Patent Publication Number: US-2013230659-A1

Title: Fine-porosity ceramic coating via spps

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2011/068225 filed Oct. 19, 2011 and claims benefit thereof, the entire content of which is hereby incorporated herein by reference. The International Application claims priority to the European application No. 10190672.5 EP filed Nov. 10, 2010, the entire contents of which is hereby incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     The invention relates to a thermal barrier layer which is applied by an SPPS (solution precursor plasma spray) process. 
     BACKGROUND OF INVENTION 
     Ceramic thermal barrier layers are frequently applied to components subject to very high thermal stress in order to increase the working temperatures. Here, the porosity plays an important role in the life of the protected ceramic layer. 
     SUMMARY OF INVENTION 
     It is therefore an object of the invention to indicate an improved ceramic layer having improved porosity. 
     The object is achieved by the features of the independent claim(s). 
     The dependent claims list further advantageous measures which can be combined with one another in any way in order to achieve further advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures show: 
         FIG. 1  a layer system, 
         FIG. 2  a turbine blade, 
         FIG. 3  a combustion chamber, 
         FIG. 4  a gas turbine, 
         FIG. 5  a list of superalloys. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The descriptions and figures merely represent examples of the invention. 
       FIG. 1  shows a layer system having a ceramic layer. 
     Such a layer system  1  is preferably a turbine blade  120 ,  130  of a turbine, in particular a gas turbine  100  ( FIG. 4 ), which is explained in more detail here as illustrating component. 
     The layer system  1  has a substrate  4 . The substrate is preferably made of a nickel-based superalloy ( FIG. 5 ). 
     The preferably metallic substrate  4  is preferably provided with a metallic bonding layer  7  to an outer ceramic layer  10 . However, there are also systems in which the ceramic layer  10  is applied directly to the substrate  4  which then also preferably has a diffusion layer in the substrate  4 . 
     A metallic bonding layer and corrosion protection layer  7  which preferably comprises an MCrAl(Y) alloy is preferably present. 
     The outer, in particular outermost, layer of the layer system  1  is the ceramic layer  10  which is present as a single layer or a double layer, with or without chemical gradients. 
     As material for the ceramic layer  10 , it is possible to use zirconium oxide or gadolinium zirconate or ytterbium zirconate, europium zirconate or lanthanum zirconate or mixed crystals. 
     Such a ceramic layer  10  is sprayed by means of a liquid precursor onto the substrate  4  or the metallic layer  7  is preferably sprayed by means of a plasma (SPPS). 
     The porosity in the range from 8% by volume to 25% by volume is set by use of salt solutions metered in different amounts. 
     The advantages of this coating method are a fine porosity distribution, the possibility of spraying nanoparticles and the easier setting of gradient composition. 
     As water-soluble salts for the SPPS process, preference is given to using the following starting materials: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Material 
                 water-soluble salts 
               
               
                   
                   
               
             
            
               
                   
                 for zirconium 
                 zirconium tetrachloride: ZrCl 4   
               
               
                   
                   
                 zirconium tetraiodide: Zrl 4   
               
               
                   
                   
                 zirconium nitrate pentahydrate: Zr(NO 3 ) 4 5H 2 O 
               
               
                   
                   
                 zirconium sulfate: Zr(SO 4 ) 2   
               
               
                   
                   
                 zirconium sulfate tetrahydrate: Zr(SO 4 ) 2 4H 2 O 
               
               
                   
                 for gadolinium 
                 gadolinium chloride: GdCl 3   
               
               
                   
                   
                 gadolinium chloride hexahydrate: GdCl 3 6H 2 O 
               
               
                   
                   
                 gadolinium bromide hexahydrate: GdBr 3 6H 2 O 
               
               
                   
                   
                 gadolinium iodide: GdI 3   
               
               
                   
                   
                 gadolinium nitrate hexahydrate: Gd(NO 3 ) 3 6H 2 O 
               
               
                   
                 for ytterbium 
                 ytterbium(II) chloride: YbCl 2   
               
               
                   
                   
                 ytterbium(III) chloride hexahydrate: YbCl 3 6H 2 O 
               
               
                   
                   
                 ytterbium(II) bromide: YbBr 2   
               
               
                   
                   
                 ytterbium(III) bromide: YbBr 3   
               
               
                   
                   
                 ytterbium(II) iodide: YbI 2   
               
               
                   
                   
                 ytterbium(III) iodide: YbI 3   
               
               
                   
                 for europium 
                 europium(II) chloride: EuCl 2   
               
               
                   
                   
                 europium(II) bromide: EuBr 2   
               
               
                   
                   
                 europium(III) bromide: EuBr 3   
               
               
                   
                   
                 europium(II) iodide: EuI 2   
               
               
                   
                   
                 europium(III) iodide: EuI 3   
               
               
                   
                   
                 europium(III) nitrate: Eu(NO 3 ) 3   
               
               
                   
                 for lanthanum 
                 lanthanum chloride heptahydrate: LaCl 3 7H 2 O 
               
               
                   
                   
                 lanthanum chloride: LaCl 3   
               
               
                   
                   
                 lanthanum bromide heptahydrate: LaBr 3 7H 2 O 
               
               
                   
                   
                 lanthanum iodide: LaI 3   
               
               
                   
                   
               
            
           
         
       
     
     For zirconium oxide, one or more of the salts for zirconium are employed. 
     For the zirconates, one or more salts for zirconium and one or more appropriate salts for Gd, La, Eu or Yb or mixtures (for mixed crystals) thereof are used. 
     Thus, for example, zirconium tetrachloride and gadolinium chloride or the hydrate are mixed with one another in one solution or by addition during spraying in order to obtain the elements gadolinium and zirconium as elements in the ceramic layer composed of a gadolinium zirconate. 
     The corresponding oxides (ZrO 2 , Gd—Zr—O, La—Zr—O, . . . ) are formed by oxidation. 
     Instead of zirconium, it is also possible to use corresponding salts of hafnium in order to produce hafnium oxide or hafnates with Gd, La, Eu or Yb. 
       FIG. 2  shows a perspective view of a rotating blade  120  or guide blade  130  of a flow engine, which extends along a longitudinal axis  121 . 
     The flow engine can be a gas turbine of an aircraft or of a power station for electricity generation, a steam turbine or a compressor. 
     The blade  120 ,  130  has, in succession along the longitudinal axis  121 , a fastening region  400 , an adjoining blade platform  403  and a blade body  406  and a blade tip  415 . 
     As guide blade  130 , the blade  130  can have a further platform (not shown) as its blade tip  415 . 
     A blade base  183  which serves for fastening the rotating blades  120 ,  130  to a shaft or a plate (not shown) is formed in the fastening region  400 . 
     The blade base  183  is, for example, configured as a hammer head. Other configurations as fir-tree or swallowtail base are possible. 
     The blade  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the blade body  406 . 
     In the case of conventional blades  120 ,  130 , solid metallic materials, in particular superalloys, are, for example, used in all regions  400 ,  403 ,  406  of the blade  120 ,  130 . 
     Such superalloys 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. 
     The blade  120 ,  130  can have been manufactured by a casting process, including by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
     Workpieces having a single-crystal structure or structures are used as components for engines which are subjected to high mechanical, thermal and/or chemical stresses in operation. 
     The manufacture of such single-crystal workpieces is carried out by, for example, directional solidification from the melt. The processes employed here are casting processes in which the liquid metallic alloy solidifies to form a single-crystal structure, i.e. a single-crystal workpiece, or directionally. 
     Here, dendritic crystals are aligned along the heat flow and form either a stem-like crystalline grain structure (columnar, i.e. grains which run along the entire length of the workpiece and are referred to here, in accordance with generally used terminology, as directionallysolidified) or a single-crystal structure, i.e. the entire workpiece consists of a single crystal. In these processes, the transition to globulitic (polycrystalline) solidification has to be avoided since transverse and longitudinal grain boundaries are necessarily formed as a result of polydirectional growth, and these nullify the good properties of the directionally solidified or single-crystal component. 
     When directionally solidified microstructures are spoken of in general, what is meant encompasses both single crystals which have no grain boundaries or at most small-angle grain boundaries and also stem-like crystal structures which have grain boundaries running in the longitudinal direction but no transverse grain boundaries. These second crystalline structures mentioned are also referred to as directionally solidified structures. 
     Such processes are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
     The blades  120 ,  130  can likewise have coatings to protect against corrosion or oxidation, e.g. (MCrAlX; M is at least one element from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and is yttrium (Y) and/or silicon and/or at least one element of the rare earths, or hafnium (Hf)). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
     The density is preferably 95% of the theoretical density. 
     A protective aluminum oxide layer (TGO=thermal grown oxide layer) is formed (as intermediate layer or as outermost layer) on the MCrAlX layer. 
     The layer composition preferably comprises Co-30Ni-28Cr-8Al-0.6Y-0.75i or Co-28Ni-24Cr-10Al-0.6Y. Apart from these cobalt-based protective layers, preference is also given to using nickel-based protective layers such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re. 
     A thermal barrier layer can be additionally present on the MCrAlX and is then preferably the outermost layer and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. it is not stabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
     The thermal barrier layer covers the entire MCrAlX layer. Stem-like grains are produced in the thermal barrier layer by means of suitable coating processes, e.g. electron beam vaporization (EB-PVD). 
     Other coating processes are conceivable, e.g. atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier layer can have porous, microcrack- or macrocrack-containing grains to improve the thermal shock resistance. The thermal barrier layer is thus preferably more porous than the MCrAlX layer. 
     Refurbishment means that components  120 ,  130  optionally have to be freed of protective layers (e.g. by sand blasting) after use. Removal of the corrosion and/or oxidation layers or products is then carried out. Cracks in the component  120 ,  130  are optionally also repaired. This is followed by recoating of the component  120 ,  130  and renewed use of the component  120 ,  130 . 
     The blade  120 ,  130  can be hollow or solid. If the blade  120 ,  130  is to be cooled, it is hollow and optionally also has film cooling holes  418  (indicated by broken lines). 
       FIG. 3  shows a combustion chamber  110  of a gas turbine. The combustion chamber  110  is, for example, configured as an annular combustion chamber in which a plurality of burners  107  arranged in the circumferential direction around an axis of rotation  102  open into a common combustion chamber space  154 , producing flames  156 . 
     For this purpose, the combustion chamber  110  in its totality is configured as an annular structure positioned around the axis of rotation  102 . 
     To achieve a comparatively high efficiency, the combustion chamber  110  is designed for a comparatively high temperature of the working medium M of from about 1000° C. to 1600° C. To make a comparatively long operating life possible even at these operating parameters which are unfavorable for the materials, the combustion chamber wall  153  is provided on its side facing the working medium M with an interior lining made up of heat shield elements  155 . 
     Each heat shield element  155  composed of an alloy is provided on the working medium side with a particularly heat-resistant protective layer (MCrAlX layer and/or ceramic coating) or is made of high-temperature-resistant material (solid ceramic bricks). 
     These protective layers can be similar to the turbine blades, i.e., for example, in MCrAlX: M is at least one element from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and is yttrium (Y) and/or silicon and/or at least one element of the rare earths, or hafnium (Hf). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
     A ceramic thermal barrier layer, for example, can be additionally present on the MCrAlX and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. it is not stabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
     Stem-shaped grains are produced in the thermal barrier layer by suitable coating processes, e.g. electron beam vaporization (EB-PVD). 
     Other coating processes are conceivable, e.g. atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier layer can have porous, microcrack- or macrocrack-containing grains to improve thermal shock resistance. 
     Refurbishment means that heat shield elements  155  optionally have to be freed of protective layers (e.g. by sand blasting) after use. Removal of the corrosion and/or oxidation layers or products is then carried out. Cracks in the heat shield element  155  are optionally also repaired. This is followed by recoating of the heat shield elements  155  and renewed use of the heat shield elements  155 . 
     Owing to the high temperatures in the interior of the combustion chamber  110 , a cooling system can additionally be provided for the heat shield elements  155  or for their holders. The heat shield elements  155  are then, for example, hollow and optionally also have cooling holes (not shown) opening into the combustion chamber space  154 . 
       FIG. 4  shows, by way of example, a gas turbine  100  in a longitudinal partial section. 
     The gas turbine  100  has, in its interior, a rotor  103  which is rotatably mounted around an axis of rotation  102  and has a shaft  101 , which is also referred to as turbine rotor. 
     Along the rotor  103  there are, in succession, an intake housing  104 , a compressor  105 , a for example torus-like combustion chamber  110 , in particular an annular combustion chamber, having a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust gas housing  109 . 
     The annular combustion chamber  110  communicates with a for example annular hot gas channel  111 . There, for example, four turbine stages  112  connected in series form the turbine  108 . 
     Each turbine stage  112  is, for example, made up of two rings of blades. Viewed in the flow direction of a working medium  113 , a row of guide blades  115  is followed by a row  125  made up of rotating blades  120  in the hot gas channel  111 . 
     The guide blades  130  are fastened to an inner housing  138  of a stator  143 , while the rotating blades  120  of a row  125  are, for example, attached by means of a turbine disk  133  to the rotor  103 . 
     A generator or a working machine (not shown) is coupled to the rotor  103 . 
     During operation of the gas turbine  100 , air  135  is drawn in through the intake housing  104  by the compressor  105  and compressed. The compressed air provided at the turbine end of the compressor  105  is conveyed to the burners  107  and mixed there with a fuel. The mixture is then burnt in the combustion chamber  110  to form the working medium  113 . From there, the working medium  113  flows along the hot gas channel  111  past the guide blades  130  and the rotating blades  120 . At the rotating blades  120 , the working medium  113  is decompressed to impart momentum, so that the rotating blades  120  drive the rotor  103  and the latter drives the working machine coupled thereto. 
     The components exposed to the hot working medium  113  are subject to thermal stresses during operation of the gas turbine  100 . The guide blades  130  and rotating blades  120  of the first, viewed in the flow direction of the working medium  113 , turbine stage  112  and also the heat shield elements lining the annular combustion chamber  110  are subject to the greatest thermal stresses. 
     In order to withstand the temperatures prevailing there, these components can be cooled by means of a cooling medium. 
     Likewise, substrates of the components can have an oriented structure, i.e. they are single crystals (SX structure) or have only longitudinally oriented grains (DS structure). 
     Materials used for the components, in particular for the turbine blade  120 ,  130  and components of the combustion chamber  110  are, for example, iron-, nickel- or cobalt-based superalloys. 
     Such superalloys are known, for example, from EP 1 204 776 B 1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
     The blades  120 ,  130  can likewise have coatings to protect against corrosion (MCrAlX; M is at least one element of the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and is yttrium (Y) and/or silicon, scandium (Sc) and/or at least one element of the rare earths or hafnium). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
     A thermal barrier layer can be additionally present on the MCrAlX and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. it is not stabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
     Stem-like grains are produced in the thermal barrier layer by suitable coating processes, e.g. electron beam vaporization (EB-PVD). 
     The guide blade  130  has a guide blade base (not shown here) facing the interior housing  138  of the turbine  108  and a guide blade head opposite the guide blade base. The guide blade head faces the rotor  103  and is fixed to a fastening ring  140  of the stator  143 .