Abstract:
Conventional methods for producing a hole in a component make use of special lasers with short laser pulse lengths. The aim of the invention is to reduce the time and money required for producing a hole. According to the inventive method, the laser pulse lengths are varied, short laser pulse lengths only being used in the area to be removed in which an influence on the throughflow or exhaust behavior is noticeable. This is, e.g., the inner surface of a diffuser of a hole that can be produced in a very precise manner using short laser pulse lengths.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2005/057030, filed Dec. 21, 2005 and claims the benefit thereof. The International Application claims the benefits of European application No. 05000729.3 filed Jan. 14, 2005, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a method for producing a hole by means of pulsed energy beams in a component, and to a device with lasers. 
       BACKGROUND OF THE INVENTION 
       [0003]    With many components, especially with cast parts, cut-outs, like recesses or through-holes, have to be subsequently produced. Especially with turbine components, which have film cooling holes for cooling, holes are subsequently added after producing the component. 
         [0004]    Such turbine components often also have coatings, like, for example, a metallic coating or intermediate coating and/or a ceramic outer coating. The film cooling holes then have to be produced through the coatings and the substrate (cast part). 
         [0005]    U.S. Pat. No. 6,172,331 and also U.S. Pat. No. 6,054,673 disclose a laser boring method in order to add holes in coating systems, wherein ultrashort laser pulse lengths are used. A laser pulse length is selected from a defined laser pulse length range, and the hole is produced by it. 
         [0006]    DE 100 63 309 A1 discloses a method for producing a cooling air opening by means of a laser, in which the laser parameters are adjusted so that material is removed by sublimating. 
         [0007]    U.S. Pat. No. 5,939,010 discloses two alternative methods for producing a plurality of holes. In the one method (FIG. 1, 2 of the US-PS), one hole is first completely produced before the next hole is produced. In the second method, the holes are produced in steps, by a first section of a first hole first being produced, then a first section of a second hole being produced, and so on (FIG. 10 of the US-PS). In this case, different pulse lengths can be used in the two methods, but the same pulse lengths are always used within one method. The two methods cannot be linked together. The cross sectional area of the region from which material is to be removed always corresponds to the cross section of the hole which is to be produced. 
         [0008]    U.S. Pat. No. 5,073,687 discloses the use of a laser for producing a hole in a component which is formed from a substrate with copper coating on both sides. In this case, a hole is first produced through a copper film by means of longer pulse durations, and then, by means of shorter pulses, a hole is produced in the substrate, which comprises a resin, wherein a hole is then produced through a copper coating on the rear side with higher power output of the laser. The cross sectional area of the region which has material removed corresponds to the cross section of the hole which is to be produced. 
         [0009]    U.S. Pat. No. 6,479,788 B1 discloses a method for producing a hole, in which in a first step longer pulse lengths are used than in a further step. The pulse duration is varied in this case, in order to produce as good as possible a rectangular shape in the hole. In this case, the cross sectional area of the beam is also increased with decreasing pulse length. 
         [0010]    The use of such ultrashort laser pulses is expensive and very time intensive on account of their low average power outputs. 
       SUMMARY OF INVENTION 
       [0011]    It is the object of the invention, therefore, to overcome this problem. 
         [0012]    The object is achieved by a method in which different pulse lengths are used, wherein an energy beam is moved in the case of the shorter pulse lengths. 
         [0013]    It is especially advantageous if shorter pulses are used only in one of the first material removal steps in order to produce optimum characteristics in an outer upper region of the joint face, since these are crucial for the outflow behavior of a medium from the hole and also for the flow circulating behavior of a medium around this hole. Inside the hole, the characteristics of the joint face are rather non-critical, so that longer pulses, which can create inhomogeneous joint faces, can be used there. 
         [0014]    It is a further object to set forth a device by which the method can be simply and quickly implemented. 
         [0015]    This object is achieved by a device according to the claims. 
         [0016]    Further advantageous measures of the method or of the device are listed in the dependent claims of the method or of the device, as the case may be. 
         [0017]    The measures which are listed in the dependent claims can be combined with each other in an advantageous manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention is explained in more detail with reference to the figures. 
           [0019]    In the drawing 
           [0020]      FIG. 1  shows a hole in a substrate, 
           [0021]      FIG. 2  shows a hole in a coating system, 
           [0022]      FIG. 3  shows a plan view of a through-hole which is to be produced, 
           [0023]      FIGS. 4 to 11  show material removal steps of the method according to the invention, 
           [0024]      FIGS. 12-15  show pieces of equipment according to the invention in order to implement the method, 
           [0025]      FIG. 16  shows a turbine blade, 
           [0026]      FIG. 17  shows a gas turbine and 
           [0027]      FIG. 18  shows a combustion chamber. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]      FIG. 1  shows a component  1  with a hole  7 . 
         [0029]    The component  1  comprises a substrate  4  (for example a cast part, or DS or SX component, as the case may be). 
         [0030]    The substrate  4  can be metallic and/or ceramic. The substrate  4  consists of a nickel-based, cobalt-based or iron-based superalloy, especially in turbine components, like, for example, turbine rotor blades  120  or stator blades  130  ( FIGS. 16 ,  17 ), heat shield elements  155  ( FIG. 18 ), and also other casing components of a steam turbine or gas turbine  100  ( FIG. 17 ), but also of an aircraft turbine. In the case of turbine blades for aircraft, the substrate  4  comprises, for example, titanium or a titanium-based alloy. 
         [0031]    The substrate  4  has a hole  7 , which for example is a through-hole. However, it can also be a blind hole. The hole  7  comprises a lower region  10  which originates from an inner side of the component  1  and which, for example, is formed symmetrically (for example circular, oval or rectangular-shaped), and an upper region  13  which is formed on an outer surface  14  of the substrate  4  as a diffuser  13 , if applicable. The diffuser  13  represents a widening of the cross section in relation to the lower region  10  of the hole  7 . 
         [0032]    The hole  7 , for example, is a film cooling hole. The inner surface  12  of the diffuser  13 , that is in the upper region of the hole  7 , should especially be smooth in order to enable an optimum outflow of a medium, especially an outflow of a cooling medium from the hole  7 , because unevenesses create unwanted turbulences and deflections. Appreciably lower demands are made on the quality of the hole surface in the lower region  10  of the hole  7 , since the flow behavior is only slightly influenced because of this. 
         [0033]      FIG. 2  shows a component  1 , which is constructed as a coating system. 
         [0034]    There is at least one coating  16  on the substrate  4 . This, for example, can be a metal alloy of the MCrAlX type, wherein M represents at least one element of the iron, cobalt or nickel group. X represents yttrium and/or at least one element of the rare earths. 
         [0035]    The coating  16  can also be ceramic. 
         [0036]    There can be yet another coating (not shown) on the MCrAlX coating, for example a ceramic coating, especially a thermal barrier coating (the MCrAlX coating is then an intermediate coating). 
         [0037]    The thermal barrier coating, for example, is a completely stabilized or partially stabilized zirconium oxide coating, especially an EB-PVD coating or plasma-sprayed (APS, LPPS, VPS), HVOF or CGS (cold gas spraying) coating. 
         [0038]    In this coating system  1 , a hole  7  with the lower region  10  and the diffuser  13  is also introduced. 
         [0039]    The aforesaid embodiments for producing the hole  7  apply to substrates  4  with and without a coating  16  or coatings  16 . 
         [0040]      FIG. 3  shows a plan view of a hole  7 . 
         [0041]    The lower region  10  could by produced by means of a cutting manufacturing method. However, in the case of the diffuser  13 , this would not be possible, or only possible at very great expense. 
         [0042]    The hole  7  can also extend at an acute angle to the surface  14  of the component  1 . 
         [0043]    Method 
         [0044]      FIGS. 4 ,  5  and  6  show material removal steps of the method according to the invention. 
         [0045]    According to the invention, energy beams  22  with different pulse lengths are used during the method. 
         [0046]    The energy beam can be an electron beam, laser beam or high pressure water jet. In the following, the use of a laser is only exemplarily dealt with. 
         [0047]    In one of the first material removal steps, shorter laser pulses (tpuls &lt;&lt;), which are less than or equal to 500 ns, especially less than or equal to 100 ns, are especially used. Laser pulse lengths in the region of picoseconds or femtoseconds can also be used. 
         [0048]    When using shorter laser pulses which are less than or equal to 500 ns (nanoseconds), especially less than or equal to 100 ns, almost no melting takes place in the region of the joint face. Therefore, no cracks are formed on the inner surface  12  of the diffuser  13 , and accurate, even geometries can be thus created. 
         [0049]    In one of the first material removal steps, a first section of the hole  7  is produced in the component  1 . This, for example, can at least partially or completely correspond to the diffuser  13  ( FIGS. 6 ,  9 ). The diffuser  13  for the most part is arranged in a ceramic coating. A shorter pulse length is especially used for producing the complete diffuser  13 . A constant shorter pulse length is especially used for producing the diffuser  13 . The time for producing the diffuser  13  in the method, for example, corresponds to the first material removal steps. 
         [0050]    When producing the diffuser  13 , a laser  19 ,  19 ′,  19 ″ with its laser beams  22 ,  22 ′,  22 ″ is moved back and forth in a lateral plane  43 , as it is shown, for example, in  FIG. 5 . The diffuser  13  is moved along a line of travel  9 , for example in meander-form, in order to remove material here in one plane (step  FIG. 4 , according to  FIG. 6 ). 
         [0051]    If a metallic intermediate coating or the substrate  4  is reached, longer laser pulse lengths (tpuls &gt;) which are greater than 100 ns, especially greater than 500 ns and especially up to 10 ms, are preferably, but not necessarily, used in order to produce the remaining lower region  10  of the hole, as it is shown in  FIG. 1  or  2 . 
         [0052]    The diffuser  13  is located at least for the most part in a ceramic coating, but it can also extend into a metallic intermediate coating  16  and/or into the metallic substrate  4 , so that even metallic material can be removed as well, in part, with shorter pulse lengths. For producing the lower region  10  of the hole  7 , mostly longer or completely longer, especially time-constant, laser pulses are especially used. The time for producing the lower region  10  corresponds to the last material removal steps in the method. 
         [0053]    When using longer laser pulses, the at least one laser  19 ,  19 ′,  19 ″ with its laser beams  22 ,  22 ′,  22 ″, for example is not moved back and forth in the plane  43 . Since the energy is distributed in the material of the coating  16  or of the substrate  4  on account of thermal conduction, and new energy is added by each laser pulse, material is extensively removed by material evaporation in a way that the surface in which the material is removed approximately corresponds to the cross sectional area A of the through-hole  7 ,  10  which is to be produced. This cross sectional area can be established by the energy power output and pulse duration, and also by the guiding of the laser beam. 
         [0054]    The laser pulse lengths of a single laser  19 , or a plurality of lasers  19 ′,  19 ″, for example can be continuously altered, for example from the beginning to the end of the method. The method begins with the removal of material on the outer surface  14 , and ends when reaching the desired depth of the hole  7 . 
         [0055]    The material, for example, is progressively removed in layers in planes  11  ( FIG. 6 ) and in an axial direction  15 . 
         [0056]    The pulse lengths can also be discontinuously altered. Two different pulse lengths are preferably used during the method. With the shorter pulse lengths (for example ≦500 ms), the at least one laser  19 ,  19 ′ is moved, and with the longer pulse lengths (for example 0.4 ms), for example it is not, because due to thermal conduction, the energy yield takes place anyway over a larger area than corresponding to the cross section of the laser beam. 
         [0057]    During machining, the remaining part of the surface can be protected by a powder coating, especially by masking according to EP 1 510593 A1. The powder (BN, ZrO2) and the grain size distribution according to EP 1 510 593 A1 are part of this disclosure. 
         [0058]    This is especially then sensible if a metallic substrate or a substrate with a metallic coating, yet which has no ceramic coating, is machined. 
         [0059]    Laser Parameters 
         [0060]    When using pulses with a defined pulse length, the power output of the laser  19 ,  19 ′,  19 ″, for example, is constant. 
         [0061]    With the longer pulse lengths, a power output of the laser  19 ,  19 ′,  19 ″ of several 100 Watts, especially 500 Watts, is used. 
         [0062]    With the shorter laser pulse lengths, a power output of the laser  19 ,  19 ′ of less than 300 Watts is used. 
         [0063]    A laser  19 ,  19 ′ with a wavelength of 532 nm, for example, is used only for producing shorter laser pulses. 
         [0064]    With the longer laser pulse lengths, a laser pulse duration of 0.4 ms and an energy (Joule) of the laser pulse of 6 J to 10 J, especially 8 J, are especially used, wherein a power output (Kilowatt) of 10 kW to 50 kW, especially 20 kW, is preferred. 
         [0065]    The shorter laser pulses have an energy in the one-digit or two-digit Millijoule range (mJ), preferably in the one-digit Millijoule range, wherein the power output used for the most part especially lies in the one-digit Kilowatt range. 
         [0066]    Number of Lasers 
         [0067]    One laser  19 , or two or more lasers  19 ′,  19 ″, as the case may be, can be used in the method, which are used simultaneously or consecutively. The similar or different lasers  19 ,  19 ′,  19 ″, for example, have different ranges with regard to their laser pulse lengths. In this way, for example a first laser  19 ′ can produce laser pulse lengths which are less than or equal to 500 ns, especially less than 100 ns, and a second laser  19 ″ can produce laser pulse lengths which are greater than 100 ns, especially greater than 500 ns. 
         [0068]    For producing a hole  7 , the first laser  19 ′ is used first. For further machining, the second laser  19 ″ is then used, or vice versa. 
         [0069]    When producing the through-hole  7 , even only one laser  19  can be used. A laser  19  is especially used which, for example, has a wavelength of 1064 nm and which can produce both the longer and the shorter laser pulses. 
         [0070]    Sequence of the Hole Regions which are to be Produced 
         [0071]      FIG. 7  shows a cross section through a hole  7 . 
         [0072]    In this case, a rough machining with laser pulse lengths which are greater than 100 ns, especially greater than 500 ns, is first carried out, and a fine machining with laser pulse lengths which are less than or equal to 500 ns, especially less than or equal to 100 ns, is carried out. 
         [0073]    The lower region  10  of the hole  7  is completely machined, and only one region of the diffuser  13  is machined, for the most part with a laser  19  which has laser pulse lengths which are greater than 100 ns, especially greater than or equal to 500 ns (first material removal steps). 
         [0074]    For completion of the hole  7  or of the diffuser  13 , as the case may be, only a thinner, outer edge region  28  in the region of the diffuser  13  has to be machined by means of a laser  19 ,  19 ′,  19 ″ which can produce laser pulse lengths which are less than or equal to 500 ns, especially less than 100 ns (last material removal steps). 
         [0075]    In this case, the laser beam is moved. 
         [0076]      FIG. 8  shows a plan view of a hole  7  of the component  1 . The different lasers  19 ,  19 ′,  19 ″ or the different laser pulse lengths of this laser  19 ,  19 ′,  19 ″, as the case may be, are used in different material removal steps. 
         [0077]    For example, a rough machining with large laser pulse lengths (&gt;100 ns, especially &gt;500 ns) is first carried out. As a result, the largest part of the hole  7  is produced. This inner region is identified by the designation  25 . Only an outer edge region  28  of the hole  7  or of the diffuser  13 , as the case may be, has to be removed in order to achieve the final dimensions of the hole  7 . 
         [0078]    In this case, the laser beam  22 ,  22 ′ is moved in the plane of the surface  14 . 
         [0079]    Not until the outer edge region  28  has been machined by means of a laser  19 ,  19 ′ with shorter laser pulse lengths (&lt;500 ns, especially &lt;100 ns), is the hole  7  or the diffuser  13  finished. 
         [0080]    The contour  29  of the diffuser  13  is consequently produced with shorter laser pulses, as a result of which the outer edge region  28  is removed in a finer and more accurate manner and so is free of cracks and fused areas. 
         [0081]    The material, for example, is removed in one plane  11  (perpendicular to the axial direction  15 ). 
         [0082]    With the longer pulse lengths, the cross section A of the region which is to be removed when producing the hole  7  can also be continuously reduced in the depth of the substrate  4  as far as A′, so that the outer edge region  28  in relation to  FIG. 7  is reduced ( FIG. 9 ). This is created by adjustments of energy and pulse duration. 
         [0083]    An alternative when producing the hole  7  is to first produce the outer edge region  28  with shorter laser pulse lengths (≦500 ns) to a depth in the axial direction  15  which partially or wholly corresponds to an extent of the diffuser  13  of the hole  7  in this direction  15  ( FIG. 10 , the inner region  25  is indicated by broken lines). 
         [0084]    In this case, the laser beam  22 ,  22 ′ in these first material removal steps is moved in the plane of the surface  14 . 
         [0085]    Therefore, almost no fused areas are produced in the region of the joint face of the diffuser  13  and no cracks are formed there, and accurate geometries can be produced in this way. 
         [0086]    Only then is the inner region  25  removed (last material removal steps) with longer laser pulse lengths (&gt;100 ns, especially &gt;500 ns). 
         [0087]    The method can be used with newly produced components  1 , which were cast for the first time. 
         [0088]    The method can also be used with components  1  which are to be refurbished. 
         [0089]    Refurbishment means that components  1  which were in use, for example are separated from coatings and after repair, like, for example, filling of cracks and removal of oxidation and corrosion products, are newly coated again. 
         [0090]    In this case, for example contaminants or coating material which was newly applied ( FIG. 11 ) and got into the holes  7 , are removed by a laser  19 ,  19 ′. Or special formings (diffusers) in the coating region are newly produced after recoating during the refurbishment. 
         [0091]    Refurbishment 
         [0092]      FIG. 11  shows the refurbishment of a hole  7 , wherein during coating of the substrate  4  with the material of the coating  16 , material is penetrated into the already existing hole  7 . 
         [0093]    For example, the deeper lying regions in the region  10  of the hole  7  can be machined with a laser which has laser pulse lengths which are greater than 100 ns, especially greater than 500 ns. These regions are identified by  25 . 
         [0094]    The more critical edge region  28 , for example in the region of the diffuser  13 , upon which there is contamination, is machined with a laser  19 ′ which has laser pulse lengths which are less than or equal to 500 ns, especially less than 100 ns. 
         [0095]    Device 
         [0096]      FIGS. 12 to 15  show exemplary devices  40  according to the invention in order to especially implement the method according to the invention. 
         [0097]    The devices  40  comprise at least one optical device  35 ,  35 ′, especially at least one lens  35 ,  35 ′ which directs at least one laser beam  22 ,  22 ′,  22 ″ onto the substrate  4  in order to produce the hole  7 . 
         [0098]    There are one, two or more lasers  19 ,  19 ′,  19 ″. 
         [0099]    The laser beams  22 ,  22 ′,  22 ″ can be guided towards the optical device  35 ,  35 ′ via mirrors  31 ,  33 . 
         [0100]    The mirrors  31 ,  33  are displaceable or rotatable, so that, for example, only one laser  19 ′,  19 ″ in each case can transmit its laser beams  22 ′ or  22 ″ onto the component  1  via the mirrors  31  or  33  and the lens  35 . 
         [0101]    The component  1 ,  120 ,  130 ,  155  or the optical device  35 ,  35 ′ or the mirrors  31 ,  33  are movable in one direction  43 , so that the laser beam  22 ,  22 ′, for example according to  FIG. 5 , is moved over the component  1 . 
         [0102]    The lasers  19 ,  19 ′,  19 ″, for example, can have a wavelength of either 1064 nm or 532 nm. The lasers  19 ′,  19 ″ can have different wavelengths: 1064 nm and 532 nm. With regard to pulse length, for example the laser  19 ′ is adjustable to pulse lengths of 0.1-5 ms; whereas the laser  19 ′ is adjustable to pulse lengths of 50-500 ns. 
         [0103]    By displacement of the mirrors  31 ,  33  ( FIG. 12 ,  13 ,  14 ), the beam of the laser  19 ′,  19 ″ with such laser pulse lengths can be coupled in each case into the component  1  via the optical device  35 , which are necessary, for example, in order to produce the outer edge region  28  or the inner region  25 . 
         [0104]      FIG. 12  shows two lasers  19 ′,  19 ″, two mirrors  31 ,  33  and an optical device in the form of a lens  35 . 
         [0105]    If, for example, the outer edge region  28  is first produced, according to  FIG. 6 , then the first laser  19 ′ with the shorter laser pulse lengths is coupled in. 
         [0106]    If then the inner region  25  is produced, then by movement of the mirror  31 , the first laser  19 ′ is decoupled, and by movement of the mirror  33 , the second laser  19 ″ with its longer laser pulse lengths is coupled in. 
         [0107]      FIG. 13  shows a similar device as in  FIG. 12 , however in this case there are two optical devices, in this case, for example, two lenses  35 ,  35 ′, which allow the laser beams  22 ′,  22 ″ of the lasers  19 ′,  19 ″ to be directed to different regions  15 ,  28  of the component  1 ,  120 ,  130 ,  155  simultaneously. 
         [0108]    If, for example, an outer edge region  28  is produced, the laser beam  22 ′ can be directed onto a first point of this sheath-form region  28 , and directed onto a second point which lies diametrically opposite the first point, so that the machining time is significantly shortened. 
         [0109]    The optical device  35  can be used for the first laser beams  22 ′, and the second optical device  35 ′ can be used for the second laser beams  22 ″. 
         [0110]    According to this device  40 , the lasers  19 ′,  19 ″ could be used consecutively or simultaneously with the same or different laser pulse lengths. 
         [0111]    In  FIG. 14 , there are no optical devices in the form of lenses, but only mirrors  31 ,  33 , which direct the laser beams  22 ′,  22 ″ onto the component  1  and by movement are used so that at least one laser beam  22 ′,  22 ″ is moved in one plane over the component. 
         [0112]    The lasers  19 ′,  19 ″ in this case can also be used simultaneously. 
         [0113]    According to this device  40 , the lasers  19 ′,  19 ″ could be used consecutively or simultaneously, with the same or different laser pulse lengths. 
         [0114]      FIG. 15  shows a device  40  with only one laser  19 , with the laser beam  22 , for example, being directed onto a component  1  via a mirror  31 . 
         [0115]    Also in this case, an optical device, for example in the form of a lens, is not necessary. The laser beam  22 , for example, is moved over the surface of the component  1  by movement of the mirror  31 . This is necessary when using shorter laser pulse lengths. With the longer laser pulse lengths, the laser beam  22  does not necessarily have to be moved, so that the mirror  31  is not moved like it is in the movement stage. 
         [0116]    In the same way, however, one lens or two lenses  35 ,  35 ′ can also be used in the device according to  FIG. 15  in order to direct the laser beam simultaneously onto different regions  25 ,  28  of the component  1 ,  120 ,  130 ,  155 . 
         [0117]    Components 
         [0118]      FIG. 16  shows in perspective view a rotor blade  120  or stator blade  130  of a turbomachine, which blade extends along a longitudinal axis  121 . 
         [0119]    The turbomachine can be a gas turbine of an aircraft or of a power plant for generation of electricity, a steam turbine, or a compressor. 
         [0120]    The blade  120 ,  130  has a fastening region  400 , a blade platform  403  which adjoins it, and also a blade airfoil  406 , which are arranged one after the other along the longitudinal axis  121 . 
         [0121]    As a stator blade  130 , the blade  130  can have an additional platform (not shown) at its blade tip  415 . 
         [0122]    In the fastening region  400 , a blade root  183  is formed, which serves for fastening of the rotor blades  120 ,  130  on a shaft or a disk (not shown). 
         [0123]    The blade root  183 , for example, is designed as an inverted T-root. Other developments as fir-tree roots or dovetail roots are possible. 
         [0124]    The blade  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the blade airfoil  406 . 
         [0125]    In conventional blades  120 ,  130 , for example solid metal materials, especially superalloys, are used in all regions  400 ,  403 ,  406  of the blade  120 ,  130 . 
         [0126]    Such superalloys, for example, are known from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these documents are part of the disclosure which refers to the chemical composition of the alloy. 
         [0127]    The blade  120 ,  130  in this case can be manufactured by means of a casting process, also by means of directional solidification, by means of a forging process, by means of a milling process, or by a combination of these processes. 
         [0128]    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. The manufacture of such single-crystal workpieces, for example, is carried out 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 thermal flux and form either a stalk-like crystal grain structure (columnar, i.e. grains which extend over the whole length of the workpiece, and which here, in accordance with the language customarily used, are referred to as directionally solidified), or a single-crystal structure, i.e. the whole workpiece comprises a single crystal. In these processes, the transition to globulitic (polycrystalline) solidification needs to be avoided, since as a result of non-directional growth transverse and longitudinal grain boundaries are inevitably formed, which negate the favorable characteristics of the directionally solidified or single-crystal component. 
         [0129]    If the text refers in general terms to directionally solidified microstructures, then this is to be understood as meaning both single crystals (5×), which have no grain boundaries or at most have small-angle grain boundaries, and also stalk-like crystal structures, which no doubt have grain boundaries which extend in the longitudinal direction but have no transverse grain boundaries. In these second-mentioned crystal structures, reference can also be made to directionally solidified microstructures (D9) (directionally solidified structures). Such processes are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these documents are part of the disclosure. 
         [0130]    Also, the blades  120 ,  130  can have coatings against corrosion or oxidation, for example (MCrAlX; M is at least one element of the iron (Fe), cobalt (Co), nickel (Ni) group, X is an active element and represents yttrium (Y) and/or silicon and/or at least one element of the rare earths, or hafnium (Hf), as the case may be). 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, which are to be part of this disclosure which refers to the chemical composition of the alloy. 
         [0131]    There can still be a thermal barrier coating on the MCrAlX, and, for example, comprises ZrO 2 , Y 2 O 4 —ZrO 2 , i.e. it is not partially or completely stabilized by yttrium oxide and/or by calcium oxide and/or by magnesium oxide. 
         [0132]    By suitable coating processes, like, for example, electron beam physical vapor deposition (EB-PVD), stalk-shaped grains are created in the thermal barrier coating. 
         [0133]    Refurbishment means that components  120 ,  130 , after their use, if necessary need to be freed of protective coatings (for example, by sand-blasting). After that, removal of the corrosion and/or oxidation coatings, or products, as the case may be, is carried out. If necessary, cracks in the component  120 ,  130  are repaired as well. Then, recoating of the component  120 ,  130  and refitting of the component  120 ,  130  is carried out. 
         [0134]    The blade  120 ,  130  can be constructed hollow or solid. If the blade  120 ,  130  is to be cooled, it is hollow and, if necessary, still has film cooling holes  418  (shown by broken lines). 
         [0135]      FIG. 17  exemplarily shows a gas turbine  100  in a longitudinal partial section. 
         [0136]    Inside, the gas turbine  100  has a rotor  103 , also described as a turbine rotor, which is rotatably mounted around a rotational axis  102 . 
         [0137]    An intake duct  104 , a compressor  105 , a combustion chamber  110 , for example a toroidal combustion chamber, especially an annular combustion chamber  106 , with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust duct  109 , are arranged in series along the rotor  103 . 
         [0138]    The annular combustion chamber  106  communicates with a hot gas passage  111 , for example an annular hot gas passage. There, turbine stages  112 , for example four turbine stages, which are connected one behind the other, form the turbine  108 . 
         [0139]    Each turbine stage  112  is formed from two blade rings. Viewed in the flow direction of a working medium  113 , a row  125  which is formed from rotor blades  120  follows a stator blade row  115  in the hot gas passage  111 . 
         [0140]    The stator blades  130  in this case are fastened on an inner casing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are attached on the rotor  103 , for example by means of a turbine disk  133 . A generator or a driven machine (not shown) is coupled to the rotor  103 . 
         [0141]    During operation of the gas turbine  100 , air  135  is inducted by the compressor  105  through the intake duct  104 , and compressed. The compressed air which is made available at the end of the compressor  105  on the turbine side is guided to the burners  107  and mixed there with a fuel. The mixture is then combusted in the combustion chamber  110 , forming the working medium  113 . The working medium  113  flows from there along the hot gas passage  111  past the stator blades  130  and the rotor blades  120 . On the rotor blades  120 , the working medium  113  expands with impulse transmitting effect, so that the rotor blades  120  drive the rotor  103 , and the latter drives the working machine which is coupled to it. 
         [0142]    The components which are exposed to the hot working medium  113  are subjected to thermal stresses during operation of the gas turbine  100 . The stator blades  130  and rotor blades  120  of the first turbine stage  112 , viewed in the flow direction of the working medium  113 , are thermally stressed most of all next to the heat shield blocks which line the annular combustion chamber  106 . 
         [0143]    In order to withstand the temperatures which prevail there, these are cooled by means of a cooling medium. 
         [0144]    Also, the substrates can have a directional structure, i.e. they are single-crystal (SX-structure) or have only longitudinally oriented grains (DS-structure). 
         [0145]    As material, iron-based, nickel-based or cobalt-based superalloys are used. 
         [0146]    Also, the blades  120 ,  130  can have coatings against corrosion (MCrAlX; M is at least one element of the iron (Fe), cobalt (Co), nickel (Ni) group, X represents yttrium (Y) and/or at least one element of the rare earths), and heat by means of a thermal barrier coating. The thermal barrier coating, for example, comprises ZrO 2 , Y 2 O 4 —ZrO 2 , i.e. it is not partially or completely stabilized by yttrium oxide and/or by calcium oxide and/or by magnesium oxide. 
         [0147]    By suitable coating methods, like, for example, electron beam physical vapor deposition (EB-PVD), stalk-shaped grains are created in the thermal barrier coating. 
         [0148]    The stator blade  130  has a stator blade root (not shown here) which faces the inner casing  138  of the turbine  108 , and a stator blade end which lies opposite the stator blade root. The stator blade end faces the rotor  103  and is fixed on a fastening ring  140  of the stator  143 . 
         [0149]      FIG. 18  shows a combustion chamber  110  of a gas turbine. The combustion chamber  110 , for example, is designed as a so-called annular combustion chamber, in which a plurality of burners  102 , which are arranged in the circumferential direction around the turbine shaft  103 , lead into a common combustion chamber space. For this purpose, the combustion chamber  110  in its entirety is designed as an annular construction which is positioned around the turbine shaft  103 . 
         [0150]    To achieve a comparatively high efficiency, the combustion chamber  110  is designed for a comparatively high temperature of the working medium M of about 1000° C. to 1600° C. In order to enable a comparatively long period in service, even at these operating parameters which are unfavorable for the materials, the combustion chamber wall  153 , on its side facing the working medium M, is provided with an inner lining which is formed from heat shield elements  155 . Each heat shield element  155  is equipped on the working medium side with an especially heat resistant protective coating or is manufactured from high temperature resistant material. On account of the high temperatures inside the combustion chamber  110 , moreover, a cooling system is provided for the heat shield elements  155  or for their mounting elements, as the case may be. 
         [0151]    The heat shield elements  155  can also have holes  7 , for example also with a diffuser  13  in order to cool the heat shield element  155  or to allow combustible gas to flow out. 
         [0152]    The materials of the combustion chamber wall and their coatings can be similar to the turbine blades.