The Tensile Creep behavior of SiC-based fibers with low oxygen content

Full text of publication follows: Owning to recent progress in the fabrication of stoichiometric fibers and their stability under neutron irradiation, SiC/SiC composites are possible candidate for nuclear applications such as structural component facing the plasma in fusion reactor or for fuel containment in Gas Fast Reactor (GFR). In this application, resistance to creep behaviour is a key factor. The creep behavior of Hi-Nicalon S and Tyranno SA3 fibers is investigated at temperatures up to 1700 deg. C. Tensile tests were carried out on a high capability fiber testing apparatus in which the fiber is heated uniformly under vacuum. Same apparatus was designed for creep testing under an irradiation beam. Analysis of initial microstructure and composition of fibers was performed using various techniques. All the fibers experienced a steady-state creep. Primary creep was found to be more or less significant depending on fiber microstructure. Steady-state creep was shown to result from grain boundary sliding. Activation energy and stress exponents were determined. Creep mechanisms are discussed on the basis of activation energy and stress exponent data. Finally, tertiary creep was observed at very high temperatures. Tertiary creep was related to volatilization of SiC. Results are discussed with respect to fiber microstructure and fiber diameter variability. (authors)