Abstract:
The invention relates to a coated turbine component adapted for exposure to a hot gas flow, comprising a component body comprising a base material, a thermal barrier coating applied to the base material, and a thermographic phosphor arranged within, on or beneath the thermal barrier coating surface adapted to emit light corresponding to a temperature of the thermographic phosphor. The invention also relates to a method for producing a coated turbine component comprising applying a first thermal barrier coating containing an activator to a component body base material, the activator providing the thermal barrier layer coating with thermographic properties such that light is emitted corresponding to a temperature of the thermographic phosphor, applying a second thermal barrier coating that does not contain the activator on top of the first thermal barrier coating, and removing a portion of the second thermal barrier coating to expose the thermographic phosphor layer underlying the second thermal barrier coating. The invention also relates to a method for producing a coated turbine component comprising applying a thermal barrier coating to a component body, trenching the thermal barrier coating to form a base at the bottom of the trench and applying a thermographic phosphor to the base of the trench.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefits of European Patent application No. EP05000728.5 filed Jan. 14, 2005, all of the applications are incorporated by reference herein in their entirety 
     FIELD OF THE INVENTION 
     The present invention relates to a coated component, which comprises a component body made from a base material and a thermal barrier coating applied to the base material, and to processes for producing this component. 
     BACKGROUND OF THE INVENTION 
     Increasing efficiency plays a central role on the road to generating energy while preserving resources and safeguarding the environment. For example, by 2025 it is aimed to increase the overall efficiency of combined-cycle power plants (a combination of gas turbine power plant and steam turbine power plant) to over 60%. To enable this objective to be achieved, it is necessary to increase the efficiency of gas turbines. 
     An important parameter in increasing the efficiency of gas turbines is the turbine inlet temperature. The current efficiency of a gas turbine of approx. 38% can be achieved with a turbine inlet temperature of 1230° C. (ISO). Increasing the efficiency of the gas turbine would require an increase in the turbine inlet temperature. For example, in order to increase the efficiency of a gas turbine to 45%, it would be necessary to increase the turbine inlet temperature to approx. 1350° C. 
     In addition to the use of improved base materials and effective cooling methods, the use of ceramic thermal barrier coatings constitutes a key technology for achieving this objective. On account of the thermally insulating action of the ceramic thermal barrier coating, the surface of the coated component can be exposed to a temperature which is several 100° C higher than without the thermal barrier coating, without the cooling conditions for the component having to be altered. A precondition for the efficient use of ceramic thermal barrier coatings (referred to below as TBCs) in gas turbines, in addition to an inexpensive process technology, is in particular the structural stability and therefore the reliability of the TBC under the conditions of use in gas turbines. For example, for gas turbines used in power plant applications, faultless functioning for over 20000 equivalent operating hours, as they are known, or more has to be ensured. Premature failure of the TBC would consequently lead to the base material of the coated turbine components overheating and possibly to catastrophic damage to the turbine. The operating loss and maintenance costs caused by turbine damage may be considerable and would ultimately cancel out the technological benefit of the TBC. 
     In future generations of high-efficiency gas turbines, the stresses will move closer and closer to the limits of the TBC&#39;s abilities. To ensure that the risk of failure is not uncontrollably increased as a result, the stress parameters which are critical for failure of the TBC have to be measured and checked in operation. Important stressing parameters in this context are the surface temperature of the TBC at critical component positions, known as hot spots, and the time dependency of the surface temperature. The latter is important in particular for the transitions between different operating states of the gas turbine, for example when running up the gas turbine. 
     Therefore, there is a demand for a suitable sensor element which is suitable for measuring temperature and heat flux in the TBC under operating conditions of a gas turbine. 
     Pyrometers and thermal imaging cameras are nowadays already in use for measuring the surface temperature of guide vanes in gas turbines. In this case, the radiation emitted by the TBC surface in a defined wavelength region, for example in the infrared or near infrared, is detected and, taking account of the emissivity and the detector sensitivity, converted into an equivalent surface temperature of the TBC. In this context, the generally inadequate knowledge of the wavelength-dependent emissivity of the TBC surface, which may be sensitively influenced inter alia by deposits on the TBC surface (for example rust), presents difficulties. 
     Another way of measuring surface temperatures is to use thermographic phosphors. A thermal barrier coating with embedded thermoluminescence indicator material and methods for determining the temperature of the thermal barrier coating are described, for example, in EP 1 105 550 B1. To determine the temperature of the thermal barrier coating, the indicator material is excited to fluoresce by means of a pulsed laser. After the excitation pulse has been switched off, the intensity of the fluorescence spectrum drops exponentially with a characteristic time constant t. For example, terbium-doped yttrium aluminum garnet (YAG:Tb) has a monotone decrease in the characteristic time constant t between 700 and 1000° C. The temperature of the indicator material and therefore of the thermal barrier coating in which it is embedded can be ascertained by measuring the time constant, provided appropriate calibration has been carried out. Under certain circumstances, different lines of the emission spectrum may have different decay constants, which may also have different temperature dependencies. 
     Instead of the time decay properties of the emission intensity of the indicator material, it is also possible to use the intensity ratio of two emission wavelengths to determine the temperature of the indicator material and therefore the temperature of the thermal barrier coating. The intensity ratio is approximately linearly dependent on the temperature of the indicator material, i.e. on the temperature of the thermal barrier coating in which the indicator material is embedded. The measuring of the temperature by means of the intensity ratio is likewise described in EP 1 105 550 B1. 
     The advantage of using measurement methods which are based on thermographic phosphors is that they are independent of the emissivity of the TBC, which is generally only inadequately known, and of the influence of surface contamination, which often influences the property of the TBC as a heat radiator. The specific properties of the emission spectrum of the phosphor, by contrast, are only slightly influenced by the emissivity and surface contamination. 
     The restriction on the thermal sensitivity of the phosphors to in each case a specific temperature range and the limited long-term stability of a thermographic phosphor under the thermal and atmospheric conditions of a gas turbine impose limits on temperature measurement by means of emission spectra of thermographic phosphors. 
     SUMMARY OF THE INVENTION 
     In light of the prior art described, it is an object of the present invention to provide a coated component and a corresponding process which are particularly suitable for temperature measurement under the thermal and atmospheric conditions of a gas turbine. 
     This object is achieved by the coated component as described in the claims. The dependent claims include advantageous configurations of the invention which can be combined in any desired way. 
     A coated component according to the invention, which is designed as a component of a structure which routes hot gases, for example a gas turbine, comprises a component body made from a base material and a thermal barrier coating (TBC) applied to the base material. In this case, the thermal barrier coating may either be applied directly to the base material or there may be what is known as a bond coat in between. Moreover, the thermal barrier coating may be formed as either a single layer or as a multiple layer. Moreover, the thermal barrier coating contains a thermographic phosphor. According to the invention, the thermal barrier coating includes at least one recess. The thermographic phosphor is arranged in the base region of the recess. Each recess has a depth and width which are selected in such a manner that its base is protected from being directly attacked by the hot gas. The dimensions of the recess which are required to achieve this effect depend in particular on the temperature of the hot gas, the position of the recess on the component and the flow conditions in the structure which routes hot gas. Suitable depths and widths for the recesses are to be determined empirically in a suitable way. 
     Arranging the thermographic phosphor in a recess in the thermal barrier coating offers the possibility of protecting the phosphor from being directly attacked by a hot gas, and therefore of protecting it from the corrosive and abrasive action of this hot gas when the coated component is used in a region of a gas turbine which routes hot gas. 
     Moreover, arranging the thermographic phosphor in the base region of the recess offers the advantage that the surface temperatures at the surface of the thermal barrier coating may also be above the range which is optimum for the thermographic phosphor. Another advantage is that the aging of the phosphor is not directly dependent on the surface temperature of the thermal barrier coating. There are also no problems caused by lack of transparency of the thermal barrier coating for the emission wavelengths of the phosphor, since there is no thermal barrier coating above the phosphor arranged at the base region. 
     If the component has at least two recesses of different depths, in the base region of which thermographic phosphors with different illumination properties are present, it is possible to measure the heat flux from the coating surface toward the base material. 
     The thermographic phosphor may in particular be selected in such a way that itself likewise has thermal barrier properties. 
     In one configuration of the coated component according to the invention, the thermographic phosphor is arranged in the interior of the thermal barrier coating. The at least one recess is then formed in such a manner that the thermographic phosphor in the region of the recess is uncovered by the latter. This can be achieved in particular by the coating having at least two layers applied above one another. In this case, at least the outermost layer has thermal barrier properties. Thermographic phosphor is arranged in a layer covered at least by the outermost layer, and the at least one recess extends through the layers arranged above a phosphor layer. This configuration offers the option of applying one or more layers containing thermographic phosphor to the component over a large area. Masks as are used for the local application of thermographic phosphors are not required. Moreover, this configuration simultaneously offers the option of determining the wear to the layers located above the layer containing phosphor when the component is operating on the basis of thermographic phosphor being uncovered at locations at which a recess should not be present. Moreover, the production of multilayer coatings can easily be incorporated in existing processes. 
     However, as an alternative to producing multilayer coatings, it is also possible for a coating to be doped with a thermographic phosphor. In this context, the term doping is to be understood as meaning the introduction of foreign substances into a coating material. In this context, the term foreign substances is to be understood as meaning substances which are not contained in the actual material composition of the coating itself. 
     In a coated component according to the invention, the thermographic phosphor can be present in the form of at least one doping which has been introduced into the thermal barrier coating at least in the region of a recess. In particular, each doping can form a doped zone which extends through the entire thermal barrier coating at a certain distance from the coating surface. The depth of the at least one recess is then selected in such a manner that a doped zone is uncovered in the region of the recess. In this configuration, large-area doping of the component can be used. There is therefore no need for masks for the doping. Moreover, it is possible to use a doped zone arranged at a certain distance from the coating surface as an indication of wear. 
     However, it is also possible for the doping to be only locally introduced into the thermal barrier coating, for example using masks. By way of example, it is thus possible to provide a coated component in which a doping is present only in the base region of the at least one recess. Local doping is of interest in particular if the introduction of the dopant influences the thermal properties of the thermal barrier coating. Influencing of this nature can generally be minimized by introducing only a small percentage of dopant into the coating. However, a small percentage of dopant also means that the emission of the phosphor has only a relatively low intensity. Therefore, a certain minimum quantity of dopant is required in order to allow reliable measurement of the temperature of the thermal barrier coating. If this minimum concentration or the desired concentration has an adverse effect on the thermal properties of the thermal barrier coating, large-area doping would not be appropriate. If the dopant is only locally arranged, however, it may be possible to accept a local deterioration in the thermal properties, in particular if the doped region of the coating is protected from direct attack from the hot gas by virtue of its position in a recess. 
     However, just a local arrangement of the thermographic phosphor can also be achieved instead of by doping by the fact that it is present as a phosphor coating applied to the base of the recess. 
     In the coated component according to the invention, the recess may in particular be configured in the form of a trench. Trench-like structures have an advantageous effect on the stability of thermal barrier coatings, which proves advantageous in particular during transitions between different operating states, with the associated thermal stresses. Accordingly, trench structures are in particular arranged in a targeted way in highly thermally stressed regions of the thermal barrier coating. In particular there, however, information about the temperature and heat flux within the thermal barrier coating is particularly important in order to detect overloading in good time and to prevent failure of the thermal barrier coating. Moreover, arranging thermographic phosphors in the base region of the trench structures allows a temperature and heat flux sensor which is integrated in the thermal barrier coating to be realized without causing considerable additional costs in production or altering the structural stability of the thermal barrier coating. The trench structures described can be produced by means of laser with a high degree of accuracy at various positions of the component, in particular including in curved regions. 
     In the coated component according to the invention, at least one metal oxide comprising at least one trivalent metal may be present as thermographic phosphor. By way of example, the metal oxide may be a perovskite with the empirical formula AA′O 3  or a pyrochlore with the empirical formula A 2 B 2   0   7 , where A and A′ represent a trivalent metal and B represents a tetravalent metal. In a further configuration, A or A′ may in particular represent a rare earth element (also known as lanthanides) or rhenium (Re), and the other may in each case represent at least one of the following elements: lanthanum, gadolinium, samarium. 
     In the component according to the invention, the thermographic phosphor may be a phosphor whose ability to light up is based on an activator which comprises at least one rare earth element. As rare earth element, it may in particular comprise at least one of the following elements: cerium (Ce), europium (Eu), dysprosium (Dy), terbium (Th). 
     The coated component according to the invention is particularly suitable for use in gas turbines. Accordingly, it may be designed as a turbine component, for example as a rotor blade or guide vane of a gas turbine installation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, properties and advantages of the present invention will emerge from the following description of exemplary embodiments with reference to the appended figures. In the drawing: 
         FIG. 1  shows by way of example a partial longitudinal section through a gas turbine. 
         FIG. 2  shows a perspective view of a rotor blade or guide vane of a gas turbine. 
         FIG. 3  shows the combustion chamber of a gas turbine. 
         FIG. 4  shows a highly diagrammatic illustration of a first exemplary embodiment of a component according to the invention. 
         FIG. 5  shows a highly diagrammatic illustration of a second exemplary embodiment of a coated component according to the invention. 
         FIG. 6  shows a highly diagrammatic illustration of a third exemplary embodiment of a coated component according to the invention. 
         FIG. 7  shows a highly diagrammatic illustration of a fourth exemplary embodiment of a coated component according to the invention. 
         FIG. 8  shows a highly diagrammatic illustration of a fifth exemplary embodiment of a coated component according to the invention. 
         FIGS. 9   a  to  9   e  show a first process for producing a coated component according to the invention. 
         FIGS. 10   a  to  10   d  show a second process for producing a coated component according to the invention. 
         FIG. 11  shows a step of a third process for producing a coated component according to the invention. 
         FIG. 12  shows by way of example the procedure used to measure the temperature of a thermal barrier coating on a guide vane of a gas turbine. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows by way of example a partial longitudinal section through a gas turbine  100 . In its interior, the gas turbine  100  has a rotor  103  which is mounted such that it can rotate about an axis of rotation  102  and is also referred to as the turbine rotor. An intake casing  104 , a compressor  105 , a for example toric combustion chamber  110 , in particular an annular combustion chamber  106 , with a plurality of coaxially arranged burners  107 , a turbine  108  and an exhaust gas casing  109  follow one another along the rotor  103 . 
     The annular combustion chamber  106  is in communication with a for example annular hot gas duct  111 . There, by way of example four successive turbine stages  112  form the turbine  108 . 
     Each turbine stage  112  is formed, for example, from two blade rings. As seen in the direction of flow of a working medium  113 , a guide vane row  115  is followed in the hot gas duct  111  by a row  125  formed from rotor blades  120 . 
     The guide vanes  130  are secured to an inner casing  138  of a stator  143 , whereas the rotor blades  120  belonging to a row  125  are arranged on the rotor  103 , for example by means of a rotor disk  133 . 
     A generator (not shown) is coupled to the rotor  103 . 
     While the gas turbine  100  is operating, air  135  is drawn in through the intake casing  104  and compressed by the compressor  105 . The compressed air provided at the turbine end of the compressor is passed to the burners  107 , where it is mixed with a fuel. The mixture is then burnt in the combustion chamber  110 , forming a working medium  113 . From there, the working medium  113  flows along the hot gas duct  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  is expanded at the rotor blades  120 , transferring its momentum, so that the rotor blades  120  drive the rotor  103  and the latter in turn drives the generator coupled to it. 
     While the gas turbine  100  is operating, the components which are exposed to the hot working medium  113  are subject to thermal stresses. The guide vanes  130  and rotor blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , together with the heat shield bricks which line the annular combustion chamber  106 , are subject to the highest thermal stresses. 
     To be able to withstand the temperatures which prevail there, they can be cooled by means of a coolant. 
     Substrates of the components may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure). 
     By way of example, iron-based, nickel-based or cobalt-based superalloys are used as material for the components, in particular for the turbine blade or vane  120 ,  130  and components of the combustion chamber  110 . Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435. or WO 00/44949; these documents form part of the disclosure. 
     The blades or vanes  120 ,  130  may also have coatings which protect against corrosion (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and represents yttrium (Y) and/or silicon and/or at least one rare earth element or hafnium). Alloys of this type are known from EP0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to form part of the present disclosure. 
     A thermal barrier coating, consisting for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, may also be present on the MCrAlX. 
     The guide vane  130  has a guide vane root (not shown here), which faces the inner housing  138  of the turbine  108 , and a guide vane head which is at the opposite end from the guide vane root. The guide vane head faces the rotor  103  and is fixed to a securing ring  140  of the stator  143 . 
       FIG. 2  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbine machine which extends along a longitudinal axis  121 . 
     The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
     The blade or vane  120 ,  130  has, in succession along the longitudinal axis  121 , a securing region  400 , an adjoining blade or vane platform  403  and a main blade or vane part  406 . As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
     A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or disk (not shown), is formed in the securing region  400 . 
     The blade or vane root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
     The blade or vane  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the main blade or vane part  406 . 
     In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade  120 ,  130 . Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these documents form part of the disclosure. The blade or vane  120 ,  130  may in this case be produced by a casting process, also by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
     Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses. Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy solidifies to form the single-crystal structure, i.e. the single-crystal workpiece, or solidifies directionally. In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, a transition to the globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal components. Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures). Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these documents form part of the disclosure. 
     The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion or oxidation (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and represents yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to form part of the present disclosure. 
     It is also possible for there to be a thermal barrier coating, consisting for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, on the MCrAlX. Columnar grains are produced in the thermal barrier coating by means of suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
     Refurbishment means that after they have been used, protective layers may have to be removed from components  120 ,  130  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component  120 ,  130  are also repaired. This is followed by recoating of the component  120 ,  130 , after which the component  120 ,  130  can be reused. 
     The blade or vane  120 ,  130  may be hollow or solid in form. If the blade or vane  120 ,  130  is to be cooled, it is hollow and may also have film-cooling holes  418  (indicated by dashed lines). 
       FIG. 3  shows a combustion chamber  110  of a gas turbine. The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  107  arranged circumferentially around the axis of rotation  102  open out into a common combustion chamber space. For this purpose, the combustion chamber  110  overall is of annular configuration positioned around the axis of rotation  102 . 
     To achieve a relatively high efficiency, the combustion chamber  110  is designed for a relatively high temperature of the working medium M of approximately 1000° C. to 1600° C. To allow a relatively long service life even with these operating parameters, which are unfavorable for the materials, the combustion chamber wall  153  is provided, on its side which faces the working medium M, with an inner lining formed from heatshield elements  155 . 
     On the working medium side, each heatshield element  155  is equipped with a particularly heat-resistant protective layer or is made from material that is able to withstand high temperatures. These may be solid ceramic bricks or alloys with MCrAlX and/or ceramic coatings. The materials of the combustion chamber wall and their coatings may be similar to the turbine blades or vanes. 
     A cooling system may also be provided for the heatshield elements  155  and/or their holding elements, on account of the high temperatures in the interior of the combustion chamber  110 . 
     The combustion chamber  110  is designed in particular to detect losses from the heatshield elements  155 . For this purpose, a number of temperature sensors  158  are positioned between the combustion chamber wall  153  and the heatshield elements  155 . 
     A first exemplary embodiment of a coated component according to the invention is illustrated in  FIG. 4 . 
     The component  1 , which is illustrated in highly diagrammatic form, is intended to be a turbine component  120 ,  130 ,  155 . The turbine component  1  is made from a base material  2 , to which a thermal barrier coating  3  has been applied. If appropriate, a bond coat may also be present between the thermal barrier coating  3  and the base material  2 . 
     When the turbine component  1 ,  120 ,  130 ,  155  is installed in a gas turbine installation, the thermal barrier coating  3  faces the region of the gas turbine installation which routes hot gas. The coating  3  ensures reduced heat exchange between the hot gas and the generally metallic base material of the turbine component  1 . In other words, the thermal barrier coating counteracts the flow of temperature in the direction of the base material  2 . 
     In particular superalloys based on nickel (Ni) or cobalt (Co) are suitable as base material  2  for the turbine component  1 . 
     Recesses, for example in the form of trenches  4 , are present in the thermal barrier coating  3 , extending from the surface  5  of the coating  3  into the coating  3  in the direction of the base material  2 , without reaching the base material  2 . Therefore, the base material  2  is covered by the thermal barrier coating  3  even in the region of the trenches  4 , but the thermal barrier coating  3  is less thick in the region of the trenches  4  than outside the trenches  4 . 
     A thermographic phosphor  7  has been applied to the base  6  of the trenches  4 . On irradiation with a suitable wavelength, this thermographic phosphor produces luminescence light, which can be detected using a suitable detector. Even if the thermal barrier coating  3  does not transmit the detected wavelength of the luminescence light, detection is nevertheless possible, since the trenches  4  allow the luminescence light to emerge from the thermographic phospor  7  into a defined spatial angle region without being impeded. The detector merely has to be arranged in this spatial angle region in order to be able to detect the luminescence light. 
     The text which follows gives examples of the material composition of the thermal barrier coating and of the thermographic phosphor  7 : 
     EXAMPLE 1 
     The thermal barrier coating  3  is made from a metal oxide in the form of a rare earth aluminate with the empirical formula Gd 0.25 La 0.75 AlO 3 . The thermographic phosphor is likewise made from a metal oxide in the form of a rare earth aluminate with the empirical formula Gd 0.25 La 0.75 AlO 3 . Unlike the material of the thermal barrier coating  3 , however, the material of the thermographic phosphor  7  is mixed with one mol % of europium oxide (Eu 2 O 3 ), with the europium functioning as an activator for the phosphor. When the thermographic phosphor  7  is excited with a wavelength of 254 nm, it-emits luminescence light with an emission maximum at approximately 610 nm. Alternatively, the activator used may also be one mol % of terbium (Tb). In this case, the thermographic phosphor  7  emits luminescence light with an emission maximum at approx. 544 nm. Other activators are possible. 
     EXAMPLE 2 
     The thermal barrier coating  3  is made from a pyrochlore. The pyrochlore is in particular a gadolinium zirconate with the empirical formula Gd 2 Zr 2 O 7 . The thermographic phosphor  7  is likewise made from this pyrochlore. Unlike the thermal barrier coating  3 , however, it is mixed with one mol % of europium oxide, the europium serving as an activator for the phosphor. Other activators are possible. 
     EXAMPLE 3 
     The thermal barrier coating  3  is made from a zirconium oxide (ZrO 2 ) stabilised with yttrium (Y). The thermographic phosphor  7  is likewise made from an yttrium-stabilized zirconium oxide, but the phosphor, unlike the thermal barrier coating  3 , is mixed with one mol % of Eu 2 O 3 , the europium serving as an activator for the phosphor. 
     As a second exemplary embodiment of a coated component according to the invention,  FIG. 5  shows a highly diagrammatic illustration of a turbine component  10 . 
     The turbine component  10  differs from the turbine component  1  only by virtue of the fact that trenches  11 ,  12  with different depths are present. The depths of the two trenches are in each case selected in such a way that none of the trenches reaches the base material  2  of the component. Moreover, different thermographic phosphors  13 ,  14  are present in the region of the trench bases  15 ,  16 . The statements which have been made in Examples 1 to 3 apply analogously to the material composition of the thermal barrier coating and of the thermographic phosphors. However, it should be noted that the thermographic phosphor  13  may differ from the thermographic phosphor  14 . 
     By way of example, the phosphor regions  13  and  14  may each be made from a metal oxide in the form of a rare earth aluminate with the empirical formula Gd 0.25 La 0.75 AlO 3 , the metal oxide of the thermographic phosphor  13  being mixed with one mol % of Eu 2 O 3 , whereas the metal oxide of the thermographic phosphor  14  is mixed with one mol % of Th. When the two thermographic phosphors  13 ,  14  are excited with laser light, two different emission wavelengths are then obtained, from which the temperature at the respective depth of the thermal barrier coating  3  can be determined. 
     As a third exemplary embodiment of a coated component according to the invention,  FIG. 6  shows a highly diagrammatic illustration of a turbine component  20 . 
     The turbine component  20  comprises a base material  2  and a thermal barrier coating  3 , to the properties of which the statements which have been made in connection with the first exemplary embodiment apply analogously. A further coating  21 , which likewise has thermal barrier properties, is arranged between the thermal barrier coating  3  and the base material  2  of the turbine component  20 . In particular, the coating  21  in the third exemplary embodiment is made from substantially the same material as the thermal barrier coating  3 , except that the material of the coating  21  is mixed with an activator, for example Th. Other activators are possible. 
     Recesses, for example in the form of trenches  24 , have been introduced into the thermal barrier coating  3 , extending as far as the coating  21  and uncovering the latter. 
     As a fourth exemplary embodiment of a coated component according to the invention,  FIG. 7  shows a highly diagrammatic illustration of a turbine component  30 . 
     The turbine component  30  comprises a base material  2  and a thermal barrier coating  3 , which substantially correspond to the base material  2  and the thermal barrier coating in the first exemplary embodiment. Unlike in the first exemplary embodiment, however, the thermal barrier coating  3  is doped with an activator. A suitable activator is, for example, terbium. The doping is mainly concentrated on a zone  32  which is located in a region of the thermal barrier coating  3  that faces the base material  2 . The doped zone  32  in particular does not extend as far as the surface  5  of the thermal barrier coating  3 . The terbium concentration in the doped zone comprises a few mol %, for example 1 mol %. 
     Trenches  34  have been introduced into the thermal barrier coating  3 , extending as far as the doped zone  32  and exposing the latter in the region of the trench bases  36 . 
     As a fifth exemplary embodiment of a coated component according to the invention,  FIG. 8  shows a highly diagrammatic illustration of a turbine component  40 . The turbine component  40  largely corresponds to the turbine component  20  from  FIG. 6 , the only difference being that it has a bond coat  41  (for example MCrAlX), which is arranged between the layer  21  and the base material of the turbine component  40 . The bond coat  41  is formed in particular as a metallic interlayer, for example in the form of a metal alloy layer. It is used to protect the base material  2  from corrosion and/or oxidation and to increase the bonding of the layer  21  on the base material  2  of the turbine component  40 . The materials properties of the thermal barrier coating  3  of the layer  21  and of the base material  2  correspond to those of the third exemplary embodiment. 
     A process for producing a coated component is illustrated by way of example in  FIGS. 9   a  to  9   e.    
     The result of this example is a coated component as described in the context of the fifth exemplary embodiment. 
     In a first step, an uncoated turbine component  50  is provided, consisting only of the base material ( FIG. 9   a ). A bond coat  51  is applied to the base material of the turbine component  50  ( FIG. 9   b ). Then, a metal oxide layer  52 , which is mixed with an activator, is applied to the bond coat  51 . Alternatively, instead of the metal oxide layer  52  it is also possible to apply a pyrochlore layer mixed with an activator ( FIG. 9   c ). In both cases, the material of the metal oxide layer  52  forms the thermographic phosphor. Finally, as the last layer, a thermal barrier coating  53  is applied to the layer  52 . It should be noted at this point that the layer  52  may also have thermal barrier properties. 
     In a final working step, trenches  55  are introduced into the thermal barrier coating  53  by means of a laser  54 . The depth of the trenches  55  and the width of the trenches  55  are set in such a manner by means of the laser beam that on the one hand the layer  52  is reached and on the other hand the trench geometry prevents the hot gas from directly attacking the layer  52  when the turbine component is operating in a gas turbine. 
     In the process according to the invention, it is also possible to dispense with the step of applying the bond coat  51  if the layer  52  is already sufficiently able to bond to the base material  50  of the turbine component. To ensure sufficient bonding, by way of example it is possible for the surface of the base material  50  to be roughened prior to the application of the layer  52 . 
       FIGS. 10   a  to  10   d  illustrate a second exemplary embodiment of a process for producing a coated component according to the invention. 
     Starting from a turbine component consisting only of base material  60  ( FIG. 10   a ), first of all a bond coat  61  is applied ( FIG. 10   b ), followed by application of a thermal barrier coating  62  ( FIG. 10   c ). After the thermal barrier coating  62  has been applied to the bond coat  61 , the thermal barrier coating  62  is doped with a suitable activator which converts the material of the thermal barrier coating  62  into a thermographic phosphor in the doped region. The doping may in this case be effected by ion bombardment with suitable elements. Energy, ion flux per unit area and duration of the doping operation are in this case selected in such a way as to form a doped zone  63  in a defined depth in the thermal barrier coating  62  ( FIG. 10   d ). A final process step involves introducing trenches  64  using a laser  65 . The depth of the trenches is in this case set in such a way that in the region of the trench bases the doped zone  63  of the thermal barrier coating  62  is uncovered. The width and depth of the trenches are also set in such a manner that during subsequent operation of the turbine component there is no attack from hot gas in the region of the trench bases. 
       FIG. 11  illustrates a modification of the second exemplary embodiment of a process for producing a coated component according to the invention. 
     Unlike in the production process illustrated with reference to  FIGS. 10   a  to  10   d , in the modification of the process, the thermal barrier coating  62  is only doped after the trenches  64  have been introduced. Moreover, prior to the introduction of the trenches  64 , a mask material  66  is deposited on the thermal barrier coating  62 . Therefore, prior to the doping, the trenches  64  extend both through the mask material  66  and also part way through the thermal barrier coating  62 . 
     After the trenches  64  have been produced, doping is carried out, which can be configured analogously to the doping in the second exemplary embodiment of the production process. The mask material  66  prevents the ions from penetrating into the regions of the thermal barrier coating  62  which are covered by the mask material  66 . Only in the region of the trenches  64  can the ions reach the material of the thermal barrier coating  62  and penetrate into the latter. The doped zones  63 ′ in the thermal barrier coating  62  are therefore concentrated on the regions below the trench bases  67 . 
     Further modifications to the production processes described are possible. For example, the first production process can be modified in such a way that the layer  52  is not produced. Instead, after the trenches have been produced, a layer of thermographic phosphor is deposited on the trench bases and fixed there, for example by being fired in. 
     Also, the trenches do not all have to be produced with the same depth. 
     The procedure involved in temperature measurement will now be described with reference to  FIG. 12  for the example of a guide vane  70  of a gas turbine. The gas turbine has a thermal barrier coating  71  and a portion  72  provided with trenches. A thermographic phosphor is arranged in the region of the trench bases. To measure the temperature, the thermographic phosphor is excited by means of UV radiation from a UV laser. In response to being excited by the laser radiation, the thermographic phosphor emits luminescence light, which is captured by means of a spectrometer  74  and converted into electrical signals by means of a photomultiplier  75  connected downstream. The electrical signals are output by the photomultiplier  75  to an analog/digital converter  76 , which converts them into digital signals and transmits them to a PC  77 . Finally, the spectrum of the luminescence light is evaluated in the PC  77 . 
     The measurement of the temperature in the thermal barrier coating  71  is effected, for example, using the intensity ratio of two wavelengths of the emission spectrum. Alternatively, it is also possible to use a pulsed laser beam, in which case the temperature in the thermal barrier coating is determined from the decay properties of the intensity. Suitable methods for determining the temperature of a thermal barrier coating from the emission spectrum of a thermographic phosphor are described in EP 1 105 550 B1. Therefore, reference is made to the methods described therein. 
     If the thermal barrier coating  71  has trenches of different depths and emission wavelenghths which originate from trenches of different depths can be distinguished from one another, the method can be used to determine the temperature in regions of the thermal barrier coating  71  which are at different distances from the surface of the coating. The heat flux flowing through the thermal barrier coating  71  can then be determined from the temperature measurements at different depths of the coating. 
     To allow the laser beam to be introduced and to allow the emission spectrum to be discharged, the housing of the gas turbine can be provided with suitable windows. 
     It should be noted that arranging the trenches at suitable locations on the coated component also increases the stability of the thermal barrier coating.