Patent Description:
Components that are exposed to high temperatures, such as a component within a gas turbine engine, typically include protective coatings. For example, components such as turbine blades, turbine vanes, blade outer air seals, combustor and compressor components typically include one or more coating layers that function to protect the component from erosion, oxidation, corrosion or the like to thereby enhance component durability and maintain efficient operation of the engine.

As an example, some conventional turbine blade outer air seals include an abradable ceramic coating that contacts tips of the turbine blades such that the blades abrade the coating upon operation of the engine. The abrasion between the outer air seal and the blade tips provide a minimum clearance between these components such that gas flow around the tips of the blades is reduced to thereby maintain engine efficiency. Over time, internal stresses can develop in the protective coating to make the coating vulnerable to cracking and spalling. Thermo-mechanical fatigue (TMF) is the overlay of a cyclical mechanical loading that leads to fatigue of a material, with a cyclical thermal loading. Thermo-mechanical fatigue is a factor that needs to be considered in the design of the coating system.

Increasing emphasis on environmental issues and fuel economy continues to drive turbine temperatures up. The higher engine operating temperatures results in an ever increasing severity of the operating environment inside a gas turbine. The severe operating environment results in more coating and base metal distress and increased maintenance costs. For example, more frequent replacement of the outer air seals.

A coating exists called a geometrically segmented abradable ceramic, (GSAC). The GSAC in development has the potential to satisfy the above described needs in many applications, however the most severe service environments still cause the ceramic surface layer of GSAC to spall. There exists a need for a further durability improvement to GSAC coating.

<CIT> discloses a segmented ceramic coating interlayer for a gas turbine disposed on a substrate comprising a plurality of surface features formed on said substrate. <CIT> discloses a further prior art thermal barrier coating for a gas turbine disposed on a substrate comprising a plurality of surface features with rounded edges formed on said substrate.

According to an aspect of the present invention, there is provided a thermal barrier coating in accordance with claim <NUM>.

Optionally, the dense layer comprises a <NUM>-<NUM> mil (<NUM>-<NUM>) thick YSZ coating.

Optionally, the metallic column top of each of the plurality of surface features comprises a radius from <NUM> to <NUM> times a thickness of the dense layer.

Optionally, the thermal barrier coating further comprises a bond coat disposed between the dense layer and the substrate.

Optionally, the bond coat comprises a thickness of from <NUM>-<NUM> mils (<NUM>-<NUM>) of MCrAlY.

Optionally, the thermally insulating topcoat comprises at least one of a porous material disposed over the dense layer between the plurality of surface features and/or the porous material disposed over the dense layer at the top of the metallic column.

Optionally, the thermally insulating topcoat covers greater than <NUM> percent of a total area of the thermal barrier coating.

According to another aspect of the present invention, there is provided a turbine engine component in accordance with claim <NUM>.

Optionally, the surface features are configured as a pattern of rounded columns that define a cell structure therebetween; wherein the pattern provides the metallic column structure a spacing that results in the surface features making up less than or equal to fifty percent of a coating area.

Optionally, the surface features comprise rounded edges at both the top and a bottom of the metallic column structure configured to reduce stress in the dense layer at both the top and a bottom of the metallic column structure of said plurality of surface features.

Optionally, the component further comprises a bond coat disposed between the dense layer and the substrate.

Optionally, the thermally insulating topcoat comprises a porous material disposed over the dense layer between the plurality of surface features and disposed over the dense layer at the top of the metallic column structure.

Optionally, the plurality of surface features can have an aspect ratio of <NUM> - <NUM> height to width.

According to another aspect of the present invention, there is provided a method of interrupting spallation for geometrically segmented coatings on a gas turbine engine component in accordance with claim <NUM>.

Optionally, the process further comprises disposing a bond coat layer between the surface and the dense layer.

Optionally, the process further comprises configuring the plurality of surface features as a pattern of rounded columns that define a cell structure therebetween; wherein the pattern provides the metallic column structure a spacing that results in the surface features making up less than or equal to fifty percent of a coating area.

Optionally, the process further comprises reducing stress in the dense ceramic layer at both the top and a bottom of the metallic column structure of said plurality of surface features.

Optionally, the thermally insulating topcoat comprises a porous material disposed over the dense layer between the plurality of surface features and disposed over the dense layer at the top of the metallic column.

Optionally, the metallic column top of each of the plurality of surface features comprises a radius from <NUM> to <NUM> times a thickness of the thermally insulating topcoat.

The present disclosure uses the inverse of the divot structure of GSAC coating and modifies it by introducing radii for reducing stress concentration at the free edges of a high toughness, dense TBC. Here, stresses are relieved by expansion joints in all three primary constituents; the metal columns, the dense TBC and the porous TBC filling between the columns. This is done by interrupting the transmission of stress with a gap (between columns) or a segmentation crack that is forced to form at regular and close spacing by the close approach of adjacent columns. Stress is further reduced at the dense TBC edges by causing a natural taper to form over a rounded (radius) edge.

The most desirable coating configuration is a column structure produced by additive manufacturing of MCrAlY composition on a superalloy substrate, <NUM>-<NUM> mils (<NUM>-<NUM>) of MCrAlY bond coat, <NUM>-<NUM> mil (<NUM>-<NUM>) dense YSZ APS coating followed by a low modulus, low conductivity YSZ or GSZ coating to fill between the columns. Low modulus and low conductivity being achieved by a combination of relatively low droplet and surface temperatures compared with the dense layer. After coating, the surface is ground smooth to remove the majority of the excess coating on the raised metallic features. The ceramic thickness on the metallic features after grinding is left at <NUM>-<NUM> mils (<NUM>-<NUM>) to maximize spallation resistance or may be left thicker if an abradable layer of the filler composition and structure is desired.

The <NUM>-<NUM> mil (<NUM>-<NUM>) HVOF bond coat layer may be used to naturally cover the radius corner on the pillars by means of the natural tendency of this high velocity process to round over edges. Alternatively, the rounded edges can be produced by machining, casting or additive methods.

Other details of the surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.

Referring now to <FIG>, selected portions of an exemplary gas turbine engine <NUM> are illustrated, such as a gas turbine engine <NUM> used for propulsion. In this example, the gas turbine engine <NUM> is circumferentially disposed about an engine centerline <NUM>. The engine <NUM> may include a fan <NUM>, a compressor <NUM>, a combustion section <NUM>, and a turbine section <NUM> that includes rotating turbine blades <NUM> and static turbine vanes <NUM>. It is to be understood that other types of engines may also benefit from the examples disclosed herein, such as engines that do not include a fan or engines having other types of compressors, combustors, and turbines.

<FIG> illustrates selected portions of the turbine section <NUM>. The turbine blades <NUM> receive a hot gas flow <NUM> from the combustion section <NUM> (<FIG>). The turbine section <NUM> includes a blade outer air seal system <NUM>, having a plurality of seal members <NUM>, or gas turbine articles, that function as an outer wall for the hot gas flow <NUM> through the turbine section <NUM>. Each seal member <NUM> is secured to a support <NUM>, which is in turn secured to a case <NUM> that generally surrounds the turbine section <NUM>. For example, a plurality of the seal members <NUM> may be arranged circumferentially about the turbine section <NUM>. It is to be understood that the seal member <NUM> is only one example of an article in the gas turbine engine and that there may be other articles within the gas turbine engine that may benefit from the examples disclosed herein.

illustrates a portion of seal member <NUM> having two circumferential sides <NUM> (one shown), a leading edge <NUM>, a trailing edge <NUM>, a radially outer side <NUM>, and a radially inner side <NUM> that is adjacent to the hot gas flow path <NUM> and blade <NUM>. It should be noted that the view in <FIG> is a small section of a part cross section. Leading edge <NUM> and trailing edge <NUM> do not necessarily have to be leading and trailing edges of the part, but rather the forward and aft edges of the section shown. In an exemplary embodiment, they can represent actual leading and trailing edges. The term "radially" as used in this disclosure relates to the orientation of a particular side with reference to the engine centerline <NUM> of the gas turbine engine <NUM>.

The seal member <NUM> includes a substrate <NUM>, a plurality of geometric surface features <NUM> (hereafter "surface features") that protrude from the substrate <NUM> on the gas path side of the seal member <NUM>. A thermally insulating topcoat <NUM> (e.g., a thermal barrier, (TBC)) can be disposed over the plurality of surface features <NUM> and substrate <NUM>. It is to be understood that the surface features <NUM> may not be shown to scale. Moreover, the substrate <NUM> may include known attachment features for mounting the seal member within the gas turbine engine <NUM>.

The thermally insulating topcoat <NUM> includes segmented portions <NUM> that are separated by faults <NUM> extending through the thickness of the thermally insulating topcoat <NUM> from the plurality of surface features <NUM>. The faults <NUM> extend from the edges or sides of the surface features <NUM> and facilitate reducing internal stresses within the thermally insulating topcoat <NUM> that may occur during manufacture or from sintering of the topcoat material at relatively high surface temperatures within the turbine section <NUM> during use in the gas turbine engine <NUM>. Depending on the composition of the topcoat <NUM>, surface temperatures of about <NUM>° F. ) and higher may cause sintering. The sintering may result in partial melting, densification, and diffusional shrinkage of the thermally insulating topcoat <NUM> and thereby induce internal stresses. The faults <NUM> provide pre-existing locations for releasing energy associated with the internal stresses (e.g., reducing shear and radial stresses). That is, the energy associated with the internal stresses may be dissipated by the faults <NUM> such that there is less energy available for causing delamination cracking between the thermally insulating topcoat <NUM> and the underlying substrate <NUM> or bond coat <NUM> and spallation.

The faults <NUM> may be produced by using the surface features <NUM>. That is, the pattern and pillar shape of the surface features <NUM> is not generally limited and may be a grid type of pattern with individual protrusions that extend from the surface of the substrate <NUM>. In any case, the dimensions of each of the plurality of surface features <NUM> may be designed with a particular ratio of a height <NUM> of the surface feature <NUM> to a width <NUM> of the surface feature <NUM>. For instance, the width <NUM> is selected such that the bond coat <NUM> (if used) and thermally insulating topcoat <NUM> can be built-up onto the tops or tips of the surface feature <NUM> during the deposition process. Likewise, the height <NUM> of surface features <NUM> is selected such that the portion of the thermally insulating topcoat <NUM> that builds-up on tops of the surface features <NUM> is discontinuous from other portions of the thermally insulating topcoat <NUM> that build-up in the valleys <NUM>, or lower recess portion, between the surface features <NUM>. As will be described with reference to an example fabrication method below, it is this discontinuity or disconnection between the portions of the thermally insulating topcoat <NUM> on the surface features <NUM> and between the surface features <NUM> that produces the fault <NUM> between the segmented portions <NUM>. In comparison, narrow widths of the surface features in combination with short heights may lead to a continuous over-coating of the thermally insulating topcoat <NUM> rather than discontinuous portions on the tops of the surface features <NUM> and in the valleys <NUM>.

A spacing <NUM> between the pluralities of surface features <NUM> may also be selected to facilitate reducing internal stresses of the thermally insulating topcoat <NUM>. As an example, the spacing <NUM> between the surface features <NUM> may be selected with regard to the thickness of the thermally insulating topcoat <NUM>, such as the thickness taken from the top of the surface features <NUM> or bond coat <NUM> to the radially inner side <NUM>, as indicated by arrow <NUM>. In some examples, a ratio of the spacing <NUM> between the surface features <NUM> to the thickness <NUM> of a thermally insulating topcoat <NUM> may be a function of the surface feature height <NUM> minus the top <NUM> radius minus a radius of the bottom <NUM> of the surface feature <NUM>. The selected spacing <NUM> may be smaller than a spacing of cracks that would occur naturally, without the faults <NUM>, which makes the thermally insulating topcoat <NUM> more resistant to spalling and delamination. Thus, different spacing <NUM> is appropriate for different thicknesses <NUM> of the thermally insulating topcoat <NUM>.

The material selected for the substrate <NUM>, bond coat <NUM> (if used), and thermally insulating topcoat <NUM> are not necessarily limited to any particular kind. For the seal member <NUM>, the substrate <NUM> may be a metal alloy, such as a nickel based alloy. The bond coat <NUM> may include any suitable type of bonding material for attaching the thermally insulating topcoat <NUM> to the substrate <NUM>. In some embodiments, the bond coat <NUM> includes a nickel alloy, platinum, gold, silver, or MCrAlY where the M includes at least one of nickel, cobalt, iron, or combination thereof, Cr is chromium, Al is aluminum and Y is yttrium. The bond coat <NUM> may be approximately <NUM>-<NUM> mils (<NUM>-<NUM>) thick, but may be thicker or thinner depending, for example, on the type of material selected and requirements of a particular application.

The thermally insulating topcoat <NUM> may be any type of ceramic material suited for providing a desired heat resistance in the gas turbine article. As an example, the thermally insulating topcoat <NUM> may be an abradable coating, such as yttria stabilized zirconia, hafnia, and/or gadolinia, gadolinia zirconate, molybdate, alumina, or combinations thereof. The topcoats <NUM> may also include porosity. While various porosities may be selected, typical porosities in a seal application include <NUM> to <NUM>% by volume. In an exemplary embodiment the topcoat <NUM> can include a <NUM> - 40v% porosity. In another exemplary embodiment the topcoat <NUM> can have a porosity of <NUM> to 25v%.

In the illustrated example, the thermally insulating topcoat <NUM> includes an abradable layer <NUM> that extends above the surface features <NUM>. In use, the tips of turbine blades <NUM> may abrade a groove in the abradable layer <NUM> such that a post-rub layer <NUM> (separated by the dotted line parallel to the radially inner side <NUM>) remains between the tips of the turbine blades <NUM> and the bond coat <NUM> or tops of the surface features <NUM>. The post-rub layer <NUM> provides thermal protection of the underlying substrate <NUM> and surface features <NUM>. In this regard, the thicknesses of the abradable layer <NUM> may be designed to meet the needs of a particular application. The abradable layer <NUM> can be machined level to produce a smooth flowpath surface <NUM>.

Alternatively, the machining can leave portions near the valleys <NUM> that can be dimpled leaving less material between the surface features <NUM>. In a further alternative embodiment the flowpath surface <NUM> can be machined to reduce a thicker application of the topcoat <NUM> resulting in thicker portions proximate the surface features or above the height of the surface features <NUM>.

In an exemplary embodiment, the topcoat <NUM> can be ground at the surface <NUM> to remove the more porous insulating layer from the dense layer on the surface features <NUM>. It is contemplated that the topcoat <NUM> can be fully or partially machined, or even ground partially into the dense layer <NUM> to a maximum of about <NUM>/<NUM> of the dense layer <NUM> thickness. If the topcoat <NUM> is ground too far in, the benefit of the rounded edges <NUM> can be lost, by leaving the rounded edges <NUM> covered by thicker dense ceramic. The intent is to have the dense layer <NUM> thickness taper to zero over the rounded edges <NUM>. The dense layer <NUM> can taper to a lesser thickness at the edges <NUM>. In an exemplary embodiment, the dense layer <NUM> can taper to <<NUM>% of the thickness at the center or generally flat top <NUM>.

The faults <NUM> may be formed during fabrication of the thermally insulating topcoat <NUM>. As an example, a thermal spray process may be used to deposit the thermally insulating topcoat <NUM> onto the substrate <NUM> and bond coat <NUM>, if used. The bond coat <NUM> may be deposited onto portions of the surface features <NUM> prior to deposition of the thermally insulating topcoat <NUM>. In this case, the deposition process may be a line-of-sight process such that the sides of the surface features include less bond coat <NUM> material or are free of any bond coat <NUM> material. That is, the bond coat <NUM> may be discontinuous over the surface of the substrate <NUM>.

For instance, the thermal spray process may be controlled to deposit the thermally insulating topcoat <NUM> such that a portion of the thermally insulating topcoat <NUM> builds-up with a dense ceramic layer TBC <NUM> on the top <NUM> of the surface features <NUM> and in the recesses <NUM> between the surface features <NUM> with a dense TBC layer <NUM> with high toughness and greater CMAS resistance due to low porosity. The dense layer <NUM> can be from <NUM>-<NUM> mils (<NUM>-<NUM>) thick and formed from dense YSZ APS coating. The dense layer <NUM> can be up to <NUM> mils (<NUM>), but most desirably <NUM>-<NUM> or <NUM>-<NUM> mils (<NUM>-<NUM> or <NUM>-<NUM>) thick. It is contemplated that the concept of dense can be having less than <NUM>% porosity. In the claimed embodiment, the density is a porosity of from <NUM>-<NUM>%, and in another example the density can be <NUM>-<NUM>% porosity, and even <NUM>-<NUM>% porosity. The dense layer <NUM> on the top of the surface features <NUM> may be dense vertically microcracked (DVC). It is understood that it would be hard to produce that vertical microcracking in the valleys <NUM>.

A low modulus, low conductivity YSZ or GSZ coating <NUM> can be used to fill between the surface features <NUM>. The thermally insulating topcoat <NUM> can be built up in the valleys <NUM> between the surface features <NUM> discontinuously from the portion on top <NUM> of the surface features <NUM> (i.e., no bridging with the topcoat on the surface features <NUM>). That is, the portion on the tops <NUM> of the surface features <NUM> is not connected to the portion between the surface features <NUM>. As the build-up of material continues, however, the portion building-up in between the surface features <NUM> eventually builds up with porous TBC to the tops <NUM> of the surface features <NUM> such that the portions between the surface feature <NUM> is laterally adjacent to the portions on the surface features <NUM>. Because of the discontinuity created by the height and width of the surface features <NUM>, the continued build-up of the portions on top <NUM> of the surface features <NUM> and between the surface features <NUM> forms the faults <NUM> between the segmented portions <NUM>.

The ceramic topcoat <NUM> can segment by cracking naturally between the pillar shaped surface features <NUM> resulting from the weak spot due to deposition and stress concentration location. Depending on the parameters of the deposition process, the faults <NUM> may be gaps between neighboring segmented portions <NUM> or discontinuities in microstructure between the neighboring portions. That is, the portions may be so close together that there is little or no gap therebetween except that there is a discontinuous plane or fault line between the segmented portions <NUM>. The radially inner side <NUM> may thereby be uneven immediately after deposition of the thermally insulating topcoat <NUM> but may be machined to provide the relatively smooth surface <NUM> as shown.

In an exemplary embodiment, the topcoat <NUM> between the surface features <NUM> can be more porous and strain tolerant and can cover greater than <NUM> percent of a coating surface area <NUM> and the surface features <NUM> cover less than or equal to <NUM> percent of surface area <NUM>. The topcoat <NUM> between the surface features <NUM> has limited width due to segmentation by the metallic surface feature <NUM> geometry and acts as columns which can dissipate stresses over significant height. The relatively thin dense topcoat portions <NUM> are configured to be spall resistant and have a cooler surface. CMAS infiltration can be limited at segmentation locations <NUM> due to cooling effect along the sides of the metallic surface features <NUM>. The tops <NUM> of the surface features <NUM> have relatively rounded column edges <NUM> configured to reduce stress concentrations at edges <NUM> of the thermally insulating topcoat <NUM>.

After partial spallation of the topcoat <NUM>, the topcoat <NUM> will remain in recesses <NUM> to reduce heat flux. The exemplary metallic surface feature <NUM> geometry is also configured to relieve local stress in the metal and has a cooler surface than a spalled region on a flat substrate. This configuration not only reduces oxidation rate of the exposed metallic due to the lower temperature relative to a generally flat surface, but also reduces propensity for thermal mechanical fatigue cracking by breaking up long range stresses by providing the relatively smaller exposed column top <NUM>. The value of reducing the stress in the metallic surface is evident when one considers that TMF cracks tend to initiate at the transition from spalled to non-spalled TBC on partially spalled flat surfaces.

Referring also to <FIG>, the plurality of surface features <NUM> may initially be a separate, metal alloy piece that is then attached to the substrate <NUM>, such as in a brazing process. Alternatively, the surface features <NUM> may be formed with the substrate <NUM> as a single, unitary piece, e.g., cast, additive manufacturing; and the like. The surface features <NUM> can be formed by casting into the base metal, forming by additive manufacturing or machining the surface features <NUM> in the surface of the base metal or as a layer of MCrAlY. In any case, the surface features <NUM> may be selected to be any of a variety of different patterns <NUM> of rounded metallic column/pillar shapes. As an example, the surface features <NUM> may be formed as a pattern of rounded columns that define a cell structure <NUM> therebetween. The patterns <NUM> can provide the metallic column surface feature <NUM> spacing that is less than or equal to fifty percent of the area being metallic. The surface features <NUM> can be configured separated to reduce the stress transmission through the metal. In an exemplary embodiment, the surface features <NUM> can optionally be formed made of MCrAlY with a base layer beneath made of MCrAlY.

The surface feature <NUM> forming process is selected to produce pillars with rounded edges <NUM> proximate the tops <NUM>. The rounded edges <NUM> at the top <NUM> of the metallic column/pillar surface feature <NUM> is necessary for producing the necessary stress relief. Rounded bottoms <NUM> may be incorporated to facilitate manufacturing or reduce stress concentration where surface features <NUM> are joined with substrate <NUM>. The rounded bottoms <NUM> can include a bottom radius of <NUM> to <NUM> times the column width <NUM>. In an exemplary embodiment, the surface features <NUM> can have an aspect ratio of <NUM> - <NUM> height to width. The top <NUM> of the surface feature <NUM> can include a radius <NUM> from <NUM> to <NUM> times the thickness of the topcoat thickness <NUM>. In another exemplary embodiment, the radius, width and height criteria of the surface feature <NUM> can include a 1x dense layer <NUM> thickness <= a radius <NUM> <= 5x dense layer <NUM> thickness. In another exemplary embodiment, 12x radius <NUM> >= surface feature width <NUM> >= 4x radius <NUM>. In another exemplary embodiment, the 1x dense layer <NUM> thickness <= surface feature height <NUM> <= 5x dense layer <NUM> thickness and the surface feature height <NUM> >= 2x the radius <NUM>. The criteria can include a 1x dense layer <NUM> thickness <= surface feature spacing <NUM> <= 5x dense layer <NUM> thickness. It can be noted that the radius <NUM> that is relevant can include the uppermost metallic interface of the surface feature <NUM>, so if there is a bond coat <NUM> present, the top of the bond coat <NUM> would be counted for the radius <NUM> dimension.

In another exemplary embodiment, the process can form rounded edges <NUM> to any degree or combination as necessary to produce the coating segmentation structure <NUM>. The rounded metallic column edges <NUM> are configured to reduce stress concentrations at edges <NUM> of the dense layer of TBC <NUM>.

Varying surface feature diameter will help to maintain design criteria for the desired ratios of coating thickness to surface feature diameter, depth and pillar spacing.

A technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes a TBC coating with high insulating factor.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes a thin ceramic portion that is naturally more erosion, CMAS and spallation resistant and has a cooler surface.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes a topcoat that is resistant to stresses associated with sintering and to CMAS.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes a topcoat that retains some insulation benefit even with partial spallation.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes a coating system that does not cause gradients in the metallic substrate that will induce TMF cracking in the event of partial spallation.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes the rounded metallic column edges reduce stress concentration at the edges of dense TBC.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes the thick ceramic portions having limited width due to segmentation by the metallic geometry and acts as columns which can dissipate stress over a significant height.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes any CMAS infiltration is limited at segmentation locations due to cooling effect along the sides of the metallic columns.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes the metallic column geometry relieves local stress and has a cooler surface than a spalled region on a flat substrate.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes after partial spallation, the ceramic topcoat will remain in the recesses to reduce heat flux.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes a reduction in the rate of blade tip to seal clearance growth and EGT margin loss.

Another technical advantage of the disclosed surface feature associated with geometrically segmented abradable ceramic (GSAC) thermal barrier coating (TBC) includes an improvement in the repairability of the coating due to less TMF cracking.

Claim 1:
A thermal barrier coating disposed on a substrate (<NUM>) of a gas turbine engine, the thermal barrier coating comprising:
a plurality of surface features (<NUM>) formed on said substrate (<NUM>) proximate an inner side (<NUM>) of said substrate (<NUM>), each of said plurality of surface features (<NUM>) comprising a metallic column having a top (<NUM>) with rounded edges (<NUM>);
a dense ceramic layer (<NUM>) disposed in a valley (<NUM>) located between each of said plurality of surface features (<NUM>), and said dense ceramic layer disposed on said top (<NUM>) and covering said rounded edges (<NUM>), wherein said dense ceramic layer (<NUM>) comprises a porosity of from <NUM>-<NUM>%; and
a thermally insulating topcoat (<NUM>) disposed over the plurality of surface features (<NUM>),
characterised in that:
a thickness of said dense ceramic layer (<NUM>) tapers to zero over said rounded edges (<NUM>).