Properties of multilayered interphases in SiC/SiC chemical-vapor-infiltrated composites with "weak" and "strong" interfaces

The interfacial properties of SiC/SiC composites with interphases that consist of (C-SiC) sequences deposited on the tibers have been determined by single-fiber push-out tests. The matrix has been reinforced with either as-received or treated Nicalon fibers. The measured interfacial properties are correlated with the fiber-coating bond strength and the number of interlayers. For the composites reinforced with as-received (weakly bonded) fibers, interfacial characteristics are extracted from the nonlinear portion of the stress-displacement curve by fitting Hsueh's push-out model. The interfacial characteristics are controlled by the carbon layer adjacent to the fiber. The resistance to interface crack growth and fiber sliding increases as the number of (C-SiC) sequences increases. For the composites reinforced with treated (strongly bonded) fibers, the push-out curves exhibit an uncommon upward curvature, which reflects different modes of interphase cracking and a contribution of fiber roughness.