EP2971240B1

EP2971240B1 - Hybrid thermal barrier coating and process of making the same

Info

Publication number: EP2971240B1
Application number: EP13878078.8A
Authority: EP
Inventors: Brian T HAZEL; David A. Litton; Michael J. Maloney
Original assignee: United Technologies Corp
Current assignee: RTX Corp
Priority date: 2013-03-14
Filing date: 2013-12-30
Publication date: 2018-11-21
Anticipated expiration: 2033-12-30
Also published as: EP2971240A1; US20160017475A1; US20180282853A1; EP2971240A4; WO2014143363A1

Description

BACKGROUND

The present disclosure relates to a thermal barrier coating for use on a turbine engine component and to a process of making the thermal barrier coating.
A thermal barrier coating (TBC) is created to meet one or more performance requirements including, but not liited to, spallation life, calcia-magnesia-alumina-silicate (CMAS) resistance, foreign object damage (FOD) resistance, erosion, and low conductivity. A turbine barrier coating is applied to a turbine engine component, such as a turbine blade/vane, to help the component withstand the relatively high temperatures of its operational environment.
TBCs are often formed using a singular coating process such as an electron beam physical vapor deposition (EB-PVD) process. For example, a TBC may be formed from two separate EB-PVD layers formed from two different materials, such as 7 wt% yttria stabilized zirconia and gadolinia stabilized zirconia in order to improve the thermal conductivity properties of the coating. The strain-tolerant columnar structure of an EB-PVD coating helps to increase the TBC spallation life. A more porous TBC however may minimize the TBC thermal conductivity and possibly the thermal radiation through the coating.
In one TBC, there is a porous outer layer over a more dense inner layer made by an EB-PVD process. In some TBCs, the two layers have different porosity levels. Such a structure can be formed by changing the coating temperature. More power equals more density but also more temperature. It is also known to form a dense vertically cracked microstructure for the TBC where the deposition is conducted at a two inch stand-off for the dense layer and a six inch stand-off for the porous layer.
EP 2 341 166 discloses a TBC on a substrate, the TBC comprising a bond coat, a ceramic coating, and a ceramic layer.
US 2011/244216 A1 discloses a combination of SPS and APS methods for deposition of multilayer thermal barrier coatings on turbine components. The applied materials comprise partially or fully YSZ as well as pyrochlores.
EP 2 336 381 A1 discloses a thermal barrier coating deposited by APS, consisting of a first 7YSZ layer and a second gadolinia stabilized zirconia layer with a porosity of 5-20 vol.%.
EP 2 450 465 A1 discloses a multilayer ceramic TBC deposited by APS, comprising an inner YSZ layer of low porosity, an intermediate YSZ layer with higher porosity than the inner layer and an outer porous layer of gadolinium zirconate.

SUMMARY

In accordance with the present disclosure, there is provided a coating according to claim 1 and a process according to claim 3.
In another and alternative embodiment, the second layer has a porosity in the range of from 10 to 40%.
In another and alternative embodiment, the first layer forming step comprises suspending a powder feedstock in a liquid suspension and injecting the powder feedstock and the suspension into a plasma jet under conditions where the first layer is formed with the strain-tolerant columnar microstructure.
In another and alternative embodiment, the second layer forming step comprises changing spray parameters so as to form the porous and radiation thermally resistant second layer.
In another and alternative embodiment, the second layer forming step comprises forming the second layer so as to have a porosity of from 10 to 40%.
In another and alternative embodiment, the first and second layer forming steps comprise using a powdered feedstock having a particle size in the range of from 10nm to 10 micrometers
In another and alternative embodiment, the first and second layer forming steps comprises using a powdered feedstock having a particle size in the range of from 10nm to 2.0 micrometers.
Other details of the hybrid thermal barrier coating and the process of making same are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a turbine engine component having a thermal barrier coating in accordance with the present disclosure deposited thereon; and
FIG. 2 illustrates a system for forming the coating on the turbine engine component.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is shown a turbine engine component 10. The turbine engine component may be any component which requires a thermal barrier coating such as a blade/vane. The turbine engine component 10 may have a substrate 12 formed from any suitable material known in the art including, but not limited to, a nickel based alloy, a cobalt based alloy, a titanium based alloy, a ceramic material, and an organo-matrix composite material.
A thermal barrier coating 14 is deposited on the substrate 12. The thermal barrier coating 14 has a first layer 16 which interfaces with the surface 18 of the substrate 12 and an outer second layer 20. The first layer 16 is formed so as to have a strain-tolerant columnar microstructure at the interface with the surface 18 of the substrate. The second layer 20 is formed to have a porous thermal conduction and radiant heat transfer resistant microstructure at an outer surface 22 of the thermal barrier coating.
The first layer 16 and the second layer 20 is formed from a material having the same composition. Each of the layers 16 and 20 is formed from a 7 wt% yttria stabilized zirconia (7YSZ).
Each of the layers 16 and 20 is formed using suspension plasma spray (SPS) technique such as that shown in FIG. 2. In this technique, a powdered feedstock is suspended in a liquid suspension 30. For example, the powdered feedstock may be 7YSZ which may be suspended in ethanol, water, or other alcohols such as methanol. The powdered feedstock may have a particle size in the range of from 10 nm to 10 micrometers mean size diameter. In another non-limiting embodiment, the particles size may be in the range of from 10 nm to 2.0 micrometers. The powdered feedstock in the suspension is injected into a plasma jet 32 created by a plasma torch 34 and thus deposited onto the substrate 12. The spray conditions are such that the first layer 16 is formed to have the desired strain tolerant columnar microstructure. The deposition technique may have a short stand off (similar to that used in dense vertically cracked coatings) and high power/enthalpy plasma conditions. After the first layer 16 has been formed, the spray conditions may be changed so as to form the second layer 20 with the porous thermal conduction and radiant heat transfer resistant microstructure. To add porosity, (1) the angle of the spray nozzle could be changed from normal relative to the surface on which the layer 20 is being deposited; (2) the stand off may be increased; and/or (3) the plasma power/enthalpy may be reduced. More porosity in the second layer 20 than in the first layer 16 creates a reduction in thermal conductivity. The second layer 20 may have a reduction of at least 10% in thermal conductivity. This may come purely from a porosity increase or a change in the structure from columnar to more splat like. An increase in porosity increases the erosion rate. A useful limit may be 10 to 40% porosity in the second layer 20.
The columnar structure SPS gives a thermal cyclic spallation resistance similar to EB-PVD (much higher than APS and higher than dense vertically cracked). Erosion is a function of porosity content and can be greater or less than EB-PVD (generally higher than APS and more like dense vertically cracked). Thermal conductivity, as discussed above, follows the porosity content.
The spray conditions are discreetly or incrementally changed throughout the spray run. The spray conditions are changed so that a continuously graded microstructure is formed where there is the strain-tolerant columnar microstructure at the interface with the substrate 12 for thermal barrier coating spallation resistance and a porous thermal conduction and radiation thermally resistant layer at the outer surface 22.
One of the advantages of the process described herein is that the thermal barrier coating can be formed using a single piece of equipment and in a single coating.
Another advantage is that one can easily change the composition of the second layer 20 so that it is different than the composition of the first layer 16. This can easily be done by changing the composition of the feedstock being injected into the plasma jet.
There has been described herein a hybrid thermal barrier coating and a process for making same.

Claims

A thermal barrier coating (14) applied to a turbine engine component (10) having a substrate (2), said coating comprising:
a first layer (16) which has a strain tolerant, columnar microstructure at an interface with the substrate for spallation resistance; and

a second layer (20) which is porous, conduction and radiation thermally resistant at an outer surface of the thermal barrier coating;

wherein there is a continuously graded microstructure from the interface to the outer surface;

wherein said first and second layers are formed from the same material;

wherein each of said first and second layers is formed from 7wt% yttria stabilized zirconia; and

wherein said first layer has a first thermal conductivity and said second layer has a second thermal conductivity which is at least 10% lower than the first thermal conductivity.
The thermal barrier coating of claim 1, wherein said second layer has a porosity in the range of from 10 to 40%.
A process for applying a thermal barrier coating (14) to a turbine engine component (10) comprising:
forming a first layer (16) which has a strain tolerant columnar microstructure at an interface of the first layer and a substrate using a suspension plasma spray technique;

forming a second layer (20) which is porous and radiation thermally resistant at an outer surface of the thermal barrier coating using said suspension plasma spray technique;

forming a continuously graded microstructure from said interface to said outer surface

wherein said first and second layer forming steps comprises forming said layers from the same material;

wherein each of said first and second layers is formed from 7wt% yttria stabilized zirconia; and

wherein said second layer forming step comprises forming said second layer with more porosity than the first layer so as to have a thermal conductivity which is at least 10% lower than a thermal conductivity of said first layer.
The process of claim 3, wherein said first layer forming step comprises suspending a powder feedstock in a liquid suspension and injecting said powder feedstock and said suspension into a plasma jet under conditions where said first layer is formed with said strain-tolerant columnar microstructure.
The process of claim 4, wherein said second layer forming step comprises changing spray parameters so as to form said porous and radiation thermally resistant second layer.
The process of claim 3, wherein said second layer forming step comprises forming said second layer so as to have a porosity of from 10 to 40%.
The process of claim 3, wherein said first and second layer forming steps comprise using a powdered feedstock having a particle size in the range of from 10nm to 10 micrometers.
The process of claim 7, wherein said first and second layer forming steps comprise using a powdered feedstock having a particle size in the range of from 10nm to 2 micrometers.