Processing And Properties Of C_f/SiC Composites Prepared By Precursor Infiltration And Pyrolysis

In this dissertation, Cf/SiC composites were fabricated by precursor infiltration and pyrolysis (PIP) route. The thesis involves three items as follow: firstly, the effects of different gas pressure on the cross-linking and pyrolysis behaviors of polycarbosilane (PCS)/divinylbenzene (DVB) were investigated, and the effects of cross-linking pressure and pyrolysis pressure in the first cycle of PIP route on the mechanical properties of Cf/SiC composites were also studied. It was found that higher gas pressure resulted in higher density of cross-linked product and higher ceramic yields, but the pressure applied in cross-linking had little effect on crystal structure of matrix. Combining pressure with infiltration and cross-linking could enhance the densification efficiency of PIP route, but Cf/SiC composites cured under atmospheric pressure in the first cycle of PIP route had better mechanical properties; The ceramic yields increased significantly with the enhancement of pyrolysis pressure, and the precursor has the highest ceramic yields of 67.2% in case of gas-pressure pyrolysis. However, the pyrolysis pressure had little effect on crystal structure of matrix. The pyrolysis pressure in the first cycle of PIP route had obvious effect on the mechanical properties of Cf/SiC composites, and when the first pyrolysis was conducted under vacuum, the resultant composite showed the highest mechanical properties, 404MPa in flexural strength and 20.2MPa?m1/2 in fracture toughness, which are 1.41 and 1.42 times respectively of those of the composite derived from gas-pressure pyrolysis.Secondly, focusing on the first cycle of PIP route, effects of different process conditions on the mechanical properties of Cf/SiC composites were also studied, and the present process conditions were optimized. The result showed that when slow cooling rate was adopted, the mechanical properties of Cf/SiC composites increased to a certain extent. when the pyrolysis temperature was below 1600℃, mechanical properties of Cf/SiC composites increased with the enhancement of pyrolysis temperature in the first cycle of PIP route, and the best process conditions in the first cycle of PIP route was pyrolysis temperature of 1600℃under vacuum. Effects of heat treatment on the T300 and JC1# carbon fibers reinforced SiC composites were studied, and effects of integration of pyrolysis temperature and pressure in the first cycle of PIP route on the mechanical properties of Cf/SiC composites on the basis of fiber heat treatment were investigated. It was found that mechanical properties of Cf/SiC composites increased greatly after heat treatment of T300 and JC1# fibers, the flexural strength of T300 Cf/SiC composites increased from 67MPa to 560MPa, and JC1# fibers Cf/SiC composites increased from 497MPa to 563MPa. And for both T300 and JC1# carbon...