CMAS-resistant protective layer

Abstract

The present invention relates to a protective layer against CMAS, to a CMAS-resistant article comprising the protective layer according to the invention, and to a process for preparing a corresponding article.

Claims

1. A protective layer against CMAS, characterized in that said protective layer consists of oxides of iron, yttrium and silicon.

2. The protective layer according to claim 1, characterized in that the layer thickness of the protective layer is from 10 μm to 200 μm.

3. A CMAS-resistant article, comprising: a basic structure made of a refractory material with a surface, a first coating on this surface, and a protective layer consisting of oxides of iron, yttrium and silicon that has been applied to this first coating.

4. The article according to claim 3, characterized by being a turbine or an inliner on the combustion chamber.

5. The article according to claim 3, characterized in that said refractory material comprises an Ni-based superalloy or SiC.

6. The article according to claim 3, characterized in that said first coating is a thermal insulation layer (TBC) or environmental barrier coating (EBC).

7. A process for preparing an article according to claim 3, characterized in that the protective layer is applied to the first coating by means of sputter technology or PVD.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) It has further been found that a protective layer that exclusively includes iron oxide, yttrium oxide and silicon oxide has properties that prevent the infiltration of CMAS into porous layers, such as TBC or EBC, in particular. At the same time, a protective layer according to the invention has a good adhesion to TBC or EBC, so that the protective layer is stable over an extended period of time.

(2) Preferably, the proportion of oxides of yttrium in the protective layer is within a range of from 25 atomic percent to 85 atomic percent, especially within a range of from 30 atomic percent to 75 atomic percent, more preferably within a range of from 40 atomic percent to 70 atomic percent. The proportion of oxides of silicon is especially within a range of from 2 atomic percent to 35 atomic percent, preferably from 5 atomic percent to 30 atomic percent, more preferably from 5 atomic percent to 25 atomic percent, or up to 20 atomic percent. More preferably according to the invention, the proportion of iron oxides in the protective layer is within a range of from 1 atomic percent to 35 atomic percent, especially from 2 atomic percent to 30 atomic percent, more preferably from 2 atomic percent to 20 atomic percent. It has been found that the above mentioned proportions are particularly suitable for forming a CMAS protective layer. The protective layer according to the invention consists only of iron, yttrium and silicon oxides. Other oxides or other additives, such as rare earths, as described, for example, in U.S. Pat. No. 9,194,242 B2 or U.S. Pat. No. 7,785,722 B2, are not contained presently, and also are not necessary to ensure protection against CMAS.

(3) Preferably, the iron oxide is Fe.sub.2O.sub.3, the silicon oxide is SiO.sub.2, and the yttrium oxide is Y.sub.2O.sub.3 in the layer according to the invention as described herein.

(4) Further, the present protective layer has no particular crystal structure. This enables the protective layer to be applied by a wide variety of coating methods as described in the prior art. No particular conditions are to be observed. Thus, the coating can be applied, for example, with PVD methods, such as magnetron atomizers or electron beam vaporization (EB-PVD), but also by means of thermal spraying methods, such as atmospheric plasma spraying (APS), or vacuum plasma spraying (VPS). What is critical for the choice of the coating method may be constructional limitations and the cost associated with the method.

(5) Preferably according to the invention, the protective layer has a layer thickness of from 10 μm to 200 μm, especially from 15 μm to 150 μm, preferably from 20 μm to 100 μm. The protective layer according to the invention reacts with the liquid CMAS and forms a crystalline layer above or immediately on the underlying layer or surface. For this reaction, a layer thickness of at least 5 μm is required. As soon as such a crystalline layer has formed immediately on the underlying surface or coating, the reaction takes place exclusively in the overlying regions of the protective layer. Thus, in contrast to the protective layers described in the prior art, CMAS cannot penetrate into porous structures below the protective layer according to the invention. Once this reaction is completed, no other reaction takes place that would affect the underlying regions in any way. A layer thickness of 10 μm is sufficient to ensure long-term protection. Layer thicknesses of more than 200 μm cause a high increase of the total layer thickness, which may be undesirable depending on the field of application. In addition, the accompanying cost and the weight are also to be considered besides the thickness. Layer thicknesses of from 10 μm to 100 μm or from 15 μm to 50 μm are sufficient to ensure long-term protection.

(6) In another embodiment, the object of the present invention is achieved by a CMAS-resistant article. According to the invention, this article includes a basic structure made of a refractory material with a surface, a first coating on this surface, and a protective layer as described above that is applied immediately to the first layer. Thus, “CMAS-resistant” means that CMAS have no adverse influence on the corresponding article in operation or use.

(7) An “article” within the meaning of the present invention is any article that is operated at high temperatures and exposed to different external influences. For example, the article is a turbine, especially a gas turbine, a turbine blade, or a turbine paddle, or an inliner on the combustion chamber of a turbine, especially a high-pressure turbine. The corresponding article also determines the basic structure. “Turbine” or “gas turbine” or “high-pressure turbine” comprises all components thereof that are exposed to high temperatures of 1000° C. or more, especially 1200° C. or more.

(8) In particular, the high-temperature material is a superalloy in operation, more preferably a nickel-based superalloy or SiC.

(9) In particular, the first coating that is present on the refractory material is a heat insulation layer (thermal barrier coating, TBC), or an EBC. Corresponding protective layers are described in the prior art, and known to the skilled person.

(10) In another embodiment, the present invention relates to a process for preparing a CMAS-resistant article, characterized in that the protective layer is applied to the first coating by means of sputter technology or PVD. In principle, any method of applying the protective layer is possible, such as EB-PVD, APS, VPS, HVOF, or sputtering methods. Differences in CMAS resistance caused by different application methods cannot be observed.

(11) In the following Example, the present invention is described in a non-limiting way.

EXAMPLE

(12) A protective layer having a thickness of 20 μm was applied to substrates of aluminum oxide using magnetron sputtering. The proportion of yttrium oxide in the protective layer according to the invention was from 48 atomic percent to 53 atomic percent, the proportion of silicon oxide was from 12 atomic percent to 15 atomic percent, the proportion of iron oxide was from 2 atomic percent to 10 atomic percent.

(13) The coatings were heated at a temperature of 700° C. over a period of 10 hours, and subsequently heated at a temperature of 1150° C. for one hour.

(14) Synthetic CMAS powder (22% by weight CaO, 8% by weight O, 8% by weight MgO, 18 % by weight Al.sub.2O.sub.3, 40% by weight SiO.sub.2, 10% by weight FeO, and 2% by weight TeO.sub.2) was applied to the protective layer. The specimen was heated at a temperature of 1250° C. for five minutes, and analyzed by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

(15) For comparison, an EB-PVD heat insulation layer (7 YSZ, a zirconium oxide stabilized with 7% by weight yttrium oxide) on a substrate of aluminum oxide was treated with the same synthetic CMAS powder, and also heated at a temperature of 1250° C. for five minutes. Here too, an analysis by means of scanning electron microscopy and EDS was performed.

(16) While the protective layer according to the invention had the effect that the liquefied CMAS could not infiltrate into the TBC, the infiltration of CMAS, especially of compounds containing calcium and silicon, into the porous structure of TBC could be clearly seen in the EDS in the comparative example.

(17) Thus, the Examples confirm that the protective layer according to the invention is capable of preventing the infiltration of CMAS into porous structures, such as those of a TBC.