Patent Application
20110293431
The invention relates to a component having a structure which differs in different places, and to a method for production.
In the single-crystal (SX) or rod-crystalline (DS) directional solidification of gas turbine blades, defect-free solidification of the blade root represents a challenge owing to the limited thermal gradients and the complex geometry in the precision casting furnace.
In order to let the blade root solidify directionally (SX, DS), a very long and cost-intensive process cycle is required. Nevertheless, a not inconsiderable number of blades fail owing to grain structure defects (for example new grains) in the root. Furthermore, SX or DS solidification is limited in respect of the blade size, so that the advantages of directionally solidified turbine blades cannot be exploited in the rows of last rotor blades.
According to the current prior art, directional solidification is carried out by the so-called Bridgeman method. In this case, blades are directionally solidified in a rod-crystalline (DS) or single-crystal (SX) fashion up to a size limited by the thermal gradients in the casting furnace. Defect-free solidification of the blade root, however, requires a very long process cycle.
In order to overcome these limitations, on the plant side attempts are being undertaken to improve the thermal gradients acting in the furnace (for example by gas cooling, cooling in a ceramic fluidized bed or in a liquid metal melt (LMC)). Alloys have furthermore been optimized in respect of their castability, although this has usually entailed a compromise in the mechanical properties.
It is an object of the invention to overcome the problems mentioned above.
The object is achieved by a component as claimed in the claims, namely by columnar (DS) or conventional (CC) solidification in a second region with single-crystal (SX) solidification of a first region, and methods as claimed in the claims.
Further advantageous measures, which may be combined with one another in any desired way in order to achieve further advantages, are listed in the dependent claims.
It has been established that an SX or DS structure is not required in the second region owing to a lower loading temperature during operation and a differently acting loading profile. To this end, however, the alloy may require chemical elements which an alloy intended for SX/DS solidification does not necessarily contain.
To this end, the alloy is advantageously to be modified in the second region (blade root), or an alloy which can accommodate the loading both in the second region (root) and the first region (blade surface) is to be used for the entire component.
The entire solidification of such a blade may be carried out in situ in a process according to the three following technical features:
1. DS-SX solidification of the blade surface (1st region) with a reduced amount of starting material (1st alloy for the blade surface, i.e. the amount for a melt that only provides the blade surface, but not the blade root);
then switching over the process parameters and adding a second alloy (different to the 1st alloy) in order to solidify the blade root (2nd region).
2. DS-SX solidification of the blade surface (1st region) with the full amount of starting material (alloy for the blade surface, blade platform and blade root, amount for a melt sufficient for the blade surface and blade root);
then switching over the process parameters and adding additional alloy elements to the alloy of the blade surface, i.e. the not yet solidified melt of the full amount of starting material;
solidifying the blade root (2nd region).
3. DS-SX solidification of the blade surface (1st region) with the full amount of starting material (a single alloy is suitable both for the blade surface and for the root and in a sufficient amount);
then switching over the process parameters and solidifying the blade root (2nd region).
The amount of starting material is the amount of material of an alloy, or two alloys, which is necessary in order to completely cast the entire component or blade.
The description and the figures merely represent exemplary embodiments of the invention.
The invention will be described merely by way of example with reference to a turbine blade 120, 130.
The blade surface region 406 preferably consists of a single-crystal structure (SX). The single-crystal structure (SX) extends from the blade tip 415 and preferably as far as the upper side 4 of the blade platform 403.
The blade platform 403 and at least the fastening region 400 preferably have a different structure, i.e. not a single-crystal structure. This may comprise: rod-shaped crystals solidified in columnar fashion (DS) or a nondirectional structure (CC structure).
Depending on the mechanical requirement, the single-crystal structure (SX) of the blade surface 406 may also extend as far as a certain thickness into the blade platform 403. In this case, a DS or CC structure begins inside the blade platform 403 (
For particularly high loads (thermal, mechanical), the entire blade platform 403 may also be solidified in single-crystal fashion, so that only the fastening region 400 has a CC or DS structure, as represented in
The blade surface 406 may likewise have an SX structure, the blade platform 403 a DS structure and the blade root 400 a CC structure (
If three structures (SX, DS, CC) are present, they may extend over different regions:
When there is SX in the blade surface 406, the blade platform 403 may likewise have DS and CC structures (as seen in the direction of the blade root 400) or SX, DS, CC structures (as seen in the direction of the blade root 400), the blade root respectively having a CC structure.
The advantages of the different structures are:
reducing the reject rate in the production of SX or DS components
significant cost reduction in the process management
utilization of SX-DS structures for larger blades and, associated with this, a possible increase in the turbine efficiency,
local optimization of the blade root or blade surface in respect of the locally acting loading profile.
The gas turbine 100 internally comprises a rotor 103, which will also be referred to as the turbine rotor, mounted so as to rotate about a rotation axis 102 and having a shaft 101.
Successively along the rotor 103, there are an intake manifold 104, a compressor 105, an e.g. toroidal combustion chamber 110, in particular a ring combustion chamber, having a plurality of burners 107 arranged coaxially, a turbine 108 and the exhaust manifold 109.
The ring combustion chamber 110 communicates with an e.g. annular hot gas channel 111. There, for example, four successively connected turbine stages 112 form the turbine 108.
Each turbine stage 112 is formed for example by two blade rings. As seen in the flow direction of a working medium 113, a guide vane row 115 is followed in the hot gas channel 111 by a row 125 formed by rotor blades 120.
The guide vanes 130 are fastened on an inner housing 138 of a stator 143 while the rotor blades 120 of a row 125 are fitted on the rotor 103, for example by means of a turbine disk 133.
Coupled to the rotor 103, there is a generator or a work engine (not shown).
During operation of the gas turbine 100, air 135 is taken in and compressed by the compressor 105 through the intake manifold 104. The compressed air provided at the turbine-side end of the compressor 105 is delivered to the burners 107 and mixed there with a fuel. The mixture is then burnt to form the working medium 113 in the combustion chamber 110. From there, the working medium 113 flows along the hot gas channel 111 past the guide vanes 130 and the rotor blades 120. At the rotor blades 120, the working medium 113 expands by imparting momentum, so that the rotor blades 120 drive the rotor 103 and this drives the work engine coupled to it.
The components exposed to the hot working medium 113 experience thermal loads during operation of the gas turbine 100. Apart from the heat shield elements lining the ring combustion chamber 110, the guide vanes 130 and rotor blades 120 of the first turbine stage 112, as seen in the flow direction of the working medium 113, are heated the most.
In order to withstand the temperatures prevailing there, they may be cooled by means of a coolant.
Substrates of the components may likewise comprise a directional structure, i.e. they are single-crystal (SX structure) or comprise only longitudinally directed grains (DS structure).
Iron-, nickel- or cobalt-based superalloys are for example used as the 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.
The blades or vanes 120, 130 may also have coatings against corrosion (MCrAlX: M is at least one element from the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon, scandium (Sc) and/or at least one rare earth element, 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, there may furthermore be a thermal barrier layer, which consists for example of ZrO2, Y2O3—ZrO2, i.e. it is not stabilized or is partially or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide.
Rod-shaped grains are produced in the thermal barrier layer by suitable coating methods, for example electron beam deposition (EB-PVD).
The guide vane 130 comprises a guide vane root (not shown here) facing the inner housing 138 of the turbine 108, and a guide vane head lying opposite the guide vane root. The guide vane head faces the rotor 103 and is fixed on a fastening ring 140 of the stator 143.
The turbomachine may be a gas turbine of an aircraft or of a power plant for electricity generation, a steam turbine or a compressor.
The blade 120, 130 comprises, successively along the longitudinal axis 121, a fastening region 400, a blade platform 403 adjacent thereto as well as a blade surface 406 and a blade tip 415.
As a guide vane 130, the vane 130 may have a further platform (not shown) at its vane tip 415.
A blade root 183 which is used to fasten the rotor blades 120, 130 on a shaft or a disk (not shown) is formed in the fastening region 400.
The blade root 183 is configured, for example, as a hammerhead. Other configurations as a firtree or dovetail root are possible.
The blade 120, 130 comprises a leading edge 409 and a trailing edge 412 for a medium which flows past the blade surface 406.
In conventional blades 120, 130, for example solid metallic materials, in particular superalloys, are used in all regions 400, 403, 406 of the blade 120, 130.
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 may in this case be manufactured by a casting method, also by means of directional solidification, by a forging method, by a machining method or combinations thereof.
Workpieces with a single-crystal structure or single-crystal structures are used as components for machines which are exposed to heavy mechanical, thermal and/or chemical loads during operation.
Such single-crystal workpieces are manufactured, for example, by directional solidification from the melts. These are casting methods in which the liquid metal alloy is solidified to form a single-crystal structure, i.e. to form the single-crystal workpiece, or is directionally solidified.
Dendritic crystals are in this case aligned along the heat flux and form either a rod crystalline grain structure (columnar, i.e. grains which extend over the entire length of the workpiece and in this case, according to general terminology usage, are referred to as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of a single crystal. It is necessary to avoid the transition to globulitic (polycrystalline) solidification in these methods, since nondirectional growth will necessarily form transverse and longitudinal grain boundaries which negate the beneficial properties of the directionally solidified or single-crystal component.
When directionally solidified structures are referred to in general, this is intended to mean both single crystals which have no grain boundaries or at most small-angle grain boundaries, and also rod crystal structures which, although they do have grain boundaries extending in the longitudinal direction, do not have any transverse grain boundaries. These latter crystalline structures are also referred to as directionally solidified structures.
Such methods are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1.
The blades 120, 130 may also have coatings against corrosion or oxidation, for example MCrAlX (M is at least one element from 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 rare earth element, 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=thermally grown oxide layer) is formed on the MCrAlX layer (as an interlayer or as the outermost layer).
The layer composition preferably comprises Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. Besides these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re.
On the MCrAlX, there may furthermore be a thermal barrier layer, which is preferably the outermost layer and consists for example of ZrO2, Y2O3—ZrO2, i.e. it is not stabilized or is partially or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide.
The thermal barrier layer covers the entire MCrAlX layer.
Rod-shaped grains are produced in the thermal barrier layer by suitable coating methods, for example electron beam deposition (EB-PVD).
Other coating methods may be envisaged, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier layer may comprise porous, micro- or macro-cracked grains for better thermal shock resistance. The thermal barrier layer is thus preferably more porous than the MCrAlX layer.
Refurbishment means that components 120, 130 may need to be stripped of protective layers (for example by sandblasting) after their use. The corrosion and/or oxidation layers or products are then removed. Optionally, cracks in the component 120, 130 are also repaired. The component 120, 130 is then recoated and the component 120, 130 is used again.
The blade 120, 130 may be designed to be a hollow or solid. If the blade 120, 130 is intended to be cooled, it will be hollow and optionally also comprise film cooling holes 418 (indicated by dashes).
| Number | Date | Country | Kind |
|---|---|---|---|
| 09000800.4 | Jan 2009 | EP | regional |
This application is the US National Stage of International Application No. PCT/EP2010/050121, filed Jan. 8, 2010 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 09000800 EP filed Jan. 21, 2009. All of the applications are incorporated by reference herein in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/050121 | 1/8/2010 | WO | 00 | 7/20/2011 |
