Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-05-19
2001-04-24
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S629000, C428S633000, C428S670000, C428S678000, C428S680000, C428S472000, C427S250000, C427S251000, C427S419100, C427S419200, C416S24100B, C416S24100B
Reexamination Certificate
active
06221512
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thermal barrier coating applied to the surface of a superalloy article e.g. a gas turbine engine turbine blade, and to a method of applying the thermal barrier coating. The invention particularly relates to ceramic thermal barrier coatings.
The constant demand for increased operating temperature in gas turbine engines was initially met by air cooling of the turbine blades and turbine vanes and the development of superalloys from which to manufacture the turbine blades and turbine vanes, both of which extended their service lives. Further temperature increases necessitated the development of ceramic coating materials with which to insulate the turbine blades and turbine vanes from the heat contained in the gases discharged from the combustion chambers, again the operating lives of the turbine blades and turbine vanes was extended.
It is known in the prior art to apply these ceramic coating materials by the thermal or plasma spray process onto a suitable bond coating, for example a MCrAlY alloy bond coating, which has been applied to the metallic substrate.
It is also known in the prior art to apply these ceramic coating materials by the physical vapor deposition process onto a suitable bond coating which has an alumina interface layer, for example a MCrAlY alloy bond coating or a diffusion aluminide bond coating, which has been applied to the metallic substrate.
It is also known in the prior art to apply these ceramic coating materials by plasma spraying or physical vapor deposition processes onto an oxide layer on the metallic substrate.
The ceramic thermal barrier coatings deposited by the physical vapor deposition process has benefits over the ceramic thermal barrier coating deposited by plasma spraying. The main benefit is improved thermal shock resistance due to the columnar structure of the ceramic thermal barrier coating produced by the physical vapor deposition process.
One problem associated with thermal barrier coatings produced by physical vapor deposition is that they suffer from spallation of the ceramic thermal barrier coating. Spallation of the ceramic thermal barrier coating is the loss of the ceramic thermal barrier coating by flaking from the bond coating due to the thermal cycling conditions. Currently it has been found that the ceramic thermal barrier coatings produced by Chromalloy United Kingdom Limited have spalled at the leading edge and trailing edge regions of the turbine blades and turbine vanes or other regions where there is a rapid change in the shape of the component.
SUMMARY OF THE INVENTION
The present invention seeks to provide a metallic article with a thermal barrier coating deposited by physical vapor deposition which is more resistant to spallation of the ceramic thermal barrier coating. The present invention also seeks to provide a method of applying a thermal barrier coating by physical vapor deposition which is more resistant to spallation of the ceramic thermal barrier coating.
Accordingly the present invention provides a metallic article comprising a bond coating on the metallic article and a ceramic thermal barrier coating on the bond coating, the ceramic thermal barrier coating comprising a plurality of columnar grains extending substantially perpendicular to the surface of the metallic article, the ceramic thermal barrier coating comprising an inner portion adjacent the bond coating, a transition portion on the inner portion and an outer portion on the transition portion, the inner portion having columnar grains grown in a competitive manner, the outer portion having columnar grains grown in a steady state manner, the transition portion having columnar grains grown in transition from competitive manner to steady state manner, in the outer portion each columnar grain having substantially constant cross-sectional area throughout its length, each columnar grain having smooth sides without the presence of sub-grains projecting therefrom and each columnar grain being separated from adjacent columnar grains by uniform clearances to minimize the stress/strain in the columnar grains and/or to minimize the stress/strain between adjacent columnar grains and thereby increase the resistance to spallation of the ceramic thermal barrier coating.
Preferably the bond coating comprises an aluminum containing bond coating on the metallic article, the aluminum containing bond coating has an alumina surface layer, the ceramic thermal barrier coating is arranged on the alumina layer.
The aluminum containing bond coating may comprise a MCrAlY bond coating, where M is at least one of cobalt, iron and nickel, or a diffusion aluminide coating.
Preferably bond coating comprises a MCrAlY bond coating on the metallic article, where M is at least one of cobalt, iron and nickel, a platinum enriched MCrAlY layer on the MCrAlY bond coating, a platinum aluminide layer on the platinum enriched MCrAlY layer, the platinum aluminide layer has an alumina surface layer, the ceramic thermal barrier coating is arranged on the alumina layer.
Alternatively the metallic article has an alumina surface layer, the ceramic thermal barrier coating is arranged on the alumina layer.
The metallic article may comprise a nickel superalloy article or a cobalt superalloy article.
The metallic article may comprise a turbine blade or a turbine vane.
The ceramic thermal barrier coating may comprise zirconia. The zirconia may be stabilized with yttria.
Preferably the outer portion is between 38% and 67% of the thickness of the ceramic thermal barrier coating. More preferably the outer portion is between 40% and 60% of the thickness of the ceramic thermal barrier coating.
Preferably the width of the columnar ceramic grains in the outer portion increases at a rate equal to or less than 2.0 micrometers per 100 micrometer length of the columnar ceramic grain. More preferably the width of the columnar ceramic grains in the outer portion increases at a rate equal to or less than 1.7 micrometers per 100 micrometer length of the columnar ceramic grain. More preferably the width of the columnar ceramic grains in the outer portion increases at a rate equal to or less than 0.24 micrometers per 100 micrometer length of the columnar ceramic grain.
The present invention also provides a method of applying a ceramic thermal barrier coating to a metallic article, comprising the steps of:—forming a bond coating on the metallic article, applying a ceramic thermal barrier coating to the bond coating by vapor deposition to form a plurality of columnar grains extend substantially perpendicular to the surface of the metallic article, the vapor deposition of the ceramic thermal barrier coating comprising depositing an inner portion adjacent the bond coating, depositing a transition portion on the inner portion and depositing an outer portion on the transition portion, the inner portion having columnar grains grown in a competitive manner, the outer portion having columnar grains grown in a steady state manner, the transition portion having columnar grains grown in transition from competitive manner to steady state manner, and in the outer portion each columnar grain having a substantially constant cross-sectional area throughout its length, each columnar grain having smooth sides without the presence of sub-grains projecting therefrom and each columnar grain being separated from adjacent columnar grains by uniform clearances to minimize the stress/strain in the columnar grain and/or to minimize the stress/strain between adjacent columnar grains and thereby increase the resistance to spallation of the ceramic thermal barrier coating.
Preferably the method comprises controlling the rate of evaporation of the ceramic, the temperature of the metallic article and the rate of rotation of the metallic article during the vapor deposition of the ceramic thermal barrier coating.
Preferably the evaporation rate of ceramic is 3 to 5 micrometers per minute, the temperature of the metallic article is 1000° C. to 1100° C. and the rate of rotation of the metallic arti
Jones Deborah
Oliff & Berridg,e PLC
Rolls-Royce plc
Young Bryant
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