Double-layer thermal barrier coating with improved bonding between ceramic layers

Abstract

The bonding capacity of the ceramic coating system (16) is improved by adapting coating parameters such as the size of the powder and changing the parameters of the spraying system.

Description

Technology Field

[0001] The present invention relates to a component having a ceramic coating system representing a two-layer ceramic coating system. The problem to be solved

[0002] The continuously increasing turbine inlet temperature (TIT) has led to the introduction of advanced thermal barrier coatings (TBCs), typically appearing as multilayer ceramic systems. These TBCs typically comprise a partially stabilized zirconia undercoating with partially high fracture toughness and one or more low-fracture ceramic topcoatings.

[0003] A very typical ceramic coating is a fully stabilized zirconia thermal barrier coating, which typically exhibits low fracture toughness, sintering resistance, and phase stability at high temperatures.

[0004] However, a fully stabilized coating is characterized by low fracture toughness and consequently low corrosion resistance, and is deposited on top of a partially stabilized zirconia coating bonded by a ceramic-ceramic interface, which may be somewhat weak and can lead to complete delamination of the top coating, thereby resulting in adverse consequences regarding the thermal protection of the underlying component.

[0005] However, the introduction of multilayer thermal protection ceramic coatings has two caveats:

[0006] i) Related low fracture toughness of fully stabilized ceramic top coatings - has a detrimental effect on the corrosion resistance of fully stabilized ceramic top coatings,

[0007] ii) Successor weak interface between the ceramic undercoating and the ceramic topcoating.

[0008] Regarding the corrosion resistance of ceramic coating systems, the solution was to apply a ceramic coating, specifically one having a segmented microstructure, namely, both a partially stabilized undercoat and a fully stabilized topcoat.

[0009] The segmented microstructure is characterized by low porosity (< 3%) and vertical cracks that travel along the coating thickness, making the segmented microstructure thermally adaptive, which means that the ceramic coating exhibits an increased ability to absorb and withstand thermal deformation. Typically, vertical cracks will extend and continue from the bottom coating to the top coating. A dense segmented microstructure can increase the corrosion resistance of the ceramic coating by at least three times.

[0010] Regarding the bonding ability of two segmented ceramic coatings, the most important factors affecting this are surface roughness and temperature control.

[0011] In terms of roughness, the segmented undercoating is generally somewhat smooth, and protrusions or cavities that can assist in mechanical interlocking are small or few. This can affect the robustness and strength of the bond between the two ceramic coatings.

[0012] Regarding temperature, ideally, a strong interface will appear when a stabilized top coating is deposited on a strongly preheated bottom coating. High temperatures will aid in the wetting and diffusion of fully stabilized particles entering the partially stabilized bottom coating. The particles will diffuse uniformly, fill almost all cavities and protrusions, and in this way improve mechanical interlocking between the two coatings.

[0013] However, homogeneous preheating of bulky components with complex geometric shapes and varying metal wall thicknesses can be difficult.

[0014] Therefore, the objective of the present invention is to improve the problems listed above. means of solving the problem

[0015] The problem is solved by the component according to claim 1.

[0016] In the dependent term, additional benefits that can be arbitrarily combined with one another to yield additional benefits are listed. Brief explanation of the drawing

[0017] The drawing illustrates a ceramic coating system of the components of the present invention. Specific details for implementing the invention

[0018] The coating is applied primarily by a spray torch that passes over the same surface multiple times by applying a layer of powder.

[0019] The present invention improves the strength and robustness of interfacial interlocking and bonding between two ceramic coatings. This improvement is achieved by achieving higher roughness on the ceramic undercoating without sacrificing the microstructure.

[0020] This can be achieved as follows:

[0021] Typically, the ceramic undercoat (10) is sprayed using finer particle powder, particularly using a powder cut, to achieve maximum melting, which ultimately reduces porosity and promotes a vertical crack appearance. The reason the surface of the coating is smooth is that the powder particles are almost completely melted, which resembles a pancake when applied.

[0022] The use of coarser particles, particularly those with a particle size exceeding 45 µm, will reduce the solubility of the particles and potentially increase the intrinsic porosity of the coating, thereby reducing the number of vertical cracks per unit length and ultimately the thermal compliance of the coating.

[0023] The solution to this is to adopt a "flash" coating approach. This refers to depositing a rough, thin coating interposed between the undercoat and the topcoat. This can be achieved in three ways:

[0024] 1. Change in injection parameters of the lower coating (10) during the last pass(s):

[0025] By adopting colder parameters during the final pass(s), the melting degree of the fine particles is significantly reduced, and the particles are deposited in a semimolten state rather than in a flat pancake-like shape. This will significantly increase the roughness without affecting the microstructure of the underlying coating. This can be achieved by reducing the secondary high-enthalpy gas flow (typically hydrogen) by at least 25%.

[0026] 2. Change in powder for the last pass(s) of the ceramic bottom coating (10).

[0027] The powder can be changed and replaced by coarser particles (especially greater than 45 µm) to adhere to the final pass(s) of the ceramic undercoating.

[0028] 3. Tilt the angle of the torch by more than 10 degrees and less than 45 degrees with respect to the vertical spray direction onto the substrate.

[0029] The inclined spray direction toward the substrate will provide a sawtooth appearance that increases surface roughness. This method can be further combined with methods 1 and 2.

[0030] Essentially, the resulting ceramic coating system (16) will include the following:

[0031] a) partially stabilized zirconia (PSZ) as a finely powdered ceramic undercoating (10) having a surface (20) on a substrate (4) or a metal bonding coat (7),

[0032] b) a thin coating of partially stabilized zirconia sprayed in the middle having a rougher surface (19) (ceramic intermediate coating (11)),

[0033] c) Fully stabilized zirconia (FSZ) as a ceramic top coating (13) sprayed with fine powder; the top coating (13) represents an outer surface (23).

[0034] The present invention is particularly intended to improve the robustness of a segmented double-layer ceramic coating system (16).

[0035] Experience shows that temperature control is important during the injection of a double-layer ceramic coating system (16), and temperature control can be somewhat difficult during the injection of large components. As a rough surface (19) is introduced between two particularly segmented coatings (10, 13), the sensitivity of the ceramic coating system (16) to temperature is reduced, providing a more robust ceramic coating system overall. Adoption of both approaches described above is relatively easy, and both approaches can be easily integrated into the injection sequence of components.

[0036] The drawing illustrates the component (1) of the present invention.

[0037] The component (1) has a metal substrate (4) which is particularly preferably a nickel or cobalt-based superalloy.

[0038] On the metal substrate (4), a metal bonding coat (7) is present, particularly on a NiCoCrAl base, which means NiCoCrAlY, NiCoCrAlYSi, NiCoCrAlYRe, NiCoCrAlYTa, etc.

[0039] On the upper part of the metal bonding coat (7), there is a ceramic coating system (16) as described above:

[0040] PSZ segmented lower coating (10)

[0041] PSZ segmented intermediate coating (11)

[0042] FSZ segmented top coating (13).

Claims

Claim 1 As a component (1), at least A substrate (4), particularly a nickel-based or cobalt-based superalloy substrate (4), Metal bonding coat (7), particularly a metal bonding coat (7) based on a NiCoCrAl composition, In a component (1) comprising a ceramic coating system (16) having a lower ceramic coating (10) and an upper ceramic coating (13), An intermediate coating (11) is positioned between the lower coating (10) and the upper coating (13), and It provides a rougher surface (19), A component (1) characterized by having a maximum thickness of 25% of the thickness of the lower coating (10) or the upper coating (13). Claim 2 A coating system according to claim 1, wherein the lower coating (10) exhibits a finer microstructure than the upper coating (13). Claim 3 A method for manufacturing the ceramic coating system of claim 1, and Step of using a torch to spray powder, To achieve maximum melting, a step of spraying the lower ceramic coating (10) using fine particle powder, in particular, As a step of applying an intermediate coating (11), By changing the injection parameters of the ceramic undercoating (10) during the last pass(s) and adopting colder parameters during the last pass(s), the melting degree of the particles is significantly reduced, and the particles are deposited in a semi-molten state rather than in a flat pancake-like shape, resulting in a significant increase in roughness. A step of depositing an intermediate coating (11) by either changing the powder for the last pass(s) of the ceramic bottom coating (10) by replacing the powder for the last pass(s) of the ceramic bottom coating (10) with coarser particles, particularly larger than 45 μm, and depositing the last pass(s) on the intermediate coating (11) on the ceramic bottom coating (10); and Finally, a step of spraying a completely stabilized ceramic top coating (13) sprayed as fine powder. A method comprising the step of tilting the angle of the torch by more than 10° and less than 45° with respect to the vertical injection direction onto the substrate. Claim 4 In a coating or method according to any one of claims 1 to 3, the ceramic undercoating (10) is a partially stabilized zirconia-based coating, particularly a segmented coating or method. Claim 5 In a coating or method according to any one of claims 1 to 4, the ceramic intermediate coating (11) is a partially stabilized zirconia-based coating, particularly a segmented coating or method. Claim 6 In a coating or method according to any one of claims 1 to 5, the ceramic top coating (13) is a fully stabilized zirconia-based coating, particularly a segmented coating or method.

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