Influence of Texture and Thickness of Pyrocarbon Coatings as Interphase on the Mechanical Behavior of Specific 2.5D SiC/SiC Composites Reinforced with Hi-Nicalon S Fibers

Abstract

In the framework of SiC/SiC composite development for nuclear applications, the influence of pyrocarbon interphase texture and thickness on the mechanical behavior both on as-processed materials and on irradiated materials is a major concern. Thus, the PyC interphase influence has to be clearly addressed to define its optimal chemical vapor infiltration processing parameters. For this purpose, specific 2.5D SiC/SiC composites reinforced with Hi-Nicalon S fibers and with two kinds of PyC texture and thickness were produced. Transmission electronic microscopy allowed PyC thickness and microstructure/texture characterizations, whereas push-out and tensile tests were employed as experimental mechanical procedures. The original result is that PyC nature directly influences the interfacial shear stress and failure mode of the weakest interface, regardless of the PyC thickness within the studied range. Adhesive failure or cohesive failure are highlighted depending on the PyC CVI deposition mechanisms. Similar post-irradiation characterizations will be required to assess the role of irradiation on the PyC microstructure/texture evolution and mechanical behavior of these materials.

Relationship between both thickness and degree of crystallisation of BN interphases and the mechanical behaviour of SiC/SiC composites

“…It has been known for several decades that the structure of the interfacial system, particularly the thickness and microstructural organisation of the interphase, has an effect on the micro-and macromechanical properties of CMCs [6][7][8][9][10][11]. In the particular case of BN interphases, work on this effect has been carried out with the first generations of fibres from the Nippon Carbon company (Tokyo, Japan), namely Nicalon TM [12] and Hi-Nicalon TM [13].…”

Impact of fiber surface gas treatments on interfacial bonding in SiC/BN/SiC minicomposites

“…The microstructural organization of layered interphase materials such as pyrocarbon or boron nitride, has an effect on interfacial debonding mechanisms and on the micro‐ and macromechanical properties of CMCs 2–4 . Therefore, it is essential to control this microstructural organization.…”

“…1 The microstructural organization of layered interphase materials such as pyrocarbon or boron nitride, has an effect on interfacial debonding mechanisms and on the microand macromechanical properties of CMCs. [2][3][4] Therefore, it is essential to control this microstructural organization. However, using Hi-Nicalon S fibers also means controlling their coupling to the interphase, as the bond between these two components must remain strong enough for the interphase to fully play its role as a mechanical fuse.…”

Polygranular image guided atomistic reconstruction: A parametric model of pyrocarbon nanostructure

“…Conversely to the formation of soot and blacks, the lower temperatures and pressures considered during pyC preparation (T ∼ 1000 • C and P ∼ 1-10 kPa), allow avoiding gas phase carbon nucleation and ensure the deposition of a dense and relatively homogeneous turbostratic carbon [2,3]. Owing to their excellent mechanical and thermal properties, high melting point and low porosity, the principal application of these materials is as constituents of continuous-fiber reinforced composite materials: as matrices of C/C composite materials for thermal protection systems and solid rocket motor parts in spatial applications [4,5] or for brakes in aeronautic or terrestrial transport [6,7], as interphases in C/SiC materials [8,9] for the same types of applications [10] or as interphases in SiC/SiC ceramic matrix composites for GenIV nuclear reactors or nuclear fusion reactors [11][12][13] . PyCs are also considered as nuclear fuel cell coatings, in the tristructural isotropic (TRISO) particle fuel cell of the high temperature reactor (HTR) technology [14], or around individual carbon nanotubes for electron emission applications or near field microscopy probes [15].…”