WO1997046734A1 - Product with a base structure consisting of a superalloy and an overlay system thereon, and process for the production thereof - Google Patents

Abstract

The invention relates to a product with a base structure consisting of a superalloy and an overlay system thereon to protect the base structure from an aggressive, hot gas. The overlay system has a ceramic heat-insulating layer with an outer surface subjected to the gas, and also contains an intermediate layer which rests on the base structure and has, according to mass proportions, the following composition of chemical elements: 35 - 60 % of rhenium, 10 - 20 % of aluminium, 0 - 10 % of gallium, 0 - 2 % in each case of silicon, hafnium and an active element such as yttrium, the rest comprising impurities resulting from the preparation and chromium. According to the invention, said intermediate layer is also obtained by plasma spraying or vapour deposition.

Description

description

Product with a body made of a superalloy and a layer system thereon and method for its production

The invention relates to a product with a base body consisting of a superalloy and a layer system thereon for protecting the base body against an aggressive hot gas, the layer system having a ceramic thermal insulation layer with an outer surface which can be exposed to the gas.

The invention relates in particular to such a certificate, which is designed as a component for one

Gas turbine, in particular as a rotor blade, guide vane or heat shield, generally as a component which is exposed to a hot flue gas during its regular operation, which can be both oxidative and corrosive.

In particular, reference is made to a product for a modern stationary gas turbine in which the flue gas can reach an average temperature of up to 1400 ° C. and in which it must be expected that a component of the type just described, despite any cooling provided exposed to a temperature up to 1000 ° C and above.

A product as described at the outset is apparent from US Pat. No. 4,321,310, US Pat. No. 4,321,311, US Pat. No. 4,055,705 and US Pat. No. 5,262,245. The products described in these patents can be viewed as alternative configurations of a basic form of a corresponding product. In any case, the product has a base made of a superalloy and an outer surface which is formed by a ceramic thermal barrier coating. Most are presented between the ceramic thermal barrier coating and the base body Embodiments a metallic adhesive layer. This adhesive layer can have a composition of the MCrAlY type, ie a composition in the manner of an alloy which has iron, cobalt and / or nickel as the basis (for which the "M" stands) and chromium, aluminum and yttrium or as further essential constituents has an element equivalent to yttrium, such as scandium or a rare earth element. The MCrAlY composition is well known in the art; it is also generally known that this composition can be further developed by adding further elements. As such further elements, silicon, hafnium, tantalum, titanium, platinum and rhenium are representative of many. Known alternative compositions for the adhesive layer are intermetallic compounds made of nickel and aluminum or platinum and aluminum.

WO 89/07159 AI, EP 0 486 489 B1 and EP 0 412 397 AI each show a layer system for protecting a base body made of a superalloy against an aggressive hot gas, which layer system is primarily metallic and one Contains a layer of an alloy of the type MCrAlY. Particularly favorable compositions for alloys of the MCrAlY type are also described, which are characterized by an additional rhenium content.

The Swiss patent specification CH 660 200 A5 describes a method for applying a high-temperature corrosion protection layer to a component consisting of a superalloy or a high-melting metal in the base body. The component is a turbine blade, the high-temperature corrosion protection layer consisting of a metallic alloy, in particular an iron-cobalt or nickel-based alloy. A coherent intermediate layer serving as a diffusion barrier for the elements forming protective oxide is placed on the metallic base body, in particular made of a nickel-based superalloy applied from a platinum metal or rhenium. The actual metallic high-temperature corrosion protection layer is applied to this intermediate layer. The intermediate layer has a thickness between 5 μm and 100 μm.

With regard to the use of rhenium in a layer system, an article "Thermal Mechanical Fatigue Behavior of Advanced Overlay Coatings" by N. Czech, F. Schmitz and W. Stamm, Materials and Manufacturing Processes HL 5 (1995) is also important. 1021. This article provides particular information regarding the effect of rhenium in a corresponding protective layer.

The protective layers of the MCrAlY type listed in the documents cited above, each with an addition of rhenium, have also been proposed for use as adhesive layers for ceramic thermal insulation layers. In this context it is particularly important that the rhenium slows down the oxidation of the adhesive layer. This results in a comparatively small growth of an oxide layer formed from components of the adhesive layer, in particular aluminum, which forms between the adhesive layer and the actual ceramic thermal insulation layer and tends to become mechanically unstable with increasing thickness; In particular, the ceramic thermal insulation layer may flake off and ultimately the entire layer system may fail.

Since the growth rate of the oxide layer between a metallic adhesive layer and a ceramic thermal barrier layer represents a factor determining the service life, an alloy with a low oxidation rate is preferred for the adhesive layer. As already mentioned, this results in the preference of the corresponding alloys containing rhenium. The ceramic thermal barrier coating is also the subject of further development with regard to its chemical composition and the structure and type of its connection to the adhesive layer. At present, thermal insulation is mainly used layer of a zirconium oxide partially or completely stabilized with yttrium oxide. Such a thermal barrier coating is produced by atmospheric plasma spraying, in which the relevant properties of the thermal barrier coating are adjusted by setting a defined porosity and a layer-like to micro-segmented structure, and by predominantly mechanical interlocking on a correspondingly porous adhesive layer. Alternatively, a thermal barrier coating is produced by a vapor deposition process, in which the thermal barrier coating has an elongation-tolerant columnar crystalline structure and a mainly chemical bond to the correspondingly smooth adhesive layer to be provided. The chemical bonding of the thermal insulation layer to the adhesive layer takes place via a thin oxide layer formed between these layers. This is, if appropriate by means of appropriately formed intermediate connections, firmly connected both to the thermal insulation layer and to the adhesive layer.

A layer system usually fails because, in addition to the oxidation of the adhesive layer, there are also thermal-mechanical alternating stresses, which can cause cracks to spread in the thermal insulation layer. In the case of a sprayed thermal insulation layer, this ultimately leads to flaking above the boundary between the ceramic and the metal, in the case of a thermal insulation layer separated from the vapor phase to flaking in the oxide layer formed between the actual thermal insulation layer and the adhesive layer. Following the flaking off of the thermal barrier coating, there is an increase in temperature on the surface of the adhesive layer, which in turn leads to rapid oxidation and the resulting rapid degradation of the adhesive layer.

It has already been explained that the addition of rhenium to an MCrAlY type adhesive layer is of considerable advantage. However, the addition of rhenium to such an adhesive layer is only possible to a limited extent, since also the addition of rhenium can lead to some embrittlement. This is also evident from the article cited.

Accordingly, the invention is based on the object of specifying a product of the type specified in the introduction, in which the use of an advantage which can result from the use of rhenium takes place in an alternative manner.

To achieve this object, a product is provided with a base body consisting of a superalloy and a layer system thereon for protecting the base body against an aggressive hot gas, the layer system having a ceramic thermal insulation layer with an outer surface which can be exposed to the gas, and wherein the thermal barrier coating rests on an intermediate layer which rests on the base body and has the following composition of chemical elements by mass fraction: rhenium 35% to 60%, aluminum 10% to 20

Gallium 0% to 10%, silicon 0% to 2%, hafnium 0% to 2%, an active element from the group containing yttrium, scandium and the rare earth elements:

0% to 2%; manufacturing-related impurities; and chrome as the rest.

Accordingly, according to the invention a special intermediate layer is provided which contains at least a substantial proportion of the rhenium content desired in the layer system. By providing this intermediate layer, the rhenium can be applied precisely where it is of particular interest because of its function as a means of reducing oxidation, namely at a boundary between the ceramic thermal barrier coating and the base body or on lying metallic adhesive layer. Since the intermediate layer can be applied thinly, its mechanical properties, in particular the question of whether it is more ductile or brittle, only play a marginal role. The intermediate layer is also comparatively rich in aluminum, optionally also gallium and / or silicon, and thus provides starting elements for forming an oxidic layer between the metallic part of the layer system and the ceramic thermal insulation layer. The material of the adhesive layer is preferably supplemented by an active element such as hafnium, yttrium or an element equivalent thereto such as scandium or the rare earth elements, since these elements make a desirable contribution to anchoring the oxidic layer mentioned to the intermediate layer.

It goes without saying that the presence of production-related impurities of the usual type and in normal proportions must always be expected; In this respect, all relevant specialist knowledge must be observed for the production of the alloy for the intermediate layer.

A preferred composition for the intermediate layer has the following composition in mass proportions: rhenium 47%; Aluminum 15%;

Yttrium 0.5%; manufacturing-related impurities; such as

Chrome as the rest.

The intermediate layer of the product preferably lies on a metallic adhesive layer which consists of an alloy of the MCrAlY type, where M stands for at least one metal from the group comprising iron, cobalt and nickel as the basis of the alloy. This alloy also preferably contains additional rhenium, preferably with a mass fraction between 1% and 15%. The intermediate layer preferably has a thickness of less than 10 μm, in particular a thickness of approximately 5 μm. This ensures that the mechanical properties of the intermediate layer, in particular any brittleness, cannot adversely affect the entire layer system.

In the product, the superalloy forming the base body is furthermore preferably a nickel-based or cobalt-based superalloy, examples of which are the generally known nickel-based superalloy IN738LC and the cobalt-based superalloy MAR-M-509 .

The intermediate layer of the product is preferably a dispersion of a phase consisting essentially of an intermetallic compound of rhenium and chromium in a metallic matrix. The intermetallic compound has in particular the approximate composition Cr ₃ Re, for which in particular chromium and rhenium with approximately equal proportions by weight must be present. The major part of the aluminum and any other elements which may be present is mainly present in the metallic matrix and is available from this matrix to form the oxide layer between the intermediate layer and the thermal insulation layer.

The heat insulation layer of the product preferably consists essentially of an at least partially stabilized zirconium oxide, which is stabilized in particular by the addition of yttrium oxide. Zirconium oxide is characterized in that its relevant mechanical properties are relatively similar to the corresponding properties of the metals and alloys used. The stabilization of the zirconium oxide serves to prevent or at least slow down a phase transition in the structure of the zirconium oxide, which could occur in pure zirconium oxide under appropriate thermal stress. The product is preferably designed as a component for a gas turbine, in particular as a rotor blade, guide blade or heat shield. In this context, the product is suitable for use in a gas turbine. This is particularly so because it can withstand a temperature of up to 1000 ° C. and beyond when exposed to an oxidizing and corrosive flue gas, as is usually formed in a stationary gas turbine.

In order to achieve the object with regard to a method, a method for producing a product with a base body consisting of a superalloy and a layer system thereon for protecting the base body against an aggressive hot gas is provided, an intermediate layer being used to form the layer system is applied to the base body and a ceramic thermal insulation layer is applied to the intermediate layer, the intermediate layer having the following composition of chemical elements according to mass proportions: rhenium 35% to 60%, aluminum 10% to 20%, gallium 0% to 10%, silicon 0% to 2 hafnium 0% to 2%, an active element from the group containing yttrium, scandium and the rare earth elements:

0% to 2%; manufacturing-related impurities; and chromium as the rest; and wherein the intermediate layer is applied by plasma spraying, in particular vacuum plasma spraying or vapor deposition.

In any case, a metallic adhesive layer is preferably first applied to the base body and then the intermediate layer is formed on the adhesive layer. Two exemplary embodiments of the invention which are regarded as particularly preferred are explained below.

1. A gas turbine component, in particular a rotor blade, a guide blade or a heat shield element, with a base body consisting of the super alloy IN738LC is provided with a metallic adhesive layer which has a composition as described in the article cited by N. Czech, F. Schmitz and W. Stamm can be seen and which in particular requires a mass fraction of rhenium in an alloy based on nickel. This adhesive layer is applied by means of vacuum plasma spraying and compacted by blasting with glass beads or the like. There is no further surface treatment, especially smoothing.

An intermediate layer of the following composition, by mass fraction, is applied to this adhesive layer: rhenium 47%; Aluminum 15%;

Yttrium 0.5%; manufacturing-related impurities; such as

Chrome as the rest.

The intermediate layer is also applied by vacuum plasma spraying, to a thickness of approximately 5 μm.

A ceramic thermal barrier coating made from partially stabilized zirconium oxide is then applied to the intermediate layer, by atmospheric plasma spraying. The

The ceramic thermal barrier coating is anchored to the intermediate layer and the adhesive layer partly by chemical bonding as already described, partly by mechanical bonding to the surface structures of the intermediate layer which remain due to the production. 2nd

An adhesive layer corresponding to the adhesive layer from the present example is applied to a gas turbine component with a base body consisting of the cobalt-based superalloy MAR-M-509 and polished after the application and blasting.

The intermediate layer is applied to the adhesive layer prepared in this way as described in the previous example, and a ceramic thermal insulation layer made of partially stabilized zirconium oxide is applied to the intermediate layer by physical vapor deposition with electron beam evaporation (EB-PVD). Before or during the application of the thermal insulation layer, care must be taken by setting suitable conditions to ensure that an oxide layer forms on the intermediate layer, to which the thermal insulation layer can adhere by chemical bonding. This heat-insulating layer has a columnar crystalline structure and is accordingly very tolerant of thermal expansion, since the columnar-shaped crystallites of the heat-insulating layer can move relatively freely against one another when the metallic structure expands from the base body and the metallic part of the layer system lying thereon. In terms of function, such a layer system is quite preferred over the layer system of the first example; it is due to its elaborate

Production, however, is significantly more expensive, so that for practical operation, based on the circumstances of the individual case, a compromise must be made between the resilience and price of the layer system to be used in each case.

In each of the examples described above, the intermediate layer is constructed in two phases; it is in the form of a dispersion of a phase consisting essentially of an intermetallic compound of rhenium and chromium in a metallic matrix. The intermetallic compound has the approximate composition Cr ₃ Re, and the metallic matrix contains the other chemical besides rhenium and chromium Elements of the composition. Aluminum, possibly also gallium and silicon, is available from the metallic matrix for the oxide formation between the intermediate layer and the thermal barrier layer.

Irrespective of its relevant mechanical properties, the intermediate layer does not significantly impair the properties of the entire layer system, since it is very thin and, due to its high rhenium content, does not allow elements to diffuse to a significant extent. Accordingly, it fits easily between the metallic adhesive layer and the ceramic thermal barrier layer. It offers all essential properties in connection with oxidation and corrosion, which the chemical element rhenium can contribute, without further rhenium having to be added to the adhesive layer and possibly impairing its properties.

The invention thus offers a powerful layer system for protecting a base body, in particular a base body of a gas turbine component, against an aggressive hot gas, at a temperature of 1000 ° C. or more.

Claims

claims 1. Product with a base body consisting of a superalloy and a layer system thereon for protecting the base body against an aggressive hot gas, wherein the layer system has a ceramic thermal barrier coating with an outer surface which can be exposed to the gas, the thermal barrier coating rests on an intermediate layer, and the intermediate layer rests on the base body and has the following composition of chemical elements in proportion to mass: Rhenium 35% to 60%, aluminum 10% to 20% gallium 0% to 10%, silicon 0% to 2%, hafnium 0% to 2%, an active element from the group containing yttrium, scandium and the elements of Rare earths: 0% to 2%; manufacturing-related impurities; and chrome as the rest. 2. Product according to claim 1, wherein the intermediate layer has the following composition by mass fraction: rhenium 47%; Aluminum 15%; Yttrium 0.5%; manufacturing-related impurities; such as Chrome as the rest. 3. Product according to claim 1 or 2, in which the intermediate layer rests on a metallic adhesive layer, the adhesive layer consisting of an alloy of the MCrAlY type, where M for at least one metal from the group containing iron, cobalt and nickel as the basis of the Alloy stands. 4. Product according to claim 3, wherein the alloy of the adhesive layer additionally contains rhenium, preferably with a mass fraction between 1% and 15%. 5. Product according to one of the preceding claims, in which the intermediate layer has a thickness of less than 10 μm, in particular of approximately 5 μm. 6. Product according to one of the preceding claims, in which the superalloy is a nickel-based or cobalt-based superalloy. 7. Product according to one of the preceding claims, wherein the intermediate layer is a dispersion of a phase consisting essentially of an intermetallic compound of rhenium and chromium in a metallic matrix. 8. Product according to one of the preceding claims, in which the heat insulation layer consists essentially of an at least partially stabilized zirconium oxide, which is stabilized in particular by the addition of yttrium oxide. 9. Product according to one of the preceding claims, which is a component for a gas turbine, in particular a rotor blade, a guide blade or a heat shield. 10. A method for producing a product with a base body consisting of a superalloy and a layer system thereon to protect the base body against an aggressive hot gas, whereby to form the Layer system, an intermediate layer is applied to the base body and a ceramic thermal barrier coating is applied to the intermediate layer, the intermediate layer having the following composition of chemical elements by mass fraction: rhenium 35% to 60%; Aluminum 10% to 20%, Gallium 0% to 10%, Silicon 0% to 2% Hafnium 0% to 2%, an active element from the group containing yttrium, scandium and the elements of the rare earths: 0% to 2%; manufacturing-related impurities; and chromium as the remainder, the intermediate layer being applied by plasma spraying, in particular vacuum plasma spraying or by vapor deposition. 11. The method according to claim 10, in which a metallic adhesive layer is first applied to the base body and then the intermediate layer is applied to the adhesive layer.