Fabrication And Properties Of Porous C_f/C Composites And C_f/C-SiC Composites Prepared Based On A Novel Pore Making Method

Porous C_f/C composites have advantages such as high specific strength,low thermal expansion coefficient,and zero wet expansion coefficient,which are conducive to manufacturing future ultra-stable and high-load structures,and will have great application value in the aerospace field.C_f/C-SiC composites have the advantages of high specific strength,high abrasion resistance,high temperature resistance,and oxidation resistance.They are widely used in thermal protection structures of transportation systems and braking systems in aerospace.In this article,the preform is impregnated with wax and puncture channels to prepare porous preforms.Based on the porous preforms,the preform channels are filled with specially designed space-holders to prepare porous C_f/C composites and the preform channels are filled with resin silicon powder slurry then reacted in situ to prepare C_f/C-SiC composites.In this paper,the preparation process of space-holders is studied,the effects of the channel diameter and channel center distance of the preform on the porous C_f/C composites are studied,and the phase composition,microstructure and mechanical properties of C _f/C-SiC composites are studied.The findings are as follows:(1)The porous preforms is prepared by a new pore-making method,which can reduce the damage of the carbon fibers and maintain the integrity of the carbon fiber.After the preform is filled with space-holders,the impregnated paraffin is completely removed by heating in a water bath.After the paraffin is removed,the space-holders can still be completely stored in the carbon fiber preform.After the preform is densified,HF can be used to corrode and filter the space-holders to obtain porous C_f/C composites;(2)The ratio of water glass to quartz sand added to the space-holders is 1:1,of which 2000 mesh quartz sand is 20%and 30-120 mesh quartz sand is 27%,its density and melting softening temperature are the highest,which can meet the preparation requirements of porous C_f/C composites;(3)The larger the channel diameter and the smaller the channel center distance of the porous preform,the higher the density of the preform,the lower the density of the struts of the prepared porous C_f/C composites,and the more it tends to generate RL pyrolytic carbon(PyC).The compressive strength of porous C_f/C composites decreases with the increase of the channel diameter and the decrease of the channel center distance of the composites.The parallel compressive strength is greater than the vertical compressive strength,which shows anisotropy;(4)The C_f/C-SiC composites is prepared by the in-situ reaction of the mixed resin and silicon powder mixed slurry in the channels of the porous preform,which can prevent Si from diffusing into the matrix,reduce the damage of Si to carbon fibers,and protect the integrity of carbon fibers;(5)The compressive strength and shear strength of C_f/C-SiC composites are significantly improved compared to pure C_f/C composites.C_f/C-SiC composites and pure C_f/C composites are pseudo-plastic fractures when parallel and vertical compression,and brittle fractures when sheared.