Processing, Fracture Toughness, and Vickers Hardness of Allylhydridopolycarbosilane‐Derived Silicon Carbide

Bulk specimens of precursor‐derived silicon carbide (SiC) suitable for mechanical‐property measurements were prepared from allylhydridopolycarbosilane (AHPCS), which is a commercially available, hyperbranched polycarbosilane. Crack‐free pellets were obtained by cold‐pressing mixtures of finely ground, 1000°C pyrolyzed, “AHPCS‐SiC” with neat AHPCS, followed by pyrolysis to 1000°C and ten subsequent reinfiltration/pyrolysis steps with the neat liquid AHPCS. Then, these pellets were heat‐treated to 1200°, 1400°, and 1600°C, followed by additional reinfiltration/pyrolysis cycles to the final respective maximum temperatures. This fabrication process simulated the production of the matrix phase for ceramic‐matrix composites via successive infiltration/pyrolysis cycles. The density of the material processed at these temperatures, measured via the Archimedes method, was 2.3, 2.5, 2.6, and 2.9 g/cm ³ , respectively, and the average open porosities of the samples were 2, 0.2, 1, and 9 vol%, respectively. The fracture toughness was measured using the single‐edge V‐notched‐beam method, and the hardness was measured via Vickers indentation. The samples had an average toughness of 1.40 ± 0.08, 1.65 ± 0.09, 1.67 ± 0.07, and 1.46 ± 0.08 MPa·m ^1/2 for the samples that were treated at 1000°, 1200°, 1400°, and 1600°C, respectively. The Vickers hardness for these samples, measured at a load of 1000 g, was 12 ± 1, 13 ± 2, 11 ± 1, and 9 ± 1 GPa, respectively.