Process for making composite materials from refractory fibers and metal

Claim 2

A process according to claim 2 wherein the piston is maintained at about 100* C below the solidus temperature of the molten metal during the initial application of the encapsulating pressure program to solidify molten metal tending to escape through leakage paths around the piston.

Claim 3

A process according to claim 2 wherein excessive cooling of the admixture prior to completion of the encapsulating pressure program is prevented by introducing a thermally insulating material between the admixture and the piston applying encapsulating pressure.

Claim 4

A process according to claim 4 and in which excessive cooling is additionally prevented by the presence of a particulate mould release agent between the mould sides and the admixture.

Claim 5

A process according to claim 4 wherein the mould and piston are unheated before the admixture is provided in the mould.

Claim 6

A process according to claim 4 wherein the mould is heated to between about 200* C and 400* C before the admixture is provided in the mould.

Claim 7

A process according to claim 1 wherein the admixture of reinforcing refractory fibers and metal are introduced into the mould as a preheated admixture of molten metal and fibers.

Claim 8

A process according to claim 8 wherein the preheated admixture is introduced into the mould contained within an envelope of metal which is solid at the pre-heating temperature.

Claim 9

A process according to claim 1 wherein the admixture of reinforcing refractory fibers and molten metal are provided in the mould by first introducing a mass of reinforcing fibers into the mould and then covering the mass with a charge of molten metal.

Claim 10

A process according to claim 10 wherein the molten metal is superheated above its melting point in order to delay the solidification of the admixture.

Claim 11

A process according to claim 10 wherein the mass of reinforcing fibers in the mould is preheated prior to the introduction of molten metal.

Claim 12

A process for the manufacture of a composite material which comprises providing in a mould an admixture of particulate reinforcing material and a molten metal, applying to the admixture an encapsulating pressure program until a desired densification is achieved, said encapsulating pressure program comprising: a first stage of infiltration pressure sufficient to force molten metal around the particulate reinforcement material to form an interconnecting network of molten metal; a second stage of increased pressure to consolidate the composite by removing microscopic voids remaining in the composite by forcing molten metal into them and causing residual trapped gases to dissolve in the metal; a third stage of pressure sufficient to ensure that as the molten matrix metal solidifies and contracts voids which tend to open as a result of metal contraction within the composite are closed by deformation of the metal matrix; and at least during initial application of the encapsulating pressure program arranging adjacent each path of potential leakage from the mould a heat sink having a heat capacity sufficient to solidify molten metal contacting the heat sink and thereby seal the leakage path.

Claim 13

A process according to claim 1 wherein the first stage infiltration pressure lies between the minimum value calculated from surface tension theory and twice that value.

Claim 14

A process according to claim 14 wherein the infiltration pressure is between about 500 psi and 1,000 psi.

Claim 15

A process according to claim 1 wherein the second stage consolidation program is between about 2,000 psi and 40,000 psi.

Claim 16

A process according to claim 1 wherein the third stage pressure is at least 2,000 psi.

Claim 17

A process according to claim 1 wherein the molten metal matrix is non-wetting in contact with the reinforcing fiber surface.

Claim 18

A process according to claim 1 wherein the molten metal matrix is an aluminum alloy.

Claim 19

A process according to claim 1 wherein the refractory reinforcing fiber is selected from the group consisting of silicon carbide and silicon nitride whiskers and carbon fibers.