EP1029101B1 - Product, especially a gas turbine component, with a ceramic heat insulating layer, and process for making the same - Google Patents

Abstract

The invention relates to a product (3), especially a component of a heat engine such as a gas turbine, which can be exposed to a hot aggressive gas (7). The product (3) has a metal base body (1) to which a ceramic heat insulating layer (4) is applied. The heat insulating layer (4) consists of a metal mixed oxide system and a lanthanum aluminate and/or calcium zirconate, whereby the calcium is replaced by a substitute element, especially strontium.

Description

The invention relates to a product which a hot, can be exposed to aggressive gas, with a metallic base body, which is a bonding agent layer forming a bonding oxide carries and has a ceramic thermal barrier coating. The invention further relates to hot gas components in thermal machines, especially in a gas turbine, to protect against a hot aggressive gas with a Thermal insulation layer are provided.

In US-PS 4,585,481 is a protective layer to protect a metallic substrate made of a superalloy High temperature oxidation and corrosion specified. For the Protective layers are used with an MCrAlY alloy. This Protective layer has 5 to 40% chromium, 8 to 35% aluminum, 0.1 up to 2% of an oxygen-active element from group IIIb of the periodic table including the lanthanides and actinides and mixtures thereof, 0.1 to 7% silicon, 0.1 to 3% Hafnium and a radical comprising nickel and / or cobalt (The percentages relate to percent by weight). The corresponding protective layers made of MCrAlY alloys are according to US-PS 4,585,481 using a Plasma spraying applied.

A gas turbine component is described in US Pat. No. 4,321,310, which is a body made of a nickel-based superalloy MAR-M-200 has. On the base material is a layer of an MCrAlY alloy, in particular one NiCoCrAlY alloy with 18% chromium, 23% cobalt, 12.5% aluminum, 0.3% yttrium and a remainder made of nickel. This layer of the MCrAlY alloy has a polished Surface on which an aluminum oxide layer is applied is. A ceramic thermal barrier coating is on this aluminum oxide layer applied, which has a stem-shaped structure having. Due to this columnar microstructure of the thermal insulation layer the crystallite columns are perpendicular to the surface of the basic body. Stabilized as a ceramic material Zirconia specified.

In US Pat. No. 5,236,787 it is stated between the base body and a ceramic thermal barrier layer an intermediate layer bring in a metal-ceramic mixture consists. As a result, the metallic part of this intermediate layer should Increase towards the base body and towards the thermal insulation layer lose weight. Conversely, the ceramic portion should accordingly low near the main body, near the thermal insulation layer be high. Yttrium oxide is used as the thermal insulation layer Stabilized zirconium oxide with proportions of cerium oxide. The intermediate layer is intended to adapt the different coefficients of thermal expansion between metallic base and ceramic thermal barrier coating can be achieved.

In US-PS 4,764,341 is the binding of a thin metal layer on a ceramic for the manufacture of electrical Circuits, so-called printed circuits, described. Nickel, cobalt, copper are used for the metal layer as well as alloys of these metals. For connection the metal layer on a ceramic substrate is on the ceramic substrate an intermediate oxide, such as aluminum oxide, Chromium oxide, titanium oxide or zirconium oxide, which applied at a sufficiently high temperature by oxidation ternary oxide incorporating an element of the metallic Coating forms.

GB 2 286 977 A1 describes a composition for an inorganic Coating described, the coating is applied to a low alloy steel and one Possesses high temperature resistance. The main characteristic of Coating is its corrosion resistance, which is due to integration of iron in the coating is reached. The coating exhibits metal oxides before a chemical reaction on, which at temperatures above 1000 ° C in spinels convert.

From US Pat. No. 4,971,839, a high-temperature protective layer comprising a metallic mixed oxide system is known, which has a perovskite structure with the chemical structural formula A _1-x B _x MO ₃ . Here, A is a metal from group IIIb of the periodic table, B is a metal from main group II (alkaline earth metals) from the periodic table and M is a metal from one of groups VIb, VIIb and VIIIb from the periodic table. The stoichiometric factor X is between 0 and 0.8. The coating is used on a temperature-resistant steel or an alloy for use at temperatures above 600 ° C, especially for a component of a gas turbine. An austenitic material based on nickel, cobalt or iron is preferably used as the base material for the component of the gas turbine.

In the article "On the development of plasma-sprayed thermal barrier coatings "by R. Sivakumar and M.P.Srivastava in: Oxidation of metals, vol. 20, Nos. 3/4, 1983, are different Specify coatings that have a zirconate. These coatings are on components made of Nimonik-75 and alternatively an adhesive layer of the type CoCrAlY by means of plasma spraying upset. There are results regarding calcium zirconates and magnesium zirconates with a cyclical temperature load specified.

The object of the invention is to provide a product with a metallic Base body and a thermal insulation layer attached to it, especially with a metallic mixed oxide system, specify.

The invention is based on the knowledge that previously used ceramic thermal insulation layers despite the use of, for example partially stabilized zirconia a thermal Have expansion coefficients that only about a maximum of 70% the coefficient of thermal expansion of the used Basic body, in particular made of a super alloy. Due to the smaller compared to the metallic base body thermal expansion coefficient result when applied with a hot gas thermal stresses. To at changing thermal load such resulting stresses counteracting this is a stretch-tolerant microstructure the thermal insulation layer is required, e.g. by Setting an appropriate porosity or a stem-shaped Structure of the thermal insulation layer. In addition, you can in a thermal barrier coating known from the prior art made of partially stabilized zirconium oxide with stabilizers how yttrium oxide, cerium oxide and lanthanum oxide tensions occur, that from a thermally induced phase transition (tetragonal in monoclinic and cubic) result. Also at an associated change in volume is a maximum permissible Surface temperature for thermal insulation layers made of zirconium oxide given.

According to the invention, the object is directed to a product solved in that the ceramic thermal barrier coating is a metallic Mixed oxide system comprising lanthanum aluminate and / or Has calcium zirconate. The thermal barrier coating is immediate or indirectly through an adhesive layer to the Basic body connected. The connection is preferably made over an oxide layer, which e.g. by oxidation of the base body or the adhesion promoter layer is formed. The connection can also or additionally via mechanical clamping, e.g. due to a roughness of the base body or the adhesion promoter layer.

These thermal insulation layers serve to extend the life of hot gas products, in particular components in gas turbines, such as blades and heat shields. The thermal barrier coating has a low thermal conductivity, a high melting point and chemical inertness. A lanthanum aluminate is also understood to mean a mixed oxide, in particular with a perovskite structure, in which the lanthanum is partially replaced by a substitute element. If necessary, it is possible that the aluminum is at least partially replaced by a further substitute element. A chemical structural formula of the type La _1-x M _x Al _1-y N _y O ₃ can be specified for the lanthanum aluminate in question. M stands for a substitute element, which preferably comes from the group of lanthanides (rare earths). N stands for chrome, for example. The substitute element is more preferably gadolinium (Gd). The substitute factor X can be up to 0.8 and is preferably in the range of about 0.5. In the range of 0.5, the thermal conductivity of such a lanthanum aluminate has a minimum, so that the thermal insulation layer thus has a particularly low thermal conductivity. The substitution factor y is preferably in the range of 0.

Additionally or alternatively, the metallic mixed oxide system has calcium zirconate, preferably in a perovskite structure, the calcium being partially replaced by at least one subtitle element, in particular strontium (Sr) or barium (Ba). A chemical structural formula of the type Ca _1-x Sr _x Zr _1-y MyO ₃ can be specified for such a calcium zirconate. The substitute factor X is greater than zero to 1, in particular greater than 0.2, and less than 0.8, and is preferably in the range of 0.5. In this area, such a calcium zirconate also has a minimum of thermal conductivity, so that the thermal conductivity of the thermal barrier coating is also particularly low. It is also possible to use a mixed oxide system with barium zirconate or strontium zirconate. (Ba _1-x X _x Zr _1-y M _y O ₃ , Sr _1-x X _x Zr _1-y MyO ₃ ), with X; Ca, Sr and Ba, respectively. M can stand for Ti or Hf.

In the following, the lanthanum aluminates and the calcium, Strontium or barium zirconate mixed crystals as ternary Oxide or pseudo-ternary oxide.

A ternary oxide here means an oxide in which oxygen (Anions) are connected to two other elements (cations) is. Under a pseudoternary oxide is a substance understood that atoms of more than two different atoms has chemical elements (cations). Here but these atoms (cations) only belong to two different ones Element groups, the atoms of each element in each of the three different element groups in crystallographically equivalent.

The ternary oxide is preferably based on elements which form materials of the perovskite material group, with appropriate mixed crystal formation and microstructure modification being made possible. Here, the two different forms of perovskites due to valence, namely perovskite A (A ²⁺ B ⁴⁺ O ₃ ) and perovskite B (A ³⁺ B ³⁺ O ₃ ), can occur. Coating materials with a perovskite structure have the general chemical structural formula ABO ₃ . Here, the ions, which are identified by the placeholder A, are smaller than the ions, which are designated by the placeholder B. The perovskite structure has four atoms in a unit cell. The perovskite structure can be characterized by the fact that the larger B ions and the O ions together form a densest cubic sphere packing in which 1/4 of the octahedral gaps are occupied by A ions. The B ions are coordinated by 12 O ions in the form of a cubic octahedron, the O ions are each adjacent to four B ions and two A ions.

The ternary oxide is preferably lanthanum aluminate (LaAlO ₃ ) or calcium zirconate (CaZrO ₃ ). These ternary oxides have a low tendency to sinter, a high thermal conductivity and a high coefficient of thermal expansion. In addition, they have high phase stability and a high melting point.

The thermal expansion coefficient of the ternary oxide is preferably between 7 x 10 ^-6 / K and 17 x 10 ^-6 / K. The thermal conductivity is preferably between 1.0 and 4.0 W / mK. The specified value ranges for expansion coefficient and thermal conductivity apply to bodies made of a ternary non-porous material. The thermal conductivity can be further reduced by specifically introducing porosities. The melting temperature is significantly more than 1750 ° C.

Calcium zirconate (CaZrO ₃ ) has an expansion coefficient at a temperature between 500 and 1500 ° C of 15 x 10 ^-6 / K and a thermal conductivity of approx. 1.7 W / mK. Lanthanum aluminate (LaAlO ₃ ) has a thermal expansion coefficient of approximately 10 x 10 ^-6 / K at a temperature in the range of approximately 500 to 1500 ° C. The thermal conductivity is around 4.0 W / mK. Lanthanum aluminate and calcium zirconate can be synthesized as perovskite by conventional methods such as the so-called mixed oxide method. After about 3 hours of reaction annealing (1400 ° C with CaZrO ₃ ; 1700 ° C with LaAlO ₃ ) in air, the ternary oxide is essentially phase-pure. A full implementation of the lanthanum oxide (La ₂ O ₃ ) used in the production certainly avoids a two-phase process. Calcium zirconate is particularly suitable due to its ease of manufacture, its favorable phases or a variable crystal chemistry, ie in particular an exchange of zirconium by titanium and hafnium. It is also sprayable. Lanthanum aluminate has a low tendency to sinter and favorable adhesive conditions, which are caused in particular by the aluminum.

The mixed oxide system can have a further oxide, the ceramic thermal barrier coating permitting a higher surface temperature and a longer service life than a thermal barrier coating made of zirconium oxide. The further oxide can be calcium oxide (CaO) or zirconium oxide (ZrO ₂ ) or a mixture thereof, in particular if the ternary oxide is calcium zirconate.

Furthermore, the ternary oxide can have magnesium oxide (MgO) or strontium oxide (SrO) as additional oxide. It is also possible for the ternary oxide to have yttrium oxide (Y ₂ O ₃ ), scandium oxide (Sc ₂ O ₃ ) or a rare earth oxide as well as a mixture of these oxides.

As a further oxide, the lanthanum aluminate can have aluminum oxide together with zirconium oxide and optionally also with yttrium oxide. Alternatively, the mixed oxide system with the ternary oxide can additionally have hafnium oxide (HfO ₂ ) and / or magnesium oxide (MgO).

The adhesion promoter layer is preferably an alloy one of the elements of the metallic mixed oxide system, in particular ternary oxides, for example lanthanum, zircon, Aluminum or other. Suitable as an adhesive layer particularly when using a base body from a Nickel-based cobalt-based, or chrome-based superalloy Alloy type MrCrAlY. M stands for one of the elements or several elements of the group comprising iron, cobalt or nickel, Cr for chrome and Al for aluminum. Y stands for yttrium, cerium, scandium or a group IIIb element the periodic table and the actinides or lanthanides. The MCrAlY alloy can contain other elements, e.g. Rhenium.

The product is preferably a component of a thermal Machine, especially a gas turbine. It can be a turbine blade, a turbine vane or heat shield a combustion chamber. With an inventive Thermal insulation layer is particularly in the case of gas turbine blades with full load operation of the gas turbine even at an operating temperature of 1250 ° C on the surface of the thermal barrier coating a service life greater than that of conventional thermal insulation layers available from zirconium oxide. A ternary oxide, in particular as a perovskite, undergoes no phase change the operating temperature of the gas temperature, which is above 1250 ° C, in particular can be up to about 1400 ° C.

The thermal insulation layer is preferably applied by atmospheric plasma spraying, especially with a predeterminable porosity. It is also possible to use the metallic one Mixed oxide system using a suitable vapor deposition process, a suitable PVD process (Physical Vapor Deposition), in particular a reactive PVD method. When applying the thermal barrier coating using a Vapor deposition process, e.g. an electron beam PVD process, if necessary, a stem structure is also achieved. In a reactive PVD process, there is a reaction in particular a transformation of the individual components a ternary oxide or a pseudoternary oxide, only during the coating process, especially immediately when hitting the product. With a non-reactive Evaporation processes are the ones that have already been pre-reacted Products, especially the ternary oxides with perovskite structure, evaporates and separate again from the steam on the Product from. The use of pre-reacted products is special especially when using a plasma spraying process advantageous.

FIG 1

Eine perspektivische Darstellung einer Gasturbinenlaufschaufel,

FIG 2, 3

jeweils einen Ausschnitt eines Querschnitts durch die Turbinenschaufel analog Figur 1,

FIG 4

eine Darstellung des Phasendiagramms von Lanthanaluminat bei Zusatz von Lanthanoxid und Aluminiumoxid, und

FIG 5

das Phasendiagramm für Kalziumzirkonat bei Zusatz von Zirkonoxid und Kalziumoxid.

The product with the thermal barrier coating is explained in more detail using the exemplary embodiments shown in the drawing. Show it:

FIG. 1

A perspective view of a gas turbine blade,

FIG 2, 3

a section of a cross section through the turbine blade analogous to FIG. 1,

FIG 4

a representation of the phase diagram of lanthanum aluminate with the addition of lanthanum oxide and aluminum oxide, and

FIG 5

the phase diagram for calcium zirconate with the addition of zirconium oxide and calcium oxide.

The gas turbine blade 3 shown in FIG. 1 has a metallic base body 1 made of a nickel-based cobalt base, or chrome-based superalloy. A coated airfoil 9 extends between a blade root 10 and a sealing strip 8. According to FIG. 2, an adhesion promoter layer 2 is applied to the base body 1. The adhesion promoter layer 2 can be an alloy of the MCrAlY type comprising chromium, aluminum, yttrium, lanthanum and / or zircon and a remainder of one or more elements from the group comprising iron, cobalt and nickel. A thermal insulation layer 4 with a metallic mixed oxide system is applied to the adhesive layer 2. The mixed oxide system here preferably has lanthanum aluminate (LaAlO ₃ ), it being possible for the lanthanum to be partially replaced by, for example, gadolinum. The mixed oxide system can alternatively have calcium zirconate with partial substitution of calcium by strontium (Ca _1-X Sr _X Zr ₂ O ₃ ). Another oxide, such as aluminum oxide or zirconium oxide, is preferably added to the ternary oxide (LaAlO ₃ , Ca ₁ -X Sr _X ZrO ₃ ). The oxide layer 5 with the bonding oxide is formed between the adhesive layer 2 and the thermal barrier layer 4. The bonding oxide is preferably formed by oxidation of the adhesion-promoting layer 2, which leads to a proportion of lanthanum oxide in the presence of lanthanum, to a proportion of zirconium oxide etc. in the case of zirconium. The oxide layer 5 provides a good connection of the thermal insulation layer 4 to the metallic base body 1 via the adhesive layer 2. When the gas turbine blade 1 is used in a gas turbine (not shown in more detail), a hot aggressive gas 7 flows past an outer surface 6 of the thermal insulation layer 4, which gas is effectively kept away from the metallic base body 1 by the ceramic thermal insulation layer 4 and the adhesive layer 2. As a result, a long service life is achieved even with changing thermal loads on the gas turbine blades.

FIG. 3 shows a layer system analogous to FIG. 2, in which an adhesion promoter layer 2 is applied to the base body 1 and the thermal insulation layer 4 is applied thereon. The adhesion promoter layer 2 has a surface that is so rough that the thermal insulation layer 4 is bonded to the adhesion promoter layer 2 and thus to the base body 1 essentially without chemical bonding by mechanical clipping. Such roughness of a surface 11 of the adhesion promoter layer 2 can already be achieved by applying the adhesion promoter layer 2, for example by vacuum spraying (plasma spraying). In the case of plasma spraying in particular, products which have already been prereacted (for example La _1-x Gd _x AlO ₃ or Ca _1-x Sr _x ZrO ₃ ) are applied to the product. This means that the products are manufactured in one work step before the actual coating and then essentially without any further chemicals. Reactions and conversions applied to the product 3. The thermal insulation layer 4 can also be attached directly to the metallic base body 1 by a corresponding roughness of the metallic base body 1. It is also possible to apply an additional bonding layer, for example with an aluminum nitride or a chromium nitride, between the adhesion promoter layer 2 and the heat insulation layer 4.

According to the phase diagram of lanthanum aluminate shown in FIG. 4 and the phase diagram of FIG Calcium zirconate can be seen that with a suitable choice of Additions of oxides have a melting temperature of well above 1750 ° C and a high phase stability without phase transition given at operating temperatures above 1250 ° C is.

Claims (14)

1. Product (3) which can be exposed to a hot aggressive gas, having a metallic base body (1), applied to which there is a ceramic thermal barrier layer (4) which contains a mixed metal oxide system comprising a lanthanum aluminate.
2. Product (3) according to Claim 1, in which the lanthanum in the lanthanum aluminate is partially replaced by at least one substitute element.
3. Product (3) according to Claim 2, in which the at least one substitute element comes from the lanthanide group, and is in particular gadolinium (Gd).
4. Product (3) which can be exposed to a hot aggressive gas, having a metallic base body (1), applied to which there is a ceramic thermal barrier layer (4) which contains a mixed metal oxide system comprising a calcium zirconate, in which calcium is partially replaced by at least one element, in particular strontium (Sr).
5. Product (3) according to one of the preceding claims, in which the substitute element replaces up to 0.8, preferably 0.5, of the lanthanum or calcium, respectively.
6. Product (3) according to one of the preceding claims, in which the mixed metal oxide system contains a further oxide.
7. Product (3) according to one of the preceding claims, in which an adhesion promoter layer (2) forming a bonding oxide is arranged between the base body (1) and the thermal barrier layer (4).
8. Product (3) according to one of the preceding claims, in which the adhesion promoter layer (2) is an alloy comprising one of the elements of the mixed metal oxide system.
9. Product (3) according to one of the preceding claims, in which the metal base body (4) contains a superalloy based on nickel, cobalt and/or chromium.
10. Product (3) according to one of the preceding claims, characterized by configuration as a component of a heat engine, in particular a gas turbine.
11. Product (3) according to Claim 10, characterized by configuration as a turbine rotor blade, turbine guide vane or heat shield of a combustion chamber.
12. Product (3) according to one of the preceding Claims, characterized in that the coefficient of thermal expansion α of the ternary oxide is between 7*10^-6/K and 17*10^-6/K.
13. Product (3) according to one of the preceding Claims, characterized in that the thermal conductivity of the ternary oxide is between 1.0 W/mK and 4.0 W/mK.
14. Process for the production of a thermal barrier layer on a product having a metallic base body, a prereacted mixed metal oxide system comprising a lanthanum aluminate and/or calcium zirconate, in which calcium is partially replaced by at least one element, in particular strontium (Sr), is applied by means of plasma spraying or an evaporation coating process.

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