Effect of increased intra-bundle spacing on mechanical behaviour of Cf- ZrB2–SiC ultra-high temperature ceramic matrix composites produced by slurry infiltration and hot pressing

A study has been carried out to examine the influence of augmented intra-bundle spacing achieved through innovative pre-treatment (heat treatment or ultrasonication) of carbon fibre (C_f) fabric, on mechanical properties of C_f-ZrB₂-SiC composites processed by ZrB₂–SiC slurry infiltration and hot pressing. Significantly enhanced C_f fabric intra-bundle spacing has facilitated homogeneous slurry infiltration, but has lowered elastic modulus, flexural strength, and fracture toughness compared to the composite with as-received C_f, because of fibre disorientation introduced during pre-treatment and its partial degradation by formation of interfacial ZrC during sintering. Notably, the composite with heat-treated C_f has shown superior fracture toughness (7.78 ± 0.4 MPa√m) and work of fracture (3043.25 ± 24.2 J/m²) compared to that containing ultra-sonicated C_f by 52.5 % and 95.7 %, respectively. Despite these variations, all the composites have exhibited non-catastrophic fracture behaviour during testing owing to the role of fibre pull-out, crack bridging, and crack deflection operating as toughening mechanisms.