WO2019175501A1

WO2019175501A1 - Composite with oxide/oxide ceramic matrix

Info

Publication number: WO2019175501A1
Application number: PCT/FR2019/050538
Authority: WO
Inventors: Pascal Diss; Florent Deliane; Natacha DUEE
Original assignee: Safran Ceramics; Irt Antoine De Saint Exupery
Priority date: 2018-03-13
Filing date: 2019-03-13
Publication date: 2019-09-19
Also published as: FR3078965B1; FR3078965A1

Abstract

The invention relates to a suspension for producing the matrix of a composite material comprising an oxide/oxide ceramic matrix, said suspension comprising, or advantageously consisting of, in weight % in relation to the total weight of the suspension: between 30% and 70%, advantageously between 40% and 60%, of a solid metal oxide filler, between 20% and 80%, advantageously between 30% and 40%, of an aqueous solvent, between 2% and 10%, advantageously between 2 and 4%, of a poloxamer having an average molar mass of between 1000 and 30000 g. mol^-1, and between 0.1% and 1.5%, advantageously between 1% and 1.5%, of a dispersant. The invention also relates to a method for producing a composite material comprising an oxide/oxide ceramic matrix using said suspension, to the composite material produced in this way, and to the use of said suspension.

Description

OXIDE / OXIDE CERAMIC MATRIX COMPOSITE

The present invention relates to the field of liquid-crystalline oxide / oxide ceramic matrix composites (CMCs).

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CMC oxide / oxide are of increasing interest for aeronautical applications. Indeed, these materials are among the serious candidates to replace certain metal parts with CMC. For reasons of lightness and durability, this last family of materials allows a significant increase in yields as well as a significant reduction of atmospheric emissions.

At the present time it is possible to propose liquid-formed CMC oxide / oxide whose mechanical properties are close to the other CMCs produced by chemical vapor infiltration.

Patent applications EP1281697, EP 1880984, GB2347113, US 4983422, US 5569422 and US 8313598 thus describe processes for the preparation of liquid-formed oxide / oxide CMCs.

Several production processes are described (filament winding, placement of strips, pre-preg, stack coating, injection, infusion ...) with their respective advantages and disadvantages with respect to the geometry of the parts, the number of steps to follow, final characteristics, etc ...

The 4 steps below are common to all the processes described in the literature:

5 - preparation of a suspension;

- introduction of the suspension into a fiber network,

- molding of the system;

- final sintering. The suspension used to impregnate the fibrous network is generally composed of:

oxide charges which will constitute the matrix after sintering,

optionally sol-gel type oxide precursors or pre¬ resin

Ceramic;

a solvent;

- a dispersant;

an organic agent intended to obtain a level of "stickiness" (stickiness) sufficient to ensure the holding of the layers during stacking, but also to guarantee the conservation of the geometry imposed on the blank during molding ( this role can also be filled by the oxide precursors).

In order to obtain, after final sintering, mechanical properties suitable for the intended applications, it is necessary to reduce, as far as possible, the final porosity of the material, and this for a single impregnation step.

For this reason, the charge rate of the suspensions formulated is high, generally close to 40% by volume. This order of magnitude is close to the critical load rate beyond which the flow of the suspension is no longer possible. In fact, beyond this critical rate, the impregnated system no longer possesses the rheology that is indispensable for a correct unwinding of the compacting step, carried out before or during molding, and intended to fix the final thickness of the piece. .

This situation results on the one hand, by the obligation to limit the quantity in fugitive elements that can generate porosity and species5 "pollutants" and on the other hand, by a permanent fight against the speed of evaporation of the solvent of so as to be in the presence of a tack time long enough to be able to drape, then mold large pieces. Indeed, the rapid drying up of the system leads to a rapid evolution of the rheology of the system with loss of:

- deformability and level of tackiness required for draping in the case of complex geometries;

5 - rheology necessary for smooth compaction and molding.

This limit generally imposes a waiting time between the stacking of the layers and the molding of at most 30 to 40 minutes and is at the origin of a high scrap rate which is not economically interesting. The inventors have surprisingly found that the use in the suspension intended to impregnate the fibers of a poloxamer whose mass average molecular weight, in particular measured by gel permeation chromatography (GPC) is between 1000 and 30000 g. mol ¹ , in particular as described in application FR 2 862 652.5 allowed, thanks to its thermogel property, to improve the rheological properties of the suspension, even with a high charge rate.

Indeed, the physical properties of this suspension evolve reversibly with temperature (the viscosity increases when the temperature increases and decreases when the temperature drops), so as to obtain a rheology adaptable to each of the steps:

- Implementation of the suspension on a fiber network (such as a woven);

- Preserving the impregnated fiber network (also called prepreg)

5 - draping or stacking

- Compaction and / or molding.

Thus, thanks to the presence of this thermogel, the impregnated layers can find the level of tackiness necessary for the realization of the draping or the stacking, then the compaction by a simple action of temperature. It is thus possible to wait several days, advantageously at least 16 days between the manufacture of the prepreg and the stages of draping or stacking and compacting and / or molding, without loss of tack and obtaining a final material (compacted and /or

Molded) having characteristics of interest in terms of porosity and fiber volume ratio.

It is certainly true that the use of starch is already described for its thermoreversibility properties to improve the rheology of a suspension that contains ceramics such as alumina or mullite (articles by Talou et al, Journal of the European Ceramic Society 31 (2011), pages 1563-1571 and Ceramics International 36 (2010) pages 1017-1026). However, starch and poloxamer are two completely different compounds. The present invention thus relates to a suspension intended for the preparation of the matrix of a ceramic / oxide ceramic matrix composite material, said suspension comprising, advantageously consisting of, in% by weight relative to the total weight of the suspension:

30% to 70%, advantageously 40 to 60%, of a solid metal oxide charge,

20% to 80%, advantageously 30 to 40%, of an aqueous solvent,

2% to 10%, advantageously 2 to 4%, of a poloxamer of which the weight average molar mass, in particular measured by gel permeation chromatography (GPC) is between 1000 and 30,000 g. mol ^'1

0.1% to 1.5%, preferably 1 to 1.5%, of a dispersant.

Oxide / oxide ceramic matrix (CMC oxide / oxide) composite materials or ceramic matrix based composite materials of oxide, are CMCs whose matrix and reinforcement are based on metal oxide.

The suspension according to the present invention therefore comprises 30 to 70%, more

Advantageously 40 to 60%, in particular 50 to 60%, by weight relative to the total weight of the suspension, of a solid metal oxide filler.

In an advantageous embodiment, the solid metal oxide filler is chosen from alumina, silica, aluminosilicates such as mullite, aluminophosphates, zirconia and their mixtures (in particular alumina-silica, mullite- silica and mullite-alumina), advantageously it is alumina.

In particular, the solid metal oxide filler is in the form of particles (in particular powder), advantageously having a number average diameter measured by laser particle size (d50 which corresponds to the size for which 50% of the population - in number of particles - has a size smaller than the value d50) of between 0.1 μm and 1 μm. It may be so the SM8 alumina powder sold by Baikowski (characteristics: d20 = 0.1 .mu.m, d50 = 0.2 .mu.m, d90 = 0.3 .mu.m, 0 BET surface area = 10 m ² / g bulk density 0.8 g / cm ³ ).

The suspension according to the present invention further comprises 20% to 80%, advantageously 25 to 60%, more preferably 30 to 50%, in particular 30 to 40%, by weight based on the total weight of the suspension, 5% by weight. aqueous solvent.

In a particular embodiment, the aqueous solvent is water, in particular demineralized water. The suspension according to the present invention further comprises 2% to 10%, advantageously 2 to 6%, more advantageously 2 to 4%, by weight relative to the total weight of the suspension, of a poloxamer whose mass average molar mass. , in particular measured by gel permeation chromatography (GPC), is between 1000 and 30000 g. mol ¹ .

The poloxamers are polyethyleneglycol-polypropylene glycol-polyethylene glycol block terpolymers.

In an advantageous embodiment, the poloxamer according to the invention is the product of the reaction between a poloxamer having an alcohol function and a diisocyanate, in particular an aromatic diisocyanate such as toluene diisocyanate. Advantageously, the poloxamer according to the invention is obtained according to the process described in application FR 2 862 652.

Thus, the poloxamer having an alcohol function, advantageously several alcohol functional groups, is reacted with an excess of diisocyanate (in particular in a stoichiometric ratio of the NCO functions of the diisocyanate / OH functions of the poloxamer between 2 and 5), in a solvent medium. miscible with water, preferably in the presence of acetone, in particular at room temperature and with stirring.

The resulting intermediate product (which has the form of a linear polymer) which comprises NCO isocyanate termini is then mixed with water. The starting solvent (acetone for example) is then evaporated for example at 40 ° C at atmospheric pressure.

The poloxamer according to the invention therefore has a solids content of less than 10%, in particular between 5 and 6% by weight, and is in the form of a gel.5 The poloxamer according to the invention is a thermogel, ie that is to say that it can form, in aqueous medium, a so-called "thermoreversible" gel, that is to say whose viscosity increases substantially when the temperature increases and decreases when the temperature decreases. It was not obvious to use the poloxamer described in application FR 2 862 652 in a suspension intended to impregnate the fibers with an oxide / oxide ceramic matrix composite material and thus intended for the preparation of the matrix of such a matrix. composite material because such

Impregnation method is not described or suggested in this document. It therefore belongs to a different domain from that according to the present invention and the person skilled in the art could not consider the benefits obtained by this use in the context of the process according to the present invention.

The process described therein has nothing to do with the pre-preg route. It is a device for infiltrating a charged suspension, which is filtered in situ. The problem of drying strata does not exist in this document. On the other hand, the method described in this document is not adapted to the production of very large fine parts: the infiltration, by a charged suspension, of large and very fine blanks presents difficulties: there is huge losses of loads to counter.

The suspension according to the present invention finally comprises 0.1% to 1.5%, advantageously 0.5 to 1.5%, more preferably 1 to 1.5%, by weight with respect to the total weight of the suspension, a dispersant.

The dispersant is a conventional dispersant in the field, such as for example an acrylic dispersant, advantageously sold under the name Duramax D3005. In an advantageous embodiment, the suspension according to the invention does not comprise a fugitive binder or not. Indeed, the poloxamer according to the invention also has the function of binder. The suspension according to the present invention may be prepared by methods that are well known to those skilled in the art, such as by mixing the various ingredients with stirring at room temperature, generally by first adding the solvent and then poloxamer, followed by the dispersant

5 and finally by the charges.

The suspension according to the present invention therefore has a variable viscosity that can be adjusted as a function of temperature. Its viscosity is thus higher at high temperatures than at low temperatures.

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The present invention furthermore relates to a process for the preparation of an oxide / oxide ceramic matrix composite material comprising the following successive stages:

a- preparation of the suspension according to the present invention;

B) introducing the suspension into a fiber network, advantageously by impregnation;

c- stacking of the strata obtained;

d- molding the system;

e- final sintering,

Recovering the oxide / oxide ceramic matrix composite material.

The fibers of step b) are metal oxide fibers such as, for example, fibers selected from alumina, silica, aluminosilicates such as mullite, aluminophosphates, zirconia and mixtures thereof (in particular blends). alumina-silica, mullite-silica and mullite-alumina), advantageously it is alumina such as that sold under the trade name Nextel 610. This fiber is composed of more than 99% alumina. Advantageously, the fibers are removed before being used. The fiber network or fibrous reinforcement of step b) according to the invention may be in the form of a woven, such as a fabric.

In an advantageous embodiment, step b) can be implemented

5 is carried out by the usual methods well known to those skilled in the art, such as, for example, by injection, infusion, coating, impregnation. In particular it is an impregnation, for example using a brush, an impregnator, a doctor-blade, or any other manual or automatic means.

In particular step b) is an impregnation and can be carried out at room temperature (20 ° C.) thanks to the presence of the poloxamer according to the invention in the suspension according to the invention which makes it possible to make the composition fairly fluid. for this step.

This step b) makes it possible to obtain different layers of impregnated fiber network5 or impregnated fabric strips. The product obtained can be a prepreg.

The method according to the present invention can comprise between steps b) and c) an intermediate step b1) of storing the fiber network 0 containing the suspension obtained in step b), in particular the impregnated fiber network. Indeed, it is possible to store it at a temperature of between 10 ° C. and 20 ° C., advantageously 10 ° C., for several days, advantageously at least one week, or even several weeks (for example 16 days) and even several months. before the implementation of step c), without there being a loss of tack, thanks to the presence of the poloxamer according to the invention in the suspension according to the invention. Indeed, the rheology of the system is no longer dependent on the evaporation of the solvent over time but depends solely on the temperature. Thus the fiber network containing the suspension obtained in step b), in particularly the impregnated fiber network, remains stackable, drapeable, compactable and moldable throughout this storage period.

The method according to the present invention can comprise between the steps

5b) and c), before or after step b1), an intermediate step b2) of cutting the fiber network containing the suspension obtained in step b), in particular the impregnated fiber network, to the desired dimensions.

Step c) of the process according to the present invention requires a greater tack of the suspension according to the invention, so that each stratum or strip of the fiber network, in particular of the fabric, sticks to the next and is therefore maintained between them. . The stacking can be done by any method well known to those skilled in the art such as draping, particularly in the case of making parts of complex geometries. Advantageously, step c) is carried out at a temperature of between 25 ° C and 40 ° C.

The method according to the present invention may comprise a step of compacting before or simultaneously with the molding step d). The compaction step is intended to fix the final thickness of the workpiece. It can be implemented by any method well known to those skilled in the art. In particular it is carried out at a temperature between 10 ° C and 20 ° C, in particular between 10 ° C and 17 ° C, so that the rheology of the suspension is adapted to this step. This thus makes it possible to increase the fiber volume ratio. This step can be performed under vacuum.

Step d) molding can be implemented by any method well known to those skilled in the art. In particular, it is implemented at a temperature between 10 ° C and 20 ° C, in particular between 10 ° C and 17 ° C. Thanks to the presence of the poloxamer according to the invention in the suspension according to the invention, it is therefore possible to mold large pieces, without this posing problems of rheology necessary for this step. This step can be performed under vacuum. The molding step imposes the desired geometry on the composite according to the invention.

The method according to the present invention may comprise between steps d) and e), an intermediate step d1) debinding. This step is generally preceded by the demolding of the part obtained in step d).

This step can be implemented by any method well known to those skilled in the art. It can be implemented at a temperature of 1100 ° C. The process according to the present invention further comprises a step s) of sintering, which can be carried out by any method well known to those skilled in the art, on the molded part obtained in step d) (generally after demolding) or the debinding piece obtained in step dl). It can be implemented at a temperature of 1100 ° C.

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Finally, the method according to the present invention comprises a step f) of recovering the oxide / oxide ceramic matrix composite material. It can be a large piece or complex geometry. Thus, in an advantageous embodiment of the process according to the invention, step b) is an impregnation carried out at room temperature, step c) is carried out at a temperature of between 25 ° C. and 40 ° C and step d) is carried out at a temperature between 10 ° C and 20 ° C. The present invention further relates to the metal oxide fiber network impregnated with the suspension according to the present invention. It is thus advantageously the intermediate product obtained in step b) of the process according to the present invention. The fiber network according to the invention may be in the form of a woven, such as a fabric. It can thus be a prepreg.

This network of fibers or prepreg can be stored at a temperature between 10 ° C and 20 ° C, preferably 10 ° C, for several days, preferably at least a week or even weeks (for example 16 days) and even several months, without loss of tack, thanks to the presence of the poloxamer according to the invention in the suspension according to the invention. Indeed, the rheology of the system is no longer dependent on the evaporation of the solvent over time but depends solely on the temperature. Thus the impregnated fiber network according to the invention remains stackable, drapeable, compactable and / or moldable throughout this storage period. It therefore has a significantly improved life in comparison with the state of the art. The present invention further relates to an oxide / oxide ceramic matrix composite material obtainable by the process according to the present invention.

Advantageously, the volume ratio (ratio between the volume occupied by the fibers and the total volume occupied by the composite material: it is obtained by dividing the mass of the texture by the density of the fibers and then dividing the result obtained by the volume of the material composite) of fibers of the oxide / oxide ceramic matrix composite material according to the invention is between 35% and 51%, in particular it is 48%. In particular its porosity, measured by buoyancy, is between 25% and 34%, more particularly it is 28%.

The composite according to the invention may have the shape of a large-sized part and / or complex geometry.

It can be used in the field of aeronautics.

Finally, the present invention relates to the use of the suspension according to the present invention for the preparation of the matrix of an oxide / oxide ceramic matrix composite material or for the preparation of a network of impregnated metal oxide fibers such as a prepreg.

The invention will be better understood on reading the example which follows which is given as an indication. EXAMPLE 1 Preparation of the Composite According to the Invention Pre-Prea:

Preparation of a suspension consisting of:

- 58.8% by weight of alumina powder SM8 marketed by Baikowski (characteristics: d20 = 0.1 .mu.m, d50 = 0.2 .mu.m, d90 = 0 0.3 pm, BET surface area = 10 m ² / g , bulk density 0.8 g / cm ³ )

37% by weight of demineralized water,

3% by weight of poloxamer prepared according to the process described in application FR 2 862 652,

5 - 1.2% by weight of Duramax D3005 acrylic dispersant.

This suspension is applied in excess to Nextel 610 tissue, either with a brush on individual layers, previously desensitized, or using an impregnator on a strip of desensimée fabric. The impregnated fabric was then stored at a temperature of about 10 ° C, and implemented 16 days later, to develop a plate, by following the following steps:

- Stacking of impregnated and cut layers at a

Temperature between 25 ° C and 40 ° C, which corresponds to the range at which the viscosity of the suspension is maximum, in order to be in the presence of the level of tack required to maintain the layers against each other,

- Tarpaulin covering for molding purposes,

0 - Draw of vacuum at 0.01 MPa, placing the blank at a temperature between 10 ° C and 17 ° C, this temperature range corresponding to the range in which the viscosity of the suspension is minimal, that is to say to say in the domain where the flow compaction of the stack, with a view to increasing the fiber volume ratio,

- Exposure of the blank undergoing vacuum draw at 95 ° C for 1 hour, per stay in the oven to remove the solvent which evaporates gradually during heating, and thus block the rheology of the system and freeze the blank to the final target geometry, 0 - Demoulding then debinding and sintering at 1100 ° C.

An oxide / oxide ceramic matrix composite plate according to the invention having a fiber volume ratio of 48% and a porosity of 28% is obtained.

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Claims

1. Suspension intended for the preparation of the matrix of an oxide / oxide ceramic matrix composite material, said suspension

Comprising, advantageously consisting of, in% by weight relative to the total weight of the suspension:

30% to 70%, advantageously 40 to 60%, of a solid metal oxide charge,

20% to 80%, advantageously 30 to 40%, of an aqueous solvent, 0 2% to 10%, advantageously 2 to 4%, of a poloxamer with a weight average molecular weight of between 1000 and 30000 g . mol ^'1

0.1% to 1.5%, preferably 1 to 1.5%, of a dispersant. 5

2. Suspension according to claim 1, characterized in that the solid metal oxide filler is selected from alumina, silica, aluminosilicates such as mullite, aluminophosphates and mixtures thereof, advantageously it is alumina . 0

3. Suspension according to any one of claims 1 or 2, characterized in that the aqueous solvent is water.

4. Suspension according to any one of claims 1 to 3, characterized in that the poloxamer is the product of the reaction between a poloxamer having an alcohol function and a diisocyanate.

Process for the preparation of an oxide / oxide ceramic matrix composite material comprising the following successive steps: a- preparation of the suspension according to any one of claims 1 to 4;

b- introducing the suspension into a fiber network, advantageously by impregnation;

5 c- stacking of the strata obtained

d- molding the system;

e- final sintering,

recovering the oxide / oxide ceramic matrix composite material. 0

6. Method according to claim 5, characterized in that step b) is an impregnation carried out at ambient temperature, in that step c) is carried out at a temperature between 25 ° C and 40 ° C. ° C and that step d) is carried out at a temperature between 10 ° C and 20 ° C.

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7. network of metal oxide fibers impregnated with the suspension according to any one of claims 1 to 4.

8. The impregnated fiber network according to claim 7, characterized in that it is a prepreg.

An oxide / oxide ceramic matrix composite material obtainable by the process of any one of claims 5 or 6.

5

10. oxide / oxide ceramic matrix composite material according to claim 9 characterized in that its fiber volume ratio is between 35% and 51% and its porosity, measured by buoyancy, between 25% and 34%

11. Use of the suspension according to any one of claims 1 to 4 for the preparation of the matrix of an oxide / oxide ceramic matrix composite material or for the preparation of a network of impregnated metal oxide fibers or a prepreg.