Method for manufacturing a part made from CMC

Abstract

Method for manufacturing a CMC, i.e. ceramic matrix composite material, part provided with at least one cutout, as well as to such a CMC part provided with at least one cutout, the method comprising the following steps: providing (E1) a fibrous reinforcement (10), forming (E2′) a cavity in a portion of the fibrous reinforcement (10), injecting (E3) a slip comprising at least a ceramic powder and a solvent, the slip being injected so as to impregnate the fibrous reinforcement (10′) and to fill the cavity of the fibrous reinforcement (10′), drying (E4) the obtained assembly, carrying out a densification (E6) by infiltration of a liquid densification material and solidification of said densification material, machining (E7) at least one cutout in the obtained blank (30) within the volume corresponding to the cavity of the fibrous reinforcement (10).

Claims

1. A method for manufacturing a CMC part provided with at least one cutout, comprising the following steps: providing a fibrous reinforcement; forming a cavity in a portion of the fibrous reinforcement; injecting a slip comprising at least a ceramic powder and a solvent, the slip being injected so as to impregnate the fibrous reinforcement and to fill the cavity of the fibrous reinforcement; drying the obtained assembly; carrying out a densification by infiltration of a liquid densification material and solidification of said densification material; and machining at least one cutout in the obtained blank within the volume corresponding to the cavity of the fibrous reinforcement, wherein the arithmetic average roughness Ra of the inner walls of the cutout machined in the blank is less than 5 μm.

2. The method according to claim 1, wherein the fibrous reinforcement is made by 3D-weaving.

3. The method according to claim 1, wherein, during the slip injection step, the slip is injected so as to further fill a volume located on the surface of the portion of the fibrous reinforcement in which the cavity has been formed.

4. The method according to claim 1, wherein the cutout machined in the blank is a groove having a width of less than 1 mm.

5. The method according to claim 1, wherein the cutout machined in the blank is a groove having a depth of at least three times greater than its width.

6. The method according to claim 1, wherein the machining step is carried out by milling, grinding and/or electrical discharge machining.

7. The method according to claim 1, further comprising a step of depositing a protective coating on at least one face of the final part which is devoid of cutout; and wherein the face of the final part in which the cutout has been machined is devoid of protective coating.

8. A method for manufacturing a CMC part provided with at least one cutout, comprising the following steps: providing a fibrous reinforcement, forming a cavity in a portion of the fibrous reinforcement, injecting a slip comprising at least a ceramic powder and a solvent, the slip being injected so as to impregnate the fibrous reinforcement and to fill the cavity of the fibrous reinforcement, drying the obtained assembly, carrying out a densification by infiltration of a liquid densification material and solidification of said densification material, and machining at least one cutout in the obtained blank within the volume corresponding to the cavity of the fibrous reinforcement, wherein the machining step is carried out by milling, grinding and/or electrical discharge machining.

9. The method according to claim 8, wherein the fibrous reinforcement is made by 3D-weaving.

10. The method according to claim 8, wherein, during the slip injection step, the slip is injected so as to further fill a volume located on the surface of the portion of the fibrous reinforcement in which the cavity has been formed.

11. The method according to claim 8, wherein the cutout machined in the blank is a groove having a width of less than 1 mm.

12. The method according to claim 8, wherein the cutout machined in the blank is a groove having a depth of at least three times greater than its width.

13. The method according to claim 8, wherein the arithmetic average roughness Ra of the inner walls of the cutout machined in the blank is less than 5 μm.

14. The method according to claim 8, further comprising a step of depositing a protective coating on at least one face of the final part which is devoid of cutout; and wherein the face of the final part in which the cutout has been machined is devoid of protective coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The appended drawings are schematic and aim above all at illustrating the principles of the invention.

(2) In these drawings, from one figure (FIG) to the other, identical elements (or parts of elements) are identified by the same reference signs. In addition, elements (or parts of elements) belonging to different exemplary embodiments but having a similar function are identified in the figures by numeral references incremented by 100, 200, etc.

(3) FIG. 1 is a sectional diagram of a turbomachine according to the present disclosure.

(4) FIG. 2 is a schematic view of a sectorized turbine ring.

(5) FIG. 3 is a perspective view of a ring sector according to the present disclosure.

(6) FIG. 4 illustrates the successive steps of a first example of a method according to the disclosure.

(7) FIG. 5 illustrates the progression of the part during this first example of method.

(8) FIG. 6 illustrates the progression of the part during a second example of a method.

DETAILED DESCRIPTION OF EMBODIMENT(S)

(9) In order to make the invention more concrete, examples of methods are described in detail hereinafter, with reference to the appended drawings. It is recalled that the invention is not limited to these examples.

(10) FIG. 1 represents, in cross-section along a vertical plane passing through its main axis A, a turbofan engine 1 according to the invention. It includes, 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.

(11) FIG. 2 illustrates the ring 60 of the high-pressure turbine 6 defining the external limit of the air flowpath within the high-pressure turbine 6. This ring 60 is divided into several substantially identical CMC sectors 61 connected by metal sealing tabs 62.

(12) FIG. 3 illustrates such a sector 61: it comprises a flowpath wall 63, an upstream flange 64 and a downstream flange 65. The flowpath wall 63, having the shape of a cylinder sector, is configured to form together with the other sectors 61 a cylindrical ring of axis A. The flowpath wall has a main inner face 63p, intended to delimit the air flowpath, an upstream end face 63m, a downstream end face 63v and two intersector lateral faces 63i.

(13) A groove 66 is formed in each intersector face 63i. These grooves 66, extending axially over practically the entire length of the flowpath wall 63, have in this example a depth of 3 mm and a width of 0.5 mm. The inner walls of the grooves 66 have an average arithmetic roughness Ra of less than 1.6 μm.

(14) The tab 62, made of a nickel or cobalt base alloy, has a length substantially equal to that of the groove 66 and a thickness slightly smaller than the latter in order to allow the insertion of the tab 62 in a groove 66.

(15) FIGS. 4 and 5 illustrate the different steps of an example of method according to the exposure making it possible to manufacture such a CMC, i.e. ceramic matrix composite material, ring sector 61. Particularly, FIG. 5 is a schematic representation not taking into account the exact shape of the part.

(16) The method begins with the weaving E1 of a fibrous preform 10 which will act as fibrous reinforcement of the sector 61. This preform 10 is preferably woven according to a 3D-weaving technique, known moreover, for example with an interlock-type weave. In this example, the preform 10 is woven with silicon carbide SiC fibers.

(17) Once the preform 10 is finished, it is shaped and undergoes an interphase deposition step E2, also known, for example of the chemical vapor deposition (CVD) type. In this example, the interphase material deposited is silicon carbide SiC. A SiC sheath is therefore formed around the fibers of the preform 10, which consolidates the preform 10 and blocks the given shape during the shaping. At the end of this interphase deposition step E2, the fibers of the preform 10 are therefore coated with an interphase sheath but the preform 10 still remains very porous.

(18) During a machining step E2′, a trench 18 is carved in each lateral face 19 of the preform 10 corresponding to the intersector faces 63i of the final sector 61. A consolidated and cut preform 10′ is then obtained.

(19) The consolidated and cut preform 10′ is then transferred in a mold to undergo a ceramic slip injection step E3. In this example, the slip comprises a solvent, here water, a ceramic powder, here silicon carbide SiC, and an organic binder, here polyvinyl alcohol.

(20) In this example, the concentration of the SiC powder in the slip is around 20% by volume. The concentration of the binder is for its part 1% by mass relative to the mass of the SiC powder in the slip.

(21) The mold is provided for its part so as to match the shape of the preform 10′ while leaving a free volume inside the trenches 18. Thus, when the slip is injected into the mold, it impregnates on the one hand the preform 10′ and fills on the other hand the free volume inside the trenches 18 of the preform 10′.

(22) A drying step E4 is then carried out to remove the solvent from the slip. In this example, it is a lyophilization step (also known as “freeze-drying”), during which the mold is suddenly brought to a negative temperature in order to solidify the solvent and then gradually heated at very low pressure so as to cause the sublimation of the solvent practically without altering the surrounding materials, the gas-phase solvent being then removed using a cold trap for example.

(23) According to one variant, the drying step E4 could comprise a step of controlled evaporation of the solvent during which the temperature of the enclosure is gradually raised from 50 to 120° C. at the rate of an increase from 1 to 5° C./min, preferably 1° C./min.

(24) According to yet another variant, the drying step E4 could comprise a Deliquoring step carried out under a pressure comprised between 50 and 100 mbar, for 1 to 2 hours.

(25) During the drying step E4, within the preform 10′, the ceramic particles of the slip decant and are deposited on the fibers of the preform as the solvent is removed, thus filling part of the porosities of the preform 10. Furthermore, within the free volume, the ceramic particles agglomerate and bond to each other under the effect in particular of the organic binder.

(26) Thus, at the end of the drying step E4, a green part 20 is obtained having a first portion 21 provided with the reinforcement formed by the fibrous preform 10 and a second portion 22, within the trenches 18 and devoid of the fibrous reinforcement 10, consisting of agglomerated ceramic powder having a compaction rate greater than 50%.

(27) The thus obtained green part 20 then undergoes an annealing and pre-sintering step E5 making it possible to strengthen the connections between the particles of the ceramic powder and therefore to strengthen the resistance of the green part 20, especially in its second portion 21.

(28) In this example, the annealing occurs under neutral gas, for example argon, at a temperature of 1400° C. for 1 hour.

(29) Once this step E5 is completed, the green part 20 is demolded and transferred to undergo a densification step E6. During this densification step E6, a liquid densification material, here silicon Si, is poured onto the green part 20: the densification material then penetrates by capillary action within the green part 20, whether in its first portion 21 or its second portion 22, and fills the residual porosities of the green part 20.

(30) After cooling and solidification of the densification material, a blank 30 is obtained which no longer has, or practically no longer has, porosities. In a manner similar to the green part, the blank 30 has a first portion 31, provided with the reinforcement formed by the fibrous preform 10 and embedded in the matrix, and a second portion 32, located within the trenches 18, devoid of the fibrous reinforcement 10 and consisting exclusively of matrix.

(31) It is then possible during a machining step E7, preferably by electrical discharge machining, to form the grooves 66 within the second portion 32, without starting the fibrous reinforcement 10, in order to obtain the final ring sector 61.

(32) Naturally, other machining operations are also possible in the second portion 32 of the blank 30 without exposing the fibers of the fibrous reinforcement 10. In addition, some faces of the ring sector 61, and in particular the main inner face 63p, can receive a thermal coating. The intersector faces 63i are for their part preferably devoid of such a thermal coating.

(33) FIG. 6 illustrates a second exemplary embodiment of the proposed method. Only the differences with the first example will be described. Particularly, the succession of the different steps remains identical to that of FIG. 3, only the slip injection step E3 being implemented differently.

(34) Thus, the method begins with the weaving E1 of a fibrous preform 110 similar to that of the first example. It undergoes an interphase deposition step E2 similar to that of the first example then a machining step E2′ similar to that of the first example leading to obtaining a consolidated and cut preform 110′ provided with trenches 118 made in each of its lateral faces 119.

(35) The consolidated and cut preform 110′ is then transferred in a mold to undergo a ceramic slip injection step E3. Similarly to the previous example, the slip comprises a solvent, here water, a ceramic powder, here silicon carbide SiC, and an organic binder, here polyvinyl alcohol, with identical concentrations.

(36) On the other hand, the mold used has a shape different from that of the first example, it is indeed provided so as to match the shape of the preform 110′ while leaving a free volume inside the trenches 18 but also on the surface of the lateral faces 119 of the preform. Thus, when the slip is injected into the mold, it impregnates on the one hand the preform 110′ and fills on the other hand the free volume left inside the trenches 118 and in front of the lateral faces 119 of the preform 110′.

(37) A drying step E4 is then carried out in a manner similar to the first example. Thus, at the end of the drying step E4, a green part 120 is obtained having a first portion 121 provided with the reinforcement formed by the fibrous preform 110 and a second portion 122, devoid of the fibrous reinforcement 110 and consisting of agglomerated ceramic powder with a compaction rate greater than 50%. The main surfaces 119 of the preform 110 are then located at the interface between these first and second portions 121, 122 of the green part 120.

(38) The green part 120 thus obtained then undergoes an annealing and pre-sintering step E5 similar to the first example. Once this step E5 is completed, the green part 120 is demolded and transferred to undergo a densification step E6 similar to the first example.

(39) After cooling and solidification of the densification material, a blank 130 is obtained which no longer has, or practically no longer has, porosities. Similarly to the green part, the blank 130 has a first portion 131, provided with the reinforcement formed by the fibrous preform 110 and embedded in the matrix, and a second portion 132, devoid of the fibrous reinforcement 110 and consisting exclusively of matrix.

(40) Particularly, since the main surfaces 119 of the preform 110 extended inside the green part 120, the densification at these lateral surfaces 119 could be complete and homogeneous, without side effect.

(41) It is then possible during a machining step E7, preferably by electrical discharge machining, to form the grooves 166 within the second portion 132, without starting the fibrous reinforcement 110, in order to obtain the final ring sector 161.

(42) In this second example, the matrix layers devoid of fibrous reinforcement obtained on the surface of the lateral faces 119 of the preform 110 allow protecting the intersector surfaces 163i of the final sector 161 without it being necessary to deposit a specific thermal coating therein.

(43) Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. Particularly, individual characteristics of the different illustrated/mentioned embodiments can be combined in additional embodiments. Therefore, the description and the drawings should be considered in an illustrative rather than restrictive sense.

(44) It is also obvious that all the characteristics described with reference to a method can be transposed, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device can be transposed, alone or in combination, to a method.