Abstract:
A pyrochlore ceramic material and a thermal barrier coating containing pyrochlore ceramic materials are provided. Using the thermal barrier coating in a single or double layer which includes magnesium and/or titanium can improve the spallation behaviour and the thermal expansion coefficient of the component onto which the thermal barrier coating is applied.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2007/056188, filed Jun. 21, 2007 and claims the benefit thereof The International Application claims the benefits of European Patent Office application No. 06020703.2 EP filed Oct. 2, 2006, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to pyrochlore materials and thermal barrier coatings with these pyrochlore materials. 
       BACKGROUND OF INVENTION 
       [0003]    Metallic components which are exposed to a high temperature must be protected against heat and corrosion. This is especially needed for parts of gas turbines like combustions chambers, turbine blades or vanes. These parts are commonly coated with an intermediated MCrAlY-layer and a ceramic thermal barrier coating (TBC) which is applied on top of the intermediate layer. 
         [0004]    It is known to use either Gd 2 Zr 2 O 7  or Gd 2 Hf 2 O 7  as thermal barrier coating. 
         [0005]    EP 0 992 603 A1 discloses (Gd, La, Y) 2  (Ti, Zr, Hf) 2  O 7  pyrochlore structures. 
         [0006]    EP 1 321 542 A1 discloses an oxide mixture of Gd 2 O 3  and HfO 2 , wherein Hafnia or gadolinia can be replaced by oxides like Zirconia, Samaria, Europia, Ytterbia or neodynia. 
       SUMMARY OF INVENTION 
       [0007]    These materials known in the state of art can also be further improved according to their thermal expansion coefficient and spallation behaviour. 
         [0008]    It is therefore the aim of the invention to solve the problem mentioned above. 
         [0009]    The problem is solved by the pyrochlore materials as given in claim  1  and a thermal barrier coating as given in claim  17 ,  19 . 
         [0010]    In the dependent claims further advantages of the invention are listed whereby the dependent claims can be combined with each other in order to achieve further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    It shows 
           [0012]      FIG. 1 ,  2  examples of layer systems, 
           [0013]      FIG. 3  a gas turbine, 
           [0014]      FIG. 4  a turbine blade or vane, 
           [0015]      FIG. 5  a combustion chamber and 
           [0016]      FIG. 6  list of superalloy. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0017]    The inventive pyrochlore material comprises: 
         [0000]      Gd 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Hf y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y-z Zr y Ti z O 7-a , 
         [0000]    wherein Gd can preferably be replaced by Sm, especially totally replaced by Sm: 
         [0000]      Sm 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-z Hf z O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Sm 2 Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y-z Zr z Ti y O 7-a    
         [0000]    with 0&lt;x&lt;2; 0&lt;y&lt;2; 0≦a≦1; 0&lt;z&lt;2; y+z&lt;2. 
         [0018]    The magnesium (Mg) can preferably be replaced by Calzium (Ca). Titanium (Ti) can preferably be replaced by Aluminium (Al). Gd 2 Zr 2-x Ti x O 7  and Sm 2-x Mg x Zr 2 O 7-a  are not claimed as pyrochlore materials. 
         [0019]    Especially the pyrochlore material consists of one of the following materials: 
         [0000]      Gd 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Hf y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y-z Zr y Ti 3 O 7-a , 
         [0000]    wherein Gd can preferably be replaced by Sm, especially totally replaced by Sm: 
         [0000]      Sm 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-z Hf z O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y-z Zr z Ti y O 7-a    
         [0000]    with 0&lt;x&lt;2; 0&lt;y&lt;2; 0≦a≦1; 0&lt;z&lt;2; y+z&lt;2. 
         [0020]    Gadolinium (Gd) or Samarium (Sm) can be replaced by Neodynium (Nd) or Europium (Eu), Ytterbium (Yb), especially totally replaced by Nd, Eu or Yb. 
         [0021]    In  FIG. 1  a component  1 ,  120 ,  130  ( FIG. 3 ,  4 ),  155  ( FIG. 5 ) is shown which comprises a substrate  4 . The substrate  4  can be a nickel- or cobalt-based super alloy. Especially a nickel-based super-alloy is used ( FIG. 6 ). 
         [0022]    On this substrate  4 , especially direct on the substrate  4  a bonding and/or protective layer  7  is applied, especially a MCrAlX-layer is used, which forms or has an oxide layer (TGO). Especially Yttrium is used (X=Y). 
         [0023]    On this intermediate layer  7  an outer single layered ceramic thermal barrier  10  coating (TBC)  10  is applied. 
         [0024]    This thermal barrier coating  10  comprises preferably one of the materials like: 
         [0000]      Gd 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Hf y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y-z Zr y Ti 3 O 7-a , 
         [0000]    wherein Gd can be replaced by Sm, especially totally replaced by Sm: 
         [0000]      Sm 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-z Hf z O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y-z Zr z Ti y O 7-a    
         [0000]    with 0&lt;x&lt;2; 0&lt;y&lt;2; 0≦a≦1; 0&lt;z&lt;2; y+z&lt;2, 
         [0025]    Gadolinium Gd) or Samarium (Sm) can be replaced by Neodynium (Nd), Europium (Eu) or by Ytterbium (Yb). Also mixtures of these materials are possible. Gd 2 Zr 2-x Ti x O 7  and Sm 2-x Mg x Zr 2 O 7-a  are not claimed as pyrochlore materials in a single layered system. 
         [0026]    Especially the thermal barrier coating  10  preferably consists of one of the materials: 
         [0000]      Gd 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Hf z O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y-z Zr y Ti z O 7-a , 
         [0000]    wherein Gd can preferably be replaced by Sm, especially totally replaced by Sm: 
         [0000]      Sm 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-z Hf z O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y-z Zr z Ti y O 7-a    
         [0000]    with 0&lt;x&lt;2; 0&lt;y&lt;2; 0≦a≦1; 0&lt;z&lt;2;y+z&lt;2. 
         [0027]    The magnesium (Mg) can preferably be replaced by Calzium (Ca). Titanium (Ti) can preferably be replaced by Aluminium (Al). 
         [0028]      FIG. 2  shows a layered ceramic barrier coating  19 , especially a two layered system which comprises, especially consists of an inner ceramic thermal barrier  13  and an outer ceramic thermal barrier  16 . Especially the ceramic thermal barrier coating  16  is the outermost coating of the layered system. 
         [0029]    The inner ceramic thermal barrier coating  13  comprises one of the materials 
         [0000]      Sm 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-z Hf z O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y-z Zr z Ti y O 7-a    
         [0000]    with 0&lt;x&lt;2; 0&lt;y&lt;2; 0≦a≦1; 0&lt;z&lt;2; y+z&lt;2. 
         [0030]    Especially the inner TBC  13  consists of one of the materials Sm 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Zr 2-z Hf z O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Zr 2-y Ti y O 7-a  or 
         [0000]      Sm 2 Hf 2-y-z Zr z Ti y O 7-a    
         [0000]    with 0&lt;x&lt;2; 0&lt;y&lt;2; 0≦a≦1; 0&lt;z&lt;2; y+z&lt;2. 
         [0031]    Especially a=x/2 is chosen. The magnesium (Mg) can preferably be replaced by Calzium (Ca). Titanium (Ti) can preferably be replaced by Aluminium (Al). The titanium (Ti) leads to reduction of spallation of the ceramic coating. The Mg leads to an adaptation of the thermal expansion coefficient to the coefficients of the superalloys and/or metallic layers. 
         [0032]    The inner ceramic thermal barrier coating  13  can also comprise or consist of YSZ. 
         [0033]    The outer ceramic thermal barrier  16  coating comprises 
         [0000]      Gd 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Hf z O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y-z Zr y Ti z O 7-a  or 
         [0000]      Gd 2 Zr 2-x Ti x O 7-a  or 
         [0000]      Gd 2 Hf 2-y Ti y O 7-a . 
         [0000]    Especially the outer TBC  16  consists of one of the materials Gd 2-x Mg x Zr 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Ti 2 O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Zr 2-y Hf z O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y Ti y O 7-a  or 
         [0000]      Gd 2-x Mg x Hf 2-y-z Zr z Ti y O 7-a  or 
         [0000]      Gd 2 Hf 2-y-z Zr y Ti z O 7-a  or 
         [0000]      Gd 2 Zr 2-x Ti x O 7-a  or 
         [0000]      Gd 2 Hf 2-y Ti y O 7-a . 
         [0034]    Titanium (Ti) can preferably be replaced by Aluminium (Al). 
         [0035]    In the layer system similar to  FIG. 1  or  FIG. 2  the ceramic barrier coating  10 ,  13 ,  16  can have a gradient in the composition. The gradient in the composition can be achieved by increasing or decreasing the values for the parameter x, y, z. 
         [0036]    The composition can also change especially gradually from Gd 2-x Mg x Hf 2 O 7-a  to Gd 2-x Mg x Hf 2-y Ti y O 7-a  and finally at the outermost surface area to Gd 2 Hf 2-y Ti y O 7-a . 
         [0037]      FIG. 1  shows a layer system  1  according to the invention. 
         [0038]    The layer system  1  comprises a metallic substrate  4 , which in particular for components used at high temperatures consists of a nickel-base or cobalt-base superalloy. 
         [0039]    Directly on the substrate  4  there is a metallic bonding layer  7 , which consists either of
       11 wt %-13 wt % cobalt, 20 wt %-22 wt % chromium, 10.5 wt %-11.5 wt %
 
aluminum,
   0.3wt %-0.5 wt % yttrium, 1.5 wt %-2.5 wt % rhenium, remainder nickel, or   24 wt %-26 wt % cobalt, 16 wt %-18 wt % chromium, 9.5 wt %-11 wt %
 
aluminum,
   0.3 wt %-0.5 wt % yttrium, 0.5 wt %-2 wt % rhenium, remainder nickel.       
 
         [0044]    Even before the application of further ceramic layers, an aluminum oxide layer has formed on this metallic bonding layer  7 , or an aluminum oxide layer of this type is formed during operation. A fully or partially stabilized zirconium oxide layer can be present as inner ceramic layer  10  on the metallic bonding layer  7  or on the aluminum oxide layer (not shown). It is preferable to use yttrium-stabilized zirconium oxide. It is also possible to use calcium oxide, cerium oxide or hafnium oxide to stabilize zirconium oxide. The zirconium oxide is preferably applied as a plasma-spray layer, but also may be applied as a columnar structure by means of electron beam physical vapor deposition. 
         [0045]      FIG. 3  shows, by way of example, a partial longitudinal section through a gas turbine  100 . In the interior, the gas turbine  100  has a rotor  103  which is mounted such that it can rotate about an axis of rotation  102  and has a shaft  101  and is also referred to as the turbine rotor. 
         [0046]    An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular an annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas housing  109  follow one another along the rotor  103 . The annular combustion chamber  110  is in communication with a, for example, annular hot-gas passage  111 , where, by way of example, four successive turbine stages  112  form the turbine  108 . Each turbine stage  112  is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium  113 , in the hot-gas passage  111  a row of guide vanes  115  is followed by a row  125  formed from rotor blades  120 . 
         [0047]    The guide vanes  130  are secured to an inner housing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are fitted to the rotor  103  for example by means of a turbine disk  133 . A generator (not shown) is coupled to the rotor  103 . 
         [0048]    While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake housing  104  and compresses it. The compressed air provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mix is then burnt in the combustion chamber  110 , forming the working medium  113 . From there, the working medium  113  flows along the hot-gas passage  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. 
         [0049]    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 elements which line the annular combustion chamber  110 , are subject to the highest thermal stresses. To be able to withstand the temperatures which prevail there, they may 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-base, nickel-base or cobalt-base 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 with regard to the chemical composition of the alloys. 
         [0050]    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 and/or hafnium). 
         [0051]    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 with regard to the chemical composition. 
         [0052]    A thermal barrier coating may also be present on the MCrAlX, consisting, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0053]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0054]    The guide vane  130  has a guide vane root (not shown here) facing the inner housing  138  of the turbine  108  and a guide vane head 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 . 
         [0055]      FIG. 4  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0056]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0057]    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 . 
         [0058]    A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or a 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 as a fir-tree root 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 . 
         [0059]    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 or vane  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 with regard to the chemical composition of the alloy. 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. 
         [0060]    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 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 component. 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 present disclosure. 
         [0061]    The blades or vanes  120 ,  130  may also have coatings protecting against corrosion or oxidation, e.g. (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 stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (HO). 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 with regard to the chemical composition of the alloy. 
         [0062]    There may also be a thermal barrier coating consisting, for example, of ZrO 2 , Y 2 O 4 —ZrO 3 , i.e. unstabilized, partially stabilized or fully 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 suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0063]    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. 
         [0064]    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  (illustrated in dashed lines).