EP1082216B1 - Product with an anticorrosion protective layer and a method for producing an anticorrosion protective layer - Google Patents

Description

The invention relates to a product with a metallic Base body and a protective layer thereon for Protection of the base body against corrosion, especially if the product is exposed to a hot, aggressive gas. The protective layer has an alloy of the MCrAlY type, where M is one or more elements from the group Iron, cobalt or nickel stands for Cr for chrome, Al for aluminum and Y for yttrium and / or an element from the group including scandium and the rare earths. The invention relates also a gas turbine blade with a protective layer and a method for producing a protective layer to protect a product against corrosion.

EP 0 486 489 B1 describes a corrosion-resistant protective coating for medium and high temperatures up to approx 1050 ° C for a gas turbine part made of a nickel base or Cobalt-based alloy specified. The protective coating shows in weight% 25 to 40% nickel, 28 - 30% chromium, 7 - 9% aluminum, 1 - 2% silicon and 0.3 to 1% at least one reactive Element of the rare earth, at least 5% cobalt as well optionally 0 to 15% of at least one of the elements from the Group consisting of rhenium, platinum, palladium, zircon, manganese, Tungsten, titanium, molybdenum, niobium, iron, hafnium, tantalum, on. In the specified specific embodiments, the Protective coating only the elements nickel, chrome, aluminum, Silicon, yttrium and additionally rhenium in one area from 1 to 15% and a remainder made of cobalt. Through the Adding the rhenium shows the corrosion properties improved.

In U.S. Patent 4,321,310 and U.S. Patent 4,321,311 and to the latter corresponding EP 0 042 872 B1 is one Gas turbine component described that a base body a nickel-based superalloy (MAR-M 200). On the base material is a layer of an MCrAlY alloy, in particular a NiCoCrAlY alloy with 18% chromium, 23% cobalt, 12.5% aluminum, 0.3% yttrium and a remainder Nickel applied. This layer made of the MCrAlY alloy has a polished surface according to US Pat. No. 4,321,310, to which an aluminum oxide layer is applied. An aluminum oxide layer also show the other two patents mentioned on. There is a ceramic on this aluminum oxide layer Thermal insulation layer applied, which is a stem-shaped Has structure.

Protective layers are also used in US Pat. No. 4,585,481 Protection of a metallic super alloy alloy substrate against high temperature oxidation and corrosion. For the protective layers are used in MCrAlY alloys. 5 to 40% chromium, 8 to 35% aluminum, 0.1 to 2% of an oxygen-active element from group IIIB of the periodic table including the lanthanides and actinides as well Mixtures thereof, 0.1 to 7% silicon, 0.1 to 3% hafnium and a radical comprising nickel and / or cobalt. The corresponding protective layers made of MCrAlY alloy according to US Pat. No. 4,585,481 by means of a plasma spraying process upset.

German laid-open specification DE 196 09 690 A1 specifies a turbine blade with a corrosion-resistant MCrAlY protective layer, in which the surface layer of the MCrAlY protective layer consists of a single-phase alloy over a large area down to a depth of 5 to 50 μm, uniformly over the entire surface layer, the single-phase alloy being produced by remelting with a pulsed electron beam. By briefly melting and rapidly cooling the protective layer so that there is no time for phase separation, the single-phase structure is achieved, which leads to the formation of uniform, uninterrupted oxide cover layers made of Al ₂ O ₃ . Compared to cover layers made of aluminum oxide with an interrupted structure, there is less tendency to spallation (flaking). In the case of cover layers with an interrupted structure with partial flaking, such damage to the oxide cover layer can be cured by immigration of aluminum from the protective layer. However, this can lead to a depletion of aluminum in the MCrAlY protective layer. By remelting with a pulsed electron beam, a manufacturing-related micro-roughness of the surface is eliminated by the process of the surface treatment and thus a heat exchange between a hot gas and the surface of the protective layer is reduced, which would allow a higher gas temperature for a gas turbine.

WO 81/01983 A1 describes a method for producing a metallic component, which has a ceramic thermal barrier coating contains, specified. This is based on a substrate a super alloy with a clean surface a thin one Layer of an McrAlY alloy applied, this layer polished, an aluminum oxide layer is applied thereon and on the aluminum oxide layer by means of a columnar ceramic layer Gas deposition (vapor deposition) produced.

EP 0 846 788 A1 relates to a product, in particular a product Gas turbine component, with a substrate on which one Protective layer made of and of an MCrAlY type alloy a ceramic thermal barrier coating is arranged. The substrate is a nickel-based superalloy that has chrome. A outer layer of the substrate is enriched with chromium, which diffuses into the substrate through a diffusion process is. The chromium has diffused into the substrate and forms a matrix that contains chromium dissolved in the nickel the gamma phase. The chromium is diffused in after the so-called "chroming" process.

EP 0 718 420 A1 describes a method for applying a Thermal insulation layer described on a component made of a super alloy. The thermal insulation layer is made of different Layers built up. The super alloy product immediately borders a layer of a platinum group metal on. This layer of the platinum group metal consists of an outer layer and an inner layer, the outer layer being the metal of the platinum group in the Gamma phase. On the outer part of the layer the metal of the platinum group is made of aluminum Coating arranged. There is a thin oxide layer on top and then a ceramic coating is placed on top of it.

From US-PS 4,321,310 and US-PS 4,321,311 are each Coating systems for a component of a turbine known in which a protective layer on the component an MCrAlY alloy is applied to which a Aluminum oxide layer as an adhesion promoter layer or Connection layer connects, and on the one ceramic Thermal insulation layer is applied. The two documents deal with this coating system underlying problem of connecting the thermal insulation layer to the MCrAlY protective layer via the aluminum oxide bonding layer. To improve the connection is according to U.S. Patent 4,321,310 provided the surface of the Polish aluminum oxide bonding layer. According to the US PS 4,321,311 will be a new one for an improved connection Microstructure of the ceramic thermal barrier coating proposed.

The object of the invention is to provide a product with a metallic Basic body and one attached to it Coating system consisting of a protective layer, one Connection layer and a heat insulation layer as well as a Process for producing such a coating system specify where a good connection of the thermal insulation layer is guaranteed.

According to the invention on a product with a metallic Basic body directed task solved in that on the body is a protective layer made of an MCrAlY alloy is applied, with a thin bonding layer Aluminum oxide and a thermal insulation layer applied thereon is, wherein the protective layer is an inner layer of a first MCrAlY alloy and an outer layer of one second MCrAlY alloy, which is predominantly in the γ phase is present, and the aluminum oxide predominantly in the α phase is present. Under an alloy of the MCrAlY type is understood to be an alloy that contains a proportion of chromium Aluminum and a reactive element such as yttrium and / or comprise at least one equivalent metal from the group Scandium and rare earth elements.

In addition or as an alternative to yttrium, other elements can be used Alloy component, such as rhenium, silicon, Hafnium, tantalum, zircon, tungsten, magnesium or niobium. In particular, a proportion of rhenium can lead to an improvement corrosion resistance. The rest contains the MCrAlY alloy one or more elements of the group Iron, cobalt and nickel, which is symbolically abbreviated to M. is.

Such an MCrAlY alloy is preferably used as Corrosion protection layer on metallic components, in particular with a base body made of a super alloy (Nickel or cobalt super alloy, possibly also iron super alloy), which is an elevated temperature and is exposed to a hot, aggressive gas. The crucial one There is an advantage of the MCrAlY alloy specified here in that they are very good as an adhesive layer for safe and permanent connection of the thermal insulation layer. In order to a coating system is produced, which both is corrosion and oxidation inhibiting and use of the product at a high temperature, for example over 1,000 ° C.

The outer layer, which has a MCrAlY alloy, which is predominantly in the γ phase takes place at an oxidation of the outer layer a growth of an aluminum oxide (thermally grown oxide) instead, which in the Areas of the γ phase of the MCrAlY alloy in the α modification is present. Already in the early stages of growing Aluminum oxide layer, the aluminum oxide is therefore predominantly in the stable α-modification. This has the advantage that compared to one growing up first in the  phase Aluminum oxide, the aluminum oxide layer with greater density, lower oxidation speed and smoother structure grows up so that a longer adhesion of the aluminum oxide layer is guaranteed on the outer layer. The invention is based on the knowledge that on a MCrAlY layer surface partial in the initial state of the oxidation or completely a  phase of the aluminum oxide is formed there, where the MCrAlY alloy is in the β phase. That in the -phase growing aluminum oxide has a low density, a high rate of oxidation and a pointed structure on, so that, although later a certain layer thickness sets the stable α-modification, a failure, i.e. chipping that can occur on the alumina layer. It is therefore particularly favorable if the MCrAlY alloy in the outer layer almost completely single-phase in the γ phase is present. This also ensures a good connection from Thermal insulation layers, in particular by means of an electron beam PVD process applied ceramic layers to one Adhesion promoter layer made of an MCrAlY alloy. The Link to the one that is essentially in the γ phase MCrAlY alloy is due to the thin aluminum oxide layer that forms much better in the stable α-modification than the connection to a MCrAlY alloy, the areas with the β phase, and was mechanically smoothed. This is due to the fact that the mechanically smoothed, predominantly MCrAlY alloy present in the β phase into one Growing a significantly thicker aluminum oxide layer in the  phase leads, due to the greater thickness and Layer growth of this aluminum oxide layer after just one chipping of the aluminum oxide layer for a shorter period of time takes place.

The second MCrAlY alloy preferably has the same chemical composition like the first MCrAlY alloy, depending on the properties of the individual alloy components also differences in a few percent by weight or a few tenths of a percent by weight of each, corresponding alloy components of the first MCrAlY alloy and the second MCrAlY alloy are present can. It is also possible that the second MCrAlY alloy additional or alternative alloying elements of the first MCrAlY alloy.

The outer layer is preferably on average between 5 microns and 50 µm thick, especially less than 20 µm. The entire middle Layer thickness of the protective layer is preferably between 100 µm and 200 µm,

Preferably, the first MCrAlY alloy and / or the second MCrAlY alloy the following alloy components (Figures in percent by weight) on: 15 to 35% chromium; 7 to 18 % Aluminum; 0.3 to 2% yttrium and / or at least one equivalent Element from the group comprising Scandium and the Rare earth elements and optionally 0 to 20% rhenium as well as other optional alloy elements such as hafnium, silicon, Tantalum, zircon, tungsten, magnesium and niobium. The amount rhenium is preferably between 1% and 20%, in particular between 5% to 11%.

A thin bonding layer consisting essentially of aluminum oxide (Al ₂ O ₃ ), which is present in the α phase, is preferably bonded to the outer layer. The connection layer preferably has a thickness between 0.3 μm and 0.6 μm at the beginning of an oxidation process. Due to a high proportion of aluminum oxide in the α-phase, preferably almost exclusively of aluminum oxide in the α-phase, the bonding layer grows with an oxidation of the MCrAlY alloy in the outer layer with a significantly lower growth rate than with a high proportion of aluminum oxide in the  phase. A connection layer which has almost exclusively aluminum oxide from the start of oxidation in the α phase is particularly advantageous, since this results in a uniform, homogeneous, low growth of the connection layer.

The thermal insulation layer applied to the connection layer preferably has a columnar microstructure, where the axis direction of the in the columnar microstructure existing crystallites essentially perpendicular to the surface of the basic body is. The thermal barrier coating preferably has a thickness of between 150 and 300 µm, preferably about 200 µm. The columnar, stem-shaped crystallites preferably have an average diameter of less than 5 µm, in particular less than 2.5µm. The thermal barrier coating preferably has a ceramic, which in particular with yttrium oxide is partially stabilized zirconium oxide. Depending on the requirements of the The product can also comprise other thermal insulation layers tertiary oxides, spinels or mullites are used.

The product is preferably a component of a gas turbine, in particular a gas turbine blade, a moving blade or a vane. With a protective layer of the above Kind as well as one over a connection layer Alumina-bonded thermal barrier coating is preferred Gas turbine blades of the first two rows of guide vanes and the first row of blades immediately downstream of one Combustion chamber of a gas turbine coated.

The outer layer of the protective layer is preferably remelted the inner layer is produced in the area of its surface, i.e. an area of the inner layer is remelted. This remelting is preferably done by electron beams or ion beams carried out, which rapidly melt without a significant change in chemical Composition of the MCrAlY alloy in the outer layer and cause the inner layer. By melting the free, i.e. untreated surface of the MCrAlY alloy of the inner layer by electron beams, ion beams or the like it is possible in the upper fringes of some Micrometers an essentially pure, temperature-stable γ phase to generate, which forms the outer layer. This γ phase causes, as already stated above, that immediately during the formation of an oxide layer on the Surface of the outer layer is a stable, dense and thin α-aluminum oxide layer, the connection layer, forms. The oxide formed by oxidation, mainly aluminum oxide, is called thermally grown oxide (thermally grown oxide, TGO). The formation of this oxide, the connection layer, can both before applying the thermal barrier coating as well as during and after the application of the thermal barrier coating respectively. The thermal barrier coating is preferred here applied by vapor deposition. Because of the low Growth rate and homogeneous structure of the thermal grown Oxides (TGO) are the tensions in the area of thermal grown oxide, the bonding layer, during a Use of the product at a high temperature in an oxidizing and corrosive environment, especially in Flow around a hot aggressive gas, reduced. Hereby the service life of thermal insulation layers is increased over the connection layer and the protective layer to the Base bodies are connected because the connection layer has flaked off due to the low growth of the thermally grown Oxide takes place at a later date.

It is also possible to make the outer layer from a liquid Phase, in particular galvanically, on a previously apply the inner layer made of a MCrAlY alloy. The inner layer can be suitably and If necessary, also by separating from a liquid phase to be applied to the base body. The second MCrAlY alloy of the outer layer has the Composition of a γ phase. The first MCrAlY alloy can be sprayed on conventionally.

The on a process of making a protective layer directed a metallic base body of a product The object is achieved in that an inner layer is applied with a first MCrAlY alloy and this inner layer in the area of its free surface like this is remelted that an outer layer is formed in which the MCrAlY alloy is essentially in the γ phase. Alternatively, you can spray on the conventionally or galvanically deposited first MCrAlY alloy, which forms the inner layer, a second MCrAlY alloy from a liquid phase, especially galvanic, are deposited, the second MCrAlY alloy being used here the outer layer forms and essentially in the γ phase is present.

The one on a gas turbine blade with a metallic one According to the invention, the basic body-directed task is achieved solved that a protective layer on the metallic base body (Adhesive layer) tied to protect against corrosion is made of an inner layer attached to the base body a first adhesive alloy and one bonded to the inner layer Has an outer layer with a second adhesive alloy, the second adhesive alloy predominantly, preferably almost completely, in the γ phase and to the Outer layer a thin bonding layer with aluminum oxide predominantly connected to the α phase and attached to it a thermal insulation layer is connected. The first adhesive alloy and the second adhesive alloy are preferably each one (same) Alloy of the type MCrAlY, modified depending on the requirement by adding one alloy element or several alloy elements, especially rhenium.

The base body preferably consists of a nickel-based or cobalt-based superalloy, possibly also an iron-based superalloy.

Based on the embodiment shown in the drawing the product, especially the gas turbine blade, with the protective layer, the connection layer and the Thermal insulation layer explained in more detail.

FIG 1

eine perspektivische Darstellung einer Gasturbinenlaufschaufel und

FIG 2

einen Ausschnitt eines Schnittes senkrecht zur Oberfläche der Gasturbinenlaufschaufel.

In a partially schematic and not to scale representation,

FIG. 1

a perspective view of a gas turbine blade and

FIG 2

a section of a section perpendicular to the surface of the gas turbine blade.

The product 1 shown in Figure 1, a gas turbine blade 1, has a metallic base body 2 a nickel-based or cobalt-based superalloy. On 2, the base body 2 serves as an adhesive layer Protective layer 3, 4 from an inner layer 3, the immediate is connected to the base body 2, and one to the Inner layer 3 attached outer layer 4 applied. The Inner layer 3 has a first alloy of the MCrAlY type and the outer layer a second alloy also of the type MCrAlY, the second alloy being essentially, preferably almost completely, in the γ phase. On this protective layer 3, 4 serving as an adhesive layer is a Thermal insulation layer 6 tied, which preferably consists of a stem-shaped ceramics, for example partially stabilized with yttrium oxide Zirconium oxide exists. Between the protective layer 3, 4 and the heat insulation layer 6 is a connection layer 5 arranged. This connection layer 5 is preferably made from a thermally grown oxide, in particular Alumina. This thermally grown oxide is already there at the beginning of the oxidation in the stable α phase before the immediate formation of the α phase at the beginning of the oxidation is caused by the γ phase in the outer layer 4. Compared to a thermally grown oxide, which is predominantly Growing up in the β phase shows that in the stable α phase growing oxide a significantly smaller layer thickness on. This not only ensures a good connection of the thermal insulation layer to the protective layer 3, 4, but also a significant extension of the service life of the thermal barrier coating 6 in that a detachment of the connection layer 5 due to a high growth rate, as in an oxide the β phase would be avoided.

On the outer surface 8 of the thermal insulation layer 6 flows in one use of the gas turbine blade 1 in one illustrated gas turbine passing a hot aggressive gas 9, which by the protective layer 3, 4 of the connection layer 5 and the thermal insulation layer 6 layer system effective from the metallic base body 2 physically and is chemically kept away. This is particularly beneficial in the case of a gas turbine blade 1 and in the case of a gas turbine guide blade, which the directly from a not shown Combustion chamber outflowing hot gas of up to over 1300 ° C is exposed.

Claims (12)

1. Product (1), in particular a component of a gas turbine, having a metallic basic body (2), to which a protective layer (3, 4) comprising an MCrAlY alloy is applied, to which layer a thin bonding layer (5) comprising aluminium oxide is applied, and then a thermal barrier coating (6) is applied to the bonding layer, M representing Fe, Ni, Co or a mixture thereof, and Y representing yttrium and/or at least one equivalent element selected from the group consisting of Scandium and the rare earths, characterized in that the protective layer (3, 4) has an inner layer (3) of a first MCrAlY alloy and an outer layer (4) of a second MCrAlY alloy, which is predominantly in the γ-phase, and in that the aluminium oxide is predominantly in the α-phase.
2. Product according to Claim 1, characterized in that the second MCrAlY alloy has the same chemical composition as the first MCrAlY alloy.
3. Product according to Claim 1 or 2, characterized in that the outer layer (4) is between 5 µm and 50 µm, in particular between 5 µm and 20 µm, thick.
4. Product according to one of the preceding claims, characterized in that the first MCrAlY alloy and/or the second MCrAlY alloy contain(s) as alloying constituents (data in per cent by weight):

   15 to 35% chromium;

   7 to 18% aluminium;

   0.3 to 2% yttrium and/or at least one equivalent element metal selected from the group consisting of scandium and the rare earths; and

   0 to 20% rhenium.
5. Product according to Claim 4, characterized in that the rhenium content is between 1% and 20%, in particular 5% and 11%.
6. Product according to one of the preceding claims, characterized in that the bonding layer (5) is between 0.3 µm and 0.6 µm thick at the beginning of an oxidation process.
7. Product according to one of the preceding claims, characterized in that the thermal barrier coating (6) has a columnar microstructure, the axial direction of the crystallites being substantially perpendicular to the surface of the basic body (1).
8. Product according to one of the preceding claims, characterized in that the thermal barrier coating (6) contains a ceramic, in particular zirconium oxide (ZrO₂), which is partially stabilized with yttrium oxide (Y₂O₃).
9. Product according to one of the preceding claims, characterized in that the outer layer (4) is produced by re-melting of the inner layer (3) in the region of its free surface, in particular by means of electron beams or ion beams.
10. Product (1) according to one of Claims 1 to 11, characterized in that the outer layer (4) is deposited from a liquid phase, in particular by electrodeposition.
11. Process for producing a coating system comprising a protective layer (3, 4), a bonding layer (5) and a thermal barrier coating (6) on a metallic basic body (2) of a product (1), characterized in that an inner layer (3) having an MCrAlY alloy is applied to the basic body (2) as protective layer (3, 4), and the inner layer (3) is re-melted in the region of its free surface, in such a way that an outer layer (4) is formed, in which the MCrAlY alloy is substantially in the γ-phase, in that the bonding layer (5) containing aluminium oxide predominantly in the α-phase is formed on the outer layer (4), and in that the thermal barrier coating (6) is applied to the bonding layer (5).
12. Process for producing a coating system comprising a protective layer (3, 4), a bonding layer (5) and a thermal barrier coating (6) on a metallic basic body (2) of a product (1), characterized in that an inner layer (3) having a first MCrAlY alloy is applied to the basic body (2) as protective layer (3, 4), and a second MCrAlY alloy is deposited on the inner layer (3) from a liquid phase, in particular by electrodeposition, this second MCrAlY alloy forming an outer layer (4) and being substantially in the γ-phase, in that the bonding layer (5) containing aluminium oxide predominantly in the α-phase is formed on the outer layer (4), and in that the thermal barrier coating (6) is applied to the bonding layer (5).

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