EP1790746A1 - Alloy, protective layer and component - Google Patents

Abstract

A cobalt alloy comprises (wt.%): nickel (9-11); chromium (22-24); aluminum (11-13); rhenium (1.5-3.5); yttrium, scandium or rare earth metal (0.5-0.7); and cobalt (to 100). Independent claims are also included for the following: (1) a protective layer for protecting a part against corrosion and/or oxidation, especially at high temperatures, comprising an alloy as above; (2) a part, especially of a gas turbine, with a protective layer as above.

Description

The invention relates to an alloy according to claim 1, a protective layer for protecting a component against corrosion and / or oxidation at high temperatures according to claim 9 and a component according to claim 10.

Protective layers for metallic components intended to increase their corrosion resistance and / or oxidation resistance are known in the art in large numbers. Most of these protective layers are known under the collective name MCrAlY, where M represents at least one of the elements selected from the group consisting of iron, cobalt and nickel and further essential components are chromium, aluminum and yttrium.

Typical coatings of this kind are from the U.S. Patents 4,005,989 and 4,034,142 known.

Efforts to increase inlet temperatures in both stationary gas turbines and aircraft engines are of great importance in the gas turbine art because inlet temperatures are important determinants of thermodynamic efficiencies achievable with gas turbines. Due to the use of specially developed alloys as base materials for components that are subject to high thermal loads such as guide vanes and rotor blades, in particular through the use of monocrystalline superalloys, inlet temperatures of well over 1000 ° C are possible. Meanwhile, the prior art allows inlet temperatures of 950 ° C and more in stationary gas turbines and 1100 ° C and more in gas turbines of aircraft engines.

Examples of the construction of a turbine blade with a monocrystalline substrate, which in turn can be complex, emerge from the WO 91/01433 A1 ,

While the physical strength of the now developed base materials for the highly loaded components with regard to possible further increases in the inlet temperatures is largely unproblematic, must be used to achieve a sufficient resistance to oxidation and corrosion on protective layers. In addition to the sufficient chemical resistance of a protective layer under the attacks that are expected of flue gases at temperatures in the order of 1000 ° C, a protective layer must also have sufficient mechanical properties, not least in view of the mechanical interaction between the protective layer and the base material , to have. In particular, the protective layer must be sufficiently ductile in order to be able to follow any deformations of the base material and not to break, since in this way points of attack for oxidation and corrosion would be created. Here, the problem typically arises that increasing the proportions of elements such as aluminum and chromium, which can improve the resistance of a protective layer against oxidation and corrosion, leads to a deterioration of the ductility of the protective layer, so that mechanical failure, in particular formation of cracks, is expected in a gas turbine usually occurring mechanical stress.

Accordingly, it is an object of the present invention to provide an alloy and a protective layer which has good high-temperature resistance in corrosion and oxidation, has good long-term stability and, in addition, a mechanical stress to be expected particularly in a gas turbine at a high temperature well adjusted.

The object is achieved by an alloy according to claim 1 and a protective layer according to claim 9.

Another object of the invention is to provide a component which has increased protection against corrosion and oxidation.

The object is also achieved by a component according to claim 10, in particular a component of a gas turbine or steam turbine, which has a protective layer of the type described above for protection against corrosion and oxidation at high temperatures.

In the dependent claims further advantageous measures are listed, which can be arbitrarily linked together to achieve further advantages.

The invention is u. a. based on the knowledge that the protective layer in the layer and in the transition region between protective layer and base material brittle rhenium precipitates shows. During operation, these brittle phases, which form increasingly with time and temperature, lead to pronounced longitudinal cracks in the layer as well as in the interface layer base material with subsequent detachment of the layer. In addition, the brittleness of the rhenium precipitates increases as a result of the interaction with carbon, which can diffuse into the layer from the base material or diffuse into the layer during a heat treatment in the furnace through the surface. Oxidation of the rhenium phases further enhances the driving force for crack formation.

Also important is the influence of cobalt as a matrix material, which determines the thermal and mechanical properties.
In particular, in the combustion of contaminated heavy oil, the use of the cobalt-based alloy as a protective layer is advantageous.

The invention will be explained in more detail below.

Figur 1

ein Schichtsystem mit einer Schutzschicht,

Figur 2

Zusammensetzungen von Superlegierungen,

Figur 3

eine Gasturbine,

Figur 4

eine Turbinenschaufel und

Figur 5

eine Brennkammer.

Show it

FIG. 1

a layer system with a protective layer,

FIG. 2

Compositions of superalloys,

FIG. 3

a gas turbine,

FIG. 4

a turbine blade and

FIG. 5

a combustion chamber.

• 22% bis 24% Chrom
• 9% bis 11% Nickel
• 11% bis 13% Aluminium
• 1,5% bis 3,5% Rhenium
• 0,5% bis 0,7% Yttrium und/oder zumindest ein äquivalentes Metall aus der Gruppe umfassend Scandium und die Elemente der Seltenen Erden,

Rest Kobalt sowie herstellungsbedingte Verunreinigungen (CoNiCrAlY).According to the invention, a protective layer 7 (FIG. 1) for protecting a component (FIG. 1) against corrosion and oxidation at a high temperature consists essentially of the following elements (indication of the proportions in wt%):

• 22% to 24% chromium
• 9% to 11% nickel
• 11% to 13% aluminum
• 1.5% to 3.5% rhenium
• 0.5% to 0.7% yttrium and / or at least one equivalent metal from the group comprising scandium and the elements of the rare earths,

Remaining cobalt as well as production-related impurities (CoNiCrAlY).

The beneficial effect of the element rhenium is exploited while preventing the formation of brittle phase. Preferably, the alloy of the protective layer 7 does not comprise silicon.
The alloy may also include ruthenium. In particular, the alloy has no further elements.

It should be noted that the proportions of the individual elements are specially tuned with regard to their effects, which are to be seen in connection with the element rhenium. If the proportions are such that no chromium-rhenium precipitates form, advantageously no brittle phases arise during the use of the protective layer, so that the runtime behavior is improved and prolonged.

This is done not only by a low chromium content, but also, taking into account the influence of aluminum on the phase formation, by accurately measuring the content of aluminum. The small and narrow range of 9wt% to 11wt% nickel surprisingly significantly and disproportionately improves the thermal and mechanical properties of the protective layer 7.

In interaction with the reduction of the brittle phases, which have a negative effect especially under higher mechanical properties, the reduction of the mechanical stresses by the selected nickel content improves the mechanical properties.

The protective layer 7, with good corrosion resistance, has a particularly good resistance to oxidation and is also distinguished by particularly good ductility properties, so that it is particularly qualified for use in a gas turbine with a further increase in the inlet temperature. There is hardly any embrittlement during operation since the layer has hardly any chromium-rhenium precipitates that become brittle during use.

In each case, it is particularly advantageous to determine the proportion of chromium to about 23% by weight, of aluminum to about 12% by weight, of nickel to about 10% by weight and the yttrium content to about 0.6% by weight. Certain fluctuations are due to large industrial production, so that yttrium contents of 0.4wt% to 0.5wt% or 0.7wt% to 0.8wt% are used and also show good properties.

The rhenium content is preferably 2.5wt% to 3.5wt%, especially 3.0wt%. An advantageous rhenium content is also 1.5wt% to 2.0wt%, especially 1.8wt%. Ruthenium can be added in addition or replace the rhenium partially or completely.
Preferably, no ruthenium is used.

An equally important role is played by the trace elements in the powder to be sprayed, which form precipitates and thus embrittle them. The powders are applied for example by plasma spraying (APS, LPPS, VPS, ...). Other methods are also conceivable (PVD, CVD, cold gas spraying).

The thickness of the protective layer 7 on the component 1 is preferably dimensioned to a value between about 100 μm and 300 μm.

The protective layer 7 can be used as an overlay (protective layer is the outer layer or as a bondcoat (protective layer is an intermediate layer).

On this protective layer 7 as a component further layers, in particular ceramic thermal barrier coatings 10 can be applied.

• 0,1% bis 0,15% Kohlenstoff
• 18% bis 22% Chrom
• 18% bis 19% Kobalt
• 0% bis 2% Wolfram
• 0% bis 4% Molybdän
• 0% bis 1,5% Tantal
• 0% bis 1% Niob
• 1% bis 3% Aluminium
• 2% bis 4% Titan
• 0% bis 0,75% Hafnium

wahlweise geringe Anteile von Bor und/oder Zirkon, Rest Nickel.In this component, the protective layer 7 is advantageously applied to a substrate 4 made of a superalloy based on nickel or cobalt.
In particular the following composition is suitable as substrate (data in wt%):

• 0.1% to 0.15% carbon
• 18% to 22% chrome
• 18% to 19% cobalt
• 0% to 2% tungsten
• 0% to 4% molybdenum
• 0% to 1.5% tantalum
• 0% to 1% niobium
• 1% to 3% aluminum
• 2% to 4% titanium
• 0% to 0.75% hafnium

optionally small amounts of boron and / or zirconium, balance nickel.

Compositions of this type are known as casting alloys under the designations GTD222, IN939, IN6203 and Udimet 500.
Further alternatives for the substrate 4 of a component 1 are listed in FIG.

The protective layer 7 is particularly suitable for protecting a component against corrosion and oxidation, while the component is acted upon by a flue gas at a material temperature of about 950 ° C., in aircraft turbines also by about 1100 ° C.

The protective layer 7 according to the invention is thus particularly qualified for protecting a component of a gas turbine 100, in particular a guide blade 120, blade 130 or other component, which is acted upon by hot gas before or in the turbine of the gas turbine.

FIG. 1 shows a layer system 1 as component 1.
The layer system 1 consists of a substrate 4.
The substrate 4 may be metallic and / or ceramic. Particularly in the case of turbine components, such as turbine runners 120 or guide vanes 130 (FIGS. 3, 4), heat shield elements 155 (FIG. 5) and other housing parts of a steam or gas turbine 100 (FIG. 3), the substrate 4 consists of a nickel , cobalt or iron based superalloy. Preferably, nickel-based superalloys are used.

On the substrate 4, the protective layer 7 according to the invention is present.
Preferably, this protective layer 7 is applied by LPPS (low pressure plasma spraying).
This can be used as outer layer (not shown) or intermediate layer (FIG. 1).
In the latter case, a ceramic thermal barrier coating 10 is present on the protective layer 7.

The protective layer 7 can be applied to newly manufactured components and remanufactured components from the refurbishment.
Refurbishment means that after use, components 1 may be separated from layers (thermal barrier coating) and corrosion and oxidation products may be removed, for example by acid treatment (acid stripping). If necessary, cracks still have to be repaired. Thereafter, such a component can be coated again because the substrate 4 is very expensive.

FIG. 3 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.
A generator or a work machine (not shown) is coupled to the rotor 103.

During operation of the gas turbine 100, air 105 is sucked in and compressed by the compressor 105 through the intake housing 104. The compressed air provided at the turbine-side end of the compressor 105 is supplied to the burners 107 where it is mixed with a fuel. The mixture is then burned to form the working fluid 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. 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 can have a directional structure, ie they are monocrystalline (SX structure) or have only longitudinal grains (DS structure).
As the material for the components, in particular for the turbine blade 120, 130 and components of the combustion chamber 110, for example, iron-, nickel- or cobalt-based superalloys are used.
Such superalloys are for example from EP 1 204 776 B1 . EP 1 306 454 . EP 1 319 729 A1 . WO 99/67435 or WO 00/44949 known; These documents are part of the disclosure regarding the chemical composition of the alloys.

The vane 130 has a guide vane foot (not shown here) facing the inner housing 138 of the turbine 108 and a vane head opposite the vane foot. The vane head is the rotor 103 facing and fixed to a mounting ring 140 of the stator 143.

FIG. 4 shows a perspective view of a moving blade 120 or guide blade 130 of a turbomachine that extends along a longitudinal axis 121.

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 consecutively a fastening region 400, a blade platform 403 adjacent thereto and an airfoil 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 designed, for example, as a hammer head. Other designs as Christmas tree or Schwalbenschwanzfuß are possible.
The blade 120, 130 has a leading edge 409 and a trailing edge 412 for a medium flowing past the airfoil 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 for example from EP 1 204 776 B1 . EP 1 306 454 . EP 1 319 729 A1 . WO 99/67435 or WO 00/44949 known; These documents are part of the disclosure regarding the chemical composition of the alloy.

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, for example, by directed solidification from the melt. These are casting methods in which the liquid metallic alloy solidifies into a monocrystalline structure, ie a single-crystal workpiece, or directionally.
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 consists of a single crystal. In these processes, it is necessary to avoid the transition to globulitic (polycrystalline) solidification, since non-directional growth necessarily produces transverse and longitudinal grain boundaries which negate the good properties of the directionally solidified or monocrystalline component.
The term generally refers to directionally solidified microstructures, which means both single crystals that have no grain boundaries or at most small angle grain boundaries, and stem crystal structures that have probably longitudinal grain boundaries but no transverse grain boundaries. These second-mentioned crystalline structures are also known as directionally solidified structures.
Such methods are known from U.S. Patent 6,024,792 and the EP 0 892 090 A1 known; these writings are part of the revelation regarding the solidification process.

Likewise, the blades 120, 130 may have layers 7 according to the invention against corrosion or oxidation.
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).

On the MCrAlX may still be present a thermal barrier coating, which is preferably the outermost layer, and consists for example of ZrO ₂ , Y ₂ O ₃ -ZrO ₂ , ie it is not, partially or completely stabilized by yttria and / or calcium oxide and / or magnesium oxide.
The thermal barrier coating covers the entire MCrAlX layer. By means of suitable coating processes, such as electron beam evaporation (EB-PVD), stalk-shaped grains are produced in the thermal barrier coating.
Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may have porous, micro- or macro-cracked grains for better thermal shock resistance. The heat-insulating layer is therefore preferably more porous than the MCrAlX layer.

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

FIG. 5 shows a combustion chamber 110 of the gas turbine 100. The combustion chamber 110 is designed, for example, as a so-called annular combustion chamber, in which a multiplicity of burners 107 arranged circumferentially about a rotation axis 102 open into a common combustion chamber space 154, which generate flames 156. 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. In order to enable a comparatively long service life even with these, for the materials unfavorable operating parameters, the combustion chamber wall 153 is provided on its side facing the working medium M side with an inner lining formed from heat shield elements 155.

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.

Each heat shield element 155 made of an alloy is equipped on the working medium side with a particularly heat-resistant protective layer (MCrA1X layer and / or ceramic coating) or is made of high-temperature-resistant material (solid ceramic stones).
These protective layers may be similar to the turbine blades.

On the MCrAlX, for example, a ceramic thermal barrier coating may be present and consists for example of ZrO ₂ , Y ₂ O ₃ -ZrO ₂ , ie it is not, partially or completely stabilized by yttria and / or calcium oxide and / or magnesium oxide.
By means of suitable coating processes, such as electron beam evaporation (EB-PVD), stalk-shaped grains are produced in the thermal barrier coating.
Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may have porous, micro- or macro-cracked grains for better thermal shock resistance.

Refurbishment means that turbine blades 120, 130, heat shield elements 155 may need to be deprotected (e.g., by sandblasting) after use. This is followed by removal of the corrosion and / or oxidation layers or products. Optionally, cracks in the turbine blade 120, 130 or the heat shield element 155 are also repaired. This is followed by a re-coating of the turbine blades 120, 130, heat shield elements 155 and a renewed use of the turbine blades 120, 130 or the heat shield elements 155.

Claims (13)

alloy
contains the following elements
(Data in wt%): 9% to 11% nickel (Ni) 22% to 24% chromium (Cr) 11% to 13% aluminum (A1) 1.5% to 3.5% rhenium (Re) 0.5% to 0.7% yttrium (Y) and / or at least one equivalent metal from the group comprising scandium (Sc) and the elements of the rare earths, Balance cobalt (Co). Alloy according to claim 1,
containing (in wt%): 10% nickel. Alloy according to claim 1 or 2,
containing (in wt%): 23% chromium. Alloy according to claim 1, 2 or 3,
containing (in wt%): 12% aluminum. Alloy according to claim 1, 2, 3 or 4,
containing (in wt%): 0.6% yttrium and / or an equivalent metal from the group comprising scandium and the rare earth elements. Alloy according to claim 1, 2, 3, 4 or 5,
containing 2.5wt% to 3.5wt% rhenium,
especially 3wt% rhenium. Alloy according to claim 1, 2, 3, 4 or 5,
containing 1.5wt% to 2wt% rhenium,
especially 1.8wt% rhenium. Alloy according to claim 1,
consisting of cobalt, nickel, chromium, aluminum, rhenium and yttrium. Protective layer for protection of a component (1, 120, 130, 138, 155) against corrosion and / or oxidation,
especially at high temperatures,
which has the composition of the alloy according to one or more of claims 1 to 8. component
in particular a component (1, 120, 130, 138, 155) of a gas turbine (100),
which has a protective layer (7) according to claim 9 for protection against corrosion and oxidation at high temperatures. Component according to claim 10,
in which a thermal barrier coating (10) is applied to the protective layer (7). Component according to claim 10 or 11,
in which a substrate (4) of the component (1, 120, 130, 138, 155) is nickel-based. Component according to claim 10 or 11,
in which a substrate (4) of the component (1, 120, 130, 138, 155) is cobalt-based.

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