SURFACE COATINGS FOR AEROSPACE ^; COMPONENTS

BACKGROUND

[0001] There are multiple challenges that factor into the design of components in aerospace applications. Components are designed, for example, to extend part life, to reduce component failure, and to operate successfully in intended applications. Aerospace applications include different types of environments, stresses (e.g., chemical, mechanical, surface, bulk, etc.), and operational envelopes.

[0002] One significant environmental condition that impacts component life is the undesirable introduction of foreign particles. These foreign particles can be anything that interfaces with the component and negatively impacts the performance of the component. Foreign particles deposit, accumulate, and aggregate differently with a component depending on the operating conditions, as will be appreciated by one skilled in the art.

[0003] Although foreign particle deposition has been a problem within the aerospace industry for a long time, the problem has become increasingly more complicated. The current environmental conditions of aerospace engines (e.g., gas turbine engines) are changing as there is an increase in the number of aircraft operating in heavy sand environments (e.g., the Middle East, India, etc.). Further, aircraft engines are‘Ingesting” additional foreign particles at increased volumes due to various operating conditions, environments, etc. Moreover, in addition to sand environments, the desired ranges of operating conditions for aerospace components is increasing, and the engines are required to perform in various different environments under broad ranges of operating conditions. Furthermore, performance expectations of engines are continually increasing (e.g., longer part life, less maintenance, etc,). The design challenges will continue as the needs of the components continue to get more challenging.

[0004] One response to counter component degradation caused by foreign particle deposition is to utilize a coating applied over the component. Coatings are widely used in aerospace applications and are applied to surfaces (external and/or internal surfaces) of many- different components to improve some component feature or to overcome operational and/or environmental conditions to which a component is exposed. Each coating application can have unique design challenges and each desired coating can have its own limitations. For example, environmental barrier coatings (EBCs) and thermal barrier coatings (TBCs) can be applied to a component to overcome a harsh environment, to improve bonding, to prevent coiTosion, to improve heat tolerance, and/or to prevent cracking. Coatings are also applied to components to mitigate or reduce the accumulation of foreign particles, as will be appreciated by those of skill in the art. Notwithstanding the applied coating, buildup of foreign particles still occurs on the component, regardless of operation or environmental conditions.

[0005] In a gas turbine engine, for example, there are a number of different components that are subject to different conditions. A gas turbine engine includes a power core that is made up of a compressor, a combustor, and a turbine, arranged in flow series with an upstream inlet and downstream exhaust. The compressor compresses air from the inlet, which is mixed with fuel m the combustor and ignited to generate hot combustion gas. The turbine extracts energy from the expanding combustion gas, and drives the compressor via a common shaft. Energy is delivered in the form of rotational energy in the shaft, reactive thrust from the exhaust, or both.

[0006] These three main sections of the gas turbine engine experience different operating and environmental conditions, and the foreign particles interfering with part performance m each section can vary. Thus, the coatings applied to components m each section may vary as well. For example, blade, vanes, and blade air seals of the compressor and turbine may he subject to calcium-magnesium-alumina-silicate (“CMAS”) particles, debris, and particulate matter passing through the flow path and such components may include different types of coatings. Nozzles, injectors, and panels of the combustor, which are generally subject to high temperatures, may be subject to coking and other foreign (soft or hard) particles, and such components may include a native or other functional coating, as will be appreciated by those of skill in the art. Notwithstanding the applied coatings, fouling of foreign particles may accumulate on the components, which can degrade component performance via cracking, micro cracking, spallation, fragmentation, or other irreversible damage.

[0007] Existing coatings that have been applied to overcome the negative consequences of foreign particle accumulation on aerospace components have been designed to mitigate the rate of deposition or delay the adhesion of the foreign particles. However, the mitigation and/or delay still renders such coatings ultimately ineffective because foreign particles will build up on the prior art coatings. Such build up is a result of the coatings wearing over time or having an initial build-up of foreign particles, which in turn reduces the efficacy of the coating, and thus additional foreign particle accumulation may occur. Further, in accordance with some prior art coatings, the coatings may exhibit an attractive property to the foreign particle, and thus the coating itself may increase the accumulation of foreign particles. Some prior art coatings have been focused on minimizing the attraction of the foreign particles, but once a first layer of foreign particles is deposited, then the accumulation of foreign particles will increase irrespective of any coating properties.

[0008] Because the operating conditions and performance expectations are continually increasing and because the mi ssions of the engines are vari ed with an increase in sand environments, there is an urgent need to improve the engine design to be more robust and more versatile. That is, although the current coatings in the industry may provide some protection, it is being discovered that such protections may fail or at least not be as effective in environments in which the components must operate. There is a need for advancement in the area of coatings such that the coating does not merely mitigate the rate of deposition but rather repels the foreign particle altogether such that deposition does not occur on the component for the variety of operating and environmental conditions in which aerospace components must operate. Such advancement may be desirable for improved component performance, reduced component failure, improved component life, and reduced component maintenance. To address the above issues, and to provide improved coatings for various applications within the aerospace industry, embodiments of the present disclosure are directed to coatings applied to substrates that repel other objects/surfaces (e.g., foreign particles) with improved efficacy as compared to prior used coatings.

BRIEF DESCRIPTION

[0009] According to some embodiments, aerospace components exposed to foreign particles during operation are provided. The aerospace components include a substrate surface and a coating material applied to the substrate surface, the coating material having properties to repel a foreign particle from a coated surface. The coating material has the following formula: Pb^lv^Nb^Sb- _f ^tgBi.giL _yyj . O^ with a, b, z, h, q, ϋ, m, and n being between 0% and 100%, L being one or more Lanthanide elemental metal (La, Ce, Pr, Nd, Prn, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu).

[0010] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the coating material comprises at least 60% lead.

[0011] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the coating material comprises 8% gold.

[0012] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the coating material is formed of primary material and a dopant material.

[0013] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the dopant material is lead.

[0014] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the dopant material has a composition of between 1 ppm and 10,000 ppm.

[0015 ] In addition to one or more of the features described above, or as an alternati v e, further embodiments of the aerospace components may include that the primary material is manganese.

[0016] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the aerospace component is a component of at least one of a fan section, a compressor section, a combustor section, a turbine section, and a gear system of a gas turbine engine.

[ 0017] In addition to one or more of the features described above, or as an alternati v e, further embodiments of the aerospace components may include that the formula is Pb _a M^Pr _Y Pm _s Ce _e NhrSb _v Pt _e BL _{e Qn} , and , b, g, d, e, z, h, q, ϋ, m, and h are between 0% and 100%.

[0018] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the substrate surface has a first permittivity value, the coating material has a second permittivity value, and the foreign particle has a third permittivity value, and the second permittivity value is greater than the first permittivity value and the third permittivity value is greater than the second permittivity value.

[0019] According to some embodiments, aerospace components that are exposed to foreign particles during operation are provided. The aerospace components include a first object having a first permittivity value and a medium formed on the first object, the medium having properties to repel a second object from the first object. The medium has a second permittivity value that is greater than the first permittivity value, the permittivity value of the medium repulses the second object having a third permittivity value, and the third permittivity value is greater than the second permittivity value.

[0020] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the first permittivity value is e > 100, the second permittivity value is 10 < e < 100, and the third permittivity value is 1 < e < 10.

[0021] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the aerospace component is a component of at least one of a fan section, a compressor section, a combustor section, a turbine section, and a gear system of a gas turbine engine

[0022] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the composition of at least one of the first object and the medium has the following formula: Rί) _a M?ΐ _b NB _z 5B _h Rί _q Bί3 (£ _m ) O _n , with a, b, z, h, q, ϋ, hi, and h being between 0% and 100%, £ being one or more Lanthanide elemental metal (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tin, Yb, Lu).

[0023] According to some embodiments, aerospace components exposed to foreign particles during operation are provided. The aerospace components include a substrate surface and a coating material applied to the substrate surface, the coating material having properties to repel a foreign particle from a coated surface. The coating is configured to generate a repulsive force greater than a normal adhesion force between the foreign particle and the coated surface

[0024] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the repulsive force is of a magnitude between 10-14 N and 10-5 N in the presence of the foreign particle.

[0025] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the aerospace component is a component of at least one of a fan section, a compressor section, a combustor section, a turbine section, and a gear system of a gas turbine engine.

[0026] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the coating material has the following formula: RB _a Mh _b NB _z XB _h Rί _q Bί (£ _gh )O _h , with a, b, z, h, Q, ΰ, hi, and n being between 0% and 100%, £ being one or more Lanthanide elemental metal (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu).

[0027 ] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the coating is configured to generate a repulsive force on the order of magnitude of 10-14 N when the foreign particle is subject to gravitational forces and the aerospace component is at rest, and the foreign particle is Iprn in size.

[0028] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the coating is configured to generate a repulsive force on the order of magnitude of 10-5 N when the foreign particle is subject to aerodynamic forces and the aerospace component is m operation, at least one of the foreign particle is 10pm in size and the foreign particle impinges upon the coating at about Mach 0.6.

[0029] According to some embodiments, aerospace components exposed to foreign particles during operation are provided. The aerospace components include a substrate surface and a means for repelling a foreign particle from the substrate surface.

[0030] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the means for repelling is a coating and at least one of (i) the coating material has the following formula: Ph _a MnpNh Sb^teBi _f JL^O _r, , with a, b, z, h, Q, ΰ, m, and n being between 0% and 100%, £ being one or more Lanthanide elemental metal (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tin, Yb, Lu), (ii) the substrate surface has a first permittivity value, the coating material has a second permittivity value, and the foreign particle has a third permittivity value, and the second permittivity' value is greater than the first permittivity value and the third permittivity value is greater than the second permittivity value, and (iii) the coating is configured to generate a repulsive force greater than a normal adhesion force between the foreign particle and the coated surface.

[0031] In addition to one or more of the features described above, or as an alternative, further embodiments of the aerospace components may include that the aerospace component is a component of at least one of a fan section, a compressor section, a combustor section, a turbine section, and a gear system of a gas turbine engine.

[0032] The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be illustrative and explanatory' in nature and non limiting. BRIEF DESCRIPTION OF THE DRAWINGS

[ 0033 ] The following descriptions should not he considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like elements may be numbered alike and:

[0034] FIG. 1 is an illustration of a force diagram identify aerodynamic forces exhibited on a substrate and a foreign particle;

[0035] FIG. 2 is an illustration of a coating material positioned between a first object and a second object;

[0036] FIG. 3A is a plot of existing example coatings used in aerospace applications illustrating an attractive force to a particle based on separation distance;

[0037] FIG. 3B is a bar graph of normalized adhesive properties of various prior art coatings;

[0038] FIG. 3C is a schematic plot of coatings that reduce attractive forces in accordance with prior art coatings;

[0039] FIG. 4A is a schematic plot illustrating the difference between a coating of the present disclosure and prior art coatings;

[0040] FIG. 4B is a schematic chart illustrating the difference in normalized adhesive forces between coatings of the present disclosure and pri or art coatings;

[0041] FIG. 5 is an illustration of an application of a repulsive coating material in accordance with an embodiment of the present disclosure;

[0042] FIG. 6 is an illustration of an application of a repulsive coating material in accordance with an embodiment of the present disclosure;

[0043] FIG. 7A is an illustration of an application of a repulsive medium in accordance with an embodiment of the present disclosure generating a force to repel a second object away from a first object;

[0044] FIG. 7B is an another illustration of an application of a repulsive medium in accordance with an embodiment of the present disclosure generating a force to repel a second object away from a first object;

[0045] FIG. 8 is an illustration of an application of a repulsive coating material in accordance with an embodiment of the present disclosure; [0046] FIG. 9 is a plot illustrating concentration levels of various components that achieve negative (repulsive) Lifshitz V an der Waais forces for CMAS particulates; and

[0047] FIG. 10 is a cross-sectional illustration of a gas turbine engine that may incorporate embodiments of the present disclosure.

DETAILED DESCRIPTION

[0048] Detailed descriptions of one or more embodiments of the disclosed apparatus and/or methods are presented herein by way of exemplification and not limitation with reference to the Figures. Illustrative embodiments pertain to the art of aerospace, and specifically to components and coating materials thereof. The term“foreign particle” as used herein refers to unwanted or undesirable particulate matter including, but not limited to, dirt, sand, dust, calcium-magnesium-alumina-silicate (“CMAS”) particles, other foreign objects, debris, component debris, and/or particles that may be present in or around a component, or as otherwise described herein. The term “component” as used herein refers to parts, assemblies, sub-assemblies, products, any elements or constituents of a part, any aerospace components, etc., including, but not limited to, gas turbine engine components or as otherwise described herein. The term“substrate” as used herein, refers to any surface of a component, especially one that may be exposed to a foreign particle (internal or external surface). The term“coating” as used herein refers to a material disposed on at least a portion of a surface of a component (i.e., substrate), or as otherwise described herein, where the disposition can occur in any number ways as is known in the art. The term“disposed” as used herein means applied, affixed, connected, attached or attracted (direct contact).

[0049] Many forces are applied to an aerospace component and/or substrates thereof during operation. A force diagram 100 of some of these forces is provided illustratively in FIG. 1. An illustrative depiction of an (aerospace) substrate 102 or surface of an aerospace component, a coating 104 (or treatment), and a foreign particle 106 and various forces impacting the substrate 102 and the foreign particle 106 is shown. A first force, Fi, indicates an aerodynamic force and is created by a gas flow (e.g., air) moving across an area at high speeds (e.g., across a surface of the substrate 102 and coating 104). The first force, F·, is indicative of aerodynamic forces that represents flow parallel to the surface, such as flow' within a boundary layer. A second force, F , indicates a normal adhesion force including, without limitation, a normal vector of an aerodynamic force, the weight of the foreign particle 106, an attractive distance-dependent intermolecular force (known as the Van der Waais force, discussed below'), and any other normal forces acting on the foreign particle 106. As will be appreciated by those of skill in the art, the normal force is a vector of force(s) that is normal to the substrate 102/coating 104. A third force, F ₃ , indicates a friction force defined as the resistant force that exists in the lateral direction between two objects, in this case between the foreign particle 106 and the substrate 102 (with or without the coating 104). Because the thickness of the aerodynamic boundary layer is greater than the diameter of the foreign particle 106, especially foreign particles havin small diameters, such as those that are below 10 microns, the velocities of the gas flow will approach zero near the surface of the substrate 102/coating 104. As such, the aerodynamic force, Fi, generated by the gas flow does not have enough momentum to dislodge a foreign particle 102 having a small diameter and thus the foreign particle 106 adheres to the substrate 102/coating 104. As illustratively shown, the third force, F ₃ , may be an order of magnitude larger than the other aerodynamic forces (e.g., first force, Fi) present where the two objects 100, 102 are at close distances. As will be appreciated by those of skill in the art, the above discussion is merely an example of forces acting upon the foreign particle 106 when it interacts with the sub substrate 102/coating 104. That is, other types of forces may also act upon the foreign particle 106, the substrate 102, and/or the coating 104, including, but not limited to, electrostatic forces, chemical bond forces, or other forces known in the industry and/or present in the interactions of the various elements of the system illustrated in FIG. 1.

[0050] The Lifshitz Van der Waals force and relationship with permittivity is now described, particularly as it relates to interactions such as shown in FIG. 1. At molecular separation distances between two materials (e.g., a few nanometers or less), quantum fluctuations create intermolecular forces between the materials that are known as Van der Waals forces. Van der Waals forces are distance-dependent interactions between atoms or molecules of the materials and such forces decay rapidly at large distances. Lifshitz theorized Van der Waals forces for macroscopic objects that are separated by short distances. The theory' predicts the forces based on optical properties, namely permittivity, of three interacting materials (e.g., object 1 (e.g., substrate), object 2 (e.g., foreign particle) and a medium (e.g., coating)). This force, as used herein, is referred to as the Lifshitz Van der Waals force (“LVDW force” or“FL _V DW”)· The LVDW force, as used herein, means the force between two object surfaces that are in close proximity to one another, e.g., 1-1000 nm, and can be referred to herein as the attractive force, particle attraction force, adhesion force, or normal adhesion force (e.g., third force F ₃ shown in FIG. 1).

[0051 ] Permittivity is a measure of the energy storing capacity, or electric field, or surface energy, exhibited by a material (e.g., substrate, coating, foreign particle, etc.) by

0 means of polarization. That is, permittivity' defines the ability of a material to propagate an electric field having a particular orientation or polarization.

[0052] The LVDW ^' force (FLVDW) between a first object (e.g. , a substrate), a medium

(e.g., a coating material), and a second object (e.g., a foreign particle) is given in Equation (1) and Equation (2) below, depending on characteristics of the second object. In Equations (1), (2), the first object has a first permittivity e _1; the medium has a second permittivity e ₂ , and the second object has a third permittivity e ₃ .

[0053] The LVDW force (FLVDW) between the two objects and the medium, w ith the second object having a surface of finite radii of curvature is:

[0054] The LVDW force (FLVDW) between the two objects and the medium, w ith the second object being flat is:

[0055] In Equations (1) and (2), R? is the radius of the second object, h is Planck’s constant, £ is the thickness of the medium, k _{B i} s the Boltzmann constant, v is dipole frequency (¾> ₁ relativistic shift frequencies), and Z' is surface temperature.

[0056] The variables of Equations (1) and (2) are shown in the illustration of FIG. 2.

In FIG. 2, an illustration of interacting objects are shown. A first object 200 is shown which may be a component for aerospace applications, such as shown and described herein. The first object 200 includes or defines a substrate 202 (e.g., surface that is exposed to interact with a foreign particle). Applied to the substrate 202 of the first object 200 is a medium 204, such as air or material of a coating. As shown, a second object 206 is shown in contact with the medium 204. The first object 200 has a respective first object radius Ri, the second object has a respective second object radius R ₂ , and the medium 204 has a thickness £. When the radii R and R ₂ are infinite, the respective object 200, 206 has a flat surface.

[0057] Given known permittivities of two objects and a medium, the LVDW force can be determined, in either case, whether the second object is curved or flat. Typically, the LVDW force is attractive because the permittivity of a vacuum or gasses (e.g., air) is 1 or coalesce to 1. Also, as noted above, the LVDW force is an order of magnitude larger than the other aerodynamic forces present where the two objects are at close distances (as shown in FIG. 1). Therefore, in accordance with embodiments of the present disclosure, given known permittivities of the first and second objects (e.g., an aerospace component and foreign particles), a medium (e.g., a coating material) can be designed to have an intermediate permittivity (and polarizability) to result in a LVDW force that is negative (i.e., repulsive). In this case, a second object will not be attractive to the first object, but rather the second object will be repulsed from the first object when the second object enters/approaches the designed medium. In the context of an aerospace component, foreign particles can be repulsed from an aerospace component having a coating material designed to exhibit a particular permittivity.

[0058] Notwithstanding the known physics upon which a coating design is premised, it is challenging to design a coating material that wall repulse foreign particles based on LVDW forces for many reasons. As noted above, the LVDW forces are an order of magnitude greater than the other aerodynamic forces contacting foreign particles present in an aerospace application. Although these forces are large, they only exist at small distances between the component and the foreign particles (e.g., on the order of nanometers). Once the foreign particle moves beyond (i.e., within) a critical separation distance, the foreign particle can sinter to the substrate, in contrast to the benefit of the repulsive coating. This force may be overlooked by one skilled m the art, and to the extent that it is not overlooked, designing for repulsion of foreign particles, where repulsion is capable only at such a close proximity between objects, is challenging

[0059] In addition, it is counterintuitive to make the LVDW forces negative. Primarily, the LVDW forces exist in the aerospace applications as a positive, attractive force (e.g., as shown in FIG. 1). While the concept of Van der Waals forces being negative is known, the present disclosure presents, in some embodiments, coating materials designed to repulse foreign particles successfully at temperatures typical to aerospace parts, including those ranging from above room temperature to higher than 1500 °C. Successful coating materials have to repulse foreign particles in the aggressive operating and environmental conditions, such as temperatures and pressures, that are required of aerospace components.

[0060] In accordance with embodiments of the present disclosure, the Gibbs free energy argument is employed to determine an affinity of the coated component surface (i.e., substrate) to the foreign particle. The Gibbs free energy represents the affinity of the substrate and the foreign object across the coating material (medium). The change in respective permittivity of materials manifests as an accumulative pressure that is maximum at the surface but decays as the foreign particle increases in distance from the surface. That is, the interaction of the foreign particle and the substrate becomes retarded over increasing distances.

[0061 ] Moreover, the types of coaling materials that are capable of exhibiting the desired permitivities are rare and difficult to identify. Moreover, utilization of such coating materials for production aerospace products further can limit the scope of potential coating materials. Successful coating materials are not temporary, volatile liquids that evaporate at particulate temperatures, such as room temperature. Rather, successful coating materials are applied to component surfaces and remain on the component during the entire operating mission and/or life of the aerospace component.

[0062] Still further, as mentioned herein, existing coating materials of aerospace components are generally known to one skilled m the art, and the typical aerospace component coating has a thickness in the range of 10s of microns. In contrast, the coatings utilized in embodiments of the present disclosure are on the order of 100s of nanometers, which is significantly thinner than existing aerospace coating materials. It is not obvious to one skilled in the art to consider coatings that are significantly thinner than most known aerospace coating materials, where such coatings can be successful in aggressive operating conditions.

[0063] Finally, the composition of foreign particles is typically not uniform. Accordingly, a design challenge may arise in determining the permittivity of a non-uniform composition of foreign particles and a successful coating material suitable for generating a repulsive force of such variable foreign particles.

[0064] For at least the above reasons, it is not obvious to design a coating based on repulsive LVDW forces. Moreover, there are significant challenges to designing such a coating that will exhibit repulsive LVDW forces and meet all the other aerospace component requirements while providing equal or superior performance to that of known coatings.

[0065 ] Given the above discussion, even though existing coatings were not designed based on the LVDW forces, existing coatings were analyzed to understand the LVDW forces present. The analysis shows that a positive or atractive LVDW force exists between existing coating materials (or uncoated substrates) and the foreign particles.

[0066] Turning to FIG. 3A, a graph 300 of selected existing coatings used in aerospace applications is shown. On plot 300, the x-axis is a separation distance £ (nm) between a coated or un coated substrate and a foreign particle interacting with the exposed surface of such substrate. On plot 300, the y-axis is a change m Gibbs Free Energy AG (J/nr) between the exposed surface of the substrate and the foreign particle interacting with the exposed surface of the substrate. In graph 300, the foreign particle is a silica particle.

[0067] A first curve 302 represents an affinity or attraction of a foreign particle toward a substrate with a coating having a composition of chromia, zircoma, and yttria. A second curve 304 represents an affinity or attraction of a foreign particle toward a substrate without a coating with the substrate having a composition of a hare super-alloy. A third curve 306 represents an affinity or attraction of a foreign particle toward a substrate with a coating having a composition of zirconium, cobalt, molybdenum, silicon, and germanium. Electromagnetic contact between the foreign particle and the exposed surface of the substrate (coated or uncoated) occurs at a distance of about 3 A (minimum of Leonard -Jones potential beyond which materials repel each other). The negative values of the change in Gibbs Free Energy AG indicate that the affinity between the exposed surface of the substrate and the foreign particle is“attractive.” Deposition is inevitable; even if the affinity is low, the rate of deposition will be non-zero. For positive values of the change in Gibbs Free Energy AG, the force becomes repulsive. The deposition is blocked due to the surface repulsion. As such, fouling may be completed blocked or prevented by using coating materials that produce a positive change in Gibbs Free Energy (AG>0).

[0068] In plot 300, a magnitude of dG/di (i.e., slope of curves 302, 304, 306) is related to a rate of deposition (thermodynamic force). Tire plot 300 illustrates that the foreign particle deposition rate to the coated or uncoated substrate is greater where the substrate and the foreign particle are closer together in distance (i.e., slope is greater closer to zero). Although the coatings may provide some utility for mitigating foreign particle deposition in decreasing the rate of deposition, the foreign particle will ultimately be deposited onto the surface of the substrate, and thus the rate of deposition is non-zero. Moreover, once a single foreign particle has been deposited and adheres to the substrate, any coating that may have been applied to the substrate provides reduced or little continued benefit, as the new' surface of the substrate now consists of foreign particles. In such cases, the additional foreign particles will adhere to the foreign particles already deposited.

[0069] FIG. 3B is a bar graph 310 of various prior art aerospace coatings illustrating normalized adhesion forces (i.e., the LVDW force). Positive values indicate an attractive LVDW force between a coating material and a foreign particle. The dashed line 312 in FIG. 3B represents a baseline coating material, wherein coating materials with greater values of normalized adhesion are operably more attractive than the baseline coating material, and those with lesser values are relatively improved coating materials as compared to the baseline coating. The theoretical JKR (Johnson, Kendall, and Roberts) model was used in approximating the LVDW forces. The JKR model approximates the LVDW forces between two objects, in this case, coating materials and the foreign particles. The JKR model, and thus the approximated LVDW forces, scales with the surface energy of the coating material multiplied by the radius of the foreign particle, as will be appreciated by those of skill in the art. Given this relationship, the existing coatings are analyzed herein by looking at the surface energy of the coating material as a predictor of the LVDW forces between foreign particles and the coating materials.

[0070] In generating the bar graph 310, the material of the foreign particles was assumed to he silica. In this illustration, the baseline (line 312) is defined by coating A which is formed of aluminum halide. Coating B is a silicon carbide (SiC) coating or a silicon nitride (S13N4) coating. Coating C is a zirconia or hafnia coating. Coating D is a rare-earth metal coating. Coating E is tantlum pentoxide, titanium dioxide, halfnium dioxide, niobium pentoxide, or yttrium oxide. Coating F is a cobalt/nickel coating. Coating G is a ferro aluminum or cobalt nickel chromium aluminum yttrium coating. Coating H is a mullite or barium strontium coating. Coating I is a calcium/rear-earth fluoride coating. Coating J is a rare-earth gallite coating (e.g., In _f Ga^Os, wherein "Lna" refers to the rare earth elements of lanthanu (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), and mixtures thereof). Coating K is a platinum or osmium coating. Coating L is an 8 wt % yttria-stabiiized zirconia coating.

Coating M is a 4 wt % yitria-stahilized zirconia coaling. Coating N is a spinel-type zinc aluminate coating. Coating O is a tantalum coating. Coating P is a coating comprised of AeAhO _?. Coating Q is a platinum aluminide coating. Coating R is a nickel-acetate tetrahydrate coating. Coating S is a nickel ferrite coating. Coating T is a chromium/aluminum coating having a 70%/30% composition.

[0071] As shown, each of the prior art coatings exhibits a positive normalized adhesion (i.e., attractive LVDW force). Although some coatings (i.e., coatings C, D, H, I, N,

O, P, and R) may perform better (be less attractive) than the baseline (i.e , coating A), each of the coatings exhibits a positive attractive force, and thus may attract foreign particles over time, and thus degrade in efficacy.

[0072] The prior art coatings tend to reduce the surface energy' of underlying substrates. The reduced surface energy- may reduce the normal adhesion force (i.e., the LVDW force) between foreign particles and the coated substrate; however, such coatings exhibiting a reduced adhesion with the foreign particles do not stop or block the deposition of a first layer of foreign particles. Rather, these coatings merely slow down the deposition process. As soon as the first layer of the foreign particles accumulates or forms on the coating, the surface energy of the coating is compromised and the surface will continue to accumulate foreign particles as if there is no coating at all. Thus, the current coatings may not block either deposition or accumulation of the foreign particles on a surface.

[0073 ] As discussed above, for existing coatings, the forces between the coating materials and the foreign particles are attractive, but also as discussed above, multiple forces are present around the coated substrate and the foreign particles. The aerodynamic forces may tend to dislodge the particles from a substrate. When comparing the aerodynamic forces with the attractive LVDW forces exhibited by the existing coating materials or uncoated substrate materials, the reduced attractive LVDW forces still remain stronger than the aerodynamic force. This is true even though the existing coating materials reduced the attractive LVDW forces over the uncoated substrate. Thus, it was observed that the existing coatings did not change the magnitude of the LVDW forces at close distances between the foreign particles and the substrates. Stated another way, the LVDW forces remained greater than the aerodynamic forces.

[0074] Turning to FIG. 3C, a bar chart of coating materials or uncoated substrate material that reduce attractive LVDW forces is shown. The x-axis represents a number of existing coating materials (or uncoated substrate material) and the y-axis represents a value of the lateral adhesion force divided by an aerodynamic force. The lateral adhesion force is a lateral Coulornbic friction force that is proportional to the coefficient of friction and the normal adhesion force. The aerodynamic force is that discussed above.

[0075] In FIG. 3C, a silica particle of 1 pm is represented as the foreign particle that contacts the coating material or uncoated substrate material indicated. The velocity of air for the analysis shown in FIG. 3C was assumed to be 50 m/s. The aerodynamic force is an order of magnitude smaller than the adhesion force, as illustratively indicated in FIG. 1. The existing coatings have compositions of bare-nickel, silica, alumina, zirconia, barium fluoride, and calcium fluoride. Aerodynamic forces tend to dislodge a foreign particle from the substrate surface (assuming the foreign particles are not sintered to the substrate material which occurs at high temperatures) if the aerodynamic force overcomes, or is greater than, the adhesion force. However, when the foreign particle adhesion is stronger than the aerodynamic force, the particle cannot be dislodged, and thus a first layer of foreign particles may be able to accumulate on the surface of the coating material or uncoated substrates.

[0076] Again, even though existing coatings were not designed with respect to considering LVDW forces, the LVDW forces are still present and are greater than the aerodynamic forces for such existing coatings. The challenge of designing coating material that utilize this strong LVDW force at close distances between a substrate and a foreign particle to repel foreign particles remains. [0077] Referring back to Equations (1), (2), above, in accordance with embodiments of the present disclosure, the LVDW force becomes repulsive rather than attractive when the permittivity of the medium is greater than one object and less than the other object (i.e., the permittivity of the medium is between the permittivity of the first and second objects). Embodiments of the present disclosure utilize the condition that the LVDW force that is present at the surface of an aerospace component is an order of magnitude larger than other aerodynamic forces present when a foreign particle is in close proximity to the component. Foreign particles can be repulsed from the aerospace component having a surface coated with a coating that is designed to exhibit a particular permittivity, thus reversing the sign of the LVDW force from positive to negative. In order to create a negative LVDW ^' force between a foreign particle and a component, the permittivity values of both objects must be determined so that intermediate permittivity of the coating can be determined.

[0078] In order to obtain a repulsive LVDW ^' force between two objects (i.e., the first object and the second object) across the medium, the permittivity of the medium, e ₂ (ίn), is required to be a value between the permittivity of the first object, s^iv), and the permittivity of the second object, e ₃ (ίn) In some embodiments of the present disclosure, the first object may be a component surface or substrate, the second object may be a foreign particle, and the medium may be a coating applied to the surface or substrate. In some embodiments of the present disclosure, the first object may be a coating, the second object may be a foreign particle, and the medium may be a surface layer of the coating, as described below. In some such embodiments, the permittivity' of a component to which the coating is applied may be ignored for purposes of generating the repulsive force described herein. The permittivities of the various objects are provided with x = iv being at imaginary' frequencies. Thus, for a repulsive LVDW force:

e ₃ (ίn) < e ₂ (ίn) < e^ίn) (3)

[0079] Equation (3) is satisfied across a wide range of imaginary frequencies, e.g., from v 0 (static) to x HO In one non-limiting embodiment, the first permittivity' value is s (iv) > 100, the second permittivity value is 10 < e ₂ < 100, and the third permittivity value is 1 < e ₃ < 10, for frequencies at approximately x = ilO ¹⁴ (i.e., on the order of magnitude thereof or about x = ilO ¹⁵ — ).

[0080] In view' of the above, in some embodiments, rather than considering the specific permittivities, the generated forces may be considered. For example, the material and/or permittivity of a coating may be selected to generate a specific repulsive force. For foreign particle repulsion, the Van der Waals force (F _V DW) must be greater than the dominant forces causing adhesion. That is, the Van der Waals force (FVDW) must be sufficient to overcome the gravitation force acting on a foreign particle when no other forces act upon the foreign particle (e.g., extreme lower bound). Further, in more extreme conditions, greater forces may act upon the foreign particles that may lead to adhesion, and thus, the Van der Waals force (F _VD w) must be greater than these forces.

[0081] For example, in some non-limiting embodiments, the coating may be configured to generate a repulsive force on an order of magnitude of about 10 ¹⁴ N. Tins repulsive force would be sufficient to repel the weight of a foreign particle having a diameter of about 1 pm. At the other end of the spectrum, a foreign particle, having a diameter of about 10 pm and subject to aerodynamic forces such that the foreign particle impinges at about Mach 0.6, may require a repulsive force on an order of magnitude of about 10 ⁵ N. As wall be appreciated by those of skill in the art, other forces may act upon the foreign particle depending on the given situation, e.g., environment, structure of the substrate/coating, etc. Accordingly, the coating may be configured to generate a repulsive force having a particular order of magnitude or range of magnitudes in the presence of a foreign particle. In one non- limiting application, a coating may be configured to generate a repulsi ve force of between 10 ³⁴ N and IQ ⁵ N in the presence of a foreign particle. As used herein, the concept/term of “repel” and “repelling” means once the coating reaches an activation condition (e.g., temperature or pressure), thus satisfying the permittivity inequality (Equation 3, above), a repulsive force is generated that is strong enough to remove particles in contact or m close proximity to the coating surface.

[0082] In addition to selecting a repulsive coating material with the desired intermediate permittivity' based on LVDW forces for an aerospace component, specific properties and characteristics of a repulsi ve coating material are designed based on the needs of a particular application of the component. As such, other factors beyond permittivity may be considered, including, but not limited to, the temperature and other operating conditions, the complexity of the composition of the foreign particles to be repulsed, and the thickness of the coating material, among other factors. Some of which will be discussed herein.

[0083] Operating temperature ranges of both an aerospace component and foreign particles that are desired to be repelled may contribute to the sel ection of th e coating material . It will be appreciated by those of skill in the art that operational temperatures may vary drastically for aerospace components. Thus, effective operating temperatures of the coating materials of embodiments of the present disclosure may be optimized for specific applications. For example, some parts of an aircraft (engine or otherwise) may be exposed to sub-zero temperatures, particularly when at cruise altitudes. In contrast, internal to the engine, temperatures may rise to very high temperatures (e.g., within or proximate to a combustion chamber and may be in excess of 1000 °C). In some such high temperature examples, the operating temperature may be beyond the melting point of the foreign particle (e.g., 100 °C, 1000 °C, above 1000 °C, etc.).

[0084] In some embodiments, the coating materials of embodiments of the present disclosure may have activation temperatures or pressures, which may be associated with the operating temperatures of the components to which the coatings are applied. That is, the coating materials of the present disclosure may be designed to activate or induce repulsion at different and/or specific temperatures (or ranges of temperatures). As will be appreciated by those of skill in the art, permittivity is a function of temperature. In some embodiments, the coating materials may be required to be heated to certain temperatures to generate the desired repulsive force. Such temperatures may be referred to as‘activation temperatures,” and as used herein, refers to an environmental temperature at which the coating material will exhibit the properties described herein (i.e., generate the repulsive force between the first and second objects). When the temperature is below the activation temperature, the repulsive force may not be generated. That is, specific operating/environmental temperatures may be required to generate the repulsive LVDW forces. In some embodiments, the activation temperature of coatings materials is 100 °C or greater. Further, for some high temperature applications within gas turbine engines, the activation temperatures may be 1000 °C or greater (e.g., for combustor section components).

[0085] In still further embodiments, low temperature activation temperatures may be provided. For example, in efforts to reduce frosting/icing at high altitude, various aerospace components may be coated with coating materials that have activation temperatures at 0 °C or less. The coating material permittivity may be selected to satisfy a specific criterion to achieve a desired result at a specific temperature (e.g., activation temperature).

[0086] In addition to activation temperatures, various pressures may be considered for activation of a coating material m accordance with embodiments of the present disclosure. Thus, in some embodiments, the coating materials may have activation pressures that, when present, exhibit the desired repulsive LVDW forces. In some embodiments, the activation pressures may be at atmospheric pressures or greater. In some embodiments, the activation pressure may be 10 bar or greater, and even above 50 bar. Further, in some embodiments and with some coating materials of the present disclosure, the partial pressure of oxygen may be important at different altitudes. Moreover, some coatings of the present disclosure may exhibit phase-transitions based on temperature and/or pressure. For example, in some such embodiments, as the coating material goes into a phase-transition, the phase-changed coating material will be exposed to the atmosphere and thus may change an oxidation state according to the partial pressure of the atmosphere. Pressure inside the coating material could be controlled through multiple adjustable characteristics of the coating simultaneously, such as by selecting the optical properties of the coating material and setting the thickness of the coating material.

[0087] Coatings of the present disclosure (i.e., repulsive LVDW force-based coatings) are designed based on the atomic level properties of the coatings. The repulsive coatings of the present disclosure can successfully perform or operate even having layers that are much smaller/thinner than one skilled in the art typically thinks about with respect to coatings used in aerospace applications. It is noted that such thin-layer coatings are not intuitively thought to be successful in such aggressive operating conditions as aerospace engine operating conditions. However, because the LVDW forces are short-range forces, only interactions between the foreign particles closest to the coated component need to be considered (i.e., at a contact area). As such, durable coating materials in accordance with the present disclosure can be thinner than 1 micron in thickness. These thin coatings survive and maintain operability and functionality at high temperatures that are experienced in aerospace applications. The thickness of the coating material may range from less than 1 nm up to about 1000 nm. In some embodiments, the thickness of the coating may be between 30 nm and 100 nm. Such thicknesses enable the repulsive LVDW forces and may provide for additional benefits as described herein.

[0088] As noted above, the foreign particles that are considered for repulsion can be a number of different items/objects/materials that may interact with an aerospace component. For example, without limitation, the foreign particle may be a chemical or material that has a chemical property (e.g., chemically inert or chemically reactive). Foreign particles can include, without limitation, sodium, calcium, magnesium, barium salt, iron, titanium, other transition metal salts, atmospheric foreign particles (including w ater soluble), other salts, insoluble compounds, sand, silica, alumina, iron oxide, titanium oxide, or other transition metal oxides in the atmosphere or air. In addition, the foreign particle may be metal, metal oxide, ceramic, plastic, glass, or other material which may release in a flow stream through a gas turbine engine or otherwise interact with a coated aerospace component. [0089] The foreign particle may take various morphologies. The foreign particle may be soft or hard surface particulates and may include small atmospheric particulates, aggregates in fuel (e.g , coke aggregates), salt scales or metal oxide scales in water in boilers, debris formations from wearing between two surfaces, etc.

[0090] Tire foreign particles may be macroscopic. The foreign particles may have sizes ranging from 500 nm or less, 1 pm or less, 100-500 pm, or even larger, in diameter or length (e.g., in at least one dimension). The foreign particles could be mono-dispersed or could be clumped or aggregated together. Clumped foreign particles could be originated from the external atmosphere in the form of aggregates or they may aggregate during or after deposition processes within the gas turbine engine. Further, the foreign particle may have various textures, e.g., rough or smooth, and could have any given geometric shape (e.g., spherical, cylindrical, planar).

[0091 ] In some instances, the foreign particles may have water content or may be dry' (i.e., lacking water content). The foreign particles may be solid, semi-solid, or in liquid state (e.g., molten foreign particles). Thus, as will be appreciated by those of skill in the art, the foreign particle may take any form and have various properties, without limitation and without departing from the scope of the present disclosure.

[0092] Because of the various operating temperatures and environment of gas turbine engines, the foreign particles may have various temperatures. For example, foreign particles within a gas turbine engine may range between -60 °C to above 1700 °C (e.g., with colder temperature at an inlet/fan and higher temperatures within a combustion section of the engine). The foreign particles may remain chemically constant as they pass through different parts of a gas turbine engine or the chemistry may alter, as will be appreciated by those of skill in the art. In some instances, the size of the foreign particles may also change as the foreign particles pass through the gas turbine engine. Further, during the operation of a gas turbine engine, foreign particles may enter the system at ground (e.g., on a runway, taxiing, etc.) or at different altitudes of flight. Further, as the foreign particles enter and flow through the gas turbine engine, the foreign particles may have velocities ranging from 0 m/s to 500 m/s or greater.

[0093 ] The coating materials may be customized or selected to achieve a desired permittivity value based on a permittivity value of a wide variety of homogenous and non- homogenous foreign particles to be repulsed from the substrate (i.e., component surface). For example, pure gold may attract all of the foreign particles. By adding some amount of low permittivity post transition metal to the gold, the overall permittivity of the coating material is reduced and repulsive conditions may arise at and beyond some critical concentrations. In order to remove ail the foreign particles, the permittivity of the coating material must be reduced below the values corresponding to the foreign particles with lowest permittivity. This ensures global or complete repulsion for all foreign particles, including the ones with lowest permittivity. In this way, coating materials of embodiments described herein may become repulsive to a range of different foreign particles with different chemistries and/or compositions.

[0094] The components to which coatings may be applied include any aerospace component, including gas turbine engine components. In addition to the types of components, the component surfaces may have any different degrees of roughness ranging from microns to nanometers in height. However, the coating materials of the present disclosure asymptotically reach to atomic scales, and thus are agnostic to surface roughness and/or texture of the component surface. Accordingly, regarding of the component, the operating condition, the environmental condition, and/or the surface texture of the component, coatings of the present disclosure may be applied thereto.

[ 0095 ] The components, or substrates thereof, may be formed from any material that is present within a gas turbine engine. For example, without limitation, the components may be formed from a pure elemental metal, a metal oxide, ceramic, an intermetallic alloy, an alloy with different compounds, refractory compounds, etc.

[0096] In gas turbine engine applications, the components may be compressor blades, air passages or clearances thereof, combustor surfaces (cold side or hot side of panels/components), turbine components, etc. As noted, the temperatures within a gas turbine engine may vary significantly, e.g., between -60 °C to 1700 °C or greater.

[0097] The substrate surface of the component could be an external surface or internal surface. Such internal surfaces may be surfaces of internal passages that may be simple or complex. In some instances, the internal surfaces may not be directly accessible for application of a coating (e.g., internal surfaces of airfoil cooling passages). The substrate surface may take any geometric shape, and may be flat, curved, sharp, blunt, vertically extending, horizontally extending, etc. The substrate surfaces of the present disclosure may include small detailed features, e.g., smaller than 1 mm. It is noted that the surface of a cooling hole (e.g., impingement hole) may define a substrate to which a coating may be applied. The above are merely for example, and are not to be limiting on the present disclosure.

[0098] The coating materials in accordance with embodiments of the present disclosure can consist of a variety of types of materials, including, without limitation, ceramics, composite ceramics, intermetallic compounds, pure metals, metal oxides, metal oxides with dopants, polymeric materials, or pure metallic elements with one, two, three or more dopants, etc., that are applied to a surface (substrate) of an aerospace component. In some embodiments, the coating may be a composite consisting of ceramics, metal oxides, metals, and/or polymers. In some embodiments, without limitation, the coating material may include lead, bismuth, manganese, scandium, cobalt, niobium, and/or praseodymium. In some embodiments, the above listed compounds may be a dopant in the coating material, with a base or other material containing the respective compounds. Further, in some embodiments, noble metals like gold and platinum may be employed as a dopant or additive to control optical properties of the coating material.

[0099] In some embodiments, the coating materials of the present disclosure may be in a solid state coating or quasi-liquid state coating. In a quasi-liquid phase, the coating material may distribute over the substrate surface to achieve a thermodynamic equilibrium thickness or distribution. Further, in some embodiments, the coating material may be in a liquid-state coating (e.g., the coating material may be a viscous quasi-liquid or a liquid). Further, the coating material may have elastic, visco-elastic, visco-plastic, or plastic properties (e.g., the coating material does not crack or spall due to fluid-like properties).

[0100] To achieve desired properties of the coating material, m accordance with embodiments herein, various alloys, dopants, or materials may be employed. For example, in some embodiments, alloys of low melting point elemental metals may be used. In some cases, a low surface melting temperature may correspond to a surface anomaly, which may be particularly true of coating materials having a thickness of 100 nm or less. In other embodiments, alloys having high melting points may be employed, with an optional dopant being employed to reduce the melting point of such alloys.

[0101 ] The composition and thickness of the coating materials of the present disclosure are determined based on the desired permittivity of the coating. The coating materi al may be one or more layers of identical, similar or different formulas of materials.

[0102] In some embodiments, the coating materials may have or comply with the following formula: RI _a M7ΐ _b Rt _Ύ Rhί _d eb _e NI _z 51 _g ,Rΐ _q Bί ₉ (£ _Ίh }O _h . In this formula a, b, g, d, e, z, h, Q, ϋ, m, and h could be between 0% and 100%, and n could be varied without bond. In this formula, O _n represents the inclusion of oxygen to form a stable metal oxide. In some embodiments, the oxygen may be included into the coating material prior to application as a coating, and in other embodiments, the oxygen may be introduced into the coating after application to a substrate (e.g., oxidation during operation). Accordingly, the compositions of the present disclosure may be stable oxides or not, depending on the particular formula and application. Further, with respect to L (the Lanthanide elemental metals), elements other than Pr, Pm, Ce may be employed, although, from the Lanthanide series, Pr, Pm and Ce are examples. For example, the formula for the coating materials may be RB _a Mh _b NB _z 5B _h Rΐ _q Bί _ϋ (£ _}h )0 _h , wherein L _m is one or more of the Lanthanide elemental metals (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, To, Dy, Ho, Er, Tin, Yb, Lu), with the same bounds on percentages as described above.

[0103] In accordance with various embodiments, in addition to repulsive properties, coating materials of the present disclosure may provide additional functions and/or have additional characteristics/properties. For example, in some embodiments, the coating material may also provide desired anti-erosion properties, anti-clogging properties, improved adhesion between interlayers, anti-corrosion, anti-frost/ice, anti-scale/salt scale fouling, anti-coke formation, etc. Thus, the repulsive properties are not to be limiting as the only beneficial properly or characteristic of the coating materials of the present disclosure.

[0104] Turning now to FIG. 4A, a plot 400 similar to that shown in FIG. 3 A, but including a curve 402 representative of a coating in accordance with an embodiment of the present disclosure, is shown. FIG. 4A is illustrative of the difference between an example embodiment of a coating of the present disclosure (curve 402) and the prior art coatings (curves 302, 304, 306). As shown, the coating in accordance with the present disclosure (curve 402) has a repulsive force (i.e., greater than zero and thus positive for the change in Gibbs Free Energy AG (J/m ² )). That is, as the separation distance i (nm) decreases, the change in Gibbs Free Energy AG (J/m ² ) of the coating m accordance with the present disclosure increases and a repulsive force is generated, thus preventing a first foreign particle from adhering to a coated surface.

[0105 ] FIG. 4B is similar to FIG. 3B and is an illustrative bar graph 410 illustrating the difference between coatings of the present disclosure (coating a and coating b) and prior art coatings (coatings A-T, discussed above). As shown, coating a and coating b each have negative normalized adhesion values, thus indicating a repulsion between a foreign particle and a substrate coated with coating a or the coating b. In this illustrative chart, coating a has a composition of 98% lead and 2% gold and coating b has a composition of 99% manganese. These compositions, when formed in accordance with the teachings described herein, exhibit repulsive LVDW forces against foreign particles that approach the coatings.

[0106] Turning now to FIGS. 5-8, illustrations of various applications of coating materials in accordance with exemplary, non-limiting embodiments of the present disclosure are shown. In FIGS. 5-8, the respective coating materials are provided to supply a repulsive LVDW force between a first and second objectis).

[0107] FIG. 5 illustrates a first object 500 having a coating material 504 applied thereto. A second object 506 is illustratively shown being repulsed from the coating material 504 due to the repulsive LVDW force. The second object 506 may have a rough surface or roughness, and yet still be repulsed.

[0108] FIG. 6 illustrates a first object 600 having a coating material 604 applied thereto. A second object 606 is illustratively shown being repulsed from the coating material 604 due to the repulsive LVDW force. In this embodiment, the second object 606 may be a chemically active object or material and it may be desirable to prevent chemical interaction and/or reaction between the first object 600 and the second object 606. The coating 604 prevents the chemically reactive second object 606 from interacting (chemically) with the first object 600. Thus no chemical reaction between the chemically reactive second object 606 and the first object 600 will occur.

[0109] FIG. 7A illustrates a first object 700 having a mediu 704 (e.g., coating) applied thereto. A second object 706 is illustratively shown being repulsed from the medium 704 due to the repulsive LVDW ^' force. In this illustration, the second object 706 is a foreign particle that essentially bounces off of or away from (is forced away from) the medium 704, thus preventing contact between the second object 706 and the first object 700. In some such embodiments, the repulsion provided by the medium 704 can prevent erosion or abrasion of the first object 700 by the second object 706.

[0110] FIG. 7B illustrates a configuration similar to that shown m FIG. 7A, but in this configuration, a first object 750 is a coating applied to a component 752. A second object 754 is repulsed from the first object 750 due to a medium 756 formed on a surface or between the first object 750 and the second object 754. In this embodiment, the medium 756 between the first object 750 and the second object 754 is a portion of the first object 750 (e.g., a surface layer). In some configurations, the medium may be a liquid or quasi-liquid layer of the coating (i.e., material of the first object 750), whereas the remainder of the first object 750 remains in substantially solid state. In some such embodiments, and as illustratively shown, the second object 754 may contact the medium 756 and interact therewith, causing an interaction shown at element 758. Such interaction may cause the repulsive force described herein to be generated, and thus repel the second object 754 away from the first object 750.

[0111 ] One example description in operation for FIG. 7B is that the first object 750 (e.g., a coating applied to the component 752) is operated at a sufficiently high temperature to form an atomically thin disordered surface layer. The atomically thin disordered surface layer may be referred to as a“melt layer,” as it is representative of an atomic level change of the structure/arrangement of atoms of the material of the first object 750 The second object 754 (e.g., a foreign particle) can interact with the“melt layer” (medium 756 shown in FIG. 7B) to form an intermediate chemical composition winch is a combination of the first object 750 (e.g., material of the coating) and the second object 754 (e.g., a foreign particle). The composition inherently has an intermediate permittivity between the permittivity of the first object 750 and the permittivity of the second object 754. Thus, the permittivity of the first object 750, the medium 756, and the second object 754 satisfy Equation (3) and a repulsive LVDW force is generated which forces the second object 754 away from the first object 750.

[0112] FIG. 8 illustrates a first object 800 having a coating material 804 applied thereto. The first object 800 defines a gap 808 with the coating material 804 coating the first object 800 about the gap 808. It is noted that in some embodiments, the first object 800 may comprise two separate elements that are located proximate each other and defining the gap 808. In other embodiments, the first object 800 may define a through-hole or aperture that is represented cross-section as the gap 808. One or more second objects 806 are illustratively shown being repulsed by the coating material 804 due to the repulsive LVDW force. As shown, the second objects 806 of the present illustration are foreign particles and may pass through the gap 808 without sticking to and/or eroding the first object 800 because the second objects 806 are repulsed by the coating material 804.

[0113] In some embodiments, matching permittivity may ensure “near-zero” adhesion. This is especially useful for applications wherein the base materials has similar optical properties as the foreign particle. Such“near-zero” coating material may slow' or reduce deposition of foreign particles. When a first layer of foreign particle is deposited onto a coating materi al, the optical properties of the coating material may be screened and thus the coating material may lose functionality. However, repulsive coating materials may ensure a sustainable anti -deposition and anti-fouling property by blocking the first layer deposition.

[0114] By applying coatings of the present disclosure to aerospace components, foreign particles can be repulsed from the aerospace component having a surface coated with a coating that is designed to exhibit a particular permittivity that is intermediate to the permittivity of the material of the aerospace component and the permittivity of the undesirable foreign particles, thus reversing the sign of the LVDW force from positive to negative. The foreign particles will levitate on the coating and could be dislodged by small disturbances such as thermal fluctuation, vibration, aero-force, etc. By designing the coating with a particular permitivity, LVDW forces repel foreign particles away from the coated component.

[01 15] In one non-limiting aero-space application, the material of the coating material is selected to repel foreign particles at 900 °C and above. In this example application, the coating material is selected and applied to repel silica particles, calcium/magnesium salts, and alumina from contacting a combustor panel of a gas turbine engine. That is, the composition of the coating material in this example is designed to repel CMAS particulates. The coating material may be formed with a lead-based formulation that is optimized with doping to achieve a desired repulsion of the CMAS particulates. For example, a coating material having 92% lead and the balance being gold was found to repel all or nearly all CMAS particulates. In one non-limiting example, a coating material having a composition of 98% lead and 2% gold may be employed for repulsion of CMAS particulates. In some embodiments, when using lead as the base for the coating material, the activation temperature may enable repulsion of foreign particles at about 750 °C and above. However, such temperature is not to be limiting, as various dopants may be employed that may alter (e.g., reduce) the activation temperature. As discussed above, the activation temperature is a temperature threshold at which the coating material will be active and repel foreign particles from the surface to which the coating material is applied.

[0116] Turning to FIG. 9, a plot 900 is shown representing the lead concentration m a coating material in accordance with the present disclosure. The lead concentration is provided along the X-axis. The plot 900 illustrates the concentration levels that achieve negative (repulsive) LVDW forces for CMAS. In plot 900, the zero line 902 represents a change in attraction to repulsion, with positive values representing an attraction between the CMAS particle and a coating material having the indicated lead content. Negative values represent a repulsive LVDW force generated by the coating material to repel the CMAS particle.

[0117] In plot 900, curve 904 is a curve for magnesium sulfate (MgS0 ₄ ) particulates, curve 1006 is a curve for silicon dioxide (Si0 ₂ ) particulates, curve 908 is a curve for di aluminum dioxide (Al ₂ 0 ₂ ) particulates, and curve 910 is a curve for calcium sulfate (CaS0 ₄ ) particulates. When the respective curve crosses from positive values to negative values, the coating material will repel the particles having the respective composition. In this embodiment, the vertical line 912 represents the lead composition of the coating material where all four CMAS particles are repelled. The line 912 is at a composition of approximately 92% lead, and in this embodiment the balance is gold. At this composition, all CMAS particles are repulsed. However, if one or more of the CMAS particles is less likely to appear, is less abundant, or less damaging to a surface, lower lead content coatings may be employed. For example, at about 60% lead composition, the magnesium sulfate (MgSCfi) particles will be repulsed by the coating material. In FIG. 9, the compositions follow': å=Pb _a MnpPr _y Pm ₈ Ce _t; ^]s ¾S^PteBi _& (L _m )C ⁾ ₁ , as discussed above.

[0118] It is noted that it is counterintuitive to choose coatings that contain lead because of negative environmental considerations associated therewith. For example, lead, although having various advantageous coating properties, has been avoided almost without exception due to the environmental and deleterious effects that using lead as a coating may have. Accordingly, those of skill in the art would readily appreciate that the suggestion of employing lead in a coatin for aerospace applications is not obvious. However, one of the benefits of the teachings of the present disclosure is that the amount of lead needed to achieve the desired optical properties of a repulsive coating material is small. Accordingly, coatings having lead may be employed in accordance with embodiments described herein, without the typical risks or negative effects of lead-based coatings.

[0119] Generating the repulsive LVDW force using coating materials of the present disclosure enables maintaining clean substrate surfaces (i.e., clean components). Even a small attraction between the first object (component) and the second object (foreign particle) may- cause“fouling,” i.e., deposition of foreign particle onto the component. Coating materials of the present disclosure demonstrate a repulsive behavior and make the fouling process unfavorable, and thus foreign particle deposition is reduced or eliminated. For example, it may be desirable to reduce or eliminate fouling at the back of a combustor panel where cooling air impinges upon the panel. Foreign particle deposition introduces an undesired thermal resistance wherein the heat transfer from the combustor panel is impaired.

[0120] As noted above, in one example embodiment, the coating material may be designed to be in a quasi-liquid state at the operating conditions of a particular application. The quasi-liquid state of the coating material may increase the reduction of the polarization or permittivity so that the coating material may begin repelling foreign particles at some critical or activation temperature. Below the activation temperature, the coating material may be a quasi-solid with a frozen dipole configuration. However, once reaching the activation temperature, the coating material may become a quasi-liquid with a disordered dipole configuration. In some such embodiments, the quasi-liquid state of the coating material may increase the repulsive LVDW force. As such, it may be desirable to design coating materials having activation temperatures that are at or near the operating conditions in which the coating material is applied.

[0121] In accordance with embodiments, of the present disclosure, the activation temperature may be customized or pre-set based on the composition of the coating material. In one non-limiting embodiment, the coating material may have a composition with individual compounds or compound oxides as listed above (e.g., Pb, Bi, Sc, Mn, Co, Nb, Pr). In one non-limiting example application, for activation temperatures of 950 °C or below, the coating material may have a primary composition of lead and bismuth that is 70% or greater (possibly, 80%, 90%, or even 95%). For higher temperature applications, e.g., above 1000 °C, the coating material may have a composition of manganese, niobium, or cobalt having a concentration of 70% or greater. In accordance with the present disclosure, a desired temperature may be selected based on a composition of the coating material. For example, without limitation, high temperature activation temperatures may be achieved using single element coating materials, whereas lower temperature activation temperatures may be achieved using alloys and/or dopants. Accordingly, a desired activation temperature may be achieved through manipulation and selection of the composition of the coating material.

[0122] As noted above, in accordance with embodiments of the present disclosure, manipulating the activation temperature of a coating material may achieved through the inclusion of dopants in the coating material. In such embodiments, the coating material may include a primary material and a dopant material. In one non-limiting example, the coating material may contain dopants with various dopant concentrations (e.g., ranging from 1 ppm to 10,000 ppm) of the above described materials. The dopant concentration may enable control of the activation temperature of the coating material. In one non-limiting example embodiment, a coating material has a composition of 99% manganese (primary material) and 1% lead or bismuth (dopant material). This specific composition may enable activation of repulsion at 900 °C or above, although the main composition is manganese. In this composition, the lead or bismuth dopant enables the use of manganese-based coating materials for lower temperature applications.

[0123 ] In some embodiments, the permittivity may be tuned at static and light frequency (simultaneously) and the coating material thickness to achieve a desired thin film pressure. The thin film pressure could be 1 MPa, 10 MPa, 100 MPa, IGPa or even higher. Tire high pressures inside the liquid thin films may control the fluidity of the coating material. Higher pressure quasi-liquid coating materials may exhibit quasi-solid behavior even at higher temperatures, such as at temperatures higher than the activation temperature.

[0124] As discussed above, coatings of the present disclosure may be applied in various aerospace applications. For example, aerospace engines, such as gas turbine engines, include a multitude of parts and components that are subject to various different operating conditions (e.g., temperature, pressure, particular or debris frequency, etc.).

[0125] Turning to FIG. IQ, a schematic illustration of a gas turbine engine 20 that includes components and parts that may be coated with coatings of the present disclosure is shown. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. The fan section 22 drives air along a bypass flow path B in a bypass duct, while the compressor section 24 drives air along a core flow path C for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines.

[0126] The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

[0127] The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a low pressure compressor 44 and a low pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary' gas turbine engine 20 is illustrated as a gear system 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a high pressure compressor 52 and high pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. An engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The engine static structure 36 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is co!!inear with their longitudinal axes.

[0128] The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The turbines 46, 54 rotation ally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48. The engine 20 can include additional components, such as heat exchangers, as will be appreciated by those of skill in the art.

[0129] Although the gas turbine engine 20 is depicted as a turbofan, it should be understood that the concepts described herein are not limited to use with the described configuration, as the teachings may be applied to other types of engines such as, but not limited to, turbojets, turboshafts, wherein an intermediate spool includes an intermediate pressure compressor (‘TPC”) between a low pressure compressor (“LPC”) and a high pressure compressor (“HPC”), and an intermediate pressure turbine (“IPT”) between the high pressure turbine (“HPT”) and the low pressure turbine (“LPT”).

[0130] Advantageously, embodiments provided herein are directed to coating materials for application to aerospace components to provide repulsive forces at/on a substrate. Advantageously, coating materials of the present disclosure may leverage reversed LVDW forces to prevent foreign particles from contacting, impacting, or otherwise interacting with a coated surface. For example, in some applications, coating materials of the present disclosure may be used to prevent foreign particle accumulation within or on components of a gas turbine engine. In other embodiments, advantageously, coating materials of the present disclosure can prevent chemical interactions between two substances (a coated substance and a foreign particle).

[0131] As used herein, the term“about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example,“about” may include a range of ± 8%, or 5%, or 2% of a given value or other percentage change as will be appreciated by those of skill in the art for the particular measurement and/or dimensions referred to herein.

[0132] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms“a,”“an,” and“the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," "radial," "axial," "circumferential," and the like are with reference to normal operational attitude and should not be considered otherwise limiting.

[0133] While the present disclosure has been described with reference to an illustrative embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.