Properties of Multilayered Interphases in SiC/SiC Chemical‐Vapor‐Infiltrated Composites with “Weak” and “Strong” Interfaces

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Abstract
The interfacial properties of SiC/SiC composites with interphases that consist of (C‐SiC) sequences deposited on the fibers 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‐coatingbond 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.