Preparation of SiC/SiC composites by hot pressing, using Tyranno-SA fiber as reinforcement

The development of advanced Tyranno SA SiC fiber with a near-stoichiometric composition and a well-crystallized microstructure has made it possible to prepare SiC/SiC composites even under harsh conditions. To assess the reinforcing effectiveness of Tyranno SA fiber at high temperature under pressure, unidirectional SiC/SiC composites were prepared by hot pressing, using pyrolytic carbon (PyC)-coated Tyranno SA fiber as a reinforcement and nanopowder SiC with sintering additives for matrix formation. The effects of sintering conditions on the microstructural evolution and mechanical properties of the composites were characterized. As the sintering temperature increased (from 1720degrees to 1780degreesC) and the sintering pressure increased (from 15 to 20 MPa), the density of the composites gradually increased. Simultaneously, the elastic modulus, the proportional limit stress, and the strength, under both bend and tensile tests, also improved. At lower temperature and/or pressure, long fiber pullout was a predominant fracture behavior, indicating relatively weak fiber/matrix bonding. However, at high temperature and/or pressure, short fiber pullout became a main fracture characteristic, indicating relatively strong fiber/matrix bonding. These phenomena were also confirmed by the characteristics of the hysteresis loops derived from the stress-strain curves produced by a tensile test with unloading-reloading cycles. In the present investigation, the reinforcement of Tyranno SA fiber is effective for providing noncatastrophic fracture behavior to composites.