Fabrication of SiC/Al composites with near-net-shape I: Preparation of SiC preforms

SiC preforms with different porosities for Al pressureless infiltrating in were prepared by oxidation bonding process deriving from micron-grade powders of SiC and graphite.The low temperature sintering mechanism of SiC preforms and the effect of graphite content on the density and dimension of the porous preforms were studied.The results show that SiC powders and graphite powders oxidize synchronously at 1 100 ℃ in air atmosphere;Crystalloid SiO2 film transformed from SiC by oxidation bonds SiC powders to each other to form a ceramic skeleton,and the sites occupied by graphite powders turn into pores when graphite powders burned out.Three dimensional co-continuous net-work of pores is achieved by original clearance among SiC powders and pores formed by graphite powders.The linear expansion of SiC preforms without any deformation is about 4% due to oxidation of SiC powders.SiC preforms with porosity ranging from 0.47 to 0.63 can be obtained by modulating graphite content.