GB2247636A

GB2247636A - The manufacture of composite materials

Info

Publication number: GB2247636A
Application number: GB9116445A
Authority: GB
Inventors: Robin Michael Kurt Young
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1990-08-03
Filing date: 1991-07-31
Publication date: 1992-03-11
Also published as: GB9116445D0

Abstract

A method of manufacturing fibre-reinforced composite materials in which a fibrous pre-form is placed in a heated die 9 in a sealed pressure chamber 1 which also contains a crucible 11 of molten material eg aluminium, to be infiltrated into the pre-form, the chamber is evacuated, the molten material is allowed to flow over the pre-form and the chamber is pressurised to cause the molten material to infiltrate the pre-form. <IMAGE>

Description

The Manufacture of Composite Materials The present invention relates to the manufacture of composite materials and more specifically to a method and apparatus for manufacturing such materials in which a porous pre-form is impregnated with a matrix material under reduced pressure.

In one process for manufacturing metal matrix composite materials, a porous pre-form is placed in a well in a massive die block, a quantity of molten liquid is run into the well in the die block and then caused to infiltrate the pre-form by means of an hydraulic ram. This process has a number of disadvantages for example, it is difficult to heat the die to a temperature sufficient to prevent premature solidification of the melt so that high degrees of superheat have to be employed, which can lead to damage of the pre-form; the die has to be massive to withstand the high pressures (5100 MPa) necessary to ensure proper infiltration of the pre-form; air and other gases may be entrapped in the preform, producing an inconsistent product, and distortion of the pre-form may occur as a result of the high pressures used.

In another process, the melt crucible and its heater are placed in a pressure vessel and a riser connects the crucible to an external heated die block. The die block is of closed form and is capable of being evacuated via a vacuum line which also connects with the pressure vessel which contains the melt crucible. A pressure line also communicates with the pressure vessel. In use, the pre-form is placed in the die block which is then closed and sealed, the pressure vessel and the die block ae evacuated and the material to be infiltrated into the pre-form is melted. When the material to be infiltrated is in a sufficiently fluid state, the pressure vessel is closed off from the vacuum line and pressurised, thus forcing the melt through the riser and into the die block.

This process is an improvement over that described previously in that the evacuation of the die block during the infiltration stage reduces somewhat the pressure required and also makes gas entrapment less likely. On the other hand, high degrees of superheat of the melt still are required and the die block still needs to be massive to withstand the applied pressure, with its attendant pre-heating problems.

The present invention seeks to overcome the disadvantages of both the previously described processes.

According to the present invention in one aspect there is provided a method of manufacturing a composite material by infiltrating a molten matrix material into a porous pre-form of reinforcing material, including the operations of placing a crucible containing a quantity of the matrix material and a die containing a porous pre-form of reinforcing material in a pressure vessel, evacuating the pressure vessel, heating both the crucible and the die to a temperature above the melting point of the matrix material, transferring the molten matrix material to the die, pressurising the pressure vessel so as to cause the matrix material to infiltrate the pre-form and cooling the die to cause the matrix material to solidify.

Also according to the invention there is provided an apparatus for manufacturing a composite material consisting of a fibre, particulate or whisker reinforced matrix material comprising a pressure vessel means whereby the pressure vessel may be evacuated or pressurised, a chamber mounted within the pressure vessel and adapted to receive a die, means for heating the die, a vent connecting tne chamber to the outside of the pressure vessel, means for admitting a pressurising medium from the pressure vessel to the chamber, a crucible, means for heating the crucible, means for transferring molten matrix material to the die, means for applying pressure to the molten matrix material when it is in the die to cause it to infiltrate a porous pre-form of reinforcing material in the die, and means for cooling the die.

In one embodiment of the invention, the crucible is positioned above the chamber and has a hole in the bottom which is normally closed by a retractable plug. The chamber has a hole in its top aligned with that in the bottom of the crucible and the die also is open and positioned beneath the holes in the crucible and chamber.

Thus when the plug is withdrawn, molten matrix material will flow from the crucible into the die under the influence of gravity alone.

In another embodiment of the invention, the matrix material is placed above the porous pre-form in the same die tube. The matrix material is melted in situ instead of being delivered separately from a melting crucible.

The reinforcing material may be filrous, woven or particulate.

The invention will now be described, by way of example, with reference to the accompanying drawing which is a diagrammatic representation of an apparatus embodying the invention.

Referring to the drawing an apparatus for the manufacture of fibre reinforced composite materials consists of a pressure vessel 1 which has a base plate 2.

A port connects the pressure vessel 1 to a vacuum pump (not shown) or a pressure accumulator, which also is not shown, via a two-way valve 4. Mounted within the pressure vessel 1 is a chamber 5. In the base of the chamber 5 is a port 6which communicates with the interior of the pressure vessel 1. Near the top of the chamber 5 is a vent 7 which passes through the base 3 of the pressure vessel 1 and includes a valve 8. Inside the chamber 5 is a die 9 which is surrounded by a heater 10. Superimposed upon the chamber 5 is an open crucible 11 which also is surrounded by a heater 12. A hole 13 in the bottom of the crucible 11 communicates with a similar hole 14 in the top of the chamber 5. The hole 13 in the crucible 11 normally is closed by a plug 15 which can be withdrawn when required by a suitable mechanism, which is not shown.

In use, a fibrous pre-form 16 is placed in the die 9 and a quantity of matrix material 17 is placed in the crucible 11, the vent valve 8 of the vent 7 is closed and the valve 4 is set to connect the pressure vessel 1 to the vacuum pump. When the pressure vessel 1 and the chamber 5 have been evacuated the port 6 is closed. The heaters 10 and 12 are switched on and both the die 9, together with the pre-form 16 and the crucible 11 are raised to a temperature above the melting point of the matrix material 17 in the crucible 11. When the matrix material is fully molten the plug 15 is withdrawn and the molten matrix material passes into the die 9 under the influence of gravity alone. When a required quantity of matrix material has passed into the die 9, the pressure vessel 1 is pressurised to cause the matrix material to infiltrate the pre-fom 16. Finally, the valve 8 is opened so that gas flows from the inside of the pressure vessel 1 past the die 9 to cool it and solidify the composite material within it. The cooling configuration is arranged so the shrinkage of one matrix during solidification is fed by one remaining liquid in one reservoir.

The placing of the die 9 within the pressure vessel 1 means that the die 9 does not have to withstand the infiltration pressure applied to the melt. As the molten matrix material 17 flows around the pre-form 16, only the preform 16 has to withstand the pressure which is applied to cause infiltration of the matrix material into the pre-form 16. As a result,the die 9 can be very lightweight in construction, so that its thermal capacity is low, heat transfer through the die 9 is rapid and control of the temperature of both the pre-form 16 and the infiltrate 9 composite is facilitated in both the heating and cooling phases. Also, the infiltration operation can be separated from the solidification stage of the process. Isothermal infiltration is possible for as long as is necessary and the solidification of the infiltrated composite can be effected by selective cooling of the die 9, which may be achieved by suitable jets or ducting arrangements for the cooling gas when it is admitted to the chamber 5. In this way it can be arranged that solidification of the molten matrix material proceeds from the bottom of the die 9 enabling still molten matrix material to flow into spaces caused by solidification shrinkage.

By way of example, the matrix material may be aluminium or an alloy thereof and the reinforcing material may be a ceramic fibre such as alumina fibres or whiskers.

Claims

1. A method of manufacturing a composite material by infiltrating a molten matrix material into a porous pre-form of a reinforcing material, including the operations of placing a die containing a porous pre-form of reinforcing material into a pressure vessel together with a quantity of matrix material in a container such that the matrix material when molten can be brought into contact with the pre-form of reinforcing material so as to infiltrate it, evacuating the pressure vessel and the die, heating the die and the matrix material to a temperature above the melting point of the matrix material, contacting the pre-form of reinforcing material with the molten matrix material, pressurising both the die and the pressure vessel so as to cause the matrix material to infiltrate the pre-form of reinforcing material and cooling the die to cause the matrix material to solidify

2.A method of manufacturing a composite material by infiltrating a molten matrix material into a porous pre-form of reinforcing material, including the operations of placing a crucible containing a quantity of the matrix material and a die containing a porous pre-form of reinforcing material in a pressure vessel, evacuating the pressure vessel, heating both the crucible and the die to a temperature above the melting point of the matrix material, transferring the molten matrix material to the die, pressurising the pressure vessel so as to cause the matrix material to infiltrate the pre-form and cooling the die to cause the matrix material to solidify.

3. A method according to claim 1 wherein the container for the matrix material is the die, the matrix material in solid form is placed in the die above the pre-form of reinforcing material and melted in situ.

4. A method according to any preceding claim wherein the bottom of the die is cooled preferentially thereby causing the matrix material to solidify first at the bottom of the die.

5. A method according to any preceding claim wherein there are included the operations of evacuating the chamber after the pre-form of reinforcing material has been infiltrated by the molten matrix material and admitting a cooling gas to the chamber so as to cool the die and cause the matrix to solidify.

6. A method according to any of claims 1 to 5 wherein the matrix material is a metal.

7. A method according to any preceding claim wherein the reinforcing material is fibrous.

8. A method according to any of claims 1 to 6 wherein the reinforcing material is particulate.

9. A method according to any preceding claim wherein the matrix material is aluminium or an alloy thereof.

10. A method according the any of claims 1 to 8 wherein the reinfrocing material is a ceramic.

11. A method according to claim 10 wherein the reinforcing material is alumina.

12. An apparatus for manufacturing a composite material consisting of a fibre, particulate or whisker reinforced matrix material comprising a pressure vessel means whereby the pressure vessel may be evacuated or pressurised, a chamber mounted within the pressure vessel and adapted to receive a die, means for heating the die, a vent connecting the chamber to the outside of the pressure vessel, means for admitting a pressurising medium from the pressure vessel to the chamber, a crucible, means for heating the crucible, means for transferring molten matrix material to the die, means for applying pressure to the molten matrix material when it is in the die to cause it to infiltrate a porous pre-form of reinforcing material in the die, and means for cooling the die.

13. An apparatus according the claim 12 wherein the crucible is positioned above the chamber, an orifice in the bottom of the crucible is arranged to communicate with another in the top of the chamber, a valve arranged to stop the passage of molten matrix material from the crucible to the chamber and means for positioning the die beneath the orifice in the top of the chamber so that on opening of the valve, molten matrix material can pass from the crucible into the die under the influence of gravity.

14. An apparatus according to claim 13 wherein the die has an open top and is positioned directly underneath the orifice in the top of the chamber.

15. An apparatus according to claim 12, 13 or 14 wherein the means for cooling the die is adapted to cool preferentially the bottom of the die thereby to cause the molten matrix material to solidify from the bottom of the die upwards.

16. An apparatus according to any of claim 12 to 15 wherein the means for cooling the die comprises means for admitting a cooling gas to the inside of the chamber.

17. A method of manufacturing a composite material substantially as hereinbefore described and with reference to the accompanying drawing.

18. An apparatus for manufacturing a composite material substantially as hereinbefore described and with reference to the accompanying drawing.