Abstract:
A turbine or compressor stage suitable for being included in airplane turbojets. According to the invention, the stage comprises a disk ( 30 ) configured to be coupled to a shaft of the turbine engine, and at least one airfoil ( 20 ), the disk ( 30 ) comprising a metal material, the airfoil ( 20 ) comprising a ceramic matrix composite material, and the stage further including an interface part ( 40 ) that is distinct from the airfoil ( 20 ) and that is configured to be fastened to the disk ( 30 ) and to fasten said at least one airfoil ( 20 ), said interface part ( 40 ) comprising a ceramic or a ceramic matrix composite material.

Description:
FIELD OF THE INVENTION 
       [0001]    The present description relates to a turbine or compressor stage and to a turbine engine including such a stage. 
         [0002]    Such a turbine stage may be included in various types of turbine engine, and most particularly in airplane turbojets. 
       STATE OF THE PRIOR ART 
       [0003]    In a conventional turbojet, the low pressure turbine generally comprises a plurality of stages, each comprising a wheel of metal blades mounted on a metal disk that is coupled to a shaft of the engine. 
         [0004]    In order to save weight relative to the metal configuration, a large amount of research and development work has been engaged to design turbine blades out of ceramic matrix composite (CMC) material. 
         [0005]    For example, designs have been proposed for single-piece bladed disks made of CMC material: nevertheless, at present, such designs are difficult to make and in particular they raise questions of mechanical strength. 
         [0006]    In other designs, the blades are made of 3D-woven CMC material and they are fastened directly to the metal disk. Nevertheless, those designs encounter difficulties with fastening the blades to the disk. Firstly, it is found that chemical interactions between the woven composite material and the metal of the disk inflicts damage to the disk. Secondly, fastening the blades to the disk concentrates high levels of mechanical stress in a small area, thereby leading to mechanical damage. Furthermore, dimensional requirements are very severe in this zone, thereby complicating the design and the fabrication of such blades. 
         [0007]    There therefore exists a real need for a turbine or compressor stage and for a turbine engine that do not suffer less or not at all from the drawbacks inherent to the above-mentioned configurations. 
       SUMMARY OF THE INVENTION 
       [0008]    The present description relates to a turbine or compressor stage for a turbine engine, the stage comprising a disk configured to be coupled to a shaft of the turbine engine, and at least one airfoil, the disk comprising a metal material, the airfoil comprising a ceramic matrix composite material, and the stage also including an interface part that is distinct from the airfoil, which part is configured to be fastened to the disk and to fasten said at least one airfoil, said interface part comprising a ceramic or a ceramic matrix composite material. 
         [0009]    In the present description, terms such as “longitudinal”, “transverse”, “bottom”, “top”, and their derivatives are defined relative to the main direction of the blade. Terms such as “axial”, “radial”, “tangential”, “inner”, “outer”, and their derivatives are defined relative to the main axis of the turbine engine; and terms such as “upstream” and “downstream” are defined relative to the flow of air through the turbine engine. 
         [0010]    This interface part makes it possible to solve a large number of difficulties that are conventionally encountered at the interface between a composite blade and a metal disk. 
         [0011]    Firstly, it is possible to decouple certain functions that are usually performed by the blades by sharing them over different elements, and in particular firstly over the airfoil and secondly over the interface part, thereby providing greater freedom in optimizing the functions that are specific to each of these parts, in particular in terms of choice of materials. Thus, it is possible to choose a first material that is suitable for the airfoil and a second material that is suitable for the interface part: in particular, it is possible to select a material for the interface part that does not give rise to any harmful chemical interaction with the metal of the disk. 
         [0012]    Furthermore, installing such an interface part serves to offset the interface zone between metal and composite material. In particular, it is possible to provide for the interface part to be fastened to the disk radially closer to the inside of the stage, where conditions are more favorable. The space available in this location is greater than in the immediate proximity of the airfoil, which is a zone that is very crowded with fastenings for all of the auxiliary members of the blade, such as the lips or the labyrinth seals, and by the presence of the inner ends of stator vanes: closer to the inside of the stage, there is thus more room for making a less complex metal/composite interface with a large surface area of contact. In addition, since the interface is further inside the stage, it is in a zone that is cooler, thereby providing thermomechanical conditions that are more favorable. 
         [0013]    In addition, by means of this interface part, it is possible to provide a metal disk of small radius such that the use of metal is limited to zones that are cooler and that require high grade mechanical characteristics, whereas the ceramic and ceramic matrix composite (CMC) materials are used in the hotter zones. 
         [0014]    It is thus also possible to benefit from a significant saving in weight, thereby contributing to reducing the specific consumption of the turbine engine. 
         [0015]    In certain embodiments, the airfoil comprises a 3D-woven composite material. This type of material is particularly suitable for airfoils as a result of its weight and its mechanical and aerodynamic properties. 
         [0016]    In certain embodiments, said interface part comprises a ceramic material, at least in its zone in contact with the disk. The inventors have found that using such a ceramic material enables the interface between the interface part and the metal disk to be more healthy. Such a ceramic material is also easier to machine than woven composite materials, thus making it possible to comply with stricter dimensional constraints. 
         [0017]    In certain embodiments, the interface part is a single piece comprising ceramic material. This provides a part that is coherent and that has good mechanical strength properties. 
         [0018]    In other embodiments, the interface part comprises a first portion of 3D-woven composite material and a second portion of ceramic material, the interface part being configured so that the first portion is not in contact with the disk. This makes it possible to benefit from the properties of the woven material, in particular its mechanical properties, while providing a healthy interface between the ceramic material and the metal of the disk. 
         [0019]    In certain embodiments, the interface part comprises a ceramic material reinforced by a central insert made of 3D-woven composite material. 
         [0020]    In other embodiments, the interface part comprises a main part of 3D-woven composite material having a contact portion of ceramic material fitted thereto, at least in the zone that comes into contact with the disk. This contact portion is preferably brazed onto the main part. 
         [0021]    In certain embodiments, the stage also includes at least one inner platform made of ceramic or ceramic matrix composite material. These platforms that are arranged in the space between blades serve to define the airflow passage and to ensure that the air flows aerodynamically while avoiding leaks. In addition, these platforms serve to isolate the inner portion of the stage from the flow of air and they thereby form a heat shield for the inner portion. 
         [0022]    This material is preferably a ceramic material. It is thus easy to make the platform even when its shape is fine or complex. 
         [0023]    In certain embodiments, the stage also has at least one lip of ceramic or of ceramic matrix composite material. Such lips, directed towards the upstream and/or downstream stator vanes of the stage serve to isolate the inner portion of the stage from the flow of air and to provide a heat shield. In addition, they help in reducing leaks, which is beneficial for the performance of the turbine. 
         [0024]    This material is preferably a ceramic material. It is then easy to make the lips even when their shape is fine or complex. 
         [0025]    In certain embodiments, the stage further comprises at least one low wall or cheekplate of ceramic material or of CMC material. In such embodiments, these walls or cheekplates serve to retain the platform and to isolate the root of the airfoil. They also serve to provide sealing against leaks between blades. This material is preferably a ceramic material. 
         [0026]    In certain embodiments, said platforms, lips, low walls, and/or cheekplates are secured to the interface part by any appropriate method. In particular they may be brazed. 
         [0027]    In other embodiments, said platforms, lips, low walls, and/or cheekplates form integral portions of the interface part. 
         [0028]    In certain embodiments, the disk does not have ventilation. This is made possible by using ceramic and CMC materials in the hottest portions that are close to the flow of air. Reducing or eliminating such ventilation constitutes a significant improvement in the performance of the turbine. 
         [0029]    In certain embodiments, the stage also includes an outer platform of ceramic material or ceramic matrix composite material at the outer end of said airfoil, and preferably made of CMC material. 
         [0030]    In certain embodiments, the outer platform includes at least one sealing portion configured to rub in sealing manner against an abradable track of the stator of the turbine engine. 
         [0031]    In certain embodiments, the platform is fitted on the tip of the blade, preferably by brazing. 
         [0032]    In other embodiments, the outer platform is formed integrally on the tip portion of the airfoil. By way of example, it may then be made by weaving one or more crossings through the airfoil using techniques that are known in the art. 
         [0033]    The top connection between the airfoil and the interface part may be constituted by a hammer attachment, a shank attachment, or by mere juxtaposition. This connection is preferably brazed and it may be reinforced by inserting by a peg. 
         [0034]    The bottom connection between the interface part and the disk may be constituted by a hammer attachment, a shank attachment, or a bolted connection. 
         [0035]    In certain embodiments, the interface part includes a fastener portion projecting towards the disk, and the disk comprises two half-disks with outer segments configured so as to co-operate with the fastener portion of the interface part so as to fasten it to the disk, the two half-disks being held pressed one against the other, preferably by bolting. 
         [0036]    In certain embodiments, the interface part has a fastener portion that is generally dovetail-shaped, and the two half-disks possess outer segments that co-operate to form a cavity in which the fastener portion of the interface part is clamped in order to fasten the interface part to the disk. 
         [0037]    In other embodiments, the interface part includes a fastener tab, and the two half-disks possess outer segments that are configured in such a manner as to lie on either side of the fastener tab of the interface part, the two half-disks and the fastener tab being fastened together by bolting or by inserting a peg. 
         [0038]    In other embodiments, the interface part has a fastener portion that is generally dovetail-shaped, and the disk includes at least one axial, transverse slot in which the fastener portion of the interface part is inserted in order to fasten it to the disk. This thus constitutes a shank attachment. Under such circumstances, the disk may be a single piece. 
         [0039]    In certain embodiments, the airfoil is extended at its inner end by a fastener portion, and the interface part includes a socket into which the fastener portion of the airfoil is engaged, the fastener portion being fastened in the socket by a retaining element inserted through said fastener portion and through at least a portion of the interface part. This retaining element is preferably a peg, and it may also be brazed. 
         [0040]    In other embodiments, the airfoil has a fastener portion that is generally dovetail-shaped, and the interface part includes a slot in which the fastener portion of the airfoil is inserted in order to fasten it to the interface part. The slot may be axial or tangential, i.e. the connection may be of the shank type or of the hammer type. The fastener portion of the airfoil may also be brazed in said slot. 
         [0041]    In certain embodiments, the interface part is configured to fasten only one airfoil. 
         [0042]    In other embodiments, the interface part is configured to fasten a plurality of airfoils: it may thus constitute a doublet or a wheel sector. 
         [0043]    In certain embodiments, the ceramic material constituting certain parts of the stage is a molded and sintered material. This enables these small parts to be made quickly and easily, even though they are often fine and complex in shape. 
         [0044]    The present description also relates to a turbine engine having at least one turbine or compressor stage in accordance with any of the embodiments described above. 
         [0045]    The above-mentioned characteristics and advantages, and others, appear on reading the following detailed description of embodiments of the proposed stage and turbine engine. This detailed description makes reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]    The accompanying drawings are diagrammatic and seek above all to illustrate the principles of the invention. 
           [0047]    In the drawings, from one figure to another, elements (or portions of an element) that are identical, are identified by the same reference sign. In addition, elements (or portions of elements) belonging to different embodiments and that are analogous in function, are identified in the figures by numerical references incremented by 100, 200, etc. 
           [0048]      FIG. 1  is an axial section view of an example of a turbojet. 
           [0049]      FIG. 2  is an axial section view of a first example of a stage of the invention. 
           [0050]      FIG. 3  is an axial section view of a second example of a stage of the invention. 
           [0051]      FIGS. 4A and 4B  show variant embodiments of the fastening of the airfoil on the interface part. 
           [0052]      FIGS. 5A and 5B  show variant embodiments of the platform and of the lips. 
           [0053]      FIGS. 6A ,  6 B, and  6 C show variant embodiments of the structure of the interface part. 
           [0054]      FIGS. 7A ,  7 B, and  7 C show variant embodiments of the fastener portion of the interface part. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0055]    In order to make the invention more concrete, examples of turbine stages of a turbine engine are described in detail below with reference to the accompanying drawings. It should be recalled that the invention is not limited to these examples. 
         [0056]      FIG. 1  is a section view on a vertical axial plane containing the main axis A of a bypass turbojet  1  of the invention. From upstream to downstream it comprises a fan  2 , a low pressure compressor  3 , a high pressure compressor  4 , a combustion chamber  5 , a high pressure turbine  6 , and a low pressure turbine  7 . 
         [0057]      FIG. 2  is a section view on the same axial plane showing a portion of the low pressure turbine  7 . This turbine  7  comprises a plurality of stages  10  in a first embodiment, each comprising a rotor  10   a  and a stator  10   b  following one after the other from upstream to downstream. Each rotor  10   a  comprises a plurality of rotor blades  11 , each comprising an airfoil  20  and an interface part  40  that are mounted on a disk  30 , which is coupled to a shaft of the turbine engine  1 . 
         [0058]    Each airfoil  20  is made of 3D-woven ceramic matrix composite (CMC) material. At its bottom end, the airfoil  20  has a dovetail-shaped fastener portion  21 . 
         [0059]    Each interface part  40  is made of ceramic material. Each interface part  40  includes at its top end a slot  41  of shape complementary to the shape of the dovetail-shaped fastener portion  21  of the airfoil  20 , and at its bottom end it includes a rod  42  terminating in a fastener portion  43  that is likewise dovetail-shaped. 
         [0060]    The disk  30  is made of metal. It comprises two half-disks  30   a  and  30   b  arranged one against the other. The outer end segment  31   a ,  31   b  of each half-disk  30   a ,  30   b  is spaced apart from the adjacent half-disk  30   a ,  30   b  so as to be C-shaped in order to co-operate with the adjacent half-disk  30   b ,  30   a  to form a cavity  32 . 
         [0061]    Thus, the airfoil  20  is mounted on the interface part  40  by means of its fastener portion  21  that is engaged and brazed in the slot  41  in the interface part  40 . The interface part  40  is itself mounted on the disk  30  by its fastener portion  43  being clamped within the cavity  32  by the outer segments  31   a  and  31   b  of the half-disks  30   a  and  30   b , which disks are held pressed against each other by means of a bolted connection  33 . 
         [0062]    The disks  30  of each stage  10  are also connected to one another in pairs by metal shrouds  34  that are bolted to the disks  30 . Advantageously, such shrouds  34  are fastened to the bolted connection  33  between the two half-disks  30   a  and  30   b.    
         [0063]    The blade  11  also has an outer platform  50  made of woven CMC material that is attached to the airfoil  20  by brazing. It could equally well be made of ceramic material. The outer platform  50  has wipers  51  configured to rub against an abradable track of the stator of the turbine  7  so as to provide the rotor  10   b  with sealing relative to the stator. 
         [0064]    The blade  11  also has an inner platform  61  with upstream and downstream lips  62  and  63  made as a single piece  60  of woven CMC material fitted on the interface part  40  by brazing. It could equally well be made of ceramic material. In this embodiment, the part  60  constituting the platform  61  and the lips  62  and  63  is attached via low walls  44  of the interface part  40  that extend radially outwards so as to be located on either side of the non-airfoil bottom portion of the airfoil  20  leading to the fastener portion  21 . 
         [0065]      FIG. 3  is a section in the same axial plane showing a portion of a second example of the low pressure turbine  7 . This turbine  7  has a plurality of stages  110  in a second embodiment. In manner identical to the first example, each rotor  110   a  has a plurality of rotor blades  111 , each comprising an airfoil  120  and an interface part  140  mounted on a disk  130  that is coupled to a shaft of the turbine engine  1 . Only the differences with the first example are described in detail. 
         [0066]    Unlike the first example, which presents a “hammer” type attachment, this second example presents a “shank” type attachment. 
         [0067]    In this second example, the dovetail  143  of the interface part  140  extends axially and no longer tangentially. 
         [0068]    The disk  130  is then made as a single piece, and in the vicinity of its outline it includes axial slots that are configured to receive the dovetail-shaped ends  143  of the interface part  140 . 
         [0069]    The two above-described configurations are only two embodiments, and they may be subjected to numerous variations. 
         [0070]    In particular, in the first-described example, the airfoil  20  is mounted on the interface part  40  with the help of a fastener portion  21  having its dovetail oriented tangentially so as to engage in the tangential slot  41  in the interface part  40 : this is a hammer-type attachment. Nevertheless, as shown in  FIG. 4A , the dovetail of the fastener portion  321  of the airfoil  320  could equally well be oriented radially; under such circumstances, the slot  341  in the interface part  340  is also oriented radially: this thus constitutes a shank-type attachment. 
         [0071]    In another variant shown in  FIG. 4B , the airfoil  320 ′ does not have a dovetail-shaped fastener portion. Instead of that, it has a fastener tab  322  extending the bottom portion of the airfoil  320 ′ with unchanging profile; this fastener tab  322  is also provided with a through orifice  323 . The interface part  340 ′ does not have a slot, but rather a radial socket  344  of shape complementary to the fastener tab  322  of the airfoil  320 ′; a through orifice  345  passes through the interface part  340 ′ and the socket  344 . Under such circumstances, the airfoil  320 ′ engages in the socket  344  of the interface part  340 ′: a peg  346  is then inserted through the orifices  345  in the interface part  340 ′ and  323  in the fastener tab  322  of the airfoil  320 ′ in order to fasten the airfoil to the interface part  340 ′. The peg  346  is then brazed in position. 
         [0072]    Certain variants relate to the inner platform and the lips. In the two examples described, a single part  60  serves to provide the inner platform  61  and the lips  62  and  63  of the blade  11 , this part  60  being fastened to the low wall  44  of the interface part  40 . Nevertheless, as shown in  FIG. 5A , in addition to the inner platform  461  and the lips  462  and  463 , such a part  460  could also include upstream and downstream vertical portions  464  acting as low walls and fastened to the body proper of the interface part  440 . 
         [0073]    In another variant, shown in  FIG. 5B , the interface part  440 ′ may be made integrally with portions  461 ′,  462 ′,  463 ′, and  464 ′ that correspond respectively to the inner platform, to the upstream lip, to the downstream lip, and to the low walls. 
         [0074]    Other variants relate to the structure of the interface part itself. In the two examples described, as in the example of  FIG. 6A , the interface part  540  is made entirely out of ceramic material. Nevertheless, and as shown in  FIG. 6B , the interface part  540 ′ could equally well have reinforcement  547  made of woven CMC material: this reinforcement  547  is substantially in the form of a plate extending tangentially over the entire length of the interface part  540 ′ and radially at least along the rod  542 ′ and in part within the body of the interface part  540 ′. The other portions of the interface part  540 ′, and in particular the flanks of the rod  542 ′ and the fastener portion  543 ′ are made of ceramic material. 
         [0075]    In another variant shown in  FIG. 6C , the interface part  540 ″ has a first portion  548  forming the body and the rod  542 ″ of the interface part  540 ″ and made of 3D-woven CMC material. The interface part  540 ″ then includes a second portion made up of two bearing surfaces  549  fitted to opposite sides of the rod  542 ″ on its fastener portion  543 ″, these bearing surfaces  549  being made of ceramic material. 
         [0076]    Finally, other variants relate to fastening the interface part on the disk. In the first embodiment described, the interface part  40  is mounted on the disk  30  with the help of a fastener portion  43  having its dovetail oriented tangentially so as to engage in the tangential slot  32  formed by the half-disks  30   a  and  30   b : this constitutes a hammer-type attachment. Nevertheless, as in the second described example and as shown in  FIG. 7A , the dovetail of the fastener portion  643  of the interface part  640  could equally well be radially oriented, and then the disk may be a single piece provided with radially oriented slots: this constitutes a shank-type attachment. 
         [0077]    In the variant shown in  FIG. 7B , the interface part  640 ′ does not have a fastener portion but includes a fastener tab  643 ′ suitable for being inserted in a U-shaped cavity in the disk; the fastener tab  643 ′ then has a through orifice  680  for passing the bolt. 
         [0000]    Nevertheless, in the variant shown in  FIG. 7C , the interface part  640 ″ could have two fastener tabs  643   a  and  643   b , each having a through orifice  680   a ,  680   b  suitable for being fastened to the disk by bolting. 
         [0078]    The embodiments described in the present description are given by way of non-limiting illustration, in the light of this description, and the person skilled in the art can easily modify these embodiments or can envisage others, while remaining within the scope of the invention. 
         [0079]    Furthermore, the various characteristics of the embodiments may be used singly or in combination with one another. When combined, these characteristics may be combined as described above or in other ways, the invention not being limited to the specific combinations described in the present description. In particular, unless specified to the contrary, any characteristic described in relation with one particular embodiment may be applied in analogous manner to another embodiment.