EP1858663A2

EP1858663A2 - Improved method for preparing metal-matrix composite and device for implementing said method

Info

Publication number: EP1858663A2
Application number: EP06726090A
Authority: EP
Inventors: Jacques Tschofen
Original assignee: Forges de Bologne
Current assignee: Forges de Bologne
Priority date: 2005-03-14
Filing date: 2006-03-14
Publication date: 2007-11-28
Also published as: WO2006097622A3; BRPI0609329B1; KR20070119016A; WO2006097622A8; UA90300C2; FR2882948A1; US20080310989A1; JP5243235B2; HK1117791A1; BRPI0609329A2; MX2007011128A; ZA200707675B; KR101366721B1; RU2449035C2; CA2600274C; JP2008533303A; FR2882948B1; CA2600274A1; WO2006097622A2; CN101142045B

Abstract

The invention mainly concerns a method for preparing metal-matrix composites including at least steps of cold-process isostatic compaction of previously mixed powders (5) and of hot-process uniaxial pressing of the compact (12) resulting from the previous step. The inventive method enables metal-matrix composites with improved properties to be obtained. The invention also concerns a device for implementing in particular the isostatic compaction step comprising a latex sheath (1) wherein the mixture of powders (5) is poured, a perforated cylindrical container (2) wherein is arranged the latex sheath (1), and means (7, 10, 11) for sealed insulation of the mixture of powders (2) contained in the sheath (1).

Description

"Improved process for preparing metal matrix composites and apparatus for carrying out such a method"

The present invention relates to a method for preparing Metallic Matrix Composites (CMMs).

The invention also relates to a device for implementing such a method. The CMMs can be aluminum alloys reinforced by particles such as, for example, particles of silicon carbide, boron carbide, alumina, or any other ceramic material.

CMMs are mainly used for the manufacture of metal parts in the field of aeronautics such as rotor parts for helicopters.

The coining of the CMM parts is performed from billets of several tens of kilograms which are obtained by compaction of previously mixed powders.

In some known processes, the main compaction step is performed by uniaxial pressing leading to the formation of strata in the billets which is disadvantageous for the mechanical properties of the metal parts obtained from these billets.

Indeed, it is necessary that each billet has a distribution as homogeneous as possible of the constituent elements, including reinforcing particles, so that the parts manufactured from these billets have the required mechanical properties.

Finally, the simplicity of a process of a CMM manufacturing process is necessary to limit the production costs of these CMMs. The method of the invention overcomes the aforementioned drawbacks and is essentially characterized in that it comprises at least the steps of: (a) cold isostatic compaction of previously mixed powders 5, and

(b) hot uniaxial pressing of the compact 12 obtained in step (a).

These two steps make it possible to lower the cost of a CMM with improved mechanical properties.

Advantageously, the powders are dry blended in a suitable mixer subjected to a pressurized gas comprising a neutral gas and oxygen.

The dry powder mixture has the advantage of being more economical than a wet mixing process and the presence of a neutral gas makes it possible to avoid the risks of explosion present during dry mixing.

Preferably, the pressure in the mixer is between 15 and 25 mbar, the neutral gas is nitrogen and the oxygen level is controlled and between 5 and 10%.

The control of the oxygen level makes it possible to limit even more the risks of explosion.

More preferably, the pressure in the mixer is 20 mbar and the oxygen level is 6%.

Preferably, the powder mixture is composed of an aluminum alloy reinforced with particles such as, for example, particles of silicon carbide, boron carbide, alumina, or any other ceramic material.

More preferably, the powder mixture comprises 94.7% by weight of aluminum, 4% by weight of copper, 1.3% by weight of magnesium and 15% by volume of silicon carbide. In addition, the powder mixture 5 undergoes a vibrating table pressing operation prior to step (a) of isostatic compaction. Also prior to step (a) of isostatic compaction, the gas contained in the mixture of packed powders 5 can be pumped out in order to obtain a solid compact 12. During the compaction step, the compaction fluid Advantageously, it comprises water and lubricating additives.

Preferably, the pressure of the compaction fluid 15 is between 1500 and 4000 Bars and more preferably the pressure is 2000 Bars.

It is also possible that the compact obtained in step (a) undergoes a degassing operation at a temperature between 100 and 450 ⁰ C, preferably 44O ⁰ C. Preferably, the step (b) uniaxial pressing to The heating is carried out at a temperature of between 400 and 600 ^° C., preferably at a temperature of 450 ^° C., and at an applied pressure of between 1000 and 3000 bar, preferably of 1800 bar. Advantageously, the billet 22 obtained in step (b) is extruded while hot.

Most advantageously, the aluminum matrix composites are reinforced with particles of silicon carbide or any other ceramic particles such as boron carbide or alumina.

The invention also relates to the billet 22 obtained by the method described above.

The invention further relates to a device for implementing step (a) of the method described above comprising:

a latex sheath 1 into which the mixture of powders 5 is poured,

a perforated cylindrical container 2 in which the latex sheath 1 is disposed, and hermetic insulation means 7, 10, 11 of the powder mixture contained in the sheath 1, in which the sheath 1, the perforated container 2 and the hermetic insulating means 7, 10, 11 form a device for the isostatic compaction 14 which is adapted to be placed in the compaction liquid 15 of the isostatic press to undergo the step (a) of isostatic compaction.

Advantageously, the hermetic insulation means 7, 10, 11 comprise at least one plug 7 made of an elastically deformable material force-fitted into the sheath 1.

Very advantageously, the hermetic insulation means 7, 10, 11 comprise the upper edge 10 of the sheath 1 which is folded towards the bottom of the sheath 1 forming an annular rim 11 resiliently bearing against the outer face 13a of the side wall 13 of the perforated container 2.

Preferably, the sheath 1 and the perforated container 2 are, prior to the step (a) of isostatic compaction, removably arranged in a cylindrical container 3.

In this case, the upper edge 10 of the sheath 1 is folded towards the bottom of the sheath 1 and elastically bears against the outer face 12a of the side wall 12 of the cylindrical container 3. Furthermore, the device of the invention may comprise means 7a for making a vacuum draw in the sheath 1 so that the gas contained in the powder mixture 5 is evacuated prior to the step

(a) isostatic compaction. The invention will be better understood and other objects, advantages and characteristics thereof will appear more clearly on reading the description which follows and which is made with reference to the accompanying drawings which show non-limiting examples of embodiment of the device. invention and in which: FIG. 1 is an exploded perspective view of the device of the invention allowing the evacuation of residual gases prior to step a) of isostatic compaction; Figure 2 is a sectional view along the line II -II of Figure 1 of the device of Figure 1 assembled; Figure 3 is an identical view of the device of Figure 2 without the container and thus disposed in the isostatic press; Figure 4 is a view of the device during the degassing step; and Figure 5 is a sectional view of the uniaxial pressing device.

The exemplary embodiment presented hereinafter adapts, without limitation, to the preparation of aluminum matrix composites reinforced with silicon carbide particles.

A mixture of pre-alloyed powders composed of 94.7% by weight of aluminum, 4% by weight of copper, 1.3% by weight of magnesium and 15% by volume of silicon carbide is dry blended in a grinder. chicken or in a conventional mixer of powders.

In order to avoid any risk of explosion during the mixing of the powders, the surrounding atmosphere comprises a neutral gas such as nitrogen at a pressure of between 15 and 25 mbar, preferably 20 mbar, as well as oxygen at a rate of between 5 and 10%, preferably 6%.

Referring to Figures 1 and 2, a latex sheath 1 is disposed in a perforated container 2 so as to leave free space between the bottom of the sheath 1 and the bottom of the perforated container 2.

The latex sheath 1 and the perforated container 2 are placed in a container 3 having a mouth 4 traversed by a channel 4a opening into the container 3, said channel 4a being intended to be connected to a vacuum pump via a pipe not shown. After sealing the device by suitable means (not shown), a slight vacuum draw is performed at the mouth 4 so that the latex sheath 1 comes to press against the walls of the perforated container 2 by defining a volume of largest possible capacity.

After having stopped the vacuum sealing of the channel 4a, the mixture of powders 5 above is poured into the sheath 1 and simultaneously packed in this sheath 1 with a vibrating table not shown.

In order to obtain an optimal seal for the following operations, the upper part 10 of the sheath 1 is arranged to protrude from the container 3 while being folded towards the bottom of the sheath 1 to form an annular edge 11 resiliently bearing against the outer face 12a of the side wall 12 of the container 3.

An approximately cylindrical nitrile plug 7 is force-fitted into the sheath 1 leaving the annular edge 11 protruding as previously described.

The arrangement of the nitrile plug 7 and that of the annular edge 11 of the sheath 1 make it possible to obtain a totally sealed system.

The nitrile plug 7 comprises a central bore 7a intended to be connected to a vacuum pump via a not shown pipe.

A vacuum draw is performed until the powder mixture 5 becomes a solid compact 12, then the vacuum is stopped by closing the channel 7a by a shutter 7b.

A filter 6, fixed on the inner face 9 of the cap

7 and in contact with the compacted powder mixture 5, prevents the dust from the powder mixture 5 to pass into the vacuum system during the draw.

With reference to FIG. 3, the device assembly for isostatic compaction 14 constituted by the compact 12, the sheath 1, the pierced container 2 and the plug 7 are extracted from the container 3, the seal being retained by the elasticity of the sheath 1 allowing, simultaneously with the extraction of the device 14 from the container 3 , that the annular edge 11 is pressed against the external face 13a of the side wall 13 of the perforated container 2.

This device 14 is immersed in the compaction liquid 15 of an isostatic press 16 comprising water and lubricating additives and is thus subjected to the cold isostatic compaction operation by applying a pressure of between 1500 and 4000. Bars preferably 2000 Bars.

The rate of rise in pressure during this step is between 20 and 50 bar per minute and the holding time at the aforementioned maximum pressure is at least one minute.

In this way, the forces exerted on the compact 12 are on its entire surface which allows to obtain uniform compaction without formation of strata or other material discontinuity.

The compact 12 obtained after the isostatic compaction operation has a density of about 85%. After this operation, the sheath 1 is extracted from the perforated container 2 and the outside of the sheath 1 and the stopper 7 are thoroughly cleaned in order to avoid any contact between the compaction liquid 15 and the compact 12. Then, the sheath 1 and the plug 7 are removed and the residues of the filter 9 are, if necessary, removed by grinding or polishing the upper part of the compact 12.

With reference to FIG. 4, the compact 12 is then placed in an aluminum tubular container 17 having a bottom wall 18. The container 17 is sealed by welding an opposite aluminum top wall 19 having an orifice 20 in which is welded a tube 21 intended to be connected to a vacuum pump. A vacuum draw is performed for about 30 minutes after checking the tightness of the aluminum container 17 and, while continuing to pump, the container 17 is placed in an oven at about 440 ⁰ C for about 12 hours for undergo a degassing operation.

As a result of this last operation, the tube 21 is closed at about 10-20 cm from the upper wall 19.

The aluminum container 17 containing the compact 12 is then rapidly placed in a tool 23 preheated to a temperature above 300 ^° C., preferably between 400 and 600 ^° C., advantageously at 450 ^° C., so that the compact 12 does not cool after the degassing step.

The aforesaid temperature is maintained throughout the duration of the uniaxial hot pressing operation.

The tooling 23 comprises a central cylindrical bore 24 of diameter approximately equal to the diameter of the container 17 so as to be able to insert the container 17 in the said bore 24. The container 17 rests on a die ejector forming part 25, for reasons explained after that which is firmly and removably attached to the inner face 26 of the central bore 24.

A punch 27 then applies a pressure of between 1000 and 3000 Bars, preferably 1800 Bars on the container 22 in the vertical direction indicated by the arrow 28 until the punch 27 no longer moves, the pressure reached being then held for about a minute. Applying vertical pressure allows the die to be centered relative to this pressure. After the uniaxial pressing operation, the punch 27 is removed and the billet 22, consisting of the compact 12 in the aluminum container 17 after the uniaxial pressing operation, is ejected from the tool 23 by an ejector 29 disposed on the side opposite the punch 27 by applying pressure in the direction of the arrow 20.

The ejection of the billet 22 from the top of the tooling is made possible by the movable die ejector 25 which slides in the central bore 24. A mechanical peeling is then performed in order to remove the aluminum layer of the container around the billet 22.

After the uniaxial pressing operation, a billet 22 of 100% density is obtained. This billet 22 is hot-extruded at a temperature of about 400 ^° C. in order to give it better cohesion and optimum mechanical properties.

The billet 22 can then be machined to produce a metal part of any form by forging, machining or any other known technique.

By the method used, the silicon carbide particles are uniformly distributed in the resulting billet which thus has improved mechanical properties.

The properties of the metal matrix composite thus obtained depend on the nature of the aluminum matrix, the degree of particle reinforcement and the heat treatment performed on the product. The breaking strength is typically greater than 500 MPa and the Young's modulus is between 95 and 130 GPa for a reinforcement ratio varying between 15 and 40% by volume.

The fatigue limit stress at 10 ⁷ cycles is between 250 and 350 MPa, which has the consequence that the mechanical parts produced from this CMM produced according to the method described above can have a lifetime multiplied by 10 compared to conventional materials.

Claims

A process for preparing metal matrix composites comprising at least one step of dry blending aluminum based alloy powders in a suitable blender subjected to a pressurized gas comprising a neutral gas and oxygen.

2. Method according to claim 1, characterized in that it further comprises the steps of: (a) cold isostatic compaction of the previously mixed powders (5), and

(b) hot uniaxial pressing of the compact (12) obtained in step (a).

A process according to any one of claims 1 to 2, wherein the pressure in the mixer is between 15 and 25 mbar, wherein the neutral gas is nitrogen and wherein the oxygen level is controlled and between 5 and 10%.

4. The method of claim 3, wherein the pressure in the mixer is 20 mbar and wherein the oxygen level is 6%.

5. Method according to any one of the preceding claims wherein the powder mixture undergoes a vibrating table tamping operation prior to step (a) of isostatic compaction.

6. Process according to any one of the preceding claims, in which, prior to step (a) of isostatic compaction, the gas contained in the mixture of packed powders (5) is evacuated by pumping in order to obtain a solid compact ( 12).

The method of any one of the preceding claims wherein the compaction fluid (15) comprises water and lubricating additives.

The method of any one of the preceding claims wherein the pressure of the compaction fluid (15) is between 1500 and 4000 Bars.

9. The method of claim 5 wherein the pressure of the compaction fluid (15) is 2000 Bars.

10. Method according to any one of the preceding claims wherein the compact obtained in step (a) undergoes a degassing operation at a temperature between 100 and 450 ⁰ C, preferably 44O ⁰ C.

11. A method according to any one of the preceding claims wherein the uniaxial hot pressing operation is carried out at a temperature between 400 and 600 ⁰ C and wherein the pressure applied is between 1000 and 3000 Bars.

12. The method of claim 18 wherein the uniaxial pressing operation is performed at a temperature of 450 ⁰ C at a pressure of 1800 Bars.

The method of any one of the preceding claims, wherein the billet obtained in step (b) is hot extruded.

14. A method according to any one of claims 1 to 15, wherein the aluminum matrix composites reinforced with silicon carbide particles or any other ceramic particles such as boron carbide or alumina.

A process according to any one of the preceding claims wherein the powder mixture comprises about 94.7% by weight of aluminum, 4% by weight of copper, 1.3% by weight of magnesium and 15% by volume of silicon carbide

16. Billette obtained by the method according to any one of claims 1 to 15.

Metal part obtained by forging, machining or any other equivalent technique from the billet of claim 16.

Apparatus for carrying out step (a) of the method according to any one of claims 1 to 15 comprising:

a latex sheath (1) into which the mixture of powders (5) is poured,

a perforated cylindrical container (2) in which the latex sheath (1) is arranged, and

hermetic isolation means (7, 10, 11) of the mixture of powders (5) contained in the sheath (1), in which the sheath (1), the perforated container (2) and the hermetic insulation means (7, 10, 11) form a device for isostatic compaction (14) which is adapted to be placed in the compaction liquid (15) of the isostatic press to undergo the step (a) of isostatic compaction.

19. Device according to claim 18, wherein the hermetic insulation means (7, 10, 11) comprise at least one plug (7) of an elastically deformable material force-fitted into the sheath (1).

20. Device according to any one of claims 18 or 19, wherein the hermetic insulation means (7, 10, 11) comprise the upper edge (10) of the sheath (1) which is folded towards the bottom of the sheath (1) forming an annular border (11) resiliently bearing against the outer face (13a) of the side wall (13) of the perforated container (2).

21. Device according to any one of claims 18 to 20, wherein the sheath (1) and the perforated container (2) are, prior to step (a) isostatic compaction, removably disposed in a cylindrical container (3).

22. Device according to claim 21, wherein the upper edge (10) of the sheath (1) is folded towards the bottom of the sheath (1) and comes resiliently bearing against the outer face (12a) of the side wall (12) of the cylindrical container (3).

23. Device according to any one of claims 21 and 22 comprising means (7a) for making a vacuum draw in the sheath (1) so that the gas contained in the powder mixture (5) is removed beforehand. step (a) of isostatic compaction.