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


  • Kevin V. Moraes,

    1. Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180
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    • Currently with Applied Materials, Inc., Santa Clara, CA 95050.

  • Leonard V. Interrante

    1. Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180
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    • *

      Member, American Ceramic Society.

  • R. Raj—contributing editor

  • This work was supported by the National Science Foundation, under Grant No.CHE-9812191.

  • Presented at the 2nd International Workshop on “Ultrahigh Temperature Polymer Derived Ceramics” (Boulder, CO, July 23-29, 2000).


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/cm3, 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·m1/2 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.