WO2021005280A1

WO2021005280A1 - Method for producing a composite material part having a silicon carbide matrix

Info

Publication number: WO2021005280A1
Application number: PCT/FR2020/051128
Authority: WO
Inventors: Stéphane Roger André GOUJARD; Inès BERDOYES
Original assignee: Safran Ceramics
Priority date: 2019-07-09
Filing date: 2020-06-29
Publication date: 2021-01-14
Also published as: FR3098513A1; FR3098513B1

Abstract

The present invention relates to the production of a composite material part having a silicon carbide matrix, comprising a first step of infiltrating a fibrous preform filled with a carbonaceous powder coated with silicon carbide, and then a second step of rising the temperature so as to react the infiltrated composition with the carbon of the powder.

Description

Title of the invention: Method of manufacturing a part made of composite material with a silicon carbide matrix

Technical area

The invention relates to a method of manufacturing a part made of a ceramic matrix composite (“Ceramic Matrix Composite”; “CMC”) in which the matrix is formed by infiltration of a composition based on silicon in the molten state. ("Melt-Infi Itration"; "MI").

Prior art

One field of application of the invention is the production of parts intended to be exposed in service to high temperatures, in particular in the aeronautical and space fields, in particular parts of hot parts of

aeronautical turbomachines, it being noted that the invention can be applied in other fields, for example in the field of industrial gas turbines.

CMC composite materials have good thermostructural properties, that is, high mechanical properties which make them suitable for constituting structural parts, and the ability to maintain these properties at high levels.

temperatures. The use of CMC materials instead of metallic materials for parts exposed in service to high temperatures has therefore been recommended, especially since these materials have a density

significantly weaker than the metallic materials for which they are substituted.

A method of manufacturing CMC parts consists in making a multilayer woven preform from silicon carbide fibers to make an interphase deposition of boron nitride BN by chemical vapor infiltration (“Chemical Vapor Infiltration”; “CVI ») Then a first densification from silicon carbide obtained by CVI. Then, a silicon carbide powder is introduced into the preform and the preform thus charged with the powder is infiltrated with molten silicon or with a molten silicon alloy. The silicon or the silicon alloy rises by capillary action and colonizes the porosity. It is possible to obtain a material whose final residual porosity is very low (conventionally less than 2%). In on the other hand, the material obtained contains a relatively large percentage of free silicon (conventionally from 14% to 20%) because this silicon has not reacted or has reacted very little with the silicon carbide powder. The part obtained exhibits satisfactory properties at high temperature but with a view to use at very high temperature, for temperatures close to 1480 ° C., this part may have limitations.

In order to reduce the free silicon, solutions have been proposed by charging the preform with a powder comprising a mixture of grains of silicon carbide and of carbon grains. In this solution, it is sought for the silicon to react with the carbon grains so as to form silicon carbide and to reduce the level of free silicon. However, complete infiltration is not always obtained with such a mixture of powders because during the infiltration the reaction of the molten silicon with the solid carbon can lead to premature blocking of the porosity and therefore to a limitation of the infiltration. On the other hand, there may be a

segregation between the grains of silicon carbide and carbon powder which leads to areas rich in silicon carbide or carbon, whereas the most favorable situation is a homogeneous mixture of carbon powder and silicon carbide.

It is therefore desirable to have a process for manufacturing a part made of composite material by infiltration in the molten state which makes it possible to reduce the level of free silicon while maintaining a low residual porosity in the part obtained.

Disclosure of the invention

The invention relates, according to a first aspect, to a method of manufacturing a part made of composite material with a silicon carbide matrix, comprising at least:

the infiltration of a fiber preform with a molten composition comprising mainly silicon by mass, a first temperature being imposed during infiltration and a powder being present in the porosity of said preform, said powder comprising grains formed of a boron-doped carbon or carbon core coated with a coating of silicon carbide, said first temperature being sufficiently low to prevent the reaction of the molten composition with the core of the grains of the powder, and - Submitting the preform thus infiltrated to a second temperature above the first temperature and sufficient to allow the reaction of the molten composition with the core of the grains of the powder and thus form silicon carbide. By “molten composition comprising predominantly silicon by mass”, it should be understood that the mass content of silicon in the molten composition is greater than or equal to 50%, for example greater than or equal to 75%, or even to 90%. The invention proposes a manufacturing method making it possible to limit the rate of free silicon while maintaining a low residual porosity in the part obtained. The method comprises a first step of infiltration of the fiber preform during which the first temperature is imposed. This step allows the colonization of the porosity of the fiber preform containing the powder by the molten composition without the latter interacting with the powder, that is to say without the latter reacting with the carbon nucleus of the powder. grains. The first temperature imposed during this first infiltration step is higher than the melting temperature of the molten composition while remaining sufficiently low to avoid the interaction between the molten composition and the powder. In fact, if too high a temperature is imposed, the molten composition penetrates through the coating of silicon carbide or this coating decomposes, which leads to the reaction between the silicon of the molten composition and the carbon of the core of the grains.

The first temperature is chosen as a function of the characteristics of the silicon carbide coating employed, namely the stoichiometric character or not of the coating, its crystalline or amorphous character and its thickness. The finer the coating of silicon carbide, the more the first temperature must be limited in order to avoid the reaction between the molten composition and the carbonaceous core of the grains of the powder. The greater the variation of the silicon carbide from a stoichiometric composition, the more the first temperature must be limited in order to avoid this reaction. The more the silicon carbide has an amorphous character (that is to say a small size of silicon carbide crystallites), the lower the first temperature must be in order to avoid the reaction.

Consequently, during the first infiltration phase, the first temperature is chosen to be sufficiently low, taking into account the characteristics of the silicon carbide coating of the grains used, in order to guarantee that this coating allows the protection of the carbonaceous core of the grains of the molten composition and prevents contact between the silicon of the molten composition and the carbonaceous core. This avoids any risk of prematurely clogging the porosity during infiltration by reaction between the molten silicon and the solid carbon - which makes it possible to obtain complete infiltration and therefore a low residual porosity in the finished part.

Once the first infiltration step is completed, the temperature to which the infiltrated preform is subjected is then increased from the first temperature to the second temperature. The temperature is thus increased to allow the penetration of the molten composition through the coating of silicon carbide or the decomposition of this coating in order to bring the silicon of the molten composition into contact with the carbonaceous core of the grains of the powder. The chemical reaction between these two elements is thus permitted and leads to the formation of silicon carbide by consuming the liquid silicon and makes it possible to obtain a part with a reduced free silicon content.

The following describes various examples according to the invention each relating to a

silicon carbide coating of the powder grains having particular characteristics and indicates for each of these examples the working ranges for the first and second temperatures.

In an exemplary embodiment, the grains of the powder have a coating of silicon carbide having:

- a stoichiometric composition with an atomic silicon content of 50% and an atomic carbon content of 50%,

- an average thickness between 20 nm and 100 nm, and

- an average size of silicon carbide crystallites of between 8 nm and 20 nm,

and the first temperature is less than or equal to 1450 ° C, and the second temperature greater than or equal to 1460 ° C.

Unless stated otherwise, an average dimension (thickness or size) designates the dimension given by the statistical particle size distribution at half the population. The average grain size thus corresponds to the size D50 of the grains and the average thickness of the coating at the median thickness of the coating on the different grains.

The average size of silicon carbide crystallites can be determined from the result of an X-ray diffractometry (XRD) test by applying Scherrer's formula. Scherrer's formula is: tmoy =

0.9A / [c.cos (20/2)] where tmoy is the average size of silicon carbide crystallites, l is the wavelength of x-rays, e is the width at half the height of a line relative to the silicon carbide measured in radians and 2Q is the position of the top of this line on the diffractogram in degrees (°). In particular cases where Scherrer's law is likely to provide approximate results, for example when there is a significant overlap between two neighboring lines, it is possible to use Rietveld's method. This method consists in simulating a

diffractogram from a crystallographic model of the sample and then adjusting the parameters of this model so that the simulated diffractogram is as close as possible to the experimental diffractogram. These steps can be carried out using specific software such as FullProf, TOPAS, MAUD and FAULTS.

As a variant, the grains of the powder have a coating of silicon carbide having:

- a quasi-stoichiometric composition with an atomic silicon content different from 50% and between 49% and 51% and an atomic carbon content different from 50% and between 51% and 49%,

- an average thickness between 30 nm and 120 nm, and

- an average size of silicon carbide crystallites of between 5 nm and 15 nm,

and the first temperature is less than or equal to 1440 ° C, and the second temperature greater than or equal to 1450 ° C.

As a further variant, the grains of the powder have a coating of silicon carbide having:

- a non-stoichiometric composition with an atomic silicon content of between 45% and 49% or between 51% and 55%, and an atomic carbon content of between 51% and 55% or between 45% and 49%,

- an average thickness between 40 nm and 150 nm, and - an average size of silicon carbide crystallites of between 3 nm and 10 nm,

and the first temperature is less than or equal to 1430 ° C, and the second temperature greater than or equal to 1440 ° C.

In an exemplary embodiment, the fiber preform comprises silicon carbide fibers having an oxygen content of less than or equal to 1% in atomic percentage.

Brief description of the drawings

[Fig. 1] FIG. 1 is a flowchart illustrating the various steps of an example of a method according to the invention.

[Fig. 2] FIG. 2 schematically illustrates a grain of a powder which can be used within the framework of the invention.

[Fig. 3] FIG. 3 illustrates an example of the change in temperature that can be implemented within the framework of the invention.

Description of embodiments

First, a fiber preform is formed (step 10). This fibrous preform is intended to form the fibrous reinforcement of the part to be obtained. The fiber preform may comprise silicon carbide fibers having, for example, an oxygen content of less than or equal to 1% in atomic percentage. The fibers used can be silicon carbide (SiC) fibers supplied under the name “Hi-Nicalon” or “Hi-Nicalon-S” by the Japanese company Nippon Carbon or “Tyranno SA3” by the company UBE. The preform may, as a variant or in combination, comprise carbon fibers.

The fiber preform can be obtained by three-dimensional weaving between a plurality of layers of warp threads and a plurality of layers of weft threads. The three-dimensional weaving produced can be an “interlock” weave, that is to say a weaving weave in which each layer of weft threads binds several layers of warp threads with all the threads of the same column of yarns. weft having the same movement in the plane of the weave. Different weaving modes that can be used are described in document WO 2006/136755.

The fiber preform can also be obtained by assembling a plurality of fiber textures. In this case, the fiber textures can be linked together, for example by stitching. The fibrous textures can in particular each be obtained from a layer or a stack of several layers of:

- one-dimensional fabric (UD),

- two-dimensional fabric (2D),

- braid,

- knitting,

- felt,

- Unidirectional sheet (UD) of son or cables or multidirectional plies (nD) obtained by superimposing several UD plies in different directions and binding of the UD plies together for example by sewing, or by chemical bonding agent.

In the case of a stack of several layers, they are linked together, for example by stitching, or by implanting wires or rigid elements.

Once the preform has been formed, an interphase of defragilization can be formed on the fibers of the preform (step 20).

In known manner, a surface treatment of the fibers prior to the formation of the interphase is preferably carried out to remove the size and a surface layer of oxide such as silica S1O2 present on the fibers. The interphase can be formed by CVI. The interphase can be monolayer or multilayer.

The interphase can comprise one or more layers of pyrolytic carbon (PyC), of boron nitride (BN), or of carbon doped with boron, noted BC (the carbon doped with boron having an atomic boron content of between 5% and 20%, the rest being carbon). The thickness of the interphase can be greater than or equal to 10 nm and for example be between 10 nm and 1000 nm. Of course, it is not outside the scope of the invention when the interphase is formed on the fibers before formation of the preform.

A consolidation phase comprising silicon carbide can then be formed in the porosity of the fiber preform in a manner known per se (step 30). The consolidation phase can be formed by chemical vapor infiltration. The consolidation phase can comprise silicon carbide, and for example comprise only silicon carbide. As a variant, the consolidation phase may comprise, in addition to the silicon carbide, a self-healing material. It is possible to choose a self-healing material containing boron, for example a ternary Si-BC system or boron carbide B ₄ C capable of forming, in the presence of oxygen, a borosilicate type glass having properties.

self-healing. The thickness of the deposit of the consolidation phase may be greater than or equal to 500 nm, for example between 1 μm and 30 μm. The outer layer of the consolidation phase (furthest from the fibers) is advantageously made of silicon carbide in order to constitute a reaction barrier between the underlying fibers and the molten silicon composition introduced subsequently.

The thickness of the consolidation phase is sufficient to consolidate the fiber preform, that is to say to bind the fibers of the preform together sufficiently so that the preform can be handled while retaining its shape without assistance. maintenance tools. After this consolidation, the preform remains porous, the initial porosity for example only being filled for a minority part by the interphase and the consolidation phase.

The powder of grains coated with silicon carbide is then introduced into the porosity of the consolidated fiber preform (step 40). To do this, the consolidated preform is impregnated with a slip containing the powder suspended in a liquid medium, for example water, a dispersant and a base. The powder can be retained in the preform by filtration or by settling optionally with the aid of pressure and / or vacuum. Use is preferably made of a powder formed of grains of average size (D50) less than or equal to 5 μm, or even less than or equal to 1 μm. The powder can typically fill 40% to 65%, for example 45% to 55%, of the porosity remaining in the material after the consolidation step. By way of illustration, this may represent from 12% to 25% of the initial porosity of the fiber preform.

The powder used is formed by a plurality of grains 100 as illustrated in FIG. 2. The grains 100 each comprise a core 102, or heart, made of carbon. or carbon doped with boron. As in the case of the above interphase, the boron-doped carbon has an atomic boron content of between 5% and 20%, the remainder being carbon. The grains 100 each further include a coating 104 of silicon carbide encapsulating the core 102. The coating 104 forms a continuous layer of silicon carbide around the core 102. The coating 104 contacts the core 102. The coating 104 defines the core. external surface SI of grain 100. The thickness e of the coating 104 and the size t of grain 100 are also shown diagrammatically in FIG. 2. The silicon carbide coating of the grains may have an atomic silicon content of between 45% and 55% and an atomic carbon content of between 45% and 55% in addition to 100%.

The coating of the grains may have an average size of silicon carbide crystallites less than or equal to 40 nanometers, for example less than or equal to 20 nanometers, for example less than or equal to 15 nanometers, or even less than or equal to 10 nanometers. The average size of silicon carbide crystallites in the coating 104 may be greater than or equal to 3 nanometers, for example greater than or equal to 5 nanometers, and for example be between 3 nanometers and 40 nanometers, for example between 3 nanometers and 20 nanometers. This average size of the silicon carbide crystallites can be between 5 nanometers and 40 nanometers, for example between 5 nanometers and 20 nanometers.

The average thickness e of the coating 104 of the grains may for example be less than or equal to 150 nm, for example less than or equal to 100 nm, for example less than or equal to 50 nm. The average thickness e of the coating 104 of the grains may for example be greater than or equal to 1 nm, for example greater than or equal to 5 nm. The average thickness e of the coating 104 of the grains may be between 1 nm and 150 nm, for example between 1 nm and 100 nm, for example between 1 nm and 50 nm. The average thickness e of the coating 104 of the grains may be between 5 nm and 150 nm, for example between 5 nm and 100 nm, for example between 5 nm and 50 nm. We have just described various characteristics which can be verified by the grains 100 of the powder. We will now provide details on the manufacture of these 100 grains.

The grains forming the powder can be formed by treating a powder of carbon, or of carbon doped with boron, by chemical vapor deposition (“Chemical Vapor Deposition”; “CVD”) of silicon carbide in a fluidized bed. Depending on the operating conditions used, the stoichiometry and the average size of the crystallites can be controlled. The duration of the deposition makes it possible to adjust the thickness of the coating - the longer the time, the greater the thickness of the coating.

According to one example, 10 grams of a carbon grain powder could be coated in the following manner. The carbon powder grains had an average size of between 1 µm and 3 µm. The carbon powder was placed in a reactor with a diameter of 50 mm and a height of 1000 mm.

The characteristics of the gas phase implemented were as follows, the gas phase included a mixture of argon (carrier gas), MTS and

of hydrogen:

- argon carrier gas: flow rate of 1000 to 4000 standard cubic centimeters per minute, preferably 2000 standard cubic centimeters per minute,

MTS gas (methyltrichlorosilane): flow rate of 100 to 200 standard cubic centimeters per minute, preferably 150 standard cubic centimeters per minute,

- hydrogen gas: flow rate of 600 to 1000 standard cubic centimeters per minute, preferably 800 standard cubic centimeters per minute.

The deposition temperature was between 900 ° C and 1000 ° C, preferably 950 ° C. The pressure in the reactor was between 300 and 600 millibars, preferably 450 millibars. The deposited thickness depends on the duration of the treatment. By way of example, a duration of one hour made it possible to deposit a thickness of about 100 nanometers.

Instead of the fluidized bed process, it is possible to employ a liquid route technique to form the coating of silicon carbide. According to this technique, a carbon or carbon powder doped with boron is first of all dispersed in a liquid phase comprising a solvent optionally containing a surfactant. The solvent can be polar or non-polar. The solvent may for example comprise at least one alcohol, such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, a mixture of these compounds. The surfactant can be anionic, cationic or nonionic. The surfactant may for example comprise at least one of:

polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide (PPO), or compounds based on acetylene diol. A precursor containing silicon is then added to the solvent in which the powder has been dispersed. For example, tetraethyl orthosilicate (TEOS) can be used as a precursor. A heat treatment is then carried out making it possible to dry the powder and to form a silica coating on the surface of the carbon or boron-doped carbon cores. The silicon carbide coating is then obtained by carburizing the silica coating by subjecting it to an atmosphere containing carbon. As a variant, a high temperature treatment could be carried out to form the coating of silicon carbide by reaction between the silica and the carbon of the powder.

Once the powder has been introduced into the preform and before infiltration by the molten composition, a heat treatment of deoxidation of the powder can be carried out. This deoxidation heat treatment can be carried out under reduced pressure. The deoxidation heat treatment can be carried out at a temperature between 1250 ° C and 1400 ° C. The silicon or silicon alloy powder intended to form the molten composition can also be subjected to this heat deoxidation treatment.

The fiber preform is then infiltrated by the composition melted at the first temperature (step 50 in FIG. 1). As indicated above, the molten composition mainly comprises molten silicon by mass. This composition may correspond to molten silicon alone or to a silicon alloy in the molten state which further contains one or more other elements such as titanium, molybdenum, boron, iron or niobium. The silicon content by mass in the molten composition can be greater than or equal to 75%, for example 90%. The preform containing the powder is then completely impregnated with the molten composition after infiltration. The molten composition infiltrates the porosity of the fiber preform and comes around the grains of the powder. As mentioned above, the infiltration is carried out at a first temperature which is sufficient to melt the molten composition but which is not too high to avoid a reaction between the silicon of the molten composition and the carbon of the grains of the powder. and thus avoid any risk of premature clogging of the porosity. The first temperature is chosen as a function of the characteristics of the coating 104 of silicon carbide grains 100 as indicated above. The first one

temperature may be less than or equal to 1450 ° C, for example less than or equal to 1440 ° C, or even less than or equal to 1430 ° C.

Once the infiltration of the preform is completed, a temperature rise step is then carried out so as to allow the chemical reaction of the silicon of the molten composition with the carbonaceous core of the grains of the powder (step 60 in FIG. 1). As indicated above, the temperature is then increased so as to crack or decompose the coating 104 of silicon carbide of the grains 100 and allow the silicon of the molten composition to come into contact with the carbonaceous core of the grains. The second temperature also depends on the characteristics of the coating 104 of silicon carbide employed but may however remain less than or equal to 1550 ° C. The second temperature can be at least 10 ° C higher than the first temperature.

The time during which the infiltrated preform is subjected to the second

temperature may be greater than or equal to 10 minutes, for example greater than or equal to 30 minutes. This duration may be less than or equal to 90 minutes. This duration can for example be between 10 minutes and 90 minutes, for example between 30 minutes and 90 minutes.

There is shown in Figure 3 in a time-temperature diagram, a succession of steps that can be implemented in the context of the invention. Once the preform has been loaded with the powder, it is first possible to carry out a powder deoxidation step (step E0) at a temperature T0 as described above. It is then possible to increase the temperature to a plateau at the first temperature T1 as described above and to carry out, at this first temperature T1, the infiltration of the preform by the molten composition (step E1). Once the infiltration is complete, the temperature can then be increased again to a plateau at the second temperature T2 as described above and carrying out, at this second temperature 12, the reaction between the silicon of the molten composition and the carbon of the grains (step E2).

In connection with the example illustrated in FIG. 1, there has thus been described a method of manufacturing a part made of composite material with a ceramic matrix which comprises at least the following steps:

- formation of a fiber preform,

- introduction of the powder into the porosity of the fiber preform, and

infiltration of the fiber preform loaded by the powder with a molten composition comprising mainly silicon by mass, a silicon carbide matrix being formed in the porosity of the fiber preform during infiltration in order to obtain the part made of composite material.

An interphase and / or a consolidation phase can be formed on the fibers after formation of the preform and before introduction of the powder as mentioned above.

As a variant, the method for manufacturing the part may include at least the following steps:

- Forming a fiber preform by assembling a plurality of fiber textures, the powder being present in the porosity of said textures, and

infiltration of the fiber preform thus obtained with a molten composition comprising mainly silicon by mass, a silicon carbide matrix being formed in the porosity of the fiber preform during infiltration in order to obtain the part made of composite material.

The expressions "between ... and ..." and "from ... to ..." must be

understand as including the limits.

Claims

[Claim 1] A method of manufacturing a part made of composite material with a silicon carbide matrix, comprising at least:

- the infiltration (50) of a fiber preform with a molten composition comprising mainly silicon by mass, a first temperature (Tl) being imposed during the infiltration and a powder being present in the porosity of said preform, said powder comprising grains (100) formed of a core (102) of carbon or boron doped carbon coated with a coating (104) of silicon carbide, said first temperature being sufficiently low to prevent the reaction of the molten composition with the core grains of the powder, and

- Submitting the preform thus infiltrated to a second temperature (T2) higher than the first temperature and sufficient to allow the reaction of the molten composition with the core of the grains of the powder and thus form silicon carbide (60).

[Claim 2] The method of claim 1, wherein the grains (100) of the powder have a coating (104) of silicon carbide having:

- an average thickness (e) between 20 nm and 100 nm, and

- an average size of silicon carbide crystallites of between 8 nm and 20 nm,

and wherein the first temperature is less than or equal to 1450 ° C, and the second temperature is greater than or equal to 1460 ° C.

[Claim 3] A method according to claim 1, wherein the grains (100) of the powder have a coating (104) of silicon carbide having:

- an average thickness between 30 nm and 120 nm, and

- an average size of silicon carbide crystallites of between 5 nm and 15 nm, and the first temperature is less than or equal to 1440 ° C, and the second temperature greater than or equal to 1450 ° C.

[Claim 4] The method of claim 1, wherein the grains (100) of the powder have a coating (104) of silicon carbide having:

- an average thickness (e) between 40 nm and 150 nm, and

- an average size of silicon carbide crystallites of between 3 nm and 10 nm,

and wherein the first temperature is less than or equal to 1430 ° C, and the second temperature is greater than or equal to 1440 ° C.

[Claim 5] A method according to any one of claims 1 to 4, wherein the fiber preform comprises silicon carbide fibers having an oxygen content of less than or equal to 1% atomic percent.