Thermal barrier coatings with low thermal conductivity

Details Thermal barrier coatings with low thermal conductivity Thermal barrier coatings with low thermal conductivity

2002-08-21

2004-05-04

McNeil, Jennifer (Department: 1775)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S632000, C428S633000, C428S702000, C428S697000, C428S699000, C428S650000, C428S680000, C416S24100B, C106S287190, C106S287200, C106S286400, C106S286800

Reexamination Certificate

active

06730422

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to thermal barrier coatings made from ceramic materials and to metallic parts having such thermal barrier coatings. The thermal barrier coatings have particular utility in gas turbine engines.
Gas turbine engines are well developed mechanisms for converting chemical potential energy, in the form of fuel, to thermal energy and then to mechanical energy for use in propelling aircraft, generating electrical power, pumping fluids, etc. At this time, the major available avenue for improved efficiency of gas turbine engines appears to be the use of higher operating temperatures. However, the metallic materials used in gas turbine engines are currently very near the upper limits of their thermal stability. In the hottest portion of modern gas turbine engines, metallic materials are used at gas temperatures above their melting points. They survive because they are air cooled. But providing air cooling reduces engine efficiency.
Accordingly, there has been extensive development of thermal barrier coatings for use with cooled gas turbine aircraft hardware. By using a thermal barrier coating, the amount of cooling air required can be substantially reduced, thus providing a corresponding increase in efficiency.
Such coatings are invariably based on ceramic. Mullite and alumina have been proposed, but zirconia is the current material of choice. Zirconia must be modified with a stabilizer to prevent the formation of the monoclinic phase. Typical stabilizers include yttria, calcia, ceria, and magnesia.
Generally speaking, metallic materials have coefficients of thermal expansion which exceed those of ceramic materials. Consequently, one of the problems that must be addressed in the development of successful thermal barrier coatings is to match the coefficient of thermal expansion of the ceramic material to the metallic substrate so that upon heating, when the substrate expands, the ceramic coating material does not crack. Zirconia has a high coefficient of thermal expansion and this is a primary reason for the success of zirconia as a thermal barrier material on metallic substrates.
Despite the success with thermal barrier coatings, there is a continuing desire for improved coatings which exhibit superior thermal insulation capabilities, especially those improved in insulation capabilities when normalized for coating density. Weight is always a critical factor when designing gas turbine engines, particularly rotating parts. Ceramic thermal barrier coatings are not load supporting materials, and consequently they add weight without increasing strength. There is a strong desire for a ceramic thermal barrier material which adds the minimum weight while providing the maximum thermal insulation capability. In addition, there are the normal desires for long life, stability and economy.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide thermal barrier coatings having low thermal conductivity.
It is a further object of the present invention to provide thermal barrier coatings as above which have utility in gas turbine engines.
The foregoing objects are attained by the thermal barrier coatings of the present invention.
In accordance with a first embodiment of the present invention, a thermal barrier coating is provided which broadly comprises at least 15 mol % of at least one lanthanide sesquioxide and the balance comprising a first oxide selected from the group consisting of zirconia, ceria, and hafnia.
In a second embodiment of the present invention, a thermal barrier coating is provided which broadly comprises an oxide present in an amount from 5 to 60 mol % with the oxide having a formula A
2
O
3
where A is selected from the group consisting of In, Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof, and the balance comprising a first oxide selected from the group consisting of zirconia, hafnia, and ceria.
In a third embodiment of the present invention, a thermal barrier coating is provided which broadly comprises a lanthanide sesquioxide and the balance comprising a first oxide selected from the group consisting of zirconia, hafnia, and ceria. The lanthanide sesquioxide is present in an amount sufficient to create more than one oxygen vacancy on average adjacent each zirconium, hafnium, and cerium ion.
In a fourth embodiment of the present invention, a thermal barrier coating is provided which broadly comprises from 15 to 60 mol % of a lanthanide sesquioxide having a formula A
2
O
3
where A is selected from the group consisting of Er, Nd, Yb, Eu, Dy, Pr, Sm, and La, and the balance zirconia.
In a fifth embodiment of the present invention, a thermal barrier coating is provided which broadly comprises at least 15 mol % yttria, and a lanthanide sesquioxide having a formula A
2
O
3
with A being selected from the group of Er, Nd, Yb, Eu, Dy, Gd, and Pr, and the balance zirconia.
In a sixth embodiment of the present invention, a thermal barrier coating is provided which broadly comprises from 9 to 15 mol % Yb
2
O
3
, and from 1.0 to 48 mol % of a lanthanide sesquioxide having a formula A
2
O
3
where A is selected from the group consisting of Er, Nd, Eu, Dy, Gd, and Pr, and the balance zirconia.
In a seventh embodiment of the present invention, a thermal barrier coating is provided which broadly comprises greater than 15 mol % Yb
2
O
3
, and a lanthanide sesquioxide having a formula A
2
O
3
where A is selected from the group consisting of Er, Nd, Eu, Dy, Gd, and Pr, and the balance zirconia.
In an eighth embodiment of the present invention, a thermal barrier coating is provided which broadly comprises from 20 to 30 mol % Sc
2
O
3
, and a lanthanide sesquioxide having a formula A
2
O
3
where A is selected from the group consisting of Er, Nd, Eu, Dy, Gd, and Pr, and the balance zirconia.
In a ninth embodiment of the present invention, a thermal barrier coating is provided which broadly comprises greater than 30 mol % Sc
2
O
3
, a lanthanide sesquioxide having a formula A
2
O
3
where A is selected from the group consisting of Nd, Eu, Dy, Gd, Er, and Pr, and the balance zirconia.
In a tenth embodiment of the present invention, a thermal barrier coating is provided which broadly comprises from 11 to 20 mol % In
2
O
3
, and a lanthanide sesquioxide having a formula A
2
O
3
where A is selected from the group consisting of Er, Nd, Eu, Dy, Gd, and Pr, and the balance zirconia.
In an eleventh embodiment of the present invention, a thermal barrier coating is provided which broadly comprises more than 20 mol % In
2
O
3
, and a lanthanide sesquioxide having a formula A
2
O
3
where A is selected from the group consisting of Er, Nd, Eu, Dy, Gd, and Pr, and the balance zirconia.
In a twelfth embodiment of the present invention, a thermal barrier coating is provided which broadly comprises from 5 to 60 mol % of at least one of La
2
O
3
and Sm
2
O
3
, and from 5 to 60 mol % of at least one oxide having a formula A
2
O
3
where A is selected from the group consisting of Sc, In, Y, Pr, Nd, Eu, Sm, Gd, dy, er, and Yb, and the balance zirconia.
The present invention also relates to an article which broadly comprises a metal substrate and one of the above thermal barrier coatings. The article may have a bond coat intermediate the metal substrate and the thermal barrier coating.
Other details of the thermal barrier coatings of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The essence of the present invention arises from the discovery that certain ceramic materials have great utility as thermal barrier coatings on metallic substrates, particularly those used to form components, such as the airfoils, of turbine engine components. These ceramic materials have such utility because they exhibit lower thermal conductivity that conventional thermal barrier coatings such as 7 weight % yttria stabilized zirconia.
In accordance with the present invention, a first embodiment of a thermal barrier co

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