FR3141170A1 - Process for manufacturing a part made of ceramic matrix composite material - Google Patents

Abstract

Method of manufacturing a part made of ceramic matrix composite material The present invention relates to a method of manufacturing a part of ceramic matrix composite material, comprising: - the formation of a matrix precursor deposit (37) of pre- densification in a porosity of a fibrous structure, comprising the deposition of a first layer (302) of silicon carbide and the deposition of a second layer of boron-doped silicon covering the first layer, - a diffusion heat treatment of the boron in solid phase by subjecting the precursor deposit thus formed to a treatment temperature of between 1350°C and 1400°C in order to form a protective barrier in a ternary Si-B-C system at the interface between the first layer and the second layer and thus obtain a pre-densified fibrous structure, and- infiltration of the pre-densified fibrous structure thus obtained by a melt infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of the pre-densified fibrous structure. Figure for abstract: Fig. 3.

Description

Process for manufacturing a part made of ceramic matrix composite material

The invention relates to the manufacture of a part made of ceramic matrix composite material (“Ceramic Matrix Composite”; “CMC”) during which the ceramic matrix is formed by infiltration of a composition based on molten silicon (“Melt- Infiltration”; “MI”). The invention proposes the presence of a protective Si-B-C barrier making it possible to protect the underlying pre-densification silicon carbide from attack by molten silicon. The composite material part thus obtained can find application as a hot part of a turbomachine, in particular an aeronautical turbomachine, such as a turbine part.

Ceramic matrix composite materials withstand temperatures ranging from 600°C to 1400°C. Due to their better resistance to high temperatures, CMCs require less cooling. This cooling traditionally comes from a sample in the compressor which impacts the efficiency of the turbomachine, CMC materials therefore make it possible to improve engine efficiency which reduces fuel consumption. Furthermore, their use contributes to optimizing the performance of turbomachines, in particular by reducing the overall mass of the turbomachine, which further contributes to a reduction in fuel consumption and therefore to a significant reduction in polluting emissions.

CMC parts can be densified by melt infiltration. In this technique, a molten silicon composition can be introduced into the porosity of a fibrous structure pre-densified by a silicon carbide deposit and loaded with silicon carbide particles. This method makes it possible to obtain a completely dense high modulus Si-SiC matrix and a composite with a high linearity limit. The composites obtained have good mechanical properties but the inventors observed a certain variability in the elongation at break which reduces the damage tolerance of the material. It is desirable to propose a solution to address this drawback.

The invention relates to a method of manufacturing a part made of ceramic matrix composite material, comprising:
- the formation of a precursor deposit of pre-densification matrix in a porosity of a fibrous structure, comprising the deposition of a first layer of silicon carbide and the deposition of a second layer of boron-doped silicon covering the first layer,
- a heat treatment for diffusion of boron in a solid phase by subjecting the precursor deposit thus formed to a treatment temperature of between 1350°C and 1400°C in order to form a protective barrier in a ternary Si-BC system at the interface between the first layer and the second layer and thus obtain a pre-densified fibrous structure, and
- the infiltration of the pre-densified fibrous structure thus obtained by a melt infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of the pre-densified fibrous structure.

The inventors noted that the variability of the fracture behavior was linked to an uncontrolled attack on the silicon carbide of the pre-densification matrix by the molten silicon in the solution of the prior art. This phenomenon can go as far as the degradation of the fibrous reinforcement and the interphase resulting in a reduction in the structural character of the composite. The invention proposes a functionalization of the pre-densification matrix so as to integrate a protective Si-B-C barrier which makes it possible to reduce the attack of the silicon carbide of the pre-densification matrix. This barrier is formed by the diffusion of boron from the second layer into the silicon carbide of the first layer during heat treatment. The protective barrier, forming an integral part of the pre-densification matrix, is distributed homogeneously in the pre-densified fibrous structure to provide protection throughout its volume and throughout infiltration. We thus obtain composite materials with much more efficient breaking behavior.

In an exemplary embodiment, a thickness of the second layer, before the heat treatment, is between 0.5 µm and 1 µm.

Such a characteristic makes it possible to obtain improved overall performance by conferring the desired protection of the silicon carbide while having a volume fraction occupied by the second layer limited so as not to substantially modify the other stages of the range, in particular in n only slightly affecting the volume fraction of the first layer which provides a large contribution of mechanical performance to the material, as well as the residual porosity of the pre-densified structure in order to avoid complicating a possible subsequent introduction of powder composition before infiltration .

In an exemplary embodiment, boron is present in an atomic proportion of between 0.05% and 1% in the second layer before the heat treatment.

Such a characteristic helps to further improve the protection of the underlying silicon carbide.

In an exemplary embodiment, the method further comprises, before the heat treatment, an introduction of a silicon carbide powder into a residual porosity of the fibrous structure provided with at least the first layer of silicon carbide.

Such a characteristic advantageously makes it possible to take advantage of the thermal diffusion treatment of boron in the solid phase which makes it possible to form the barrier described above to also carry out deoxidation of the powder in order to improve wetting by the molten silicon.

In particular, the silicon carbide powder can be introduced into the residual porosity of the fibrous structure provided with the precursor deposit.

In this case, the silicon carbide powder is introduced after the deposition of the first layer of silicon carbide and the second layer of silicon doped with boron but we do not depart from the scope of the invention when the carbide powder of silicon is introduced between the first and second layers. In the latter case, an additional protective barrier made of a ternary Si-B-C system is also formed at the interface between the silicon carbide powder and the second layer, in addition to the protective barrier at the interface between the first layer and the second layer described above.

In an exemplary embodiment, the treatment temperature is between 1370°C and 1390°C.

In an exemplary embodiment, the infiltration composition comprises boron.

Such a characteristic advantageously makes it possible to further protect the underlying silicon carbide.

In an exemplary embodiment, the fibrous structure is provided with an interphase of boron nitride on which the first layer is deposited during the formation of the precursor deposit.

The presence of a boron nitride interphase advantageously makes it possible to deflect cracks which may appear in the matrix of the composite part in operation so as to preserve the fibrous reinforcement, and to provide resistance to oxidation.

In an exemplary embodiment, the fibrous structure comprises a fibrous reinforcement formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers.

In an exemplary embodiment, the part is a turbomachine part.

The part may be a turbine part, for example an aircraft engine turbine part. The part can for example be a turbomachine blade, a turbine ring sector or a distributor.

There is a flowchart showing a succession of steps of an example of a method according to the invention.

There represents, schematically and partially, an example of a fibrous structure provided with a precursor deposit of pre-densification matrix which can be implemented within the framework of the invention.

There represents, schematically and partially, the fibrous structure of the after the boron diffusion heat treatment.

An example of a method of manufacturing a part made of CMC material according to the invention will now be described in connection with the flowchart of the and the architectures illustrated in Figures 2 and 3.

A first step S10 of the process may consist of forming the fibrous structure by implementing one or more textile operations such as three-dimensional weaving. The fibrous structure can be formed from ceramic wires, for example silicon carbide wires. The fibrous structure can constitute the fibrous reinforcement 10 of the composite material part to be obtained. Examples of usable silicon carbide wires may be wires marketed under the reference “Nicalon”, “Hi-Nicalon”, “Hi-Nicalon-S” or Tyranno SA3 from the company UBE Industries. The ceramic yarns of the fibrous structure may have an oxygen content less than or equal to 1% in atomic percentage. “Hi-Nicalon-S” threads, for example, have such a characteristic. By “three-dimensional weaving” or “3D weaving”, we must understand a mode of weaving by which at least some of the warp threads bind weft threads on several weft layers. A reversal of roles between warp and weft is possible in the present text and must be considered as also covered by the claims. The fibrous structure can for example have an interlock weave. By "weave or interlock fabric", we must understand a 3D weave weave in which each layer of warp threads links several layers of weft threads with all the threads of the same warp column having the same movement in the plane of the armor. It is also possible to start from fibrous textures such as two-dimensional fabrics or unidirectional webs, and to obtain the fibrous structure by draping such fibrous textures on a form. These textures can possibly be linked together, for example by sewing or implantation of threads to form the fibrous structure.

In a step S20, an interphase 20 of defragmentation can be formed by chemical vapor infiltration (“Chemical Vapor Infiltration”) on the threads of the fibrous structure. The fibrous structure can be positioned in conformation tooling allowing it to be shaped into the shape of the part to be obtained during the deposition of the interphase. The thickness e ₂₀ of the interphase can for example be between 10 nm and 1000 nm, and for example between 200 nm and 500 nm. After formation of the interphase, the fibrous structure remains porous, the initial accessible porosity being filled for only a minority part by the interphase. The interphase can be single-layer or multi-layer. The interphase may comprise at least one layer of pyrolytic carbon (PyC), boron nitride (BN), boron nitride doped with silicon (BN(Si), with silicon in a mass proportion of between 5% and 40 %, the complement being boron nitride) or carbon doped with boron (BC, with boron in an atomic proportion of between 5% and 20%, the complement being carbon). The interphase here has a function of weakening the composite material which promotes the deflection of possible cracks reaching the interphase after having propagated in the matrix, preventing or delaying the rupture of fibers by such cracks. Alternatively, it will be noted that it is possible to form the interphase on the wires before the formation of the fibrous structure, that is to say before implementation of step S10.

A step S30 of forming a silicon carbide deposit is then carried out. This step S30 can be separated into two phases. During the first phase, the fibrous structure is still in the conformation tooling and a consolidation layer 301 of silicon carbide is deposited on the interphase 20 and the fibrous reinforcement 10. The consolidation layer 301 can be deposited in contact of the interphase 20. This layer has sufficient thickness to sufficiently bind the fibers so that the structure retains its shape without assistance from the holding tooling. This layer provides protection to the interphase against oxidation and can be formed by chemical vapor infiltration in a manner known per se, for example from a gas phase comprising methyltrichlorosilane (MTS) and hydrogen (H ₂ ). The thickness e ₃₀₁ of the consolidation layer 301 may be greater than or equal to 0.1 µm, for example between 0.1 µm and 5 µm. During the second phase, the fibrous structure consolidated and shaped into the part to be obtained can be removed from the tooling and the formation of the precursor deposit 35 of the pre-densification matrix can be initiated by depositing a first layer 302 of this in silicon carbide. The first layer 302 can be deposited in contact with the consolidation layer 301. The thickness e ₃₀₂ of the first layer 302 may be greater than the thickness e ₃₀₁ of the consolidation layer 301. This first layer of silicon carbide provides a large contribution of mechanical performance to the composite material and provides protection against the molten silicon used during subsequent infiltration. The thickness e ₃₀₂ of the first layer 302 may be greater than or equal to 1 µm, for example between 1 µm and 20 µm. As for the consolidation layer, the first layer of the precursor deposit can be formed by chemical vapor infiltration in a manner known per se. Generally speaking, the precursor deposit can be formed by chemical vapor infiltration. According to a variant not illustrated, the layer 301 could be omitted and the first layer 302 of the precursor deposit could be directly formed on the interphase 20.

The formation of the precursor deposit can be continued by forming the second layer 40 of boron-doped silicon on the first layer 302 (step S40). This layer 40 is intended to provide boron allowing the formation of the Si-BC protective barrier after the diffusion heat treatment in order to protect the underlying silicon carbide from attack by molten silicon. In the example of the , the precursor deposit 35 comprises a single second layer 40 of silicon doped with boron. The second layer 40 can be deposited in contact with the first layer 302. In the example illustrated, the precursor deposit 35 comprises only the first 302 and the second 40 layers. The thickness e40 of the second layer 40 can be between 0.5 µm and 1 µm. Boron may be present in an atomic proportion of between 0.05% and 1% in the second layer 40 before the diffusion heat treatment of the boron, the complement possibly being silicon. The second layer 40 may correspond to a binary eutectic composition of silicon and boron. The residual porosity of the fibrous structure provided with the precursor deposit 35 can be between 20% and 40%, for example between 30% and 35%. The second layer 40 can be formed by chemical vapor infiltration. It is possible to use a mixture of a first gaseous precursor comprising silicon, for example chosen from SiCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl, SiH ₄ , CH ₃ SiCl ₃ or CH ₃ SiH ₃ , and a second gaseous precursor comprising boron, for example chosen from BCl ₃ , BF ₃ or B ₂ H ₆ . The relative ratios of precursors are adjusted based on their reactivity. The second layer 40 can be formed by imposing a temperature between 700°C and 1200°C. The second layer 40 can be formed in a medium at a pressure less than or equal to 200 mbar, for example between 1 mbar and 200 mbar to promote good infiltration of the deposit. In an exemplary embodiment, a combination of SiHCl ₃ and BCl ₃ can be used in ratios of between 1/1 and 100/1 at a temperature of 1000°C and a pressure of 100 mbar.

The process continues by introducing a powder composition into a residual porosity of the structure provided with the precursor deposit 35 (step S50). This powdery composition can be introduced into the fibrous structure by slurry-cast method in a manner known per se. The powder composition may comprise a silicon carbide powder and/or a carbon powder and/or a boron carbide powder. According to one example, the powder composition comprises silicon carbide powder, and optionally carbon powder and/or boron carbide powder.

It is then possible to carry out during step S60 the heat treatment for diffusion of the boron comprising the application of a temperature between 1350°C and 1400°C, for example between 1370°C and 1390°C, for example between 1375°C and 1385°C in particular at around 1380°C. Generally speaking, this temperature can be applied for a period of at least 30 minutes. Whatever the embodiment considered, the heat treatment can be carried out under vacuum or under a pressure less than or equal to 100 mbar of a neutral gas. During the heat treatment, the boron of the second layer 40 diffuses towards the first layer 302 to form a barrier 38 in a ternary Si-B-C system at the interface between the first layer 302 and the second layer 40. After the diffusion heat treatment , we obtain a second layer 402 depleted in boron which has an atomic proportion of boron lower than the atomic proportion of boron in the second layer 40 before this heat treatment. The reduction in the atomic proportion of boron in the second layer 40 following the heat treatment can be greater than or equal to 80%, or even 90%. According to one example, substantially all of the boron in the second layer 40 can be consumed following the heat treatment. The protective barrier 38 may have a thickness e38 greater than or equal to 1 nm, for example between 1 nm and 30 nm. In the example considered, the heat treatment also allows deoxidation of the silicon carbide powder previously introduced.

After the diffusion heat treatment, the pre-densification matrix 37 is obtained which successively comprises the first layer 302, the protective barrier 38 and the second layer 402 depleted in boron or substantially devoid of boron. In the example illustrated, the second layer 402 defines an external surface Sext of the pre-densification matrix, that is to say it forms the layer furthest from the fibrous reinforcement 10 during infiltration. Thus during infiltration, no other layer is interposed between layer 402 and the infiltration composition. The residual porosity volume rate of the pre-densified fibrous structure loaded with the powder composition may be less than or equal to 25%, for example between 15% and 25%. An embodiment has been described in which the powder composition is introduced after formation of the second layer 40 of boron-doped silicon but we do not depart from the scope of the invention when the powder composition is introduced after formation of the first layer 302 but before formation of the second layer 40 with subsequent diffusion heat treatment. In this case, the second layer 40 covers the silicon carbide powder as well as the first layer 302. The silicon carbide powder is interposed between the first 302 and the second layer 40. Generally speaking, the powder composition, which can at least comprise silicon carbide powder, can be introduced after the deposition of the second layer before or after the diffusion heat treatment, or be introduced between the deposition of the first layer and the second layer.

After introduction of the powder composition, step S70 is carried out during which the residual porosity is infiltrated with a melt infiltration composition comprising at least silicon so as to form a ceramic matrix in the porosity of the fibrous structure. . The formation of this ceramic matrix can make it possible to finalize the densification of the part. This infiltration step corresponds to a melt infiltration step. The infiltration composition may consist of pure molten silicon or alternatively be in the form of a molten alloy of silicon and one or more other constituents. The infiltration composition may comprise a majority of silicon by mass, that is to say have a silicon mass content greater than or equal to 50%. The infiltration composition may for example have a silicon mass content greater than or equal to 75%. The constituent(s) present within the silicon alloy can be chosen from B, Al, Mo, Ti, Ge and their mixtures. When the powder composition comprises carbon particles, a chemical reaction can occur between the infiltration composition and these carbon particles during infiltration resulting in the formation of silicon carbide.

After step S70, we obtain a part made of CMC material. Such a part made of CMC material can be a static or rotating part of a turbomachine. Examples of turbomachine parts have been mentioned above. Such a part may additionally be coated with an environmental or thermal barrier coating before use.

The expression “between… and…” must be understood as including the limits.

Claims (10)

Process for manufacturing a part made of ceramic matrix composite material, comprising:
- the formation of a precursor deposit (35) of pre-densification matrix (37) in a porosity of a fibrous structure, comprising the deposition of a first layer (302) of silicon carbide and the deposition of a second layer (40) of boron-doped silicon covering the first layer,
- a heat treatment (S60) for diffusion of boron in the solid phase by subjecting the precursor deposit thus formed to a treatment temperature of between 1350°C and 1400°C in order to form a protective barrier (38) in a ternary system Si- BC at the interface between the first layer and the second layer and thus obtain a pre-densified fibrous structure, and
- the infiltration (S70) of the pre-densified fibrous structure thus obtained by a melt infiltration composition comprising silicon in order to form a ceramic matrix in a residual porosity of the pre-densified fibrous structure. Method according to claim 1, in which a thickness (e40) of the second layer (40), before the heat treatment (S60), is between 0.5 µm and 1 µm. Method according to claim 1 or 2, in which the boron is present in an atomic proportion of between 0.05% and 1% in the second layer (40) before the heat treatment. Method according to any one of claims 1 to 3, in which the method further comprises, before the heat treatment (S60), an introduction (S50) of a silicon carbide powder into a residual porosity of the fibrous structure provided at least of the first layer (302) of silicon carbide. Method according to claim 4, in which the silicon carbide powder is introduced into the residual porosity of the fibrous structure provided with the precursor deposit (35). Process according to any one of claims 1 to 5, in which the treatment temperature is between 1370°C and 1390°C. A method according to any of claims 1 to 6, wherein the infiltration composition comprises boron. Method according to any one of claims 1 to 7, in which the fibrous structure is provided with an interphase (20) of boron nitride on which the first layer (302) is deposited during the formation of the precursor deposit (35) . A method according to any one of claims 1 to 8, wherein the fibrous structure comprises a fibrous reinforcement (10) formed by three-dimensional weaving or from a plurality of two-dimensional fibrous layers. Method according to any one of claims 1 to 9, in which the part is a turbomachine part.