SiC/SiC minicomposites with structure-graded BN interphases

Abstract

BN interphases in SiC/SiC minicomposites were produced by infiltration of fibre tows from BF 3 -NH 3 -H 2 gaseous system. During interphase one-step processing, the tow travels through a reactor containing a succession of different hot areas. By TEM characterization, the BN interphases were found to be made of a structural gradient: from isotropic to highly anisotropic. The very first coating is poorly organised and allows protecting the fibre from a further chemical attack by the reactant mixture. The minicomposites were tensile tested at room temperature with unloading-reloading cycles. The BN interphases act as mechanical fuses; the fibre/matrix bonding intensity ranges from weak to rather strong depending on the tow travelling rate during interphase infiltration. The specimen lifetimes at 700°C under a constant tensile loading were measured in dry and moist air. Compared to a pyrocarbon reference interphase, the BN interphases significantly improve the oxidation resistance of the SiC/SiC minicomposites.

Single‐ and Multilayered Interphases in SiC/SiC Composites Exposed to Severe Environmental Conditions: An Overview

“…One way to solve the corrosion problem and to play with the mechanical fuse location could be to deposit BN in a temperature gradient (TG‐CVI). Jacques et al 42 have fabricated 1D‐SiC/BN/SiC minicomposites with a radial crystallinity gradient by simply passing a Hi‐Nicalon tow through a three‐temperature zones furnace. Under optimized conditions, in terms of fiber progression speed, the FI bonding was strong (crack deflection occurring within BN interphase (Fig.…”

A comparative study on Cf/PyC/SiC minicomposites prepared via CVI process for hypersonic engine application

“…The long duration of the matrix densification process involved in the fabrication of 2D/3D test specimens for property evaluation is the major concern for the initial selection of a fiber/matrix system. Minicomposite approach, using 1D CMC has been developed with an aim to reduce the time required for the initial selection of fiber/matrix system in material development . The approach has the following advantages: (i) reducing the densification time by employing a 1D yarn as the fiber preform, (ii) 1D architecture, which avoids fiber orientation effects on tensile strength, and (iii) easy application of micromechanical models over the mechanical test data.…”

The improvement in the mechanical and thermal properties of SiC/SiC composites by introducing CNTs into the PyC interface

“…These properties are highly dependant on their three constituents: the fibres, matrix and interface. In SiC/SiC composites, the interface plays a key role in their behaviour, such as preventing early failure of fibres, transferring load and heat between the fibres and matrix, and releasing part of the residual thermal stresses [6][7][8][9][10]. The most commonly used interfacial material in SiC/SiC composites for fusion/fission reactors is pyrocarbon (PyC) [11][12][13].…”