Patent Application
20180355477
The application relates generally to coating systems for gas turbine engine components, and more particularly to thermal coating systems including an aluminide layer.
The hot surfaces (i.e. those exposed to prolonged elevated temperatures) of metal components in gas turbine engines are frequently coated with a Thermal Coating System (TCS)—sometimes called Thermal Barrier Coating (TBC). The remaining surfaces (i.e. cold surfaces) of such components are also frequently coated with a layer of oxidation resistant coating, such as an aluminide coating.
Known TCS thus generally include a ceramic layer on the hot surface and an aluminide layer only on the cold surface of the metal substrate. It is generally assumed that contamination (by other coating materials, such as aluminide coating for example) of the TCS reduces its spallation life. To avoid contamination of the TCS coating on the hot surface during application of the aluminide coating on the cold surface, the hot surface of the component is typically masked to prevent any of the aluminide coating to contaminate the hot side surface. However, masking processes are time and cost intensive, and thus greatly increase the production cost of the gas turbine coated component.
There is accordingly provided a method of applying a thermal coating to a gas turbine engine component, the method comprising the steps of: applying a first aluminide layer to a hot surface of the component, the hot surface in use adapted to be exposed to a hot environment of the gas turbine engine; applying a second aluminide layer to a cold surface of the component, the cold surface opposed to the hot surface; applying a first bond layer over the first aluminide layer on the hot surface of the component; applying a second bond layer over the aluminide layer on the cold surface of the component; and applying a ceramic layer on the first bond layer on the hot surface of the component.
There is also provided a coated component of a gas turbine engine having a hot side adapted to be exposed to hot combustion gases and a cold side opposite the hot side, the coated component comprising: a metallic substrate forming a base structure of the coated component, the metallic substrate having a first surface on the hot side of the coated component and a second surface on the cold side of the coated component; and a thermal coating system on the metallic substrate, the thermal coating system including: a first aluminide layer in direct contact with the second surface on the cold side of the coated component; and a first bond layer overlying the first aluminide layer on the cold side of the coated component.
There is further provided a combustor of a gas turbine engine comprising: a combustor liner having annular walls interconnected at upstream ends thereof to form a dome end of the combustor, the annular walls radially spaced apart to define a combustion chamber therebetween, each of the annular walls having an inner surface on a hot side of the combustor liner and an outer surface on a cold side of the combustor liner; a first aluminide layer in direct contact with at least a portion of the outer surface of the combustor walls on the cold side of the combustor liner; and a first bond layer overlying at least a portion of the first aluminide layer on the outer surface of the combustor walls on the cold side of the combustor liner.
Reference is now made to the accompanying figures in which:
According to an aspect, there is provided a coated component 10 of a gas turbine engine 11.
Referring to
In a particular embodiment, illustrated in
In a particular embodiment, the metallic substrate 38 forms a base structure of the coated component 10. The metallic substrate 38 can be one of a nickel-base alloy substrate, a cobalt-base alloy substrate, and a titanium-base alloy substrate. As used herein, “nickel-base”, “cobalt-base” , and “titanium-base” mean that the composition of the substrate has respectively more nickel, cobalt and titanium present than any other element. The metallic substrate 38 can define a panel, such as a combustor heat shield, a combustor liner, an exhaust wall, or a turbine blade. In a particular embodiment, the metallic substrate 38 is the combustor liner 20 as shown in
Referring to
The thermal coating system 40, is applied to the first and the second surfaces 46, 48. In a particular embodiment, the thermal coating system 40 on the first surface 46 on the hot side 42 provides with thermal insulation while, on the second surface 48 on the cold side 44, the thermal coating system provides resistance to oxidation.
As shown in
A burner rig test can be conducted with 16 uncooled pins with various coatings, or just bare metal pins, mounted onto a carousel rotating at about 200 rpm. The carousel is put in front of a flame at control gas temperature of 2000° F. so that all the pins are under the same heat load. The assembly comprising the pins and the carousel can be alternately heated by the flame (57 minutes) and cooled by a cooler stream of air at 100° F. (3 minutes). The samples can be subjected to hundreds of thermal cycles, and every 40-80 cycles the surface condition of the pins can be studies with SEM and dimensions to determine the relative oxidation depth.
Still referring to
The chemical composition of the first and second aluminide layers 50, 54 can be similar. For example, the first and second aluminide layers 50, 54 can be applied in a single deposition process and therefore have the same chemical composition.
In a particular embodiment, the second aluminide layer 54 has an aluminum content of less than 50 wt % based on total weight of the aluminide layer. In a more particular embodiment, the second aluminide layer 54 has an aluminum content of between 20 and 40 wt %. More particularly still, the second aluminide layer 54 may have an aluminum content of between 25 and 35 wt %. The second aluminide layer 54 can further include silicon. The second aluminide layer 54 can also include other additives, such as, but not limited to, Yttrium, Hafnium, Chromium, or precious metals. In a particular embodiment, the second aluminide layer 54 has a thickness of from 0.0002 to 0.004 inch. In one particular embodiment, the second aluminide layer 54 has a thickness of about 0.004 inch.
In a particular embodiment, at least one of an outer surface 56, 58 of the first and the second aluminide layers 50, 54 can be roughened and/or packed before applying any additional layer thereon. The roughened outer surface 56, 58 preferably have a roughness of from about 80 Ra to about 150 Ra. The roughness can be similar to the roughness of the first and the second surface 46, 48 upon which the first and the second aluminide layers 50, 54 are applied. Roughening the outer surfaces 56, 58 improves the adherence of overlying coating layers. In a particular embodiment, both outer surfaces 56, 58 are roughened. Also, both outer surfaces 56, 58 can be packed.
Also shown in
In a particular embodiment, the second bond layer 60 has a composition similar to the composition of the first bond layer 52, as described herein. For example, the first and the second bond layers 52, 60 can be applied in a single deposition step and therefore have the same composition.
In a particular embodiment, the ceramic layer 62 comprises coating materials that are capable of reducing heat flow to the metallic substrate 38. The ceramic layer 62 must form a thermal barrier and, as a consequence, has a melting point of at least 2000° F. (1093° C.). Coating materials used in the ceramic layer 62 can comprise aluminum oxide (Al2O3), in unhydrated and/or hydrated forms. The ceramic layer 62 can also include zirconias, and more particularly chemically stabilized zirconias (yttria-stabilized zirconias, ceria-stabilized zirconias, calcia-stabilized zirconias, scandia-stabilized zirconias, magnesia-stabilized zirconias, india-stabilized zirconias, ytterbia-stabilized zirconias or mixture thereof). In addition, the ceramic layer 62 is preferably from 0.01″ to 0.015 inch thick.
In contrast with the common understanding, which assumes that any contamination of the thermal coating system on the hot side of the coated component is to be avoided, it has been shown that the presence of the second aluminide layer 54 underlying the second bond layer 60 and the ceramic layer 62 provides improvement of the spallation life of the thermal coating system 40 on the hot side 42 of the coated component 10. Extensive burner rig tests that simulate the combustor hot environment can be done to assess the improvement in spallation life. More particularly, the spallation life of the thermal coating system 40 can be improved up to four time compared with conventional thermal coating systems, without aluminide layer.
Turning now to
As show in
As shown in
The bond layer is applied over the aluminide layer on the cold side of the component so that the resistance to oxidation provided by the aluminide layer is improved of up to 70%.
Finally, still referring to
Now referring to
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, any suitable material having the properties described with respect to the aluminide layer, bond layer or ceramic layer may be used. Any suitable method of applying the different layers may be used. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
