Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1998-12-16
2001-02-06
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S141000, C428S148000, C428S629000, C428S632000, C428S633000, C428S635000, C428S670000, C428S678000, C416S24100B, C427S248100, C427S255190, C427S566000, C427S567000
Reexamination Certificate
active
06183884
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 vapour 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 vapour deposition processes onto an oxide layer on the metallic substrate.
The ceramic thermal barrier coatings deposited by the physical vapour deposition process have 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 vapour deposition process.
One problem associated with thermal barrier coatings produced by physical vapour deposition is that the the thermal conductivity is greater than the thermal conductivity of the same thermal barrier coating produced by plasma spraying.
It is known from International patent application WO9318199A to produce a columnar ceramic thermal barrier coating which comprises a plurality of layers with interfaces between the adjacent layers. Each columnar grain extends perpendicularly to the surface of the metallic article. Each columnar grain has a plurality of layers and adjacent layers have different structures. The interfaces between adjacent layers decreases the thermal conductivity of the ceramic thermal barrier coating. These layers are produced by alternate physical vapour deposition and plasma assisted physical vapour deposition.
SUMMARY OF THE INVENTION
The present invention seeks to provide a metallic article having a columnar ceramic thermal barrier coating in which the ceramic thermal barrier coating has reduced thermal conductivity. The present invention also seeks to provide a method of applying a ceramic thermal barrier coating by physical vapour deposition to produce a columnar ceramic thermal barrier coating which has reduced thermal conductivity.
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 perpendicularly to the surface of the metallic article, each columnar grain having a plurality of layers having sub-grains extending at an acute angle to the surface of the metallic article to form voids between adjacent sub-grains, the voids being arranged at an acute angle to the surface of the metallic article and thereby reduce the thermal conductivity of the ceramic thermal barrier coating.
Preferably each columnar grain has at least one further layer having sub-grains extending perpendicularly to the surface of the article, the at least one layer having sub-grains extending perpendicularly to the surface of the article being arranged further from the surface of the article than the plurality of layers having sub-grains extending at an acute angle to the surface of the article to increase the erosion resistance of the ceramic thermal barrier coating.
Preferably there are a plurality of layers having sub-grains extending at an acute angle to the surface of the metallic article to form voids between adjacent sub-grains and a plurality of layers having sub-grains extending perpendicularly to the surface of the metallic article.
Preferably the layers having sub-grains extending at an acute angle to the surface of the metallic article to form voids between adjacent sub-grains are arranged alternately with the further layers having sub-grains extending perpendicularly to the surface of the metallic article.
The sub-grains in adjacent layers with sub-grains extending at an acute angle to the surface of the metallic article may be arranged at different angles. The sub-grains in adjacent layers with sub-grains extending at an acute angle to the surface of the metallic article may be arranged at progressively decreasing acute angles.
Preferably the sub-grains in the at least one layer having sub-grains extending at an acute angle to the surface of the metallic article are arranged at an angle between 10° and 60°, more preferably at an angle between 20° and 45°, preferably at an angle of 30°.
Preferably the bond coating comprises an aluminium containing bond coating on the metallic article, the aluminium containing bond coating has an alumina surface layer, the ceramic thermal barrier coating is arranged on the alumina layer.
The aluminium containing bond coating may comprise a CrAlY bond coating or a diffusion aluminide coating.
Preferably the bond coating comprises a MCrAlY bond coating on the metallic article, 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 stabilised with yttria.
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 vapour deposition such that a plurality of columnar grains extend substantially perpendicularly to the surface of the metallic article, the vapour deposition process including a first deposition mode comprising depositing the ceramic such that a plurality of layers are formed in each columnar ceramic grain, the plurality of layers have sub-grains extending at an acute angle to the surface of the metallic article to form voids between adjacent sub-grains, the voids being arranged at an acute angle to the surface of the metallic article and thereby reduce the thermal conductivity of the ceramic thermal barrier coating.
Preferably the vapour deposition process includes a second mode comprising depositing the ceramic such that at least one further layer is formed in each columnar ceramic grain, the at least one further layer having sub-grains extending perpendicularly to the surface of the article, the at least one further layer having sub-grains extending perpendicularly to the surface of the article being arranged further from the surface of the article than the plurality of layers having sub-grains extending at an acute angle to the surface of the article to increase the erosion resistance of the ceramic thermal barrier coat
Oliff & Berridg,e PLC
Rolls-Royce plc
Speer Timothy M.
Young Bryant
LandOfFree
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