Calcium-Magnesium-Aluminum-Silicate Resistant Overlay Coating

Abstract

The present invention relates to a CMAS-resistant overlay coating (240) comprising at least one CMAS-resistant layer, the overlay coating (240) i. disposed on a surface (11a) of a substrate (10a) comprising or consisting of a material susceptible to CMAS corrosion, ii. comprising a metal oxide matrix, and iii. having at least a partially vertical columnar structure. Furthermore, at least one non-oxidized metal component selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium is embedded in the metal oxide matrix. Furthermore, the present invention relates to a substrate (10a) having the CMAS-resistant overlay coating (240) in question on a surface (231) of a material susceptible to CMAS corrosion. The present invention also relates to a CAE process for forming such a CMAS-resistant overlay coating (240) on a surface (231) of a material susceptible to CMAS corrosion.

Description

[Technical field]

[0001] The present invention relates to a calcium-magnesium-aluminium-silicate (CMAS)-resistant overlay coating and to a cathodic arc deposition (CAE) process for forming such a CMAS-resistant overlay coating on the surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion. Furthermore, the present invention relates to a substrate comprising or consisting of a material susceptible to CMAS corrosion and having the CMAS-resistant overlay coating in question on the surface of at least one substrate layer, the substrate being in particular obtained or obtainable by the process described above. [Background technology]

[0002] To increase the operating temperatures of stationary and aero gas turbines, and thereby increase turbine efficiency, complex cooling systems for the turbine blades are required. Such systems are typically achieved by thermal barrier coating (TBC) systems that include internal cooling channels, cooling holes to generate a film of cooling gas on the blade surface, and a ceramic top coating that exhibits low thermal conductivity to maximize the temperature gradient from the coating surface to the coating-blade interface.

[0003] For thermal insulation, conventional TBC systems include a porous or strain-resistant ceramic top coating, also commonly referred to as a thermal barrier coating. Typically, a yttria-stabilized zirconia (YSZ)-based thermal barrier coating is placed on a thermally grown oxide (TGO) layer. The latter is then placed on a bond coat (BC) layer. Two non-limiting examples of conventional thermal barrier coating compositions are 7 wt% yttria-stabilized zirconia (7YSZ) and 8 wt% yttria-stabilized zirconia (8YSZ). YSZ-based thermal barrier coatings are characterized by their high toughness and low thermal conductivity up to high temperatures. They are usually deposited by atmospheric plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD). APS results in a dense vertical or horizontal crack structure, while EB-PVD results in a columnar structure that can withstand the significant thermal expansion mismatch between the metal blade and the ceramic coating. For this reason, columnar structures are preferred for aero-engine applications, despite the relatively high manufacturing costs.

[0004] Melt deposits based on calcium-magnesium-aluminium-silicates (CMAS), originating from atmospheric dust ingested by the intake air and deposited on surfaces in the hot gas path of gas turbines, are recognized as a key factor affecting the durability of conventional thermal barrier coatings. Moreover, they are a fundamental barrier to progress in the field of gas turbine technology. The reason is as follows: Most CMAS deposits melt at temperatures around or above 1.200 °C. As a result, when engine operating temperatures increase (e.g. aircraft takeoff or landing), a glassy melt based on CMAS is formed, which attacks the thermal barrier coating, which is typically a YSZ layer. The melt can chemically dissolve the thermal barrier coating, usually followed by the precipitation of new phases effectively destroying the columnar or vane-like structure of the thermal barrier coating. Alternatively or additionally, the CMAS melt can penetrate the porous or columnar structure of the thermal barrier coating, i.e. the void spaces that accommodate the strain incompatibility with the metal substrate, and solidify upon engine shutdown. As a result, the tolerance of the thermal barrier coating to the thermal expansion of the turbine blade is greatly reduced, leading to cracking and delamination of the thermal barrier coating. The penetration of the CMAS melt can also extend into the BC layer, whereby the melt chemically interacts with the TGO layer. This results in delamination along the TGO layer and potentially promoting creep cavitation within the BC layer, with the delamination crack path propagating through the metal rather than the ceramic layer. (See for example C.G.Levi, J.W.Hutchinson, M.-H.Vidal-Setif, C.A.Johnson, MRS Bulletin 2012, 37, 932-941).

[0005] Various strategies have been developed to mitigate CMAS-induced degradation and corrosion, respectively. The most promising strategy to date attempts to increase the reactivity between the thermal barrier coating and the CMAS melt by applying a CMAS-reactive thermal barrier coating. This consumes the melt while the crystalline reaction products form a dense layer, blocking the path for further melt penetration. In other words, the crystalline reaction products form a CMAS-resistant layer.

[0006] Most of the CMAS reactive thermal barrier coatings known from the prior art are based on rare earth zirconates, mainly containing the rare earth elements gadolinium (Gd), ytterbium (Yb) or samarium (Sm). Disadvantageously, these CMAS reactive thermal barrier coatings are typically less tough than conventional thermal barrier coatings based on YSZ compositions. CMAS reactive thermal barrier coatings are therefore only provided in addition to conventional thermal barrier coatings, i.e. as a top layer on top of a YSZ-based or low-k thermal barrier coating. To form such CMAS reactive thermal barrier coatings, the same techniques are applied in each case as the deposition of the underlying thermal barrier coating, i.e. APS or EB-PVD.

[0007] However, this approach has the disadvantage that the material costs are quite high, mainly because two rare earth metal-containing layers are required, and the separation and isolation of the rare earth metals is complicated and time-consuming. Moreover, the process of forming such a CMAS reactive top layer is also relatively costly.

[0008] In summary, from an economical and ecological point of view, previously known CMAS-reactive thermal barrier coating compositions, CMAS-resistant top layers based thereon, as well as methods for forming such CMAS-resistant top layers, are relatively unsatisfactory. Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to overcome the above and other drawbacks of the state of the art and to provide a CMAS-resistant overlay coating that is relatively inexpensive, versatile and durable, regardless of the surface properties, especially the surface texture. In particular, the CMAS-resistant overlay coating shall exhibit good mechanical stability and adhesion to the respective underlying layers, especially under thermal cycling up to 1.600 ° C. Furthermore, the present invention relates to a substrate comprising or consisting of a material susceptible to CMAS corrosion, having a CMAS-resistant overlay coating that exhibits good mechanical stability and adhesion to the respective underlying layers, especially under thermal cycling up to 1.600 ° C. on the surface. Another object of the present invention is a process for forming such a CMAS-resistant overlay coating on the surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion. The process should be relatively versatile with respect to the surface properties, especially the surface texture, simple, relatively cost-effective, energy-saving and easily scalable for industrial applications. [Means for solving the problem]

[0010] The main features of the invention are set forth in the appended claims. According to a first aspect of the present invention, the object is to provide a calcium-magnesium-aluminium-silicate (CMAS)-resistant overlay coating comprising at least one CMAS-resistant layer, the CMAS-resistant overlay coating comprising: i. disposed on a surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion; ii. a metal oxide matrix, a metal oxide matrix, wherein at least one unoxidized metal component selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium is embedded in said metal oxide matrix; iii. having at least a partial vertical columnar structure; The solution is a calcium-magnesium-aluminum-silicate (CMAS) resistant overlay coating.

[0011] Within the scope of the present invention, the terms "CMAS-resistant overlay coating" and "overlay coating" and "protective layer" are used synonymously.

[0012] The term "surface" refers to any surface area, regardless of surface properties, particularly regardless of surface texture. Furthermore, the term "surface of a substrate" refers to any surface of a single layer substrate or any surface of a multi-layer substrate. In particular, the term "surface of a substrate" refers to the top surface of a single layer material, the top surface of a multi-layer substrate, and the top surface of any layer included in a multi-layer substrate, such that the top surface of a laminate substrate and the top surface of a substrate layer of a top surface of a laminate substrate are the same. The CMAS-resistant overlay coatings disposed on the top surface of the top substrate layer of the multi-layer substrate and the top surface of the multi-layer substrate, respectively, are also disposed on the underlying substrate layer.

[0013] A "substrate comprising or consisting of a material susceptible to CMAS corrosion" can be a single layer substrate comprising or consisting of one or more materials susceptible to CMAS corrosion. A multi-layer substrate may consist of a base layer, e.g., a superalloy, and a conventional thermal barrier coating (TBC) system.

[0014] The term "thermal barrier coating system", abbreviated as TBC system, used in the context of the invention described herein, refers to a multilayer material comprising or consisting of a porous or strain-resistant ceramic top coating, also commonly referred to as thermal barrier coating, a thermally grown oxide (TGO) layer and a bond coat (BC) layer, the ceramic top coating being disposed on the TGO layer and the BC layer being disposed between the substrate, e.g. a gas turbine blade, and the TGO layer. In particular, the BC layer is disposed between the top layer of the substrate, e.g. a gas turbine blade, and the TGO layer. In the following, this type of TBC system is also referred to as a conventional thermal barrier coating system. Furthermore, the ceramic top coating, which is included in this type of TBC system and is typically YSZ-based, is also referred to as a conventional thermal barrier coating.

[0015] Within the scope of the present invention, the term "layer" is synonymous with the term "film" and does not provide any information regarding layer or film thickness. Furthermore, layers do not necessarily have a uniform thickness. However, if a layer thickness is specified, this layer thickness is intended to be present in at least a portion of the respective layer, i.e., at its maximum thickness.

[0016] According to the present invention, a "material susceptible to CMAS corrosion" is, for example, a metal, a superalloy, a ceramic material or a ceramic matrix composite (CMC), or a combination thereof. The CMC may, for example, include or consist of a SiC-based CMC.

[0017] The metal oxide matrix may comprise one or more stoichiometric metal oxides and / or one or more non-stoichiometric, in particular oxygen-deficient, metal oxides.

[0018] Surprisingly, the inventors have found that under thermal cycling, the CMAS-resistant overlay coating according to the first aspect of the invention exhibits very good mechanical stability and excellent adhesion to the immediately underlying material surface, even when temperatures of 1.500° C. or higher, especially up to 1.600° C. are applied. This is due in particular to the thermally induced formation of an impermeable barrier layer involving unoxidized metallic components from the CMAS-resistant overlay coating diffusing to the interface between the overlay coating and the overlying molten CMAS material, as described below: The overlay coating according to the first aspect of the invention, when heated at high temperatures, i.e. at temperatures above about 1.000° C., can release the contained non-oxidized metal components, i.e. aluminum and / or chromium and / or one or more metal components including or consisting of aluminum and chromium embedded in a metal oxide matrix. Briefly, the non-oxidized metal components then diffuse to the top surface of the CMAS-resistant overlay coating and the bottom surface of the liquid CMAS layer, respectively, and react with the elements and / or components of the CMAS material, e.g. calcium, magnesium, magnesium oxide and silicon. Thereby, an impermeable barrier layer is formed that has a higher melting temperature than the CMAS material, thus effectively preventing the liquid CMAS material from penetrating into the respective underlying substrate, which may include, for example, a TBC system, and / or reacting with the components of the respective underlying one or more substrate layers, e.g. during operation of a gas turbine.

[0019] The formation of the CMAS-resistant overlay coatings presented herein, the high temperature behavior, and the manifold advantages associated with the application of such overlay coatings are illustrated below with the example of a particular conventional TBC system, however the following description is equally applicable when there is no conventional thermal barrier coating, for example a TGO layer coated with a CMAS-resistant overlay coating.

[0020] In general, the CMAS-resistant overlay coating according to the first aspect of the invention may be disposed by a physical vapor deposition process on the surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion. In particular, the overlay coating is disposed on top of a conventional TBC system, i.e., typically on top of a YSZ-based thermal barrier coating. When the overlay coating according to the first aspect of the invention is disposed on top of a TGO layer, the conventional thermal barrier coating may usually be omitted, depending in particular on the layer thickness of the overlay coating.

[0021] Carrying out a cathodic arc evaporation (CAE) process as a reactive PVD process, thereby combining thin film deposition or coating, respectively, with a reactive gas plasma, has been found to be the best approach, i.e. the most versatile, simple, cost-effective and energy-saving process, for forming and depositing a protective layer according to the first aspect of the invention described herein. In general, depending on the target material, in particular its material composition, and the oxygen partial pressure controlled and / or influenced by the gas flow controller and the arc current, the CMAS-resistant overlay coating comprises: i. a metal oxide matrix comprising Al-O species or Cr-O species or Al-Cr-O species, or a mixture thereof; and ii. at least one non-oxidized metal component embedded in the metal oxide matrix and selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium. In particular, the formation of the non-oxidized metal component in the metal oxide matrix of the CMAS-resistant overlay coating can be particularly influenced and / or controlled by the target material composition and - to some extent - by the oxygen partial pressure controlled and / or influenced by the gas flow controller and the arc current. Thus, if desired, the formation of intermetallic compounds containing or consisting of, for example, aluminum and chromium can be promoted. After deposition and prior to exposure to high temperatures, the CMAS-resistant overlay coatings presented herein contain non-oxidized metallic components, i.e., aluminum and / or chromium and / or components containing or consisting of aluminum and chromium, which can be verified by X-ray diffraction (XRD) analysis.

[0022] Upon heating at high temperatures, typically around or above 1.000°C, more typically around or above 1.200°C, in particular around or above 1.300°C, droplets of unoxidized metal components embedded in the metal oxide matrix of the CMAS-resistant overlay coating, in particular in the lower zone of the overlay coating, selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium, diffuse to the top surface of the overlay coating in contact with the overlying CMAS layer. The metal components consisting of aluminum and chromium, for example Al8Cr5, decompose into their elements, whereby at least a portion of them can be oxidized to one or more Al-O and / or Cr-O compounds. The diffusion of chromium and / or aluminum results in the following:

[0023] 1. The self-limiting oxidation of aluminum or non-stoichiometric Al-O species, respectively, leads to the formation of a corundum (Al2O3) layer in the lower zone of the overlay coating, particularly at and / or near the interface between the top region of the conventional thermal barrier coating and the bottom region of the CMAS-resistant overlay coating. Advantageously, due to the formation of the corundum layer, an increase in volume and thus a densification and closure of grain boundaries in the lower zone of the overlay coating is observed, particularly at and / or near the interface between the top region of the conventional thermal barrier coating and the bottom region of the CMAS-resistant overlay coating.

[0024] 2. Transformation of the at least partially vertical columnar structure of the protective layer present before deposition and after heating into a porous vertical columnar structure upon heating. Beneficially, this results in strain-tolerant properties and behavior, respectively, of the overlay coating presented herein, especially at and / or near the top surface of the underlying conventional YSZ-based thermal barrier coating. The main advantage of the development of a porous and vertical columnar structure is that not only is very good strain tolerance and therefore mechanical stability of the CMAS-resistant overlay coating observed under thermal cycling, but also excellent adhesion of the overlay coating to the immediately underlying conventional thermal barrier coating.

[0025] 3. When the overlay coating is in contact with the CMAS material heated to a temperature above its melting point, for example about 1.200 to about 1.300 °C, a chemical reaction takes place in the reaction zone, i.e. the area between the top region of the overlay coating and the bottom region of the CMAS material. Indeed, a chemical reaction takes place between the aluminum (Al) and / or chromium (Cr) and / or aluminum chromium (Al-Cr) released by the CMAS-resistant overlay coating and the elements and / or constituents of the CMAS material, in particular magnesium (Mg) and / or magnesium oxide (MgO). This results in an impermeable barrier layer comprising Al-Mg-O species and / or Cr-Mg-O species and / or Al-Cr-Mg-O species. The barrier layer may comprise MgAlO4 and / or MgCrO4. Advantageously, the barrier layer formed in the reaction zone or essentially the same or identical to the reaction zone comprises at least one layer of a material or mixture of materials exhibiting a higher melting temperature than the CMAS material. Thus, the barrier layer acts as an efficient diffusion barrier for the TBC system against penetration and / or degradation by elements and / or constituents contained in the CMAS layer.

[0026] The level of oxygen deficiency and the amount of unoxidized metal components, respectively, can be easily determined by adjusting the oxygen flow rate during the CAE process. As a result, the oxidation of aluminum and / or chromium is "self-limiting" in the sense that oxidation is possible only as long as oxygen gas is available. The amount of oxygen can then be determined as previously described.

[0027] It is worth mentioning that the lower and upper zones may be formed as two merged regions rather than as two regions strictly separated by a defined interface.

[0028] Additionally, it should be noted that if some of the chromium diffused from the CMAS-resistant overlay coating does not undergo chemical reaction with elements and / or constituents of the CMAS melt, the chromium may be oxidized to one or more Cr-O compounds that are volatile at a given elevated temperature.

[0029] Another main advantage of the CMAS-resistant overlay coatings disclosed herein is that they function as an alternative to conventional thermal barrier coatings, i.e., they are suitable to be placed directly on top of a TGO layer in the absence of a conventional thermal barrier coating, typically based on YSZ. Furthermore, the CMAS-resistant overlay coating according to the first aspect of the invention functions as a protective top layer. This is particularly true for the overlay coating according to the first aspect of the invention, which has a minimum layer thickness of about 50 μm, advantageously in the range of about 50 μm to about 300 μm.

[0030] In view of the above, it can be said that the overlay coating according to the first aspect of the present invention is relatively inexpensive, versatile and durable, regardless of surface properties, particularly surface texture.

[0031] According to a preferred embodiment of the overlay coating according to the first aspect of the present invention it is provided that the CMAS-resistant overlay coating is free of rare earth metals.

[0032] In this context, the term "rare earth metal-free" means that the CMAS-resistant overlay coating contains rare earth metals in an amount up to 10 atomic percent, preferably less than 10 atomic percent, more preferably less than 9 atomic percent, and most preferably less than 8 atomic percent.

[0033] "Atomic percentage", hereinafter abbreviated as at.%, is a measure of the proportion of all rare earth metal atoms contained in the overlay coating composition relative to the total number of atoms.

[0034] A further embodiment of the overlay coating presented herein provides that the metal oxide matrix comprises at least one oxide species containing aluminum and / or chromium. In another embodiment of the overlay coating according to the first aspect of the invention, the metal oxide matrix comprises an oxide species selected from the group consisting of Al-O, Cr-O and Al-Cr-O species, and mixtures thereof. Advantageously, the metal oxide matrix comprises an oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide, and non-stoichiometric, oxygen-deficient aluminum chromium oxide, aluminum oxide (Al2O3), chromium oxide (Cr2O3) and aluminum chromium oxide (Al,Cr)2O3, and mixtures thereof.

[0035] Non-stoichiometric oxygen species indicate a non-stoichiometric ratio between aluminum and / or chromium and oxygen. In other words, non-stoichiometric oxygen-deficient aluminum oxide contains a combination of aluminum oxide (Al2O3) and aluminum, i.e., an excess of aluminum. This is equally true for non-stoichiometric oxygen-deficient chromium oxide. In the case of non-stoichiometric oxygen-deficient aluminum chromium oxide, there is a combination of aluminum chromium oxide (Al,Cr)2O3 and chromium and / or aluminum.

[0036] The level of oxygen deficiency and the amount of unoxidized metal components, respectively, can be easily determined by adjusting the oxygen flow rate during the CAE process.

[0037] A further embodiment of the overlay coating according to the first aspect of the invention described herein provides that the CMAS-resistant overlay coating comprises a lower zone and an upper zone, where the lower zone comprises an oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide and non-stoichiometric, oxygen-deficient aluminum chromium oxide, and mixtures thereof, and the upper zone typically comprises aluminum oxide (Al2O3), chromium oxide (Cr2O3) and aluminum chromium oxide (Al,Cr)2O, in addition to oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide and non-stoichiometric, oxygen-deficient aluminum chromium oxide, and mixtures thereof. 3、 and mixtures thereof, or a mixture of at least one of the foregoing non-stoichiometric oxides with at least one of the foregoing stoichiometric oxides.

[0038] According to another embodiment of the overlay coating according to the first aspect of the invention, the metallic components comprising or consisting of aluminum and chromium are, independently of one another, in the form of an alloy, an intermetallic compound or a solid solution. Advantageously, it is provided that the metallic components comprising or consisting of aluminum and chromium comprise or consist of Al1Cr2 or Al8Cr5, or combinations or mixtures thereof.

[0039] Another preferred embodiment of the overlay coating presented herein provides that the non-oxidized aluminum and / or non-oxidized chromium and / or non-oxidized aluminum chromium are in the form of metallic droplets.

[0040] In a further embodiment of the overlay coating according to the first aspect of the present invention, the overlay coating may provide elemental aluminum and / or elemental chromium and / or aluminum chromium at a temperature in the range of 1.000°C to 1.600°C, advantageously in the range of 1.100°C to 1.500°C, more advantageously in the range of 1.150°C to 1.450°C.

[0041] According to another important embodiment of the overlay coating according to the first aspect of the invention described herein, the vertical columnar structure of the CMAS-resistant overlay coating comprises: - extending partially through the thickness of the CMAS-resistant overlay coating, advantageously about 50% or more of the thickness, or essentially the entire or entire thickness of the CMAS-resistant overlay coating; and / or extending partially across the width of the CMAS-resistant overlay coating, or across essentially the entire or entire width of the CMAS-resistant overlay coating.

[0042] If the vertical columnar structures extend only partially through the thickness of the CMAS-resistant overlay coating, the vertical structures may be at least partially interrupted in the vertical direction.If the vertical columnar structures extend only partially across the width of the CMAS-resistant overlay coating, the vertical structures may be at least partially interrupted in the horizontal direction.

[0043] Another embodiment of the overlay coating according to the first aspect of the invention provides that the CMAS-resistant overlay coating has a layer thickness in the range of 5 μm to 300 μm, advantageously in the range of 10 μm to 250 μm, more advantageously in the range of 15 μm to 150 μm, in particular in the range of 20 μm to 100 μm.

[0044] In a further embodiment of the overlay coating according to the first aspect of the invention, the CMAS-resistant overlay coating serves as a top layer on a conventional, in particular YSZ-based, thermal barrier coating. A minimum layer thickness of the overlay coating of about 5 μm is then required. Advantageously, the CMAS-resistant overlay coating has a layer thickness in the range of 5 μm to 49 μm, more advantageously in the range of 5 μm to 45 μm, preferably in the range of 5 μm to 40 μm. For example, the overlay coating has a layer thickness in the range of 10 μm to 35 μm or in the range of 15 μm to 30 μm. The overlay coating may also have a layer thickness of 6 μm or 7 μm or 8 μm or 9 μm or 11 μm or 12 μm or 13 μm or 14 μm or 16 μm or 17 μm or 18 μm or 19 μm or 20 μm or 21 μm or 22 μm or 23 μm or 24 μm or 25 μm or 26 μm or 27 μm or 28 μm or 29 μm or 31 μm or 32 μm or 33 μm or 34 μm or 36 μm or 37 μm or 38 μm or 39 μm or 41 μm or 42 μm or 43 μm or 44 μm or 46 μm or 47 μm or 48 μm.

[0045] Another important embodiment of the overlay coating according to the first aspect of the present invention provides that the CMAS-resistant overlay coating i. has a layer thickness in the range of 50 μm to 300 μm, and ii. functions as both a thermal barrier coating and a top layer.

[0046] Advantageously, this embodiment of the CMAS-resistant overlay coating according to the first aspect of the invention provides that the overlay coating is used as a further protective top layer as an alternative to conventional, typically YSZ-based, thermal barrier coatings. The overlay coating is therefore applied in the absence of a conventional thermal barrier coating, i.e. without an underlying conventional thermal barrier coating, but usually with an underlying TGO layer. Advantageously, even with layer thicknesses in the range of 50 μm to 300 μm, the CMAS-resistant overlay coating is very cost-effective, since only relatively inexpensive aluminum and / or chromium are required instead of cost-intensive rare earth metals. Another main advantage over the prior art is that the overlay coating shows very good mechanical stability under thermal cycling and excellent adhesion to the underlying layer, usually a TGO layer, even when temperatures of 1.500 °C and above, especially up to 1.600 °C, are applied.

[0047] Another embodiment of the overlay coating provides that the CMAS-resistant overlay coating functions both as a thermal barrier coating and as a top layer and has a layer thickness in the range of 50 μm to 295 μm, more advantageously in the range of 50 μm to 150 μm, preferably in the range of 50 μm to 100 μm. For example, the overlay coating has a layer thickness in the range of 55 μm to 95 μm or in the range of 60 μm to 90 μm. The overlay coating can also have a layer thickness of 65 μm or 70 μm or 75 μm or 80 μm or 85 μm or 105 μm or 110 μm or 115 μm or 120 μm or 125 μm or 130 μm or 135 μm or 140 μm or 145 μm or 155 μm or 160 μm or 165 μm or 170 μm or 175 μm or 180 μm or 185 μm. The layer may have a layer thickness of 190 μm or 200 μm or 205 μm or 210 μm or 215 μm or 220 μm or 225 μm or 230 μm or 235 μm or 240 μm or 245 μm or 250 μm or 255 μm or 260 μm or 265 μm or 270 μm or 275 μm or 280 μm or 285 μm or 290 μm.

[0048] According to a second aspect of the present invention, the above problem is solved by a substrate comprising or consisting of a material susceptible to CMAS corrosion, the substrate comprising: i. comprises or consists of at least one substrate layer comprising or consisting of a material susceptible to CMAS corrosion; ii. having a CMAS-resistant overlay coating on at least one surface of the substrate layer.

[0049] In particular, at least one of the overlay coatings is a CMAS-resistant overlay coating according to one or more of the above-mentioned embodiments in the context of the first aspect of the invention. If two or more overlay coatings are provided, preferably all of them are CMAS-resistant overlay coatings according to one or more of the above-mentioned embodiments, whereby each overlay coating is in particular formed and deposited respectively by applying a process according to the third aspect of the invention described below.

[0050] Whether or not the overlay coating is formed and deposited by a process according to one or more of the process embodiments described below, respectively, the CMAS-resistant overlay coating may be: i. a metal oxide matrix, a metal oxide matrix, wherein at least one unoxidized metal component selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium is embedded in the metal oxide matrix; ii. have at least a partial vertical columnar structure;

[0051] Within the scope of the present invention, the terms "CMAS-resistant overlay coating" and "overlay coating" and "protective layer" are used synonymously.

[0052] The terms "surface", "layer" and "thermal barrier coating system" are as defined above in relation to the first aspect of the invention.

[0053] "Material susceptible to CMAS corrosion" is as defined above in the context of the first aspect of the invention.

[0054] The metal oxide matrix may comprise one or more stoichiometric metal oxides and / or one or more non-stoichiometric, in particular oxygen-deficient, metal oxides.

[0055] Details regarding the formation and high temperature behavior of CMAS-resistant overlay coatings disposed on a surface of at least one layer of a substrate as described herein, and details regarding the manifold advantages associated with the application of such overlay coatings, particularly according to one or more of the above-described embodiments, are detailed above in the context of the first aspect of the invention and below in relation to the third aspect of the invention.

[0056] Surprisingly, under thermal cycling, the CMAS-resistant overlay coating, particularly according to the first aspect of the invention, disposed on the surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion, i.e. on at least one surface of a substrate layer, shows very good mechanical stability and excellent adhesion to the immediately underlying material surface, even when temperatures of 1.500° C. or higher, particularly up to 1.600° C. are applied. This is due in particular to the formation of an impermeable barrier layer involving unoxidized metallic components from the CMAS-resistant overlay coating that have diffused to the interface between the overlay coating and the immediately overlying molten CMAS material, as explained below.

[0057] When heated at high temperatures, i.e., at temperatures above about 1.000° C., the overlay coating can release the contained non-oxidized metal components, i.e., aluminum and / or chromium and / or metal components including or consisting of aluminum and chromium embedded in a metal oxide matrix. Briefly, the non-oxidized metal components then diffuse to the top surface of the CMAS-resistant overlay coating and the bottom surface of the liquid CMAS layer, respectively, and react with the elements and / or components of the CMAS material, e.g., calcium, magnesium, magnesium oxide, and silicon. Thereby, an impermeable barrier layer is formed that has a higher melting temperature than the CMAS material, thus effectively inhibiting the liquid CMAS material from penetrating into the respective underlying substrate layer, e.g., a TBC system, and / or reacting with the components of the respective underlying substrate layer, e.g., during operation of a gas turbine.

[0058] In an important embodiment of the substrate according to the second aspect of the invention, the material susceptible to CMAS corrosion is selected from the group consisting of metals, superalloys, ceramic materials and ceramic matrix composites (CMCs), and combinations thereof. Alternatively or complementary, at least one of the substrate layers comprises or consists of a CMC comprising or consisting of a SiC-based CMC.

[0059] According to another embodiment of the substrate according to the second aspect of the invention described herein, the substrate comprises a base layer, in particular a metal or metal alloy, for example a superalloy, - a thermal barrier coating (TBC) system comprising a YSZ-based thermal barrier coating disposed on a thermally grown oxide (TGO) layer; It comprises or consists of:

[0060] In a complementary embodiment of the substrate, the TBC system includes a bond coat (BC) layer disposed between the base layer and the TGO layer.

[0061] An alternative embodiment is a substrate comprising: a base layer, in particular a metal or metal alloy, for example a superalloy, a bond coat (BC) layer and a TGO layer, the BC layer being disposed between the base layer and the TGO layer; The present invention provides a method for manufacturing a semiconductor device, comprising the steps of:

[0062] A further embodiment of the substrate according to the second aspect of the invention provides that the base layer is part of a turbine, in particular a gas turbine, such as a turbine blade, a combustion chamber, in particular a turbine inlet of a high pressure turbine.

[0063] Yet another embodiment of the substrate according to the second aspect of the invention described herein provides that the BC layer comprises or consists of a material selected from the group consisting of NiCoCrAlY, Pt-modified diffusion aluminides and glass ceramics. Alternatively, the BC layer may comprise a material selected from the group consisting of NiCoCrAlY and Pt-modified diffusion aluminides.

[0064] According to a preferred embodiment of the substrate disclosed herein, it is provided that the CMAS-resistant overlay coating is free of rare earth metals, meaning that the CMAS-resistant overlay coating contains rare earth metals in an amount of up to 10 atomic percent, preferably less than 10 atomic percent, more preferably less than 9 atomic percent, and most preferably less than 8 atomic percent.

[0065] The term "atomic percentage" is defined above. Another embodiment of the substrate according to the second aspect of the invention described herein provides that the metal oxide matrix comprised in the CMAS-resistant overlay coating comprises at least one oxide species containing aluminum and / or chromium. In another embodiment of the substrate, the metal oxide matrix comprises an oxide species selected from the group consisting of Al-O, Cr-O and Al-Cr-O species, and mixtures thereof. Advantageously, the metal oxide matrix comprises an oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide, and non-stoichiometric, oxygen-deficient aluminum chromium oxide, aluminum oxide (Al2O3), chromium oxide (Cr2O3) and aluminum chromium oxide (Al,Cr)2O3, and mixtures thereof.

[0066] Non-stoichiometric oxygen species indicate a non-stoichiometric ratio between aluminum and / or chromium and oxygen. In other words, non-stoichiometric oxygen-deficient aluminum oxide contains a combination of aluminum oxide (Al2O3) and aluminum, i.e., an excess of aluminum. This is equally true for non-stoichiometric oxygen-deficient chromium oxide. In the case of non-stoichiometric oxygen-deficient aluminum chromium oxide, there is a combination of aluminum chromium oxide (Al,Cr)2O3 with chromium and / or aluminum.

[0067] The level of oxygen deficiency and the amount of unoxidized metal components, respectively, can be easily determined by adjusting the oxygen flow rate during the CAE process.

[0068] Yet another embodiment of the substrate according to the second aspect of the invention provides that the CMAS-resistant overlay coating comprises a lower zone and an upper zone, where the lower zone comprises an oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide and non-stoichiometric, oxygen-deficient aluminum chromium oxide, and mixtures thereof, and the upper zone typically comprises aluminum oxide (Al2O3), chromium oxide (Cr2O3) and aluminum chromium oxide (Al,Cr)2O, in addition to oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide and non-stoichiometric, oxygen-deficient aluminum chromium oxide, and mixtures thereof. 3、 and mixtures thereof, or a mixture of at least one of the foregoing non-stoichiometric oxides with at least one of the foregoing stoichiometric oxides.

[0069] The lower and upper zones may be formed as two merged regions rather than as two regions strictly separated by a defined interface.

[0070] According to a further embodiment of the substrate according to the second aspect of the invention presented herein, the metal components comprising or consisting of aluminum and chromium are, independently of one another, in the form of an alloy, an intermetallic compound or a solid solution. In an advantageous embodiment, it is provided that the non-oxidized metal components comprising or consisting of aluminum and chromium embedded in the metal oxide matrix of the CMAS-resistant overlay coating comprise or consist of Al1Cr2 or Al8Cr5, or combinations or mixtures thereof.

[0071] Another preferred embodiment of the substrate disclosed herein provides that the non-oxidized aluminum and / or non-oxidized chromium and / or non-oxidized aluminum chromium are in the form of metal droplets.

[0072] In another embodiment of the substrate according to the second aspect of the present invention, the overlay coating may provide elemental aluminum and / or elemental chromium and / or aluminum chromium at a temperature in the range of 1.000°C to 1.600°C, advantageously in the range of 1.100°C to 1.500°C, and more advantageously in the range of 1.150°C to 1.450°C.

[0073] According to another important embodiment of the substrate according to the second aspect of the invention described herein, the vertical columnar structure of the CMAS-resistant overlay coating comprises: - extending partially through the thickness of the CMAS-resistant overlay coating, advantageously about 50% or more of the thickness, or through essentially the entire or entire thickness of the CMAS-resistant overlay coating; and / or extending partially across the width of the CMAS-resistant overlay coating, or across essentially the entire or entire width of the CMAS-resistant overlay coating.

[0074] If the vertical columnar structures extend only partially through the thickness of the CMAS-resistant overlay coating, the vertical structures may be at least partially interrupted in the vertical direction.If the vertical columnar structures extend only partially across the width of the CMAS-resistant overlay coating, the vertical structures may be at least partially interrupted in the horizontal direction.

[0075] Another embodiment of the substrate according to the second aspect of the invention provides that the CMAS-resistant overlay coating has a layer thickness in the range of 5 μm to 300 μm, advantageously in the range of 10 μm to 250 μm, more advantageously in the range of 15 μm to 150 μm, in particular in the range of 20 μm to 100 μm.

[0076] In a further embodiment of the substrate according to the second aspect of the invention, the CMAS-resistant overlay coating serves as a top layer on a conventional, in particular YSZ-based, thermal barrier coating. A minimum layer thickness of the overlay coating of about 5 μm is then required. Advantageously, the CMAS-resistant overlay coating has a layer thickness in the range of 5 μm to 49 μm, more advantageously in the range of 5 μm to 45 μm, preferably in the range of 5 μm to 40 μm. For example, the overlay coating has a layer thickness in the range of 10 μm to 35 μm or in the range of 15 μm to 30 μm. The overlay coating may also have a layer thickness of 6 μm or 7 μm or 8 μm or 9 μm or 11 μm or 12 μm or 13 μm or 14 μm or 16 μm or 17 μm or 18 μm or 19 μm or 20 μm or 21 μm or 22 μm or 23 μm or 24 μm or 25 μm or 26 μm or 27 μm or 28 μm or 29 μm or 31 μm or 32 μm or 33 μm or 34 μm or 36 μm or 37 μm or 38 μm or 39 μm or 41 μm or 42 μm or 43 μm or 44 μm or 46 μm or 47 μm or 48 μm.

[0077] Another important embodiment of the substrate according to the second aspect of the present invention provides that the CMAS-resistant overlay coating i. has a layer thickness in the range of 50 μm to 300 μm, and ii. functions as both a thermal barrier coating and a top layer.

[0078] Advantageously, this embodiment of the substrate according to the second aspect of the invention provides that the overlay coating is used as a further protective top layer as an alternative to a conventional, typically YSZ-based, thermal barrier coating. The overlay coating is therefore applied in the absence of a conventional thermal barrier coating, i.e. without an underlying conventional thermal barrier coating. Advantageously, even with layer thicknesses in the range of 50 μm to 300 μm, the CMAS-resistant overlay coating is very cost-effective, since only relatively inexpensive aluminum and / or chromium are required instead of cost-intensive rare earth metals. Another main advantage over the prior art is that the overlay coating shows very good mechanical stability under thermal cycling and excellent adhesion to the underlying layer, typically a TGO layer, even when temperatures of 1.500 °C and above, especially up to 1.600 °C, are applied.

[0079] Another embodiment of the substrate according to the second aspect of the invention provides that the CMAS-resistant overlay coating functions both as a thermal barrier coating and as a top layer and has a layer thickness in the range of 50 μm to 295 μm, more advantageously in the range of 50 μm to 150 μm, preferably in the range of 50 μm to 100 μm. For example, the overlay coating has a layer thickness in the range of 55 μm to 95 μm or in the range of 60 μm to 90 μm. The overlay coating may also have a layer thickness of 65 μm or 70 μm or 75 μm or 80 μm or 85 μm or 105 μm or 110 μm or 115 μm or 120 μm or 125 μm or 130 μm or 135 μm or 140 μm or 145 μm or 155 μm or 160 μm or 165 μm or 170 μm or 175 μm or 180 μm or 185 μm. The layer may have a layer thickness of 190 μm or 200 μm or 205 μm or 210 μm or 215 μm or 220 μm or 225 μm or 230 μm or 235 μm or 240 μm or 245 μm or 250 μm or 255 μm or 260 μm or 265 μm or 270 μm or 275 μm or 280 μm or 285 μm or 290 μm.

[0080] Overall, the substrates disclosed herein can be said to be particularly durable since they have a CMAS-resistant overlay coating on the surface, particularly on its top surface. The behavior of the overlay coating at high temperatures results in the formation of an impermeable barrier layer that effectively protects the respective underlying substrate, including the TBC system, from penetration and / or degradation, for example, by liquid CMAS materials. Therefore, the application of a CMAS-resistant overlay coating, advantageously according to one or more of the above-mentioned embodiments, is particularly beneficial from both an economical and an ecological point of view.

[0081] According to a third aspect of the present invention, the above problem is solved by a cathodic arc deposition (CAE) process for forming a CMAS-resistant overlay coating on a surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion, the overlay coating comprising at least one CMAS-resistant layer. The process comprises: A. Providing a target for use as a cathode material, the target material comprising or consisting of aluminum and / or chromium; B. providing a process gas that comprises or consists of oxygen; C. evaporating aluminum and / or chromium from the target material provided in step A; D. reacting the evaporated aluminum and / or chromium evaporated in step C with the process gas supplied in step B; and E. Depositing the reaction product of step D as a CMAS-resistant overlay coating on the surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion, i.e. on the surface of at least one substrate layer, in particular until the CMAS-resistant overlay coating has a desired layer thickness. Includes.

[0082] The terms "CMAS-resistant overlay coating" and "overlay coating" and "protective layer" are used interchangeably.

[0083] The terms "surface," "material susceptible to CMAS corrosion," and "substrate comprising or consisting of a material susceptible to CMAS corrosion" are as defined above.

[0084] Within the scope of the present invention, the term "layer" is synonymous with the term "film" and does not provide any information regarding layer or film thickness. Furthermore, layers do not necessarily have a uniform thickness. However, if a layer thickness is specified, this layer thickness is intended to be present in at least a portion of the respective layer, i.e., at its maximum thickness.

[0085] The process according to the third aspect of the invention provides that the formation and deposition of the CMAS-resistant overlay coating, in particular the overlay coating according to one or more embodiments according to the first aspect of the invention, are performed by a CAE method, respectively. The latter is carried out as a reactive physical vapor deposition (PVD) process, combining thin film deposition or thin film coating, respectively, with a reactive gas plasma in an arc evaporation device. The latter typically comprises a target material operable as a cathode during arc evaporation. Furthermore, the arc evaporation device may also comprise at least one electrode operable as an anode during arc evaporation. The arc evaporation device is placed in a vacuum chamber of the coating device. To carry out the CAE process, means are usually used that ignite a high current discharge, establish a plasma, form an arc with a spot that moves across the surface of the target, thereby tearing electrons from the target material, more precisely from the surface of the target material. Due to the heat generated at the spot, the target material is evaporated and atomized, respectively, and deposited on a surface provided for this purpose. The arc evaporation device is therefore also called a coating source or a plasma source. The terms "evaporator", "coating source" and "plasma source" are commonly used as synonyms.

[0086] When applying the process according to the third aspect of the invention, the formation of the metal oxide matrix contained in the CMAS-resistant overlay coating according to the first aspect of the invention is achieved by carrying out CAE as a reactive PVD process. In step C of this process, the metal components, i.e. aluminum and / or chromium, are evaporated from a single elemental target material consisting of aluminum or chromium or from a multi-elemental target material comprising or consisting of aluminum and chromium provided in step A. Step D provides that the evaporated aluminum and / or chromium reacts with a process gas comprising or consisting of oxygen, which is introduced in step D into the coating chamber. As a result, in step E, the ceramic oxide material, which is the reaction product of step D, is deposited as a CMAS-resistant overlay coating on the surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion, in particular on the top surface of the substrate.

[0087] It should be noted that steps B and C do not have to be carried out as separate steps, but may instead be included in step D. However, when steps B and C are carried out in two steps, the order described is not mandatory. Moreover, from the very nature of the CAE process described herein, it is clear that steps B, C, D and E should be repeated until an overlay coating having a desired layer thickness is formed on each surface of the substrate, i.e. on at least one surface of the substrate layer comprising or consisting of a material susceptible to CMAS corrosion. It is clear that the reaction product of step D, including in particular steps B and C, may be deposited according to step E and may be simultaneously reacted again according to step D.

[0088] In summary, it is a major advantage of the process according to the third aspect of the present invention that it provides a CMAS-resistant overlay coating that can provide elemental aluminum and / or elemental chromium and / or aluminum chromium at temperatures in the range of 1.000°C to 1.600°C, advantageously in the range of 1.100°C to 1.500°C, and more advantageously in the range of 1.150°C to 1.550°C.

[0089] In general, depending on the target material, particularly its material composition, and the oxygen partial pressure controlled and / or influenced by the gas flow controller and the arc current, the CMAS-resistant overlay coating comprises: i. a metal oxide matrix comprising at least one oxidizing species, particularly comprising aluminum and / or chromium, more particularly selected from the group consisting of Al-O species and / or Cr-O species and / or Al-Cr-O species; and ii. at least one non-oxidized metal component embedded in the metal oxide matrix and selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium.

[0090] In particular, the metal oxide matrix comprises an oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide, and non-stoichiometric, oxygen-deficient aluminum chromium oxide, aluminum oxide (Al2O3), chromium oxide (Cr2O3), and aluminum chromium oxide (Al,Cr)2O3, or mixtures thereof.

[0091] Thereby, the non-stoichiometric oxygen species indicates a non-stoichiometric ratio between aluminum and / or chromium and oxygen. In other words, the non-stoichiometric oxygen-deficient aluminum oxide contains a combination of aluminum oxide and aluminum, i.e., an excess of aluminum. This is equally true for the non-stoichiometric oxygen-deficient chromium oxide. In the case of the non-stoichiometric oxygen-deficient aluminum chromium oxide, there is a combination of aluminum chromium oxide with chromium and / or aluminum.

[0092] In the CMAS-resistant layer deposited in step E, the non-oxidized metal components comprising or consisting of aluminum and chromium are, independently of one another, in the form of an alloy, an intermetallic compound or a solid solution. In particular, the non-oxidized aluminum, the non-oxidized chromium and the non-oxidized metal components comprising or consisting of aluminum and chromium are in the form of metal droplets. Advantageously, the non-oxidized metal components comprising or consisting of aluminum and chromium comprise or consist of Al1Cr2 or Al8Cr5, or combinations or mixtures thereof.

[0093] Advantageously, the CMAS-resistant overlay coating deposited in step E typically comprises a lower zone and an upper zone. The lower zone then comprises an oxide species selected from the group consisting of non-stoichiometric oxygen-deficient aluminum oxide, non-stoichiometric oxygen-deficient chromium oxide and non-stoichiometric oxygen-deficient aluminum chromium oxide, and mixtures thereof. The upper zone also typically comprises an oxide species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide and non-stoichiometric, oxygen-deficient aluminum chromium oxide, and mixtures thereof, as well as a stoichiometric oxide species selected from the group consisting of aluminum oxide (Al2O3), chromium oxide (Cr2O3) and aluminum chromium oxide (Al,Cr)2O3, or a mixture of at least one of the aforementioned non-stoichiometric oxides and at least one of the aforementioned stoichiometric oxides.

[0094] The above-mentioned intermetallic compounds or solid solutions are obtained according to the Al-Cr phase diagram, the composition of which depends on the respective target material. For example, the target material Al 70 Cr 30 In the case of (70 at.% Al and 30 at.% Cr), metallic droplets of Al8Cr5 can be detected in the CMAS-resistant overlay coating, which, according to the Al-Cr binary phase diagram, shows a transition to the liquid phase at about 1.300 °C. Alternatively or supplementally, especially Al 50 Cr 50If a target composition of (50 at.% Al and 50 at.% Cr) is selected, metal droplets with a higher chromium content and therefore a higher transition temperature to the liquid phase, e.g. Al1Cr2, can be detected in the CMAS-resistant overlay coating after its deposition, i.e. by XRD analysis. At high temperatures of about 1.300 °C, the aluminum-chromium metal component with one of the above-mentioned compositions, for example, begins to decompose into its elements, whereby at least a part of them can be oxidized to one or more Al-O and / or Cr-O compounds. This is a major difference compared to pure aluminum droplets or metal droplets containing a substantially larger atomic percentage of aluminum than chromium. The latter show a higher thermal stability at the aforementioned temperatures. The decomposition of the aluminum-chromium component is accompanied by the diffusion of chromium towards the top surface of the CMAS-resistant overlay coating. If part of the chromium does not react with the components and / or elements contained in the CMAS material in contact with the CMAS-resistant overlay coating, the chromium can be oxidized to one or more Cr-O compounds that are volatile at high temperatures.

[0095] An embodiment of the process according to the third aspect of the invention provides that the target material comprises or consists of aluminium and / or chromium, the chromium being present in an amount of at least 15 atomic percent, advantageously in an amount of at least 20 atomic percent, in particular in an amount of at least 25 atomic percent.

[0096] A further embodiment of the process according to the third aspect of the invention is characterized in that the target material comprises i. consisting essentially of aluminum and chromium; or ii. Consists entirely of aluminum and chromium To provide.

[0097] "Atomic percentage" is abbreviated as at.% and is a measure of the ratio of one type of atom, here chromium, to the total number of atoms, i.e., aluminum and chromium, for example, if the target material consists entirely of aluminum and chromium. If the target material consists essentially of aluminum and chromium, these two elements are present in the target material in an amount of at least 97 at.%, preferably at least 98 at.%, and more preferably at least 99 at.%.

[0098] Preferably, the target material is free of rare earth metals in the sense that only trace amounts of rare earth metals may be present in the target material, the term "trace amount" meaning an amount below the threshold of the relevant analytical method, e.g., inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0099] In a further embodiment of the process according to the third aspect of the invention, the oxygen partial pressure is in the range of 0.001 Pa to 10 Pa.

[0100] Advantageously, the oxygen deficiency level of the non-stoichiometric, oxygen-deficient metal oxide, in particular the non-stoichiometric, oxygen-deficient aluminum oxide and / or the non-stoichiometric, oxygen-deficient chromium oxide and / or the non-stoichiometric, oxygen-deficient aluminum chromium oxide, respectively, contained in the CMAS-resistant overlay coating deposited in step E, can be determined by simply adjusting the oxygen flow rate during the CAE process according to the third aspect of the present invention.

[0101] In a preferred embodiment of the process according to the third aspect of the invention, a CMAS-resistant overlay coating according to one or more embodiments of the first aspect of the invention is deposited in step E onto a surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion. The CMAS-resistant overlay coating is thereby preferably deposited on a substrate according to one or more embodiments according to the second aspect of the invention.

[0102] In particular, the CMAS-resistant overlay coating deposited in step E of the process described herein comprises i. comprises at least one CMAS-resistant layer; ii. a metal oxide matrix, a metal oxide matrix, wherein at least one unoxidized metal component selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium is embedded in the metal oxide matrix; iii. having at least a partial vertical columnar structure;

[0103] Advantageously, the vertical columnar structure of the CMAS-resistant overlay coating deposited in Step E is generally - extending partially through the thickness of the CMAS-resistant overlay coating, advantageously about 50% or more of the thickness, or essentially the entire or entire thickness of the CMAS-resistant overlay coating; and / or extending partially across the width of the CMAS-resistant overlay coating, or across essentially the entire or entire width of the CMAS-resistant overlay coating.

[0104] If the vertical columnar structures extend only partially through the thickness of the CMAS-resistant overlay coating, the vertical structures may be at least partially interrupted in the vertical direction.If the vertical columnar structures extend only partially across the width of the CMAS-resistant overlay coating, the vertical structures may be at least partially interrupted in the horizontal direction.

[0105] In another embodiment of the process according to the third aspect of the invention, step E is carried out until the CMAS-resistant overlay coating has a layer thickness in the range of 5 μm to 300 μm, advantageously in the range of 10 μm to 250 μm, more advantageously in the range of 15 μm to 150 μm, in particular in the range of 20 μm to 100 μm.

[0106] In a further embodiment of the process according to the third aspect of the invention, in step E, a CMAS-resistant overlay coating is deposited on the surface of a thermal barrier coating, in particular a conventional, in particular YSZ-based, coating, in order to act as a top layer on such a thermal barrier coating. In particular, the CMAS-resistant overlay coating is deposited on the top surface of the thermal barrier coating. In the aforementioned case, step E is carried out until the CMAS-resistant overlay coating has a layer thickness of about 5 μm. Advantageously, step E is carried out until the CMAS-resistant overlay coating has a layer thickness in the range of 5 μm to 49 μm, more advantageously in the range of 5 μm to 45 μm, preferably in the range of 5 μm to 40 μm. For example, step E is carried out until the overlay coating has a layer thickness in the range of 10 μm to 35 μm or in the range of 15 μm to 30 μm. The overlay coating may also have a layer thickness of 6 μm or 7 μm or 8 μm or 9 μm or 11 μm or 12 μm or 13 μm or 14 μm or 16 μm or 17 μm or 18 μm or 19 μm or 20 μm or 21 μm or 22 μm or 23 μm or 24 μm or 25 μm or 26 μm or 27 μm or 28 μm or 29 μm or 31 μm or 32 μm or 33 μm or 34 μm or 36 μm or 37 μm or 38 μm or 39 μm or 41 μm or 42 μm or 43 μm or 44 μm or 46 μm or 47 μm or 48 μm.

[0107] Another alternative or complementary embodiment of the process according to the third aspect of the invention provides that in step E, a CMAS-resistant overlay coating is deposited on the surface of the thermally grown oxide layer, having a layer thickness in the range of 50 μm to 300 μm. In particular, the CMAS-resistant overlay coating is deposited on the top surface of the TGO layer. In the aforementioned case, in step E, the CMAS-resistant overlay coating functions both as a thermal barrier coating and as a protective top layer. Advantageously, the overlay coating is used as a replacement for a conventional, typically YSZ-based, thermal barrier coating, and further as a protective top layer. Thus, the overlay coating is applied in the absence of a conventional thermal barrier coating, i.e. in the absence of an underlying conventional thermal barrier coating. Advantageously, even with a layer thickness in the range of 50 μm to 300 μm, the CMAS-resistant overlay coating obtained by one or more embodiments of the straightforward, relatively cost-effective and energy-saving process described herein is very cost-effective, since only relatively inexpensive aluminum and / or chromium are required instead of costly rare earth metals. Another major advantage over the prior art is that the overlay coatings show very good mechanical stability under thermal cycling and excellent adhesion to the underlying layer, which is usually a TGO layer, even when temperatures above 1.500°C, especially up to 1.600°C, are applied.

[0108] Another embodiment of the process provides that step E is carried out until the CMAS-resistant overlay coating has a layer thickness in the range of 50 μm to 250 μm, more advantageously in the range of 50 μm to 150 μm, preferably in the range of 50 μm to 100 μm. For example, step E is carried out until the overlay coating has a layer thickness in the range of 55 μm to 95 μm or in the range of 60 μm to 90 μm. The overlay coating may also have a layer thickness of 65 μm or 70 μm or 75 μm or 80 μm or 85 μm or 105 μm or 110 μm or 115 μm or 120 μm or 125 μm or 130 μm or 135 μm or 140 μm or 145 μm or 155 μm or 160 μm or 165 μm or 170 μm or 175 μm or 180 μm or 185 μm or 190 μm or 200 μm or 205 μm or 210 μm or 215 μm or 220 μm or 225 μm or 230 μm or 235 μm or 240 μm or 245 μm or 260 μm or 265 μm or 270 μm or 275 μm or 280 μm or 285 μm or 290 μm or 295 μm.

[0109] According to another embodiment of the process according to the third aspect of the present invention, the substrate comprising or consisting of a material susceptible to CMAS corrosion comprises or consists of at least one substrate layer. Thereby, at least one of the substrate layers comprises or consists of a material susceptible to CMAS corrosion. Typically, the material susceptible to CMAS corrosion is selected from the group consisting of metals, superalloys, ceramic materials and ceramic matrix composites (CMCs), and combinations thereof. Alternatively or complementary, at least one of the substrate layers comprises or consists of a CMC comprising or consisting of a SiC-based CMC.

[0110] A further embodiment of the process according to the third aspect of the invention is a process comprising: A base layer; - a thermal barrier coating (TBC) system comprising a YSZ-based thermal barrier coating disposed on a thermally grown oxide (TGO) layer; The present invention provides a method for manufacturing a semiconductor device, comprising the steps of:

[0111] In a complementary embodiment of the process, the TBC system included in the substrate includes a bond coat (BC) layer disposed between the base layer and the TGO layer.

[0112] Another embodiment of the process according to the third aspect of the invention is a process comprising the steps of: A base layer; a bond coat (BC) layer and a TGO layer, the BC layer being disposed between the base layer and the TGO layer; The present invention provides a method for manufacturing a semiconductor device, comprising the steps of:

[0113] A further embodiment of the process according to the third aspect of the invention provides that the base layer of the substrate is part of a turbine, in particular a gas turbine, such as a turbine blade, a combustion chamber, in particular a turbine inlet of a high pressure turbine.

[0114] Yet another embodiment of the process according to the third aspect of the invention described herein provides that the BC layer comprises or consists of a material selected from the group consisting of NiCoCrAlY, Pt modified diffusion aluminides and glass ceramics. Alternatively, the BC layer may comprise a material selected from the group consisting of NiCoCrAlY and Pt modified diffusion aluminides.

[0115] In summary, the process according to the third aspect of the invention for forming a CMAS-resistant overlay coating, in particular an overlay coating according to the first aspect of the invention, on a surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion is versatile with respect to surface properties, in particular surface texture, simple, relatively cost-effective, energy-saving and easily scalable to industrial applications.

[0116] The invention will now be described in more detail by the following figures and examples which are considered to be illustrative and do not limit the invention or the claims. [Brief description of the drawings]

[0117] [Figure 1] Schematic of a substrate comprising: a) a TBC system and an overlay coating; b) the TBC system and the overlay coating in contact with a CMAS layer; c) the TBC system and the overlay coating in contact with the CMAS layer exposed to a temperature above its melting point; and d) a TGO layer as a top substrate layer having an overlay coating on top of it. [Diagram 2] FIG. 1 is a cross-sectional scanning electron microscope (X-SEM) image of an upper region of a conventional thermal barrier coating having an overlay coating according to a first embodiment of the present invention, taken after exposing the overlay coating to a CMAS material at a temperature of about 1.300° C. for several hours and cooling to room temperature. [Diagram 3] 3 is an enlarged cross-sectional view of FIG. 2 showing the top region of the conventional thermal barrier coating and the bottom region of the overlay coating according to FIG. 2. [Figure 4] 3 is an enlarged cross-sectional view of FIG. 2 showing an upper region of the overlay coating and a reaction zone located between the uppermost region of the overlay coating and the lowermost region of the CMAS material. [Diagram 5] FIG. 5 is an enlarged cross-sectional view of FIG. 4, with the zones inspected by energy dispersive X-ray spectroscopy (EDS) line scan analysis marked. [Figure 6] Figure 5. Overlay of EDS spectra as a result of line scan analysis performed within the zone. [Figure 7] Image from Figure 5, where the zones examined by EDS line scan analysis are marked. [Figure 8] Figure 7. Overlay of EDS spectra as a result of line scan analysis performed within the zone according to Figure 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0118] The left side of FIG. 1 shows a schematic diagram of a multi-layer substrate 10a consisting of a base layer 100, in particular a metal or metal alloy, and a TBC system 20. The TBC system consists of a BC layer 210, a TGO layer 220, a conventional thermal barrier coating 230, usually made of YSZ material, and a CMAS-resistant overlay coating 240 serving as a top layer, for example a CMAS-resistant overlay coating according to the first embodiment of the invention. For example, the CMAS-resistant overlay coating 240 according to the first embodiment of the invention has a layer thickness in the range of about 5 μm to about 49 μm when serving as a top layer, as shown in FIG. 1a. However, depending on its layer thickness T of the CMAS-resistant overlay coating 240 according to the invention presented herein, it may function both as a thermal barrier coating and as a top layer (FIG. 1d). In particular, when the layer thickness T of the CMAS-resistant overlay coating 240 is in the range of about 50 μm to about 300 μm, it can serve both as a replacement for a conventional thermal barrier coating and as a protective top layer. This is particularly beneficial since rare earth metals may be omitted.

[0119] The substrate 10a, having a top surface 11a and consisting of four substrate layers 100, 210, 220, 230, namely the base layer 100 having a top surface 101 and the TBC system 20 having a top surface 21, is the most prominent multi-layer substrate that includes or consists of several materials susceptible to CMAS corrosion. The TBC system 20 shown in FIG. 1a consists of three substrate layers 210, 220, 230, namely the BC layer 210 having a top surface 211, the TGO layer 220 having a top surface 221, and the thermal barrier coating 230 having a top surface 231. Thus, the top surfaces 11a, 21 and 231 are identical. According to FIG. 1a, the CMAS-resistant overlay coating 240 serves as a top layer on the substrate 10a, namely on the top surface 231 of the conventional thermal barrier coating 230. However, the CMAS-resistant overlay coating 240 according to the first aspect of the invention may also be used on other types of multi-layer substrates, or on single layer substrates that include or consist of one or more materials that are susceptible to CMAS corrosion, are exposed to high temperatures, and thus require protection against CMAS corrosion. Examples of materials that are susceptible to CMAS corrosion are metals, superalloys, particularly nickel-, cobalt-, and titanium-based alloys, ceramic materials, ceramic matrix composites (CMCs), such as SiC-based CMCs, and combinations thereof.

[0120] In Fig. 1d, an example of another multi-layer substrate 10b with a top surface 11b is shown. The substrate 10b consists of only three substrate layers 100, 210, 220, namely a base layer 100 with a top surface 101, a BC layer 210 with a top surface 211, and a TGO layer 220 with a top surface 221. This makes the top surfaces 11b and 221 identical. There is no conventional thermal barrier coating 230 as shown in Fig. 1a. Instead, a CMAS-resistant overlay coating 240 is provided with a larger layer thickness T compared to that included in the TBC system 240 shown in Fig. 1a. Thus, in the case of Fig. 1d, the overlay coating 240 functions as both a thermal barrier coating and a protective layer. In other words, the overlay coating 240 is used as a replacement for a conventional, typically YSZ-based, thermal barrier coating, and also as a protective top layer. Advantageously, even though the layer thickness T of overlay coating 240 as shown in FIG. 1d is preferably in the range of about 50 μm to about 300 μm, CMAS-resistant overlay coating 240 is very cost-effective because only relatively inexpensive aluminum and / or chromium are required instead of cost-intensive rare earth metals.

[0121] The CMAS-resistant overlay coating 240 according to the first aspect of the present invention comprises a rare earth metal-free metal oxide matrix. At least one unoxidized metal component selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium is embedded in the metal oxide matrix. The metal oxide of the CMAS-resistant overlay coating 240 may comprise an oxidizing species selected from the group consisting of Al-O species, Cr-O species, and Al-Cr-O species, and mixtures thereof. In particular, immediately after its formation, the CMAS-resistant overlay coating 240 comprises a lower zone and an upper zone, the lower zone typically comprising an oxidizing species selected from the group consisting of non-stoichiometric, oxygen-deficient aluminum oxide, non-stoichiometric, oxygen-deficient chromium oxide, and non-stoichiometric, oxygen-deficient aluminum chromium oxide, or mixtures thereof. Also, the upper zone typically comprises at least one oxide species selected from the group of aluminum oxide (Al2O3), chromium oxide (Cr2O3) and aluminum chromium oxide (Al,Cr)2O3, in addition to non-stoichiometric oxygen-deficient aluminum oxide and / or non-stoichiometric oxygen-deficient chromium oxide and / or non-stoichiometric oxygen-deficient aluminum chromium oxide, or a mixture of at least one of the aforementioned non-stoichiometric oxides with at least one of the aforementioned stoichiometric oxides. Furthermore, the CMAS-resistant overlay coating 240 has a vertical columnar structure extending partially through the thickness T of the CMAS-resistant overlay coating 240, advantageously through about 50% or more of the thickness T, or through essentially the entire or entire thickness T of the CMAS-resistant overlay coating 240. As an alternative or complementary columnar structure, it extends partially through the width W of the CMAS-resistant overlay coating 240, or essentially the entire or entire width W of the CMAS-resistant overlay coating 240. Furthermore, the layer thickness T of the CMAS-resistant overlay coating 240 may be 5 μm to 300 μm inclusive. Advantageously, it is in the range of 10 μm to 250 μm, more advantageously in the range of 15 μm to 150 μm, in particular in the range of 20 μm to 100 μm.Independently of its layer thickness, the overlay coating 240 can provide elemental aluminum and / or elemental chromium and / or aluminum chromium at temperatures in the range of 1.000°C to 1.600°C, advantageously in the range of 1.100°C to 1.500°C, more advantageously in the range of 1.150°C to 1.450°C. The CMAS-resistant overlay coating 240 according to the first aspect of the invention, having a layer thickness T in the range of about 50 μm to about 300 μm, can function both as a thermal barrier coating and as a top layer, advantageously up to 1.600°C. It is a great advantage over the prior art that the overlay coating 240 according to the first aspect of the invention shows very good mechanical stability and excellent adhesion to the respective underlying layer, i.e. the conventional thermal barrier coating 230 (Figure 1a) or the TGO layer 220 (Figure 1d), even when temperatures of 1.500°C and above, especially up to 1.600°C, are applied, for example under thermal cycling.

[0122] The formation of non-oxidized metal components within the metal oxide matrix of the CMAS-resistant overlay coating 240 can be particularly influenced and / or controlled by the target material composition and - to some extent - by the oxygen partial pressure, which is controlled and / or influenced by the gas flow controller and the arc current. Thus, the formation of intermetallic compounds containing or consisting of aluminum and chromium can be promoted, if desired. After deposition and prior to exposure to high temperatures, the CMAS-resistant overlay coating 240 presented herein includes non-oxidized metal components, i.e., aluminum and / or chromium and / or components containing or consisting of aluminum and chromium, which can be evidenced by X-ray diffraction (XRD).

[0123] In Figures 1b and 1c, the CMAS-resistant overlay coating 240 is in contact with the CMAS layer 30, which contains, among other things, airborne dust and / or sand. While the protective layer 240 in Figures 1a, 1b and 1d, respectively, is not exposed to high temperatures, i.e., temperatures above several hundred degrees Celsius, the CMAS-resistant overlay coating 240 in Figure 1c is exposed to temperatures above the melting point of the CMAS layer 30, typically around or above about 1,200°C.

[0124] Assuming that the overlay coating 240 disposed on the top surface 21 of the TBC system 20 of Figures 1a, 1b and 1c and on the top surface 221 of the TGO layer 220 of Figure 1d, respectively, is a CMAS-resistant overlay coating 240 according to the first embodiment of the present invention, upon heating at high temperatures, typically around or above 1.000°C, more typically around or above 1.200°C, in particular around or above 1.300°C, the following occurs: droplets of non-oxidized metal components, especially in the lower zone of the overlay coating 240, embedded in the metal oxide matrix of the CMAS-resistant overlay coating 240 and selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium, diffuse to the top surface 241 of the overlay coating 240. The non-oxidized metal components consisting of aluminum and chromium, for example Al8Cr5, decompose into their elements, whereby at least a portion of them can be oxidized to one or more Al-O and / or Cr-O compounds. The diffusion of chromium and / or aluminum results in the following:

[0125] 1. The self-limiting oxidation of aluminum or the non-stoichiometric Al-O species, respectively, results in the formation of a corundum (Al2O3) layer in the lower zone of the overlay coating 240, particularly at and / or near the interface between the top region of the conventional thermal barrier coating 230 (FIG. 1a) and the top region of the TGO layer 220 (FIG. 1d), respectively, and in the bottom region of the CMAS-resistant overlay coating 240.

[0126] As a benefit of the formation of the corundum layer, an increase in volume, and therefore densification and closure of grain boundaries within the lower zone of the overlay coating 240 is observed, particularly at and / or near the interface between the top region of the conventional thermal barrier coating 230 and the top region of the TGO layer 220, and the bottom region of the CMAS-resistant overlay coating 240, respectively.

[0127] 2. Changing the vertical columnar structures in the overlay coating 240 to porous vertical columnar structures.

[0128] This results in strain tolerant properties and behavior of the overlay coating 240, particularly at and / or near the top surface 231 of the underlying conventional thermal barrier coating 230 and the top surface 221 of the underlying TGO layer 220, respectively.

[0129] Advantageously, the porous and vertical columnar structure not only provides very good strain tolerance and therefore mechanical stability of the CMAS-resistant overlay coating 240 under thermal cycling, but also achieves excellent adhesion to the underlying conventional thermal barrier coating 230 and the underlying TGO layer 220, respectively.

[0130] 3. When the overlay coating 240 is in contact with one or more materials of the CMAS layer 30 heated to a temperature above its melting point, for example about 1.200 to about 1.300 °C, a chemical reaction takes place in the reaction zone 40, i.e. in the area between the top region of the overlay coating 240 and the bottom region of the CMAS layer 30. More precisely, a chemical reaction takes place between aluminum (Al) and / or chromium (Cr) and / or aluminum chromium (Al-Cr) diffused towards the top surface 241 of the CMAS-resistant overlay coating 240 and elements and / or constituents of the CMAS layer 30, in particular magnesium (Mg) and / or magnesium oxide (MgO). This results in a barrier layer comprising Al-Mg-O species and / or Cr-Mg-O species and / or Al-Cr-Mg-O species. The barrier layer may comprise MgAlO4 and / or MgCrO4.

[0131] Beneficially, the barrier layer formed within reaction zone 40 or essentially the same or identical to reaction zone 40 comprises at least one layer of a material or mixture of materials exhibiting a higher melting temperature than the material of CMAS layer 30. The barrier layer thus acts as a diffusion barrier for substrate 10a or 10b and the included layers (substrate 10a: 210, 220, 230; substrate 10b: 210, 220), respectively, against penetration and / or degradation by elements and / or constituents included in CMAS layer 30.

[0132] If a portion of the chromium does not chemically react with elements and / or components of the CMAS layer 30 in contact with the CMAS-resistant overlay coating 240, the chromium may be oxidized to one or more Cr-O compounds that are volatile at a given elevated temperature.

[0133] From the above, it becomes apparent that other overlay coatings, which can be free of elemental Al and / or Cr at high temperatures, can also be applied to protect substrates that include or consist of materials susceptible to CMAS corrosion.

[0134] The above behavior and advantages of the CMAS-resistant overlay coating 240 according to the first aspect of the invention are presented below by way of examples. It should be noted that the layers referred to in the context of the examples do not necessarily have a uniform thickness. However, when a layer thickness is specified, this layer thickness is present in at least a portion of the layer, i.e. as a maximum thickness.

[0135] Figures 2 to 8 show an example of a CMAS-resistant overlay coating 240 according to the first embodiment of the invention, formed and deposited, respectively, by a cathodic arc evaporation (CAE) process according to the third embodiment of the invention, as shown in Figure 1a, which is the top layer on a multi-layer substrate. The latter consists of a base layer 100 and a conventional TBC system 20, which consists of a BC layer 210, a TGO layer 220 and a conventional thermal barrier coating 230. In a next step, the CMAS-resistant overlay coating 240 was exposed to the CMAS layer 30 at a temperature of about 1.300 °C for several hours. After cooling the molten CMAS material 30 to room temperature, the upper region of the TBC system 20, i.e. the top region of the conventional thermal barrier coating 230, as well as the reaction zone 40 located between the top region of the overlay coating 240 and the bottom region of the CMAS layer 30 were investigated. Standard methods such as cross-sectional scanning electron microscopy (X-SEM) and energy dispersive X-ray spectroscopy (EDS) line scan analysis were applied. The results are shown in Figures 2 to 8. It should be noted that it makes no difference whether the conventional thermal barrier coating 230 is made of 7 wt. % yttria stabilized zirconia (7YSZ) or 8 wt. % yttria stabilized zirconia (8YSZ).

[0136] The lower half of FIG. 2 shows an X-SEM image of the top region of the conventional thermal barrier coating 230. It can be seen that the top surface 231 of the conventional thermal barrier coating 230 is coated with an overlay coating 240 according to the first embodiment of the present invention, having a layer thickness T of about 20 μm. As can be seen from the X-SEM image in FIG. 2, the top region of the conventional thermal barrier coating 230 still shows the columnar feather structure characteristic of the conventional thermal barrier coating 230 formed by EB-PVD. The CMAS-resistant overlay coating 240 has a porous vertical columnar structure and morphology, respectively. In the left region of the SEM image, relatively large cavities in the CMAS-resistant overlay coating 240 are visible, which are due to larger metal droplets that have disappeared by diffusion during thermal cycling. However, the determining factor in the development of the porous structure of the overlay coating 240 is the outward diffusion of much smaller metal droplets upon heating at a temperature of about 1,300° C. in addition to the columnar structure of the overlay coating 240 already present after deposition on the top surface 231 of the conventional thermal barrier coating 230. The latter results in the relatively fine porous structure of the CMAS-resistant overlay coating 240. In the top region of the X-SEM image, the reaction zone 40 is visible after cooling from about 1,300° C. to room temperature.

[0137] Figure 3 shows an enlarged cross section of Figure 2, more precisely the top area of ​​the conventional thermal barrier coating 230 and the bottom area of ​​the overlay coating 240 according to the first embodiment of the invention. A very good adhesion of the CMAS-resistant overlay coating 240 to the conventional thermal barrier coating 230 is shown. Furthermore, in addition to the columnar structure of the overlay coating 240 already present after deposition on the top surface 231 of the conventional thermal barrier coating 230, the development of a porous structure of the overlay coating 240 is seen due to the outward diffusion of smaller metal droplets upon heating at a temperature of about 1.300 °C. The latter is essential to achieve the strain-resistant properties and therefore the mechanical stability of the overlay coating 240.

[0138] FIG. 4 shows an enlarged cross section of FIG. 2, more precisely the upper region of the overlay coating 240, as well as the reaction zone 40 (not shown in FIG. 4) located between the top region of the overlay coating 240 and the bottom region of the CMAS layer 30. It should be noted that the upper region of the CMAS-resistant overlay coating 240 is not necessarily identical to the above-mentioned upper zone of the overlay coating 240. However, there may be an overlap between the upper region of the overlay coating 240 and the upper zone. The reaction zone 40 is formed during a chemical reaction between aluminum (Al) and / or chromium (Cr) and / or aluminum chromium (Al-Cr) diffused towards the top surface 241 of the CMAS-resistant overlay coating 240 and elements and / or constituents of the CMAS layer 30, in particular magnesium (Mg) and / or magnesium oxide (MgO). This results in a barrier layer comprising Al-Mg-O species and / or Cr-Mg-O species and / or Al-Cr-Mg-O species, and possibly MgAlO4 and / or MgCrO4. The reaction zone 40 was examined by energy dispersive X-ray spectroscopy (EDS) line scan analysis (see Figures 7 and 8).

[0139] In FIG. 5, an enlarged cross section of FIG. 4 is shown, in which zones extending along an approximately vertical axis from the top region of the CMAS-resistant overlay coating 240 to the bottom region of the reaction zone 40 are marked. The chemical composition of the marked zones was determined by EDS line scan analysis. In FIG. 6, an overlay of the EDS spectra obtained for the main elements, namely Al, Cr, O, Mg, Si and Ca, is shown, showing the chemical composition of the scanned zone. The x-axis represents the position (in μm) of each element, namely Al, Cr, O, Mg, Si and Ca, in the marked zone, where 0 μm relates to the bottom of the scanned zone and the start of the line scan, respectively, and 12 μm (number 12 is not shown in FIG. 6) relates to the top of the scanned zone and the end of the line scan, respectively. The atomic percentage of the elements at each position in the scanned zone is plotted on the y-axis. Within the first section of the scanned zone (0 μm to about 6 μm), the elements contained in the CMAS-resistant overlay coating 240 were detected. In a second section (from about 6 μm to about 9 μm) directly adjacent to the first section, the elements Al, Cr, O and Mg were identified, which are typical of the reaction zone 40, in this case having a thickness of about 3 μm. In a third section (from about 9 μm to about 12 μm) directly adjacent to the second section, the elements contained in the CMAS layer 30 were detected, namely in particular Ca, Si and O, as well as Cr. It is worth mentioning that, with regard to the composition of the reaction zone 40, it is not possible to distinguish between Al originating from the CMAS layer 30 and Al diffused from the CMAS-resistant overlay coating 240. However, the reaction zone 40 could be clearly determined by the detected Cr.

[0140] FIG. 7 shows the image of FIG. 5, in which zones extending along an axis essentially parallel to the top surface 241 of the CMAS-resistant overlay coating 240 have been marked. The chemical composition of the marked zones within the reaction zone 40 was determined by EDS line scan analysis. In FIG. 8, an overlay of the EDS spectra obtained for the main elements, namely Al, Cr, O, Mg, Si and Ca, is shown, showing the chemical composition of the scan zone. The x-axis represents the position (μm) of each element, namely Al, Cr, O, Mg, Si and Ca, within the marked zone, with 0 μm relating to the left limit of the scan zone and the start of the line scan, respectively, and 16 μm relating to the right limit of the scan zone and the end of the line scan, respectively. The atomic percentage of the elements at each position within the scan zone is plotted on the y-axis. From FIG. 8, it can be seen that a correlation exists between the Cr and Mg intensities, indicating that a chemical reaction occurs at least between these two elements.

[0141] In summary, this example illustrates the well-adhered and strain-resistant CMAS-resistant overlay coating 240 according to the first aspect of the invention, its high-temperature properties and behavior, respectively, and its advantages when in contact with the elements and / or constituents of the CMAS layer 30 at high temperatures, in the range of 1.000°C to 1.600°C, for example at a temperature of about 1.300°C, the overlay coating 240 can provide and release elemental aluminum and / or elemental chromium and / or aluminum-chromium, respectively. The elemental aluminum and elemental chromium are in the form of droplets, while the non-oxidized metallic components consisting of aluminum and chromium may be independent of each other in the form of alloys, intermetallic compounds or solid solutions. In the reaction zone 40, i.e. the region between the top region of the overlay coating 240 and the bottom region of the CMAS layer 30, the provided aluminum and / or chromium chemically react with the elements and / or constituents of the CMAS layer 30, in particular magnesium (Mg) and / or magnesium oxide (MgO). This results in a barrier layer comprising Al-Mg-O and / or Cr-Mg-O and / or Al-Cr-Mg-O species. The barrier layer may comprise MgAlO4 and / or MgCrO4. Advantageously, the barrier layer formed in or essentially the same as or identical to the reaction zone 40 comprises at least one layer of a material or mixture of materials exhibiting a higher melting temperature than the materials comprised in the CMAS layer 30. The barrier layer therefore prevents further penetration of elements and / or constituents of the CMAS layer 30 into the underlying substrate 10a comprising the TBC system 20. EXAMPLES

[0142] Methods and Materials Cathodic Arc Evaporation (CAE) The CAE was carried out using an INNOVA batch coating system from Oerlikon Balzers Coating AG. The skilled artisan knows how to do this and can apply this knowledge without departing from the scope of the claims.

[0143] Cross-sectional scanning electron microscopy (X-SEM) Cross sections analyzed with a Zeiss LEO 1530 scanning electron microscope (SEM) were obtained by ion milling.

[0144] Energy Dispersive X-ray Spectroscopy (EDS) The elemental composition of the cross sections analyzed by SEM was determined by energy dispersive X-ray spectroscopy (EDS) on a Zeiss LEO 1530 SEM.

[0145] Example 1: Formation of an approximately 20 μm thick CMAS-resistant overlay coating according to the first aspect of the invention on a conventional thermal barrier coating by a process according to the third aspect of the invention described herein An aluminum chromium target (70 at.% Al, 30 at.% Cr) was operated in the vacuum chamber of a cathodic arc evaporation system with oxygen as the reactive gas, and the partial pressure of oxygen gas in the chamber was 1.0 Pa. Evaporation of the target material was initiated by ignition of the cathodic arc. The evaporated target material reacted with the oxygen gas to form a CMAS-resistant overlay coating on top of the YSZ-based thermal barrier coating, which was the top layer of the TBC system.

[0146] Example 2: Formation of a Barrier Layer Containing a CMAS-Resistant Overlay Coating According to Example 1 CMAS ash powder was dispersed on the CMAS-resistant coating layer formed according to Example 1. The substrate obtained in Example 1 was then heated in air at a temperature of 1,300° C. for 1 hour to form a barrier layer.

[0147] The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0148] As can be seen, the present invention relates to a well-adhered, strain-tolerant, CMAS-resistant overlay coating comprising at least one CMAS-resistant layer, the overlay coating being i. disposed on a surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion, i.e. on at least one surface of the substrate layer, ii. comprising a metal oxide matrix, and iii. having at least a partially vertical columnar structure. Furthermore, at least one non-oxidized metal component selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium is embedded in the metal oxide matrix. Furthermore, the present invention relates to a substrate having the CMAS-resistant overlay coating in question on the surface of the substrate comprising or consisting of a material susceptible to CMAS corrosion. The present invention also relates to a CAE process for forming such a CMAS-resistant overlay coating on the surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion.

[0149] Advantageously, the CMAS-resistant overlay coating according to the first aspect of the present invention is capable of releasing elemental aluminum and / or elemental chromium and / or aluminum chromium at elevated temperatures at which the overlying CMAS material layer melts, for example at temperatures in the range of 1.000°C to 1.600°C, advantageously in the range of 1.100°C to 1.500°C, more advantageously in the range of 1.150°C to 1.450°C.

[0150] Briefly, a barrier layer that prevents further penetration of CMAS contaminants into the underlying substrate and underlying layers of the substrate, and in particular into at least one layer of a TBC system included in the substrate, is formed by: 1. Deposition of a CMAS-resistant overlay coating on a surface of a substrate comprising or consisting of a material susceptible to CMAS corrosion, the overlay coating comprising a metal oxide matrix and having at least a partially vertical columnar structure, with metal components comprising or consisting of aluminum and / or chromium and / or aluminum and chromium embedded in the metal oxide matrix; 2. Outward diffusion of unoxidized metallic components to the top surface of the overlay coating in contact with the overlying CMAS material layer; 3. Chemical reaction of the released aluminum and / or chromium with the elements and / or constituents of the CMAS material, in particular magnesium (Mg) and / or magnesium oxide (MgO).

[0151] All of the features and advantages emerging from the claims, the specification and the drawings, including the design details, the spatial arrangement and the procedural steps, may be essential to the invention individually or in various combinations. [Explanation of symbols]

[0152] 10a,10b Base material 11a,11b Top surface 100 Base Layer 101 Top surface 20 TBC series 21 Top surface 210 BC layer 211 Top surface 220 TGO layer 221 Top surface 230 Thermal barrier coating 231 Top surface 240 Overlay Coating 241 Top surface 30 CMAS layers; CMAS materials 40 Reaction Zone T Overlay Coating Thickness W Overlay coating width

Claims

1. 1. A calcium-magnesium-aluminum-silicate (CMAS)-resistant overlay coating (240) comprising at least one CMAS-resistant layer, said CMAS-resistant overlay coating (240) comprising: i. disposed on a surface (101, 211, 221, 231) of a substrate (10a, 10b) that includes a material susceptible to CMAS corrosion or on a surface (101, 211, 221, 231) of a substrate (10a, 10b) that consists of a material susceptible to CMAS corrosion; ii. a metal oxide matrix, a metal oxide matrix, wherein at least one unoxidized metal component selected from the group consisting of aluminum, chromium, and metal components comprising or consisting of aluminum and chromium is embedded in said metal oxide matrix; iii. At least partially having a vertical columnar structure; Calcium-Magnesium-Aluminum-Silicate (CMAS) resistant overlay coating (240).

2. The overlay coating (240) of claim 1 , wherein the CMAS-resistant overlay coating (240) is free of rare earth metals.

3. The overlay coating (240) of claim 1, wherein the metal oxide matrix comprises at least one oxide species containing aluminum and / or chromium.

4. 2. The overlay coating of claim 1, wherein the metal oxide matrix comprises oxide species selected from the group consisting of Al-O, Cr-O and Al-Cr-O species, and mixtures thereof.

5. The metal oxide matrix may be selected from the group consisting of non-stoichiometric oxygen-deficient aluminum oxide, non-stoichiometric oxygen-deficient chromium oxide, and non-stoichiometric oxygen-deficient aluminum chromium oxide, aluminum oxide (Al ２ O ３ ), chromium oxide (Cr ２ O ３ ) and aluminum chromium oxide (Al, Cr) ２ O ３ 10. The overlay coating of claim 1, comprising an oxidizing species selected from the group consisting of:

6. the CMAS-resistant overlay coating (240) comprising a lower zone and an upper zone; i. the lower zone comprises an oxidizing species selected from the group consisting of non-stoichiometric oxygen-deficient aluminum oxide, non-stoichiometric oxygen-deficient chromium oxide, and non-stoichiometric oxygen-deficient aluminum chromium oxide, and mixtures thereof; ii. The upper zone is made of aluminum oxide (Al ２ O ３ ), chromium oxide (Cr ２ O ３ ) and aluminum chromium oxide (Al, Cr) ２ O ３ 10. The overlay coating of claim 1, comprising a stoichiometric oxidizing species selected from the group consisting of:

7. 10. The overlay coating of claim 1, wherein the metallic components comprising or consisting of aluminum and chromium are, independently of one another, in the form of an alloy, an intermetallic compound, or a solid solution.

8. The metal component containing aluminum and chromium or the metal component consisting of aluminum and chromium is Al １ Cr ２ Or Al ８ Cr ５ or a combination or mixture thereof, or Al １ Cr ２ and Al ８ Cr ５ The overlay coating (240) of claim 1, comprising:

9. 10. The overlay coating (240) of claim 1, wherein the non-oxidized aluminum and / or non-oxidized chromium and / or non-oxidized aluminum chromium is in the form of metallic droplets.

10. The overlay coating (240) of any of the preceding claims, wherein the CMAS-resistant overlay coating (240) is capable of providing elemental aluminum and / or elemental chromium and / or aluminum chromium at temperatures ranging from 1.000°C to 1.600°C.

11. The vertical columnar structures of the CMAS-resistant overlay coating (240) are - extending partially through the thickness (T) of said CMAS-resistant overlay coating (240) or through essentially the entire or entire thickness (T) of said CMAS-resistant overlay coating (240); and / or The overlay coating (240) of claim 1, extending partially across a width (W) of the CMAS-resistant overlay coating (240) or across essentially the entire or entire width (W) of the CMAS-resistant overlay coating (240).

12. The overlay coating (240) of claim 1, wherein the CMAS-resistant overlay coating (240) has a layer thickness (T) in the range of 5 μm to 300 μm.

13. The overlay coating (240) of claim 1 , wherein the CMAS-resistant overlay coating (240) functions as a top layer over a conventional thermal barrier coating.

14. said CMAS-resistant overlay coating (240) i. has a layer thickness (T) in the range of 50 μm to 300 μm; ii. acts as both a thermal barrier coating and a top layer; The overlay coating (240) of claim 1.

15. A substrate (10a, 10b) comprising or consisting of a material susceptible to CMAS corrosion, said substrate (10a, 10b) comprising: i. at least one substrate layer (100, 210, 220, 230) comprising or consisting of a material susceptible to CMAS corrosion; A substrate (10a, 10b) having a CMAS-resistant overlay coating (240) according to claim 1 on at least one surface (101, 211, 221, 231) of said substrate layer (100, 210, 220, 230).

16. 16. The substrate (10a, 10b) of claim 15, wherein the material susceptible to CMAS corrosion is selected from the group consisting of metals, superalloys, ceramic materials and ceramic matrix composites (CMCs), and combinations thereof.

17. 16. The substrate (10a, 10b) of claim 15, wherein at least one of the substrate layers (100, 210, 220, 230) comprises a CMC that includes or consists of a SiC-based CMC, or consists of a CMC that includes or consists of a SiC-based CMC.

18. i. The substrate (10a) a base layer (100), a thermal barrier coating (TBC) system (20) comprising a YSZ-based thermal barrier coating (230) disposed on a thermally grown oxide (TGO) layer (220), or consisting of said base layer (100) and said thermal barrier coating (TBC) system (20); ii. The substrate (10b) a base layer (100), a bond coat (BC) layer (210) and a TGO layer (220), said BC layer (210) being arranged between said base layer (100) and said TGO layer (220), or alternatively consisting of said base layer (100) and said bond coat (BC) layer (210) and said TGO layer (220); A substrate (10a, 10b) according to claim 15.

19. The substrate (10a, 10b) according to claim 18, wherein the base layer (100) is part of a turbine, in particular a gas turbine.

20. 20. The substrate (10a) of claim 18, wherein the TBC system (20) comprises a bond coat (BC) layer (210) disposed between the base layer (100) and the TGO layer (220).

21. 20. The substrate (10a, 10b) of claim 18, wherein the BC layer (210) comprises or consists of a material selected from the group consisting of NiCoCrAlY, Pt-modified diffusion aluminides and glass ceramics.

22. A cathodic arc evaporation (CAE) process for forming a CMAS-resistant overlay coating (240) on a surface (101, 211, 221, 231) of a substrate (10a, 10b) that includes or consists of a material susceptible to CMAS corrosion, said overlay coating (240) comprising at least one CMAS-resistant layer, said process comprising: A. Providing a target for use as a cathode material, the target material comprising or consisting of aluminum and / or chromium; B. Providing a process gas that includes or consists of oxygen; C. evaporating aluminum and / or chromium from the target material provided in step A; D. Reacting the evaporated aluminum and / or chromium evaporated in step C with the process gas provided in step B; and E. depositing the reaction product of step D as a CMAS-resistant overlay coating (240) on a surface (101, 211, 221, 231) of a substrate (10a, 10b) that includes or is made of a material susceptible to CMAS corrosion.

23. 23. The process of claim 22, wherein the CMAS-resistant overlay coating (240) is as defined in claim 1.

24. 23. The process according to claim 22, wherein the substrate (10a, 10b) is as defined in claim 15.

25. 23. The process of claim 22, wherein the target material comprises or consists of aluminum and / or chromium, with chromium being present in an amount of at least 15 atomic percent.

26. The target material is i. consisting essentially of aluminum and chromium, or ii. consists entirely of aluminum and chromium; 23. The process of claim 22.

27. 23. The process of claim 22, wherein the oxygen partial pressure is in the range of 0.001 Pa to 10 Pa.

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