JP2016540890A - Modified thermal barrier composite coating - Google Patents

Abstract

A novel coating system is provided that allows a single coating structure to exhibit properties that were previously considered mutually exclusive. Depending on the position in the coating, a unique approach to tailor specific properties of the coating structure is chosen to match and complement the specially designed undercoat with a columnar macrostructure and the undercoat Provided with a second coating layer. The resulting composite coating system can maintain thermomechanical compatibility while improving various bulk and / or free surface properties of the composite coating system. [Selection figure] None

Description

  The present invention relates generally to the field of thermal barrier composite coatings utilized to protect substrate materials from high temperatures and corrosive environments.

  It is known that a thermal barrier coating (hereinafter referred to as “TBC”) applied on a substrate suppresses the flow of heat to the substrate. TBC is commonly utilized to protect alloy components of gas turbine engines that are exposed to hot combustion gases.

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

  As an alternative, the thermal barrier coating can be applied by atmospheric plasma spraying (APS) derived 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. The spray of molten particles is directed against the substrate surface, which solidifies upon impact to create a coating. Conventional as-deposited APS microstructures are known to be characterized by superposition of splats of material. The boundary between the splats may be tightly joined or separated by a gap resulting in some porosity. APS coatings are generally cheaper to apply than EB-PVD coatings and provide better thermal and chemical seals to the surrounding environment than columnar particle structures. However, the gaps between splats in the APS microstructure immediately after deposition tend to become densified when exposed to high temperatures. Such densification can result in shorter operating lifetimes in a gas turbine environment due to repeated thermal cycling that induces the accumulation of thermal stresses in the coating that can ultimately cause fracture. There is.

  Columnar structures can be produced by using an APS process (ie, a thermal spray process performed under ambient temperature and pressure conditions) that utilizes nano-sized powders that are generally supplied by solution or suspension means. The gap between the columns can provide strain relief. 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 conventional post-deposition APS microstructures, these coatings have disadvantages including: Low erosion resistance when adjusted to have a low column density; direct thermal path along the column gap; and / or inter-columnar gaps and low column interior Potential low resistance to chemical penetration due to low intra-columnar densities.

  In view of the shortcomings of conventional TBC, there are the following unmet needs for TBC. That is, it is possible to maintain adhesion to 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 path of contaminant penetration.

  The invention may include any of the following aspects in various combinations, and may 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 present invention also provides a unique approach to tailoring specific properties of the coating structure depending on the position within the coating.

In a first aspect, a modified thermal barrier composite coating is provided comprising:
A first coating layer bonded to the surface of the substrate, said first coating layer having a macro-columnar shape characterized by a predetermined distribution of peaks and valleys at the corresponding free surface Including improved macro joint features, creating an improved mechanical bond between the first layer and the second layer;
The columnar features are derived from a nano-sized and / or sub-micron sized splat precursor suspension to form a thermomechanically compatible interface on the substrate surface, the splats comprising: Randomly oriented to produce an isotropic crystal orientation for the first coating;
The splats include non-equal axis columnar grains that grow opposite to the direction of heat flow during cooling to produce anisotropic grain orientation;
The second coating layer is bonded to the corresponding free surface of the first coating layer, and the second coating layer in the bulk and / or free surface is at least as compared to the first coating layer. Has one improved coating property.

In a second aspect, a modified thermal barrier composite coating is provided comprising:
A first coating layer bonded to the smooth surface of the substrate, said first coating layer having a size of less than about 10 μm;
The first coating layer includes macro-columnar features characterized by a predetermined distribution of peaks and valleys on the corresponding free surface, and improved mechanical coupling between the first layer and the second layer Make;
The columnar features are derived from a nano-sized and / or sub-micron-sized splat precursor suspension to form a thermomechanically compatible interface on the substrate surface, the splats being randomly oriented Creating an isotropic crystal orientation for the first coating;
The splats include non-equal axis columnar grains that grow opposite to the direction of heat flow during cooling to produce anisotropic grain orientation;
The second layer includes 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 the densified coating has an improved mechanical erosion barrier compared to the first coating layer.

In a third aspect, a modified thermal barrier composite coating is provided comprising:
A first coating layer bonded to the smooth surface of the substrate, said first coating layer having a size of less than about 10 μm;
The first coating layer includes macro-columnar features characterized by a predetermined distribution of peaks and valleys on the corresponding free surface, and improved mechanical coupling between the first layer and the second layer Make;
The columnar features are derived from a nano-sized and / or sub-micron-sized splat precursor suspension to form a thermomechanically compatible interface on the substrate surface, the splats being randomly oriented Creating an isotropic crystal orientation for the first coating;
The splats include non-equal axis columnar grains that grow opposite to the direction of heat flow during cooling to produce anisotropic grain orientation;
The second layer includes 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 the dense layer The modified coating is derived from a dry powder applied by atmospheric spraying, the coating comprising partially melted particles and fully melted particles, which is improved compared to the first coating layer. With a mechanical erosion barrier.

  The foregoing and other aspects, features and advantages of the present invention will become more apparent from the more detailed description thereof set forth below, taken in conjunction with the following drawings.

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

  FIG. 1b shows an optical 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.

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

Fig. 4 illustrates an exemplary composite coating system according to another embodiment of the invention. In this figure, the second coating layer is an environmental barrier coating.

Fig. 4 illustrates an exemplary composite coating system according to yet another embodiment of the present invention. In this figure, the second coating layer is DVC.

Fig. 4 illustrates an exemplary composite coating system according to yet another embodiment of the present invention. In this figure, the second coating layer is an abradable coating.

2 shows an optical micrograph of a columnar composite coating system prepared according to the principles of the present invention.

2 shows an optical micrograph of another columnar composite coating system prepared according to the principles of the present invention.

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.

  Objects and advantages of the present invention will be better understood from the following detailed description of the preferred embodiments associated therewith. The disclosure herein relates to novel TBC composite coatings for various applications. The coatings of the present invention are particularly suitable for high temperature applications, including but not limited to gas turbines. The present disclosure is presented herein in various embodiments and with reference to various aspects and features of the invention.

  The relationship and function of the various elements of the present invention will be better understood with the following detailed description. This detailed description contemplates features, aspects, and embodiments in various substitutions and combinations as included within the scope of this disclosure. Accordingly, the present disclosure may comprise or consist of any of these specific features, aspects, and embodiments, or one or more selected combinations and substitutions thereof, Or it can be specified as consisting essentially of them.

  A new TBC composite coating system has been found with significantly improved performance characteristics. As described herein, the TBC of the present 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 weight percent (wt%), based on the total weight of the formulation, unless otherwise noted.

  The TBC of the present invention provides a unique alternative to traditional TBC. Specifically, the TBC of the present invention is designed to interact synergistically to create and maintain excellent thermomechanical compatibility in terms of adhesion and bond strength at the coating-substrate interface. A first layer and a second layer selected to be compatible with each other. At the same time, it improves selected coating properties at the bulk and / or free surface of the composite coating structure. The term “thermomechanical compliance” as used herein and throughout this specification is intended to prevent delamination from thermal shock impact during repeated heating and cooling (ie, “thermal cycling”). And is intended to indicate the function of the first coating layer so as to sufficiently maintain the adhesion and bonding strength to the substrate surface. Thermal shock impact is created by thermal cycling that occurs when using a coated substrate in a high temperature environment such as, for example, a gas turbine application. In this way, the composite coating structure can be continuously changed in the first and / or second layer, or from some location in the first coating layer in the second coating layer. Adjusted to have one or more selected characteristics that can vary discretely to position. Selected bulk properties may include, for example, bond strength, thermal conductivity, erosion resistance, corrosion resistance, and thermomechanical compatibility.

  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 present invention having macro-columnar features. FIG. 1b is an optical micrograph showing the first coating layer 100 at a higher magnification. FIGS. 1 a and 1 b show a first coating layer 100 bonded to a substrate 110. In forming the composite coating system, the first coating layer 100 serves as a base coat for the second coating layer deposited thereon. It should be understood that the terms “first coating layer” and “undercoat layer” are used interchangeably throughout this specification. FIGS. 1 a and 1 b show that the first coating layer 100 has macro-columnar features 120. The macro columnar feature 120 is a feature of a microstructure. The microstructure features include nano-sized and / or sub-micron splats derived from a precursor suspension 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 microparticles described herein can be effectively suspended and transported to the substrate to be processed without substantial agglomeration to produce a coating. The majority of the precursor material is preferably splats that are partially melted and / or completely melted before impacting the substrate 110. Any resulting particles that resolidify before impacting the substrate 110 tend to remain trapped in the splats that surround them. The splats are randomly oriented to produce an isotropic crystal orientation in the first coating or undercoat layer 100. The portion of the splat bonded to the surface of the substrate 110 forms a thermomechanical compatible interface. The thermomechanical compatible interface may remain attached to the surface during the thermal cycling conditions typically encountered by TBC.

  FIGS. 1a and 1b show that the controlled porosity amount is not only built-in inside the macro-columnar feature 120, but also the macro-columnar feature 120 configured adjacently. It is further shown that it is built in between. The built-in porosity of the columnar undercoat 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 a conventional TBC.

  FIGS. 1a and 1b show that the macro-columnar feature 120 of the undercoat layer 100 has unique features characterized by peaks 130 and valleys 140 along the free surface of the first coating layer. As used herein, the term “free surfaces” as used in connection with the undercoat layer 100 may 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. It should be understood that the terms “topcoat layer” and “second coating layer” are used interchangeably throughout this specification. The peaks 130 and valleys 140 are better seen in the higher magnification FIG. Without being bound by any theory, the peaks 130 and valleys 140 create an improved bond and thermomechanical compatibility between the undercoat layer 100 and the subsequent topcoat or second coating layer. Thus, it is considered that the characteristics of the undercoat layer 100 are improved. The peaks 130 and valleys 140 can be created to have a selected distribution and pattern based on the control of the thermal spray process and coating media conditions. In a preferred embodiment, as seen in FIG. 1b, peaks 130 and valleys 140 create a random distribution, creating a jagged and serpentine irregular free surface. The degree of tortoise of the underlying coat layer 100 required may depend on several factors, including its end use and the type of second coating layer bonded thereto. Generally speaking, during actual use of the composite coating, the serpentine properties are sufficient to create a preferred interface where the second coating can be applied and maintain its adhesion. FIGS. 1 a and 1 b show that the width and height of each of the peaks 130 and valleys 140 are substantially non-uniform in order to increase serpentineness 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-axial. The particles are made by cooling and unidirectional solidification while in contact with the substrate 110 to create an anisotropic crystal orientation. The solidified particles within the splat are generally aligned and grow in a preferred direction to obtain unidirectional orientation. Thereby, a localized texture is created.

  The fine microstructure features of the undercoat layer 100 may be less than 25 microns (μm) in size, more preferably less than about 10 microns (μm). Thereby, the adhesiveness on the base material 110 can be improved and it can be made smooth. In another embodiment, the microstructure characteristics of the undercoat are in the range of about 10 μm to about 50 nm in size, or less than 50 nm. A smooth substrate as used herein is intended to mean a surface having a roughness (referred to as “Ra”) of less than about 125 μin. In one embodiment, the undercoat layer 100 of the present invention may be applied onto a smooth substrate surface characterized by a Ra between about 25 μin and about 80 μin. Prior to thermal spraying of the first coating layer 100 onto the substrate 110, surface treatment of the substrate surface is therefore not required. This is in contrast to conventional thermal barrier coatings that generally cannot adhere to smooth surfaces that do not roughen the substrate surface. Roughening is particularly detrimental 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 and form an oxide layer in a high temperature environment and to be spalled. As a result of the accumulation of residual thermal stress inside the roughened oxide layer, spalling is emphasized.

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

  Since the undercoat layer 100 is designed with a controlled amount of built-in porosity to improve thermomechanical compatibility during thermal cycling, the TBC composite of the present invention is compatible with conventional TBCs. In comparison, a long life can be achieved. The combination of the built-in porosity and the tortuous interface bounded along the free surface of the undercoat layer 100 can also improve the thermal insulation properties of the composite coating.

  Because the undercoat layer 100 is relatively small in size (ie, sub-micron or smaller), it can be prepared by suspending the precursor material in a liquid carrier during a thermal spray process using a plasma torch. The thermal spraying process using a plasma torch effectively deposits submicron particles on a substrate without causing particle agglomeration that typically occurs when submicron particles are used as a dry powder. Can be coated. Suitable liquid carriers may include an aqueous solvent or a solvent that is a fuel. Specifically, suitable solvent materials include, for example, water, ethanol, methanol, ethylene glycol, kerosene, and propylene, but are not limited thereto. The exact plasma torch conditions selected will depend on several parameters. The parameters include the specific type of torch utilized and the specific coating media selected for the base coat and top coat, as will be appreciated by those skilled in the art.

  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 cerates can be used with other oxides that may be stabilized with yttria or other stabilizers such as ceria. The present invention also contemplates zirconium oxide, yttrium oxide, aluminum oxide or any other type of suitable rare earth oxide.

  The columnar particle structure is thermomechanically compatible, but generally the columnar particle structure itself cannot create the desired properties of TBC. For these reasons, in accordance with the principles of the present invention, as shown in FIG. 2, a second coating layer or topcoat 200 that conforms to the undercoat layer 100 of FIGS. 1a and 1b can be bonded thereto, Has been found to produce a novel TBC composite coating system 220 in accordance with the principles of the present invention. For simplicity and to convey the diversity of inventive aspects of the composite coating structure of the present invention, the topcoat 200 of FIG. 2 is shown as an illustration rather than as a photomicrograph. Here, any suitable topcoat 200 that complementarily and conformably couples with the undercoat 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 shown in detail in FIGS. May be. The serpentine free edge or surface of the undercoat layer 100 provides an effective interface 210 for bonding with the second coating layer. In this way, one or more missing properties of the first coating layer 100 can be offset or compensated 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 characteristic. For example, the first coating layer 100 by itself includes an unacceptably high level of porosity, at the expense of not being able to effectively suppress heat flow to the surface of the substrate 110. , Improve thermomechanical compatibility. Selecting a second coating layer 200 that has a sufficiently low thermal conductivity compared to the first coating layer 100 to compensate or offset this particular missing characteristic of the first coating layer 100. it can. Because the second coating layer 200 can be exposed to the high temperature environment of components such as internal combustion engines, its low thermal conductivity suppresses heat flow much more effectively than the first coating layer 100. . Further, the excellent compatibility of the first coating layer 100 prevents the direct bonding between the second coating layer 200 and the substrate 110 and maintains the continuous integrity of the composite coating structure 220. In other words, a direct bond between the second coating layer 200 and the smooth or roughened substrate surface 110 will cause crushing and reduce the operational life of the coated part.

  In accordance with the principles of the present invention, a modified composite TBC composite structure 200 is created by careful selection of suitable and complementary first and second coating layers 100 and 200, respectively. Even if the properties of the modified TBC composite structure 200 are not necessarily present in the first coating layer or the second coating layer, the first TBC composite structure 200 has a first TBC composite structure 200 in comparison with a conventional TBC material. By combining this layer and the second layer, the overall performance of the TBC can be synergistically improved.

  In accordance with the principles of the present invention, various types of second coating layers can be applied to the serpentine interface of the first coating layer. Of particular importance is the selection of a suitable second coating layer, as shown in the examples, to reduce the overall bulk and free surface of the composite coating system without sacrificing loss of thermal compatibility. The property is to be improved. Possible composite coating systems contemplated by the present invention are shown in FIGS. 3-6 are intended to exemplify certain aspects of the composite coating, and in the process of doing so, are not representative of the macrostructure and / or microstructure coating morphology of the composite coating system. Please understand that this is not always the case.

  FIG. 3 shows a composite coating system 300 comprising a densified columnar coating as a second coating layer 320 and a porous columnar coating 310 as an undercoat or 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 that is larger 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 at its free surface and / or bulk region. The undercoat 310 is a first coating layer and has a columnar structure directly coupled to the smooth base material 330. A columnar undercoat structure 310 is illustrated in FIGS. 1a and 1b. As shown and shown in FIGS. 1a and 1b, the undercoat layer 310 has a built-in porosity due to the characteristics of its macro columnar structure. The porous undercoat 310 has a greater porosity than the densified columnar coating 320, thereby the thermomechanical required to extend the life of the composite coating system 300 compared to a conventional composite TBC system. Provide conformity.

  In the composite coating system 300 of FIG. 3, the density within the column is graded through the thickness of the coating. The density can be graded in several ways. In one embodiment, the density along the path starting from some location inside either the first coating layer 310 or the portion adjacent to the interface between the first coating layer 310 and the second coating layer 320. Will increase. The grading can occur continuously or discretely. It should be understood that other coating properties may also change in stages.

  The densified columnar coating 320 preferably has a greater thickness than the first coating layer 310 to further improve erosion resistance. This combination, i.e., the combination of excellent thermomechanical compatibility provided by the first coating layer 310 and 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 superior erosion resistance not previously possible with conventional TBC composite systems.

  Another embodiment of the present invention is shown in FIG. FIG. 4 consists of an environmental barrier coating (EBC) topcoat 420 as a second coating layer and a porous columnar coating 410 as an undercoat or first coating layer bonded to a smooth substrate 430. A composite coating system 400 is shown. Environmental barrier topcoat 420 blocks the path of contaminant penetration into the coat that can induce corrosion of 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 the same as the porosity of the first coating layer 310 of FIG. Alternatively, the base coat 410 may modify its free surface as needed to produce a customized distribution of customized peaks and valleys. Thereby, the desired meandering can be created at the interface and bonding and adhesion with the topcoat 420 can be promoted to allow adaptation with the environmental barrier topcoat 420.

  Yet another embodiment of the present invention is shown in FIG. FIG. 5 shows a composite coating consisting of a densely vertically cracked (DVC) topcoat 520 as a second coating layer and a porous columnar coating 510 as an undercoat or first coating layer. System 500 is shown. The DVC topcoat 520 utilizes a dense vertical crack microstructure to create a dense barrier for erosion resistance. The DVC topcoat 520 may serve as an EBC in some cases. The base coat 510 bonds to the smooth substrate 530 and maintains a level of thermomechanical compatibility that cannot be achieved by the DVC topcoat 520 itself. Furthermore, 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 the bonding interface. In this way, a compatible composite coating system 500 can be customized and provided with superior erosion resistance not previously possible with conventional TBC composite systems.

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

  Applicants have conducted several experiments by performing a furnace cycle test (FCT), as described in the examples below, to determine the thermomechanical compatibility of the modified composite TBC of the present invention. Compared with other materials. In all FCT tests, a smooth Ni-based superalloy substrate having a surface roughness Ra of about 25-40 μin was used. The substrate surface was not previously roughened and was lightly polished to remove any impurities on its free surface prior to coating. 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 commercial Progressive Surface 100HE ™ plasma torch was used to prepare the SPS undercoat. The SPS undercoat was used for the baseline coating of Comparative Examples 1 and 2; for the SPS undercoat and SPS topcoat of Example 1, and for the SPS undercoat of Example 2. The torch conditions for each of these coatings prepared using a Progressive Surface 100HE ™ plasma torch included a gas flow and chemicals of argon 180 scfh; nitrogen 120 scfh; and hydrogen 120 scfh. The torch was operated at power levels of 100-105 kW and 450-500 amps. The feed rate of the suspension raw material was about 40 to 50 mL / min. The feedstock used was an ethanol suspension of about 7-8 wt% submicron sized YSZ particles. The suspension was injected radially into the plasma stream from outside the Progressive Surface 100HE ™. The torch was rastered for a selected number of passes, traversing the part at a constant surface speed until it accumulated to the desired coating thickness.

  A topcoat for 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% submicron sized YSZ particles. Plasma spray conditions were operated with a feedstock of 90 grams / minute. The total current used was in the range of 150-170 amps. The main torch gas flow was 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. and holding at that temperature for 50 minutes, followed by cooling the coated sample to 75 ° F. in 10 minutes. It was. The average number of FCT cycles completed under such conditions was measured for each coating tested. The coating was considered to fail after it was determined that 20% of the total coating area was crushed from the substrate. It is desirable to have a large number of FCT cycles before failure.

  Coated samples were prepared from the modified composite TBC of the present 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 having a median size of 50 microns. The alumina particles impinged on the coated sample at a room temperature of 20 ° C. and a particle velocity of 200 ft / sec. An erosion rate has been established for the test sample based on exposure to the set mass of the alumina erosion medium. In other words, the mass of the eroded coating material per mass of alumina erosion medium is determined. It is desirable that the erosion rate is low.

  All coated samples tested were evaluated for particle macrostructure using an optical microscope.

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

  The resulting coating contained macro-columnar features. The features of the pillars were generally uniform with each other in the width direction over the entire surface of the substrate. The features were similar to each other in height. A regular and smooth interface with uniform coating thickness was created.

  To evaluate the thermomechanical performance of the non-composite coating, an FCT cycle was performed. The average number of 850 FCT cycles was completed as indicated by the bar labeled “Columnar SPS Baseline” in FIG.

  In addition, coated non-composite samples were prepared for mechanical erosion testing. The erosion rate was determined in units of mg of eroded test material per gram of alumina particles impinging on the coated surface. As shown by the bar labeled “Columnar SPS Baseline” in FIG. 10, this sample shows the worst behavior of all the materials tested, as evidenced by an erosion rate of about 1.05 mg / g. It was.

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

[Comparative Example 2] (Non-Composite APS DVC)
A non-composite coating was prepared from 7-8 wt% YSZ dry powder feed (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 having a surface roughness Ra of about 25-40 μin. The APS DVC coating was observed to show poor quality and coverage. The coating quality was too poor to produce any substantial coating. A maximum thickness of only 1 mil was obtained in the area that could be considered adhesion.

  To evaluate the thermomechanical performance of the non-composite coating, an FCT cycle was performed. As indicated by the bar labeled “APS DVC” in FIG. 9, the coating peeled after only a total of 20 cycles.

  In addition, coated non-composite samples were prepared for mechanical erosion testing. The erosion rate was determined in units of mg of eroded test material per gram of alumina particles impinging on the coated surface. As shown by the bar labeled “APS DVC” in FIG. 10, the uncomplexed sample exhibited an erosion rate between about 0.2-0.25 mg / g.

  The results of these FCT 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 composite A”) was prepared. A base coat layer was prepared from 7 to 8 wt% of yttria-stabilized zirconia (YSZ) raw material. 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 having a surface roughness Ra of about 25-40 μin. The coating thickness of the undercoat was 6-7 mil.

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

  The composite coating system produced and obtained is shown in FIG. The composite 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 serpentine interface provides improved mechanical bonding between the first and second coating layers. Provided.

  To evaluate the thermomechanical performance of the composite coating, an FCT cycle was performed. The average number of FCT cycles between 800-850 cycles was completed as indicated by the bar labeled “Columnar SPS Complex A” in FIG. The vertical line extending from the top of the bar indicates the standard deviation of the sample set for each test. According to the standard deviation, it was shown that the columnar SPS composite 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 attracted attention. Therefore, it was concluded that the columnar SPS composite A maintains 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 units of mg of eroded test material per gram of alumina particles impinging on the coated surface. As shown by the bar labeled “Columnar SPS Complex A” in FIG. 10, this sample exhibited an erosion rate of about 0.3-0.35 mg / g. The results of this erosion test indicated an improvement in erosion rate resistance of about 70% compared to the coated sample of Comparative Example 1.

  In contrast to the baseline coating of Comparative Example 1, the columnar SPS composite A coating also exhibited the additional benefit of having 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 composite B”) was prepared. A base coat 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 having a surface roughness Ra of about 25-40 μin. The coating thickness of the undercoat was 6-7 mil.

  A topcoat layer was prepared from a feed of 7-8 wt% YSZ dry powder having 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 total 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 more dense and provided a barrier to mechanical erosion.

  To evaluate the thermomechanical performance of the composite coating, an FCT cycle was performed. As shown by the bar labeled “Columnar SPS Composite 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 indicates the standard deviation of the sample set for each test. According to the standard deviation, it was shown that the columnar SPS composite 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 attracted attention. Therefore, it was concluded that the columnar SPS composite 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 units of mg of eroded test material per gram of alumina particles impinging on the coated surface. As indicated by the bar labeled “Columnar SPS Complex B” in FIG. 10, this sample exhibited an erosion rate slightly below 0.2 mg / g. This result indicated 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 composite B coating also exhibited the additional advantage of superior erosion resistance while maintaining sufficient FCT performance.

  The inventive composite coatings 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. Furthermore, the composite coating of the present invention has the ability to bind and adhere to a smooth substrate surface (eg, less than 100 μin Ra) while maintaining a thermal conductivity value consistent with thermal spray coating. . Furthermore, in comparison with other typical thermal spray processes, the TBC of the present invention is produced in a low cost range. Generally speaking, the traditional TBC's ability to maintain thermomechanical compatibility during repeated thermal shock cycling is notable for erosion resistance and other properties in the bulk and / or free surface of the coated sample. It was possible only at the expense of a reduction. A specially designed first coating layer having a non-uniform columnar macrostructure and bonded to a smooth substrate roughness is adapted to the first coating layer on top of it. Examples 1 and 2 show that a second coating can be applied next.

  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 in the bulk and / or free surface of the resulting composite coating structure. Thus, for features that were previously recognized as mutually exclusive properties due to competing design considerations, the present invention provides an improved combination of these properties (e.g., thermomechanical adaptation). And a TBC composite structure having erosion resistance / corrosion resistance).

  It should be understood that any suitable top coating can be utilized to provide the desired bulk and free surface coating properties as desired for specific TBC applications and other types of applications. The free surface of the specially designed undercoat may be modified as needed to ensure proper bonding of the particular topcoat. For example, in some top coats, proper bonding of the top coat would require increasing the serpentine nature of the free surface of the undercoat (ie, the lack of height and width of adjacent peaks and valleys). Increase uniformity).

  The properties of the first coating layer are selectively tuned by the features of the macrostructure, as shown in FIGS. 1a and 1b. Of particular importance in the function of the present invention is to maintain adhesion and bond strength with a smooth substrate during thermal cycling, thereby allowing conventional thermal barrier coatings (eg, DVC, abradable coatings). , Environmental barrier coatings or densified columnar coatings—both typically fail to maintain sustained adhesion and bond strength during thermal cycling) have superior thermomechanical compatibility Is to produce material.

  It will be understood that various modifications and changes can be readily made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited to the precise forms and details shown and described herein, but is limited to nothing less than the full invention disclosed and claimed herein. Is intended.

Claims (21)

A modified thermal barrier composite coating comprising:
A first coating layer bonded to the surface of the substrate, said first coating layer comprising macro-columnar features characterized by a predetermined distribution of peaks and valleys on the corresponding free surface; Creating an improved mechanical bond between the second layers;
The columnar features are derived from a nano-sized and / or sub-micron-sized splat precursor suspension to form a thermomechanically compatible interface on the substrate surface, the splats being randomly oriented Creating an isotropic crystal orientation for the first coating;
The splats include non-equal axis columnar grains that grow opposite to the direction of heat flow during cooling to produce anisotropic grain orientation;
The second coating layer is bonded to the corresponding free surface of the first coating layer, and the second coating layer in the bulk and / or free surface is at least as compared to the first coating layer. Has one improved coating property.   The modified thermal barrier composite coating of claim 1, wherein the coating properties are selected from the group consisting of thermal conductivity, erosion resistance, corrosion resistance, and thermomechanical compatibility.   The modified thermal barrier composite coating of claim 1, wherein the first coating layer further has a built-in porosity in a greater amount than the second coating.   The second coating layer is selected from the group consisting of a dense longitudinal crack coating, an abradable coating, an environmental barrier coating, a densified columnar coating, an atmospheric plasma spray coating, and any combination thereof. Modified thermal barrier composite coating.   The modified thermal barrier composite coating of claim 1, wherein the substrate comprises a smooth surface.   The modified thermal barrier composite coating of claim 1, wherein at least a portion of the peaks and valleys have substantially non-uniform widths and heights to form a serpentine interface.   The coating property changes continuously and stepwise in the second coating layer, the coating property having a first value at a first location adjacent to the interface of the first and second coating layers. The characteristic varies from the first value along a path starting at the first position and extending in a direction toward a point on the free surface of the second coating layer; The modified thermal barrier composite coating of claim 1.   The coating characteristic 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, the coating characteristic The modified thermal barrier composite coating of claim 1, wherein is discretely changing from the first value to the second value.   The modified thermal barrier composite coating of claim 1, wherein the first coating layer comprises microstructure features less than about 25 microns.   The modified thermal barrier composite coating of claim 1, wherein the first coating layer comprises microstructure features ranging from about 10 microns to about 50 nm. A modified thermal barrier composite coating comprising:
A first coating layer bonded to the smooth surface of the substrate, said first coating layer having a size of less than about 10 μm;
The first coating layer includes macro-columnar features characterized by a predetermined distribution of peaks and valleys on the corresponding free surface, and improved mechanical coupling between the first layer and the second layer Make;
The columnar features are derived from a nano-sized and / or sub-micron-sized splat precursor suspension to form a thermomechanically compatible interface on the substrate surface, the splats being randomly oriented Creating an isotropic crystal orientation for the first coating;
The splats include non-equal axis columnar grains that grow opposite to the direction of heat flow during cooling to produce anisotropic grain orientation;
The second layer includes 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 the dense layer The modified coating has an improved mechanical erosion barrier compared to the first coating layer.   The modified thermal barrier composite coating of claim 11, wherein the microstructure features of the first coating layer have a size of less than about 10 μm and greater than about 50 nm.   The modified thermal barrier composite coating of claim 11, wherein the densified coating is derived from a second precursor suspension of nano-sized and / or sub-micron sized particles.   12. The modified thermal barrier composite coating of claim 11, wherein the predetermined distribution of peaks and valleys is arranged to form a serpentine irregular interface.   The modified thermal barrier composite coating of claim 1, wherein the first coating layer has a built-in porosity in a greater amount than the densified coating. A modified thermal barrier composite coating comprising:
A first coating layer bonded to the smooth surface of the substrate, said first coating layer having a size of less than about 10 μm;
The first coating layer includes macro-columnar features characterized by a predetermined distribution of peaks and valleys on the corresponding free surface, and improved mechanical coupling between the first layer and the second layer Make;
The columnar features are derived from a nano-sized and / or sub-micron-sized splat precursor suspension to form a thermomechanically compatible interface on the substrate surface, the splats being randomly oriented Creating an isotropic crystal orientation for the first coating;
The splats include non-equal axis columnar grains that grow opposite to the direction of heat flow during cooling to produce anisotropic grain orientation;
The second layer includes 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 the dense layer The coating is derived from a dry powder applied by atmospheric spraying, said coating comprising partially melted particles and fully melted particles, improved mechanical erosion compared to the first coating layer Has a barrier.   The modified thermal barrier composite coating of claim 16, wherein the particles of the densified coating layer have a size greater than about 10 μm.   The modified thermal barrier composite coating of claim 16, wherein the smooth surface has a Ra of less than about 125 μin.   The modified thermal barrier composite coating of claim 18, wherein the smooth surface has a Ra of less than about 80 μin.   The modification of claim 16, wherein the densified coating layer has at least one improved coating property compared to the first coating layer, and wherein the improved coating property is stepwise changed. Quality thermal barrier composite coating.   The modified thermal barrier composite coating of claim 16, wherein the densified coating layer produces a dense vertically cracked microstructure.