Process for densifying a porous preform
Selective CVI and silicification method for CMC parts addresses the thermostability issue by minimizing free silicon, enhancing operating temperature and reducing costs and time.
Patent Information
- Application Number
- FR2023011622
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-10-26
- Publication Date
- 2025-10-31
- Estimated Expiration
- 2043-10-26
AI Technical Summary
CMC material parts produced using conventional methods contain free silicon, limiting their thermostability and operating temperature due to silicon flow at low temperatures, especially in components like turbomachine turbine blades.
A method involving selective CVI densification for high-temperature-exposed parts and silicification for lower-temperature-exposed parts, minimizing free silicon content by controlling temperature and thickness differences during matrix deposition.
This approach raises the operating temperature of CMC parts while reducing manufacturing costs and time, ensuring high-temperature stability with minimal silicon content.
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Abstract
Description
Title of the invention: Method for densifying a porous preform technical field
[0001] The invention relates to the manufacture of parts in carbide-based ceramic matrix composite (CMC) material. Previous technique
[0002] A well-known process for manufacturing parts from CMC material comprises the following steps:
[0003] - consolidation of a porous preform carried out by chemical infiltration in phase gaseous (CVI) of a carbide phase, for example SiC,
[0004] - injection of a ceramic powder slip, for example of SiC, into the porous preform (“Slurry Cast” or “Slurry Transfer Molding”) in order to break down the porosity in the preform,
[0005] - infiltration of the preform with a molten silicon-based composition of in order to fill the porosity still present in the preform, densification process known as MI process ("Melt Infiltration").
[0006] Such a process is described in particular in document US2019337859.
[0007] However, CMC material parts produced using this process contain a quantity of free silicon introduced during the infiltration step, which limits the thermostability of the material because the silicon begins to flow at temperatures as low as 1300°C. This limits the operating temperature of the part, even if only a portion of it is exposed to high temperatures, as is the case, for example, with a turbomachine turbine blade where the blade portion is subjected to high thermomechanical loads because it is located in the flow path, while the root portion is exposed to lower temperatures.
[0008] Consequently, there is a need to manufacture parts from carbide-based ceramic matrix composite material that allows for raising the maximum operating temperature of these parts while controlling manufacturing cost and time. Description of the invention
[0009] To this end, the present invention proposes a method for densifying a porous preform comprising at least a first part and a second part, the method comprising the following steps: - deposition of a first phase of carbide matrix in the porous preform by chemical infiltration in the gas phase (CVI), - deposition of a second matrix phase in the second part of the preform porous by infiltration of said second part with a molten silicon-based composition, the second part being heated to a temperature above the melting temperature of the silicon-based composition while the first part is maintained at a temperature below the melting temperature of the silicon-based composition during the deposition of the second matrix phase.
[0010] This gives us a part made of hybrid matrix CMC composite material with one or more parts whose matrix is obtained solely by CVI and which consequently have a very low free silicon content and one or more other parts whose matrix is composed of a CVI phase and a silicide phase which have a higher free silicon content.
[0011] It is thus possible to produce parts in CMC composite material by minimizing the presence of free silicon in the area(s) of the part most subjected to thermal stress.
[0012] This raises the operating temperature of such parts while reducing their cost and manufacturing time. Indeed, CVI densification is a lengthy and energy-intensive process compared to densification by silicification, i.e., by infiltration with a molten silicon-based composition. By reserving purely CVI densification for only the part(s) of the final part intended to be exposed to high temperatures, it is possible to complete the densification of the other part(s) by silicification, which is a much shorter and less expensive process than CVI.
[0013] According to a particular feature of the process of the invention, during the deposition of the second matrix phase, the second part of the preform is brought into contact with the molten silicon-based composition. The preform is placed in a furnace comprising a silicon-based composition. The furnace further comprises a heating system configured to locally heat the silicon composition and the second part of the preform to a temperature above the melting temperature of the silicon-based composition. A portion of the first part of the preform adjacent to the second part of the preform may also be subjected to a cooling flow to facilitate the formation of a solidification front that halts the progression of the molten silicon-based composition in the first part.
[0014] According to another particular feature of the process of the invention, during the deposition of the first phase of matrix by chemical infiltration in the gas phase, the first part of the porous preform is heated to a temperature higher than the temperature to which the second part of said porous preform is heated.
[0015] According to another particular feature of the process of the invention, during the deposition of the first matrix phase by chemical infiltration in the gas phase, the The first and second parts of the porous preform are heated to the same temperature, and the second part of the porous preform has a greater thickness than the first part. Preferably, the second part of the porous preform has a thickness at least 50% greater than the thickness of the first part. For example, the thickness of the second part of the porous preform is between 150% and 400% of the thickness of the first part.
[0016] According to another particular feature of the process of the invention, the first part of the porous preform has, after the deposition of the first phase of carbide matrix by chemical infiltration in the gas phase, a porosity rate of less than or equal to 15%, preferably less than or equal to 5%, or even less than or equal to 1%.
[0017] According to another particular feature of the process of the invention, the first part of the porous preform corresponds to a preform part of a blade of a turbomachine blade while the second part of the porous preform corresponds to a root part of the turbomachine blade.
[0018] According to another particular feature of the process of the invention, the porous preform is made in one piece by three-dimensional weaving or by draping of unidirectional layers. Brief description of the drawings
[0019] [Fig-1] Fig. 1 is a schematic cross-sectional view of a treatment plant by chemical infiltration in the gaseous phase used for the implementation of a process according to the invention,
[0020] [Fig.2] Fig.2 is a schematic cross-sectional view of a furnace for infiltration treatment of a molten silicon-based composition used for implementing a process according to the invention,
[0021] [Fig.3] The [Fig.3] is a schematic view of a part made of hybrid matrix CMC composite material obtained after processing in respectively the installation of [Fig.1] and the furnace of [Fig.2]. Description of the implementation methods
[0022] The invention applies generally to the densification of porous preforms combining chemical gas infiltration (CVI) of a carbide-based matrix and infiltration by a molten silicon-based composition ("melt infiltration"). The invention therefore applies to the manufacture of parts made of carbide-based ceramic matrix composite (CMC) material such as SiC / SiC, SiC / SiBC, or SiC / SiC-SiBC.
[0023] The densification process begins with the deposition of a first phase of carbide matrix in a porous preform 20 by chemical infiltration in the gas phase (CVI) as shown in [Fig. 1].
[0024] The porous preform 20 corresponds to a fibrous texture that has possibly been shaped. For the production of the porous preforms 20, one can use, for example, SiC fiber yarns such as those marketed by the Japanese company Nippon Carbon under the name "Hi-Nicalon S".
[0025] The porous preform can also be made from one of the following textures:
[0026] - three-dimensional (3D) weaving or multilayer weaving,
[0027] - two-dimensional (2D) fabric,
[0028] - braid,
[0029] - knitting,
[0030] - felt,
[0031] - unidirectional (UD) ribbon of wires or cables or multidirectional (nD) ribbon obtained by superimposing several UD layers in different directions.
[0032] The porous preform can also be made by a combination of several of the textures mentioned above.
[0033] A porous preform made up of several superimposed layers of UD or 2D fabric, braid, knit, felt, sheets, cables or other materials can also be used, which layers are linked together for example by sewing, by implantation of threads or rigid elements or by needle punching.
[0034] Where the preform is produced in whole or in part by three-dimensional weaving, or multilayer weaving, the weave may be of the interlock type, but other three-dimensional or multilayer weaves may be used, such as multi-plain or multi-satin weaves. Reference may be made to document WO 2006 / 136755.
[0035] CVI treatment is a well-known process for densifying porous preforms to produce parts made of CMC composite material. The preform(s) to be densified are placed in a reaction chamber of a CVI installation where they are heated. A reactive gas containing one or more gaseous precursors of the matrix material is introduced into the reaction chamber. The temperature and pressure in the installation are adjusted to allow the reactive gas to diffuse within the porosity of the preforms and form a deposit of the matrix material by decomposition of one or more components of the reactive gas or by reaction between several components, these components forming the matrix precursor. The process is carried out under reduced pressure to promote the diffusion of the reactive gases within the preforms.The transformation temperature of the precursor(s) to form the matrix material, such as a carbide, is in most cases between 900°C and 1200°C. For example, such a process is described in [reference missing]. US patent 9,845,534.
[0036] As illustrated in [Fig. 1], a porous preform 20 is placed in a gaseous chemical infiltration treatment (GCI) installation or furnace 100 delimited by an enclosure 110 comprising a cylindrical side wall 111, a bottom wall 112, and a top wall 113. The GCI treatment installation 100 includes a gas inlet 101 located at a first end of the installation, a preheating chamber 150, a reaction chamber 120, and a gas outlet 130. The gas inlet 101 includes a port 102 connected to a reactive gas line 140. The preheating chamber 150 includes several multi-perforated trays 151, 152, and 153 and is located between the gas inlet 101 and a first end 121 of the reaction chamber 120. The gas outlet 130 is present at a second end 122 of the installation opposite to the first end.The CVI treatment facility can, of course, include several gas inlets.
[0037] In the example described here, the gas exhaust outlet 130 includes a gas phase depletion module having vents 131 connected to a gas exhaust line (not shown in [Fig.1]) connected to the enclosure 110 of the installation.
[0038] Still in the example described here, only one porous preform 20 is present in the reaction chamber 120 of the installation. However, it is possible to place several porous preforms in the reaction chamber. In this case, a load of several preforms is prepared in advance and placed in the reaction chamber of the installation.
[0039] The CVI 100 processing unit also includes heating means. In the example described here, the unit is heated by induction. More specifically, the cylindrical side wall 111 of the enclosure 110 includes an armature, or susceptor 1110, for example made of graphite, which is coupled to inductors 1112 and 1113 located outside the unit and each consisting of at least one induction coil. An insulator 1111 is interposed between the inductors 1112 and 1113 and the susceptor 1110. As is well known, the CVI 100 processing unit is heated by warming the susceptor 1110 when the inductors 1112 and 1113 are supplied with an alternating voltage. For this purpose, the coil(s) of each inductor are connected to an alternating voltage generator (not shown).The magnetic field created by the inductors 1112 and 1113 induces an electric current in the susceptor 1110, which, through Joule heating, heats the susceptor. The porous preform(s) inside the enclosure 110 are heated by radiation. The inductors 1112 and 1113 respectively define first and second heating zones 132 and 133 within the enclosure 110.
[0040] The heating of the CVI 100 treatment unit can be provided by other means, such as electric heating elements consisting, for example, of heating resistors embedded in the side wall of the enclosure. The heating elements can also be arranged to delineate more than two heating zones.
[0041] According to the invention, the porous preform 20 comprises a first part 21 and a second part 22, the first part 21 being intended to be densified only by the deposition of a first phase of carbide matrix by CVI. For this purpose, the first part 21 of the porous preform 20 is positioned in the first heating zone 132 while the second part 22 of the preform is positioned in the second heating zone 133. The temperature in the first and second heating zones 132 and 133 being controlled respectively by the inductors 1112 and 1113, it is possible to heat the first part 21 of the preform present in the first heating zone 132 to a temperature higher than the temperature to which the second part 22 of the preform 20 is heated in the second heating zone 133 and thus promote the deposition kinetics of the matrix phase in the first part 21 of the preform.In other words, by heating the first part 21 to a temperature higher than the temperature to which the second part 22 is heated during CVI, a larger quantity of carbide matrix is deposited in the first part 21 for the same CVI treatment time of the porous preform 20.
[0042] In the case of electric heating means consisting for example of heating resistors embedded in the side wall of the enclosure, the electric heating means are configured to heat the first heating zone 132 to a temperature higher than the heating temperature of the second heating zone 133.
[0043] A gas stream 11, containing a gaseous carbide precursor, for example methyltrichlorosilane (MTS) or monomethylsilane (MMS) yielding SiC by decomposition, is admitted into the reaction chamber 120 through the reactive gas line 140 and the injection port 102. The gas stream 11 is preheated during its circulation in the preheating chamber 150 before being introduced into the reaction chamber 120. The gas stream 11 flows through the porous preform 20 present in the reaction chamber from the preheating chamber 150 to the gas outlet 130. The by-products 12 resulting from the decomposition of the gas stream 10 are discharged through the gas outlet 130. A SiC matrix is deposited in the porosity of the preform 20 by decomposition of the gas stream 11.The programmed CVI processing temperatures in the first and second heating zones 132 and 133 are maintained for a determined period corresponding to the CVI densification level. that we wish to achieve in the first and second parts 21 and 22 of the porous preform 20, this duration being generally calculated as a function of the deposition kinetics and a target porosity rate.
[0044] The first carbide matrix phase may, in particular, correspond to a silicon carbide (SiC) matrix, a Si-BC ternary system (SiBC), or a combination of the two (SiC / SiBC). For the deposition of a SiC matrix phase by CVI, monomethylsilane (MMS) or methyltrichlorosilane (MTS), as previously mentioned, can be used, yielding SiC by decomposition. For the deposition of a SiBC phase by CVI, the gas phase consists of a mixture of precursors of the elements Si, B, and C, to which a reducing element such as hydrogen (H2) is added. The carbon and silicon elements can be generated by precursors belonging respectively to the hydrocarbon and silane or chlorosilane families. The boron element is generated by a borane or a halide, such as boron trichloride (BC13).
[0045] At the end of the CVI treatment, the second part 22 of the porous preform 20 may have a higher porosity rate than the first part 21 of the porous preform 20. Preferably, the first part 21 has a porosity rate less than or equal to 15%, preferably less than or equal to 5%, or even less than 1%, while the second part 22 still has a porosity rate greater than or equal to 15%, preferably between 15% and 35%.
[0046] The densification of the first part by deposition of the first phase of carbide matrix by CVI can optionally be completed by an additional deposition carried out after the deposition of a second phase of matrix in the second part 22 of the porous preform 20 as described below.
[0047] Local heating of the first part 21 of the porous preform 20 to a temperature higher than the heating temperature of the second part 22 of the preform can also be achieved by using a local susceptor 160, for example a graphite cylinder, which will admit the induced currents from the inductor 1112 and thus preferentially heat the first part 21 of the porous preform 20. In this case, the CVI processing installation may include only one inductor.
[0048] In the case where the second part of the porous preform has a greater thickness than the first part of said porous preform, it is possible to heat both parts to the same temperature during the CVI treatment. Indeed, due to the difference in thickness, the densification rate of the first part, i.e., the porosity filling rate, will be greater than the densification rate of the thicker second part, assuming identical deposition kinetics throughout the porous preform. At the end of the CVI treatment, the second part of the porous preform has a higher porosity rate than the first part of the porous preform. In this case, the second part of the preform The porous preform preferably has a thickness at least 50% greater than the thickness of the first part of the porous preform. The thickness of the second part of the porous preform is, for example, between 150% and 400% of the thickness of the first part of the porous preform. In this case as well, the CVI processing installation may include only one inductor or one resistive heater, this heating element being common to both the first and second parts of the porous preform.
[0049] Once the CVI treatment is completed, a second matrix phase is deposited in the second part 22 of the porous preform 20 by infiltrating said second part with a molten silicon-based composition.
[0050] Figure 2 shows a cross-sectional view of a furnace 200 according to an embodiment of the invention that can be used to infiltrate the second part 22 of the porous preform with a molten silicon-based composition. The furnace 200 comprises a hermetically sealed chamber 210 inside which is a crucible 204 having an internal volume containing a molten silicon-based composition 206. Hereinafter, "silicon-based composition" means a composition comprising silicon in a minimum mass content of 85%. The silicon-based composition may, in particular, comprise a silicon alloy. It may comprise boron in a mass content of between 1% and 15%. The crucible 204 may be made of a ceramic material.The furnace 200 is here equipped with an induction heating system 240 comprising an induction coil 242 and a susceptor 244 arranged around the crucible 204 and the second part 22 of the porous preform 20 within the furnace chamber 210. The heating system further includes, as is known, a high-frequency generator 236 connected to the coil 242 so as to generate a variable magnetic field using the coil. The susceptor 244 can, for example, be a graphite cylinder. The furnace 200 can also be equipped with a vacuum pump 238 in fluidic communication with the interior of the chamber 210, so as to achieve vacuum infiltration. It should be noted that a different type of furnace than the one illustrated can be used; in particular, the furnace can include a resistive heating system instead of an inductive one.The oven 200 includes a device for measuring the mass of the preform 20, corresponding here to a balance 220 of the load cell type, to which the preform 20 is suspended by means of the interface rod 221.
[0051] The furnace 200 further includes a displacement device comprising, in this case, a cylinder 224 having a rod 226 on which the crucible 204 is mounted. In this example, the cylinder 224 is located outside the furnace chamber 210, below the chamber 210. In this way, the cylinder 224 allows the crucible 204 to be moved vertically within the furnace chamber 210, specifically towards the second part 22 of the preform 20. Thus, the crucible 204 is translationally mobile. vertical in enclosure 210. In an unillustrated variant, the crucible can be fixedly mounted in the furnace, and the preform can be mobile in vertical translation.
[0052] In the illustrated example, the furnace 200 also includes a control system 228 for the relative position between the preform and the crucible, which is configured to control the cylinder 224 according to the evolution of the mass of the preform 20 as measured by the scale 220. The control system 228 can receive electrical signals as input from the scale 220, and send control signals as output to the cylinder 224.
[0053] The infiltration of the second part 22 of the preform 20 is achieved by bringing said second part into contact with the molten silicon composition 206, which infiltrates the porosity of the preform by capillary action. The contact can be direct, i.e., the preform is directly immersed in the bath of the molten silicon composition, or indirect, by bringing the preform into contact with one or more drains (not shown in [Fig. 2]) which are themselves in contact with the bath of the molten silicon composition, which is then conveyed to the preform by capillary action. The contact or non-contact of the preform with the molten silicon composition, and consequently the control of the infiltration of the preform by the molten metal, is achieved by controlling the actuator 224.The infiltration of the second part 22 of the preform 20 by the molten silicon-based composition 206 ends when the balance 220 measures a predetermined mass gain corresponding to the desired level of densification of the second part 22.
[0054] According to the invention, during infiltration by the molten silicon-based composition, the second part 22 is heated to a temperature above the melting temperature of the silicon-based composition while the first part 21 is maintained at a temperature below the melting temperature of the silicon-based composition.
[0055] To this end, the induction heating system 240 is configured to locally heat the silicon composition and the second part of the preform to a temperature above the melting temperature of the silicon-based composition. More specifically, the susceptor 244 has a height H244 such as to surround the crucible 204 and the second part 22 of the preform 20 in its infiltration position, i.e., when the second part 22 is in direct or indirect contact via one or more drains with the bath of the molten silicon-based composition 206.In this way, the silicon-based composition and the second part 22 of the preform can be heated to a temperature above the melting temperature of the silicon-based composition, the first part 21 of the preform located outside the susceptor 244 being maintained at a temperature below the melting temperature of the silicon-based composition during the deposition of the . Second matrix phase. The molten silicon composition 206 seeps by capillary action into the second part 22 and then solidifies upon contact with the first part 21, which is at a temperature lower than the melting point of the composition. A solidification front then forms at the interface between the first and second parts 21 and 22, preventing the molten silicon composition from progressing into the first part 21. In the case of a furnace using another type of heating, such as a resistive heating system, it is configured to heat only the silicon composition and the second part 22 of the preform to a temperature higher than the melting point of the silicon composition.
[0056] After infiltration of the second part 22 with a composition based on molten silicon, we obtain, as illustrated in [Fig.3], a part 30 comprising a first part 31 corresponding to the first part 21 of the preform 20 densified only by the first phase of carbide matrix deposited by CVI and a second part 32 corresponding to the second part 22 of the preform 20 densified both by the first phase of carbide matrix and by the second phase of silicon-based matrix.
[0057] The first part 31 obtained by the process of the invention has a low volumetric content of free silicon, typically less than or equal to 15%, preferably less than 5%, and possibly less than 1%, which is significantly lower than that of the second part 32. The final volumetric content of free silicon in the second part 32 is equivalent to its porosity. The first part 31 can therefore be exposed to very high temperatures exceeding 1300°C without risk of degradation of the material of the part.
[0058] As illustrated in [Fig.2], at least a portion of the first part 21 of the preform 20 adjacent to the second part 22 of the preform can be subjected to a cooling flow in order to facilitate the formation of the solidification front at the interface between the first and second parts 21 and 22. In this case, the furnace 200 further includes a conduit 250 connected to a cooling source (not shown in [Fig.2]) to project a cooling flow 261 onto the portion of the first part 21 of the preform 20 adjacent to the second part 22.
[0059] The process of the invention finds advantageous application in the manufacture of composite material parts, only one or more of which are intended to be subjected to high temperatures, typically exceeding 1300°C, as is the case, for example, with a turbomachine turbine blade, the blade portion of which is subjected to high thermomechanical loads because it is located in the duct, while the root portion is exposed to lower temperatures. In this case, the first part of the porous preform corresponds to a preform portion. The first part of the preform corresponds to a portion of the turbine blade, and the second part of the porous preform corresponds to a portion of the turbine blade's root. The process of the invention can, of course, be applied to the manufacture of other types of composite material parts, such as turbine ring sectors that have an annular base or tub thicker than its flanges or mounting lugs, or distributor sectors that have blade portions thinner than the inner and outer platforms.
Claims
Demands
1. A method for densifying a porous preform (20) comprising at least a first part (21) and a second part (22), the method comprising the following steps: - deposition of a first carbide matrix phase in the porous preform by chemical infiltration in the gas phase, - deposition of a second matrix phase in the second part (22) of the porous preform (20) by infiltration of said second part with a molten silicon-based composition (206), the second part (22) being heated to a temperature above the melting temperature of the silicon-based composition while the first part (21) is maintained at a temperature below the melting temperature of the silicon-based composition during the deposition of the second matrix phase.
2. A method according to claim 1, wherein, during the deposition of the second matrix phase, the second part (22) of the porous preform (20) is brought into contact with the molten silicon-based composition (206), the porous preform (20) being placed in a furnace (200) comprising a silicon-based composition, the furnace further comprising a heating system (240) configured to locally heat the silicon composition and the second part (22) of the porous preform to a temperature above the melting temperature of the silicon-based composition.
3. A method according to claim 2, wherein at least a portion of the first part (21) of the porous preform (20) adjacent to the second part (22) of the porous preform is subjected to a cooling flow (251).
4. A method according to any one of claims 1 to 3, wherein, during the deposition of the first matrix phase by chemical infiltration in the gas phase, the first part (21) of the porous preform (20) is heated to a temperature higher than the temperature to which the second part (22) of said porous preform is heated.
5. A method according to any one of claims 1 to 3, wherein, during the deposition of the first matrix phase by gas-phase chemical infiltration, the first and second parts (21, 22) of the porous preform (20) are heated to the same temperature and wherein the second part (22) of the porous preform has a thickness greater than the thickness of the first part (21) of said porous preform.
6. A method according to claim 5, wherein the second part (22) of the porous preform (20) preferably has a thickness at least 50% greater than the thickness of the first part (21) of the porous preform.
7. Method according to claim 5 or 6, wherein the first part (21) of the porous preform (20) corresponds to a preform portion of a turbine blade and wherein the second part (22) of the porous preform corresponds to a root portion of the turbine blade.
8. A method according to any one of claims 1 to 7, wherein the first part (21) of the porous preform (20) has, after deposition of the first phase of carbide matrix by chemical infiltration in the gas phase, a porosity rate of less than or equal to 15%, preferably less than or equal to 5%, more preferably less than or equal to 1%.
9. A method according to any one of claims 1 to 8, wherein the porous preform (20) is made in one piece by three-dimensional weaving or by draping unidirectional layers.