Study On Gel-casting For Preparing SiC Preform For High Volume Fraction SiC_p/Al Composite

Aluminum-based silicon carbide composites with a volume content of Si C above 40%(collectively called high volume fraction Si Cp/Al composite)have excellent mechanical properties and thermal properties such as low density,high specific strength and specific stiffness,low coefficient of linear expansion and high thermal conductivity.It has a great application prospect in the fields of aerospace payload manufacturing and high-power electronic control device manufacturing and so on.The combination of gel-casting and pressureless infiltration can be used for the preparation of high volume fraction Si Cp/Al with near-net size.In this process,the preparation of Si C reinforcement phase green body is a crucial part.If the prepared Si C slurry cannot meet the requirement of gel-casting,the properties of the composites will be reduced.In this paper,through the research on the influence factors of the rheological properties of gel-casting and the solidification process of the slurry,a high solid content Si C slurry satisfying the requirements of gel casting technology is obtained.Si C preform was obtained after pre-sintering and oxidation,and high volume Si Cp/Al composite was fabricated by pressureless infiltration process.The main contents of this paper are as follows:(1)The effects of p H value,dispersant and solid content on the rheological properties of Si C slurry were studied.The 12.8?m Si C powder was selected,the p H value of the slurry is 10,the content of polymer dispersant PEG6000 is 1 wt.%,the solid content is 48 Vol.%,and the viscosity of slurry is below 2.2 Pa·s,the requirements of gelasting process will be satisfied;(2)The mechanism of slurry gel process and the effect of catalyst and initiator dosage on the gelasting time of Si C slurry were studied.When the amount of catalyst was 1.8m L/L and the dosage of initiator was 0.48g/L,the gelasting time of Si C slurry was 15 min,which met the requirements of gel casting process;(3)The TG-DSC of of the pre-sintering process of Si C preform body was tested,and a reasonable pre-sintering process was established to prevent cracking of the green body during pre-sintering;(4)The Microstructure and crystal type of Si O2 oxide layer on the surface of Si C particles at different pre-oxidation temperatures were studied.The Si O2 oxide layer on the surface of Si C particles was amorphous after pre-oxidation below 850 °C.When the temperature above 850 °C,the Si O2 oxide layer would crystallize and change from amorphous state to crystalline state.After the phase transition,the structure of the Si O2 oxide layer would become loose,which may affect the compactness of the Si Cp/Al composite.(5)The fracture morphology of high volume fraction Si Cp/Al composites prepared from the above-mentioned Si C preforms was analyzed.It was found that the main mechanism of fracture failure of composites were enhanced phase cleavage mechanism and matrix control mechanism.The properties of the composite were tested.The properties of the composites were tested.The density of the composites was 2.921g·cm-3,the modulus of elasticity was 193.3GPa,the bending strength was 360 MPa and the coefficient of thermal expansion was 8.3×10-6/?(20?~75?).