Hi-Nicalon/SiC minicomposites with (pyrocarbon/SiC)n nanoscale multilayered interphases

SiC/SiC minicomposites that comprise different pyrocarbon/silicon carbide ((PyC/SiC)(n)) multilayered interphases and a tow of SIC fibers (Hi-Nicalon) have been prepared via pressure-pulsed chemical vapor infiltration. Pyrocarbon and SIC were deposited from propane and a CH3SiCl3/H-2 mixture, respectively. The microstructure of the interphases:has been investigated using transmission electron microscopy. The mechanical tensile behavior of the minicomposites at room temperature exhibits the classical features of tough composites, regardless of the characteristics of the (PyC/SiC) sequences. The interfacial shear stress has been determined from the width of hysteresis loops upon unloading/reloading and from the crack-spacing distance at saturation. All the experimental data indicate that the strength of the fiber/interphase interfaces is rather weak (similar to 50 MPa).