Process for preparation of composite materials containing nonmetallic particles in a metallic matrix

Claim 1

A method for preparing a composite of a metallic alloy reinforced with particles of a carbon containing, nonmetallic refractory material, comprising: roasting the particles of the refractory material in an oxidizing environment to form a zone at the surface of the particles wherein the carbon content is less than about 25 percent of its initial level, the depth of the zone being at least about 50 Angstroms below the surface of the particles; melting the metallic alloy; adding the roasted particles to the molten metal; mixing together the molten metal and the particles of the nonmetallic material to wet the molten metal to the particles, under conditions that the particles are distributed throughout the volume of the melt and the particles and the metallic melt are sheared past each other to promote wetting of the particles by the melt, said mixing to occur while minimizing the introduction of any gas into, and while minimizing the retention of any gas within, the mixture of particles and molten metal, and at a temperature whereat the particles do not substantially chemically degrade in the molten metal in the time required to complete said step of mixing; and casting the resulting mixture at a casting temperature sufficiently high that substantially no solid metal is present.

Claim 2

A method for preparing a composite of a metallic alloy reinforced with particles of a carbon containing, nonmetallic refractory material, comprising: roasting the particles of the refractory material in an oxidizing environment to form a zone at the surface of the particles wherein the carbon content is less than about 25 percent of its initial level, the depth of the zone being at least about 50 Angstroms below the surface of the particles; melting the metallic alloy; adding the roasted particles to the molten metal; mixing together the molten metal and the particles of the nonmetallic material to wet the molten metal to the particles, under conditions that the particles are distributed throughout the volume of the melt and the particles and the metallic melt are sheared past each other to promote wetting of the particles by the melt, said mixing to occur while minimizing the introduction of any gas into, and while minimizing the retention of any gas within, the mixture of particles and molten metal, and at a temperature whereat the particles do not substantially chemically degrade in the molten metal in the time required to complete said step of mixing; and casting the resulting mixture at a casting temperature sufficiently high that substantially no solid metal is present.

Claim 12

A method for preparing a composite of aluminum alloy reinforced with silicon carbide particles, comprising: roasting the silicon carbide particles at a temperature of at least about 800° C. in a gaseous source of oxygen, for a time sufficient to form a zone at the surface of the particles wherein the carbon content is less than about 25 percent of its initial level, the depth of the zone being at least about 50 Angstroms below the surface of the particles; forming a mixture of the molten aluminum alloy and the roasted particles; maintaining the mixture in a temperature range of from about the liquidus temperature of the metallic material to a temperature whereat the particles do not substantially degrade during the time required for the subsequent processing steps; mixing together the particles and the molten metal for a time sufficient to wet the molten metal to the particles and to distribute the particles throughout the molten metal, using a rotating dispersing impeller immersed in the molten mixture to shear the particles and the molten metal past each other while minimizing the introduction of any gas into the mixture and while minimizing the retention of any gas already present in the mixture, said step of mixing to occur with a vacuum applied to the mixture; and casting the resulting mixture.

Claim 13

A method for preparing a composite of aluminum alloy reinforced with silicon carbide particles, comprising: roasting the silicon carbide particles at a temperature of at least about 800° C. in a gaseous source of oxygen, for a time sufficient to form a zone at the surface of the particles wherein the carbon content is less than about 25 percent of its initial level, the depth of the zone being at least about 50 Angstroms below the surface of the particles; forming a mixture of the molten aluminum alloy and the roasted particles; maintaining the mixture in a temperature range of from about the liquidus temperature of the metallic material to a temperature whereat the particles do not substantially degrade during the time required for the subsequent processing steps; mixing together the particles and the molten metal for a time sufficient to wet the molten metal to the particles and to distribute the particles throughout the molten metal, using a rotating dispersing impeller immersed in the molten mixture to shear the particles and the molten metal past each other while minimizing the introduction of any gas into the mixture and while minimizing the retention of any gas already present in the mixture, said step of mixing to occur with a vacuum applied to the mixture; and casting the resulting mixture.