FR2758146A1 - Composite carbon@ fibre reinforced materials with mixed carbon@-metal matrix - Google Patents

Abstract

Composite material comprising a fibrous carbon reinforcement in a mixed matrix comprising a first carbon component and a second metallic component is claimed.

Description

COMPOSITE MATERIAL WITH CARBON REINFORCEMENT IN A MATRIX
MIXED CARBON-METAL AND PROCESS FOR PRODUCING THE SAME
DESCRIPTION
Technical area
The subject of the present invention is a composite material with a carbon reinforcement, which can be used in particular for space applications requiring significant dimensional stability.

 These applications include, in particular, space platforms for optical purposes, and more specifically optical instrument support structures for space observation satellites that require increasingly high performance.

The market for these future observation telescopes shows that the composite materials used will have even greater dimensional stability and have the following properties
a coefficient of thermal expansion very close to O (a <<10-7 C l);
- highest elastic modulus possible
- a significant thermal conductivity; and
an interlaminar shear stress value comparable to that measured on organic composite materials.

 Such composite materials can also be used in the field of electronics because of their excellent athermic conductivity.

State of the art
Among the materials likely to have these properties, there are known composite materials of carbon-carbon type, that is to say carbon fiber reinforcement in a carbon matrix. Such materials exhibit property isotropy, low density and, when made from high strength carbon (HR) fibers, a coefficient of thermal expansion close to 0, but their performance is limited by their low level. thermal conductivity, their low elastic modulus (E <60 Gpa) due to the use of high strength carbon fibers (HR) and their insufficient interlaminar shear stress.

Composite materials of this type are described for example in FR-A-2 668 479 and
FR-A-2,669,623.

More recently, other composite materials have been proposed comprising a carbon fiber reinforcement associated with a metal matrix, for example based on magnesium, as described in US Pat.
FR-A-2 695 409 and FR-A-2 698 582. Such materials have interesting mechanical properties, a high thermal conductivity, but their dimensional stability is insufficient because of the high coefficient of thermal expansion of the metal matrix. Moreover, they are sensitive to atmospheric corrosion.

Presentation of the invention
The present invention specifically relates to a composite material with carbon reinforcement which has improved properties compared to those of composite materials of the same type comprising a carbon matrix or a metal matrix.

 According to the invention, the composite material comprises a fibrous reinforcement of carbon fibers arranged in a mixed matrix comprising a first carbon component and a second metal component.

 According to the invention, the second metal component may be any type of metal, metal alloy or intermetallic compound. Aluminum, magnesium, copper and their alloys as well as intermetallic compounds of the Aine type, TiAl can be used in particular. Suitable alloys are aluminum magnesium alloys and magnesium zirconium alloys.

 Aluminum or an aluminum-magnesium alloy containing 10% by weight of magnesium can be used in particular.

 In the composite material of the invention, the addition of a metallic constituent to the carbon matrix makes it possible to improve the performance of the composite material, in particular as regards its coefficient of thermal expansion, its thermal conductivity and its mechanical properties.

 Indeed, the introduction of a metal component with a high coefficient of thermal expansion in a carbon-carbon composite material which has a negative coefficient of thermal expansion, makes it possible to increase this coefficient of thermal expansion to reach the required value, close to 0, for applications requiring high stability, especially in the space domain.

 Moreover, thanks to the addition of this metallic constituent, it is possible to use carbon fibers with high modulus and very high modulus because it is possible to compensate for the high negativity of their coefficient of thermal expansion by varying the content of metallic constituent of the matrix and thereby obtain a higher elastic modulus. Moreover, the addition of a metallic constituent of high conductivity makes it possible to increase the thermal conductivity of the material.

 Thus, by appropriately selecting the metal component used for the matrix and its content in the composite material, the properties of the material can be set to appropriate values.

 Generally, the metal component content of the composite material is 0.5 to 60% by volume relative to the volume of said material.

According to a preferred embodiment of the invention, the composite material comprises in volume
40 to 70% fibrous reinforcement,
10 to 45% of the first carbon component of the matrix, and
5 to 25% of the second metal component of the matrix.

 In particular, the content of the second metal component of the matrix is chosen so that the coefficient of thermal expansion of the composite is from 0 to 10-7 C-1.

 In the composite material of the invention, the fibrous reinforcement consists of carbon fibers which may be carbon fibers, or carbon fibers covered with a layer of silicon carbide or carbonitride.

 When carbon fibers are used, these may be high-strength (HR), high modulus (HM) or very high modulus (THM) carbon fibers made from various precursors. Preferably, carbon fibers manufactured either from polyacrylonitrile precursors (fibers ex-PAN) or from a precursor pitch of petroleum or coal (fibers ex-pitch) are used.

In the fiber reinforcement, the fibers can be unidirectional (UD), that is to say that all the fibers are oriented in the same direction, or quasi-unidirectional, some fibers being in the cross direction at 90 "to maintain the reinforcement Fiber-formed, bidirectional (2D), tridirectional (3D) and multidirectional reinforcements may also be used In the case of fibrous reinforcement made up of bidirectional fibers, these may consist of stacked unidirectional sheets arranged alternately In two directions, it is also possible to use fibrous reinforcements constituted by woven reinforcements such as that described in
FR-A-2 610 951 which is generally designated by the abbreviation 2.5 D, or that described in
FR-A-2612950 which is generally designated by the abbreviation 3D evo.

 The carbon component of the matrix is generally carbon obtained, either by liquid pyrolysis and graphitation of precursors consisting of thermosetting organic resins and / or by pitch, or by gaseous deposition of pyrocarbon and graphitation.

 The composite material of the invention can be easily manufactured from a preform of carbon-carbon type porous composite material comprising a fibrous reinforcement of carbon fibers arranged in a matrix of the first carbon component, having a porosity of 0.5 to 60%, by introducing the second metal component in the porosity of this preform to fill at least part of this second metal component.

 The porous preform can be prepared by conventional carbon deposition techniques in fibrous reinforcement. Preferably, the preform is obtained by performing one or more cycles of impregnation of a fibrous reinforcement of carbon fibers using precursors of the carbon component of the matrix.

 These precursors may be either thermosetting organic resins or pitch, or a hydrocarbon gas which pyrolytically pyrolyzes.

 Thus, for producing the porous preform, starting from unidirectional carbon fibers, almost unidirectional or multidirectional, in the form of woven or non-woven substrate, which will constitute the reinforcement of the composite material, and is formed in this reinforcement the carbon matrix .

 Generally, commercial carbon fibers are intended for the production of organic matrix composites for which strong fiber-matrix bonds are necessary. Also, the fiber manufacturer grafts on the surface of the fibers functional groups -C-OH, -C = o and -COOH so as to allow the formation of strong bonds with plastics. In the case of the composite materials of the invention which are carbon-carbon composites, strong fiber-matrix bonds lead to brittle materials, which is undesirable.

Also, before making the composite material, it is therefore preferred to eliminate the oxhydryl functions on the surface of fibers. This can be done by a heat treatment, for example to 900 C under a neutral atmosphere. It is also possible to proceed with the desizing of the fibers by washing in acetone. This size is a surface organic coating applied to facilitate the handling of the locks, which is not desirable in the case of carbon-carbon composites. After this preliminary step, the carbon matrix can be formed around the fibrous reinforcement, from organic resins, from pitch or from both.

 According to the invention, it is possible to carry out one or more impregnation cycles of the fibrous reinforcement, each cycle comprising a step of impregnating the fibrous reinforcement by means of an organic resin or pitch, followed by a step of pyrolysis.

 After this or these impregnation cycles, a graphitation is then carried out, ie a thermal treatment under neutral gas at a temperature of 1600 to 2600 ° C.

 The conditions used for the impregnation and pyrolysis steps of the impregnation cycle or cycles depend in particular on the precursor used, as will be seen below.

1) Densification from organic resins
The thermosetting organic resins are precursors by pyrolysis of isotropic and low density glassy carbon. However, the carbon yield varies greatly depending on the nature of the carbon skeleton of the starting polymer. When the temperature rises, the increasingly strong bonds are progressively broken down: first the bonds between polymer chains, then the bonds of aliphatic groups which lose their heteroatoms, and finally the intramolecular aliphatic bonds which reorganize themselves. by dehydrogenating to give aromatic carbon structures more and more dense.

 The carbon yield is higher when the polymer consists of more stable (aromatic) and more branched molecules with stronger (aromatic) bonds. The best result is obtained with so-called crosslinked infinite molecules that are also infusible.

 These polymers are generally produced by condensation reactions and develop molecules extending in the three directions of space. This is the case of resol type phenolic resins and furan resins. In the case of phenolic resins, the coke yield is about 56%.

 The amorphous nature of the carbon thus produced results from the preservation, during the pyrolysis process, of a large part of the unordered carbon skeleton of the original polymer, as well as the absence of mobility of the carbon atoms. The vitreous carbon is made of very small graphitic domains (USB formed of stacks of graphitic planes over very short distances of the order of a few aromatic nuclei) unrelated to a large distance and leaving a significant microporosity between them. The density of the coke is about 1.54, a density lower than that of graphite which is 2.25. The vitreous coke is not graphitable, that is to say that by treatment at high temperature, for example at a temperature above 2400 ° C, the carbon atoms do not acquire sufficient mobility to reorganize and give graphite.

In the case of these organic resins, the densification step comprises several steps which are
a) formation of the carbon / resin form,
b) pyrolysis of the carbon / resin form,
- c) a stabilizing heat treatment.

 The first step has two variants depending on the type of fibrous substrate used.

In the case of a woven substrate (type 2.5D and 3D) the operations are as follows
No. 1: Tooling the substrate so as to maintain its shape.
No. 2: Impregnation with the liquid resin (or in solution) by the vacuum / pressure method.
No. 3: polymerization of the resin.

In the case of a 2D substrate made by draping fabrics, the following operations are performed
No. 1: production of a prepreg with the resin.

The prepreg is obtained by soaking the fabric in the liquid resin or in solution, spinning, drying, and then pre-polymerization of the resin (gelling) to bring it into a state allowing it to stick without casting.
n "2: draping of the tissues on a form and placing under bladder.
n03: vacuum polymerization and external pressure in an autoclave.

2) Densification from pitch
Pitch is the final residue of the distillation process of oils or coal tars.

It consists of a complex mixture of heavy aromatic molecules having from 3 to several tens of aromatic rings. It is therefore a thermoplastic material with a behavior of glass characterized by its softening point.

 Pyrolysis of pitch is carried out in the liquid phase. As the temperature rises, the first breaks in molecules occur for the less stable bonds. There is then a recombination (condensation) of these elements leading to increasingly heavy and aromatic molecules, and therefore more stable.

 Aromatic molecules are plans. From a certain dimension, they are arranged between them by moving closer together and orienting themselves in parallel, thus constituting small domains of semi-crystals (liquid crystals). These domains of liquid crystals are organized in the form of spheres (mesophases) dispersed in the isotropic phase. These spheres grow gradually at the expense of the isotropic phase, then coalesce to completely invade the entire range to 450 ° C. This is then in solid form and is semi-coke.

 The particularity of pitch coke is therefore its anisotropic character with a pregraphic organization. By subsequent treatment at high temperature, this imperfect organization improves to a nearly perfect graphitic structure over large areas with a density close to that of graphite (2.25).

 However, from a technological point of view, the disadvantage of pitch is its thermoplastic character. This is responsible for an extremely low coke volume yield due to the foaming of pitch during pyrolysis. This difficulty can be circumvented by carrying out a pyrolysis under isostatic pressure in hyperclaves, whose pressure is about 100 MPa. This process is expensive and limits the dimensions of the workpieces.

 According to the invention, the use of the hyperclave is avoided by using a method of densification of the pitch without pressure.

Also, the invention also relates to a method for manufacturing a composite material comprising a fibrous reinforcement and a carbon matrix formed from pitch, comprising the following steps
impregnation of the fibrous reinforcement with liquefied pitch or in solution in a solvent,
heat treating the fibrous reinforcement impregnated at a temperature of 340 ° C to 360 ° C to bring the softening point of the pitch to a value of 240-260 ° C,
oxidation of the pitch at a temperature of 200 ° C. to 240 ° C. for 100 to 200 hours,
pyrolysis of the pitch under inert gas at atmospheric pressure, and
- graphitation.

 In this case, the pitch is firstly heat-treated to bring it to a softening point of about 240 ° C., then air-dried at about 200 ° C., which has the effect of make it infusible and give it the same behavior as pyrolysis resin, but this method requires the use of a high-performance reactor capable of providing a good vacuum and a temperature of 400 ° C.

 Two alternative methods to the previous method can be used.

The first technique applies when the substrate is a 2D substrate made by layering. It has the following steps
a): making a prepreg, the fabrics are impregnated in the matured pitch.
b): stacking of the prepreg on a shape and pressage towards 270 "C.
c): oxidation of the pitch to make it infusible under air at 200 ° C for 100 hours.
d): pyrolysis at atmospheric pressure.

The second technique that applies to a thin-walled part, that is to say a thickness of 1 to 5 mm, or <5 mm, to a subsequent impregnation cycle on a material already stiffened by carbon obtained from organic resins or pitch, comprises the following steps
a) impregnation with liquid pitch and maturation of the pitch
b) crushing the pitch; and
c) gentle pyrolysis of the pitch with a very long thermal cycle of 250 "C to 450 C which allows the gas to diffuse thus avoiding creating an internal pressure of the gas which would expel the pitch to the outside of the fibrous reinforcement.

 According to the invention, the carbon component of the matrix may be formed by mixed techniques, for example by producing a first impregnation cycle with an organic resin and then one or more impregnation cycles from pitch and or organic resin. . It is also possible to start with a first impregnation cycle using pitch followed by impregnation cycles using organic resin and / or pitch.

 This method of manufacturing the carbon component of the matrix is very advantageous because it makes it possible to adjust to the desired value the porosity of the porous carbon preform, ie the quantity of metallic constituent that can be included later, and thus to control the final properties of the composite material, such as its thermal conductivity, its coefficient of thermal expansion and its mechanical properties.

 After production of the porous carbon preform, the second metal component is introduced into the porosity of this preform so as to fill it at least in part with this metallic constituent and form the composite matrix of the composite material.

 This introduction can be carried out by infiltration of the second metallic constituent in the liquid phase under pressure, for example by isostatic pressing under low pressure (70 to 100 bar).

 Generally, this operation is carried out as follows.

 The porous carbon preform is placed in an enclosure and heated to the desired temperature, and then the preheated metal component is pressurized into the enclosure at the desired temperature to effect infiltration of the preform by the liquid metal component. The cooling is then carried out, followed by depressurization of the enclosure.

The temperatures of the molten metal component and the heated preform are chosen depending on the nature of the metal component used. Generally, to limit the reactions at the carbon interfaces, the temperature of the preform during the infiltration is limited. In order to maintain sufficient wettability of the carbon matrix by the metal component, it is overheated before infiltration. In the case of a second metallic constituent consisting of an aluminum and magnesium alloy, the following infiltration conditions can be used
temperature of the metallic constituent: 700 C,
temperature of the preform: 650 ° C.

 maximum pressure: 6 MPa.

- average cooling rate: 75 "C min
Other characteristics and advantages of the invention will appear better on reading the following examples, given of course by way of illustration and not limitation, with reference to the accompanying drawings.

Brief description of the drawing
Figure 1 shows schematically the device used for the production of a preimpregnated sheet of unidirectional carbon fibers.

Detailed description of the embodiments
The examples which follow illustrate the manufacture of composite materials according to the invention.

Example 1
In this example, a composite material is prepared from a reinforcement of unidirectional carbon fibers obtained from pitch, forming the carbon component of the matrix from an organic resin in a single step, and then infiltrating the porous preform with an alloy of aluminum and magnesium.

 The carbon fibers used are ex-pitch fibers of very high modulus (K135 2U fibers marketed by Mitsusbishi Kasei). They have a density of 2.14, a Young's modulus E of 624 GPa, a tensile strength of 3472 MPa and a corresponding elongation of 1.7%.

The fibers are first treated chemically and thermally in a neutral atmosphere to achieve a desizing and then impregnated with resin by passing them in a bath containing an alcoholic solution of phenolic resin type
Ablaphene RA101 provided by Rhône Poulenc.

It is a formophenolic resin, Resol type, in aqueous solution, which has the following characteristics
Viscosity at 20 C (CP) 700-850
Density at 20 C .................. approx. 1.20
Dry extract at 160 ° C (%) 67-73 pH 7.5-8.1
Phenol free (%) ........... .... 19-22
Gel time at 1250C (min) 22-30
Coke rate (%) ................ approx. 59
In Figure 1, there is shown the technique used for this impregnation. In this figure, we see that the fibers initially wound on a cylindrical mandrel 1, are unwound and transferred by a system of pulleys (3a, 3b, 3c, 3d, 3e) in a tank 5 containing the alcohol solution of resin.

At the outlet of the tank, they are directly wound on a flat mandrel 7 Teflon to form sheets of unidirectional fibers.

 After drying in an oven at 60 ° C. and then gelling for 15 minutes at 100 ° C., the web is pressed with a Teflon roll before cutting it and then storing it between embossed plastic sheets. The resin content is about 40% by weight.

 The plies are then stacked to obtain a reinforcement of desired thickness, respecting the mirror symmetry, that is to say by simply alternating the plies located on the side of the mandrel, then on the outer side. A stack of four sheets is thus produced which is subjected to vacuum pressing. This gives a carbon fiber content of 70%.

The whole is then subjected to a cooking cycle carried out as follows
- rise to 60 ° C at a rate of 3 C per minute, then plateau for 2 hours at 60 ° C,
- rise to 80 C at a rate of 2 "C per minute, then maintain this temperature for 2 hours,
- rise to 100 C at a rate of 1 "C per minute, then maintain this temperature for 1 hour,
- rise to 120 ° C at a rate of 2 ° C per minute, then maintain this temperature for 2 hours,
- rise to 150 ° C at a rate of 2 C per minute, then maintain this temperature for 30 minutes,
rising to 180 ° C. at a rate of 2 ° C. per minute, then maintaining this temperature for 1 hour, and
- natural cooling.

After this firing cycle, the resin is pyrolyzed, which is carried out in a neutral medium under a nitrogen sweep. This pyrolysis is carried out as follows
- rise to a temperature of 180 ° C at a speed of 5 C per minute,
- rise to 200 C at a speed of 2 C per minute,
- rise to 350 C at a rate of 1 C per minute, then maintain this temperature for 2 hours,
- rise to 400 C at a rate of 0.5 "C per minute, then maintain this temperature for 30 minutes,
- rise to 450 C at a rate of 0.5 "C per minute, then maintain this temperature for 30 minutes,
- rise to 500 ° C at a rate of 0.5 ° C per minute, then
- rise to 900 ° C at a rate of 2 ° C per minute.

 High temperature graphitation is then carried out at 24000.degree.

 During this treatment, the characteristics of the carbon fibers, which were already well graphitized, are modified very little.

 Although the vitreous carbon matrix is not graphitable, the difference in expansion between the fibers and the matrix generates stresses that cause graphitization of the interfacial area and reduce adhesion between the fibers and the matrix.

Moreover, this treatment increases the microcracking of the matrix and thus helps to open the porosities. The open porosity rate of the material then increases from 19 to 21% after this graphitation treatment.

 The porous preform thus obtained has a density of 1.68.

 It is then infiltrated with aluminum using an aluminum alloy and AG10 magnesium supplied by the company Brefond, which contains 10% by weight of magnesium.

 The use of this alloy makes it possible to obtain a melting temperature of the alloy lower than that of pure aluminum (600 ° C. for the alloy instead of 660 ° C. for pure aluminum), to attenuate the chemical reactions at the fiber-matrix interface because magnesium is inert to carbon and to obtain a density lower than that of aluminum (2.57 for alloy instead of 2.7 for aluminum).

The conditions used for this infiltration are as follows
temperature of the metallic constituent: 700 ° C.
temperature of the preform: 650 C
- maximum pressure: 6 MPa
- average cooling rate: 75 "C.min-1.

The composite material obtained comprises
- 60% fibrous reinforcement
- 19% carbon, and
- 19.3% of metallic constituent.

 The density of the material before and after infiltration is determined, as is the thermal conductivity in the plane and the cross direction, its Young's modulus E and its breaking stress o.

Thermal conductivity is measured from the following characteristics
thermal diffusivity a from a pellet with a diameter of 16 + 0.5 mm by carrying out a measurement under vacuum between 20 and 100 C,
- specific heat capacity Cp from a pellet with a diameter of 4.9 + 0.1 mm by carrying out the measurement under nitrogen with a kinetics of S "C.min- '(between 20 and 100 C), and
the density p at 20 C.

The thermal conductivity k is deduced from the following relationship kaxpx Cp
The measurements were made in the cross direction, therefore in the direction perpendicular to the fibers and in the plane, therefore in the direction of the fibers. The results obtained are given in the attached Table 1.

 The mechanical properties of the material are also determined by testing it in 4-point bending for the Young's modulus and the tensile stress (60-20 mm rest) and in close-supported bending for interlaminar shear strength (10 mm supports). ). The results obtained are given in the attached Table 1.

Example 2
In this example, a carbon-reinforced composite material is prepared from ex-pitch fibers.
K135 identical to those of Example 1, by producing the porous preform in the same way as in the ex

After cooling the pitch, the preform is removed from the pitch matrix and placed in an oven to undergo the next pyrolysis cycle.
rising to 200 ° C. at a rate of 10 ° C. per minute and then maintaining this temperature for 1 hour,
- rise to 350 ° C at a rate of 1 ° C per minute, then maintain this temperature for 5 hours,
- rise to 380 ° C at a rate of 1 ° C per minute, then maintain this temperature for 5 hours,
- rise to 400 ° C at a rate of 1 ° C per minute, then maintain this temperature for 5 hours,
rise to 420 ° C. at a rate of 1 ° C. per minute, then maintain this temperature for 3 hours,
- rise to 440 C at a rate of 1 C per minute, then maintain this temperature for 3 hours, and
- rise to 900 C at a speed of 5 C per minute.

 The material is then graphitized at 2400 ° C., a porosity of the porous preform of 10% is also obtained after redensification by pitch while it was 21% in Example 1. The density of the preform is 1.9 and the fiber ratio is 46%.

 The infiltration operation of the preform with the Al-Mg alloy is then carried out under the same conditions as those of Example 1.

This gives a composite material containing
- 46% of fibers,
- 44% carbon, and
- 9% AlMg alloy.

 The properties of the material obtained are given in Table 1.

Example 3
This example illustrates the production of a composite material comprising a reinforcement consisting of a two-dimensional fabric of carbon fibers obtained from polyacrylonitrile (ex-PAN) in a mixed carbon matrix obtained from RA101 resin and aluminum alloy -magnesium.

The fibers used in this example are high strength T300 fibers manufactured by
Toray from polyacrylonitrile. The reinforcement is formed of webs of fabric which is a satin of 5 made from this T300K fiber (3,000 filaments per wick). The properties of the starting fiber are as follows
- density: 1.76
- Young's modulus: 230 GPa
- breaking load: 3530 MPa
- elongation at break: 1.5 t.

 The carbon fabric is first impregnated in a solution of 75% by weight of RA101 resin and 25% by weight of ethanol.

 After wringing, drying and gelling for 15 minutes at 100 ° C., a prepreg containing about 40% of resin and 6% by mass of volatile material is obtained, 4 sheets of fabric are stacked in accordance with the mirror symmetry as in FIG. Example 1, and then the stack is subjected to pressing so as to have a fiber content of 65% and baking performed in the following manner.

The press is preheated to 80 ° C and held at 80 ° C for 10 minutes after closing, then increased to 1200 ° C in 1 hour, and 180 ° C in 1 hour.
(speed of 1 ° C per minute).

 The pyrolysis and graphitation are then carried out under the same conditions as those of Example 1. This gives a porous preform having a fiber content of 60%, a density of 1.4 and an open porosity before graphitation of 22%. and 26% after graphitation.

 Finally the infiltration of the metallic component is carried out under the same conditions as those of Example 1.

The composite material obtained comprises
- 60% fiber,
- 14% carbon, and
- 24.5% aluminum-magnesium alloy,
The properties of this material are given in Table 1.

Example 4
This example illustrates the manufacture of a composite material comprising a two-dimensional fabric reinforcement of ex-PAN carbon fibers, and a mixed coke matrix obtained from RA101 resin and aluminum-magnesium alloy.

 In this example, the same procedure as in Example 3 is followed, but a second impregnation cycle is carried out with the phenolic resin RA101 after the first impregnation and pyrolysis cycle of this resin, and before the graphitation.

 For this purpose, the porous preform obtained in Example 3, before graphitization, is impregnated with matured and dehydrated phenolic resin RA101 at 60 ° C. under vacuum for approximately 4 hours, and the preform is then removed from the impregnation tank. it is drained and then subjected to cooking under the following conditions, which are identical to those of Example 1.

- rise to 60 "C at a rate of 3" C per minute, then maintain this temperature for 2 hours,
- rise to 80 ° C at a rate of 2 ° C per minute, then maintain this temperature for 2 hours,
- rise to 100 ° C at a rate of 1 ° C per minute, then maintain this temperature for 1 hour,
- rise to 1200C at a rate of 2 "C per minute, then maintain this temperature for 2 hours,
- rise to 1500C at a rate of 2 "C per minute, then maintain this temperature for 30 minutes,
rising to 180 ° C. at a rate of 2 ° C. per minute, then maintaining this temperature for 1 hour, and
- natural cooling.

 The material is then subjected to pyrolysis, then to graphitation at 2400 ° C. and infiltration with the aluminum-magnesium alloy as in Example 1.

 After graphitation, the preform has an open porosity of 15% (26% in Example 3) whereas it was 14% before graphitation (22% in Example 3). The density of the porous preform is 1.55.

The composite material obtained comprises
- 50% of fibers,
- 35% carbon, and
- 14% aluminum-magnesium alloy.

 The properties of this material are given in Table 1.

Example 5
This example illustrates the manufacture of a composite material from a T300J carbon fiber reinforcement in the form of a 2.5D fabric with a mixed carbon matrix obtained from pitch and aluminum-magnesium alloy.

The carbon fiber used is a fiber
T300J high strength obtained from polyacrylonitrile (ex-PAN) manufactured by Toray.

These fibers are put in the form of a 2.5D fabric formed of 7 layers, using the technique described in FR-A-2 610 951 and T300J-6K fibers (6000 filaments per wick). The properties of this fiber are as follows
- density: 1.78
- Young's modulus: 230 GPa
- breaking load: 4210 MPa
- elongation at break: 1.8%.

 This fiber undergoes a partial graphitation at 2400 ° C before the 2.5 D fabric is made, its density then increases from 1.78 to 1.94, and its Young's modulus from 230 to 400 GPa.

The carbon matrix is then produced from pitch by arranging the woven reinforcement in a yoke made of grids making it possible to slightly compress the reinforcement to prevent its defibration in the liquid pitch. The assembly is placed in an impregnation tank with crushed pitch and the tank is placed in a vacuum oven where impregnation with pitch is carried out at 250 ° C. under a pressure of less than 500.
Pa. After impregnation, the material is demolded, it is cut off and it is crumbled. The pitch is then cured in an oven under a nitrogen sweep, operating as follows
- rise to 250 ° C at a rate of 10 C per minute, then maintain this temperature for 1 hour,
- rise to 300 ° C at a rate of 1 ° C per minute, then maintain this temperature for 2 hours,
rising to 350 ° C. at a rate of 1 ° C. per minute, then maintaining this temperature for 2 hours, and
rising to 380 ° C. at a rate of 0.5 ° C. per minute and then maintaining this temperature for 3 hours.

 The softening point is roughly determined by measuring the temperature at which a metal point can be sunk into the preform, at about 2500 ° C.

 The material is then pressed in hot press at 260 ° C. At this temperature, given its softening point towards 250 ° C., the pitch remains very viscous, which avoids the risk of wringing the material. The pitch being in excess, the pressing is carried out between grids which make it possible to evacuate the pitch which flows, one thus obtains a zero porosity rate.

 The pitch is then subjected to oxidation.

It is carried out at 200 ° C. in the air for 100 hours.

This temperature is low enough that the shrinkage of the pitch causes a large cracking thereof, and is sufficiently high that the kinetics of oxidation is not too low.

Pyrolysis is then carried out in a nitrogen flushing furnace operating as follows
- rise to 280 ° C at a rate of 7 per minute, then maintain this temperature for 2 hours,
- rise to 300 ° C at a rate of 2 C per minute, then maintain this temperature for 2 hours,
- rise to 350 C at a speed of 5 C per minute, then maintain this temperature for 2 hours,
rising to 450 ° C. at a rate of 3 ° C. per minute, then maintaining this temperature for 2 hours, and
- rise to 900 ° C at a rate of 3 ° C per minute.

After pyrolysis, the material has a fiber content of 50%. A graphitization is then carried out at 2400 ° C., as in Example 1. The porosity of the material increases because of the graphitization of the carbon matrix, as can be seen below.

<SEP> 2.5 <SEP> D <SEP> 2.5D
<tb><SEP> before <SEP> graphitation <SEP> after <SEP> graphitation
<tb><SEP> rate <SEP> of <SEP> fiber <SEP> 50 <SEP>% <SEP> 50 <SEP>%
<tb> density <SEP> apparent <SEP> 1.40 <SEP> 1.40
<tb> porosity <SEP> open
<tb><SEP> measured <SEP> 20 <SEP>% <SEP> 23 <SEP>%
<Tb>
The matrix is then infiltrated with the aluminum-magnesium alloy under the same conditions as those of the preceding examples.

The characteristics of the composite material obtained are given in Table 1. This material comprises
- 50% carbon fiber,
- 27% carbon, and
- 22% aluminum-magnesium alloy.

 The coefficient of thermal expansion of this material is 2.6 × 10 -6. C-1 between 30 and 800C.

 The results of Examples 1 to 5 show the advantage of the carbon-metal composite matrix of the invention, which makes it possible to control the properties of the material obtained. Indeed, the porosity of the porous preforms can be controlled during the impregnation cycles with resins and / or pitch, which makes it possible to control the amount of metal which will then be infiltrated to form the mixed matrix.

 In the attached Table 2, the mechanical characteristics of the materials according to the invention as well as those of material of the prior art comprising a reinforcement of carbon fibers of one-dimensional or two-dimensional 2D in an aluminum matrix have been given, and those of carbon-carbon materials in which the reinforcement is two-dimensional or 2.5D. In view of this table, it is noted that it is possible to improve the thermal conductivity, the elastic modulus and the interlaminar shear stress, by using the mixed matrix of the invention.

TABLE 1

Ex <SEP> Fibers <SEP> Reinforcement <SEP> Matrix <SEP> Mass <SEP> Porosity <SEP> Module <SEP> Constraint <SEP> Constraint <SEP> Conductivity <SEP> Thermal
<tb> C <SEP> volume <SEP> (%) <SEP> of Young <SEP> to <SEP><SEP> of <SEP> (W / m C)
<tb> E (GPa) <SEP> rupture <SEP> shear
<tb> (flexion <SEP> 4
<tb> points
<tb># (MPa) <SEP># (MPa) <SEP> Plan <SEP> through
<tb> 1 <SEP> ex-pitch <SEP> unidirectional <SEP> Resin
<tb> K135 <SEP> 2U <SEP> RA101 <SEP> 2.23 <SEP> 1.7 <SEP> 376 <SEP> 525 <SEP> 30 <SEP> 352.4 <SEP> 15.3
<tb> 2 <SEP> Ex-pitch <SEP> Resin
<tb> K135 <SEP> 2U <SEP> RA101 <SEP> 2.30 <SEP> 1 <SEP> 356 <SEP> 560 <SEP> 28 <SEP> 414 <SEP> 20.8
<tb> pitch
<tb> 3 <SEP> Ex-Pan <SEP> Tissue <SEP> 2D <SEP> Resin
<tb> T300 <SEP> RA101 <SEP> 2.05 <SEP> 1.5 <SEP> 120 <SEP> 440 <SEP> 31 <SEP> 73 <SEP> 19.3
<tb> 4 <SEP> Ex-Pan <SEP> Fabric <SEP> Resin
<tb> T300 <SEP> 2D <SEP> RA101 <SEP> 2.06 <SEP> 1 <SEP> 114 <SEP> 393 <SEP> 23 <SEP> 150 <SEP> 20.5
<tb> 5 <SEP> Ex-Pan <SEP> Fabric
<tb> T <SEP> 300 <SEQ> 2.5D <SEP> Brak <SEP> 1.99 <SEP> 1 <SEP> 73 <SEP> 391 <SEP> 21 <SEP> No <SEP> measured
<tb> TABLE 2

Constraint <SEP> Constraint
<tb> Material <SEP> composite <SEP> Density <SEP> Module <SEP> to <SEP><SEP> of
<tb> Yound <SEP> rupture <SEP> shear
<tb> E <SEP> (Gpa) <SEP>#R (MPa) <SEP># (MPa)
<tb> (flex <SEP> 4 <SEP> points)
<tb> Invention <SEP> (ex <SEP> 1 <SEP> to <SEP> 5) <SEP> 1.99 <SEP> - <SEP> 2.30 <SEP> 73 <SEP> - <SEP> 376 <SEP> 391 <SEP> - <SEP> 560 <SEP> 21 <SEP> - <SEP> 31
<tb> Reinforcement <SEP> in <SEP> fibers <SEP> of <SEP> carbon <SEP> quasi <SEP> UD
<tb> in <SEP> one <SEP> matrix <SEP> Al <SEP> 2,3 <SEP> 300 <SEQ> 688 <SEP> 48
<tb> Reinforcement <SEP> tissue <SEP> 2D <SEP> of <SEP> fibers <SEP> of <SEP> C <SEP> in
<tb> a <SEP> template <SEP> Al. <SEP> 2,3 <SEP> 104 (L) <SEP> 297 (L) <SEP> 94
<tb> 27 (T) <SEP> 103 (T)
<tb> Reinforcement <SEP> fabric <SEP> of <SEP> fibers <SEP> of <SEP> carbon <SEP> 2D
<tb> in <SEP> a <SEP> matrix <SEP> of <SEP> carbon <SEP> 1.6 <SEP> 90 <SEP> 200 <SEP> 14-18
<tb> Reinforcement <SEP> in <SEP><SEP> fabric of <SEP><SEP> carbon fiber <SEP>
<tb> 2.5D <SEP> in <SEP> one <SEP> matrix <SEP> of <SEP> carbon <SEP> 1.6 <SEP> 93 <SEP> 232 <SEP> 10
<tb> (meaning <SEP> string)
<tb> L Longitudinal T Travers

Claims (19)

 Composite material comprising a fibrous reinforcement of carbon fibers arranged in a mixed matrix comprising a first carbon component and a second metal component.  The material of claim 1, wherein the second metal component is a metal, a metal alloy, or an intermetallic compound.  3. The material of claim 1 wherein the second metal component is aluminum or an aluminum magnesium alloy.  4. Material according to any one of claims 1 to 3, wherein the content of second metal component is 0.5 to 60% by volume relative to the volume of said material.  5. Material according to any one of claims 1 to 3, comprising by volume  40 to 70% fibrous reinforcement,  10 to 45% of the first carbon component of the matrix, and  5 to 25% of the second metal component of the matrix.  The material of any of claims 1 to 5, wherein the content of the second metal component is such that the coefficient of thermal expansion of the material is in the range of 0 to 10-7. C-1.  The material of any one of claims 1 to 6, wherein the fibrous reinforcement is unidirectional or near-unidirectional, bi-directional or multidirectional carbon fibers, or a woven carbon fiber substrate.  The material of claim 7, wherein the carbon fibers are derived from polyacrylonitrile precursors or pitch.  9. Material according to any one of claims 1 to 8, wherein the carbon component is graphitized carbon obtained by pyrolysis and graphitation of a thermosetting organic resin and / or pitch.  10. A method of manufacturing a composite material comprising a fibrous reinforcement of carbon fibers and a mixed matrix of a first carbon component and a second metal component, comprising the following steps  a) preparing a preform of carbon-carbon type porous composite material comprising a fibrous reinforcement of carbon fibers arranged in a matrix of the first carbonaceous component, having a porosity of 0.5 to 60%, and  b) introducing the second metal component in the porosity of the preform obtained in a) to fill at least part of this second metal component.  11. The method of claim 10, wherein preparing the preform of porous composite material by performing at least one impregnating cycle comprising impregnating a fibrous reinforcement of carbon fibers with a thermosetting organic resin followed by pyrolysis of the resin, and then performing a graphitation.  12. The method of claim 11, wherein before graphitization is carried out at least one additional impregnation cycle by pitch followed by pyrolysis pitch.  13. The method of claim 10, wherein preparing the preform of porous composite material by performing at least one impregnating cycle comprising impregnating a fibrous reinforcement of carbon fibers with liquid pitch, followed by pyrolysis. pitch, and then performing a graphitation.  The process according to claim 13, wherein after impregnation with pitch and before pyrolysis, the pitch is subjected to a thermal cure treatment followed by an oxidation treatment.  15. The method of claim 13 or 14, wherein before graphitization is carried out at least one complementary impregnation cycle with a thermosetting resin followed by pyrolysis of the resin.  16. A method according to any one of claims 11 to 15, wherein the number of impregnation cycles is chosen according to the porosity that is to be obtained.  17. A method according to any one of claims 10 to 16, wherein the fibrous reinforcement is obtained from precursor carbon fibers consisting of polyacrylonitrile or pitch.  18. The method of any one of claims 11 or 15 wherein the thermosetting organic resin is a formophenolic resin.  19. A method of manufacturing a composite material comprising a fibrous reinforcement and a carbon matrix formed from pitch, comprising the following steps  impregnation of the fibrous reinforcement with liquefied pitch or in solution in a solvent,  heat treatment of the fibrous reinforcement impregnated at a temperature of 340 ° C to 360 ° C to bring the softening point of the pitch to a value of 240-260 ° C,  oxidation of the pitch at a temperature of 200 ° C. to 240 ° C. for 100 to 200 hours;  pyrolysis of the pitch under inert gas at atmospheric pressure, and  - graphitation.