EP2245204B1 - Method for making parts with an insert made of a metal-matrix composite material - Google Patents

Abstract

The invention relates to a method for making a metal part that comprises a reinforcement (15) made of ceramic fibres. The method comprises the following steps: forming at least one annular-shaped insert (15) by assembling a bundle of metal-coated fibres; placing the insert into a hollow metal mould (10) such that the insert is spaced between the walls (10a, 10b) of the mould; filling the mould with a metal powder; generating vacuum in the mould and closing the same; hot isostatic compressing the assembly at a temperature and under a pressure sufficient for binding the powder particles between them and for binding the insert fibres between them; removing the mould and optionally machining to the desired shape.

Description

The present invention relates to a method of manufacturing a metal part having a reinforcement of metal matrix composite material of the ceramic fiber type in a metal matrix.

In the field of aeronautics in particular we seek to achieve parts with optimal mechanical properties for a mass as low as possible. For this purpose is incorporated in some parts an insert made of composite material with a metal matrix. This material comprises ceramic fibers, of silicon carbide for example, embedded in a metal matrix, such as a titanium alloy. Ceramic fibers have the property of a very high tensile strength and compression greater than the metal. The metal matrix provides a binder function with the part as well as protection and insulation of the fibers.

A known method of manufacturing such parts with reinforcement comprises producing a coil of wire coated around a mandrel. The coil is then incorporated in a container or metal main body in which a groove forming a housing has been previously machined. The depth of the groove is greater than the height of the winding. A lid is placed on the container and welded to its periphery. The cover has a post complementary shape to that of the groove, and its height is adapted to that of the coil placed in the groove so as to fill the groove. A hot isostatic pressing step is then carried out during which the winding is compacted by the tenon. The metallic sheaths of the coated wires are welded together and with the walls of the groove by diffusion to form a dense set composed of metal alloy in which the ceramic fibers extend annularly. The resulting part is then machined to the desired shape.

In order to simplify the manufacture of such a part, and instead of manufacturing the insert separately and then to transfer it into the groove of the main body, the patent FR 2886290 on behalf of Snecma proposes to carry out the winding directly on the main body. Instead of a groove, there are two shoulders in it. The first has a bearing surface for the direct winding of a coated wire. This surface is parallel to the winding direction. When the winding is completed, the groove is reconstructed by placing a piece on the main body which is shaped complementary to that of a second shoulder forming a step relative to the first shoulder. Then we have the cover with the pin on the insert that has just wound and compacts the whole.

The manufacturing techniques reported above involve precise machining of the housing and after completion of the part blank with compression of the insert and welding of the elements together, a machining operation to obtain the part. These operations thus imply not only a machining of a large amount of material but also delicate machining to carry out. For these reasons the manufacturing cost of this type of part is important and it is desirable to reduce it as much as possible.

The present invention therefore aims to improve the manufacture of a part with a reinforcement of this type so as to reduce the cost.

The steps of the process according to the invention are set forth in claim 1.

By using powder technology according to a hot isostatic pressing technique, parts can be produced directly: having both high dimensional accuracy, high mechanical performance, and excellent metallurgical homogeneity. In addition, the geometry of the piece resulting from the process can be chosen so that it is closer to the final piece, requiring no or little machining operation.

The method allows the use of one or more inserts of various shapes depending on the shape of the piece and the desired reinforcement. Each insert can thus be annular. It may be more particularly axisymmetric or have at least one rectilinear portion. When the insert is rectilinear, in the form of a straight segment, it has preferably been formed from coated yarns subjected to hot isostatic compression treatment together.

When at least two inserts are available in the mold; these can be superimposed. The arrangement is a function of the structure of the part to be manufactured and the expected mechanical properties.

In order to limit the machining operations on the blank obtained, pads are provided inside the mold which reduce the volume to be filled by the metal powder in the areas where the material will be removed by machining. These studs delimit cavities in said metal part between the reinforced zones: by the ceramic fibers.

The patent is known EP 1,669,144 which relates to the manufacture of a metal article, such as a hollow fan blade with an internal reinforcement by powder metallurgy as well. However, the process involves the production of a preform: then the shaping of the latter to make the hollow article. Such a method is not suitable for the implementation of the invention.

We know the document GB 2.280.909 which relates to the manufacture of a metal part comprising reinforcements of ceramic fibers. The coated metal fibers are wound on a support. The whole is covered with a sheet and the whole is subjected to hot isostatic compression. However, such a technique does not allow the manufacture of parts from a hollow mold in which there is a prefabricated insert. The two documents EP 997.549 and DE 4,335,557 do not disclose the formation of an insert from a plurality of fibers.

• La figure 1 représente un conteneur de l'art antérieur pour la réalisation d'une pièce de forme allongée et avec un insert en matériau composite à matrice céramique,
• La figure 2 représente vu de dessus un moule pour la réalisation de pièces conformément à l'invention sans son couvercle.
• La figure 3 représente vu de côté en coupe longitudinale le moule de la figure 2.
• La figure 4 représente vu de côté en coupe longitudinale un autre mode de support de l'insert dans le moule.
• La figure 5 représente vu de côté en coupe longitudinale une variante de moule pour l'obtention d'une pièce possédant plus de matière.
• La figure 6 représente la pièce obtenue dans un moule du type de la figure 5 vue en transparence et avec une partie arrachée.
• La figure 7 représente vu de côté en coupe longitudinale une autre variante de moule pour l'obtention d'une pièce symétrique.
• La figure 8 représente la pièce obtenue dans un moule du type de la figure 7, vue en transparence et avec une partie arrachée.
• La figure 9 représente la pièce obtenue dans un moule du type de celui des figures 2, 3, 4 et 5, vue en transparence.

Other features and advantages of the invention will emerge from reading the following description with reference to the accompanying drawings in which:

• The figure 1 represents a container of the prior art for producing an elongated piece and with an insert made of a ceramic matrix composite material,
• The figure 2 is seen from above a mold for producing parts according to the invention without its cover.
• The figure 3 is seen from the side in longitudinal section the mold of the figure 2 .
• The figure 4 is seen from side in longitudinal section another way of supporting the insert in the mold.
• The figure 5 is a side view in longitudinal section of a mold variant for obtaining a part having more material.
• The figure 6 represents the piece obtained in a mold of the type of the figure 5 seen in transparency and with part torn off.
• The figure 7 is seen from side in longitudinal section another mold variant for obtaining a symmetrical part.
• The figure 8 represents the piece obtained in a mold of the type of the figure 7 , seen in transparency and with part torn off.
• The figure 9 represents the part obtained in a mold of the type of Figures 2, 3 , 4 and 5 , seen in transparency.

Referring to the figure 1 , there is shown a container 4 of the prior art, of elongate shape, for producing a piece with a metal matrix composite insert. A groove 41 has been machined in the container to receive an insert 3. The groove and the insert are of complementary shape so that the insert is fit without play in the groove. A cover 5 covers the assembly and has a projecting surface not visible in the figure to form a bearing on the insert in the groove. The assembly is evacuated, the lid is electron beam welded for example. Then the assembly is placed in a suitable chamber where it is carried out isostatic hot pressing by subjecting it to a high pressure and a high temperature (1000 ° C and 1000 bar). The manufacturing techniques with an insert comprising at least one rectilinear portion are described in the patent applications FR 07/05453 and FR 07/05454 of July 26, 2007 in the name of the plaintiff.

The blank thus produced is then machined to obtain the desired shape. As shown in the above patent applications, parts having complex shapes such as aircraft landing gear elements can be obtained.

The solution of the invention makes it possible to obtain such parts more economically.

On the one hand, a steel mold is prepared with a hollow shape close to that of the part to be manufactured.

The Figures 2 and 3 show such a mold 10 for producing a generally elongate piece. This mold is hollow with a flat bottom 10a and a wall 10b of determined thickness and height corresponding to the thickness of the finished part. It comprises studs 11, 12 and 13 inside the cavity. According to the example of this figure the pads are at a height that allows them to come into contact with a lid 14 closing the mold. The height may however be less as shown on the figure 5 .

An insert 15 is placed in the mold. This insert here comprises two rectilinear portions between two half-circle portions. In the case of this type of insert, the straight portions may be parallel or not and the semicircular portions may be of the same diameter or not.

The insert is made, without limitation, according to one of the methods taught by the FR 2886290 . This includes the structure of the coated yarns, their manufacture, the manufacture of a bonded ply of coated yarns, the joining of this ply either to the metal support on which it is wound or to the lower ply, the welding of yarns by laser or by contact between two electrodes. Insofar as the insert comprises at least one rectilinear portion, it is more particularly made according to one of the methods presented in the FR 07/05453 or FR 07/05454 of July 26, 2007 in the name of the plaintiff. Thus the insert can be obtained from a plurality of coated wires each comprising a ceramic fiber coated with a metal sheath with a winding step around a part of revolution, a part of the winding being effected in one direction. straight. In the case where the insert forms a rectilinear segment, it can be obtained from an insert blank with a rectilinear portion which is compacted and then cut into straight segments.

The insert is positioned inside the cavity being spaced apart from the walls of the mold. One way to hold the insert in the mold is to arrange it on a support 16 which, if necessary, is of width corresponding to that of the insert and over the entire length of the latter or on pawns distributed under the insert. This support is preferably in the same metal as the powder.

According to a variant, the support may consist of a L-shaped section piece 16 'as shown in FIG. figure 4 . In this case, the support is advantageously constituted by the mandrel on which the coated wire has been wound to form the insert as described in the patent. FR2886920 which is not part of this invention.

The mold is filled with metal powder 18. In this type of application the metal may be a titanium alloy such as TA6V alloy or a nickel alloy such as the unknown 625 or a stainless steel. It is an alloy in a granulometric form suitable for use in powder metallurgy.

The powder can be introduced into the mold in part before the introduction of the insert, with pre-compaction if necessary. Then the mold is filled.

The lid 14 is placed on the mold thus filled and the cavity is evacuated. The enclosure is finally sealed tightly by welding.

The mold thus prepared is placed in a hot isostatic compression chamber. The chamber thus makes it possible to maintain the workpiece at a temperature of 1000 ° C. and a pressure of 1000 bars for several hours. Under these conditions the mold is deformed due to the volume reduction between 20 and 25% of both the insert and the powder.

After this operation, the powder is completely densified and no porosity remains. All the parts in contact are welded by soldering diffusion. The coated wires are welded together forming a matrix within which the ceramic fibers are contained. The metal constituting the matrix of the insert is the same as that constituting the powder. It may be distinct, however.

The mold is then removed by selective acid or mechanical dissolution. If necessary, the workpiece is machined to obtain the desired shape.

This method makes it possible to vary the production of the parts. In the example above, the studs extend over the entire height of the mold cavity. A minimum of material was used. We obtain a part 20, such as that represented in figure 9 with openings 21, 22, and 23 through. The integrated insert 15 in the mass is visible by transparency.

We have shown on the figure 9 an example of a piece that can be made by implementing the invention. Its cost of production is reduced by about 30% compared to a technique involving machining after hot compression.

In the example of the figure 5 , the pads 51, 52, 53 of the mold 50 extend only in part over the height of the mold cavity. We obtain a piece 50 'with lightened parts 51' 52 '53' but no through opening as seen on the figure 6 . The insert is visible by transparency in the figure

In the example of the figure 7 a mold 70 and its associated cover 71 are used which have symmetrical pads 72, 73 with respect to a median wall 74. The molding 70 'of the figure 8 is symmetrical.

Claims (9)

1. Method for manufacturing a metal part (20; 50'; 70') which is reinforced by ceramic fibres, comprising the following successive steps:

   - formation of at least one insert (15) by assembling metal-coated ceramic fibres into a bundle;

   - introduction of the insert (15) into a hollow metal mould (10; 50; 70) in such a way that the insert (15) is arranged inside the cavity at a distance from the walls (10a, 10b) of the mould;

   - filling of the mould (10; 50; 70) with a metal powder (18);

   - positioning of a lid which closes the mould;

   - creation of a vacuum inside the chamber and tight closure of the mould (10; 50; 70) by welding;

   - hot isostatic pressing of the assembly at a temperature and a pressure that are sufficient to bond the powder particles and the coated fibres of the insert (15);

   - removal of the mould (10; 50; 70) and optionally machining to the desired shape.
2. Method according to the preceding claim, wherein the insert (15) is annular in shape, in particular axisymmetric in shape.
3. Method according to claim 1, wherein the insert (15) has at least one straight portion.
4. Method according to claim 1, wherein the insert (15) is straight and formed from coated threads jointly subjected to a hot isostatic pressing treatment.
5. Method according to any one of the preceding claims, wherein the insert (15) is arranged inside the mould (10) by means of a support (16, 16').
6. Method according to the preceding claim, wherein the support (16) is the mandrel for winding the insert.
7. Method according to any one of the preceding claims, wherein at least two inserts are arranged inside the mould.
8. Method according to the preceding claim, wherein the two inserts are arranged in such a way that they are superposed.
9. Method according to any one of the preceding claims, wherein projections (11, 12, 13; 51, 52, 53; 72, 73) are provided inside the mould (10, 50, 70), the projections defining the cavities in said metal part between the zones reinforced by the ceramic fibres.

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