Processing, fracture toughness, and vickers hardness of allylhyd ridopolycarbosilane-derived silicon carbide

Bulk specimens of precursor-derived silicon carbide NO 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, 1000degreesC pyrolyzed, AHPCS-SiC with neat AHPCS, followed by pyrolysis to 1000degreesC and ten subsequent reinfiltration/pyrolysis steps with the neat liquid AHPCS. Then, these pellets were heat-treated to 1200degrees, 1400degrees, and 1600degreesC, 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 1000degrees, 1200degrees, 1400degrees, and 1600degreesC, 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.