Effect of intermediate heat treatment on mechanical properties of SiCf/SiC composites with BN interphase prepared by ICVI

SiCf/SiC composites with BN interface were prepared through isothermal–isobaric chemical vapour infiltration process. Room temperature mechanical properties such as tensile, flexural, inter-laminar shear strength and fracture toughness (KIC) were studied for the composites. The tensile strength of the SiCf/SiC composites with stabilised BN interface was almost 3.5 times higher than that of SiCf/SiC composites with un-stabilised BN interphase. The fracture toughness is similarly enhanced to 23 MPa m1/2 by stabilisation treatment. Fibre push-through test results showed that the interfacial bond strength between fibre and matrix for the composite with un-stabilised BN interface was too strong (>48 MPa) and it has been modified to a weaker bond (10 MPa) due to intermediate heat treatment. In the case of composite in which BN interface was subjected to thermal treatment soon after the interface coating, the interfacial bond strength between fibre and matrix was relatively stronger (29 MPa) and facilitated limited fibre pull-out.