FR3159965A1 - Manufacturing process of a CMC part - Google Patents

Abstract

Method for manufacturing a CMC part The invention relates to a method for manufacturing a composite material part comprising the following steps: - infiltrating a fiber preform (135) with an infiltration composition (133) comprising at least liquid silicon and via a melt infiltration method, said infiltration being carried out at an infiltration temperature (TI), - cooling said fiber preform (135), the method being characterized in that the cooling of the fiber preform (135) after infiltration is carried out by exposing the fiber preform (135) to a temperature gradient, between a first temperature (T1) and a second temperature (T2), the second temperature (T2) being at least 50°C lower than the first temperature (T1); and - ablation of at least a portion of the fiber preform (135) exposed to the first temperature (T1) during cooling. Figure for abstract: Fig 2.

Description

Manufacturing process of a CMC part

The present invention relates to a method for manufacturing a part made of ceramic matrix composite material.

Ceramic matrix composites (CMC) 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 draw in the compressor which impacts the efficiency of the turbomachine, CMC materials therefore 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.

These advantages explain the industrial interest in developing such ceramic matrix composite materials.

A known method for manufacturing such a part is infiltration with molten silicon, often called "MI" for the English acronym "Melt Infiltration".

In such a method, a fiber preform is impregnated with an infiltration composition generally comprising molten silicon to form the matrix of the CMC material within the porosity of the fiber preform. Generally, to carry out the infiltration, one end of the preform is dipped into a bath of infiltration composition, so that the latter fills the porosity of the preform by capillarity.

Such a method is satisfactory industrially, but improvements remain desirable.

In particular, infiltration compositions that include silicon are denser in the solid state than in the liquid state. Thus, their cooling and solidification cause part of the liquid infiltration composition to escape in the form of drops that solidify on the surface of the part, thus forming nodules. These nodules then cause significant difficulties since they modify the dimensions of the part beyond the tolerances and degrade the adhesion of any surface coating subsequently deposited.

Similarly, the appearance and growth of nodules can cause cracks in the area of the part where they appear. In addition, removing these nodules by sandblasting or machining is slow, laborious, and therefore expensive; it can also affect the material health of the final part.

Consequently, in order to combat the appearance of such nodules, certain solutions have been considered. One of these aims to modify the composition of the densification material or ceramic slip used in conventional infiltration processes with molten silicon, for example by adding diamond particles, sources of carbon which will consume the excess silicon to form SiC. However, it is not always possible or desirable to modify the composition of the slip in this way.

Another option is to provide a sacrificial layer of ceramic slip all around the intermediate part in order to protect the final part, and in particular its reinforcement, during sandblasting or machining of the nodules. However, naturally, such an option results in significant overconsumption of raw materials and requires complete machining of the final part, which is long and tedious.

Alternatively, it is possible to add thermal masses to the locations where nodules are desired to form. However, this alternative does not completely eliminate nodules, but only ensures that the appearance of nodules is concentrated in locations where they are expected. In addition, this solution also limits the maximum quantity of parts that can be loaded into a densification furnace.

There is therefore a real need for a process for manufacturing a CMC part that allows for better control of the densification stage of the part and that is free, at least in part, from the drawbacks inherent in the aforementioned known methods. There is also a need for an installation that allows such a process to be implemented.

The invention aims precisely to meet the needs formulated above.

According to a first of its aspects, the invention proposes a method for manufacturing a part made of composite material comprising the following steps:
- the infiltration of a fiber preform by an infiltration composition comprising at least liquid silicon and via a molten infiltration method, said infiltration being carried out at an infiltration temperature,
- cooling of said fiber preform,
the method being characterized in that the cooling of the fiber preform after infiltration is carried out by exposing the fiber preform to a temperature gradient, between a first temperature and a second temperature, the second temperature being at least 50°C lower than the first temperature; and
- the removal of at least a portion of the fibrous preform exposed to the first temperature during cooling.

Thus, the process makes it possible to obtain a part made of ceramic matrix composite (CMC) material having mechanical properties and a surface finish at least identical to those of the prior art and at reduced costs.

In fact, the nodules and cracks formed during cooling are concentrated in the area of the part which cools the slowest, i.e. the one which is exposed to the first temperature.

In fact, the rest of the room is exposed to a lower temperature, between the second temperature and the first temperature.

In addition, the ablation step thus makes it possible to eliminate nodules and any cracks to achieve an improved part compared to parts of the prior art. For this, the ablation step is preferably carried out for the portion of the part exposed to the first temperature throughout the cooling period.

For example, the ablation step can allow the removal of an area of the preform which will be called “sacrificial”.

For example, such a zone may extend over a height of a few millimeters to a few centimeters and over the entire thickness of the preform, for example less than or equal to 5 mm, or even less than or equal to 15 mm, or even less than or equal to 25 mm, or even less than or equal to 50 mm, or even less than or equal to 100 mm.

In one embodiment of a method, the sacrificial area of the preform may extend from the area of the preform disposed in the infiltration composition for the purposes of the infiltration step over a height as described above.

The size of the sacrificial zone represents an optimum between the need for a small sacrificial portion, which reduces the cost of the process by minimizing the amount of material left behind, and the need for a larger sacrificial portion to ensure that all silicon nodules that may have formed are removed.

The process thus makes it possible to manufacture CMC materials more quickly and economically, in particular because it does not require complete machining of the final part to remove silicon nodules, nor crack control.

According to a particular characteristic of the process, the fiber preform may have a thickness greater than or equal to 15 mm.

The usual meaning of the field is given here and in the application to the expression "thickness", that is to say the smallest dimension in which the fibrous preform extends, in other words the minimum distance to be covered to cross the preform from one side to the other.

In one embodiment, the thickness of the preform may not be constant, but nevertheless always be greater than or equal to 15 mm.

It is for such parts that the process is most advantageous. Indeed, it is for parts whose thickness is greater than or equal to 15 mm that the nodules observed during the production of prior art processes are most likely to create strong stresses when solidifying, which can go as far as degrading the fibrous texture.

On the contrary, and as described, the process allows the nodules and stresses created during cooling to be located in a portion of the preform exposed to the first temperature, which will be removed at the end of the process.

This makes it easier to manufacture thick CMC parts without cracks or surface defects.

For the purposes of the process, the infiltration temperature must be higher than the melting temperature of the infiltration composition.

In one embodiment and depending on the infiltration composition chosen, the infiltration temperature may be greater than or equal to 1400°C, or even greater than or equal to 1450°C.

The infiltration temperature is chosen according to the melting temperature of the infiltration composition and may, for example, be at least 10°C higher, or even at least 30°C higher or even at least 50°C higher than the melting temperature of the infiltration composition.

Depending on a particular characteristic of the process, the infiltration temperature may be greater than or equal to 1450°C, or even greater than or equal to 1400°C.

An infiltration temperature greater than or equal to 1450°C allows the infiltration composition to be maintained in the molten state throughout the infiltration stage.

In one embodiment, the first temperature may be greater than or equal to 1450°C, or even greater than or equal to 1400°C, for example between 1400°C and 1450°C.

According to a particular characteristic of the process, the first temperature can be between the infiltration temperature and 1400°C.

In one embodiment, the first temperature may be equal to the infiltration temperature.

In one embodiment, the first temperature may be at least 10°C, or even at least 30°C, or even at least 50°C lower than the melting temperature of the infiltration composition.

Such embodiments allow an optimum for the solidification of the infiltration composition while ensuring that the temperature difference with the second temperature nevertheless allows excellent control of the solidification front in the preform.

In one embodiment, the second temperature may be 50°C, or even 100°C, or even 200°C lower than the first temperature.

According to a particular characteristic of the process, the second temperature may be less than or equal to 1350°C, or even less than or equal to 1300°C, or even less than or equal to 1250°C.

As described, however, the cooling is carried out with a difference between the first and second temperatures greater than or equal to 50°C, or even greater than or equal to 100°C, or even greater than or equal to 200°C.

A difference greater than or equal to 50°C between the first temperature and the second temperature allows optimal control of the solidification front during the cooling stage.

Further increasing the temperature difference between the first temperature and the second temperature can influence the speed of movement of the solidification front in the part.

For example, the cooling step can be carried out by placing the fiber preform between a first heated enclosure, for example the one in which the infiltration step was carried out, and a second unheated enclosure, the two enclosures being separated by a sealing member during the infiltration step.

In such an embodiment, and although the second enclosure is not heated, the opening of the closure member nevertheless allows the hot atmosphere of the first enclosure to invade the second, thus establishing the desired thermal gradient.

This embodiment is the most economical because it allows the establishment of a gradient passively, without having to supply energy to the second enclosure.

In one embodiment, the cooling step can be carried out by placing the fiber preform between a first heated enclosure, for example the one in which the infiltration step was carried out, and a second heated enclosure but independently, the two enclosures being for example separated by a sealing member during the infiltration step.

In this way, the temperature of the first and second enclosures is perfectly controlled, and the desired thermal gradient is thus achieved.

Such a temperature difference is sufficient to guarantee a cooling front ensuring that silicon nodules are formed in the portion of the part that sees the first temperature for the longest time.

Depending on a particular characteristic of the process, the duration of the infiltration step can be between a few minutes and a few hours, for example between 10 minutes and 6 hours.

If the infiltration step duration is too short, the preform may not be fully infiltrated. On the contrary, if the infiltration step duration is too long, the fiber texture may be damaged by the infiltration compound.

According to a particular characteristic of the process, the duration of the cooling step can be between 10 minutes and 24 hours.

In one embodiment, neither the first nor the second temperature varies during a cooling step according to the method of the invention.

In one embodiment the first and/or the second temperature may vary and preferably decrease during the cooling step of a method of the invention.

It is however understood that the temperature difference between the first and second temperatures must remain greater than or equal to 50°C, or even greater than or equal to 100°C, or even greater than or equal to 200°C.

In one embodiment, the cooling step is carried out at a cooling ramp, preferably constant. In other words, the first and second temperatures may decrease accordingly during the cooling step.

This embodiment then makes it possible to minimize internal stresses in the part, while ensuring that the advantages described above for exposing a part to a temperature gradient are retained.

In one embodiment of the method, the latter may comprise, after the cooling step described, an additional cooling step, ensuring a return to ambient temperature of the formed part.

Preferably, this additional cooling step is undertaken when all of the infiltration composition has solidified in the fibrous preform.

In such an embodiment, an additional cooling step may be performed between the cooling step and the ablation step.

For such an additional cooling step, it is not necessary to maintain any temperature difference between two portions of the preform unlike the cooling step described above.

For example, the additional cooling step can be achieved by exposing the densified part to room temperature.

Preferably, the additional cooling step is carried out under reduced pressure, or under a controlled atmosphere.

Preferably, the ablation step is carried out at room temperature, for example outside the enclosure used for infiltration.

In one embodiment, the fibrous preform may comprise fibers of silicon carbide, carbon, or a mixture thereof.

In one embodiment, the fiber preform may be the preform of an aeronautical part, for example a part chosen from a turbine blade, a ring sector, a distributor or even a combustion chamber or a portion of one of these parts.

The invention proposes, according to another of its aspects, a furnace for the siliciding of at least one fibrous preform comprising:
- an upper enclosure without heating means;
- a lower enclosure, having a heating means and further comprising a support capable of receiving an infiltration composition comprising molten silicon and a displacement member capable of moving the fiber preform from the lower enclosure to the upper enclosure,
the furnace being characterized in that the displacement member is configured to allow the displacement of the fiber preform from the lower enclosure to the upper enclosure through an opening provided between the lower enclosure and the upper enclosure, and further characterized in that it comprises a closing member capable of closing the opening between the lower enclosure and the upper enclosure.

Such an oven is particularly suitable for obtaining a part made of ceramic matrix composite (CMC) material, in particular by implementing a process such as that just described.

Such an oven allows in particular controlled cooling of the preform, ensuring that the part closest to the lower enclosure cools the most slowly, because it is exposed to the highest temperature throughout the cooling stage.

It is to the credit of the inventors to have determined that the upper enclosure, devoid of heating means, made it possible, by its proximity to the lower enclosure, to establish a sufficient temperature gradient for carrying out a process as described above, and this without creating an additional energy cost to be provided during the infiltration stage thanks to the sealing element.

According to a particular characteristic of the furnace, the displacement member can be integral with the closure member. Thanks to this characteristic, it is possible to simultaneously move the closure member and the preform, linked to the displacement member.

Generally speaking, the presence of the shutter makes it possible to limit the size of the lower enclosure and thus reduce the heating requirements of the oven.

According to a particular characteristic of the oven, the support can extend in a plane and the oven can comprise a displacement member configured to move the preform along an axis orthogonal to said plane.

In one embodiment, the preform may be disposed on the displacement member so that this area where the nodules are concentrated can be eliminated before use of said part.

In such a furnace configuration, the displacement member allows the preform to be brought closer to the upper enclosure. In doing so, the preform is exposed to a temperature gradient which allows the nodules and any cracks to be concentrated in a predetermined area of the preform.

In fact, the upper enclosure is devoid of heating means so that it is at a lower temperature than that of the lower enclosure of the oven.

By bringing the preform closer to the upper or middle enclosure of the displacement member, we therefore ensure the presence of the temperature gradient, necessary for cooling the process described above and making it possible to obtain improved properties for the composite material part.

Depending on a particular characteristic of the furnace, it can be configured to implement the infiltration and cooling steps of the process described above.

In fact, the furnace allows on the one hand to carry out the siliciding in the lower chamber, then to carry out the cooling step by placing the infiltrated preform between the lower chamber and the upper chamber.

Since the upper chamber is devoid of heating means, the latter is at a lower temperature than that of the lower chamber which has been heated for the purposes of infiltration.

Thus, by placing the preform between the lower enclosure and the upper enclosure once the infiltration of the preform is complete, and by controlling the heating means of the lower enclosure, it can be ensured that the preform cools by being exposed to a temperature gradient, between a first temperature and a second temperature, the second temperature being at least 50°C lower than the first temperature.

In this embodiment, the lower enclosure having been heated for the purposes of infiltration is at a first temperature and the upper enclosure not having its own heating means is at a second temperature, lower than the first.

FIG. 1 There FIG. 1 is a schematic representation of the furnace according to one embodiment of the invention.

FIG. 2 There FIG. 2 is a schematic representation of the furnace of the FIG. 1 in a configuration different from that represented in FIG. 1 .

FIG. 3 There FIG. 3 is a schematic representation of the evolution of the solidification front during the cooling of a preform infiltrated with CMC according to a method of the invention.

The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

There FIG. 1 represents an oven 100 according to one embodiment of the invention. Such an oven comprises an upper enclosure 120 and a lower enclosure 110. Said lower enclosure 110 comprises at least one heating means 111 while the upper enclosure 120 is devoid of heating means.

According to a particular characteristic of the oven according to the invention, the heating means 111 can be inductive or resistive depending on the particular choices for the design of the oven 100.

Likewise, the FIG. 1 represents the heating means 111 outside the lower enclosure 110 but this is not restrictive of the invention.

The lower enclosure 110 further comprises a support 130 capable of receiving an infiltration composition comprising molten silicon 133.

In the embodiment shown, the support comprises a crucible 134, which contains a bath of an infiltration composition 133.

On the FIG. 1 , a preform 135 is dipped into said bath of an infiltration composition 133.

There FIG. 1 represents the fibrous preform 135 directly in contact with the infiltration composition 133. This is not necessary and in one embodiment, a drain can be interposed between the portion of the fibrous preform 135 and the infiltration composition 133. Such a drain must allow the infiltration composition to rise by capillarity in the fibrous preform, without having to directly expose the latter to the composition.

The crucible 134 may be made of a ceramic material. The infiltration composition 133 may, for example, be silicon or a silicon alloy, which may optionally include boron.

In an embodiment that is not the one shown, the oven 100 may be provided with a vacuum pump configured to maintain a reduced pressure in the lower enclosure 110 and/or the upper enclosure 120.

Such a vacuum pump then makes it possible to carry out the vacuum infiltration process.

The number of porous fibrous preforms 135 arranged on the support 130 is in no way limiting.

In one embodiment, the support may comprise a plurality of fibrous preforms 135, for example between 2 and 10 fibrous preforms.

Thus, it is possible to carry out the infiltration and/or cooling of several preforms 135 simultaneously, which allows a gain in terms of profitability and cost.

For the purposes of simplification, an embodiment is described below which comprises only one preform, one support 130 and one displacement member 131.

The furnace 100 also comprises a moving member 131 configured to move the porous fibrous preform 135 from the lower enclosure 110 to the upper enclosure 120.

However, the advantages described here for embodiments in which the displacement member 131 would allow the displacement of several preforms 135, or in which several displacement members 131 would be present can be transposed to these embodiments.

This movement is carried out through an opening 121 provided between the lower enclosure 110 and the upper enclosure 120.

The number of openings 121 provided and of movement members 131 is not limiting.

In an embodiment which is not the one shown, the oven may comprise several openings 121 arranged between the lower chamber 110 and the upper chamber 120 in order to allow the passage of each of a porous fibrous preform 135.

In an embodiment which is not shown, the oven may comprise one or more openings 121 arranged between the lower chamber 110 and the upper chamber 120, each allowing the passage of several porous fibrous preforms 135.

According to a particular characteristic of the oven, the oven 100 may comprise several displacement members 131, for example one displacement member 131 per fiber preform 135.

A closure member 140 for said opening 121 is provided in the oven 100. In the context where several openings 121 can be provided between the lower enclosure 110 and the upper enclosure 120, several closure members 140 can also be envisaged.

In one embodiment, which is that illustrated in figures 1 and 2, the displacement member 131 is integral with the support 130. Thus, it is possible to move both the support 130 and the preform 135. This embodiment is however not limiting and embodiments in which only the preform 135 would be moved by the displacement member 131 are not excluded.

For example, in an embodiment of the furnace that is not illustrated, the displacement member 131 may carry the porous fibrous preform 135.

In an embodiment not shown, the furnace 100 may also comprise a system for controlling the relative position between the preforms 135 and the crucible 134. For example, the movement of the movement member 131 may be controlled to extract the preform 135 from the bath of infiltration composition 133 placed on the support 130.

The control system can be, for example, a PLC or a computer equipped with an input/output acquisition card. The control system can receive electrical signals from the mass measuring device as input and send control signals to the holding arm.

In one embodiment, the displacement member 131 can be integral with the closure member 140. Thus, it is possible to simultaneously move the porous fiber preform 135 and the closure member 140. In addition, thanks to this characteristic, the movement of the preform 135 can be optimally controlled.

According to a particular characteristic of the oven illustrated in the figures, the support 130 can extend in an XZ plane.

According to a particular characteristic of the furnace, the displacement member 131 may comprise a movable rod 132. Said movable rod 132 may be configured to move the porous fibrous preform 135, along a Y axis orthogonal to the XZ plane of the support 130.

There FIG. 1 illustrates an oven 100 for which the displacement member 131 is positioned so that the preform 135 is present in the lower enclosure 110.

There FIG. 2 illustrates the same oven 100 in which the displacement member 131 is positioned so that the fiber preform 135 is located for the most part in the upper enclosure 120.

It should however be understood that the displacement member 131 allows the preform 135 to take all positions, and it is precisely the displacement of the preform 135 between the lower enclosure 110 and the upper enclosure 120 which allows the exposure of the preform to a temperature difference.

As illustrated, the closure member 140 may be able to move along a Y axis orthogonal to the XZ plane of the support 130.

The oven 100 may further comprise at least one device for measuring the mass of the preforms 135. In particular, this device may correspond to a scale of the weighing type.

In one embodiment, such a measuring device may be added to the displacement member 131. In such a case, the displacement member 131 may be configured to control the displacement as a function of the change in the mass of the preform 135 as measured by the mass measuring device.

For example, the movement member 131 may be configured to set the preform 135 in motion when it reaches a target mass, corresponding to that for which the porosity of the preform 135 is optimally filled by the infiltration composition to begin cooling.

Such an embodiment makes it possible to ensure that the transition between the infiltration step and the cooling step is made once the preform 135 has its porosity filled optimally.

According to a particular feature of the oven, the oven may include a temperature control device configured to control the temperature of the lower enclosure 110.

In one embodiment, the upper enclosure 120 and/or the lower enclosure 110 may include a temperature sensor.

According to a particular characteristic of the furnace, the furnace may comprise a movement control device configured to control the speed of movement of the preform 135 between the lower enclosure 110 and the upper enclosure 120.

Depending on the geometry of the part to be manufactured, the speed of movement of the preform 135 between the lower enclosure 110 and the upper enclosure 120 can thus be controlled. It is thus possible to optimally control the speed of movement of the solidification front of the infiltration composition in the preform 135.

According to a particular characteristic, the lower enclosure 110 may comprise a thermal insulating material disposed between the lower enclosure 110 and the upper enclosure 120.

This embodiment allows for better passive control of the temperature of the upper enclosure, which has no heating means, but whose temperature is influenced by its proximity to the lower enclosure.

An example of the method for siliciding a fiber preform 135 is now described. In a first step, the preform 135 is infiltrated with an infiltration composition 133 inside the lower enclosure 110 of an oven 100 as illustrated in the FIG. 1 .

Preferably, to carry out this step, the closure member closes the passage existing between the lower enclosure 110 and the upper enclosure 120. This in fact makes it possible to reduce the heating requirements of the process by reducing the size of the enclosure in which the infiltration takes place.

In the mode shown, the infiltration of the porous preforms 135 is carried out by bringing said porous fibrous preform 135, for example the lower end of the preform 135, into contact with the surface 133a of the bath of an infiltration composition 133 which may for example be silicon or a silicon alloy, the infiltration composition 133 infiltrating the porosity of the preform 135 by capillarity.

According to a particular characteristic of the furnace and of the method, the contacting or not of the preform 135 with the infiltration composition 133 and, consequently, the control of the infiltration of the preform 135 by the infiltration composition 133 is carried out by the displacement member 131.

In one embodiment, the infiltration of the preform 135 by the infiltration composition of the bath 133 is monitored, for example by a mass measuring device which is capable of detecting a predetermined mass gain corresponding to the desired level of densification for the preform 135.

Depending on a particular characteristic of the furnace and the process, the infiltration temperature T _I is greater than or equal to 1450°C.

According to a particular characteristic of the furnace and the process, the first temperature T ₁ is between the infiltration temperature T _I and 1400°C.

Alternatively, the first temperature T ₁ may be greater than or equal to 1400°C, or even greater than or equal to 1450°C.

According to a particular characteristic of the furnace and the process, the second temperature T ₂ is less than or equal to 1350°C, or even less than or equal to 1300°C, or even less than or equal to 1250°C.

As described, cooling of the fiber preform 135 is accomplished by exposing the fiber preform 135 to a temperature gradient.

Such a "temperature gradient" is intended to mean that the preform is immersed in a non-uniform temperature field so that two parts of the preform are arranged, one at a first temperature T ₁ and the other at a second temperature T ₂ lower by at least 50°C, or even at least 100°C, or even at least 200°C, than the first temperature T ₁ .

In other words, at least a portion of the preform 135 is exposed for cooling to a second temperature T ₂ lower by at least 50°C, or even at least 100°C, or even at least 200°C, than the first temperature T ₁ to which another portion of the part is exposed.

If such a method is carried out in an oven 100 described above, such a cooling step can be carried out by opening the opening 121 between the lower enclosure 110 and the upper enclosure 120, for example by removing the closure member 140, and by placing the infiltrated preform 135 between the lower enclosure 110 and the upper enclosure 120.

In such an embodiment, the temperature difference between the temperature of the lower enclosure 110 and the temperature of the upper enclosure 120 is at least 50°C, which ensures that the temperature field has the desired gradient. This temperature gradient makes it possible to control the solidification front 136 during the cooling step of the infiltrated preform 135.

In fact, the solidification of the silicon takes place first in the coldest zone of the preform 135.

In one embodiment, the cooling step can be done by decreasing or even stopping the heating supply to the lower enclosure.

In this way and due to inherent thermal losses, the first and second temperatures may decrease during the cooling step of a method of the invention.

However, this reduction in the first and second temperatures can be controlled, and the gradient to which the preform is exposed remains at least greater than 50°C, throughout the cooling stage.

Alternatively, the first temperature may be maintained throughout the cooling step, but chosen to be slightly lower than the melting temperature of the infiltration composition.

In this way, the solidification of the infiltration composition also takes place from the portion of the preform exposed to the second temperature and up to the portion exposed to the first temperature, but without the need to reduce the first or second temperature during the cooling step.

In an alternative embodiment, the method may be carried out in an oven was not as on the FIG. 2 .

For example, such an oven may include a heated upper chamber, which then allows very precise control of the second temperature.

The method of the invention can thus be implemented in an even more advantageous manner.

There FIG. 3 shows an example of the evolution of the solidification front 136 of an infiltrated preform 135 during the cooling step. The solidification front 136 moves in the infiltrated preform over time.

You must read the FIG. 3 as different states of progress of the solidification of the infiltration composition in a preform 135 which would be arranged as illustrated in FIG. 2 , in which the lower enclosure would be at the first temperature T ₁ and the upper enclosure 120 at the temperature T ₂ .

There FIG. 3 represents a solidified portion 141 which progresses from the portion of the preform exposed to the second temperature T ₂ towards the portion of the preform exposed to the first temperature T ₁ .

The silicon nodules and any cracks form at the end of solidification, in the part where the infiltration composition solidifies last. In the preform 135 of the example shown, a sacrificial zone 137 has been provided where the silicon nodules and cracks are concentrated at the end of cooling.

In one embodiment, the sacrificial zone 137 generally comprises a height greater than the height of the area of the preform dipped into the bath of an infiltration composition 133 during the infiltration step.

Indeed, it is to the credit of the inventors to have understood that this characteristic also ensures an excellent surface condition of the preform once the sacrificial zone 137 has been removed.

Indeed, it has been identified that contact with molten silicon could lead to a degraded surface condition.

Thus, during the step of eliminating the sacrificial zone 137, all the nodules and cracks will be eliminated from the preform.

In one embodiment, the ablation step can be carried out after a second step of cooling the preform, making it possible to bring the temperature of the densified preform back to room temperature.

In one embodiment, such a second cooling step may be performed by exposing the preform to air at room temperature.

For such a second cooling step, it is no longer necessary to expose the preform to a temperature gradient. Indeed, once the infiltration composition has solidified in the preform as described above, the advantages of the first cooling step, i.e. the concentration of nodules and possible cracks in the desired area of the preform, will be ensured.

The process which has just been described thus makes it possible to obtain parts made of CMC material comprising a fibrous reinforcement densified by a matrix having mechanical properties and a surface condition superior to those of the prior art, due to the better control of the growth of silicon nodules and any cracks in the associated preform.

Claims (10)

Method of manufacturing a part in composite material comprising the following steps:
- the infiltration of a fibrous preform (135) by an infiltration composition (133) comprising at least liquid silicon and via a molten infiltration method, said infiltration being carried out at an infiltration temperature (T _I ),
- cooling said fiber preform (135),
the method being characterized in that the cooling of the fibrous preform (135) after infiltration is carried out by exposing the fibrous preform (135) to a temperature gradient, between a first temperature (T ₁ ) and a second temperature (T ₂ ), the second temperature (T ₂ ) being at least 50°C lower than the first temperature (T ₁ ); and
- the ablation of at least a portion of the fibrous preform (135) exposed to the first temperature (T ₁ ) during cooling. Method according to claim 1 in which the fibrous preform (135) has a thickness greater than or equal to 15 mm. Method according to claim 1 or 2, wherein said first temperature (T ₁ ) is greater than or equal to 1400 °C. Method according to any one of claims 1 to 3, wherein said second temperature (T ₂ ) is less than or equal to 1350 °C. Method according to any one of claims 1 to 4, wherein the duration of said infiltration step is between 10 minutes and 6 hours. A method according to any one of claims 1 to 5, wherein the duration of said cooling step is between 10 minutes and 24 hours. Oven (100) for the siliciding of at least one fibrous preform comprising:
- an upper enclosure (120) without heating means;
- a lower enclosure (110), having a heating means (111) and further comprising a support (130) capable of receiving an infiltration composition comprising molten silicon (133) and a displacement member (131) capable of moving the fiber preform from the lower enclosure (110) to the upper enclosure (120),
the furnace (100) being characterized in that the displacement member (131) is configured to allow the displacement of the fiber preform (135) from the lower enclosure (110) to the upper enclosure (120) through an opening (121) provided between the lower enclosure (110) and the upper enclosure (120), and further characterized in that it comprises a closing member (140) capable of closing the opening (121) between the lower enclosure (110) and the upper enclosure (120). Oven (100) according to claim 7, wherein said displacement member (131) is integral with said closure member (140). Oven according to any one of claims 7 or 8, wherein said support (130) extends in a plane (XZ) and wherein the oven (100) comprises a displacement member (131) configured to move the preform (135) along an axis orthogonal (Y) to said plane (XZ). Oven according to any one of claims 7 to 9 configured to implement the infiltration and cooling steps of the method for manufacturing a part made of composite material according to any one of claims 1 to 6.