Effects of dry and wet air oxidation on tensile properties of SiC/BN/SiC minicomposites

Abstract This study investigates the effects of dry and wet air oxidation on the tensile behavior of unidirectional SiC/BN/SiC minicomposites, with a particular focus on how environmental conditions and pre‐cracking influence strength retention and failure modes. The pristine minicomposites exhibit high strength and failure strain, attributed to effective fiber coatings and preservation of fiber strength throughout processing. Oxidation at 1000°C without pre‐cracking in dry air causes only minor degradation and is associated with a transition from transverse matrix cracking with distributed fiber fracture to a shear‐driven failure mode. In wet air, the same shear‐driven mode occurs but with a significantly lower failure strain. The most severe degradation is observed when pre‐cracking precedes oxidation; bonding between fibers and with the matrix eliminates interfacial sliding, resulting in a dramatic reduction in failure strain. The work identifies three distinct fracture regimes controlled by the interplay of fiber waviness, oxidation conditions, and mechanical loading history.