Influence of the interphase properties on the mechanical behaviour of SiC/PyC/SiC_f composites

摘要

SiC/SiC composites are commonly used for high-temperature engineering applications due to their excellent specific mechanical properties at elevated temperatures. Their good microstructural stability under high-energy neutron irradiation makes them attractive to be used as blanket components in fusion or structural material in fission reactors [1-5]. In the frame of nuclear applications, their mechanical properties remain however a drawback and must be adjusted to resist to neutronic irradiation. This mechanical behaviour of the composite depends on the fiber/matrix (F/M) bonding. Among the parameters influencing the mechanical properties of the composite, the nature of the C/SiC interface and/or the surface characteristics of the SiC fibers appear to be predominant. The SiC surface characteristics depend on the fibers type [13-16]. Two fibers types appear interesting to be used in SiC/SiC composites devoted to neutron irradiation: the fibers named Hi-Nicalon S and SA3 Tyranno [6, 7]. The mechanical behaviour of CVI SiC/SiC composites reinforced with Hi-Nicalon S (noted HNS) or SA3 fibers (noted TSA3) were investigated on minicomposite (unidirectional composite reinforced with single tows) test specimen. Tensile tests and push-out tests were done in order to determine the interfacial shear strength. The surface properties of SiC fibers were investigated in relation with the mechanical behaviour of the corresponding composite in order to identify the predominant surface characteristics responsible for the mechanical behaviour. The surface morphology and the chemical characteristics were determined using several characterization techniques. The results are discussed in order to highlight the importance of the SiC surface properties on the F/M coupling.