Oxidizing environment influence on the mechanical properties and microstructure of 2DSiC/BN/SiC composites processed by ICVI

Abstract

2DSiC SiC composites have been elaborated with BN interphases of different thicknesses which were deposited on treated 1 Nicalon ™ fibers by isothermal-isobaric chemical vapor infiltration from BCl 3NH 3H 2 mixtures. Their mechanical behavior was investigated at 600 °C in air and compared to the results obtained on similar SiC/C/SiC composites. Although these materials exhibit similar stress and strain values at rupture when loaded at room temperature, whatever the interphase, their thermomechanical resistance depends on stress type, i.e. static or dynamic. Under static fatigue the BN interphases are more efficient than the pyrocarbon (PyC) ones. Thin BN interphases tend to maintain the interfacial properties. This result could be explained by the larger microcrack distances in the tows supporting the main part of the load, according to a lower interfacial sliding resistance. In contrast the materials with a PyC interphase, which have a much higher interfacial shear resistance at room temperature, exhibit better thermomechanical behavior under dynamic fatigue at 600 ° C. The mechanical characteristics are related to the evolution of the fibermatrix interfacial zone which has been studied by SEM, TEM and EELS.