JP7097668B2 - Modified heat shield composite coating - Google Patents

Description

The present invention relates to the field of thermal barrier coatings, which are generally used to protect substrate materials from high temperature and corrosive environments.

The heat shield coating (hereinafter referred to as "TBC") applied on the base material is known to suppress the flow of heat to the base material. TBC is commonly used to protect the alloy components of gas turbine engines exposed to high temperature combustion gases.

TBC can be deposited by vapor phase processes such as physical vapor deposition (PVD). Such PVD coatings are typically produced under process conditions designed to promote nucleation and growth of individual, dense, columnar particles that provide a compatible microstructure. Columnar particles are separated by small gaps that can relieve the stress of the coating. However, the gap between the columns can provide a path for the penetration of contaminants and thus can induce corrosion of the undercoat and / or substrate material.

As an alternative, thermal barrier coatings can be applied by atmospheric plasma spraying (APS) from a source of dry powder. The APS coating is formed by heating a gas-propelled spray of powdered metal oxide or non-oxide material with a plasma spray torch. The spray is heated to a temperature at which the powder particles are in a molten state. A spray of molten particles is directed against the surface of the substrate, which solidifies during collision to create a coating. It is known that the conventional as-deposited APS microstructure is characterized by superimposing splats of material. Boundaries between splats may be tightly joined or separated by gaps to provide some porosity. APS coatings are generally cheaper to apply than EB-PVD coatings and provide better thermal and chemical seals to the ambient environment than columnar particle structures. However, the gaps between the splats in the APS microstructure immediately after deposition tend to become dense when exposed to high temperatures. Such densification results in shorter operating life in gas turbine environments due to repeated thermal cycling that induces the accumulation of thermal stresses in the coating that can ultimately cause crushing. There is.

Columnar structures can be produced by using an APS process (ie, a thermal spraying process performed under ambient temperature and pressure conditions), generally utilizing nano-sized powders supplied by means of solution or suspension. The gap between the columns can provide strain reduction. When the plasma flow and particle size are adjusted to the desired range of interaction, overlapping layers of deposited material can flow together to form a columnar array of adjacent particle layers. While such columnar structures have several advantages when compared to the conventional microstructure of APS immediately after deposition, these coatings have drawbacks, including: That is, low erosion resistance when adjusted to have a low intra-column density; direct heat path along the inter-column gaps; and / or inter-column gaps and low intra-column gaps. Potentially low resistance to chemiosmosis due to low intra-column densities.

In view of the shortcomings of conventional TBC, there are the following requirements that are not met for TBC: That is, it is possible to maintain adhesion with the substrate during thermal cycling, while suppressing heat flow toward the substrate surface and inducing corrosion and / or erosion of the substrate surface. There is a need for a TBC with a Compliant Structure that allows the integrity of the substrate to be protected by blocking the infiltration route of contaminants.

The invention may include any of the following aspects in various combinations, and may also include any other aspect of the invention described herein below.

The present invention provides a coating system that allows a single coating structure to exhibit properties that were previously considered mutually exclusive. The invention also provides a unique approach for adjusting certain properties of the coating structure depending on its location within the coating.

In the first aspect, a modified thermal barrier composite coating is provided, including:
The first coating layer bonded to the surface of the substrate, said first coating layer, is a macrocolumnar feature characterized by a predetermined distribution of peaks and valleys on the corresponding free surface. Includes macrocolumnar features and creates improved mechanical bonds between the first and second layers;
The columnar features are derived from a suspension of nano-sized and / or submicron-sized splats, forming a thermomechanically compatible interface on the surface of the substrate. Randomly oriented to produce isotropic crystal orientation for the first coating;
The splats contain non-isotropic columnar particles that grow in the opposite direction of the heat flow during cooling, producing an anisotropic crystalline particle orientation;
The second coating layer is bonded to the corresponding free surface of the first coating layer, and the second coating layer on the bulk and / or free surface is at least compared to the first coating layer. It has one improved coating property.

In the second aspect, a modified thermal barrier composite coating is provided, including:
The first coating layer bonded to the smooth surface of the substrate, said first coating layer, has a size smaller than about 10 μm;
The first coating layer contains macrocolumnar features characterized by a predetermined distribution of peaks and valleys on the corresponding free surface, with improved mechanical bonding between the first and second layers. Make;
The columnar features are derived from a suspension of nano-sized and / or submicron-sized splats, forming a thermomechanically compatible interface on the surface of the substrate, with the splats randomly oriented. And generate isotropic crystal orientation for the first coating;
The splats contain non-isotropic columnar particles that grow in the opposite direction of the heat flow during cooling, producing an anisotropic crystalline particle orientation;
The second layer comprises a densely coated coating layer bonded to the corresponding free surface of the first coating layer, wherein the densified coating has a lower porosity than the first coating layer. The densified coating has an improved mechanical erosion barrier as compared to the first coating layer.

In a third aspect, a modified thermal barrier composite coating is provided, including:
The first coating layer bonded to the smooth surface of the substrate, said first coating layer, has a size smaller than about 10 μm;
The first coating layer contains macrocolumnar features characterized by a predetermined distribution of peaks and valleys on the corresponding free surface, with improved mechanical bonding between the first and second layers. Make;
The columnar features are derived from a suspension of nano-sized and / or submicron-sized splats, forming a thermomechanically compatible interface on the surface of the substrate, with the splats randomly oriented. And generate isotropic crystal orientation for the first coating;
The splats contain non-isotropic columnar particles that grow in the opposite direction of the heat flow during cooling, producing an anisotropic crystalline particle orientation;
The second layer comprises a densified coating layer bonded to the corresponding free surface of the first coating layer, the densified coating having a lower porosity than the first coating layer and said dense. The chemical coating is derived from a dry powder applied by atmospheric spraying, the coating containing partially melted particles and fully melted particles, which are improved compared to the first coating layer. Has a mechanical erosion barrier.

The above and other aspects, features and advantages of the invention will become even more apparent from their more detailed description that follows, shown in combination with the drawings below.

FIG. 1a shows an optical micrograph of a representative first coating layer of the present invention having a columnar particle macrostructure.

FIG. 1b shows a light micrograph of the columnar particle coating of FIG. 1a at high magnification.

In general, any suitable second coating layer that can be bonded to the free surface of the first coating layer of FIGS. 1a and 1b is illustrated.

An exemplary composite coating system according to an embodiment of the present invention is illustrated. In this figure, the second coating layer is a dense columnar coating.

An exemplary composite coating system according to another embodiment of the invention is illustrated. In this figure, the second coating layer is an environmental barrier coating.

An exemplary composite coating system according to yet another embodiment of the present invention is illustrated. In this figure, the second coating layer is DVC.

An exemplary composite coating system according to yet another embodiment of the present invention is illustrated. In this figure, the second coating layer is an abradable coating.

An optical micrograph of a columnar composite coating system prepared according to the principle of the present invention is shown.

An optical micrograph of another columnar composite coating system prepared according to the principles of the present invention is shown.

The results of various furnace cycle tests are plotted and compared for different thermal barrier coating materials.

The results of various mechanical erosion resistance tests are plotted and compared for different thermal barrier coating materials.

The objects and advantages of the present invention are better understood from the detailed description of the following preferred embodiments relating thereto. The disclosure herein relates to novel TBC composite coatings for a variety of uses. The coatings of the present invention are particularly suitable for high temperature applications, including but not limited to gas turbines. The present disclosure is set forth herein in various embodiments and with reference to various aspects and features of the invention.

The relationships and functions of the various elements of the invention are better understood by the following detailed description. This detailed description envisions features, embodiments, and embodiments in various substitution forms and combinations as included within the scope of the present disclosure. Accordingly, the present disclosure comprises or comprises any of such specific features, embodiments, and embodiments thereof, or selected combinations and substitutions thereof. Or it can be specified as being composed essentially of them.

A novel TBC composite coating system has been found with significantly improved performance characteristics. As described herein, the TBCs of the invention can achieve improved performance in the context of other types of materials, including conventional thermal barrier materials. It should be understood that all compositions are expressed as percent by weight (wt%) based on the total weight of the formulation, unless otherwise noted.

The TBC of the present invention provides a unique alternative to the conventional TBC. Specifically, the TBCs of the invention interact synergistically to create and maintain excellent thermomechanical compatibility in terms of adhesion and bond strength at the coating-base material interface. Includes a first layer and a second layer selected to fit each other. At the same time, it improves the selected coating properties on the bulk and / or free surface of the composite coating structure. The term "thermomechanical compatibility" as used herein and throughout the specification is used to prevent separation from thermal shock impact during repeated heating and cooling (ie, "thermal cycling"). It is intended to refer to the function of the first coating layer such that the adhesion to the surface of the substrate and the bond strength are sufficiently maintained. Thermal shock impact is created by thermal cycling that occurs when using coated substrates in high temperature environments, such as in gas turbine applications. In this way, the composite coating structure can change continuously in the first and / or second layer, or from one position in the first coating layer to one in the second coating layer. It is tuned to have one or more selected properties that can vary discretely to position. The bulk properties selected may include, for example, bond strength, thermal conductivity, erosion resistance, corrosion resistance, thermomechanical compatibility, and the like.

An exemplary first coating layer is shown in FIGS. 1a and 1b. FIG. 1a shows an optical micrograph of a representative first coating layer 100 of the invention, which has the characteristics of macrocolumnarity. FIG. 1b is an optical micrograph showing the first coating layer 100 at a higher magnification. 1a and 1b show the first coating layer 100 bonded to the substrate 110. In the formation of the composite coating system, the first coating layer 100 serves as a base coat for the second coating layer deposited on it. It should be understood that the terms "first coating layer" and "undercoat layer" are used interchangeably throughout this specification. 1a and 1b show that the first coating layer 100 has macro-columnar features 120. The macro columnar feature 120 comprises microstructure features. Its microstructural features include nano-sized and / or sub-micron-sized splats derived from precursor suspensions of nano-sized and / or sub-micron-sized precursor particles. The term liquid suspension as used herein is to be understood as intended to refer to suspension plasma spraying (SPS). Thereby, the fine particles described herein can be effectively suspended and transported to the substrate to be treated without substantial agglomeration to form a coating. The majority of the precursor material is preferably splats that have partially melted and / or completely melted before colliding with the substrate 110. Any particles obtained that resolidify prior to impacting the substrate 110 tend to be trapped and retained within the splats surrounding them. The splats are randomly oriented to produce an isotropic crystal orientation within the first coating or undercoat layer 100. A portion of the splats bonded to the surface of the substrate 110 forms a thermomechanically compatible interface. The thermomechanically compatible interface may remain attached to the surface during the thermal cycling conditions typically encountered by TBC.

1a and 1b show that the controlled amount of porosity is not only built-in within the macrocolumnar feature 120, but also adjacent to the macrocolumnar feature 120. It is further shown that it is built in between. The built-in porosity of the columnar substrate coat layer 100 can further improve thermomechanical compatibility during thermal cycling. As a result, the undercoat layer 100 can help extend the life of the TBC of the present invention as compared to that of conventional TBC.

1a and 1b show that the macrocolumnar feature 120 of the undercoat layer 100 has the distinctive unique feature of peaks 130 and valleys 140 along the free surface of the first coating layer. As used herein, the term "free surfaces" used in connection with the undercoat layer 100 can be combined with a topcoat or a second coating layer, as described below. It is intended to refer to a portion of the first coating layer 100 that can be made. It should be understood that the terms "topcoat layer" and "second coating layer" are used interchangeably throughout this specification. The peaks 130 and 140 are better seen in FIG. 1b at higher magnification. Without being bound by any theory, peaks 130 and valleys 140 create improved bonding and thermomechanical compatibility between the underlying coat layer 100 and the subsequent topcoat or second coating layer. In this way, it is considered that the characteristics of the base coat layer 100 are improved. The peaks 130 and 140 can be created to have a selected distribution and pattern based on control of the thermal spraying process and coating medium conditions. In a preferred embodiment, as seen in FIG. 1b, the peaks 130 and valleys 140 form a random distribution, creating a jagged and meandering irregular free surface. The degree of tortuosity of the underlying coat layer 100 required may depend on several factors, including its end use and the type of second coating layer attached thereto. Generally speaking, in actual use of the composite coating, its meandering property is sufficient to create a favorable interface where the second coating can be applied and its adhesion can be maintained. 1a and 1b show that the widths and heights of the peaks 130 and the valleys 140 are substantially non-uniform in order to increase meandering along the free surface of the first coating layer 100. ing.

The microstructure of the undercoat is defined by the splats and the particles contained within the splats. The particles are substantially non-isoaxial. The particles are formed by cooling and unidirectionally solidifying while in contact with the substrate 110, creating an anisotropic crystal orientation. The solidified particles in the splat are generally aligned and grow in a preferred direction to obtain unidirectional orientation. Thereby, a localized texture is created.

The fine microstructure feature of the undercoat layer 100 may be less than 25 microns (μm) in size, more preferably less than about 10 microns (μm). As a result, the adhesion on the base material 110 can be improved and smoothed. In another embodiment, the microstructure of the undercoat is characterized by a size ranging from about 10 μm to about 50 nm, or less than 50 nm. The smooth substrate used herein is intended to mean a surface having a roughness of less than about 125 μin (referred to as “Ra”). In one embodiment, the undercoat layer 100 of the present invention may be applied on a smooth substrate surface characterized by Ra between about 25 μin and about 80 μin. No surface treatment of the substrate surface is therefore required prior to spraying the first coating layer 100 onto the substrate 110. This is in contrast to conventional thermal barrier coatings, which generally cannot adhere to smooth surfaces that are not roughened on the surface of the substrate. The roughening treatment is particularly harmful to metal substrates such as gas turbine blades that are exposed to high temperature environments. The metal surface of the substrate has a tendency to oxidize to form an oxide layer and to be crushed (spall) in a high temperature environment. Fragmentation is emphasized as a result of the accumulation of residual thermal stress inside the roughened oxide layer.

Thus, the first coating layer 100 not only binds to the smooth substrate surface, but also maintains thermomechanical compatibility with the substrate 110 during the rigorous thermal cycling that occurs during its useful life. be able to. Thereby, the life of coated parts such as gas turbine assemblies can be extended without the need for repair and / or repair work.

Since the undercoat layer 100 is designed with a controlled amount of built-in porosity to improve thermomechanical compatibility during thermal cycling, the TBC composites of the present invention can be made into conventional TBCs. In comparison, a long life can be achieved. The combination of the built-in porosity and the tortous interfacial boundary along the free surfaces of the undercoat layer 100 can also improve the thermal insulation properties of the composite coating.

Since the undercoat layer 100 is relatively small in size (ie, submicron or less), it can be prepared by suspending the precursor material in a liquid carrier during the spraying process using a plasma torch. According to a thermal spraying process using a plasma torch, particles of submicron or smaller are effectively deposited or deposited on a substrate without causing particle aggregation that can typically occur when submicron particles are used as a dry powder. Can be covered. A suitable liquid carrier may contain an aqueous solvent or a solvent that is a fuel. Specifically, suitable solvent materials include, but are not limited to, water, ethanol, methanol, ethylene glycol, kerosene and propylene. The exact plasma torch conditions selected will depend on several parameters. The parameters include, as will be recognized by those skilled in the art, the particular type of torch utilized, as well as the particular coating medium selected for the undercoat and topcoat.

Various thermal barrier precursor materials such as any suitable ceramic or cermet coating material can be utilized to make the first coating layer 100. In one embodiment, a ceramic material, such as a stabilized zirconia material, may be used. Other examples include yttria-stabilized zirconia. In addition, oxides such as hafnates and scavengers can be used with yttrium or other oxides that may be stabilized with other stabilizers (eg, ceria, etc.). The present invention also contemplates zirconium oxide, yttrium oxide, aluminum oxide or any other suitable rare earth oxide.

Although the columnar particle structure has thermomechanical compatibility, in general, the columnar particle structure itself cannot produce the desired properties of TBC. For these reasons, as shown in FIG. 2, according to the principles of the present invention, a second coating layer or topcoat 200 compatible with the undercoat layer 100 of FIGS. 1a and 1b can be bonded thereto. Therefore, it was found that a novel TBC composite coating system 220 is produced according to the principle of the present invention. The top coat 200 of FIG. 2 is shown as an illustration rather than a photomicrograph for the purpose of simplifying and conveying the variety of aspects of the invention of the composite coating structure of the present invention. Here, any suitable top coat 200 that complementarily and conformably binds to the base coat 100 can be selected. For example, as shown in FIG. 2, the topcoat 200 may be selected as a dense TBD, abradable coating, or as any other TBC as detailed in FIGS. 3-6. May be. The meandering free end or free surface of the undercoat layer 100 provides an effective interface 210 for bonding to the second coating layer. In this way, one or more missing properties of the first coating layer 100 can be offset or compensated for by selecting a suitable second coating layer 200 that is also not missing. Thereby, the overall performance of the TBC composite coating system 200 can be improved with respect to that particular missing property. For example, the first coating layer 100 by itself contains an unacceptably high level of porosity at the expense of the porosity not being able to effectively suppress heat flow to the surface of the substrate 110. , Improve thermomechanical compatibility. To compensate for or offset this particular missing property of the first coating layer 100, it is possible to select a second coating layer 200 that has sufficiently lower thermal conductivity than the first coating layer 100. can. Since the second coating layer 200 may be exposed to the high temperature environment of parts such as internal combustion engines, its low thermal conductivity suppresses heat flow much more effectively than the first coating layer 100. .. Moreover, the excellent compatibility of the first coating layer 100 prevents the direct coupling between the second coating layer 200 and the substrate 110 to be achieved and maintains the sustained integrity of the composite coating structure 220. In other words, a direct coupling between the second coating layer 200 and the smooth or roughened substrate surface 110 will cause crushing and shorten the working life of the coated component.

By careful selection of compatible and complementary first and second coating layers 100 and 200 respectively according to the principles of the invention, a modified composite TBC composite structure 200 is produced. Even if the characteristics of the modified TBC composite structure 200 are not always present in the first coating layer or the second coating layer, the first is in comparison with the conventional TBC material. By combining the first layer and the second layer, the overall performance of the TBC can be synergistically improved.

According to the principles of the present invention, various types of second coating layers can be applied to the meandering interface of the first coating layer. Of particular importance is the selection of a suitable second coating layer, as shown in the examples, of the overall bulk and free surface of the composite coating system without sacrificing loss of thermal compatibility. The characteristics are improved. Possible composite coating systems intended by the present invention are shown in FIGS. 3-6. 3-6 are intended to illustrate certain aspects of the composite coating and do not represent the macrostructured and / or microstructured coating forms of the composite coating system in the process of doing so. Please understand that it is not always the case.

FIG. 3 shows a composite coating system 300 comprising a densely formed columnar coating as a second coating layer 320 and a porous columnar coating 310 as an undercoat or a first coating layer. The densified columnar coating 320 may be applied over the porous columnar undercoat 310 by any suitable process. In one embodiment, the densified columnar coating 320 is derived from a suspension of particles having a median size greater than the median size of the first coating layer 310. The densified columnar coating 320 has a higher density and lower porosity than the undercoat layer 310. As a result, the densified columnar coating 320 provides erosion resistance on its free surface and / or bulk region. The undercoat 310 is the first coating layer and has a columnar structure directly coupled to the smooth substrate 330. The columnar base coat structure 310 is shown in FIGS. 1a and 1b. As described and shown in FIGS. 1a and 1b, the undercoat layer 310 has a built-in porosity due to the characteristics of its macrocolumnar structure. The porous undercoat 310 has a higher porosity than the densified columnar coating 320, thereby the thermomechanical required to extend the life of the composite coating system 300 compared to conventional composite TBC systems. Provide compatibility.

In the composite coating system 300 of FIG. 3, the density in the column is graded throughout the thickness of the coating. Density can be graded in several ways. In one embodiment, the density of the first coating layer 310 or the portion adjacent to the interface of the first coating layer 310 and the second coating layer 320 along a path starting from a position within either of them. Will increase. Grading can occur continuously or discretely. It should be understood that other coating properties may also change over time.

The densified columnar coating 320 preferably has a larger thickness than the first coating layer 310 in order to further improve erosion resistance. This combination, ie, the combination of the excellent thermomechanical compatibility provided by the first coating layer 310 with the improved coating properties in the bulk and / or free surface provided by the second coating layer 320. A compatible composite coating system 300 has been created, with excellent corrosion resistance not previously possible with conventional TBC composite systems.

Another embodiment of the present invention is shown in FIG. FIG. 4 comprises an environmental barrier coating (EBC) topcoat 420 as a second coating layer and a base coat or a porous columnar coating 410 as a first coating layer that binds to a smooth substrate 430. The composite coating system 400 is shown. The environmental barrier top coat 420 blocks the path of permeation of contaminants into the coat, which can induce corrosion of the substrate surface 430. The corrosion resistance of the second coating layer 420 is higher than the corrosion resistance of the first coating layer 410. The porous columnar coating 410 may be substantially identical to the porosity of the first coating layer 310 in FIG. Alternatively, the undercoat 410 may optionally modify its free surface to produce a predetermined distribution of customized peaks and valleys. Thereby, the desired meandering can be created at the interface, the binding and adhesion with the topcoat 420 can be promoted, and the compatibility with the environmental barrier topcoat 420 can be made possible.

Yet another embodiment of the present invention is shown in FIG. FIG. 5 shows a composite coating comprising a densely cracked (DVC) topcoat 520 as a second coating layer and a porous columnar coating 510 as a base coat or first coating layer. The system 500 is shown. The DVC topcoat 520 utilizes a dense longitudinal crack microstructure to create a dense barrier for erosion resistance. The DVC top coat 520 may serve as an EBC in some cases. The undercoat 510 binds to the smooth substrate 530 and maintains a level of thermomechanical compatibility that cannot be achieved by the DVC topcoat 520 itself. Further, the erosion resistance of the second coating layer 520 is higher than the erosion resistance of the first coating layer 510. The first coating layer 510 is relatively more porous and columnar. The free surface may be modified in comparison to the free surface of FIGS. 3 and 4 to allow compatibility with the DVC topcoat 520 at its bonding interface. In this way, the compatible composite coating system 500 is customized and made with excellent erosion resistance not previously possible with conventional TBC composite systems.

Yet another embodiment of the present invention is shown in FIG. FIG. 6 is a composite coating system consisting of an abradable topcoat 620 as a second coating layer and a base coat that binds to a smooth substrate 630 or a porous columnar coating 610 as a first coating layer. 600 is shown. The abradable topcoat 620 is selected to match the free surface of the undercoat 610 at the meandering interface. In use, the abradable topcoat 620 provides a seal, while the columnar undercoat 610 maintains thermomechanical compatibility and adhesion. In this way, a compatible composite coating system 600 is made with excellent sealing properties not previously possible with conventional TBC composite systems.

Applicants conducted several experiments by performing a Reactor Cycle Test (FCT), as described in the Examples below, to determine the thermomechanical suitability of the modified composite TBC of the invention. Compared with other materials. All FCT tests used a smooth Ni-based superalloy substrate with a surface roughness Ra of about 25-40 μin. The surface of the substrate was not pre-roughened and was lightly polished prior to coating to remove any impurities on its free surface. A fine mesh medium was used to obtain the final surface roughness. Its surface roughness was in the surface range of about 25-40 μin.

A commercially available Progressive Surface 100HE ™ plasma torch was used to prepare the SPS undercoat. The SPS base coat was used for the baseline coating of Comparative Examples 1 and 2; for the SPS base coat and SPS top coat of Example 1; and for the SPS base coat of Example 2. The torch conditions when preparing each of these coatings using a Progressive Surface 100HE ™ plasma torch included a gas stream of argon 180 scfh; nitrogen 120 scfh; and hydrogen 120 scfh and chemicals. The torch was operated at power levels of 100-105 kW and 450-500 amps. The feed rate of the suspension material was about 40-50 mL / min. The feedstock used was an ethanol suspension of approximately 7-8 wt% submicron-sized YSZ particles. A radial suspension was injected into the plasma stream from outside the Liquid Surface 100HE ™. The torch was rastered for the number of pass selections, traversing the part at a constant surface velocity until it accumulated to the desired coating thickness.

A topcoat for the APS dense vertical crack (DVC) coating in Example 2 was made using a PST1100 series torch. The feedstock used in the torch was an ethanol suspension of about 7-8 wt% YSZ particles of submicron size. Plasma spraying conditions were manipulated with a feedstock of 90 grams / min. The total current used was in the range of 150-170 amps. The main torch gas streams were 90 scfh torch gas; 90 scfh argon; and 40 scfh hydrogen gas.

Each FCT cycle consists of exposing the coated sample to a high temperature of 2075 ° F, holding it at that temperature for 50 minutes, and then cooling the coated sample to 75 ° F in 10 minutes. rice field. The average number of FCT cycles completed under these conditions was measured for each coating tested. The coating was considered to fail after determining that 20% of the total coating area was crushed from the substrate. It is desirable that the number of FCT cycles before failure is large.

Coated samples were prepared from the modified composite TBC of the invention and various other materials and tested for resistance to mechanical erosion. Each mechanical erosion test was performed under controlled conditions consisting of exposing the coated sample to angular alumina particles with a median size of 50 microns. The alumina particles were impinged at a particle rate of 200 ft / sec at room temperature of 20 ° C. The erosion rate has been established for the test sample based on the exposure to the set mass of the alumina erosion medium. In other words, the mass of the coating material to be eroded is determined per mass of the alumina erosion medium. It is desirable that the erosion rate is low.

Particle macrostructures were evaluated using light microscopy for all coated samples tested.

[Comparative Example 1] (Non-composite columnar SPS structure)
A non-composite coating was prepared (referred to as a columnar SPS baseline) from a 7-8 wt% yttria-stabilized zirconia (YSZ) feed material in an ethanol-based suspension. The material had a submicron size with a diameter of about 330 nm. The material was suspended in an ethanol-based suspension and then sprayed onto a smooth substrate with a surface roughness Ra of approximately 25-40 μin (thermally sprayed). A coating thickness of about 12-15 mil was obtained.

The coating obtained contained macro-columnar features. The characteristics of the columns were generally uniform with each other in the width direction over the entire surface of the substrate. The characteristics were similar to each other in height. Created a regular, smooth interface with a uniform coating thickness.

An FCT cycle was performed to evaluate the thermomechanical performance of the non-composite coating. As indicated by the bar labeled "Columnar SPS Baseline" in FIG. 9, the average number of approximately 850 FCT cycles was completed.

In addition, coated non-composite samples were prepared for mechanical erosion testing. The erosion rate was determined in mg of eroded test material per gram of alumina particles colliding with the coated surface. This sample showed the worst behavior of all the materials tested, as evidenced by the erosion rate of about 1.05 mg / g, as indicated by the bar labeled "Columnar SPS Baseline" in FIG. rice field.

The results of these FCTs and erosion tests showed conventional TBC materials.

[Comparative Example 2] (Non-composite APS DVC)
A non-composite coating was prepared from a feedstock of 7-8 wt% YSZ dry powder (referred to as APS DVC). The material had a median particle size of 22-62 μm. The material was sprayed by APS onto a smooth substrate with a surface roughness Ra of about 25-40 μin. It was observed that the APS DVC coating showed poor quality and coverage. The quality of the coating was so poor that it did not produce any substantial coating. A maximum thickness of only 1 mil was obtained in the area that could be considered adhesion.

An FCT cycle was performed to evaluate the thermomechanical performance of the non-composite coating. The coating peeled off after only a total of 20 cycles, as indicated by the bar labeled "APS DVC" in FIG.

In addition, coated non-composite samples were prepared for mechanical erosion testing. The erosion rate was determined in mg of eroded test material per gram of alumina particles colliding with the coated surface. As indicated by the bar labeled "APS DVC" in FIG. 10, the non-complex sample showed an erosion rate between about 0.2 and 0.25 mg / g.

The results of these FCTs and erosion tests showed conventional TBC materials.

[Example 1] (composite structure)
As shown in FIG. 7, a composite coating system (referred to as “columnar SPS complex A”) was prepared. An undercoat layer was prepared from a raw material of 7-8 wt% yttria-stabilized zirconia (YSZ). The undercoat material had a median particle size of about 330 nm. The undercoat material was suspended in an ethanol-based suspension and then sprayed onto a smooth substrate with a surface roughness Ra of approximately 25-40 μin. The coating thickness of the base coat was 6 to 7 mil.

A topcoat layer was prepared from 7-8 wt% YSZ feed material. The topcoat material had a median particle size of about 2 μm. The topcoat material was suspended in a liquid carrier of an ethanol-based suspension and then sprayed onto a substrate. The coating thickness of the top coat was 4-5 mil. The thickness of the composite coating was 10-12 mil.

The resulting composite coating system is shown in FIG. The complex contained a porous, macro-columnar undercoat and a dense, macro-columnar topcoat. The undercoat layer maintains the thermomechanical compatibility of the coating layer on the smooth substrate surface, while the meandering interface provides improved mechanical bonding between the first and second coating layers. Provided.

An FCT cycle was performed to evaluate the thermomechanical performance of the composite coating. As indicated by the bar labeled "Columnar SPS Complex A" in FIG. 9, the average number of FCT cycles between 800 and 850 cycles was completed. The vertical line extending from the top of the bar shows the standard deviation of the sample set for each test. The standard deviation showed that the columnar SPS complex A had the same FCT performance as the columnar SPS baseline (Comparative Example 1), and no statistical difference was observed between the two coatings. However, it was noticed. Therefore, it was concluded that the columnar SPS complex A maintained the same FCT performance as the columnar SPS baseline (Comparative Example 1).

In addition, coated composite samples were prepared for mechanical erosion testing. The erosion rate was determined in mg of eroded test material per gram of alumina particles colliding with the coated surface. As indicated by the bar labeled "Columnar SPS Complex A" in FIG. 10, this sample exhibited an erosion rate of approximately 0.3-0.35 mg / g. The results of this erosion test showed that the resistance to erosion rate was improved by about 70% in comparison with the coated sample of Comparative Example 1.

In contrast to the baseline coating of Comparative Example 1, the columnar SPS complex A coating also showed the additional advantage of excellent erosion resistance while maintaining sufficient FCT performance.

[Example 2] (composite structure)
As shown in FIG. 8, a composite coating system (referred to as “columnar SPS complex B”) was prepared. An undercoat layer was prepared from a raw material of 7-8 wt% yttria-stabilized zirconia (YSZ). The undercoat material had a median particle size of about 330 nm. The undercoat material was suspended in an ethanol-based suspension and then sprayed onto a smooth substrate with a surface roughness Ra of approximately 25-40 μin. The coating thickness of the base coat was 6 to 7 mil.

A topcoat layer was prepared from a feedstock of 7-8 wt% YSZ dry powder with an average particle size between 22-62 μm. The topcoat material was sprayed onto a smooth substrate surface by atmospheric plasma spraying (APS) to produce an APS dense vertical crack (DVC) topcoat. The thickness of the APS DVC topcoat was about 8 mils and the overall thickness of the composite coating was about 14-15 mils.

The resulting composite coating system is shown in FIG. The first coating or undercoat layer was more porous and provided thermomechanical compatibility. The second coating or topcoat layer was denser and provided a barrier against mechanical erosion.

An FCT cycle was performed to evaluate the thermomechanical performance of the composite coating. As indicated by the bar labeled "Columnar SPS Complex B" in FIG. 9, the average number of FCT cycles of about 800 cycles was completed. The vertical line extending from the top of the bar shows the standard deviation of the sample set for each test. The standard deviation showed that the columnar SPS complex B had the same FCT performance as the columnar SPS baseline (Comparative Example 1), and no statistical difference was observed between the two coatings. However, it was noticed. Therefore, it was concluded that the columnar SPS complex B maintained the same FCT performance as the columnar SPS baseline (Comparative Example 1).

In addition, coated composite samples were prepared for mechanical erosion testing. The erosion rate was determined in mg of eroded test material per gram of alumina particles colliding with the coated surface. As indicated by the bar labeled "Columnar SPS Complex B" in FIG. 10, this sample showed an erosion rate slightly below 0.2 mg / g. This result showed that the erosion rate resistance was improved by about 80% in comparison with the coated sample of Comparative Example 1.

In contrast to the baseline coating of Comparative Example 1, the columnar SPS complex B coating also showed the additional advantage of excellent erosion resistance while maintaining sufficient FCT performance.

The composite coatings of the present invention of Examples 1 and 2 have the function of maintaining the thermomechanical compatibility of the non-composite columnar coating (Comparative Example 1), while at the same time improving the APS DVC (Comparative Example 2). The above example shows that erosion resistance is achieved. In addition, the composite coatings of the invention have the ability to bond and adhere to smooth substrate surfaces (eg Ra less than 100 μin) while maintaining thermal conductivity values consistent with thermal spray coatings. .. Moreover, in comparison with other typical thermal spraying processes, the TBCs of the present invention are produced at low cost. Generally speaking, the traditional TBC's ability to maintain thermomechanical compatibility during repeated thermal shock cycling is remarkable for erosion resistance and other properties on the bulk and / or free surface of the coated sample. It was only possible at the expense of reduction. A specially designed first coating layer, which has a non-uniform columnar macrostructure and binds to a smooth substrate roughness, is compatible with and above the first coating layer. Examples 1 and 2 show that the next second coating applied to is possible.

The second coating is selected to complement the first coating layer. Complementation of such a first coating layer is due to the fact that one or more property improvements are shown on the bulk and / or free surface of the resulting composite coating structure. Thus, with respect to properties previously recognized as mutually exclusive properties due to conflicting design considerations, the present invention presents an improved combination of these properties (eg, thermomechanical adaptation). To provide a TBC composite structure having resistance and corrosion resistance / corrosion resistance).

It should be appreciated that any suitable top coating can be utilized to provide the desired bulk and free surface coating properties as desired for a particular TBC application or other type of application. The free surface of the specially designed undercoat may be modified as needed to ensure proper bonding of a particular topcoat. For example, in the case of some topcoats, it may be necessary to increase the meandering nature of the free surface of the undercoat (ie, the height and width of adjacent peaks and valleys) for proper bonding of the topcoat. Increases uniformity).

The properties of the first coating layer are selectively adjusted by the characteristics of the macrostructure, as shown in FIGS. 1a and 1b. Of particular importance in the functionality of the present invention is to maintain smooth substrate adhesion and bond strength during thermal cycling, thereby providing conventional thermal barrier coatings (eg, DVC, abradable coatings). , Environmental barrier coatings or densified columnar coatings-both typically unable to maintain sustained adhesion and bond strength during thermal cycling) have excellent thermomechanical compatibility. Is to produce the material.

It will be appreciated that various modifications and modifications can be easily made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited to the exact form and details described and described herein, and is not limited to anything less than the whole of the invention disclosed and subsequently claimed herein. Intended.

Claims (4)

A modified thermal barrier composite coating that includes:
A first coating layer bonded to the surface of a gas turbine blade with a roughness Ra of less than 3.18 μm (125 μin), said first coating layer is characterized by a predetermined distribution of peaks and valleys on the corresponding free surface. Includes macro-columnar features to be attached, creating a interface between the first coating layer and the second coating layer;
The macrocolumnar features include nano-sized and / or submicron-sized splats that form a thermomechanically compatible interface on the surface of the substrate, the splats being randomly oriented in the first coating layer. death;
The second coating layer is attached to the corresponding free surface of the first coating layer, and the second coating layer on the bulk and / or free surface is at least compared to the first coating layer. It has one improved coating property, said coating property comprising a lower porosity than the first coating layer and an improved mechanical erosion barrier compared to the first coating layer. .. The modified thermal barrier composite coating of claim 1, wherein at least a portion of the peaks and valleys has a non-uniform width and height to form the meandering interface. The coating properties change continuously and stepwise within the second coating layer, and the coating properties have the first value at the first position adjacent to the interface between the first and second coating layers. The coating property varies from the first value along a path that begins at the first position and extends in the direction towards a point on the free surface of the second coating layer. The modified heat shield composite coating according to claim 1. The coating property has a first value at a first position adjacent to the surface of the substrate and a second value at a point along the free surface of the second coating layer. However, the modified heat-shielding composite coating according to claim 1, wherein the value is discretely changed from the first value to the second value.

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