Blade with a root provided with an Anti-wear coating

Abstract

Blade for a turbomachine, comprising an airfoil part (12) and a blade root (11), the blade root (11) comprising at least one bearing surface (22) configured to cooperate with a fastening device (31) of the turbomachine (1), wherein at least the blade root (11) is made of TiAl, and wherein the bearing surface (22) is provided with an anti-wear coating, this anti-wear coating being made of a nickel-based alloy comprising at least 9.5% by mass of Co and / or at least 14% by mass of Cr.

Description

BLADE WITH FOOT EQUIPPED WITH AN ANTI-WEAR COATING Technical Field

[0001] This disclosure relates to a turbomachine blade, as well as a turbomachine module and a turbomachine, the root of which is provided with an anti-wear coating. Such a blade can be fitted to any type of turbomachine, and in particular an aircraft turbojet. Prior art

[0002] Turbomachine blades are typically mounted on a rotating disk secured to one of the turbomachine's power shafts. More specifically, the blades typically include a dovetail blade root designed to engage in radial cells formed on the circumference of the disk. For example, document FR 2 890 126 describes such a configuration.

[0003] In such a configuration, surfaces of the blade root bearing surfaces are in permanent contact with the cell retaining surfaces. Therefore, due to the friction caused in particular by the vibrations of the turbomachine in operation, there is significant and rapid wear of the blade root bearing surfaces and / or the cell retaining surfaces.

[0004] To reduce the impact of such a phenomenon, it is known to install a foil between the blade root and the disc cell. Depending on the configurations, such a foil can help lubricate the contact between the blade root, the foil and the cell and therefore reduce wear caused by friction. Such a foil can also be configured to be worn more easily than the bearing surfaces of the blade root and the retaining surfaces of the disc cell: in fact, in such a case, the foil is worn first, sparing the bearing surfaces and the retaining surfaces; it is then easy to replace the foil when its wear becomes too significant.

[0005] However, it occasionally happens that foils disengage from their sockets during operation of the turbomachine. The blade root rubs then again directly on the retaining surfaces of the cell, which results in premature wear of the blade root, with damage severe enough to require complete replacement of the damaged blade.

[0006] This phenomenon is even more critical for certain new generation engines whose blades are made of titanium aluminide (TiAl). Indeed, TiAl wears quickly and more easily than Inconel 718 (registered trademark), which is the material frequently used to make rotating discs. It also wears more easily than nickel-based alloys such as DS200 or R77, which are other alloys used for certain blades.

[0007] Another known option to mitigate this wear phenomenon is to protect the blade root bearing surfaces with a lubricating varnish, for example the lubricating varnish known as Surf-Kote Lob-1800-G (registered trademark). However, this option is very expensive and not very robust in terms of manufacturing. In particular, such a varnish must be applied manually, by brush or airbrush to narrow and difficult-to-access areas.

[0008] There is therefore a real need for a turbomachine blade, as well as for a turbomachine module and a turbomachine, which are free, at least in part, from the drawbacks inherent in the aforementioned known configurations. Statement of the invention

[0009] The present disclosure relates to a blade for a turbomachine, comprising a blade portion, and a blade root, the blade root comprising at least one bearing surface configured to cooperate with a device for fixing the turbomachine, in which at least the blade root is made essentially of TiAI, and in which the bearing surface is provided with an anti-wear coating, this anti-wear coating being made essentially of a Nickel-based alloy comprising at least 9.5% by mass of Co and / or at least 14% by mass of Cr. The anti-wear coating may also comprise at least one of the elements chosen from Fe, Ni, S, P, C, Zr, B in trace form.

[0010] Thanks to such an anti-wear coating, it is possible to effectively protect the bearing surfaces of the blade root. In particular, tests carried out by the inventors show that the corresponding materials exhibit good friction behavior at high temperatures with much lower wear levels than existing configurations without coating or in the presence of foil.

[0011] Such an anti-wear coating then makes foil superfluous and, unlike the latter, does not present any risk of disengagement. In addition, such an anti-wear coating has sufficient anti-wear performance on its own, without the need to apply a lubricating varnish over it.

[0012] Furthermore, if necessary, when wear becomes too severe, such an anti-wear coating can be stripped and reconditioned, without it being necessary to replace the entire blade. Repair is therefore easy and inexpensive.

[0013] In some embodiments, the anti-wear coating is made essentially from a Nickel-Cobalt based alloy. Indeed, upon exposure to heat, these alloys form oxides, in particular cobalt oxides, which play a role of dry lubrication at the contact surface.

[0014] In some embodiments, the anti-wear coating is made essentially of a nickel-based alloy.

[0015] In certain embodiments, the anti-wear coating is made essentially from an alloy comprising at least 3% by mass, and preferably between 3 and 30% by mass, of Molybdenum. Preferably, when the alloy is Nickel or Nickel-Cobalt based, the Molybdenum content does not exceed 5% by mass. The addition of molybdenum to the composition makes it possible to form molybdenum oxides which extend the temperature range over which dry lubrication is effective.

[0016] In certain embodiments, the anti-wear coating is made essentially from an alloy comprising at least 3% by mass, and preferably between 3 and 5% by mass, of Silicon. Similarly to molybdenum, the addition of silicon to the composition makes it possible to form silicon oxides which extend the temperature range over which dry lubrication is effective.

[0017] In some embodiments, the alloy of the anti-wear coating comprises carbide particles, preferably chromium carbide. The carbide particles, due to their hardness, make it possible to limit the consumption of the anti-wear coating during friction. The chromium carbide particles are particularly suitable in the context of a nickel-based alloy, preferably comprising a high chromium content: in fact, such alloys have a certain ductility forming a good matrix for the carbide particles.

[0018] In some embodiments, the anti-wear coating is made essentially of one of the following alloys, René 80 (registered trademark), Cr3C2-Ni20Cr or Inconel 718 (registered trademark). These three alloys have shown very good results during tests carried out by the inventors.

[0019] In some embodiments, the anti-wear coating comprises a thickness of between 0.1 and 1.5 mm, preferably between 0.1 and 1.0 mm, more preferably between 0.1 and 0.3 mm. Such thicknesses are suitable to ensure a good interface with the disc socket.

[0020] In some embodiments, the anti-wear coating is present only on all of the blade's bearing surfaces. The coating is thus deposited only where it is useful, which limits the cost of the operation. In addition, the deposition of a coating may not be desired in certain areas for reasons of dimensional constraints or mechanical strength of the part.

[0021] In some embodiments, the anti-wear coating is devoid of a protective varnish. In other words, the anti-wear coating is directly exposed to the external environment of the blade, and therefore in contact with the retaining surfaces of the disc when the blade is mounted. Indeed, the tests have demonstrated that it was possible to obtain equally good, or even better, results with such anti-wear coatings compared to configurations using a lubricating varnish. It is therefore possible to do without a long and tedious step of applying such a varnish.

[0022] In some embodiments, the anti-wear coating is deposited by thermal spraying, preferably by plasma spraying.

[0023] In some embodiments, the blade further comprises a blade head comprising at least one heel surface, said heel surface being provided with an anti-wear coating of the same nature as the anti-wear coating of the blade root. Thus, it is possible to use the same material to protect both the blade root and the blade head: this simplifies the manufacturing process of the blade.

[0024] In certain embodiments, said blade is a moving blade. Indeed, friction, and therefore the wear phenomenon, is greater when the blade rotates in the turbomachine.

[0025] In some embodiments, said blade is a turbine blade. Indeed, the wear phenomenon is more significant at high temperature.

[0026] The present disclosure also relates to a turbomachine module, comprising a disk, comprising a plurality of cells, and a plurality of blades according to any one of the preceding embodiments, the blade root of each blade being engaged in a cell of the disk so that the bearing surfaces of the blade root are in contact with retaining surfaces of the cell.

[0027] In some embodiments, the turbomachine module is devoid of foil at the interface between the blade roots and the disk.

[0028] The present disclosure also relates to a turbomachine, comprising a turbomachine blade or module according to any of the preceding embodiments.

[0029] In this presentation, the terms "longitudinal", "transverse", "lower", "upper" and their derivatives are defined with respect to direction main axis of the blades; the terms "axial", "radial", "tangential", "internal", "external" and their derivatives are defined in relation to the main axis of the turbomachine; "axial plane" means a plane passing through the main axis of the turbomachine and "radial plane" means a plane perpendicular to this main axis; finally, the terms "upstream" and "downstream" are defined in relation to the circulation of air in the turbomachine.

[0030] In this presentation, a material is considered to be based on an element when this element represents the majority element, by mass, in the composition of the material.

[0031] In the present disclosure, it is considered that a part or part of a part is made essentially of a given material when it is formed at least 80%, preferably 90%, more preferably 99%, by this material.

[0032] The above-mentioned features and advantages, as well as others, will become apparent from the following detailed description of examples of embodiments of the proposed blade. This detailed description refers to the attached drawings.

[0033] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. Brief description of the drawings

[0034] The attached drawings are schematic and are intended primarily to illustrate the principles of the presentation.

[0035] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference signs.

[0036] [Fig. 1] Figure 1 is a schematic axial section of an example of a turbomachine.

[0037] [Fig. 2] Figure 2 is a perspective view of an example of a blade.

[0038] [Fig. 3] Figure 3 is an enlarged view of the blade root of Figure 2.

[0039] [Fig. 4] Figure 4 schematically illustrates a rotating disk.

[0040] [Fig. 5] Figure 5 schematically illustrates a test device.

[0041] [Fig. 6] Figure 6 illustrates the results of initial tests carried out by the inventors.

[0042] [Fig. 7] Figure 7 illustrates the results of second tests carried out by the inventors. Description of the embodiments

[0043] In order to make the disclosure more concrete, an example of a blade is described in detail below, with reference to the attached drawings. It is recalled that the invention is not limited to this example.

[0044] Fig. 1 represents, in section along a vertical plane passing through its main axis A, a double-flow turbojet 1 according to the description. It comprises, from upstream to downstream according to the circulation of the air flow, 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.

[0045] Fig. 2 shows in more detail a moving blade 10 of the low-pressure turbine 7. This blade 10 comprises a blade root 11, a blade part 12 and a blade head 13. An internal platform 14 is provided at the interface between the blade root 11 and the blade part 12. The internal platform 14 extends, on each side, upstream and downstream, by radial walls 15 each provided with an axial spoiler 16.

[0046] As best seen in Fig. 3, the blade root 11 comprises an axially extending dovetail portion 20 having a neck 21, diverging lateral surfaces 22 forming bearing surfaces, and a lower surface 23.

[0047] The blade head 13 for its part comprises an external platform 17 and, on each side in the circumferential direction, heel surfaces 18 intended to fit with the heel surfaces of the adjacent blades when the blades are mounted.

[0048] Fig. 4 illustrates the rotating disc 30 on which the moving blade 10 is intended to be mounted. A plurality of cells 31 are made in the outer surface of the disc 30: these cells 31 are rectilinear and extend axially from upstream to downstream along the entire length of the disc 30. They are furthermore regularly distributed all around the axis A of the disc 30. In this way, each cell 31 defines with its neighbor a tooth 32 which thus also extends axially from upstream to downstream along the entire length of the disc 30. Each cell 31 has a bottom 33, two converging lateral surfaces 34, forming retaining surfaces, and a narrowed opening 35.

[0049] The moving blade 10 is mounted on the disc 30 by engaging the dovetail portion 20 of its root 11 in a cell 31 of the disc 30. Thus, the width of the opening 35 is designed to correspond substantially to the width of the neck 21 of the blade root 11. Therefore, in the mounted state, the bearing surfaces 22 of the blade root 11 are in contact with the retaining surfaces 34 of the cell 31 of the disc 30.

[0050] In the present invention, at least the blade root 11, and preferably the entire moving blade 10, is made essentially of TiAI, possibly shot-peened. The disc 30 is made essentially of Inconel 718 (registered trademark), preferably shot-peened.

[0051] In order to protect the bearing surfaces 22 of the blade root 11 against wear caused by friction with the retaining surfaces 34 of the disc 30, the bearing surfaces 22 of the blade root 11 are provided with an anti-wear coating. Several materials are possible for producing this anti-wear coating: in a first example, the anti-wear coating is made of Cr3C2-Ni20Cr; in a second example, the anti-wear coating is made of René 80; in a third example, the anti-wear coating is made of Inconel 718 (registered trademark).

[0052] In all these examples, the anti-wear coating can be deposited by plasma spraying; however, in other examples, other spraying modes would be possible, for example hypersonic thermal spraying (HVOF), detonation gun or even arc wire. The thickness of the coating is between 0.1 and 0.3 mm; preferably, this thickness is determined so as to ensure permanent contact between the bearing surfaces 22 of the blade 10 and the retaining surfaces 34 of the disk 30. The other surfaces of the blade root 11 are devoid of such a coating: they are in fact masked during the plasma projection step. Furthermore, it should be noted that, in these examples, no additional lubricating varnish is deposited over this anti-wear coating.

[0053] A similar anti-wear coating may be deposited on the heel surfaces 18 of the blade head 13 in order to protect them from wear caused by contact with the heel surfaces of adjacent blades.

[0054] Tests highlighting the performance of the different examples of anti-wear coatings will now be described.

[0055] Fig. 5 illustrates a part of the test device 40 used during these tests. This test device 40 thus comprises a fixed punch 41, against which a movable button 42 is pressed. During the test, an actuator (not shown) pushes the button 42 against the punch 41 in a plane contact while moving it along an alternating rectilinear path, along the surface of the punch 41.

[0056] Several configurations were tested. Three configurations E1, E2 and E3 are configurations according to the disclosure, implementing anti-wear coatings comprising materials from among those presented above. Two configurations C1 and C2 are comparative configurations for which the substrate has no protection. Comparative configuration C3 provides a simple lubricating varnish. Comparative configuration C4 corresponds to the situation in which a foil made of HS25 alloy (registered trademark) is inserted between the blade root 11 and the cell 31 of the disk 30. Finally, comparative configurations C5 to C7 provide other types of anti-wear coatings associated with a lubricating varnish.Thus, in each of the tests carried out with the exception of configuration C4, punch 41 was made of Inconel 718 (registered trademark) to correspond to the material of disc 30; in the comparative test according to configuration C4, punch 41 was made of HS25 to correspond to the usual material of an interlayer foil. The different configurations tested are presented in detail in the table below.

[0057] [Table 1]

[0058] In each of these tests, the average pressure exerted on button 42 was equal to 212 MPa; the deflection of button 42 from its central position was equal to ±1 OOpm; the frequency of the reciprocating movement was equal to 20 Hz; the test duration was equal to 50,000 cycles, or 42 minutes; and the test temperature was equal to 625 °C.

[0059] For each configuration tested, the average friction coefficient and the worn volumes were measured, i.e. the volumes lost respectively by the punch 41 and the button 42.

[0060] The measured values ​​for the friction coefficients of the different configurations tested are shown in the graph in Fig. 6. It can be seen that the friction coefficients of the three configurations according to the description E1, E2, E3 are lower than the friction coefficients of the comparative configurations C1 and C2 in which the substrate is devoid of any protection; these friction coefficients are also lower than in the comparative configuration C3 corresponding to the situation in which a HS25 alloy foil is inserted between the blade root 11 and the cell 31 of the disc 30. It is also noted that the friction coefficients of these three configurations E1, E2 and E3 are comparable to the friction coefficients of the comparative configurations C5 to C7 using a coating of another type associated with a lubricating varnish.

[0061] The measured values ​​for the used volumes of the different configurations tested are represented on the graph in Fig.7: the volume lost per button is represented with small dots, in the lower part of each bar, while the volume lost by the punch is represented with hatching, in the upper part of each bar; the value indicated at the top of each bar therefore corresponds to the total lost volume.

[0062] It is then noted that the total used volumes are very much lower in the configurations according to the description E1, E2, E3 compared to the comparative configurations C1 and C2 in which the substrate is not protected; or again compared to the comparative configuration C3 corresponding to the situation in which a HS25 alloy foil is inserted between the blade root 11 and the cell 31 of the disc 30. It is also noted that the volume lost by the button 42 in the configurations E1, E2 and E3 is always lower than the volume lost by the button 42 in the comparative configurations C5 to C7 using a coating of another type associated with a lubricating varnish. Incidentally, it is also noted thanks to the comparative configuration C3 that a simple lubricating varnish, used alone, is insufficient to effectively protect the substrate.

[0063] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0064] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. A blade for a turbomachine, comprising a blade portion (12), and a blade root (11), the blade root (11) comprising at least one bearing surface (22) configured to cooperate with a fixing device (31) of the turbomachine (1), in which at least the blade root (11) is made of TiAI, and in which the bearing surface (22) is provided with an anti-wear coating, this anti-wear coating being made of a Nickel-based alloy comprising at least 9.5% by mass of Co and / or at least 14% by mass of Cr.

2. Blade according to claim 1, in which the anti-wear coating is made from an alloy comprising at least 3% by mass, and preferably between 3 and 30% by mass, of Molybdenum.

3. Blade according to claim 1 or 2, in which the anti-wear coating is made from an alloy comprising at least 3% by mass, and preferably between 3 and 5% by mass, of Silicon.

4. A blade according to any one of claims 1 to 3, wherein the alloy of the anti-wear coating comprises carbide particles, preferably chromium carbide.

5. A blade according to any one of claims 1 to 4, wherein the anti-wear coating is made from one of the following alloys: René 80, Cr3C2-Ni20Cr or Inconel 718 (registered trademark).

6. A blade according to any one of claims 1 to 5, wherein the anti-wear coating comprises a thickness of between 0.1 and 1.5 mm, preferably between 0.1 and 1.0 mm, more preferably between 0.1 and 0.3 mm.

7. A blade according to any one of claims 1 to 6, wherein the anti-wear coating is free of a protective varnish.

8. A blade according to any one of claims 1 to 7, wherein the anti-wear coating is deposited by thermal spraying, preferably by plasma spraying.

9. A turbomachine module, comprising a disc (30), comprising a plurality of cells (31), and a plurality of blades (10) according to any one of claims 1 to 8, the blade root (11) of each blade (10) being engaged in a cell (31) of the disc (30) so that the bearing surfaces (22) of the blade root (21) are in contact with retaining surfaces (34) of the cell (31).

10. A turbomachine, comprising a blade (10) according to any one of claims 1 to 8 or a turbomachine module (7) according to claim 9.

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