Influence of Strong Fiber/Coating Interfaces on the Mechanical Behavior and Lifetime of Hi-Nicalon/(PyC/SiC)n/SiC Minicomposites

Hi-Nicalon fiber-reinforced silicon carbide matrix minicomposites (Hi-Nicalon/SiC) with nanoscale multilayered (PyC/SiC) _n fiber coatings (also referred to as interphases) have been manufactured via pressure pulse chemical vapor infiltration (P-CVI). Fiber/coating interfaces were strengthened by using treated fibers. The microstructures of the interphases as well as the propagation and deflection of cracks in the interfacial region were investigated by SEM and TEM. Interfacial shear stress was estimated using various methods based on either the width of hysteresis loops on unloading–reloading, crack spacing, or fitting of the force–deformation curve using a micromechanics-based model. Tensile behavior at room temperature and lifetime in static fatigue in air at 700°C were related to the interphase/interface characteristics.