High-temperature flexural strength of I-CVI processed Cf/SiC composites with variable interphases

•The Cf/SiC composites having single layer PyC and multilayered [(PyC/SiC)n=4] interphases are processed by I-CVI method.•The effect of interphase type and SiC-CVD seal coating on the high temperature (1200oC) flexural properties is investigated.•Uncoated and seal coated Cf/SiC composites with multilayered interphase showed higher flexural strength and displacement.•The fractured surfaces of tested samples are analyzed in detail to study the fracture phenomena.•A mechanism is proposed for the increase of flexural properties of Cf/SiC composites having multilayered interphase.