Patent Application
20180305824
The following relates to protection of a thermal barrier coating against corrosion, which comprises hollow aluminum oxide spheres and can further comprise a glass-like outer protective layer.
Components which are, in order to lower the metal temperature, coated with thermal barrier coatings composed of partially stabilized zirconia or gadolinium zirconate are present in the hot gas path. The present-day surface temperatures of the ceramics in combination with impurities such as CMAS lead to chemical attacks on the ceramics and also to intrusion of liquid phases into the pores of the ceramic. At the same time, the abrasion of compressor abradables can leave one-off nickel deposits on the layers. This, too, leads to TBC spalling as a result of reduced thermal expansion. There has hitherto not been any system to protect against this multiple attack in the long term.
Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:
The drawing and the description merely present working examples of embodiments of the invention.
The inventive step is application of a layer composed of aluminum particles, in particular by means of a slip.
The present problem is solved in the following way: a layer of pure aluminum particles or aluminum/titanium group metal or metal oxide particles containing 2-20% of titanium group metal, preferably zirconium, hafnium or titanium, and with additions of up to 5% of semimetal, in particular boron, silicon or germanium, is applied to the thermal barrier coating by spraying-on of a slip. The aluminum particles/zirconium oxide particles can have a diameter in the range from 1 to 125 μm, but particles in a smaller diameter range (2-40 μm) are desirable in most cases. The thickness of the applied particle layer can be in the range from 5 to 150 μm. This layer is optimally applied as slip. However, other methods are also possible. Hollow alumina spheres which comprise the further oxides as composite structure and due to this structure have good ductility in operation are formed from the aluminum particles by means of a suitable heat treatment (matched to the respective coating system consisting of base material, bonding layer and TBC). The addition of boron, silicon and/or germanium increases the diffusion activity of the elements and ultimately leads to increased adhesion of the additional protective layer. The titanium group oxides increase the mechanical compatibility and the resistance to CMAS attack.
A second optional layer has the composition of a low-melting, viscous glass whose melting point is preferably lower than or in the region of the melting point of the diffusing metal in the underlying layer. The glass comprises, in particular, essentially SiO2 and preferably contains accompanying elements such as magnesium (Mg), calcium (Ca) or else boron (B) and/or sodium (Na) which are relevant for setting the melting point.
The glass can also be formed only during the heat treatment in an oxygen-containing atmosphere from a silazane, siloxane or silicone polymer as precursor. This precursor can contain inorganic fillers in order to set the shrinkage and degradation behavior and the resistance to CMAS attack.
In any case, oxidation of the aluminum particles can be carried out by means of the additional layer of the glass without pure aluminum particles which run along the surface of the system blocking holes in the component during the heat treatment.
In addition, the “migration” of aluminum/titanium group metal particles (which can lead to blocking of the cooling air holes) on the surface of the thermal barrier coating during the heat treatment can be prevented by two processes. Firstly, this occurrence can be prevented by polymer masking of the holes or else by application of SiO2 to the particle layer. The SiO2 layer has, only in the initial state, the task of assisting the formation of alumina/zirconia layers and preventing such particles from running about. The SiO2 layer will then largely delaminate during operation because of the brittleness and the actual protective layer can take over the protective action.
The inventive step lies in the composition and the application of the aluminum/titanium group metal particles in combination with semimetal additions and in the application of a further supplementary layer of SiO2. Relatively high contents of Zr of >20% also lead to lower adhesion of the layers. As a result, oxidation of the aluminum/zirconium particles can be carried out without the pure aluminum particles which run along the surface of the system blocking the cooling air holes during the heat treatment. The use of polymer masking can also be carried out as an alternative. Boron strengthens the chemical bonding-on of the supplementary layer.
Concentration ranges: Al; Zr<20% by weight, B<6% by weight.
The substrate 4 is, in particular, metallic and in particular comprises a nickel- or cobalt-based superalloy.
An optional metallic bonding layer 7 is present on the substrate 4. This is in particular a coating layer, in particular a coating layer based on NiCoCrAlY.
During further coating, or as a result of deliberate oxidation or at least during operation, an oxide layer (TGO), which is not shown in more detail here, forms on this bonding layer 7.
A ceramic thermal barrier coating 10 is present on this thermally grown oxide layer (TGO) or on the metallic bonding layer 7. This ceramic thermal barrier coating can be made up of a single layer, in particular of zirconium oxide, or of two layers comprising zirconium oxide and a pyrochlore or “DVC” layers.
According to embodiments of the invention, an outer ceramic corrosion protection layer 13′ composed of aluminum oxide, in particular hollow aluminum oxide spheres 14 is present on the ceramic thermal barrier coating 10 (
To produce the coating system, a layer of aluminum particles, in particular having particle sizes of from 1 μm to 50 μm, is applied to the ceramic thermal barrier coating 10, in particular by means of a slip, vapor deposition, sputtering, etc.
This layer can have a layer thickness in the range from a few microns up to 300 μm, in particular not more than 200 μm, very particularly preferably not more than 100 μm.
Additions of aluminum (Al) are preferred: in particular at least one element Z selected from the group I boron (B), gallium (Ga) and/or germanium (Ge) and/or, in addition to aluminum (Al), at least one element selected from the group II zirconium (Zr), titanium (Ti), tantalum (Ta), niobium (Nb) and/or hafnium (Hf) is applied as mixture of materials and/or oxidized or has been oxidized for the corrosion layer (13′, 13″, 13′″).
In addition, silicon (Si) and/or magnesium (Mg) can be concomitantly applied and/or be present in the mixture of materials.
The following combinations are at least possible:
Ge/Ga means: germanium and/or gallium, i.e. Ge, Ga or Ge+Ga.
Elements of the group I and II can in each case be present and be used as mixtures of two, three, . . . or all elements of the groups I, II.
This layer is intended to prevent the intrusion of the CMAS (CMAF) layer and also react with the CMAS (CMAF). As a result of a heat treatment, aluminum oxide and a reaction layer between thermal barrier coating and aluminum layer are formed. The alumina applied in this way has a lower coefficient of expansion and in combination with the nickel (Ni), which originates from the compressor abradable, part of the aluminum oxide flakes off. The remaining layer then protects against the intrusion of liquid deposits.
The inventive step also lies in the application of the different particle sizes of the aluminum oxide which firstly provides protection against Ni deposits and also against CMAS. Since the deposits of nickel (Ni) occur only briefly and at the beginning of the operating time, a layer which has a short-term effect here and a layer having a long-term action against CMAS or similar attacks are present.
The layer of the aluminum oxide or the oxidation and/or optionally glass is in each case at least 20% thinner than the ceramic layer system 10.
The glass can be, in particular, silicon oxide, in particular SiO2.
Instead of aluminum (Al), it is also possible to use aluminum (Al) and zirconium, (Zr) (
Zirconium (Zr) improves the adhesion of the protective layer to the thermal barrier coating. In addition, zirconium (Zr) reduces the viscosity of the CMAS and prevents or slows the infiltration of the CMAS and thus increases the life of the layer system.
Furthermore, at least one element from the group consisting of boron (B), gallium (Ga) and/or germanium (Ge) and optionally silicon (Si) is additionally present.
A glass layer as described above can also be or have been applied on top of the layer of aluminum oxide/zirconium oxide or on top of the metallic aluminum/zirconium or on top of aluminum and an element Z.
The heat treatment to form aluminum oxide or aluminum oxide/zirconium oxide or aluminum oxide and oxide of the element Z can be carried out by means of a first use of the component or by means of preceding heat treatment before first use or after it has been installed in a machine for high-temperature use.
Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.
For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 221 751.5 | Nov 2015 | DE | national |
This application claims priority to PCT Application No. PCT/EP2016/074278, having a filing date of Oct. 11, 2016, based on German Application No. 10 2015 221 751.5, having a filing date of Nov. 5, 2015, the entire contents both of which are hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/074278 | 10/11/2016 | WO | 00 |
