Abstract:
A method for producing gas turbine components, in particular blades, blade sections or rotors with integral blades for a jet engine is provided. The method comprises at least the following steps: preparation of at least one metallic powder and at least one expanding agent; mixing of the metallic powder or each metallic powder with the expanding agent or each expanding agent; compression of the resultant mixture to form at least one semi-finished product; expansion of the semi-finished product or each semi-finished product by heating to achieve a defined degree of expansion; termination of the expansion process by cooling, once the defined degree of expansion has been reached.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for manufacturing gas turbine components. 
     BACKGROUND 
     Modern gas turbines, in particular aircraft engines, must meet the highest demands with regard to reliability, weight, performance, cost-effectiveness, and service life. In particular in civil aviation, aircraft engines have been developed over the previous decades which fully meet the above-mentioned requirements and have reached a high degree of technological perfection. Among other things, material selection, the search for new, suitable materials, and the search for new manufacturing methods play a decisive role in the development of aircraft engines. 
     The most important materials used today for aircraft engines or other gas turbines are titanium alloys, nickel alloys (also known as super alloys), and high-strength steels. High-strength steels are used for shaft components, gear components, compressor housings, and turbine housings. Titanium alloys are typical materials for compressor components. Nickel alloys are suitable for the hot components of the aircraft engine. 
     Precision casting and forging are primarily known from the related art as manufacturing methods for gas turbine components made of titanium alloys, nickel alloys, or other alloys. All highly stressed gas turbine components such as blades for a compressor are forged components. In contrast, rotating blades and guide blades of the turbine are as a rule designed as precision cast components. 
     For reducing the weight of gas turbine components it is known from the related art to use metal matrix composite materials (known as MMC materials). High-strength fibers are embedded in the metal material of such MMC materials. However, the manufacture of gas turbine components using such MMC materials is expensive. Moreover, rotating blades of a gas turbine rotor, for example, cannot be manufactured using such MMC materials, since rotating blades made of MMC materials have only limited strength vis-à-vis bird strike, for example. 
     Another approach for reducing weight known from the related art is to design gas turbine components as hollow components. Blades are already manufactured as hollow blades with the aid of diffusion welding. However, such diffusion-welded hollow blades are expensive. 
     SUMMARY OF THE INVENTION 
     Since blades made of MMC materials have insufficient strength vis-à-vis bird strike, for example, and hollow blades are too expensive, an object of the present invention is to propose alternative options for reducing weight. The mass of guide blades and rotating blades contributes considerably to the total weight of a gas turbine, in particular an aircraft engine. If the weight of the rotating blades can be reduced, then the rotor can also have a lighter design since the rotor has to absorb lower centrifugal forces when the weight of the rotating blades is reduced. The lighter an aircraft engine can be designed, the more favorable is the thrust to weight ratio of the aircraft engine which in turn represents a decisive competitive criterion for aircraft engines. 
     On this basis, an object of the present invention is to propose a novel method for manufacturing gas turbine components. 
     The method according to the present invention for manufacturing gas turbine components, in particular blades, blade segments, or rotors having integral blades for an aircraft engine includes at least the following steps: providing at least one metal powder and at least one foaming agent; mixing the metal powder or each metal powder with the foaming agent or each foaming agent; compacting the resulting mixture to form at least one precursor; foaming the precursor or each precursor by heating up to a defined degree of foaming; terminating the foaming process by cooling when the defined degree of foaming is reached. 
     According to the present invention, a method to design gas turbine components, in particular guide blades and rotating blades for a compressor or a turbine of an aircraft engine, using metal foam at least partially is provided. Use of metal foams represents a cost-effective alternative compared to hollow blades, a clear weight reduction being implementable due to the porosity of the metal foam. 
     According to an advantageous refinement of the present invention, the precursor is foamed in a mold, the mold being actively heated and actively cooled during the foaming process in order to obtain a gas turbine component having a closed and supporting exterior wall of a defined wall thickness. 
     The method according to the present invention is preferably used for manufacturing a blade, in particular a compressor blade or a turbine blade for an aircraft engine, the respective precursor being foamed in a mold, and at least one supporting and/or function-relevant component made of a non-foamable material being at least partially surrounded by foam or embedded in foam during the foaming process of the precursor. The supporting and/or function-relevant component may be, for example, a blade root made of a non-foamable material which is partially embedded in foam or surrounded by foam. For manufacturing an integrally bladed rotor, for example, multiple blades manufactured in this way may be fixedly joined with a forged or cast rotor carrier via a joining process, in particular via soldering or welding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention, without being limited thereto, are explained in greater detail on the basis of the drawing. 
         FIG. 1  shows a block diagram for elucidating the method according to the present invention for manufacturing gas turbine components; 
         FIG. 2  shows a cross section of a blade of a gas turbine according to the present invention in a first exemplary embodiment of the present invention; 
         FIG. 3  shows a cross section of a blade of a gas turbine according to the present invention in a second exemplary embodiment of the present invention; 
         FIG. 4  shows a cross section of a blade of a gas turbine according to the present invention in a third exemplary embodiment of the present invention; 
         FIG. 5  shows a cross section of a blade of a gas turbine according to the present invention in another exemplary embodiment of the present invention, and 
         FIG. 6  shows a cross section of a blade of a gas turbine according to the present invention in another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is subsequently explained in greater detail with reference to  FIGS. 1 through 6 ,  FIGS. 2 through 6  each showing a cross section of rotating blades of a gas turbine, i.e., an aircraft engine, which are manufactured using the method according to the present invention. 
     The approach of the method according to the present invention for manufacturing a guide blade or a rotating blade or for manufacturing a guide blade segment or a rotating blade segment for an aircraft engine is that in a first step  10  of the method a metal powder is provided and in a second step  11  a foaming agent is provided. The provided metal powder is preferably a metal powder on the basis of an aluminum alloy, or a titanium alloy, or a nickel alloy. It is also possible to use a metal powder on the basis of a cobalt alloy or an iron alloy. Furthermore, metal powders made of intermetallic titanium-aluminum alloys may be used. Titanium hydride in particular is provided as the foaming agent. 
     The provided metal powder and the provided foaming agent are mixed in a step  12 . The mixture of metal powder and foaming agent resulting from the mixing process is subsequently compacted to form a precursor. Compacting may be carried out either according to step  13  by extrusion or according to step  14  by axial hot pressing. At the end of the compacting process according to step  13  or step  14  there is a precursor which is indicated in the flow diagram of  FIG. 1  by step  15 . The precursor is externally virtually indistinguishable from a conventional metal; however, it contains the foaming agent and is therefore foamable. 
     For manufacturing the gas turbine component, the precursor present in step  15  is heated according to step  16  in particular to just above its melting point so that the metal is melted and gas is released from the foaming agent. Foaming of the precursor is triggered by the gas release from the foaming agent. The foaming process is carried out until a defined degree of foaming is reached. As soon as the defined degree of foaming is reached, the foaming process is terminated in such a way that cooling below the melting point of the used metal powder is carried out. The foaming process triggered by heating the precursor above the melting point of the metal powder and the corresponding termination of the foaming process by cooling below the melting point of the metal powder are both indicated by step  16 . 
     Subsequent to step  16 , surface machining or other processing or surface finishing of the manufactured gas turbine component may be carried out according to step  17 . This, however, is optional. 
     Furthermore,  FIG. 1  shows, according to a step  18 , that in addition to the metal powder provided according to step  10  and the foaming agent provided according to step  11  other elements may be mixed with the metal powder and the foaming agent in step  12 . The other elements may be, for example, an additional metal powder having a different melting point or different powder granularity, a different foaming agent, or also ceramic particles, ceramic fibers, or other inorganic or organic elements. 
     Under consideration of the preferred manufacture of blades for aircraft engines, some of the method steps roughly mentioned above are subsequently discussed in greater detail. This is essentially step  16  relating to foaming the precursor. 
       FIG. 2  shows a cross section through a blade  19  of an aircraft engine designed according to the present invention, i.e., through a vane  20  of the blade. According to  FIG. 2  and according to the present invention, blade  19  is made of metal foam, at least partially; in the exemplary embodiment in  FIG. 2 , an inner core  21  of blade  19  has a porous design and an exterior wall  22  of the blade has a closed design. For manufacturing such a blade  19  having a porous core  21  and a closed and supporting exterior wall  22 , a corresponding, foamable precursor is foamed in a mold during step  16 . The mold is an actively heatable and actively coolable mold. Heating devices and cooling devices are thus assigned to the mold, the heating devices and cooling devices being activatable by a control device; the temperature of the mold may follow a predefined temperature profile with the aid of the heating and cooling devices. The mold is a hollow mold made of sheet steel, for example, the precursor to be foamed filling the mold completely after the foaming process. The mold is removed after the foaming process. In this way, the closed and supporting exterior wall  22  may be obtained. 
       FIG. 3  shows a blade  23 , i.e., a cross section through a vane  24  of blade  23  according to a second exemplary embodiment of the present invention. In the exemplary embodiment in  FIG. 3 , blade  23  is also made of metal foam, at least partially, blade  23  having a porous core  25  as well as a closed and supporting exterior wall  26 . According to  FIG. 3 , supporting or function-relevant components made of a non-foamable material are integrated into core  25  of blade  23 ; these components, according to step  16 , are partly or completely surrounded by foam or embedded in foam during the foaming process. In the exemplary embodiment in  FIG. 3 , a total of five such supporting or function-relevant components are at least partially foamed into core  25 , i.e., a component  27  in the area of a flow inlet edge of blade  23 , a component  28  in the area of a flow outlet edge of blade  23 , and another three components  29 ,  30 , and  31  in the interior of vane  24 . Components  27  through  31  foamed into vane  24  may either be made of the same material as the metal foam or may be made of another material. It is thus possible, that when a metal foam on the basis of a titanium alloy is used, the other components  27  through  31  are also made of a titanium alloy. However, it is also possible that components  27  through  31  are components made of another metal alloy or components made of a ceramic material. When individual blades are produced, which are mounted on a rotor via a blade root, it is preferred according to the present invention, during the foaming process according to step  16 , to foam a blade root made of a non-foamable material into the precursor during foaming of same. 
     Furthermore, it is the object of the present invention to manufacture a blade for an aircraft engine in such a way that a hollow body, which is formed by a fiber-reinforced metal or a fiber-reinforced plastic or from an intermetallic alloy, is filled with a metal foam during step  16  and the metal foam and the hollow body are subsequently melted together to form a firmly bonded composite.  FIG. 4  shows a blade  32 , i.e., a vane  33  of same, the blade being formed from a metallic hollow body  34 , the metallic hollow body being filled by a core  35  made of metal foam, and core  35  is joined firmly bonded with hollow body  34 . Hollow body  34  in  FIG. 3  is a hollow body having a one-piece design. The exterior geometry of blade  32  is determined by the exterior geometry of hollow body  34 . 
       FIG. 5  shows another exemplary embodiment of a blade  36  manufactured according to the present invention, i.e., a cross section through a vane  37  of same. In the exemplary embodiment in  FIG. 5 , a first part  38  of blade  36 , which forms the flow inlet side of blade  36 , is manufactured by filling a hollow body  39  with a core  40  made of metal foam, core  40  made of metal foam being form-fittingly connected to hollow body  39 . As in the exemplary embodiment in  FIG. 4 , a second part  41  of blade  36  is manufactured by filling a hollow body  42  with a core  43  made of metal foam, core  43  being firmly bonded with hollow body  42 . In blade  36  having such a two-part design, both hollow bodies  39  and  42  have preferably a different material composition, as do cores  40  and  43 . Cores  40  and  43  may not only be made of a different metal alloy, but they also may have a different porosity. Both parts  38  and  41  of blade  36  may be connected by a joining process, e.g., via welding or soldering. 
     Many additional alternatives are possible within the scope of the present invention. It is the object of the present invention to mix metal powders having different melting points with the foaming agent in order to ensure a locally variable rigidity or strength of the blades. Moreover, it is the object of the present invention to use metal powders having different powder granularities in order to influence the porosity of the resulting metal foam in a targeted manner. Furthermore, ceramic powders or also ceramic fibers may be mixed with a metal powder and the foaming agent and subsequently compacted to form a foamable precursor. This makes it also possible to influence the stability of the metal foam or the component to be formed in a targeted manner. 
       FIG. 6  shows another exemplary embodiment of a blade  44  manufactured according to the present invention, i.e., a cross section through a vane  45  of blade  44 . The exemplary embodiment in  FIG. 6  is in essence identical to the exemplary embodiment in  FIG. 5 . The same reference numerals are used for the same components in order to avoid unnecessary repeats. The exemplary embodiment in  FIG. 6  differs from the exemplary embodiment in  FIG. 5  by the fact that function-relevant components  46  are integrated into core  43  of second part  41  of blade  44  by surrounding same by foam. The function-relevant components  46  are hollow bodies which are used as flow channels for the controlled removal by blowing or suction of a flow medium from the main flow channel of the gas turbine. Using the present invention, blades having integrated flow channels are thus manufacturable in a simple manner. 
     Different exemplary embodiments of blades designed according to the present invention have been described in connection with  FIGS. 2 through 6 . According to the present invention, blade segments made up of multiple individual blades as well as rotors having integral blades are also manufacturable, of course. Rotors having integral blades may be manufactured, for example, by mounting individual blades according to the exemplary embodiments in  FIGS. 2 through 6  on forged or cast disc-shaped or ring-shaped rotor carriers via blade feet which are appropriately partially foamed into the blades. The blades on the rotor carrier may be mounted via soldering or welding or other joining processes. It should be pointed out again that, according to the present invention, individual blades as well as blade segments for rotors having integral blades may be manufactured entirely or partially using metal foam. The blades may be guide blades or rotating blades and the blade segments may be guide blade segments or rotating blade segments for a compressor or a turbine of an aircraft engine. Moreover, flow ribs or blades for fans may be manufactured according to the present invention. 
     As mentioned above, a gas turbine component manufactured according to the present invention may be subjected to subsequent processing or finishing as described in step  17 . For example, the surfaces of blades may be coated with an oxidation protection layer or a corrosion protection layer during step  17  according to the present invention. Moreover, the manufactured components may be subjected to post-forging. Furthermore, covering the components manufactured using foaming technology with sheet metal, fiber-reinforced layers, or foils made of fiber-reinforced metal is possible. 
     According to the present invention, it is thus proposed to manufacture reduced-weight blades, blade segments, or rotors having integral blades by at least partially making the blades or blade segments of metal foam. The present invention provides a cost-effective alternative to the manufacture of diffusion-welded hollow blades. Blades, blade segments, or rotors having integral blades made of metal foam are, moreover, more impact-tolerant than similar gas turbine components made of MMC materials.