Novel MMC microstructures prepared by melt infiltration of reticulated ceramic preforms

Alumina/aluminium composites with an interpenetrating microstructure were m ade by infiltrating an alumina preform which had the structure of a reticul ated ceramic foam. Low density preforms (6% relative density) with porous s truts were prepared from a polyurethane suspension of alumina powder which was pyrolysed and partially sintered after foaming. Higher density preforms consisted of ceramic foams with open cells and dense struts. All these pre forms were infiltrated with 6061 aluminium alloy using a modified squeeze e aster fitted with a vacuum system and fine control of speed and pressure. S uch MMCs had a microstructure in which two 3D networks were interpenetratin g, One was either a ceramic reinforced alloy (50 vol.-% reinforcement) or a dense ceramic phase while the other was the unreinforced ahoy, The microst ructure of the preform fitted an established relationship between the ratio of window diameter to cell diameter k and void volume fraction V-p. In add ition, a short fibre foam was made to compare with the traditional fibre pr eforms, V-p. In addition, a short fibre foam MST/4571.