Abstract:
A honeycomb seal is provided. The honeycomb seal is in one part with a substrate so that there is no brazing is needed. Furthermore, a better corrosion resistance is gained by the substrate having a coating comprising iron, chromium, aluminum and/or yttrium, especially applied by vapour deposition. A method for producing a honeycomb seal is also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2009/061054, filed Aug. 27, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 02020602.5 EP filed Oct. 8, 2008. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a honeycomb seal and a method to produce it. 
       BACKGROUND OF INVENTION 
       [0003]    Honeycomb seals are utilized to minimize the leakage in gas pressures inside an engine particularly between stator and rotor of turbines. 
         [0004]    The current method of manufacture consists of casting a material with a defined recess. These pieces are called backing plates (substrate). 
         [0005]    Honeycomb materials are fabricated from very thin, light sheet metal pieces, welded and shaped to resemble the honeycomb of a honeybee. These structures are skived, a method of thin cutting, into thin sheets having the same depth as the recess which has been cast into the backing plates. The honeycomb pieces are then brazed into the recesses. Sometimes the honeycomb is filled with abrasive materials to lengthen the life. 
         [0006]    There are several problems with honeycomb seals. Since the brazing is at the bottom of the recess it is hidden and cannot be inspected readily. Occasionally a void in the braze occurs. These seals can then tear off and jump into vulnerable knife edge seals which have been prepared to interface with the honeycomb. In this way the seal fails. 
         [0007]    Secondly, the knife edge seals and the honeycombs are subjected to the corrosive atmosphere of the combustion gases in the engine. Particularly, the very thin honeycomb structures can be affected by sulfur in the fuel, suffering sulfidation. If they become embrittled, they may fracture and exit the engine, leaving the seal less effective at controlling gas pressures than before. For these reasons, there is a need for a more robust manufacturing method and a more corrosion resistance seal and seal material. 
       SUMMARY OF INVENTION 
       [0008]    It is therefore the task of the invention to overcome this problem. 
         [0009]    The problem is solved by a honeycomb cell seal according to the claims and a method to produce it by the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the dependent claims further advantageous embodiments of the invention are shown which can be combined arbitrarily with each other in order to get further advantages. 
           [0011]    It shows: 
           [0012]      FIG. 1  honeycomb cells, 
           [0013]      FIG. 2  schematically a way to produce a honeycomb seal, 
           [0014]      FIG. 3  a tool to produce on honeycomb seal, 
           [0015]      FIG. 4 ,  5  examples of honeycomb seals, 
           [0016]    FIG.  6 , 7 , 8 , 9 , 10 , 11  some embodiments of a honeycomb seal with a coating, 
           [0017]      FIG. 12  gas turbine 
           [0018]      FIG. 13  a blade in a perspective view and 
           [0019]      FIG. 14  a list of superalloys. 
       
    
    
       [0020]    The figures and the description are only embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0021]      FIG. 1  shows several honeycomb cells  13  which have the geometry of a honeycomb (hexagonal). 
         [0022]    One honeycomb cell  13  consists preferably of six side walls  10 . Two honeycomb cells  13  of a honeycomb seal have preferably a common side wall  10 . 
         [0023]      FIG. 2  shows schematically one inventive way to produce the honeycomb seal  1 . 
         [0024]    In one aspect of this invention, a substrate  4 , especially a casting  4  is made which has the identical outside dimensions as a casting in the state of the art, except that there is no recess to be filled with a fragile honeycomb material. In this case, the hexagonal shaped honeycomb cells are formed preferably by EDM machining, very preferably by repeated EDM machining, in the manner one accustomed to this technique would do. Because the seal and the casting are now monolithic, there are no opportunities for a braze process or any other connecting technology to fail. The seal overall is stronger. 
         [0025]    A substrate  4  which is preferably a steel or stainless steel has a thickness h. 
         [0026]    By machining this substrate  4 , preferably by EDM, the honeycomb cells  13  are produced by removing material from the outer surface  28  of the substrate  4 . Therefore the honeycomb cells  13  are in one part with the substrate  4 ′, which can be derived from the fact that the total height h of the honeycomb cells  13  together with the remaining height of the substrate  4 ′ with the honeycomb cells  13  has still the same thickness h. 
         [0027]    The honeycomb cells  13  are not brazed on the substrate  4 ′. 
         [0028]    In  FIG. 3  a complementary arrangement of honeycomb cells  13  is schematically shown which is preferably used as machining tool  25 . 
         [0029]    Such a tool  25  shows preferably several stamps  7  which have the same form as a pocket of one honeycomb cell  13  (hexagonal shape) with a certain gap  31  between the stamps  7 , which corresponds to the thickness of the side walls  10  of the honeycomb cell  13 . Because the honeycomb seal  22  has a curved form, e.g. a ring, the tool  25  is preferably also curved (not shown). 
         [0030]    Also only one stamp  7  can be used for EDM machining the seal. 
         [0031]    The honeycomb seal  16  can be produced on a ring  16  ( FIG. 4 ) or on ring segments  19  ( FIG. 5 ), which form together a ring  16 ′ which will be a similar ring as it is shown in  FIG. 4 . Both will be a part of a housing cooperating with moving parts like blades  120 . 
         [0032]    The segment  19  shows several honeycomb cells  13 . 
         [0033]    In addition following the EDM operation it is preferred to etch the total overall piece (substrate  4 ′) in an acid mixture to remove the EDM recast layer that is foamed by the EDM operation. There are several mixtures of acids for performing this operation. The acid mixture used is a function of the materials that the casting has been made. These techniques are well known by those who perform this art. One difference here is that preferably the principles of the direct DC coupling of the piece which has been cast will be utilizing. Principles of EDM machinery of a piece of graphite according to the principles in U.S. Pat. No. 6,294,072 B1 dated Sep. 25, 2001 are applying. 
         [0034]    It is preferably to perform the etching to remove as much recast as possible. 
         [0035]    Other tools for machining the honeycomb cells  13  into the substrate  4  like laser, electron beams are also possible. 
         [0036]    Following the etching, the substrate  4 ′ is preferably submitted to coating, especially a sequential CVD coating via vapor phase to convert the casting alloy from whatever its chemical constituents are preferably to a FeCrAlY. To perform this operation, it is preferably to shield the rear portions of the substrate from the CVD gases. 
         [0037]    The first CVD operation will preferably be to apply a large weight fraction of iron (Fe) to the hexagonal machined pockets, if the substrate is not iron-based, especially if it is Ni-based. Following this operation, then a vapor phase (CrAlY or Cr, Al, Y or Cr+Y, Al or Al+Y, Cr, . . . ) coating will be applied. This coating will preferably not utilize masking materials, because it is the desire to fully coat the piece all over. 
         [0038]    It was recognized that iron is a better getter or CrAlY is a better getter than Nickel based superalloys. This coating operation is preferably followed by a heat treatment for the purpose of ductilization and reformation of the basic and inherent γγ′ phases within the nickel based superalloy. 
         [0039]    In  FIG. 6  a partial cross section of a substrate  4 ′ with one honeycomb cell  13  is shown, which form a honeycomb seal  1 . 
         [0040]    According to the invention the sidewalls  10  comprise preferably a Fe-base metallic material, especially steel or stainless steel or a nickel based superalloy. 
         [0041]    This steel (as an exemplary example) is then exposed to alloying elements Cr, Al and Y ( FIG. 7 ) to form by diffusion a FeCrAlY, here a FeCrAlY diffusion area  8  inside the side wall  10  (FIG.  7 → FIG. 8 ). The diffusion area  8  is only a part of the side wall  10 . 
         [0042]    The diffusion can preferably also be throughout the wall  10  (FIG.  7 → FIG. 9 ). This means that nothing of the original composition of the side wall  10  is left. The sidewall  10 ′ especially consists of a FeCrAlY alloy. 
         [0043]    Preferably first chromium can be deposition followed by deposition of aluminum, especially doped with Yttrium (Y). 
         [0044]    Aluminizing can be performed preferably by the well known pack cementation process or other methods. 
         [0045]    Preferably Yttrium is coated together with aluminum. 
         [0046]    Preferably other alloying elements like Hafnium, titanium or silicon can be added. 
         [0047]    The alloying elements are preferably exposed to the substrate by a vapour process, preferably by CVD. 
         [0048]    During exposure the elements can be used together or one by one. 
         [0049]    Since iron is recognized as a getter for aluminum at least, then the addition of a thick aluminide coating or a thick chromide coating followed by an aluminide coating could be tailored to provide the correct chemistry to meet the composition of FeCrAlY inside the diffusion area ( 8 ). 
         [0050]    After a following heat treatment for diffusion, a relative soft and ductile steel of a honeycomb seal was converted into a relatively brittle FeCrAlY via CVD. 
         [0051]    The amount of Cr, Al and Y to be diffused into the substrate depends on the amount of Cr, Al (other base elements) already present in the substrate, especially the steel or Fe-based material. This can be controlled by exposure time, temperature and concentration. 
       EXAMPLES 
       [0052]    A: 
         [0000]    providing a substrate  4  with honeycomb cells  13 
 
aluminizing
 
optionally a heat treatment to promote diffusion of Al into substrate
 
chromizing
 
optionally a heat treatment to promote diffusion of Cr in Al and into substrate
 
         [0053]    B: 
         [0000]    providing a substrate  4  with honeycomb cells  13 
 
aluminizing
 
chromizing
 
a heat treatment to promote diffusion of Cr, Al
 
         [0054]    C: 
         [0000]    providing a substrate  4  with honeycomb cells  13  and with a braze between honeycomb  13 
 
cells and substrate  4 
 
chromizing
 
aluminizing
 
optionally a heat treatment to promote diffusion of Cr, Al
 
         [0055]    D: 
         [0000]    providing a substrate  4  with honeycomb cells  13  and with a braze between honeycomb  13 
 
cells and substrate  4 
 
aluminizing
 
chromizing
 
optionally a heat treatment to promote diffusion of Cr, Al
 
         [0056]    E: 
         [0000]    providing a substrate  4  with honeycomb cells  13 
 
chromizing
 
aluminizing
 
a heat treatment to promote diffusion of Cr, Al
 
         [0057]    F: 
         [0000]    providing a substrate  4  with honeycomb cells  13 
 
chromizing
 
optionally a heat treatment to promote diffusion of Al in substrate
 
aluminizing
 
optionally a heat treatment to promote diffusion of Cr in Al and into substrate
 
         [0058]    By this sequence the advantage of a ductile and easily to be manufactured steel can be used to form the honeycomb cells and adapt it into shrouds. After that a reduced ductility is not a problem anymore because no further bending or mechanical stresses due to manufacturing are induced. 
         [0059]    According to another example of the invention a protective FeCrAlY coating  7  is applied on the iron board sidewalls  10  ( FIG. 10 ) as an overlay coating. 
         [0060]    Both types of overlay and diffusion coating are also possible. 
         [0061]    The composition of the coating  7  or diffusion area  8  comprises chromium, aluminum (Al) and yttrium (Y) and balance M, especially iron (Fe). Especially the FeCrAlY alloy or coating  7  consists of Fe, Cr, Al and Y. 
         [0062]    Optionally the MCrAlY alloy or coating  7 ,  8  can contain titanium (Ti), Hafnium (Hf), and/or silicon (Si) which enhance the corrosion/oxidation behavior of the alloyed or coated steel. Hafnium (Hf) stabilizes the aluminum oxide which is formed on the outside surface of the MCrAlY alloy wherein silicon (Si) will permit the formation of an aluminum silicate phase. 
         [0063]    The phrase “contain” means that the amount of such an element is at least two times higher that the impurity level of this element in a MCrAlY alloy or at least two times higher than the measuring accuracy depending on which is higher. 
         [0064]    Especially the MCrAlY alloy or coating  7  consists of Fe, Cr, Al, Y and at least one element of the group Ti, Hf and/or Si. 
         [0065]    Preferred ranges of the elements (in wt %) are 18% to 35% Cr, 3% to 15% Al, 0,2% to 2% Yttrium and for the optional additions up to 3% titanium, up to 3% hafnium and/or up to 3% silicon. 
         [0066]    Adding the low side, the balance would be iron 80% by weight, and on the high side 39% by weight. 
         [0067]    All combinations with the optional elements are preferred embodiments: 
         [0068]    That means: MCrAlY, especially M=Fe: 
         [0000]    
       
         
           
             
               + 
               Ti 
             
             + 
             Hf 
             + 
             Si 
             + 
             Ti 
             + 
             Hf 
             + 
             Ti 
             + 
             Si 
             + 
             Hf 
             + 
             Si 
             + 
             Hf 
             + 
             Si 
             + 
             Ti 
             + 
             Hf 
             + 
             
               Si 
               . 
             
           
         
       
     
         [0069]    These seven combinations of the elements of the alloy can be on exclusive (consist) or non-exclusive (comprise) listing of the MCrAlY or coating  7 . 
         [0070]    The FeCrAlY coating  7  or diffusion area  8  preferably does not contain nickel (Ni) and/or does not contain cobalt (Co). 
         [0071]    The MCrAlY coating  7  can be applied by a coating or exposure process known in the state of the art by using the adequate alloy of MCrAlY or preferably by coating the elements Cr, Al and Y and/or the optional elements separately and fottning by diffusion this MCrAlY diffusion area. 
         [0072]    Especially, a CVD coating process is used to coat the honeycomb cells  13  of the honeycomb seals  1 . 
         [0073]    Especially, the honeycomb cell  13  can be filled with an abradable material, especially a ceramic  19  in order to have a further improvement of the abrasion behavior of the honeycomb seal  1  ( FIG. 11 ). 
         [0074]    The material of the side walls  10  of the honeycomb cells  1  is preferably steel or stainless steel. 
         [0075]      FIG. 12  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
         [0076]    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 , has a shaft  101  and is also referred to as the turbine rotor. 
         [0077]    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 . 
         [0078]    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  faint the turbine  108 . 
         [0079]    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 . 
         [0080]    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 . 
         [0081]    A generator (not shown) is coupled to the rotor  103 . 
         [0082]    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. 
         [0083]    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  110 , are subject to the highest thermal stresses. 
         [0084]    To be able to withstand the temperatures which prevail there, they can be cooled by means of a coolant. 
         [0085]    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). 
         [0086]    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 . 
         [0087]    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. 
         [0088]    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 . 
         [0089]    The Substrate  4  is a ring or segment of a ring in which the honeycomb cell structure is machined in. 
         [0090]    This removes the need of braise a honeycomb to a substrate and reduces the number of joints in this circumference and therefore producing the leakage paths. 
         [0091]      FIG. 13  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbo machine, which extends along a longitudinal axis  121 . 
         [0092]    The turbo machine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0093]    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 well as a blade or vane tip  415 . 
         [0094]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0095]    A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or disk (not shown) is foil led in the securing region  400 . 
         [0096]    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. 
         [0097]    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 . 
         [0098]    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 . 
         [0099]    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. 
         [0100]    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. 
         [0101]    Work pieces 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. 
         [0102]    Single-crystal work pieces 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 work piece, or solidifies directionally. 
         [0103]    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 work piece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire work piece 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. 
         [0104]    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). 
         [0105]    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 with regard to the solidification process. 
         [0106]    The blades or vanes  120 ,  130  may likewise 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 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 with regard to the chemical composition of the alloy. 
         [0107]    The density is preferably 95% of the theoretical density. 
         [0108]    A protective aluminum oxide layer (TGO=thermally grown oxide layer) forms on the MCrAlX layer (as an intermediate layer or an outermost layer). 
         [0109]    It is also possible for a thermal barrier coating, 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, which is preferably the outermost layer, to be present on the MCrAlX. 
         [0110]    The thermal barrier coating covers the entire MCrAlX layer. 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). 
         [0111]    Other coating processes are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include porous grains which have microcracks or macrocracks for improving its resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer. 
         [0112]    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).