FR3052164A1 - MANUFACTURING A CMC PIECE WITH RETOUCHING INDICATIONS - Google Patents

Abstract

The invention relates to a manufacturing method (S) of a piece of ceramic matrix or at least partially ceramic composite material comprising the steps of: - providing a fibrous preform (S1), - filling (S2) the fibrous preform with a ceramic matrix or at least partially ceramic so as to obtain an intermediate piece of composite material, - demolding (S3) the intermediate piece, - retouching the intermediate piece by applying a slip comprising at least one ceramic filler on all or part of the surface of the intermediate piece, and - apply a heat treatment (S5) to the intermediate piece to obtain a final piece.

Description

FIELD OF THE INVENTION The invention relates to the production of ceramic matrix or at least partly ceramic composite material parts, hereinafter referred to as CMC material.

A field of application of the invention is the production of parts intended to be exposed in service at high temperatures in an oxidizing atmosphere, particularly in the aeronautical and space fields, in particular parts of hot parts of aeronautical turbomachines, being noted that the invention can be applied in other fields, for example the field of industrial gas turbines.

BACKGROUND

Ceramic matrix or at least partially ceramic composite materials have good thermostructural properties, i.e., high mechanical properties that make them suitable for forming structural parts, and the ability to maintain these properties at high temperatures. The use of these materials instead of metal materials for parts exposed in service at high temperatures has been recommended, especially since CMC materials have a density significantly lower than the metal materials to which they substitute.

A first well-known method for manufacturing parts made of CMC material comprises the production of a fibrous preform from a woven fibrous texture, the preform being consolidated by injection of a ceramic matrix into a cavity formed of two half-shells .

A second method, well known as the poly-flex process, consists in shaping a fiber preform on a tool having a surface having the desired profile of the final product. The preform is then covered by a deformable impermeable membrane and the slip is injected between the membrane and the preform. On the other side of the membrane, isostatic pressure is exerted on the membrane by a fluid which causes a deformation of the face of the membrane located opposite the preform. This fluid forces the matrix between the fibers. Such a method is for example described in US Pat. No. 7,866,969.

According to a third known method, the CMC material can be obtained by infiltration under vacuum (or aspiration of submicron powder, APS). In this method, a fibrous reinforcement is placed on a filter, a ceramic suspension in aqueous media is poured on the upper surface of the reinforcement, a pressure is applied on the free surface of the suspension to make it penetrate the reinforcement and a vacuum is made under the underside of the filter to remove water in liquid form.

However, whatever its manufacturing process, the demolding step of the piece of CMC material turns out to be a critical operation. Indeed, the part is not in its final stage at the time of demolding, a high temperature heat treatment still to be applied thereafter to give the CMC material its final characteristics. As a result, agglomerates consisting of several grains (which will be consolidated only during the future heat treatment) can be detached from the surface of the CMC part and form indications.

It has therefore been proposed to apply a release agent and / or a fabric comprising polytetrafluoroethylene (PTFE - marketed under the trademark Teflon® in particular) in order to reduce the risk of indications appearing. However, indications may still appear punctually, especially in the parts of the CMC material part undergoing strong stresses to demoulding.

SUMMARY OF THE INVENTION

An object of the invention is therefore to provide a method of manufacturing a piece of ceramic matrix or at least partially ceramic composite material which eliminates the indications that may appear on the surface of the finished part and thus reduces the risk of scrapping the part.

For this, the invention proposes a method of manufacturing a piece of ceramic matrix or at least partially ceramic composite material comprising the following steps: - providing a fiber preform, - filling the fiber preform with a ceramic matrix or at least partially ceramic so as to obtain an intermediate piece of composite material, - unmolding the intermediate piece, and - apply heat treatment to the intermediate piece to obtain a final piece.

The manufacturing method further comprises a step of retouching all or part of a surface of the intermediate part, said retouching step comprising an application of a slip comprising at least one ceramic filler on all or part of the surface of the intermediate piece.

Some preferred but non-limiting characteristics of the manufacturing process are as follows, taken individually or in combination: the step of heat treatment of the intermediate part is carried out after the retouching step, the slip is applied by dipping all or part of the surface of the intermediate piece in a slip bath, - the method further comprises a step of homogenizing the slip deposited on the surface of the intermediate part which has been quenched by vibrations, - a viscosity of the slip bath during the retouching step is between 100 mPa.s and 500 mPa.s, - the slip is applied using a gun and / or a brush, - a viscosity of the slip at the same time. retouching step is less than or equal to 100 mPa.s, - the method further comprises a step of drying in an oven of the intermediate part prior to the treatment step thermal, - the method further comprises a step of rectification of all or part of the intermediate piece before the heat treatment step, and / or - a volume ratio of the ceramic charge of the slip is between 5% and 50% .

BRIEF DESCRIPTION OF THE DRAWINGS Other features, objects and advantages of the present invention will appear better on reading the detailed description which follows, and with reference to the single appended figure given by way of non-limiting examples and on which has been shown a flowchart of a method of manufacturing a part according to an embodiment of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

In order to produce a piece of ceramic matrix or at least partially ceramic (CMC matrix) composite material, the method S comprises a first step in which the CMC matrix is deposited by a liquid process according to a conventional method S, such as the RTM process, poly-flex process, APS process or any other equivalent.

For this, conventionally, a fibrous preform is placed S1 in a mold or on a tool then filled S2 with the ceramic matrix or at least partially ceramic so as to obtain an intermediate piece. If appropriate, a release agent is coated on the walls of the mold or tool and / or a fabric comprising polytetrafluoroethylene is placed on the preform to reduce the risk of forming indications on the intermediate part.

This intermediate part is then demolded S3 and then undergoes a heat treatment S5 (sintering type) at a temperature greater than or equal to 800 ° C to give the piece its final characteristics.

The filling, demolding and heat treatment steps being conventional, they will not be further detailed here.

In what follows, will be designated by "intermediate piece" CMC material part after step S2 filling the fiber preform (and solvent evacuation) with the ceramic matrix or at least partially ceramic but before application of heat treatment S5 , as opposed to the "final part" which corresponds to the CMC part after S5 heat treatment.

When the intermediate piece has indications, that is to say that one or more agglomerates of ceramic or partial ceramic matrix are detached from the surface of the intermediate piece, the method S further comprises a step S4 retouching the intermediate piece during which a slurry comprising a ceramic filler is applied on all or part of the surface of the intermediate piece. In other words, either the slip is applied over the entire surface of the intermediate piece, or the slip is applied only in the areas of the intermediate part in which the indications are formed and which must be retouched.

A slip comprising a ceramic filler is a ceramic powder present in a solution, typically an aqueous or organic solution. In what follows, the invention will be described in the case of an aqueous solution. This is not, however, limiting. The powder may in particular comprise one or more of the following materials: carbide, for example silicon carbide SiC, and / or boride, for example titanium diboride TiB 2, and / or nitride, for example S3Ni4 silicon nitride, and / or an oxide of alumina or zirconia.

The volume ratio of the ceramic powder (or filler) in the slip depends on the ceramic powder used in said slip and may be between 5% and 50%.

The ceramic charge of the slip may comprise the same material as the ceramic matrix of the intermediate piece, or alternatively comprise a different material.

In one embodiment, the powder may have a sub-micron particle size to facilitate step S2 of filling.

This step S4 retouching is carried out before step S5 heat treatment. The S4 application of the slip may be carried out by dipping all or part of the surface of the intermediate piece in a slip bath comprising ceramic fillers. For this purpose, either an area to be retouched or the complete intermediate part is soaked in the slip bath.

In order to ensure a good recovery of the area to be retouched or the intermediate part by dipping, the viscosity of the slip bath is between 100 mPa.s and 500 mPa.s. The measurement of the viscosity is carried out here with a Brookfield viscometer at room temperature (between 20 ° C. and 23 ° C.) in the solvent of the slip, at a rotation speed of 100 rpm in a tank having a tank volume of 150. mL. The thickness of the ceramic charge deposit applied to the immersed surface of the intermediate piece may, optionally, then be homogenized. For this, the intermediate piece may for example be vibrated, typically using a basket or vibrating table (e).

Alternatively, the application S4 of the slip can be performed using a gun or a brush on all or part of the intermediate piece.

For this, the viscosity of the slip is preferably less than or equal to 100 mPa.s.

In an alternative embodiment, the intermediate piece can be drained in order to avoid a local surplus of material in areas of the intermediate piece that does not require retouching. This dewatering step can in particular be preferred when the slip is applied over the entire surface of the intermediate piece.

After application of the slip, the intermediate part can be dried. For example, the drying step may be carried out in an oven, for example at a temperature of between 40 ° C. and 90 ° C. in order to prevent the water from being evaporated too rapidly (creation of bubbles) for a period of time. between 1h and 10h, depending on the size of the room and the temperature. To determine if the part is dry, a mass tracking can be carried out until mass stabilization.

If necessary, when the thickness of the ceramic charge deposit obtained by application of the slip is too great in relation to the dimensions required for the part, the intermediate part may be ground prior to the heat treatment step, for example by sanding to remove excess material. The grinding step may in particular be carried out after drying of the intermediate piece.

Claims (10)

1. A method of manufacturing (S) a piece of ceramic matrix or at least partially ceramic composite material comprising the following steps: - providing a fibrous preform (S1), - filling (S2) the fiber preform with a ceramic matrix or at least partially made of ceramic so as to obtain an intermediate piece of ceramic matrix or at least partially ceramic composite material, - demolding (S3) the intermediate piece, and - applying a heat treatment (S5) to the intermediate piece in order to to obtain a final part, the manufacturing method (S) being characterized in that it further comprises a retouching step (S4) of all or part of a surface of the intermediate part, said retouching step (S4) comprising applying a slip comprising at least one ceramic filler on all or part of the surface of the intermediate piece. 2. Manufacturing method (S) according to claim 1, wherein the heat treatment step (S5) of the intermediate piece is performed after the retouching step (S4). 3. Manufacturing process (S) according to one of claims 1 or 2, wherein the slip is applied (S4) by dipping all or part of the surface of the intermediate piece in a slip bath. 4. Manufacturing process (S) according to claim 3, further comprising a step of homogenizing the slip deposited on the surface of the intermediate piece which has been quenched by vibration. 5. Manufacturing process (S) according to one of claims 3 or 4, wherein a viscosity of the slip bath during the step (S4) retouching is between 100 mPa.s and 500 mPa.s. 6. Manufacturing process (S) according to one of claims 1 or 2, wherein the slip is applied (S4) with a gun and / or a brush. 7. Manufacturing process (S) according to claim 6, wherein a viscosity of the slip during the retouching step is less than or equal to 100 mPa.s. 8. Manufacturing process (S) according to one of claims 3 to 7, further comprising a step of drying in an oven of the intermediate piece prior to the heat treatment step (S5). 9. Manufacturing method (S) according to one of claims 1 to 8, further comprising a step of grinding all or part of the intermediate piece before the step (S5) of heat treatment. 10. Manufacturing process (S) according to one of claims 1 to 9, wherein a volume rate of the ceramic load of the slip is between 5% and 50%.