Adhesion between Nextel 312(TM) fibers and Blackglas(TM) silicon oxycarbide and its effect on composite properties

Increasing demand for high strength, light weight composite structures for use in gas turbine engine applications has fueled interest in ceramic matrix composites. CMC's typically exhibit high strength with low ductility and often require expensive manufacturing processes, however, a polymer precursor to a ceramic matrix reinforced with continuous ceramic fibers offers high strength coupled with ductile fracture modes. Fabricated with conventional epoxy composite tooling, a Silicon Oxycarbide reinforced with a Boron Nitride treated aluminoborosilicate fibers is capable of meeting 1300°F service environments found in gas turbine engines. This continuously fiber reinforced CMC lends its improved toughness to controlled fiber pull-out during failure which is created through the Boron Nitride interphase. This work characterizes fiber-matrix adhesion of untreated and BN treated Nextel 312(TM) fibers through fiber pull-out and indentation testing. Contact angle and wettability measurements also are assessed. Flexure and short beam shear testing of both unidirectional and woven composites were used to verify adhesion observations. Environmental Electron Scanning Microscopy (ESEM) performed in conjunction with composite processing provided insight to matrix cracking and fiber-matrix differential expansion effects. This work served to quantify performance gains associated with the BN treatment of Nextel 312(TM) composites.