Hi-Nicalon<SUP>TM</SUP> Fiber-Reinforced CVI-SiC Matrix Composites: I Effects of PyC and PyC-SiC Multilayers on the Fracture Behaviors and Flexural Properties

Abstract

The flexural properties of 2D plain-woven Hi-Nicalon TM 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 CH 3 SiCl 3 (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.

Hi-Nicalon<SUP>TM</SUP> Fiber-Reinforced CVI-SiC Matrix Composites: II Interfacial Shear Strength and Its Effects on the Flexural Properties

“…The composite with 150 nm PyC layer yielded an ISS ∼ 200 MPa, which seems to be the optimum value in term of the PLS for the 2D plain-woven Hi-Nicalon/SiC composites. These findings are in good agreement with the results in the study 4) on the flexural properties of these composites that the PLS showed sharp increase with the increase of the PyC layer thickness till ∼ 150 nm, and then decreased gradually. When the PyC layer was thicker than ∼ 200 nm, the PLS showed little change with the PyC layer thickness.…”

“…When single PyC or PyC-SiC multilayers were employed, the ISS was drastically decreased. It was found in the flexural properties study of these composites 4) that the interfacial debonding/sliding took place mostly at the interface adjacent to the first PyC layer (most near to the fiber). Rebillat et al 8) has also reported that the interfacial characteristics seemed to be related to the thickness of the first carbon layer on the fibers in as-received Nicalon fiber reinforced CVI SiC/SiC composites with (C-SiC) n interlayers.…”

“…3) In a companion study, 4) the flexural properties and fracture behaviors of a series of Hi-Nicalon fiber reinforced CVISiC/SiC composites with various PyC or PyC-SiC multilayers were investigated. The results showed significant effects of the various interlayers on the strength and interfacial crack behaviors of the materials.…”

Mechanical Properties of Chemically Vapor-Infiltrated Silicon Carbide Structural Composites with Thin Carbon Interphases for Fusion and Advanced Fission Applications

“…For conventional CVI-SiC/SiC composite systems, an optimum PyC interphase thickness range of 150-300 nm is reported for the best fracture behavior. [23][24][25][26] However, for application in fusion blankets, the minimum use of carbon constituents is preferred to optimize irradiation stability, chemical compatibility with coolants and/or breeding materials, tritium permeability, and electrical conductivity. The Generation Materials Transactions, Vol.…”

Flexural Strength of a Plain-Woven Tyranno-SA Fiber-Reinforced SiC Matrix Composite

“…During the past several tens of years, many efforts have been done to develop continuous silicon carbide fibers reinforced silicon carbide matrix (SiC/ SiC) composites for use in energy conversion systems, aviation and aerospace systems, etc. [1][2][3][4] SiC/SiC composites usually exhibit relatively large scatter in strength 5,6) because of the statistic distributions of the flaws and pores in the materials. Therefore, fabrication of SiC/SiC composites with dense and space homogeneous matrix densification is critical and remains one of the main current issues, especially when it comes to the evaluation of the strength and reliability of SiC/ SiC composites, which is necessary for critical engineering applications.…”