The manufacture of composite materials

Metal matrix composite is made by assembling pre-forms of porous reinforcing material with an array of separator plates 22 in a die in a pressure vessel, and infiltrating molten metal matrix material. Pre-evacuation followed by pressurisation when the molten metal matrix material is introduced into the die aids the infiltration. Re-introduction of gas during initial heating prior to melting speeds the heat-up process. The porous reinforcing material comprises particulate material in which the particle size is selected and controlled such that the majority of the particles have a size at or close to one of two different sizes (Fig.1). In producing a composite material by infiltrating a molten matrix material into a porous pre-form of a reinforcing material a perforated closure member 21a is used to cover the pre-form in a die. On heating the die the metal matrix melts and passes through the perforated closure member to infiltrate the pre-form.