Hi-NicalonTM Fiber-Reinforced CVI-SiC Matrix Composites: I Effects of PyC and PyC-SiC Multilayers on the Fracture Behaviors and Flexural Properties

The flexural properties of 2D plain-woven Hi-NicalonTM fiber reinforced SiC/SiC composites with various PyC and PyC-SiC multilayers were studied at ambient temperature. The composites were fabricated by chemical vapor infiltration process (CVI). The interlayers were deposited by isothermal CVI process from methane for PyC layer and CH3SiCl3 (MTS) for SiC layer. The effects of the various interlayers on the fracture behaviors and flexural properties were investigated. The PyC layer thickness showed significant influence on the flexural strength and an optimum PyC layer thickness was defined to be ∼ 150 nm. Fiber/matrix interfacial debonding occurred at the very fiber surface for single PyC layered composites while several interfacial debonding and cracking behaviors were observed with the PyC-SiC multilayered composites.