

Welding beam (10),

in particular a laser beam,

is covered,

in particular in which the melt (16) is overlapped.

3. The method according to claim 1 or 2,

in the supplied powder (7) is applied in layers.

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

wherein the substrate (4) comprises a nickel-based superalloy,

which in particular has columnar grains,

in particular, has a monocrystalline structure.

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

in which the diameter of the powder particles (7) is so small

that in the welding laser beam (10) in particular

completely melt and a sufficiently high

Have temperature.

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

in which the temperature of the molten powder particles (7) is 20 ° C above the melting temperature of the powder particles (7). The method of claim 1, 2, 3, 4, 5 or 6, wherein a laser is used for welding.

The method of claim 1, 2, 3, 4, 5, 6 or 7, wherein:

A: absorptivity of substrate,

I _L : laser intensity,

V _v : scan speed,

X: thermal conductivity of the substrate.