Bilayer thermal barrier coating

Abstract

The invention relates to a two layered TBC system (1) comprising a metallic substrate (4), a ceramic bottom layer (10) on the metallic substrate (4), which is made of either PSZ, or (2 – 10)wt% Yb2O3 + (2 – 10)wt% Y2O3 / ZrO2 or (2 – 10)wt% Er2O3 + (2 – 10)wt% Y2O3 / ZrO2 or (2 – 10)wt% (Yb2O3 + Er2O3) + (2 – 10)wt% Y2O3 / ZrO2 and a ceramic top layer (13) on the ceramic bottom layer (10), wherein the ceramic top layer (13) is made of either (2 – 50)wt% (Yb2O3 + Y2O3) / ZrO2 or (2 – 50)wt% (Er2O3 + Y2O3) / ZrO2 or (2 – 50)wt% (Yb2O3 + Er2O3 + Y2O3) / ZrO2.

Description

[0001]2023PF12243 1 Bilayer TBC The invention relates to a bilayer TBC with different amounts of stabilizers. Thermal barrier coatings (TBC) are designed to fulfill the demanding working conditions of first stage components of high-efficient gas turbines. It is known that one method to enhance the efficiency of these engines is the increase of Turbine Inlet Temperature (TIT), which represents an increment of the temperature of these deposited on the surface of the turbine airfoils and the walls of the combustor. Often Yttrium stabilized Zirconia (YSZ) is used. But there is a certain instability of the standard 8YSZ coating, which is of a PSZ type (PSZ = Partially stabilized Zirconia) to remain stable at extreme high temperatures and to remain stable for a long period of time. There are also known limitations of the standard 8YSZ - TBCs, like the phase transfor- mation at T > 1473K. Thus, the use of a bilayer TBC with a top layer of a chemical composition capable to with- stand the phase transformation and to remain stable for a long period of time at extreme high temperatures is needed. It is known that other TBC`s are using a 20YSZ (= FSZ, Fully Stabilized Zirconia), or a Ta2O5containing TBC to solve this issue. EP 944746 B1 discloses Gadolinium Zirconate as TBC and EP 1707653 B1 the same ma- terial with YSZ as ceramic adhesion layer. It is therefore the aim of the invention to solve this problem. The problem is solved by a bilayer TBC according to claim 1. In the subclaims further advantages are listed which can be combined arbitrarily with each other to yield further advantages. The figure shows one example of a bilayer TBC. 2023PF12243 2 The figure and the description are only embodiments of the invention. The use of a stabilizer such as Y2O3 and / or Er2O3 and / or Yb2O3 containing YSZ coating shows enhanced manufacturability and thermo-mechanical performance of the TBC sys- tem. This material shows enhanced E-Modulus and coefficient of thermal expansion than the 48YSZ and also 20YSZ. The proposed chemical compositions enhances the melting behavior of the powder parti- cles, improving the manufacture robustness of the coatings which lead to an extended pro- cess window. A higher cohesion of the particles ends up in an improved performance of the coating in all, high and low thermally loaded regions of the coated components. Fur- thermore, an high amount of heavy rare earth (RE) elements leads to a reduction in the thermal conductivity of the top layer of a ceramic coating system. The figure shows a bilayer TBC 15 with a ceramic bottom layer 10 and a ceramic top layer 13. The whole component 1 has a substrate 4 which is preferably a nickel based superalloy. Between the substrate 4 and the bilayer TBC 15 there is metallic bond coat 7 which also improves oxidation resistance, such as NiCoCrAlY-X (X=Ta, Si oder Hf) and especially no Rhenium (Re) or no Ruthenium (Ru). It is proposed the use of following bilayer TBC System 15. For the ceramic bottom layer 10 there are four options: Option BA: P-YSZ, especially 8wt% Y2O3– ZrO2Option BB: (2 – 10)wt% Yb2O3 / (2 – 10)wt% Y2O3 / ZrO2 Option BC: (2 – 10)wt% Er2O3 / (2 – 10)wt% Y2O3 / ZrO2 Option BD: (2 – 10)wt% ( Yb2O3+ Er2O3) / (2 – 10) wt% Y2O3 / ZrO2. For the ceramic top layer 13 there are three options: Option TA: (2 – 50)wt% (Yb2O3+ Y2O3) / ZrO2Option TB: (2 – 50)wt% (Er2O3+ Y2O3) / ZrO2Option TC: (2 – 50)wt% (Yb2O3 + Er2O3 + Y2O3) / ZrO2, 2023PF12243 3 wherein the amount of at least one stabilizer of the ceramic top layer 13 is different by at least 5%, especially by at least 10%, compared to the same of stabilizer of the ceramic bot- tom layer 10 or vice versa, e.g. if the amount of Yb2O3 is 8,0wt% in the ceramic top layer 13, the amount of Yb2O3is at least 8,4% or maximum 7,6% in the ceramic bottom layer. Preferably the total amount of stabilizers of the ceramic top layer 13 is at least 5%, espe- cially at least 10% higher than the total amount of stabilizers in the ceramic bottom layer 10. Preferably the ceramic top layer 13 is a FSZ. Hafnia HfO2 can also be used as stabilizer in addition to Ytterbia or Erbia, that will mean: It is proposed the use of a following bilayer TBC System 15. For the ceramic bottom layer 10 there are 4 options: Option BA: P-YSZ, especially 8 wt% Y2O3 – ZrO2 Option BB: (2 – 10)wt% Yb2O3 / (2 – 10)wt% Y2O3 / (0.1 – 2)wt% HfO2 / ZrO2Option BC: (2 – 10)wt% Er2O3 / (2 – 10)wt% Y2O3 / (0.1 – 2)wt% HfO2 / ZrO2 Option BD: (2 – 10)wt% (Yb2O3 + Er2O3) / (2 – 10)wt% Y2O3 / (0.1 – 2)wt% HfO2 / ZrO2 For the ceramic top layer 13 there are 3 options: Option TA: (2 – 50)wt% (Yb2O3 + Y2O3 + HfO2) / ZrO2 Option TB: (2 – 50)wt% (Er2O3+ Y2O3+ HfO2) / ZrO2Option TC: (2 – 50)wt% (Yb2O3+ Er2O3+ Y2O3+ HfO2) / ZrO2, wherein the amount of at least one stabilizer of the ceramic top layer 13 is different by at least 5%, especially by at least 10%. compared to the same of stabilizer of bottom layer 10 or vice versa. Preferably the total amount of stabilizers of the ceramic top layer 13 is at least 5%, espe- cially at least 10% higher than the total amount of stabilizers in the bottom layer 10. Preferably the ceramic top layer 13 is a FSZ. 2023PF12243 4 Preferably the amount of HfO2is between 0,2Gew.% to 1,8wt% Hafnia (HfO2), very especially between 0,2Gew.% to 1,6Gew.% Hafnia (HfO2). Alumina Al2O3can also be used as fracture toughener in addition; that will mean: It is proposed the use of a following bilayer TBC System 15. For the ceramic bottom layer 10 there are four options: Option BA: P-YSZ, especially 8 wt% Y2O3– ZrO2Option BB: (2 – 10)wt% Yb2O3 / (2 – 10)wt% Y2O3 / (0.2 – 3)wt% Al2O3 / ZrO2 Option BC: (2 – 10)wt% Er2O3 / 2 – 10) wt% Y2O3 / (0.2 – 3)wt% Al2O3 / ZrO2Option BD: (2 – 10)wt% (Yb2O3+ Er2O3) / (2 – 10) wt% Y2O3 / (0.2 – 3)wt% Al2O3 / ZrO2 For the ceramic top layer 13 there are also three options: Option TA: (2 – 50)wt% (Yb2O3 + Y2O3 + Al2O3) / ZrO2 Option TB: (2 – 50)wt% (Er2O3 + Y2O3 + Al2O3) / ZrO2 Option TC: (2 – 50)wt% (Yb2O3+ Er2O3+ Y2O3+ Al2O3) / ZrO2, wherein the amount of at least one stabilizer of the ceramic top layer 13 is different by at least 5%, especially by at least 10% compared to the same of stabilizer of the ceramic bot- tom layer 10 or vice versa. Preferably the total amount of stabilizers of the ceramic top layer 13 is at least 5%, espe- cially at least 10%, higher than the total amount of stabilizers in the ceramic bottom layer 10. Preferably the ceramic top layer 13 is a FSZ. Preferably the amount of Al2O3 is between 0,2wt% to 1,5wt% Al2O3, very especially between 0,2wt% to 1,2wt% Al2O3. Another advantage is reached by using Alumina Al2O3in amount of >1,7wt% bis 3,0wt% Alumina (Al2O3), especially > 2,0wt% bis 2,5wt% Alumina (Al2O3). 2023PF12243 5 The advantages of adding Alumina Al2O3or Hafnia HfO2can be combined. For the ceramic bottom layer 10 there are four options: (in wt%): Option BA: P-YSZ, especially 8 wt% Y2O3 – ZrO2 Option BB: (2 – 10)wt% Yb2O3 / (2 – 10)wt% Y2O3 / (0.2% - 3%) Al2O3+ (0.2% - 2wt%) HfO2 / ZrO2 Option BC: (2 – 10)wt% Er2O3 / 2 – 10) wt% Y2O3 / (0.2% - 3%) Al2O3 + (0.2% - 2wt%) HfO2 / ZrO2Option BD: (2 – 10)wt% (Yb2O3+ Er2O3) / (2 – 10) wt% Y2O3 / (0.2% - 3%) Al2O3+ (0.2% - 2wt%) HfO2 / ZrO2 For the ceramic top layer 13 there are three options. Option TA: (2 – 50)wt% (Yb2O3 + Y2O3 + Al2O3 + HfO2 ) ZrO2 Option TB: (2 – 50)wt% (Er2O3 + Y2O3 + Al2O3 + HfO2 ) ZrO2 Option TC: (2 – 50)wt% (Yb2O3+ Er2O3+ Y2O3+ Al2O3+ HfO2) / ZrO2, wherein the amount of at least one stabilizer of the top layer 13 is different by at least 5%, especially by at least 10%, compared to the same of stabilizer of ceramic bottom layer 10 or vice versa, e.g. if the amount of Y2O3is 6,0wt% in the top layer 13, the amount of Y2O3is at least 6,3% or maximum 5,7% in the ceramic bottom layer 10. Preferably the total amount of stabilizers of the ceramic top layer 13 is at least 5%, espe- cially at least 10%, higher than the total amount of stabilizers in the ceramic bottom layer 10. Preferably the ceramic top layer is a FSZ. Preferably the bottom layer 10 is partially stabilized Zirconia (PSZ) to adapt the differ- ences in thermal expension. Therefore, possible combinations are possible (just the constituents): for option BB of the ceramic bottom layer 10 and option TA of the top layer 13 Yb2O3 / Y2O3 / Al2O3 / HfO2 / ZrO2Yb2O3 / Y2O3 / Al2O3 / ZrO2 Yb2O3 / Y2O3 / HfO2 / ZrO2 2023PF12243 6 Yb2O3 / Y2O3 / ZrO2; for option BC of the ceramic bottom layer 10 and option TB of the top layer 13 Er2O3 / Y2O3 / ZrO2Er2O3 / Y2O3 / HfO2 / ZrO2 Er2O3 / Y2O3 / Al2O3 / ZrO2 Er2O3 / Y2O3 / Al2O3 / HfO2 / ZrO2; for option BD of the ceramic bottom layer 10 and option TC of the top layer 13 Yb2O3 / Er2O3 / Y2O3 / Al2O3 / ZrO2Yb2O3 / Er2O3 / Y2O3 / HfO2 / ZrO2Yb2O3 / Er2O3 / Y2O3 / Al2O3 / HfO2 / ZrO2 Yb2O3 / Er2O3 / Y2O3 / ZrO2. Preferably Zirconia ZrO2 is balancing the compositions of the ceramic layers (10, 13) ex- cept some unavoidable impurities of the examples given above. The ceramic top layer 15 have a preferred thickness of max.1000µm and can preferably be manufactured with Plasma Spraying, HVOF, Physical Vapor Deposition (PVD) tech- nologies or other coating methods. As substrate 4 a nickel or cobalt based superalloy is used for a substate. On top on this metallic substrate a bond coat 7 of NiCoCrAl – X (X=Y, Re, Ta, Si and / or Hf) is preferably applied. Preferably a NiCoCrAlYTa composition is used. Good results were yielded with ^ Ceramic bottom layer 10: Y2O3 / ZrO2 and ceramic top layer 13: Yb2O3 / Y2O3 / Al2O3 / HfO2 / ZrO2 ^ Ceramic bottom layer 10: Yb2O3 / Y2O3 / ZrO2and ceramic top layer 13: Yb2O3 / Y2O3 / Al2O3 / HfO2 / ZrO2 2023PF12243 7 ^ Ceramic bottom layer10: Yb2O3 / Y2O3 / HfO2 / ZrO2 and ceramic top layer 13: Yb2O3 / Y2O3 / Al2O3 / HfO2 / ZrO2. Favorable examples (EX) (in wt%) of stabilizers (ST) in the ceramic bottom layer 10 are given in following table ST / EX 1 2 3 4 5 6 7 Y2O3 7,7 7,5 5,2 2,2 6,3 8.9 4,2 Yb2O3 2,0 2,0 3,0 - - 1,5 5,5 Er203 - - - 7,7 3,0 8,0 4,0 Hf02 - - 0,3 1,6 1,2 1,4 0,8 Al2O3 - - 2,8 2,3 2,5 1,5 1,2 . Favorable examples (EX) (in wt%) of stabilizes in the ceramic top layer 13 are given in following table ST / EX 1 2 3 4 5 6 7 Y2O3 8,2 8,6 7,7 6,9 9,0 5,7 8,2 Yb2O3 10,2 15,0 20 7,0 17 30 14 Er203 - - - 11 8,3 2,2 21 Hf02 - - 0,5 1,9 1,5 1,7 1.2 Al2O3 - - 3,0 2,8 0,5 1,2 1,8

Claims

2023PF12243 8 Patentansprüche / Patent claims 1. Two layered TBC system (1), comprising a metallic substrate (4), especially comprising a nickel base or cobalt based superalloy, a ceramic bottom layer (10) on the metallic substrate (4), which is made of either PSZ, especially 8 wt% Y2O3 – ZrO2 or (2 – 10)wt% Yb2O3+ (2 – 10)wt% Y2O3 / ZrO2or (2 – 10)wt% Er2O3 + (2 – 10)wt% Y2O3 / ZrO2 or (2 – 10)wt% (Yb2O3 + Er2O3) + (2 – 10)wt% Y2O3 / ZrO2 and a ceramic top layer (13) on the ceramic bottom layer (13) wherein the ceramic top layer (13) is made of either (2 – 50)wt% (Yb2O3+ Y2O3) / ZrO2or (2 – 50)wt% (Er2O3 + Y2O3) / ZrO2 or (2 – 50)wt% (Yb2O3+ Er2O3+ Y2O3) / ZrO2.

2. Two layered TBC system according to claim 1, wherein a NiCoCrAlX (X=Y, Ta, Si, Ta, Re) is applied on the metallic substrate (4), especially a NiCoCrAlYTa coating.

3. Two layered TBC system according to claim 1 or 2, wherein in addition to Ytterbia and / or Erbia the ceramic bottom layer (10) or the ceramic top layer (13)2023PF12243 9 comprises between 0,2Gew.% to 1,8wt% Hafnia (HfO2), especially between 0,2Gew.% to 1,6Gew.% Hafnia (HfO2).

4. Two layered TBC system according to any of the claims 1, 2 or 3, wherein in addition to Ytterbia and / or Erbia the ceramic bottom layer (10) or the ceramic top layer (13) comprises between 0,2wt% to 1,5wt% Al2O3, very especially between 0,2wt% to 1,2wt% Al2O3.

5. Two layered TBC system according to any of the claims 1, 2, 3 or 4, wherein in addition to Ytterbia and / or Erbia the ceramic bottom layer (10) or the ceramic top layer (13) comprises > 1,7wt% bis 3,0wt% Alumina (Al2O3), especially > 2,0wt% bis 2,5wt% Alumina (Al2O3).

6. Two layered TBC system according to any of the claims 1, 2, 3, 4 or 5, wherein the amount of at least one stabilizer of the ceramic top layer (13) is differ- ent by at least 5%, especially different by at least 10%, compared to the same stabilizer of the ceramic bottom layer (10) or vice versa.

7. Two layered TBC system according to any of the claims 1, 2, 3, 4, 5 or 6, wherein the ceramic top layer (15) is a fully stabilized Zirconia (FSZ).

8. Two layered TBC system according to any of the claims 1, 2, 3, 4, 5, 6 or 7, wherein the total amount of stabilizers of the ceramic top layer (13) is at least 5%, especially at least 10% higher, than the total amount of stabilizers in the ceramic bottom layer (10).

9. Two layered TBC system according to any of the claims 1, 2, 3, 4, 5, 6, 7 or 8, wherein the ceramic bottom layer (10) is a partially stabilized Zirconia (PSZ).2023PF12243 10 10. Two layered TBC system according to any of the claims 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the amount of Zirconia is balancing the composition of the ceramic layers (10, 13) except some unavoidable impurities.

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