Forming a ceramic coating that smoothes the surface using a temperature-controlled gas flow

Abstract

To provide a method and a coating system (100) that use a temperature controlled gas flow (142) to smooth a surface (114, 166, 170) of thermal barrier coating (TBC) (112).SOLUTION: Thermal spray coating unit (110) coats a TBC (112) on a surface (114, 166, 170). The thermal spray coating unit (110) creates a flow of TBC material (124) towards the surface (114, 166, 170). A surface (114, 166, 170) of uncured TBC material (144) on the surface (114, 166, 170) is smoothed by transmitting a flow of temperature controlled gas (142) across the uncured TBC material (144) on the surface (114, 166, 170) after the thermal spray coating of the TBC (112) on the surface (114, 166, 170). The cured TBC (112) has a smoother surface (114, 166, 170) that requires much less polishing to attain a desired surface roughness.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to coating processes, and more specifically to a method of thermally spraying a ceramic, such as a thermal barrier coating (TBC), onto a metallic component and transmitting a temperature-controlled gas flow across the surface to smooth the ceramic.

Background Art

[0002] Ceramics are widely used for surface coatings. For example, ceramics can be used as thermal barrier coatings (TBCs) that can be applied to various metallic components in turbomachinery, protecting the underlying metal from high operating temperatures. TBCs can be applied, for example, to turbine blades, nozzles, and shrouds within a gas turbine to protect from the heat of combustion gases within the gas turbine. As the geometric shapes of metallic components in turbomachinery become more complex and the operating temperatures of turbines increase, thicker TBCs have been adopted. Thicker TBCs present challenges in maintaining a smooth TBC surface that does not affect performance. Typically, the surface roughness of a TBC is a result of a combination of the spraying angle relative to the surface being coated and surface contaminants by unmelted or partially melted powder particles that are subsequently coated thereon. Increasing the thickness of the TBC coating worsens the surface roughness. Currently, the problem of surface roughness is addressed by expensive surface polishing, such as using a diamond-coated disk, to remove the surface roughness and achieve the desired surface finish.

Summary of the Invention

[0003] A first aspect of the present disclosure is thermal spray coating a ceramic on a surface, the thermal spray coating creating a flow of ceramic material towards the surface and smoothing a layer of at least partially molten ceramic material on the surface by transmitting a flow of temperature-controlled gas across the entirety of the at least partially molten ceramic material on the surface during thermal spray coating of the ceramic on the surface, and solidifying the ceramic, and provides a method including these steps.

[0004] A second aspect of the present disclosure is a thermal spray coating unit for applying a thermal barrier coating (TBC) over an entire surface, the thermal spray coating unit creating a flow of TBC material, an actuator operably coupled to the thermal spray coating unit and moving the thermal spray coating unit across the entire surface, and a gas nozzle configured to transmit a temperature-controlled gas flow across the entirety of at least partially molten TBC material on the surface when the thermal spray coating unit applies the TBC material on the surface, the gas nozzle being movable with the thermal spray coating unit, and provides a coating system including these components.

[0005] Exemplary aspects of the present disclosure are designed to solve the problems described herein and / or other problems not considered.

[0006] These and other features of the present disclosure will be more readily understood from the following detailed description of various aspects of the present disclosure in conjunction with the accompanying drawings that illustrate various embodiments of the present disclosure.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0008] It should be noted that the drawings of the present disclosure are not necessarily drawn to scale. The drawings are intended to illustrate only typical aspects of the present disclosure and should not, therefore, be considered as limiting the scope of the present disclosure. In the drawings, like reference numerals represent like elements among the drawings.

[0009] 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. The terms “comprise” and / or “comprising,” when used herein, specify the presence of the 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, elements, components, and / or groups thereof. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and this description includes instances where the event occurs and instances where it does not.

[0010] When an element or layer is referred to as being "on," "engaged with," "connected to," or "coupled to" another element or layer, it may be directly on, engaged with, connected to, or coupled to the other element or layer, or intervening elements or layers may be present. Conversely, when an element is referred to as being "directly on," "directly engaged with," "directly connected to," or "directly coupled to" another element or layer, intervening elements or layers may not be present. Other terms used to describe the relationship between elements should be interpreted in a similar manner (e.g., "directly between" for "between," "directly adjacent to" for "adjacent to," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0011] Embodiments of the present disclosure provide a method and a coating system for smoothing a ceramic layer, such as a thermal barrier coating (TBC) to be applied, using a temperature-controlled gas flow. A thermal spray coating unit coats a surface with a ceramic. The thermal spray coating unit creates a flow of ceramic material towards the surface. A layer of at least partially molten ceramic material on the surface is smoothed by transmitting a temperature-controlled gas flow over the entire layer of at least partially molten ceramic material on the surface after the thermal spray coating of the ceramic on the surface. The solidified ceramic can be thicker and have a smoother surface than if the gas flow was not used. In one non-limiting example, the smoother surface can be about 200 rA compared to a conventional 400 rA. Thus, the ceramic can be made thicker and the polishing required to achieve the desired surface roughness is much less.

[0012] Referring to the drawings, FIG. 1 shows a schematic side view of a coating system 100 according to an embodiment of the present disclosure. As shown, the coating system 100 includes a thermal spray coating unit 110 that applies a ceramic such as a thermal barrier coating (TBC) 112 over the entire surface 114. The teachings of the present disclosure can be applied to any ceramic material, but the present disclosure refers to the TBC 112 for purposes of illustration. As used herein, a “surface” can be the base material or substrate of a component, an intermediate coating on the base material or substrate, or the surface of a precursor layer of the TBC. That is, the surface 114 can be the surface of a component 120 (e.g., a metal, ceramic layer, multi-material ceramic layer, etc.), or a layer on the component 120, such as a bond coat 122 on a metal component 120, or the surface of a precursor layer of the TBC. The metal component 120 can include any currently known or later developed metal for use in a turbomachine, such as a superalloy or a ceramic. As used herein, a “superalloy” refers to an alloy having a number of excellent physical properties compared to conventional alloys, such as, but not limited to, high mechanical strength, high thermal creep deformation resistance, such as Rene 108, CM247, Haynes alloys, Incalloy, MP98T, TMS alloys, CMSX single crystal alloys. In one embodiment, a superalloy in which the teachings of the present disclosure can be particularly advantageous is a superalloy having a high gamma prime (γ’) value. “Gamma prime” (γ’) is the primary strengthening phase of nickel-based alloys. Exemplary high gamma prime superalloys include, but are not limited to, Rene 108, N5, GTD 444, MarM 247, and IN 738.

[0013] The thermal spray coating unit 110 creates a flow of the TBC material 124, e.g., a jet plume of a ceramic material. The thermal spray coating unit 110 can employ any currently known or later developed thermal process to inject the TBC material 124, or any other desired ceramic, onto the surface 114. In one embodiment, the thermal spray coating unit 110 can include a plasma spray unit. In other embodiments, the thermal spray coating unit 110 may include an arc spray unit, a combustion spray unit, or a high velocity oxygen fuel (HVOF) coating unit. The thermal spray coating unit 110 can also include any of various low pressure coating systems.

[0014] The bond coating 122, when used, can include any currently known or later developed bond coat material, such as, but not limited to, nickel or platinum aluminide, nickel chromium aluminum yttrium (NiCrAlY), or nickel cobalt chromium aluminum yttrium (NiCoCrAlY). The bond coating 122 can have a thickness of less than, for example, 500 microns. Optionally, the bond coating 122 and the TBC 112 can be used together. The TBC 112 can include any currently known or later developed ceramic TBC material, such as, but not limited to, yttria stabilized zirconia (YSZ), mullite, and alumina. The TBC 112 can also include additional layers (not shown), such as thermally grown oxides. The TBC 112 can have various porosities and / or densities. The TBC 112 may be densely cracked vertically. As described above, the geometric shape of the complex metal component 120 may require a thicker TBC 112. For this purpose, the TBC 112 can have a thickness in the range of, for example, about 0.127 millimeters (mm) (0.005 inches) to about 2.54 mm (0.1 inches), depending on the type of material applied. The TBC 112 and the bond coating 122 may be present over the entire surface 114 of the metal component 120 or only over a portion of the surface 114.

[0015] Coating system 100 may also be operably coupled to a thermal spray coating unit 110, i.e., include an actuator 130 that moves the thermal spray coating unit 110 across the surface 114 when coating the surface 114. Actuator 130 may include any currently known or later developed actuator system that enables controlled movement of the thermal spray coating unit 110, such as a linear actuator, a motor, a robotic system 132 (shown in phantom lines), etc. Although shown at an angle substantially perpendicular to the surface 114, actuator 130 may also include an angle adjustment actuator (see arrow A) configured to control the angle of incidence of the thermal spray coating unit 110 with respect to the surface, i.e., the angle of the flow of the TBC material 124 with respect to the surface 114. The angle of incidence may make it possible to create various TBC attributes, such as density, porosity, thickness, etc.

[0016] Coating system 100 can also include a gas nozzle 140 configured to convey a temperature-controlled gas stream 142 over at least the partially molten TBC material 144 (or other ceramic) on the surface 114, i.e., when or after the thermal spray coating unit 110 applies the TBC material 124 onto the surface 114. "Partially molten" indicates that at least a portion of the TBC material 144 is not solidified, e.g., is semi-molten. Since the temperature-controlled gas stream 142 impinges on the at least partially molten TBC material 144, it smooths the surface of the material. More specifically, the gas stream 142 smooths a portion of the peaks of the at least partially molten TBC material 144 and makes the peaks smaller. This can also remove unmelted or partially melted powder particles present on the surface 114. The temperature-controlled gas stream 142 may be provided from any currently known or later developed source, such as a pump (shown), a pressurized supply, etc. The temperature-controlled gas stream 142 can include air or an inert gas such as argon or nitrogen. A thermal controller 150 can be provided to control the temperature of the temperature-controlled gas. The thermal controller 150 can include any suitable form of heat exchanger for the gas used, such as an air conditioner, a heater, etc. The temperature can be in the range of, for example, about 204.4 degrees Celsius (°C) (400°F) to about 1093.3 °C (2000°F). The temperature can be selected based on many factors, including but not limited to the ability to create the desired smoothing without affecting the solidification of the TBC material in some cases, the ability to reduce surface roughness, the type of gas, the type of TBC material, the applied chamber environment, etc. For example, as schematically indicated by the coupling element 160, the gas nozzle 140 can be directly coupled to the thermal spray coating unit 110 to move together or can be configured to move with the thermal spray coating unit 110. In this way, when the thermal spray coating unit 110 advances, the gas nozzle 140 also advances. The distance between the gas nozzle 140 and the thermal spray coating unit 110 can be predefined or can vary during use, e.g., depending on the geometry of the metal component 120.

[0017] The coating system 100 may also include an angle adjustment actuator 160 (schematically shown by arrow 162) operably coupled to the gas nozzle 140 to control the angle of attack of the temperature-controlled gas stream 142 relative to the flow of the TBC material 124. In one embodiment, the angle adjustment actuator 160 controls the angle of attack α of the temperature-controlled gas stream 142 to be between 5° and 85° relative to the flow of the TBC material 124. The angle of attack α may be predefined or may vary during use, for example, depending on the thickness of the TBC 112 and / or the geometric shape of the metal component 120.

[0018] Figure 3 shows a block diagram of a method 300 according to an embodiment of the present disclosure. During operation, in process 310 as shown in FIG. 3, the coating system 100 thermally spray coats a TBC 112 (or other ceramic), such as yttria-stabilized zirconia (YSZ), mullite, and alumina, onto the surface 114. That is, the thermal spray coating unit 110 creates a flow of the TBC material 124 towards the surface 114, for example, using plasma spraying of the TBC material 124. The TBC material 124 on the surface 114 can have a thickness of, for example, about 0.127 millimeters (mm) (0.005 inches) to 2.54 mm (0.1 inches), depending on the material. When this is done, in process 312 of FIG. 3, a layer of at least partially molten TBC material 144 on the surface 114 is smoothed by transmitting a flow of a temperature-controlled gas stream 142 over the entire at least partially molten TBC material 144 on the surface 114 after the thermal spray coating of the TBC on the surface. Processes P10 and P12 may be performed simultaneously. The gas nozzle 140 for transmitting a flow of temperature-controlled gas over the entire surface 114 can move with the thermal spray coating unit 110 for plasma spray coating the TBC 112 because the gas nozzle 140 is either coupled to the thermal spray coating unit 110 or configured to move together therewith as the thermal spray coating unit 110 moves over the surface 114. As described above, the temperature-controlled gas stream 142 can include air or an inert gas such as argon or nitrogen and can have a temperature in the range of, for example, about 204.4 degrees Celsius (°C) (400°F) to about 1093.3 °C (2000°F). The transmission of the flow of the temperature-controlled gas stream 142 can include controlling the angle of incidence of the flow with respect to the flow of the TBC material 124 to optimize the smoothing. The angle of incidence α of the flow of the temperature-controlled gas stream 142 is between 5° and 85° with respect to the flow of the TBC material 124. The pressure of the temperature-controlled gas stream 142 can also be controlled, for example, between about 0.034 megapascals (MPa) (5 pounds per square inch (psi)) and about 0.82 MPa (120 psi). Other parameters of the temperature-controlled gas stream 142, such as the flow rate, can also be controlled.

[0019] Once completed, in process 314 of FIG. 3, the TBC 112 (or other ceramic) can be solidified. The solidification may include any currently known or later developed solidification process, such as doing nothing (atmospheric progression), cooling, heating, drying, exposure to a particular type of light, etc. The necessary curing process can follow the solidification. Conventionally, the TBC 112 would have a surface roughness of about 400 Ra after solidification. Roughness can be quantified by the variation in direction from the ideal level of the surface. A large variation results in a rough surface, and a small variation results in a smooth surface. As described in American Society of Mechanical Engineers (ASME) B46.1, Ra is the arithmetic mean of the absolute values of the profile height deviations from the mean line recorded within the evaluation length. That is, Ra is the average of a series of individual measurements of the minimum and maximum heights of the surface. The formation of the TBC 112 according to embodiments of the present disclosure can result in a roughness of about 200 Ra, thereby significantly reducing the polishing required to achieve a desired surface roughness, for example, of 40 Ra. FIG. 2 shows a polished surface 170 of the TBC 112 for further smoothing the surface of the TBC. The polishing may be performed using any currently known or later developed polishing system 172, for example, using a diamond-coated disk.

[0020] Embodiments of the method according to the present disclosure not only clean the surface of the metal component 120, but also smooth the peaks of the layer of at least partially molten TBC material 144 by creating a cross-room jet of a temperature-controlled gas stream 142 to smooth the peaks. As a result, the final TBC surface is much smoother.

[0021] As used throughout this specification and the claims, the language representing approximation can be applied to modify any quantitative expression that can vary within a reasonable extent without causing a change in the relevant basic function. Thus, values modified by terms such as "about," "approximately," and "substantially" are not limited to the precisely stated value. In at least some examples, the language representing approximation can correspond to the accuracy of the equipment used to measure the value. Here, as well as throughout this specification and the claims, limitations of ranges are combinable and / or replaceable, and such ranges are identified and include all sub-ranges subsumed therein, unless the context and language specifically indicate otherwise. "About" applied to a particular value of a range can be applied to both values and can indicate + / - 10% of the stated value, unless specifically dependent on the accuracy of the equipment used to measure the value.

[0022] All corresponding structures, materials, acts, and equivalents of the means-plus-function or step-plus-function elements in the following claims are intended to include any structure, material, or act for performing the recited function in combination with other claimed elements specifically recited for performing that function. The description of the present disclosure has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the disclosure to the forms disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present disclosure. The present embodiments have been chosen and described in order to best explain the principles of the disclosure and its practical application, to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

Description of Reference Numerals

[0023] 100 Coating System 110 Thermal Spray Coating Unit 112 Thermal Barrier Coating (TBC) 114 Surface 120 Metal Component 122 Bond coating, bond coat 124 TBC material 130 Actuator 132 Robot system 140 Gas nozzle 142 Temperature-controlled gas flow 144 At least partially molten TBC material 150 Thermal controller 160 Bonding element, angle adjustment actuator 166 Surface 170 Polished surface 172 Polishing system 300 Method 310 Process 312 Process 314 Process

Claims

1. A step (310) of thermally spraying a ceramic (112) onto a surface (114, 166, 170), wherein the thermal spraying creates a flow of ceramic material (124) towards the surface (114, 166, 170); A step (312) of smoothing a layer of at least partially molten ceramic material (124) on the surface (114, 166, 170) by transmitting a flow of temperature-controlled gas (142) across the entire at least partially molten ceramic material (144) on the surface (114, 166, 170) during the thermal spraying of the ceramic (112) on the surface (114, 166, 170); A step (314) of solidifying the ceramic (112); A method (300) comprising the above steps.

2. The method (300) according to claim 1, wherein the temperature-controlled gas (142) comprises at least one of air, argon, and nitrogen.

3. The method (300) according to claim 1, wherein the temperature-controlled gas (142) has a temperature in the range of 204.4°C to 1093.3°C.

4. The method (300) according to claim 1, wherein transmitting the flow of the temperature-controlled gas (142) comprises controlling the angle of incidence of the flow of the temperature-controlled gas (142) relative to the flow of the ceramic material (124).

5. The method (300) according to claim 4, wherein the angle of incidence of the flow of the temperature-controlled gas (142) is 5° to 85° relative to the flow of the ceramic material (124).

6. The method (300) according to claim 1, further comprising a step of polishing the surface (114, 166, 170) to further smooth the surface (114, 166, 170) of the ceramic (112).

7. The method (300) according to claim 1, further comprising a step of moving a gas nozzle (140) for transmitting a flow of the temperature-controlled gas (142) across the entire surface (114, 166, 170) together with the thermal spraying unit (110) for thermally spraying the ceramic (112) when the thermal spraying unit (110) moves over the surface (114, 166, 170).

8. The method (300) according to claim 1, wherein the surface (114, 166, 170) has a surface roughness of 200 Ra after the curing.

9. The method (300) according to claim 1, wherein the thermal spray coating includes plasma spraying the ceramic material (124).

10. The method (300) according to claim 1, wherein the ceramic material (124) includes yttria-stabilized zirconia (YSZ), mullite, and alumina.

11. The method (300) according to claim 1, wherein the ceramic material (124) on the surface (114, 166, 170) has a thickness in the range of 0.127 mm to 2.54 mm.

12. A coating system (100), wherein the coating system (100) comprises a thermal spray coating unit (110) that applies a thermal barrier coating (TBC) (112) to the entire surface (114, 166, 170), the thermal spray coating unit (110) creating a flow of TBC material (124); an actuator (130) operably coupled to the thermal spray coating unit (110) and moving the thermal spray coating unit (110) across the entire surface (114, 166, 170); a gas nozzle (140) configured to convey a temperature-controlled gas flow (142) across the entire uncured TBC material (144) on the surface (114, 166, 170) after the thermal spray coating unit (110) applies the TBC material (124) onto the surface (114, 166, 170), the gas nozzle (140) being operably coupled to the thermal spray coating unit (110) and moving therewith A coating system (100).

13. The coating system (100) according to claim 12, wherein the temperature-controlled gas (142) includes at least one of air, argon, and nitrogen.

14. The coating system (100) according to claim 13, further comprising a thermal controller (150) for controlling the temperature of the temperature-controlled gas (142), the temperature being in the range of 204.4 °C to 1093.3 °C.

15. The coating system (100) according to claim 14, further comprising an angle adjustment actuator (162) operably coupled to the gas nozzle (140) to control the angle of incidence of the temperature-controlled gas flow (142) with respect to the flow of the TBC material (124).

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