Thermal spray powders for erosion resistant CMAS coatings, erosion resistant CMAS coatings and methods of fabricating the same

Abstract

The present invention relates to new and improved thermal barrier coating compositions that are also erosion resistant to CMAS attack at high temperatures. More specifically, this invention provides ceramic powder compositions which, when applied as thermal barriers in aviation-based or land-based turbine components, have improved erosion resistance, and also resistance to the attack by molten CMAS deposits. Currently used ceramic compositions based on Pyrochlores of the type Ln2Zr2O7 (where Ln= Gd, La, Sm, Nd, Eu and / or Yb) and / or high Yttria containing Zirconia powders / coatings (e.g., 38 wt% Yttria to 55 wt% Yttria) are improved by the addition of 0.1-10 wt% of graphene and or graphene oxide.

Description

[0001] THERMAL SPRAY POWDERS FOR EROSION RESISTANT CMAS COATINGS, EROSION RESISTANT CMAS COATINGS AND METHODS OF FABRICATING THE SAME

[0002] FIELD OF INVENTION:

[0003] The present invention relates to thermal Barrier coating compositions (TBC) that are erosion resistant to Calcium-Magnesium-Alumino-Silicate (CMAS) attack at high temperatures. More specifically, this invention provides ceramic powder compositions which when applied as thermal Barriers in aviation-based or land-based turbine components resist the erosion attack by molten CMAS deposits. The present invention also relates to methods of fabricating erosion resistant CMAS coatings.

[0004] BACKGROUND OF THE INVENTION:

[0005] In the past, focus has been on the thermal barrier coatings based on 6-8 wt% Yttria stabilized Zirconia powders. Such thermal barrier coatings are well known and are applied by several thermal Spray methods onto gas turbine hot section components to protect the superalloy substrates enabling operation at higher inlet temperatures and higher efficiency. Common thermal spray methods include air plasma spray / shrouded plasma spray, suspension plasma spray (SPS) and other methods.

[0006] Although these coatings have performed excellently for many decades, they have suffered significant degradation due to the erosion reactions with molten silicates when operated in dusty, sand particles enriched environments. The molten silicates deposited on the thermal barrier coating compositions (TBC’s) react with the stabilized Zirconia and cause premature erosive failure. Mechanisms of such failure are well documented in open literature.

[0007] More recently, compositions based on Pyrochlores (A2B2O7) have improved the resistance to such attacks. A prime example of such a composition is Gd2Zr2O? ceramic. US 10,322,976 and US 10,934,217 disclose that this is applied in multilayer structures on 6-7 Yttria Stabilized Zirconia (YSZ) compositions.Another well-known ceramic is high Yttria containing Zirconia (ex. 38% to 55% Yttria) stabilized Zirconia which has also shown resistance to CMAS attack.

[0008] For example, currently used ceramic compositions are based on Pyrochlores of the type LmZnCh (where Ln= Gd, La, Sm, Nd, Eu and / or Yb) and / or high Yttria containing Zirconia powders / coatings (e.g., 38 wt% Yttria to 55 wt% Yttria).

[0009] Notwithstanding these developments, there is a need to further improve the erosion resistance of the Pyrochores and high Zirconia coatings against CMAS attack.

[0010] OBJECTIVES OF THE INVENTION:

[0011] An objective of the present invention is to provide new and improved thermal barrier coating compositions that are resistant to Calcium-Magnesium-Alumino-Silicate (CMAS) attack at high temperatures.

[0012] Another objective of the present invention is to provide ceramic powder compositions which when applied as thermal barriers in aviation-based or land-based turbine components have improved erosion performance and also resistance to the attack by molten CMAS deposits.

[0013] Yetanother objective ofthe present invention is to incorporate 0.1-10% graphene and / or graphene oxide into the powders, enabling thermal spray application of coatings with enhanced resistance to erosion and CMAS attack.

[0014] Yet another objective of the present invention is to provide a composite thermal spray powder that can be applied using conventional thermal spray methods to form an erosion resistant CMAS layer on existing TBC coating systems.

[0015] Yet another objective of the present invention is to apply such powders on porous YSZ coatings using Air Plasma Spray (APS) or onto dense vertically cracked (DVC) coatings.

[0016] In the present invention, the focus is on providing new and improved ceramic compositions based on Pyrochlores of the type LmZnCh (where Ln= Gd, La, Sm, Nd,Euand / or Yb) and / or high Yttria containing Zirconia powders / coatings (e.g., 38 wt% Yttria to 55 wt% Yttria) improved by the addition of 0.1-10 wt% of graphene and or graphene oxide.

[0017] Other objectives and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

[0018] SUMMARY OF THE INVENTION:

[0019] A primary embodiment of the present invention is new and improved thermal barrier coating compositions that are resistant to erosive CMAS attack at high temperatures. More specifically, this invention provides ceramic powder compositions which when applied as thermal barrier coatings in aviation-based or land-based turbine components have improved erosion resistance and also resistance to the attack by molten CMAS deposits.

[0020] Currently used ceramic compositions based on Pyrochlores of the type LmZnO? (where Ln= Gd, La, Sm, Nd, Eu and / or Yb) and / or high Yttria containing Zirconia powders / coatings (e.g., 38 wt% Yttria to 55 wt% Yttria) are improved by the addition of 0.1-10 wt% of graphene and or graphene oxide. For example, the Pyrochlores of the type LmZnO? will have 0.1 - 10% graphene / graphene oxide added in its composition. Thus, the invented composition will have LmZnCh (90 - 99.9%) and balance graphene / graphene oxide (0.1-10%). Similarly, the high Yttria containing Zirconia powders will have 90 to 99.9% of ZrO2-38 to 55%Y20s and balance of 0.1-10% of graphene or graphene oxide.

[0021] In yet another embodiment of the present invention, methods of preparing thermal spray powders containing graphene or graphene oxide using spray dry agglomeration methods and other well-known composite powder cladding techniques such as mechanical cladding using binder agglomeration methods have been disclosed.

[0022] In yet another embodiment of the present invention, method of making erosion resistant CMAS coatings containing graphene or graphene oxide using thermal spray processes, Atmospheric Plasma Spray / shrouded plasma spray methods have been disclosed.In yet another embodiment of the present disclosure, improved erosion resistant CMAS coatings containing graphene and or graphene oxide used in gas turbine components have been disclosed.

[0023] In yet another embodiment of the present disclosure, improved erosion resistant CMAS coatings are produced by the Atmospheric plasma spray (APS) process. Invented powders are fed into an Air Plasma Spray gun. Parameters such as Plasma Power, gas flows, powder feed rates, spray distance, and powder injection are adjusted to produce the coatings with a desired porosity (usually around 10% porosity). These Parameters vary according to the type of commercially available plasma guns and are available from the manufacturers of the gun. Adjustments to the parameters are usually done to adjust the porosity levels and, in some cases, to increase deposition efficiency of the coating.

[0024] BRIEF DESCRIPTION OF THE FIGURES:

[0025] Figures 1 (a) and (b) illustrate Scanning electron micrographs (SEMs) of the Graphene added 48% YSZ powder.

[0026] Figure 1 (c) illustrates an EDAX analysis of the powder showing the presence of graphene (carbon).

[0027] DETAILED DESCRIPTION OF INVENTION:

[0028] For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where explicitly specified to the contrary. It is noted that, unless otherwise stated, all percentages given in this specification refer to percentages by weight of the total composition.

[0029] Thus, before describing the present invention in detail, it is to be understood that this invention is not limited to particularly exemplified compositions or process parameters that may of course, vary. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to limit the scope of the invention in any manner.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the case of conflict, the present document, including definitions will control.

[0031] It must be noted that, as used in this specification the singular forms “a,” “an” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a “solvent” may include two or more such solvents.

[0032] The terms “preferred”, “preferably” and “optionally” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

[0033] The various elements, steps and processing techniques that may be involved in the present disclosure are described herein for a thorough understanding of a person skilled in the art.

[0034] CERAMIC POWDER COMPOSITIONS

[0035] Ceramic powder is made up of ceramic particles and additives that make a powder easier to work with when applying ceramic thermal barrier coatings.

[0036] CALCIUM-MAGNESIUM-ALUMINO-SILICATE (CMAS)

[0037] Calcium-Magnesium-Alumino-Silicate minerals are usually referred to as silicon-containing sand dust and volcano ash materials that are carried by the intake air into gas turbines and their deposits often react at high temperatures (more than 1200°C) with the engine turbine coating systems and components.

[0038] CALCIUM-MAGNESIUM-ALUMINO-SILICATE (CMAS) ATTACK

[0039] The attack of calcium, magnesium, alumina, and silicate (CMAS) has been identified as a major cause of thermal barrier coating failure. The CMAS attack refers to a form of molten siliceous residue that is produced in aeroengines at high temperatures. CMAS sticks to the surface of TBCs and can seriously erode the TBC coatings, leading to TBC failures.THERMAL BARRIER COATINGS

[0040] A thin covering of a substance with extremely low heat conductivity is called a thermal barrier coating. It forms a thermal barrier layer between the superalloy blade and the hot gases coming from the gas turbine combustor when applied to a turbine blade.

[0041] SPRAY DRY AGGLOMERATION TECHNIQUES

[0042] Small micron-sized particles are mixed into slurry with a binder and other surfactants. This slurry is atomized inside a dry chamber where several finer particles get agglomerated to larger particles in a dry form.

[0043] Ceramic powder compositions are gaining interest in the field of coating compositions. During component manufacture, the convenience of using a powder is enhanced by ceramic powder particles and additives.

[0044] A primary embodiment of the invention is a ceramic composition for thermal spraying comprising:

[0045] • a ceramic phase selected from (i) pyrochlores of formula LmZnOy, where Ln comprises one or more of Gd, La, Sm, Nd, Eu, and Yb; and (ii) high-yttria zirconia comprising Zrt stabilized with 38 wt% yttria to 55 wt% yttria; and

[0046] • a carbonaceous additive comprising graphene and / or graphene oxide in an amount of 0.1 to 10 wt% based on total composition,

[0047] wherein a coating formed from the composition exhibits improved erosion resistance to molten calcium-magnesium-alumino-silicate (CMAS) infiltration at temperatures >1200°C.

[0048] In an embodiment of the present invention, new and improved thermal barrier coating compositions that are resistant to erosive CMAS attack at high temperatures are disclosed. More specifically, this invention provides ceramic powder compositions which when applied as thermal barrier coatings in aviation-based or land-based turbine components have improved erosion resistance and also resistance to the attack by molten CMAS deposits.In another embodiment of the ceramic composition is that the pyrochlore is Gd2Zr20y.

[0049] In another embodiment of the ceramic composition, the high-yttria zirconia comprises 38 wt% yttria stabilized zirconia.

[0050] In another embodiment of the ceramic composition, the high-yttria zirconia comprises 55 wt% yttria stabilized zirconia.

[0051] In another embodiment of the ceramic composition, the high-yttria zirconia comprises Yttria between 38 and 55 wt% .

[0052] In another embodiment of the ceramic composition, the graphene oxide to graphene mass ratio is between 90:10 and 10:90.

[0053] In another embodiment of the ceramic composition, the graphene and / or graphene oxide is present as platelets having an average lateral size of 0.2 to 10 pm and thickness of 0.3 to 10 nm.

[0054] In another embodiment of the ceramic composition, the ceramic phase consists essentially of LmZnOy and unavoidable impurities, present at 99.0-99.9 wt% of the total composition exclusive of the graphene and / or graphene oxide.

[0055] A secondary embodiment of the invention is the thermal spray powder comprising agglomerated particles each including:

[0056] • primary ceramic particles of a material; and

[0057] • graphene and / or graphene oxide distributed within or on the agglomerate, the agglomerated particles having a D50 of 10-90 pm and a tap density of 0.8-3.5 g / cm3suitable for atmospheric plasma spraying.

[0058] In another embodiment of the thermal spray powder, the agglomerated particles are produced by spray-dry agglomeration of sub-45 pm ceramic feed with an aqueous oralcoholic binder and subsequent thermal conditioning to retain graphene and / or graphene oxide functionality.

[0059] In yet another embodiment of the present invention, method of making erosion resistant CMAS coatings containing graphene or graphene oxide using thermal spray processes, Atmospheric Plasma Spray / shrouded plasma spray methods have been disclosed.

[0060] In yet another embodiment of the present disclosure, improved erosion resistant CMAS coatings containing graphene and or graphene oxide used in gas turbine components have been disclosed.

[0061] In yet another embodiment of the present disclosure, improved erosion resistant CMAS coatings are produced by the Atmospheric plasma spray (APS) process. Invented powders are fed into an Air Plasma Spray gun. Parameters such as Plasma Power, gas flows, powder feed rates, spray distance, and powder injection are adjusted to produce the coatings with a desired porosity (usually around 10% porosity). These Parameters vary according to the type of commercially available plasma guns and are available from the manufacturers of the gun. Adjustments to the parameters are usually done to adjust the porosity levels and, in some cases, to increase deposition efficiency of the coating.

[0062] A third embodiment of the invention is an erosion resistant CMAS thermal barrier coating on a turbine component comprising:

[0063] • a ceramic topcoat deposited from a powder by atmospheric plasma spraying or shrouded plasma spraying; and

[0064] • optionally, an underlying yttria-stabilized zirconia layer and a bond coat on a metallic superalloy substrate,

[0065] wherein the topcoat contains 0.1-10 wt% graphene and / or graphene oxide and exhibits at least 5-15 vol% open or closed porosity tailored by spray parameters for CMAS erosion resistance.Another embodiment of the erosion resistant CMAS thermal barrier coating wherein the topcoat consists of Gd2Zr2O? with 0.1-10 wt% graphene and / or graphene oxide and has a lamellar microstructure.

[0066] Another embodiment of the erosion resistant CMAS thermal barrier coating wherein the coating is configured as a top layer over a porous APS YSZ or a dense vertically cracked (DVC) YSZ layer.

[0067] In yet another embodiment of the present invention, methods of preparing thermal spray powders containing graphene or graphene oxide using spray dry agglomeration methods and other well-known composite powder cladding techniques such as mechanical cladding using binder agglomeration methods have been disclosed.

[0068] A fourth embodiment of the current invention is a method of making a thermal spray powder comprising:

[0069] • providing ceramic particles of LmZnCh and / or high-yttria zirconia (38 wt% to 55 wt% yttria);

[0070] • dispersing graphene and / or graphene oxide in a liquid to form a slurry with the ceramic particles;

[0071] • spray-drying the slurry to form agglomerates with 0.1-10 wt% graphene and / or graphene oxide; and

[0072] • heat-treating the agglomerates to achieve handling strength while retaining graphene and / or graphene oxide structure.

[0073] In another embodiment of the method of making a thermal spray powder, a mechanical cladding of graphene and / or graphene oxide onto ceramic particles using a resinous binder agglomeration technique in a mixer and subsequently removing the solvent to get an agglomerated dry powder.

[0074] Yet another embodiment of the current invention is a method of making erosion resistant CMAS thermal barrier coating comprising:• feeding a powder into an atmospheric plasma spray or shrouded plasma spray gun; and

[0075] • depositing a topcoat onto a turbine component at spray parameters selected to achieve 5-15 vol% porosity and a thickness of 50-1000 pm,

[0076] wherein the deposited topcoat contains 0.1-10 wt% graphene and / or graphene oxide and is configured to resist erosive CMAS infiltration at >1200°C.

[0077] Another embodiment of the method wherein parameters comprise plasma power, gas flows, powder feed rate, stand-off distance, and injection angle adjusted to control pore architecture and deposition efficiency typical of APS processing windows.

[0078] Another embodiment of the method comprises depositing the topcoat over an existing porous YSZ or DVC YSZ layer of a thermal barrier system.

[0079] While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined by the appended claims. The following examples are provided for purposes of illustration only and are not to be construed as limiting the invention.

[0080] TECHNICAL ADVANCES AND ECONOMIC SIGNIFICANCE

[0081] The present invention described herein above has several technical advantages including, but not limited to the realization of new and improved thermal barrier coating compositions that are erosion resistant to CMAS attack at high temperatures. The ceramic powder compositions provided herein when applied as thermal barrier coatings in aviation-based or land-based turbine components, have increased erosion resistance and also resist the attack by molten CMAS deposits.

[0082] EXAMPLE:

[0083] This example illustrates the preparation of a CMAS resistant 48 wt% Yttria Stabilized Zirconia (48YSZ) powder incorporating 1 wt% of Graphene powder suitable for making an improved erosion resistant thermal sprayed CMAS coating. 1000 grams of a commercially available Yttria Stabilized Zirconia ceramic powder comprising nominallyZrO2 (Balance) -Yttria (48 wt%) with a nominal particle size in the range 45 to 110 microns was used as a starting material.

[0084] 30 grams of commercially available polyvinyl pyrrolidone (PVP) was mixed with 650 ml of Iso propyl alcohol (1PA) for 15 to 20 minutes. 10 grams of graphene powder was added to the PVP / 1PA solution slowly along with mechanical mixing for 5 to 10 minutes. This mixture of graphene in the PVP solution was additionally subjected to probe sonification in a pulse mode for 5 minutes. The pre weighed ceramic 48YSZ powder (1000 grams) was added to the graphene containing PVP solution slowly in 15 to 20 minutes while continuously stirring. The graphene solution was kept on a pre-heated water bath maintained at 60 deg C during the stirring. The stirring continued until the ceramic powder coated with graphene material was completely dry. The final product security screened to remove some larger lumps and used for plasma spraying.

[0085] COMPARATIVE STUDY:

[0086] In order to determine the benefits of the 1 wt% graphene containing Ceramic powder, plasma coatings were prepared side by side with the 1 wt% Graphene containing powder (as prepared above) and a prior art powder without any addition of Graphene.

[0087] Air Plasma Sprayed coatings were applied on specially cleaned steel substrates of 3 inches X 1 inch X 1 / 8-inch thickness. A commercially available 95 Nickel-5wt% Al bond coat(Metco 450NS) was initially applied to a thickness of200 microns. The ceramic based CMAS coatings (with and without 1 wt% Graphene) were separately applied by Air Plasma Spray process for thickness up to 550 microns.

[0088] Table 1: Plasma Spray Parameters

[0089]

[0090]

[0091] COATING TESTS:

[0092] Plasma spray coatings were tested by Nano Indentation tests to determine a) Modulus of Elasticity and b) Hardness. The details of testing are as follows:

[0093] The analysis was completed in a third party institute - M / s Industron Technical Services Pvt. Ltd., based in Trivandrum, Kerala.

[0094] Equipment Used: T1980 TriboIndenter

[0095] Transducer: nanoDMA 111 transducer

[0096] Tip: Berkovich probe

[0097] A polished surface sample is mounted on a flat substrate, over which a diamond tip indent is positioned to make the indent. The Force load applied is ImN. 5 indentations are made on each sample. The indentation technique is quasistatic i.e., the loading to unloading happens at a slow rate. Here the load of ImN is gradually applied over a period of 5s and held for 2s. The load is again released over a period of 5s. The indent depth or displacement is measured as a function of force applied. Based on this, calculations are done to arrive at the Modulus and Hardness values.

[0098] Test Results

[0099] Test results are shown in Table 2 below:Table 2:

[0100]

[0101] As shown in the test results, the coatings of the current invention showed a reduced Elastic Modulus by 4.27 percent and a surprising increase in Hardness by 26 percent. It is well known in the high temperature ceramic coatings technology that any reduction in Elastic Modulus is an improvement of thermal shock resistance as well high temperature life of the coating. At the same time, an increase in the hardness of 26 percent is very surprising and represents a significant improvement of erosion resistance of the coating. These results are surprisingly novel and can contribute to the improved life of CMAS coatings.

Claims

CLAIMS:

1. A ceramic composition for thermal spraying comprising:• a ceramic phase selected from (i) pyrochlores of formula LmZnOy, where Ln comprises one or more of Gd, La, Sm, Nd, Eu, and Yb; and (ii) high -yttria zirconia comprising ZrCh stabilized with 38 wt% yttria to 55 wt% yttria; and• a carbonaceous additive comprising graphene and / or graphene oxide in an amount of 0.1 to 10 wt% based on total composition,wherein a coating formed from the composition exhibits improved erosion resistance to molten calcium-magnesium-alumino-silicate (CMAS) infiltration at temperatures >1200°C.

2. The composition as claimed in claim 1, wherein the pyrochlore is Gd2Zr20y.

3. The composition as claimed in claim 1, wherein the high-yttria zirconia comprises 38 wt% yttria stabilized zirconia.

4. The composition as claimed in claim 1, wherein the high-yttria zirconia comprises 55 wt% yttria stabilized zirconia.

5. The composition as claimed in claim 1, wherein the high-yttria zirconia comprises Yttria between 38 and 55 wt%.

6. The composition as claimed in any of claims 1-5, wherein the graphene oxide to graphene mass ratio is between 90:10 and 10:90.

7. The composition as claimed in any of claims 1-6, wherein the graphene and / or graphene oxide is present as platelets having an average lateral size of 0.2 to 10 pm and thickness of 0.3 to 10 nm.

8. The composition as claimed in any of claims 1-7, wherein the ceramic phase consists essentially of LmZnOy and unavoidable impurities, present at 99.0-99.9 wt% of the total composition exclusive of the graphene and / or graphene oxide.

9. A thermal spray powder comprising agglomerated particles each including:• primary ceramic particles of the composition as claimed in any of claims 1-8; and • graphene and / or graphene oxide distributed within or on the agglomerate, the agglomerated particles having a D50 of 10-90 pm and a tap density of 0.8-3.5 g / cm3 suitable for atmospheric plasma spraying.

10. The thermal spray powder as claimed in claim 9, wherein the agglomerated particles are produced by spray-dry agglomeration of sub-45 pm ceramic feedwith an aqueous or alcoholic binder and subsequent thermal conditioning to retain graphene and / or graphene oxide functionality.

11. An erosion resistant CMAS thermal barrier coating on a turbine component comprising:• a ceramic topcoat deposited from the thermal spray powder as claimed in any of claims 9-10 by atmospheric plasma spraying or shrouded plasma spraying; and • optionally, an underlying yttria-stabilized zirconia layer and a bond coat on a metallic superalloy substrate,wherein the topcoat contains 0.1-10 wt% graphene and / or graphene oxide and exhibits at least 5-15 vol% open or closed porosity tailored by spray parameters for CMAS erosion resistance.

12. The erosion resistant CMAS thermal barrier coating as claimed in claim 11, wherein the topcoat consists of Gd2Zr2O? with 0.1-10 wt% graphene and / or graphene oxide and has a lamellar microstructure.

13. The erosion resistant CMAS thermal barrier coating as claimed in any of claims 11 - 12, configured as a top layer over a porous APS YSZ or a dense vertically cracked (DVC) YSZ layer.

14. A method of making a thermal spray powder comprising:• providing ceramic particles of Ln2Zr2O7 and / or high-yttria zirconia (38 wt% to 55 wt% yttria);• dispersing graphene and / or graphene oxide in a liquid to form a slurry with the ceramic particles;• spray-drying the slurry to form agglomerates with 0.1-10 wt% graphene and / or graphene oxide; and• heat-treating the agglomerates to achieve handling strength while retaining graphene and / or graphene oxide structure.

15. A method of making a thermal spray powder comprising a mechanical cladding of graphene and / or graphene oxide onto ceramic particles using a resinous binder agglomeration technique in a mixer and subsequently removing the solvent to get an agglomerated dry powder.

16. A method of making erosion resistant CMAS thermal barrier coating comprising:• feeding a powder as claimed in any of claims 9-10 into an atmospheric plasma spray or shrouded plasma spray gun; and• depositing a topcoat onto a turbine component at spray parameters selected to achieve 5-15 vol% porosity and a thickness of 50-1000 pm,wherein the deposited topcoat contains 0.1-10 wt% graphene and / or graphene oxide and is configured to resist erosive CMAS infiltration at >1200°C.

17. The method as claimed in claim 16, wherein spray parameters comprise plasma power, gas flows, powder feed rate, stand-off distance, and injection angle adjusted to control pore architecture and deposition efficiency typical of APS processing windows.

18. The method as claimed in claim 16 or 17, further comprising depositing the topcoat over an existing porous YSZ or DVC YSZ layer of a thermal barrier system.

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