EP0922779B1 - Metal matrix composite bodies with high stiffness and high stability in a longitudinal direction - Google Patents

Description

Technical area

The invention relates to an elongated part, made of a composite material including a matrix metallic based on aluminum or magnesium, as well as continuous carbon fibers arranged in layers superimposed.

Throughout the text the expression "fibers continuous "means fibers of great length, which extend continuously from one end to the other of the room or on its entire periphery or its periphery, according to the orientation given to the fibers inside the room.

Furthermore, the expression "elongated piece" means any part (plate, rod, tube, etc.) with greater dimension in one direction given, called "longitudinal direction", according to which efforts must be transmitted.

In addition, the term "tablecloth" here means, by convention, any layer of woven or non-woven fibers, whatever its manufacturing method (draping, winding, etc.).

The part in composite material with metallic matrix according to the invention is particularly suitable for uses in the space industry and, from more generally, to any use involving a great dimensional stability.

State of the art

The different structural parts of the satellites, probes and other devices intended for use in space are subject to constraints, in particular mechanical and thermal, particularly severe.

Thus, during assembly and testing at soil, the effects of gravity, humidity and temperature should be carefully monitored.

During the launch phase, the launcher transmits thrust forces to the spacecraft and intense vibrations.

Finally, when the machine is operational, it undergoes very significant temperature variations, depending on whether its different faces are lit or not by the sun. To this constraint is added the placing under vacuum of the machine, which can result in a release of moisture.

In the presence of all these constraints, the realization structural parts pose a delicate problem, especially when they are used to support high precision devices such as these mirrors belonging to optical systems.

In this context, it does not currently exist of material having, in itself, stability sufficient dimension and rigidity to achieve structural parts capable of supporting the aforementioned constraints, while ensuring the precision of positioning required. This is why these regulators more or less complex thermals are sometimes associated to such rooms.

So the metal parts always have a non-zero coefficient of expansion, which translates by positioning instability when the part undergoes thermal variations. In addition, the stiffness of purely metallic parts is generally insufficient for the application considered.

Parts made of matrix composite material organic are much less sensitive to variations temperatures and may exhibit rigidity raised in the longitudinal direction of the workpiece. However, they have the notable disadvantage, when they arrive in a vacuum, to gradually desorb the water they adsorbed when they found on earth. This progressive desorption is translated by dimensional variations of the part. It requires following very penalizing procedures during the manufacture of the spacecraft. She drives also to equip this machine with more or less complex to reposition the devices high precision, when in space. However, these are delicate operations and energy consuming, which can affect reliability of the machine and reduce its lifespan.

The use of parts made of composite material with a metallic matrix makes it possible, thanks to the presence of continuous fibers, to substantially increase the rigidity, compared to purely metallic parts. In addition, the problems of dimensional variations due to desorbtion in a vacuum are eliminated. These advantages are explained, in particular, in the article "High Stable Advanced Materials For Space Telescope, An Application Of Metal Matrix Composites" by C. Désagulier et al., IAF-96-I.3.01, in the case of fiber composites. carbon-aluminum and carbon-magnesium fibers. More precisely, this article recommends the use of fibers with ultra-high modulus carbon, and it announces that an elementary ply or "fold" having a coefficient of longitudinal thermal expansion αL of 1.10 ^-6 / ° C (magnesium matrix) or 1.27.10 ^-6 / ° C (aluminum matrix) and an EL longitudinal traction module of 280 GPa (magnesium matrix) or 302 GPa (aluminum matrix) could be obtained.

However, no technique is suggested with regard to the production of a thick part (set of plies) which must have a practically zero coefficient of longitudinal thermal expansion αL, that is to say the absolute value of which is preferably less than 0.2.10 ^-6 / ° C.

In document EP-A-0 164 536, it is proposed a composite material formed of carbon fibers and of a metallic matrix of a magnesium alloy containing aluminum, zirconium and zinc. For make this material, we introduce a beam of high-strength parallel carbon fibers in a elongated stainless steel case, preheated to about 700 ° C and placed in the cavity of a mold pressure foundry, preheated to about 200 ° C, so that the opening of the case is oriented to the top. The molten magnesium alloy is then poured into the cavity, at around 700 ° C, then a piston also preheated to around 200 ° C, is pressed on the top of the mold, in order to compress the molten alloy and to force it to enter the fiber bundle, when the device cools down. After ascent of the piston, the solidified part is extracted towards the high by a pusher. The final piece is obtained by machining during which the housing is eliminated.

Statement of the invention

The subject of the invention is precisely a part made of a metal matrix composite material, the original design allows it to present both high rigidity and great dimensional stability, in particular so that it can be used in space, to support high precision devices.

According to a first embodiment of the invention, this result is obtained by means of a part made of a metal matrix composite material, elongated shape in a given direction, characterized by the fact that it comprises from 35% to 45% by volume of an aluminum alloy matrix and, respectively, from 65% to 55% by volume of continuous fibers carbon arranged in successive layers in parallel in said direction, at least about 90% of carbon fibers being ultra high modulus fibers having a tensile modulus at least equal to approximately 650 GPa, said ultra-high modulus fibers being oriented to 0 ° ± 5 ° in about 25% to about 60% of the water tables, and between ± 20 ° and ± 40 ° in the other layers, compared to said direction.

In this case, the alloy-based matrix aluminum is preferably made of an AG10 type alloy, containing in particular approximately 10% by volume of magnesium.

Advantageously, ultra high modulus fibers are then oriented at 0 ° ± 5 ° in 45% to 55% of tablecloths and, preferably, in about 50% of the tablecloths.

In addition, ultra-high modulus fibers are advantageously oriented around ± 25 ° in the others plies.

According to a second embodiment of the invention, the characteristics targeted are achieved using a piece of matrix composite material metallic, elongated in a given direction, comprising an alloy matrix based on magnesium and continuous carbon fibers, arranged in successive layers parallel to said direction, characterized in that it comprises, respectively, 35% to 45% by volume of said matrix and from 65% to 55% by volume of said fibers, at least about 90% of the carbon fibers being ultra high modulus fibers, having a tensile modulus at least equal to approximately 650 GPa, said ultra-high modulus fibers being oriented at 0 ° ± 5 ° with respect to said direction in at least 90% of the tablecloths.

In this case, the alloy matrix based on magnesium is preferably an alloy of the type GA9Z1, containing in particular around 9% by volume aluminum.

Advantageously, ultra high modulus fibers are then oriented at 0 ° ± 5 ° in about 100% of plies.

In both embodiments, the parts have almost perfect stability at least in the longitudinal direction. In fact, like all metallic or metallic matrix parts, there is no adsorption of moisture on the ground, so that its dimensions do not change when the part is placed in a vacuum. In addition, thanks to the characteristics specific to the material according to the invention, the coefficient of thermal expansion αL in the longitudinal direction is practically zero. Indeed, its absolute value is less than 0.2.10 ^-6 / ° C, or close to this value.

Furthermore, a part according to the invention has a high specific stiffness in the direction longitudinal above. More specifically, the rigidity specific in this direction being defined as the ratio between the longitudinal traction module EL and the relative density ρ, this ratio is, in in most cases, more than 100 MPa.

Preferably, at least some of the tablecloths are fabrics, for example of the taffeta type, comprising around 90% of warp threads, made up of continuous ultra high modulus carbon fibers and about 10% of weft threads, made up of other continuous carbon fibers, of lower modulus. The weft yarns have the particular function of maintaining the sons of chain.

Preferably, the sheets are arranged according to mirror symmetry with respect to a longitudinal surface median, parallel to the longitudinal direction.

Detailed description of preferred embodiments of the invention

According to the invention, for a room of elongated shape presents both a very large specific stiffness and dimensional stability practically perfect in the direction of its length, this part must be made of a composite material with metal matrix having characteristics well determined.

The expression "very high specific rigidity in the direction of its length ", means a relationship between the tensile modulus EL and the relative density ρ generally greater than 100 GPa in this direction. In the preferred embodiments which will be described, this objective is achieved since the rigidity specific measured in the longitudinal direction is, as the case may be, 119 GPa (aluminum-based matrix) or 197 (magnesium base matrix).

In a comparable manner, the expression "practically perfect dimensional stability in the direction of its length" means that the absolute value of the coefficient of longitudinal thermal expansion αL is generally less than 0.2.10 ^-6 / ° C. In the preferred embodiments, this result is also achieved, since the absolute value of the measured coefficient of longitudinal thermal expansion is, as the case may be, 0.08.10 ^-6 / ° C (aluminum-based matrix) or 0 , 01.10 ^-6 / ° C (magnesium-based matrix).

According to the invention, the composite material used to make an elongated piece includes an aluminum-based alloy matrix or magnesium, as well as continuous carbon fibers which are arranged in successive layers, in parallel to the longitudinal direction of the part.

More precisely, the matrix and the fibers make up approximately 40% and approximately 60% of the total volume of the room. If the room includes one or several inserts made of another material, by metallic example, this volume proportion does not concerns that the part of the part made of material composite. In practice, the expressions "approximately 40% "and" approximately, 60% "means that the matrix represents from 35% to 45% of the total volume of the part and that the fibers respectively represent 65% at 55% of this same volume.

In a first preferred embodiment of the invention, the alloy in which the matrix is an aluminum alloy containing in particular about 10% by volume of magnesium. Such an alloy is generally known under the name "AG10 alloy".

In this first embodiment of the invention, at least about 90% of the continuous fibers carbon are ultra high fibers. module, i.e. fibers whose tensile modulus is at least equal to around 650 GPa. More specifically, the. continuous carbon fibers are "K139" fibers of the MITSUBISHI Company.

In addition, ultra high carbon fibers module are oriented between -5 ° and + 5 ° relative to the longitudinal direction of the part in 45 to 55% tablecloths. In the remaining layers, that is to say respectively in 55 to 45% of the sheets, the fibers of ultra high modulus carbon are alternately oriented in either direction between 20 ° and 40 ° by relative to the longitudinal direction of the part.

In the first preferred embodiment, the part comprises an even number of layers of fibers and these layers are arranged in a mirror symmetry by relative to a median longitudinal area of the part, parallel to the longitudinal direction. This surface is flat or cylindrical, depending on whether the part has a rectangular or circular section, respectively.

In each of the layers, the fibers with ultra high modulus are parallel to each other and they extend from one end to the other of the room, according to the longitudinal direction thereof.

A part in accordance with the invention is produced by first making a fibrous preform, then by infiltrating this preform of the alloy forming the matrix. The completion of the fiber preform depends on the shape of the part to be manufactured. In particular, ultra high modulus fibers can be used alone (in the case of a winding), in association with others fibers (in the case of a fabric), or by combining these two processes.

When all the layers are formed only ultra high modulus fibers, parallel between them in each layer, all of the carbon fibers forming the fibrous matrix is made of ultra ultra fibers high modulus. Conversely, when all the layers are are in the form of a fabric in which the ultra high modulus fibers make up the chain, about 90% of the fibers in the fibrous matrix are ultra high modulus fibers. In some cases, a part of the sheets is formed only of fibers with ultra high modulus and the other layers are formed of tissue. According to the percentage of the tablecloths of each category, the percentage of ultra high modulus fibers in the fibrous preform is then between approximately 90% and 100%.

In the case of the example described, the fibers with ultra high modulus are woven to maintain these fibers together, in the sheet considered, for ensure satisfactory manufacture of the part. For ensure this maintenance, a fabric is then produced, by taffeta type example, comprising about 90% of chain yarns made up of carbon fibers ultra high modulus and around 10% of weft yarns, made up of other continuous carbon fibers, lesser module. In the first embodiment described, these other fibers are fibers of the type "M40" or "M50" from the company TORAY.

A piece of matrix composite material metal according to the invention is manufactured by pressure foundry.

According to this technique, we place in the same airtight container, comparable to an autoclave, a crucible containing blocks of the alloy intended to form the matrix of the part, as well as a mold in which the fiber preform was previously introduced previously manufactured according to the arrangement previously described.

During a first step, we vacuum inside the container and the mold, we heat the crucible containing the metal alloy blocks and we preheats the mold.

When the alloy contained in the crucible is completely melted, it is transferred inside the mold. This transfer is carried out automatically in pressurizing the container to a pressure level generally between approximately 30 bars and approximately 100 bars.

As soon as the mold is filled, cooling of the room is accelerated by bringing in a cooling element in contact with a wall of the mold. As long as the temperature did not drop below the temperature solidification of the alloy, the pressure is kept in the container to compensate for the natural shrinking of metal.

For more details on the main known techniques for implementing this method, usefully refer to the article "Pressure Infiltration Casting of Metal Matrix Composites "by Arnold J. COOK and Paul S. WERNER, in "Materials Science and Engineering" A 144 (October 1991) pages 189 to 206.

In the first embodiment of the invention, six different pieces, numbered 1 to 6, of composite material with a metal matrix, of elongated parallelepiped shape, were produced by this pressure foundry technique. The pieces numbered 1 to 5 had the same dimensions of 260mm x 130mm x 3mm. The piece numbered 6 had dimensions of 160 mm x 80 mm x 3 mm. All the parts presented the same matrix in AG10. They differed essentially in the structure of their fibrous preform. Indeed, if each of these preforms was formed of sixteen (pieces 1 to 5) or ten (piece 6) sheets of fabric each including 90% of K139 fibers and 10% of fibers M40 (pieces 1 to 5) or M50 (piece 6), the orientation of the ultra high modulus K139 fibers was different from one preform to another. This orientation is given in Table I. Part no. Draping (K139 fiber) Draping sequence 1 Almost one-way / 2 25% fiber at 0 °
75% fiber ± 30 ° (+ 30 °; + 30 °; + 30 °; 0 °; -30 °; -30 °; -30 °; 0 °; 0 °; -30 °; -30 °; -30 °; 0 °; + 30 °, + 30 °, + 30 °) 3 25% fiber at 0 °
75% fiber ± 22 ° (+ 22 °; + 22 °; + 22 °; 0 °; -22 °; -22 °; -22 °, 0 °; 0 °; -22 °; -22 °; -22 °; 0 °; + 22 °, + 22 °, + 22 °) 4 50% fiber at 0 °
50% of fibers ± 30 ° (-30 °; 0 °; + 30 °; 0 °; -30 °; 0 °; + 30 °; 0 °; 0 °; + 30 °; 0 °; -30 °; 0 °; + 30 °; 0 °, -30 °) 5 50% fiber at 0 °
50% of fibers ± 25 ° (-25 °; 0 °; + 25 °; 0 °; -25 °; 0 °; + 25 °; 0 °; 0 ° + 25 °; 0 °; -25 °; 0 °; + 25 °; 0 °, -25 °) 6 60% fiber at 0 °
40% fiber ± 32 (0, 32 °, 0, -32 °, 0, 0, -32 °, 0, 32 °, 0)

The preforms defined in Table I correspond to reference parts, allowing show the importance of fiber orientation to inside the composite material, to get the desired result.

• température du bain de métal constitué par l'alliage d'aluminium AG10 : 720°C;
• température de la préforme : 670°C ;
• pression maximale d'infiltration : 60 bars ;
• montée en pression : 1 bar/s ;
• vitesse moyenne de refroidissement : environ 50°C/min.

From the preforms thus produced, each of the parts was then produced, using the pressure foundry technique, under identical production conditions. These conditions are as follows:

• temperature of the metal bath constituted by the aluminum alloy AG10: 720 ° C;
• preform temperature: 670 ° C;
• maximum infiltration pressure: 60 bars;
• pressure build-up: 1 bar / s;
• average cooling rate: around 50 ° C / min.

Test pieces were then cut with the diamond wheel in each of the pieces thus obtained, to allow in particular mechanical tests and physical measurements.

Before cutting the test pieces, the quality of infiltration of fibrous preforms by the alloy was checked both by radiography X-rays and metallographic observations. These checks revealed very good infiltration of the preform and the absence of a foundry defect.

Mechanical tests carried out on test pieces machined in parts are mainly tensile tests. Physical measurements concern in particular the coefficient of thermal expansion in the transverse direction; the coefficient of expansion thermal in the longitudinal direction and the fiber volume fraction.

Physical measurements showed that the density of the composite was always between 2.26 g / cm ³ and 2.30 g / cm ³ .

The results of the mechanical tests and of the physical measurements carried out on each of the test pieces, at ambient temperature (approximately 20 ° C.), are collated in Table II.

In this Table, the expression "sense L" means longitudinal direction, the expression "sense T" means transverse direction and the values given between parentheses indicate the number of tests performed at every time.

The results presented in Table II show that the coefficient of thermal expansion αL in the longitudinal direction decreases progressively in absolute value, from part 1 to part 5, parts 2, 3 and 6 having a coefficient of thermal expansion substantially of equal value, in this direction. Only parts 4 and 5 have a coefficient αL less than 0.2.10 ^-6 / ° C, in the longitudinal direction. Furthermore, only parts 1, 5 and 6 have a specific rigidity in the longitudinal direction EL / ρ greater than 100 GPa.

In the first embodiment of the invention, Exhibit 5 therefore presents the best compromise in order to obtain both a high rigidity and a great stability in the longitudinal direction.

In a second preferred embodiment of the invention, the matrix is made of an alloy with magnesium base, containing in particular approximately 9% in volume of aluminum. This alloy is GA9Z1 High type Purity.

As in the first embodiment described, the matrix and the continuous carbon fibers have respective volume ratios of approximately 40% and around 60%.

In the example, chosen to illustrate this second embodiment of the invention, one realizes a preform from a stack of layers of tissue. The fabric comprises approximately 90% by volume of ultra-high modulus carbon fibers, type K 139, placed in the longitudinal direction, and 10% of carbon fibers type M 50, placed in the direction transverse, in order to hold the fibers K 139.

The stack of fabric layers is made of in such a way that, in all the layers, the fibers to ultra high modulus are oriented at 0 ° ± 5 ° from to the longitudinal direction of the part.

• température, du bain d'alliage de magnésium GA9Z1 : 750°C ;
• température de la préforme : 750°C ;
• pression maximale d'infiltration : 60 bars ;
• montée en pression : 1 bar/s ;
• vitesse moyenne de refroidissement : environ 25°C/min.

As in the first embodiment described, the part is manufactured by pressure foundry, under the following conditions:

• temperature of the GA9Z1 magnesium alloy bath: 750 ° C;
• preform temperature: 750 ° C;
• maximum infiltration pressure: 60 bars;
• pressure build-up: 1 bar / s;
• average cooling rate: around 25 ° C / min.

Samples of the part obtained, called "piece 7" have been cut to perform the same mechanical and physical measurements only on parts 1 to 6 illustrating the first embodiment of the invention.

The density of the part 7 was determined at 1.95 g / cm ³ by physical measurements.

Table III gives, at room temperature (approximately 20 ° C.), the results of the mechanical and physical measurements carried out (the notations are the same as in Table II). Measured characteristics Symbol Exhibit 7 Young's modulus L (GPa) EL 384 (3) Absolute value of the thermal expansion coefficient in direction L (10-6 / ° C) aL 0.01 (4) Absolute value of the thermal expansion coefficient in direction T (10-6 / ° C) αT 5.33 (3) Fiber volume rate (%) vf 58.3 ± 2.5 (3)

The observation in Table III shows that the part 7 has, in absolute value, a coefficient of thermal expansion αL, in the longitudinal direction, much less than 0.2.10 ^-6 / ° C. In addition, the specific rigidity EL / ρ in the longitudinal direction is much greater than 100 GPa. The objectives sought are therefore also achieved by this second embodiment of the invention, since the orientation of the fibers is at 0 ° ± 5 ° in at least 90% of the sheets.

In conclusion, the parts made of composite material with metal matrix according to the invention have mechanical and physical characteristics that allow to consider their use especially in the space industry, for all applications requiring both high rigidity and excellent stability in a longitudinal direction of the room.

Claims (12)

1. Composite, metal matrix material part, which is elongated in a given direction, comprising 35 to 45 volume % of an aluminium-based alloy matrix and, respectively, 65 to 55 volume % of continuous carbon fibres arranged as successive sheets parallel to said direction, at least approximately 90% of the carbon fibres being ultra-high modulus fibres having a rupture modulus of at least approximately 650 GPa, said ultra-high modulus fibres being oriented at 0° + 5° in approximately 25% to approximately 60% of the sheets, and between ± 20° and ± 40° in the other sheets, with respect to said direction.
2. Part according to claim 1, wherein the matrix is of an aluminium-based alloy containing approximately 10 vol.% magnesium.
3. Part according to any one of the preceding claims, wherein the ultra-high modulus fibres are oriented at 0° ± 5° in 45 to 55% of the sheets.
4. Part according to claim 3, wherein the ultra-high modulus fibres are oriented at 0° ± 5° in approximately 50% of the sheets.
5. Part according to any one of the preceding claims, wherein the ultra-high modulus fibres are oriented at approximately ± 25° in the other sheets.
6. Composite, metal matrix material part, elongated in a given direction comprising, an alloy matrix based on magnesium and continuous carbon fibres, arranged in successive sheets parallel to said direction, characterized in that it comprises respectively, 35 to 45 volume % of said matrix and 65 to 55 volume % of said fibres, at least approximately 90% of the carbon fibres being ultra-high modulus fibres having a rupture modulus of at least approximately 650 GPa, said ultra-high modulus fibres being oriented at 0° ± 5° relative to said direction in at least 90% of the sheets.
7. Part according to claim 6, wherein the matrix is of magnesium-based alloy containing approximately 9 vol.% aluminium.
8. Part according to either of the claims 6 and 7, wherein the ultra-high modulus fibres are oriented at 0° ± 5° in approximately 100% of the sheets.
9. Part according to any one of the preceding claims, wherein at least some of the sheets are fabrics comprising approximately 90% warp yarns, constituted by said continuous, ultra-high modulus, carbon fibres and approximately 10% weft yarns, constituted by other continuous carbon fibres with a lower modulus.
10. Part according to any one of the preceding claims, wherein the ultra-high modulus fibres extend from one end to the other of the part, in accordance with said direction.
11. Part according to any one of the preceding claims, wherein the sheets are arranged in accordance with a mirror symmetry with respect to a median, longitudinal surface, parallel to said direction.
12. Part according to any one of the preceding claims, belonging to a spacecraft.