HK1117791B - Improved method for preparing metal-matrix composite and device for implementing said method - Google Patents

Description

Improved method for preparing metal matrix composite and apparatus using the same

The present invention relates to a method for preparing a metal matrix Composite (CMM).

The invention also relates to a device for carrying out the method.

The metal matrix Composite (CMM) may be an aluminum alloy reinforced with particles of, for example, silicon carbide, boron carbide, alumina, or any other ceramic material.

Metal matrix composites are mainly used for the manufacture of metal parts in the aeronautical field, such as rotor parts for helicopters.

Parts made of metal matrix Composite (CMM) are press-formed on the basis of a billet weighing several tens of kilograms, which is obtained by pressing (compacting) a premixed powder.

In some known processes, the main step of pressing (or "forming") is accomplished by uniaxial pressing, which results in the formation of sheets (strates) inside the blanks, which are detrimental to the mechanical properties of the metal parts obtained by stamping from these blanks.

In practice, each billet needs to distribute its constituent components, in particular the reinforcing particles, as uniformly as possible in order to give the required mechanical properties to the parts produced on the basis of these billets.

Finally, simplification of the metal matrix Composite (CMM) manufacturing process is essential in order to limit the production costs of these metal matrix composites.

The method of the invention, which makes up for the above-mentioned drawbacks, is essentially characterized in that it comprises at least the following steps:

(a) cold isostatic pressing (isostatic pressing ) of the premixed powder 5, and

(b) hot uniaxial pressing (compact) the compact (or compact)12 resulting from step (a).

These two steps allow for the production of metal matrix composites with improved mechanical properties at minimal cost.

Advantageously, the powders are dry mixed (m langer sec) in a suitable mixer in a pressurized gas (or pressure gas) containing a neutral (or inert) gas and oxygen.

Dry mixing powders has the advantage of being more economical than wet mixing methods, and the presence of a neutral (inert) gas makes it possible to avoid the risk of explosion during dry mixing.

The pressure in the mixer is preferably between 15 and 25 mBar (mBar), the neutral (inert) gas is nitrogen and the oxygen proportion is controlled between 5% and 10%.

The control of the oxygen ratio also makes it possible to reduce (limit) the risk of explosions.

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

The powder mixture 5 is preferably composed of an aluminum alloy reinforced with particles such as silicon carbide, boron carbide, alumina, or other ceramic materials.

More preferably, the powder mixture 5 includes (a metal mixture of) 94.7% by mass of aluminum, 4% by mass of copper, 1.3% by mass of magnesium, and 15% by volume of silicon carbide.

Further, the powder mixture 5 is subjected to a compaction process on a vibrating table before the isostatic forming step (a).

Also, before the isostatic molding step (a), the gas contained in the compacted powder mixture 5 is discharged by pumping so as to obtain a solid compact (un compact) 12.

In the molding (pressing) step, the molding fluid (compressed fluid) 15 preferably contains water and a lubricant additive.

The pressure of the forming fluid is preferably between 1500 and 4000 bar, more preferably 2000 bar.

It is also possible to envisage subjecting the compact obtained in step (a) to a degassing step at a temperature of between 100 and 450 ℃, preferably 440 ℃.

Preferably, the uniaxial pressing step (b) is carried out at a temperature of between 400 and 600 ℃, preferably 450 ℃, and at an applied pressure of between 1000 and 3000 bar, preferably 1800 bar.

Advantageously, the billet obtained in step (b) is hot extruded.

Very advantageously, the aluminum matrix composite is reinforced (renforcer) by silicon carbide particles or other ceramic particles such as boron carbide or alumina.

The invention also relates to a blank 22 obtained with the above method.

Furthermore, the present invention also relates to an apparatus for carrying out step (a) of the above method, comprising:

a rubber casing (casing made of rubber) 1 into which the powder mixture 5 is poured,

a perforated cylindrical container 2 inside which a rubber casing 1 is arranged, and

sealing and isolating means (or sealing and isolating devices) 7, 10, 11 for sealing and isolating the powder mixture 5 in the rubber casing 1,

wherein the outer shell 1, the perforated container 2 and the sealed partition means 7, 10, 11 form a device 14 for isostatic forming, which device 14 can be placed in a pressing liquid 15 of an isostatic press to undergo the isostatic forming step (a).

Advantageously, the seal-isolating means 7, 10, 11 comprise at least one plug 7 of elastically deformable material, which is force-fitted in the housing 1.

Advantageously, the sealing and separating means 7, 10, 11 comprise an upper edge 10 of the casing 1 folded towards the bottom of the casing 1 to form a ring-shaped edge 11 elastically pressed against the outer surface 13a of the side wall 13 of the perforated container 2.

Preferably, the outer shell 1 and the perforated cylindrical container 2 are removably arranged in a cylindrical cartridge (content) 3 before the isostatic forming step (a).

In this case, the upper end edge 10 of the housing 1 is folded toward the bottom of the housing 1 and elastically pressed against the outer surface 12a of the side wall 12 of the cylindrical barrel 3.

Furthermore, the apparatus of the invention may be provided with means 7a for effecting evacuation (evacuation) of the enclosure 1 in order to evacuate the gas contained in the powder mixture 5 prior to the isostatic shaping step (a).

The objects, advantages and features of the invention will become more apparent upon reading the following description and upon reference to the drawings which illustrate a non-limiting example of a particular embodiment of the device of the invention, in which:

FIG. 1 is a perspective exploded view of the device of the invention, which makes it possible to evacuate the residual gases before the isostatic shaping step (a);

FIG. 2 is a cross-sectional view of the assembled device of FIG. 1 along line II-II of FIG. 1;

FIG. 3 is the same view as the apparatus of FIG. 2, except without the drum and arranged in an isostatic press (la press isotatic);

figure 4 is a view of the device in the venting phase; while

FIG. 5 is a cross-sectional view of a uniaxial pressing apparatus.

The non-limiting examples described below are suitable for preparing aluminum matrix composites reinforced with silicon carbide particles.

The premixed powder mixture 5, consisting of (a metal mixture of) 94.7% by mass of aluminum, 4% by mass of copper, 1.3% by mass of magnesium, and 15% by volume of silicon carbide, is dry-mixed in a ball mill or a conventional powder mixer.

To avoid any risk of explosion during the mixing of the powders, the ambient gas contains a neutral (inert) gas such as nitrogen at a pressure of between 15 and 25 mbar, preferably 20 mbar, and oxygen in a proportion of between 5 and 10%, preferably 6%.

Referring to fig. 1 and 2, a rubber casing 1 is placed inside a perforated container 2 so that a free space is left between the bottom of the casing 1 and the bottom of the perforated container 2.

The rubber housing 1 and the perforated container 2 are placed in a cartridge 3 comprising a conduit outlet 4 through which a conduit 4a leads into the container 3, which conduit 4a is connected to a vacuum pump via a pipe. The tube is not shown in the figure.

After sealing the closure using suitable means (not shown), vacuum is applied at the outlet 4 of the duct to draw the rubber casing 1 against the wall of the perforated container 2 to define a maximum volume.

After the evacuation has been stopped through the blocked pipe 4a, the powder mixture 5 is poured into the housing 1 and the powder mixture is compacted in this housing 1 by means of a vibrating table (not shown).

For optimum sealing in the following process, the upper end portion 10 of the casing 1 is arranged beyond the cartridge 3 and folded towards the bottom of the casing 1 so as to form an annular edge, which abuts elastically against the outer surface 12a of the side wall 12 of the cartridge 3.

A generally cylindrical nitrile plug 7 is forced into the housing 1 to leave an annular rim 11 which, as described above, is convex.

The arrangement of the nitrile plug 7 and the annular rim 11 of the housing 1 makes it possible to obtain a completely sealed system.

The nitrile plug 7 includes a central bore 7a for connection to a vacuum pump via a tube (not shown).

Vacuum pumping is performed until the powder mixture 5 becomes a solid compact 12, and then the vacuum pumping is stopped by blocking the pipe 7a with the plug 7 b.

A filter 6 is fixed on the inner surface 9 of the plug 7 in contact with the compacted powder mixture 5, so that dust from the powder mixture 5 is prevented from entering the vacuum system during evacuation.

Referring to figure 3, the whole of the compact 12, housing 1, apertured container 2 and plug 7 forming the isostatic moulding means 14 is removed from the drum 3, the seal ensured by the resilience of the housing 1 being such that the annular rim 11 abuts against the outer surface 13a of the side wall 13 of the apertured container 2 whilst the means 14 is removed from the drum 3.

This device 14 is immersed in a forming liquid 15 of an isostatic press 16, which contains water and lubricant additives and undergoes a cold isostatic forming process by applying a pressure between 1500 and 4000 bar, preferably 2000 bar.

In this step, the rate of rise of pressure is between 20 and 50 bar per minute, while the above-mentioned maximum pressure is maintained for a period of at least 1 minute.

In this way, the pressure applied to the compact 12 is applied over its entire surface, which allows for uniform compaction without the formation of sheets or other material discontinuities.

The compact 12 obtained after the isostatic pressing process has a density of about 85%.

After this procedure, the casing 1 is removed from the perforated container 2 and the exterior of the casing 1 and the plug 7 are carefully cleaned to avoid any contact with the forming liquid 15 and the compact 12.

Subsequently, the housing 1 and the plug 7 are removed, and if necessary, the filter residue 9 is removed by grinding or polishing the upper part of the compact 12.

Referring to fig. 4, the compact 12 is then housed in a tubular barrel 17 of aluminum material with a bottom wall 18.

The cylinder 17 is closed by welding an opposite upper wall 19 of aluminum material, which has a hole 20 inside of which is welded a tube 21 intended to be connected to a vacuum pump.

After checking the sealability of the aluminum material cylinder 17, vacuum suction was performed for about 30 minutes and pumping (suction) was continued, and the cylinder 17 was placed in an oven at about 440 ℃ for about 12 hours to perform a degassing process.

After this process is complete, the tube 21 is closed at about 10-20cm of the upper wall 19.

The aluminium material barrel 17 containing the compact 12 is then quickly placed into a pre-heated apparatus (outer) 23 at a temperature greater than 300 c, preferably between 400 and 600 c, preferably 450 c, so that the compact 12 does not cool after the degassing step.

The above temperature is maintained throughout the hot uniaxial pressing operation.

The device 23 is provided with a central cylindrical hole 24 having a diameter approximately equal to the diameter of the cartridge 17, so that the cartridge 17 can be inserted in said hole 24.

For reasons explained later, the cartridge 17 rests on a member forming the base ejector 25, which is fixedly or removably fixed to the inner surface 26 of the central bore 24.

A punch 27 then applies a pressure to the barrel 22 in the vertical direction indicated by the arrow, between 1000 and 3000 bar, preferably 1800 bar, until the punch 27 is no longer moved, maintaining the pressure reached for a period of about 1 minute.

The vertically applied pressure can keep the substrate (matrix) relatively centered under this pressure.

After the uniaxial pressing process, the punch 27 is pulled out, and the blank 22 composed of the compact 22 accommodated in the aluminum cylinder 17 after the uniaxial pressing process is ejected out of the apparatus 23 by applying a pressing force in the direction indicated by the arrow 20 by an ejector 29 provided on the opposite side of the punch 27.

The blank 22 can be ejected from the upper part of the apparatus by sliding a movable matrix ejector (female ejector pin) 25 in the central hole 24.

A mechanical peeling process is then performed to remove the aluminum layer of the drum around the blank 22.

After the uniaxial pressing process, a blank 22 having a density of 100% is obtained.

This billet 22 is hot extruded at a temperature of about 400 c to give the billet better cohesion and optimum mechanical properties.

The blank 22 may then be machined to form a metal part by forging, machining, or any other known technique.

By adopting this method, the silicon carbide particles are uniformly distributed in the obtained blank, which exhibits improved mechanical properties.

The properties of the metal matrix composite obtained in this way depend on the characteristics of the aluminium matrix, the proportion of reinforcing particles and the heat treatment applied to the product.

For reinforcement rates varying between 15 and 40% by volume, the breaking strength is generally higher than 500Mpa and the young's modulus is between 95 and 130 Gpa.

10⁷Period of timeThe fatigue limit stress (Contraint Limite) is between 250 and 350MPa, which results in that mechanical parts made on the basis of metal matrix composites made according to the above method can have a service life 10 times longer than conventional materials.

Claims (16)

1. Method for the preparation of a metal matrix composite material comprising at least one mixing step, dry mixing an aluminium based alloy powder in a suitable mixer, this mixer being under a pressurised gas, said gas containing a neutral gas and oxygen, said method further comprising the steps of:

(a) cold isostatic pressing of the premixed powder (5), and

(a1) degassing the compact obtained by step (a) at a temperature between 100 and 450 ℃ for 12 hours,

(a2) rapidly placing the degassed compacts into a pre-heated apparatus at a temperature greater than 300 ℃ so that the degassed compacts do not cool after the degassing step,

(b) hot uniaxial pressing the compact (12) obtained in step (a2), maintaining the temperature at more than 300 ℃ throughout the hot uniaxial pressing operation, an

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

2. The process according to claim 1, the pressure in the mixer being 20 mbar and the proportion of oxygen being 6%.

3. The method according to any of the preceding claims, wherein the pre-mixed powder (5) is subjected to a compaction process on a vibrating table before the isostatic forming step (a).

4. A method according to claim 3, wherein, prior to said isostatic forming step (a), the gas contained in the compacted pre-mixed powder (5) is expelled by pumping so as to obtain a solid compact (12).

5. The method of claim 4, wherein the isostatic forming step (a) comprises immersing in a forming fluid (15) comprising water and a lubricious additive.

6. A method according to claim 5, wherein the pressure of the forming fluid (15) is between 1500 and 4000 bar.

7. A method according to claim 6, wherein the pressure of the forming fluid (15) is 2000 bar.

8. The method of claim 1, wherein the compact obtained in step (a) is subjected to a degassing procedure at a temperature of 440 ℃.

9. The method according to claim 1, wherein the hot uniaxial pressing procedure is performed at a temperature between 400 ℃ and 600 ℃ and wherein the applied pressure is between 1000 and 3000 bar.

10. The method according to claim 9, wherein the hot uniaxial pressing process is performed at a temperature of 450 ℃ and a pressure of 1800 bar.

11. The method of claim 1, wherein the billet obtained in step (b) is hot extruded.

12. The method of claim 1, wherein the metal matrix composite is an aluminum matrix composite reinforced with ceramic particles.

13. The method of claim 12, wherein the ceramic particles are silicon carbide, boron carbide, or alumina particles.

14. The method of claim 1, wherein the powder comprises:

a premixed powder mixture containing 94.7% by mass of aluminum, 4% by mass of copper, 1.3% by mass of magnesium,

and 15% by volume of silicon carbide.

15. Blank obtained according to the method of any one of the preceding claims 1 to 14.

16. Metal part obtained by forging or machining techniques based on a blank according to claim 15.