Abstract:
A high-temperature component made of a nickel super-alloy has the following composition in wt %: 11-13% of Cr, 3-5% of W, 0.5-2.5% of Mo, 3-5% of Al, 3-5% of Ti, 3-7% of Ta, 1-5% of Re and a remainder of nickel.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of copending application Ser. No. 10/059,541, filed Jan. 29, 2002, which was a continuation of copending International Application No. PCT/EP00/07079, filed Jul. 24, 2000, which designated the United States. This application also claims priority of European Application 99 114 278.7 filed Jul. 29, 1999. The prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0002]     The invention relates to a high-temperature-resistant component made from a nickel-base superalloy. The invention also relates to a process for producing the component.  
         [0003]     German Published, Non-Prosecuted Patent Application DE 23 33 775 B2 describes a process for the heat treatment of a nickel alloy. The nickel alloy includes up to 0.3% of carbon, 11-15% of chromium, 8-12% of cobalt, 1-2.5% of molybdenum, 3-10% of tungsten, 3.5-10% of tantalum, 3.5-4.5% of titanium, 3-4% of aluminum, 0.005-0.025% of boron, 0.05-0.4% of zirconium and a remainder of nickel. Furthermore, the alloy additionally includes 0.01-3% of hafnium, so that a block-like carbide formation and a finely dispersed precipitation of an Ni 3 (Al,Ti) phase is achieved through a suitable heat treatment. There is no mention of rhenium or ruthenium being added.  
         [0004]     U.S. Pat. No. 5,611,670 discloses a rotor blade for a gas turbine. The rotor blade has a monocrystalline platform area and a monocrystalline blade part. A securing area of the blade is constructed with a directionally solidified structure. The blade is cast from a superalloy which has the following composition, in percent by weight: up to 0.2% of carbon, 5-14% of chromium, 4-7% of aluminum, 2-15% of tungsten, 0.5-5% of titanium, up to 3% of niobium, up to 6% of molybdenum, up to 12% of tantalum, up to 10.5% of cobalt, up to 2% of hafnium, up to 4% of rhenium, up to 0.035% of boron, up to 0.035% of zirconium and a remainder of nickel. Those wide ranges are used to specify alloy compositions which are suitable, in principle, for proposed gas turbine blades, but do not indicate a composition range which is appropriate with a view to a particular resistance to oxidation and corrosion or strength.  
         [0005]     European Patent EP 0 297 785 B1 has disclosed a nickel-base superalloy for single crystals. The superalloy has the following composition, in percent by weight: 6-15% of chromium, 5-12% of tungsten, 0.01-4% of rhenium, 3-9% of tantalum, 0.5-2% of titanium, 4-7% of aluminum and optionally 0.5-3% of molybdenum. This superalloy results both in a resistance to high-temperature cracking and in a resistance to corrosion. The titanium content must not exceed 2% by weight in order not to impair the resistance to corrosion.  
         [0006]     U.S. Pat. No. 5,122,206 has disclosed a nickel-base superalloy which has a particularly narrow coexistence zone for the solid and liquid phases and is therefore particularly suitable for a single-crystal casting process. The alloy has the following composition, in percent by weight: 10-30% of chromium, 0.1-5% of niobium, 0.1-8% of titanium, 0.1-8% of aluminum, 0.05-0.5% of copper or, instead of copper, 0.1-3% of tantalum. In the former case, hafnium or rhenium may optionally also be present, in an amount of from 0.05-3%, while in the latter case 0.05-0.5% of copper may also be present instead of rhenium or hafnium. Furthermore, it is optionally possible to provide 0.05-3% of molybdenum or tungsten.  
       SUMMARY OF THE INVENTION  
       [0007]     It is accordingly an object of the invention to provide a high-temperature-resistant component and a process for producing the high-temperature-resistant component, which overcome the hereinafore-mentioned disadvantages of the heretofore-known products and processes of this general type and in which the component is made from a nickel-base superalloy that has particularly favorable properties with regard to its ability to withstand high temperatures, its resistance to oxidation and corrosion and its stability with respect to the formation of intermetallic phases which have the effect of reducing ductility.  
         [0008]     With the foregoing and other objects in view there is provided, in accordance with the invention, a high-temperature-resistant component. The component comprises a nickel-base superalloy having a composition including the following elements, in percent by weight:  
                                       11-13%   chromium       3-5%   tungsten       0.5-2.5%   molybdenum       3-5%   aluminum       3-5%   titanium       3-7%   tantalum        0-12%   cobalt       0-1%   niobium       0-2%   hafnium       0-1%   zirconium         0-0.05%   boron         0-0.2%   carbon       1-5%   rhenium, and                  
 
 a remainder of Ni and impurities. 
 
         [0009]     The superalloy of the component described above has been specified for the first time, in terms of its composition, in such a way that the component has particularly favorable properties with regard to its ability to withstand high temperatures, its resistance to oxidation and corrosion and with regard to stability with respect to the formation of intermetallic phases which have the effect of reducing ductility. Extensive experiments made it possible to determine the specific composition described herein, through the use of which the desired, above-mentioned properties are satisfied to a surprisingly high degree. In particular, the invention is based on a chromium-rich superalloy which acquires a high strength through the addition of rhenium. The formation of embrittling intermetallic phases, which is promoted by rhenium, is controlled by the subtle balance with the other elements in the composition.  
         [0010]     In accordance with another feature of the invention, the rhenium content is preferably at least 2% by weight.  
         [0011]     It is possible for the superalloy to also have a content of ruthenium of 0.1 to 5 wt %. The addition of ruthenium in particular enables the tendency to form embrittling intermetallic phases to be reduced further. It has proven expedient to add ruthenium particularly with a rhenium content of over 2% by weight. In accordance with a further feature of the invention, in this case, the maximum ruthenium content is preferably 3% by weight, and the minimum ruthenium content is 0.1% by weight.  
         [0012]     In accordance with an added feature of the invention, the cobalt content of the superalloy is preferably up to 12% by weight.  
         [0013]     In accordance with an additional feature of the invention, the superalloy preferably contains at most 1% by weight of niobium.  
         [0014]     In a preferred composition, the cobalt content of the superalloy is lower than 12% by weight, while the niobium content is at most 1% by weight. Preferably, 0-2% by weight of hafnium and/or 0-1% by weight of zirconium and/or 0-0.05% by weight of boron and/or 0-0.2% by weight of carbon are included in the superalloy.  
         [0015]     In accordance with a further feature of the invention, the component preferably has a directionally solidified grain structure. In a directionally solidified structure of this type, the grain boundaries are oriented substantially along one axis. This results in a particularly high strength along this axis.  
         [0016]     In accordance with an added feature of the invention, the component preferably has a monocrystalline structure. The monocrystalline structure avoids strength-reducing grain boundaries in the component and results in a particularly high strength.  
         [0017]     In accordance with an additional feature of the invention, the component is constructed as a gas turbine blade. A gas turbine blade is a component which is exposed to particularly high demands in terms of its ability to withstand high temperatures and its resistance to oxidation/corrosion.  
         [0018]     With the objects of the invention in view, there is additionally provided a process for producing a component from a superalloy in accordance with the above-described embodiments, through the use of a conventional casting process. A fine-grained precision-cast structure is achieved for the component in a conventional casting process of this type. This casting process is particularly inexpensive.  
         [0019]     With the objects of the invention in view, there is also provided a process for producing a component from a superalloy having the above composition, in which the superalloy is cooled in such a way that it solidifies directionally or in single crystal form, with the cooling taking place in vacuo through the use of a liquid cooling metal. A process of this type, which is known as liquid metal cooling, considerably improves the quality and speed of the casting process. Cooling takes place only by radiation, especially in vacuo. The cooling capacity is considerably increased by a liquid cooling metal. This allows the solidification process, in which the component that is to be solidified is cooled along a component axis, to be optimized for solidification which is as flawless and rapid as possible.  
         [0020]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0021]     Although the invention is illustrated and described herein as embodied in a high-temperature-resistant component and a process for producing the high-temperature-resistant component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0022]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a fragmentary, diagrammatic, elevational view of a gas turbine blade;  
         [0024]      FIG. 2  is a cross-sectional view of an apparatus for carrying out a process for producing a gas turbine blade;  
         [0025]      FIG. 3  is a table showing alloy compositions; and  
         [0026]      FIG. 4  is another table showing alloy compositions. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a high-temperature-resistant component, which is constructed as a gas turbine blade  1 . The gas turbine blade  1  has a blade part  3 , a platform  5  and a securing area  7 . The gas turbine blade  1  is produced in directionally solidified form in a casting process, as a result of which grain boundaries  9  that are oriented along a blade axis  8  are formed.  
         [0028]     The gas turbine blade  1  is produced from a nickel-base superalloy which has one of the compositions listed in tables shown in  FIGS. 3 and 4 . The tables seen in  FIGS. 3 and 4  contain the content in percent by weight of one element in each column, for twelve different alloys L 1 -L 12 . The remainder, making a total of up to 100%, is nickel and inevitable impurities. A portion of cobalt of between 6 and 10% and a content of zirconium of between 0 and 0.1% is especially advantageous.  
         [0029]      FIG. 2  shows a melt  101  of a metal, in particular of a superalloy, for the production of turbine blades  1  in a casting mold  102 . The casting mold  102  is to be immersed in a bath  103  of a liquid cooling medium, preferably tin, an inorganic salt or boron oxide, for the purpose of cooling. A liquid cooling medium  103 A is at a second temperature, which is lower than a first temperature of the melt  101 . The bath  103  is covered by a covering layer  104 , which is formed of a free-flowing, thermally insulating bulk material including spherical solid bodies  105 ,  106  (hollow beads  105  and solid beads  106 ). The hollow beads  105  preferably are formed of a ceramic material, such as silicon dioxide/aluminum oxide (mullite). The solid beads  106  preferably are formed of a material such as aluminum oxide, magnesium oxide or zirconium oxide. The solid bodies made from a solid material may also include, for example, particles  106  of a commercially available powder. The covering layer  104  considerably reduces the introduction of heat into the bath  103  from a heating zone  107 , in which the casting mold  102  containing the melt  101  is initially held. The casting mold  102  is at a very high first temperature, in particular 1600° C., in the heating zone  107 . A high temperature drop, corresponding to a particularly high temperature gradient, is established in the interior of the covering layer  104 . Heat is introduced into the melt  101  and the casting mold  102  following the heating zone  107  and heat is dissipated from the melt  101  and the casting mold  102  in the bath  103 . Therefore, a high temperature gradient is likewise established in the melt  101  in the area where the casting mold  102  passes through the covering layer  104 . A high temperature gradient of this nature results in directional solidification of the melt  101  to form a workpiece or a plurality of workpieces, in particular a turbine blade  1 , with a columnar crystal or a single crystal microstructure. The casting mold  102  can be moved into the bath  103  through the use of a holding frame  111 .  
         [0030]     Particularly preferred alloys have the following composition:  
                                                           Al: 3.4;   Cr: 12.5%;   Co: 9%;           Mo: 1.9%;   W: 4%;   Ta: 4%;           Ti: 3.9%;   Re: 3%   C: 0.08%;           B: 125 ppm;   Zr: 80 ppm;   Hf: &lt;100 ppm;           Ni: bal.           Al: 3.6-4;   Cr: 12.5%;   Co: 9%;           Mo: 1.9%;   W: 4%;   Ta: 6%;           Ti: 3.9%;   C: 0.08%;   B: 125 ppm;           Zr: 80 ppm;   Hf: &lt;100 ppm;   Ni: bal.           Al: 3.8;   Cr: 12%;   Co: 4%;           Mo: 1.5%;   W: 3.5%;   Ta: 6%;           Ti: 3.9%;   Re: 2.5%   C: 0.08%;           B: 125 ppm;   Zr: 80 ppm;   Hf: &lt;100 ppm;           Ni: bal.           Al: 3.8;   Cr: 12%;   Co: 4%;           Mo: 1.5%;   W: 3.5%;   Ta: 6%;           Ti: 3.9%;   Re: 2.5%   Ru: 1%;           C: 0.08%;   B: 25 ppm;   Zr: 80 ppm;           Hf: &lt;100 ppm;   Ni: bal.           Al: 3.8;   Cr: 12%;   Co: 4%;           Mo: 1.9%;   W: 4%;   Ta: 6%;           Ti: 3.9%;   Re: 1.5%   C: 0.08%;           B: 125 ppm;   Zr: 80 ppm;   Hf: &lt;100 ppm;           Ni: bal.