FR3145972A1 - OVEN AND METHOD FOR DENSIFYING A PART MADE OF CMC MATERIAL - Google Patents

Abstract

Furnace (50) for densifying a part (30) made of ceramic matrix composite material, this furnace (50) comprising: - a first chamber (52) comprising a cavity (54) configured to receive the part (30) as well as a crucible (56) comprising a ceramic material for densifying this part, - a second chamber (58) in which the first chamber (52) is located as well as heating elements (60), - at least one device (62) for creating a vacuum in said cavity (54), - at least one device (64) for measuring the temperature in said second chamber (58), and - at least one unit (66) for controlling the furnace, and in particular its heating elements (60) and devices (62, 64), characterized in that said first chamber (52) is equipped with a filter (82) for effluents (84).

Description

OVEN AND METHOD FOR DENSIFYING A PART MADE OF CMC MATERIAL Technical field of the invention

The present invention relates to an oven and a method for densifying a part made of CMC material, i.e. a ceramic matrix composite material (for example SiC/SiC).

Technical background

Such a densification process can be used in particular in the aeronautics sector in order to manufacture parts capable of withstanding high

temperatures. This is particularly the case for parts forming the turbine(s) of an aircraft turbomachine, for example the sectors of the rings used to delimit the external periphery of a turbine vein.

In order to withstand these very high temperatures, the ring sectors are made of CMC. In a typical manufacturing process for this type of part,

A preform is woven using ceramic fibers, for example silicon carbide (SiC).

This preform is then shaped in a former and an interphase is deposited on the surface of the ceramic fibers, using a CVI ( Chemical Vapor Infiltration ) process for example. The preform is removed from the former and a second densification by a CVI process can be carried out to deposit silicon carbide on the preform.

In a second step, a slip comprising ceramic particles, for example SiC, suspended in a solvent, is injected into the preform. Once the solvent has been removed by drying, the ceramic particles thus deposited undergo a heat treatment which makes it possible to obtain an intermediate part having a certain porosity.

A densification step is then carried out by infiltration then solidification of a liquid densification material, generally liquid silicon, in the intermediate part.

This densification is carried out in an oven which typically includes:

- a first chamber comprising a cavity configured to receive the part as well as a crucible comprising the densification material,

- a second chamber in which the first chamber is located and heating elements configured to heat the densification material above a melting temperature of the densification material, and

- cavity vacuum and temperature measurement devices.

During this densification, effluents are generated and include, for example, silicon (Si) vapours and silicon monoxide (SiO). These effluents have been found to degrade the furnace and accelerate its ageing. This is particularly the case for the insulating materials of the furnace and the aforementioned devices, which can react with these effluents and degrade.

The present invention aims to provide a solution to this problem, which is simple, effective and economical.

The invention relates to an oven for the densification of a part made of ceramic matrix composite material, this oven comprising:

- a first chamber comprising a cavity configured to receive the part as well as a crucible comprising a ceramic material for densifying this part,

- a second chamber in which the first chamber is located as well as heating elements configured to heat the densification material above a melting temperature of the ceramic densification material,

- at least one device for placing said cavity under vacuum,

- at least one device for measuring the temperature in said second chamber, and

- at least one control unit for the oven, and in particular for its heating elements and devices,

characterized in that said first chamber is equipped with an effluent filter.

The present invention thus proposes to filter the effluents so as to retain the particles or compounds likely to accelerate the aging of the furnace, or to degrade these particles or compounds. Chemical degradation reactions can for example occur between compounds of the effluents and the material(s) of the filter.

In this application, effluent means a gas caused by the heating of the densification material and/or by the products used during heating or located in the furnace. Filter means an element capable of retaining or degrading particles or compounds of an effluent.

It is therefore understood that the oven according to the invention will have an improved service life compared to ovens of the prior art.

• le filtre à effluents comprend plusieurs couches superposées ;
• les couches sont différentes ;
• les couches sont identiques ;
• le filtre ou chacune des couches est réalisé dans un matériau choisi parmi du carbone et de l’alumine par exemple ;
• le filtre est recouvert d’une grille ou est porté par une cassette, de préférence en molybdène ;
• le filtre ou chacune des couches a une forme générale parallélépipédique dont la longueur est comprise entre 20 et 80cm, et la largeur est comprise entre 20 et 80cm ;
• le filtre ou chacune des couches a une épaisseur comprise entre 5 et 30mm.
• le filtre est situé en sortie de la première chambre, c’est-à-dire au niveau d’une sortie d’effluents ou d’un passage de sortie de gaz de la première chambre ; dans le cas où la sortie serait située au sommet de la chambre, le filtre serait situé au sommet de la chambre ; selon la géométrie du four, le filtre pourrait être placé ailleurs qu’au sommet ;

The oven according to the invention may also have one or more of the following characteristics, taken alone or in combination with each other:

• the effluent filter consists of several superimposed layers;
• the layers are different;
• the layers are identical;
• the filter or each of the layers is made of a material chosen from carbon and alumina for example;
• the filter is covered with a grid or is carried by a cassette, preferably made of molybdenum;
• the filter or each of the layers has a general parallelepiped shape whose length is between 20 and 80cm, and the width is between 20 and 80cm;
• the filter or each of the layers has a thickness between 5 and 30mm.
• the filter is located at the outlet of the first chamber, i.e. at an effluent outlet or a gas outlet passage of the first chamber; in the case where the outlet is located at the top of the chamber, the filter would be located at the top of the chamber; depending on the geometry of the furnace, the filter could be placed elsewhere than at the top;

-- the oven comprises a third chamber in which the first chamber is located, this third chamber having for example a generally cylindrical shape with a diameter greater than or equal to 1m, or even 2m, and a height greater than or equal to 1m, or even 2m;

-- the rooms are spaced apart from each other;

-- the heating elements are resistive bars;

• le four comprend en outre un plateau mobile verticalement qui est logé dans la première chambre et qui est relié à un actionneur relié à ladite au moins une unité.

-- said at least one measuring device is a thermocouple;

• the oven further comprises a vertically movable tray which is housed in the first chamber and which is connected to an actuator connected to said at least one unit.

The present invention also relates to a method for densifying a part made of ceramic matrix composite material, using an oven as described above, comprising the steps of:

(a) suspending or placing a part above a crucible in the first chamber, the part comprising a reinforcement embedded in a ceramic matrix, the reinforcement being obtained by weaving silicon carbide fibres, and the crucible comprising a silicon-based mixture as a densification material, and

b) heating said mixture to a temperature above a melting temperature of said mixture, which is for example greater than or equal to 1400°C.

The part is for example an aeronautical part.

Brief description of the figures

Other features and advantages of the invention will become apparent upon reading the detailed description which follows, for the understanding of which reference will be made to the appended drawings in which:

there is a block diagram illustrating steps in a process for manufacturing a part made of CMC material,

there is a schematic view of an oven according to the invention for densifying a part made of CMC material, and

there is a schematic perspective view of an effluent filter for a furnace of the .

Detailed description of the invention

There illustrates the different stages of an example of a process according to the presentation for manufacturing a part in CMC, i.e. in ceramic matrix composite material.

The process begins with the weaving E1 of a fibrous preform 10 which will act as a fibrous reinforcement for the part. This preform 10 is preferably woven using a 3D weaving technique, known elsewhere, for example with an interlock type weave. In this example, the preform 10 is woven with silicon carbide (SiC) fibers.

Once the preform 10 is finished, it is shaped and undergoes an interphase deposition step E2, known elsewhere, for example as CVI or chemical vapor deposition (also known as CVD for “ Chemical Vapor Deposition ”). In this example, the deposited interphase material is boron nitride (BN). A BN sheath is therefore formed around the fibers of the preform 10, which consolidates the preform 10 and blocks the shape given during shaping.

At the end of this interphase deposition step E2, a consolidated preform 10’ is obtained whose fibers are coated with an interphase sheath. The consolidated preform 10’ remains, however, still very porous.

An additional step of predensification of the preform can take place and involves depositing silicon carbide on the preform by CVI.

The preform 10’ thus consolidated is then transferred into a mold to undergo a step E3 of injecting a ceramic slip. In this example, the slip comprises a solvent, here water, a ceramic powder, here silicon carbide (SiC), and an organic binder, here polyvinyl alcohol. During this step E3, one or more filters are placed in contact with the preform 10’ and retain the ceramic particles of the slip.

In this example, the concentration of SiC powder in the slip is approximately 20% by volume. The concentration of the binder is 1% by mass relative to the mass of SiC powder in the slip.

The mold is designed to fit the shape of the 10’ preform.

A drying step E4 is then carried out to remove the solvent from the slip. This involves, for example, drying in an oven, with a temperature between 60 and 110°C. In addition, drying can be carried out in the mold or outside the mold.

During the drying step E4, within the preform 10’, the ceramic particles of the slip decant and are deposited on the fibers of the preform 10’ as the solvent is removed, thus filling a portion of the porosities of the preform 10’. A green part 20 is then obtained.

The raw part 20 thus obtained then undergoes a densification step which comprises two sub-steps, namely an annealing and pre-sintering sub-step E5 and a densification sub-step E6.

The annealing and pre-sintering sub-step makes it possible to strengthen the connections between the particles of the ceramic powder and therefore to reinforce the strength of the raw part 20.

In this example, the annealing preferably takes place under vacuum for several hours, at a predetermined temperature. The duration of the annealing depends in particular on the temperature applied. An intermediate part 30 formed of a ceramic matrix enclosing the preform 10’ is then obtained.

In another example, the annealing could be done under neutral gas, for example argon.

During the densification sub-step E6, the part 30 is held in suspension or placed above a crucible containing liquid silicon, acting as a liquid densification material.

In suspension, the part 30 has a generally lower part immersed in the liquid of the crucible. During this densification step E6, the part 30 is lowered until its lower end comes into contact with the liquid silicon, or the crucible is raised until this contact is obtained. This contact allows the silicon to penetrate by capillarity within the part 30 in order to fill the residual porosities of the part 30 and thus densify it.

When placed, the part 30 is located on a drain which rests on the bottom of the crucible and is immersed in the liquid of the crucible. This drain can be a porous part configured to convey the liquid by capillarity to the part. This porous part is preferably made of carbon.

This densification sub-step E6 is carried out at a temperature higher than a melting temperature of the mixture, which is preferably greater than or equal to 1400°C, and is for example 1450°C. The temperature during sub-step E6 is higher than the temperature during sub-step E5.

Once the infiltration is complete, a cooling step E7 begins. During this cooling step, the temperature of the cavity in which the part is located is reduced according to a cooling ramp which is between 800°C and 20°C/h, and which is for example 600°C/h until reaching a cavity temperature of for example between 1100°C and 1250°C.

After cooling and solidification of the silicon, a raw part 40 is obtained which no longer has, or practically no longer has, any porosities.

There illustrates an oven 50 according to the invention for implementing the densification step E6.

This 50 oven includes:

- a first chamber 52 comprising a cavity 54 configured to receive the part 30 as well as the crucible 56 comprising the densification material,

- a second chamber 58 in which the first chamber 52 is located as well as heating elements 60 configured to heat the densification material to the aforementioned temperature (which is higher than the melting temperature (1410-1420°C for silicon) of the densification material),

- at least one device 62 for creating a vacuum in the cavity 54,

- at least one device 64 for measuring the temperature in the second chamber 58, and

- at least one unit 66 for controlling the oven 50, and in particular its heating elements 60 and devices 62, 64.

The cavity 54 of the first chamber 52 is advantageously sealed and the vacuum device 62 makes it possible to achieve a vacuum in this cavity 54 of the order of 10 ^-6 bars for example, although this example is not limiting. The vacuum device 62 comprises one or more pumps for example.

Room 30 is suspended in the cavity 54 and arranged above the crucible 56 as mentioned above, or placed on a drain as mentioned above.

The first chamber 52 may have a general parallelepiped shape and for example a cubic shape.

The furnace 50 is generally configured to move the part 30 toward the crucible 56, or the crucible 56 toward the part 30, to impregnate the part 30 with the liquid silicon, as also discussed in the foregoing.

In the example shown, it is the crucible 56 which is moved upwards and towards the part 30 by means of a vertically movable plate 68 which is housed in the first chamber 52 and which is connected to an actuator 70 connected to the unit 66. The crucible 56 rests on the plate 68.

The second chamber 58 is preferably an insulation or insulating chamber, that is, it preferably comprises thermally insulating materials.

The second chamber 58 may have a general parallelepiped shape and for example a cubic shape.

The heating elements 60 are, for example, in the form of bars, which are arranged on each side of the first chamber 52 and which are preferably resistive bars supplied with electricity by the unit 66.

The or each temperature measuring device 64 is for example a thermocouple also connected to the unit 66. The or each device 64 measures the temperature in the second chamber 58n, which makes it possible to estimate by calculation the temperature in the cavity 54.

The oven 50 may further comprise a third chamber 72 in which the second chamber 58 is located.

The third chamber 72 may have a generally cylindrical shape.

This third chamber 72 has for example a diameter greater than or equal to 1m, or even 2m, and a height greater than or equal to 1m, or even 2m.

In the example shown, it can be seen that the chambers 52, 58, 72 are spaced apart from each other, and are thus separated from each other by air gaps.

The first chamber 52 of the oven 50 according to the invention is equipped with at least one effluent filter 80, that is to say a filter 80 intended to be passed through by the effluents 82 generated during the densification of the part 30.

In the example shown, the filter 80 is located at the top of the first chamber 52, as in the example shown. It is for example located at the level of a gas evacuation chimney.

The filter 80 may comprise several superimposed layers 80a, 80b, …, 80i, as is better seen in the . These layers 80a, 80b, …, 80i are different or may alternatively be identical. Each of the layers may thus have a particular function, and may for example target the decomposition or retention of a particular compound or particle.

The geometric parameters (porosity, specific surface area, pore diameter, etc.) of the filter 80 and the layers 80a, 80b, …, 80i are preferably chosen to promote exchanges between the effluents and the filter while limiting pressure losses.

The filter 80 or each of the layers 80a, 80b, …, 80i is made of a material chosen from carbon and alumina.

For carbon layers, these may be, for example, Kreca Flet® C and G layers marketed by Kureha, or Calcarb® Graphite Soft Felt layers marketed by Mersen. These layers were originally marketed for their thermal insulation function.

The carbon is intended to react with silicon monoxide to generate carbon monoxide and silicon carbide instead, according to the following formula.

2C + SIO -> SiC + CO

Alumina is intended to react with silicon vapors to form silicon dioxide and aluminum according to the following formula.

2Al ₂ O3 + 3Si -> 3SiO ₂ + 4 Al

The filter 80 can be covered with a grid 84 or be carried by a cassette 86, preferably made of molybdenum so as not to deteriorate on contact with the effluents 82.

The filter 80 or each of the layers 80a, 80b, …, 80i may have a general parallelepiped shape whose length is between 20 and 80cm, and whose width is between 20 and 80cm.

The filter 80 or each of the layers 80a, 80b, …, 80i may have a thickness E of between 5 and 30 mm. The thicknesses E of the layers may be identical or different.

The present invention is particularly advantageous for the manufacture of a CMC part of the SiC/SiC type although other types of CMC can be obtained.

The present invention further relates to a method of densifying a CMC part 30, also called a siliciding method, using the oven 50. This method essentially comprises the aforementioned steps consisting of:

a) suspending or placing the part 30 above the crucible 56 in the first chamber 52, the crucible 56 preferably comprising a silicon-based mixture as densification material, and

b) heating this mixture to a temperature above a melting temperature of said mixture. This step b) may include a preliminary sub-step of annealing the part, at a temperature below the melting temperature of the mixture.

Claims (12)

Oven (50) for the densification of a part (30) made of ceramic matrix composite material, this oven (50) comprising:
- a first chamber (52) comprising a cavity (54) configured to receive the part (30) as well as a crucible (56) comprising a ceramic material for densifying this part,
- a second chamber (58) in which the first chamber (52) is located as well as heating elements (60) configured to heat the densification material above a melting temperature of the ceramic densification material,
- at least one device (62) for placing said cavity (54) under vacuum,
- at least one device (64) for measuring the temperature in said second chamber (58), and
- at least one unit (66) for controlling the oven, and in particular its heating elements (60) and devices (62, 64),
characterized in that said first chamber (52) is equipped with a filter (82) for effluents (84). Oven (50) according to claim 1, in which the effluent filter (80) comprises several superimposed layers (80a, 80b, …, 80i). Oven (50) according to claim 2, wherein the layers (80a, 80b, …, 80i) are different. Oven (50) according to claim 2, wherein the layers (80a, 80b, …, 80i) are identical. Oven (50) according to one of the preceding claims, in which the filter (80) or each of the layers (80a, 80b, …, 80i) is made of a material chosen from carbon and alumina. Oven (50) according to one of the preceding claims, in which the filter (80) is covered with a grid (84) or is carried by a cassette (86), preferably made of molybdenum. Oven (50) according to one of the preceding claims, in which the filter (80) or each of the layers (80a, 80b, …, 80i) has a generally parallelepiped shape whose length is between 20 and 80cm, and whose width is between 20 and 80cm. Oven (50) according to one of the preceding claims, in which the filter (80) or each of the layers (80a, 80b, …, 80i) has a thickness of between 5 and 30 mm. Oven (50) according to one of the preceding claims, in which the filter (80) is located at the top of the first chamber (82). Oven (50) according to one of the preceding claims, wherein it further comprises a vertically movable tray (68) which is housed in the first chamber (52) and which is connected to an actuator (70) connected to said at least one unit (66). Method for densifying a part (30) made of ceramic matrix composite material, by means of an oven (50) according to one of the preceding claims, comprising the steps of:
a) suspending or placing a part (30) above a crucible (56) in the first chamber (52), the part (30) comprising a reinforcement embedded in a ceramic matrix, the reinforcement being obtained by weaving silicon carbide fibers, and the crucible (56) comprising a silicon-based mixture as densification material, and
b) heating said mixture to a temperature above a melting temperature of said mixture. Method according to the preceding claim, in which the part (30) is an aeronautical part.