FR3039838A1 - PROCESS FOR MANUFACTURING A PIECE OF COMPOSITE MATERIAL - Google Patents

Abstract

The invention relates to a method for producing a composite material part (15) comprising a fibrous reinforcement densified by a metal matrix (14).

Description

BACKGROUND OF THE INVENTION The invention relates to a method for manufacturing a metal matrix composite part.

Reinforcement of metal parts by long fibers based on a ceramic material such as silicon carbide has been envisaged in order to improve the mechanical properties (elastic limit, modulus dYoung) of these parts. However, the integration of long fibers in a metal matrix by conventional shaping processes (foundry, forging, machining) is complex. In addition, the cohesion between the fibers and the metal matrix is generally low, due to either a weak diffusion between these two elements or a reaction between the fibers and the matrix.

One solution for improving the cohesion of the fibers with the metal matrix consists in using fibers consisting of a core of ceramic material and a metal sheath surrounding this core. The sheath may for example have been deposited by high speed coating. A heat diffusion welding treatment can then be performed to secure the fibers to a pre-shaped part, for example forged and / or machined. Such a solution is for example described in document FR 2 886 180. This solution works but it requires a large succession of operations: shaping of the initial part, machining of grooves to introduce the fibers, welding of a cover for close the workpiece, and heat diffusion welding treatment. In addition, in this type of solution, the distribution of the fibers requires each time specific operations, making their distribution in multiple positions relatively long to achieve.

There is therefore a need for more simple methods for producing metal matrix composite parts reinforced with ceramic fibers while retaining satisfactory mechanical properties for the parts obtained.

OBJECT AND SUMMARY OF THE INVENTION To this end, the invention proposes, according to a first aspect, a method of manufacturing a composite material part comprising a fiber reinforcement densified by a metal matrix, the method comprising at least the following steps: a) introducing a composition comprising at least one powder of a metal alloy and a binder into a molding cavity in which a plurality of fibers are present in order to obtain a blank of the part to be manufactured, the fibers comprising a core in ceramic material coated with a metal sheath and being held in at least one predefined orientation in the molding cavity, the melting temperature Ti of said alloy and the melting temperature T2 of the metal sheath of the fibers satisfying the following condition: Ti | / Ti <25%, b) machining of the blank to obtain a preform of the part to be manufactured, c) removal of the binder present in the preform a in order to obtain a debonded preform, and d) heat treatment of the debonded preform in order to obtain the piece of composite material during which the metallic sheath of the fibers is assembled with the powder of the metal alloy by diffusion bonding and during which the powder of the metal alloy is sintered to form the metal matrix.

Unless otherwise stated, the melting temperatures Ti and T2 are expressed in ° C (degrees Celsius). Unless otherwise stated, the size noted | A | denotes the absolute value of magnitude A.

The fact that the temperatures Ti and T2 satisfy the inequality above makes it possible to guarantee good compatibility between the metal sheath of the fibers and the powder of the metal alloy in order to achieve efficient diffusion welding and to obtain a good quality interface. between the fibers and the metal matrix thus making it possible to have a part having the desired mechanical properties.

The fact of using a composition comprising a powder of a metal alloy advantageously makes it possible to significantly simplify the manufacture of the composite material part, particularly because of the possibility of using the same heat treatment step both to form the metal matrix as well as to make the sheath of the fibers integral with the metal matrix. Obtaining parts with satisfactory mechanical properties by such a simplified process is made possible by the use of materials having particular melting temperatures to ensure effective diffusion welding as mentioned above.

The powder of the metal alloy may be present in the composition in a volume content of between 50% and 80% and the binder may be present in the composition in a volume content of between 20% and 50%.

Preferably, the following condition can be verified: | T2 - Til / Ti <15%.

The fact of verifying this inequality advantageously makes it possible to further improve the quality of the diffusion welding carried out allowing the assembly of the metal sheath of the fibers with the metal matrix and thus to further improve the mechanical properties of the parts obtained. The core of the fibers may, for example, be silicon carbide, zirconia or alumina.

Preferably, the metal sheath of the fibers and said alloy may each consist mainly of a mass of the same metal element.

In other words, it is necessary in this case to understand that the metal sheath of the fibers consists of at least 50% by weight of a chemical element X and that the metal alloy is made up of at least 50% by weight of this material. same element X.

Such an embodiment advantageously makes it possible to further improve the compatibility between the metal sheath of the fibers and the metal matrix of the part obtained.

In particular, the material forming the metal sheath of the fibers may be identical to said alloy.

In an exemplary embodiment, the metal sheath of all or part of the fibers may be in the form of a continuous layer of a metallic material.

In an exemplary embodiment, the metal sheath of all or part of the fibers may be in the form of a plurality of metal strands surrounding the core, for example helically wound around the core.

In an exemplary embodiment, the fibers may include a first set of fibers extending along a first direction and a second set of fibers extending along a second direction not parallel to the first direction.

Alternatively, all the fibers may be parallel to each other.

In an exemplary embodiment, the molding cavity may be defined between a mold and a mold-against and all or part of the fibers may extend through channels in the wall of the mold and / or counter-mold.

In an exemplary embodiment, the molding cavity may be defined between a mold and a counter-mold and all or part of the fibers may be held between the mold and the counter-mold.

In an exemplary embodiment, the composition may be injected into the molding cavity during step a). In this case, the blank is formed by carrying out a metal injection molding process.

The implementation of such a technique to form the blank advantageously makes it possible to further simplify the process insofar as it is thus possible to obtain a blank substantially having the desired ribs and consequently to reduce the duration of the blank. subsequent machining.

In an exemplary embodiment, said metal alloy is chosen from: titanium-based alloys, nickel-based alloys, cobalt-based alloys, aluminum-based alloys or steels.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will emerge from the following description of particular embodiments of the invention, given by way of non-limiting example, with reference to the appended drawings, in which: FIGS IA to IG represent different steps of an exemplary method according to the invention, - Figures 2A and 2B show the structure of the fibers used in the example method illustrated in Figures IA to IG, - Figures 3A and 3B represent a variant of fiber structure that can be implemented in the context of a method according to the invention, - Figure 4 shows a longitudinal section in plan view showing the positioning of the fibers in the molding cavity in the context of the step illustrated in FIG. 1C, FIGS. 5A to 5D illustrate steps of a variant of the method according to the invention, and FIG. 6 illustrates a detail of the assembly. lustrous in Figure 5C.

Detailed description of embodiments

FIGS. 1A to 1G show the implementation of the different steps of an exemplary method according to the invention. In Figures IA to 1D, the mold 1 and the counter-mold 2 are observed in longitudinal section. FIG. 1A shows a mold 1 and a counter mold 2 that can be used in the context of the present invention. Channels 7a and 7b are formed in the wall of the mold 1 and against the mold 3. Fibers are intended to be positioned in these channels 7a and 7b as will be detailed below. More specifically, the mold 1 and the counter mold 3 each have a plurality of pairs of channels, each of these couples comprising a first channel 7a and a second channel 7b. The first channel 7a and the second channel 7b of the same pair each extend in the same direction denoted by X1 in FIG. 1A for an example of a pair of channels.

First of all, the positioning of the fibers 10 in the channels 7a and 7b formed in the mold 1 and in the counter mold 2. In the example illustrated in FIG. 1B, each fiber 10 is positioned in the first 7a and 7b. second 7b channels of the same couple. Once positioned, the fibers 10 extend substantially rectilinearly (in a straight line). The positioning of the fibers 10 through the channels 7a and 7b will allow to maintain the latter in predefined orientations in the mold cavity. The fibers 10 may be introduced into the channels 7a and 7b by "bundles" of fibers or individually.

FIGS. 2A and 2B show the structure of the fibers 10 used. Fig. 2A is a view of a fiber 10 in cross-section and Fig. 2B is a view of this fiber 10 in longitudinal section. The fibers 10 each comprise a core of ceramic material 10a coated with a metal sheath 10b. The metallic material forming the sheath 10b may be a metal or a metal alloy. In the illustrated example, the metal sheath 10b is in the form of a continuous layer of a metallic material, for example obtained by a high-speed coating process (EGV). The core of ceramic material 10a may for example be alumina, zirconia or silicon carbide. The core 10a may for example have a diameter (greater transverse dimension) greater than or equal to 1 μm, for example between 1 μm and 140 μm. The thickness of the metal sheath 10b may, for its part, be greater than or equal to 1 μm, for example between 1 μm and 140 μm. As will be detailed below, the metal sheath is intended to form the interface between the core of the fibers 10 and the metal matrix of the piece of composite material obtained.

FIGS. 3A and 3B show a variant of fiber 10 'that can be used in the context of the method according to the invention. In this variant, the metal sheath 10'b is in the form of a plurality of metal strands 10'c surrounding the core 10'a. The metal strands 10'c can each be wound around the core 10'a. The diameter of the core 10'a and the thickness of the metal sheath 10'b may be as described above in connection with Figures 2A and 2B. In the configuration illustrated in Figures 3A and 3B, at least six metal strands 10'c can surround the core 10'a fibers 10 '.

Once the fibers are positioned, the counter-mold 2 is placed on the mold 1 and is fixed thereto as illustrated in FIG. In this configuration, the mold 1 and the counter mold 2 define the molding cavity 3 which has the shape of the blank to manufacture. The molding cavity 3 is defined between the mold 1 and the counter-mold 2. An injection point 4 is present between the mold 1 and the counter-mold 2. Due to the placement of the fibers 10 in the channels 7a and 7b these latter are maintained in a plurality of predefined orientations in the molding cavity 3 (see in particular direction Xi in FIG. 1C for an example of fiber). In other words, the fibers 10 are distributed, in the illustrated example, into several sets of fibers each extending along a different direction. The channels 7a and 7b each open into the molding cavity 3. The channels 7a and 7b are distributed along the height of the molding cavity 3. As illustrated in FIG. 4, the channels 7a and 7b are also distributed according to the width of the molding cavity 3 in the example in question. There is shown an example in which a plurality of pairs of channels 7a and 7b are present but it is not beyond the scope of the invention when only one pair of channels is present.

In the example illustrated in FIG. 1C in particular, the fibers 10 extend along the length of the molding cavity 3. In a variant that is not illustrated, it is possible, for example, for fibers to be positioned according to the width or height of the mold. the molding cavity. The present invention is not limited to a particular fiber arrangement in the molding cavity.

An injection composition 5 is injected under pressure into the molding cavity 3 in order to obtain a blank of the part to be manufactured (see FIG. 1D). The injection composition 5 comprises a powder of a metal alloy and a binder. In the example considered, a metal injection molding process is used to obtain the blank of the part to be manufactured. The metal injection molding process is a technique known per se. The metal alloy used in the injection composition 5 may, for example, be a titanium-based alloy, a nickel-based alloy, a cobalt-based alloy, an aluminum-based alloy, or an aluminum alloy. steel. Unless stated otherwise, a material said to be "based on a chemical element X" has the element X in a mass content greater than or equal to 50%.

The binder may be chosen from: paraffins, thermoplastic resins, agar gel, cellulose, polyethylene, polyethylene glycol, polypropylene, stearic acid, polyoxymethylene and mixtures thereof. The volume content of the metal alloy powder in the injection composition may for example be between 50% and 80%. The volume content of the binder in the injection composition may for example be between 20% and 50%. The injection composition 5 may first be mixed at a temperature between 150 ° C and 200 ° C in a neutral atmosphere for example, and may then be injected into the molding cavity 3 at such a temperature.

In the illustrated example, the injection composition 5 is injected into the molding cavity 3 through a single injection point 4. Of course, it is not beyond the scope of the present invention when the composition of injection is injected into the molding cavity through a plurality of injection points allowing simultaneous injection or not of the injection composition in several parts of the molding cavity. During the injection, the mold 1 and the counter-mold 2 can be regulated in temperature. The mold 1 and the counter mold 2 can, for example, be maintained at a temperature between 30 ° C and 70 ° C to promote cooling of the blank. The blank thus produced is said in a "green state" or plastic. It is advantageous to perform the injection of the injection composition 5 in a molding cavity 3 in which the vacuum has been made, in order to facilitate the injection and to ensure the homogeneity of the blank that will be formed. In a variant not shown, the composition comprising the powder of the metal alloy and the binder can be introduced by pouring into the mold cavity (introduction under the effect of gravity and not by injection).

Once the injection is made, the blank 6 is demolded as shown in Figure 1E. The fibers 10 may extend from a first end 16a of the blank 6 to a second end 16b of the blank located on the opposite side to the first end 16a. The fibers 10 present in the blank 6 may have zones of over-lengths 11 and 12 extending beyond the blank 6. In the example illustrated, the zones of over-lengths 11 and 12 extend from opposite ends 16a and 16b of the blank 6. In general, the fibers 10 are positioned along the mechanical stress axes of the part to be obtained. The blank is then machined in the green state to remove the over-length zones 11 and 12, the burrs and the core (s) of the injection point (s) (step b)). After completion of this machining operation, a preform 7 is obtained from the part to be manufactured (see FIG. 1F). This preform 7 comprises at least the powder of the metal alloy, the binder and the fibers. The powder of the metal alloy may, for example, have a grain size D90 less than or equal to 150 μm (i.e. in this case at least 90% of the grains of the powder have a size less than or equal to 150 μm).

As mentioned above, the metal alloy and the material constituting the fiber sheath are not chosen arbitrarily. Indeed, the melting temperature Ti of said alloy and the melting temperature T2 of the metal sheath of the fibers satisfy the following condition: | T2 - Til / Ti <25%. The verification of this inequality concerning the relative difference between T2 and Ti advantageously makes it possible to ensure good diffusion bonding of the metal sheath of the fibers with the metal matrix formed from the powder of the metal alloy and, consequently, to optimize the mechanical properties of the part obtained.

Advantageously, the following combinations can be implemented: nickel-based metal alloy and metal sheath of nickel-based fibers, iron-based metal alloy and metallic sheath of iron-based fibers, metal alloy based on of titanium and metallic sheath of titanium-based fibers, - cobalt-based metal alloy and metallic sheath of cobalt-based fibers, - iron-based metallic alloy and metallic sheath of nickel-based fibers, - metallic alloy with nickel base and metallic sheath of iron-based fibers, - cobalt-based metal alloy and metal sheath of nickel-based fibers, - nickel-based metal alloy and metallic sheath of cobalt-based fibers.

Some examples of possible combinations that can be implemented in the context of the invention are given below: metal sheath of TiAl 48-2-2 fibers with metal alloy in TiAl 48-2-2, metallic sheath Ta6V fibers with metal alloy in TiAI 48-2-2, metallic sheath of titanium fibers T40 with metal alloy in TiAI 48-2-2, metallic sheath of Inconel® 718 fibers with metal alloy in Inconel® 718 - Inconel® 625 metal fiber sheath with Inconel® 718 metal alloy, - Nickel fiber metal sheath with Inconel® 718 metal alloy, - Nickel fiber metal sheath with 304L stainless steel metal alloy, - Metallic sheath 304L stainless steel fiber with 304L stainless steel metal alloy, - 316L stainless steel fiber sheath with 304L stainless steel metal alloy.

Preferably, the metal alloy and the metal sheath of the fibers may each be based on the same metal element. In particular, the material constituting the metal sheath of the fibers may be identical to the material constituting the metal alloy.

The preform obtained after implementation of step b) is then debinding (step c)). During debinding, there is selective removal of the binder present in the preform. It is possible to perform during step c) a chemical debinding of the preform during which it is brought into contact with one or more solvents for solubilizing all or part of the binder. Alternatively or in combination, it is possible to perform during step c) thermal debinding. In this case, thermal debinding can be performed in a sintering chamber so as not to have to move the preform between step c) and step d). Thermal debinding can be performed after implementation of chemical debinding. The conditions for debinding used in the context of the present invention are known per se.

A step d) of heat treatment of the debonded preform is then carried out in order to obtain the piece 15 made of metal matrix composite material 14 (see FIG. During step d), the metal sheath of the fibers is assembled with the powder of the metal alloy by diffusion bonding and the powder of the metal alloy is sintered to form the metal matrix. It is possible, for example, during step d) to impose on the debinding preform a treatment temperature greater than or equal to 1200 ° C., for example between 1250 ° C. and 1350 ° C. The duration during which this treatment temperature is imposed may for example be greater than or equal to 120 minutes, for example between 120 minutes and 180 minutes. Step d) makes it possible to densify the powder of the metal alloy and to create bonds between the metal sheaths of the fibers and the metal matrix. As explained above, the fact of introducing sheathed fibers with a material compatible with the metal matrix makes it possible to improve the cohesion of the fibers with the metal matrix, thus optimizing the mechanical behavior of the part obtained.

The part intended to be formed in the context of the process of the invention may for example be a turbomachine blade. As a variant, said part may have an axisymmetric shape and for example constitute a turbine ring, segmented or not.

FIGS. 5A to 5D show steps of an alternative embodiment of a method according to the invention. FIG. 5A (seen from above) and FIG. 5B (longitudinal sectional view) show a set of fibers 10 positioned on a mold 25. The fibers 10 are positioned on two lateral walls 31 and 32 of the mold 25 As illustrated, each of the side walls 31 and 32 has openings 31a and 32a. Once the fibers have been positioned in this way, the counter-mold 26 is placed on the mold 25. The counter mold 26 has two side walls 35 and 36. The side walls 35 and 36 also have openings 35a and 36a. As illustrated, the side walls 35 and 36 of the counter-mold 26 each have a plurality of teeth 39 between which the fibers 10 are accommodated and thus making it possible to keep the fibers 10 in the desired orientation (see FIG. in section at the side walls 31 and 35). In this embodiment, the fibers 10 are held between the mold 25 and against the mold 26 and are parallel to each other. The fibers are in this embodiment maintained in a predefined orientation corresponding to the direction X2 here oriented along the length of the molding cavity (see Figure 5C).

The openings 35a and 36a are positioned opposite openings 31a and 32a. The counter mold 26 is then fixed to the mold 25 by fastening elements 41 and 42 in the form of screw-nut systems in the example shown (see Figure 5D). The process is then continued in a manner similar to that described above by injecting an injection composition through the injection orifices 40, machining, debinding and sintering.

Example

Firstly, a mixture of a metal powder and a binder is produced. This mixture is composed of 60% by volume of a metal powder of the Ta6V alloy and 40% by volume of a mixture of polyethylene glycol, polyethylene and polypropylene constituting the binder. The size D90 of the Ta6V metal powder used was less than 35 μm and this powder was obtained by atomization under argon.

Fibers were positioned in a mold and a counter-mold to obtain a structure similar to that shown in Figure 1C. The fibers used consisted of a central core of silicon carbide 80 microns in diameter and a pure titanium sheath (99% titanium content in the sheath greater than 99%) of a thickness of 10 microns. The titanium sheath was deposited on the ceramic cores by high speed coating. The fibers were positioned in a number to obtain a volume fraction of 1% of fibers (10 fibers per 100 mm 2 section).

A blank was obtained by injection into the mold cavity of the mixture of Ta6V powder and binder. The injection temperature of the mixture was of the order of 190 ° C and the molds were cooled to about 50 ° C. The mold was then opened to extract the resulting blank, the over-length areas of the fibers were cut, the blank was deburred and the injection cores were removed to obtain a preform of the blank. piece to get.

The preform then underwent a first chemical debinding step by immersion in a demineralized water bath while stirring the bath. The bath temperature was 60 ° C. and this debinding step was carried out for 24 hours.

Once debinding with demineralised water carried out, the partially debonded preform was placed on a zirconia plate and introduced into an oven in order to undergo a heat treatment to heat finalize debinding. The heat treatment was then continued in order to sinter the powder of the metal alloy in order to form the matrix of the part as well as to secure the metal sheath of the fibers to said matrix. An argon atmosphere at 20 mbar pressure was imposed during this heat treatment. The heat treatment carried out had the following characteristics: - passage from 20 ° C to 200 ° C with a ramp at 5 ° C / minute, - passage from 200 ° C to 350 ° C with a ramp at 2 ° C / minute and 1 hour holding at 350 ° C, - passage from 350 ° C to 470 ° C with a ramp at 2 ° C / minute and 1 hour of maintenance at 470 ° C, - passage from 470 ° C to 1250 ° C with a ramp to 5 ° C / minute and 3 hours of holding at 1250 ° C, - passage from 1250 ° C to 80 ° C with a cooling ramp at 10 ° C / minute.

Once this heat treatment has been performed, the part obtained has been removed from the oven. The part can then possibly be machined to adjust its shape and dimensions to the desired application. The expression "understood between ... and ..." or "from ... to ..." must be understood as including the boundaries.

Claims (12)

A method of manufacturing a composite material part (15) comprising a fibrous reinforcement densified by a metal matrix (14), the method comprising at least the following steps: a) introducing a composition (5) comprising at least a powder of a metal alloy and a binder in a molding cavity in which a plurality of fibers are present to obtain a blank (6) of the workpiece, the fibers comprising a core (10a, 10'a) of ceramic material coated with a metal sheath (10b; 10'b) and being held in at least one predefined orientation (Xi; X2) in the molding cavity (3; 30), the melting temperature Ti of said alloy and the temperature T2 melting of the metal sheath of the fibers satisfying the following condition: | T2 - Til / Ti <25%, b) machining of the blank (6) to obtain a preform (7) of the part to be manufactured, c ) removing the binder present in the preform (7) in order to obtain a debinding preform, and d) heat treatment of the debonded preform in order to obtain the composite material part (15) during which the metallic sheath of the fibers is assembled with the powder of the metal alloy by diffusion bonding and during which the powder of the metal alloy is sintered to form the metal matrix (14). The method of claim 1, wherein the following condition is satisfied: T2-Ti | / Ti <15%. 3. Method according to any one of claims 1 or 2, wherein the metal sheath (10b; 10'b) of the fibers (10; 100 and said alloy are each constituted mainly by mass of the same metal element. 4. The method of claim 3, wherein the material forming the metal sheath (10b; 10'b) of the fibers (10; 100 is identical to said alloy. 5. Method according to any one of claims 1 to 4, wherein the metal sheath (10b) of all or part of the fibers (10) is in the form of a continuous layer of a metallic material. 6. A method according to any one of claims 1 to 5, wherein the metal sheath (10'b) of all or part of the fibers (100 is in the form of a plurality of metal strands (10'c) surrounding the soul (10'a). The method of any one of claims 1 to 6, wherein the fibers comprise a first set of fibers extending along a first direction and a second set of fibers extending along a second direction. not parallel to the first direction. 8. A process according to any one of claims 1 to 6, wherein all the fibers are parallel to each other. Method according to any one of claims 1 to 8, wherein the molding cavity (3) is defined between a mold (1) and a counter-mold (2) and in which all or part of the fibers (10) extend through channels (7a; 7b) formed in the wall of the mold (1) and / or counter-mold (2). Method according to any one of claims 1 to 9, wherein the molding cavity (3) is defined between a mold (1) and a counter-mold (2) and wherein all or part of the fibers (10) are held between the mold (25) and the counter mold (26). 11. A method according to any one of claims 1 to 10, wherein the composition (5) is injected into the molding cavity (3; 30) in step a). The method according to any one of claims 1 to 11, wherein said metal alloy is selected from: titanium-based alloys, nickel-based alloys, cobalt-based alloys, alloys based on aluminum or steels.