Chemical vapor infiltration densification method using single stack for semi-forced flow

Abstract

The invention relates to a method for densifying a porous annular substrate (21) having a central channel (21a) by chemical vapor infiltration, comprising at least the following steps: providing a stack (20) of porous annular substrates (21); providing a plurality of individual modules (30), the individual modules (30) comprising a stack (20) disposed on support plates (31), each support plate having a perforated injection tube (33), each injection tube mounted on a gas inlet opening (32); forming a stack of individual modules (30), aligning the stacked individual modules (30) in a sealing manner by means of an annular seal (35) arranged between the injection tube (33) of the second individual module (30b) and the gas inlet opening (32) of the first individual module (30a) cooperating therewith, and injecting a gas phase into the internal volume (24) of each stack (20) of porous annular substrate (21), the gas phase comprises a gaseous precursor of a matrix material to be deposited in the pores of the substrate (21).

Description

Technical Field

[0001] The present invention relates to the production of composite parts comprising porous annular substrates densified by chemical vapor infiltration (CVI), and more particularly to the production of parts having a central channel.

[0002] The invention is particularly, but not exclusively, suitable for the production of annular brake friction disks or diverging nozzles for rocket engines made of thermostructural composite materials. Background Art

[0003] Thermostructural composites are noteworthy for their excellent mechanical properties and their ability to maintain these properties at high temperatures. Typical examples of thermostructural composites are carbon-carbon (CC) composites, which include a porous reinforcing matrix of carbon fibers densified by a carbon matrix, and ceramic matrix composites (CMCs), which include a porous reinforcing matrix of refractory fibers (such as carbon or ceramic) densified by a ceramic matrix (such as silicon carbide).

[0004] CC composites are commonly used in aircraft brake friction discs due to their high energy friction properties, non-brittleness, thermal properties (conductivity and heat capacity), and density.

[0005] Densification of a porous substrate by chemical vapor infiltration (CVI) consists in placing an annular preform in a reaction chamber of an infiltration device and introducing into the reaction chamber a gas phase, one or more of whose components form a precursor of the matrix material, to be deposited in the substrate to ensure its densification. The infiltration conditions, in particular the composition and flow rate of the gas phase, as well as the temperature and pressure in the chamber are chosen to allow the gas phase to diffuse in the accessible internal pores of the substrate, thereby depositing the desired material therein, either by decomposition of the gas phase components or by reaction between several of its components. Document FR 2,834,713 describes such a method and a device for implementing it.

[0006] The conditions for chemical vapor infiltration of pyrolytic carbon are already known to those skilled in the art. The carbon precursor is an alkane, an alkyl or an alkene, usually propane, methane or a mixture of the two. For example, the infiltration is carried out at a temperature of about 1000° C. and a pressure of about 1 kPa.

[0007] A gas phase containing the precursor of the material to be deposited in the preform is introduced at one longitudinal end of the reaction chamber, while the residual gas is evacuated at the opposite end, being withdrawn from this end by means of pumping means.

[0008] The reactors used for conducting research and development on the penetration of brake friction discs have a load configuration that usually consists of a stack of plates, each carrying one stack of discs. These are so-called "single-stack" furnaces. This configuration differs from industrial loads produced in large reactors, where the plates carry several stacks of discs side by side, so-called "multi-stack" furnaces.

[0009] In both cases, the disks are separated by intermediate supports called spacers, and the plates include openings aligned with the central channels of the disks so that the reactive gas phase circulates in each stack, which then passes through the disks to densify it. An upper plate is located above the load and closes the internal space of each stack. The plates supporting the stack of disks are fixed by vertical rods.

[0010] The traditional densification method used in industry and suitable for R&D furnaces is oriented flow.

[0011] Figure 1 A known example of a single stack of trays that can be used in a reaction chamber (commonly referred to as a "densification furnace") is shown.

[0012] The chamber 1 has a cylindrical symmetry about an axis Z. The load comprises a stack of individual modules 2, each of which comprises a single stack 3 of porous annular substrates 4 supported by a lower support plate 5. The plate 5 comprises an opening 6 aligned with a central channel 7 of the substrate 4 so that a reactive gas phase circulates in each stack 3, which then passes through the substrate 4 to densify it. An annular cover disc 8 is mounted above each stack 3, and each individual module 2 also comprises a vertical rod 9 extending between the support plate 5 of the individual module 2 and the support plate 5 of the individual module 2 above. The vertical rod 9 is used to bear the mass of the upper support plate 5, so that the support plate 5 can be ensured to remain in the proper position.

[0013] Figure 1 Schematic diagram of the hot zone of the directional flow load. The hot zone includes from bottom to top: the reaction gas mixture inlet 10, then the preheating zone 11, which can raise the gas temperature to the densification temperature, and finally the load zone 12. At the top of the furnace, at the base cover 13, a chimney 14 is installed in the cover 13, and the waste gas generated by the deposition reaction is discharged through the chimney 14.

[0014] On each plate 5 there is a stack of substrates 4 separated by spacers 15, each stack having a cover disc 8 on top to limit leakage.

[0015] The gas at the end of the preheating zone 11 enters each column of stacks 3 of substrates 4. The gas passes from the inside of the column of substrates 4 to the outside via leaks constituted by the pores of each preform 4, the gaps between the substrates 4 created by the spacers 15 and the channels between the plates 5.

[0016] Document FR 2,821,859 discloses a chemical vapor infiltration densification method for porous substrates, in particular using semi-forced flow. In order to adapt to the semi-forced flow described in this document, it is necessary to control the leakage between the substrates and also the leakage in the channels between the plates. In other words, in addition to controlling the leakage related to the porosity of the preform 4, controlling other leakages can also improve the densification kinetics: this is the implementation of the so-called "semi-forced flow" method.

[0017] The implementation of semi-forced flow consists in providing calibrated leakage channels between the inside and outside of the substrate array, which involves sealing the free areas left when implementing the current directed flow method: these areas are located in particular at the junctions between the inter-disc spacers and the support plates of the lower stack and the upper individual modules.

[0018] As the preform densifies between the inside of the stack (where the gas arrives) and the outside, a pressure gradient will build up and increase. The installation of a calibrated leak must allow this pressure gradient to be limited in order to avoid soot deposition inside the substrate stack due to excessive pressure. Monitoring the pressure gradient, which reflects the progress of densification, is therefore essential for the performance of the cycle.

[0019] Leakage in the inter-plate channels is the most difficult to control because the stack heights of the porous annular substrates are not the same. If the seal at the top of each stack is not well controlled, the pressure differential required to force the gas into the pores of the substrate 2 cannot be achieved.

[0020] It is also known from patent FR 3,084,892 to replace the rods with gas distributors, which make it possible to simultaneously perform the functions of bearing the load (function previously performed by the rods), directing the gas (cold), which avoids cooling plates, and gas distribution at the level of the preforms. Summary of the invention

[0021] The object of the present invention is to provide a technical solution for implementing a densification method which allows improving the distribution of the reaction gases in the load zone of a densification furnace and which allows generally reducing the densification gradient between substrates located at different positions in the load zone, without affecting the load capacity of the furnace, or even increasing its load capacity.

[0022] One object of the present invention is to provide a method for densifying a porous annular substrate having a central channel by pressure gradient chemical vapor infiltration, the method comprising at least the following steps:

[0023] - providing a stack of a plurality of porous annular substrates, each stack comprising an inner volume formed by a central channel of the stacked substrates,

[0024] - providing a plurality of individual modules, each of which comprises a support plate and a single stack of porous annular substrates arranged on the support plate, the support plate having a gas inlet opening and an injection tube mounted on the gas inlet opening, the injection tube extending into the inner volume of the stack between a first tube end connected to the support plate and a free second tube end, the injection tube also comprising a gas injection hole opening into the inner volume,

[0025] - forming a stack of individual modules in the chamber of the densification furnace, each first individual module being stacked on a second individual module, the gas inlet opening of the support plate of a first individual module being in communication with the second end of the injection pipe of the second individual module stacked thereon, so as to allow gas circulation between the individual modules, and

[0026] - Injecting a gas phase comprising a gaseous precursor of the matrix material to be deposited in the pores of the substrates into the inner volume of each porous annular substrate stack.

[0027] According to a general feature of the present invention, in each individual module, each first porous annular substrate is supported on a second porous annular substrate, or on a support plate, by a sealing ring, which provides a radial seal between the first porous annular substrate and the second porous annular substrate or between the first porous annular substrate and the support plate.

[0028] In other words, each individual module comprises a plurality of sealing rings, each sealing ring being placed in a support between two consecutive porous annular substrates or between a porous annular substrate and a support plate.

[0029] A “radial seal” is understood to mean a seal which prevents gas from circulating radially between the internal volume of the stack and the outside of the stack.

[0030] Therefore, the present invention can better control the circulation of gas around the porous annular substrate, thereby improving the distribution of gas in the furnace chamber.

[0031] Furthermore, in each individual module, each sealing ring is coupled to an annular spacer having an inner diameter equal to the inner diameter of the porous annular substrate.

[0032] The annular spacer allows the sealing ring to be centred, thereby facilitating its positioning.

[0033] The thickness of each annular spacer is less than the thickness of the sealing ring to which it is coupled. This thickness ratio has the advantage of ensuring that the porous annular substrate is supported on the sealing ring. This ensures a radial seal. In addition, this thickness ratio has the advantage of allowing the gas phase to circulate freely around the porous annular substrate.

[0034] In an exemplary embodiment, each stack includes at least one cover disk supported on a porous annular substrate at the top of the stack by a sealing ring that provides a radial seal between the cover disk and the porous annular substrate at the top of the stack.

[0035] Each stack may further comprise a deformable annular seal arranged to be compressed between the cover disc and the support plate of the upper individual module.

[0036] The deformable annular seal is made of, for example, carbon fiber felt.

[0037] Furthermore, each stack may also include an expanded graphite disk disposed between the deformable annular seal and the support plate of the upper individual module. The expanded graphite disk prevents the deformable annular seal from sticking to the support plate above.

[0038] According to a first embodiment, in each individual module, a sealing ring is arranged at the radial outer periphery of the porous annular substrate.

[0039] According to the second embodiment, in each individual module, the sealing rings are alternately disposed at the radial outer circumference of the porous annular substrate and the radial inner circumference of the porous annular substrate along the direction in which the porous annular substrates are stacked.

[0040] These two embodiments can maximize the contact surface of the porous annular substrate with the gas phase.

[0041] The sealing ring is made of e.g. Made.

[0042] The annular spacer can also be made of Made.

[0043] For example, each sealing ring is welded to the annular spacer to which it is coupled. The welding facilitates the formation of the stack.

[0044] According to a particular embodiment, the method further comprises placing a solid cover on top of the stack of individual modules. The solid cover compresses the deformable elements, in particular the sealing rings and the deformable annular seals.

[0045] According to a specific embodiment, the method also includes a sealing alignment step of the stacked individual modules, including: for each first individual module stacked on a second individual module, inserting the second end of the injection pipe of the second individual module into the gas inlet opening of the first individual module stacked on the second individual module, and an annular seal is arranged between the second end of the injection pipe of the second individual module and the gas inlet opening of the first individual module stacked on the second individual module.

[0046] In an exemplary embodiment, for each individual module, the support plate may include a first face and a second face opposite to the first face, the stack of individual modules being arranged on the first face, the gas inlet opening may include a truncated conical shape having a first diameter formed on the second face of the support plate and a second diameter smaller than the first diameter formed on the first face of the support plate or between the first face and the second face, and the second end of the injection pipe may include a complementary truncated conical shape that matches the truncated conical shape of the gas inlet opening.

[0047] The injection tube thus forms the male centering means and the gas inlet opening forms the female centering means, which cooperate together to ensure good centering of the individual modules with respect to each other.

[0048] Preferably, each support plate may include a centering ring on its first face, the centering ring being centered on the gas opening and shaped to receive the injection tube.

[0049] The centering ring thus facilitates and optimizes the assembly of the injection pipe on the support plate.

[0050] In one example of implementation of the method, the method may further comprise the step of arranging the stack of individual modules on a carrying shell, the carrying shell being arranged on a preheating zone of the densification furnace.

[0051] In an exemplary embodiment, each individual module may include an annular foot disposed between a support plate of the individual module and a stack of porous annular substrates of the individual module, the annular foot having a radial groove that forms a channel between a central cavity of the annular foot and an outer side of the annular foot along a direction orthogonal to a direction in which the porous annular substrates are stacked.

[0052] According to a particular embodiment, the step of injecting the gaseous phase into the internal volume of each stack comprises maintaining a pressure difference between the internal volume of the stack and the outside of the stack of 0-100 mbar.

[0053] In an exemplary embodiment, each porous annular substrate may include carbon.

[0054] In one embodiment, each porous annular substrate may constitute a fiber brake friction disc preform. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] [ Figure 1 ] Figure 1 , it has been described that an example of supporting a porous annular substrate according to the prior art is shown very schematically.

[0056] [ Figure 2 ] Figure 2 A cross-sectional view schematically shows an example of a stack of porous annular substrates according to the present invention.

[0057] [ Figure 3 ] Figure 3 A cross-sectional view of a densification furnace according to the invention is schematically shown.

[0058] [ Figure 4 ] Figure 4 A top view of the annular foot is schematically shown.

[0059] [ Figure 5 ] Figure 5 A cross-section of the annular foot is schematically shown. DETAILED DESCRIPTION

[0060] The chemical vapor infiltration densification method according to the present invention first comprises the following steps: providing a plurality of stacks of porous annular substrates to be treated by chemical vapor infiltration.

[0061] Figure 2 A cross-sectional view of an example of a stack 20 of porous annular substrates 21 is shown. The porous annular substrates 21 have cylindrical symmetry and are stacked along a first direction Z. Each porous annular substrate 21 extends mainly in a plane perpendicular to the first direction Z. Figure 2 The cross section shown in 20 includes a first direction Z and a second direction X perpendicular to the first direction Z. The first direction Z coincides with the rotational symmetry axis of the porous annular substrate 21 , and the second direction X corresponds to a radial direction.

[0062] Therefore, each porous annular substrate 21 of the stack 20 has an annular shape with a central channel 21a. Each porous annular substrate 21 is disposed on an assembly including an annular spacer 22 and a sealing ring 23. The radial outer diameter of the annular spacer 22 is smaller than the radial outer diameter of the porous annular substrate 21, and the diameters of the orifices of the annular spacer 22 and the porous annular substrate 21 are equal.

[0063] Each annular spacer 22 is surrounded by a sealing ring 23 in a plane perpendicular to the first direction Z. The thickness of the sealing ring 23 measured along the first direction Z is greater than the thickness of the annular spacer 22, so each porous annular substrate 21 is located on the sealing ring 23. The annular spacer 22 is used to center the sealing ring 23 in the first direction Z.

[0064] The alternating stack of porous annular substrates 21 and sealing rings 23 forms an inner volume 24 of the stack 20 in the center of the stack 20 .

[0065] Furthermore, the top of the stack 20 is closed by an annular cover disc 25. The cover disc 25 is placed on the stack via an annular spacer 22 and a sealing ring 23. The stack also includes a deformable annular seal 26 made of compressed carbon fiber felt placed on the cover disc 25, and an expanded graphite disc 27 arranged on the deformable annular seal 26 to prevent the deformable annular seal 26 from adhering to the support plate above.

[0066] The stack 20 also comprises an annular secondary sealing ring 28, also made of compressed carbon fiber felt, which is located directly on the annular spacer 22 supporting the cover disk 25. The secondary sealing ring 28 covers the portion of the annular spacer 22 not covered by the cover disk 25.

[0067] The chemical vapor infiltration densification method according to the invention then comprises a step of providing a plurality of individual modules 30 .

[0068] Figure 3 A cross-sectional view of a densification furnace according to the invention is schematically shown.

[0069] The densification furnace 40 according to the invention comprises a plurality of stacks of individual modules 30. Each individual module 30 comprises a support plate 31 on which a stack 20 of porous annular substrates is arranged by means of annular feet 29 arranged between the support plate 31 and the stack 20 of the same individual module 30.

[0070] like Figure 4 and Figure 5 As shown, Figure 4 and Figure 5 A top view and a cross-sectional view of the annular foot 29 are shown, the annular foot 29 comprising a radial groove 295 which forms a passage between a central cavity 290 of the annular foot 29 and the outside of the annular foot 29 in the radial direction.

[0071] like Figure 3 As shown, the support plate 31 of the individual module 30 comprises a gas inlet opening 32 and an injection pipe 33 mounted on the gas inlet opening 32 and extending into the inner volume 24 of the stack 20 between a first pipe end 33a connected to the support plate 31 and a free second pipe end 33b.

[0072] The injection pipe 33 also includes a gas injection hole 34 leading to the inner volume 24 .

[0073] The chemical vapor infiltration densification method according to the invention then comprises a step of forming a stack of individual modules 30 in a chamber of a densification furnace 40 .

[0074] Figure 3 A support plate 31 of a first individual module 30a to be stacked on a second individual module 30b is shown.

[0075] The step of forming a stack of individual modules 30 also includes a step of sealing and aligning the stacked individual modules 30. Figure 3 As shown, to achieve alignment, the second end 33b of the injection pipe 33 of the second individual module 30b is inserted into the gas inlet opening 32 of the first individual module 30a.

[0076] In order to seal the joint between the injection pipe 33 of the second individual module 30b and the gas inlet opening 32 of the first individual module 30a, the second individual module 30a also includes an annular seal 35, which is arranged between the second end 33b of the injection pipe 33 of the second individual module 30b and the gas inlet opening 32 of the first individual module 30a.

[0077] More specifically, each support plate 31 includes a first face 31a and a second face 31b opposite to the first face 31a, on which the stack 20 is disposed. The gas inlet opening 32 has a frustoconical shape having a first diameter d1 formed in the second face 31b of the support plate 31 and a second diameter d2 formed between the first face 31a and the second face 31b of the support plate 31 and smaller than the first diameter d1.

[0078] The second end 33b of each injection tube 33 comprises a truncated conical shape complementary to the truncated conical shape of the gas inlet opening 32, such that the two truncated conical shapes cooperate with each other. The complementary truncated conical shape of the second end 33b of the injection tube 33 comprises a third diameter that is greater than a fourth diameter, the fourth diameter being measured at the free end, while the first diameter is measured at the proximal end coupled to the rest of the injection tube 33, in particular the proximal end coupled to the main portion 33c.

[0079] like Figure 3 As shown, in order to improve the sealing of the stack of individual modules 30, the deformable annular seal 26 is dimensioned to fill the gap between the cover plate 25 of the stack 20 of the second individual module 30b and the support plate 31 of the first individual module 30a along the first direction Z.

[0080] The chemical vapor infiltration densification method according to the invention then comprises a step of arranging the stack of individual modules 30 on a carrying shell 42 arranged on a preheating zone 44 of a densification furnace 40 .

[0081] The chemical vapor infiltration densification method according to the invention then consists in placing a solid cover 46 on top of the stack of individual modules 30 .

[0082] The chemical vapor infiltration densification method according to the invention then comprises a step of injecting a gas phase containing a gaseous precursor of the matrix material to be deposited in the pores of the substrate 21 into the internal volume 24 of each stack 20 of porous annular substrates 21. The injection of the gas Figure 3 denoted by arrow G. The step of injecting gas into the internal volume 24 of the stack 20 preferably comprises adjusting the pressure difference between the internal volume 24 of the stack 20 and the outside of the stack. The pressure difference is preferably kept between 0 and 100 mbar. Such a range makes it possible to ensure the flow of the gas phase around the porous annular substrate 21 while avoiding the deposition of soot.

Claims

1. A method for densifying a porous annular substrate (21) having a central channel (21a) by pressure gradient chemical vapor infiltration, the method comprising at least the following steps: - providing a plurality of stacks (20) of porous annular substrates (21), each stack (20) comprising an inner volume (24) formed by a central channel (21a) of the stacked substrates (21), - providing a plurality of individual modules (30), each of which comprises a support plate (31) and a single stack (20) of porous annular substrates (21) arranged on the support plate (31), the support plate (31) comprising a gas inlet opening (32) and an injection pipe (33), the injection pipe being mounted on the gas inlet opening (32) and extending into an inner volume (24) of the stack (20), the inner volume being arranged on the support plate (31) between a first pipe end (33a) connected to the support plate (31) and a free second pipe end (33b), the injection pipe (33) also comprising a gas injection hole (34) leading to the inner volume (24), - forming a stack of individual modules (30) in the chamber of the densification furnace (40), each first individual module (30a) being stacked on a second individual module (30b), the gas inlet opening (32) of the first individual module (30a) being in communication with the second end (33b) of the injection pipe (33) of the second individual module (30b) stacked thereon, so as to allow gas to circulate between the individual modules (30), and - injecting into the inner volume (24) of each stack (20) of porous annular substrates (21) a gas phase comprising a gaseous precursor of the matrix material to be deposited in the pores of the substrates (21), It is characterized in that In each individual module (30), each first porous annular substrate (21) is supported on a second porous annular substrate (21) or on a support plate (31) through a sealing ring (23), and the sealing ring (23) provides radial sealing between the first porous annular substrate (21) and the second porous annular substrate (21) or between the first porous annular substrate (21) and the support plate (31). Each sealing ring (23) is coupled to an annular spacer (22), and the inner diameter of the annular spacer (22) is equal to the inner diameter of the porous annular substrate (21). Each annular spacer (22) is surrounded by the sealing ring (23) connected to it in a plane perpendicular to the stacking direction of the porous annular substrates (21), and the thickness of the annular spacer (22) is less than the thickness of the sealing ring (23) coupled to it.

2. The method according to claim 1, wherein: Each stack (20) includes at least one cover disk (25), which is supported on a porous annular substrate (21) at the top of the stack (20) by a sealing ring (23), and the sealing ring (23) provides a radial seal between the cover disk (25) and the porous annular substrate (21) at the top of the stack (20).

3. The method according to claim 2, wherein: Each stack (20) also comprises a deformable annular seal (26) arranged to be compressed between the cover disc (25) and the support plate (31) of the upper individual module (30).

4. The method according to any one of claims 1 to 3, wherein: In each individual module (30), a sealing ring (23) is provided on the radial outer periphery of the porous annular substrate (21).

5. The method according to any one of claims 1 to 3, wherein: In each individual module (30), the sealing rings (23) are alternately arranged on the radial outer periphery of the porous annular substrate (21) and the radial inner periphery of the porous annular substrate (21) along the stacking direction of the porous annular substrates.

6. The method according to any one of claims 1 to 5, wherein: The sealing ring (23) is Made.

7. The method according to any one of claims 1 to 6, wherein: Each sealing ring (23) is welded to the annular spacer (22) coupled thereto.

8. The method according to any one of claims 1 to 7, further comprising a step of sealing alignment of the stacked individual modules (30), comprising: For each first individual module (30a) stacked on a second individual module (30b), the second end (33b) of the injection pipe (33) of the second individual module (30b) is inserted into the gas inlet opening (32) of the first individual module (30a) stacked on the second individual module (30b), and an annular seal (35) is arranged between the second end (33b) of the injection pipe (33) of the second individual module (30b) and the gas inlet opening (32) of the first individual module (30a) stacked on the second individual module (30b).

9. The method according to claim 8, wherein: For each individual module (30), the support plate (31) comprises a first face (31a) supporting the stack (20) of individual modules (30) and a second face (31b) opposite to the first face (31a), the gas inlet opening (32) comprises a truncated cone shape having a first diameter (d1) formed at the second face (31b) of the support member (31) and a second diameter (d2) smaller than the first diameter (d1) and formed at the first face (31a) of the support plate (31) or between the first face (31a) and the second face (31b), and the second end (33b) of the injection pipe (33) comprises a complementary truncated cone shape matching the truncated cone shape of the gas inlet opening (32).

10. The method according to any one of claims 1 to 9, further comprising the step of arranging the stack of individual modules (30) on a carrying shell (42) arranged in a preheating zone (44) of a densification furnace (40).

11. The method according to any one of claims 1 to 10, wherein: Each individual module (30) includes an annular foot (29), which is arranged between a support plate (31) of the individual module and a stack (20) of porous annular substrates (21) of the individual module (30), and the annular foot has a radial groove, which forms a channel between the central cavity of the annular foot and the outer side of the annular foot along a direction (X) orthogonal to the direction of the stacking of the porous annular substrates.

12. The method according to any one of claims 1 to 11, wherein each porous annular substrate (21) comprises carbon.

13. The method according to any one of claims 1 to 12, wherein each porous annular substrate (21) constitutes a fiber brake friction disk preform.

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