Microstructures and mechanical properties of C-f/SiC composites by precursor pyrolysis-hot pressing

C-f/SiC composites were prepared by polymeric precursor pyrolysis-hot press ing with AIN and Y2O3 as additives. The effects of sintering temperature an d additives on the microstructures and mechanical properties of the composi tes were investigated. During sintering, Y2O3 reacted with the pyrolysis pr oducts from the PCS and the oxides on the surfaces of the AIN and SiC grain s, forming a liquid-phase assisting the densification of the composites. So , in combination with SiC-AlN solid solution formed through a reaction-diss olution-precipitation process, the composite sintered at the temperature as low as 1750 degrees C had showed higher density and better mechanical prop erties. The highest flexural strength and fracture toughness, 691.6 MPa and 20.7 MPa.m(1/2)?, respectively, were obtained at the composite sintered at 1800 degrees C. This could be explained by desirable fiber/matrix interfac ial bonding resulting from the formation of the carbon-rich fiber/matrix in terphase containing a certain number of SiC-AlN solid solution grains. In s pite of a tough-like failure mode, the composite sintered at 1700 degrees C exhibited much lower mechanical properties, which was attributed to that t he fiber/matrix interfacial bonding was too weak to effectively transfer lo ad from matrix to fibers. And the composite sintered at temperatures above 1850 degrees C displayed brittle behavior because of the strongly bonded fi ber/matrix intel faces as well as degradation of the fibers. (C) 2000 Elsev ier Science S.A. All rights reserved.