Assessment of flexural properties of oxide/oxide ceramic matrix composites with tailored porosity

This study investigates the effect of porosity on the flexural properties of ceramic-oxide composites manufactured by a precursor infiltration and pyrolysis process. The composite porosity decreased from 35.89% to 25.85% over seven infiltration cycles. The flexural strength exhibited a non-monotonic relationship with porosity, peaking at approximately 350MPa (at 30.71% porosity after three cycles) before decreasing. This peak strength corresponded to a non-brittle failure mode, characterised by a porous matrix and single fibre pull-out. Further cycles (5 and 7) reduced porosity, leading to a more densified matrix and tightly packed fibre bundles. This increased density resulted in decreased flexural strength and a transition to a brittle failure mode. In contrast, the flexural modulus increased continuously as porosity decreased.