Patent Application
20190032189
The present disclosure relates to a method for the deposition of a thermal spray coating over a columnar or dense vertically cracked thermal barrier coatings, such as for use on or the repair of turbine engine components on which an electron beam physical vapor deposition (EB-PVD) thermal barrier coating has been previously deposited.
Thermal barrier coatings (“TBC”) are typically used in articles that operate at or are exposed to high temperatures. Aviation turbines and land-based turbines, for example, may include one or more components protected by the thermal barrier coatings. Under normal conditions of operation, coated components may be susceptible to various types of damage, including erosion, oxidation, and attack from environmental contaminants.
For turbine components, environmental contaminant compositions of particular concern are those containing oxides of calcium, magnesium, aluminum, silicon, and mixtures thereof; dirt, ash, and dust ingested by gas turbine engines, for instance, are often made up of such compounds. These oxides often combine to form contaminant compositions comprising mixed calcium-magnesium-aluminum-silicon-oxide systems (Ca—Mg—Al—Si—O), hereafter referred to as “CMAS.” At the high turbine operating temperatures, these environmental contaminants can adhere to the hot thermal barrier coating surface, and thus cause damage to the thermal barrier coating. For example, CMAS can form compositions that are liquid or molten at the operating temperatures of the turbines. The molten CMAS composition can dissolve the thermal barrier coating, or can fill its porous structure by infiltrating the pores, channels, cracks, or other cavities in the coating. Upon cooling, the infiltrated CMAS composition solidifies and reduces the coating strain tolerance, thus initiating and propagating cracks that may cause delamination and spalling of the coating material. This may further result in partial or complete loss of the thermal protection provided to the underlying metal substrate of the part or component. Further, spallation of the thermal barrier coating may create hot spots in the metal substrate leading to premature component failure. Premature component failure can lead to unscheduled maintenance as well as parts replacement resulting in reduced performance, and increased operating and servicing costs.
However, routine maintenance of a TBC includes washing and reapplying the TBC material onto the component. Such operations require either engine disassembly or an engine wash process such that a new TBC can be applied onto the surface of the component(s). Such a disassembly processes, causes downtime in the engine leading to loss of service for extended periods of time. Alternatively, flushing the internal components of the engine with detergents and other cleaning agents can introduce other unwanted issues to the engine.
Thus, there is a need for improved coating systems that provide protection to thermal barrier coatings from the adverse effects of environmental contaminants, when operated at or exposed to high temperatures. In particular, there is a need for improved coating systems, and methods for making such coatings, that provide protection from the adverse effects of deposited CMAS.
Aspects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
A coated component is generally provided. In one embodiment, the coated component includes a substrate having a surface with a coating system thereon. The coating system may include a columnar thermal barrier coating (TBC) over the surface of the substrate, with the columnar TBC including surface-connected voids. An intermediate layer is over the columnar TBC layer. The intermediate layer has a surface opposite of the columnar TBC that is rougher than the surface of the columnar TBC. A second TBC is over the intermediate layer.
A method is also provided for forming a coating system on a surface of a substrate. In one embodiment, a columnar thermal barrier coating is formed over the surface of the substrate such that the columnar TBC has surface-connected voids and has a surface with a first surface roughness. An air plasma spray intermediate layer is formed over the columnar such that the intermediate layer has a surface opposite of the columnar TBC that has a second surface roughness that is rougher than the first surface roughness of the columnar TBC. Optionally, a second TBC may then be formed over the APS intermediate layer.
These and other features, aspects and advantages will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain certain principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended Figs., in which:
Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
As used herein, the term “coating” refers to a material disposed on at least a portion of an underlying surface in a continuous or discontinuous manner. Further, the term “coating” does not necessarily mean a uniform thickness of the disposed material, and the disposed material may have a uniform or a variable thickness. The term “coating” may refer to a single layer of the coating material or may refer to a plurality of layers of the coating material. The coating material may be the same or different in the plurality of layers.
In the present disclosure, when a layer is being described as “on” or “over” another layer or substrate, it is to be understood that the layers can either be directly contacting each other or have another layer or feature between the layers, unless expressly stated to the contrary. Thus, these terms are simply describing the relative position of the layers to each other and do not necessarily mean “on top of” since the relative position above or below depends upon the orientation of the device to the viewer.
A coated component is generally provided that includes a thermal barrier coating (TBC) having an intermediate layer for improving adhesion of additional TBCs thereon, along with methods of its formation and use. Referring to
Generally, the columnar TBC 24 has a surface 25 that is relatively smooth, which leads to difficulties in adhering additional layers thereon (particularly for an air plasma spray (APS) coating). In order to improve adherence to the surface 25 of the columnar TBC 24, the intermediate layer 26 is formed over the columnar TBC 24 to have a surface 27 that is rougher (in terms of surface roughness) than the surface 25 of the columnar TBC 24.
Each of the layers of the coating system 20 is described in greater detail below. The coating system 20 may be utilized with any suitable substrate 12. For example, the substrate 12 may be a turbine component, such as an airfoil (e.g., of a turbine blade). However, it is to be understood that the substrate 12 is not limited to any particular shape or component. In one embodiment, the substrate 12 is formed from a metal or a metal alloy. Examples include metals such as nickel, cobalt, titanium, aluminum, zirconium, and copper. Examples of metal alloys include nickel-base alloys, cobalt-base alloys, titanium-base alloys, iron-base alloys, steels, stainless steels, and aluminum-base alloys. In particular embodiments, the substrate 12 is formed from a superalloy material, such as nickel-base superalloys, cobalt-base superalloys, to name a few. In one particular embodiment, the substrate 12 is formed from a nickel-based alloy. Nickle-based superalloys are commercially available under the trade name RENE® is a non-limiting example that is particularly beneficial to be used for the engine components.
As shown in
The bond coating 22 may have a thickness of about 2.5 μm to about 400 μm and may be applied as an additive layer to the substrate 12 or may be diffused into the substrate giving an inhomogeneous composition which is engineered to have a gradient in properties. However, it is noted that all coating layers within the coating system 20 can vary in thickness depending on location on the part.
A thermally grown oxide layer 23 is shown on the bond coating 22. Generally, the thermally grown oxide layer 23 includes an oxide of the material of the bond coating 22. For example, when the bond coating 22 includes aluminum in its construction, the thermally grown oxide (TGO) layer 23 may include an aluminum oxide (e.g., Al2O, AlO, Al2O3, etc., or mixtures thereof). In certain embodiments, the thermally grown oxide layer 23 generally has a thickness of up to about 10 μm (e.g., about 0.01 μm to about 6 μm) and can be a natural product of thermal exposures during processing of subsequent layers or can be designed to be thicker by heat treating the part. The TGO layer may not be uniform dependent on the underlying bond coating 22, processing methods, and exposure conditions.
A columnar TBC 24 is on the optional bond coat 22. In one embodiment, the columnar TBC 24 is formed from electron beam physical vapor deposition (EB-PVD), and may be described as an EB-PVD TBC layer. The columnar TBC 24 includes voids 30, which may span the entire thickness of the columnar TBC 24. The voids 30 may be intentionally formed within the columnar TBC 24, and may be defined in the form of cracks, grain boundaries, or other porosity. In some embodiments, voids 30 include substantially vertically oriented (from the perspective of a cross-sectional view as in
As stated above, the columnar TBC 24 has a surface 25 that is relatively smooth, which leads to difficulties in adhering additional layers thereon. For example, the surface 25 of the columnar TBC 24 may have a surface roughness (Ra) that is about 2.5 micrometer (μm or microns) or less (e.g., about 1 μm or less) in the areas excluding the space formed by the voids 30.
The columnar TBC 24 having a columnar structure is typically more suitable for turbine airfoil applications (e.g., blades and vanes) to provide strain tolerant, as well as erosion and impact resistant coatings. A porous structure, especially (though not exclusively) a structure incorporating vertically oriented and/or columnar features as noted above, may be one of the factors that provides for strain tolerance by the thermal barrier coatings during thermal cycling. Further, the porous structure may provide for stress reduction due to the differences between the coefficient of thermal expansion (CTE) of the coating and the CTE of the underlying bond coating/substrate.
The columnar TBC 24 generally includes a ceramic thermal barrier material, which may be independently selected from the ceramic material of other layers within the coating system 20. That is, in certain embodiments, the ceramic material of the columnar TBC 24 and the other layers (e.g., the columnar TBC 24) may be a substantially identical, in terms of chemical composition, with the intermediate layer 26 and/or the TBC layer 28. However, in other embodiments, the ceramic material of the columnar TBC 24 can be different, in terms of chemical composition, than the intermediate layer 26 and/or the TBC layer 28. Suitable ceramic thermal barrier coating materials include various types of oxides, such as hafnium oxide (“hafnia”) or zirconium oxide (“zirconia”), in particular stabilized hafnia or stabilized zirconia, and blends including one or both of these. Examples of stabilized zirconia include without limitation yttria-stabilized zirconia, ceria-stabilized zirconia, calcia-stabilized zirconia, scandia-stabilized zirconia, magnesia-stabilized zirconia, india-stabilized zirconia, ytterbia-stabilized zirconia, lanthana-stabilized zirconia, gadolinia-stabilized zirconia, as well as mixtures of such stabilized zirconia. Similar stabilized hafnia compositions are known in the art and suitable for use in embodiments described herein.
In certain embodiments, columnar TBC 24 includes yttria-stabilized zirconia. Suitable yttria-stabilized zirconia may include from about 1 weight percent to about 60 weight percent yttria (based on the combined weight of yttria and zirconia), and more typically from about 3 weight percent to about 20 weight percent yttria. An example yttria-stabilized zirconia thermal barrier coating includes about 7% yttria and about 93% zirconia. These types of zirconia may further include one or more of a second metal (e.g., a lanthanide or actinide) oxide, such as dysprosia, erbia, europia, gadolinia, neodymia, praseodymia, urania, and hafnia, to further reduce thermal conductivity of the thermal barrier coating material. In some embodiments, the thermal barrier coating material may further include an additional metal oxide, such as, titania.
Suitable ceramic thermal barrier coating materials may also include pyrochlores of general formula A2B2O7 where A is a metal having a valence of 3+ or 2+(e.g., gadolinium, aluminum, cerium, lanthanum or yttrium) and B is a metal having a valence of 4+ or 5+(e.g., hafnium, titanium, cerium or zirconium) where the sum of the A and B valences is 7. Representative materials of this type include gadolinium zirconate, lanthanum titanate, lanthanum zirconate, yttrium zirconate, lanthanum hafnate, cerium hafnate, and lanthanum cerate.
The columnar TBC 24 may include the ceramic thermal barrier coating material in an amount of up to 100 weight percent. In some embodiments, the columnar TBC 24 includes the ceramic thermal barrier coating material in a range from about 95 weight percent to 100 weight percent and more particularly from about 98 weight percent to 100 weight percent. The selected composition of columnar TBC 24 may depend upon one or more factors, including the composition of the optional, adjacent bond coating 22 (if present), the coefficient of thermal expansion (CTE) characteristics desired for columnar TBC 24, and the thermal barrier properties desired for columnar TBC 24.
The thickness of columnar TBC 24 may depend upon the substrate 12 and/or the intended use for the component 10. In one embodiment, columnar TBC 24 has a thickness in a range of from about 25 microns to about 2000 microns. In certain embodiments, columnar TBC 24 has a thickness in a range of from about 25 microns to about 1500 microns (e.g., about 25 microns to about 1000 microns).
As stated above, the intermediate layer 26 is formed on the surface 25 of the columnar TBC 24. In the shown embodiment, the intermediate layer 26 is formed directly on the surface 25 of the columnar TBC 24 without any other layers therebetween. However, in other embodiments, additional layers may be present.
Generally, the intermediate layer 26 is formed to define a surface 27 that is rougher (in terms of surface roughness) than the surface 25 of the columnar TBC 24. For example, the surface 27 of the intermediate layer 26 has, in one embodiment, a surface roughness (Ra) that is about 2 μm or greater, such as about 2.5 μm or greater, (e.g., about 2.5 μm to about 6.5 μm, such as about 3 μm to about 6 μm). The increased surface roughness of the surface 27 of the intermediate layer 26 increases the ability of subsequently deposited layers (e.g., an APS TBC layer) to bond within the coating system.
The intermediate layer 26 may be formed to a thickness that is sufficient to transition the relatively smooth surface 25 of the columnar TBC 24 to a rougher surface 27 defined by the intermediate layer 26 while adding minimal thickness to the coating system 20. In one embodiment, the intermediate layer 26 may have a thickness that is less than the thickness of the columnar TBC 24. For example, in certain embodiments, the intermediate layer 26 may have a thickness that is less than half (e.g., about 1% to about 50%) of the thickness of the columnar TBC 24, such as about 1% to about 25% of the thickness of the columnar TBC 24 (e.g., about 1% to about 10% of the thickness of the columnar TBC 24). For example, when the columnar TBC 24 has a thickness of about 25 microns to about 500 microns, the intermediate layer 26 may have a thickness of about 4 microns to about 500 microns.
Such an APS coating may be formed by heating a gas-propelled spray of microparticles (e.g., a powdered metal oxide or non-oxide material) with a plasma spray torch. The spray of microparticles is heated to a temperature at which the particles become molten, and is directed against the deposition surface (i.e., surface 25 of the columnar TBC 24) where the microparticles solidify upon impact to create the intermediate layer 26. The microparticles are generally carried via a gas injected into a plasma spray torch that melts the particles and deposits them in melted form onto the surface 25 of the columnar TBC 24. As the melted microparticles impact the surface 25 at high velocity, they solidify into a thin, substantially uniform, coating as they cool.
In one embodiment, the microparticles are deposited onto a heated substrate such that the surface 25 of the columnar TBC 24 has a surface temperature of about 90° C. to about 650° C. to ensure good adhesion between the surface 25 and the melted microparticles forming the intermediate layer 26. For example, the surface 25 of the columnar TBC 24 may be preheated using the plasma jet before the microparticles are added.
The microparticles useful in forming the intermediate layer 26 may range in size from about 0.1 μm to about 100 microns in average diameter (e.g., about 10 μm to about 80 μm). Because of the size and composition of the microparticles, the spray forms a plurality of non-uniform splats on the columnar TBC 24 that ultimately combine to form the APS intermediate layer 26. The exact thickness and size of the splats depend on the initial size of the microparticles used in the air plasma spray and the plasma spray conditions.
During APS deposition, the density of the resulting intermediate layer 26 may be controlled by varying the particles size, the flame temperature, the surface temperature of the substrate, the nozzle distance, and/or the velocity of the particles, among other variables. For example, the density of the APS layer formed may be increased (i.e., the porosity of the layer may be decreased) by increasing the temperature of APS (e.g., the flame temperature and/or substrate temperature), decreasing the particle size, increasing the particle velocity, etc.
In one embodiment, the intermediate layer 26 is formed via APS to have a microstructure formed by spraying fully melted splats of material such that the inter-splat boundaries are tightly joined to minimize porosity (i.e., maximize density). That is, the inter-splat gaps in the intermediate layer 26 are minimized during deposition of the fully melted splats via the APS process to form a dense microstructure. Thus, the intermediate layer 26 may have a porosity that is less than the porosity of the columnar TBC 24 and/or less than the porosity of the subsequently deposited TBC 28. In one embodiment, for example, the intermediate layer 26 is deposited with porosity of about 10% or less (e.g., about 0.1% to about 10%), such as about 5% or less (e.g., about 0.1% to about 5%). The fully melted splats improve the adhesion with the smooth surface 25 of the columnar TBC 24, and provide the surface 27 with increased roughness to enable good bonding of the intermediate layer with the subsequently deposited TBC layers (e.g., thermal spray coatings). As such, the improved splat contact and the dense coating microstructure result in the good adhesion between the intermediate layer 26 and the underlying TBC 24 (e.g., a EB-PVD TBC layer), as well as with subsequently deposited layers.
The microparticles utilized to form the intermediate layer 26 may include any suitable materials, such as described above with respect to the columnar TBC 24, such as ytterbium, yttria, hafnium, tantalum and/or zirconium, combinations thereof, and oxides thereof. That is, in particular embodiments, the microparticles may include a ceramic thermal barrier material, which may be independently selected from the ceramic material of the columnar TBC 24. However, in certain embodiments, the ceramic material of the columnar TBC 24 and the intermediate layer 26 are substantially identical in terms of chemical composition. In other embodiments, the ceramic material of the columnar TBC 24 and the intermediate layer 26 are different in terms of chemical composition.
Suitable intermediate layer 26 materials include various types of oxides, such as hafnium oxide (“hafnia”) or zirconium oxide (“zirconia”), in particular stabilized hafnia or stabilized zirconia, and blends including one or both of these. Examples of stabilized zirconia include without limitation yttria-stabilized zirconia, ceria-stabilized zirconia, calcia-stabilized zirconia, scandia-stabilized zirconia, magnesia-stabilized zirconia, india-stabilized zirconia, ytterbia-stabilized zirconia, lanthana-stabilized zirconia, gadolinia-stabilized zirconia, as well as mixtures of such stabilized zirconia. Similar stabilized hafnia compositions are known in the art and suitable for use in embodiments described herein. In certain embodiments, the intermediate layer 26 includes yttria-stabilized zirconia. In some embodiments, the intermediate layer 26 material may further include an additional metal oxide, such as, titania. Suitable ceramic intermediate layer 26 materials may also include pyrochlores of general formula A2B2O7 (as described above), such as gadolinium zirconate, lanthanum titanate, lanthanum zirconate, yttrium zirconate, lanthanum hafnate, cerium hafnate, lanthanum cerate, Y2SiO5, Yb2SiO5, Y2Si2O7, Yb2Si2O7, or combinations thereof.
The intermediate layer 26 may include the ceramic TBC layer material in an amount of up to 100 weight percent. In some embodiments, the intermediate layer 26 includes the ceramic TBC layer material in a range from about 95 weight percent to about 100 weight percent and more particularly from about 98 weight percent to about 100 weight percent. The selected composition of intermediate layer 26 may depend upon one or factors, including the composition of the adjacent columnar TBC 24, the coefficient of thermal expansion (CTE) characteristics desired for intermediate layer 26, and the thermal barrier properties desired for intermediate layer 26.
As stated above, a subsequent TBC 28 may be applied onto the intermediate layer 26, with the surface 27 providing improved adhesion thereto. In one embodiment, the second TBC 28 may also be formed via APS but with different processing parameters to increase the porosity of the TBC 28 compared to the porosity of the intermediate layer 26. For example, the density of the APS layer formed may be decreased (i.e., the porosity of the layer may be increased) by decreasing the temperature of APS (e.g., the flame temperature and/or substrate temperature), increasing the particle size, decreasing the particle velocity, etc.
In one embodiment, the TBC 28 is formed via APS to have a microstructure formed by spraying partially melted splats of material such that the inter-splat boundaries may be separated by gaps resulting in some porosity. Thus, the TBC 28 may have a porosity that is greater than the porosity of the intermediate layer 26. In one embodiment, for example, the TBC 28 is deposited with porosity of about 10% to about 25%. Additionally, the partially melted splats have good adhesion with the rough surface 27 of the intermediate layer 26.
Such an APS coating may be formed by heating a gas-propelled spray of microparticles with a plasma spray torch as described above with respect to the intermediate layer 26, and may be applied onto a heated substrate such that the surface 27 of the intermediate layer has a surface temperature of about 90° C. to about 225° C. to ensure good adhesion between the surface 27 and the partially melted microparticles forming the TBC 28. For example, the surface 27 may be preheated using the plasma jet before the microparticles are added.
The microparticles useful in forming the TBC 28 may range in size from about 0.1 μm to about 100 microns in average diameter (e.g., about 10 μm to about 80 μm). Because of the size and composition of the microparticles, the spray forms a plurality of non-uniform splats on the intermediate layer 26 that ultimately combine to form the TBC 28. The exact thickness and size of the splats depend on the initial size of the microparticles used in the air plasma spray and the plasma spray conditions.
The microparticles utilized to form the TBC 28 may include any suitable materials, such as described above with respect to the columnar TBC 24 and/or the intermediate layer 26, such as ytterbium, yttria, hafnium, tantalum and/or zirconium, combinations thereof, and oxides thereof. That is, in particular embodiments, the microparticles may include a ceramic thermal barrier material, which may be independently selected from the ceramic material of the intermediate layer 26. However, in certain embodiments, the ceramic material of the intermediate layer 26 and the TBC 28 are substantially identical in terms of chemical composition. In other embodiments, the ceramic material of the intermediate layer 26 and the TBC 28 are different in terms of chemical composition.
Suitable TBC 28 materials include various types of oxides, such as hafnium oxide (“hafnia”) or zirconium oxide (“zirconia”), in particular stabilized hafnia or stabilized zirconia, and blends including one or both of these. Examples of stabilized zirconia include without limitation yttria-stabilized zirconia, ceria-stabilized zirconia, calcia-stabilized zirconia, scandia-stabilized zirconia, magnesia-stabilized zirconia, india-stabilized zirconia, ytterbia-stabilized zirconia, lanthana-stabilized zirconia, gadolinia-stabilized zirconia, as well as mixtures of such stabilized zirconia. Similar stabilized hafnia compositions are known in the art and suitable for use in embodiments described herein. In certain embodiments, the TBC 28 includes yttria-stabilized zirconia. In some embodiments, the TBC 28 material may further include an additional metal oxide, such as, titania. Suitable ceramic TBC 2 materials may also include pyrochlores of general formula A2B2O7 (as described above), such as gadolinium zirconate, lanthanum titanate, lanthanum zirconate, yttrium zirconate, lanthanum hafnate, cerium hafnate, lanthanum cerate, Y2SiO5, Yb2SiO5, Y2Si2O7, Yb2Si2O7, or combinations thereof.
The TBC 28 may include the ceramic TBC layer material in an amount of up to 100 weight percent. In some embodiments, the TBC 28 includes the ceramic TBC layer material in a range from about 95 weight percent to about 100 weight percent and more particularly from about 98 weight percent to about 100 weight percent. The selected composition of TBC 28 may depend upon one or factors, including the composition of the adjacent intermediate layer 26, the coefficient of thermal expansion (CTE) characteristics desired for TBC 28, and the thermal barrier properties desired for TBC 28.
The thickness of the TBC 28 may depend upon the substrate 12 on which it is deposited, and/or the type of component 10 formed. In particular embodiments, the thickness of TBC 28 may depend upon the thickness of the underlaying intermediate layer 26, but is typically less than half of the total thickness of the coating system 20. In some embodiments, the TBC 28 is greater than the thickness of the intermediate layer 26. In particular embodiments, for instance, the TBC 28 when present may have a thickness that is about 0.5 times to about 5 times thicker than the intermediate layer 26 to provide sufficient barrier coating system 20. For example, the TBC 28 may have a thickness of about 25 microns to about 500 microns.
As stated above, the coating system 20 is generally disposed over a surface 14 of the substrate 12 to form the component 10. In particular embodiments, the component 10 may be any component that is subject to service in a high-temperature environment, such as a component of a gas turbine assembly (e.g., within a hot gas path therein). Examples of such components include, but are not limited to, components that include turbine airfoils such as blades and vanes, and combustion components such as liners and transition pieces.
Methods are also generally provided for forming a coating system on the surface of a substrate in order to make a coated component, such as component 10 described above. For example,
This written description uses exemplary embodiments to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
